Squashed 'third_party/boostorg/optional/' content from commit 155ad59
Change-Id: I4ad7a1e7b295a6136c5a0d7b6c11700e76b939b5
git-subtree-dir: third_party/boostorg/optional
git-subtree-split: 155ad5911e5683cc87d34363f8304b60a30a8345
diff --git a/.gitattributes b/.gitattributes
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+* text=auto !eol svneol=native#text/plain
+*.gitattributes text svneol=native#text/plain
+
+# Scriptish formats
+*.bat text svneol=native#text/plain
+*.bsh text svneol=native#text/x-beanshell
+*.cgi text svneol=native#text/plain
+*.cmd text svneol=native#text/plain
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+*.php text svneol=native#text/x-php
+*.pl text svneol=native#text/x-perl
+*.pm text svneol=native#text/x-perl
+*.py text svneol=native#text/x-python
+*.sh eol=lf svneol=LF#text/x-sh
+configure eol=lf svneol=LF#text/x-sh
+
+# Image formats
+*.bmp binary svneol=unset#image/bmp
+*.gif binary svneol=unset#image/gif
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+*.tif binary svneol=unset#image/tiff
+*.tiff binary svneol=unset#image/tiff
+*.svg text svneol=native#image/svg%2Bxml
+
+# Data formats
+*.pdf binary svneol=unset#application/pdf
+*.avi binary svneol=unset#video/avi
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+*.rtf binary svneol=unset#text/rtf
+*.sln text svneol=native#text/plain
+*.swf binary svneol=unset#application/x-shockwave-flash
+*.tgz binary svneol=unset#application/gzip
+*.vcproj text svneol=native#text/xml
+*.vcxproj text svneol=native#text/xml
+*.vsprops text svneol=native#text/xml
+*.wav binary svneol=unset#audio/wav
+*.xls binary svneol=unset#application/vnd.ms-excel
+*.zip binary svneol=unset#application/zip
+
+# Text formats
+.htaccess text svneol=native#text/plain
+*.bbk text svneol=native#text/xml
+*.cmake text svneol=native#text/plain
+*.css text svneol=native#text/css
+*.dtd text svneol=native#text/xml
+*.htm text svneol=native#text/html
+*.html text svneol=native#text/html
+*.ini text svneol=native#text/plain
+*.log text svneol=native#text/plain
+*.mak text svneol=native#text/plain
+*.qbk text svneol=native#text/plain
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+TODO text svneol=native#text/plain
+
+# Code formats
+*.c text svneol=native#text/plain
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diff --git a/.travis.yml b/.travis.yml
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--- /dev/null
+++ b/.travis.yml
@@ -0,0 +1,199 @@
+# Copyright 2016, 2017 Peter Dimov
+# Distributed under the Boost Software License, Version 1.0.
+# (See accompanying file LICENSE_1_0.txt or copy at http://boost.org/LICENSE_1_0.txt)
+
+language: cpp
+
+sudo: false
+
+python: "2.7"
+
+branches:
+ only:
+ - master
+ - develop
+ - /feature\/.*/
+
+env:
+ matrix:
+ - BOGUS_JOB=true
+
+matrix:
+
+ exclude:
+ - env: BOGUS_JOB=true
+
+ include:
+ - os: linux
+ compiler: g++
+ env: TOOLSET=gcc COMPILER=g++ CXXSTD=03,11
+
+ - os: linux
+ compiler: g++-4.7
+ env: TOOLSET=gcc COMPILER=g++-4.7 CXXSTD=03,11
+ addons:
+ apt:
+ packages:
+ - g++-4.7
+ sources:
+ - ubuntu-toolchain-r-test
+
+ - os: linux
+ compiler: g++-4.8
+ env: TOOLSET=gcc COMPILER=g++-4.8 CXXSTD=03,11
+ addons:
+ apt:
+ packages:
+ - g++-4.8
+ sources:
+ - ubuntu-toolchain-r-test
+ - os: linux
+ compiler: g++-4.9
+ env: TOOLSET=gcc COMPILER=g++-4.9 CXXSTD=03,11
+ addons:
+ apt:
+ packages:
+ - g++-4.9
+ sources:
+ - ubuntu-toolchain-r-test
+
+ - os: linux
+ compiler: g++-5
+ env: TOOLSET=gcc COMPILER=g++-5 CXXSTD=03,11,14,1z
+ addons:
+ apt:
+ packages:
+ - g++-5
+ sources:
+ - ubuntu-toolchain-r-test
+
+ - os: linux
+ compiler: g++-6
+ env: TOOLSET=gcc COMPILER=g++-6 CXXSTD=03,11,14,1z
+ addons:
+ apt:
+ packages:
+ - g++-6
+ sources:
+ - ubuntu-toolchain-r-test
+
+ - os: linux
+ dist: trusty
+ compiler: g++-7
+ env: TOOLSET=gcc COMPILER=g++-7 CXXSTD=03,11,14,17
+ addons:
+ apt:
+ packages:
+ - g++-7
+ sources:
+ - ubuntu-toolchain-r-test
+
+ - os: linux
+ compiler: clang++
+ env: TOOLSET=clang COMPILER=clang++ CXXSTD=03,11
+
+ - os: linux
+ compiler: clang++-3.5
+ env: TOOLSET=clang COMPILER=clang++-3.5 CXXSTD=03,11,14,1z
+ addons:
+ apt:
+ packages:
+ - clang-3.5
+ - libstdc++-4.9-dev
+ sources:
+ - ubuntu-toolchain-r-test
+ - llvm-toolchain-precise-3.5
+
+ - os: linux
+ compiler: clang++-3.6
+ env: TOOLSET=clang COMPILER=clang++-3.6 CXXSTD=03,11,14,1z
+ addons:
+ apt:
+ packages:
+ - clang-3.6
+ sources:
+ - ubuntu-toolchain-r-test
+ - llvm-toolchain-precise-3.6
+
+ - os: linux
+ compiler: clang++-3.7
+ env: TOOLSET=clang COMPILER=clang++-3.7 CXXSTD=03,11,14,1z
+ addons:
+ apt:
+ packages:
+ - clang-3.7
+ sources:
+ - ubuntu-toolchain-r-test
+ - llvm-toolchain-precise-3.7
+
+ - os: linux
+ compiler: clang++-3.8
+ env: TOOLSET=clang COMPILER=clang++-3.8 CXXSTD=03,11,14,1z
+ addons:
+ apt:
+ packages:
+ - clang-3.8
+ - libstdc++-4.9-dev
+ sources:
+ - ubuntu-toolchain-r-test
+ - llvm-toolchain-precise-3.8
+
+ - os: linux
+ compiler: clang++-3.9
+ env: TOOLSET=clang COMPILER=clang++-3.9 CXXSTD=03,11,14,1z
+ addons:
+ apt:
+ packages:
+ - clang-3.9
+ - libstdc++-4.9-dev
+ sources:
+ - ubuntu-toolchain-r-test
+ - llvm-toolchain-precise-3.9
+
+ - os: linux
+ compiler: clang++-4.0
+ env: TOOLSET=clang COMPILER=clang++-4.0 CXXSTD=03,11,14,1z
+ addons:
+ apt:
+ packages:
+ - clang-4.0
+ sources:
+ - ubuntu-toolchain-r-test
+ - llvm-toolchain-trusty-4.0
+
+ - os: linux
+ compiler: clang++-5.0
+ env: TOOLSET=clang COMPILER=clang++-5.0 CXXSTD=03,11,14,1z
+ addons:
+ apt:
+ packages:
+ - clang-5.0
+ sources:
+ - ubuntu-toolchain-r-test
+ - llvm-toolchain-trusty-5.0
+
+ - os: osx
+ compiler: clang++
+ env: TOOLSET=clang COMPILER=clang++ CXXSTD=03,11,14,1z
+
+install:
+ - BOOST_BRANCH=develop && [ "$TRAVIS_BRANCH" == "master" ] && BOOST_BRANCH=master || true
+ - cd ..
+ - git clone -b $BOOST_BRANCH --depth 1 https://github.com/boostorg/boost.git boost-root
+ - cd boost-root
+ - git submodule update --init tools/build
+ - git submodule update --init libs/config
+ - git submodule update --init tools/boostdep
+ - cp -r $TRAVIS_BUILD_DIR/* libs/optional
+ - python tools/boostdep/depinst/depinst.py optional
+ - ./bootstrap.sh
+ - ./b2 headers
+
+script:
+ - |-
+ echo "using $TOOLSET : : $COMPILER ;" > ~/user-config.jam
+ - ./b2 libs/optional/test toolset=$TOOLSET cxxstd=$CXXSTD
+
+notifications:
+ email:
+ on_success: always
diff --git a/README.md b/README.md
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--- /dev/null
+++ b/README.md
@@ -0,0 +1,15 @@
+optional
+========
+
+A library for representing optional (nullable) objects in C++.
+
+```cpp
+optional<int> readInt(); // this function may return either an int or a not-an-int
+
+if (optional<int> oi = readInt()) // did I get a real int
+ cout << "my int is: " << *oi; // use my int
+else
+ cout << "I have no int";
+```
+
+For more information refer to the documentation provided with this library.
diff --git a/doc/00_optional.qbk b/doc/00_optional.qbk
new file mode 100644
index 0000000..00b6096
--- /dev/null
+++ b/doc/00_optional.qbk
@@ -0,0 +1,106 @@
+[library Boost.Optional
+ [quickbook 1.4]
+ [authors [Cacciola Carballal, Fernando Luis]]
+ [copyright 2003-2007 Fernando Luis Cacciola Carballal]
+ [copyright 2014-2018 Andrzej Krzemieński]
+ [category miscellaneous]
+ [id optional]
+ [dirname optional]
+ [purpose
+ Discriminated-union wrapper for optional values
+ ]
+ [source-mode c++]
+ [license
+Distributed under the Boost Software License, Version 1.0.
+(See accompanying file LICENSE_1_0.txt or copy at
+[@http://www.boost.org/LICENSE_1_0.txt])
+ ]
+]
+
+[/ Macros will be used for links so we have a central place to change them ]
+
+
+[/ Cited Boost resources ]
+
+[def __BOOST_VARIANT__ [@../../../variant/index.html Boost.Variant]]
+[def __BOOST_TUPLE__ [@../../../tuple/index.html Boost.Tuple]]
+[def __BOOST_TRIBOOL__ [@../../../../doc/html/tribool.html boost::tribool]]
+
+[def __OPTIONAL_POINTEE__ [@../../../utility/OptionalPointee.html `OptionalPointee`]]
+[def __COPY_CONSTRUCTIBLE__ [@../../../utility/CopyConstructible.html `CopyConstructible`]]
+[def __MOVE_CONSTRUCTIBLE__ `MoveConstructible`]
+[def __FUNCTION_EQUAL_POINTEES__ [@../../../utility/OptionalPointee.html#equal `equal_pointees()`]]
+[def __FUNCTION_LESS_POINTEES__ [@../../../utility/OptionalPointee.html#less `less_pointees()`]]
+
+[def __IN_PLACE_FACTORY_HPP__ [@../../../../boost/utility/in_place_factory.hpp in_place_factory.hpp]]
+[def __TYPED_IN_PLACE_FACTORY_HPP__ [@../../../../boost/utility/typed_in_place_factory.hpp typed_in_place_factory.hpp]]
+
+[/ Other web resources ]
+
+[def __HASKELL__ [@http://www.haskell.org/ Haskell]]
+[def __SGI_DEFAULT_CONSTRUCTIBLE__ [@http://www.sgi.com/tech/stl/DefaultConstructible.html `DefaultConstructible`]]
+[def __SGI_LESS_THAN_COMPARABLE__ [@http://www.sgi.com/tech/stl/LessThanComparable.html `LessThanComparable`]]
+[def __SGI_EQUALITY_COMPARABLE__ [@http://www.sgi.com/tech/stl/EqualityComparable.html `EqualityComparable`]]
+[def __SGI_GENERATOR__ [@http://www.sgi.com/tech/stl/Generator.html `Generator`]]
+
+
+[/ Icons ]
+
+[def __SPACE__ [$images/space.png]]
+[def __GO_TO__ [$images/callouts/R.png]]
+
+
+[section Introduction]
+Class template `optional` is a wrapper for representing 'optional' (or 'nullable') objects who may not (yet) contain a valid value. Optional objects offer full value semantics; they are good for passing by value and usage inside STL containers. This is a header-only library.
+
+[heading Problem]
+Suppose we want to read a parameter form a config file which represents some integral value, let's call it `"MaxValue"`. It is possible that this parameter is not specified; such situation is no error. It is valid to not specify the parameter and in that case the program is supposed to behave slightly differently. Also, suppose that any possible value of type `int` is a valid value for `"MaxValue"`, so we cannot just use `-1` to represent the absence of the parameter in the config file.
+
+[heading Solution]
+
+This is how you solve it with `boost::optional`:
+
+ #include <boost/optional.hpp>
+
+ boost::optional<int> getConfigParam(std::string name); // return either an int or a `not-an-int`
+
+ int main()
+ {
+ if (boost::optional<int> oi = getConfigParam("MaxValue")) // did I get a real int?
+ runWithMax(*oi); // use my int
+ else
+ runWithNoMax();
+ }
+
+[endsect]
+
+[include 01_quick_start.qbk]
+[section Tutorial]
+[include 10_motivation.qbk]
+[include 11_development.qbk]
+[include 12_when_to_use.qbk]
+[include 13_relational_operators.qbk]
+[include 14_io.qbk]
+[include 15_optional_references.qbk]
+[include 16_in_place_factories.qbk]
+[include 17_gotchas.qbk]
+[include 18_exception_safety.qbk]
+[include 19_type_requirements.qbk]
+[include 1A_on_performance.qbk]
+[endsect]
+[section:reference Reference]
+[include 21_ref_none.qbk]
+[include 22_ref_bad_optional_access.qbk]
+[include 23_ref_optional_io.qbk]
+[include 24_ref_optional_fwd.qbk]
+[section Header <boost/optional/optional.hpp>]
+[include 27_ref_optional_synopsis.qbk]
+[include 28_ref_optional_semantics.qbk]
+[endsect]
+[include 29_ref_optional_convenience.qbk]
+[endsect]
+[include 90_dependencies.qbk]
+[include 91_relnotes.qbk]
+[include 92_acknowledgments.qbk]
+
+
diff --git a/doc/01_quick_start.qbk b/doc/01_quick_start.qbk
new file mode 100644
index 0000000..6bfc398
--- /dev/null
+++ b/doc/01_quick_start.qbk
@@ -0,0 +1,158 @@
+[/
+ Boost.Optional
+
+ Copyright (c) 2003-2007 Fernando Luis Cacciola Carballal
+ Copyright (c) 2014 Andrzej Krzemienski
+
+ Distributed under the Boost Software License, Version 1.0.
+ (See accompanying file LICENSE_1_0.txt or copy at
+ http://www.boost.org/LICENSE_1_0.txt)
+]
+
+
+[section Quick Start]
+
+[section Optional return values]
+
+Let's write and use a converter function that converts a `std::string` to an `int`. It is possible that for a given string (e.g. `"cat"`) there exists no value of type `int` capable of representing the conversion result. We do not consider such situation an error. We expect that the converter can be used only to check if the conversion is possible. A natural signature for this function can be:
+
+ #include <boost/optional.hpp>
+ boost::optional<int> convert(const std::string& text);
+
+All necessary functionality can be included with one header `<boost/optional.hpp>`. The above function signature means that the function can either return a value of type `int` or a flag indicating that no value of `int` is available. This does not indicate an error. It is like one additional value of `int`. This is how we can use our function:
+
+ const std::string& text = /*... */;
+ boost::optional<int> oi = convert(text); // move-construct
+ if (oi) // contextual conversion to bool
+ int i = *oi; // operator*
+
+In order to test if `optional` contains a value, we use the contextual conversion to type `bool`. Because of this we can combine the initialization of the optional object and the test into one instruction:
+
+ if (boost::optional<int> oi = convert(text))
+ int i = *oi;
+
+We extract the contained value with `operator*` (and with `operator->` where it makes sense). An attempt to extract the contained value of an uninitialized optional object is an ['undefined behaviour] (UB). This implementation guards the call with `BOOST_ASSERT`. Therefore you should be sure that the contained value is there before extracting. For instance, the following code is reasonably UB-safe:
+
+ int i = *convert("100");
+
+This is because we know that string value `"100"` converts to a valid value of `int`. If you do not like this potential UB, you can use an alternative way of extracting the contained value:
+
+ try {
+ int j = convert(text).value();
+ }
+ catch (const boost::bad_optional_access&) {
+ // deal with it
+ }
+
+This version throws an exception upon an attempt to access a non-existent contained value. If your way of dealing with the missing value is to use some default, like `0`, there exists a yet another alternative:
+
+ int k = convert(text).value_or(0);
+
+This uses the `atoi`-like approach to conversions: if `text` does not represent an integral number just return `0`. Finally, you can provide a callback to be called when trying to access the contained value fails:
+
+ int fallback_to_default()
+ {
+ cerr << "could not convert; using -1 instead" << endl;
+ return -1;
+ }
+
+ int l = convert(text).value_or_eval(fallback_to_default);
+
+This will call the provided callback and return whatever the callback returns. The callback can have side effects: they will only be observed when the optional object does not contain a value.
+
+Now, let's consider how function `convert` can be implemented.
+
+ boost::optional<int> convert(const std::string& text)
+ {
+ std::stringstream s(text);
+ int i;
+ if ((s >> i) && s.get() == std::char_traits<char>::eof())
+ return i;
+ else
+ return boost::none;
+ }
+
+Observe the two return statements. `return i` uses the converting constructor that can create `optional<T>` from `T`. Thus constructed optional object is initialized and its value is a copy of `i`. The other return statement uses another converting constructor from a special tag `boost::none`. It is used to indicate that we want to create an uninitialized optional object.
+
+[endsect]
+
+[section Optional automatic variables]
+
+We could write function `convert` in a slightly different manner, so that it has a single `return`-statement:
+
+ boost::optional<int> convert(const std::string& text)
+ {
+ boost::optional<int> ans;
+ std::stringstream s(text);
+ int i;
+ if ((s >> i) && s.get() == std::char_traits<char>::eof())
+ ans = i;
+
+ return ans;
+ }
+
+The default constructor of `optional` creates an unitialized optional object. Unlike with `int`s you cannot have an `optional<int>` in an indeterminate state. Its state is always well defined. Instruction `ans = i` initializes the optional object. It uses the 'mixed' assignment from `int`. In general, for `optional<T>`, when an assignment from `T` is invoked, it can do two things. If the optional object is not initialized (our case here), it initializes the contained value using `T`'s copy constructor. If the optional object is already initialized, it assigns the new value to it using `T`'s copy assignment.
+[endsect]
+
+[section Optional data members]
+
+Suppose we want to implement a ['lazy load] optimization. This is because we do not want to perform an expensive initialization of our `Resource` until (if at all) it is really used. We can do it this way:
+
+ class Widget
+ {
+ mutable boost::optional<const Resource> resource_;
+
+ public:
+ Widget() {}
+
+ const Resource& getResource() const // not thread-safe
+ {
+ if (resource_ == boost::none)
+ resource_.emplace("resource", "arguments");
+
+ return *resource_;
+ }
+ };
+
+`optional`'s default constructor creates an uninitialized optional. No call to `Resource`'s default constructor is attempted. `Resource` doesn't have to be __SGI_DEFAULT_CONSTRUCTIBLE__. In function `getResource` we first check if `resource_` is initialized. This time we do not use the contextual conversion to `bool`, but a comparison with `boost::none`. These two ways are equivalent. Function `emplace` initializes the optional in-place by perfect-forwarding the arguments to the constructor of `Resource`. No copy- or move-construction is involved here. `Resource` doesn't even have to be `MoveConstructible`.
+
+[note Function `emplace` is only available on compilers that support rvalue references and variadic templates. If your compiler does not support these features and you still need to avoid any move-constructions, use [link boost_optional.tutorial.in_place_factories In-Place Factories].]
+
+[endsect]
+
+[section Bypassing unnecessary default construction]
+
+Suppose we have class `Date`, which does not have a default constructor: there is no good candidate for a default date. We have a function that returns two dates in form of a `boost::tuple`:
+
+ boost::tuple<Date, Date> getPeriod();
+
+In other place we want to use the result of `getPeriod`, but want the two dates to be named: `begin` and `end`. We want to implement something like 'multiple return values':
+
+ Date begin, end; // Error: no default ctor!
+ boost::tie(begin, end) = getPeriod();
+
+The second line works already, this is the capability of __BOOST_TUPLE__ library, but the first line won't work. We could set some invented initial dates, but it is confusing and may be an unacceptable cost, given that these values will be overwritten in the next line anyway. This is where `optional` can help:
+
+ boost::optional<Date> begin, end;
+ boost::tie(begin, end) = getPeriod();
+
+It works because inside `boost::tie` a move-assignment from `T` is invoked on `optional<T>`, which internally calls a move-constructor of `T`.
+[endsect]
+
+[section Storage in containers]
+
+Suppose you want to ask users to choose some number (an `int`). One of the valid responses is to choose nothing, which is represented by an uninitialized `optional<int>`. You want to make a histogram showing how many times each choice was made. You can use an `std::map`:
+
+ std::map<boost::optional<int>, int> choices;
+
+ for (int i = 0; i < LIMIT; ++i) {
+ boost::optional<int> choice = readChoice();
+ ++choices[choice];
+ }
+
+This works because `optional<T>` is __SGI_LESS_THAN_COMPARABLE__ whenever `T` is __SGI_LESS_THAN_COMPARABLE__. In this case the state of being uninitialized is treated as a yet another value of `T`, which is compared less than any value of `T`.
+[endsect]
+
+[endsect]
+
+
diff --git a/doc/10_motivation.qbk b/doc/10_motivation.qbk
new file mode 100644
index 0000000..fe5b6da
--- /dev/null
+++ b/doc/10_motivation.qbk
@@ -0,0 +1,80 @@
+[/
+ Boost.Optional
+
+ Copyright (c) 2003-2007 Fernando Luis Cacciola Carballal
+ Copyright (c) 2014 Andrzej Krzemienski
+
+ Distributed under the Boost Software License, Version 1.0.
+ (See accompanying file LICENSE_1_0.txt or copy at
+ http://www.boost.org/LICENSE_1_0.txt)
+]
+
+[section Motivation]
+
+Consider these functions which should return a value but which might not have
+a value to return:
+
+* (A) `double sqrt(double n );`
+* (B) `char get_async_input();`
+* (C) `point polygon::get_any_point_effectively_inside();`
+
+There are different approaches to the issue of not having a value to return.
+
+A typical approach is to consider the existence of a valid return value as a
+postcondition, so that if the function cannot compute the value to return, it
+has either undefined behavior (and can use assert in a debug build) or uses a
+runtime check and throws an exception if the postcondition is violated. This
+is a reasonable choice for example, for function (A), because the lack of a
+proper return value is directly related to an invalid parameter (out of domain
+argument), so it is appropriate to require the callee to supply only parameters
+in a valid domain for execution to continue normally.
+
+However, function (B), because of its asynchronous nature, does not fail just
+because it can't find a value to return; so it is incorrect to consider such
+a situation an error and assert or throw an exception. This function must
+return, and somehow, must tell the callee that it is not returning a meaningful
+value.
+
+A similar situation occurs with function (C): it is conceptually an error to
+ask a ['null-area] polygon to return a point inside itself, but in many
+applications, it is just impractical for performance reasons to treat this as
+an error (because detecting that the polygon has no area might be too expensive
+to be required to be tested previously), and either an arbitrary point
+(typically at infinity) is returned, or some efficient way to tell the callee
+that there is no such point is used.
+
+There are various mechanisms to let functions communicate that the returned
+value is not valid. One such mechanism, which is quite common since it has
+zero or negligible overhead, is to use a special value which is reserved to
+communicate this. Classical examples of such special values are `EOF`,
+`string::npos`, points at infinity, etc...
+
+When those values exist, i.e. the return type can hold all meaningful values
+['plus] the ['signal] value, this mechanism is quite appropriate and well known.
+Unfortunately, there are cases when such values do not exist. In these cases,
+the usual alternative is either to use a wider type, such as `int` in place of
+`char`; or a compound type, such as `std::pair<point,bool>`.
+
+Returning a `std::pair<T,bool>`, thus attaching a boolean flag to the result
+which indicates if the result is meaningful, has the advantage that can be
+turned into a consistent idiom since the first element of the pair can be
+whatever the function would conceptually return. For example, the last two
+functions could have the following interface:
+
+ std::pair<char,bool> get_async_input();
+ std::pair<point,bool> polygon::get_any_point_effectively_inside();
+
+These functions use a consistent interface for dealing with possibly nonexistent
+results:
+
+ std::pair<point,bool> p = poly.get_any_point_effectively_inside();
+ if ( p.second )
+ flood_fill(p.first);
+
+However, not only is this quite a burden syntactically, it is also error prone
+since the user can easily use the function result (first element of the pair)
+without ever checking if it has a valid value.
+
+Clearly, we need a better idiom.
+
+[endsect]
diff --git a/doc/11_development.qbk b/doc/11_development.qbk
new file mode 100644
index 0000000..de5d00d
--- /dev/null
+++ b/doc/11_development.qbk
@@ -0,0 +1,251 @@
+[/
+ Boost.Optional
+
+ Copyright (c) 2003-2007 Fernando Luis Cacciola Carballal
+
+ Distributed under the Boost Software License, Version 1.0.
+ (See accompanying file LICENSE_1_0.txt or copy at
+ http://www.boost.org/LICENSE_1_0.txt)
+]
+
+[section Design Overview]
+
+[section The models]
+
+In C++, we can ['declare] an object (a variable) of type `T`, and we can give this
+variable an ['initial value] (through an ['initializer]. (cf. 8.5)).
+When a declaration includes a non-empty initializer (an initial value is given),
+it is said that the object has been initialized.
+If the declaration uses an empty initializer (no initial value is given), and
+neither default nor value initialization applies, it is said that the object is
+[*uninitialized]. Its actual value exist but has an ['indeterminate initial value]
+(cf. 8.5/11).
+`optional<T>` intends to formalize the notion of initialization (or lack of it)
+allowing a program to test whether an object has been initialized and stating
+that access to the value of an uninitialized object is undefined behavior. That
+is, when a variable is declared as `optional<T>` and no initial value is given,
+the variable is ['formally] uninitialized. A formally uninitialized optional object
+has conceptually no value at all and this situation can be tested at runtime. It
+is formally ['undefined behavior] to try to access the value of an uninitialized
+optional. An uninitialized optional can be assigned a value, in which case its initialization state changes to initialized. Furthermore, given the formal
+treatment of initialization states in optional objects, it is even possible to
+reset an optional to ['uninitialized].
+
+In C++ there is no formal notion of uninitialized objects, which means that
+objects always have an initial value even if indeterminate.
+As discussed on the previous section, this has a drawback because you need
+additional information to tell if an object has been effectively initialized.
+One of the typical ways in which this has been historically dealt with is via
+a special value: `EOF`, `npos`, -1, etc... This is equivalent to adding the
+special value to the set of possible values of a given type. This super set of
+`T` plus some ['nil_t]—where `nil_t` is some stateless POD—can be modeled in modern
+languages as a [*discriminated union] of T and nil_t. Discriminated unions are
+often called ['variants]. A variant has a ['current type], which in our case is either
+`T` or `nil_t`.
+Using the __BOOST_VARIANT__ library, this model can be implemented in terms of `boost::variant<T,nil_t>`.
+There is precedent for a discriminated union as a model for an optional value:
+the __HASKELL__ [*Maybe] built-in type constructor. Thus, a discriminated union
+`T+nil_t` serves as a conceptual foundation.
+
+A `variant<T,nil_t>` follows naturally from the traditional idiom of extending
+the range of possible values adding an additional sentinel value with the
+special meaning of ['Nothing]. However, this additional ['Nothing] value is largely
+irrelevant for our purpose since our goal is to formalize the notion of
+uninitialized objects and, while a special extended value can be used to convey
+that meaning, it is not strictly necessary in order to do so.
+
+The observation made in the last paragraph about the irrelevant nature of the
+additional `nil_t` with respect to [_purpose] of `optional<T>` suggests an
+alternative model: a ['container] that either has a value of `T` or nothing.
+
+As of this writing I don't know of any precedent for a variable-size
+fixed-capacity (of 1) stack-based container model for optional values, yet I
+believe this is the consequence of the lack of practical implementations of
+such a container rather than an inherent shortcoming of the container model.
+
+In any event, both the discriminated-union or the single-element container
+models serve as a conceptual ground for a class representing optional—i.e.
+possibly uninitialized—objects.
+For instance, these models show the ['exact] semantics required for a wrapper
+of optional values:
+
+Discriminated-union:
+
+* [*deep-copy] semantics: copies of the variant implies copies of the value.
+* [*deep-relational] semantics: comparisons between variants matches both
+current types and values
+* If the variant's current type is `T`, it is modeling an ['initialized] optional.
+* If the variant's current type is not `T`, it is modeling an ['uninitialized]
+optional.
+* Testing if the variant's current type is `T` models testing if the optional
+is initialized
+* Trying to extract a `T` from a variant when its current type is not `T`, models
+the undefined behavior of trying to access the value of an uninitialized optional
+
+Single-element container:
+
+* [*deep-copy] semantics: copies of the container implies copies of the value.
+* [*deep-relational] semantics: comparisons between containers compare container
+size and if match, contained value
+* If the container is not empty (contains an object of type `T`), it is modeling
+an ['initialized] optional.
+* If the container is empty, it is modeling an ['uninitialized] optional.
+* Testing if the container is empty models testing if the optional is
+initialized
+* Trying to extract a `T` from an empty container models the undefined behavior
+of trying to access the value of an uninitialized optional
+
+[endsect]
+
+[section The semantics]
+
+Objects of type `optional<T>` are intended to be used in places where objects of
+type `T` would but which might be uninitialized. Hence, `optional<T>`'s purpose is
+to formalize the additional possibly uninitialized state.
+From the perspective of this role, `optional<T>` can have the same operational
+semantics of `T` plus the additional semantics corresponding to this special
+state.
+As such, `optional<T>` could be thought of as a ['supertype] of `T`. Of course, we
+can't do that in C++, so we need to compose the desired semantics using a
+different mechanism.
+Doing it the other way around, that is, making `optional<T>` a ['subtype] of `T`
+is not only conceptually wrong but also impractical: it is not allowed to
+derive from a non-class type, such as a built-in type.
+
+We can draw from the purpose of `optional<T>` the required basic semantics:
+
+* [*Default Construction:] To introduce a formally uninitialized wrapped
+object.
+* [*Direct Value Construction via copy:] To introduce a formally initialized
+wrapped object whose value is obtained as a copy of some object.
+* [*Deep Copy Construction:] To obtain a new yet equivalent wrapped object.
+* [*Direct Value Assignment (upon initialized):] To assign a value to the
+wrapped object.
+* [*Direct Value Assignment (upon uninitialized):] To initialize the wrapped
+object with a value obtained as a copy of some object.
+* [*Assignment (upon initialized):] To assign to the wrapped object the value
+of another wrapped object.
+* [*Assignment (upon uninitialized):] To initialize the wrapped object with
+value of another wrapped object.
+* [*Deep Relational Operations (when supported by the type T):] To compare
+wrapped object values taking into account the presence of uninitialized states.
+* [*Value access:] To unwrap the wrapped object.
+* [*Initialization state query:] To determine if the object is formally
+initialized or not.
+* [*Swap:] To exchange wrapped objects. (with whatever exception safety
+guarantees are provided by `T`'s swap).
+* [*De-initialization:] To release the wrapped object (if any) and leave the
+wrapper in the uninitialized state.
+
+Additional operations are useful, such as converting constructors and
+converting assignments, in-place construction and assignment, and safe
+value access via a pointer to the wrapped object or null.
+
+[endsect]
+
+[section The Interface]
+
+Since the purpose of optional is to allow us to use objects with a formal
+uninitialized additional state, the interface could try to follow the
+interface of the underlying `T` type as much as possible. In order to choose
+the proper degree of adoption of the native `T` interface, the following must
+be noted: Even if all the operations supported by an instance of type `T` are
+defined for the entire range of values for such a type, an `optional<T>`
+extends such a set of values with a new value for which most
+(otherwise valid) operations are not defined in terms of `T`.
+
+Furthermore, since `optional<T>` itself is merely a `T` wrapper (modeling a `T`
+supertype), any attempt to define such operations upon uninitialized optionals
+will be totally artificial w.r.t. `T`.
+
+This library chooses an interface which follows from `T`'s interface only for
+those operations which are well defined (w.r.t the type `T`) even if any of the
+operands are uninitialized. These operations include: construction,
+copy-construction, assignment, swap and relational operations.
+
+For the value access operations, which are undefined (w.r.t the type `T`) when
+the operand is uninitialized, a different interface is chosen (which will be
+explained next).
+
+Also, the presence of the possibly uninitialized state requires additional
+operations not provided by `T` itself which are supported by a special interface.
+
+[heading Lexically-hinted Value Access in the presence of possibly
+uninitialized optional objects: The operators * and ->]
+
+A relevant feature of a pointer is that it can have a [*null pointer value].
+This is a ['special] value which is used to indicate that the pointer is not
+referring to any object at all. In other words, null pointer values convey
+the notion of nonexistent objects.
+
+This meaning of the null pointer value allowed pointers to became a ['de
+facto] standard for handling optional objects because all you have to do
+to refer to a value which you don't really have is to use a null pointer
+value of the appropriate type. Pointers have been used for decades—from
+the days of C APIs to modern C++ libraries—to ['refer] to optional (that is,
+possibly nonexistent) objects; particularly as optional arguments to a
+function, but also quite often as optional data members.
+
+The possible presence of a null pointer value makes the operations that
+access the pointee's value possibly undefined, therefore, expressions which
+use dereference and access operators, such as: `( *p = 2 )` and `( p->foo() )`,
+implicitly convey the notion of optionality, and this information is tied to
+the ['syntax] of the expressions. That is, the presence of operators `*` and `->`
+tell by themselves —without any additional context— that the expression will
+be undefined unless the implied pointee actually exist.
+
+Such a ['de facto] idiom for referring to optional objects can be formalized
+in the form of a concept: the __OPTIONAL_POINTEE__ concept.
+This concept captures the syntactic usage of operators `*`, `->` and
+contextual conversion to `bool` to convey the notion of optionality.
+
+However, pointers are good to [_refer] to optional objects, but not particularly
+good to handle the optional objects in all other respects, such as initializing
+or moving/copying them. The problem resides in the shallow-copy of pointer
+semantics: if you need to effectively move or copy the object, pointers alone
+are not enough. The problem is that copies of pointers do not imply copies of
+pointees. For example, as was discussed in the motivation, pointers alone
+cannot be used to return optional objects from a function because the object
+must move outside from the function and into the caller's context.
+
+A solution to the shallow-copy problem that is often used is to resort to
+dynamic allocation and use a smart pointer to automatically handle the details
+of this. For example, if a function is to optionally return an object `X`, it can
+use `shared_ptr<X>` as the return value. However, this requires dynamic allocation
+of `X`. If `X` is a built-in or small POD, this technique is very poor in terms of
+required resources. Optional objects are essentially values so it is very
+convenient to be able to use automatic storage and deep-copy semantics to
+manipulate optional values just as we do with ordinary values. Pointers do
+not have this semantics, so are inappropriate for the initialization and
+transport of optional values, yet are quite convenient for handling the access
+to the possible undefined value because of the idiomatic aid present in the
+__OPTIONAL_POINTEE__ concept incarnated by pointers.
+
+
+[heading Optional<T> as a model of OptionalPointee]
+
+For value access operations `optional<>` uses operators `*` and `->` to
+lexically warn about the possibly uninitialized state appealing to the
+familiar pointer semantics w.r.t. to null pointers.
+
+[caution
+However, it is particularly important to note that `optional<>` objects
+are not pointers. [_`optional<>` is not, and does not model, a pointer].
+]
+
+For instance, `optional<>` does not have shallow-copy so does not alias:
+two different optionals never refer to the ['same] value unless `T` itself is
+a reference (but may have ['equivalent] values).
+The difference between an `optional<T>` and a pointer must be kept in mind,
+particularly because the semantics of relational operators are different:
+since `optional<T>` is a value-wrapper, relational operators are deep: they
+compare optional values; but relational operators for pointers are shallow:
+they do not compare pointee values.
+As a result, you might be able to replace `optional<T>` by `T*` on some
+situations but not always. Specifically, on generic code written for both,
+you cannot use relational operators directly, and must use the template
+functions __FUNCTION_EQUAL_POINTEES__ and __FUNCTION_LESS_POINTEES__ instead.
+
+[endsect]
+
+[endsect]
diff --git a/doc/12_when_to_use.qbk b/doc/12_when_to_use.qbk
new file mode 100644
index 0000000..80dff54
--- /dev/null
+++ b/doc/12_when_to_use.qbk
@@ -0,0 +1,37 @@
+
+[section When to use Optional]
+
+It is recommended to use `optional<T>` in situations where there is exactly one, clear (to all parties) reason for having no value of type `T`, and where the lack of value is as natural as having any regular value of `T`. One example of such situation is asking the user in some GUI form to optionally specify some limit on an `int` value, but the user is allowed to say 'I want the number not to be constrained by the maximum'.
+For another example, consider a config parameter specifying how many threads the application should launch. Leaving this parameter unspecified means that the application should decide itself. For yet another example, consider a function returning the index of the smallest element in a `vector`. We need to be prepared for the situation, where the `vector` is empty. Therefore a natural signature for such function would be:
+
+ template <typename T>
+ optional<size_t> find_smallest_elem(const std::vector<T>& vec);
+
+Here, having received an empty `vec` and having no `size_t` to return is not a ['failure] but a ['normal], albeit irregular, situation.
+
+Another typical situation is to indicate that we do not have a value yet, but we expect to have it later. This notion can be used in implementing solutions like lazy initialization or a two-phase initialization.
+
+`optional` can be used to take a non-__SGI_DEFAULT_CONSTRUCTIBLE__ type `T` and create a sibling type with a default constructor. This is a way to add a ['null-state] to any type that doesn't have it already.
+
+Sometimes type `T` already provides a built-in null-state, but it may still be useful to wrap it into `optional`. Consider `std::string`. When you read a piece of text from a GUI form or a DB table, it is hardly ever that the empty string indicates anything else but a missing text. And some data bases do not even distinguish between a null string entry and a non-null string of length 0. Still, it may be practical to use `optional<string>` to indicate in the returned type that we want to treat the empty string in a special dedicated program path:
+
+ if(boost::optional<std::string> name = ask_user_name()) {
+ assert(*name != "");
+ logon_as(*name);
+ }
+ else {
+ skip_logon();
+ }
+
+In the example above, the assertion indicates that if we choose to use this technique, we must translate the empty string state to an optional object with no contained value (inside function `ask_user_name`).
+
+[heading Not recommended usages]
+
+It is not recommended to use `optional` to indicate that we were not able to compute a value because of a ['failure]. It is difficult to define what a failure is, but it usually has one common characteristic: an associated information on the cause of the failure. This can be the type and member data of an exception object, or an error code. It is a bad design to signal a failure and not inform about the cause. If you do not want to use exceptions, and do not like the fact that by returning error codes you cannot return the computed value, you can use [@https://github.com/ptal/Boost.Expected Expected] library. It is sort of __BOOST_VARIANT__ that contains either a computed value or a reason why the computation failed.
+
+Sometimes the distinction into what is a failure and what is a valid but irregular result is blurry and depends on a particular usage and personal preference. Consider a function that converts a `string` to an `int`. Is it a failure that you cannot convert? It might in some cases, but in other you may call it exactly for the purpose of figuring out if a given `string` is convertible, and you are not even interested in the resulting value. Sometimes when a conversion fails you may not consider it a failure, but you need to know why it cannot be converted; for instance at which character it is determined that the conversion is impossible. In this case returning `optional<T>` will not suffice. Finally, there is a use case where an input string that does not represent an `int` is not a failure condition, but during the conversion we use resources whose acquisition may fail. In that case the natural representation is to both return `optional<int>` and signal failure:
+
+ optional<int> convert1(const string& str); // throws
+ expected<ErrorT, optional<int>> convert2(const string& str); // return either optional or error
+
+[endsect]
diff --git a/doc/13_relational_operators.qbk b/doc/13_relational_operators.qbk
new file mode 100644
index 0000000..861a4e8
--- /dev/null
+++ b/doc/13_relational_operators.qbk
@@ -0,0 +1,37 @@
+
+[section Relational operators]
+
+Type `optional<T>` is __SGI_EQUALITY_COMPARABLE__ whenever `T` is __SGI_EQUALITY_COMPARABLE__. Two optional objects containing a value compare in the same way as their contained values. The uninitialized state of `optional<T>` is treated as a distinct value, equal to itself, and unequal to any value of type `T`:
+
+ boost::optional<int> oN = boost::none;
+ boost::optional<int> o0 = 0;
+ boost::optional<int> o1 = 1;
+
+ assert(oN != o0);
+ assert(o1 != oN);
+ assert(o0 != o1);
+ assert(oN == oN);
+ assert(o0 == o0);
+
+The converting constructor from `T` as well as from `boost::none` implies the existence and semantics of the mixed comparison between `T` and `optional<T>` as well as between `none_t` and `optionl<T>`:
+
+ assert(oN != 0);
+ assert(o1 != boost::none);
+ assert(o0 != 1);
+ assert(oN == boost::none);
+ assert(o0 == 0);
+
+This mixed comparison has a practical interpretation, which is occasionally useful:
+
+ boost::optional<int> choice = ask_user();
+ if (choice == 2)
+ start_procedure_2();
+
+In the above example, the meaning of the comparison is 'user chose number 2'. If user chose nothing, he didn't choose number 2.
+
+In case where `optional<T>` is compared to `none`, it is not required that `T` be __SGI_EQUALITY_COMPARABLE__.
+
+In a similar manner, type `optional<T>` is __SGI_LESS_THAN_COMPARABLE__ whenever `T` is __SGI_LESS_THAN_COMPARABLE__. The optional object containing no value is compared less than any value of `T`. To illustrate this, if the default ordering of `size_t` is {`0`, `1`, `2`, ...}, the default ordering of `optional<size_t>` is {`boost::none`, `0`, `1`, `2`, ...}. This order does not have a practical interpretation. The goal is to have any semantically correct default ordering in order for `optional<T>` to be usable in ordered associative containers (wherever `T` is usable).
+
+Mixed relational operators are the only case where the contained value of an optional object can be inspected without the usage of value accessing function (`operator*`, `value`, `value_or`).
+[endsect]
diff --git a/doc/14_io.qbk b/doc/14_io.qbk
new file mode 100644
index 0000000..0fb4e89
--- /dev/null
+++ b/doc/14_io.qbk
@@ -0,0 +1,37 @@
+
+[section IO operators]
+
+It is possible to use `optional<T>` with IO streams, provided that `T` can be used with streams. IOStream operators are defined in a separate header.
+
+``
+#include <iostream>
+#include <boost/optional/optional_io.hpp>
+
+int main()
+{
+ boost::optional<int> o1 = 1, oN = boost::none;
+ std::cout << o1;
+ std::cin >> oN;
+}
+``
+
+The current implementation does not guarantee any particular output. What it guarantees is that if streaming out and then back in `T` gives the same value, then streaming out and then back in `optional<T>` will also give back the same result:
+
+``
+#include <cassert>
+#include <sstream>
+#include <boost/optional/optional_io.hpp>
+
+int main()
+{
+ boost::optional<int> o1 = 1, oN = boost::none;
+ boost::optional<int> x1, x2;
+ std::stringstream s;
+ s << o1 << oN;
+ s >> x1 >> x2;
+ assert (o1 == x1);
+ assert (oN == x2);
+}
+``
+
+[endsect]
diff --git a/doc/15_optional_references.qbk b/doc/15_optional_references.qbk
new file mode 100644
index 0000000..acb1226
--- /dev/null
+++ b/doc/15_optional_references.qbk
@@ -0,0 +1,123 @@
+
+[section Optional references]
+
+[section Overview]
+
+This library allows the template parameter `T` to be of reference type:
+`T&`, and to some extent, `T const&`.
+
+However, since references are not real objects some restrictions apply and
+some operations are not available in this case:
+
+* Converting constructors
+* Converting assignment
+* InPlace construction
+* InPlace assignment
+* Value-access via pointer
+
+Also, even though `optional<T&>` treats it wrapped pseudo-object much as
+a real value, a true real reference is stored so aliasing will ocurr:
+
+* Copies of `optional<T&>` will copy the references but all these references
+will nonetheless refer to the same object.
+* Value-access will actually provide access to the referenced object
+rather than the reference itself.
+
+[caution On compilers that do not conform to Standard C++ rules of reference binding, some operations on optional references are disabled in order to prevent subtle bugs. For more details see [link boost_optional.dependencies_and_portability.optional_reference_binding Dependencies and Portability section].]
+
+[heading Rvalue references]
+
+Rvalue references and lvalue references to const have the ability in C++ to extend the life time of a temporary they bind to. Optional references do not have this capability, therefore to avoid surprising effects it is not possible to initialize an optional references from a temporary. Optional rvalue references are disabled altogether. Also, the initialization and assignment of an optional reference to const from rvalue reference is disabled.
+
+ const int& i = 1; // legal
+ optional<const int&> oi = 1; // illegal
+
+[endsect]
+
+[section Rebinding semantics for assignment of optional references]
+
+If you assign to an ['uninitialized ] `optional<T&>` the effect is to bind (for
+the first time) to the object. Clearly, there is no other choice.
+
+ int x = 1 ;
+ int& rx = x ;
+ optional<int&> ora ;
+ optional<int&> orb(x) ;
+ ora = orb ; // now 'ora' is bound to 'x' through 'rx'
+ *ora = 2 ; // Changes value of 'x' through 'ora'
+ assert(x==2);
+
+If you assign to a bare C++ reference, the assignment is forwarded to the
+referenced object; its value changes but the reference is never rebound.
+
+ int a = 1 ;
+ int& ra = a ;
+ int b = 2 ;
+ int& rb = b ;
+ ra = rb ; // Changes the value of 'a' to 'b'
+ assert(a==b);
+ b = 3 ;
+ assert(ra!=b); // 'ra' is not rebound to 'b'
+
+Now, if you assign to an ['initialized ] `optional<T&>`, the effect is to
+[*rebind] to the new object instead of assigning the referee. This is unlike
+bare C++ references.
+
+ int a = 1 ;
+ int b = 2 ;
+ int& ra = a ;
+ int& rb = b ;
+ optional<int&> ora(ra) ;
+ optional<int&> orb(rb) ;
+ ora = orb ; // 'ora' is rebound to 'b'
+ *ora = 3 ; // Changes value of 'b' (not 'a')
+ assert(a==1);
+ assert(b==3);
+
+[heading Rationale]
+
+Rebinding semantics for the assignment of ['initialized ] `optional` references has
+been chosen to provide [*consistency among initialization states] even at the
+expense of lack of consistency with the semantics of bare C++ references.
+It is true that `optional<U>` strives to behave as much as possible as `U`
+does whenever it is initialized; but in the case when `U` is `T&`, doing so would
+result in inconsistent behavior w.r.t to the lvalue initialization state.
+
+Imagine `optional<T&>` forwarding assignment to the referenced object (thus
+changing the referenced object value but not rebinding), and consider the
+following code:
+
+ optional<int&> a = get();
+ int x = 1 ;
+ int& rx = x ;
+ optional<int&> b(rx);
+ a = b ;
+
+What does the assignment do?
+
+If `a` is ['uninitialized], the answer is clear: it binds to `x` (we now have
+another reference to `x`).
+But what if `a` is already ['initialized]? it would change the value of the
+referenced object (whatever that is); which is inconsistent with the other
+possible case.
+
+If `optional<T&>` would assign just like `T&` does, you would never be able to
+use Optional's assignment without explicitly handling the previous
+initialization state unless your code is capable of functioning whether
+after the assignment, `a` aliases the same object as `b` or not.
+
+That is, you would have to discriminate in order to be consistent.
+
+If in your code rebinding to another object is not an option, then it is very
+likely that binding for the first time isn't either. In such case, assignment
+to an ['uninitialized ] `optional<T&>` shall be prohibited. It is quite possible
+that in such a scenario it is a precondition that the lvalue must be already
+initialized. If it isn't, then binding for the first time is OK
+while rebinding is not which is IMO very unlikely.
+In such a scenario, you can assign the value itself directly, as in:
+
+ assert(!!opt);
+ *opt=value;
+
+[endsect]
+[endsect]
diff --git a/doc/16_in_place_factories.qbk b/doc/16_in_place_factories.qbk
new file mode 100644
index 0000000..d9df24d
--- /dev/null
+++ b/doc/16_in_place_factories.qbk
@@ -0,0 +1,139 @@
+
+[section In-Place Factories]
+
+One of the typical problems with wrappers and containers is that their
+interfaces usually provide an operation to initialize or assign the
+contained object as a copy of some other object. This not only requires the
+underlying type to be __COPY_CONSTRUCTIBLE__, but also requires the existence of
+a fully constructed object, often temporary, just to follow the copy from:
+
+ struct X
+ {
+ X ( int, std::string ) ;
+ } ;
+
+ class W
+ {
+ X wrapped_ ;
+
+ public:
+
+ W ( X const& x ) : wrapped_(x) {}
+ } ;
+
+ void foo()
+ {
+ // Temporary object created.
+ W ( X(123,"hello") ) ;
+ }
+
+A solution to this problem is to support direct construction of the
+contained object right in the container's storage.
+In this scheme, the user only needs to supply the arguments to the
+constructor to use in the wrapped object construction.
+
+ class W
+ {
+ X wrapped_ ;
+
+ public:
+
+ W ( X const& x ) : wrapped_(x) {}
+ W ( int a0, std::string a1) : wrapped_(a0,a1) {}
+ } ;
+
+ void foo()
+ {
+ // Wrapped object constructed in-place
+ // No temporary created.
+ W (123,"hello") ;
+ }
+
+A limitation of this method is that it doesn't scale well to wrapped
+objects with multiple constructors nor to generic code were the constructor
+overloads are unknown.
+
+The solution presented in this library is the family of [*InPlaceFactories]
+and [*TypedInPlaceFactories].
+These factories are a family of classes which encapsulate an increasing
+number of arbitrary constructor parameters and supply a method to construct
+an object of a given type using those parameters at an address specified by
+the user via placement new.
+
+For example, one member of this family looks like:
+
+ template<class T,class A0, class A1>
+ class TypedInPlaceFactory2
+ {
+ A0 m_a0 ; A1 m_a1 ;
+
+ public:
+
+ TypedInPlaceFactory2( A0 const& a0, A1 const& a1 ) : m_a0(a0), m_a1(a1) {}
+
+ void construct ( void* p ) { new (p) T(m_a0,m_a1) ; }
+ } ;
+
+A wrapper class aware of this can use it as:
+
+ class W
+ {
+ X wrapped_ ;
+
+ public:
+
+ W ( X const& x ) : wrapped_(x) {}
+ W ( TypedInPlaceFactory2 const& fac ) { fac.construct(&wrapped_) ; }
+ } ;
+
+ void foo()
+ {
+ // Wrapped object constructed in-place via a TypedInPlaceFactory.
+ // No temporary created.
+ W ( TypedInPlaceFactory2<X,int,std::string>(123,"hello")) ;
+ }
+
+The factories are divided in two groups:
+
+* [_TypedInPlaceFactories]: those which take the target type as a primary
+template parameter.
+* [_InPlaceFactories]: those with a template `construct(void*)` member
+function taking the target type.
+
+Within each group, all the family members differ only in the number of
+parameters allowed.
+
+This library provides an overloaded set of helper template functions to
+construct these factories without requiring unnecessary template parameters:
+
+ template<class A0,...,class AN>
+ InPlaceFactoryN <A0,...,AN> in_place ( A0 const& a0, ..., AN const& aN) ;
+
+ template<class T,class A0,...,class AN>
+ TypedInPlaceFactoryN <T,A0,...,AN> in_place ( T const& a0, A0 const& a0, ..., AN const& aN) ;
+
+In-place factories can be used generically by the wrapper and user as follows:
+
+ class W
+ {
+ X wrapped_ ;
+
+ public:
+
+ W ( X const& x ) : wrapped_(x) {}
+
+ template< class InPlaceFactory >
+ W ( InPlaceFactory const& fac ) { fac.template <X>construct(&wrapped_) ; }
+
+ } ;
+
+ void foo()
+ {
+ // Wrapped object constructed in-place via a InPlaceFactory.
+ // No temporary created.
+ W ( in_place(123,"hello") ) ;
+ }
+
+The factories are implemented in the headers: __IN_PLACE_FACTORY_HPP__ and __TYPED_IN_PLACE_FACTORY_HPP__
+
+[endsect]
diff --git a/doc/17_gotchas.qbk b/doc/17_gotchas.qbk
new file mode 100644
index 0000000..5cfa36b
--- /dev/null
+++ b/doc/17_gotchas.qbk
@@ -0,0 +1,111 @@
+[section Gotchas]
+
+[section A note about optional<bool>]
+
+`optional<bool>` should be used with special caution and consideration.
+
+First, it is functionally similar to a tristate boolean (false, maybe, true)
+—such as __BOOST_TRIBOOL__— except that in a tristate boolean, the maybe state
+[_represents a valid value], unlike the corresponding state of an uninitialized
+`optional<bool>`.
+It should be carefully considered if an `optional<bool>` instead of a `tribool`
+is really needed.
+
+Second, although `optional<>` provides a contextual conversion to `bool` in C++11,
+ this falls back to an implicit conversion on older compilers. This conversion refers
+ to the initialization state and not to the contained value. Using `optional<bool>`
+ can lead to subtle errors due to the implicit `bool` conversion:
+
+ void foo ( bool v ) ;
+ void bar()
+ {
+ optional<bool> v = try();
+
+ // The following intended to pass the value of 'v' to foo():
+ foo(v);
+ // But instead, the initialization state is passed
+ // due to a typo: it should have been foo(*v).
+ }
+
+The only implicit conversion is to `bool`, and it is safe in the sense that
+typical integral promotions don't apply (i.e. if `foo()` takes an `int`
+instead, it won't compile).
+
+Third, mixed comparisons with `bool` work differently than similar mixed comparisons between pointers and `bool`, so the results might surprise you:
+
+ optional<bool> oEmpty(none), oTrue(true), oFalse(false);
+
+ if (oEmpty == none); // renders true
+ if (oEmpty == false); // renders false!
+ if (oEmpty == true); // renders false!
+
+ if (oFalse == none); // renders false
+ if (oFalse == false); // renders true!
+ if (oFalse == true); // renders false
+
+ if (oTrue == none); // renders false
+ if (oTrue == false); // renders false
+ if (oTrue == true); // renders true
+
+In other words, for `optional<>`, the following assertion does not hold:
+
+ assert((opt == false) == (!opt));
+[endsect]
+
+[section Moved-from `optional`]
+
+When an optional object that contains a value is moved from (is a source of move constructor or assignment) it still contains a value and its contained value is left in a moved-from state. This can be illustrated with the following example.
+
+ optional<std::unique_ptr<int>> opi {std::make_unique<int>(1)};
+ optional<std::unique_ptr<int>> opj = std::move(opi);
+ assert (opi);
+ assert (*opi == nullptr);
+
+Quite a lot of people expect that when an object that contains a value is moved from, its contained value should be destroyed. This is not so, for performance reasons. Current semantics allow the implementation of `boost::opiotnal<T>` to be trivially copyable when `T` is trivial.
+[endsect]
+
+[section Mixed relational comparisons]
+
+Because `T` is convertible to `optional<T>` and because `opiotnal<T>` is __SGI_LESS_THAN_COMPARABLE__ when `T` is __SGI_LESS_THAN_COMPARABLE__,
+you can sometimes get an unexpected runtime result where you would rather expect a compiler error:
+
+ optional<double> Flight_plan::weight(); // sometimes no weight can be returned
+
+ bool is_aircraft_too_heavy(Flight_plan const& p)
+ {
+ return p.weight() > p.aircraft().max_weight(); // compiles!
+ } // returns false when the optional contains no value
+
+[endsect]
+
+[section False positive with -Wmaybe-uninitialized]
+
+Sometimes on GCC compilers below version 5.1 you may get an -Wmaybe-uninitialized warning when copiling with option -02 on a perfectly valid `boost::optional` usage. For instance in this program:
+
+ #include <boost/optional.hpp>
+
+ boost::optional<int> getitem();
+
+ int main(int argc, const char *[])
+ {
+ boost::optional<int> a = getitem();
+ boost::optional<int> b;
+
+ if (argc > 0)
+ b = argc;
+
+ if (a != b)
+ return 1;
+
+ return 0;
+ }
+
+This is a bug in the compiler. As a workaround (provided in [@http://stackoverflow.com/questions/21755206/how-to-get-around-gcc-void-b-4-may-be-used-uninitialized-in-this-funct this Stack Overflow question]) use the following way of initializing an optional containing no value:
+
+ boost::optional<int> b = boost::make_optional(false, int());
+
+This is obviously redundant, but makes the warning disappear.
+
+[endsect]
+
+[endsect]
\ No newline at end of file
diff --git a/doc/18_exception_safety.qbk b/doc/18_exception_safety.qbk
new file mode 100644
index 0000000..331104b
--- /dev/null
+++ b/doc/18_exception_safety.qbk
@@ -0,0 +1,57 @@
+
+[section Exception Safety Guarantees]
+
+This library assumes that `T`'s destructor does not throw exceptions. If it does, the behaviour of many operations on `optional<T>` is undefined.
+
+The following mutating operations never throw exceptions:
+
+* `optional<T>::operator= ( none_t ) noexcept`
+* `optional<T>::reset() noexcept`
+
+In addition, the following constructors and the destructor never throw exceptions:
+
+* `optional<T>::optional() noexcept`
+* `optional<T>::optional( none_t ) noexcept`
+
+
+Regarding the following assignment functions:
+
+* `optional<T>::operator= ( optional<T> const& )`
+* `optional<T>::operator= ( T const& )`
+* `template<class U> optional<T>::operator= ( optional<U> const& )`
+* `template<class InPlaceFactory> optional<T>::operator= ( InPlaceFactory const& )`
+* `template<class TypedInPlaceFactory> optional<T>::operator= ( TypedInPlaceFactory const& ) `
+* `optional<T>::reset( T const& )`
+
+They forward calls to the corresponding `T`'s constructors or assignments (depending on whether the optional object is initialized or not); so if both `T`'s constructor and the assignment provide strong exception safety guarantee, `optional<T>`'s assignment also provides strong exception safety guarantee; otherwise we only get the basic guarantee. Additionally, if both involved `T`'s constructor and the assignment never throw, `optional<T>`'s assignment also never throws.
+
+Unless `T`'s constructor or assignment throws, assignments to `optional<T>` do not throw anything else on its own. A throw during assignment never changes the initialization state of any optional object involved:
+
+
+ optional<T> opt1(val1);
+ optional<T> opt2(val2);
+ assert(opt1);
+ assert(opt2);
+
+ try
+ {
+ opt1 = opt2; // throws
+ }
+ catch(...)
+ {
+ assert(opt1);
+ assert(opt2);
+ }
+
+This also applies to move assignments/constructors. However, move operations are made no-throw more often.
+
+Operation `emplace` provides basic exception safety guarantee. If it throws, the optional object becomes uninitialized regardless of its initial state, and its previous contained value (if any) is destroyed. It doesn't call any assignment or move/copy constructor on `T`.
+
+[heading Swap]
+
+Unless `swap` on optional is customized, its primary implementation forwards calls to `T`'s `swap` or move constructor (depending on the initialization state of the optional objects). Thus, if both `T`'s `swap` and move constructor never throw, `swap` on `optional<T>` never throws. similarly, if both `T`'s `swap` and move constructor offer strong guarantee, `swap` on `optional<T>` also offers a strong guarantee.
+
+In case `swap` on optional is customized, the call to `T`'s move constructor are replaced with the calls to `T`'s default constructor followed by `swap`. (This is more useful on older compilers that do not support move semantics, when one wants to acheive stronger exception safety guarantees.) In this case the exception safety guarantees for `swap` are reliant on the guarantees of `T`'s `swap` and default constructor
+[endsect]
+
+
diff --git a/doc/19_type_requirements.qbk b/doc/19_type_requirements.qbk
new file mode 100644
index 0000000..033a6eb
--- /dev/null
+++ b/doc/19_type_requirements.qbk
@@ -0,0 +1,38 @@
+
+[section Type requirements]
+
+The very minimum requirement of `optional<T>` is that `T` is a complete type and that it has a publicly accessible destructor. `T` doesn't even need to be constructible. You can use a very minimum interface:
+
+ optional<T> o; // uninitialized
+ assert(o == none); // check if initialized
+ assert(!o); //
+ o.value(); // always throws
+
+But this is practically useless. In order for `optional<T>` to be able to do anything useful and offer all the spectrum of ways of accessing the contained value, `T` needs to have at least one accessible constructor. In that case you need to initialize the optional object with function `emplace()`, or if your compiler does not support it, resort to [link boost_optional.tutorial.in_place_factories In-Place Factories]:
+
+ optional<T> o;
+ o.emplace("T", "ctor", "params");
+
+If `T` is __MOVE_CONSTRUCTIBLE__, `optional<T>` is also __MOVE_CONSTRUCTIBLE__ and can be easily initialized from an rvalue of type `T` and be passed by value:
+
+ optional<T> o = make_T();
+ optional<T> p = optional<T>();
+
+If `T` is __COPY_CONSTRUCTIBLE__, `optional<T>` is also __COPY_CONSTRUCTIBLE__ and can be easily initialized from an lvalue of type `T`:
+
+ T v = make_T();
+ optional<T> o = v;
+ optional<T> p = o;
+
+If `T` is not `MoveAssignable`, it is still possible to reset the value of `optional<T>` using function `emplace()`:
+
+ optional<const T> o = make_T();
+ o.emplace(make_another_T());
+
+If `T` is `Moveable` (both __MOVE_CONSTRUCTIBLE__ and `MoveAssignable`) then `optional<T>` is also `Moveable` and additionally can be constructed and assigned from an rvalue of type `T`.
+
+Similarly, if `T` is `Copyable` (both __COPY_CONSTRUCTIBLE__ and `CopyAssignable`) then `optional<T>` is also `Copyable` and additionally can be constructed and assigned from an lvalue of type `T`.
+
+`T` ['is not] required to be __SGI_DEFAULT_CONSTRUCTIBLE__.
+
+[endsect]
diff --git a/doc/1A_on_performance.qbk b/doc/1A_on_performance.qbk
new file mode 100644
index 0000000..968b18f
--- /dev/null
+++ b/doc/1A_on_performance.qbk
@@ -0,0 +1,156 @@
+
+[section Performance considerations]
+
+Technical details aside, the memory layout of `optional<T>` for a generic `T` is more-less this:
+
+ template <typename T>
+ class optional
+ {
+ bool _initialized;
+ std::aligned_storage_t<sizeof(t), alignof(T)> _storage;
+ };
+
+Lifetime of the `T` inside `_storage` is manually controlled with placement-`new`s and pseudo-destructor calls. However, for scalar `T`s we use a different way of storage, by simply holding a `T`:
+
+ template <typename T>
+ class optional
+ {
+ bool _initialized;
+ T _storage;
+ };
+
+We call it a ['direct] storage. This makes `optional<T>` a trivially-copyable type for scalar `T`s. This only works for compilers that support defaulted functions (including defaulted move assignment and constructor). On compilers without defaulted functions we still use the direct storage, but `optional<T>` is no longer recognized as trivially-copyable. Apart from scalar types, we leave the programmer a way of customizing her type, so that it is reconized by `optional` as candidate for optimized storage, by specializing type trait `boost::opitonal_config::optional_uses_direct_storage_for`:
+
+ struct X // not trivial
+ {
+ X() {}
+ };
+
+ namespace boost { namespace optional_config {
+
+ template <> struct optional_uses_direct_storage_for<X> : boost::true_type {};
+
+ }}
+
+
+[heading Controlling the size]
+
+For the purpose of the following analysis, considering memory layouts, we can think of it as:
+
+ template <typename T>
+ class optional
+ {
+ bool _initialized;
+ T _storage;
+ };
+
+Given type `optional<int>`, and assuming that `sizeof(int) == 4`, we will get `sizeof(optional<int>) == 8`. This is so because of the alignment rules, for our two members we get the following alignment:
+
+[$images/opt_align1.png]
+
+This means you can fit twice as many `int`s as `optional<int>`s into the same space of memory. Therefore, if the size of the objects is critical for your application (e.g., because you want to utilize your CPU cache in order to gain performance) and you have determined you are willing to trade the code clarity, it is recommended that you simply go with type `int` and use some 'magic value' to represent ['not-an-int], or use something like [@https://github.com/akrzemi1/markable `markable`] library.
+
+Even if you cannot spare any value of `int` to represent ['not-an-int] (e.g., because every value is useful, or you do want to signal ['not-an-int] explicitly), at least for `Trivial` types you should consider storing the value and the `bool` flag representing the ['null-state] separately. Consider the following class:
+
+ struct Record
+ {
+ optional<int> _min;
+ optional<int> _max;
+ };
+
+Its memory layout can be depicted as follows:
+
+[$images/opt_align2.png]
+
+This is exactly the same as if we had the following members:
+
+ struct Record
+ {
+ bool _has_min;
+ int _min;
+ bool _has_max;
+ int _max;
+ };
+
+But when they are stored separately, we at least have an option to reorder them like this:
+
+ struct Record
+ {
+ bool _has_min;
+ bool _has_max;
+ int _min;
+ int _max;
+ };
+
+Which gives us the following layout (and smaller total size):
+
+[$images/opt_align3.png]
+
+Sometimes it requires detailed consideration what data we make optional. In our case above, if we determine that both minimum and maximum value can be provided or not provided together, but one is never provided without the other, we can make only one optional memebr:
+
+ struct Limits
+ {
+ int _min;
+ int _max;
+ };
+
+ struct Record
+ {
+ optional<Limits> _limits;
+ };
+
+This would give us the following layout:
+
+[$images/opt_align4.png]
+
+[heading Optional function parameters]
+
+Having function parameters of type `const optional<T>&` may incur certain unexpected run-time cost connected to copy construction of `T`. Consider the following code.
+
+ void fun(const optional<Big>& v)
+ {
+ if (v) doSomethingWith(*v);
+ else doSomethingElse();
+ }
+
+ int main()
+ {
+ optional<Big> ov;
+ Big v;
+ fun(none);
+ fun(ov); // no copy
+ fun(v); // copy constructor of Big
+ }
+
+No copy elision or move semantics can save us from copying type `Big` here. Not that we need any copy, but this is how `optional` works. In order to avoid copying in this case, one could provide second overload of `fun`:
+
+ void fun(const Big& v)
+ {
+ doSomethingWith(v);
+ }
+
+ int main()
+ {
+ optional<Big> ov;
+ Big v;
+ fun(ov); // no copy
+ fun(v); // no copy: second overload selected
+ }
+
+Alternatively, you could consider using an optional reference instead:
+
+ void fun(optional<const Big&> v) // note where the reference is
+ {
+ if (v) doSomethingWith(*v);
+ else doSomethingElse();
+ }
+
+ int main()
+ {
+ optional<Big> ov;
+ Big v;
+ fun(none);
+ fun(ov); // doesn't compile
+ fun(v); // no copy
+ }
+[endsect]
diff --git a/doc/21_ref_none.qbk b/doc/21_ref_none.qbk
new file mode 100644
index 0000000..011eff7
--- /dev/null
+++ b/doc/21_ref_none.qbk
@@ -0,0 +1,31 @@
+[/
+ Boost.Optional
+
+ Copyright (c) 2003-2007 Fernando Luis Cacciola Carballal
+ Copyright (c) 2015 Andrzej Krzemienski
+
+ Distributed under the Boost Software License, Version 1.0.
+ (See accompanying file LICENSE_1_0.txt or copy at
+ http://www.boost.org/LICENSE_1_0.txt)
+]
+
+[section Header <boost/none.hpp>]
+
+[section Synopsis]
+```
+namespace boost {
+
+class none_t {/* see below */};
+
+const none_t none (/* see below */);
+
+} // namespace boost
+```
+
+Class `none_t` is meant to serve as a tag for selecting appropriate overloads of from `optional`'s interface. It is an empty, trivially copyable class with disabled default constructor.
+
+Constant `none` is used to indicate an optional object that does not contain a value in initialization, assignment and relational operations of `optional`.
+
+[endsect]
+
+[endsect]
diff --git a/doc/22_ref_bad_optional_access.qbk b/doc/22_ref_bad_optional_access.qbk
new file mode 100644
index 0000000..e929134
--- /dev/null
+++ b/doc/22_ref_bad_optional_access.qbk
@@ -0,0 +1,40 @@
+[/
+ Boost.Optional
+
+ Copyright (c) 2003-2007 Fernando Luis Cacciola Carballal
+ Copyright (c) 2015 Andrzej Krzemienski
+
+ Distributed under the Boost Software License, Version 1.0.
+ (See accompanying file LICENSE_1_0.txt or copy at
+ http://www.boost.org/LICENSE_1_0.txt)
+]
+
+[section Header <boost/optional/bad_optional_access.hpp>]
+
+[section Synopsis]
+```
+namespace boost {
+
+class bad_optional_access : public std::logic_error
+{
+public:
+ bad_optional_access(); ``[link reference_bad_optional_access_constructor __GO_TO__]``
+};
+
+} // namespace boost
+```
+[endsect]
+
+[section Detailed semantics]
+
+__SPACE__
+
+[#reference_bad_optional_access_constructor]
+
+`bad_optional_access();`
+
+* [*Effect:] Constructs an object of class `bad_optional_access`.
+* [*Postconditions:] `what()` returns an implementation-defined NTBS.
+
+[endsect]
+[endsect]
diff --git a/doc/23_ref_optional_io.qbk b/doc/23_ref_optional_io.qbk
new file mode 100644
index 0000000..a9425d4
--- /dev/null
+++ b/doc/23_ref_optional_io.qbk
@@ -0,0 +1,74 @@
+[/
+ Boost.Optional
+
+ Copyright (c) 2003-2007 Fernando Luis Cacciola Carballal
+ Copyright (c) 2015 Andrzej Krzemienski
+
+ Distributed under the Boost Software License, Version 1.0.
+ (See accompanying file LICENSE_1_0.txt or copy at
+ http://www.boost.org/LICENSE_1_0.txt)
+]
+
+[section:io_header Header <boost/optional/optional_io.hpp>]
+
+[section:io_synop Synopsis]
+```
+#include <istream>
+#include <ostream>
+#include <boost/optional/optional.hpp>
+
+namespace boost {
+
+template <class CharType, class CharTrait, class T>
+ std::basic_ostream<CharType, CharTrait>&
+ operator<<(std::basic_ostream<CharType, CharTrait>& out, optional<T> const& v); ``[link reference_operator_ostream __GO_TO__]``
+
+ template <class CharType, class CharTrait>
+ std::basic_ostream<CharType, CharTrait>&
+ operator<<(std::basic_ostream<CharType, CharTrait>& out, none_t const&); ``[link reference_operator_ostream_none __GO_TO__]``
+
+template<class CharType, class CharTrait, class T>
+ std::basic_istream<CharType, CharTrait>&
+ operator>>(std::basic_istream<CharType, CharTrait>& in, optional<T>& v); ``[link reference_operator_istream __GO_TO__]``
+
+} // namespace boost
+```
+
+[endsect]
+
+[section:io_semantics Detailed semantics]
+
+
+[#reference_operator_ostream]
+
+
+`template <class CharType, class CharTrait, class T>` [br]
+\u00A0\u00A0\u00A0\u00A0`std::basic_ostream<CharType, CharTrait>&` [br]
+\u00A0\u00A0\u00A0\u00A0`operator<<(std::basic_ostream<CharType, CharTrait>& out, optional<T> const& v);`
+
+* [*Effect:] Outputs an implementation-defined string. The output contains the information about whether the optional object contains a value or not. If `v` contains a value, the output contains result of calling `out << *v`.
+* [*Returns:] `out`.
+
+__SPACE__
+[#reference_operator_ostream_none]
+
+`template <class CharType, class CharTrait, class T>` [br]
+\u00A0\u00A0\u00A0\u00A0`std::basic_ostream<CharType, CharTrait>&` [br]
+\u00A0\u00A0\u00A0\u00A0`operator<<(std::basic_ostream<CharType, CharTrait>& out, none_t);`
+
+* [*Effect:] Outputs an implementation-defined string.
+* [*Returns:] `out`.
+
+__SPACE__
+[#reference_operator_istream]
+
+`template <class CharType, class CharTrait, class T>` [br]
+\u00A0\u00A0\u00A0\u00A0`std::basic_ostream<CharType, CharTrait>&` [br]
+\u00A0\u00A0\u00A0\u00A0`operator>>(std::basic_istream<CharType, CharTrait>& in, optional<T>& v);`
+
+* [*Requires:] `T` is __SGI_DEFAULT_CONSTRUCTIBLE__ and __MOVE_CONSTRUCTIBLE__.
+* [*Effect:] Reads the value of optional object from `in`. If the string representation indicates that the optional object should contain a value, `v` contains a value and its contained value is obtained as if by default-constructing an object `o` of type `T` and then calling `in >> o`; otherwise `v` does not contain a value, and the previously contained value (if any) has been destroyed.
+* [*Returns:] `out`.
+
+[endsect]
+[endsect]
diff --git a/doc/24_ref_optional_fwd.qbk b/doc/24_ref_optional_fwd.qbk
new file mode 100644
index 0000000..03187f9
--- /dev/null
+++ b/doc/24_ref_optional_fwd.qbk
@@ -0,0 +1,32 @@
+[/
+ Boost.Optional
+
+ Copyright (c) 2003-2007 Fernando Luis Cacciola Carballal
+ Copyright (c) 2015 Andrzej Krzemienski
+
+ Distributed under the Boost Software License, Version 1.0.
+ (See accompanying file LICENSE_1_0.txt or copy at
+ http://www.boost.org/LICENSE_1_0.txt)
+]
+
+[section Header <boost/optional/optional_fwd.hpp>]
+
+[section Synopsis]
+```
+namespace boost {
+
+template <class T> class optional ;
+
+template <class T> void swap ( optional<T>& , optional<T>& );
+
+template <class T> struct optional_swap_should_use_default_constructor ;
+
+} // namespace boost
+```
+
+This header only contains declarations.
+
+[endsect]
+
+
+[endsect]
diff --git a/doc/27_ref_optional_synopsis.qbk b/doc/27_ref_optional_synopsis.qbk
new file mode 100644
index 0000000..7114b43
--- /dev/null
+++ b/doc/27_ref_optional_synopsis.qbk
@@ -0,0 +1,295 @@
+[/
+ Boost.Optional
+
+ Copyright (c) 2003-2007 Fernando Luis Cacciola Carballal
+
+ Distributed under the Boost Software License, Version 1.0.
+ (See accompanying file LICENSE_1_0.txt or copy at
+ http://www.boost.org/LICENSE_1_0.txt)
+]
+
+
+[#ref_header_optional_optional_hpp] [section:header_optional_optional Synopsis]
+
+ ```// In Header: <`[@boost:/boost/optional/optional.hpp boost/optional/optional.hpp]'''<phrase role="comment">></phrase>'''``
+
+ namespace boost {
+
+ class in_place_init_t { /* see below */ } ; ``[link reference_in_place_init __GO_TO__]``
+ const in_place_init_t in_place_init ( /* see below */ ) ;
+
+ class in_place_init_if_t { /*see below*/ } ; ``[link reference_in_place_init_if __GO_TO__]``
+ const in_place_init_if_t in_place_init_if ( /*see below*/ ) ;
+
+ template <class T>
+ class optional ; ``[link reference_operator_template __GO_TO__]``
+
+ template <class T>
+ class optional<T&> ; ``[link reference_operator_template_spec __GO_TO__]``
+
+ template<class T> inline bool operator == ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_equal_optional_optional __GO_TO__]``
+
+ template<class T> inline bool operator != ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_not_equal_optional_optional __GO_TO__]``
+
+ template<class T> inline bool operator < ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_less_optional_optional __GO_TO__]``
+
+ template<class T> inline bool operator > ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_greater_optional_optional __GO_TO__]``
+
+ template<class T> inline bool operator <= ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_less_or_equal_optional_optional __GO_TO__]``
+
+ template<class T> inline bool operator >= ( optional<T> const& x, optional<T> const& y ) ; ``[link reference_operator_compare_greater_or_equal_optional_optional __GO_TO__]``
+
+ template<class T> inline bool operator == ( optional<T> const& x, none_t ) noexcept ; ``[link reference_operator_compare_equal_optional_none __GO_TO__]``
+
+ template<class T> inline bool operator != ( optional<T> const& x, none_t ) noexcept ; ``[link reference_operator_compare_not_equal_optional_none __GO_TO__]``
+
+ template<class T> inline optional<T> make_optional ( T const& v ) ; ``[link reference_make_optional_value __GO_TO__]``
+
+ template<class T> inline optional<std::decay_t<T>> make_optional ( T && v ) ; ``[link reference_make_optional_rvalue __GO_TO__]``
+
+ template<class T> inline optional<T> make_optional ( bool condition, T const& v ) ; ``[link reference_make_optional_bool_value __GO_TO__]``
+
+ template<class T> inline optional<std::decay_t<T>> make_optional ( bool condition, T && v ) ; ``[link reference_make_optional_bool_rvalue __GO_TO__]``
+
+ template<class T> inline auto get_optional_value_or ( optional<T> const& opt, typename optional<T>::reference_const_type def ) -> typename optional<T>::reference_const_type; ``[link reference_free_get_value_or __GO_TO__]``
+
+ template<class T> inline auto get_optional_value_or ( optional<T> const& opt, typename optional<T>::reference_type def ) -> typename optional<T>::reference_type ; ``[link reference_free_get_value_or __GO_TO__]``
+
+ template<class T> inline T const& get ( optional<T> const& opt ) ; ``[link reference_optional_get __GO_TO__]``
+
+ template<class T> inline T& get ( optional<T> & opt ) ; ``[link reference_optional_get __GO_TO__]``
+
+ template<class T> inline T const* get ( optional<T> const* opt ) ; ``[link reference_optional_get __GO_TO__]``
+
+ template<class T> inline T* get ( optional<T>* opt ) ; ``[link reference_optional_get __GO_TO__]``
+
+ template<class T> inline auto get_pointer ( optional<T> const& opt ) -> ``['see below]``; ``[link reference_free_get_pointer __GO_TO__]``
+
+ template<class T> inline auto get_pointer ( optional<T> & opt ) -> ``['see below]``; ``[link reference_free_get_pointer __GO_TO__]``
+
+ template<class T> inline void swap( optional<T>& x, optional<T>& y ) ; ``[link reference_swap_optional_optional __GO_TO__]``
+
+ template<class T> inline void swap( optional<T&>& x, optional<T&>& y ) ; ``[link reference_swap_optional_reference __GO_TO__]``
+
+ } // namespace boost
+
+
+[endsect]
+
+
+[section:header_optional_in_place_init Initialization tags]
+
+[#reference_in_place_init]
+[#reference_in_place_init_if]
+
+ namespace boost {
+
+ class in_place_init_t { /* see below */ } ;
+ const in_place_init_t in_place_init ( /* see below */ ) ;
+
+ class in_place_init_if_t { /*see below*/ } ;
+ const in_place_init_if_t in_place_init_if ( /*see below*/ ) ;
+
+ }
+
+Classes `in_place_init_t` and `in_place_init_if_t` are empty clsses. Their purpose is to control overload resolution in the initialization of optional objects.
+They are empty, trivially copyable classes with disabled default constructor.
+
+[endsect]
+
+[section:header_optional_optional_values Optional Values]
+
+[#reference_operator_template]
+
+ template <class T>
+ class optional
+ {
+ public :
+
+ typedef T value_type ;
+ typedef T & reference_type ;
+ typedef T const& reference_const_type ;
+ typedef T && rval_reference_type ;
+ typedef T * pointer_type ;
+ typedef T const* pointer_const_type ;
+
+ optional () noexcept ; ``[link reference_optional_constructor __GO_TO__]``
+
+ optional ( none_t ) noexcept ; ``[link reference_optional_constructor_none_t __GO_TO__]``
+
+ optional ( T const& v ) ; ``[link reference_optional_constructor_value __GO_TO__]``
+
+ optional ( T&& v ) ; ``[link reference_optional_constructor_move_value __GO_TO__]``
+
+ optional ( bool condition, T const& v ) ; ``[link reference_optional_constructor_bool_value __GO_TO__]``
+
+ optional ( optional const& rhs ) ; ``[link reference_optional_constructor_optional __GO_TO__]``
+
+ optional ( optional&& rhs ) noexcept(``['see below]``) ; ``[link reference_optional_move_constructor_optional __GO_TO__]``
+
+ template<class U> explicit optional ( optional<U> const& rhs ) ; ``[link reference_optional_constructor_other_optional __GO_TO__]``
+
+ template<class U> explicit optional ( optional<U>&& rhs ) ; ``[link reference_optional_move_constructor_other_optional __GO_TO__]``
+
+ template<class... Args> explicit optional ( in_place_init_t, Args&&... args ) ; ``[link reference_optional_in_place_init __GO_TO__]``
+
+ template<class... Args> explicit optional ( in_place_init_if_t, bool condition, Args&&... args ) ; ``[link reference_optional_in_place_init_if __GO_TO__]``
+
+ template<class InPlaceFactory> explicit optional ( InPlaceFactory const& f ) ; ``[link reference_optional_constructor_factory __GO_TO__]``
+
+ template<class TypedInPlaceFactory> explicit optional ( TypedInPlaceFactory const& f ) ; ``[link reference_optional_constructor_factory __GO_TO__]``
+
+ optional& operator = ( none_t ) noexcept ; ``[link reference_optional_operator_equal_none_t __GO_TO__]``
+
+ optional& operator = ( T const& v ) ; ``[link reference_optional_operator_equal_value __GO_TO__]``
+
+ optional& operator = ( T&& v ) ; ``[link reference_optional_operator_move_equal_value __GO_TO__]``
+
+ optional& operator = ( optional const& rhs ) ; ``[link reference_optional_operator_equal_optional __GO_TO__]``
+
+ optional& operator = ( optional&& rhs ) noexcept(``['see below]``) ; ``[link reference_optional_operator_move_equal_optional __GO_TO__]``
+
+ template<class U> optional& operator = ( optional<U> const& rhs ) ; ``[link reference_optional_operator_equal_other_optional __GO_TO__]``
+
+ template<class U> optional& operator = ( optional<U>&& rhs ) ; ``[link reference_optional_operator_move_equal_other_optional __GO_TO__]``
+
+ template<class... Args> void emplace ( Args&&... args ) ; ``[link reference_optional_emplace __GO_TO__]``
+
+ template<class InPlaceFactory> optional& operator = ( InPlaceFactory const& f ) ; ``[link reference_optional_operator_equal_factory __GO_TO__]``
+
+ template<class TypedInPlaceFactory> optional& operator = ( TypedInPlaceFactory const& f ) ; ``[link reference_optional_operator_equal_factory __GO_TO__]``
+
+ T const& get() const ; ``[link reference_optional_get __GO_TO__]``
+ T& get() ; ``[link reference_optional_get __GO_TO__]``
+
+ T const* operator ->() const ; ``[link reference_optional_operator_arrow __GO_TO__]``
+ T* operator ->() ; ``[link reference_optional_operator_arrow __GO_TO__]``
+
+ T const& operator *() const& ; ``[link reference_optional_operator_asterisk __GO_TO__]``
+ T& operator *() & ; ``[link reference_optional_operator_asterisk __GO_TO__]``
+ T&& operator *() && ; ``[link reference_optional_operator_asterisk_move __GO_TO__]``
+
+ T const& value() const& ; ``[link reference_optional_value __GO_TO__]``
+ T& value() & ; ``[link reference_optional_value __GO_TO__]``
+ T&& value() && ; ``[link reference_optional_value_move __GO_TO__]``
+
+ template<class U> T value_or( U && v ) const& ; ``[link reference_optional_value_or __GO_TO__]``
+ template<class U> T value_or( U && v ) && ; ``[link reference_optional_value_or_move __GO_TO__]``
+
+ template<class F> T value_or_eval( F f ) const& ; ``[link reference_optional_value_or_call __GO_TO__]``
+ template<class F> T value_or_eval( F f ) && ; ``[link reference_optional_value_or_call_move __GO_TO__]``
+
+ template<class F> auto map( F f ) const& -> ``['see below]``; ``[link reference_optional_map __GO_TO__]``
+ template<class F> auto map( F f ) & -> ``['see below]``; ``[link reference_optional_map __GO_TO__]``
+ template<class F> auto map( F f ) && -> ``['see below]``; ``[link reference_optional_map_move __GO_TO__]``
+
+ template<class F> auto flat_map( F f ) const& -> ``['see below]``; ``[link reference_optional_flat_map __GO_TO__]``
+ template<class F> auto flat_map( F f ) & -> ``['see below]``; ``[link reference_optional_flat_map __GO_TO__]``
+ template<class F> auto flat_map( F f ) && -> ``['see below]``; ``[link reference_optional_flat_map_move __GO_TO__]``
+
+ T const* get_ptr() const ; ``[link reference_optional_get_ptr __GO_TO__]``
+ T* get_ptr() ; ``[link reference_optional_get_ptr __GO_TO__]``
+
+ bool has_value() const noexcept ; ``[link reference_optional_operator_bool __GO_TO__]``
+
+ explicit operator bool() const noexcept ; ``[link reference_optional_operator_bool __GO_TO__]``
+
+ bool operator!() const noexcept ; ``[link reference_optional_operator_not __GO_TO__]``
+
+ // deprecated methods
+
+ // (deprecated)
+ void reset() noexcept ; ``[link reference_optional_reset __GO_TO__]``
+
+ // (deprecated)
+ void reset ( T const& ) ; ``[link reference_optional_reset_value __GO_TO__]``
+
+ // (deprecated)
+ bool is_initialized() const ; ``[link reference_optional_is_initialized __GO_TO__]``
+
+ // (deprecated)
+ T const& get_value_or( T const& default ) const ; ``[link reference_optional_get_value_or_value __GO_TO__]``
+ };
+
+
+[endsect]
+
+
+[section:header_optional_optional_refs Optional References]
+
+[#reference_operator_template_spec]
+ template <class T>
+ class optional<T&> // specilization for lvalue references
+ {
+ public :
+
+ typedef T& value_type;
+ typedef T& reference_type;
+ typedef T& reference_const_type; // no const propagation
+ typedef T& rval_reference_type;
+ typedef T* pointer_type;
+ typedef T* pointer_const_type; // no const propagation
+
+ optional () noexcept ; ``[link reference_optional_ref_default_ctor __GO_TO__]``
+
+ optional ( none_t ) noexcept ; ``[link reference_optional_ref_default_ctor __GO_TO__]``
+
+ template<class R> optional(R&& r) noexcept ; ``[link reference_optional_ref_value_ctor __GO_TO__]``
+
+ template <class R> optional(bool cond, R&& r) noexcept ; ``[link reference_optional_ref_cond_value_ctor __GO_TO__]``
+
+ optional ( optional const& rhs ) noexcept ; ``[link reference_optional_ref_copy_ctor __GO_TO__]``
+
+ template<class U> explicit optional ( optional<U&> const& rhs ) noexcept ; ``[link reference_optional_ref_ctor_from_opt_U __GO_TO__]``
+
+ optional& operator = ( none_t ) noexcept ; ``[link reference_optional_ref_assign_none_t __GO_TO__]``
+
+ optional& operator = ( optional const& rhs ) noexcept; ``[link reference_optional_ref_copy_assign __GO_TO__]``
+
+ template<class U> optional& operator = ( optional<U&> const& rhs ) noexcept ; ``[link reference_optional_ref_assign_optional_U __GO_TO__]``
+
+ template<class R> optional& operator = (R&& r) noexcept ; ``[link reference_optional_ref_assign_R __GO_TO__]``
+
+ template<class R> void emplace ( R&& r ) noexcept ; ``[link reference_optional_ref_emplace_R __GO_TO__]``
+
+ T& get() const ; ``[link reference_optional_ref_get __GO_TO__]``
+ T& operator *() const ; ``[link reference_optional_ref_get __GO_TO__]``
+
+ T* operator ->() const ; ``[link reference_optional_ref_arrow __GO_TO__]``
+
+ T& value() const& ; ``[link reference_optional_ref_value __GO_TO__]``
+
+ template<class R> T& value_or( R && r ) const noexcept ; ``[link reference_optional_ref_value_or __GO_TO__]``
+
+ template<class F> T& value_or_eval( F f ) const ; ``[link reference_optional_ref_value_or_eval __GO_TO__]``
+
+ template<class F> auto map( F f ) const -> ``['see below]``; ``[link reference_optional_ref_map __GO_TO__]``
+
+ template<class F> auto flat_map( F f ) const -> ``['see below]``; ``[link reference_optional_ref_flat_map __GO_TO__]``
+
+ T* get_ptr() const noexcept ; ``[link reference_optional_ref_get_ptr __GO_TO__]``
+
+ bool has_value() const noexcept ; ``[link reference_optional_ref_operator_bool __GO_TO__]``
+
+ explicit operator bool() const noexcept ; ``[link reference_optional_ref_operator_bool __GO_TO__]``
+
+ bool operator!() const noexcept ; ``[link reference_optional_ref_operator_not __GO_TO__]``
+
+ // deprecated methods
+
+ // (deprecated)
+ void reset() noexcept ; ``[link reference_optional_ref_reset __GO_TO__]``
+
+ // (deprecated)
+ template<class R> void reset ( R && r ) noexcept ; ``[link reference_optional_ref_reset_value __GO_TO__]``
+
+ // (deprecated)
+ bool is_initialized() const noexcept ; ``[link reference_optional_ref_is_initialized __GO_TO__]``
+
+ // (deprecated)
+ template<class R> T& get_value_or( R && r ) constnoexcept; ``[link reference_optional_ref_get_value_or_value __GO_TO__]``
+
+ private:
+ T* ref; // exposition only
+ };
+[endsect]
diff --git a/doc/28_ref_optional_semantics.qbk b/doc/28_ref_optional_semantics.qbk
new file mode 100644
index 0000000..6ce0d2e
--- /dev/null
+++ b/doc/28_ref_optional_semantics.qbk
@@ -0,0 +1,1411 @@
+[/
+ Boost.Optional
+
+ Copyright (c) 2003-2007 Fernando Luis Cacciola Carballal
+
+ Distributed under the Boost Software License, Version 1.0.
+ (See accompanying file LICENSE_1_0.txt or copy at
+ http://www.boost.org/LICENSE_1_0.txt)
+]
+
+
+[section Detailed Semantics - Optional Values]
+
+[note
+The following section contains various `assert()` which are used only to show
+the postconditions as sample code. It is not implied that the type `T` must
+support each particular expression but that if the expression is supported,
+the implied condition holds.
+]
+
+
+__SPACE__
+
+[#reference_optional_constructor]
+
+[: `optional<T>::optional() noexcept;`]
+
+* [*Effect:] Default-Constructs an `optional`.
+* [*Postconditions:] `*this` is [_uninitialized].
+* [*Notes:] T's default constructor [_is not] called.
+* [*Example:]
+``
+optional<T> def ;
+assert ( !def ) ;
+``
+
+__SPACE__
+
+[#reference_optional_constructor_none_t]
+
+[: `optional<T>::optional( none_t ) noexcept;`]
+
+* [*Effect:] Constructs an `optional` uninitialized.
+* [*Postconditions:] `*this` is [_uninitialized].
+* [*Notes:] `T`'s default constructor [_is not] called. The expression
+`boost::none` denotes an instance of `boost::none_t` that can be used as
+the parameter.
+* [*Example:]
+``
+#include <boost/none.hpp>
+optional<T> n(none) ;
+assert ( !n ) ;
+``
+
+__SPACE__
+
+[#reference_optional_constructor_value]
+
+[: `optional<T>::optional( T const& v )`]
+
+* [*Requires:] `is_copy_constructible<T>::value` is `true`.
+* [*Effect:] Directly-Constructs an `optional`.
+* [*Postconditions:] `*this` is [_initialized] and its value is a ['copy]
+of `v`.
+* [*Throws:] Whatever `T::T( T const& )` throws.
+* [*Notes: ] `T::T( T const& )` is called.
+* [*Exception Safety:] Exceptions can only be thrown during
+`T::T( T const& );` in that case, this constructor has no effect.
+* [*Example:]
+``
+T v;
+optional<T> opt(v);
+assert ( *opt == v ) ;
+``
+
+
+__SPACE__
+
+[#reference_optional_constructor_move_value]
+
+[: `optional<T>::optional( T&& v )`]
+
+* [*Requires:] `is_move_constructible<T>::value` is `true`.
+* [*Effect:] Directly-Move-Constructs an `optional`.
+* [*Postconditions:] `*this` is [_initialized] and its value is move-constructed from `v`.
+* [*Throws:] Whatever `T::T( T&& )` throws.
+* [*Notes: ] `T::T( T&& )` is called.
+* [*Exception Safety:] Exceptions can only be thrown during
+`T::T( T&& );` in that case, the state of `v` is determined by exception safety guarantees for `T::T(T&&)`.
+* [*Example:]
+``
+T v1, v2;
+optional<T> opt(std::move(v1));
+assert ( *opt == v2 ) ;
+``
+
+
+__SPACE__
+
+[#reference_optional_constructor_bool_value]
+
+[: `optional<T>::optional( bool condition, T const& v ) ;` ]
+
+* If condition is true, same as:
+
+[: `optional<T>::optional( T const& v )`]
+
+* otherwise, same as:
+
+[: `optional<T>::optional()`]
+
+
+__SPACE__
+
+[#reference_optional_constructor_optional]
+
+[: `optional<T>::optional( optional const& rhs );`]
+
+* [*Requires:] `is_copy_constructible<T>::value` is `true`.
+* [*Effect:] Copy-Constructs an `optional`.
+* [*Postconditions:] If rhs is initialized, `*this` is initialized and
+its value is a ['copy] of the value of `rhs`; else `*this` is uninitialized.
+* [*Throws:] Whatever `T::T( T const& )` throws.
+* [*Notes:] If rhs is initialized, `T::T(T const& )` is called.
+* [*Exception Safety:] Exceptions can only be thrown during
+`T::T( T const& );` in that case, this constructor has no effect.
+* [*Example:]
+``
+optional<T> uninit ;
+assert (!uninit);
+
+optional<T> uinit2 ( uninit ) ;
+assert ( uninit2 == uninit );
+
+optional<T> init( T(2) );
+assert ( *init == T(2) ) ;
+
+optional<T> init2 ( init ) ;
+assert ( init2 == init ) ;
+``
+
+
+__SPACE__
+
+[#reference_optional_move_constructor_optional]
+
+[: `optional<T>::optional( optional&& rhs ) noexcept(`['see below]`);`]
+
+* [*Requires:] `is_move_constructible<T>::value` is `true`.
+* [*Effect:] Move-constructs an `optional`.
+* [*Postconditions:] If `rhs` is initialized, `*this` is initialized and
+its value is move constructed from `rhs`; else `*this` is uninitialized.
+* [*Throws:] Whatever `T::T( T&& )` throws.
+* [*Remarks:] The expression inside `noexcept` is equivalent to `is_nothrow_move_constructible<T>::value`.
+* [*Notes:] If `rhs` is initialized, `T::T( T && )` is called.
+* [*Exception Safety:] Exceptions can only be thrown during
+`T::T( T&& );` in that case, `rhs` remains initialized and the value of `*rhs` is determined by exception safety of `T::T(T&&)`.
+* [*Example:]
+``
+optional<std::unique_ptr<T>> uninit ;
+assert (!uninit);
+
+optional<std::unique_ptr<T>> uinit2 ( std::move(uninit) ) ;
+assert ( uninit2 == uninit );
+
+optional<std::unique_ptr<T>> init( std::uniqye_ptr<T>(new T(2)) );
+assert ( **init == T(2) ) ;
+
+optional<std::unique_ptr<T>> init2 ( std::move(init) ) ;
+assert ( init );
+assert ( *init == nullptr );
+assert ( init2 );
+assert ( **init2 == T(2) ) ;
+``
+
+
+__SPACE__
+
+[#reference_optional_constructor_other_optional]
+
+[: `template<U> explicit optional<T>::optional( optional<U> const& rhs );`]
+
+* [*Effect:] Copy-Constructs an `optional`.
+* [*Postconditions:] If `rhs` is initialized, `*this` is initialized and its
+value is a ['copy] of the value of rhs converted to type `T`; else `*this` is
+uninitialized.
+* [*Throws:] Whatever `T::T( U const& )` throws.
+* [*Notes: ] `T::T( U const& )` is called if `rhs` is initialized, which requires a
+valid conversion from `U` to `T`.
+* [*Exception Safety:] Exceptions can only be thrown during `T::T( U const& );`
+in that case, this constructor has no effect.
+* [*Example:]
+``
+optional<double> x(123.4);
+assert ( *x == 123.4 ) ;
+
+optional<int> y(x) ;
+assert( *y == 123 ) ;
+``
+
+__SPACE__
+
+[#reference_optional_move_constructor_other_optional]
+
+[: `template<U> explicit optional<T>::optional( optional<U>&& rhs );`]
+
+* [*Effect:] Move-constructs an `optional`.
+* [*Postconditions:] If `rhs` is initialized, `*this` is initialized and its
+value is move-constructed from `*rhs`; else `*this` is
+uninitialized.
+* [*Throws:] Whatever `T::T( U&& )` throws.
+* [*Notes: ] `T::T( U&& )` is called if `rhs` is initialized, which requires a
+valid conversion from `U` to `T`.
+* [*Exception Safety:] Exceptions can only be thrown during `T::T( U&& );`
+in that case, `rhs` remains initialized and the value of `*rhs` is determined by exception safety guarantee of `T::T( U&& )`.
+* [*Example:]
+``
+optional<double> x(123.4);
+assert ( *x == 123.4 ) ;
+
+optional<int> y(std::move(x)) ;
+assert( *y == 123 ) ;
+``
+
+__SPACE__
+
+[#reference_optional_in_place_init]
+
+[: `template<class... Args> explicit optional<T>::optional( in_place_init_t, Args&&... ars );`]
+
+* [*Requires:] `is_constructible_v<T, Args&&...>` is `true`.
+* [*Effect:] Initializes the contained value as if direct-non-list-initializing an object of type `T` with the
+arguments `std::forward<Args>(args)...`.
+* [*Postconditions:] `*this` is initialized.
+* [*Throws:] Any exception thrown by the selected constructor of `T`.
+* [*Notes: ] `T` need not be __MOVE_CONSTRUCTIBLE__. On compilers that do not suppor variadic templates or rvalue references, this constuctor is available in limited functionality. For details [link optional_emplace_workaround see here].
+
+* [*Example:]
+``
+// creates an std::mutex using its default constructor
+optional<std::mutex> om {in_place_init};
+assert (om);
+
+// creates a unique_lock by calling unique_lock(*om, std::defer_lock)
+optional<std::unique_lock<std::mutex>> ol {in_place_init, *om, std::defer_lock};
+assert (ol);
+assert (!ol->owns_lock());
+``
+
+__SPACE__
+
+[#reference_optional_in_place_init_if]
+
+[: `template<class... Args> explicit optional<T>::optional( in_place_init_if_t, bool condition, Args&&... ars );`]
+
+* [*Requires:] `is_constructible_v<T, Args&&...>` is `true`.
+* [*Effect:] If `condition` is `true`, initializes the contained value as if direct-non-list-initializing an object of type `T` with the arguments `std::forward<Args>(args)...`.
+* [*Postconditions:] `bool(*this) == condition`.
+* [*Throws:] Any exception thrown by the selected constructor of `T`.
+* [*Notes: ] `T` need not be __MOVE_CONSTRUCTIBLE__. On compilers that do not suppor variadic templates or rvalue references, this constuctor is available in limited functionality. For details [link optional_emplace_workaround see here].
+
+* [*Example:]
+``
+optional<std::vector<std::string>> ov1 {in_place_init_if, false, 3, "A"};
+assert (!ov1);
+
+optional<std::vector<std::string>> ov2 {in_place_init_if, true, 3, "A"};
+assert (ov2);
+assert (ov2->size() == 3);
+``
+
+__SPACE__
+
+[#reference_optional_constructor_factory]
+
+[: `template<InPlaceFactory> explicit optional<T>::optional( InPlaceFactory const& f );`]
+[: `template<TypedInPlaceFactory> explicit optional<T>::optional( TypedInPlaceFactory const& f );`]
+
+* [*Effect:] Constructs an `optional` with a value of `T` obtained from the
+factory.
+* [*Postconditions: ] `*this` is [_initialized] and its value is ['directly given]
+from the factory `f` (i.e., the value [_is not copied]).
+* [*Throws:] Whatever the `T` constructor called by the factory throws.
+* [*Notes:] See [link boost_optional.tutorial.in_place_factories In-Place Factories]
+* [*Exception Safety:] Exceptions can only be thrown during the call to
+the `T` constructor used by the factory; in that case, this constructor has
+no effect.
+* [*Example:]
+``
+class C { C ( char, double, std::string ) ; } ;
+
+C v('A',123.4,"hello");
+
+optional<C> x( in_place ('A', 123.4, "hello") ); // InPlaceFactory used
+optional<C> y( in_place<C>('A', 123.4, "hello") ); // TypedInPlaceFactory used
+
+assert ( *x == v ) ;
+assert ( *y == v ) ;
+``
+
+__SPACE__
+
+[#reference_optional_operator_equal_none_t]
+
+[: `optional& optional<T>::operator= ( none_t ) noexcept;`]
+
+* [*Effect:] If `*this` is initialized destroys its contained value.
+* [*Postconditions: ] `*this` is uninitialized.
+
+__SPACE__
+
+[#reference_optional_operator_equal_value]
+
+[: `optional& optional<T>::operator= ( T const& rhs ) ;`]
+
+* [*Effect:] Assigns the value `rhs` to an `optional`.
+* [*Postconditions: ] `*this` is initialized and its value is a ['copy] of `rhs`.
+* [*Throws:] Whatever `T::operator=( T const& )` or `T::T(T const&)` throws.
+* [*Notes:] If `*this` was initialized, `T`'s assignment operator is used,
+otherwise, its copy-constructor is used.
+* [*Exception Safety:] In the event of an exception, the initialization
+state of `*this` is unchanged and its value unspecified as far as `optional`
+is concerned (it is up to `T`'s `operator=()`). If `*this` is initially
+uninitialized and `T`'s ['copy constructor] fails, `*this` is left properly
+uninitialized.
+* [*Example:]
+``
+T x;
+optional<T> def ;
+optional<T> opt(x) ;
+
+T y;
+def = y ;
+assert ( *def == y ) ;
+opt = y ;
+assert ( *opt == y ) ;
+``
+
+
+__SPACE__
+
+[#reference_optional_operator_move_equal_value]
+
+[: `optional& optional<T>::operator= ( T&& rhs ) ;`]
+
+* [*Effect:] Moves the value `rhs` to an `optional`.
+* [*Postconditions: ] `*this` is initialized and its value is moved from `rhs`.
+* [*Throws:] Whatever `T::operator=( T&& )` or `T::T(T &&)` throws.
+* [*Notes:] If `*this` was initialized, `T`'s move-assignment operator is used,
+otherwise, its move-constructor is used.
+* [*Exception Safety:] In the event of an exception, the initialization
+state of `*this` is unchanged and its value unspecified as far as `optional`
+is concerned (it is up to `T`'s `operator=()`). If `*this` is initially
+uninitialized and `T`'s ['move constructor] fails, `*this` is left properly
+uninitialized.
+* [*Example:]
+``
+T x;
+optional<T> def ;
+optional<T> opt(x) ;
+
+T y1, y2, yR;
+def = std::move(y1) ;
+assert ( *def == yR ) ;
+opt = std::move(y2) ;
+assert ( *opt == yR ) ;
+``
+
+
+__SPACE__
+
+[#reference_optional_operator_equal_optional]
+
+[: `optional& optional<T>::operator= ( optional const& rhs ) ;`]
+
+* [*Requires:] `T` is __COPY_CONSTRUCTIBLE__ and `CopyAssignable`.
+* [*Effects:]
+[table
+ []
+ [[][[*`*this` contains a value]][[*`*this` does not contain a value]]]
+ [[[*`rhs` contains a value]][assigns `*rhs` to the contained value][initializes the contained value as if direct-initializing an object of type `T` with `*rhs`]]
+ [[[*`rhs` does not contain a value]][destroys the contained value by calling `val->T::~T()`][no effect]]
+]
+* [*Returns:] `*this`;
+* [*Postconditions:] `bool(rhs) == bool(*this)`.
+* [*Exception Safety:] If any exception is thrown, the initialization state of `*this` and `rhs` remains unchanged.
+If an exception is thrown during the call to `T`'s copy constructor, no effect.
+If an exception is thrown during the call to `T`'s copy assignment, the state of its contained value is as defined by the exception safety guarantee of `T`'s copy assignment.
+* [*Example:]
+``
+T v;
+optional<T> opt(v);
+optional<T> def ;
+
+opt = def ;
+assert ( !def ) ;
+// previous value (copy of 'v') destroyed from within 'opt'.
+``
+
+
+__SPACE__
+
+[#reference_optional_operator_move_equal_optional]
+
+[: `optional& optional<T>::operator= ( optional&& rhs ) noexcept(`['see below]`);`]
+
+* [*Requires:] `T` is __MOVE_CONSTRUCTIBLE__ and `MoveAssignable`.
+* [*Effects:]
+[table
+ []
+ [[][[*`*this` contains a value]][[*`*this` does not contain a value]]]
+ [[[*`rhs` contains a value]][assigns `std::move(*rhs)` to the contained value][initializes the contained value as if direct-initializing an object of type `T` with `std::move(*rhs)`]]
+ [[[*`rhs` does not contain a value]][destroys the contained value by calling `val->T::~T()`][no effect]]
+]
+* [*Returns:] `*this`;
+* [*Postconditions:] `bool(rhs) == bool(*this)`.
+* [*Remarks:] The expression inside `noexcept` is equivalent to `is_nothrow_move_constructible<T>::value && is_nothrow_move_assignable<T>::value`.
+* [*Exception Safety:] If any exception is thrown, the initialization state of `*this` and `rhs` remains unchanged. If an exception is
+thrown during the call to `T`'s move constructor, the state of `*rhs` is determined by the exception safety guarantee
+of `T`'s move constructor. If an exception is thrown during the call to T's move-assignment, the state of `**this` and `*rhs` is determined by the exception safety guarantee of T's move assignment.
+* [*Example:]
+``
+optional<T> opt(T(2)) ;
+optional<T> def ;
+
+opt = def ;
+assert ( def ) ;
+assert ( opt ) ;
+assert ( *opt == T(2) ) ;
+``
+
+
+__SPACE__
+
+
+[#reference_optional_operator_equal_other_optional]
+
+[: `template<U> optional& optional<T>::operator= ( optional<U> const& rhs ) ;`]
+
+* [*Effect:]
+[table
+ []
+ [[][[*`*this` contains a value]][[*`*this` does not contain a value]]]
+ [[[*`rhs` contains a value]][assigns `*rhs` to the contained value][initializes the contained value as if direct-initializing an object of type `T` with `*rhs`]]
+ [[[*`rhs` does not contain a value]][destroys the contained value by calling `val->T::~T()`][no effect]]
+]
+* [*Returns:] `*this`.
+* [*Postconditions:] `bool(rhs) == bool(*this)`.
+* [*Exception Safety:] If any exception is thrown, the result of the expression `bool(*this)` remains unchanged.
+If an exception is thrown during the call to `T`'s constructor, no effect.
+If an exception is thrown during the call to `T`'s assignment, the state of its contained value is as defined by the exception safety guarantee of `T`'s copy assignment.
+* [*Example:]
+``
+T v;
+optional<T> opt0(v);
+optional<U> opt1;
+
+opt1 = opt0 ;
+assert ( *opt1 == static_cast<U>(v) ) ;
+``
+
+__SPACE__
+
+[#reference_optional_operator_move_equal_other_optional]
+
+[: `template<U> optional& optional<T>::operator= ( optional<U>&& rhs ) ;`]
+
+* [*Effect:]
+[table
+ []
+ [[][[*`*this` contains a value]][[*`*this` does not contain a value]]]
+ [[[*`rhs` contains a value]][assigns `std::move(*rhs)` to the contained value][initializes the contained value as if direct-initializing an object of type `T` with `std::move(*rhs)`]]
+ [[[*`rhs` does not contain a value]][destroys the contained value by calling `val->T::~T()`][no effect]]
+]
+* [*Returns:] `*this`.
+* [*Postconditions:] `bool(rhs) == bool(*this)`.
+* [*Exception Safety:] If any exception is thrown, the result of the expression `bool(*this)` remains unchanged.
+If an exception is thrown during the call to `T`'s constructor, no effect.
+If an exception is thrown during the call to `T`'s assignment, the state of its contained value is as defined by the exception safety guarantee of `T`'s copy assignment.
+* [*Example:]
+``
+T v;
+optional<T> opt0(v);
+optional<U> opt1;
+
+opt1 = std::move(opt0) ;
+assert ( opt0 );
+assert ( opt1 )
+assert ( *opt1 == static_cast<U>(v) ) ;
+``
+
+__SPACE__
+
+[#reference_optional_emplace]
+
+[: `template<class... Args> void optional<T>::emplace( Args&&... args );`]
+
+* [*Requires:] The compiler supports rvalue references and variadic templates.
+* [*Effect:] If `*this` is initialized calls `*this = none`.
+ Then initializes in-place the contained value as if direct-initializing an object
+ of type `T` with `std::forward<Args>(args)...`.
+* [*Postconditions: ] `*this` is [_initialized].
+* [*Throws:] Whatever the selected `T`'s constructor throws.
+* [*Exception Safety:] If an exception is thrown during the initialization of `T`, `*this` is ['uninitialized].
+* [*Notes:] `T` need not be __MOVE_CONSTRUCTIBLE__ or `MoveAssignable`. On compilers that do not suppor variadic templates or rvalue references, this function is available in limited functionality. For details [link optional_emplace_workaround see here].
+* [*Example:]
+``
+T v;
+optional<const T> opt;
+opt.emplace(0); // create in-place using ctor T(int)
+opt.emplace(); // destroy previous and default-construct another T
+opt.emplace(v); // destroy and copy-construct in-place (no assignment called)
+``
+
+__SPACE__
+
+[#reference_optional_operator_equal_factory]
+
+[: `template<InPlaceFactory> optional<T>& optional<T>::operator=( InPlaceFactory const& f );`]
+[: `template<TypedInPlaceFactory> optional<T>& optional<T>::operator=( TypedInPlaceFactory const& f );`]
+
+* [*Effect:] Assigns an `optional` with a value of `T` obtained from the
+factory.
+* [*Postconditions: ] `*this` is [_initialized] and its value is ['directly given]
+from the factory `f` (i.e., the value [_is not copied]).
+* [*Throws:] Whatever the `T` constructor called by the factory throws.
+* [*Notes:] See [link boost_optional.tutorial.in_place_factories In-Place Factories]
+* [*Exception Safety:] Exceptions can only be thrown during the call to
+the `T` constructor used by the factory; in that case, the `optional` object
+will be reset to be ['uninitialized].
+
+__SPACE__
+
+[#reference_optional_reset_value]
+
+[: `void optional<T>::reset( T const& v ) ;`]
+* [*Deprecated:] same as `operator= ( T const& v) ;`
+
+__SPACE__
+
+[#reference_optional_reset]
+
+[: `void optional<T>::reset() noexcept ;`]
+* [*Deprecated:] Same as `operator=( none_t );`
+
+__SPACE__
+
+[#reference_optional_get]
+
+[: `T const& optional<T>::get() const ;`]
+[: `T& optional<T>::get() ;`]
+
+[: `inline T const& get ( optional<T> const& ) ;`]
+[: `inline T& get ( optional<T> &) ;`]
+
+* [*Requires:] `*this` is initialized
+* [*Returns:] A reference to the contained value
+* [*Throws:] Nothing.
+* [*Notes:] The requirement is asserted via `BOOST_ASSERT()`.
+
+
+__SPACE__
+
+[#reference_optional_operator_asterisk]
+
+[: `T const& optional<T>::operator*() const& ;`]
+[: `T& optional<T>::operator*() &;`]
+
+* [*Requires:] `*this` is initialized
+* [*Returns:] A reference to the contained value
+* [*Throws:] Nothing.
+* [*Notes:] The requirement is asserted via `BOOST_ASSERT()`. On compilers that do not support ref-qualifiers on member functions these two overloads are replaced with the classical two: a `const` and non-`const` member functions.
+* [*Example:]
+``
+T v ;
+optional<T> opt ( v );
+T const& u = *opt;
+assert ( u == v ) ;
+T w ;
+*opt = w ;
+assert ( *opt == w ) ;
+``
+
+__SPACE__
+
+[#reference_optional_operator_asterisk_move]
+
+[: `T&& optional<T>::operator*() &&;`]
+
+* [*Requires:] `*this` contains a value.
+* [*Effects:] Equivalent to `return std::move(*val);`.
+* [*Notes:] The requirement is asserted via `BOOST_ASSERT()`. On compilers that do not support ref-qualifiers on member functions this overload is not present.
+
+
+__SPACE__
+
+[#reference_optional_value]
+
+[: `T const& optional<T>::value() const& ;`]
+[: `T& optional<T>::value() & ;`]
+
+* [*Effects:] Equivalent to `return bool(*this) ? *val : throw bad_optional_access();`.
+* [*Notes:] On compilers that do not support ref-qualifiers on member functions these two overloads are replaced with the classical two: a `const` and non-`const` member functions.
+* [*Example:]
+``
+T v ;
+optional<T> o0, o1 ( v );
+assert ( o1.value() == v );
+
+try {
+ o0.value(); // throws
+ assert ( false );
+}
+catch(bad_optional_access&) {
+ assert ( true );
+}
+``
+
+__SPACE__
+
+[#reference_optional_value_move]
+
+[: `T&& optional<T>::value() && ;`]
+
+* [*Effects:] Equivalent to `return bool(*this) ? std::move(*val) : throw bad_optional_access();`.
+* [*Notes:] On compilers that do not support ref-qualifiers on member functions this overload is not present.
+
+__SPACE__
+
+
+[#reference_optional_value_or]
+
+[: `template<class U> T optional<T>::value_or(U && v) const& ;`]
+
+* [*Effects:] Equivalent to `if (*this) return **this; else return std::forward<U>(v);`.
+* [*Remarks:] If `T` is not __COPY_CONSTRUCTIBLE__ or `U &&` is not convertible to `T`, the program is ill-formed.
+* [*Notes:] On compilers that do not support ref-qualifiers on member functions this overload is replaced with the `const`-qualified member function. On compilers without rvalue reference support the type of `v` becomes `U const&`.
+
+__SPACE__
+
+[#reference_optional_value_or_move]
+
+[: `template<class U> T optional<T>::value_or(U && v) && ;`]
+
+* [*Effects:] Equivalent to `if (*this) return std::move(**this); else return std::forward<U>(v);`.
+* [*Remarks:] If `T` is not __MOVE_CONSTRUCTIBLE__ or `U &&` is not convertible to `T`, the program is ill-formed.
+* [*Notes:] On compilers that do not support ref-qualifiers on member functions this overload is not present.
+
+__SPACE__
+
+[#reference_optional_value_or_call]
+
+[: `template<class F> T optional<T>::value_or_eval(F f) const& ;`]
+
+* [*Requires:] `T` is __COPY_CONSTRUCTIBLE__ and `F` models a __SGI_GENERATOR__ whose result type is convertible to `T`.
+* [*Effects:] `if (*this) return **this; else return f();`.
+* [*Notes:] On compilers that do not support ref-qualifiers on member functions this overload is replaced with the `const`-qualified member function.
+* [*Example:]
+``
+int complain_and_0()
+{
+ clog << "no value returned, using default" << endl;
+ return 0;
+}
+
+optional<int> o1 = 1;
+optional<int> oN = none;
+
+int i = o1.value_or_eval(complain_and_0); // fun not called
+assert (i == 1);
+
+int j = oN.value_or_eval(complain_and_0); // fun called
+assert (i == 0);
+``
+
+__SPACE__
+
+[#reference_optional_value_or_call_move]
+
+[: `template<class F> T optional<T>::value_or_eval(F f) && ;`]
+
+* [*Requires:] `T` is __MOVE_CONSTRUCTIBLE__ and `F` models a __SGI_GENERATOR__ whose result type is convertible to `T`.
+* [*Effects:] `if (*this) return std::move(**this); else return f();`.
+* [*Notes:] On compilers that do not support ref-qualifiers on member functions this overload is not present.
+
+__SPACE__
+
+[#reference_optional_map]
+
+[: `template<class F> auto optional<T>::map(F f) const& -> `['see below]` ;`]
+[: `template<class F> auto optional<T>::map(F f) & -> `['see below]` ;`]
+
+* [*Effects:] `if (*this) return f(**this); else return none;`
+* [*Notes:] The return type of these overloads is `optional<decltype(f(**this))>`. On compilers that do not support ref-qualifiers on member functions, these two (as well as the next one) overloads are replaced with good old const and non-const overloads.
+* [*Example:]
+``
+auto length = [](const string& s){ return s.size(); };
+optional<string> o1 {}, o2 {"cat"};
+optional<size_t> os1 = o1.map(length), os2 = o2.map(length);
+assert ( !os1 ) ;
+assert ( os2 ) ;
+assert ( *os2 == 3 ) ;
+``
+
+__SPACE__
+
+[#reference_optional_map_move]
+
+[: `template<class F> auto optional<T>::map(F f) && -> `['see below]` ;`]
+
+* [*Effects:] `if (*this) return f(std::move(**this)); else return none;`
+* [*Notes:] The return type of this overload is `optional<decltype(f(istd::move(**this)))>`.
+
+__SPACE__
+
+[#reference_optional_flat_map]
+
+[: `template<class F> auto optional<T>::flat_map(F f) const& -> `['see below]` ;`]
+[: `template<class F> auto optional<T>::flat_map(F f) & -> `['see below]` ;`]
+
+* [*Requires:] The return type of expression `f(**this)` is `optional<U>` for some object or reference type `U`.
+* [*Effects:] `if (*this) return f(**this); else return none;`
+* [*Notes:] The return type of these overloads is `optional<U>`. On compilers that do not support ref-qualifiers on member functions, these two (as well as the next one) overloads are replaced with good old const and non-const overloads.
+* [*Example:]
+``
+optional<char> first_char(const string& s) {
+ return s.empty() ? none : optional<char>(s[0]);
+};
+optional<string> o1 {}, o2 {"cat"};
+optional<char> os1 = o1.flat_map(first_char), os2 = o2.flat_map(first_char);
+assert ( !os1 ) ;
+assert ( os2 ) ;
+assert ( *os2 == 'c' ) ;
+``
+__SPACE__
+
+[#reference_optional_flat_map_move]
+
+[: `template<class F> auto optional<T>::flat_map(F f) && -> `['see below]` ;`]
+
+* [*Requires:] The return type of expression `f(std::move(**this))` is `optional<U>` for some object or reference type `U`.
+* [*Effects:] `if (*this) return f(std::move(**this)); else return none;`
+* [*Notes:] The return type of this overload is `optional<U>`.
+
+__SPACE__
+
+[#reference_optional_get_value_or_value]
+
+[: `T const& optional<T>::get_value_or( T const& default) const ;`]
+[: `T& optional<T>::get_value_or( T& default ) ;`]
+
+* [*Deprecated:] Use `value_or()` instead.
+* [*Returns:] A reference to the contained value, if any, or `default`.
+* [*Throws:] Nothing.
+* [*Example:]
+``
+T v, z ;
+optional<T> def;
+T const& y = def.get_value_or(z);
+assert ( y == z ) ;
+
+optional<T> opt ( v );
+T const& u = opt.get_value_or(z);
+assert ( u == v ) ;
+assert ( u != z ) ;
+``
+
+
+__SPACE__
+
+[#reference_optional_get_ptr]
+
+[: `T const* optional<T>::get_ptr() const ;`]
+[: `T* optional<T>::get_ptr() ;`]
+
+* [*Returns:] If `*this` is initialized, a pointer to the contained value;
+else `0` (['null]).
+* [*Throws:] Nothing.
+* [*Notes:] The contained value is permanently stored within `*this`, so you
+should not hold nor delete this pointer
+* [*Example:]
+``
+T v;
+optional<T> opt(v);
+optional<T> const copt(v);
+T* p = opt.get_ptr() ;
+T const* cp = copt.get_ptr();
+assert ( p == get_pointer(opt) );
+assert ( cp == get_pointer(copt) ) ;
+``
+
+__SPACE__
+
+[#reference_optional_operator_arrow]
+
+[: `T const* optional<T>::operator ->() const ;`]
+[: `T* optional<T>::operator ->() ;`]
+
+* [*Requires: ] `*this` is initialized.
+* [*Returns:] A pointer to the contained value.
+* [*Throws:] Nothing.
+* [*Notes:] The requirement is asserted via `BOOST_ASSERT()`.
+* [*Example:]
+``
+struct X { int mdata ; } ;
+X x ;
+optional<X> opt (x);
+opt->mdata = 2 ;
+``
+
+__SPACE__
+
+[#reference_optional_operator_bool]
+
+[: `explicit optional<T>::operator bool() const noexcept ;`]
+[: `bool optional<T>::has_value() const noexcept ;`]
+
+* [*Returns:] `get_ptr() != 0`.
+* [*Notes:] On compilers that do not support explicit conversion operators this falls back to safe-bool idiom.
+* [*Example:]
+``
+optional<T> def ;
+assert ( def == 0 );
+optional<T> opt ( v ) ;
+assert ( opt );
+assert ( opt != 0 );
+``
+
+__SPACE__
+
+[#reference_optional_operator_not]
+
+[: `bool optional<T>::operator!() noexcept ;`]
+
+* [*Returns:] If `*this` is uninitialized, `true`; else `false`.
+* [*Notes:] This operator is provided for those compilers which can't
+use the ['unspecified-bool-type operator] in certain boolean contexts.
+* [*Example:]
+``
+optional<T> opt ;
+assert ( !opt );
+*opt = some_T ;
+
+// Notice the "double-bang" idiom here.
+assert ( !!opt ) ;
+``
+
+__SPACE__
+
+[#reference_optional_is_initialized]
+
+[: `bool optional<T>::is_initialized() const ;`]
+
+* [*Deprecated:] Same as `explicit operator bool () ;`
+
+
+[endsect]
+
+[section Detailed Semantics - Optional References]
+
+__SPACE__
+
+[#reference_optional_ref_default_ctor]
+
+[: `optional<T&>::optional() noexcept;`]
+[: `optional<T&>::optional(none_t) noexcept;`]
+
+* [*Postconditions:] `bool(*this) == false`; `*this` refers to nothing.
+
+
+__SPACE__
+
+[#reference_optional_ref_value_ctor]
+
+[: `template<class R> optional<T&>::optional(R&& r) noexcept;`]
+* [*Postconditions:] `bool(*this) == true`; `addressof(**this) == addressof(r)`.
+* [*Remarks:] Unless `R` is an lvalue reference, the program is ill-formed. This constructor does not participate in overload resolution if `decay<R>` is an instance of `boost::optional`.
+* [*Notes:] This constructor is declared `explicit` on compilers that do not correctly suport binding to const lvalues of integral types. For more details [link optional_reference_binding see here].
+* [*Example:]
+``
+T v;
+T& vref = v ;
+optional<T&> opt(vref);
+assert ( *opt == v ) ;
+++ v ; // mutate referee
+assert (*opt == v);
+``
+
+__SPACE__
+
+[#reference_optional_ref_cond_value_ctor]
+
+[: `template<class R> optional<T&>::optional(bool cond, R&& r) noexcept;`]
+* [*Effects: ] Initializes `ref` with expression `cond ? addressof(r) : nullptr`.
+* [*Postconditions:] `bool(*this) == cond`; If `bool(*this)`, `addressof(**this) == addressof(r)`.
+* [*Remarks:] Unless `R` is an lvalue reference, the program is ill-formed. This constructor does not participate in overload resolution if `decay<R>` is an instance of `boost::optional`.
+
+__SPACE__
+
+[#reference_optional_ref_copy_ctor]
+
+[: `optional<T&>::optional ( optional const& rhs ) noexcept ;`]
+
+* [*Effects: ] Initializes `ref` with expression `rhs.ref`.
+
+* [*Postconditions:] `bool(*this) == bool(rhs)`.
+
+* [*Example:]
+``
+optional<T&> uninit ;
+assert (!uninit);
+
+optional<T&> uinit2 ( uninit ) ;
+assert ( uninit2 == uninit );
+
+T v = 2 ; T& ref = v ;
+optional<T> init(ref);
+assert ( *init == v ) ;
+
+optional<T> init2 ( init ) ;
+assert ( *init2 == v ) ;
+
+v = 3 ;
+
+assert ( *init == 3 ) ;
+assert ( *init2 == 3 ) ;
+``
+
+__SPACE__
+
+[#reference_optional_ref_ctor_from_opt_U]
+
+[: `template<class U> explicit optional<T&>::optional ( optional<U&> const& rhs ) noexcept ;`]
+
+* [*Requires:] `is_convertible<U&, T&>::value` is `true`.
+
+* [*Effects: ] Initializes `ref` with expression `rhs.ref`.
+
+* [*Postconditions:] `bool(*this) == bool(rhs)`.
+
+
+__SPACE__
+
+[#reference_optional_ref_assign_none_t]
+
+[: `optional<T&>::operator= ( none_t ) noexcept ;`]
+
+* [*Effects: ] Assigns `ref` with expression `nullptr`.
+
+* [*returns:] `*this`.
+
+* [*Postconditions:] `bool(*this) == false`.
+
+
+
+[#reference_optional_ref_copy_assign]
+
+[: `optional& optional<T&>::operator= ( optional const& rhs ) noexcept ;`]
+
+* [*Effects: ] Assigns `ref` with expression `rhs.ref`.
+
+* [*returns:] `*this`.
+
+* [*Postconditions:] `bool(*this) == bool(rhs)`.
+
+* [*Notes:] This behaviour is called ['rebinding semantics]. See [link boost_optional.tutorial.optional_references.rebinding_semantics_for_assignment_of_optional_references here] for details.
+
+* [*Example:]
+``
+int a = 1 ;
+int b = 2 ;
+T& ra = a ;
+T& rb = b ;
+optional<int&> def ;
+optional<int&> ora(ra) ;
+optional<int&> orb(rb) ;
+
+def = orb ; // binds 'def' to 'b' through 'rb' wrapped within 'orb'
+assert ( *def == b ) ;
+*def = ora ; // changes the value of 'b' to a copy of the value of 'a'
+assert ( b == a ) ;
+int c = 3;
+int& rc = c ;
+optional<int&> orc(rc) ;
+ora = orc ; // REBINDS ora to 'c' through 'rc'
+c = 4 ;
+assert ( *ora == 4 ) ;
+``
+
+
+[#reference_optional_ref_assign_optional_U]
+
+[: `template<class U> optional& optional<T&>::operator= ( optional<U&> const& rhs ) noexcept ;`]
+
+* [*Requires:] `is_convertible<U&, T&>::value` is `true`.
+
+* [*Effects: ] Assigns `ref` with expression `rhs.ref`.
+
+* [*returns:] `*this`.
+
+* [*Postconditions:] `bool(*this) == bool(rhs)`.
+
+
+__SPACE__
+
+[#reference_optional_ref_assign_R]
+
+[: `template<class R> optional& optional<T&>::operator= ( R&& r ) noexcept ;`]
+
+* [*Effects: ] Assigns `ref` with expression `r`.
+
+* [*returns:] `*this`.
+
+* [*Postconditions:] `bool(*this) == true`.
+
+* [*Remarks:] Unless `R` is an lvalue reference, the program is ill-formed. This function does not participate in overload resolution if `decay<R>` is an instance of `boost::optional`.
+
+* [*Example:]
+``
+int a = 1 ;
+int b = 2 ;
+T& ra = a ;
+T& rb = b ;
+optional<int&> def ;
+optional<int&> opt(ra) ;
+
+def = rb ; // binds 'def' to 'b' through 'rb'
+assert ( *def == b ) ;
+*def = a ; // changes the value of 'b' to a copy of the value of 'a'
+assert ( b == a ) ;
+int c = 3;
+int& rc = c ;
+opt = rc ; // REBINDS to 'c' through 'rc'
+c = 4 ;
+assert ( *opt == 4 ) ;
+``
+
+__SPACE__
+
+[#reference_optional_ref_emplace_R]
+
+[: `void optional<T&>::emplace( R&& r ) noexcept ;`]
+* [*Effects: ] Assigns `ref` with expression `r`.
+* [*Postconditions:] `bool(*this) == true`.
+* [*Remarks:] Unless `R` is an lvalue reference, the program is ill-formed. This function does not participate in overload resolution if `decay<R>` is an instance of `boost::optional`.
+
+__SPACE__
+
+[#reference_optional_ref_get]
+[: `T& optional<T&>::get() const ;`]
+[: `T& optional<T&>::operator *() const ;`]
+* [*Requires:] `bool(*this) == true`.
+* [*Effects: ] Returns `*ref`.
+* [*Throws: ] Nothing.
+* [*Example:]
+``
+T v ;
+T& vref = v ;
+optional<T&> opt ( vref );
+T const& vref2 = *opt;
+assert ( vref2 == v ) ;
+++ v ;
+assert ( *opt == v ) ;
+``
+
+__SPACE__
+
+[#reference_optional_ref_arrow]
+[: `T* optional<T&>::operator -> () const ;`]
+* [*Requires:] `bool(*this) == true`.
+* [*Effects: ] Returns `ref`.
+* [*Throws: ] Nothing.
+
+__SPACE__
+
+[#reference_optional_ref_value]
+[: `T& optional<T&>::value() const ;`]
+* [*Effects:] Equivalent to `return bool(*this) ? *val : throw bad_optional_access();`.
+
+__SPACE__
+
+[#reference_optional_ref_value_or]
+[: `template<class R> T& optional<T&>::value_or( R&& r ) const noexcept;`]
+* [*Effects:] Equivalent to `if (*this) return **this; else return r;`.
+* [*Remarks:] Unless `R` is an lvalue reference, the program is ill-formed.
+
+__SPACE__
+
+[#reference_optional_ref_value_or_eval]
+[: `template<class F> T& optional<T&>::value_or( F f ) const ;`]
+* [*Effects:] Equivalent to `if (*this) return **this; else return f();`.
+* [*Remarks:] Unless `decltype(f())` is an lvalue reference, the program is ill-formed.
+
+__SPACE__
+
+[#reference_optional_ref_map]
+[: `template<class F> auto optional<T&>::map( F f ) const -> `['see below]`;`]
+* [*Effects:] Equivalent to `if (*this) return f(**this); else return none;`.
+* [*Remarks:] The return type of this function is `optional<decltype(f(**this))>`.
+
+__SPACE__
+
+[#reference_optional_ref_flat_map]
+[: `template<class F> auto optional<T&>::flat_map( F f ) const -> `['see below]`;`]
+* [*Requires:] The return type of expression `f(**this)` is `optional<U>` for some object or reference type `U`.
+* [*Effects:] Equivalent to `if (*this) return f(**this); else return none;`.
+* [*Remarks:] The return type of this function is `optional<U>`.
+
+__SPACE__
+
+[#reference_optional_ref_get_ptr]
+[: `T* optional<T&>::get_ptr () const noexcept;`]
+* [*Returns:] `ref`.
+
+__SPACE__
+
+[#reference_optional_ref_operator_bool]
+[: `bool has_value() const noexcept;`]
+[: `optional<T&>::operator bool () const noexcept;`]
+* [*Returns:] `bool(ref)`.
+
+__SPACE__
+
+[#reference_optional_ref_operator_not]
+[: `optional<T&>::operator ! () const noexcept;`]
+* [*Returns:] `!bool(ref)`.
+
+__SPACE__
+
+[#reference_optional_ref_reset]
+[: `void optional<T&>::reset() noexcept;`]
+* [*Effects:] Use `*this = none` instead.
+* [*Remarks:] This function is depprecated.
+
+__SPACE__
+
+[#reference_optional_ref_reset_value]
+[: `template<class R> void optional<T&>::reset ( R&& r) noexcept;`]
+* [*Effects:] Equivalent to `*this = std::forward<R>(r)`.
+* [*Remarks:] This function is depprecated.
+
+__SPACE__
+
+[#reference_optional_ref_is_initialized]
+[: `bool optional<T&>::is_initialized() const noexcept;`]
+* [*Effects:] Equivalent to `return bool(*this)`.
+* [*Remarks:] This function is depprecated.
+
+__SPACE__
+
+[#reference_optional_ref_get_value_or_value]
+[: `template<class R> T& optional<T&>::get_value_or( R&& r ) const noexcept;`]
+* [*Effects:] Equivalent to `return value_or(std::forward<R>(r);`.
+* [*Remarks:] This function is depprecated.
+
+[endsect]
+
+
+[section Detailed Semantics - Free Functions]
+
+
+__SPACE__
+
+[#reference_make_optional_value]
+
+[: `optional<T> make_optional( T const& v )`]
+
+* [*Returns: ] `optional<T>(v)` for the ['deduced] type `T` of `v`.
+* [*Example:]
+``
+template<class T> void foo ( optional<T> const& opt ) ;
+
+foo ( make_optional(1+1) ) ; // Creates an optional<int>
+``
+
+__SPACE__
+
+[#reference_make_optional_rvalue]
+
+[: `optional<std::decay_t<T>> make_optional( T && v )`]
+
+* [*Returns: ] `optional<std::decay_t<T>>(std::move(v))` for the ['deduced] type `T` of `v`.
+
+
+__SPACE__
+
+[#reference_make_optional_bool_value]
+
+[: `optional<T> make_optional( bool condition, T const& v )`]
+
+* [*Returns: ] `optional<T>(condition, v)` for the ['deduced] type `T` of `v`.
+* [*Example:]
+``
+optional<double> calculate_foo()
+{
+ double val = compute_foo();
+ return make_optional(is_not_nan_and_finite(val),val);
+}
+
+optional<double> v = calculate_foo();
+if ( !v )
+ error("foo wasn't computed");
+``
+
+__SPACE__
+
+[#reference_make_optional_bool_rvalue]
+
+[: `optional<std::decay_t<T>> make_optional( bool condition, T && v )`]
+
+* [*Returns: ] `optional<std::decay_t<T>>(condition, std::move(v))` for the ['deduced] type `T` of `v`.
+
+
+__SPACE__
+
+[#reference_operator_compare_equal_optional_optional]
+
+[: `bool operator == ( optional<T> const& x, optional<T> const& y );`]
+
+* [*Requires:] `T` shall meet requirements of __SGI_EQUALITY_COMPARABLE__.
+* [*Returns:] If both `x` and `y` are initialized, `(*x == *y)`. If only
+`x` or `y` is initialized, `false`. If both are uninitialized, `true`.
+* [*Notes:] This definition guarantees that `optional<T>` not containing a value is compared unequal to any `optional<T>` containing any value, and equal to any other `optional<T>` not containing a value.
+Pointers have shallow relational operators while `optional` has deep relational operators. Do not use `operator==` directly in generic code which expect to be given either an `optional<T>` or a pointer; use
+__FUNCTION_EQUAL_POINTEES__ instead
+* [*Example:]
+``
+optional<T> oN, oN_;
+optional<T> o1(T(1)), o1_(T(1));
+optional<T> o2(T(2));
+
+assert ( oN == oN ); // Identity implies equality
+assert ( o1 == o1 ); //
+
+assert ( oN == oN_ ); // Both uninitialized compare equal
+
+assert ( oN != o1 ); // Initialized unequal to initialized.
+
+assert ( o1 == o1_ ); // Both initialized compare as (*lhs == *rhs)
+assert ( o1 != o2 ); //
+``
+
+__SPACE__
+
+[#reference_operator_compare_less_optional_optional]
+
+[: `bool operator < ( optional<T> const& x, optional<T> const& y );`]
+
+* [*Requires:] Expression `*x < *y` shall be well-formed and its result shall be convertible to `bool`.
+* [*Returns:] `(!y) ? false : (!x) ? true : *x < *y`.
+* [*Notes:] This definition guarantees that `optional<T>` not containing a value is ordered as less than any `optional<T>` containing any value, and equivalent to any other `optional<T>` not containing a value.
+Pointers have shallow relational operators while `optional` has deep relational operators. Do not use `operator<` directly in generic code
+which expect to be given either an `optional<T>` or a pointer; use __FUNCTION_LESS_POINTEES__ instead. `T` need not be __SGI_LESS_THAN_COMPARABLE__. Only single `operator<` is required. Other relational operations are defined in terms of this one. If `T`'s `operator<` satisfies the axioms of __SGI_LESS_THAN_COMPARABLE__ (transitivity, antisymmetry and irreflexivity), `optinal<T>` is __SGI_LESS_THAN_COMPARABLE__.
+* [*Example:]
+``
+optional<T> oN, oN_;
+optional<T> o0(T(0));
+optional<T> o1(T(1));
+
+assert ( !(oN < oN) ); // Identity implies equivalence
+assert ( !(o1 < o1) );
+
+assert ( !(oN < oN_) ); // Two uninitialized are equivalent
+assert ( !(oN_ < oN) );
+
+assert ( oN < o0 ); // Uninitialized is less than initialized
+assert ( !(o0 < oN) );
+
+assert ( o1 < o2 ) ; // Two initialized compare as (*lhs < *rhs)
+assert ( !(o2 < o1) ) ;
+assert ( !(o2 < o2) ) ;
+``
+
+__SPACE__
+
+[#reference_operator_compare_not_equal_optional_optional]
+
+[: `bool operator != ( optional<T> const& x, optional<T> const& y );`]
+
+* [*Returns: ] `!( x == y );`
+
+__SPACE__
+
+[#reference_operator_compare_greater_optional_optional]
+
+[: `bool operator > ( optional<T> const& x, optional<T> const& y );`]
+
+* [*Returns: ] `( y < x );`
+
+__SPACE__
+
+[#reference_operator_compare_less_or_equal_optional_optional]
+
+[: `bool operator <= ( optional<T> const& x, optional<T> const& y );`]
+
+* [*Returns: ] `!( y < x );`
+
+__SPACE__
+
+[#reference_operator_compare_greater_or_equal_optional_optional]
+
+[: `bool operator >= ( optional<T> const& x, optional<T> const& y );`]
+
+* [*Returns: ] `!( x < y );`
+
+__SPACE__
+
+[#reference_operator_compare_equal_optional_none]
+
+[: `bool operator == ( optional<T> const& x, none_t ) noexcept;`]
+[: `bool operator == ( none_t, optional<T> const& x ) noexcept;`]
+
+* [*Returns:] `!x`.
+* [*Notes:] `T` need not meet requirements of __SGI_EQUALITY_COMPARABLE__.
+
+
+__SPACE__
+
+[#reference_operator_compare_not_equal_optional_none]
+
+[: `bool operator != ( optional<T> const& x, none_t ) noexcept;`]
+[: `bool operator != ( none_t, optional<T> const& x ) noexcept;`]
+
+* [*Returns: ] `bool(x);`
+
+
+__SPACE__
+
+
+[#reference_free_get_pointer]
+[: `auto get_pointer ( optional<T>& o ) -> typename optional<T>::pointer_type ;`]
+[: `auto get_pointer ( optional<T> const& o ) -> typename optional<T>::pointer_const_type ;`]
+* [*Returns:] `o.get_ptr()`.
+* [*Throws:] Nothing.
+
+__SPACE__
+
+
+[#reference_free_get_value_or]
+[: `auto get_optional_value_or ( optional<T>& o, typename optional<T>::reference_type def ) -> typename optional<T>::reference_type ;`]
+[: `auto get_optional_value_or ( optional<T> const& o, typename optional<T>::reference_const_type def ) -> typename optional<T>::reference_const_type ;`]
+* [*Returns:] `o.get_value_or(def)`.
+* [*Throws:] Nothing.
+* [*Remarks:] This function is deprecated.
+
+__SPACE__
+
+[#reference_swap_optional_optional]
+
+[: `void swap ( optional<T>& x, optional<T>& y ) ;`]
+
+* [*Requires:] Lvalues of type `T` shall be swappable and `T` shall be __MOVE_CONSTRUCTIBLE__.
+* [*Effects:]
+[table
+ []
+ [[][[*`*this` contains a value]][[*`*this` does not contain a value]]]
+ [[[*`rhs` contains a value]][calls `swap(*(*this), *rhs)`][initializes the contained value of `*this` as if direct-initializing an object of type `T` with the expression `std::move(*rhs)`, followed by `rhs.val->T::~T()`, `*this` contains a value and `rhs` does not contain a value]]
+ [[[*`rhs` does not contain a value]][initializes the contained value of `rhs` as if direct-initializing an object of type `T` with the expression `std::move(*(*this))`, followed by `val->T::~T()`, `*this` does not contain a value and `rhs` contains a value][no effect]]
+]
+* [*Postconditions:] The states of `x` and `y` interchanged.
+* [*Throws:] If both are initialized, whatever `swap(T&,T&)` throws. If only
+one is initialized, whatever `T::T ( T&& )` throws.
+* [*Example:]
+``
+T x(12);
+T y(21);
+optional<T> def0 ;
+optional<T> def1 ;
+optional<T> optX(x);
+optional<T> optY(y);
+
+boost::swap(def0,def1); // no-op
+
+boost::swap(def0,optX);
+assert ( *def0 == x );
+assert ( !optX );
+
+boost::swap(def0,optX); // Get back to original values
+
+boost::swap(optX,optY);
+assert ( *optX == y );
+assert ( *optY == x );
+``
+
+__SPACE__
+
+[#reference_swap_optional_reference]
+[: `void swap ( optional<T&>& x, optional<T&>& y ) noexcept ;`]
+
+* [*Postconditions:] `x` refers to what `y` refererred to before the swap (if anything). `y` refers to whatever `x` referred to before the swap.
+
+* [*Example:]
+``
+T x(12);
+T y(21);
+
+optional<T&> opt0;
+optional<T&> optX (x);
+optional<T&> optY (y);
+
+boost::swap(optX, optY);
+assert (addressof(*optX) == addressof(y));
+assert (addressof(*optY) == addressof(x));
+
+boost::swap(opt0, optX);
+assert ( opt0 );
+assert ( !optX );
+assert (addressof(*opt0) == addressof(y));
+``
+
+[endsect]
diff --git a/doc/29_ref_optional_convenience.qbk b/doc/29_ref_optional_convenience.qbk
new file mode 100644
index 0000000..63b4732
--- /dev/null
+++ b/doc/29_ref_optional_convenience.qbk
@@ -0,0 +1,17 @@
+[/
+ Boost.Optional
+
+ Copyright (c) 2003-2007 Fernando Luis Cacciola Carballal
+ Copyright (c) 2015 Andrzej Krzemienski
+
+ Distributed under the Boost Software License, Version 1.0.
+ (See accompanying file LICENSE_1_0.txt or copy at
+ http://www.boost.org/LICENSE_1_0.txt)
+]
+
+[section Header <boost/optional.hpp>]
+
+This is an alias for header [link boost_optional.reference.header__boost_optional_optional_hpp_.header_optional_optional `<boost/optional/optional.hpp>`].
+
+
+[endsect]
diff --git a/doc/90_dependencies.qbk b/doc/90_dependencies.qbk
new file mode 100644
index 0000000..b5fa97c
--- /dev/null
+++ b/doc/90_dependencies.qbk
@@ -0,0 +1,116 @@
+[/
+ Boost.Optional
+
+ Copyright (c) 2003-2007 Fernando Luis Cacciola Carballal
+
+ Distributed under the Boost Software License, Version 1.0.
+ (See accompanying file LICENSE_1_0.txt or copy at
+ http://www.boost.org/LICENSE_1_0.txt)
+]
+
+
+[section Dependencies and Portability]
+
+[section Dependencies]
+The implementation uses the following other Boost modules:
+
+# assert
+# config
+# core
+# detail
+# move
+# mpl
+# static_assert
+# throw_exception
+# type_traits
+# utility
+
+[endsect]
+
+[section Emplace operations in older compilers][#optional_emplace_workaround]
+
+Certain constructors and functions in the interface of `optional` perform a 'perfect forwarding' of arguments:
+
+ template<class... Args> optional(in_place_init_t, Args&&... args);
+ template<class... Args> optional(in_place_init_if_t, bool condition, Args&&... args);
+ template<class... Args> void emplace(Args&&... args);
+
+On compilers that do not support variadic templates, each of these functions is substituted with two overloads, one forwarding a single argument, the other forwarding zero arguments. This forms the following set:
+
+ template<class Arg> optional(in_place_init_t, Arg&& arg);
+ optional(in_place_init_t);
+
+ template<class Arg> optional(in_place_init_if_t, bool condition, Arg&& arg);
+ optional(in_place_init_if_t, bool condition);
+
+ template<class Arg> void emplace(Arg&& arg);
+ void emplace();
+
+On compilers that do not support rvalue references, each of these functions is substituted with three overloadss: taking `const` and non-`const` lvalue reference, and third forwarding zero arguments. This forms the following set:
+
+ template<class Arg> optional(in_place_init_t, const Arg& arg);
+ template<class Arg> optional(in_place_init_t, Arg& arg);
+ optional(in_place_init_t);
+
+ template<class Arg> optional(in_place_init_if_t, bool condition, const Arg& arg);
+ template<class Arg> optional(in_place_init_if_t, bool condition, Arg& arg);
+ optional(in_place_init_if_t, bool condition);
+
+ template<class Arg> void emplace(const Arg& arg);
+ template<class Arg> void emplace(Arg& arg);
+ void emplace();
+
+This workaround addressess about 40% of all use cases. If this is insufficient, you need to resort to using [link boost_optional.tutorial.in_place_factories In-Place Factories].
+[endsect]
+
+[section Optional Reference Binding][#optional_reference_binding]
+
+A number of compilers incorrectly treat const lvalues of integral type as rvalues, and create an illegal temporary when binding to an lvalue reference to const in some expressions. This could result in creating an optional lvalue reference that is in fact bound to an unexpected temporary rather than to the intended object. In order to prevent hard to find run-time bugs, this library performs compile-time checks to prevent expressions that would otherwise bind an optional reference to an unexpected temporary. As a consequence, on certain compilers certain pieces of functionality in optional references are missing. In order to maintain a portability of your code across diferent compilers, it is recommended that you only stick to the minimum portable interface of optional references: prefer direct-initialization and copy assignment of optional references to copy-initialization and assignment from `T&`:
+
+ const int i = 0;
+ optional<const int&> or1;
+ optional<const int&> or2 = i; // caution: not portable
+ or1 = i; // caution: not portable
+
+ optional<const int&> or3(i); // portable
+ or1 = optional<const int&>(i); // portable
+
+Compilers known to have these deficiencies include GCC versions 4.2, 4.3, 4.4, 4.5, 5.1, 5.2; QCC 4.4.2; MSVC versions 8.0, 9.0, 10.0, 11.0, 12.0. In order to check if your compiler correctly implements reference binding use this test program.
+
+ #include <cassert>
+
+ const int global_i = 0;
+
+ struct TestingReferenceBinding
+ {
+ TestingReferenceBinding(const int& ii)
+ {
+ assert(&ii == &global_i);
+ }
+
+ void operator=(const int& ii)
+ {
+ assert(&ii == &global_i);
+ }
+
+ void operator=(int&&) // remove this if your compiler doesn't have rvalue refs
+ {
+ assert(false);
+ }
+ };
+
+ int main()
+ {
+ const int& iref = global_i;
+ assert(&iref == &global_i);
+
+ TestingReferenceBinding ttt = global_i;
+ ttt = global_i;
+
+ TestingReferenceBinding ttt2 = iref;
+ ttt2 = iref;
+ }
+
+[endsect]
+
+[endsect]
\ No newline at end of file
diff --git a/doc/91_relnotes.qbk b/doc/91_relnotes.qbk
new file mode 100644
index 0000000..b7d410f
--- /dev/null
+++ b/doc/91_relnotes.qbk
@@ -0,0 +1,99 @@
+[/
+ Boost.Optional
+
+ Copyright (c) 2015, 2016 Andrzej Krzemienski
+
+ Distributed under the Boost Software License, Version 1.0.
+ (See accompanying file LICENSE_1_0.txt or copy at
+ http://www.boost.org/LICENSE_1_0.txt)
+]
+
+
+[section:relnotes Release Notes]
+
+[heading Boost Release 1.68]
+
+* Added member function `has_value()` for compatibility with `std::optional` ([@https://github.com/boostorg/optional/issues/52 issue #52]).
+* Added member function `map()` for transforming `optional<T>` into `optional<U>` using a function of type `T -> U`.
+* Added member function `flat_map()` for transforming `optional<T>` into `optional<U>` using a function of type `T -> optonal<U>`.
+
+
+[heading Boost Release 1.67]
+
+* Fixed [@https://github.com/boostorg/optional/issues/46 issue #46].
+* Fixed `-Wzero-as-null-pointer-constant` warnings.
+
+
+[heading Boost Release 1.66]
+
+* On newer compilers `optional` is now trivially-copyable for scalar `T`s. This uses a different storage (just `T` rather than `aligned_storage`). We require the compiler to support defaulted functions.
+* Changed the implementation of `operator==` to get rid of the `-Wmaybe-uninitialized` false-positive warning from GCC.
+
+[heading Boost Release 1.63]
+* Added two new in-place constructors. They work similarly to `emplace()` functions: they initialize the contained value by perfect-forwarding the obtained arguments. One constructor always initializes the contained value, the other based on a boolean condition.
+* Syntax `o = {}` now correctly un-initializes optional, just like in `std::optional`.
+* Fixed [@https://svn.boost.org/trac/boost/ticket/12203 Trac #12203].
+* Fixed [@https://svn.boost.org/trac/boost/ticket/12563 Trac #12563].
+
+
+[heading Boost Release 1.62]
+
+* Fixed [@https://svn.boost.org/trac/boost/ticket/12179 Trac #12179].
+
+
+[heading Boost Release 1.61]
+
+* Now `boost::optional` is specialized for reference parameters. This addresses a couple of issues:
+ * the `sizeof` of optional reference is that of a pointer,
+ * some bugs connected to copying optional references are gone,
+ * all run-time bugs caused by incorrect reference binding on some compilers are now turned into compile-time errors,
+ * you can swap optional references: it is like swapping pointers: shalow, underlying objects are not affected,
+ * optional references to abstract types work.
+* Documented nested typedefs ([@https://svn.boost.org/trac/boost/ticket/5193 Trac #5193]).
+* Made the perfect-forwarding constructor SFINAE-friendly, which fixes [@https://svn.boost.org/trac/boost/ticket/12002 Trac #12002]. However, this only works in the newer platforms that correctly implement C++11 `<type_traits>`.
+* Fixed [@https://svn.boost.org/trac/boost/ticket/10445 Trac #10445].
+
+
+[heading Boost Release 1.60]
+
+* Changed the implementation of `boost::none` again. Now it is a const object with internal linkage (as any other tag). This fixes [@https://svn.boost.org/trac/boost/ticket/11203 Trac #11203].
+
+
+[heading Boost Release 1.59]
+
+* For C++03 compilers, added 0-argument overload for member function `emplace()`, and therewith removed the dependency on `<boost/utility/in_place_factory.hpp>`.
+* Fixed [@https://svn.boost.org/trac/boost/ticket/11241 Trac #11241].
+
+[heading Boost Release 1.58]
+
+* `boost::none_t` is no longer convertible from literal `0`. This avoids a bug where `optional<rational<int>> oi = 0;` would initialize an optional object with no contained value.
+* Improved the trick that prevents streaming out `optional` without header `optional_io.hpp` by using safe-bool idiom. This addresses [@https://svn.boost.org/trac/boost/ticket/10825 Trac #10825].
+* IOStream operators are now mentioned in documentation.
+* Added a way to manually disable move semantics: just define macro `BOOST_OPTIONAL_CONFIG_NO_RVALUE_REFERENCES`. This can be used to work around [@https://svn.boost.org/trac/boost/ticket/10399 Trac #10399].
+* It is no longer possible to assign `optional<U>` to `optional<T>` when `U` is not assignable or convertible to `T` ([@https://svn.boost.org/trac/boost/ticket/11087 Trac #11087]).
+* Value accessors now work correctly on rvalues of `optional<T&>` ([@https://svn.boost.org/trac/boost/ticket/10839 Trac #10839]).
+
+
+[heading Boost Release 1.57]
+
+* [@https://github.com/boostorg/optional/pull/9 Git pull #9]: ['"Supply `<string>` to fix C++03 compile error on `logic_error("...")`"].
+
+
+[heading Boost Release 1.56]
+
+* Added support for rvalue references. Now `optional<T>` works with moveable but non-copyable `T`'s,
+* Improved `swap` (now uses move operations),
+* Added function `emplace()`. This is the last of the requests from [@https://svn.boost.org/trac/boost/ticket/1841 Trac #1841],
+* `optional` is moveable, including conditional `noexcept` specifications, which make it `move_if_noexcept`-friendly,
+* Using explicit operator bool() on platforms that support it ([@https://svn.boost.org/trac/boost/ticket/4227 Trac #4227]) (breaking change),
+* Forward declaration of `operator<<(ostream&, optional const&)` to prevent inadvertent incorrect serialization of optional objects,
+* Removed deprecated function `reset()` from examples ([@https://svn.boost.org/trac/boost/ticket/9005 Trac #9005]),
+* Equality comparison with `boost::none` does not require that `T` be EqualityComparable,
+* Optional rvalue references are explicitly disallowed,
+* Binding temporaries to optional references is explicitly disallowed (breaking change),
+* More ways to access the contained value, functions `value()`, `value_or()`, `value_or_eval()`,
+* Updated and reorganized documentation, added tutorial and quick guide sections.
+
+
+
+[endsect][/ relnotes]
diff --git a/doc/92_acknowledgments.qbk b/doc/92_acknowledgments.qbk
new file mode 100644
index 0000000..f337ce2
--- /dev/null
+++ b/doc/92_acknowledgments.qbk
@@ -0,0 +1,62 @@
+[/
+ Boost.Optional
+
+ Copyright (c) 2003-2007 Fernando Luis Cacciola Carballal
+
+ Distributed under the Boost Software License, Version 1.0.
+ (See accompanying file LICENSE_1_0.txt or copy at
+ http://www.boost.org/LICENSE_1_0.txt)
+]
+
+
+[section:acknowledgements Acknowledgements]
+
+[heading Pre-formal review]
+
+* Peter Dimov suggested the name 'optional', and was the first to point out
+the need for aligned storage.
+* Douglas Gregor developed 'type_with_alignment', and later Eric Friedman
+coded 'aligned_storage', which are the core of the optional class
+implementation.
+* Andrei Alexandrescu and Brian Parker also worked with aligned storage
+techniques and their work influenced the current implementation.
+* Gennadiy Rozental made extensive and important comments which shaped the
+design.
+* Vesa Karvonen and Douglas Gregor made quite useful comparisons between
+optional, variant and any; and made other relevant comments.
+* Douglas Gregor and Peter Dimov commented on comparisons and evaluation
+in boolean contexts.
+* Eric Friedman helped understand the issues involved with aligned storage,
+move/copy operations and exception safety.
+* Many others have participated with useful comments: Aleksey Gurotov,
+Kevlin Henney, David Abrahams, and others I can't recall.
+
+[heading Post-formal review]
+
+* William Kempf carefully considered the originally proposed interface
+and suggested the new interface which is currently used. He also started and
+fueled the discussion about the analogy optional<>/smart pointer and about
+relational operators.
+* Peter Dimov, Joel de Guzman, David Abrahams, Tanton Gibbs and Ian Hanson
+focused on the relational semantics of optional (originally undefined);
+concluding with the fact that the pointer-like interface doesn't make it a
+pointer so it shall have deep relational operators.
+* Augustus Saunders also explored the different relational semantics between
+optional<> and a pointer and developed the OptionalPointee concept as an aid
+against potential conflicts on generic code.
+* Joel de Guzman noticed that optional<> can be seen as an API on top of
+variant<T,nil_t>.
+* Dave Gomboc explained the meaning and usage of the Haskell analog to
+optional<>: the Maybe type constructor (analogy originally pointed out by
+David Sankel).
+* Other comments were posted by Vincent Finn, Anthony Williams, Ed Brey,
+Rob Stewart, and others.
+* Joel de Guzman made the case for the support of references and helped
+with the proper semantics.
+* Mat Marcus shown the virtues of a value-oriented interface, influencing
+the current design, and contributed the idea of "none".
+* Vladimir Batov's design of Boost.Convert library motivated the development
+of value accessors for `optional`: functions `value`, `value_or`, `value_or_eval`.
+
+[endsect]
+
diff --git a/doc/Jamfile.v2 b/doc/Jamfile.v2
new file mode 100644
index 0000000..2fc6463
--- /dev/null
+++ b/doc/Jamfile.v2
@@ -0,0 +1,53 @@
+# Boost.Optional
+#
+# Copyright (c) 2003-2007 Fernando Luis Cacciola Carballal
+#
+# Distributed under the Boost Software License, Version 1.0.
+# (See accompanying file LICENSE_1_0.txt or copy at
+# http://www.boost.org/LICENSE_1_0.txt)
+
+
+# Quickbook
+# -----------------------------------------------------------------------------
+
+using boostbook ;
+import quickbook ;
+
+path-constant images : html ;
+
+xml optional
+ :
+ 00_optional.qbk
+ ;
+
+install images
+ :
+ images/opt_align1.png
+ images/opt_align2.png
+ images/opt_align3.png
+ images/opt_align4.png
+ :
+ <location>html/images
+ ;
+
+boostbook standalone
+ :
+ optional
+ :
+ <format>html:<xsl:param>boost.root=../../../..
+ <format>html:<xsl:param>boost.libraries=../../../../libs/libraries.htm
+ <xsl:param>chapter.autolabel=0
+ <xsl:param>chunk.section.depth=8
+ <xsl:param>toc.section.depth=2
+ <xsl:param>toc.max.depth=2
+ <xsl:param>generate.section.toc.level=1
+ <format>pdf:<xsl:param>img.src.path=$(images)/
+ <format>pdf:<xsl:param>boost.url.prefix=http://www.boost.org/doc/libs/release/libs/optional/doc/html
+ <format>docbook:<auto-index-internal>on
+ ;
+
+###############################################################################
+alias boostdoc ;
+explicit boostdoc ;
+alias boostrelease : standalone ;
+explicit boostrelease ;
diff --git a/doc/html/boost_optional/a_note_about_optional_bool_.html b/doc/html/boost_optional/a_note_about_optional_bool_.html
new file mode 100644
index 0000000..64f37f6
--- /dev/null
+++ b/doc/html/boost_optional/a_note_about_optional_bool_.html
@@ -0,0 +1,108 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>A note about optional<bool></title>
+<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../index.html" title="Chapter 1. Boost.Optional">
+<link rel="up" href="../index.html" title="Chapter 1. Boost.Optional">
+<link rel="prev" href="detailed_semantics.html" title="Detailed Semantics">
+<link rel="next" href="exception_safety_guarantees.html" title="Exception Safety Guarantees">
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+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
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+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../index.html">Home</a></td>
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+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../more/index.htm">More</a></td>
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+<a accesskey="p" href="detailed_semantics.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="exception_safety_guarantees.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="boost_optional.a_note_about_optional_bool_"></a><a class="link" href="a_note_about_optional_bool_.html" title="A note about optional<bool>">A note about
+ optional<bool></a>
+</h2></div></div></div>
+<p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span></code> should
+ be used with special caution and consideration.
+ </p>
+<p>
+ First, it is functionally similar to a tristate boolean (false, maybe, true)
+ —such as <a href="../../../../../doc/html/tribool.html" target="_top">boost::tribool</a>—
+ except that in a tristate boolean, the maybe state <span class="underline">represents
+ a valid value</span>, unlike the corresponding state of an uninitialized
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span></code>. It
+ should be carefully considered if an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span></code>
+ instead of a <code class="computeroutput"><span class="identifier">tribool</span></code> is really
+ needed.
+ </p>
+<p>
+ Second, although <code class="computeroutput"><span class="identifier">optional</span><span class="special"><></span></code>
+ provides a contextual conversion to <code class="computeroutput"><span class="keyword">bool</span></code>
+ in C++11, this falls back to an implicit conversion on older compilers. This
+ conversion refers to the initialization state and not to the contained value.
+ Using <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span></code> can
+ lead to subtle errors due to the implicit <code class="computeroutput"><span class="keyword">bool</span></code>
+ conversion:
+ </p>
+<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">foo</span> <span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="keyword">void</span> <span class="identifier">bar</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span> <span class="identifier">v</span> <span class="special">=</span> <span class="keyword">try</span><span class="special">();</span>
+
+ <span class="comment">// The following intended to pass the value of 'v' to foo():</span>
+ <span class="identifier">foo</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+ <span class="comment">// But instead, the initialization state is passed</span>
+ <span class="comment">// due to a typo: it should have been foo(*v).</span>
+<span class="special">}</span>
+</pre>
+<p>
+ The only implicit conversion is to <code class="computeroutput"><span class="keyword">bool</span></code>,
+ and it is safe in the sense that typical integral promotions don't apply (i.e.
+ if <code class="computeroutput"><span class="identifier">foo</span><span class="special">()</span></code>
+ takes an <code class="computeroutput"><span class="keyword">int</span></code> instead, it won't
+ compile).
+ </p>
+<p>
+ Third, mixed comparisons with <code class="computeroutput"><span class="keyword">bool</span></code>
+ work differently than similar mixed comparisons between pointers and <code class="computeroutput"><span class="keyword">bool</span></code>, so the results might surprise you:
+ </p>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span> <span class="identifier">oEmpty</span><span class="special">(</span><span class="identifier">none</span><span class="special">),</span> <span class="identifier">oTrue</span><span class="special">(</span><span class="keyword">true</span><span class="special">),</span> <span class="identifier">oFalse</span><span class="special">(</span><span class="keyword">false</span><span class="special">);</span>
+
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oEmpty</span> <span class="special">==</span> <span class="identifier">none</span><span class="special">);</span> <span class="comment">// renders true</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oEmpty</span> <span class="special">==</span> <span class="keyword">false</span><span class="special">);</span> <span class="comment">// renders false!</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oEmpty</span> <span class="special">==</span> <span class="keyword">true</span><span class="special">);</span> <span class="comment">// renders false!</span>
+
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oFalse</span> <span class="special">==</span> <span class="identifier">none</span><span class="special">);</span> <span class="comment">// renders false</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oFalse</span> <span class="special">==</span> <span class="keyword">false</span><span class="special">);</span> <span class="comment">// renders true!</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oFalse</span> <span class="special">==</span> <span class="keyword">true</span><span class="special">);</span> <span class="comment">// renders false</span>
+
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oTrue</span> <span class="special">==</span> <span class="identifier">none</span><span class="special">);</span> <span class="comment">// renders false</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oTrue</span> <span class="special">==</span> <span class="keyword">false</span><span class="special">);</span> <span class="comment">// renders false</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oTrue</span> <span class="special">==</span> <span class="keyword">true</span><span class="special">);</span> <span class="comment">// renders true</span>
+</pre>
+<p>
+ In other words, for <code class="computeroutput"><span class="identifier">optional</span><span class="special"><></span></code>, the following assertion does not hold:
+ </p>
+<pre class="programlisting"><span class="identifier">assert</span><span class="special">((</span><span class="identifier">opt</span> <span class="special">==</span> <span class="keyword">false</span><span class="special">)</span> <span class="special">==</span> <span class="special">(!</span><span class="identifier">opt</span><span class="special">));</span>
+</pre>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="detailed_semantics.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="exception_safety_guarantees.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
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+</html>
diff --git a/doc/html/boost_optional/acknowledgements.html b/doc/html/boost_optional/acknowledgements.html
new file mode 100644
index 0000000..c6f9f2f
--- /dev/null
+++ b/doc/html/boost_optional/acknowledgements.html
@@ -0,0 +1,130 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Acknowledgements</title>
+<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../index.html" title="Boost.Optional">
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+</div>
+<div class="section">
+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="boost_optional.acknowledgements"></a><a class="link" href="acknowledgements.html" title="Acknowledgements">Acknowledgements</a>
+</h2></div></div></div>
+<h4>
+<a name="boost_optional.acknowledgements.h0"></a>
+ <span class="phrase"><a name="boost_optional.acknowledgements.pre_formal_review"></a></span><a class="link" href="acknowledgements.html#boost_optional.acknowledgements.pre_formal_review">Pre-formal
+ review</a>
+ </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ Peter Dimov suggested the name 'optional', and was the first to point out
+ the need for aligned storage.
+ </li>
+<li class="listitem">
+ Douglas Gregor developed 'type_with_alignment', and later Eric Friedman
+ coded 'aligned_storage', which are the core of the optional class implementation.
+ </li>
+<li class="listitem">
+ Andrei Alexandrescu and Brian Parker also worked with aligned storage techniques
+ and their work influenced the current implementation.
+ </li>
+<li class="listitem">
+ Gennadiy Rozental made extensive and important comments which shaped the
+ design.
+ </li>
+<li class="listitem">
+ Vesa Karvonen and Douglas Gregor made quite useful comparisons between
+ optional, variant and any; and made other relevant comments.
+ </li>
+<li class="listitem">
+ Douglas Gregor and Peter Dimov commented on comparisons and evaluation
+ in boolean contexts.
+ </li>
+<li class="listitem">
+ Eric Friedman helped understand the issues involved with aligned storage,
+ move/copy operations and exception safety.
+ </li>
+<li class="listitem">
+ Many others have participated with useful comments: Aleksey Gurotov, Kevlin
+ Henney, David Abrahams, and others I can't recall.
+ </li>
+</ul></div>
+<h4>
+<a name="boost_optional.acknowledgements.h1"></a>
+ <span class="phrase"><a name="boost_optional.acknowledgements.post_formal_review"></a></span><a class="link" href="acknowledgements.html#boost_optional.acknowledgements.post_formal_review">Post-formal
+ review</a>
+ </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ William Kempf carefully considered the originally proposed interface and
+ suggested the new interface which is currently used. He also started and
+ fueled the discussion about the analogy optional<>/smart pointer
+ and about relational operators.
+ </li>
+<li class="listitem">
+ Peter Dimov, Joel de Guzman, David Abrahams, Tanton Gibbs and Ian Hanson
+ focused on the relational semantics of optional (originally undefined);
+ concluding with the fact that the pointer-like interface doesn't make it
+ a pointer so it shall have deep relational operators.
+ </li>
+<li class="listitem">
+ Augustus Saunders also explored the different relational semantics between
+ optional<> and a pointer and developed the OptionalPointee concept
+ as an aid against potential conflicts on generic code.
+ </li>
+<li class="listitem">
+ Joel de Guzman noticed that optional<> can be seen as an API on top
+ of variant<T,nil_t>.
+ </li>
+<li class="listitem">
+ Dave Gomboc explained the meaning and usage of the Haskell analog to optional<>:
+ the Maybe type constructor (analogy originally pointed out by David Sankel).
+ </li>
+<li class="listitem">
+ Other comments were posted by Vincent Finn, Anthony Williams, Ed Brey,
+ Rob Stewart, and others.
+ </li>
+<li class="listitem">
+ Joel de Guzman made the case for the support of references and helped with
+ the proper semantics.
+ </li>
+<li class="listitem">
+ Mat Marcus shown the virtues of a value-oriented interface, influencing
+ the current design, and contributed the idea of "none".
+ </li>
+<li class="listitem">
+ Vladimir Batov's design of Boost.Convert library motivated the development
+ of value accessors for <code class="computeroutput"><span class="identifier">optional</span></code>:
+ functions <code class="computeroutput"><span class="identifier">value</span></code>, <code class="computeroutput"><span class="identifier">value_or</span></code>, <code class="computeroutput"><span class="identifier">value_or_eval</span></code>.
+ </li>
+</ul></div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="relnotes.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/acknowledgments.html b/doc/html/boost_optional/acknowledgments.html
new file mode 100644
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@@ -0,0 +1,125 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Acknowledgments</title>
+<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
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+<link rel="up" href="../index.html" title="Boost.Optional">
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+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td>
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+<td align="center"><a href="../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
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+</div>
+<div class="section">
+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="boost_optional.acknowledgments"></a><a class="link" href="acknowledgments.html" title="Acknowledgments">Acknowledgments</a>
+</h2></div></div></div>
+<h4>
+<a name="boost_optional.acknowledgments.h0"></a>
+ <span class="phrase"><a name="boost_optional.acknowledgments.pre_formal_review"></a></span><a class="link" href="acknowledgments.html#boost_optional.acknowledgments.pre_formal_review">Pre-formal
+ review</a>
+ </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ Peter Dimov suggested the name 'optional', and was the first to point out
+ the need for aligned storage.
+ </li>
+<li class="listitem">
+ Douglas Gregor developed 'type_with_alignment', and later Eric Friedman
+ coded 'aligned_storage', which are the core of the optional class implementation.
+ </li>
+<li class="listitem">
+ Andrei Alexandrescu and Brian Parker also worked with aligned storage techniques
+ and their work influenced the current implementation.
+ </li>
+<li class="listitem">
+ Gennadiy Rozental made extensive and important comments which shaped the
+ design.
+ </li>
+<li class="listitem">
+ Vesa Karvonen and Douglas Gregor made quite useful comparisons between
+ optional, variant and any; and made other relevant comments.
+ </li>
+<li class="listitem">
+ Douglas Gregor and Peter Dimov commented on comparisons and evaluation
+ in boolean contexts.
+ </li>
+<li class="listitem">
+ Eric Friedman helped understand the issues involved with aligned storage,
+ move/copy operations and exception safety.
+ </li>
+<li class="listitem">
+ Many others have participated with useful comments: Aleksey Gurotov, Kevlin
+ Henney, David Abrahams, and others I can't recall.
+ </li>
+</ul></div>
+<h4>
+<a name="boost_optional.acknowledgments.h1"></a>
+ <span class="phrase"><a name="boost_optional.acknowledgments.post_formal_review"></a></span><a class="link" href="acknowledgments.html#boost_optional.acknowledgments.post_formal_review">Post-formal
+ review</a>
+ </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ William Kempf carefully considered the originally proposed interface and
+ suggested the new interface which is currently used. He also started and
+ fueled the discussion about the analogy optional<>/smart pointer
+ and about relational operators.
+ </li>
+<li class="listitem">
+ Peter Dimov, Joel de Guzman, David Abrahams, Tanton Gibbs and Ian Hanson
+ focused on the relational semantics of optional (originally undefined);
+ concluding with the fact that the pointer-like interface doesn't make it
+ a pointer so it shall have deep relational operators.
+ </li>
+<li class="listitem">
+ Augustus Saunders also explored the different relational semantics between
+ optional<> and a pointer and developed the OptionalPointee concept
+ as an aid against potential conflicts on generic code.
+ </li>
+<li class="listitem">
+ Joel de Guzman noticed that optional<> can be seen as an API on top
+ of variant<T,nil_t>.
+ </li>
+<li class="listitem">
+ Dave Gomboc explained the meaning and usage of the Haskell analog to optional<>:
+ the Maybe type constructor (analogy originally pointed out by David Sankel).
+ </li>
+<li class="listitem">
+ Other comments were posted by Vincent Finn, Anthony Williams, Ed Brey,
+ Rob Stewart, and others.
+ </li>
+<li class="listitem">
+ Joel de Guzman made the case for the support of references and helped with
+ the proper semantics.
+ </li>
+<li class="listitem">
+ Mat Marcus shown the virtues of a value-oriented interface, influencing
+ the current design, and contributed the idea of "none".
+ </li>
+</ul></div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="dependencies_and_portability/optional_reference_binding.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a>
+</div>
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+</html>
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+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Dependencies and Portability</title>
+<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
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+</div>
+<div class="section">
+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="boost_optional.dependencies_and_portability"></a><a class="link" href="dependencies_and_portability.html" title="Dependencies and Portability">Dependencies
+ and Portability</a>
+</h2></div></div></div>
+<div class="toc"><dl class="toc">
+<dt><span class="section"><a href="dependencies_and_portability.html#boost_optional.dependencies_and_portability.dependencies">Dependencies</a></span></dt>
+<dt><span class="section"><a href="dependencies_and_portability/emplace_operations_in_older_compilers.html">Emplace
+ operations in older compilers</a></span></dt>
+<dt><span class="section"><a href="dependencies_and_portability/optional_reference_binding.html">Optional
+ Reference Binding</a></span></dt>
+</dl></div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.dependencies_and_portability.dependencies"></a><a class="link" href="dependencies_and_portability.html#boost_optional.dependencies_and_portability.dependencies" title="Dependencies">Dependencies</a>
+</h3></div></div></div>
+<p>
+ The implementation uses the following other Boost modules:
+ </p>
+<div class="orderedlist"><ol class="orderedlist" type="1">
+<li class="listitem">
+ assert
+ </li>
+<li class="listitem">
+ config
+ </li>
+<li class="listitem">
+ core
+ </li>
+<li class="listitem">
+ detail
+ </li>
+<li class="listitem">
+ move
+ </li>
+<li class="listitem">
+ mpl
+ </li>
+<li class="listitem">
+ static_assert
+ </li>
+<li class="listitem">
+ throw_exception
+ </li>
+<li class="listitem">
+ type_traits
+ </li>
+<li class="listitem">
+ utility
+ </li>
+</ol></div>
+</div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="reference/header__boost_optional_hpp_.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="dependencies_and_portability/emplace_operations_in_older_compilers.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/dependencies_and_portability/emplace_operations_in_older_compilers.html b/doc/html/boost_optional/dependencies_and_portability/emplace_operations_in_older_compilers.html
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@@ -0,0 +1,90 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Emplace operations in older compilers</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../index.html" title="Boost.Optional">
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+<link rel="next" href="optional_reference_binding.html" title="Optional Reference Binding">
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+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="optional_reference_binding.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.dependencies_and_portability.emplace_operations_in_older_compilers"></a><a class="link" href="emplace_operations_in_older_compilers.html" title="Emplace operations in older compilers">Emplace
+ operations in older compilers</a>
+</h3></div></div></div>
+<p>
+ <a name="optional_emplace_workaround"></a>Certain constructors and functions
+ in the interface of <code class="computeroutput"><span class="identifier">optional</span></code>
+ perform a 'perfect forwarding' of arguments:
+ </p>
+<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_t</span><span class="special">,</span> <span class="identifier">Args</span><span class="special">&&...</span> <span class="identifier">args</span><span class="special">);</span>
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_if_t</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">Args</span><span class="special">&&...</span> <span class="identifier">args</span><span class="special">);</span>
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">(</span><span class="identifier">Args</span><span class="special">&&...</span> <span class="identifier">args</span><span class="special">);</span>
+</pre>
+<p>
+ On compilers that do not support variadic templates, each of these functions
+ is substituted with two overloads, one forwarding a single argument, the
+ other forwarding zero arguments. This forms the following set:
+ </p>
+<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">></span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_t</span><span class="special">,</span> <span class="identifier">Arg</span><span class="special">&&</span> <span class="identifier">arg</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_t</span><span class="special">);</span>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">></span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_if_t</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">Arg</span><span class="special">&&</span> <span class="identifier">arg</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_if_t</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">);</span>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">(</span><span class="identifier">Arg</span><span class="special">&&</span> <span class="identifier">arg</span><span class="special">);</span>
+<span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">();</span>
+</pre>
+<p>
+ On compilers that do not support rvalue references, each of these functions
+ is substituted with three overloadss: taking <code class="computeroutput"><span class="keyword">const</span></code>
+ and non-<code class="computeroutput"><span class="keyword">const</span></code> lvalue reference,
+ and third forwarding zero arguments. This forms the following set:
+ </p>
+<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">></span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_t</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">Arg</span><span class="special">&</span> <span class="identifier">arg</span><span class="special">);</span>
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">></span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_t</span><span class="special">,</span> <span class="identifier">Arg</span><span class="special">&</span> <span class="identifier">arg</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_t</span><span class="special">);</span>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">></span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_if_t</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="keyword">const</span> <span class="identifier">Arg</span><span class="special">&</span> <span class="identifier">arg</span><span class="special">);</span>
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">></span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_if_t</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">Arg</span><span class="special">&</span> <span class="identifier">arg</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special">(</span><span class="identifier">in_place_init_if_t</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">);</span>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">Arg</span><span class="special">&</span> <span class="identifier">arg</span><span class="special">);</span>
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">Arg</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">(</span><span class="identifier">Arg</span><span class="special">&</span> <span class="identifier">arg</span><span class="special">);</span>
+<span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">();</span>
+</pre>
+<p>
+ This workaround addressess about 40% of all use cases. If this is insufficient,
+ you need to resort to using <a class="link" href="../tutorial/in_place_factories.html" title="In-Place Factories">In-Place
+ Factories</a>.
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="optional_reference_binding.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/dependencies_and_portability/optional_reference_binding.html b/doc/html/boost_optional/dependencies_and_portability/optional_reference_binding.html
new file mode 100644
index 0000000..7a191d2
--- /dev/null
+++ b/doc/html/boost_optional/dependencies_and_portability/optional_reference_binding.html
@@ -0,0 +1,107 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Optional Reference Binding</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../index.html" title="Boost.Optional">
+<link rel="up" href="../dependencies_and_portability.html" title="Dependencies and Portability">
+<link rel="prev" href="emplace_operations_in_older_compilers.html" title="Emplace operations in older compilers">
+<link rel="next" href="../relnotes.html" title="Release Notes">
+</head>
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+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
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+<a accesskey="p" href="emplace_operations_in_older_compilers.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../relnotes.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.dependencies_and_portability.optional_reference_binding"></a><a class="link" href="optional_reference_binding.html" title="Optional Reference Binding">Optional
+ Reference Binding</a>
+</h3></div></div></div>
+<p>
+ <a name="optional_reference_binding"></a>A number of compilers incorrectly
+ treat const lvalues of integral type as rvalues, and create an illegal temporary
+ when binding to an lvalue reference to const in some expressions. This could
+ result in creating an optional lvalue reference that is in fact bound to
+ an unexpected temporary rather than to the intended object. In order to prevent
+ hard to find run-time bugs, this library performs compile-time checks to
+ prevent expressions that would otherwise bind an optional reference to an
+ unexpected temporary. As a consequence, on certain compilers certain pieces
+ of functionality in optional references are missing. In order to maintain
+ a portability of your code across diferent compilers, it is recommended that
+ you only stick to the minimum portable interface of optional references:
+ prefer direct-initialization and copy assignment of optional references to
+ copy-initialization and assignment from <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span></code>:
+ </p>
+<pre class="programlisting"><span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&></span> <span class="identifier">or1</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&></span> <span class="identifier">or2</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">;</span> <span class="comment">// caution: not portable</span>
+<span class="identifier">or1</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">;</span> <span class="comment">// caution: not portable</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&></span> <span class="identifier">or3</span><span class="special">(</span><span class="identifier">i</span><span class="special">);</span> <span class="comment">// portable</span>
+<span class="identifier">or1</span> <span class="special">=</span> <span class="identifier">optional</span><span class="special"><</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&>(</span><span class="identifier">i</span><span class="special">);</span> <span class="comment">// portable</span>
+</pre>
+<p>
+ Compilers known to have these deficiencies include GCC versions 4.2, 4.3,
+ 4.4, 4.5, 5.1, 5.2; QCC 4.4.2; MSVC versions 8.0, 9.0, 10.0, 11.0, 12.0.
+ In order to check if your compiler correctly implements reference binding
+ use this test program.
+ </p>
+<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span>
+
+<span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">global_i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
+
+<span class="keyword">struct</span> <span class="identifier">TestingReferenceBinding</span>
+<span class="special">{</span>
+ <span class="identifier">TestingReferenceBinding</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&</span> <span class="identifier">ii</span><span class="special">)</span>
+ <span class="special">{</span>
+ <span class="identifier">assert</span><span class="special">(&</span><span class="identifier">ii</span> <span class="special">==</span> <span class="special">&</span><span class="identifier">global_i</span><span class="special">);</span>
+ <span class="special">}</span>
+
+ <span class="keyword">void</span> <span class="keyword">operator</span><span class="special">=(</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&</span> <span class="identifier">ii</span><span class="special">)</span>
+ <span class="special">{</span>
+ <span class="identifier">assert</span><span class="special">(&</span><span class="identifier">ii</span> <span class="special">==</span> <span class="special">&</span><span class="identifier">global_i</span><span class="special">);</span>
+ <span class="special">}</span>
+
+ <span class="keyword">void</span> <span class="keyword">operator</span><span class="special">=(</span><span class="keyword">int</span><span class="special">&&)</span> <span class="comment">// remove this if your compiler doesn't have rvalue refs</span>
+ <span class="special">{</span>
+ <span class="identifier">assert</span><span class="special">(</span><span class="keyword">false</span><span class="special">);</span>
+ <span class="special">}</span>
+<span class="special">};</span>
+
+<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="keyword">const</span> <span class="keyword">int</span><span class="special">&</span> <span class="identifier">iref</span> <span class="special">=</span> <span class="identifier">global_i</span><span class="special">;</span>
+ <span class="identifier">assert</span><span class="special">(&</span><span class="identifier">iref</span> <span class="special">==</span> <span class="special">&</span><span class="identifier">global_i</span><span class="special">);</span>
+
+ <span class="identifier">TestingReferenceBinding</span> <span class="identifier">ttt</span> <span class="special">=</span> <span class="identifier">global_i</span><span class="special">;</span>
+ <span class="identifier">ttt</span> <span class="special">=</span> <span class="identifier">global_i</span><span class="special">;</span>
+
+ <span class="identifier">TestingReferenceBinding</span> <span class="identifier">ttt2</span> <span class="special">=</span> <span class="identifier">iref</span><span class="special">;</span>
+ <span class="identifier">ttt2</span> <span class="special">=</span> <span class="identifier">iref</span><span class="special">;</span>
+<span class="special">}</span>
+</pre>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="emplace_operations_in_older_compilers.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../relnotes.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/detailed_semantics.html b/doc/html/boost_optional/detailed_semantics.html
new file mode 100644
index 0000000..b93515f
--- /dev/null
+++ b/doc/html/boost_optional/detailed_semantics.html
@@ -0,0 +1,1975 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Detailed Semantics</title>
+<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../index.html" title="Chapter 1. Boost.Optional">
+<link rel="up" href="../index.html" title="Chapter 1. Boost.Optional">
+<link rel="prev" href="synopsis.html" title="Synopsis">
+<link rel="next" href="dependencies_and_portability.html" title="Dependencies and Portability">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="synopsis.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="dependencies_and_portability.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="boost_optional.detailed_semantics"></a><a class="link" href="detailed_semantics.html" title="Detailed Semantics">Detailed Semantics</a>
+</h2></div></div></div>
+<p>
+ Because <code class="computeroutput"><span class="identifier">T</span></code> might be of reference
+ type, in the sequel, those entries whose semantic depends on <code class="computeroutput"><span class="identifier">T</span></code> being of reference type or not will be
+ distinguished using the following convention:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ If the entry reads: <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code><span class="emphasis"><em>(not
+ a ref)</em></span><code class="computeroutput"><span class="special">></span></code>, the
+ description corresponds only to the case where <code class="computeroutput"><span class="identifier">T</span></code>
+ is not of reference type.
+ </li>
+<li class="listitem">
+ If the entry reads: <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code>, the description corresponds only
+ to the case where <code class="computeroutput"><span class="identifier">T</span></code> is
+ of reference type.
+ </li>
+<li class="listitem">
+ If the entry reads: <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>, the description is the same for both
+ cases.
+ </li>
+</ul></div>
+<div class="note"><table border="0" summary="Note">
+<tr>
+<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../doc/src/images/note.png"></td>
+<th align="left">Note</th>
+</tr>
+<tr><td align="left" valign="top"><p>
+ The following section contains various <code class="computeroutput"><span class="identifier">assert</span><span class="special">()</span></code> which are used only to show the postconditions
+ as sample code. It is not implied that the type <code class="computeroutput"><span class="identifier">T</span></code>
+ must support each particular expression but that if the expression is supported,
+ the implied condition holds.
+ </p></td></tr>
+</table></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<h4>
+<a name="boost_optional.detailed_semantics.h0"></a>
+ <span class="phrase"><a name="boost_optional.detailed_semantics.optional_class_member_functions"></a></span><a class="link" href="detailed_semantics.html#boost_optional.detailed_semantics.optional_class_member_functions">optional
+ class member functions</a>
+ </h4>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">()</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Default-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">uninitialized</span>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> T's default constructor <span class="underline">is not</span> called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">def</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_none_t"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>
+ uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">uninitialized</span>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>'s
+ default constructor <span class="underline">is not</span> called.
+ The expression <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code> denotes an instance of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none_t</span></code> that can be used as the parameter.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">none</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">n</span><span class="special">(</span><span class="identifier">none</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">n</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_copy_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>
+ is <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Directly-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
+ and its value is a <span class="emphasis"><em>copy</em></span> of <code class="computeroutput"><span class="identifier">v</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span>
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span>
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code>
+ is called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">);</span></code> in that case, this constructor
+ has no effect.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">ref</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Directly-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
+ and its value is an instance of an internal type wrapping the reference
+ <code class="computeroutput"><span class="identifier">ref</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">vref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">vref</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">++</span> <span class="identifier">v</span> <span class="special">;</span> <span class="comment">// mutate referee</span>
+<span class="identifier">assert</span> <span class="special">(*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span><span class="special">);</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_move_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span>
+ <span class="identifier">v</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>
+ is <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Directly-Move-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
+ and its value is move-constructed from <code class="computeroutput"><span class="identifier">v</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span>
+ <span class="identifier">T</span><span class="special">&&</span>
+ <span class="special">)</span></code> throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span>
+ <span class="identifier">T</span><span class="special">&&</span>
+ <span class="special">)</span></code> is called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">);</span></code>
+ in that case, the state of <code class="computeroutput"><span class="identifier">v</span></code>
+ is determined by exception safety guarantees for <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span><span class="special">&&)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v1</span><span class="special">,</span> <span class="identifier">v2</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">v1</span><span class="special">));</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v2</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="identifier">ref</span> <span class="special">)</span> <span class="special">=</span> <span class="keyword">delete</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> This constructor is deleted
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_bool_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="special">::</span><span class="identifier">optional</span><span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ If condition is true, same as:
+ </li></ul></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="special">::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">v</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ otherwise, same as:
+ </li></ul></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">()</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="special">::</span><span class="identifier">optional</span><span class="special">()</span></code>
+ </p></blockquote></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">optional</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_copy_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>
+ is <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Copy-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If rhs is initialized,
+ <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is a <span class="emphasis"><em>copy</em></span> of the value
+ of <code class="computeroutput"><span class="identifier">rhs</span></code>; else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is
+ uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span>
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If rhs is initialized, <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code>
+ is called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">);</span></code> in that case, this constructor
+ has no effect.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">uninit</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">uninit</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init</span><span class="special">(</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">init</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">init</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">optional</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Copy-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is another reference to the same object referenced
+ by <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>;
+ else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, both <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ and <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>
+ will reefer to the same object (they alias).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">uninit</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">uninit</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span>
+
+<span class="identifier">T</span> <span class="identifier">v</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">ref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init</span><span class="special">(</span><span class="identifier">ref</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">init</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">v</span> <span class="special">=</span> <span class="number">3</span> <span class="special">;</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init2</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_move_constructor_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">optional</span><span class="special">&&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">(</span></code><span class="emphasis"><em>see below</em></span><code class="computeroutput"><span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>
+ is <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Move-constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is move constructed from <code class="computeroutput"><span class="identifier">rhs</span></code>;
+ else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span>
+ <span class="identifier">T</span><span class="special">&&</span>
+ <span class="special">)</span></code> throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span>
+ <span class="special">&&</span> <span class="special">)</span></code>
+ is called. The expression inside <code class="computeroutput"><span class="keyword">noexcept</span></code>
+ is equivalent to <code class="computeroutput"><span class="identifier">is_nothrow_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">);</span></code>
+ in that case, <code class="computeroutput"><span class="identifier">rhs</span></code> remains
+ initialized and the value of <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is determined by exception safety
+ of <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span><span class="special">&&)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">uninit</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">uninit</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">init</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">uniqye_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="keyword">new</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">init</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">init</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="keyword">nullptr</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">init2</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">optional</span> <span class="special">&&</span>
+ <span class="identifier">rhs</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Move-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is another reference to the same object referenced
+ by <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>;
+ else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, both <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ and <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>
+ will reefer to the same object (they alias).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">uninit</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">uninit</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span>
+
+<span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">v</span><span class="special">(</span><span class="keyword">new</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">init</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">init</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="special">*</span><span class="identifier">v</span> <span class="special">=</span> <span class="number">3</span> <span class="special">;</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init2</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Copy-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is a <span class="emphasis"><em>copy</em></span> of the value
+ of rhs converted to type <code class="computeroutput"><span class="identifier">T</span></code>;
+ else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span>
+ <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span>
+ <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code>
+ is called if <code class="computeroutput"><span class="identifier">rhs</span></code> is initialized,
+ which requires a valid conversion from <code class="computeroutput"><span class="identifier">U</span></code>
+ to <code class="computeroutput"><span class="identifier">T</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">);</span></code> in that case, this constructor
+ has no effect.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">x</span><span class="special">(</span><span class="number">123.4</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">==</span> <span class="number">123.4</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">y</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span><span class="special">(</span> <span class="special">*</span><span class="identifier">y</span> <span class="special">==</span> <span class="number">123</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_move_constructor_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&&</span>
+ <span class="identifier">rhs</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Move-constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is move constructed from <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>; else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span>
+ <span class="identifier">U</span><span class="special">&&</span>
+ <span class="special">)</span></code> throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span>
+ <span class="identifier">U</span><span class="special">&&</span>
+ <span class="special">)</span></code> is called if <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, which requires a valid conversion from <code class="computeroutput"><span class="identifier">U</span></code>
+ to <code class="computeroutput"><span class="identifier">T</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">);</span></code>
+ in that case, <code class="computeroutput"><span class="identifier">rhs</span></code> remains
+ initialized and the value of <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is determined by exception safety
+ guarantee of <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">x</span><span class="special">(</span><span class="number">123.4</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">==</span> <span class="number">123.4</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">y</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">x</span><span class="special">))</span> <span class="special">;</span>
+<span class="identifier">assert</span><span class="special">(</span> <span class="special">*</span><span class="identifier">y</span> <span class="special">==</span> <span class="number">123</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_factory"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">InPlaceFactory</span><span class="special">></span>
+ <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">InPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">TypedInPlaceFactory</span><span class="special">></span>
+ <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">TypedInPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>
+ with a value of <code class="computeroutput"><span class="identifier">T</span></code> obtained
+ from the factory.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
+ and its value is <span class="emphasis"><em>directly given</em></span> from the factory
+ <code class="computeroutput"><span class="identifier">f</span></code> (i.e., the value <span class="underline">is not copied</span>).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever the <code class="computeroutput"><span class="identifier">T</span></code>
+ constructor called by the factory throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> See <a class="link" href="tutorial/in_place_factories.html" title="In-Place Factories">In-Place
+ Factories</a>
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during the call to the <code class="computeroutput"><span class="identifier">T</span></code>
+ constructor used by the factory; in that case, this constructor has no
+ effect.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">C</span> <span class="special">{</span> <span class="identifier">C</span> <span class="special">(</span> <span class="keyword">char</span><span class="special">,</span> <span class="keyword">double</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">)</span> <span class="special">;</span> <span class="special">}</span> <span class="special">;</span>
+
+<span class="identifier">C</span> <span class="identifier">v</span><span class="special">(</span><span class="char">'A'</span><span class="special">,</span><span class="number">123.4</span><span class="special">,</span><span class="string">"hello"</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">C</span><span class="special">></span> <span class="identifier">x</span><span class="special">(</span> <span class="identifier">in_place</span> <span class="special">(</span><span class="char">'A'</span><span class="special">,</span> <span class="number">123.4</span><span class="special">,</span> <span class="string">"hello"</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// InPlaceFactory used</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">C</span><span class="special">></span> <span class="identifier">y</span><span class="special">(</span> <span class="identifier">in_place</span><span class="special"><</span><span class="identifier">C</span><span class="special">>(</span><span class="char">'A'</span><span class="special">,</span> <span class="number">123.4</span><span class="special">,</span> <span class="string">"hello"</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// TypedInPlaceFactory used</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">y</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_equal_none_t"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized destroys its contained
+ value.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_equal_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">rhs</span> <span class="special">)</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Assigns the value <code class="computeroutput"><span class="identifier">rhs</span></code> to an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized and its value is a
+ <span class="emphasis"><em>copy</em></span> of <code class="computeroutput"><span class="identifier">rhs</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code> or <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&)</span></code> throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s
+ assignment operator is used, otherwise, its copy-constructor is used.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> In the event of an exception,
+ the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is unchanged and its value unspecified
+ as far as <code class="computeroutput"><span class="identifier">optional</span></code> is concerned
+ (it is up to <code class="computeroutput"><span class="identifier">T</span></code>'s <code class="computeroutput"><span class="keyword">operator</span><span class="special">=()</span></code>).
+ If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initially uninitialized and <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <span class="emphasis"><em>copy constructor</em></span> fails, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is left properly uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">T</span> <span class="identifier">y</span><span class="special">;</span>
+<span class="identifier">def</span> <span class="special">=</span> <span class="identifier">y</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">y</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">rhs</span> <span class="special">)</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> (Re)binds the wrapped reference.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized and it references the
+ same object referenced by <code class="computeroutput"><span class="identifier">rhs</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized, it is <span class="emphasis"><em>rebound</em></span>
+ to the new object. See <a class="link" href="tutorial/rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">here</a>
+ for details on this behavior.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">ra</span><span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">def</span> <span class="special">=</span> <span class="identifier">rb</span> <span class="special">;</span> <span class="comment">// binds 'def' to 'b' through 'rb'</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">b</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">*</span><span class="identifier">def</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span> <span class="comment">// changes the value of 'b' to a copy of the value of 'a'</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">b</span> <span class="special">==</span> <span class="identifier">a</span> <span class="special">)</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">c</span> <span class="special">=</span> <span class="number">3</span><span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">rc</span> <span class="special">=</span> <span class="identifier">c</span> <span class="special">;</span>
+<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">rc</span> <span class="special">;</span> <span class="comment">// REBINDS to 'c' through 'rc'</span>
+<span class="identifier">c</span> <span class="special">=</span> <span class="number">4</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="number">4</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_move_equal_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Moves the value <code class="computeroutput"><span class="identifier">rhs</span></code> to an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized and its value is moved
+ from <code class="computeroutput"><span class="identifier">rhs</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code>
+ or <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span>
+ <span class="special">&&)</span></code> throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s
+ move-assignment operator is used, otherwise, its move-constructor is used.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> In the event of an exception,
+ the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is unchanged and its value unspecified
+ as far as <code class="computeroutput"><span class="identifier">optional</span></code> is concerned
+ (it is up to <code class="computeroutput"><span class="identifier">T</span></code>'s <code class="computeroutput"><span class="keyword">operator</span><span class="special">=()</span></code>).
+ If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initially uninitialized and <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <span class="emphasis"><em>move constructor</em></span> fails, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is left properly uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">T</span> <span class="identifier">y1</span><span class="special">,</span> <span class="identifier">y2</span><span class="special">,</span> <span class="identifier">yR</span><span class="special">;</span>
+<span class="identifier">def</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">y1</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">yR</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">y2</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">yR</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span>
+ <span class="identifier">rhs</span> <span class="special">)</span>
+ <span class="special">=</span> <span class="keyword">delete</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> This assignment operator is deleted.
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_equal_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">rhs</span> <span class="special">)</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Assigns another <code class="computeroutput"><span class="identifier">optional</span></code> to an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is a <span class="emphasis"><em>copy</em></span> of the value
+ of <code class="computeroutput"><span class="identifier">rhs</span></code>; else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is
+ uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="keyword">operator</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&)</span></code>
+ or <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span></code> throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If both <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="identifier">rhs</span></code>
+ are initially initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <span class="emphasis"><em>assignment operator</em></span> is used. If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initially initialized but <code class="computeroutput"><span class="identifier">rhs</span></code> is uninitialized, <code class="computeroutput"><span class="identifier">T</span></code>'s
+ [destructor] is called. If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initially uninitialized but <code class="computeroutput"><span class="identifier">rhs</span></code> is initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <span class="emphasis"><em>copy constructor</em></span> is called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> In the event of an exception,
+ the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is unchanged and its value unspecified
+ as far as optional is concerned (it is up to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <code class="computeroutput"><span class="keyword">operator</span><span class="special">=()</span></code>).
+ If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initially uninitialized and <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <span class="emphasis"><em>copy constructor</em></span> fails, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is left properly uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+
+<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">def</span> <span class="special">)</span> <span class="special">;</span>
+<span class="comment">// previous value (copy of 'v') destroyed from within 'opt'.</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">rhs</span> <span class="special">)</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> (Re)binds thee wrapped reference.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized and it references the
+ same object referenced by <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>; otherwise, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized (and references no
+ object).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized and so is <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>,
+ <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is <span class="emphasis"><em>rebound</em></span> to the new object. See <a class="link" href="tutorial/rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">here</a>
+ for details on this behavior.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">ora</span><span class="special">(</span><span class="identifier">ra</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">orb</span><span class="special">(</span><span class="identifier">rb</span><span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">def</span> <span class="special">=</span> <span class="identifier">orb</span> <span class="special">;</span> <span class="comment">// binds 'def' to 'b' through 'rb' wrapped within 'orb'</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">b</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">*</span><span class="identifier">def</span> <span class="special">=</span> <span class="identifier">ora</span> <span class="special">;</span> <span class="comment">// changes the value of 'b' to a copy of the value of 'a'</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">b</span> <span class="special">==</span> <span class="identifier">a</span> <span class="special">)</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">c</span> <span class="special">=</span> <span class="number">3</span><span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">rc</span> <span class="special">=</span> <span class="identifier">c</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">orc</span><span class="special">(</span><span class="identifier">rc</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">ora</span> <span class="special">=</span> <span class="identifier">orc</span> <span class="special">;</span> <span class="comment">// REBINDS ora to 'c' through 'rc'</span>
+<span class="identifier">c</span> <span class="special">=</span> <span class="number">4</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">ora</span> <span class="special">==</span> <span class="number">4</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_move_equal_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">(</span></code><span class="emphasis"><em>see below</em></span><code class="computeroutput"><span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Move-assigns another <code class="computeroutput"><span class="identifier">optional</span></code> to an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is moved from <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>, <code class="computeroutput"><span class="identifier">rhs</span></code>
+ remains initialized; else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="keyword">operator</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span>
+ <span class="special">)</span></code> or <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span>
+ <span class="identifier">T</span> <span class="special">&&</span>
+ <span class="special">)</span></code> throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If both <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="identifier">rhs</span></code>
+ are initially initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <span class="emphasis"><em>move assignment operator</em></span> is used. If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is
+ initially initialized but <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is uninitialized, <code class="computeroutput"><span class="identifier">T</span></code>'s [destructor]
+ is called. If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initially uninitialized but <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s <span class="emphasis"><em>move
+ constructor</em></span> is called. The expression inside <code class="computeroutput"><span class="keyword">noexcept</span></code>
+ is equivalent to <code class="computeroutput"><span class="identifier">is_nothrow_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span>
+ <span class="special">&&</span> <span class="identifier">is_nothrow_move_assignable</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> In the event of an exception,
+ the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is unchanged and its value unspecified
+ as far as optional is concerned (it is up to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <code class="computeroutput"><span class="keyword">operator</span><span class="special">=()</span></code>).
+ If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initially uninitialized and <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <span class="emphasis"><em>move constructor</em></span> fails, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is left properly uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+
+<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">def</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&&</span>
+ <span class="identifier">rhs</span> <span class="special">)</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Same as <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">)</span></code>.
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_equal_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">rhs</span> <span class="special">)</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Assigns another convertible optional
+ to an optional.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is a <span class="emphasis"><em>copy</em></span> of the value
+ of <code class="computeroutput"><span class="identifier">rhs</span></code> <span class="emphasis"><em>converted</em></span>
+ to type <code class="computeroutput"><span class="identifier">T</span></code>; else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is
+ uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code> or <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span>
+ <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If both <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and rhs are initially initialized,
+ <code class="computeroutput"><span class="identifier">T</span></code>'s <span class="emphasis"><em>assignment
+ operator</em></span> (from <code class="computeroutput"><span class="identifier">U</span></code>)
+ is used. If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initially initialized but <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is uninitialized, <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <span class="emphasis"><em>destructor</em></span> is called. If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initially uninitialized but rhs
+ is initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s <span class="emphasis"><em>converting
+ constructor</em></span> (from <code class="computeroutput"><span class="identifier">U</span></code>)
+ is called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> In the event of an exception,
+ the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is unchanged and its value unspecified
+ as far as optional is concerned (it is up to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <code class="computeroutput"><span class="keyword">operator</span><span class="special">=()</span></code>).
+ If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initially uninitialized and <code class="computeroutput"><span class="identifier">T</span></code>'s
+ converting constructor fails, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is left properly uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt0</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">opt1</span><span class="special">;</span>
+
+<span class="identifier">opt1</span> <span class="special">=</span> <span class="identifier">opt0</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt1</span> <span class="special">==</span> <span class="keyword">static_cast</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_move_equal_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&&</span>
+ <span class="identifier">rhs</span> <span class="special">)</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Move-assigns another convertible
+ optional to an optional.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is moved from the value of <code class="computeroutput"><span class="identifier">rhs</span></code>;
+ else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">)</span></code>
+ or <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If both <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="identifier">rhs</span></code>
+ are initially initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <span class="emphasis"><em>assignment operator</em></span> (from <code class="computeroutput"><span class="identifier">U</span><span class="special">&&</span></code>) is used. If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initially initialized but <code class="computeroutput"><span class="identifier">rhs</span></code> is uninitialized, <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <span class="emphasis"><em>destructor</em></span> is called. If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initially uninitialized but <code class="computeroutput"><span class="identifier">rhs</span></code> is initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <span class="emphasis"><em>converting constructor</em></span> (from <code class="computeroutput"><span class="identifier">U</span><span class="special">&&</span></code>) is called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> In the event of an exception,
+ the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is unchanged and its value unspecified
+ as far as optional is concerned (it is up to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <code class="computeroutput"><span class="keyword">operator</span><span class="special">=()</span></code>).
+ If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initially uninitialized and <code class="computeroutput"><span class="identifier">T</span></code>'s
+ converting constructor fails, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is left properly uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt0</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">opt1</span><span class="special">;</span>
+
+<span class="identifier">opt1</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">opt0</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt1</span> <span class="special">==</span> <span class="keyword">static_cast</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_emplace"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">emplace</span><span class="special">(</span> <span class="identifier">Args</span><span class="special">...&&</span>
+ <span class="identifier">args</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> The compiler supports rvalue
+ references and variadic templates.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized calls <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span> <span class="special">=</span>
+ <span class="identifier">none</span></code>. Then initializes in-place
+ the contained value as if direct-initializing an object of type <code class="computeroutput"><span class="identifier">T</span></code> with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">Args</span><span class="special">>(</span><span class="identifier">args</span><span class="special">)...</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever the selected <code class="computeroutput"><span class="identifier">T</span></code>'s constructor throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ need not be <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>
+ or <code class="computeroutput"><span class="identifier">MoveAssignable</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> If an exception is thrown
+ during the initialization of <code class="computeroutput"><span class="identifier">T</span></code>,
+ <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is <span class="emphasis"><em>uninitialized</em></span>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_equal_factory"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">InPlaceFactory</span><span class="special">></span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">InPlaceFactory</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">f</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">TypedInPlaceFactory</span><span class="special">></span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">TypedInPlaceFactory</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">f</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Assigns an <code class="computeroutput"><span class="identifier">optional</span></code>
+ with a value of <code class="computeroutput"><span class="identifier">T</span></code> obtained
+ from the factory.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
+ and its value is <span class="emphasis"><em>directly given</em></span> from the factory
+ <code class="computeroutput"><span class="identifier">f</span></code> (i.e., the value <span class="underline">is not copied</span>).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever the <code class="computeroutput"><span class="identifier">T</span></code>
+ constructor called by the factory throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> See <a class="link" href="tutorial/in_place_factories.html" title="In-Place Factories">In-Place
+ Factories</a>
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during the call to the <code class="computeroutput"><span class="identifier">T</span></code>
+ constructor used by the factory; in that case, the <code class="computeroutput"><span class="identifier">optional</span></code>
+ object will be reset to be <span class="emphasis"><em>uninitialized</em></span>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_reset_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">reset</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Deprecated:</strong></span> same as <code class="computeroutput"><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">v</span><span class="special">)</span>
+ <span class="special">;</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_reset"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">reset</span><span class="special">()</span> <span class="keyword">noexcept</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Deprecated:</strong></span> Same as <code class="computeroutput"><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">none_t</span> <span class="special">);</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_get"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get</span><span class="special">()</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">get</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span>
+ <span class="special">&)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> A reference to the contained
+ value
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The requirement is asserted via
+ <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">get</span><span class="special">()</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">get</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
+ <span class="special">&)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <span class="underline">The</span>
+ reference contained.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The requirement is asserted via
+ <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_asterisk"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">*()</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">*()</span> <span class="special">&;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">*()</span> <span class="special">&&;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> A reference to the contained
+ value
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The requirement is asserted via
+ <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
+ On compilers that do not support ref-qualifiers on member functions these
+ three overloads are replaced with the classical two: a <code class="computeroutput"><span class="keyword">const</span></code>
+ and non-<code class="computeroutput"><span class="keyword">const</span></code> member functions.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">);</span>
+<span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">u</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">opt</span><span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">u</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">T</span> <span class="identifier">w</span> <span class="special">;</span>
+<span class="special">*</span><span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">w</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">w</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">*()</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">*()</span> <span class="special">&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">*()</span> <span class="special">&&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <span class="underline">The</span>
+ reference contained.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The requirement is asserted via
+ <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
+ On compilers that do not support ref-qualifiers on member functions these
+ three overloads are replaced with the classical two: a <code class="computeroutput"><span class="keyword">const</span></code>
+ and non-<code class="computeroutput"><span class="keyword">const</span></code> member functions.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">vref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">vref</span> <span class="special">);</span>
+<span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">vref2</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">opt</span><span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">vref2</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">++</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span><span class="special">()</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span><span class="special">()</span> <span class="special">&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span><span class="special">()</span> <span class="special">&&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> A reference to the contained
+ value, if <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> An instance of <code class="computeroutput"><span class="identifier">bad_optional_access</span></code>,
+ if <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is not initialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ ref-qualifiers on member functions these three overloads are replaced with
+ the classical two: a <code class="computeroutput"><span class="keyword">const</span></code>
+ and non-<code class="computeroutput"><span class="keyword">const</span></code> member functions.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o0</span><span class="special">,</span> <span class="identifier">o1</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span><span class="special">.</span><span class="identifier">value</span><span class="special">()</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">);</span>
+
+<span class="keyword">try</span> <span class="special">{</span>
+ <span class="identifier">o0</span><span class="special">.</span><span class="identifier">value</span><span class="special">();</span> <span class="comment">// throws</span>
+ <span class="identifier">assert</span> <span class="special">(</span> <span class="keyword">false</span> <span class="special">);</span>
+<span class="special">}</span>
+<span class="keyword">catch</span><span class="special">(</span><span class="identifier">bad_optional_access</span><span class="special">&)</span> <span class="special">{</span>
+ <span class="identifier">assert</span> <span class="special">(</span> <span class="keyword">true</span> <span class="special">);</span>
+<span class="special">}</span>
+</pre>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </li>
+</ul></div>
+<a name="reference_optional_value_or"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or</span><span class="special">(</span><span class="identifier">U</span> <span class="special">&&</span>
+ <span class="identifier">v</span><span class="special">)</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or</span><span class="special">(</span><span class="identifier">U</span> <span class="special">&&</span>
+ <span class="identifier">v</span><span class="special">)</span> <span class="special">&&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ is CopyConstructible.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> First overload: <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">?</span> <span class="special">**</span><span class="keyword">this</span> <span class="special">:</span> <span class="keyword">static_cast</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">))</span></code>.
+ second overload: <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">?</span>
+ <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(**</span><span class="keyword">this</span><span class="special">)</span> <span class="special">:</span>
+ <span class="keyword">static_cast</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">))</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Any exception thrown by the selected
+ constructor of <code class="computeroutput"><span class="identifier">T</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ ref-qualifiers on member functions these three overloads are replaced with
+ the classical two: a <code class="computeroutput"><span class="keyword">const</span></code>
+ and non-<code class="computeroutput"><span class="keyword">const</span></code> member functions.
+ On compilers without rvalue reference support the type of <code class="computeroutput"><span class="identifier">v</span></code> becomes <code class="computeroutput"><span class="identifier">U</span>
+ <span class="keyword">const</span><span class="special">&</span></code>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_get_value_or_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_value_or</span><span class="special">(</span>
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="keyword">default</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_value_or</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&</span>
+ <span class="keyword">default</span> <span class="special">)</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">get_optional_value_or</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">o</span><span class="special">,</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="keyword">default</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get_optional_value_or</span>
+ <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>&</span>
+ <span class="identifier">o</span><span class="special">,</span> <span class="identifier">T</span><span class="special">&</span> <span class="keyword">default</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Deprecated:</strong></span> Use <code class="computeroutput"><span class="identifier">value_or</span><span class="special">()</span></code> instead.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> A reference to the contained
+ value, if any, or <code class="computeroutput"><span class="keyword">default</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">,</span> <span class="identifier">z</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span><span class="special">;</span>
+<span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">=</span> <span class="identifier">def</span><span class="special">.</span><span class="identifier">get_value_or</span><span class="special">(</span><span class="identifier">z</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">y</span> <span class="special">==</span> <span class="identifier">z</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">);</span>
+<span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">u</span> <span class="special">=</span> <span class="identifier">get_optional_value_or</span><span class="special">(</span><span class="identifier">opt</span><span class="special">,</span><span class="identifier">z</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">u</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">u</span> <span class="special">!=</span> <span class="identifier">z</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_get_ptr"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_ptr</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">*</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">*</span> <span class="identifier">get_pointer</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">*</span> <span class="identifier">get_pointer</span>
+ <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span>
+ <span class="special">&)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized, a pointer to the contained
+ value; else <code class="computeroutput"><span class="number">0</span></code> (<span class="emphasis"><em>null</em></span>).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The contained value is permanently
+ stored within <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>,
+ so you should not hold nor delete this pointer
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span> <span class="identifier">copt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">T</span><span class="special">*</span> <span class="identifier">p</span> <span class="special">=</span> <span class="identifier">opt</span><span class="special">.</span><span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">;</span>
+<span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">cp</span> <span class="special">=</span> <span class="identifier">copt</span><span class="special">.</span><span class="identifier">get_ptr</span><span class="special">();</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">p</span> <span class="special">==</span> <span class="identifier">get_pointer</span><span class="special">(</span><span class="identifier">opt</span><span class="special">)</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">cp</span> <span class="special">==</span> <span class="identifier">get_pointer</span><span class="special">(</span><span class="identifier">copt</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_arrow"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span> <span class="special">->()</span>
+ <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">*</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span> <span class="special">->()</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> A pointer to the contained value.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The requirement is asserted via
+ <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">X</span> <span class="special">{</span> <span class="keyword">int</span> <span class="identifier">mdata</span> <span class="special">;</span> <span class="special">}</span> <span class="special">;</span>
+<span class="identifier">X</span> <span class="identifier">x</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">X</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span><span class="identifier">x</span><span class="special">);</span>
+<span class="identifier">opt</span><span class="special">-></span><span class="identifier">mdata</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_bool"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span> <span class="keyword">bool</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">!=</span> <span class="number">0</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ explicit conversion operators this falls back to safe-bool idiom.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">def</span> <span class="special">==</span> <span class="number">0</span> <span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt</span> <span class="special">!=</span> <span class="number">0</span> <span class="special">);</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_not"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">!()</span> <span class="keyword">noexcept</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized, <code class="computeroutput"><span class="keyword">true</span></code>;
+ else <code class="computeroutput"><span class="keyword">false</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> This operator is provided for those
+ compilers which can't use the <span class="emphasis"><em>unspecified-bool-type operator</em></span>
+ in certain boolean contexts.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">opt</span> <span class="special">);</span>
+<span class="special">*</span><span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">some_T</span> <span class="special">;</span>
+
+<span class="comment">// Notice the "double-bang" idiom here.</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!!</span><span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_is_initialized"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">is_initialized</span><span class="special">()</span>
+ <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Deprecated:</strong></span> Same as <code class="computeroutput"><span class="keyword">explicit</span>
+ <span class="keyword">operator</span> <span class="keyword">bool</span>
+ <span class="special">()</span> <span class="special">;</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<h4>
+<a name="boost_optional.detailed_semantics.h1"></a>
+ <span class="phrase"><a name="boost_optional.detailed_semantics.free_functions"></a></span><a class="link" href="detailed_semantics.html#boost_optional.detailed_semantics.free_functions">Free
+ functions</a>
+ </h4>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_make_optional_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="identifier">make_optional</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">v</span><span class="special">)</span></code> for the <span class="emphasis"><em>deduced</em></span> type
+ <code class="computeroutput"><span class="identifier">T</span></code> of <code class="computeroutput"><span class="identifier">v</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">foo</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">foo</span> <span class="special">(</span> <span class="identifier">make_optional</span><span class="special">(</span><span class="number">1</span><span class="special">+</span><span class="number">1</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> <span class="comment">// Creates an optional<int></span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_make_optional_bool_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="identifier">make_optional</span><span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">condition</span><span class="special">,</span><span class="identifier">v</span><span class="special">)</span></code>
+ for the <span class="emphasis"><em>deduced</em></span> type <code class="computeroutput"><span class="identifier">T</span></code>
+ of <code class="computeroutput"><span class="identifier">v</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">calculate_foo</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="keyword">double</span> <span class="identifier">val</span> <span class="special">=</span> <span class="identifier">compute_foo</span><span class="special">();</span>
+ <span class="keyword">return</span> <span class="identifier">make_optional</span><span class="special">(</span><span class="identifier">is_not_nan_and_finite</span><span class="special">(</span><span class="identifier">val</span><span class="special">),</span><span class="identifier">val</span><span class="special">);</span>
+<span class="special">}</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">v</span> <span class="special">=</span> <span class="identifier">calculate_foo</span><span class="special">();</span>
+<span class="keyword">if</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">v</span> <span class="special">)</span>
+ <span class="identifier">error</span><span class="special">(</span><span class="string">"foo wasn't computed"</span><span class="special">);</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">==</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ shall meet requirements of <code class="computeroutput"><span class="identifier">EqualityComparable</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> If both <code class="computeroutput"><span class="identifier">x</span></code>
+ and <code class="computeroutput"><span class="identifier">y</span></code> are initialized,
+ <code class="computeroutput"><span class="special">(*</span><span class="identifier">x</span>
+ <span class="special">==</span> <span class="special">*</span><span class="identifier">y</span><span class="special">)</span></code>. If
+ only <code class="computeroutput"><span class="identifier">x</span></code> or <code class="computeroutput"><span class="identifier">y</span></code> is initialized, <code class="computeroutput"><span class="keyword">false</span></code>.
+ If both are uninitialized, <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> Pointers have shallow relational
+ operators while <code class="computeroutput"><span class="identifier">optional</span></code>
+ has deep relational operators. Do not use <code class="computeroutput"><span class="keyword">operator</span>
+ <span class="special">==</span></code> directly in generic code which
+ expect to be given either an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> or a pointer; use <a href="../../../../utility/OptionalPointee.html#equal" target="_top"><code class="computeroutput"><span class="identifier">equal_pointees</span><span class="special">()</span></code></a>
+ instead
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">(</span><span class="number">12</span><span class="special">);</span>
+<span class="identifier">T</span> <span class="identifier">y</span><span class="special">(</span><span class="number">12</span><span class="special">);</span>
+<span class="identifier">T</span> <span class="identifier">z</span><span class="special">(</span><span class="number">21</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def0</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def1</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">optX</span><span class="special">(</span><span class="identifier">x</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">optY</span><span class="special">(</span><span class="identifier">y</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">optZ</span><span class="special">(</span><span class="identifier">z</span><span class="special">);</span>
+
+<span class="comment">// Identity always hold</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">def0</span> <span class="special">==</span> <span class="identifier">def0</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">optX</span> <span class="special">==</span> <span class="identifier">optX</span> <span class="special">);</span>
+
+<span class="comment">// Both uninitialized compare equal</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">def0</span> <span class="special">==</span> <span class="identifier">def1</span> <span class="special">);</span>
+
+<span class="comment">// Only one initialized compare unequal.</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">def0</span> <span class="special">!=</span> <span class="identifier">optX</span> <span class="special">);</span>
+
+<span class="comment">// Both initialized compare as (*lhs == *rhs)</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">optX</span> <span class="special">==</span> <span class="identifier">optY</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">optX</span> <span class="special">!=</span> <span class="identifier">optZ</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_less_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special"><</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ shall meet requirements of <code class="computeroutput"><span class="identifier">LessThanComparable</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> If <code class="computeroutput"><span class="identifier">y</span></code>
+ is not initialized, <code class="computeroutput"><span class="keyword">false</span></code>.
+ If <code class="computeroutput"><span class="identifier">y</span></code> is initialized and
+ <code class="computeroutput"><span class="identifier">x</span></code> is not initialized,
+ <code class="computeroutput"><span class="keyword">true</span></code>. If both <code class="computeroutput"><span class="identifier">x</span></code> and <code class="computeroutput"><span class="identifier">y</span></code>
+ are initialized, <code class="computeroutput"><span class="special">(*</span><span class="identifier">x</span>
+ <span class="special"><</span> <span class="special">*</span><span class="identifier">y</span><span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> Pointers have shallow relational
+ operators while <code class="computeroutput"><span class="identifier">optional</span></code>
+ has deep relational operators. Do not use <code class="computeroutput"><span class="keyword">operator</span>
+ <span class="special"><</span></code> directly in generic code which
+ expect to be given either an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> or a pointer; use <a href="../../../../utility/OptionalPointee.html#less" target="_top"><code class="computeroutput"><span class="identifier">less_pointees</span><span class="special">()</span></code></a>
+ instead.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">(</span><span class="number">12</span><span class="special">);</span>
+<span class="identifier">T</span> <span class="identifier">y</span><span class="special">(</span><span class="number">34</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">optX</span><span class="special">(</span><span class="identifier">x</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">optY</span><span class="special">(</span><span class="identifier">y</span><span class="special">);</span>
+
+<span class="comment">// Identity always hold</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">def</span> <span class="special"><</span> <span class="identifier">def</span><span class="special">)</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">optX</span> <span class="special">==</span> <span class="identifier">optX</span> <span class="special">);</span>
+
+<span class="comment">// Both uninitialized compare equal</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">def0</span> <span class="special">==</span> <span class="identifier">def1</span> <span class="special">);</span>
+
+<span class="comment">// Only one initialized compare unequal.</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">def0</span> <span class="special">!=</span> <span class="identifier">optX</span> <span class="special">);</span>
+
+<span class="comment">// Both initialized compare as (*lhs == *rhs)</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">optX</span> <span class="special">==</span> <span class="identifier">optY</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">optX</span> <span class="special">!=</span> <span class="identifier">optZ</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_not_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">!=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
+ <span class="identifier">x</span> <span class="special">==</span>
+ <span class="identifier">y</span> <span class="special">);</span></code>
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_greater_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">></span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">(</span>
+ <span class="identifier">y</span> <span class="special"><</span>
+ <span class="identifier">x</span> <span class="special">);</span></code>
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_less_or_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special"><=</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
+ <span class="identifier">y</span> <span class="special"><</span>
+ <span class="identifier">x</span> <span class="special">);</span></code>
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_greater_or_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">>=</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
+ <span class="identifier">x</span><span class="special"><</span><span class="identifier">y</span> <span class="special">);</span></code>
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+</ul></div>
+<a name="reference_operator_compare_equal_optional_none"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">==</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">none_t</span>
+ <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">!</span><span class="identifier">x</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ need not meet requirements of <code class="computeroutput"><span class="identifier">EqualityComparable</span></code>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_not_equal_optional_none"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">!=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">none_t</span>
+ <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
+ <span class="identifier">x</span> <span class="special">==</span>
+ <span class="identifier">y</span> <span class="special">);</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_swap_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">swap</span>
+ <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span>
+ <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> If both <code class="computeroutput"><span class="identifier">x</span></code>
+ and <code class="computeroutput"><span class="identifier">y</span></code> are initialized,
+ calls <code class="computeroutput"><span class="identifier">swap</span><span class="special">(*</span><span class="identifier">x</span><span class="special">,*</span><span class="identifier">y</span><span class="special">)</span></code> using <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">swap</span></code>.
+ If only one is initialized, say <code class="computeroutput"><span class="identifier">x</span></code>,
+ calls: <code class="computeroutput"><span class="identifier">y</span><span class="special">.</span><span class="identifier">reset</span><span class="special">(*</span><span class="identifier">x</span><span class="special">);</span> <span class="identifier">x</span><span class="special">.</span><span class="identifier">reset</span><span class="special">();</span></code> If none is initialized, does nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> The states of <code class="computeroutput"><span class="identifier">x</span></code> and <code class="computeroutput"><span class="identifier">y</span></code>
+ interchanged.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> If both are initialized, whatever
+ <code class="computeroutput"><span class="identifier">swap</span><span class="special">(</span><span class="identifier">T</span><span class="special">&,</span><span class="identifier">T</span><span class="special">&)</span></code>
+ throws. If only one is initialized, whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span>
+ <span class="special">)</span></code> throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If both are initialized, <code class="computeroutput"><span class="identifier">swap</span><span class="special">(</span><span class="identifier">T</span><span class="special">&,</span><span class="identifier">T</span><span class="special">&)</span></code>
+ is used unqualified but with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">swap</span></code>
+ introduced in scope. If only one is initialized, <code class="computeroutput"><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code> and <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span>
+ <span class="identifier">T</span><span class="special">&&</span>
+ <span class="special">)</span></code> is called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> If both are initialized,
+ this operation has the exception safety guarantees of <code class="computeroutput"><span class="identifier">swap</span><span class="special">(</span><span class="identifier">T</span><span class="special">&,</span><span class="identifier">T</span><span class="special">&)</span></code>.
+ If only one is initialized, it has the same basic guarantee as <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span>
+ <span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">(</span><span class="number">12</span><span class="special">);</span>
+<span class="identifier">T</span> <span class="identifier">y</span><span class="special">(</span><span class="number">21</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def0</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def1</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">optX</span><span class="special">(</span><span class="identifier">x</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">optY</span><span class="special">(</span><span class="identifier">y</span><span class="special">);</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">def1</span><span class="special">);</span> <span class="comment">// no-op</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">optX</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def0</span> <span class="special">==</span> <span class="identifier">x</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">optX</span> <span class="special">);</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">optX</span><span class="special">);</span> <span class="comment">// Get back to original values</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">optX</span><span class="special">,</span><span class="identifier">optY</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">optX</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">optY</span> <span class="special">==</span> <span class="identifier">x</span> <span class="special">);</span>
+</pre>
+ </li>
+</ul></div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
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+<div class="section">
+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="boost_optional.development"></a><a class="link" href="development.html" title="Development">Development</a>
+</h2></div></div></div>
+<div class="toc"><dl class="toc">
+<dt><span class="section"><a href="development.html#boost_optional.development.the_models">The models</a></span></dt>
+<dt><span class="section"><a href="development.html#boost_optional.development.the_semantics">The semantics</a></span></dt>
+<dt><span class="section"><a href="development.html#boost_optional.development.the_interface">The Interface</a></span></dt>
+</dl></div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.development.the_models"></a><a class="link" href="development.html#boost_optional.development.the_models" title="The models">The models</a>
+</h3></div></div></div>
+<p>
+ In C++, we can <span class="emphasis"><em>declare</em></span> an object (a variable) of type
+ <code class="computeroutput"><span class="identifier">T</span></code>, and we can give this variable
+ an <span class="emphasis"><em>initial value</em></span> (through an <span class="emphasis"><em>initializer</em></span>.
+ (cf. 8.5)). When a declaration includes a non-empty initializer (an initial
+ value is given), it is said that the object has been initialized. If the
+ declaration uses an empty initializer (no initial value is given), and neither
+ default nor value initialization applies, it is said that the object is
+ <span class="bold"><strong>uninitialized</strong></span>. Its actual value exist but
+ has an <span class="emphasis"><em>indeterminate initial value</em></span> (cf. 8.5/11). <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> intends
+ to formalize the notion of initialization (or lack of it) allowing a program
+ to test whether an object has been initialized and stating that access to
+ the value of an uninitialized object is undefined behavior. That is, when
+ a variable is declared as <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ and no initial value is given, the variable is <span class="emphasis"><em>formally</em></span>
+ uninitialized. A formally uninitialized optional object has conceptually
+ no value at all and this situation can be tested at runtime. It is formally
+ <span class="emphasis"><em>undefined behavior</em></span> to try to access the value of an
+ uninitialized optional. An uninitialized optional can be assigned a value,
+ in which case its initialization state changes to initialized. Furthermore,
+ given the formal treatment of initialization states in optional objects,
+ it is even possible to reset an optional to <span class="emphasis"><em>uninitialized</em></span>.
+ </p>
+<p>
+ In C++ there is no formal notion of uninitialized objects, which means that
+ objects always have an initial value even if indeterminate. As discussed
+ on the previous section, this has a drawback because you need additional
+ information to tell if an object has been effectively initialized. One of
+ the typical ways in which this has been historically dealt with is via a
+ special value: <code class="computeroutput"><span class="identifier">EOF</span></code>, <code class="computeroutput"><span class="identifier">npos</span></code>, -1, etc... This is equivalent to
+ adding the special value to the set of possible values of a given type. This
+ super set of <code class="computeroutput"><span class="identifier">T</span></code> plus some
+ <span class="emphasis"><em>nil_t</em></span>—where <code class="computeroutput"><span class="identifier">nil_t</span></code>
+ is some stateless POD—can be modeled in modern languages as a <span class="bold"><strong>discriminated union</strong></span> of T and nil_t. Discriminated
+ unions are often called <span class="emphasis"><em>variants</em></span>. A variant has a <span class="emphasis"><em>current
+ type</em></span>, which in our case is either <code class="computeroutput"><span class="identifier">T</span></code>
+ or <code class="computeroutput"><span class="identifier">nil_t</span></code>. Using the <a href="../../../../variant/index.html" target="_top">Boost.Variant</a> library, this model
+ can be implemented in terms of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">variant</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span><span class="identifier">nil_t</span><span class="special">></span></code>.
+ There is precedent for a discriminated union as a model for an optional value:
+ the <a href="http://www.haskell.org/" target="_top">Haskell</a> <span class="bold"><strong>Maybe</strong></span>
+ built-in type constructor. Thus, a discriminated union <code class="computeroutput"><span class="identifier">T</span><span class="special">+</span><span class="identifier">nil_t</span></code>
+ serves as a conceptual foundation.
+ </p>
+<p>
+ A <code class="computeroutput"><span class="identifier">variant</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span><span class="identifier">nil_t</span><span class="special">></span></code> follows naturally from the traditional
+ idiom of extending the range of possible values adding an additional sentinel
+ value with the special meaning of <span class="emphasis"><em>Nothing</em></span>. However,
+ this additional <span class="emphasis"><em>Nothing</em></span> value is largely irrelevant
+ for our purpose since our goal is to formalize the notion of uninitialized
+ objects and, while a special extended value can be used to convey that meaning,
+ it is not strictly necessary in order to do so.
+ </p>
+<p>
+ The observation made in the last paragraph about the irrelevant nature of
+ the additional <code class="computeroutput"><span class="identifier">nil_t</span></code> with
+ respect to <span class="underline">purpose</span> of <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> suggests
+ an alternative model: a <span class="emphasis"><em>container</em></span> that either has a
+ value of <code class="computeroutput"><span class="identifier">T</span></code> or nothing.
+ </p>
+<p>
+ As of this writing I don't know of any precedent for a variable-size fixed-capacity
+ (of 1) stack-based container model for optional values, yet I believe this
+ is the consequence of the lack of practical implementations of such a container
+ rather than an inherent shortcoming of the container model.
+ </p>
+<p>
+ In any event, both the discriminated-union or the single-element container
+ models serve as a conceptual ground for a class representing optional—i.e.
+ possibly uninitialized—objects. For instance, these models show the <span class="emphasis"><em>exact</em></span>
+ semantics required for a wrapper of optional values:
+ </p>
+<p>
+ Discriminated-union:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>deep-copy</strong></span> semantics: copies of the variant
+ implies copies of the value.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>deep-relational</strong></span> semantics: comparisons
+ between variants matches both current types and values
+ </li>
+<li class="listitem">
+ If the variant's current type is <code class="computeroutput"><span class="identifier">T</span></code>,
+ it is modeling an <span class="emphasis"><em>initialized</em></span> optional.
+ </li>
+<li class="listitem">
+ If the variant's current type is not <code class="computeroutput"><span class="identifier">T</span></code>,
+ it is modeling an <span class="emphasis"><em>uninitialized</em></span> optional.
+ </li>
+<li class="listitem">
+ Testing if the variant's current type is <code class="computeroutput"><span class="identifier">T</span></code>
+ models testing if the optional is initialized
+ </li>
+<li class="listitem">
+ Trying to extract a <code class="computeroutput"><span class="identifier">T</span></code>
+ from a variant when its current type is not <code class="computeroutput"><span class="identifier">T</span></code>,
+ models the undefined behavior of trying to access the value of an uninitialized
+ optional
+ </li>
+</ul></div>
+<p>
+ Single-element container:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>deep-copy</strong></span> semantics: copies of the container
+ implies copies of the value.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>deep-relational</strong></span> semantics: comparisons
+ between containers compare container size and if match, contained value
+ </li>
+<li class="listitem">
+ If the container is not empty (contains an object of type <code class="computeroutput"><span class="identifier">T</span></code>), it is modeling an <span class="emphasis"><em>initialized</em></span>
+ optional.
+ </li>
+<li class="listitem">
+ If the container is empty, it is modeling an <span class="emphasis"><em>uninitialized</em></span>
+ optional.
+ </li>
+<li class="listitem">
+ Testing if the container is empty models testing if the optional is initialized
+ </li>
+<li class="listitem">
+ Trying to extract a <code class="computeroutput"><span class="identifier">T</span></code>
+ from an empty container models the undefined behavior of trying to access
+ the value of an uninitialized optional
+ </li>
+</ul></div>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.development.the_semantics"></a><a class="link" href="development.html#boost_optional.development.the_semantics" title="The semantics">The semantics</a>
+</h3></div></div></div>
+<p>
+ Objects of type <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ are intended to be used in places where objects of type <code class="computeroutput"><span class="identifier">T</span></code>
+ would but which might be uninitialized. Hence, <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>'s
+ purpose is to formalize the additional possibly uninitialized state. From
+ the perspective of this role, <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ can have the same operational semantics of <code class="computeroutput"><span class="identifier">T</span></code>
+ plus the additional semantics corresponding to this special state. As such,
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> could
+ be thought of as a <span class="emphasis"><em>supertype</em></span> of <code class="computeroutput"><span class="identifier">T</span></code>.
+ Of course, we can't do that in C++, so we need to compose the desired semantics
+ using a different mechanism. Doing it the other way around, that is, making
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> a
+ <span class="emphasis"><em>subtype</em></span> of <code class="computeroutput"><span class="identifier">T</span></code>
+ is not only conceptually wrong but also impractical: it is not allowed to
+ derive from a non-class type, such as a built-in type.
+ </p>
+<p>
+ We can draw from the purpose of <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ the required basic semantics:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Default Construction:</strong></span> To introduce a
+ formally uninitialized wrapped object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Direct Value Construction via copy:</strong></span>
+ To introduce a formally initialized wrapped object whose value is obtained
+ as a copy of some object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Deep Copy Construction:</strong></span> To obtain a
+ new yet equivalent wrapped object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Direct Value Assignment (upon initialized):</strong></span>
+ To assign a value to the wrapped object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Direct Value Assignment (upon uninitialized):</strong></span>
+ To initialize the wrapped object with a value obtained as a copy of some
+ object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Assignment (upon initialized):</strong></span> To assign
+ to the wrapped object the value of another wrapped object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Assignment (upon uninitialized):</strong></span> To
+ initialize the wrapped object with value of another wrapped object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Deep Relational Operations (when supported by the
+ type T):</strong></span> To compare wrapped object values taking into account
+ the presence of uninitialized states.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Value access:</strong></span> To unwrap the wrapped
+ object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Initialization state query:</strong></span> To determine
+ if the object is formally initialized or not.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Swap:</strong></span> To exchange wrapped objects. (with
+ whatever exception safety guarantees are provided by <code class="computeroutput"><span class="identifier">T</span></code>'s
+ swap).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>De-initialization:</strong></span> To release the wrapped
+ object (if any) and leave the wrapper in the uninitialized state.
+ </li>
+</ul></div>
+<p>
+ Additional operations are useful, such as converting constructors and converting
+ assignments, in-place construction and assignment, and safe value access
+ via a pointer to the wrapped object or null.
+ </p>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.development.the_interface"></a><a class="link" href="development.html#boost_optional.development.the_interface" title="The Interface">The Interface</a>
+</h3></div></div></div>
+<p>
+ Since the purpose of optional is to allow us to use objects with a formal
+ uninitialized additional state, the interface could try to follow the interface
+ of the underlying <code class="computeroutput"><span class="identifier">T</span></code> type
+ as much as possible. In order to choose the proper degree of adoption of
+ the native <code class="computeroutput"><span class="identifier">T</span></code> interface, the
+ following must be noted: Even if all the operations supported by an instance
+ of type <code class="computeroutput"><span class="identifier">T</span></code> are defined for
+ the entire range of values for such a type, an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ extends such a set of values with a new value for which most (otherwise valid)
+ operations are not defined in terms of <code class="computeroutput"><span class="identifier">T</span></code>.
+ </p>
+<p>
+ Furthermore, since <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ itself is merely a <code class="computeroutput"><span class="identifier">T</span></code> wrapper
+ (modeling a <code class="computeroutput"><span class="identifier">T</span></code> supertype),
+ any attempt to define such operations upon uninitialized optionals will be
+ totally artificial w.r.t. <code class="computeroutput"><span class="identifier">T</span></code>.
+ </p>
+<p>
+ This library chooses an interface which follows from <code class="computeroutput"><span class="identifier">T</span></code>'s
+ interface only for those operations which are well defined (w.r.t the type
+ <code class="computeroutput"><span class="identifier">T</span></code>) even if any of the operands
+ are uninitialized. These operations include: construction, copy-construction,
+ assignment, swap and relational operations.
+ </p>
+<p>
+ For the value access operations, which are undefined (w.r.t the type <code class="computeroutput"><span class="identifier">T</span></code>) when the operand is uninitialized, a
+ different interface is chosen (which will be explained next).
+ </p>
+<p>
+ Also, the presence of the possibly uninitialized state requires additional
+ operations not provided by <code class="computeroutput"><span class="identifier">T</span></code>
+ itself which are supported by a special interface.
+ </p>
+<h5>
+<a name="boost_optional.development.the_interface.h0"></a>
+ <span class="phrase"><a name="boost_optional.development.the_interface.lexically_hinted_value_access_in_the_presence_of_possibly_untitialized_optional_objects__the_operators___and___gt_"></a></span><a class="link" href="development.html#boost_optional.development.the_interface.lexically_hinted_value_access_in_the_presence_of_possibly_untitialized_optional_objects__the_operators___and___gt_">Lexically-hinted
+ Value Access in the presence of possibly untitialized optional objects: The
+ operators * and -></a>
+ </h5>
+<p>
+ A relevant feature of a pointer is that it can have a <span class="bold"><strong>null
+ pointer value</strong></span>. This is a <span class="emphasis"><em>special</em></span> value which
+ is used to indicate that the pointer is not referring to any object at all.
+ In other words, null pointer values convey the notion of nonexistent objects.
+ </p>
+<p>
+ This meaning of the null pointer value allowed pointers to became a <span class="emphasis"><em>de
+ facto</em></span> standard for handling optional objects because all you have
+ to do to refer to a value which you don't really have is to use a null pointer
+ value of the appropriate type. Pointers have been used for decades—from
+ the days of C APIs to modern C++ libraries—to <span class="emphasis"><em>refer</em></span>
+ to optional (that is, possibly nonexistent) objects; particularly as optional
+ arguments to a function, but also quite often as optional data members.
+ </p>
+<p>
+ The possible presence of a null pointer value makes the operations that access
+ the pointee's value possibly undefined, therefore, expressions which use
+ dereference and access operators, such as: <code class="computeroutput"><span class="special">(</span>
+ <span class="special">*</span><span class="identifier">p</span> <span class="special">=</span> <span class="number">2</span> <span class="special">)</span></code>
+ and <code class="computeroutput"><span class="special">(</span> <span class="identifier">p</span><span class="special">-></span><span class="identifier">foo</span><span class="special">()</span> <span class="special">)</span></code>, implicitly
+ convey the notion of optionality, and this information is tied to the <span class="emphasis"><em>syntax</em></span>
+ of the expressions. That is, the presence of operators <code class="computeroutput"><span class="special">*</span></code>
+ and <code class="computeroutput"><span class="special">-></span></code> tell by themselves
+ —without any additional context— that the expression will be undefined
+ unless the implied pointee actually exist.
+ </p>
+<p>
+ Such a <span class="emphasis"><em>de facto</em></span> idiom for referring to optional objects
+ can be formalized in the form of a concept: the <a href="../../../../utility/OptionalPointee.html" target="_top">OptionalPointee</a>
+ concept. This concept captures the syntactic usage of operators <code class="computeroutput"><span class="special">*</span></code>, <code class="computeroutput"><span class="special">-></span></code>
+ and contextual conversion to <code class="computeroutput"><span class="keyword">bool</span></code>
+ to convey the notion of optionality.
+ </p>
+<p>
+ However, pointers are good to <span class="underline">refer</span>
+ to optional objects, but not particularly good to handle the optional objects
+ in all other respects, such as initializing or moving/copying them. The problem
+ resides in the shallow-copy of pointer semantics: if you need to effectively
+ move or copy the object, pointers alone are not enough. The problem is that
+ copies of pointers do not imply copies of pointees. For example, as was discussed
+ in the motivation, pointers alone cannot be used to return optional objects
+ from a function because the object must move outside from the function and
+ into the caller's context.
+ </p>
+<p>
+ A solution to the shallow-copy problem that is often used is to resort to
+ dynamic allocation and use a smart pointer to automatically handle the details
+ of this. For example, if a function is to optionally return an object <code class="computeroutput"><span class="identifier">X</span></code>, it can use <code class="computeroutput"><span class="identifier">shared_ptr</span><span class="special"><</span><span class="identifier">X</span><span class="special">></span></code>
+ as the return value. However, this requires dynamic allocation of <code class="computeroutput"><span class="identifier">X</span></code>. If <code class="computeroutput"><span class="identifier">X</span></code>
+ is a built-in or small POD, this technique is very poor in terms of required
+ resources. Optional objects are essentially values so it is very convenient
+ to be able to use automatic storage and deep-copy semantics to manipulate
+ optional values just as we do with ordinary values. Pointers do not have
+ this semantics, so are inappropriate for the initialization and transport
+ of optional values, yet are quite convenient for handling the access to the
+ possible undefined value because of the idiomatic aid present in the <a href="../../../../utility/OptionalPointee.html" target="_top">OptionalPointee</a> concept
+ incarnated by pointers.
+ </p>
+<h5>
+<a name="boost_optional.development.the_interface.h1"></a>
+ <span class="phrase"><a name="boost_optional.development.the_interface.optional_lt_t_gt__as_a_model_of_optionalpointee"></a></span><a class="link" href="development.html#boost_optional.development.the_interface.optional_lt_t_gt__as_a_model_of_optionalpointee">Optional<T>
+ as a model of OptionalPointee</a>
+ </h5>
+<p>
+ For value access operations <code class="computeroutput"><span class="identifier">optional</span><span class="special"><></span></code> uses operators <code class="computeroutput"><span class="special">*</span></code>
+ and <code class="computeroutput"><span class="special">-></span></code> to lexically warn
+ about the possibly uninitialized state appealing to the familiar pointer
+ semantics w.r.t. to null pointers.
+ </p>
+<div class="warning"><table border="0" summary="Warning">
+<tr>
+<td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../../../doc/src/images/warning.png"></td>
+<th align="left">Warning</th>
+</tr>
+<tr><td align="left" valign="top"><p>
+ However, it is particularly important to note that <code class="computeroutput"><span class="identifier">optional</span><span class="special"><></span></code> objects are not pointers. <span class="underline"><code class="computeroutput"><span class="identifier">optional</span><span class="special"><></span></code> is not, and does not model, a pointer</span>.
+ </p></td></tr>
+</table></div>
+<p>
+ For instance, <code class="computeroutput"><span class="identifier">optional</span><span class="special"><></span></code>
+ does not have shallow-copy so does not alias: two different optionals never
+ refer to the <span class="emphasis"><em>same</em></span> value unless <code class="computeroutput"><span class="identifier">T</span></code>
+ itself is a reference (but may have <span class="emphasis"><em>equivalent</em></span> values).
+ The difference between an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ and a pointer must be kept in mind, particularly because the semantics of
+ relational operators are different: since <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ is a value-wrapper, relational operators are deep: they compare optional
+ values; but relational operators for pointers are shallow: they do not compare
+ pointee values. As a result, you might be able to replace <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ by <code class="computeroutput"><span class="identifier">T</span><span class="special">*</span></code>
+ on some situations but not always. Specifically, on generic code written
+ for both, you cannot use relational operators directly, and must use the
+ template functions <a href="../../../../utility/OptionalPointee.html#equal" target="_top"><code class="computeroutput"><span class="identifier">equal_pointees</span><span class="special">()</span></code></a>
+ and <a href="../../../../utility/OptionalPointee.html#less" target="_top"><code class="computeroutput"><span class="identifier">less_pointees</span><span class="special">()</span></code></a>
+ instead.
+ </p>
+</div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="tutorial.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="synopsis.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
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diff --git a/doc/html/boost_optional/discussion.html b/doc/html/boost_optional/discussion.html
new file mode 100644
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@@ -0,0 +1,128 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Discussion</title>
+<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../index.html" title="Chapter 1. Boost.Optional">
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+<link rel="prev" href="quick_start.html" title="Quick Start">
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+</div>
+<div class="section">
+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="boost_optional.discussion"></a><a class="link" href="discussion.html" title="Discussion">Discussion</a>
+</h2></div></div></div>
+<p>
+ Consider these functions which should return a value but which might not have
+ a value to return:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ (A) <code class="computeroutput"><span class="keyword">double</span> <span class="identifier">sqrt</span><span class="special">(</span><span class="keyword">double</span> <span class="identifier">n</span> <span class="special">);</span></code>
+ </li>
+<li class="listitem">
+ (B) <code class="computeroutput"><span class="keyword">char</span> <span class="identifier">get_async_input</span><span class="special">();</span></code>
+ </li>
+<li class="listitem">
+ (C) <code class="computeroutput"><span class="identifier">point</span> <span class="identifier">polygon</span><span class="special">::</span><span class="identifier">get_any_point_effectively_inside</span><span class="special">();</span></code>
+ </li>
+</ul></div>
+<p>
+ There are different approaches to the issue of not having a value to return.
+ </p>
+<p>
+ A typical approach is to consider the existence of a valid return value as
+ a postcondition, so that if the function cannot compute the value to return,
+ it has either undefined behavior (and can use assert in a debug build) or uses
+ a runtime check and throws an exception if the postcondition is violated. This
+ is a reasonable choice for example, for function (A), because the lack of a
+ proper return value is directly related to an invalid parameter (out of domain
+ argument), so it is appropriate to require the callee to supply only parameters
+ in a valid domain for execution to continue normally.
+ </p>
+<p>
+ However, function (B), because of its asynchronous nature, does not fail just
+ because it can't find a value to return; so it is incorrect to consider such
+ a situation an error and assert or throw an exception. This function must return,
+ and somehow, must tell the callee that it is not returning a meaningful value.
+ </p>
+<p>
+ A similar situation occurs with function (C): it is conceptually an error to
+ ask a <span class="emphasis"><em>null-area</em></span> polygon to return a point inside itself,
+ but in many applications, it is just impractical for performance reasons to
+ treat this as an error (because detecting that the polygon has no area might
+ be too expensive to be required to be tested previously), and either an arbitrary
+ point (typically at infinity) is returned, or some efficient way to tell the
+ callee that there is no such point is used.
+ </p>
+<p>
+ There are various mechanisms to let functions communicate that the returned
+ value is not valid. One such mechanism, which is quite common since it has
+ zero or negligible overhead, is to use a special value which is reserved to
+ communicate this. Classical examples of such special values are <code class="computeroutput"><span class="identifier">EOF</span></code>, <code class="computeroutput"><span class="identifier">string</span><span class="special">::</span><span class="identifier">npos</span></code>, points
+ at infinity, etc...
+ </p>
+<p>
+ When those values exist, i.e. the return type can hold all meaningful values
+ <span class="emphasis"><em>plus</em></span> the <span class="emphasis"><em>signal</em></span> value, this mechanism
+ is quite appropriate and well known. Unfortunately, there are cases when such
+ values do not exist. In these cases, the usual alternative is either to use
+ a wider type, such as <code class="computeroutput"><span class="keyword">int</span></code> in place
+ of <code class="computeroutput"><span class="keyword">char</span></code>; or a compound type, such
+ as <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">point</span><span class="special">,</span><span class="keyword">bool</span><span class="special">></span></code>.
+ </p>
+<p>
+ Returning a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span><span class="keyword">bool</span><span class="special">></span></code>, thus attaching a boolean flag to the result
+ which indicates if the result is meaningful, has the advantage that can be
+ turned into a consistent idiom since the first element of the pair can be whatever
+ the function would conceptually return. For example, the last two functions
+ could have the following interface:
+ </p>
+<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span><span class="keyword">bool</span><span class="special">></span> <span class="identifier">get_async_input</span><span class="special">();</span>
+<span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">point</span><span class="special">,</span><span class="keyword">bool</span><span class="special">></span> <span class="identifier">polygon</span><span class="special">::</span><span class="identifier">get_any_point_effectively_inside</span><span class="special">();</span>
+</pre>
+<p>
+ These functions use a consistent interface for dealing with possibly nonexistent
+ results:
+ </p>
+<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">point</span><span class="special">,</span><span class="keyword">bool</span><span class="special">></span> <span class="identifier">p</span> <span class="special">=</span> <span class="identifier">poly</span><span class="special">.</span><span class="identifier">get_any_point_effectively_inside</span><span class="special">();</span>
+<span class="keyword">if</span> <span class="special">(</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">second</span> <span class="special">)</span>
+ <span class="identifier">flood_fill</span><span class="special">(</span><span class="identifier">p</span><span class="special">.</span><span class="identifier">first</span><span class="special">);</span>
+</pre>
+<p>
+ However, not only is this quite a burden syntactically, it is also error prone
+ since the user can easily use the function result (first element of the pair)
+ without ever checking if it has a valid value.
+ </p>
+<p>
+ Clearly, we need a better idiom.
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="quick_start.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="development.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
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+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Examples</title>
+<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
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+<link rel="prev" href="detailed_semantics.html" title="Detailed Semantics">
+<link rel="next" href="optional_references.html" title="Optional references">
+</head>
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+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../index.html">Home</a></td>
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+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
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+</div>
+<div class="section">
+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="boost_optional.examples"></a><a class="link" href="examples.html" title="Examples">Examples</a>
+</h2></div></div></div>
+<div class="toc"><dl class="toc">
+<dt><span class="section"><a href="examples.html#boost_optional.examples.optional_return_values">Optional
+ return values</a></span></dt>
+<dt><span class="section"><a href="examples.html#boost_optional.examples.optional_local_variables">Optional
+ local variables</a></span></dt>
+<dt><span class="section"><a href="examples.html#boost_optional.examples.optional_data_members">Optional
+ data members</a></span></dt>
+<dt><span class="section"><a href="examples.html#boost_optional.examples.bypassing_expensive_unnecessary_default_construction">Bypassing
+ expensive unnecessary default construction</a></span></dt>
+</dl></div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.examples.optional_return_values"></a><a class="link" href="examples.html#boost_optional.examples.optional_return_values" title="Optional return values">Optional
+ return values</a>
+</h3></div></div></div>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">char</span><span class="special">></span> <span class="identifier">get_async_input</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="keyword">if</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">queue</span><span class="special">.</span><span class="identifier">empty</span><span class="special">()</span> <span class="special">)</span>
+ <span class="keyword">return</span> <span class="identifier">optional</span><span class="special"><</span><span class="keyword">char</span><span class="special">>(</span><span class="identifier">queue</span><span class="special">.</span><span class="identifier">top</span><span class="special">());</span>
+ <span class="keyword">else</span> <span class="keyword">return</span> <span class="identifier">optional</span><span class="special"><</span><span class="keyword">char</span><span class="special">>();</span> <span class="comment">// uninitialized</span>
+<span class="special">}</span>
+
+<span class="keyword">void</span> <span class="identifier">receive_async_message</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="keyword">char</span><span class="special">></span> <span class="identifier">rcv</span> <span class="special">;</span>
+ <span class="comment">// The safe boolean conversion from 'rcv' is used here.</span>
+ <span class="keyword">while</span> <span class="special">(</span> <span class="special">(</span><span class="identifier">rcv</span> <span class="special">=</span> <span class="identifier">get_async_input</span><span class="special">())</span> <span class="special">&&</span> <span class="special">!</span><span class="identifier">timeout</span><span class="special">()</span> <span class="special">)</span>
+ <span class="identifier">output</span><span class="special">(*</span><span class="identifier">rcv</span><span class="special">);</span>
+<span class="special">}</span>
+</pre>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.examples.optional_local_variables"></a><a class="link" href="examples.html#boost_optional.examples.optional_local_variables" title="Optional local variables">Optional
+ local variables</a>
+</h3></div></div></div>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">string</span><span class="special">></span> <span class="identifier">name</span> <span class="special">;</span>
+<span class="keyword">if</span> <span class="special">(</span> <span class="identifier">database</span><span class="special">.</span><span class="identifier">open</span><span class="special">()</span> <span class="special">)</span>
+<span class="special">{</span>
+ <span class="identifier">name</span> <span class="special">=</span> <span class="identifier">database</span><span class="special">.</span><span class="identifier">lookup</span><span class="special">(</span><span class="identifier">employer_name</span><span class="special">)</span> <span class="special">;</span>
+<span class="special">}</span>
+<span class="keyword">else</span>
+<span class="special">{</span>
+ <span class="keyword">if</span> <span class="special">(</span> <span class="identifier">can_ask_user</span> <span class="special">)</span>
+ <span class="identifier">name</span> <span class="special">=</span> <span class="identifier">user</span><span class="special">.</span><span class="identifier">ask</span><span class="special">(</span><span class="identifier">employer_name</span><span class="special">)</span> <span class="special">;</span>
+<span class="special">}</span>
+
+<span class="keyword">if</span> <span class="special">(</span> <span class="identifier">name</span> <span class="special">)</span>
+ <span class="identifier">print</span><span class="special">(*</span><span class="identifier">name</span><span class="special">);</span>
+<span class="keyword">else</span> <span class="identifier">print</span><span class="special">(</span><span class="string">"employer's name not found!"</span><span class="special">);</span>
+</pre>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.examples.optional_data_members"></a><a class="link" href="examples.html#boost_optional.examples.optional_data_members" title="Optional data members">Optional
+ data members</a>
+</h3></div></div></div>
+<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">figure</span>
+<span class="special">{</span>
+ <span class="keyword">public</span><span class="special">:</span>
+
+ <span class="identifier">figure</span><span class="special">()</span>
+ <span class="special">{</span>
+ <span class="comment">// data member 'm_clipping_rect' is uninitialized at this point.</span>
+ <span class="special">}</span>
+
+ <span class="keyword">void</span> <span class="identifier">clip_in_rect</span> <span class="special">(</span> <span class="identifier">rect</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rect</span> <span class="special">)</span>
+ <span class="special">{</span>
+ <span class="special">....</span>
+ <span class="identifier">m_clipping_rect</span> <span class="special">=</span> <span class="identifier">rect</span> <span class="special">;</span> <span class="comment">// initialized here.</span>
+ <span class="special">}</span>
+
+ <span class="keyword">void</span> <span class="identifier">draw</span> <span class="special">(</span> <span class="identifier">canvas</span><span class="special">&</span> <span class="identifier">cvs</span> <span class="special">)</span>
+ <span class="special">{</span>
+ <span class="keyword">if</span> <span class="special">(</span> <span class="identifier">m_clipping_rect</span> <span class="special">)</span>
+ <span class="identifier">do_clipping</span><span class="special">(*</span><span class="identifier">m_clipping_rect</span><span class="special">);</span>
+
+ <span class="identifier">cvs</span><span class="special">.</span><span class="identifier">drawXXX</span><span class="special">(..);</span>
+ <span class="special">}</span>
+
+ <span class="comment">// this can return NULL.</span>
+ <span class="identifier">rect</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">get_clipping_rect</span><span class="special">()</span> <span class="special">{</span> <span class="keyword">return</span> <span class="identifier">get_pointer</span><span class="special">(</span><span class="identifier">m_clipping_rect</span><span class="special">);</span> <span class="special">}</span>
+
+ <span class="keyword">private</span> <span class="special">:</span>
+
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">rect</span><span class="special">></span> <span class="identifier">m_clipping_rect</span> <span class="special">;</span>
+
+<span class="special">};</span>
+</pre>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.examples.bypassing_expensive_unnecessary_default_construction"></a><a class="link" href="examples.html#boost_optional.examples.bypassing_expensive_unnecessary_default_construction" title="Bypassing expensive unnecessary default construction">Bypassing
+ expensive unnecessary default construction</a>
+</h3></div></div></div>
+<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">ExpensiveCtor</span> <span class="special">{</span> <span class="special">...</span> <span class="special">}</span> <span class="special">;</span>
+<span class="keyword">class</span> <span class="identifier">Fred</span>
+<span class="special">{</span>
+ <span class="identifier">Fred</span><span class="special">()</span> <span class="special">:</span> <span class="identifier">mLargeVector</span><span class="special">(</span><span class="number">10000</span><span class="special">)</span> <span class="special">{}</span>
+
+ <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">ExpensiveCtor</span><span class="special">></span> <span class="special">></span> <span class="identifier">mLargeVector</span> <span class="special">;</span>
+<span class="special">}</span> <span class="special">;</span>
+</pre>
+</div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="detailed_semantics.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="optional_references.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/exception_safety_guarantees.html b/doc/html/boost_optional/exception_safety_guarantees.html
new file mode 100644
index 0000000..2537918
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@@ -0,0 +1,170 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Exception Safety Guarantees</title>
+<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../index.html" title="Chapter 1. Boost.Optional">
+<link rel="up" href="../index.html" title="Chapter 1. Boost.Optional">
+<link rel="prev" href="a_note_about_optional_bool_.html" title="A note about optional<bool>">
+<link rel="next" href="type_requirements.html" title="Type requirements">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="a_note_about_optional_bool_.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="type_requirements.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="boost_optional.exception_safety_guarantees"></a><a class="link" href="exception_safety_guarantees.html" title="Exception Safety Guarantees">Exception Safety
+ Guarantees</a>
+</h2></div></div></div>
+<p>
+ This library assumes that <code class="computeroutput"><span class="identifier">T</span></code>'s
+ destructor does not throw exceptions. If it does, the behaviour of many operations
+ on <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> is
+ undefined.
+ </p>
+<p>
+ The following mutating operations never throw exceptions:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span></code>
+ </li>
+<li class="listitem">
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">reset</span><span class="special">()</span> <span class="keyword">noexcept</span></code>
+ </li>
+</ul></div>
+<p>
+ In addition, the following constructors and the destructor never throw exceptions:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">()</span>
+ <span class="keyword">noexcept</span></code>
+ </li>
+<li class="listitem">
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span></code>
+ </li>
+</ul></div>
+<p>
+ Regarding the following assignment functions:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code>
+ </li>
+<li class="listitem">
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code>
+ </li>
+<li class="listitem">
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code>
+ </li>
+<li class="listitem">
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">InPlaceFactory</span><span class="special">></span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">InPlaceFactory</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span></code>
+ </li>
+<li class="listitem">
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">TypedInPlaceFactory</span><span class="special">></span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">TypedInPlaceFactory</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span> </code>
+ </li>
+<li class="listitem">
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">reset</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code>
+ </li>
+</ul></div>
+<p>
+ They forward calls to the corresponding <code class="computeroutput"><span class="identifier">T</span></code>'s
+ constructors or assignments (depending on whether the optional object is initialized
+ or not); so if both <code class="computeroutput"><span class="identifier">T</span></code>'s constructor
+ and the assignment provide strong exception safety guarantee, <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>'s assignment
+ also provides strong exception safety guarantee; otherwise we only get the
+ basic guarantee. Additionally, if both involved <code class="computeroutput"><span class="identifier">T</span></code>'s
+ constructor and the assignment never throw, <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>'s
+ assignment also never throws.
+ </p>
+<p>
+ Unless <code class="computeroutput"><span class="identifier">T</span></code>'s constructor or assignment
+ throws, assignments to <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ do not throw anything else on its own. A throw during assignment never changes
+ the initialization state of any optional object involved:
+ </p>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt1</span><span class="special">(</span><span class="identifier">val1</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt2</span><span class="special">(</span><span class="identifier">val2</span><span class="special">);</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">opt1</span><span class="special">);</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">opt2</span><span class="special">);</span>
+
+<span class="keyword">try</span>
+<span class="special">{</span>
+ <span class="identifier">opt1</span> <span class="special">=</span> <span class="identifier">opt2</span><span class="special">;</span> <span class="comment">// throws</span>
+<span class="special">}</span>
+<span class="keyword">catch</span><span class="special">(...)</span>
+<span class="special">{</span>
+ <span class="identifier">assert</span><span class="special">(</span><span class="identifier">opt1</span><span class="special">);</span>
+ <span class="identifier">assert</span><span class="special">(</span><span class="identifier">opt2</span><span class="special">);</span>
+<span class="special">}</span>
+</pre>
+<p>
+ This also applies to move assignments/constructors. However, move operations
+ are made no-throw more often.
+ </p>
+<p>
+ Operation <code class="computeroutput"><span class="identifier">emplace</span></code> provides
+ basic exception safety guarantee. If it throws, the optional object becomes
+ uninitialized regardless of its initial state, and its previous contained value
+ (if any) is destroyed. It doesn't call any assignment or move/copy constructor
+ on <code class="computeroutput"><span class="identifier">T</span></code>.
+ </p>
+<h4>
+<a name="boost_optional.exception_safety_guarantees.h0"></a>
+ <span class="phrase"><a name="boost_optional.exception_safety_guarantees.swap"></a></span><a class="link" href="exception_safety_guarantees.html#boost_optional.exception_safety_guarantees.swap">Swap</a>
+ </h4>
+<p>
+ Unless <code class="computeroutput"><span class="identifier">swap</span></code> on optional is
+ customized, its primary implementation forwards calls to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <code class="computeroutput"><span class="identifier">swap</span></code> or move constructor (depending
+ on the initialization state of the optional objects). Thus, if both <code class="computeroutput"><span class="identifier">T</span></code>'s <code class="computeroutput"><span class="identifier">swap</span></code>
+ and move constructor never throw, <code class="computeroutput"><span class="identifier">swap</span></code>
+ on <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> never
+ throws. similarly, if both <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <code class="computeroutput"><span class="identifier">swap</span></code> and move constructor offer
+ strong guarantee, <code class="computeroutput"><span class="identifier">swap</span></code> on
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> also
+ offers a strong guarantee.
+ </p>
+<p>
+ In case <code class="computeroutput"><span class="identifier">swap</span></code> on optional is
+ customized, the call to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ move constructor are replaced with the calls to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ default constructor followed by <code class="computeroutput"><span class="identifier">swap</span></code>.
+ (This is more useful on older compilers that do not support move semantics,
+ when one wants to acheive stronger exception safety guarantees.) In this case
+ the exception safety guarantees for <code class="computeroutput"><span class="identifier">swap</span></code>
+ are reliant on the guarantees of <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <code class="computeroutput"><span class="identifier">swap</span></code> and default constructor
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="a_note_about_optional_bool_.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="type_requirements.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/implementation_notes.html b/doc/html/boost_optional/implementation_notes.html
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index 0000000..48d476c
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+++ b/doc/html/boost_optional/implementation_notes.html
@@ -0,0 +1,55 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Implementation Notes</title>
+<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../index.html" title="Chapter 1. Boost.Optional">
+<link rel="up" href="../index.html" title="Chapter 1. Boost.Optional">
+<link rel="prev" href="type_requirements.html" title="Type requirements">
+<link rel="next" href="dependencies_and_portability.html" title="Dependencies and Portability">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="type_requirements.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="dependencies_and_portability.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="boost_optional.implementation_notes"></a><a class="link" href="implementation_notes.html" title="Implementation Notes">Implementation Notes</a>
+</h2></div></div></div>
+<p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> is
+ currently implemented using a custom aligned storage facility built from <code class="computeroutput"><span class="identifier">alignment_of</span></code> and <code class="computeroutput"><span class="identifier">type_with_alignment</span></code>
+ (both from Type Traits). It uses a separate boolean flag to indicate the initialization
+ state. Placement new with <code class="computeroutput"><span class="identifier">T</span></code>'s
+ copy/move constructor and <code class="computeroutput"><span class="identifier">T</span></code>'s
+ destructor are explicitly used to initialize, copy, move and destroy optional
+ values. As a result, <code class="computeroutput"><span class="identifier">T</span></code>'s default
+ constructor is effectively by-passed, but the exception guarantees are basic.
+ It is planned to replace the current implementation with another with stronger
+ exception safety, such as a future <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">variant</span></code>.
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="type_requirements.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="dependencies_and_portability.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/in_place_factories.html b/doc/html/boost_optional/in_place_factories.html
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@@ -0,0 +1,196 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>In-Place Factories</title>
+<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../index.html" title="Chapter 1. Boost.Optional">
+<link rel="up" href="../index.html" title="Chapter 1. Boost.Optional">
+<link rel="prev" href="detailed_semantics.html" title="Detailed Semantics">
+<link rel="next" href="a_note_about_optional_bool_.html" title="A note about optional<bool>">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="detailed_semantics.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="a_note_about_optional_bool_.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="boost_optional.in_place_factories"></a><a class="link" href="in_place_factories.html" title="In-Place Factories">In-Place Factories</a>
+</h2></div></div></div>
+<p>
+ One of the typical problems with wrappers and containers is that their interfaces
+ usually provide an operation to initialize or assign the contained object as
+ a copy of some other object. This not only requires the underlying type to
+ be <a href="../../../../utility/CopyConstructible.html" target="_top">Copy Constructible</a>,
+ but also requires the existence of a fully constructed object, often temporary,
+ just to follow the copy from:
+ </p>
+<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">X</span>
+<span class="special">{</span>
+ <span class="identifier">X</span> <span class="special">(</span> <span class="keyword">int</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">}</span> <span class="special">;</span>
+
+<span class="keyword">class</span> <span class="identifier">W</span>
+<span class="special">{</span>
+ <span class="identifier">X</span> <span class="identifier">wrapped_</span> <span class="special">;</span>
+
+ <span class="keyword">public</span><span class="special">:</span>
+
+ <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">X</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span> <span class="special">)</span> <span class="special">:</span> <span class="identifier">wrapped_</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">{}</span>
+<span class="special">}</span> <span class="special">;</span>
+
+<span class="keyword">void</span> <span class="identifier">foo</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="comment">// Temporary object created.</span>
+ <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">X</span><span class="special">(</span><span class="number">123</span><span class="special">,</span><span class="string">"hello"</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">}</span>
+</pre>
+<p>
+ A solution to this problem is to support direct construction of the contained
+ object right in the container's storage. In this scheme, the user only needs
+ to supply the arguments to the constructor to use in the wrapped object construction.
+ </p>
+<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">W</span>
+<span class="special">{</span>
+ <span class="identifier">X</span> <span class="identifier">wrapped_</span> <span class="special">;</span>
+
+ <span class="keyword">public</span><span class="special">:</span>
+
+ <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">X</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span> <span class="special">)</span> <span class="special">:</span> <span class="identifier">wrapped_</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">{}</span>
+ <span class="identifier">W</span> <span class="special">(</span> <span class="keyword">int</span> <span class="identifier">a0</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">a1</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">wrapped_</span><span class="special">(</span><span class="identifier">a0</span><span class="special">,</span><span class="identifier">a1</span><span class="special">)</span> <span class="special">{}</span>
+<span class="special">}</span> <span class="special">;</span>
+
+<span class="keyword">void</span> <span class="identifier">foo</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="comment">// Wrapped object constructed in-place</span>
+ <span class="comment">// No temporary created.</span>
+ <span class="identifier">W</span> <span class="special">(</span><span class="number">123</span><span class="special">,</span><span class="string">"hello"</span><span class="special">)</span> <span class="special">;</span>
+<span class="special">}</span>
+</pre>
+<p>
+ A limitation of this method is that it doesn't scale well to wrapped objects
+ with multiple constructors nor to generic code were the constructor overloads
+ are unknown.
+ </p>
+<p>
+ The solution presented in this library is the family of <span class="bold"><strong>InPlaceFactories</strong></span>
+ and <span class="bold"><strong>TypedInPlaceFactories</strong></span>. These factories
+ are a family of classes which encapsulate an increasing number of arbitrary
+ constructor parameters and supply a method to construct an object of a given
+ type using those parameters at an address specified by the user via placement
+ new.
+ </p>
+<p>
+ For example, one member of this family looks like:
+ </p>
+<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span><span class="keyword">class</span> <span class="identifier">A0</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">A1</span><span class="special">></span>
+<span class="keyword">class</span> <span class="identifier">TypedInPlaceFactory2</span>
+<span class="special">{</span>
+ <span class="identifier">A0</span> <span class="identifier">m_a0</span> <span class="special">;</span> <span class="identifier">A1</span> <span class="identifier">m_a1</span> <span class="special">;</span>
+
+ <span class="keyword">public</span><span class="special">:</span>
+
+ <span class="identifier">TypedInPlaceFactory2</span><span class="special">(</span> <span class="identifier">A0</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">a0</span><span class="special">,</span> <span class="identifier">A1</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">a1</span> <span class="special">)</span> <span class="special">:</span> <span class="identifier">m_a0</span><span class="special">(</span><span class="identifier">a0</span><span class="special">),</span> <span class="identifier">m_a1</span><span class="special">(</span><span class="identifier">a1</span><span class="special">)</span> <span class="special">{}</span>
+
+ <span class="keyword">void</span> <span class="identifier">construct</span> <span class="special">(</span> <span class="keyword">void</span><span class="special">*</span> <span class="identifier">p</span> <span class="special">)</span> <span class="special">{</span> <span class="keyword">new</span> <span class="special">(</span><span class="identifier">p</span><span class="special">)</span> <span class="identifier">T</span><span class="special">(</span><span class="identifier">m_a0</span><span class="special">,</span><span class="identifier">m_a1</span><span class="special">)</span> <span class="special">;</span> <span class="special">}</span>
+ <span class="special">}</span> <span class="special">;</span>
+</pre>
+<p>
+ A wrapper class aware of this can use it as:
+ </p>
+<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">W</span>
+<span class="special">{</span>
+ <span class="identifier">X</span> <span class="identifier">wrapped_</span> <span class="special">;</span>
+
+ <span class="keyword">public</span><span class="special">:</span>
+
+ <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">X</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span> <span class="special">)</span> <span class="special">:</span> <span class="identifier">wrapped_</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">{}</span>
+ <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">TypedInPlaceFactory2</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">fac</span> <span class="special">)</span> <span class="special">{</span> <span class="identifier">fac</span><span class="special">.</span><span class="identifier">construct</span><span class="special">(&</span><span class="identifier">wrapped_</span><span class="special">)</span> <span class="special">;</span> <span class="special">}</span>
+<span class="special">}</span> <span class="special">;</span>
+
+<span class="keyword">void</span> <span class="identifier">foo</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="comment">// Wrapped object constructed in-place via a TypedInPlaceFactory.</span>
+ <span class="comment">// No temporary created.</span>
+ <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">TypedInPlaceFactory2</span><span class="special"><</span><span class="identifier">X</span><span class="special">,</span><span class="keyword">int</span><span class="special">,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">>(</span><span class="number">123</span><span class="special">,</span><span class="string">"hello"</span><span class="special">))</span> <span class="special">;</span>
+<span class="special">}</span>
+</pre>
+<p>
+ The factories are divided in two groups:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="underline">TypedInPlaceFactories</span>: those which
+ take the target type as a primary template parameter.
+ </li>
+<li class="listitem">
+ <span class="underline">InPlaceFactories</span>: those with a template
+ <code class="computeroutput"><span class="identifier">construct</span><span class="special">(</span><span class="keyword">void</span><span class="special">*)</span></code> member
+ function taking the target type.
+ </li>
+</ul></div>
+<p>
+ Within each group, all the family members differ only in the number of parameters
+ allowed.
+ </p>
+<p>
+ This library provides an overloaded set of helper template functions to construct
+ these factories without requiring unnecessary template parameters:
+ </p>
+<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">A0</span><span class="special">,...,</span><span class="keyword">class</span> <span class="identifier">AN</span><span class="special">></span>
+<span class="identifier">InPlaceFactoryN</span> <span class="special"><</span><span class="identifier">A0</span><span class="special">,...,</span><span class="identifier">AN</span><span class="special">></span> <span class="identifier">in_place</span> <span class="special">(</span> <span class="identifier">A0</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">a0</span><span class="special">,</span> <span class="special">...,</span> <span class="identifier">AN</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">aN</span><span class="special">)</span> <span class="special">;</span>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span><span class="keyword">class</span> <span class="identifier">A0</span><span class="special">,...,</span><span class="keyword">class</span> <span class="identifier">AN</span><span class="special">></span>
+<span class="identifier">TypedInPlaceFactoryN</span> <span class="special"><</span><span class="identifier">T</span><span class="special">,</span><span class="identifier">A0</span><span class="special">,...,</span><span class="identifier">AN</span><span class="special">></span> <span class="identifier">in_place</span> <span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">a0</span><span class="special">,</span> <span class="identifier">A0</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">a0</span><span class="special">,</span> <span class="special">...,</span> <span class="identifier">AN</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">aN</span><span class="special">)</span> <span class="special">;</span>
+</pre>
+<p>
+ In-place factories can be used generically by the wrapper and user as follows:
+ </p>
+<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">W</span>
+<span class="special">{</span>
+ <span class="identifier">X</span> <span class="identifier">wrapped_</span> <span class="special">;</span>
+
+ <span class="keyword">public</span><span class="special">:</span>
+
+ <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">X</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span> <span class="special">)</span> <span class="special">:</span> <span class="identifier">wrapped_</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">{}</span>
+
+ <span class="keyword">template</span><span class="special"><</span> <span class="keyword">class</span> <span class="identifier">InPlaceFactory</span> <span class="special">></span>
+ <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">InPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">fac</span> <span class="special">)</span> <span class="special">{</span> <span class="identifier">fac</span><span class="special">.</span><span class="keyword">template</span> <span class="special"><</span><span class="identifier">X</span><span class="special">></span><span class="identifier">construct</span><span class="special">(&</span><span class="identifier">wrapped_</span><span class="special">)</span> <span class="special">;</span> <span class="special">}</span>
+
+<span class="special">}</span> <span class="special">;</span>
+
+<span class="keyword">void</span> <span class="identifier">foo</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="comment">// Wrapped object constructed in-place via a InPlaceFactory.</span>
+ <span class="comment">// No temporary created.</span>
+ <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">in_place</span><span class="special">(</span><span class="number">123</span><span class="special">,</span><span class="string">"hello"</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">}</span>
+</pre>
+<p>
+ The factories are implemented in the headers: <a href="../../../../../boost/utility/in_place_factory.hpp" target="_top">in_place_factory.hpp</a>
+ and <a href="../../../../../boost/utility/typed_in_place_factory.hpp" target="_top">typed_in_place_factory.hpp</a>
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="detailed_semantics.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="a_note_about_optional_bool_.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
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+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
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+<link rel="home" href="../index.html" title="Chapter 1. Boost.Optional">
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+</div>
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+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="boost_optional.motivation"></a><a class="link" href="motivation.html" title="Motivation">Motivation</a>
+</h2></div></div></div>
+<p>
+ Consider these functions which should return a value but which might not have
+ a value to return:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ (A) <code class="computeroutput"><span class="keyword">double</span> <span class="identifier">sqrt</span><span class="special">(</span><span class="keyword">double</span> <span class="identifier">n</span> <span class="special">);</span></code>
+ </li>
+<li class="listitem">
+ (B) <code class="computeroutput"><span class="keyword">char</span> <span class="identifier">get_async_input</span><span class="special">();</span></code>
+ </li>
+<li class="listitem">
+ (C) <code class="computeroutput"><span class="identifier">point</span> <span class="identifier">polygon</span><span class="special">::</span><span class="identifier">get_any_point_effectively_inside</span><span class="special">();</span></code>
+ </li>
+</ul></div>
+<p>
+ There are different approaches to the issue of not having a value to return.
+ </p>
+<p>
+ A typical approach is to consider the existence of a valid return value as
+ a postcondition, so that if the function cannot compute the value to return,
+ it has either undefined behavior (and can use assert in a debug build) or uses
+ a runtime check and throws an exception if the postcondition is violated. This
+ is a reasonable choice for example, for function (A), because the lack of a
+ proper return value is directly related to an invalid parameter (out of domain
+ argument), so it is appropriate to require the callee to supply only parameters
+ in a valid domain for execution to continue normally.
+ </p>
+<p>
+ However, function (B), because of its asynchronous nature, does not fail just
+ because it can't find a value to return; so it is incorrect to consider such
+ a situation an error and assert or throw an exception. This function must return,
+ and somehow, must tell the callee that it is not returning a meaningful value.
+ </p>
+<p>
+ A similar situation occurs with function (C): it is conceptually an error to
+ ask a <span class="emphasis"><em>null-area</em></span> polygon to return a point inside itself,
+ but in many applications, it is just impractical for performance reasons to
+ treat this as an error (because detecting that the polygon has no area might
+ be too expensive to be required to be tested previously), and either an arbitrary
+ point (typically at infinity) is returned, or some efficient way to tell the
+ callee that there is no such point is used.
+ </p>
+<p>
+ There are various mechanisms to let functions communicate that the returned
+ value is not valid. One such mechanism, which is quite common since it has
+ zero or negligible overhead, is to use a special value which is reserved to
+ communicate this. Classical examples of such special values are <code class="computeroutput"><span class="identifier">EOF</span></code>, <code class="computeroutput"><span class="identifier">string</span><span class="special">::</span><span class="identifier">npos</span></code>, points
+ at infinity, etc...
+ </p>
+<p>
+ When those values exist, i.e. the return type can hold all meaningful values
+ <span class="emphasis"><em>plus</em></span> the <span class="emphasis"><em>signal</em></span> value, this mechanism
+ is quite appropriate and well known. Unfortunately, there are cases when such
+ values do not exist. In these cases, the usual alternative is either to use
+ a wider type, such as <code class="computeroutput"><span class="keyword">int</span></code> in place
+ of <code class="computeroutput"><span class="keyword">char</span></code>; or a compound type, such
+ as <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">point</span><span class="special">,</span><span class="keyword">bool</span><span class="special">></span></code>.
+ </p>
+<p>
+ Returning a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span><span class="keyword">bool</span><span class="special">></span></code>, thus attaching a boolean flag to the result
+ which indicates if the result is meaningful, has the advantage that can be
+ turned into a consistent idiom since the first element of the pair can be whatever
+ the function would conceptually return. For example, the last two functions
+ could have the following interface:
+ </p>
+<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span><span class="keyword">bool</span><span class="special">></span> <span class="identifier">get_async_input</span><span class="special">();</span>
+<span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">point</span><span class="special">,</span><span class="keyword">bool</span><span class="special">></span> <span class="identifier">polygon</span><span class="special">::</span><span class="identifier">get_any_point_effectively_inside</span><span class="special">();</span>
+</pre>
+<p>
+ These functions use a consistent interface for dealing with possibly nonexistent
+ results:
+ </p>
+<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">point</span><span class="special">,</span><span class="keyword">bool</span><span class="special">></span> <span class="identifier">p</span> <span class="special">=</span> <span class="identifier">poly</span><span class="special">.</span><span class="identifier">get_any_point_effectively_inside</span><span class="special">();</span>
+<span class="keyword">if</span> <span class="special">(</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">second</span> <span class="special">)</span>
+ <span class="identifier">flood_fill</span><span class="special">(</span><span class="identifier">p</span><span class="special">.</span><span class="identifier">first</span><span class="special">);</span>
+</pre>
+<p>
+ However, not only is this quite a burden syntactically, it is also error prone
+ since the user can easily use the function result (first element of the pair)
+ without ever checking if it has a valid value.
+ </p>
+<p>
+ Clearly, we need a better idiom.
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
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+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Optional references</title>
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+</div>
+<div class="section">
+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="boost_optional.optional_references"></a><a class="link" href="optional_references.html" title="Optional references">Optional references</a>
+</h2></div></div></div>
+<p>
+ This library allows the template parameter <code class="computeroutput"><span class="identifier">T</span></code>
+ to be of reference type: <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span></code>, and to some extent, <code class="computeroutput"><span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">&</span></code>.
+ </p>
+<p>
+ However, since references are not real objects some restrictions apply and
+ some operations are not available in this case:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ Converting constructors
+ </li>
+<li class="listitem">
+ Converting assignment
+ </li>
+<li class="listitem">
+ InPlace construction
+ </li>
+<li class="listitem">
+ InPlace assignment
+ </li>
+<li class="listitem">
+ Value-access via pointer
+ </li>
+</ul></div>
+<p>
+ Also, even though <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code>
+ treats it wrapped pseudo-object much as a real value, a true real reference
+ is stored so aliasing will ocurr:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ Copies of <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code>
+ will copy the references but all these references will nonetheless refer
+ to the same object.
+ </li>
+<li class="listitem">
+ Value-access will actually provide access to the referenced object rather
+ than the reference itself.
+ </li>
+</ul></div>
+<div class="warning"><table border="0" summary="Warning">
+<tr>
+<td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../../../doc/src/images/warning.png"></td>
+<th align="left">Warning</th>
+</tr>
+<tr><td align="left" valign="top"><p>
+ On compilers that do not conform to Standard C++ rules of reference binding,
+ operations on optional references might give adverse results: rather than
+ binding a reference to a designated object they may create an unexpected
+ temporary and bind to it. For more details see <a class="link" href="dependencies_and_portability/optional_reference_binding.html" title="Optional Reference Binding">Dependencies
+ and Portability section</a>.
+ </p></td></tr>
+</table></div>
+<h4>
+<a name="boost_optional.optional_references.h0"></a>
+ <span class="phrase"><a name="boost_optional.optional_references.rvalue_references"></a></span><a class="link" href="optional_references.html#boost_optional.optional_references.rvalue_references">Rvalue
+ references</a>
+ </h4>
+<p>
+ Rvalue references and lvalue references to const have the ability in C++ to
+ extend the life time of a temporary they bind to. Optional references do not
+ have this capability, therefore to avoid surprising effects it is not possible
+ to initialize an optional references from a temporary. Optional rvalue references
+ are disabled altogether. Also, the initialization and assignment of an optional
+ reference to const from rvalue reference is disabled.
+ </p>
+<pre class="programlisting"><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span> <span class="comment">// legal</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&></span> <span class="identifier">oi</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span> <span class="comment">// illegal</span>
+</pre>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="detailed_semantics.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="rebinding_semantics_for_assignment_of_optional_references.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/quick_start.html b/doc/html/boost_optional/quick_start.html
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+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Quick Start</title>
+<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
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+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="boost_optional.quick_start"></a><a class="link" href="quick_start.html" title="Quick Start">Quick Start</a>
+</h2></div></div></div>
+<div class="toc"><dl class="toc">
+<dt><span class="section"><a href="quick_start.html#boost_optional.quick_start.optional_return_values">Optional
+ return values</a></span></dt>
+<dt><span class="section"><a href="quick_start/optional_automatic_variables.html">Optional
+ automatic variables</a></span></dt>
+<dt><span class="section"><a href="quick_start/optional_data_members.html">Optional
+ data members</a></span></dt>
+<dt><span class="section"><a href="quick_start/bypassing_unnecessary_default_construction.html">Bypassing
+ unnecessary default construction</a></span></dt>
+<dt><span class="section"><a href="quick_start/storage_in_containers.html">Storage
+ in containers</a></span></dt>
+</dl></div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.quick_start.optional_return_values"></a><a class="link" href="quick_start.html#boost_optional.quick_start.optional_return_values" title="Optional return values">Optional
+ return values</a>
+</h3></div></div></div>
+<p>
+ Let's write and use a converter function that converts a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code>
+ to an <code class="computeroutput"><span class="keyword">int</span></code>. It is possible that
+ for a given string (e.g. <code class="computeroutput"><span class="string">"cat"</span></code>)
+ there exists no value of type <code class="computeroutput"><span class="keyword">int</span></code>
+ capable of representing the conversion result. We do not consider such situation
+ an error. We expect that the converter can be used only to check if the conversion
+ is possible. A natural signature for this function can be:
+ </p>
+<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">optional</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">convert</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&</span> <span class="identifier">text</span><span class="special">);</span>
+</pre>
+<p>
+ All necessary functionality can be included with one header <code class="computeroutput"><span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">optional</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>.
+ The above function signature means that the function can either return a
+ value of type <code class="computeroutput"><span class="keyword">int</span></code> or a flag
+ indicating that no value of <code class="computeroutput"><span class="keyword">int</span></code>
+ is available. This does not indicate an error. It is like one additional
+ value of <code class="computeroutput"><span class="keyword">int</span></code>. This is how we
+ can use our function:
+ </p>
+<pre class="programlisting"><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&</span> <span class="identifier">text</span> <span class="special">=</span> <span class="comment">/*... */</span><span class="special">;</span>
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">oi</span> <span class="special">=</span> <span class="identifier">convert</span><span class="special">(</span><span class="identifier">text</span><span class="special">);</span> <span class="comment">// move-construct</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oi</span><span class="special">)</span> <span class="comment">// contextual conversion to bool</span>
+ <span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">oi</span><span class="special">;</span> <span class="comment">// operator*</span>
+</pre>
+<p>
+ In order to test if <code class="computeroutput"><span class="identifier">optional</span></code>
+ contains a value, we use the contextual conversion to type <code class="computeroutput"><span class="keyword">bool</span></code>. Because of this we can combine the initialization
+ of the optional object and the test into one instruction:
+ </p>
+<pre class="programlisting"><span class="keyword">if</span> <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">oi</span> <span class="special">=</span> <span class="identifier">convert</span><span class="special">(</span><span class="identifier">text</span><span class="special">))</span>
+ <span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">oi</span><span class="special">;</span>
+</pre>
+<p>
+ We extract the contained value with <code class="computeroutput"><span class="keyword">operator</span><span class="special">*</span></code> (and with <code class="computeroutput"><span class="keyword">operator</span><span class="special">-></span></code> where it makes sense). An attempt to
+ extract the contained value of an uninitialized optional object is an <span class="emphasis"><em>undefined
+ behaviour</em></span> (UB). This implementation guards the call with <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span></code>. Therefore you should be sure
+ that the contained value is there before extracting. For instance, the following
+ code is reasonably UB-safe:
+ </p>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">convert</span><span class="special">(</span><span class="string">"100"</span><span class="special">);</span>
+</pre>
+<p>
+ This is because we know that string value <code class="computeroutput"><span class="string">"100"</span></code>
+ converts to a valid value of <code class="computeroutput"><span class="keyword">int</span></code>.
+ If you do not like this potential UB, you can use an alternative way of extracting
+ the contained value:
+ </p>
+<pre class="programlisting"><span class="keyword">try</span> <span class="special">{</span>
+ <span class="keyword">int</span> <span class="identifier">j</span> <span class="special">=</span> <span class="identifier">convert</span><span class="special">(</span><span class="identifier">text</span><span class="special">).</span><span class="identifier">value</span><span class="special">();</span>
+<span class="special">}</span>
+<span class="keyword">catch</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">bad_optional_access</span><span class="special">&)</span> <span class="special">{</span>
+ <span class="comment">// deal with it</span>
+<span class="special">}</span>
+</pre>
+<p>
+ This version throws an exception upon an attempt to access a non-existent
+ contained value. If your way of dealing with the missing value is to use
+ some default, like <code class="computeroutput"><span class="number">0</span></code>, there exists
+ a yet another alternative:
+ </p>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">k</span> <span class="special">=</span> <span class="identifier">convert</span><span class="special">(</span><span class="identifier">text</span><span class="special">).</span><span class="identifier">value_or</span><span class="special">(</span><span class="number">0</span><span class="special">);</span>
+</pre>
+<p>
+ This uses the <code class="computeroutput"><span class="identifier">atoi</span></code>-like approach
+ to conversions: if <code class="computeroutput"><span class="identifier">text</span></code> does
+ not represent an integral number just return <code class="computeroutput"><span class="number">0</span></code>.
+ Finally, you can provide a callback to be called when trying to access the
+ contained value fails:
+ </p>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">fallback_to_default</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="identifier">cerr</span> <span class="special"><<</span> <span class="string">"could not convert; using -1 instead"</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span>
+ <span class="keyword">return</span> <span class="special">-</span><span class="number">1</span><span class="special">;</span>
+<span class="special">}</span>
+
+<span class="keyword">int</span> <span class="identifier">l</span> <span class="special">=</span> <span class="identifier">convert</span><span class="special">(</span><span class="identifier">text</span><span class="special">).</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">fallback_to_default</span><span class="special">);</span>
+</pre>
+<p>
+ This will call the provided callback and return whatever the callback returns.
+ The callback can have side effects: they will only be observed when the optional
+ object does not contain a value.
+ </p>
+<p>
+ Now, let's consider how function <code class="computeroutput"><span class="identifier">convert</span></code>
+ can be implemented.
+ </p>
+<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">convert</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&</span> <span class="identifier">text</span><span class="special">)</span>
+<span class="special">{</span>
+ <span class="identifier">std</span><span class="special">::</span><span class="identifier">stringstream</span> <span class="identifier">s</span><span class="special">(</span><span class="identifier">text</span><span class="special">);</span>
+ <span class="keyword">int</span> <span class="identifier">i</span><span class="special">;</span>
+ <span class="keyword">if</span> <span class="special">((</span><span class="identifier">s</span> <span class="special">>></span> <span class="identifier">i</span><span class="special">)</span> <span class="special">&&</span> <span class="identifier">s</span><span class="special">.</span><span class="identifier">get</span><span class="special">()</span> <span class="special">==</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">char_traits</span><span class="special"><</span><span class="keyword">char</span><span class="special">>::</span><span class="identifier">eof</span><span class="special">())</span>
+ <span class="keyword">return</span> <span class="identifier">i</span><span class="special">;</span>
+ <span class="keyword">else</span>
+ <span class="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span><span class="special">;</span>
+<span class="special">}</span>
+</pre>
+<p>
+ Observe the two return statements. <code class="computeroutput"><span class="keyword">return</span>
+ <span class="identifier">i</span></code> uses the converting constructor
+ that can create <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ from <code class="computeroutput"><span class="identifier">T</span></code>. Thus constructed
+ optional object is initialized and its value is a copy of <code class="computeroutput"><span class="identifier">i</span></code>.
+ The other return statement uses another converting constructor from a special
+ tag <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code>. It is used to indicate that we want
+ to create an uninitialized optional object.
+ </p>
+</div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../index.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="quick_start/optional_automatic_variables.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
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+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Bypassing unnecessary default construction</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../index.html" title="Boost.Optional">
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+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.quick_start.bypassing_unnecessary_default_construction"></a><a class="link" href="bypassing_unnecessary_default_construction.html" title="Bypassing unnecessary default construction">Bypassing
+ unnecessary default construction</a>
+</h3></div></div></div>
+<p>
+ Suppose we have class <code class="computeroutput"><span class="identifier">Date</span></code>,
+ which does not have a default constructor: there is no good candidate for
+ a default date. We have a function that returns two dates in form of a <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">tuple</span></code>:
+ </p>
+<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">tuple</span><span class="special"><</span><span class="identifier">Date</span><span class="special">,</span> <span class="identifier">Date</span><span class="special">></span> <span class="identifier">getPeriod</span><span class="special">();</span>
+</pre>
+<p>
+ In other place we want to use the result of <code class="computeroutput"><span class="identifier">getPeriod</span></code>,
+ but want the two dates to be named: <code class="computeroutput"><span class="identifier">begin</span></code>
+ and <code class="computeroutput"><span class="identifier">end</span></code>. We want to implement
+ something like 'multiple return values':
+ </p>
+<pre class="programlisting"><span class="identifier">Date</span> <span class="identifier">begin</span><span class="special">,</span> <span class="identifier">end</span><span class="special">;</span> <span class="comment">// Error: no default ctor!</span>
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">tie</span><span class="special">(</span><span class="identifier">begin</span><span class="special">,</span> <span class="identifier">end</span><span class="special">)</span> <span class="special">=</span> <span class="identifier">getPeriod</span><span class="special">();</span>
+</pre>
+<p>
+ The second line works already, this is the capability of <a href="../../../../../tuple/index.html" target="_top">Boost.Tuple</a>
+ library, but the first line won't work. We could set some invented initial
+ dates, but it is confusing and may be an unacceptable cost, given that these
+ values will be overwritten in the next line anyway. This is where <code class="computeroutput"><span class="identifier">optional</span></code> can help:
+ </p>
+<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="identifier">Date</span><span class="special">></span> <span class="identifier">begin</span><span class="special">,</span> <span class="identifier">end</span><span class="special">;</span>
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">tie</span><span class="special">(</span><span class="identifier">begin</span><span class="special">,</span> <span class="identifier">end</span><span class="special">)</span> <span class="special">=</span> <span class="identifier">getPeriod</span><span class="special">();</span>
+</pre>
+<p>
+ It works because inside <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">tie</span></code> a
+ move-assignment from <code class="computeroutput"><span class="identifier">T</span></code> is
+ invoked on <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>,
+ which internally calls a move-constructor of <code class="computeroutput"><span class="identifier">T</span></code>.
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="optional_data_members.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../quick_start.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="storage_in_containers.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/quick_start/optional_automatic_variables.html b/doc/html/boost_optional/quick_start/optional_automatic_variables.html
new file mode 100644
index 0000000..f7b6664
--- /dev/null
+++ b/doc/html/boost_optional/quick_start/optional_automatic_variables.html
@@ -0,0 +1,75 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Optional automatic variables</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../index.html" title="Boost.Optional">
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+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../index.html">Home</a></td>
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+<hr>
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+<a accesskey="p" href="../quick_start.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../quick_start.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="optional_data_members.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.quick_start.optional_automatic_variables"></a><a class="link" href="optional_automatic_variables.html" title="Optional automatic variables">Optional
+ automatic variables</a>
+</h3></div></div></div>
+<p>
+ We could write function <code class="computeroutput"><span class="identifier">convert</span></code>
+ in a slightly different manner, so that it has a single <code class="computeroutput"><span class="keyword">return</span></code>-statement:
+ </p>
+<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">convert</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&</span> <span class="identifier">text</span><span class="special">)</span>
+<span class="special">{</span>
+ <span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">ans</span><span class="special">;</span>
+ <span class="identifier">std</span><span class="special">::</span><span class="identifier">stringstream</span> <span class="identifier">s</span><span class="special">(</span><span class="identifier">text</span><span class="special">);</span>
+ <span class="keyword">int</span> <span class="identifier">i</span><span class="special">;</span>
+ <span class="keyword">if</span> <span class="special">((</span><span class="identifier">s</span> <span class="special">>></span> <span class="identifier">i</span><span class="special">)</span> <span class="special">&&</span> <span class="identifier">s</span><span class="special">.</span><span class="identifier">get</span><span class="special">()</span> <span class="special">==</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">char_traits</span><span class="special"><</span><span class="keyword">char</span><span class="special">>::</span><span class="identifier">eof</span><span class="special">())</span>
+ <span class="identifier">ans</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">;</span>
+
+ <span class="keyword">return</span> <span class="identifier">ans</span><span class="special">;</span>
+<span class="special">}</span>
+</pre>
+<p>
+ The default constructor of <code class="computeroutput"><span class="identifier">optional</span></code>
+ creates an unitialized optional object. Unlike with <code class="computeroutput"><span class="keyword">int</span></code>s
+ you cannot have an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span></code>
+ in an indeterminate state. Its state is always well defined. Instruction
+ <code class="computeroutput"><span class="identifier">ans</span> <span class="special">=</span>
+ <span class="identifier">i</span></code> initializes the optional object.
+ It uses the 'mixed' assignment from <code class="computeroutput"><span class="keyword">int</span></code>.
+ In general, for <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>,
+ when an assignment from <code class="computeroutput"><span class="identifier">T</span></code>
+ is invoked, it can do two things. If the optional object is not initialized
+ (our case here), it initializes the contained value using <code class="computeroutput"><span class="identifier">T</span></code>'s
+ copy constructor. If the optional object is already initialized, it assigns
+ the new value to it using <code class="computeroutput"><span class="identifier">T</span></code>'s
+ copy assignment.
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../quick_start.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../quick_start.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="optional_data_members.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/quick_start/optional_data_members.html b/doc/html/boost_optional/quick_start/optional_data_members.html
new file mode 100644
index 0000000..a06aa10
--- /dev/null
+++ b/doc/html/boost_optional/quick_start/optional_data_members.html
@@ -0,0 +1,94 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Optional data members</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../index.html" title="Boost.Optional">
+<link rel="up" href="../quick_start.html" title="Quick Start">
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+<link rel="next" href="bypassing_unnecessary_default_construction.html" title="Bypassing unnecessary default construction">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="optional_automatic_variables.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../quick_start.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="bypassing_unnecessary_default_construction.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.quick_start.optional_data_members"></a><a class="link" href="optional_data_members.html" title="Optional data members">Optional
+ data members</a>
+</h3></div></div></div>
+<p>
+ Suppose we want to implement a <span class="emphasis"><em>lazy load</em></span> optimization.
+ This is because we do not want to perform an expensive initialization of
+ our <code class="computeroutput"><span class="identifier">Resource</span></code> until (if at
+ all) it is really used. We can do it this way:
+ </p>
+<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">Widget</span>
+<span class="special">{</span>
+ <span class="keyword">mutable</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">const</span> <span class="identifier">Resource</span><span class="special">></span> <span class="identifier">resource_</span><span class="special">;</span>
+
+<span class="keyword">public</span><span class="special">:</span>
+ <span class="identifier">Widget</span><span class="special">()</span> <span class="special">{}</span>
+
+ <span class="keyword">const</span> <span class="identifier">Resource</span><span class="special">&</span> <span class="identifier">getResource</span><span class="special">()</span> <span class="keyword">const</span> <span class="comment">// not thread-safe</span>
+ <span class="special">{</span>
+ <span class="keyword">if</span> <span class="special">(</span><span class="identifier">resource_</span> <span class="special">==</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span><span class="special">)</span>
+ <span class="identifier">resource_</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">(</span><span class="string">"resource"</span><span class="special">,</span> <span class="string">"arguments"</span><span class="special">);</span>
+
+ <span class="keyword">return</span> <span class="special">*</span><span class="identifier">resource_</span><span class="special">;</span>
+ <span class="special">}</span>
+<span class="special">};</span>
+</pre>
+<p>
+ <code class="computeroutput"><span class="identifier">optional</span></code>'s default constructor
+ creates an uninitialized optional. No call to <code class="computeroutput"><span class="identifier">Resource</span></code>'s
+ default constructor is attempted. <code class="computeroutput"><span class="identifier">Resource</span></code>
+ doesn't have to be <a href="http://www.sgi.com/tech/stl/DefaultConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">DefaultConstructible</span></code></a>. In function
+ <code class="computeroutput"><span class="identifier">getResource</span></code> we first check
+ if <code class="computeroutput"><span class="identifier">resource_</span></code> is initialized.
+ This time we do not use the contextual conversion to <code class="computeroutput"><span class="keyword">bool</span></code>,
+ but a comparison with <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code>.
+ These two ways are equivalent. Function <code class="computeroutput"><span class="identifier">emplace</span></code>
+ initializes the optional in-place by perfect-forwarding the arguments to
+ the constructor of <code class="computeroutput"><span class="identifier">Resource</span></code>.
+ No copy- or move-construction is involved here. <code class="computeroutput"><span class="identifier">Resource</span></code>
+ doesn't even have to be <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>.
+ </p>
+<div class="note"><table border="0" summary="Note">
+<tr>
+<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../doc/src/images/note.png"></td>
+<th align="left">Note</th>
+</tr>
+<tr><td align="left" valign="top"><p>
+ Function <code class="computeroutput"><span class="identifier">emplace</span></code> is only
+ available on compilers that support rvalue references and variadic templates.
+ If your compiler does not support these features and you still need to
+ avoid any move-constructions, use <a class="link" href="../tutorial/in_place_factories.html" title="In-Place Factories">In-Place
+ Factories</a>.
+ </p></td></tr>
+</table></div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="optional_automatic_variables.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../quick_start.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="bypassing_unnecessary_default_construction.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
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diff --git a/doc/html/boost_optional/quick_start/optional_return_values.html b/doc/html/boost_optional/quick_start/optional_return_values.html
new file mode 100644
index 0000000..9ad85ef
--- /dev/null
+++ b/doc/html/boost_optional/quick_start/optional_return_values.html
@@ -0,0 +1,135 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Optional return values</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../../index.html" title="Chapter 1. Boost.Optional">
+<link rel="up" href="../quick_start.html" title="Quick Start">
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+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../index.html">Home</a></td>
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+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../quick_start.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../quick_start.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="optional_automatic_variables.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.quick_start.optional_return_values"></a><a class="link" href="optional_return_values.html" title="Optional return values">Optional
+ return values</a>
+</h3></div></div></div>
+<p>
+ Let's write and use a converter function that converts an a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code>
+ to an <code class="computeroutput"><span class="keyword">int</span></code>. It is possible that
+ for a given string (e.g. <code class="computeroutput"><span class="string">"cat"</span></code>)
+ there exist no value of type <code class="computeroutput"><span class="keyword">int</span></code>
+ capable of representing the conversion result. We do not consider such situation
+ an error. We expect that the converter can be used only to check if the conversion
+ is possible. A natural signature for this function can be:
+ </p>
+<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">optional</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">optionl</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">convert</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&</span> <span class="identifier">text</span><span class="special">);</span>
+</pre>
+<p>
+ All necessary functionality can be included with one header <code class="computeroutput"><span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">optional</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>.
+ The above function signature means that the function can either return a
+ value of type <code class="computeroutput"><span class="keyword">int</span></code> or a flag
+ indicating that no value of <code class="computeroutput"><span class="keyword">int</span></code>
+ is available. This does not indicate an error. It is like one additional
+ value of <code class="computeroutput"><span class="keyword">int</span></code>. This is how we
+ can use our function:
+ </p>
+<pre class="programlisting"><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&</span> <span class="identifier">text</span> <span class="special">=</span> <span class="comment">/*... */</span><span class="special">;</span>
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">optionl</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">oi</span> <span class="special">=</span> <span class="identifier">convert</span><span class="special">(</span><span class="identifier">text</span><span class="special">);</span> <span class="comment">// move-construct</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oi</span><span class="special">)</span> <span class="comment">// contextual conversion to bool</span>
+ <span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">oi</span><span class="special">;</span> <span class="comment">// operator*</span>
+</pre>
+<p>
+ In order to test if <code class="computeroutput"><span class="identifier">optional</span></code>
+ contains a value, we use the contextual conversion to type <code class="computeroutput"><span class="keyword">bool</span></code>. Because of this we can combine the initialization
+ of the optional object and the test into one instruction:
+ </p>
+<pre class="programlisting"><span class="keyword">if</span> <span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optionl</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">oi</span> <span class="special">=</span> <span class="identifier">convert</span><span class="special">(</span><span class="identifier">text</span><span class="special">))</span>
+ <span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">oi</span><span class="special">;</span>
+</pre>
+<p>
+ We extract the contained value with <code class="computeroutput"><span class="keyword">operator</span><span class="special">*</span></code> (and with <code class="computeroutput"><span class="keyword">operator</span><span class="special">-></span></code> where it makes sense). An attempt to
+ extract the contained value of an uninitialized optional object is an <span class="emphasis"><em>undefined
+ behaviour</em></span> (UB). This implementation guards the call with <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span></code>. Therefore you should be sure
+ that the contained value is there before extracting. For instance, the following
+ code is reasonably UB-safe:
+ </p>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">convert</span><span class="special">(</span><span class="string">"100"</span><span class="special">);</span>
+</pre>
+<p>
+ This is because we know that string value <code class="computeroutput"><span class="string">"100"</span></code>
+ converts to a valid value of <code class="computeroutput"><span class="keyword">int</span></code>.
+ If you do not like this potential UB, you can use an alternative way of extracting
+ the contained value:
+ </p>
+<pre class="programlisting"><span class="keyword">try</span> <span class="special">{</span>
+ <span class="keyword">int</span> <span class="identifier">j</span> <span class="special">=</span> <span class="identifier">convert</span><span class="special">(</span><span class="identifier">text</span><span class="special">).</span><span class="identifier">value</span><span class="special">();</span>
+<span class="special">}</span>
+<span class="keyword">catch</span> <span class="special">(</span><span class="keyword">const</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">bad_optional_access</span><span class="special">&)</span> <span class="special">{</span>
+ <span class="comment">// deal with it</span>
+<span class="special">}</span>
+</pre>
+<p>
+ This version throws an exception upon an attempt to access a non-existent
+ contained value. If your way of dealing with the missing value is to use
+ some default, like <code class="computeroutput"><span class="number">0</span></code>, there exists
+ a yet another alternative:
+ </p>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">k</span> <span class="special">=</span> <span class="identifier">convert</span><span class="special">(</span><span class="identifier">text</span><span class="special">).</span><span class="identifier">value_or</span><span class="special">(</span><span class="number">0</span><span class="special">);</span>
+</pre>
+<p>
+ This uses the <code class="computeroutput"><span class="identifier">atoi</span></code>-like approach
+ to conversions: if <code class="computeroutput"><span class="identifier">text</span></code> does
+ not represent an integral number just return <code class="computeroutput"><span class="number">0</span></code>.
+ Now, let's consider how function <code class="computeroutput"><span class="identifier">convert</span></code>
+ can be implemented.
+ </p>
+<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optionl</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">convert</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">&</span> <span class="identifier">text</span><span class="special">)</span>
+<span class="special">{</span>
+ <span class="identifier">std</span><span class="special">::</span><span class="identifier">stringstream</span> <span class="identifier">s</span><span class="special">(</span><span class="identifier">text</span><span class="special">);</span>
+ <span class="keyword">int</span> <span class="identifier">i</span><span class="special">;</span>
+ <span class="keyword">if</span> <span class="special">((</span><span class="identifier">s</span> <span class="special">>></span> <span class="identifier">i</span><span class="special">)</span> <span class="special">&&</span> <span class="identifier">s</span><span class="special">.</span><span class="identifier">get</span><span class="special">()</span> <span class="special">==</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">char_traits</span><span class="special"><</span><span class="keyword">char</span><span class="special">>::</span><span class="identifier">eof</span><span class="special">())</span>
+ <span class="keyword">return</span> <span class="identifier">i</span><span class="special">;</span>
+ <span class="keyword">else</span>
+ <span class="keyword">return</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span><span class="special">;</span>
+<span class="special">}</span>
+</pre>
+<p>
+ Observe the two return statements. <code class="computeroutput"><span class="keyword">return</span>
+ <span class="identifier">i</span></code> uses the converting constructor
+ that can create <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ from <code class="computeroutput"><span class="identifier">T</span></code>. Thus constructed
+ optional object is initialized and its value is a copy of <code class="computeroutput"><span class="identifier">i</span></code>.
+ The other return statement uses another converting constructor from a special
+ tag <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code>. It is used to indicate that we want
+ to create an uninitialized optional object.
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../quick_start.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../quick_start.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="optional_automatic_variables.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
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new file mode 100644
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@@ -0,0 +1,64 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Storage in containers</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../index.html" title="Boost.Optional">
+<link rel="up" href="../quick_start.html" title="Quick Start">
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+<link rel="next" href="../../optional/tutorial.html" title="Tutorial">
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+<td align="center"><a href="../../../../../../index.html">Home</a></td>
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+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.quick_start.storage_in_containers"></a><a class="link" href="storage_in_containers.html" title="Storage in containers">Storage
+ in containers</a>
+</h3></div></div></div>
+<p>
+ Suppose you want to ask users to choose some number (an <code class="computeroutput"><span class="keyword">int</span></code>).
+ One of the valid responses is to choose nothing, which is represented by
+ an uninitialized <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span></code>.
+ You want to make a histogram showing how many times each choice was made.
+ You can use an <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span></code>:
+ </p>
+<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">map</span><span class="special"><</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">>,</span> <span class="keyword">int</span><span class="special">></span> <span class="identifier">choices</span><span class="special">;</span>
+
+<span class="keyword">for</span> <span class="special">(</span><span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span> <span class="identifier">i</span> <span class="special"><</span> <span class="identifier">LIMIT</span><span class="special">;</span> <span class="special">++</span><span class="identifier">i</span><span class="special">)</span> <span class="special">{</span>
+ <span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">choice</span> <span class="special">=</span> <span class="identifier">readChoice</span><span class="special">();</span>
+ <span class="special">++</span><span class="identifier">choices</span><span class="special">[</span><span class="identifier">choice</span><span class="special">];</span>
+<span class="special">}</span>
+</pre>
+<p>
+ This works because <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ is <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a> whenever <code class="computeroutput"><span class="identifier">T</span></code> is <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a>. In this case
+ the state of being uninitialized is treated as a yet another value of <code class="computeroutput"><span class="identifier">T</span></code>, which is compared less than any value
+ of <code class="computeroutput"><span class="identifier">T</span></code>.
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="bypassing_unnecessary_default_construction.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../quick_start.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/rebinding_semantics_for_assignment_of_optional_references.html b/doc/html/boost_optional/rebinding_semantics_for_assignment_of_optional_references.html
new file mode 100644
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+++ b/doc/html/boost_optional/rebinding_semantics_for_assignment_of_optional_references.html
@@ -0,0 +1,148 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Rebinding semantics for assignment of optional references</title>
+<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../index.html" title="Chapter 1. Boost.Optional">
+<link rel="up" href="../index.html" title="Chapter 1. Boost.Optional">
+<link rel="prev" href="optional_references.html" title="Optional references">
+<link rel="next" href="in_place_factories.html" title="In-Place Factories">
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+<td align="center"><a href="../../../../../index.html">Home</a></td>
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+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
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+</tr></table>
+<hr>
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+<a accesskey="p" href="optional_references.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="in_place_factories.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="boost_optional.rebinding_semantics_for_assignment_of_optional_references"></a><a class="link" href="rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">Rebinding
+ semantics for assignment of optional references</a>
+</h2></div></div></div>
+<p>
+ If you assign to an <span class="emphasis"><em>uninitialized </em></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code>
+ the effect is to bind (for the first time) to the object. Clearly, there is
+ no other choice.
+ </p>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">x</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">rx</span> <span class="special">=</span> <span class="identifier">x</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">ora</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">orb</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">ora</span> <span class="special">=</span> <span class="identifier">orb</span> <span class="special">;</span> <span class="comment">// now 'ora' is bound to 'x' through 'rx'</span>
+<span class="special">*</span><span class="identifier">ora</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span> <span class="comment">// Changes value of 'x' through 'ora'</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">x</span><span class="special">==</span><span class="number">2</span><span class="special">);</span>
+</pre>
+<p>
+ If you assign to a bare C++ reference, the assignment is forwarded to the referenced
+ object; its value changes but the reference is never rebound.
+ </p>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
+<span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">rb</span> <span class="special">;</span> <span class="comment">// Changes the value of 'a' to 'b'</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">a</span><span class="special">==</span><span class="identifier">b</span><span class="special">);</span>
+<span class="identifier">b</span> <span class="special">=</span> <span class="number">3</span> <span class="special">;</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">ra</span><span class="special">!=</span><span class="identifier">b</span><span class="special">);</span> <span class="comment">// 'ra' is not rebound to 'b'</span>
+</pre>
+<p>
+ Now, if you assign to an <span class="emphasis"><em>initialized </em></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code>,
+ the effect is to <span class="bold"><strong>rebind</strong></span> to the new object
+ instead of assigning the referee. This is unlike bare C++ references.
+ </p>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">ora</span><span class="special">(</span><span class="identifier">ra</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">orb</span><span class="special">(</span><span class="identifier">rb</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">ora</span> <span class="special">=</span> <span class="identifier">orb</span> <span class="special">;</span> <span class="comment">// 'ora' is rebound to 'b'</span>
+<span class="special">*</span><span class="identifier">ora</span> <span class="special">=</span> <span class="number">3</span> <span class="special">;</span> <span class="comment">// Changes value of 'b' (not 'a')</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">a</span><span class="special">==</span><span class="number">1</span><span class="special">);</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">b</span><span class="special">==</span><span class="number">3</span><span class="special">);</span>
+</pre>
+<h4>
+<a name="boost_optional.rebinding_semantics_for_assignment_of_optional_references.h0"></a>
+ <span class="phrase"><a name="boost_optional.rebinding_semantics_for_assignment_of_optional_references.rationale"></a></span><a class="link" href="rebinding_semantics_for_assignment_of_optional_references.html#boost_optional.rebinding_semantics_for_assignment_of_optional_references.rationale">Rationale</a>
+ </h4>
+<p>
+ Rebinding semantics for the assignment of <span class="emphasis"><em>initialized </em></span>
+ <code class="computeroutput"><span class="identifier">optional</span></code> references has been
+ chosen to provide <span class="bold"><strong>consistency among initialization states</strong></span>
+ even at the expense of lack of consistency with the semantics of bare C++ references.
+ It is true that <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span></code> strives
+ to behave as much as possible as <code class="computeroutput"><span class="identifier">U</span></code>
+ does whenever it is initialized; but in the case when <code class="computeroutput"><span class="identifier">U</span></code>
+ is <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span></code>,
+ doing so would result in inconsistent behavior w.r.t to the lvalue initialization
+ state.
+ </p>
+<p>
+ Imagine <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code>
+ forwarding assignment to the referenced object (thus changing the referenced
+ object value but not rebinding), and consider the following code:
+ </p>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">a</span> <span class="special">=</span> <span class="identifier">get</span><span class="special">();</span>
+<span class="keyword">int</span> <span class="identifier">x</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">rx</span> <span class="special">=</span> <span class="identifier">x</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">b</span><span class="special">(</span><span class="identifier">rx</span><span class="special">);</span>
+<span class="identifier">a</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
+</pre>
+<p>
+ What does the assignment do?
+ </p>
+<p>
+ If <code class="computeroutput"><span class="identifier">a</span></code> is <span class="emphasis"><em>uninitialized</em></span>,
+ the answer is clear: it binds to <code class="computeroutput"><span class="identifier">x</span></code>
+ (we now have another reference to <code class="computeroutput"><span class="identifier">x</span></code>).
+ But what if <code class="computeroutput"><span class="identifier">a</span></code> is already <span class="emphasis"><em>initialized</em></span>?
+ it would change the value of the referenced object (whatever that is); which
+ is inconsistent with the other possible case.
+ </p>
+<p>
+ If <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code>
+ would assign just like <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span></code>
+ does, you would never be able to use Optional's assignment without explicitly
+ handling the previous initialization state unless your code is capable of functioning
+ whether after the assignment, <code class="computeroutput"><span class="identifier">a</span></code>
+ aliases the same object as <code class="computeroutput"><span class="identifier">b</span></code>
+ or not.
+ </p>
+<p>
+ That is, you would have to discriminate in order to be consistent.
+ </p>
+<p>
+ If in your code rebinding to another object is not an option, then it is very
+ likely that binding for the first time isn't either. In such case, assignment
+ to an <span class="emphasis"><em>uninitialized </em></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code>
+ shall be prohibited. It is quite possible that in such a scenario it is a precondition
+ that the lvalue must be already initialized. If it isn't, then binding for
+ the first time is OK while rebinding is not which is IMO very unlikely. In
+ such a scenario, you can assign the value itself directly, as in:
+ </p>
+<pre class="programlisting"><span class="identifier">assert</span><span class="special">(!!</span><span class="identifier">opt</span><span class="special">);</span>
+<span class="special">*</span><span class="identifier">opt</span><span class="special">=</span><span class="identifier">value</span><span class="special">;</span>
+</pre>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="optional_references.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="in_place_factories.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/reference/acknowledgements.html b/doc/html/boost_optional/reference/acknowledgements.html
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@@ -0,0 +1,131 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Acknowledgements</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../../index.html" title="Boost.Optional">
+<link rel="up" href="../../optional/reference.html" title="Reference">
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+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
+</tr></table>
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+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.reference.acknowledgements"></a><a class="link" href="acknowledgements.html" title="Acknowledgements">Acknowledgements</a>
+</h3></div></div></div>
+<h5>
+<a name="boost_optional.reference.acknowledgements.h0"></a>
+ <span class="phrase"><a name="boost_optional.reference.acknowledgements.pre_formal_review"></a></span><a class="link" href="acknowledgements.html#boost_optional.reference.acknowledgements.pre_formal_review">Pre-formal
+ review</a>
+ </h5>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ Peter Dimov suggested the name 'optional', and was the first to point
+ out the need for aligned storage.
+ </li>
+<li class="listitem">
+ Douglas Gregor developed 'type_with_alignment', and later Eric Friedman
+ coded 'aligned_storage', which are the core of the optional class implementation.
+ </li>
+<li class="listitem">
+ Andrei Alexandrescu and Brian Parker also worked with aligned storage
+ techniques and their work influenced the current implementation.
+ </li>
+<li class="listitem">
+ Gennadiy Rozental made extensive and important comments which shaped
+ the design.
+ </li>
+<li class="listitem">
+ Vesa Karvonen and Douglas Gregor made quite useful comparisons between
+ optional, variant and any; and made other relevant comments.
+ </li>
+<li class="listitem">
+ Douglas Gregor and Peter Dimov commented on comparisons and evaluation
+ in boolean contexts.
+ </li>
+<li class="listitem">
+ Eric Friedman helped understand the issues involved with aligned storage,
+ move/copy operations and exception safety.
+ </li>
+<li class="listitem">
+ Many others have participated with useful comments: Aleksey Gurotov,
+ Kevlin Henney, David Abrahams, and others I can't recall.
+ </li>
+</ul></div>
+<h5>
+<a name="boost_optional.reference.acknowledgements.h1"></a>
+ <span class="phrase"><a name="boost_optional.reference.acknowledgements.post_formal_review"></a></span><a class="link" href="acknowledgements.html#boost_optional.reference.acknowledgements.post_formal_review">Post-formal
+ review</a>
+ </h5>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ William Kempf carefully considered the originally proposed interface
+ and suggested the new interface which is currently used. He also started
+ and fueled the discussion about the analogy optional<>/smart pointer
+ and about relational operators.
+ </li>
+<li class="listitem">
+ Peter Dimov, Joel de Guzman, David Abrahams, Tanton Gibbs and Ian Hanson
+ focused on the relational semantics of optional (originally undefined);
+ concluding with the fact that the pointer-like interface doesn't make
+ it a pointer so it shall have deep relational operators.
+ </li>
+<li class="listitem">
+ Augustus Saunders also explored the different relational semantics between
+ optional<> and a pointer and developed the OptionalPointee concept
+ as an aid against potential conflicts on generic code.
+ </li>
+<li class="listitem">
+ Joel de Guzman noticed that optional<> can be seen as an API on
+ top of variant<T,nil_t>.
+ </li>
+<li class="listitem">
+ Dave Gomboc explained the meaning and usage of the Haskell analog to
+ optional<>: the Maybe type constructor (analogy originally pointed
+ out by David Sankel).
+ </li>
+<li class="listitem">
+ Other comments were posted by Vincent Finn, Anthony Williams, Ed Brey,
+ Rob Stewart, and others.
+ </li>
+<li class="listitem">
+ Joel de Guzman made the case for the support of references and helped
+ with the proper semantics.
+ </li>
+<li class="listitem">
+ Mat Marcus shown the virtues of a value-oriented interface, influencing
+ the current design, and contributed the idea of "none".
+ </li>
+<li class="listitem">
+ Vladimir Batov's design of Boost.Convert library motivated the development
+ of value accessors for <code class="computeroutput"><span class="identifier">optional</span></code>:
+ functions <code class="computeroutput"><span class="identifier">value</span></code>, <code class="computeroutput"><span class="identifier">value_or</span></code>, <code class="computeroutput"><span class="identifier">value_or_eval</span></code>.
+ </li>
+</ul></div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2016 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="relnotes.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a>
+</div>
+</body>
+</html>
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+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Dependencies and Portability</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../../index.html" title="Boost.Optional">
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+<link rel="next" href="dependencies_and_portability/optional_reference_binding.html" title="Optional Reference Binding">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
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+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
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+<a accesskey="p" href="header__boost_optional_optional_hpp_/header__boost_optional_hpp_.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="dependencies_and_portability/optional_reference_binding.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.reference.dependencies_and_portability"></a><a class="link" href="dependencies_and_portability.html" title="Dependencies and Portability">Dependencies
+ and Portability</a>
+</h3></div></div></div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.dependencies_and_portability.dependencies"></a><a class="link" href="dependencies_and_portability.html#boost_optional.reference.dependencies_and_portability.dependencies" title="Dependencies">Dependencies</a>
+</h4></div></div></div>
+<p>
+ The implementation uses the following other Boost modules:
+ </p>
+<div class="orderedlist"><ol class="orderedlist" type="1">
+<li class="listitem">
+ assert
+ </li>
+<li class="listitem">
+ config
+ </li>
+<li class="listitem">
+ core
+ </li>
+<li class="listitem">
+ detail
+ </li>
+<li class="listitem">
+ move
+ </li>
+<li class="listitem">
+ mpl
+ </li>
+<li class="listitem">
+ static_assert
+ </li>
+<li class="listitem">
+ throw_exception
+ </li>
+<li class="listitem">
+ type_traits
+ </li>
+<li class="listitem">
+ utility
+ </li>
+</ol></div>
+</div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2016 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="header__boost_optional_optional_hpp_/header__boost_optional_hpp_.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="dependencies_and_portability/optional_reference_binding.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/reference/dependencies_and_portability/optional_reference_binding.html b/doc/html/boost_optional/reference/dependencies_and_portability/optional_reference_binding.html
new file mode 100644
index 0000000..16c1637
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@@ -0,0 +1,100 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Optional Reference Binding</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../dependencies_and_portability.html" title="Dependencies and Portability">
+<link rel="prev" href="../dependencies_and_portability.html" title="Dependencies and Portability">
+<link rel="next" href="../relnotes.html" title="Release Notes">
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+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../dependencies_and_portability.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../dependencies_and_portability.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../relnotes.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.dependencies_and_portability.optional_reference_binding"></a><a class="link" href="optional_reference_binding.html" title="Optional Reference Binding">Optional
+ Reference Binding</a>
+</h4></div></div></div>
+<p>
+ On compilers that do not conform to Standard C++ rules of reference binding,
+ operations on optional references might give adverse results: rather than
+ binding a reference to a designated object they may create an unexpected
+ temporary and bind to it. Compilers known to have these deficiencies include
+ GCC versions 4.2, 4.3, 4.4, 4.5; QCC 4.4.2; MSVC versions 8.0, 9.0, 10.0,
+ 11.0, 12.0. On these compilers prefer using direct-initialization and copy
+ assignment of optional references to copy-initialization and assignment
+ from <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span></code>:
+ </p>
+<pre class="programlisting"><span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&></span> <span class="identifier">or1</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&></span> <span class="identifier">or2</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">;</span> <span class="comment">// not portable</span>
+<span class="identifier">or1</span> <span class="special">=</span> <span class="identifier">i</span><span class="special">;</span> <span class="comment">// not portable</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&></span> <span class="identifier">or3</span><span class="special">(</span><span class="identifier">i</span><span class="special">);</span> <span class="comment">// portable</span>
+<span class="identifier">or1</span> <span class="special">=</span> <span class="identifier">optional</span><span class="special"><</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&>(</span><span class="identifier">i</span><span class="special">);</span> <span class="comment">// portable</span>
+</pre>
+<p>
+ In order to check if your compiler correctly implements reference binding
+ use this test program.
+ </p>
+<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span>
+
+<span class="keyword">const</span> <span class="keyword">int</span> <span class="identifier">global_i</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
+
+<span class="keyword">struct</span> <span class="identifier">TestingReferenceBinding</span>
+<span class="special">{</span>
+ <span class="identifier">TestingReferenceBinding</span><span class="special">(</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&</span> <span class="identifier">ii</span><span class="special">)</span>
+ <span class="special">{</span>
+ <span class="identifier">assert</span><span class="special">(&</span><span class="identifier">ii</span> <span class="special">==</span> <span class="special">&</span><span class="identifier">global_i</span><span class="special">);</span>
+ <span class="special">}</span>
+
+ <span class="keyword">void</span> <span class="keyword">operator</span><span class="special">=(</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&</span> <span class="identifier">ii</span><span class="special">)</span>
+ <span class="special">{</span>
+ <span class="identifier">assert</span><span class="special">(&</span><span class="identifier">ii</span> <span class="special">==</span> <span class="special">&</span><span class="identifier">global_i</span><span class="special">);</span>
+ <span class="special">}</span>
+
+ <span class="keyword">void</span> <span class="keyword">operator</span><span class="special">=(</span><span class="keyword">int</span><span class="special">&&)</span> <span class="comment">// remove this if your compiler doesn't have rvalue refs</span>
+ <span class="special">{</span>
+ <span class="identifier">assert</span><span class="special">(</span><span class="keyword">false</span><span class="special">);</span>
+ <span class="special">}</span>
+<span class="special">};</span>
+
+<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="keyword">const</span> <span class="keyword">int</span><span class="special">&</span> <span class="identifier">iref</span> <span class="special">=</span> <span class="identifier">global_i</span><span class="special">;</span>
+ <span class="identifier">assert</span><span class="special">(&</span><span class="identifier">iref</span> <span class="special">==</span> <span class="special">&</span><span class="identifier">global_i</span><span class="special">);</span>
+
+ <span class="identifier">TestingReferenceBinding</span> <span class="identifier">ttt</span> <span class="special">=</span> <span class="identifier">global_i</span><span class="special">;</span>
+ <span class="identifier">ttt</span> <span class="special">=</span> <span class="identifier">global_i</span><span class="special">;</span>
+
+ <span class="identifier">TestingReferenceBinding</span> <span class="identifier">ttt2</span> <span class="special">=</span> <span class="identifier">iref</span><span class="special">;</span>
+ <span class="identifier">ttt2</span> <span class="special">=</span> <span class="identifier">iref</span><span class="special">;</span>
+<span class="special">}</span>
+</pre>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2016 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../dependencies_and_portability.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../dependencies_and_portability.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../relnotes.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
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+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
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+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.reference.header__boost_optional_bad_optional_access_hpp_"></a><a class="link" href="header__boost_optional_bad_optional_access_hpp_.html" title="Header <boost/optional/bad_optional_access.hpp>">Header
+ <boost/optional/bad_optional_access.hpp></a>
+</h3></div></div></div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.header__boost_optional_bad_optional_access_hpp_.synopsis"></a><a class="link" href="header__boost_optional_bad_optional_access_hpp_.html#boost_optional.reference.header__boost_optional_bad_optional_access_hpp_.synopsis" title="Synopsis">Synopsis</a>
+</h4></div></div></div>
+<p>
+</p>
+<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
+
+<span class="keyword">class</span> <span class="identifier">bad_optional_access</span> <span class="special">:</span> <span class="keyword">public</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">logic_error</span>
+<span class="special">{</span>
+<span class="keyword">public</span><span class="special">:</span>
+ <span class="identifier">bad_optional_access</span><span class="special">();</span> <a class="link" href="header__boost_optional_bad_optional_access_hpp_/detailed_semantics.html#reference_bad_optional_access_constructor"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+<span class="special">};</span>
+
+<span class="special">}</span> <span class="comment">// namespace boost</span>
+</pre>
+<p>
+ </p>
+</div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="header__boost_optional_bad_optional_access_hpp_/detailed_semantics.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/reference/header__boost_optional_bad_optional_access_hpp_/detailed_semantics.html b/doc/html/boost_optional/reference/header__boost_optional_bad_optional_access_hpp_/detailed_semantics.html
new file mode 100644
index 0000000..b182324
--- /dev/null
+++ b/doc/html/boost_optional/reference/header__boost_optional_bad_optional_access_hpp_/detailed_semantics.html
@@ -0,0 +1,60 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Detailed semantics</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../header__boost_optional_bad_optional_access_hpp_.html" title="Header <boost/optional/bad_optional_access.hpp>">
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+<link rel="next" href="../io_header.html" title="Header <boost/optional/optional_io.hpp>">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../../index.html">Home</a></td>
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+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../header__boost_optional_bad_optional_access_hpp_.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../header__boost_optional_bad_optional_access_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../io_header.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.header__boost_optional_bad_optional_access_hpp_.detailed_semantics"></a><a class="link" href="detailed_semantics.html" title="Detailed semantics">Detailed
+ semantics</a>
+</h4></div></div></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<p>
+ <a name="reference_bad_optional_access_constructor"></a><code class="computeroutput"><span class="identifier">bad_optional_access</span><span class="special">();</span></code>
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Constructs an object of class
+ <code class="computeroutput"><span class="identifier">bad_optional_access</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="identifier">what</span><span class="special">()</span></code> returns an implementation-defined
+ NTBS.
+ </li>
+</ul></div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../header__boost_optional_bad_optional_access_hpp_.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../header__boost_optional_bad_optional_access_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../io_header.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/reference/header__boost_optional_hpp_.html b/doc/html/boost_optional/reference/header__boost_optional_hpp_.html
new file mode 100644
index 0000000..c8d6b9e
--- /dev/null
+++ b/doc/html/boost_optional/reference/header__boost_optional_hpp_.html
@@ -0,0 +1,47 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Header <boost/optional.hpp></title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../index.html" title="Boost.Optional">
+<link rel="up" href="../../optional/reference.html" title="Reference">
+<link rel="prev" href="header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html" title="Detailed Semantics - Free Functions">
+<link rel="next" href="../dependencies_and_portability.html" title="Dependencies and Portability">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.reference.header__boost_optional_hpp_"></a><a class="link" href="header__boost_optional_hpp_.html" title="Header <boost/optional.hpp>">Header
+ <boost/optional.hpp></a>
+</h3></div></div></div>
+<p>
+ This is an alias for header <a class="link" href="../../optional/reference/header__boost_optional_optional_hpp_.html#boost_optional.reference.header__boost_optional_optional_hpp_.header_optional_optional" title="Synopsis"><code class="computeroutput"><span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">optional</span><span class="special">/</span><span class="identifier">optional</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code></a>.
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../dependencies_and_portability.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/reference/header__boost_optional_optional_fwd_hpp_.html b/doc/html/boost_optional/reference/header__boost_optional_optional_fwd_hpp_.html
new file mode 100644
index 0000000..ee81dd9
--- /dev/null
+++ b/doc/html/boost_optional/reference/header__boost_optional_optional_fwd_hpp_.html
@@ -0,0 +1,66 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Header <boost/optional/optional_fwd.hpp></title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../index.html" title="Boost.Optional">
+<link rel="up" href="../../optional/reference.html" title="Reference">
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+<link rel="next" href="../../optional/reference/header__boost_optional_optional_hpp_.html" title="Header <boost/optional/optional.hpp>">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
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+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="io_header/io_semantics.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.reference.header__boost_optional_optional_fwd_hpp_"></a><a class="link" href="header__boost_optional_optional_fwd_hpp_.html" title="Header <boost/optional/optional_fwd.hpp>">Header
+ <boost/optional/optional_fwd.hpp></a>
+</h3></div></div></div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.header__boost_optional_optional_fwd_hpp_.synopsis"></a><a class="link" href="header__boost_optional_optional_fwd_hpp_.html#boost_optional.reference.header__boost_optional_optional_fwd_hpp_.synopsis" title="Synopsis">Synopsis</a>
+</h4></div></div></div>
+<p>
+</p>
+<pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
+
+<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">class</span> <span class="identifier">optional</span> <span class="special">;</span>
+
+<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">swap</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="special">);</span>
+
+<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">struct</span> <span class="identifier">optional_swap_should_use_default_constructor</span> <span class="special">;</span>
+
+<span class="special">}</span> <span class="comment">// namespace boost</span>
+</pre>
+<p>
+ </p>
+<p>
+ This header only contains declarations.
+ </p>
+</div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="io_header/io_semantics.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html b/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html
new file mode 100644
index 0000000..b7d25f5
--- /dev/null
+++ b/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics.html
@@ -0,0 +1,2423 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Detailed Semantics</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../../../optional/reference/header__boost_optional_optional_hpp_.html" title="Header <boost/optional/optional.hpp>">
+<link rel="prev" href="header_optional_optional_refs.html" title="Optional References">
+<link rel="next" href="header__boost_optional_hpp_.html" title="Header <boost/optional.hpp>">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="header_optional_optional_refs.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="header__boost_optional_hpp_.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.header__boost_optional_optional_hpp_.detailed_semantics"></a><a class="link" href="detailed_semantics.html" title="Detailed Semantics">Detailed
+ Semantics</a>
+</h4></div></div></div>
+<p>
+ Because <code class="computeroutput"><span class="identifier">T</span></code> might be of reference
+ type, in the sequel, those entries whose semantic depends on <code class="computeroutput"><span class="identifier">T</span></code> being of reference type or not will
+ be distinguished using the following convention:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ If the entry reads: <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code><span class="emphasis"><em>(not
+ a ref)</em></span><code class="computeroutput"><span class="special">></span></code>,
+ the description corresponds only to the case where <code class="computeroutput"><span class="identifier">T</span></code>
+ is not of reference type.
+ </li>
+<li class="listitem">
+ If the entry reads: <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code>, the description corresponds
+ only to the case where <code class="computeroutput"><span class="identifier">T</span></code>
+ is of reference type.
+ </li>
+<li class="listitem">
+ If the entry reads: <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>, the description is the same for
+ both cases.
+ </li>
+</ul></div>
+<div class="note"><table border="0" summary="Note">
+<tr>
+<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../../doc/src/images/note.png"></td>
+<th align="left">Note</th>
+</tr>
+<tr><td align="left" valign="top"><p>
+ The following section contains various <code class="computeroutput"><span class="identifier">assert</span><span class="special">()</span></code> which are used only to show the postconditions
+ as sample code. It is not implied that the type <code class="computeroutput"><span class="identifier">T</span></code>
+ must support each particular expression but that if the expression is
+ supported, the implied condition holds.
+ </p></td></tr>
+</table></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<h6>
+<a name="boost_optional.reference.header__boost_optional_optional_hpp_.detailed_semantics.h0"></a>
+ <span class="phrase"><a name="boost_optional.reference.header__boost_optional_optional_hpp_.detailed_semantics.optional_class_member_functions"></a></span><a class="link" href="detailed_semantics.html#boost_optional.reference.header__boost_optional_optional_hpp_.detailed_semantics.optional_class_member_functions">optional
+ class member functions</a>
+ </h6>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">()</span>
+ <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Default-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">uninitialized</span>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> T's default constructor <span class="underline">is not</span> called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">def</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_none_t"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">none_t</span> <span class="special">)</span>
+ <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Constructs an <code class="computeroutput"><span class="identifier">optional</span></code> uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">uninitialized</span>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>'s
+ default constructor <span class="underline">is not</span> called.
+ The expression <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code>
+ denotes an instance of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none_t</span></code>
+ that can be used as the parameter.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">none</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">n</span><span class="special">(</span><span class="identifier">none</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">n</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_copy_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>
+ is <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Directly-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
+ and its value is a <span class="emphasis"><em>copy</em></span> of <code class="computeroutput"><span class="identifier">v</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span></code> throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span></code> is called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">);</span></code> in that case, this constructor
+ has no effect.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">ref</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Directly-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
+ and its value is an instance of an internal type wrapping the reference
+ <code class="computeroutput"><span class="identifier">ref</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">vref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">vref</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">++</span> <span class="identifier">v</span> <span class="special">;</span> <span class="comment">// mutate referee</span>
+<span class="identifier">assert</span> <span class="special">(*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span><span class="special">);</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_move_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="identifier">v</span>
+ <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>
+ is <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Directly-Move-Constructs an
+ <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
+ and its value is move-constructed from <code class="computeroutput"><span class="identifier">v</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code>
+ is called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">);</span></code>
+ in that case, the state of <code class="computeroutput"><span class="identifier">v</span></code>
+ is determined by exception safety guarantees for <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span><span class="special">&&)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v1</span><span class="special">,</span> <span class="identifier">v2</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">v1</span><span class="special">));</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v2</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">T</span><span class="special">&&</span>
+ <span class="identifier">ref</span> <span class="special">)</span>
+ <span class="special">=</span> <span class="keyword">delete</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> This constructor is deleted
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_bool_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span>
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
+ <span class="special">::</span><span class="identifier">optional</span><span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span>
+ <span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">v</span> <span class="special">)</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ If condition is true, same as:
+ </li></ul></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
+ <span class="special">::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ otherwise, same as:
+ </li></ul></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">()</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
+ <span class="special">::</span><span class="identifier">optional</span><span class="special">()</span></code>
+ </p></blockquote></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">optional</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">rhs</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_copy_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>
+ is <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Copy-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If rhs is initialized,
+ <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is a <span class="emphasis"><em>copy</em></span> of the
+ value of <code class="computeroutput"><span class="identifier">rhs</span></code>; else
+ <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span></code> throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If rhs is initialized, <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code>
+ is called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">);</span></code> in that case, this constructor
+ has no effect.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">uninit</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">uninit</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init</span><span class="special">(</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">init</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">init</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">optional</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span>
+ <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Copy-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is another reference to the same object
+ referenced by <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>;
+ else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, both <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> will refer to the same object
+ (they alias).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">uninit</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">uninit</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span>
+
+<span class="identifier">T</span> <span class="identifier">v</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">ref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init</span><span class="special">(</span><span class="identifier">ref</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">init</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">v</span> <span class="special">=</span> <span class="number">3</span> <span class="special">;</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init2</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_move_constructor_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">optional</span><span class="special">&&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">(</span></code><span class="emphasis"><em>see below</em></span><code class="computeroutput"><span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>
+ is <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Move-constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is move constructed from <code class="computeroutput"><span class="identifier">rhs</span></code>; else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> The expression inside <code class="computeroutput"><span class="keyword">noexcept</span></code> is equivalent to <code class="computeroutput"><span class="identifier">is_nothrow_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="special">&&</span>
+ <span class="special">)</span></code> is called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">);</span></code>
+ in that case, <code class="computeroutput"><span class="identifier">rhs</span></code> remains
+ initialized and the value of <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is determined by exception safety
+ of <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span><span class="special">&&)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">uninit</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">uninit</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">init</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">uniqye_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="keyword">new</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">init</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">init</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="keyword">nullptr</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">init2</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">optional</span> <span class="special">&&</span>
+ <span class="identifier">rhs</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Move-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is another reference to the same object
+ referenced by <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>;
+ else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, both <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> will refer to the same object
+ (they alias).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">uninit</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">uninit</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span>
+
+<span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">v</span><span class="special">(</span><span class="keyword">new</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">init</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">init</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="special">*</span><span class="identifier">v</span> <span class="special">=</span> <span class="number">3</span> <span class="special">;</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init2</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Copy-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is a <span class="emphasis"><em>copy</em></span> of the
+ value of rhs converted to type <code class="computeroutput"><span class="identifier">T</span></code>;
+ else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span></code> throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span></code> is called if <code class="computeroutput"><span class="identifier">rhs</span></code> is initialized, which requires
+ a valid conversion from <code class="computeroutput"><span class="identifier">U</span></code>
+ to <code class="computeroutput"><span class="identifier">T</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">);</span></code> in that case, this constructor
+ has no effect.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">x</span><span class="special">(</span><span class="number">123.4</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">==</span> <span class="number">123.4</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">y</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span><span class="special">(</span> <span class="special">*</span><span class="identifier">y</span> <span class="special">==</span> <span class="number">123</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_move_constructor_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&&</span>
+ <span class="identifier">rhs</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Move-constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is move-constructed from <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>;
+ else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">)</span></code>
+ is called if <code class="computeroutput"><span class="identifier">rhs</span></code> is
+ initialized, which requires a valid conversion from <code class="computeroutput"><span class="identifier">U</span></code>
+ to <code class="computeroutput"><span class="identifier">T</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">);</span></code>
+ in that case, <code class="computeroutput"><span class="identifier">rhs</span></code> remains
+ initialized and the value of <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is determined by exception safety
+ guarantee of <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span>
+ <span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">x</span><span class="special">(</span><span class="number">123.4</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">==</span> <span class="number">123.4</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">y</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">x</span><span class="special">))</span> <span class="special">;</span>
+<span class="identifier">assert</span><span class="special">(</span> <span class="special">*</span><span class="identifier">y</span> <span class="special">==</span> <span class="number">123</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_factory"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">InPlaceFactory</span><span class="special">></span>
+ <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">InPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">TypedInPlaceFactory</span><span class="special">></span>
+ <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">TypedInPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Constructs an <code class="computeroutput"><span class="identifier">optional</span></code> with a value of <code class="computeroutput"><span class="identifier">T</span></code> obtained from the factory.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
+ and its value is <span class="emphasis"><em>directly given</em></span> from the factory
+ <code class="computeroutput"><span class="identifier">f</span></code> (i.e., the value
+ <span class="underline">is not copied</span>).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever the <code class="computeroutput"><span class="identifier">T</span></code> constructor called by the factory
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> See <a class="link" href="../../tutorial/in_place_factories.html" title="In-Place Factories">In-Place
+ Factories</a>
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during the call to the <code class="computeroutput"><span class="identifier">T</span></code>
+ constructor used by the factory; in that case, this constructor has
+ no effect.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">C</span> <span class="special">{</span> <span class="identifier">C</span> <span class="special">(</span> <span class="keyword">char</span><span class="special">,</span> <span class="keyword">double</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">)</span> <span class="special">;</span> <span class="special">}</span> <span class="special">;</span>
+
+<span class="identifier">C</span> <span class="identifier">v</span><span class="special">(</span><span class="char">'A'</span><span class="special">,</span><span class="number">123.4</span><span class="special">,</span><span class="string">"hello"</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">C</span><span class="special">></span> <span class="identifier">x</span><span class="special">(</span> <span class="identifier">in_place</span> <span class="special">(</span><span class="char">'A'</span><span class="special">,</span> <span class="number">123.4</span><span class="special">,</span> <span class="string">"hello"</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// InPlaceFactory used</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">C</span><span class="special">></span> <span class="identifier">y</span><span class="special">(</span> <span class="identifier">in_place</span><span class="special"><</span><span class="identifier">C</span><span class="special">>(</span><span class="char">'A'</span><span class="special">,</span> <span class="number">123.4</span><span class="special">,</span> <span class="string">"hello"</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// TypedInPlaceFactory used</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">y</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_equal_none_t"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">none_t</span>
+ <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized destroys its contained
+ value.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_equal_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">rhs</span> <span class="special">)</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Assigns the value <code class="computeroutput"><span class="identifier">rhs</span></code> to an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized and its value is
+ a <span class="emphasis"><em>copy</em></span> of <code class="computeroutput"><span class="identifier">rhs</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span></code> or <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s assignment operator is used,
+ otherwise, its copy-constructor is used.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> In the event of
+ an exception, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is unchanged and its value unspecified
+ as far as <code class="computeroutput"><span class="identifier">optional</span></code>
+ is concerned (it is up to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <code class="computeroutput"><span class="keyword">operator</span><span class="special">=()</span></code>).
+ If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initially uninitialized and <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <span class="emphasis"><em>copy constructor</em></span> fails, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is left properly uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">T</span> <span class="identifier">y</span><span class="special">;</span>
+<span class="identifier">def</span> <span class="special">=</span> <span class="identifier">y</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">y</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> (Re)binds the wrapped reference.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized and it references
+ the same object referenced by <code class="computeroutput"><span class="identifier">rhs</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized, it is <span class="emphasis"><em>rebound</em></span>
+ to the new object. See <a class="link" href="../../tutorial/rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">here</a>
+ for details on this behavior.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">ra</span><span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">def</span> <span class="special">=</span> <span class="identifier">rb</span> <span class="special">;</span> <span class="comment">// binds 'def' to 'b' through 'rb'</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">b</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">*</span><span class="identifier">def</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span> <span class="comment">// changes the value of 'b' to a copy of the value of 'a'</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">b</span> <span class="special">==</span> <span class="identifier">a</span> <span class="special">)</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">c</span> <span class="special">=</span> <span class="number">3</span><span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">rc</span> <span class="special">=</span> <span class="identifier">c</span> <span class="special">;</span>
+<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">rc</span> <span class="special">;</span> <span class="comment">// REBINDS to 'c' through 'rc'</span>
+<span class="identifier">c</span> <span class="special">=</span> <span class="number">4</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="number">4</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_move_equal_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Moves the value <code class="computeroutput"><span class="identifier">rhs</span></code> to an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized and its value is
+ moved from <code class="computeroutput"><span class="identifier">rhs</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code>
+ or <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span> <span class="special">&&)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s move-assignment operator is used,
+ otherwise, its move-constructor is used.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> In the event of
+ an exception, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is unchanged and its value unspecified
+ as far as <code class="computeroutput"><span class="identifier">optional</span></code>
+ is concerned (it is up to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <code class="computeroutput"><span class="keyword">operator</span><span class="special">=()</span></code>).
+ If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initially uninitialized and <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <span class="emphasis"><em>move constructor</em></span> fails, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is left properly uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">T</span> <span class="identifier">y1</span><span class="special">,</span> <span class="identifier">y2</span><span class="special">,</span> <span class="identifier">yR</span><span class="special">;</span>
+<span class="identifier">def</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">y1</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">yR</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">y2</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">yR</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="special">=</span>
+ <span class="keyword">delete</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> This assignment operator is
+ deleted.
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_equal_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">rhs</span> <span class="special">)</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ is <a href="../../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a> and <code class="computeroutput"><span class="identifier">CopyAssignable</span></code>.
+ </li>
+<li class="listitem">
+<p class="simpara">
+ <span class="bold"><strong>Effects:</strong></span>
+ </p>
+<div class="informaltable"><table class="table">
+<colgroup>
+<col>
+<col>
+<col>
+</colgroup>
+<thead><tr></tr></thead>
+<tbody>
+<tr>
+<td>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ assigns <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>
+ to the contained value
+ </p>
+ </td>
+<td>
+ <p>
+ initializes the contained value as if direct-initializing
+ an object of type <code class="computeroutput"><span class="identifier">T</span></code>
+ with <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ does not contain a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ destroys the contained value by calling <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>
+ </p>
+ </td>
+<td>
+ <p>
+ no effect
+ </p>
+ </td>
+</tr>
+</tbody>
+</table></div>
+</li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>;
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> If any exception
+ is thrown, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="identifier">rhs</span></code>
+ remains unchanged. If an exception is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s copy constructor, no effect.
+ If an exception is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ copy assignment, the state of its contained value is as defined by
+ the exception safety guarantee of <code class="computeroutput"><span class="identifier">T</span></code>'s
+ copy assignment.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+
+<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">def</span> <span class="special">)</span> <span class="special">;</span>
+<span class="comment">// previous value (copy of 'v') destroyed from within 'opt'.</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
+ <span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> (Re)binds thee wrapped reference.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and it references the same object referenced by <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>;
+ otherwise, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is uninitialized (and references no object).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized and so is <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>,
+ <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is <span class="emphasis"><em>rebound</em></span> to the new object. See <a class="link" href="../../tutorial/rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">here</a>
+ for details on this behavior.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">ora</span><span class="special">(</span><span class="identifier">ra</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">orb</span><span class="special">(</span><span class="identifier">rb</span><span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">def</span> <span class="special">=</span> <span class="identifier">orb</span> <span class="special">;</span> <span class="comment">// binds 'def' to 'b' through 'rb' wrapped within 'orb'</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">b</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">*</span><span class="identifier">def</span> <span class="special">=</span> <span class="identifier">ora</span> <span class="special">;</span> <span class="comment">// changes the value of 'b' to a copy of the value of 'a'</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">b</span> <span class="special">==</span> <span class="identifier">a</span> <span class="special">)</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">c</span> <span class="special">=</span> <span class="number">3</span><span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">rc</span> <span class="special">=</span> <span class="identifier">c</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">orc</span><span class="special">(</span><span class="identifier">rc</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">ora</span> <span class="special">=</span> <span class="identifier">orc</span> <span class="special">;</span> <span class="comment">// REBINDS ora to 'c' through 'rc'</span>
+<span class="identifier">c</span> <span class="special">=</span> <span class="number">4</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">ora</span> <span class="special">==</span> <span class="number">4</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_move_equal_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">(</span></code><span class="emphasis"><em>see below</em></span><code class="computeroutput"><span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ is <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>
+ and <code class="computeroutput"><span class="identifier">MoveAssignable</span></code>.
+ </li>
+<li class="listitem">
+<p class="simpara">
+ <span class="bold"><strong>Effects:</strong></span>
+ </p>
+<div class="informaltable"><table class="table">
+<colgroup>
+<col>
+<col>
+<col>
+</colgroup>
+<thead><tr></tr></thead>
+<tbody>
+<tr>
+<td>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ assigns <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code> to the contained value
+ </p>
+ </td>
+<td>
+ <p>
+ initializes the contained value as if direct-initializing
+ an object of type <code class="computeroutput"><span class="identifier">T</span></code>
+ with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ does not contain a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ destroys the contained value by calling <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>
+ </p>
+ </td>
+<td>
+ <p>
+ no effect
+ </p>
+ </td>
+</tr>
+</tbody>
+</table></div>
+</li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>;
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> The expression inside <code class="computeroutput"><span class="keyword">noexcept</span></code> is equivalent to <code class="computeroutput"><span class="identifier">is_nothrow_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span> <span class="special">&&</span>
+ <span class="identifier">is_nothrow_move_assignable</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> If any exception
+ is thrown, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="identifier">rhs</span></code>
+ remains unchanged. If an exception is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s move constructor, the state of
+ <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>
+ is determined by the exception safety guarantee of <code class="computeroutput"><span class="identifier">T</span></code>'s
+ move constructor. If an exception is thrown during the call to T's
+ move-assignment, the state of <code class="computeroutput"><span class="special">**</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is determined by the exception
+ safety guarantee of T's move assignment.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+
+<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">def</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
+ <span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Same as <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">rhs</span> <span class="special">)</span></code>.
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_equal_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+<p class="simpara">
+ <span class="bold"><strong>Effect:</strong></span>
+ </p>
+<div class="informaltable"><table class="table">
+<colgroup>
+<col>
+<col>
+<col>
+</colgroup>
+<thead><tr></tr></thead>
+<tbody>
+<tr>
+<td>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ assigns <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>
+ to the contained value
+ </p>
+ </td>
+<td>
+ <p>
+ initializes the contained value as if direct-initializing
+ an object of type <code class="computeroutput"><span class="identifier">T</span></code>
+ with <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ does not contain a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ destroys the contained value by calling <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>
+ </p>
+ </td>
+<td>
+ <p>
+ no effect
+ </p>
+ </td>
+</tr>
+</tbody>
+</table></div>
+</li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> If any exception
+ is thrown, the result of the expression <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code> remains unchanged. If an exception
+ is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ constructor, no effect. If an exception is thrown during the call to
+ <code class="computeroutput"><span class="identifier">T</span></code>'s assignment, the
+ state of its contained value is as defined by the exception safety
+ guarantee of <code class="computeroutput"><span class="identifier">T</span></code>'s copy
+ assignment.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt0</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">opt1</span><span class="special">;</span>
+
+<span class="identifier">opt1</span> <span class="special">=</span> <span class="identifier">opt0</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt1</span> <span class="special">==</span> <span class="keyword">static_cast</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_move_equal_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+<p class="simpara">
+ <span class="bold"><strong>Effect:</strong></span>
+ </p>
+<div class="informaltable"><table class="table">
+<colgroup>
+<col>
+<col>
+<col>
+</colgroup>
+<thead><tr></tr></thead>
+<tbody>
+<tr>
+<td>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ assigns <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code> to the contained value
+ </p>
+ </td>
+<td>
+ <p>
+ initializes the contained value as if direct-initializing
+ an object of type <code class="computeroutput"><span class="identifier">T</span></code>
+ with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ does not contain a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ destroys the contained value by calling <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>
+ </p>
+ </td>
+<td>
+ <p>
+ no effect
+ </p>
+ </td>
+</tr>
+</tbody>
+</table></div>
+</li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> If any exception
+ is thrown, the result of the expression <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code> remains unchanged. If an exception
+ is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ constructor, no effect. If an exception is thrown during the call to
+ <code class="computeroutput"><span class="identifier">T</span></code>'s assignment, the
+ state of its contained value is as defined by the exception safety
+ guarantee of <code class="computeroutput"><span class="identifier">T</span></code>'s copy
+ assignment.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt0</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">opt1</span><span class="special">;</span>
+
+<span class="identifier">opt1</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">opt0</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt0</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt1</span> <span class="special">)</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt1</span> <span class="special">==</span> <span class="keyword">static_cast</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_emplace"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span>
+ <span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">emplace</span><span class="special">(</span>
+ <span class="identifier">Args</span><span class="special">...&&</span>
+ <span class="identifier">args</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> The compiler supports rvalue
+ references and variadic templates.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized calls <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span> <span class="special">=</span> <span class="identifier">none</span></code>.
+ Then initializes in-place the contained value as if direct-initializing
+ an object of type <code class="computeroutput"><span class="identifier">T</span></code>
+ with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">Args</span><span class="special">>(</span><span class="identifier">args</span><span class="special">)...</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever the selected <code class="computeroutput"><span class="identifier">T</span></code>'s constructor throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> If an exception
+ is thrown during the initialization of <code class="computeroutput"><span class="identifier">T</span></code>,
+ <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is <span class="emphasis"><em>uninitialized</em></span>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ need not be <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>
+ or <code class="computeroutput"><span class="identifier">MoveAssignable</span></code>.
+ On compilers that do not support variadic templates, the signature
+ falls back to two overloads:<code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span>
+ <span class="identifier">Arg</span><span class="special">></span>
+ <span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">(</span><span class="identifier">Arg</span><span class="special">&&</span> <span class="identifier">arg</span><span class="special">)</span></code> and <code class="computeroutput"><span class="keyword">void</span>
+ <span class="identifier">emplace</span><span class="special">()</span></code>.
+ On compilers that do not support rvalue references, the signature falls
+ back to three overloads: taking <code class="computeroutput"><span class="keyword">const</span></code>
+ and non-<code class="computeroutput"><span class="keyword">const</span></code> lvalue reference,
+ and third with empty function argument list.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">;</span>
+<span class="identifier">opt</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">(</span><span class="number">0</span><span class="special">);</span> <span class="comment">// create in-place using ctor T(int)</span>
+<span class="identifier">opt</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">();</span> <span class="comment">// destroy previous and default-construct another T</span>
+<span class="identifier">opt</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> <span class="comment">// destroy and copy-construct in-place (no assignment called)</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_equal_factory"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">InPlaceFactory</span><span class="special">></span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">InPlaceFactory</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">f</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">TypedInPlaceFactory</span><span class="special">></span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">TypedInPlaceFactory</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">f</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Assigns an <code class="computeroutput"><span class="identifier">optional</span></code>
+ with a value of <code class="computeroutput"><span class="identifier">T</span></code> obtained
+ from the factory.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
+ and its value is <span class="emphasis"><em>directly given</em></span> from the factory
+ <code class="computeroutput"><span class="identifier">f</span></code> (i.e., the value
+ <span class="underline">is not copied</span>).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever the <code class="computeroutput"><span class="identifier">T</span></code> constructor called by the factory
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> See <a class="link" href="../../tutorial/in_place_factories.html" title="In-Place Factories">In-Place
+ Factories</a>
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during the call to the <code class="computeroutput"><span class="identifier">T</span></code>
+ constructor used by the factory; in that case, the <code class="computeroutput"><span class="identifier">optional</span></code>
+ object will be reset to be <span class="emphasis"><em>uninitialized</em></span>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_reset_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">reset</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Deprecated:</strong></span> same as <code class="computeroutput"><span class="keyword">operator</span><span class="special">=</span>
+ <span class="special">(</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">v</span><span class="special">)</span>
+ <span class="special">;</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_reset"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">reset</span><span class="special">()</span> <span class="keyword">noexcept</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Deprecated:</strong></span> Same as <code class="computeroutput"><span class="keyword">operator</span><span class="special">=(</span>
+ <span class="identifier">none_t</span> <span class="special">);</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_get"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get</span><span class="special">()</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">get</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get</span>
+ <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span>
+ <span class="special">&)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> A reference to the contained
+ value
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The requirement is asserted
+ via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">get</span><span class="special">()</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">get</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get</span>
+ <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="special">&)</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <span class="underline">The</span>
+ reference contained.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The requirement is asserted
+ via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_asterisk"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">*()</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">*()</span> <span class="special">&;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> A reference to the contained
+ value
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The requirement is asserted
+ via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
+ On compilers that do not support ref-qualifiers on member functions
+ these two overloads are replaced with the classical two: a <code class="computeroutput"><span class="keyword">const</span></code> and non-<code class="computeroutput"><span class="keyword">const</span></code>
+ member functions.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">);</span>
+<span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">u</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">opt</span><span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">u</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">T</span> <span class="identifier">w</span> <span class="special">;</span>
+<span class="special">*</span><span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">w</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">w</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_asterisk_move"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">*()</span> <span class="special">&&;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">val</span><span class="special">);</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The requirement is asserted
+ via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
+ On compilers that do not support ref-qualifiers on member functions
+ this overload is not present.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">*()</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">*()</span>
+ <span class="special">&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">*()</span>
+ <span class="special">&&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <span class="underline">The</span>
+ reference contained.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The requirement is asserted
+ via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
+ On compilers that do not support ref-qualifiers on member functions
+ these three overloads are replaced with the classical two: a <code class="computeroutput"><span class="keyword">const</span></code> and non-<code class="computeroutput"><span class="keyword">const</span></code>
+ member functions.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">vref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">vref</span> <span class="special">);</span>
+<span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">vref2</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">opt</span><span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">vref2</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">++</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span><span class="special">()</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span><span class="special">()</span> <span class="special">&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">?</span> <span class="special">*</span><span class="identifier">val</span> <span class="special">:</span> <span class="keyword">throw</span> <span class="identifier">bad_optional_access</span><span class="special">();</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ ref-qualifiers on member functions these two overloads are replaced
+ with the classical two: a <code class="computeroutput"><span class="keyword">const</span></code>
+ and non-<code class="computeroutput"><span class="keyword">const</span></code> member functions.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o0</span><span class="special">,</span> <span class="identifier">o1</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span><span class="special">.</span><span class="identifier">value</span><span class="special">()</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">);</span>
+
+<span class="keyword">try</span> <span class="special">{</span>
+ <span class="identifier">o0</span><span class="special">.</span><span class="identifier">value</span><span class="special">();</span> <span class="comment">// throws</span>
+ <span class="identifier">assert</span> <span class="special">(</span> <span class="keyword">false</span> <span class="special">);</span>
+<span class="special">}</span>
+<span class="keyword">catch</span><span class="special">(</span><span class="identifier">bad_optional_access</span><span class="special">&)</span> <span class="special">{</span>
+ <span class="identifier">assert</span> <span class="special">(</span> <span class="keyword">true</span> <span class="special">);</span>
+<span class="special">}</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_value_move"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span><span class="special">()</span> <span class="special">&&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">?</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">val</span><span class="special">)</span> <span class="special">:</span> <span class="keyword">throw</span> <span class="identifier">bad_optional_access</span><span class="special">();</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ ref-qualifiers on member functions this overload is not present.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_value_or"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or</span><span class="special">(</span><span class="identifier">U</span> <span class="special">&&</span>
+ <span class="identifier">v</span><span class="special">)</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">if</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="special">**</span><span class="keyword">this</span><span class="special">;</span> <span class="keyword">else</span> <span class="keyword">return</span>
+ <span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">);</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> If <code class="computeroutput"><span class="identifier">T</span></code>
+ is not <a href="../../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a> or <code class="computeroutput"><span class="identifier">U</span> <span class="special">&&</span></code>
+ is not convertible to <code class="computeroutput"><span class="identifier">T</span></code>,
+ the program is ill-formed.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ ref-qualifiers on member functions this overload is replaced with the
+ <code class="computeroutput"><span class="keyword">const</span></code>-qualified member
+ function. On compilers without rvalue reference support the type of
+ <code class="computeroutput"><span class="identifier">v</span></code> becomes <code class="computeroutput"><span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span></code>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_value_or_move"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or</span><span class="special">(</span><span class="identifier">U</span> <span class="special">&&</span>
+ <span class="identifier">v</span><span class="special">)</span>
+ <span class="special">&&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">if</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(**</span><span class="keyword">this</span><span class="special">);</span> <span class="keyword">else</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">);</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> If <code class="computeroutput"><span class="identifier">T</span></code>
+ is not <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>
+ or <code class="computeroutput"><span class="identifier">U</span> <span class="special">&&</span></code>
+ is not convertible to <code class="computeroutput"><span class="identifier">T</span></code>,
+ the program is ill-formed.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ ref-qualifiers on member functions this overload is not present.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_value_or_call"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">F</span> <span class="identifier">f</span><span class="special">)</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ is <a href="../../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a> and <code class="computeroutput"><span class="identifier">F</span></code> models a <a href="http://www.sgi.com/tech/stl/Generator.html" target="_top"><code class="computeroutput"><span class="identifier">Generator</span></code></a> whose result type
+ is convertible to <code class="computeroutput"><span class="identifier">T</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> <code class="computeroutput"><span class="keyword">if</span>
+ <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="special">**</span><span class="keyword">this</span><span class="special">;</span> <span class="keyword">else</span> <span class="keyword">return</span> <span class="identifier">f</span><span class="special">();</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ ref-qualifiers on member functions this overload is replaced with the
+ <code class="computeroutput"><span class="keyword">const</span></code>-qualified member
+ function.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">complain_and_0</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="identifier">clog</span> <span class="special"><<</span> <span class="string">"no value returned, using default"</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span>
+ <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
+<span class="special">}</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">o1</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">oN</span> <span class="special">=</span> <span class="identifier">none</span><span class="special">;</span>
+
+<span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="identifier">o1</span><span class="special">.</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">complain_and_0</span><span class="special">);</span> <span class="comment">// fun not called</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">i</span> <span class="special">==</span> <span class="number">1</span><span class="special">);</span>
+
+<span class="keyword">int</span> <span class="identifier">j</span> <span class="special">=</span> <span class="identifier">oN</span><span class="special">.</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">complain_and_0</span><span class="special">);</span> <span class="comment">// fun called</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">i</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_value_or_call_move"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">F</span> <span class="identifier">f</span><span class="special">)</span> <span class="special">&&</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ is <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>
+ and <code class="computeroutput"><span class="identifier">F</span></code> models a <a href="http://www.sgi.com/tech/stl/Generator.html" target="_top"><code class="computeroutput"><span class="identifier">Generator</span></code></a>
+ whose result type is convertible to <code class="computeroutput"><span class="identifier">T</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> <code class="computeroutput"><span class="keyword">if</span>
+ <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(**</span><span class="keyword">this</span><span class="special">);</span> <span class="keyword">else</span> <span class="keyword">return</span>
+ <span class="identifier">f</span><span class="special">();</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ ref-qualifiers on member functions this overload is not present.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_get_value_or_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_value_or</span><span class="special">(</span>
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="keyword">default</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_value_or</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&</span> <span class="keyword">default</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">get_optional_value_or</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">o</span><span class="special">,</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="keyword">default</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get_optional_value_or</span>
+ <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>&</span>
+ <span class="identifier">o</span><span class="special">,</span>
+ <span class="identifier">T</span><span class="special">&</span>
+ <span class="keyword">default</span> <span class="special">)</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Deprecated:</strong></span> Use <code class="computeroutput"><span class="identifier">value_or</span><span class="special">()</span></code> instead.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> A reference to the contained
+ value, if any, or <code class="computeroutput"><span class="keyword">default</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">,</span> <span class="identifier">z</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span><span class="special">;</span>
+<span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">=</span> <span class="identifier">def</span><span class="special">.</span><span class="identifier">get_value_or</span><span class="special">(</span><span class="identifier">z</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">y</span> <span class="special">==</span> <span class="identifier">z</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">);</span>
+<span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">u</span> <span class="special">=</span> <span class="identifier">get_optional_value_or</span><span class="special">(</span><span class="identifier">opt</span><span class="special">,</span><span class="identifier">z</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">u</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">u</span> <span class="special">!=</span> <span class="identifier">z</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_get_ptr"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_ptr</span><span class="special">()</span>
+ <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">*</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">*</span>
+ <span class="identifier">get_pointer</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">*</span> <span class="identifier">get_pointer</span>
+ <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span>
+ <span class="special">&)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized, a pointer to the
+ contained value; else <code class="computeroutput"><span class="number">0</span></code>
+ (<span class="emphasis"><em>null</em></span>).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The contained value is permanently
+ stored within <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>,
+ so you should not hold nor delete this pointer
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span> <span class="identifier">copt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">T</span><span class="special">*</span> <span class="identifier">p</span> <span class="special">=</span> <span class="identifier">opt</span><span class="special">.</span><span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">;</span>
+<span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">cp</span> <span class="special">=</span> <span class="identifier">copt</span><span class="special">.</span><span class="identifier">get_ptr</span><span class="special">();</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">p</span> <span class="special">==</span> <span class="identifier">get_pointer</span><span class="special">(</span><span class="identifier">opt</span><span class="special">)</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">cp</span> <span class="special">==</span> <span class="identifier">get_pointer</span><span class="special">(</span><span class="identifier">copt</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_arrow"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span> <span class="special">->()</span>
+ <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">*</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span>
+ <span class="special">->()</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> A pointer to the contained
+ value.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The requirement is asserted
+ via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">X</span> <span class="special">{</span> <span class="keyword">int</span> <span class="identifier">mdata</span> <span class="special">;</span> <span class="special">}</span> <span class="special">;</span>
+<span class="identifier">X</span> <span class="identifier">x</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">X</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span><span class="identifier">x</span><span class="special">);</span>
+<span class="identifier">opt</span><span class="special">-></span><span class="identifier">mdata</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_bool"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span>
+ <span class="keyword">bool</span><span class="special">()</span>
+ <span class="keyword">const</span> <span class="keyword">noexcept</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">!=</span> <span class="number">0</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ explicit conversion operators this falls back to safe-bool idiom.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">def</span> <span class="special">==</span> <span class="number">0</span> <span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt</span> <span class="special">!=</span> <span class="number">0</span> <span class="special">);</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_not"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">!()</span> <span class="keyword">noexcept</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized, <code class="computeroutput"><span class="keyword">true</span></code>; else <code class="computeroutput"><span class="keyword">false</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> This operator is provided for
+ those compilers which can't use the <span class="emphasis"><em>unspecified-bool-type
+ operator</em></span> in certain boolean contexts.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">opt</span> <span class="special">);</span>
+<span class="special">*</span><span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">some_T</span> <span class="special">;</span>
+
+<span class="comment">// Notice the "double-bang" idiom here.</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!!</span><span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_is_initialized"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">is_initialized</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Deprecated:</strong></span> Same as <code class="computeroutput"><span class="keyword">explicit</span> <span class="keyword">operator</span>
+ <span class="keyword">bool</span> <span class="special">()</span>
+ <span class="special">;</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<h6>
+<a name="boost_optional.reference.header__boost_optional_optional_hpp_.detailed_semantics.h1"></a>
+ <span class="phrase"><a name="boost_optional.reference.header__boost_optional_optional_hpp_.detailed_semantics.free_functions"></a></span><a class="link" href="detailed_semantics.html#boost_optional.reference.header__boost_optional_optional_hpp_.detailed_semantics.free_functions">Free
+ functions</a>
+ </h6>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_make_optional_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="identifier">make_optional</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">v</span><span class="special">)</span></code> for the <span class="emphasis"><em>deduced</em></span>
+ type <code class="computeroutput"><span class="identifier">T</span></code> of <code class="computeroutput"><span class="identifier">v</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">foo</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">foo</span> <span class="special">(</span> <span class="identifier">make_optional</span><span class="special">(</span><span class="number">1</span><span class="special">+</span><span class="number">1</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> <span class="comment">// Creates an optional<int></span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_make_optional_bool_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="identifier">make_optional</span><span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span>
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">condition</span><span class="special">,</span><span class="identifier">v</span><span class="special">)</span></code> for the <span class="emphasis"><em>deduced</em></span>
+ type <code class="computeroutput"><span class="identifier">T</span></code> of <code class="computeroutput"><span class="identifier">v</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">calculate_foo</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="keyword">double</span> <span class="identifier">val</span> <span class="special">=</span> <span class="identifier">compute_foo</span><span class="special">();</span>
+ <span class="keyword">return</span> <span class="identifier">make_optional</span><span class="special">(</span><span class="identifier">is_not_nan_and_finite</span><span class="special">(</span><span class="identifier">val</span><span class="special">),</span><span class="identifier">val</span><span class="special">);</span>
+<span class="special">}</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">v</span> <span class="special">=</span> <span class="identifier">calculate_foo</span><span class="special">();</span>
+<span class="keyword">if</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">v</span> <span class="special">)</span>
+ <span class="identifier">error</span><span class="special">(</span><span class="string">"foo wasn't computed"</span><span class="special">);</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">==</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ shall meet requirements of <a href="http://www.sgi.com/tech/stl/EqualityComparable.html" target="_top"><code class="computeroutput"><span class="identifier">EqualityComparable</span></code></a>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> If both <code class="computeroutput"><span class="identifier">x</span></code>
+ and <code class="computeroutput"><span class="identifier">y</span></code> are initialized,
+ <code class="computeroutput"><span class="special">(*</span><span class="identifier">x</span>
+ <span class="special">==</span> <span class="special">*</span><span class="identifier">y</span><span class="special">)</span></code>.
+ If only <code class="computeroutput"><span class="identifier">x</span></code> or <code class="computeroutput"><span class="identifier">y</span></code> is initialized, <code class="computeroutput"><span class="keyword">false</span></code>.
+ If both are uninitialized, <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> This definition guarantees
+ that <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ not containing a value is compared unequal to any <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> containing any value, and equal
+ to any other <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> not containing a value. Pointers
+ have shallow relational operators while <code class="computeroutput"><span class="identifier">optional</span></code>
+ has deep relational operators. Do not use <code class="computeroutput"><span class="keyword">operator</span><span class="special">==</span></code> directly in generic code which expect
+ to be given either an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> or a pointer; use <a href="../../../../../../utility/OptionalPointee.html#equal" target="_top"><code class="computeroutput"><span class="identifier">equal_pointees</span><span class="special">()</span></code></a>
+ instead
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">oN</span><span class="special">,</span> <span class="identifier">oN_</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o1</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">)),</span> <span class="identifier">o1_</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">));</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o2</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">));</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">==</span> <span class="identifier">oN</span> <span class="special">);</span> <span class="comment">// Identity implies equality</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">==</span> <span class="identifier">o1</span> <span class="special">);</span> <span class="comment">//</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">==</span> <span class="identifier">oN_</span> <span class="special">);</span> <span class="comment">// Both uninitialized compare equal</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">!=</span> <span class="identifier">o1</span> <span class="special">);</span> <span class="comment">// Initialized unequal to initialized.</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">==</span> <span class="identifier">o1_</span> <span class="special">);</span> <span class="comment">// Both initialized compare as (*lhs == *rhs)</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">!=</span> <span class="identifier">o2</span> <span class="special">);</span> <span class="comment">//</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_less_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special"><</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> Expression <code class="computeroutput"><span class="special">*</span><span class="identifier">x</span> <span class="special"><</span> <span class="special">*</span><span class="identifier">y</span></code> shall be well-formed and its result
+ shall be convertible to <code class="computeroutput"><span class="keyword">bool</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">(!</span><span class="identifier">y</span><span class="special">)</span> <span class="special">?</span> <span class="keyword">false</span> <span class="special">:</span> <span class="special">(!</span><span class="identifier">x</span><span class="special">)</span> <span class="special">?</span> <span class="keyword">true</span> <span class="special">:</span> <span class="special">*</span><span class="identifier">x</span> <span class="special"><</span>
+ <span class="special">*</span><span class="identifier">y</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> This definition guarantees
+ that <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ not containing a value is ordered as less than any <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> containing any value, and equivalent
+ to any other <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> not containing a value. Pointers
+ have shallow relational operators while <code class="computeroutput"><span class="identifier">optional</span></code>
+ has deep relational operators. Do not use <code class="computeroutput"><span class="keyword">operator</span><span class="special"><</span></code> directly in generic code which
+ expect to be given either an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> or a pointer; use <a href="../../../../../../utility/OptionalPointee.html#less" target="_top"><code class="computeroutput"><span class="identifier">less_pointees</span><span class="special">()</span></code></a>
+ instead. <code class="computeroutput"><span class="identifier">T</span></code> need not
+ be <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a>. Only
+ single <code class="computeroutput"><span class="keyword">operator</span><span class="special"><</span></code>
+ is required. Other relational operations are defined in terms of this
+ one. If <code class="computeroutput"><span class="identifier">T</span></code>'s <code class="computeroutput"><span class="keyword">operator</span><span class="special"><</span></code>
+ satisfies the axioms of <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a> (transitivity,
+ antisymmetry and irreflexivity), <code class="computeroutput"><span class="identifier">optinal</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> is <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">oN</span><span class="special">,</span> <span class="identifier">oN_</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o0</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">0</span><span class="special">));</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o1</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">));</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN</span> <span class="special"><</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// Identity implies equivalence</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o1</span> <span class="special"><</span> <span class="identifier">o1</span><span class="special">)</span> <span class="special">);</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN</span> <span class="special"><</span> <span class="identifier">oN_</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// Two uninitialized are equivalent</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN_</span> <span class="special"><</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special"><</span> <span class="identifier">o0</span> <span class="special">);</span> <span class="comment">// Uninitialized is less than initialized</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o0</span> <span class="special"><</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special"><</span> <span class="identifier">o2</span> <span class="special">)</span> <span class="special">;</span> <span class="comment">// Two initialized compare as (*lhs < *rhs)</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o2</span> <span class="special"><</span> <span class="identifier">o1</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o2</span> <span class="special"><</span> <span class="identifier">o2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_not_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">!=</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
+ <span class="identifier">x</span> <span class="special">==</span>
+ <span class="identifier">y</span> <span class="special">);</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_greater_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">></span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">(</span>
+ <span class="identifier">y</span> <span class="special"><</span>
+ <span class="identifier">x</span> <span class="special">);</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_less_or_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special"><=</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
+ <span class="identifier">y</span> <span class="special"><</span>
+ <span class="identifier">x</span> <span class="special">);</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_greater_or_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">>=</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
+ <span class="identifier">x</span> <span class="special"><</span>
+ <span class="identifier">y</span> <span class="special">);</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_equal_optional_none"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">==</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">none_t</span> <span class="special">)</span>
+ <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">==</span> <span class="special">(</span>
+ <span class="identifier">none_t</span><span class="special">,</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">!</span><span class="identifier">x</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ need not meet requirements of <a href="http://www.sgi.com/tech/stl/EqualityComparable.html" target="_top"><code class="computeroutput"><span class="identifier">EqualityComparable</span></code></a>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_not_equal_optional_none"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">!=</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">none_t</span> <span class="special">)</span>
+ <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">!=</span> <span class="special">(</span>
+ <span class="identifier">none_t</span><span class="special">,</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
+ <span class="identifier">x</span> <span class="special">==</span>
+ <span class="identifier">y</span> <span class="special">);</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_swap_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">swap</span>
+ <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">y</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> Lvalues of type <code class="computeroutput"><span class="identifier">T</span></code> shall be swappable and <code class="computeroutput"><span class="identifier">T</span></code> shall be <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>.
+ </li>
+<li class="listitem">
+<p class="simpara">
+ <span class="bold"><strong>Effects:</strong></span>
+ </p>
+<div class="informaltable"><table class="table">
+<colgroup>
+<col>
+<col>
+<col>
+</colgroup>
+<thead><tr></tr></thead>
+<tbody>
+<tr>
+<td>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ calls <code class="computeroutput"><span class="identifier">swap</span><span class="special">(*(*</span><span class="keyword">this</span><span class="special">),</span> <span class="special">*</span><span class="identifier">rhs</span><span class="special">)</span></code>
+ </p>
+ </td>
+<td>
+ <p>
+ initializes the contained value of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> as if direct-initializing
+ an object of type <code class="computeroutput"><span class="identifier">T</span></code>
+ with the expression <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code>, followed by <code class="computeroutput"><span class="identifier">rhs</span><span class="special">.</span><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>,
+ <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ contains a value and <code class="computeroutput"><span class="identifier">rhs</span></code>
+ does not contain a value
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ does not contain a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ initializes the contained value of <code class="computeroutput"><span class="identifier">rhs</span></code>
+ as if direct-initializing an object of type <code class="computeroutput"><span class="identifier">T</span></code> with the expression
+ <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*(*</span><span class="keyword">this</span><span class="special">))</span></code>,
+ followed by <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value
+ and <code class="computeroutput"><span class="identifier">rhs</span></code> contains
+ a value
+ </p>
+ </td>
+<td>
+ <p>
+ no effect
+ </p>
+ </td>
+</tr>
+</tbody>
+</table></div>
+</li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> The states of <code class="computeroutput"><span class="identifier">x</span></code> and <code class="computeroutput"><span class="identifier">y</span></code>
+ interchanged.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> If both are initialized, whatever
+ <code class="computeroutput"><span class="identifier">swap</span><span class="special">(</span><span class="identifier">T</span><span class="special">&,</span><span class="identifier">T</span><span class="special">&)</span></code>
+ throws. If only one is initialized, whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">(</span><span class="number">12</span><span class="special">);</span>
+<span class="identifier">T</span> <span class="identifier">y</span><span class="special">(</span><span class="number">21</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def0</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def1</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">optX</span><span class="special">(</span><span class="identifier">x</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">optY</span><span class="special">(</span><span class="identifier">y</span><span class="special">);</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">def1</span><span class="special">);</span> <span class="comment">// no-op</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">optX</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def0</span> <span class="special">==</span> <span class="identifier">x</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">optX</span> <span class="special">);</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">optX</span><span class="special">);</span> <span class="comment">// Get back to original values</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">optX</span><span class="special">,</span><span class="identifier">optY</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">optX</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">optY</span> <span class="special">==</span> <span class="identifier">x</span> <span class="special">);</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_swap_optional_reference"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">swap</span>
+ <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&</span> <span class="identifier">y</span>
+ <span class="special">)</span> <span class="keyword">noexcept</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="identifier">x</span></code>
+ refers to what <code class="computeroutput"><span class="identifier">y</span></code> refererred
+ to before the swap (if anything). <code class="computeroutput"><span class="identifier">y</span></code>
+ refers to whatever <code class="computeroutput"><span class="identifier">x</span></code>
+ referred to before the swap.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">(</span><span class="number">12</span><span class="special">);</span>
+<span class="identifier">T</span> <span class="identifier">y</span><span class="special">(</span><span class="number">21</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">opt0</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">optX</span> <span class="special">(</span><span class="identifier">x</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">optY</span> <span class="special">(</span><span class="identifier">y</span><span class="special">);</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">optX</span><span class="special">,</span> <span class="identifier">optY</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">optX</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">y</span><span class="special">));</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">optY</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">x</span><span class="special">));</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">opt0</span><span class="special">,</span> <span class="identifier">optX</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt0</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">optX</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">opt0</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">y</span><span class="special">));</span>
+</pre>
+ [endsect]
+ </li>
+</ul></div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2016 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="header_optional_optional_refs.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="header__boost_optional_hpp_.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
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+</html>
diff --git a/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics____free_functions.html b/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics____free_functions.html
new file mode 100644
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--- /dev/null
+++ b/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics____free_functions.html
@@ -0,0 +1,447 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Detailed Semantics -- Free Functions</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
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+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.header__boost_optional_optional_hpp_.detailed_semantics____free_functions"></a><a class="link" href="detailed_semantics____free_functions.html" title="Detailed Semantics -- Free Functions">Detailed
+ Semantics -- Free Functions</a>
+</h4></div></div></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_make_optional_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">make_optional</span><span class="special">(</span>
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">v</span><span class="special">)</span></code> for the <span class="emphasis"><em>deduced</em></span>
+ type <code class="computeroutput"><span class="identifier">T</span></code> of <code class="computeroutput"><span class="identifier">v</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">foo</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">foo</span> <span class="special">(</span> <span class="identifier">make_optional</span><span class="special">(</span><span class="number">1</span><span class="special">+</span><span class="number">1</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> <span class="comment">// Creates an optional<int></span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_make_optional_bool_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="identifier">make_optional</span><span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span>
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">condition</span><span class="special">,</span><span class="identifier">v</span><span class="special">)</span></code> for the <span class="emphasis"><em>deduced</em></span>
+ type <code class="computeroutput"><span class="identifier">T</span></code> of <code class="computeroutput"><span class="identifier">v</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">calculate_foo</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="keyword">double</span> <span class="identifier">val</span> <span class="special">=</span> <span class="identifier">compute_foo</span><span class="special">();</span>
+ <span class="keyword">return</span> <span class="identifier">make_optional</span><span class="special">(</span><span class="identifier">is_not_nan_and_finite</span><span class="special">(</span><span class="identifier">val</span><span class="special">),</span><span class="identifier">val</span><span class="special">);</span>
+<span class="special">}</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">v</span> <span class="special">=</span> <span class="identifier">calculate_foo</span><span class="special">();</span>
+<span class="keyword">if</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">v</span> <span class="special">)</span>
+ <span class="identifier">error</span><span class="special">(</span><span class="string">"foo wasn't computed"</span><span class="special">);</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">==</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ shall meet requirements of <a href="http://www.sgi.com/tech/stl/EqualityComparable.html" target="_top"><code class="computeroutput"><span class="identifier">EqualityComparable</span></code></a>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> If both <code class="computeroutput"><span class="identifier">x</span></code>
+ and <code class="computeroutput"><span class="identifier">y</span></code> are initialized,
+ <code class="computeroutput"><span class="special">(*</span><span class="identifier">x</span>
+ <span class="special">==</span> <span class="special">*</span><span class="identifier">y</span><span class="special">)</span></code>.
+ If only <code class="computeroutput"><span class="identifier">x</span></code> or <code class="computeroutput"><span class="identifier">y</span></code> is initialized, <code class="computeroutput"><span class="keyword">false</span></code>.
+ If both are uninitialized, <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> This definition guarantees
+ that <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ not containing a value is compared unequal to any <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> containing any value, and equal
+ to any other <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> not containing a value. Pointers
+ have shallow relational operators while <code class="computeroutput"><span class="identifier">optional</span></code>
+ has deep relational operators. Do not use <code class="computeroutput"><span class="keyword">operator</span><span class="special">==</span></code> directly in generic code which expect
+ to be given either an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> or a pointer; use <a href="../../../../../../utility/OptionalPointee.html#equal" target="_top"><code class="computeroutput"><span class="identifier">equal_pointees</span><span class="special">()</span></code></a>
+ instead
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">oN</span><span class="special">,</span> <span class="identifier">oN_</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o1</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">)),</span> <span class="identifier">o1_</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">));</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o2</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">));</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">==</span> <span class="identifier">oN</span> <span class="special">);</span> <span class="comment">// Identity implies equality</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">==</span> <span class="identifier">o1</span> <span class="special">);</span> <span class="comment">//</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">==</span> <span class="identifier">oN_</span> <span class="special">);</span> <span class="comment">// Both uninitialized compare equal</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">!=</span> <span class="identifier">o1</span> <span class="special">);</span> <span class="comment">// Initialized unequal to initialized.</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">==</span> <span class="identifier">o1_</span> <span class="special">);</span> <span class="comment">// Both initialized compare as (*lhs == *rhs)</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">!=</span> <span class="identifier">o2</span> <span class="special">);</span> <span class="comment">//</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_less_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special"><</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> Expression <code class="computeroutput"><span class="special">*</span><span class="identifier">x</span> <span class="special"><</span> <span class="special">*</span><span class="identifier">y</span></code> shall be well-formed and its result
+ shall be convertible to <code class="computeroutput"><span class="keyword">bool</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">(!</span><span class="identifier">y</span><span class="special">)</span> <span class="special">?</span> <span class="keyword">false</span> <span class="special">:</span> <span class="special">(!</span><span class="identifier">x</span><span class="special">)</span> <span class="special">?</span> <span class="keyword">true</span> <span class="special">:</span> <span class="special">*</span><span class="identifier">x</span> <span class="special"><</span>
+ <span class="special">*</span><span class="identifier">y</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> This definition guarantees
+ that <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ not containing a value is ordered as less than any <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> containing any value, and equivalent
+ to any other <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> not containing a value. Pointers
+ have shallow relational operators while <code class="computeroutput"><span class="identifier">optional</span></code>
+ has deep relational operators. Do not use <code class="computeroutput"><span class="keyword">operator</span><span class="special"><</span></code> directly in generic code which
+ expect to be given either an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> or a pointer; use <a href="../../../../../../utility/OptionalPointee.html#less" target="_top"><code class="computeroutput"><span class="identifier">less_pointees</span><span class="special">()</span></code></a>
+ instead. <code class="computeroutput"><span class="identifier">T</span></code> need not
+ be <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a>. Only
+ single <code class="computeroutput"><span class="keyword">operator</span><span class="special"><</span></code>
+ is required. Other relational operations are defined in terms of this
+ one. If <code class="computeroutput"><span class="identifier">T</span></code>'s <code class="computeroutput"><span class="keyword">operator</span><span class="special"><</span></code>
+ satisfies the axioms of <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a> (transitivity,
+ antisymmetry and irreflexivity), <code class="computeroutput"><span class="identifier">optinal</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> is <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">oN</span><span class="special">,</span> <span class="identifier">oN_</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o0</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">0</span><span class="special">));</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o1</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">));</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN</span> <span class="special"><</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// Identity implies equivalence</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o1</span> <span class="special"><</span> <span class="identifier">o1</span><span class="special">)</span> <span class="special">);</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN</span> <span class="special"><</span> <span class="identifier">oN_</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// Two uninitialized are equivalent</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN_</span> <span class="special"><</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special"><</span> <span class="identifier">o0</span> <span class="special">);</span> <span class="comment">// Uninitialized is less than initialized</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o0</span> <span class="special"><</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special"><</span> <span class="identifier">o2</span> <span class="special">)</span> <span class="special">;</span> <span class="comment">// Two initialized compare as (*lhs < *rhs)</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o2</span> <span class="special"><</span> <span class="identifier">o1</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o2</span> <span class="special"><</span> <span class="identifier">o2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_not_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">!=</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
+ <span class="identifier">x</span> <span class="special">==</span>
+ <span class="identifier">y</span> <span class="special">);</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_greater_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">></span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">(</span>
+ <span class="identifier">y</span> <span class="special"><</span>
+ <span class="identifier">x</span> <span class="special">);</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_less_or_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special"><=</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
+ <span class="identifier">y</span> <span class="special"><</span>
+ <span class="identifier">x</span> <span class="special">);</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_greater_or_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">>=</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
+ <span class="identifier">x</span> <span class="special"><</span>
+ <span class="identifier">y</span> <span class="special">);</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_equal_optional_none"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">==</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">none_t</span> <span class="special">)</span>
+ <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">==</span> <span class="special">(</span>
+ <span class="identifier">none_t</span><span class="special">,</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">!</span><span class="identifier">x</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ need not meet requirements of <a href="http://www.sgi.com/tech/stl/EqualityComparable.html" target="_top"><code class="computeroutput"><span class="identifier">EqualityComparable</span></code></a>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_not_equal_optional_none"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">!=</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">none_t</span> <span class="special">)</span>
+ <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">!=</span> <span class="special">(</span>
+ <span class="identifier">none_t</span><span class="special">,</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
+ <span class="identifier">x</span> <span class="special">==</span>
+ <span class="identifier">y</span> <span class="special">);</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_swap_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">swap</span>
+ <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">y</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> Lvalues of type <code class="computeroutput"><span class="identifier">T</span></code> shall be swappable and <code class="computeroutput"><span class="identifier">T</span></code> shall be <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>.
+ </li>
+<li class="listitem">
+<p class="simpara">
+ <span class="bold"><strong>Effects:</strong></span>
+ </p>
+<div class="informaltable"><table class="table">
+<colgroup>
+<col>
+<col>
+<col>
+</colgroup>
+<thead><tr></tr></thead>
+<tbody>
+<tr>
+<td>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ calls <code class="computeroutput"><span class="identifier">swap</span><span class="special">(*(*</span><span class="keyword">this</span><span class="special">),</span> <span class="special">*</span><span class="identifier">rhs</span><span class="special">)</span></code>
+ </p>
+ </td>
+<td>
+ <p>
+ initializes the contained value of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> as if direct-initializing
+ an object of type <code class="computeroutput"><span class="identifier">T</span></code>
+ with the expression <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code>, followed by <code class="computeroutput"><span class="identifier">rhs</span><span class="special">.</span><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>,
+ <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ contains a value and <code class="computeroutput"><span class="identifier">rhs</span></code>
+ does not contain a value
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ does not contain a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ initializes the contained value of <code class="computeroutput"><span class="identifier">rhs</span></code>
+ as if direct-initializing an object of type <code class="computeroutput"><span class="identifier">T</span></code> with the expression
+ <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*(*</span><span class="keyword">this</span><span class="special">))</span></code>,
+ followed by <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value
+ and <code class="computeroutput"><span class="identifier">rhs</span></code> contains
+ a value
+ </p>
+ </td>
+<td>
+ <p>
+ no effect
+ </p>
+ </td>
+</tr>
+</tbody>
+</table></div>
+</li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> The states of <code class="computeroutput"><span class="identifier">x</span></code> and <code class="computeroutput"><span class="identifier">y</span></code>
+ interchanged.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> If both are initialized, whatever
+ <code class="computeroutput"><span class="identifier">swap</span><span class="special">(</span><span class="identifier">T</span><span class="special">&,</span><span class="identifier">T</span><span class="special">&)</span></code>
+ throws. If only one is initialized, whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">(</span><span class="number">12</span><span class="special">);</span>
+<span class="identifier">T</span> <span class="identifier">y</span><span class="special">(</span><span class="number">21</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def0</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def1</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">optX</span><span class="special">(</span><span class="identifier">x</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">optY</span><span class="special">(</span><span class="identifier">y</span><span class="special">);</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">def1</span><span class="special">);</span> <span class="comment">// no-op</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">optX</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def0</span> <span class="special">==</span> <span class="identifier">x</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">optX</span> <span class="special">);</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">optX</span><span class="special">);</span> <span class="comment">// Get back to original values</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">optX</span><span class="special">,</span><span class="identifier">optY</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">optX</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">optY</span> <span class="special">==</span> <span class="identifier">x</span> <span class="special">);</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_swap_optional_reference"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">swap</span>
+ <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&</span> <span class="identifier">y</span>
+ <span class="special">)</span> <span class="keyword">noexcept</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="identifier">x</span></code>
+ refers to what <code class="computeroutput"><span class="identifier">y</span></code> refererred
+ to before the swap (if anything). <code class="computeroutput"><span class="identifier">y</span></code>
+ refers to whatever <code class="computeroutput"><span class="identifier">x</span></code>
+ referred to before the swap.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">(</span><span class="number">12</span><span class="special">);</span>
+<span class="identifier">T</span> <span class="identifier">y</span><span class="special">(</span><span class="number">21</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">opt0</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">optX</span> <span class="special">(</span><span class="identifier">x</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">optY</span> <span class="special">(</span><span class="identifier">y</span><span class="special">);</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">optX</span><span class="special">,</span> <span class="identifier">optY</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">optX</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">y</span><span class="special">));</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">optY</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">x</span><span class="special">));</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">opt0</span><span class="special">,</span> <span class="identifier">optX</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt0</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">optX</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">opt0</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">y</span><span class="special">));</span>
+</pre>
+ [endsect]
+ </li>
+</ul></div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2016 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="detailed_semantics____optional_references.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="header__boost_optional_hpp_.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics____optional_references.html b/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics____optional_references.html
new file mode 100644
index 0000000..7eedfab
--- /dev/null
+++ b/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics____optional_references.html
@@ -0,0 +1,57 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Detailed Semantics -- Optional References</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../../../optional/reference/header__boost_optional_optional_hpp_.html" title="Header <boost/optional/optional.hpp>">
+<link rel="prev" href="detailed_semantics____optional_values.html" title="Detailed Semantics -- Optional Values">
+<link rel="next" href="detailed_semantics____free_functions.html" title="Detailed Semantics -- Free Functions">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td>
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+<td align="center"><a href="../../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
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+<a accesskey="p" href="detailed_semantics____optional_values.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="detailed_semantics____free_functions.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.header__boost_optional_optional_hpp_.detailed_semantics____optional_references"></a><a class="link" href="detailed_semantics____optional_references.html" title="Detailed Semantics -- Optional References">Detailed
+ Semantics -- Optional References</a>
+</h4></div></div></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_default_ctor"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><&>::</span><span class="identifier">optional</span><span class="special">()</span>
+ <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><&>::</span><span class="identifier">optional</span><span class="special">(</span><span class="identifier">none_t</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> refers to nothing.
+ </li></ul></div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2016 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="detailed_semantics____optional_values.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="detailed_semantics____free_functions.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics____optional_values.html b/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics____optional_values.html
new file mode 100644
index 0000000..5fd6391
--- /dev/null
+++ b/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics____optional_values.html
@@ -0,0 +1,1983 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Detailed Semantics -- Optional Values</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../../../optional/reference/header__boost_optional_optional_hpp_.html" title="Header <boost/optional/optional.hpp>">
+<link rel="prev" href="header_optional_optional_refs.html" title="Optional References">
+<link rel="next" href="detailed_semantics____optional_references.html" title="Detailed Semantics -- Optional References">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="header_optional_optional_refs.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="detailed_semantics____optional_references.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.header__boost_optional_optional_hpp_.detailed_semantics____optional_values"></a><a class="link" href="detailed_semantics____optional_values.html" title="Detailed Semantics -- Optional Values">Detailed
+ Semantics -- Optional Values</a>
+</h4></div></div></div>
+<div class="note"><table border="0" summary="Note">
+<tr>
+<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../../doc/src/images/note.png"></td>
+<th align="left">Note</th>
+</tr>
+<tr><td align="left" valign="top"><p>
+ The following section contains various <code class="computeroutput"><span class="identifier">assert</span><span class="special">()</span></code> which are used only to show the postconditions
+ as sample code. It is not implied that the type <code class="computeroutput"><span class="identifier">T</span></code>
+ must support each particular expression but that if the expression is
+ supported, the implied condition holds.
+ </p></td></tr>
+</table></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">()</span>
+ <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Default-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">uninitialized</span>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> T's default constructor <span class="underline">is not</span> called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">def</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_none_t"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">none_t</span> <span class="special">)</span>
+ <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Constructs an <code class="computeroutput"><span class="identifier">optional</span></code> uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">uninitialized</span>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>'s
+ default constructor <span class="underline">is not</span> called.
+ The expression <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code>
+ denotes an instance of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none_t</span></code>
+ that can be used as the parameter.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">none</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">n</span><span class="special">(</span><span class="identifier">none</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">n</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_copy_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>
+ is <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Directly-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
+ and its value is a <span class="emphasis"><em>copy</em></span> of <code class="computeroutput"><span class="identifier">v</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span></code> throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span></code> is called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">);</span></code> in that case, this constructor
+ has no effect.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">ref</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Directly-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
+ and its value is an instance of an internal type wrapping the reference
+ <code class="computeroutput"><span class="identifier">ref</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">vref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">vref</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">++</span> <span class="identifier">v</span> <span class="special">;</span> <span class="comment">// mutate referee</span>
+<span class="identifier">assert</span> <span class="special">(*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span><span class="special">);</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_move_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="identifier">v</span>
+ <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>
+ is <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Directly-Move-Constructs an
+ <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
+ and its value is move-constructed from <code class="computeroutput"><span class="identifier">v</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code>
+ is called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">);</span></code>
+ in that case, the state of <code class="computeroutput"><span class="identifier">v</span></code>
+ is determined by exception safety guarantees for <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span><span class="special">&&)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v1</span><span class="special">,</span> <span class="identifier">v2</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">v1</span><span class="special">));</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v2</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">T</span><span class="special">&&</span>
+ <span class="identifier">ref</span> <span class="special">)</span>
+ <span class="special">=</span> <span class="keyword">delete</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> This constructor is deleted
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_bool_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span>
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
+ <span class="special">::</span><span class="identifier">optional</span><span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span>
+ <span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">v</span> <span class="special">)</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ If condition is true, same as:
+ </li></ul></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
+ <span class="special">::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ otherwise, same as:
+ </li></ul></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">()</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
+ <span class="special">::</span><span class="identifier">optional</span><span class="special">()</span></code>
+ </p></blockquote></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">optional</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">rhs</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_copy_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>
+ is <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Copy-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If rhs is initialized,
+ <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is a <span class="emphasis"><em>copy</em></span> of the
+ value of <code class="computeroutput"><span class="identifier">rhs</span></code>; else
+ <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span></code> throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If rhs is initialized, <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code>
+ is called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">);</span></code> in that case, this constructor
+ has no effect.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">uninit</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">uninit</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init</span><span class="special">(</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">init</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">init</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">optional</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span>
+ <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Copy-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is another reference to the same object
+ referenced by <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>;
+ else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, both <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> will refer to the same object
+ (they alias).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">uninit</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">uninit</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span>
+
+<span class="identifier">T</span> <span class="identifier">v</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">ref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init</span><span class="special">(</span><span class="identifier">ref</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">init</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">v</span> <span class="special">=</span> <span class="number">3</span> <span class="special">;</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init2</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_move_constructor_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span> </code><span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">optional</span><span class="special">&&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">(</span></code><span class="emphasis"><em>see below</em></span><code class="computeroutput"><span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>
+ is <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Move-constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is move constructed from <code class="computeroutput"><span class="identifier">rhs</span></code>; else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> The expression inside <code class="computeroutput"><span class="keyword">noexcept</span></code> is equivalent to <code class="computeroutput"><span class="identifier">is_nothrow_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="special">&&</span>
+ <span class="special">)</span></code> is called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">);</span></code>
+ in that case, <code class="computeroutput"><span class="identifier">rhs</span></code> remains
+ initialized and the value of <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is determined by exception safety
+ of <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span><span class="special">&&)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">uninit</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">uninit</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">init</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">uniqye_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="keyword">new</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">init</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">init</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="keyword">nullptr</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">init2</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">optional</span> <span class="special">&&</span>
+ <span class="identifier">rhs</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Move-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is another reference to the same object
+ referenced by <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>;
+ else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, both <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> will refer to the same object
+ (they alias).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">uninit</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">uninit</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span>
+
+<span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">v</span><span class="special">(</span><span class="keyword">new</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">init</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">init</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="special">*</span><span class="identifier">v</span> <span class="special">=</span> <span class="number">3</span> <span class="special">;</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init2</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Copy-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is a <span class="emphasis"><em>copy</em></span> of the
+ value of rhs converted to type <code class="computeroutput"><span class="identifier">T</span></code>;
+ else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span></code> throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span></code> is called if <code class="computeroutput"><span class="identifier">rhs</span></code> is initialized, which requires
+ a valid conversion from <code class="computeroutput"><span class="identifier">U</span></code>
+ to <code class="computeroutput"><span class="identifier">T</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">);</span></code> in that case, this constructor
+ has no effect.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">x</span><span class="special">(</span><span class="number">123.4</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">==</span> <span class="number">123.4</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">y</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span><span class="special">(</span> <span class="special">*</span><span class="identifier">y</span> <span class="special">==</span> <span class="number">123</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_move_constructor_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&&</span>
+ <span class="identifier">rhs</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Move-constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is move-constructed from <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>;
+ else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">)</span></code>
+ is called if <code class="computeroutput"><span class="identifier">rhs</span></code> is
+ initialized, which requires a valid conversion from <code class="computeroutput"><span class="identifier">U</span></code>
+ to <code class="computeroutput"><span class="identifier">T</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">);</span></code>
+ in that case, <code class="computeroutput"><span class="identifier">rhs</span></code> remains
+ initialized and the value of <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is determined by exception safety
+ guarantee of <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span>
+ <span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">x</span><span class="special">(</span><span class="number">123.4</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">==</span> <span class="number">123.4</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">y</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">x</span><span class="special">))</span> <span class="special">;</span>
+<span class="identifier">assert</span><span class="special">(</span> <span class="special">*</span><span class="identifier">y</span> <span class="special">==</span> <span class="number">123</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_factory"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">InPlaceFactory</span><span class="special">></span>
+ <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">InPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">TypedInPlaceFactory</span><span class="special">></span>
+ <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">TypedInPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Constructs an <code class="computeroutput"><span class="identifier">optional</span></code> with a value of <code class="computeroutput"><span class="identifier">T</span></code> obtained from the factory.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
+ and its value is <span class="emphasis"><em>directly given</em></span> from the factory
+ <code class="computeroutput"><span class="identifier">f</span></code> (i.e., the value
+ <span class="underline">is not copied</span>).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever the <code class="computeroutput"><span class="identifier">T</span></code> constructor called by the factory
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> See <a class="link" href="../../tutorial/in_place_factories.html" title="In-Place Factories">In-Place
+ Factories</a>
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during the call to the <code class="computeroutput"><span class="identifier">T</span></code>
+ constructor used by the factory; in that case, this constructor has
+ no effect.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">C</span> <span class="special">{</span> <span class="identifier">C</span> <span class="special">(</span> <span class="keyword">char</span><span class="special">,</span> <span class="keyword">double</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">)</span> <span class="special">;</span> <span class="special">}</span> <span class="special">;</span>
+
+<span class="identifier">C</span> <span class="identifier">v</span><span class="special">(</span><span class="char">'A'</span><span class="special">,</span><span class="number">123.4</span><span class="special">,</span><span class="string">"hello"</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">C</span><span class="special">></span> <span class="identifier">x</span><span class="special">(</span> <span class="identifier">in_place</span> <span class="special">(</span><span class="char">'A'</span><span class="special">,</span> <span class="number">123.4</span><span class="special">,</span> <span class="string">"hello"</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// InPlaceFactory used</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">C</span><span class="special">></span> <span class="identifier">y</span><span class="special">(</span> <span class="identifier">in_place</span><span class="special"><</span><span class="identifier">C</span><span class="special">>(</span><span class="char">'A'</span><span class="special">,</span> <span class="number">123.4</span><span class="special">,</span> <span class="string">"hello"</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// TypedInPlaceFactory used</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">y</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_equal_none_t"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">none_t</span>
+ <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized destroys its contained
+ value.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_equal_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">rhs</span> <span class="special">)</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Assigns the value <code class="computeroutput"><span class="identifier">rhs</span></code> to an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized and its value is
+ a <span class="emphasis"><em>copy</em></span> of <code class="computeroutput"><span class="identifier">rhs</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span></code> or <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s assignment operator is used,
+ otherwise, its copy-constructor is used.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> In the event of
+ an exception, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is unchanged and its value unspecified
+ as far as <code class="computeroutput"><span class="identifier">optional</span></code>
+ is concerned (it is up to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <code class="computeroutput"><span class="keyword">operator</span><span class="special">=()</span></code>).
+ If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initially uninitialized and <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <span class="emphasis"><em>copy constructor</em></span> fails, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is left properly uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">T</span> <span class="identifier">y</span><span class="special">;</span>
+<span class="identifier">def</span> <span class="special">=</span> <span class="identifier">y</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">y</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> (Re)binds the wrapped reference.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized and it references
+ the same object referenced by <code class="computeroutput"><span class="identifier">rhs</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized, it is <span class="emphasis"><em>rebound</em></span>
+ to the new object. See <a class="link" href="../../tutorial/rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">here</a>
+ for details on this behavior.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">ra</span><span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">def</span> <span class="special">=</span> <span class="identifier">rb</span> <span class="special">;</span> <span class="comment">// binds 'def' to 'b' through 'rb'</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">b</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">*</span><span class="identifier">def</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span> <span class="comment">// changes the value of 'b' to a copy of the value of 'a'</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">b</span> <span class="special">==</span> <span class="identifier">a</span> <span class="special">)</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">c</span> <span class="special">=</span> <span class="number">3</span><span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">rc</span> <span class="special">=</span> <span class="identifier">c</span> <span class="special">;</span>
+<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">rc</span> <span class="special">;</span> <span class="comment">// REBINDS to 'c' through 'rc'</span>
+<span class="identifier">c</span> <span class="special">=</span> <span class="number">4</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="number">4</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_move_equal_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Moves the value <code class="computeroutput"><span class="identifier">rhs</span></code> to an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized and its value is
+ moved from <code class="computeroutput"><span class="identifier">rhs</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code>
+ or <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span> <span class="special">&&)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s move-assignment operator is used,
+ otherwise, its move-constructor is used.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> In the event of
+ an exception, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is unchanged and its value unspecified
+ as far as <code class="computeroutput"><span class="identifier">optional</span></code>
+ is concerned (it is up to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <code class="computeroutput"><span class="keyword">operator</span><span class="special">=()</span></code>).
+ If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initially uninitialized and <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <span class="emphasis"><em>move constructor</em></span> fails, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is left properly uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">T</span> <span class="identifier">y1</span><span class="special">,</span> <span class="identifier">y2</span><span class="special">,</span> <span class="identifier">yR</span><span class="special">;</span>
+<span class="identifier">def</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">y1</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">yR</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">y2</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">yR</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="special">=</span>
+ <span class="keyword">delete</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> This assignment operator is
+ deleted.
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_equal_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">rhs</span> <span class="special">)</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ is <a href="../../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a> and <code class="computeroutput"><span class="identifier">CopyAssignable</span></code>.
+ </li>
+<li class="listitem">
+<p class="simpara">
+ <span class="bold"><strong>Effects:</strong></span>
+ </p>
+<div class="informaltable"><table class="table">
+<colgroup>
+<col>
+<col>
+<col>
+</colgroup>
+<thead><tr></tr></thead>
+<tbody>
+<tr>
+<td>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ assigns <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>
+ to the contained value
+ </p>
+ </td>
+<td>
+ <p>
+ initializes the contained value as if direct-initializing
+ an object of type <code class="computeroutput"><span class="identifier">T</span></code>
+ with <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ does not contain a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ destroys the contained value by calling <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>
+ </p>
+ </td>
+<td>
+ <p>
+ no effect
+ </p>
+ </td>
+</tr>
+</tbody>
+</table></div>
+</li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>;
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> If any exception
+ is thrown, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="identifier">rhs</span></code>
+ remains unchanged. If an exception is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s copy constructor, no effect.
+ If an exception is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ copy assignment, the state of its contained value is as defined by
+ the exception safety guarantee of <code class="computeroutput"><span class="identifier">T</span></code>'s
+ copy assignment.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+
+<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">def</span> <span class="special">)</span> <span class="special">;</span>
+<span class="comment">// previous value (copy of 'v') destroyed from within 'opt'.</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
+ <span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> (Re)binds thee wrapped reference.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and it references the same object referenced by <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>;
+ otherwise, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is uninitialized (and references no object).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized and so is <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>,
+ <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is <span class="emphasis"><em>rebound</em></span> to the new object. See <a class="link" href="../../tutorial/rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">here</a>
+ for details on this behavior.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">ora</span><span class="special">(</span><span class="identifier">ra</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">orb</span><span class="special">(</span><span class="identifier">rb</span><span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">def</span> <span class="special">=</span> <span class="identifier">orb</span> <span class="special">;</span> <span class="comment">// binds 'def' to 'b' through 'rb' wrapped within 'orb'</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">b</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">*</span><span class="identifier">def</span> <span class="special">=</span> <span class="identifier">ora</span> <span class="special">;</span> <span class="comment">// changes the value of 'b' to a copy of the value of 'a'</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">b</span> <span class="special">==</span> <span class="identifier">a</span> <span class="special">)</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">c</span> <span class="special">=</span> <span class="number">3</span><span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">rc</span> <span class="special">=</span> <span class="identifier">c</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">orc</span><span class="special">(</span><span class="identifier">rc</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">ora</span> <span class="special">=</span> <span class="identifier">orc</span> <span class="special">;</span> <span class="comment">// REBINDS ora to 'c' through 'rc'</span>
+<span class="identifier">c</span> <span class="special">=</span> <span class="number">4</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">ora</span> <span class="special">==</span> <span class="number">4</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_move_equal_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">(</span></code><span class="emphasis"><em>see below</em></span><code class="computeroutput"><span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ is <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>
+ and <code class="computeroutput"><span class="identifier">MoveAssignable</span></code>.
+ </li>
+<li class="listitem">
+<p class="simpara">
+ <span class="bold"><strong>Effects:</strong></span>
+ </p>
+<div class="informaltable"><table class="table">
+<colgroup>
+<col>
+<col>
+<col>
+</colgroup>
+<thead><tr></tr></thead>
+<tbody>
+<tr>
+<td>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ assigns <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code> to the contained value
+ </p>
+ </td>
+<td>
+ <p>
+ initializes the contained value as if direct-initializing
+ an object of type <code class="computeroutput"><span class="identifier">T</span></code>
+ with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ does not contain a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ destroys the contained value by calling <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>
+ </p>
+ </td>
+<td>
+ <p>
+ no effect
+ </p>
+ </td>
+</tr>
+</tbody>
+</table></div>
+</li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>;
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> The expression inside <code class="computeroutput"><span class="keyword">noexcept</span></code> is equivalent to <code class="computeroutput"><span class="identifier">is_nothrow_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span> <span class="special">&&</span>
+ <span class="identifier">is_nothrow_move_assignable</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> If any exception
+ is thrown, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="identifier">rhs</span></code>
+ remains unchanged. If an exception is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s move constructor, the state of
+ <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>
+ is determined by the exception safety guarantee of <code class="computeroutput"><span class="identifier">T</span></code>'s
+ move constructor. If an exception is thrown during the call to T's
+ move-assignment, the state of <code class="computeroutput"><span class="special">**</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is determined by the exception
+ safety guarantee of T's move assignment.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+
+<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">def</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
+ <span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Same as <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">rhs</span> <span class="special">)</span></code>.
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_equal_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+<p class="simpara">
+ <span class="bold"><strong>Effect:</strong></span>
+ </p>
+<div class="informaltable"><table class="table">
+<colgroup>
+<col>
+<col>
+<col>
+</colgroup>
+<thead><tr></tr></thead>
+<tbody>
+<tr>
+<td>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ assigns <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>
+ to the contained value
+ </p>
+ </td>
+<td>
+ <p>
+ initializes the contained value as if direct-initializing
+ an object of type <code class="computeroutput"><span class="identifier">T</span></code>
+ with <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ does not contain a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ destroys the contained value by calling <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>
+ </p>
+ </td>
+<td>
+ <p>
+ no effect
+ </p>
+ </td>
+</tr>
+</tbody>
+</table></div>
+</li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> If any exception
+ is thrown, the result of the expression <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code> remains unchanged. If an exception
+ is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ constructor, no effect. If an exception is thrown during the call to
+ <code class="computeroutput"><span class="identifier">T</span></code>'s assignment, the
+ state of its contained value is as defined by the exception safety
+ guarantee of <code class="computeroutput"><span class="identifier">T</span></code>'s copy
+ assignment.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt0</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">opt1</span><span class="special">;</span>
+
+<span class="identifier">opt1</span> <span class="special">=</span> <span class="identifier">opt0</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt1</span> <span class="special">==</span> <span class="keyword">static_cast</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_move_equal_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+<p class="simpara">
+ <span class="bold"><strong>Effect:</strong></span>
+ </p>
+<div class="informaltable"><table class="table">
+<colgroup>
+<col>
+<col>
+<col>
+</colgroup>
+<thead><tr></tr></thead>
+<tbody>
+<tr>
+<td>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ assigns <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code> to the contained value
+ </p>
+ </td>
+<td>
+ <p>
+ initializes the contained value as if direct-initializing
+ an object of type <code class="computeroutput"><span class="identifier">T</span></code>
+ with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ does not contain a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ destroys the contained value by calling <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>
+ </p>
+ </td>
+<td>
+ <p>
+ no effect
+ </p>
+ </td>
+</tr>
+</tbody>
+</table></div>
+</li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> If any exception
+ is thrown, the result of the expression <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code> remains unchanged. If an exception
+ is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ constructor, no effect. If an exception is thrown during the call to
+ <code class="computeroutput"><span class="identifier">T</span></code>'s assignment, the
+ state of its contained value is as defined by the exception safety
+ guarantee of <code class="computeroutput"><span class="identifier">T</span></code>'s copy
+ assignment.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt0</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">opt1</span><span class="special">;</span>
+
+<span class="identifier">opt1</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">opt0</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt0</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt1</span> <span class="special">)</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt1</span> <span class="special">==</span> <span class="keyword">static_cast</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_emplace"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span>
+ <span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">emplace</span><span class="special">(</span>
+ <span class="identifier">Args</span><span class="special">...&&</span>
+ <span class="identifier">args</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> The compiler supports rvalue
+ references and variadic templates.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized calls <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span> <span class="special">=</span> <span class="identifier">none</span></code>.
+ Then initializes in-place the contained value as if direct-initializing
+ an object of type <code class="computeroutput"><span class="identifier">T</span></code>
+ with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">Args</span><span class="special">>(</span><span class="identifier">args</span><span class="special">)...</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever the selected <code class="computeroutput"><span class="identifier">T</span></code>'s constructor throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> If an exception
+ is thrown during the initialization of <code class="computeroutput"><span class="identifier">T</span></code>,
+ <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is <span class="emphasis"><em>uninitialized</em></span>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ need not be <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>
+ or <code class="computeroutput"><span class="identifier">MoveAssignable</span></code>.
+ On compilers that do not support variadic templates, the signature
+ falls back to two overloads:<code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span>
+ <span class="identifier">Arg</span><span class="special">></span>
+ <span class="keyword">void</span> <span class="identifier">emplace</span><span class="special">(</span><span class="identifier">Arg</span><span class="special">&&</span> <span class="identifier">arg</span><span class="special">)</span></code> and <code class="computeroutput"><span class="keyword">void</span>
+ <span class="identifier">emplace</span><span class="special">()</span></code>.
+ On compilers that do not support rvalue references, the signature falls
+ back to three overloads: taking <code class="computeroutput"><span class="keyword">const</span></code>
+ and non-<code class="computeroutput"><span class="keyword">const</span></code> lvalue reference,
+ and third with empty function argument list.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">;</span>
+<span class="identifier">opt</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">(</span><span class="number">0</span><span class="special">);</span> <span class="comment">// create in-place using ctor T(int)</span>
+<span class="identifier">opt</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">();</span> <span class="comment">// destroy previous and default-construct another T</span>
+<span class="identifier">opt</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> <span class="comment">// destroy and copy-construct in-place (no assignment called)</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_equal_factory"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">InPlaceFactory</span><span class="special">></span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">InPlaceFactory</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">f</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">TypedInPlaceFactory</span><span class="special">></span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">TypedInPlaceFactory</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">f</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Assigns an <code class="computeroutput"><span class="identifier">optional</span></code>
+ with a value of <code class="computeroutput"><span class="identifier">T</span></code> obtained
+ from the factory.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
+ and its value is <span class="emphasis"><em>directly given</em></span> from the factory
+ <code class="computeroutput"><span class="identifier">f</span></code> (i.e., the value
+ <span class="underline">is not copied</span>).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever the <code class="computeroutput"><span class="identifier">T</span></code> constructor called by the factory
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> See <a class="link" href="../../tutorial/in_place_factories.html" title="In-Place Factories">In-Place
+ Factories</a>
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during the call to the <code class="computeroutput"><span class="identifier">T</span></code>
+ constructor used by the factory; in that case, the <code class="computeroutput"><span class="identifier">optional</span></code>
+ object will be reset to be <span class="emphasis"><em>uninitialized</em></span>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_reset_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">reset</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Deprecated:</strong></span> same as <code class="computeroutput"><span class="keyword">operator</span><span class="special">=</span>
+ <span class="special">(</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">v</span><span class="special">)</span>
+ <span class="special">;</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_reset"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">reset</span><span class="special">()</span> <span class="keyword">noexcept</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Deprecated:</strong></span> Same as <code class="computeroutput"><span class="keyword">operator</span><span class="special">=(</span>
+ <span class="identifier">none_t</span> <span class="special">);</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_get"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get</span><span class="special">()</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">get</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get</span>
+ <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span>
+ <span class="special">&)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> A reference to the contained
+ value
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The requirement is asserted
+ via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">get</span><span class="special">()</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">get</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get</span>
+ <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="special">&)</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <span class="underline">The</span>
+ reference contained.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The requirement is asserted
+ via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_asterisk"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">*()</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">*()</span> <span class="special">&;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> A reference to the contained
+ value
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The requirement is asserted
+ via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
+ On compilers that do not support ref-qualifiers on member functions
+ these two overloads are replaced with the classical two: a <code class="computeroutput"><span class="keyword">const</span></code> and non-<code class="computeroutput"><span class="keyword">const</span></code>
+ member functions.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">);</span>
+<span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">u</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">opt</span><span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">u</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">T</span> <span class="identifier">w</span> <span class="special">;</span>
+<span class="special">*</span><span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">w</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">w</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_asterisk_move"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span><span class="special">*()</span> <span class="special">&&;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">val</span><span class="special">);</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The requirement is asserted
+ via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
+ On compilers that do not support ref-qualifiers on member functions
+ this overload is not present.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">*()</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">*()</span>
+ <span class="special">&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">*()</span>
+ <span class="special">&&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <span class="underline">The</span>
+ reference contained.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The requirement is asserted
+ via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
+ On compilers that do not support ref-qualifiers on member functions
+ these three overloads are replaced with the classical two: a <code class="computeroutput"><span class="keyword">const</span></code> and non-<code class="computeroutput"><span class="keyword">const</span></code>
+ member functions.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">vref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">vref</span> <span class="special">);</span>
+<span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">vref2</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">opt</span><span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">vref2</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">++</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span><span class="special">()</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span><span class="special">()</span> <span class="special">&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">?</span> <span class="special">*</span><span class="identifier">val</span> <span class="special">:</span> <span class="keyword">throw</span> <span class="identifier">bad_optional_access</span><span class="special">();</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ ref-qualifiers on member functions these two overloads are replaced
+ with the classical two: a <code class="computeroutput"><span class="keyword">const</span></code>
+ and non-<code class="computeroutput"><span class="keyword">const</span></code> member functions.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o0</span><span class="special">,</span> <span class="identifier">o1</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span><span class="special">.</span><span class="identifier">value</span><span class="special">()</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">);</span>
+
+<span class="keyword">try</span> <span class="special">{</span>
+ <span class="identifier">o0</span><span class="special">.</span><span class="identifier">value</span><span class="special">();</span> <span class="comment">// throws</span>
+ <span class="identifier">assert</span> <span class="special">(</span> <span class="keyword">false</span> <span class="special">);</span>
+<span class="special">}</span>
+<span class="keyword">catch</span><span class="special">(</span><span class="identifier">bad_optional_access</span><span class="special">&)</span> <span class="special">{</span>
+ <span class="identifier">assert</span> <span class="special">(</span> <span class="keyword">true</span> <span class="special">);</span>
+<span class="special">}</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_value_move"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span><span class="special">()</span> <span class="special">&&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">?</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">val</span><span class="special">)</span> <span class="special">:</span> <span class="keyword">throw</span> <span class="identifier">bad_optional_access</span><span class="special">();</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ ref-qualifiers on member functions this overload is not present.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_value_or"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or</span><span class="special">(</span><span class="identifier">U</span> <span class="special">&&</span>
+ <span class="identifier">v</span><span class="special">)</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">if</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="special">**</span><span class="keyword">this</span><span class="special">;</span> <span class="keyword">else</span> <span class="keyword">return</span>
+ <span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">);</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> If <code class="computeroutput"><span class="identifier">T</span></code>
+ is not <a href="../../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a> or <code class="computeroutput"><span class="identifier">U</span> <span class="special">&&</span></code>
+ is not convertible to <code class="computeroutput"><span class="identifier">T</span></code>,
+ the program is ill-formed.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ ref-qualifiers on member functions this overload is replaced with the
+ <code class="computeroutput"><span class="keyword">const</span></code>-qualified member
+ function. On compilers without rvalue reference support the type of
+ <code class="computeroutput"><span class="identifier">v</span></code> becomes <code class="computeroutput"><span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span></code>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_value_or_move"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or</span><span class="special">(</span><span class="identifier">U</span> <span class="special">&&</span>
+ <span class="identifier">v</span><span class="special">)</span>
+ <span class="special">&&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">if</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(**</span><span class="keyword">this</span><span class="special">);</span> <span class="keyword">else</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">);</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> If <code class="computeroutput"><span class="identifier">T</span></code>
+ is not <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>
+ or <code class="computeroutput"><span class="identifier">U</span> <span class="special">&&</span></code>
+ is not convertible to <code class="computeroutput"><span class="identifier">T</span></code>,
+ the program is ill-formed.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ ref-qualifiers on member functions this overload is not present.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_value_or_call"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">F</span> <span class="identifier">f</span><span class="special">)</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ is <a href="../../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a> and <code class="computeroutput"><span class="identifier">F</span></code> models a <a href="http://www.sgi.com/tech/stl/Generator.html" target="_top"><code class="computeroutput"><span class="identifier">Generator</span></code></a> whose result type
+ is convertible to <code class="computeroutput"><span class="identifier">T</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> <code class="computeroutput"><span class="keyword">if</span>
+ <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="special">**</span><span class="keyword">this</span><span class="special">;</span> <span class="keyword">else</span> <span class="keyword">return</span> <span class="identifier">f</span><span class="special">();</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ ref-qualifiers on member functions this overload is replaced with the
+ <code class="computeroutput"><span class="keyword">const</span></code>-qualified member
+ function.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">complain_and_0</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="identifier">clog</span> <span class="special"><<</span> <span class="string">"no value returned, using default"</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span>
+ <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
+<span class="special">}</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">o1</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">oN</span> <span class="special">=</span> <span class="identifier">none</span><span class="special">;</span>
+
+<span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="identifier">o1</span><span class="special">.</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">complain_and_0</span><span class="special">);</span> <span class="comment">// fun not called</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">i</span> <span class="special">==</span> <span class="number">1</span><span class="special">);</span>
+
+<span class="keyword">int</span> <span class="identifier">j</span> <span class="special">=</span> <span class="identifier">oN</span><span class="special">.</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">complain_and_0</span><span class="special">);</span> <span class="comment">// fun called</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">i</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_value_or_call_move"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">F</span> <span class="identifier">f</span><span class="special">)</span> <span class="special">&&</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ is <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>
+ and <code class="computeroutput"><span class="identifier">F</span></code> models a <a href="http://www.sgi.com/tech/stl/Generator.html" target="_top"><code class="computeroutput"><span class="identifier">Generator</span></code></a>
+ whose result type is convertible to <code class="computeroutput"><span class="identifier">T</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> <code class="computeroutput"><span class="keyword">if</span>
+ <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(**</span><span class="keyword">this</span><span class="special">);</span> <span class="keyword">else</span> <span class="keyword">return</span>
+ <span class="identifier">f</span><span class="special">();</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ ref-qualifiers on member functions this overload is not present.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_get_value_or_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_value_or</span><span class="special">(</span>
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="keyword">default</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_value_or</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&</span> <span class="keyword">default</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">get_optional_value_or</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">o</span><span class="special">,</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="keyword">default</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get_optional_value_or</span>
+ <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>&</span>
+ <span class="identifier">o</span><span class="special">,</span>
+ <span class="identifier">T</span><span class="special">&</span>
+ <span class="keyword">default</span> <span class="special">)</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Deprecated:</strong></span> Use <code class="computeroutput"><span class="identifier">value_or</span><span class="special">()</span></code> instead.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> A reference to the contained
+ value, if any, or <code class="computeroutput"><span class="keyword">default</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">,</span> <span class="identifier">z</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span><span class="special">;</span>
+<span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">=</span> <span class="identifier">def</span><span class="special">.</span><span class="identifier">get_value_or</span><span class="special">(</span><span class="identifier">z</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">y</span> <span class="special">==</span> <span class="identifier">z</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">);</span>
+<span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">u</span> <span class="special">=</span> <span class="identifier">get_optional_value_or</span><span class="special">(</span><span class="identifier">opt</span><span class="special">,</span><span class="identifier">z</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">u</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">u</span> <span class="special">!=</span> <span class="identifier">z</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_get_ptr"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_ptr</span><span class="special">()</span>
+ <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">*</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">*</span>
+ <span class="identifier">get_pointer</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">*</span> <span class="identifier">get_pointer</span>
+ <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">></span>
+ <span class="special">&)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized, a pointer to the
+ contained value; else <code class="computeroutput"><span class="number">0</span></code>
+ (<span class="emphasis"><em>null</em></span>).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The contained value is permanently
+ stored within <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>,
+ so you should not hold nor delete this pointer
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span> <span class="identifier">copt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">T</span><span class="special">*</span> <span class="identifier">p</span> <span class="special">=</span> <span class="identifier">opt</span><span class="special">.</span><span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">;</span>
+<span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">cp</span> <span class="special">=</span> <span class="identifier">copt</span><span class="special">.</span><span class="identifier">get_ptr</span><span class="special">();</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">p</span> <span class="special">==</span> <span class="identifier">get_pointer</span><span class="special">(</span><span class="identifier">opt</span><span class="special">)</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">cp</span> <span class="special">==</span> <span class="identifier">get_pointer</span><span class="special">(</span><span class="identifier">copt</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_arrow"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code>
+ <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span> <span class="special">->()</span>
+ <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">*</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span></code> <span class="emphasis"><em>(not a ref)</em></span><code class="computeroutput"><span class="special">>::</span><span class="keyword">operator</span>
+ <span class="special">->()</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> A pointer to the contained
+ value.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The requirement is asserted
+ via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">X</span> <span class="special">{</span> <span class="keyword">int</span> <span class="identifier">mdata</span> <span class="special">;</span> <span class="special">}</span> <span class="special">;</span>
+<span class="identifier">X</span> <span class="identifier">x</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">X</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span><span class="identifier">x</span><span class="special">);</span>
+<span class="identifier">opt</span><span class="special">-></span><span class="identifier">mdata</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_bool"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span>
+ <span class="keyword">bool</span><span class="special">()</span>
+ <span class="keyword">const</span> <span class="keyword">noexcept</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">!=</span> <span class="number">0</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ explicit conversion operators this falls back to safe-bool idiom.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">def</span> <span class="special">==</span> <span class="number">0</span> <span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt</span> <span class="special">!=</span> <span class="number">0</span> <span class="special">);</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_not"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">!()</span> <span class="keyword">noexcept</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized, <code class="computeroutput"><span class="keyword">true</span></code>; else <code class="computeroutput"><span class="keyword">false</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> This operator is provided for
+ those compilers which can't use the <span class="emphasis"><em>unspecified-bool-type
+ operator</em></span> in certain boolean contexts.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">opt</span> <span class="special">);</span>
+<span class="special">*</span><span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">some_T</span> <span class="special">;</span>
+
+<span class="comment">// Notice the "double-bang" idiom here.</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!!</span><span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_is_initialized"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">is_initialized</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Deprecated:</strong></span> Same as <code class="computeroutput"><span class="keyword">explicit</span> <span class="keyword">operator</span>
+ <span class="keyword">bool</span> <span class="special">()</span>
+ <span class="special">;</span></code>
+ </li></ul></div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2016 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="header_optional_optional_refs.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="detailed_semantics____optional_references.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html b/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html
new file mode 100644
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+++ b/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___free_functions.html
@@ -0,0 +1,521 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Detailed Semantics - Free Functions</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
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+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.header__boost_optional_optional_hpp_.detailed_semantics___free_functions"></a><a class="link" href="detailed_semantics___free_functions.html" title="Detailed Semantics - Free Functions">Detailed
+ Semantics - Free Functions</a>
+</h4></div></div></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_make_optional_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">make_optional</span><span class="special">(</span>
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">v</span><span class="special">)</span></code> for the <span class="emphasis"><em>deduced</em></span>
+ type <code class="computeroutput"><span class="identifier">T</span></code> of <code class="computeroutput"><span class="identifier">v</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">foo</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">foo</span> <span class="special">(</span> <span class="identifier">make_optional</span><span class="special">(</span><span class="number">1</span><span class="special">+</span><span class="number">1</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span> <span class="comment">// Creates an optional<int></span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_make_optional_rvalue"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">decay_t</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span>
+ <span class="identifier">make_optional</span><span class="special">(</span>
+ <span class="identifier">T</span> <span class="special">&&</span>
+ <span class="identifier">v</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">decay_t</span><span class="special"><</span><span class="identifier">T</span><span class="special">>>(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">v</span><span class="special">))</span></code> for the <span class="emphasis"><em>deduced</em></span>
+ type <code class="computeroutput"><span class="identifier">T</span></code> of <code class="computeroutput"><span class="identifier">v</span></code>.
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_make_optional_bool_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">make_optional</span><span class="special">(</span>
+ <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="identifier">condition</span><span class="special">,</span> <span class="identifier">v</span><span class="special">)</span></code> for the <span class="emphasis"><em>deduced</em></span>
+ type <code class="computeroutput"><span class="identifier">T</span></code> of <code class="computeroutput"><span class="identifier">v</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">calculate_foo</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="keyword">double</span> <span class="identifier">val</span> <span class="special">=</span> <span class="identifier">compute_foo</span><span class="special">();</span>
+ <span class="keyword">return</span> <span class="identifier">make_optional</span><span class="special">(</span><span class="identifier">is_not_nan_and_finite</span><span class="special">(</span><span class="identifier">val</span><span class="special">),</span><span class="identifier">val</span><span class="special">);</span>
+<span class="special">}</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">v</span> <span class="special">=</span> <span class="identifier">calculate_foo</span><span class="special">();</span>
+<span class="keyword">if</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">v</span> <span class="special">)</span>
+ <span class="identifier">error</span><span class="special">(</span><span class="string">"foo wasn't computed"</span><span class="special">);</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_make_optional_bool_rvalue"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">decay_t</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span>
+ <span class="identifier">make_optional</span><span class="special">(</span>
+ <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">T</span> <span class="special">&&</span> <span class="identifier">v</span>
+ <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">decay_t</span><span class="special"><</span><span class="identifier">T</span><span class="special">>>(</span><span class="identifier">condition</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">v</span><span class="special">))</span></code> for the <span class="emphasis"><em>deduced</em></span>
+ type <code class="computeroutput"><span class="identifier">T</span></code> of <code class="computeroutput"><span class="identifier">v</span></code>.
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">==</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ shall meet requirements of <a href="http://www.sgi.com/tech/stl/EqualityComparable.html" target="_top"><code class="computeroutput"><span class="identifier">EqualityComparable</span></code></a>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> If both <code class="computeroutput"><span class="identifier">x</span></code>
+ and <code class="computeroutput"><span class="identifier">y</span></code> are initialized,
+ <code class="computeroutput"><span class="special">(*</span><span class="identifier">x</span>
+ <span class="special">==</span> <span class="special">*</span><span class="identifier">y</span><span class="special">)</span></code>.
+ If only <code class="computeroutput"><span class="identifier">x</span></code> or <code class="computeroutput"><span class="identifier">y</span></code> is initialized, <code class="computeroutput"><span class="keyword">false</span></code>.
+ If both are uninitialized, <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> This definition guarantees
+ that <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ not containing a value is compared unequal to any <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> containing any value, and equal
+ to any other <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> not containing a value. Pointers
+ have shallow relational operators while <code class="computeroutput"><span class="identifier">optional</span></code>
+ has deep relational operators. Do not use <code class="computeroutput"><span class="keyword">operator</span><span class="special">==</span></code> directly in generic code which expect
+ to be given either an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> or a pointer; use <a href="../../../../../../utility/OptionalPointee.html#equal" target="_top"><code class="computeroutput"><span class="identifier">equal_pointees</span><span class="special">()</span></code></a>
+ instead
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">oN</span><span class="special">,</span> <span class="identifier">oN_</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o1</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">)),</span> <span class="identifier">o1_</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">));</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o2</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">));</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">==</span> <span class="identifier">oN</span> <span class="special">);</span> <span class="comment">// Identity implies equality</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">==</span> <span class="identifier">o1</span> <span class="special">);</span> <span class="comment">//</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">==</span> <span class="identifier">oN_</span> <span class="special">);</span> <span class="comment">// Both uninitialized compare equal</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special">!=</span> <span class="identifier">o1</span> <span class="special">);</span> <span class="comment">// Initialized unequal to initialized.</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">==</span> <span class="identifier">o1_</span> <span class="special">);</span> <span class="comment">// Both initialized compare as (*lhs == *rhs)</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special">!=</span> <span class="identifier">o2</span> <span class="special">);</span> <span class="comment">//</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_less_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special"><</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> Expression <code class="computeroutput"><span class="special">*</span><span class="identifier">x</span> <span class="special"><</span> <span class="special">*</span><span class="identifier">y</span></code> shall be well-formed and its result
+ shall be convertible to <code class="computeroutput"><span class="keyword">bool</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">(!</span><span class="identifier">y</span><span class="special">)</span> <span class="special">?</span> <span class="keyword">false</span> <span class="special">:</span> <span class="special">(!</span><span class="identifier">x</span><span class="special">)</span> <span class="special">?</span> <span class="keyword">true</span> <span class="special">:</span> <span class="special">*</span><span class="identifier">x</span> <span class="special"><</span>
+ <span class="special">*</span><span class="identifier">y</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> This definition guarantees
+ that <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ not containing a value is ordered as less than any <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> containing any value, and equivalent
+ to any other <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> not containing a value. Pointers
+ have shallow relational operators while <code class="computeroutput"><span class="identifier">optional</span></code>
+ has deep relational operators. Do not use <code class="computeroutput"><span class="keyword">operator</span><span class="special"><</span></code> directly in generic code which
+ expect to be given either an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> or a pointer; use <a href="../../../../../../utility/OptionalPointee.html#less" target="_top"><code class="computeroutput"><span class="identifier">less_pointees</span><span class="special">()</span></code></a>
+ instead. <code class="computeroutput"><span class="identifier">T</span></code> need not
+ be <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a>. Only
+ single <code class="computeroutput"><span class="keyword">operator</span><span class="special"><</span></code>
+ is required. Other relational operations are defined in terms of this
+ one. If <code class="computeroutput"><span class="identifier">T</span></code>'s <code class="computeroutput"><span class="keyword">operator</span><span class="special"><</span></code>
+ satisfies the axioms of <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a> (transitivity,
+ antisymmetry and irreflexivity), <code class="computeroutput"><span class="identifier">optinal</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> is <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">oN</span><span class="special">,</span> <span class="identifier">oN_</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o0</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">0</span><span class="special">));</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o1</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">1</span><span class="special">));</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN</span> <span class="special"><</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// Identity implies equivalence</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o1</span> <span class="special"><</span> <span class="identifier">o1</span><span class="special">)</span> <span class="special">);</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN</span> <span class="special"><</span> <span class="identifier">oN_</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// Two uninitialized are equivalent</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">oN_</span> <span class="special"><</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">oN</span> <span class="special"><</span> <span class="identifier">o0</span> <span class="special">);</span> <span class="comment">// Uninitialized is less than initialized</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o0</span> <span class="special"><</span> <span class="identifier">oN</span><span class="special">)</span> <span class="special">);</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span> <span class="special"><</span> <span class="identifier">o2</span> <span class="special">)</span> <span class="special">;</span> <span class="comment">// Two initialized compare as (*lhs < *rhs)</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o2</span> <span class="special"><</span> <span class="identifier">o1</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!(</span><span class="identifier">o2</span> <span class="special"><</span> <span class="identifier">o2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_not_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">!=</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
+ <span class="identifier">x</span> <span class="special">==</span>
+ <span class="identifier">y</span> <span class="special">);</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_greater_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">></span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">(</span>
+ <span class="identifier">y</span> <span class="special"><</span>
+ <span class="identifier">x</span> <span class="special">);</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_less_or_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special"><=</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
+ <span class="identifier">y</span> <span class="special"><</span>
+ <span class="identifier">x</span> <span class="special">);</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_greater_or_equal_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">>=</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="special">!(</span>
+ <span class="identifier">x</span> <span class="special"><</span>
+ <span class="identifier">y</span> <span class="special">);</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_equal_optional_none"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">==</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">none_t</span> <span class="special">)</span>
+ <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">==</span> <span class="special">(</span>
+ <span class="identifier">none_t</span><span class="special">,</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">!</span><span class="identifier">x</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ need not meet requirements of <a href="http://www.sgi.com/tech/stl/EqualityComparable.html" target="_top"><code class="computeroutput"><span class="identifier">EqualityComparable</span></code></a>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_operator_compare_not_equal_optional_none"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">!=</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">none_t</span> <span class="special">)</span>
+ <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="keyword">operator</span>
+ <span class="special">!=</span> <span class="special">(</span>
+ <span class="identifier">none_t</span><span class="special">,</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Returns: </strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">x</span><span class="special">);</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_free_get_pointer"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">auto</span> <span class="identifier">get_pointer</span>
+ <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">o</span>
+ <span class="special">)</span> <span class="special">-></span>
+ <span class="keyword">typename</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">pointer_type</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">auto</span> <span class="identifier">get_pointer</span>
+ <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">o</span> <span class="special">)</span> <span class="special">-></span> <span class="keyword">typename</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">pointer_const_type</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="identifier">o</span><span class="special">.</span><span class="identifier">get_ptr</span><span class="special">()</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_free_get_value_or"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">auto</span> <span class="identifier">get_optional_value_or</span>
+ <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">o</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">reference_type</span> <span class="identifier">def</span>
+ <span class="special">)</span> <span class="special">-></span>
+ <span class="keyword">typename</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">reference_type</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">auto</span> <span class="identifier">get_optional_value_or</span>
+ <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">o</span><span class="special">,</span> <span class="keyword">typename</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">reference_const_type</span> <span class="identifier">def</span>
+ <span class="special">)</span> <span class="special">-></span>
+ <span class="keyword">typename</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">reference_const_type</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="identifier">o</span><span class="special">.</span><span class="identifier">get_value_or</span><span class="special">(</span><span class="identifier">def</span><span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> This function is deprecated.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_swap_optional_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">swap</span>
+ <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">y</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> Lvalues of type <code class="computeroutput"><span class="identifier">T</span></code> shall be swappable and <code class="computeroutput"><span class="identifier">T</span></code> shall be <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>.
+ </li>
+<li class="listitem">
+<p class="simpara">
+ <span class="bold"><strong>Effects:</strong></span>
+ </p>
+<div class="informaltable"><table class="table">
+<colgroup>
+<col>
+<col>
+<col>
+</colgroup>
+<thead><tr></tr></thead>
+<tbody>
+<tr>
+<td>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ calls <code class="computeroutput"><span class="identifier">swap</span><span class="special">(*(*</span><span class="keyword">this</span><span class="special">),</span> <span class="special">*</span><span class="identifier">rhs</span><span class="special">)</span></code>
+ </p>
+ </td>
+<td>
+ <p>
+ initializes the contained value of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> as if direct-initializing
+ an object of type <code class="computeroutput"><span class="identifier">T</span></code>
+ with the expression <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code>, followed by <code class="computeroutput"><span class="identifier">rhs</span><span class="special">.</span><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>,
+ <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ contains a value and <code class="computeroutput"><span class="identifier">rhs</span></code>
+ does not contain a value
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ does not contain a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ initializes the contained value of <code class="computeroutput"><span class="identifier">rhs</span></code>
+ as if direct-initializing an object of type <code class="computeroutput"><span class="identifier">T</span></code> with the expression
+ <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*(*</span><span class="keyword">this</span><span class="special">))</span></code>,
+ followed by <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value
+ and <code class="computeroutput"><span class="identifier">rhs</span></code> contains
+ a value
+ </p>
+ </td>
+<td>
+ <p>
+ no effect
+ </p>
+ </td>
+</tr>
+</tbody>
+</table></div>
+</li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> The states of <code class="computeroutput"><span class="identifier">x</span></code> and <code class="computeroutput"><span class="identifier">y</span></code>
+ interchanged.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> If both are initialized, whatever
+ <code class="computeroutput"><span class="identifier">swap</span><span class="special">(</span><span class="identifier">T</span><span class="special">&,</span><span class="identifier">T</span><span class="special">&)</span></code>
+ throws. If only one is initialized, whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">(</span><span class="number">12</span><span class="special">);</span>
+<span class="identifier">T</span> <span class="identifier">y</span><span class="special">(</span><span class="number">21</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def0</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def1</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">optX</span><span class="special">(</span><span class="identifier">x</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">optY</span><span class="special">(</span><span class="identifier">y</span><span class="special">);</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">def1</span><span class="special">);</span> <span class="comment">// no-op</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">optX</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def0</span> <span class="special">==</span> <span class="identifier">x</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">optX</span> <span class="special">);</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">def0</span><span class="special">,</span><span class="identifier">optX</span><span class="special">);</span> <span class="comment">// Get back to original values</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">optX</span><span class="special">,</span><span class="identifier">optY</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">optX</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">optY</span> <span class="special">==</span> <span class="identifier">x</span> <span class="special">);</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_swap_optional_reference"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">swap</span>
+ <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>&</span> <span class="identifier">y</span>
+ <span class="special">)</span> <span class="keyword">noexcept</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="identifier">x</span></code>
+ refers to what <code class="computeroutput"><span class="identifier">y</span></code> refererred
+ to before the swap (if anything). <code class="computeroutput"><span class="identifier">y</span></code>
+ refers to whatever <code class="computeroutput"><span class="identifier">x</span></code>
+ referred to before the swap.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">(</span><span class="number">12</span><span class="special">);</span>
+<span class="identifier">T</span> <span class="identifier">y</span><span class="special">(</span><span class="number">21</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">opt0</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">optX</span> <span class="special">(</span><span class="identifier">x</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">optY</span> <span class="special">(</span><span class="identifier">y</span><span class="special">);</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">optX</span><span class="special">,</span> <span class="identifier">optY</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">optX</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">y</span><span class="special">));</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">optY</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">x</span><span class="special">));</span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">swap</span><span class="special">(</span><span class="identifier">opt0</span><span class="special">,</span> <span class="identifier">optX</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt0</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">optX</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">addressof</span><span class="special">(*</span><span class="identifier">opt0</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">y</span><span class="special">));</span>
+</pre>
+ </li>
+</ul></div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="detailed_semantics___optional_references.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../header__boost_optional_hpp_.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___optional_references.html b/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___optional_references.html
new file mode 100644
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--- /dev/null
+++ b/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___optional_references.html
@@ -0,0 +1,557 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Detailed Semantics - Optional References</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../../../optional/reference/header__boost_optional_optional_hpp_.html" title="Header <boost/optional/optional.hpp>">
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+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
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+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="detailed_semantics___optional_values.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="detailed_semantics___free_functions.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.header__boost_optional_optional_hpp_.detailed_semantics___optional_references"></a><a class="link" href="detailed_semantics___optional_references.html" title="Detailed Semantics - Optional References">Detailed
+ Semantics - Optional References</a>
+</h4></div></div></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_default_ctor"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">()</span>
+ <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span><span class="identifier">none_t</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">false</span></code>; <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> refers to nothing.
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_value_ctor"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">></span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span><span class="identifier">R</span><span class="special">&&</span> <span class="identifier">r</span><span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">true</span></code>; <code class="computeroutput"><span class="identifier">addressof</span><span class="special">(**</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">r</span><span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> Unless <code class="computeroutput"><span class="identifier">R</span></code>
+ is an lvalue reference, the program is ill-formed. This constructor
+ does not participate in overload resolution if <code class="computeroutput"><span class="identifier">decay</span><span class="special"><</span><span class="identifier">R</span><span class="special">></span></code> is an instance of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> This constructor is declared
+ <code class="computeroutput"><span class="keyword">explicit</span></code> on compilers
+ that do not correctly suport binding to const lvalues of integral types.
+ For more details <a class="link" href="../../dependencies_and_portability/optional_reference_binding.html#optional_reference_binding">see here</a>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">vref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">vref</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">++</span> <span class="identifier">v</span> <span class="special">;</span> <span class="comment">// mutate referee</span>
+<span class="identifier">assert</span> <span class="special">(*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span><span class="special">);</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_cond_value_ctor"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">></span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span><span class="special">(</span><span class="keyword">bool</span> <span class="identifier">cond</span><span class="special">,</span> <span class="identifier">R</span><span class="special">&&</span>
+ <span class="identifier">r</span><span class="special">)</span>
+ <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects: </strong></span> Initializes <code class="computeroutput"><span class="identifier">ref</span></code> with expression <code class="computeroutput"><span class="identifier">cond</span> <span class="special">?</span>
+ <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">r</span><span class="special">)</span> <span class="special">:</span> <span class="keyword">nullptr</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">cond</span></code>; If <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>, <code class="computeroutput"><span class="identifier">addressof</span><span class="special">(**</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">addressof</span><span class="special">(</span><span class="identifier">r</span><span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> Unless <code class="computeroutput"><span class="identifier">R</span></code>
+ is an lvalue reference, the program is ill-formed. This constructor
+ does not participate in overload resolution if <code class="computeroutput"><span class="identifier">decay</span><span class="special"><</span><span class="identifier">R</span><span class="special">></span></code> is an instance of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span></code>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_copy_ctor"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span> <span class="special">(</span>
+ <span class="identifier">optional</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="keyword">noexcept</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects: </strong></span> Initializes <code class="computeroutput"><span class="identifier">ref</span></code> with expression <code class="computeroutput"><span class="identifier">rhs</span><span class="special">.</span><span class="identifier">ref</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">uninit</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">uninit</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span>
+
+<span class="identifier">T</span> <span class="identifier">v</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">ref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init</span><span class="special">(</span><span class="identifier">ref</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">init</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">v</span> <span class="special">=</span> <span class="number">3</span> <span class="special">;</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init2</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_ctor_from_opt_U"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="keyword">explicit</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">optional</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">&></span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">rhs</span> <span class="special">)</span>
+ <span class="keyword">noexcept</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_convertible</span><span class="special"><</span><span class="identifier">U</span><span class="special">&,</span> <span class="identifier">T</span><span class="special">&>::</span><span class="identifier">value</span></code>
+ is <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effects: </strong></span> Initializes <code class="computeroutput"><span class="identifier">ref</span></code> with expression <code class="computeroutput"><span class="identifier">rhs</span><span class="special">.</span><span class="identifier">ref</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span></code>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_assign_none_t"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">none_t</span>
+ <span class="special">)</span> <span class="keyword">noexcept</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects: </strong></span> Assigns <code class="computeroutput"><span class="identifier">ref</span></code>
+ with expression <code class="computeroutput"><span class="keyword">nullptr</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">false</span></code>.
+ </li>
+</ul></div>
+<a name="reference_optional_ref_copy_assign"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">rhs</span> <span class="special">)</span>
+ <span class="keyword">noexcept</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects: </strong></span> Assigns <code class="computeroutput"><span class="identifier">ref</span></code>
+ with expression <code class="computeroutput"><span class="identifier">rhs</span><span class="special">.</span><span class="identifier">ref</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> This behaviour is called <span class="emphasis"><em>rebinding
+ semantics</em></span>. See <a class="link" href="../../tutorial/optional_references/rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">here</a>
+ for details.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">ora</span><span class="special">(</span><span class="identifier">ra</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">orb</span><span class="special">(</span><span class="identifier">rb</span><span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">def</span> <span class="special">=</span> <span class="identifier">orb</span> <span class="special">;</span> <span class="comment">// binds 'def' to 'b' through 'rb' wrapped within 'orb'</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">b</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">*</span><span class="identifier">def</span> <span class="special">=</span> <span class="identifier">ora</span> <span class="special">;</span> <span class="comment">// changes the value of 'b' to a copy of the value of 'a'</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">b</span> <span class="special">==</span> <span class="identifier">a</span> <span class="special">)</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">c</span> <span class="special">=</span> <span class="number">3</span><span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">rc</span> <span class="special">=</span> <span class="identifier">c</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">orc</span><span class="special">(</span><span class="identifier">rc</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">ora</span> <span class="special">=</span> <span class="identifier">orc</span> <span class="special">;</span> <span class="comment">// REBINDS ora to 'c' through 'rc'</span>
+<span class="identifier">c</span> <span class="special">=</span> <span class="number">4</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">ora</span> <span class="special">==</span> <span class="number">4</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<a name="reference_optional_ref_assign_optional_U"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">&></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="keyword">noexcept</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_convertible</span><span class="special"><</span><span class="identifier">U</span><span class="special">&,</span> <span class="identifier">T</span><span class="special">&>::</span><span class="identifier">value</span></code>
+ is <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effects: </strong></span> Assigns <code class="computeroutput"><span class="identifier">ref</span></code>
+ with expression <code class="computeroutput"><span class="identifier">rhs</span><span class="special">.</span><span class="identifier">ref</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span></code>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_assign_R"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">R</span><span class="special">&&</span> <span class="identifier">r</span>
+ <span class="special">)</span> <span class="keyword">noexcept</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects: </strong></span> Assigns <code class="computeroutput"><span class="identifier">ref</span></code>
+ with expression <code class="computeroutput"><span class="identifier">r</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> Unless <code class="computeroutput"><span class="identifier">R</span></code>
+ is an lvalue reference, the program is ill-formed. This function does
+ not participate in overload resolution if <code class="computeroutput"><span class="identifier">decay</span><span class="special"><</span><span class="identifier">R</span><span class="special">></span></code> is an instance of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">ra</span><span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">def</span> <span class="special">=</span> <span class="identifier">rb</span> <span class="special">;</span> <span class="comment">// binds 'def' to 'b' through 'rb'</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">b</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">*</span><span class="identifier">def</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span> <span class="comment">// changes the value of 'b' to a copy of the value of 'a'</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">b</span> <span class="special">==</span> <span class="identifier">a</span> <span class="special">)</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">c</span> <span class="special">=</span> <span class="number">3</span><span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">rc</span> <span class="special">=</span> <span class="identifier">c</span> <span class="special">;</span>
+<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">rc</span> <span class="special">;</span> <span class="comment">// REBINDS to 'c' through 'rc'</span>
+<span class="identifier">c</span> <span class="special">=</span> <span class="number">4</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="number">4</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_emplace_R"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">emplace</span><span class="special">(</span> <span class="identifier">R</span><span class="special">&&</span> <span class="identifier">r</span>
+ <span class="special">)</span> <span class="keyword">noexcept</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects: </strong></span> Assigns <code class="computeroutput"><span class="identifier">ref</span></code>
+ with expression <code class="computeroutput"><span class="identifier">r</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> Unless <code class="computeroutput"><span class="identifier">R</span></code>
+ is an lvalue reference, the program is ill-formed. This function does
+ not participate in overload resolution if <code class="computeroutput"><span class="identifier">decay</span><span class="special"><</span><span class="identifier">R</span><span class="special">></span></code> is an instance of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span></code>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_get"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span> <span class="special">*()</span>
+ <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effects: </strong></span> Returns <code class="computeroutput"><span class="special">*</span><span class="identifier">ref</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws: </strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">T</span><span class="special">&</span> <span class="identifier">vref</span> <span class="special">=</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">vref</span> <span class="special">);</span>
+<span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">vref2</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">opt</span><span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">vref2</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">++</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_arrow"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">*</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span> <span class="special">-></span>
+ <span class="special">()</span> <span class="keyword">const</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effects: </strong></span> Returns <code class="computeroutput"><span class="identifier">ref</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws: </strong></span> Nothing.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">value</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">?</span> <span class="special">*</span><span class="identifier">val</span> <span class="special">:</span> <span class="keyword">throw</span> <span class="identifier">bad_optional_access</span><span class="special">();</span></code>.
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_value_or"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">></span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">value_or</span><span class="special">(</span> <span class="identifier">R</span><span class="special">&&</span> <span class="identifier">r</span>
+ <span class="special">)</span> <span class="keyword">const</span>
+ <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">if</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="special">**</span><span class="keyword">this</span><span class="special">;</span> <span class="keyword">else</span> <span class="keyword">return</span>
+ <span class="identifier">r</span><span class="special">;</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> Unless <code class="computeroutput"><span class="identifier">R</span></code>
+ is an lvalue reference, the program is ill-formed.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_value_or_eval"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">value_or</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">if</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="special">**</span><span class="keyword">this</span><span class="special">;</span> <span class="keyword">else</span> <span class="keyword">return</span>
+ <span class="identifier">f</span><span class="special">();</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> Unless <code class="computeroutput"><span class="keyword">decltype</span><span class="special">(</span><span class="identifier">f</span><span class="special">())</span></code> is an lvalue reference, the program
+ is ill-formed.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_map"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="keyword">auto</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">map</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="keyword">const</span> <span class="special">-></span> </code><span class="emphasis"><em>see below</em></span><code class="computeroutput"><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">if</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="identifier">f</span><span class="special">(**</span><span class="keyword">this</span><span class="special">);</span> <span class="keyword">else</span> <span class="keyword">return</span> <span class="identifier">none</span><span class="special">;</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> The return type of this function
+ is <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">decltype</span><span class="special">(</span><span class="identifier">f</span><span class="special">(**</span><span class="keyword">this</span><span class="special">))></span></code>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_flat_map"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="keyword">auto</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">flat_map</span><span class="special">(</span>
+ <span class="identifier">F</span> <span class="identifier">f</span>
+ <span class="special">)</span> <span class="keyword">const</span>
+ <span class="special">-></span> </code><span class="emphasis"><em>see below</em></span><code class="computeroutput"><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> The return type of expression
+ <code class="computeroutput"><span class="identifier">f</span><span class="special">(**</span><span class="keyword">this</span><span class="special">)</span></code>
+ is <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span></code>
+ for some object or reference type <code class="computeroutput"><span class="identifier">U</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">if</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="identifier">f</span><span class="special">(**</span><span class="keyword">this</span><span class="special">);</span> <span class="keyword">else</span> <span class="keyword">return</span> <span class="identifier">none</span><span class="special">;</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> The return type of this function
+ is <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span></code>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_get_ptr"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">*</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">get_ptr</span> <span class="special">()</span>
+ <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="identifier">ref</span></code>.
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_operator_bool"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="identifier">has_value</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span> <span class="keyword">bool</span>
+ <span class="special">()</span> <span class="keyword">const</span>
+ <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">ref</span><span class="special">)</span></code>.
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_operator_not"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="keyword">operator</span> <span class="special">!</span> <span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">!</span><span class="keyword">bool</span><span class="special">(</span><span class="identifier">ref</span><span class="special">)</span></code>.
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_reset"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">reset</span><span class="special">()</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Use <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span> <span class="special">=</span> <span class="identifier">none</span></code> instead.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> This function is depprecated.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_reset_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">reset</span> <span class="special">(</span> <span class="identifier">R</span><span class="special">&&</span>
+ <span class="identifier">r</span><span class="special">)</span>
+ <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">R</span><span class="special">>(</span><span class="identifier">r</span><span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> This function is depprecated.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_is_initialized"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">is_initialized</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> This function is depprecated.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_ref_get_value_or_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">></span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&>::</span><span class="identifier">get_value_or</span><span class="special">(</span> <span class="identifier">R</span><span class="special">&&</span> <span class="identifier">r</span>
+ <span class="special">)</span> <span class="keyword">const</span>
+ <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="identifier">value_or</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">R</span><span class="special">>(</span><span class="identifier">r</span><span class="special">);</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> This function is depprecated.
+ </li>
+</ul></div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="detailed_semantics___optional_values.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="detailed_semantics___free_functions.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___optional_values.html b/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/detailed_semantics___optional_values.html
new file mode 100644
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@@ -0,0 +1,1788 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Detailed Semantics - Optional Values</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../../../optional/reference/header__boost_optional_optional_hpp_.html" title="Header <boost/optional/optional.hpp>">
+<link rel="prev" href="header_optional_optional_refs.html" title="Optional References">
+<link rel="next" href="detailed_semantics___optional_references.html" title="Detailed Semantics - Optional References">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
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+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="header_optional_optional_refs.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="detailed_semantics___optional_references.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.header__boost_optional_optional_hpp_.detailed_semantics___optional_values"></a><a class="link" href="detailed_semantics___optional_values.html" title="Detailed Semantics - Optional Values">Detailed
+ Semantics - Optional Values</a>
+</h4></div></div></div>
+<div class="note"><table border="0" summary="Note">
+<tr>
+<td rowspan="2" align="center" valign="top" width="25"><img alt="[Note]" src="../../../../../../../doc/src/images/note.png"></td>
+<th align="left">Note</th>
+</tr>
+<tr><td align="left" valign="top"><p>
+ The following section contains various <code class="computeroutput"><span class="identifier">assert</span><span class="special">()</span></code> which are used only to show the postconditions
+ as sample code. It is not implied that the type <code class="computeroutput"><span class="identifier">T</span></code>
+ must support each particular expression but that if the expression is
+ supported, the implied condition holds.
+ </p></td></tr>
+</table></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">()</span>
+ <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Default-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">uninitialized</span>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> T's default constructor <span class="underline">is not</span> called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">def</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_none_t"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">none_t</span> <span class="special">)</span>
+ <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Constructs an <code class="computeroutput"><span class="identifier">optional</span></code> uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">uninitialized</span>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>'s
+ default constructor <span class="underline">is not</span> called.
+ The expression <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code>
+ denotes an instance of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none_t</span></code>
+ that can be used as the parameter.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">none</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">n</span><span class="special">(</span><span class="identifier">none</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">n</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_copy_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>
+ is <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Directly-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
+ and its value is a <span class="emphasis"><em>copy</em></span> of <code class="computeroutput"><span class="identifier">v</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span></code> throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span></code> is called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">);</span></code> in that case, this constructor
+ has no effect.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_move_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">T</span><span class="special">&&</span>
+ <span class="identifier">v</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>
+ is <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Directly-Move-Constructs an
+ <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
+ and its value is move-constructed from <code class="computeroutput"><span class="identifier">v</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code>
+ is called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">);</span></code>
+ in that case, the state of <code class="computeroutput"><span class="identifier">v</span></code>
+ is determined by exception safety guarantees for <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span><span class="special">&&)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v1</span><span class="special">,</span> <span class="identifier">v2</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">v1</span><span class="special">));</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">v2</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_bool_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ If condition is true, same as:
+ </li></ul></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ otherwise, same as:
+ </li></ul></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">()</span></code>
+ </p></blockquote></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">optional</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span>
+ <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_copy_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>
+ is <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Copy-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If rhs is initialized,
+ <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is a <span class="emphasis"><em>copy</em></span> of the
+ value of <code class="computeroutput"><span class="identifier">rhs</span></code>; else
+ <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span></code> throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If rhs is initialized, <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code>
+ is called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">);</span></code> in that case, this constructor
+ has no effect.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">uninit</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">uninit</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init</span><span class="special">(</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">init</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">init</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_move_constructor_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">optional</span><span class="special">&&</span>
+ <span class="identifier">rhs</span> <span class="special">)</span>
+ <span class="keyword">noexcept</span><span class="special">(</span></code><span class="emphasis"><em>see
+ below</em></span><code class="computeroutput"><span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>
+ is <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Move-constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is move constructed from <code class="computeroutput"><span class="identifier">rhs</span></code>; else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> The expression inside <code class="computeroutput"><span class="keyword">noexcept</span></code> is equivalent to <code class="computeroutput"><span class="identifier">is_nothrow_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span> <span class="special">&&</span>
+ <span class="special">)</span></code> is called.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">);</span></code>
+ in that case, <code class="computeroutput"><span class="identifier">rhs</span></code> remains
+ initialized and the value of <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is determined by exception safety
+ of <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span><span class="special">&&)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">uninit</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">uninit</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">uinit2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">uninit</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">uninit2</span> <span class="special">==</span> <span class="identifier">uninit</span> <span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">init</span><span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">uniqye_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>(</span><span class="keyword">new</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="identifier">T</span><span class="special">>></span> <span class="identifier">init2</span> <span class="special">(</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">init</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">init</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">init</span> <span class="special">==</span> <span class="keyword">nullptr</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">init2</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">**</span><span class="identifier">init2</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span>
+ <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Copy-Constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is a <span class="emphasis"><em>copy</em></span> of the
+ value of rhs converted to type <code class="computeroutput"><span class="identifier">T</span></code>;
+ else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span></code> throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span></code> is called if <code class="computeroutput"><span class="identifier">rhs</span></code> is initialized, which requires
+ a valid conversion from <code class="computeroutput"><span class="identifier">U</span></code>
+ to <code class="computeroutput"><span class="identifier">T</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">);</span></code> in that case, this constructor
+ has no effect.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">x</span><span class="special">(</span><span class="number">123.4</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">==</span> <span class="number">123.4</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">y</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span><span class="special">(</span> <span class="special">*</span><span class="identifier">y</span> <span class="special">==</span> <span class="number">123</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_move_constructor_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&&</span> <span class="identifier">rhs</span>
+ <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Move-constructs an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> If <code class="computeroutput"><span class="identifier">rhs</span></code>
+ is initialized, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initialized and its value is move-constructed from <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>;
+ else <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">)</span></code>
+ is called if <code class="computeroutput"><span class="identifier">rhs</span></code> is
+ initialized, which requires a valid conversion from <code class="computeroutput"><span class="identifier">U</span></code>
+ to <code class="computeroutput"><span class="identifier">T</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span> <span class="special">);</span></code>
+ in that case, <code class="computeroutput"><span class="identifier">rhs</span></code> remains
+ initialized and the value of <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is determined by exception safety
+ guarantee of <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span> <span class="identifier">U</span><span class="special">&&</span>
+ <span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">x</span><span class="special">(</span><span class="number">123.4</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">==</span> <span class="number">123.4</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">y</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">x</span><span class="special">))</span> <span class="special">;</span>
+<span class="identifier">assert</span><span class="special">(</span> <span class="special">*</span><span class="identifier">y</span> <span class="special">==</span> <span class="number">123</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_in_place_init"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span>
+ <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">in_place_init_t</span><span class="special">,</span> <span class="identifier">Args</span><span class="special">&&...</span> <span class="identifier">ars</span>
+ <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_constructible_v</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">Args</span><span class="special">&&...></span></code> is <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Initializes the contained
+ value as if direct-non-list-initializing an object of type <code class="computeroutput"><span class="identifier">T</span></code> with the arguments <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">Args</span><span class="special">>(</span><span class="identifier">args</span><span class="special">)...</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Any exception thrown by the
+ selected constructor of <code class="computeroutput"><span class="identifier">T</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ need not be <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>.
+ On compilers that do not suppor variadic templates or rvalue references,
+ this constuctor is available in limited functionality. For details
+ <a class="link" href="../../dependencies_and_portability/emplace_operations_in_older_compilers.html#optional_emplace_workaround">see here</a>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="comment">// creates an std::mutex using its default constructor</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">mutex</span><span class="special">></span> <span class="identifier">om</span> <span class="special">{</span><span class="identifier">in_place_init</span><span class="special">};</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">om</span><span class="special">);</span>
+
+<span class="comment">// creates a unique_lock by calling unique_lock(*om, std::defer_lock)</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_lock</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">mutex</span><span class="special">>></span> <span class="identifier">ol</span> <span class="special">{</span><span class="identifier">in_place_init</span><span class="special">,</span> <span class="special">*</span><span class="identifier">om</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">defer_lock</span><span class="special">};</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">ol</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">ol</span><span class="special">-></span><span class="identifier">owns_lock</span><span class="special">());</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_in_place_init_if"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span>
+ <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">in_place_init_if_t</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span>
+ <span class="identifier">Args</span><span class="special">&&...</span>
+ <span class="identifier">ars</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">is_constructible_v</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span> <span class="identifier">Args</span><span class="special">&&...></span></code> is <code class="computeroutput"><span class="keyword">true</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> If <code class="computeroutput"><span class="identifier">condition</span></code>
+ is <code class="computeroutput"><span class="keyword">true</span></code>, initializes the
+ contained value as if direct-non-list-initializing an object of type
+ <code class="computeroutput"><span class="identifier">T</span></code> with the arguments
+ <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">Args</span><span class="special">>(</span><span class="identifier">args</span><span class="special">)...</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">==</span> <span class="identifier">condition</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Any exception thrown by the
+ selected constructor of <code class="computeroutput"><span class="identifier">T</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes: </strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ need not be <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>.
+ On compilers that do not suppor variadic templates or rvalue references,
+ this constuctor is available in limited functionality. For details
+ <a class="link" href="../../dependencies_and_portability/emplace_operations_in_older_compilers.html#optional_emplace_workaround">see here</a>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">>></span> <span class="identifier">ov1</span> <span class="special">{</span><span class="identifier">in_place_init_if</span><span class="special">,</span> <span class="keyword">false</span><span class="special">,</span> <span class="number">3</span><span class="special">,</span> <span class="string">"A"</span><span class="special">};</span>
+<span class="identifier">assert</span> <span class="special">(!</span><span class="identifier">ov1</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">>></span> <span class="identifier">ov2</span> <span class="special">{</span><span class="identifier">in_place_init_if</span><span class="special">,</span> <span class="keyword">true</span><span class="special">,</span> <span class="number">3</span><span class="special">,</span> <span class="string">"A"</span><span class="special">};</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">ov2</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">ov2</span><span class="special">-></span><span class="identifier">size</span><span class="special">()</span> <span class="special">==</span> <span class="number">3</span><span class="special">);</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_constructor_factory"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">InPlaceFactory</span><span class="special">></span>
+ <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">InPlaceFactory</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">f</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">TypedInPlaceFactory</span><span class="special">></span>
+ <span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span> <span class="identifier">TypedInPlaceFactory</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">f</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Constructs an <code class="computeroutput"><span class="identifier">optional</span></code> with a value of <code class="computeroutput"><span class="identifier">T</span></code> obtained from the factory.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
+ and its value is <span class="emphasis"><em>directly given</em></span> from the factory
+ <code class="computeroutput"><span class="identifier">f</span></code> (i.e., the value
+ <span class="underline">is not copied</span>).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever the <code class="computeroutput"><span class="identifier">T</span></code> constructor called by the factory
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> See <a class="link" href="../../tutorial/in_place_factories.html" title="In-Place Factories">In-Place
+ Factories</a>
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during the call to the <code class="computeroutput"><span class="identifier">T</span></code>
+ constructor used by the factory; in that case, this constructor has
+ no effect.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">C</span> <span class="special">{</span> <span class="identifier">C</span> <span class="special">(</span> <span class="keyword">char</span><span class="special">,</span> <span class="keyword">double</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">)</span> <span class="special">;</span> <span class="special">}</span> <span class="special">;</span>
+
+<span class="identifier">C</span> <span class="identifier">v</span><span class="special">(</span><span class="char">'A'</span><span class="special">,</span><span class="number">123.4</span><span class="special">,</span><span class="string">"hello"</span><span class="special">);</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">C</span><span class="special">></span> <span class="identifier">x</span><span class="special">(</span> <span class="identifier">in_place</span> <span class="special">(</span><span class="char">'A'</span><span class="special">,</span> <span class="number">123.4</span><span class="special">,</span> <span class="string">"hello"</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// InPlaceFactory used</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">C</span><span class="special">></span> <span class="identifier">y</span><span class="special">(</span> <span class="identifier">in_place</span><span class="special"><</span><span class="identifier">C</span><span class="special">>(</span><span class="char">'A'</span><span class="special">,</span> <span class="number">123.4</span><span class="special">,</span> <span class="string">"hello"</span><span class="special">)</span> <span class="special">);</span> <span class="comment">// TypedInPlaceFactory used</span>
+
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">x</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">y</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_equal_none_t"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">none_t</span>
+ <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized destroys its contained
+ value.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_equal_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Assigns the value <code class="computeroutput"><span class="identifier">rhs</span></code> to an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized and its value is
+ a <span class="emphasis"><em>copy</em></span> of <code class="computeroutput"><span class="identifier">rhs</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span></code> or <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s assignment operator is used,
+ otherwise, its copy-constructor is used.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> In the event of
+ an exception, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is unchanged and its value unspecified
+ as far as <code class="computeroutput"><span class="identifier">optional</span></code>
+ is concerned (it is up to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <code class="computeroutput"><span class="keyword">operator</span><span class="special">=()</span></code>).
+ If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initially uninitialized and <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <span class="emphasis"><em>copy constructor</em></span> fails, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is left properly uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">T</span> <span class="identifier">y</span><span class="special">;</span>
+<span class="identifier">def</span> <span class="special">=</span> <span class="identifier">y</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">y</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_move_equal_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Moves the value <code class="computeroutput"><span class="identifier">rhs</span></code> to an <code class="computeroutput"><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized and its value is
+ moved from <code class="computeroutput"><span class="identifier">rhs</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="special">)</span></code>
+ or <code class="computeroutput"><span class="identifier">T</span><span class="special">::</span><span class="identifier">T</span><span class="special">(</span><span class="identifier">T</span> <span class="special">&&)</span></code>
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> was initialized, <code class="computeroutput"><span class="identifier">T</span></code>'s move-assignment operator is used,
+ otherwise, its move-constructor is used.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> In the event of
+ an exception, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is unchanged and its value unspecified
+ as far as <code class="computeroutput"><span class="identifier">optional</span></code>
+ is concerned (it is up to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <code class="computeroutput"><span class="keyword">operator</span><span class="special">=()</span></code>).
+ If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is initially uninitialized and <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <span class="emphasis"><em>move constructor</em></span> fails, <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is left properly uninitialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">x</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">T</span> <span class="identifier">y1</span><span class="special">,</span> <span class="identifier">y2</span><span class="special">,</span> <span class="identifier">yR</span><span class="special">;</span>
+<span class="identifier">def</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">y1</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">def</span> <span class="special">==</span> <span class="identifier">yR</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">y2</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">yR</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_equal_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">rhs</span> <span class="special">)</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ is <a href="../../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a> and <code class="computeroutput"><span class="identifier">CopyAssignable</span></code>.
+ </li>
+<li class="listitem">
+<p class="simpara">
+ <span class="bold"><strong>Effects:</strong></span>
+ </p>
+<div class="informaltable"><table class="table">
+<colgroup>
+<col>
+<col>
+<col>
+</colgroup>
+<thead><tr></tr></thead>
+<tbody>
+<tr>
+<td>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ assigns <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>
+ to the contained value
+ </p>
+ </td>
+<td>
+ <p>
+ initializes the contained value as if direct-initializing
+ an object of type <code class="computeroutput"><span class="identifier">T</span></code>
+ with <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ does not contain a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ destroys the contained value by calling <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>
+ </p>
+ </td>
+<td>
+ <p>
+ no effect
+ </p>
+ </td>
+</tr>
+</tbody>
+</table></div>
+</li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>;
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> If any exception
+ is thrown, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="identifier">rhs</span></code>
+ remains unchanged. If an exception is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s copy constructor, no effect.
+ If an exception is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ copy assignment, the state of its contained value is as defined by
+ the exception safety guarantee of <code class="computeroutput"><span class="identifier">T</span></code>'s
+ copy assignment.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+
+<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">def</span> <span class="special">)</span> <span class="special">;</span>
+<span class="comment">// previous value (copy of 'v') destroyed from within 'opt'.</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_move_equal_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">(</span></code><span class="emphasis"><em>see below</em></span><code class="computeroutput"><span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ is <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>
+ and <code class="computeroutput"><span class="identifier">MoveAssignable</span></code>.
+ </li>
+<li class="listitem">
+<p class="simpara">
+ <span class="bold"><strong>Effects:</strong></span>
+ </p>
+<div class="informaltable"><table class="table">
+<colgroup>
+<col>
+<col>
+<col>
+</colgroup>
+<thead><tr></tr></thead>
+<tbody>
+<tr>
+<td>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ assigns <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code> to the contained value
+ </p>
+ </td>
+<td>
+ <p>
+ initializes the contained value as if direct-initializing
+ an object of type <code class="computeroutput"><span class="identifier">T</span></code>
+ with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ does not contain a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ destroys the contained value by calling <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>
+ </p>
+ </td>
+<td>
+ <p>
+ no effect
+ </p>
+ </td>
+</tr>
+</tbody>
+</table></div>
+</li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>;
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> The expression inside <code class="computeroutput"><span class="keyword">noexcept</span></code> is equivalent to <code class="computeroutput"><span class="identifier">is_nothrow_move_constructible</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span> <span class="special">&&</span>
+ <span class="identifier">is_nothrow_move_assignable</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> If any exception
+ is thrown, the initialization state of <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="identifier">rhs</span></code>
+ remains unchanged. If an exception is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s move constructor, the state of
+ <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>
+ is determined by the exception safety guarantee of <code class="computeroutput"><span class="identifier">T</span></code>'s
+ move constructor. If an exception is thrown during the call to T's
+ move-assignment, the state of <code class="computeroutput"><span class="special">**</span><span class="keyword">this</span></code> and <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code> is determined by the exception
+ safety guarantee of T's move assignment.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">))</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+
+<span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">def</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">T</span><span class="special">(</span><span class="number">2</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_equal_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+<p class="simpara">
+ <span class="bold"><strong>Effect:</strong></span>
+ </p>
+<div class="informaltable"><table class="table">
+<colgroup>
+<col>
+<col>
+<col>
+</colgroup>
+<thead><tr></tr></thead>
+<tbody>
+<tr>
+<td>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ assigns <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>
+ to the contained value
+ </p>
+ </td>
+<td>
+ <p>
+ initializes the contained value as if direct-initializing
+ an object of type <code class="computeroutput"><span class="identifier">T</span></code>
+ with <code class="computeroutput"><span class="special">*</span><span class="identifier">rhs</span></code>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ does not contain a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ destroys the contained value by calling <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>
+ </p>
+ </td>
+<td>
+ <p>
+ no effect
+ </p>
+ </td>
+</tr>
+</tbody>
+</table></div>
+</li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> If any exception
+ is thrown, the result of the expression <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code> remains unchanged. If an exception
+ is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ constructor, no effect. If an exception is thrown during the call to
+ <code class="computeroutput"><span class="identifier">T</span></code>'s assignment, the
+ state of its contained value is as defined by the exception safety
+ guarantee of <code class="computeroutput"><span class="identifier">T</span></code>'s copy
+ assignment.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt0</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">opt1</span><span class="special">;</span>
+
+<span class="identifier">opt1</span> <span class="special">=</span> <span class="identifier">opt0</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt1</span> <span class="special">==</span> <span class="keyword">static_cast</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_move_equal_other_optional"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&&</span> <span class="identifier">rhs</span>
+ <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+<p class="simpara">
+ <span class="bold"><strong>Effect:</strong></span>
+ </p>
+<div class="informaltable"><table class="table">
+<colgroup>
+<col>
+<col>
+<col>
+</colgroup>
+<thead><tr></tr></thead>
+<tbody>
+<tr>
+<td>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> does not contain a value</strong></span>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ contains a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ assigns <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code> to the contained value
+ </p>
+ </td>
+<td>
+ <p>
+ initializes the contained value as if direct-initializing
+ an object of type <code class="computeroutput"><span class="identifier">T</span></code>
+ with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">rhs</span><span class="special">)</span></code>
+ </p>
+ </td>
+</tr>
+<tr>
+<td>
+ <p>
+ <span class="bold"><strong><code class="computeroutput"><span class="identifier">rhs</span></code>
+ does not contain a value</strong></span>
+ </p>
+ </td>
+<td>
+ <p>
+ destroys the contained value by calling <code class="computeroutput"><span class="identifier">val</span><span class="special">-></span><span class="identifier">T</span><span class="special">::~</span><span class="identifier">T</span><span class="special">()</span></code>
+ </p>
+ </td>
+<td>
+ <p>
+ no effect
+ </p>
+ </td>
+</tr>
+</tbody>
+</table></div>
+</li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions:</strong></span> <code class="computeroutput"><span class="keyword">bool</span><span class="special">(</span><span class="identifier">rhs</span><span class="special">)</span> <span class="special">==</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> If any exception
+ is thrown, the result of the expression <code class="computeroutput"><span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span></code> remains unchanged. If an exception
+ is thrown during the call to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ constructor, no effect. If an exception is thrown during the call to
+ <code class="computeroutput"><span class="identifier">T</span></code>'s assignment, the
+ state of its contained value is as defined by the exception safety
+ guarantee of <code class="computeroutput"><span class="identifier">T</span></code>'s copy
+ assignment.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt0</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="identifier">opt1</span><span class="special">;</span>
+
+<span class="identifier">opt1</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">opt0</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt0</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt1</span> <span class="special">)</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt1</span> <span class="special">==</span> <span class="keyword">static_cast</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_emplace"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span>
+ <span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">emplace</span><span class="special">(</span> <span class="identifier">Args</span><span class="special">&&...</span> <span class="identifier">args</span>
+ <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> The compiler supports rvalue
+ references and variadic templates.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized calls <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span> <span class="special">=</span> <span class="identifier">none</span></code>.
+ Then initializes in-place the contained value as if direct-initializing
+ an object of type <code class="computeroutput"><span class="identifier">T</span></code>
+ with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">Args</span><span class="special">>(</span><span class="identifier">args</span><span class="special">)...</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever the selected <code class="computeroutput"><span class="identifier">T</span></code>'s constructor throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> If an exception
+ is thrown during the initialization of <code class="computeroutput"><span class="identifier">T</span></code>,
+ <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>
+ is <span class="emphasis"><em>uninitialized</em></span>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ need not be <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>
+ or <code class="computeroutput"><span class="identifier">MoveAssignable</span></code>.
+ On compilers that do not suppor variadic templates or rvalue references,
+ this function is available in limited functionality. For details <a class="link" href="../../dependencies_and_portability/emplace_operations_in_older_compilers.html#optional_emplace_workaround">see here</a>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">;</span>
+<span class="identifier">opt</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">(</span><span class="number">0</span><span class="special">);</span> <span class="comment">// create in-place using ctor T(int)</span>
+<span class="identifier">opt</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">();</span> <span class="comment">// destroy previous and default-construct another T</span>
+<span class="identifier">opt</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> <span class="comment">// destroy and copy-construct in-place (no assignment called)</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_equal_factory"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">InPlaceFactory</span><span class="special">></span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">InPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="identifier">TypedInPlaceFactory</span><span class="special">></span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=(</span> <span class="identifier">TypedInPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span> <span class="special">);</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Assigns an <code class="computeroutput"><span class="identifier">optional</span></code>
+ with a value of <code class="computeroutput"><span class="identifier">T</span></code> obtained
+ from the factory.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Postconditions: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is <span class="underline">initialized</span>
+ and its value is <span class="emphasis"><em>directly given</em></span> from the factory
+ <code class="computeroutput"><span class="identifier">f</span></code> (i.e., the value
+ <span class="underline">is not copied</span>).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Whatever the <code class="computeroutput"><span class="identifier">T</span></code> constructor called by the factory
+ throws.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> See <a class="link" href="../../tutorial/in_place_factories.html" title="In-Place Factories">In-Place
+ Factories</a>
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Exception Safety:</strong></span> Exceptions can only
+ be thrown during the call to the <code class="computeroutput"><span class="identifier">T</span></code>
+ constructor used by the factory; in that case, the <code class="computeroutput"><span class="identifier">optional</span></code>
+ object will be reset to be <span class="emphasis"><em>uninitialized</em></span>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_reset_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">reset</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Deprecated:</strong></span> same as <code class="computeroutput"><span class="keyword">operator</span><span class="special">=</span>
+ <span class="special">(</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">v</span><span class="special">)</span>
+ <span class="special">;</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_reset"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">void</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">reset</span><span class="special">()</span> <span class="keyword">noexcept</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Deprecated:</strong></span> Same as <code class="computeroutput"><span class="keyword">operator</span><span class="special">=(</span>
+ <span class="identifier">none_t</span> <span class="special">);</span></code>
+ </li></ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_get"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">get</span><span class="special">()</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="identifier">get</span> <span class="special">(</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">inline</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get</span>
+ <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="special">&)</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> A reference to the contained
+ value
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The requirement is asserted
+ via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_asterisk"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">*()</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">*()</span>
+ <span class="special">&;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> A reference to the contained
+ value
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The requirement is asserted
+ via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
+ On compilers that do not support ref-qualifiers on member functions
+ these two overloads are replaced with the classical two: a <code class="computeroutput"><span class="keyword">const</span></code> and non-<code class="computeroutput"><span class="keyword">const</span></code>
+ member functions.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">);</span>
+<span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">u</span> <span class="special">=</span> <span class="special">*</span><span class="identifier">opt</span><span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">u</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">T</span> <span class="identifier">w</span> <span class="special">;</span>
+<span class="special">*</span><span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">w</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">opt</span> <span class="special">==</span> <span class="identifier">w</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_asterisk_move"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">*()</span>
+ <span class="special">&&;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> contains a value.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">val</span><span class="special">);</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The requirement is asserted
+ via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
+ On compilers that do not support ref-qualifiers on member functions
+ this overload is not present.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span><span class="special">()</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span><span class="special">()</span> <span class="special">&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">?</span> <span class="special">*</span><span class="identifier">val</span> <span class="special">:</span> <span class="keyword">throw</span> <span class="identifier">bad_optional_access</span><span class="special">();</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ ref-qualifiers on member functions these two overloads are replaced
+ with the classical two: a <code class="computeroutput"><span class="keyword">const</span></code>
+ and non-<code class="computeroutput"><span class="keyword">const</span></code> member functions.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o0</span><span class="special">,</span> <span class="identifier">o1</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">o1</span><span class="special">.</span><span class="identifier">value</span><span class="special">()</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">);</span>
+
+<span class="keyword">try</span> <span class="special">{</span>
+ <span class="identifier">o0</span><span class="special">.</span><span class="identifier">value</span><span class="special">();</span> <span class="comment">// throws</span>
+ <span class="identifier">assert</span> <span class="special">(</span> <span class="keyword">false</span> <span class="special">);</span>
+<span class="special">}</span>
+<span class="keyword">catch</span><span class="special">(</span><span class="identifier">bad_optional_access</span><span class="special">&)</span> <span class="special">{</span>
+ <span class="identifier">assert</span> <span class="special">(</span> <span class="keyword">true</span> <span class="special">);</span>
+<span class="special">}</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_value_move"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value</span><span class="special">()</span> <span class="special">&&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">return</span> <span class="keyword">bool</span><span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="special">?</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(*</span><span class="identifier">val</span><span class="special">)</span> <span class="special">:</span> <span class="keyword">throw</span> <span class="identifier">bad_optional_access</span><span class="special">();</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ ref-qualifiers on member functions this overload is not present.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_value_or"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or</span><span class="special">(</span><span class="identifier">U</span> <span class="special">&&</span>
+ <span class="identifier">v</span><span class="special">)</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">if</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="special">**</span><span class="keyword">this</span><span class="special">;</span> <span class="keyword">else</span> <span class="keyword">return</span>
+ <span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">);</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> If <code class="computeroutput"><span class="identifier">T</span></code>
+ is not <a href="../../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a> or <code class="computeroutput"><span class="identifier">U</span> <span class="special">&&</span></code>
+ is not convertible to <code class="computeroutput"><span class="identifier">T</span></code>,
+ the program is ill-formed.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ ref-qualifiers on member functions this overload is replaced with the
+ <code class="computeroutput"><span class="keyword">const</span></code>-qualified member
+ function. On compilers without rvalue reference support the type of
+ <code class="computeroutput"><span class="identifier">v</span></code> becomes <code class="computeroutput"><span class="identifier">U</span> <span class="keyword">const</span><span class="special">&</span></code>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_value_or_move"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or</span><span class="special">(</span><span class="identifier">U</span> <span class="special">&&</span>
+ <span class="identifier">v</span><span class="special">)</span>
+ <span class="special">&&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> Equivalent to <code class="computeroutput"><span class="keyword">if</span> <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(**</span><span class="keyword">this</span><span class="special">);</span> <span class="keyword">else</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">forward</span><span class="special"><</span><span class="identifier">U</span><span class="special">>(</span><span class="identifier">v</span><span class="special">);</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Remarks:</strong></span> If <code class="computeroutput"><span class="identifier">T</span></code>
+ is not <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>
+ or <code class="computeroutput"><span class="identifier">U</span> <span class="special">&&</span></code>
+ is not convertible to <code class="computeroutput"><span class="identifier">T</span></code>,
+ the program is ill-formed.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ ref-qualifiers on member functions this overload is not present.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_value_or_call"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">F</span> <span class="identifier">f</span><span class="special">)</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ is <a href="../../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a> and <code class="computeroutput"><span class="identifier">F</span></code> models a <a href="http://www.sgi.com/tech/stl/Generator.html" target="_top"><code class="computeroutput"><span class="identifier">Generator</span></code></a> whose result type
+ is convertible to <code class="computeroutput"><span class="identifier">T</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> <code class="computeroutput"><span class="keyword">if</span>
+ <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="special">**</span><span class="keyword">this</span><span class="special">;</span> <span class="keyword">else</span> <span class="keyword">return</span> <span class="identifier">f</span><span class="special">();</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ ref-qualifiers on member functions this overload is replaced with the
+ <code class="computeroutput"><span class="keyword">const</span></code>-qualified member
+ function.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">complain_and_0</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="identifier">clog</span> <span class="special"><<</span> <span class="string">"no value returned, using default"</span> <span class="special"><<</span> <span class="identifier">endl</span><span class="special">;</span>
+ <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
+<span class="special">}</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">o1</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">oN</span> <span class="special">=</span> <span class="identifier">none</span><span class="special">;</span>
+
+<span class="keyword">int</span> <span class="identifier">i</span> <span class="special">=</span> <span class="identifier">o1</span><span class="special">.</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">complain_and_0</span><span class="special">);</span> <span class="comment">// fun not called</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">i</span> <span class="special">==</span> <span class="number">1</span><span class="special">);</span>
+
+<span class="keyword">int</span> <span class="identifier">j</span> <span class="special">=</span> <span class="identifier">oN</span><span class="special">.</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">complain_and_0</span><span class="special">);</span> <span class="comment">// fun called</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">i</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_value_or_call_move"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">value_or_eval</span><span class="special">(</span><span class="identifier">F</span> <span class="identifier">f</span><span class="special">)</span> <span class="special">&&</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ is <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>
+ and <code class="computeroutput"><span class="identifier">F</span></code> models a <a href="http://www.sgi.com/tech/stl/Generator.html" target="_top"><code class="computeroutput"><span class="identifier">Generator</span></code></a>
+ whose result type is convertible to <code class="computeroutput"><span class="identifier">T</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> <code class="computeroutput"><span class="keyword">if</span>
+ <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(**</span><span class="keyword">this</span><span class="special">);</span> <span class="keyword">else</span> <span class="keyword">return</span>
+ <span class="identifier">f</span><span class="special">();</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ ref-qualifiers on member functions this overload is not present.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_map"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="keyword">auto</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">map</span><span class="special">(</span><span class="identifier">F</span> <span class="identifier">f</span><span class="special">)</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">-></span>
+ </code><span class="emphasis"><em>see below</em></span><code class="computeroutput"> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="keyword">auto</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">map</span><span class="special">(</span><span class="identifier">F</span> <span class="identifier">f</span><span class="special">)</span> <span class="special">&</span> <span class="special">-></span> </code><span class="emphasis"><em>see below</em></span><code class="computeroutput">
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> <code class="computeroutput"><span class="keyword">if</span>
+ <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="identifier">f</span><span class="special">(**</span><span class="keyword">this</span><span class="special">);</span> <span class="keyword">else</span> <span class="keyword">return</span>
+ <span class="identifier">none</span><span class="special">;</span></code>
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The return type of these overloads
+ is <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">decltype</span><span class="special">(</span><span class="identifier">f</span><span class="special">(**</span><span class="keyword">this</span><span class="special">))></span></code>.
+ On compilers that do not support ref-qualifiers on member functions,
+ these two (as well as the next one) overloads are replaced with good
+ old const and non-const overloads.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">auto</span> <span class="identifier">length</span> <span class="special">=</span> <span class="special">[](</span><span class="keyword">const</span> <span class="identifier">string</span><span class="special">&</span> <span class="identifier">s</span><span class="special">){</span> <span class="keyword">return</span> <span class="identifier">s</span><span class="special">.</span><span class="identifier">size</span><span class="special">();</span> <span class="special">};</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">string</span><span class="special">></span> <span class="identifier">o1</span> <span class="special">{},</span> <span class="identifier">o2</span> <span class="special">{</span><span class="string">"cat"</span><span class="special">};</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">size_t</span><span class="special">></span> <span class="identifier">os1</span> <span class="special">=</span> <span class="identifier">o1</span><span class="special">.</span><span class="identifier">map</span><span class="special">(</span><span class="identifier">length</span><span class="special">),</span> <span class="identifier">os2</span> <span class="special">=</span> <span class="identifier">o2</span><span class="special">.</span><span class="identifier">map</span><span class="special">(</span><span class="identifier">length</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">os1</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">os2</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">os2</span> <span class="special">==</span> <span class="number">3</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_map_move"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="keyword">auto</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">map</span><span class="special">(</span><span class="identifier">F</span> <span class="identifier">f</span><span class="special">)</span> <span class="special">&&</span>
+ <span class="special">-></span> </code><span class="emphasis"><em>see below</em></span><code class="computeroutput">
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> <code class="computeroutput"><span class="keyword">if</span>
+ <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="identifier">f</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(**</span><span class="keyword">this</span><span class="special">));</span> <span class="keyword">else</span> <span class="keyword">return</span>
+ <span class="identifier">none</span><span class="special">;</span></code>
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The return type of this overload
+ is <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">decltype</span><span class="special">(</span><span class="identifier">f</span><span class="special">(</span><span class="identifier">istd</span><span class="special">::</span><span class="identifier">move</span><span class="special">(**</span><span class="keyword">this</span><span class="special">)))></span></code>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_flat_map"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="keyword">auto</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">flat_map</span><span class="special">(</span><span class="identifier">F</span> <span class="identifier">f</span><span class="special">)</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">-></span>
+ </code><span class="emphasis"><em>see below</em></span><code class="computeroutput"> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="keyword">auto</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">flat_map</span><span class="special">(</span><span class="identifier">F</span> <span class="identifier">f</span><span class="special">)</span> <span class="special">&</span> <span class="special">-></span> </code><span class="emphasis"><em>see below</em></span><code class="computeroutput">
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> The return type of expression
+ <code class="computeroutput"><span class="identifier">f</span><span class="special">(**</span><span class="keyword">this</span><span class="special">)</span></code>
+ is <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span></code>
+ for some object or reference type <code class="computeroutput"><span class="identifier">U</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> <code class="computeroutput"><span class="keyword">if</span>
+ <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="identifier">f</span><span class="special">(**</span><span class="keyword">this</span><span class="special">);</span> <span class="keyword">else</span> <span class="keyword">return</span>
+ <span class="identifier">none</span><span class="special">;</span></code>
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The return type of these overloads
+ is <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span></code>.
+ On compilers that do not support ref-qualifiers on member functions,
+ these two (as well as the next one) overloads are replaced with good
+ old const and non-const overloads.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">char</span><span class="special">></span> <span class="identifier">first_char</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">string</span><span class="special">&</span> <span class="identifier">s</span><span class="special">)</span> <span class="special">{</span>
+ <span class="keyword">return</span> <span class="identifier">s</span><span class="special">.</span><span class="identifier">empty</span><span class="special">()</span> <span class="special">?</span> <span class="identifier">none</span> <span class="special">:</span> <span class="identifier">optional</span><span class="special"><</span><span class="keyword">char</span><span class="special">>(</span><span class="identifier">s</span><span class="special">[</span><span class="number">0</span><span class="special">]);</span>
+<span class="special">};</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">string</span><span class="special">></span> <span class="identifier">o1</span> <span class="special">{},</span> <span class="identifier">o2</span> <span class="special">{</span><span class="string">"cat"</span><span class="special">};</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">char</span><span class="special">></span> <span class="identifier">os1</span> <span class="special">=</span> <span class="identifier">o1</span><span class="special">.</span><span class="identifier">flat_map</span><span class="special">(</span><span class="identifier">first_char</span><span class="special">),</span> <span class="identifier">os2</span> <span class="special">=</span> <span class="identifier">o2</span><span class="special">.</span><span class="identifier">flat_map</span><span class="special">(</span><span class="identifier">first_char</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">os1</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">os2</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">*</span><span class="identifier">os2</span> <span class="special">==</span> <span class="char">'c'</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </li>
+</ul></div>
+<a name="reference_optional_flat_map_move"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="keyword">auto</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">flat_map</span><span class="special">(</span><span class="identifier">F</span> <span class="identifier">f</span><span class="special">)</span> <span class="special">&&</span>
+ <span class="special">-></span> </code><span class="emphasis"><em>see below</em></span><code class="computeroutput">
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> The return type of expression
+ <code class="computeroutput"><span class="identifier">f</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(**</span><span class="keyword">this</span><span class="special">))</span></code>
+ is <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span></code>
+ for some object or reference type <code class="computeroutput"><span class="identifier">U</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effects:</strong></span> <code class="computeroutput"><span class="keyword">if</span>
+ <span class="special">(*</span><span class="keyword">this</span><span class="special">)</span> <span class="keyword">return</span> <span class="identifier">f</span><span class="special">(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(**</span><span class="keyword">this</span><span class="special">));</span> <span class="keyword">else</span> <span class="keyword">return</span>
+ <span class="identifier">none</span><span class="special">;</span></code>
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The return type of this overload
+ is <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span></code>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_get_value_or_value"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">get_value_or</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="keyword">default</span><span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">get_value_or</span><span class="special">(</span>
+ <span class="identifier">T</span><span class="special">&</span>
+ <span class="keyword">default</span> <span class="special">)</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Deprecated:</strong></span> Use <code class="computeroutput"><span class="identifier">value_or</span><span class="special">()</span></code> instead.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> A reference to the contained
+ value, if any, or <code class="computeroutput"><span class="keyword">default</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">,</span> <span class="identifier">z</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span><span class="special">;</span>
+<span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">=</span> <span class="identifier">def</span><span class="special">.</span><span class="identifier">get_value_or</span><span class="special">(</span><span class="identifier">z</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">y</span> <span class="special">==</span> <span class="identifier">z</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">);</span>
+<span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">u</span> <span class="special">=</span> <span class="identifier">opt</span><span class="special">.</span><span class="identifier">get_value_or</span><span class="special">(</span><span class="identifier">z</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">u</span> <span class="special">==</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">u</span> <span class="special">!=</span> <span class="identifier">z</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_get_ptr"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">get_ptr</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">*</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">get_ptr</span><span class="special">()</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized, a pointer to the
+ contained value; else <code class="computeroutput"><span class="number">0</span></code>
+ (<span class="emphasis"><em>null</em></span>).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The contained value is permanently
+ stored within <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code>,
+ so you should not hold nor delete this pointer
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span> <span class="identifier">copt</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="identifier">T</span><span class="special">*</span> <span class="identifier">p</span> <span class="special">=</span> <span class="identifier">opt</span><span class="special">.</span><span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">;</span>
+<span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">cp</span> <span class="special">=</span> <span class="identifier">copt</span><span class="special">.</span><span class="identifier">get_ptr</span><span class="special">();</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">p</span> <span class="special">==</span> <span class="identifier">get_pointer</span><span class="special">(</span><span class="identifier">opt</span><span class="special">)</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">cp</span> <span class="special">==</span> <span class="identifier">get_pointer</span><span class="special">(</span><span class="identifier">copt</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_arrow"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span>
+ <span class="special">->()</span> <span class="keyword">const</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="identifier">T</span><span class="special">*</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span> <span class="special">->()</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires: </strong></span> <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is initialized.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> A pointer to the contained
+ value.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Throws:</strong></span> Nothing.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> The requirement is asserted
+ via <code class="computeroutput"><span class="identifier">BOOST_ASSERT</span><span class="special">()</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">X</span> <span class="special">{</span> <span class="keyword">int</span> <span class="identifier">mdata</span> <span class="special">;</span> <span class="special">}</span> <span class="special">;</span>
+<span class="identifier">X</span> <span class="identifier">x</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">X</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span><span class="identifier">x</span><span class="special">);</span>
+<span class="identifier">opt</span><span class="special">-></span><span class="identifier">mdata</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_bool"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">explicit</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span>
+ <span class="keyword">bool</span><span class="special">()</span>
+ <span class="keyword">const</span> <span class="keyword">noexcept</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">has_value</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">!=</span> <span class="number">0</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> On compilers that do not support
+ explicit conversion operators this falls back to safe-bool idiom.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">def</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">def</span> <span class="special">==</span> <span class="number">0</span> <span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">(</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt</span> <span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="identifier">opt</span> <span class="special">!=</span> <span class="number">0</span> <span class="special">);</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_operator_not"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">!()</span> <span class="keyword">noexcept</span>
+ <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> If <code class="computeroutput"><span class="special">*</span><span class="keyword">this</span></code> is uninitialized, <code class="computeroutput"><span class="keyword">true</span></code>; else <code class="computeroutput"><span class="keyword">false</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Notes:</strong></span> This operator is provided for
+ those compilers which can't use the <span class="emphasis"><em>unspecified-bool-type
+ operator</em></span> in certain boolean contexts.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Example:</strong></span>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt</span> <span class="special">;</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!</span><span class="identifier">opt</span> <span class="special">);</span>
+<span class="special">*</span><span class="identifier">opt</span> <span class="special">=</span> <span class="identifier">some_T</span> <span class="special">;</span>
+
+<span class="comment">// Notice the "double-bang" idiom here.</span>
+<span class="identifier">assert</span> <span class="special">(</span> <span class="special">!!</span><span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span>
+</pre>
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span>
+ </p>
+<a name="reference_optional_is_initialized"></a><div class="blockquote"><blockquote class="blockquote"><p>
+ <code class="computeroutput"><span class="keyword">bool</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">is_initialized</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span></code>
+ </p></blockquote></div>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <span class="bold"><strong>Deprecated:</strong></span> Same as <code class="computeroutput"><span class="keyword">explicit</span> <span class="keyword">operator</span>
+ <span class="keyword">bool</span> <span class="special">()</span>
+ <span class="special">;</span></code>
+ </li></ul></div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="header_optional_optional_refs.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="detailed_semantics___optional_references.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/header__boost_optional_hpp_.html b/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/header__boost_optional_hpp_.html
new file mode 100644
index 0000000..8496d37
--- /dev/null
+++ b/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/header__boost_optional_hpp_.html
@@ -0,0 +1,47 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Header <boost/optional.hpp></title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../../../optional/reference/header__boost_optional_optional_hpp_.html" title="Header <boost/optional/optional.hpp>">
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+<link rel="next" href="../dependencies_and_portability.html" title="Dependencies and Portability">
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+<a accesskey="p" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../dependencies_and_portability.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.header__boost_optional_optional_hpp_.header__boost_optional_hpp_"></a><a class="link" href="header__boost_optional_hpp_.html" title="Header <boost/optional.hpp>">Header
+ <boost/optional.hpp></a>
+</h4></div></div></div>
+<p>
+ This is an alias for header <a class="link" href="../../../optional/reference/header__boost_optional_optional_hpp_.html#boost_optional.reference.header__boost_optional_optional_hpp_.header_optional_optional" title="Synopsis"><code class="computeroutput"><span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">optional</span><span class="special">/</span><span class="identifier">optional</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code></a>.
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2016 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
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+<a accesskey="p" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../dependencies_and_portability.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
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diff --git a/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/header_optional_in_place_init.html b/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/header_optional_in_place_init.html
new file mode 100644
index 0000000..be67b67
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+++ b/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/header_optional_in_place_init.html
@@ -0,0 +1,61 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Initialization tags</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../../../optional/reference/header__boost_optional_optional_hpp_.html" title="Header <boost/optional/optional.hpp>">
+<link rel="prev" href="../../../optional/reference/header__boost_optional_optional_hpp_.html" title="Header <boost/optional/optional.hpp>">
+<link rel="next" href="header_optional_optional_values.html" title="Optional Values">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
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+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="header_optional_optional_values.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.header__boost_optional_optional_hpp_.header_optional_in_place_init"></a><a class="link" href="header_optional_in_place_init.html" title="Initialization tags">Initialization
+ tags</a>
+</h4></div></div></div>
+<a name="reference_in_place_init"></a><a name="reference_in_place_init_if"></a><pre class="programlisting"><span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
+
+<span class="keyword">class</span> <span class="identifier">in_place_init_t</span> <span class="special">{</span> <span class="comment">/* see below */</span> <span class="special">}</span> <span class="special">;</span>
+<span class="keyword">const</span> <span class="identifier">in_place_init_t</span> <span class="identifier">in_place_init</span> <span class="special">(</span> <span class="comment">/* see below */</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="keyword">class</span> <span class="identifier">in_place_init_if_t</span> <span class="special">{</span> <span class="comment">/*see below*/</span> <span class="special">}</span> <span class="special">;</span>
+<span class="keyword">const</span> <span class="identifier">in_place_init_if_t</span> <span class="identifier">in_place_init_if</span> <span class="special">(</span> <span class="comment">/*see below*/</span> <span class="special">)</span> <span class="special">;</span>
+
+<span class="special">}</span>
+</pre>
+<p>
+ Classes <code class="computeroutput"><span class="identifier">in_place_init_t</span></code>
+ and <code class="computeroutput"><span class="identifier">in_place_init_if_t</span></code>
+ are empty clsses. Their purpose is to control overload resolution in the
+ initialization of optional objects. They are empty, trivially copyable
+ classes with disabled default constructor.
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="header_optional_optional_values.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/header_optional_optional_refs.html b/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/header_optional_optional_refs.html
new file mode 100644
index 0000000..43b0c0a
--- /dev/null
+++ b/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/header_optional_optional_refs.html
@@ -0,0 +1,119 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Optional References</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../../../optional/reference/header__boost_optional_optional_hpp_.html" title="Header <boost/optional/optional.hpp>">
+<link rel="prev" href="header_optional_optional_values.html" title="Optional Values">
+<link rel="next" href="detailed_semantics___optional_values.html" title="Detailed Semantics - Optional Values">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="header_optional_optional_values.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="detailed_semantics___optional_values.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.header__boost_optional_optional_hpp_.header_optional_optional_refs"></a><a class="link" href="header_optional_optional_refs.html" title="Optional References">Optional
+ References</a>
+</h4></div></div></div>
+<a name="reference_operator_template_spec"></a><pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
+<span class="keyword">class</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span> <span class="comment">// specilization for lvalue references</span>
+<span class="special">{</span>
+<span class="keyword">public</span> <span class="special">:</span>
+
+ <span class="keyword">typedef</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">value_type</span><span class="special">;</span>
+ <span class="keyword">typedef</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">reference_type</span><span class="special">;</span>
+ <span class="keyword">typedef</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">reference_const_type</span><span class="special">;</span> <span class="comment">// no const propagation</span>
+ <span class="keyword">typedef</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">rval_reference_type</span><span class="special">;</span>
+ <span class="keyword">typedef</span> <span class="identifier">T</span><span class="special">*</span> <span class="identifier">pointer_type</span><span class="special">;</span>
+ <span class="keyword">typedef</span> <span class="identifier">T</span><span class="special">*</span> <span class="identifier">pointer_const_type</span><span class="special">;</span> <span class="comment">// no const propagation</span>
+
+ <span class="identifier">optional</span> <span class="special">()</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_default_ctor"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_default_ctor"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">></span> <span class="identifier">optional</span><span class="special">(</span><span class="identifier">R</span><span class="special">&&</span> <span class="identifier">r</span><span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_value_ctor"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">></span> <span class="identifier">optional</span><span class="special">(</span><span class="keyword">bool</span> <span class="identifier">cond</span><span class="special">,</span> <span class="identifier">R</span><span class="special">&&</span> <span class="identifier">r</span><span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_cond_value_ctor"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">optional</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_copy_ctor"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">&></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_ctor_from_opt_U"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_assign_none_t"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_copy_assign"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">&></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_assign_optional_U"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span><span class="identifier">R</span><span class="special">&&</span> <span class="identifier">r</span><span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_assign_R"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">emplace</span> <span class="special">(</span> <span class="identifier">R</span><span class="special">&&</span> <span class="identifier">r</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_emplace_R"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_get"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+ <span class="identifier">T</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">*()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_get"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">T</span><span class="special">*</span> <span class="keyword">operator</span> <span class="special">->()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_arrow"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">T</span><span class="special">&</span> <span class="identifier">value</span><span class="special">()</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">></span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">value_or</span><span class="special">(</span> <span class="identifier">R</span> <span class="special">&&</span> <span class="identifier">r</span> <span class="special">)</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_value_or"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">value_or_eval</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_value_or_eval"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="keyword">auto</span> <span class="identifier">map</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="keyword">const</span> <span class="special">-></span> <span class="emphasis"><em>see below</em></span><span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_map"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="keyword">auto</span> <span class="identifier">flat_map</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="keyword">const</span> <span class="special">-></span> <span class="emphasis"><em>see below</em></span><span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_flat_map"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">T</span><span class="special">*</span> <span class="identifier">get_ptr</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_get_ptr"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">bool</span> <span class="identifier">has_value</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_operator_bool"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">explicit</span> <span class="keyword">operator</span> <span class="keyword">bool</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_operator_bool"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">!()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_operator_not"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="comment">// deprecated methods</span>
+
+ <span class="comment">// (deprecated)</span>
+ <span class="keyword">void</span> <span class="identifier">reset</span><span class="special">()</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_reset"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="comment">// (deprecated)</span>
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">reset</span> <span class="special">(</span> <span class="identifier">R</span> <span class="special">&&</span> <span class="identifier">r</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_reset_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="comment">// (deprecated)</span>
+ <span class="keyword">bool</span> <span class="identifier">is_initialized</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_is_initialized"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="comment">// (deprecated)</span>
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">R</span><span class="special">></span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get_value_or</span><span class="special">(</span> <span class="identifier">R</span> <span class="special">&&</span> <span class="identifier">r</span> <span class="special">)</span> <span class="identifier">constnoexcept</span><span class="special">;</span> <a class="link" href="detailed_semantics___optional_references.html#reference_optional_ref_get_value_or_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+<span class="keyword">private</span><span class="special">:</span>
+ <span class="identifier">T</span><span class="special">*</span> <span class="identifier">ref</span><span class="special">;</span> <span class="comment">// exposition only</span>
+<span class="special">};</span>
+</pre>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="header_optional_optional_values.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="detailed_semantics___optional_values.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/header_optional_optional_values.html b/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/header_optional_optional_values.html
new file mode 100644
index 0000000..5e1edff
--- /dev/null
+++ b/doc/html/boost_optional/reference/header__boost_optional_optional_hpp_/header_optional_optional_values.html
@@ -0,0 +1,154 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Optional Values</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../../../optional/reference/header__boost_optional_optional_hpp_.html" title="Header <boost/optional/optional.hpp>">
+<link rel="prev" href="header_optional_in_place_init.html" title="Initialization tags">
+<link rel="next" href="header_optional_optional_refs.html" title="Optional References">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td>
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+<a name="boost_optional.reference.header__boost_optional_optional_hpp_.header_optional_optional_values"></a><a class="link" href="header_optional_optional_values.html" title="Optional Values">Optional
+ Values</a>
+</h4></div></div></div>
+<a name="reference_operator_template"></a><pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
+<span class="keyword">class</span> <span class="identifier">optional</span>
+<span class="special">{</span>
+<span class="keyword">public</span> <span class="special">:</span>
+
+ <span class="keyword">typedef</span> <span class="identifier">T</span> <span class="identifier">value_type</span> <span class="special">;</span>
+ <span class="keyword">typedef</span> <span class="identifier">T</span> <span class="special">&</span> <span class="identifier">reference_type</span> <span class="special">;</span>
+ <span class="keyword">typedef</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">reference_const_type</span> <span class="special">;</span>
+ <span class="keyword">typedef</span> <span class="identifier">T</span> <span class="special">&&</span> <span class="identifier">rval_reference_type</span> <span class="special">;</span>
+ <span class="keyword">typedef</span> <span class="identifier">T</span> <span class="special">*</span> <span class="identifier">pointer_type</span> <span class="special">;</span>
+ <span class="keyword">typedef</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">pointer_const_type</span> <span class="special">;</span>
+
+ <span class="identifier">optional</span> <span class="special">()</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_constructor"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_constructor_none_t"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_constructor_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_constructor_move_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span> <span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_constructor_bool_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">optional</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_constructor_optional"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">(</span><span class="emphasis"><em>see below</em></span><span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_move_constructor_optional"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_constructor_other_optional"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_move_constructor_other_optional"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">in_place_init_t</span><span class="special">,</span> <span class="identifier">Args</span><span class="special">&&...</span> <span class="identifier">args</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_in_place_init"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">in_place_init_if_t</span><span class="special">,</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">Args</span><span class="special">&&...</span> <span class="identifier">args</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_in_place_init_if"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">InPlaceFactory</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">InPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_constructor_factory"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">TypedInPlaceFactory</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">TypedInPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_constructor_factory"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_equal_none_t"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_equal_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_move_equal_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_equal_optional"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">(</span><span class="emphasis"><em>see below</em></span><span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_move_equal_optional"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_equal_other_optional"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_move_equal_other_optional"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">emplace</span> <span class="special">(</span> <span class="identifier">Args</span><span class="special">&&...</span> <span class="identifier">args</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_emplace"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">InPlaceFactory</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">InPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_equal_factory"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">TypedInPlaceFactory</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">TypedInPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_equal_factory"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_get"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+ <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get</span><span class="special">()</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_get"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="keyword">operator</span> <span class="special">->()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_arrow"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+ <span class="identifier">T</span><span class="special">*</span> <span class="keyword">operator</span> <span class="special">->()</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_arrow"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">*()</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_asterisk"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+ <span class="identifier">T</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">*()</span> <span class="special">&</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_asterisk"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+ <span class="identifier">T</span><span class="special">&&</span> <span class="keyword">operator</span> <span class="special">*()</span> <span class="special">&&</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_asterisk_move"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">value</span><span class="special">()</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+ <span class="identifier">T</span><span class="special">&</span> <span class="identifier">value</span><span class="special">()</span> <span class="special">&</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+ <span class="identifier">T</span><span class="special">&&</span> <span class="identifier">value</span><span class="special">()</span> <span class="special">&&</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_value_move"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">value_or</span><span class="special">(</span> <span class="identifier">U</span> <span class="special">&&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_value_or"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">value_or</span><span class="special">(</span> <span class="identifier">U</span> <span class="special">&&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">&&</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_value_or_move"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">value_or_eval</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_value_or_call"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">value_or_eval</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">&&</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_value_or_call_move"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="keyword">auto</span> <span class="identifier">map</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">-></span> <span class="emphasis"><em>see below</em></span><span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_map"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="keyword">auto</span> <span class="identifier">map</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">&</span> <span class="special">-></span> <span class="emphasis"><em>see below</em></span><span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_map"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="keyword">auto</span> <span class="identifier">map</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">&&</span> <span class="special">-></span> <span class="emphasis"><em>see below</em></span><span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_map_move"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="keyword">auto</span> <span class="identifier">flat_map</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">-></span> <span class="emphasis"><em>see below</em></span><span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_flat_map"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="keyword">auto</span> <span class="identifier">flat_map</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">&</span> <span class="special">-></span> <span class="emphasis"><em>see below</em></span><span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_flat_map"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">F</span><span class="special">></span> <span class="keyword">auto</span> <span class="identifier">flat_map</span><span class="special">(</span> <span class="identifier">F</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">&&</span> <span class="special">-></span> <span class="emphasis"><em>see below</em></span><span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_flat_map_move"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">get_ptr</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_get_ptr"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+ <span class="identifier">T</span><span class="special">*</span> <span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_get_ptr"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">bool</span> <span class="identifier">has_value</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_bool"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">explicit</span> <span class="keyword">operator</span> <span class="keyword">bool</span><span class="special">()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_bool"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">!()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_operator_not"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="comment">// deprecated methods</span>
+
+ <span class="comment">// (deprecated)</span>
+ <span class="keyword">void</span> <span class="identifier">reset</span><span class="special">()</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_reset"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="comment">// (deprecated)</span>
+ <span class="keyword">void</span> <span class="identifier">reset</span> <span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_reset_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="comment">// (deprecated)</span>
+ <span class="keyword">bool</span> <span class="identifier">is_initialized</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_is_initialized"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="comment">// (deprecated)</span>
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">get_value_or</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="keyword">default</span> <span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics___optional_values.html#reference_optional_get_value_or_value"><span class="inlinemediaobject"><img src="../../../images/callouts/R.png" alt="R"></span></a>
+<span class="special">};</span>
+</pre>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="header_optional_in_place_init.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../../optional/reference/header__boost_optional_optional_hpp_.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="header_optional_optional_refs.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/reference/io_header.html b/doc/html/boost_optional/reference/io_header.html
new file mode 100644
index 0000000..fd8599f
--- /dev/null
+++ b/doc/html/boost_optional/reference/io_header.html
@@ -0,0 +1,72 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Header <boost/optional/optional_io.hpp></title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
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+<link rel="next" href="io_header/io_semantics.html" title="Detailed semantics">
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+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
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+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
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+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="header__boost_optional_bad_optional_access_hpp_/detailed_semantics.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="io_header/io_semantics.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.reference.io_header"></a><a class="link" href="io_header.html" title="Header <boost/optional/optional_io.hpp>">Header <boost/optional/optional_io.hpp></a>
+</h3></div></div></div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.io_header.io_synop"></a><a class="link" href="io_header.html#boost_optional.reference.io_header.io_synop" title="Synopsis">Synopsis</a>
+</h4></div></div></div>
+<p>
+</p>
+<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">istream</span><span class="special">></span>
+<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">ostream</span><span class="special">></span>
+<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">optional</span><span class="special">/</span><span class="identifier">optional</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
+
+<span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
+
+<span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">CharType</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">CharTrait</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
+ <span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special"><</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">>&</span>
+ <span class="keyword">operator</span><span class="special"><<(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special"><</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">>&</span> <span class="identifier">out</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span><span class="special">);</span> <a class="link" href="io_header/io_semantics.html#reference_operator_ostream"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">CharType</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">CharTrait</span><span class="special">></span>
+ <span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special"><</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">>&</span>
+ <span class="keyword">operator</span><span class="special"><<(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special"><</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">>&</span> <span class="identifier">out</span><span class="special">,</span> <span class="identifier">none_t</span> <span class="keyword">const</span><span class="special">&);</span> <a class="link" href="io_header/io_semantics.html#reference_operator_ostream_none"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">CharType</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">CharTrait</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
+ <span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_istream</span><span class="special"><</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">>&</span>
+ <span class="keyword">operator</span><span class="special">>>(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_istream</span><span class="special"><</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">>&</span> <span class="identifier">in</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">v</span><span class="special">);</span> <a class="link" href="io_header/io_semantics.html#reference_operator_istream"><span class="inlinemediaobject"><img src="../../images/callouts/R.png" alt="R"></span></a>
+
+<span class="special">}</span> <span class="comment">// namespace boost</span>
+</pre>
+<p>
+ </p>
+</div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="header__boost_optional_bad_optional_access_hpp_/detailed_semantics.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="io_header/io_semantics.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/reference/io_header/io_semantics.html b/doc/html/boost_optional/reference/io_header/io_semantics.html
new file mode 100644
index 0000000..2e8ed56
--- /dev/null
+++ b/doc/html/boost_optional/reference/io_header/io_semantics.html
@@ -0,0 +1,112 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Detailed semantics</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../io_header.html" title="Header <boost/optional/optional_io.hpp>">
+<link rel="prev" href="../io_header.html" title="Header <boost/optional/optional_io.hpp>">
+<link rel="next" href="../header__boost_optional_optional_fwd_hpp_.html" title="Header <boost/optional/optional_fwd.hpp>">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
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+</tr></table>
+<hr>
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+<a accesskey="p" href="../io_header.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../io_header.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../header__boost_optional_optional_fwd_hpp_.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.reference.io_header.io_semantics"></a><a class="link" href="io_semantics.html" title="Detailed semantics">Detailed
+ semantics</a>
+</h4></div></div></div>
+<p>
+ <a name="reference_operator_ostream"></a><code class="computeroutput"><span class="keyword">template</span>
+ <span class="special"><</span><span class="keyword">class</span>
+ <span class="identifier">CharType</span><span class="special">,</span>
+ <span class="keyword">class</span> <span class="identifier">CharTrait</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span></code>
+ <br>     <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special"><</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">>&</span></code> <br>     <code class="computeroutput"><span class="keyword">operator</span><span class="special"><<(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special"><</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">>&</span>
+ <span class="identifier">out</span><span class="special">,</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span><span class="special">);</span></code>
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Outputs an implementation-defined
+ string. The output contains the information about whether the optional
+ object contains a value or not. If <code class="computeroutput"><span class="identifier">v</span></code>
+ contains a value, the output contains result of calling <code class="computeroutput"><span class="identifier">out</span> <span class="special"><<</span>
+ <span class="special">*</span><span class="identifier">v</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="identifier">out</span></code>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> <a name="reference_operator_ostream_none"></a>
+ </p>
+<p>
+ <code class="computeroutput"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">CharType</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">CharTrait</span><span class="special">,</span>
+ <span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span></code> <br>     <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special"><</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">>&</span></code>
+ <br>     <code class="computeroutput"><span class="keyword">operator</span><span class="special"><<(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special"><</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">>&</span> <span class="identifier">out</span><span class="special">,</span> <span class="identifier">none_t</span><span class="special">);</span></code>
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Outputs an implementation-defined
+ string.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="identifier">out</span></code>.
+ </li>
+</ul></div>
+<p>
+ <span class="inlinemediaobject"><img src="../../../images/space.png" alt="space"></span> <a name="reference_operator_istream"></a>
+ </p>
+<p>
+ <code class="computeroutput"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">class</span> <span class="identifier">CharType</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">CharTrait</span><span class="special">,</span>
+ <span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span></code> <br>     <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_ostream</span><span class="special"><</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">>&</span></code>
+ <br>     <code class="computeroutput"><span class="keyword">operator</span><span class="special">>>(</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">basic_istream</span><span class="special"><</span><span class="identifier">CharType</span><span class="special">,</span> <span class="identifier">CharTrait</span><span class="special">>&</span> <span class="identifier">in</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">v</span><span class="special">);</span></code>
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Requires:</strong></span> <code class="computeroutput"><span class="identifier">T</span></code>
+ is <a href="http://www.sgi.com/tech/stl/DefaultConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">DefaultConstructible</span></code></a> and
+ <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Effect:</strong></span> Reads the value of optional
+ object from <code class="computeroutput"><span class="identifier">in</span></code>. If
+ the string representation indicates that the optional object should
+ contain a value, <code class="computeroutput"><span class="identifier">v</span></code>
+ contains a value and its contained value is obtained as if by default-constructing
+ an object <code class="computeroutput"><span class="identifier">o</span></code> of type
+ <code class="computeroutput"><span class="identifier">T</span></code> and then calling
+ <code class="computeroutput"><span class="identifier">in</span> <span class="special">>></span>
+ <span class="identifier">o</span></code>; otherwise <code class="computeroutput"><span class="identifier">v</span></code> does not contain a value, and the
+ previously contained value (if any) has been destroyed.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Returns:</strong></span> <code class="computeroutput"><span class="identifier">out</span></code>.
+ </li>
+</ul></div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../io_header.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../io_header.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../header__boost_optional_optional_fwd_hpp_.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
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diff --git a/doc/html/boost_optional/reference/relnotes.html b/doc/html/boost_optional/reference/relnotes.html
new file mode 100644
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+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Release Notes</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../../index.html" title="Boost.Optional">
+<link rel="up" href="../../optional/reference.html" title="Reference">
+<link rel="prev" href="dependencies_and_portability/optional_reference_binding.html" title="Optional Reference Binding">
+<link rel="next" href="acknowledgements.html" title="Acknowledgements">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
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+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="dependencies_and_portability/optional_reference_binding.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="acknowledgements.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.reference.relnotes"></a><a class="link" href="relnotes.html" title="Release Notes">Release Notes</a>
+</h3></div></div></div>
+<h5>
+<a name="boost_optional.reference.relnotes.h0"></a>
+ <span class="phrase"><a name="boost_optional.reference.relnotes.boost_release_x_xx"></a></span><a class="link" href="relnotes.html#boost_optional.reference.relnotes.boost_release_x_xx">Boost Release
+ X.XX</a>
+ </h5>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ Now <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span></code> is specialized for reference
+ parameters. This way the <code class="computeroutput"><span class="keyword">sizeof</span></code>
+ of optional reference is that of a pointer, and a number of bugs is avoided.
+ </li></ul></div>
+<h5>
+<a name="boost_optional.reference.relnotes.h1"></a>
+ <span class="phrase"><a name="boost_optional.reference.relnotes.boost_release_1_60"></a></span><a class="link" href="relnotes.html#boost_optional.reference.relnotes.boost_release_1_60">Boost Release
+ 1.60</a>
+ </h5>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ Changed the implementation of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code>
+ again. Now it is a const object with internal linkage (as any other tag).
+ This fixes <a href="https://svn.boost.org/trac/boost/ticket/11203" target="_top">Trac
+ #11203</a>.
+ </li></ul></div>
+<h5>
+<a name="boost_optional.reference.relnotes.h2"></a>
+ <span class="phrase"><a name="boost_optional.reference.relnotes.boost_release_1_59"></a></span><a class="link" href="relnotes.html#boost_optional.reference.relnotes.boost_release_1_59">Boost Release
+ 1.59</a>
+ </h5>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ For C++03 compilers, added 0-argument overload for member function <code class="computeroutput"><span class="identifier">emplace</span><span class="special">()</span></code>,
+ and therewith removed the dependency on <code class="computeroutput"><span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">utility</span><span class="special">/</span><span class="identifier">in_place_factory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>.
+ </li>
+<li class="listitem">
+ Fixed <a href="https://svn.boost.org/trac/boost/ticket/11241" target="_top">Trac
+ #11241</a>.
+ </li>
+</ul></div>
+<h5>
+<a name="boost_optional.reference.relnotes.h3"></a>
+ <span class="phrase"><a name="boost_optional.reference.relnotes.boost_release_1_58"></a></span><a class="link" href="relnotes.html#boost_optional.reference.relnotes.boost_release_1_58">Boost Release
+ 1.58</a>
+ </h5>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none_t</span></code> is no longer convertible from
+ literal <code class="computeroutput"><span class="number">0</span></code>. This avoids a
+ bug where <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">rational</span><span class="special"><</span><span class="keyword">int</span><span class="special">>></span>
+ <span class="identifier">oi</span> <span class="special">=</span>
+ <span class="number">0</span><span class="special">;</span></code>
+ would initialize an optional object with no contained value.
+ </li>
+<li class="listitem">
+ Improved the trick that prevents streaming out <code class="computeroutput"><span class="identifier">optional</span></code>
+ without header <code class="computeroutput"><span class="identifier">optional_io</span><span class="special">.</span><span class="identifier">hpp</span></code>
+ by using safe-bool idiom. This addresses <a href="https://svn.boost.org/trac/boost/ticket/10825" target="_top">Trac
+ #10825</a>.
+ </li>
+<li class="listitem">
+ IOStream operators are now mentioned in documentation.
+ </li>
+<li class="listitem">
+ Added a way to manually disable move semantics: just define macro <code class="computeroutput"><span class="identifier">BOOST_OPTIONAL_CONFIG_NO_RVALUE_REFERENCES</span></code>.
+ This can be used to work around <a href="https://svn.boost.org/trac/boost/ticket/10399" target="_top">Trac
+ #10399</a>.
+ </li>
+<li class="listitem">
+ It is no longer possible to assign <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span></code> to <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> when <code class="computeroutput"><span class="identifier">U</span></code>
+ is not assignable or convertible to <code class="computeroutput"><span class="identifier">T</span></code>
+ (<a href="https://svn.boost.org/trac/boost/ticket/11087" target="_top">Trac #11087</a>).
+ </li>
+<li class="listitem">
+ Value accessors now work correctly on rvalues of <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code> (<a href="https://svn.boost.org/trac/boost/ticket/10839" target="_top">Trac
+ #10839</a>).
+ </li>
+</ul></div>
+<h5>
+<a name="boost_optional.reference.relnotes.h4"></a>
+ <span class="phrase"><a name="boost_optional.reference.relnotes.boost_release_1_57"></a></span><a class="link" href="relnotes.html#boost_optional.reference.relnotes.boost_release_1_57">Boost Release
+ 1.57</a>
+ </h5>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <a href="https://github.com/boostorg/optional/pull/9" target="_top">Git pull #9</a>:
+ <span class="emphasis"><em>"Supply <code class="computeroutput"><span class="special"><</span><span class="identifier">string</span><span class="special">></span></code>
+ to fix C++03 compile error on <code class="computeroutput"><span class="identifier">logic_error</span><span class="special">(</span><span class="string">"..."</span><span class="special">)</span></code>"</em></span>.
+ </li></ul></div>
+<h5>
+<a name="boost_optional.reference.relnotes.h5"></a>
+ <span class="phrase"><a name="boost_optional.reference.relnotes.boost_release_1_56"></a></span><a class="link" href="relnotes.html#boost_optional.reference.relnotes.boost_release_1_56">Boost Release
+ 1.56</a>
+ </h5>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ Added support for rvalue references. Now <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> works with moveable but non-copyable
+ <code class="computeroutput"><span class="identifier">T</span></code>'s,
+ </li>
+<li class="listitem">
+ Improved <code class="computeroutput"><span class="identifier">swap</span></code> (now uses
+ move operations),
+ </li>
+<li class="listitem">
+ Added function <code class="computeroutput"><span class="identifier">emplace</span><span class="special">()</span></code>. This is the last of the requests from
+ <a href="https://svn.boost.org/trac/boost/ticket/1841" target="_top">Trac #1841</a>,
+ </li>
+<li class="listitem">
+ <code class="computeroutput"><span class="identifier">optional</span></code> is moveable,
+ including conditional <code class="computeroutput"><span class="keyword">noexcept</span></code>
+ specifications, which make it <code class="computeroutput"><span class="identifier">move_if_noexcept</span></code>-friendly,
+ </li>
+<li class="listitem">
+ Using explicit operator bool() on platforms that support it (<a href="https://svn.boost.org/trac/boost/ticket/4227" target="_top">Trac
+ #4227</a>) (breaking change),
+ </li>
+<li class="listitem">
+ Forward declaration of <code class="computeroutput"><span class="keyword">operator</span><span class="special"><<(</span><span class="identifier">ostream</span><span class="special">&,</span> <span class="identifier">optional</span>
+ <span class="keyword">const</span><span class="special">&)</span></code>
+ to prevent inadvertent incorrect serialization of optional objects,
+ </li>
+<li class="listitem">
+ Removed deprecated function <code class="computeroutput"><span class="identifier">reset</span><span class="special">()</span></code> from examples (<a href="https://svn.boost.org/trac/boost/ticket/9005" target="_top">Trac
+ #9005</a>),
+ </li>
+<li class="listitem">
+ Equality comparison with <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code>
+ does not require that <code class="computeroutput"><span class="identifier">T</span></code>
+ be EqualityComparable,
+ </li>
+<li class="listitem">
+ Optional rvalue references are explicitly disallowed,
+ </li>
+<li class="listitem">
+ Binding temporaries to optional references is explicitly disallowed (breaking
+ change),
+ </li>
+<li class="listitem">
+ More ways to access the contained value, functions <code class="computeroutput"><span class="identifier">value</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">value_or</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">value_or_eval</span><span class="special">()</span></code>,
+ </li>
+<li class="listitem">
+ Updated and reorganized documentation, added tutorial and quick guide
+ sections.
+ </li>
+</ul></div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2016 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="dependencies_and_portability/optional_reference_binding.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="acknowledgements.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/relnotes.html b/doc/html/boost_optional/relnotes.html
new file mode 100644
index 0000000..f074211
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+++ b/doc/html/boost_optional/relnotes.html
@@ -0,0 +1,293 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Release Notes</title>
+<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../index.html" title="Boost.Optional">
+<link rel="up" href="../index.html" title="Boost.Optional">
+<link rel="prev" href="dependencies_and_portability/optional_reference_binding.html" title="Optional Reference Binding">
+<link rel="next" href="acknowledgements.html" title="Acknowledgements">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="dependencies_and_portability/optional_reference_binding.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="acknowledgements.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="boost_optional.relnotes"></a><a class="link" href="relnotes.html" title="Release Notes">Release Notes</a>
+</h2></div></div></div>
+<h4>
+<a name="boost_optional.relnotes.h0"></a>
+ <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_68"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_68">Boost
+ Release 1.68</a>
+ </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ Added member function <code class="computeroutput"><span class="identifier">has_value</span><span class="special">()</span></code> for compatibility with <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">optional</span></code> (<a href="https://github.com/boostorg/optional/issues/52" target="_top">issue
+ #52</a>).
+ </li>
+<li class="listitem">
+ Added member function <code class="computeroutput"><span class="identifier">map</span><span class="special">()</span></code> for transforming <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> into <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span></code> using a function of type <code class="computeroutput"><span class="identifier">T</span> <span class="special">-></span> <span class="identifier">U</span></code>.
+ </li>
+<li class="listitem">
+ Added member function <code class="computeroutput"><span class="identifier">flat_map</span><span class="special">()</span></code> for transforming <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> into <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span></code> using a function of type <code class="computeroutput"><span class="identifier">T</span> <span class="special">-></span> <span class="identifier">optonal</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span></code>.
+ </li>
+</ul></div>
+<h4>
+<a name="boost_optional.relnotes.h1"></a>
+ <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_67"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_67">Boost
+ Release 1.67</a>
+ </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ Fixed <a href="https://github.com/boostorg/optional/issues/46" target="_top">issue
+ #46</a>.
+ </li>
+<li class="listitem">
+ Fixed <code class="computeroutput"><span class="special">-</span><span class="identifier">Wzero</span><span class="special">-</span><span class="identifier">as</span><span class="special">-</span><span class="identifier">null</span><span class="special">-</span><span class="identifier">pointer</span><span class="special">-</span><span class="identifier">constant</span></code> warnings.
+ </li>
+</ul></div>
+<h4>
+<a name="boost_optional.relnotes.h2"></a>
+ <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_66"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_66">Boost
+ Release 1.66</a>
+ </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ On newer compilers <code class="computeroutput"><span class="identifier">optional</span></code>
+ is now trivially-copyable for scalar <code class="computeroutput"><span class="identifier">T</span></code>s.
+ This uses a different storage (just <code class="computeroutput"><span class="identifier">T</span></code>
+ rather than <code class="computeroutput"><span class="identifier">aligned_storage</span></code>).
+ We require the compiler to support defaulted functions.
+ </li>
+<li class="listitem">
+ Changed the implementation of <code class="computeroutput"><span class="keyword">operator</span><span class="special">==</span></code> to get rid of the <code class="computeroutput"><span class="special">-</span><span class="identifier">Wmaybe</span><span class="special">-</span><span class="identifier">uninitialized</span></code> false-positive warning
+ from GCC.
+ </li>
+</ul></div>
+<h4>
+<a name="boost_optional.relnotes.h3"></a>
+ <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_63"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_63">Boost
+ Release 1.63</a>
+ </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ Added two new in-place constructors. They work similarly to <code class="computeroutput"><span class="identifier">emplace</span><span class="special">()</span></code>
+ functions: they initialize the contained value by perfect-forwarding the
+ obtained arguments. One constructor always initializes the contained value,
+ the other based on a boolean condition.
+ </li>
+<li class="listitem">
+ Syntax <code class="computeroutput"><span class="identifier">o</span> <span class="special">=</span>
+ <span class="special">{}</span></code> now correctly un-initializes
+ optional, just like in <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">optional</span></code>.
+ </li>
+<li class="listitem">
+ Fixed <a href="https://svn.boost.org/trac/boost/ticket/12203" target="_top">Trac #12203</a>.
+ </li>
+<li class="listitem">
+ Fixed <a href="https://svn.boost.org/trac/boost/ticket/12563" target="_top">Trac #12563</a>.
+ </li>
+</ul></div>
+<h4>
+<a name="boost_optional.relnotes.h4"></a>
+ <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_62"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_62">Boost
+ Release 1.62</a>
+ </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ Fixed <a href="https://svn.boost.org/trac/boost/ticket/12179" target="_top">Trac #12179</a>.
+ </li></ul></div>
+<h4>
+<a name="boost_optional.relnotes.h5"></a>
+ <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_61"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_61">Boost
+ Release 1.61</a>
+ </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ Now <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span></code> is specialized for reference
+ parameters. This addresses a couple of issues:
+ <div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: circle; ">
+<li class="listitem">
+ the <code class="computeroutput"><span class="keyword">sizeof</span></code> of optional
+ reference is that of a pointer,
+ </li>
+<li class="listitem">
+ some bugs connected to copying optional references are gone,
+ </li>
+<li class="listitem">
+ all run-time bugs caused by incorrect reference binding on some compilers
+ are now turned into compile-time errors,
+ </li>
+<li class="listitem">
+ you can swap optional references: it is like swapping pointers: shalow,
+ underlying objects are not affected,
+ </li>
+<li class="listitem">
+ optional references to abstract types work.
+ </li>
+</ul></div>
+ </li>
+<li class="listitem">
+ Documented nested typedefs (<a href="https://svn.boost.org/trac/boost/ticket/5193" target="_top">Trac
+ #5193</a>).
+ </li>
+<li class="listitem">
+ Made the perfect-forwarding constructor SFINAE-friendly, which fixes <a href="https://svn.boost.org/trac/boost/ticket/12002" target="_top">Trac #12002</a>.
+ However, this only works in the newer platforms that correctly implement
+ C++11 <code class="computeroutput"><span class="special"><</span><span class="identifier">type_traits</span><span class="special">></span></code>.
+ </li>
+<li class="listitem">
+ Fixed <a href="https://svn.boost.org/trac/boost/ticket/10445" target="_top">Trac #10445</a>.
+ </li>
+</ul></div>
+<h4>
+<a name="boost_optional.relnotes.h6"></a>
+ <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_60"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_60">Boost
+ Release 1.60</a>
+ </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ Changed the implementation of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code>
+ again. Now it is a const object with internal linkage (as any other tag).
+ This fixes <a href="https://svn.boost.org/trac/boost/ticket/11203" target="_top">Trac
+ #11203</a>.
+ </li></ul></div>
+<h4>
+<a name="boost_optional.relnotes.h7"></a>
+ <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_59"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_59">Boost
+ Release 1.59</a>
+ </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ For C++03 compilers, added 0-argument overload for member function <code class="computeroutput"><span class="identifier">emplace</span><span class="special">()</span></code>,
+ and therewith removed the dependency on <code class="computeroutput"><span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">utility</span><span class="special">/</span><span class="identifier">in_place_factory</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span></code>.
+ </li>
+<li class="listitem">
+ Fixed <a href="https://svn.boost.org/trac/boost/ticket/11241" target="_top">Trac #11241</a>.
+ </li>
+</ul></div>
+<h4>
+<a name="boost_optional.relnotes.h8"></a>
+ <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_58"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_58">Boost
+ Release 1.58</a>
+ </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none_t</span></code> is no longer convertible from
+ literal <code class="computeroutput"><span class="number">0</span></code>. This avoids a bug
+ where <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">rational</span><span class="special"><</span><span class="keyword">int</span><span class="special">>></span> <span class="identifier">oi</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span></code> would
+ initialize an optional object with no contained value.
+ </li>
+<li class="listitem">
+ Improved the trick that prevents streaming out <code class="computeroutput"><span class="identifier">optional</span></code>
+ without header <code class="computeroutput"><span class="identifier">optional_io</span><span class="special">.</span><span class="identifier">hpp</span></code>
+ by using safe-bool idiom. This addresses <a href="https://svn.boost.org/trac/boost/ticket/10825" target="_top">Trac
+ #10825</a>.
+ </li>
+<li class="listitem">
+ IOStream operators are now mentioned in documentation.
+ </li>
+<li class="listitem">
+ Added a way to manually disable move semantics: just define macro <code class="computeroutput"><span class="identifier">BOOST_OPTIONAL_CONFIG_NO_RVALUE_REFERENCES</span></code>.
+ This can be used to work around <a href="https://svn.boost.org/trac/boost/ticket/10399" target="_top">Trac
+ #10399</a>.
+ </li>
+<li class="listitem">
+ It is no longer possible to assign <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span></code> to <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> when <code class="computeroutput"><span class="identifier">U</span></code>
+ is not assignable or convertible to <code class="computeroutput"><span class="identifier">T</span></code>
+ (<a href="https://svn.boost.org/trac/boost/ticket/11087" target="_top">Trac #11087</a>).
+ </li>
+<li class="listitem">
+ Value accessors now work correctly on rvalues of <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code> (<a href="https://svn.boost.org/trac/boost/ticket/10839" target="_top">Trac
+ #10839</a>).
+ </li>
+</ul></div>
+<h4>
+<a name="boost_optional.relnotes.h9"></a>
+ <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_57"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_57">Boost
+ Release 1.57</a>
+ </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; "><li class="listitem">
+ <a href="https://github.com/boostorg/optional/pull/9" target="_top">Git pull #9</a>:
+ <span class="emphasis"><em>"Supply <code class="computeroutput"><span class="special"><</span><span class="identifier">string</span><span class="special">></span></code>
+ to fix C++03 compile error on <code class="computeroutput"><span class="identifier">logic_error</span><span class="special">(</span><span class="string">"..."</span><span class="special">)</span></code>"</em></span>.
+ </li></ul></div>
+<h4>
+<a name="boost_optional.relnotes.h10"></a>
+ <span class="phrase"><a name="boost_optional.relnotes.boost_release_1_56"></a></span><a class="link" href="relnotes.html#boost_optional.relnotes.boost_release_1_56">Boost
+ Release 1.56</a>
+ </h4>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ Added support for rvalue references. Now <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> works with moveable but non-copyable
+ <code class="computeroutput"><span class="identifier">T</span></code>'s,
+ </li>
+<li class="listitem">
+ Improved <code class="computeroutput"><span class="identifier">swap</span></code> (now uses
+ move operations),
+ </li>
+<li class="listitem">
+ Added function <code class="computeroutput"><span class="identifier">emplace</span><span class="special">()</span></code>. This is the last of the requests from
+ <a href="https://svn.boost.org/trac/boost/ticket/1841" target="_top">Trac #1841</a>,
+ </li>
+<li class="listitem">
+ <code class="computeroutput"><span class="identifier">optional</span></code> is moveable, including
+ conditional <code class="computeroutput"><span class="keyword">noexcept</span></code> specifications,
+ which make it <code class="computeroutput"><span class="identifier">move_if_noexcept</span></code>-friendly,
+ </li>
+<li class="listitem">
+ Using explicit operator bool() on platforms that support it (<a href="https://svn.boost.org/trac/boost/ticket/4227" target="_top">Trac
+ #4227</a>) (breaking change),
+ </li>
+<li class="listitem">
+ Forward declaration of <code class="computeroutput"><span class="keyword">operator</span><span class="special"><<(</span><span class="identifier">ostream</span><span class="special">&,</span> <span class="identifier">optional</span>
+ <span class="keyword">const</span><span class="special">&)</span></code>
+ to prevent inadvertent incorrect serialization of optional objects,
+ </li>
+<li class="listitem">
+ Removed deprecated function <code class="computeroutput"><span class="identifier">reset</span><span class="special">()</span></code> from examples (<a href="https://svn.boost.org/trac/boost/ticket/9005" target="_top">Trac
+ #9005</a>),
+ </li>
+<li class="listitem">
+ Equality comparison with <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code>
+ does not require that <code class="computeroutput"><span class="identifier">T</span></code>
+ be EqualityComparable,
+ </li>
+<li class="listitem">
+ Optional rvalue references are explicitly disallowed,
+ </li>
+<li class="listitem">
+ Binding temporaries to optional references is explicitly disallowed (breaking
+ change),
+ </li>
+<li class="listitem">
+ More ways to access the contained value, functions <code class="computeroutput"><span class="identifier">value</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">value_or</span><span class="special">()</span></code>, <code class="computeroutput"><span class="identifier">value_or_eval</span><span class="special">()</span></code>,
+ </li>
+<li class="listitem">
+ Updated and reorganized documentation, added tutorial and quick guide sections.
+ </li>
+</ul></div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="dependencies_and_portability/optional_reference_binding.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="acknowledgements.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
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+</body>
+</html>
diff --git a/doc/html/boost_optional/synopsis.html b/doc/html/boost_optional/synopsis.html
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+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
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+</div>
+<div class="section">
+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="boost_optional.synopsis"></a><a class="link" href="synopsis.html" title="Synopsis">Synopsis</a>
+</h2></div></div></div>
+<pre class="programlisting"><code class="computeroutput"><span class="comment">// In Header: <</span></code><a href="../../../../../boost/optional/optional.hpp" target="_top">boost/optional/optional.hpp</a><span class="comment">></span>
+
+<span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span>
+<span class="keyword">class</span> <span class="identifier">optional</span>
+<span class="special">{</span>
+ <span class="keyword">public</span> <span class="special">:</span>
+
+ <span class="comment">// (If T is of reference type, the parameters and results by reference are by value)</span>
+
+ <span class="identifier">optional</span> <span class="special">()</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_constructor"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_constructor_none_t"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_constructor_value"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_constructor_move_value"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="comment">// [new in 1.34]</span>
+ <span class="identifier">optional</span> <span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_constructor_bool_value"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">optional</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_constructor_optional"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">(</span><span class="emphasis"><em>see below</em></span><span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_move_constructor_optional"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_constructor_other_optional"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_move_constructor_other_optional"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">InPlaceFactory</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">InPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_constructor_factory"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">TypedInPlaceFactory</span><span class="special">></span> <span class="keyword">explicit</span> <span class="identifier">optional</span> <span class="special">(</span> <span class="identifier">TypedInPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_constructor_factory"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_operator_equal_none_t"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_operator_equal_value"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span><span class="special">&&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_operator_move_equal_value"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_operator_equal_optional"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">optional</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special">&&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="keyword">noexcept</span><span class="special">(</span><span class="emphasis"><em>see below</em></span><span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_operator_move_equal_optional"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_operator_equal_other_optional"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">>&&</span> <span class="identifier">rhs</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_operator_move_equal_other_optional"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span><span class="special">...</span> <span class="identifier">Args</span><span class="special">></span> <span class="keyword">void</span> <span class="identifier">emplace</span> <span class="special">(</span> <span class="identifier">Args</span><span class="special">...&&</span> <span class="identifier">args</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_emplace"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">InPlaceFactory</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">InPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_operator_equal_factory"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">TypedInPlaceFactory</span><span class="special">></span> <span class="identifier">optional</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">=</span> <span class="special">(</span> <span class="identifier">TypedInPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">f</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_operator_equal_factory"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">get</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_get"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+ <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get</span><span class="special">()</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_get"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="keyword">operator</span> <span class="special">->()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_operator_arrow"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+ <span class="identifier">T</span><span class="special">*</span> <span class="keyword">operator</span> <span class="special">->()</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_operator_arrow"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">*()</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_operator_asterisk"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+ <span class="identifier">T</span><span class="special">&</span> <span class="keyword">operator</span> <span class="special">*()</span> <span class="special">&;</span> <a class="link" href="detailed_semantics.html#reference_optional_operator_asterisk"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+ <span class="identifier">T</span><span class="special">&&</span> <span class="keyword">operator</span> <span class="special">*()</span> <span class="special">&&;</span> <a class="link" href="detailed_semantics.html#reference_optional_operator_asterisk"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">value</span><span class="special">()</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_value"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+ <span class="identifier">T</span><span class="special">&</span> <span class="identifier">value</span><span class="special">()</span> <span class="special">&</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_value"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+ <span class="identifier">T</span><span class="special">&&</span> <span class="identifier">value</span><span class="special">()</span> <span class="special">&&</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_value"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">value_or</span><span class="special">(</span> <span class="identifier">U</span> <span class="special">&&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_value_or"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+ <span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">T</span> <span class="identifier">value_or</span><span class="special">(</span> <span class="identifier">U</span> <span class="special">&&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">&&</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_value_or"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">get_ptr</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_get_ptr"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+ <span class="identifier">T</span><span class="special">*</span> <span class="identifier">get_ptr</span><span class="special">()</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_get_ptr"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">explicit</span> <span class="keyword">operator</span> <span class="keyword">bool</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_operator_bool"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="keyword">bool</span> <span class="keyword">operator</span><span class="special">!()</span> <span class="keyword">const</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_operator_not"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="comment">// deprecated methods</span>
+
+ <span class="comment">// (deprecated)</span>
+ <span class="keyword">void</span> <span class="identifier">reset</span><span class="special">()</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_reset"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="comment">// (deprecated)</span>
+ <span class="keyword">void</span> <span class="identifier">reset</span> <span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_reset_value"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="comment">// (deprecated)</span>
+ <span class="keyword">bool</span> <span class="identifier">is_initialized</span><span class="special">()</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_is_initialized"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+ <span class="comment">// (deprecated)</span>
+ <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">get_value_or</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="keyword">default</span> <span class="special">)</span> <span class="keyword">const</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_get_value_or_value"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+<span class="special">};</span>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">==</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_operator_compare_equal_optional_optional"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">!=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_operator_compare_not_equal_optional_optional"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special"><</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_operator_compare_less_optional_optional"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">></span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_operator_compare_greater_optional_optional"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special"><=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_operator_compare_less_or_equal_optional_optional"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">>=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_operator_compare_greater_or_equal_optional_optional"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">==</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_operator_compare_equal_optional_none"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">inline</span> <span class="keyword">bool</span> <span class="keyword">operator</span> <span class="special">!=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">none_t</span> <span class="special">)</span> <span class="keyword">noexcept</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_operator_compare_not_equal_optional_none"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">inline</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">make_optional</span> <span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_make_optional_value"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">inline</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">make_optional</span> <span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">condition</span><span class="special">,</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_make_optional_bool_value"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">get_optional_value_or</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">opt</span><span class="special">,</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="keyword">default</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_get_value_or_value"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">get</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_get"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">inline</span> <span class="identifier">T</span><span class="special">&</span> <span class="identifier">get</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="special">&</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_get"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">get</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_get"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">inline</span> <span class="identifier">T</span><span class="special">*</span> <span class="identifier">get</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>*</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_get"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">inline</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">*</span> <span class="identifier">get_pointer</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_get_ptr"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">inline</span> <span class="identifier">T</span><span class="special">*</span> <span class="identifier">get_pointer</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="special">&</span> <span class="identifier">opt</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_optional_get_ptr"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">></span> <span class="keyword">inline</span> <span class="keyword">void</span> <span class="identifier">swap</span><span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">x</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">y</span> <span class="special">)</span> <span class="special">;</span> <a class="link" href="detailed_semantics.html#reference_swap_optional_optional"><span class="inlinemediaobject"><img src="../images/callouts/R.png" alt="R"></span></a>
+
+<span class="special">}</span> <span class="comment">// namespace boost</span>
+</pre>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="tutorial/type_requirements.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="detailed_semantics.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/tutorial.html b/doc/html/boost_optional/tutorial.html
new file mode 100644
index 0000000..8f033e8
--- /dev/null
+++ b/doc/html/boost_optional/tutorial.html
@@ -0,0 +1,523 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Tutorial</title>
+<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../index.html" title="Chapter 1. Boost.Optional">
+<link rel="up" href="../index.html" title="Chapter 1. Boost.Optional">
+<link rel="prev" href="quick_start.html" title="Quick Start">
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+<a name="boost_optional.tutorial"></a><a class="link" href="tutorial.html" title="Tutorial">Tutorial</a>
+</h2></div></div></div>
+<div class="toc"><dl class="toc">
+<dt><span class="section"><a href="tutorial.html#boost_optional.tutorial.motivation">Motivation</a></span></dt>
+<dt><span class="section"><a href="tutorial.html#boost_optional.tutorial.design_overview">Design Overview</a></span></dt>
+</dl></div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.tutorial.motivation"></a><a class="link" href="tutorial.html#boost_optional.tutorial.motivation" title="Motivation">Motivation</a>
+</h3></div></div></div>
+<p>
+ Consider these functions which should return a value but which might not
+ have a value to return:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ (A) <code class="computeroutput"><span class="keyword">double</span> <span class="identifier">sqrt</span><span class="special">(</span><span class="keyword">double</span> <span class="identifier">n</span> <span class="special">);</span></code>
+ </li>
+<li class="listitem">
+ (B) <code class="computeroutput"><span class="keyword">char</span> <span class="identifier">get_async_input</span><span class="special">();</span></code>
+ </li>
+<li class="listitem">
+ (C) <code class="computeroutput"><span class="identifier">point</span> <span class="identifier">polygon</span><span class="special">::</span><span class="identifier">get_any_point_effectively_inside</span><span class="special">();</span></code>
+ </li>
+</ul></div>
+<p>
+ There are different approaches to the issue of not having a value to return.
+ </p>
+<p>
+ A typical approach is to consider the existence of a valid return value as
+ a postcondition, so that if the function cannot compute the value to return,
+ it has either undefined behavior (and can use assert in a debug build) or
+ uses a runtime check and throws an exception if the postcondition is violated.
+ This is a reasonable choice for example, for function (A), because the lack
+ of a proper return value is directly related to an invalid parameter (out
+ of domain argument), so it is appropriate to require the callee to supply
+ only parameters in a valid domain for execution to continue normally.
+ </p>
+<p>
+ However, function (B), because of its asynchronous nature, does not fail
+ just because it can't find a value to return; so it is incorrect to consider
+ such a situation an error and assert or throw an exception. This function
+ must return, and somehow, must tell the callee that it is not returning a
+ meaningful value.
+ </p>
+<p>
+ A similar situation occurs with function (C): it is conceptually an error
+ to ask a <span class="emphasis"><em>null-area</em></span> polygon to return a point inside
+ itself, but in many applications, it is just impractical for performance
+ reasons to treat this as an error (because detecting that the polygon has
+ no area might be too expensive to be required to be tested previously), and
+ either an arbitrary point (typically at infinity) is returned, or some efficient
+ way to tell the callee that there is no such point is used.
+ </p>
+<p>
+ There are various mechanisms to let functions communicate that the returned
+ value is not valid. One such mechanism, which is quite common since it has
+ zero or negligible overhead, is to use a special value which is reserved
+ to communicate this. Classical examples of such special values are <code class="computeroutput"><span class="identifier">EOF</span></code>, <code class="computeroutput"><span class="identifier">string</span><span class="special">::</span><span class="identifier">npos</span></code>,
+ points at infinity, etc...
+ </p>
+<p>
+ When those values exist, i.e. the return type can hold all meaningful values
+ <span class="emphasis"><em>plus</em></span> the <span class="emphasis"><em>signal</em></span> value, this mechanism
+ is quite appropriate and well known. Unfortunately, there are cases when
+ such values do not exist. In these cases, the usual alternative is either
+ to use a wider type, such as <code class="computeroutput"><span class="keyword">int</span></code>
+ in place of <code class="computeroutput"><span class="keyword">char</span></code>; or a compound
+ type, such as <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">point</span><span class="special">,</span><span class="keyword">bool</span><span class="special">></span></code>.
+ </p>
+<p>
+ Returning a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span><span class="keyword">bool</span><span class="special">></span></code>, thus attaching a boolean flag to the
+ result which indicates if the result is meaningful, has the advantage that
+ can be turned into a consistent idiom since the first element of the pair
+ can be whatever the function would conceptually return. For example, the
+ last two functions could have the following interface:
+ </p>
+<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span><span class="keyword">bool</span><span class="special">></span> <span class="identifier">get_async_input</span><span class="special">();</span>
+<span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">point</span><span class="special">,</span><span class="keyword">bool</span><span class="special">></span> <span class="identifier">polygon</span><span class="special">::</span><span class="identifier">get_any_point_effectively_inside</span><span class="special">();</span>
+</pre>
+<p>
+ These functions use a consistent interface for dealing with possibly nonexistent
+ results:
+ </p>
+<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">point</span><span class="special">,</span><span class="keyword">bool</span><span class="special">></span> <span class="identifier">p</span> <span class="special">=</span> <span class="identifier">poly</span><span class="special">.</span><span class="identifier">get_any_point_effectively_inside</span><span class="special">();</span>
+<span class="keyword">if</span> <span class="special">(</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">second</span> <span class="special">)</span>
+ <span class="identifier">flood_fill</span><span class="special">(</span><span class="identifier">p</span><span class="special">.</span><span class="identifier">first</span><span class="special">);</span>
+</pre>
+<p>
+ However, not only is this quite a burden syntactically, it is also error
+ prone since the user can easily use the function result (first element of
+ the pair) without ever checking if it has a valid value.
+ </p>
+<p>
+ Clearly, we need a better idiom.
+ </p>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.tutorial.design_overview"></a><a class="link" href="tutorial.html#boost_optional.tutorial.design_overview" title="Design Overview">Design Overview</a>
+</h3></div></div></div>
+<div class="toc"><dl class="toc">
+<dt><span class="section"><a href="tutorial.html#boost_optional.tutorial.design_overview.the_models">The
+ models</a></span></dt>
+<dt><span class="section"><a href="tutorial.html#boost_optional.tutorial.design_overview.the_semantics">The
+ semantics</a></span></dt>
+<dt><span class="section"><a href="tutorial.html#boost_optional.tutorial.design_overview.the_interface">The
+ Interface</a></span></dt>
+</dl></div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.tutorial.design_overview.the_models"></a><a class="link" href="tutorial.html#boost_optional.tutorial.design_overview.the_models" title="The models">The
+ models</a>
+</h4></div></div></div>
+<p>
+ In C++, we can <span class="emphasis"><em>declare</em></span> an object (a variable) of type
+ <code class="computeroutput"><span class="identifier">T</span></code>, and we can give this
+ variable an <span class="emphasis"><em>initial value</em></span> (through an <span class="emphasis"><em>initializer</em></span>.
+ (cf. 8.5)). When a declaration includes a non-empty initializer (an initial
+ value is given), it is said that the object has been initialized. If the
+ declaration uses an empty initializer (no initial value is given), and
+ neither default nor value initialization applies, it is said that the object
+ is <span class="bold"><strong>uninitialized</strong></span>. Its actual value exist
+ but has an <span class="emphasis"><em>indeterminate initial value</em></span> (cf. 8.5/11).
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ intends to formalize the notion of initialization (or lack of it) allowing
+ a program to test whether an object has been initialized and stating that
+ access to the value of an uninitialized object is undefined behavior. That
+ is, when a variable is declared as <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> and no initial value is given, the
+ variable is <span class="emphasis"><em>formally</em></span> uninitialized. A formally uninitialized
+ optional object has conceptually no value at all and this situation can
+ be tested at runtime. It is formally <span class="emphasis"><em>undefined behavior</em></span>
+ to try to access the value of an uninitialized optional. An uninitialized
+ optional can be assigned a value, in which case its initialization state
+ changes to initialized. Furthermore, given the formal treatment of initialization
+ states in optional objects, it is even possible to reset an optional to
+ <span class="emphasis"><em>uninitialized</em></span>.
+ </p>
+<p>
+ In C++ there is no formal notion of uninitialized objects, which means
+ that objects always have an initial value even if indeterminate. As discussed
+ on the previous section, this has a drawback because you need additional
+ information to tell if an object has been effectively initialized. One
+ of the typical ways in which this has been historically dealt with is via
+ a special value: <code class="computeroutput"><span class="identifier">EOF</span></code>,
+ <code class="computeroutput"><span class="identifier">npos</span></code>, -1, etc... This is
+ equivalent to adding the special value to the set of possible values of
+ a given type. This super set of <code class="computeroutput"><span class="identifier">T</span></code>
+ plus some <span class="emphasis"><em>nil_t</em></span>—where <code class="computeroutput"><span class="identifier">nil_t</span></code>
+ is some stateless POD—can be modeled in modern languages as a <span class="bold"><strong>discriminated union</strong></span> of T and nil_t. Discriminated
+ unions are often called <span class="emphasis"><em>variants</em></span>. A variant has a
+ <span class="emphasis"><em>current type</em></span>, which in our case is either <code class="computeroutput"><span class="identifier">T</span></code> or <code class="computeroutput"><span class="identifier">nil_t</span></code>.
+ Using the <a href="../../../../variant/index.html" target="_top">Boost.Variant</a>
+ library, this model can be implemented in terms of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">variant</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span><span class="identifier">nil_t</span><span class="special">></span></code>. There is precedent for a discriminated
+ union as a model for an optional value: the <a href="http://www.haskell.org/" target="_top">Haskell</a>
+ <span class="bold"><strong>Maybe</strong></span> built-in type constructor. Thus,
+ a discriminated union <code class="computeroutput"><span class="identifier">T</span><span class="special">+</span><span class="identifier">nil_t</span></code>
+ serves as a conceptual foundation.
+ </p>
+<p>
+ A <code class="computeroutput"><span class="identifier">variant</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span><span class="identifier">nil_t</span><span class="special">></span></code> follows naturally from the traditional
+ idiom of extending the range of possible values adding an additional sentinel
+ value with the special meaning of <span class="emphasis"><em>Nothing</em></span>. However,
+ this additional <span class="emphasis"><em>Nothing</em></span> value is largely irrelevant
+ for our purpose since our goal is to formalize the notion of uninitialized
+ objects and, while a special extended value can be used to convey that
+ meaning, it is not strictly necessary in order to do so.
+ </p>
+<p>
+ The observation made in the last paragraph about the irrelevant nature
+ of the additional <code class="computeroutput"><span class="identifier">nil_t</span></code>
+ with respect to <span class="underline">purpose</span> of <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ suggests an alternative model: a <span class="emphasis"><em>container</em></span> that either
+ has a value of <code class="computeroutput"><span class="identifier">T</span></code> or nothing.
+ </p>
+<p>
+ As of this writing I don't know of any precedent for a variable-size fixed-capacity
+ (of 1) stack-based container model for optional values, yet I believe this
+ is the consequence of the lack of practical implementations of such a container
+ rather than an inherent shortcoming of the container model.
+ </p>
+<p>
+ In any event, both the discriminated-union or the single-element container
+ models serve as a conceptual ground for a class representing optional—i.e.
+ possibly uninitialized—objects. For instance, these models show the
+ <span class="emphasis"><em>exact</em></span> semantics required for a wrapper of optional
+ values:
+ </p>
+<p>
+ Discriminated-union:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>deep-copy</strong></span> semantics: copies of the
+ variant implies copies of the value.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>deep-relational</strong></span> semantics: comparisons
+ between variants matches both current types and values
+ </li>
+<li class="listitem">
+ If the variant's current type is <code class="computeroutput"><span class="identifier">T</span></code>,
+ it is modeling an <span class="emphasis"><em>initialized</em></span> optional.
+ </li>
+<li class="listitem">
+ If the variant's current type is not <code class="computeroutput"><span class="identifier">T</span></code>,
+ it is modeling an <span class="emphasis"><em>uninitialized</em></span> optional.
+ </li>
+<li class="listitem">
+ Testing if the variant's current type is <code class="computeroutput"><span class="identifier">T</span></code>
+ models testing if the optional is initialized
+ </li>
+<li class="listitem">
+ Trying to extract a <code class="computeroutput"><span class="identifier">T</span></code>
+ from a variant when its current type is not <code class="computeroutput"><span class="identifier">T</span></code>,
+ models the undefined behavior of trying to access the value of an uninitialized
+ optional
+ </li>
+</ul></div>
+<p>
+ Single-element container:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>deep-copy</strong></span> semantics: copies of the
+ container implies copies of the value.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>deep-relational</strong></span> semantics: comparisons
+ between containers compare container size and if match, contained value
+ </li>
+<li class="listitem">
+ If the container is not empty (contains an object of type <code class="computeroutput"><span class="identifier">T</span></code>), it is modeling an <span class="emphasis"><em>initialized</em></span>
+ optional.
+ </li>
+<li class="listitem">
+ If the container is empty, it is modeling an <span class="emphasis"><em>uninitialized</em></span>
+ optional.
+ </li>
+<li class="listitem">
+ Testing if the container is empty models testing if the optional is
+ initialized
+ </li>
+<li class="listitem">
+ Trying to extract a <code class="computeroutput"><span class="identifier">T</span></code>
+ from an empty container models the undefined behavior of trying to
+ access the value of an uninitialized optional
+ </li>
+</ul></div>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.tutorial.design_overview.the_semantics"></a><a class="link" href="tutorial.html#boost_optional.tutorial.design_overview.the_semantics" title="The semantics">The
+ semantics</a>
+</h4></div></div></div>
+<p>
+ Objects of type <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> are intended to be used in places where
+ objects of type <code class="computeroutput"><span class="identifier">T</span></code> would
+ but which might be uninitialized. Hence, <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>'s purpose is to formalize the additional
+ possibly uninitialized state. From the perspective of this role, <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ can have the same operational semantics of <code class="computeroutput"><span class="identifier">T</span></code>
+ plus the additional semantics corresponding to this special state. As such,
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ could be thought of as a <span class="emphasis"><em>supertype</em></span> of <code class="computeroutput"><span class="identifier">T</span></code>. Of course, we can't do that in C++,
+ so we need to compose the desired semantics using a different mechanism.
+ Doing it the other way around, that is, making <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> a <span class="emphasis"><em>subtype</em></span> of
+ <code class="computeroutput"><span class="identifier">T</span></code> is not only conceptually
+ wrong but also impractical: it is not allowed to derive from a non-class
+ type, such as a built-in type.
+ </p>
+<p>
+ We can draw from the purpose of <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> the required basic semantics:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Default Construction:</strong></span> To introduce
+ a formally uninitialized wrapped object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Direct Value Construction via copy:</strong></span>
+ To introduce a formally initialized wrapped object whose value is obtained
+ as a copy of some object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Deep Copy Construction:</strong></span> To obtain
+ a new yet equivalent wrapped object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Direct Value Assignment (upon initialized):</strong></span>
+ To assign a value to the wrapped object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Direct Value Assignment (upon uninitialized):</strong></span>
+ To initialize the wrapped object with a value obtained as a copy of
+ some object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Assignment (upon initialized):</strong></span> To
+ assign to the wrapped object the value of another wrapped object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Assignment (upon uninitialized):</strong></span> To
+ initialize the wrapped object with value of another wrapped object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Deep Relational Operations (when supported by
+ the type T):</strong></span> To compare wrapped object values taking into
+ account the presence of uninitialized states.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Value access:</strong></span> To unwrap the wrapped
+ object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Initialization state query:</strong></span> To determine
+ if the object is formally initialized or not.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Swap:</strong></span> To exchange wrapped objects.
+ (with whatever exception safety guarantees are provided by <code class="computeroutput"><span class="identifier">T</span></code>'s swap).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>De-initialization:</strong></span> To release the
+ wrapped object (if any) and leave the wrapper in the uninitialized
+ state.
+ </li>
+</ul></div>
+<p>
+ Additional operations are useful, such as converting constructors and converting
+ assignments, in-place construction and assignment, and safe value access
+ via a pointer to the wrapped object or null.
+ </p>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.tutorial.design_overview.the_interface"></a><a class="link" href="tutorial.html#boost_optional.tutorial.design_overview.the_interface" title="The Interface">The
+ Interface</a>
+</h4></div></div></div>
+<p>
+ Since the purpose of optional is to allow us to use objects with a formal
+ uninitialized additional state, the interface could try to follow the interface
+ of the underlying <code class="computeroutput"><span class="identifier">T</span></code> type
+ as much as possible. In order to choose the proper degree of adoption of
+ the native <code class="computeroutput"><span class="identifier">T</span></code> interface,
+ the following must be noted: Even if all the operations supported by an
+ instance of type <code class="computeroutput"><span class="identifier">T</span></code> are
+ defined for the entire range of values for such a type, an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ extends such a set of values with a new value for which most (otherwise
+ valid) operations are not defined in terms of <code class="computeroutput"><span class="identifier">T</span></code>.
+ </p>
+<p>
+ Furthermore, since <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> itself is merely a <code class="computeroutput"><span class="identifier">T</span></code>
+ wrapper (modeling a <code class="computeroutput"><span class="identifier">T</span></code> supertype),
+ any attempt to define such operations upon uninitialized optionals will
+ be totally artificial w.r.t. <code class="computeroutput"><span class="identifier">T</span></code>.
+ </p>
+<p>
+ This library chooses an interface which follows from <code class="computeroutput"><span class="identifier">T</span></code>'s
+ interface only for those operations which are well defined (w.r.t the type
+ <code class="computeroutput"><span class="identifier">T</span></code>) even if any of the operands
+ are uninitialized. These operations include: construction, copy-construction,
+ assignment, swap and relational operations.
+ </p>
+<p>
+ For the value access operations, which are undefined (w.r.t the type <code class="computeroutput"><span class="identifier">T</span></code>) when the operand is uninitialized,
+ a different interface is chosen (which will be explained next).
+ </p>
+<p>
+ Also, the presence of the possibly uninitialized state requires additional
+ operations not provided by <code class="computeroutput"><span class="identifier">T</span></code>
+ itself which are supported by a special interface.
+ </p>
+<h6>
+<a name="boost_optional.tutorial.design_overview.the_interface.h0"></a>
+ <span class="phrase"><a name="boost_optional.tutorial.design_overview.the_interface.lexically_hinted_value_access_in_the_presence_of_possibly_untitialized_optional_objects__the_operators___and___gt_"></a></span><a class="link" href="tutorial.html#boost_optional.tutorial.design_overview.the_interface.lexically_hinted_value_access_in_the_presence_of_possibly_untitialized_optional_objects__the_operators___and___gt_">Lexically-hinted
+ Value Access in the presence of possibly untitialized optional objects:
+ The operators * and -></a>
+ </h6>
+<p>
+ A relevant feature of a pointer is that it can have a <span class="bold"><strong>null
+ pointer value</strong></span>. This is a <span class="emphasis"><em>special</em></span> value
+ which is used to indicate that the pointer is not referring to any object
+ at all. In other words, null pointer values convey the notion of nonexistent
+ objects.
+ </p>
+<p>
+ This meaning of the null pointer value allowed pointers to became a <span class="emphasis"><em>de
+ facto</em></span> standard for handling optional objects because all you
+ have to do to refer to a value which you don't really have is to use a
+ null pointer value of the appropriate type. Pointers have been used for
+ decades—from the days of C APIs to modern C++ libraries—to <span class="emphasis"><em>refer</em></span>
+ to optional (that is, possibly nonexistent) objects; particularly as optional
+ arguments to a function, but also quite often as optional data members.
+ </p>
+<p>
+ The possible presence of a null pointer value makes the operations that
+ access the pointee's value possibly undefined, therefore, expressions which
+ use dereference and access operators, such as: <code class="computeroutput"><span class="special">(</span>
+ <span class="special">*</span><span class="identifier">p</span>
+ <span class="special">=</span> <span class="number">2</span> <span class="special">)</span></code> and <code class="computeroutput"><span class="special">(</span>
+ <span class="identifier">p</span><span class="special">-></span><span class="identifier">foo</span><span class="special">()</span> <span class="special">)</span></code>, implicitly convey the notion of optionality,
+ and this information is tied to the <span class="emphasis"><em>syntax</em></span> of the
+ expressions. That is, the presence of operators <code class="computeroutput"><span class="special">*</span></code>
+ and <code class="computeroutput"><span class="special">-></span></code> tell by themselves
+ —without any additional context— that the expression will be undefined
+ unless the implied pointee actually exist.
+ </p>
+<p>
+ Such a <span class="emphasis"><em>de facto</em></span> idiom for referring to optional objects
+ can be formalized in the form of a concept: the <a href="../../../../utility/OptionalPointee.html" target="_top">OptionalPointee</a>
+ concept. This concept captures the syntactic usage of operators <code class="computeroutput"><span class="special">*</span></code>, <code class="computeroutput"><span class="special">-></span></code>
+ and contextual conversion to <code class="computeroutput"><span class="keyword">bool</span></code>
+ to convey the notion of optionality.
+ </p>
+<p>
+ However, pointers are good to <span class="underline">refer</span>
+ to optional objects, but not particularly good to handle the optional objects
+ in all other respects, such as initializing or moving/copying them. The
+ problem resides in the shallow-copy of pointer semantics: if you need to
+ effectively move or copy the object, pointers alone are not enough. The
+ problem is that copies of pointers do not imply copies of pointees. For
+ example, as was discussed in the motivation, pointers alone cannot be used
+ to return optional objects from a function because the object must move
+ outside from the function and into the caller's context.
+ </p>
+<p>
+ A solution to the shallow-copy problem that is often used is to resort
+ to dynamic allocation and use a smart pointer to automatically handle the
+ details of this. For example, if a function is to optionally return an
+ object <code class="computeroutput"><span class="identifier">X</span></code>, it can use <code class="computeroutput"><span class="identifier">shared_ptr</span><span class="special"><</span><span class="identifier">X</span><span class="special">></span></code>
+ as the return value. However, this requires dynamic allocation of <code class="computeroutput"><span class="identifier">X</span></code>. If <code class="computeroutput"><span class="identifier">X</span></code>
+ is a built-in or small POD, this technique is very poor in terms of required
+ resources. Optional objects are essentially values so it is very convenient
+ to be able to use automatic storage and deep-copy semantics to manipulate
+ optional values just as we do with ordinary values. Pointers do not have
+ this semantics, so are inappropriate for the initialization and transport
+ of optional values, yet are quite convenient for handling the access to
+ the possible undefined value because of the idiomatic aid present in the
+ <a href="../../../../utility/OptionalPointee.html" target="_top">OptionalPointee</a>
+ concept incarnated by pointers.
+ </p>
+<h6>
+<a name="boost_optional.tutorial.design_overview.the_interface.h1"></a>
+ <span class="phrase"><a name="boost_optional.tutorial.design_overview.the_interface.optional_lt_t_gt__as_a_model_of_optionalpointee"></a></span><a class="link" href="tutorial.html#boost_optional.tutorial.design_overview.the_interface.optional_lt_t_gt__as_a_model_of_optionalpointee">Optional<T>
+ as a model of OptionalPointee</a>
+ </h6>
+<p>
+ For value access operations <code class="computeroutput"><span class="identifier">optional</span><span class="special"><></span></code> uses operators <code class="computeroutput"><span class="special">*</span></code>
+ and <code class="computeroutput"><span class="special">-></span></code> to lexically warn
+ about the possibly uninitialized state appealing to the familiar pointer
+ semantics w.r.t. to null pointers.
+ </p>
+<div class="warning"><table border="0" summary="Warning">
+<tr>
+<td rowspan="2" align="center" valign="top" width="25"><img alt="[Warning]" src="../../../../../doc/src/images/warning.png"></td>
+<th align="left">Warning</th>
+</tr>
+<tr><td align="left" valign="top"><p>
+ However, it is particularly important to note that <code class="computeroutput"><span class="identifier">optional</span><span class="special"><></span></code> objects are not pointers. <span class="underline"><code class="computeroutput"><span class="identifier">optional</span><span class="special"><></span></code> is not, and does not model, a
+ pointer</span>.
+ </p></td></tr>
+</table></div>
+<p>
+ For instance, <code class="computeroutput"><span class="identifier">optional</span><span class="special"><></span></code> does not have shallow-copy so does
+ not alias: two different optionals never refer to the <span class="emphasis"><em>same</em></span>
+ value unless <code class="computeroutput"><span class="identifier">T</span></code> itself is
+ a reference (but may have <span class="emphasis"><em>equivalent</em></span> values). The
+ difference between an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> and a pointer must be kept in mind,
+ particularly because the semantics of relational operators are different:
+ since <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ is a value-wrapper, relational operators are deep: they compare optional
+ values; but relational operators for pointers are shallow: they do not
+ compare pointee values. As a result, you might be able to replace <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ by <code class="computeroutput"><span class="identifier">T</span><span class="special">*</span></code>
+ on some situations but not always. Specifically, on generic code written
+ for both, you cannot use relational operators directly, and must use the
+ template functions <a href="../../../../utility/OptionalPointee.html#equal" target="_top"><code class="computeroutput"><span class="identifier">equal_pointees</span><span class="special">()</span></code></a>
+ and <a href="../../../../utility/OptionalPointee.html#less" target="_top"><code class="computeroutput"><span class="identifier">less_pointees</span><span class="special">()</span></code></a>
+ instead.
+ </p>
+</div>
+</div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="quick_start.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="synopsis.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
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diff --git a/doc/html/boost_optional/tutorial/a_note_about_optional_bool_.html b/doc/html/boost_optional/tutorial/a_note_about_optional_bool_.html
new file mode 100644
index 0000000..ffd5c3d
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@@ -0,0 +1,108 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>A note about optional<bool></title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../../index.html" title="Boost.Optional">
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+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
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+</tr></table>
+<hr>
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+<a accesskey="p" href="in_place_factories.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="exception_safety_guarantees.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.tutorial.a_note_about_optional_bool_"></a><a class="link" href="a_note_about_optional_bool_.html" title="A note about optional<bool>">A
+ note about optional<bool></a>
+</h3></div></div></div>
+<p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span></code> should
+ be used with special caution and consideration.
+ </p>
+<p>
+ First, it is functionally similar to a tristate boolean (false, maybe, true)
+ —such as <a href="../../../../../../doc/html/tribool.html" target="_top">boost::tribool</a>—
+ except that in a tristate boolean, the maybe state <span class="underline">represents
+ a valid value</span>, unlike the corresponding state of an uninitialized
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span></code>.
+ It should be carefully considered if an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span></code>
+ instead of a <code class="computeroutput"><span class="identifier">tribool</span></code> is really
+ needed.
+ </p>
+<p>
+ Second, although <code class="computeroutput"><span class="identifier">optional</span><span class="special"><></span></code> provides a contextual conversion
+ to <code class="computeroutput"><span class="keyword">bool</span></code> in C++11, this falls
+ back to an implicit conversion on older compilers. This conversion refers
+ to the initialization state and not to the contained value. Using <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span></code> can
+ lead to subtle errors due to the implicit <code class="computeroutput"><span class="keyword">bool</span></code>
+ conversion:
+ </p>
+<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">foo</span> <span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="keyword">void</span> <span class="identifier">bar</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span> <span class="identifier">v</span> <span class="special">=</span> <span class="keyword">try</span><span class="special">();</span>
+
+ <span class="comment">// The following intended to pass the value of 'v' to foo():</span>
+ <span class="identifier">foo</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+ <span class="comment">// But instead, the initialization state is passed</span>
+ <span class="comment">// due to a typo: it should have been foo(*v).</span>
+<span class="special">}</span>
+</pre>
+<p>
+ The only implicit conversion is to <code class="computeroutput"><span class="keyword">bool</span></code>,
+ and it is safe in the sense that typical integral promotions don't apply
+ (i.e. if <code class="computeroutput"><span class="identifier">foo</span><span class="special">()</span></code>
+ takes an <code class="computeroutput"><span class="keyword">int</span></code> instead, it won't
+ compile).
+ </p>
+<p>
+ Third, mixed comparisons with <code class="computeroutput"><span class="keyword">bool</span></code>
+ work differently than similar mixed comparisons between pointers and <code class="computeroutput"><span class="keyword">bool</span></code>, so the results might surprise you:
+ </p>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span> <span class="identifier">oEmpty</span><span class="special">(</span><span class="identifier">none</span><span class="special">),</span> <span class="identifier">oTrue</span><span class="special">(</span><span class="keyword">true</span><span class="special">),</span> <span class="identifier">oFalse</span><span class="special">(</span><span class="keyword">false</span><span class="special">);</span>
+
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oEmpty</span> <span class="special">==</span> <span class="identifier">none</span><span class="special">);</span> <span class="comment">// renders true</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oEmpty</span> <span class="special">==</span> <span class="keyword">false</span><span class="special">);</span> <span class="comment">// renders false!</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oEmpty</span> <span class="special">==</span> <span class="keyword">true</span><span class="special">);</span> <span class="comment">// renders false!</span>
+
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oFalse</span> <span class="special">==</span> <span class="identifier">none</span><span class="special">);</span> <span class="comment">// renders false</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oFalse</span> <span class="special">==</span> <span class="keyword">false</span><span class="special">);</span> <span class="comment">// renders true!</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oFalse</span> <span class="special">==</span> <span class="keyword">true</span><span class="special">);</span> <span class="comment">// renders false</span>
+
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oTrue</span> <span class="special">==</span> <span class="identifier">none</span><span class="special">);</span> <span class="comment">// renders false</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oTrue</span> <span class="special">==</span> <span class="keyword">false</span><span class="special">);</span> <span class="comment">// renders false</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oTrue</span> <span class="special">==</span> <span class="keyword">true</span><span class="special">);</span> <span class="comment">// renders true</span>
+</pre>
+<p>
+ In other words, for <code class="computeroutput"><span class="identifier">optional</span><span class="special"><></span></code>, the following assertion does not
+ hold:
+ </p>
+<pre class="programlisting"><span class="identifier">assert</span><span class="special">((</span><span class="identifier">opt</span> <span class="special">==</span> <span class="keyword">false</span><span class="special">)</span> <span class="special">==</span> <span class="special">(!</span><span class="identifier">opt</span><span class="special">));</span>
+</pre>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2016 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="in_place_factories.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="exception_safety_guarantees.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
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@@ -0,0 +1,184 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Design Overview</title>
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+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../index.html" title="Boost.Optional">
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+<link rel="next" href="design_overview/the_semantics.html" title="The semantics">
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+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="design_overview/the_semantics.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.tutorial.design_overview"></a><a class="link" href="design_overview.html" title="Design Overview">Design Overview</a>
+</h3></div></div></div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.tutorial.design_overview.the_models"></a><a class="link" href="design_overview.html#boost_optional.tutorial.design_overview.the_models" title="The models">The
+ models</a>
+</h4></div></div></div>
+<p>
+ In C++, we can <span class="emphasis"><em>declare</em></span> an object (a variable) of type
+ <code class="computeroutput"><span class="identifier">T</span></code>, and we can give this
+ variable an <span class="emphasis"><em>initial value</em></span> (through an <span class="emphasis"><em>initializer</em></span>.
+ (cf. 8.5)). When a declaration includes a non-empty initializer (an initial
+ value is given), it is said that the object has been initialized. If the
+ declaration uses an empty initializer (no initial value is given), and
+ neither default nor value initialization applies, it is said that the object
+ is <span class="bold"><strong>uninitialized</strong></span>. Its actual value exist
+ but has an <span class="emphasis"><em>indeterminate initial value</em></span> (cf. 8.5/11).
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ intends to formalize the notion of initialization (or lack of it) allowing
+ a program to test whether an object has been initialized and stating that
+ access to the value of an uninitialized object is undefined behavior. That
+ is, when a variable is declared as <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> and no initial value is given, the
+ variable is <span class="emphasis"><em>formally</em></span> uninitialized. A formally uninitialized
+ optional object has conceptually no value at all and this situation can
+ be tested at runtime. It is formally <span class="emphasis"><em>undefined behavior</em></span>
+ to try to access the value of an uninitialized optional. An uninitialized
+ optional can be assigned a value, in which case its initialization state
+ changes to initialized. Furthermore, given the formal treatment of initialization
+ states in optional objects, it is even possible to reset an optional to
+ <span class="emphasis"><em>uninitialized</em></span>.
+ </p>
+<p>
+ In C++ there is no formal notion of uninitialized objects, which means
+ that objects always have an initial value even if indeterminate. As discussed
+ on the previous section, this has a drawback because you need additional
+ information to tell if an object has been effectively initialized. One
+ of the typical ways in which this has been historically dealt with is via
+ a special value: <code class="computeroutput"><span class="identifier">EOF</span></code>,
+ <code class="computeroutput"><span class="identifier">npos</span></code>, -1, etc... This is
+ equivalent to adding the special value to the set of possible values of
+ a given type. This super set of <code class="computeroutput"><span class="identifier">T</span></code>
+ plus some <span class="emphasis"><em>nil_t</em></span>—where <code class="computeroutput"><span class="identifier">nil_t</span></code>
+ is some stateless POD—can be modeled in modern languages as a <span class="bold"><strong>discriminated union</strong></span> of T and nil_t. Discriminated
+ unions are often called <span class="emphasis"><em>variants</em></span>. A variant has a
+ <span class="emphasis"><em>current type</em></span>, which in our case is either <code class="computeroutput"><span class="identifier">T</span></code> or <code class="computeroutput"><span class="identifier">nil_t</span></code>.
+ Using the <a href="../../../../../variant/index.html" target="_top">Boost.Variant</a>
+ library, this model can be implemented in terms of <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">variant</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span><span class="identifier">nil_t</span><span class="special">></span></code>. There is precedent for a discriminated
+ union as a model for an optional value: the <a href="http://www.haskell.org/" target="_top">Haskell</a>
+ <span class="bold"><strong>Maybe</strong></span> built-in type constructor. Thus,
+ a discriminated union <code class="computeroutput"><span class="identifier">T</span><span class="special">+</span><span class="identifier">nil_t</span></code>
+ serves as a conceptual foundation.
+ </p>
+<p>
+ A <code class="computeroutput"><span class="identifier">variant</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span><span class="identifier">nil_t</span><span class="special">></span></code> follows naturally from the traditional
+ idiom of extending the range of possible values adding an additional sentinel
+ value with the special meaning of <span class="emphasis"><em>Nothing</em></span>. However,
+ this additional <span class="emphasis"><em>Nothing</em></span> value is largely irrelevant
+ for our purpose since our goal is to formalize the notion of uninitialized
+ objects and, while a special extended value can be used to convey that
+ meaning, it is not strictly necessary in order to do so.
+ </p>
+<p>
+ The observation made in the last paragraph about the irrelevant nature
+ of the additional <code class="computeroutput"><span class="identifier">nil_t</span></code>
+ with respect to <span class="underline">purpose</span> of <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ suggests an alternative model: a <span class="emphasis"><em>container</em></span> that either
+ has a value of <code class="computeroutput"><span class="identifier">T</span></code> or nothing.
+ </p>
+<p>
+ As of this writing I don't know of any precedent for a variable-size fixed-capacity
+ (of 1) stack-based container model for optional values, yet I believe this
+ is the consequence of the lack of practical implementations of such a container
+ rather than an inherent shortcoming of the container model.
+ </p>
+<p>
+ In any event, both the discriminated-union or the single-element container
+ models serve as a conceptual ground for a class representing optional—i.e.
+ possibly uninitialized—objects. For instance, these models show the
+ <span class="emphasis"><em>exact</em></span> semantics required for a wrapper of optional
+ values:
+ </p>
+<p>
+ Discriminated-union:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>deep-copy</strong></span> semantics: copies of the
+ variant implies copies of the value.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>deep-relational</strong></span> semantics: comparisons
+ between variants matches both current types and values
+ </li>
+<li class="listitem">
+ If the variant's current type is <code class="computeroutput"><span class="identifier">T</span></code>,
+ it is modeling an <span class="emphasis"><em>initialized</em></span> optional.
+ </li>
+<li class="listitem">
+ If the variant's current type is not <code class="computeroutput"><span class="identifier">T</span></code>,
+ it is modeling an <span class="emphasis"><em>uninitialized</em></span> optional.
+ </li>
+<li class="listitem">
+ Testing if the variant's current type is <code class="computeroutput"><span class="identifier">T</span></code>
+ models testing if the optional is initialized
+ </li>
+<li class="listitem">
+ Trying to extract a <code class="computeroutput"><span class="identifier">T</span></code>
+ from a variant when its current type is not <code class="computeroutput"><span class="identifier">T</span></code>,
+ models the undefined behavior of trying to access the value of an uninitialized
+ optional
+ </li>
+</ul></div>
+<p>
+ Single-element container:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>deep-copy</strong></span> semantics: copies of the
+ container implies copies of the value.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>deep-relational</strong></span> semantics: comparisons
+ between containers compare container size and if match, contained value
+ </li>
+<li class="listitem">
+ If the container is not empty (contains an object of type <code class="computeroutput"><span class="identifier">T</span></code>), it is modeling an <span class="emphasis"><em>initialized</em></span>
+ optional.
+ </li>
+<li class="listitem">
+ If the container is empty, it is modeling an <span class="emphasis"><em>uninitialized</em></span>
+ optional.
+ </li>
+<li class="listitem">
+ Testing if the container is empty models testing if the optional is
+ initialized
+ </li>
+<li class="listitem">
+ Trying to extract a <code class="computeroutput"><span class="identifier">T</span></code>
+ from an empty container models the undefined behavior of trying to
+ access the value of an uninitialized optional
+ </li>
+</ul></div>
+</div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="design_overview/the_semantics.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/tutorial/design_overview/the_interface.html b/doc/html/boost_optional/tutorial/design_overview/the_interface.html
new file mode 100644
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+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>The Interface</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
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+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../../index.html">Home</a></td>
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+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
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+<a accesskey="p" href="the_semantics.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../design_overview.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../when_to_use_optional.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.tutorial.design_overview.the_interface"></a><a class="link" href="the_interface.html" title="The Interface">The
+ Interface</a>
+</h4></div></div></div>
+<p>
+ Since the purpose of optional is to allow us to use objects with a formal
+ uninitialized additional state, the interface could try to follow the interface
+ of the underlying <code class="computeroutput"><span class="identifier">T</span></code> type
+ as much as possible. In order to choose the proper degree of adoption of
+ the native <code class="computeroutput"><span class="identifier">T</span></code> interface,
+ the following must be noted: Even if all the operations supported by an
+ instance of type <code class="computeroutput"><span class="identifier">T</span></code> are
+ defined for the entire range of values for such a type, an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ extends such a set of values with a new value for which most (otherwise
+ valid) operations are not defined in terms of <code class="computeroutput"><span class="identifier">T</span></code>.
+ </p>
+<p>
+ Furthermore, since <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> itself is merely a <code class="computeroutput"><span class="identifier">T</span></code>
+ wrapper (modeling a <code class="computeroutput"><span class="identifier">T</span></code> supertype),
+ any attempt to define such operations upon uninitialized optionals will
+ be totally artificial w.r.t. <code class="computeroutput"><span class="identifier">T</span></code>.
+ </p>
+<p>
+ This library chooses an interface which follows from <code class="computeroutput"><span class="identifier">T</span></code>'s
+ interface only for those operations which are well defined (w.r.t the type
+ <code class="computeroutput"><span class="identifier">T</span></code>) even if any of the operands
+ are uninitialized. These operations include: construction, copy-construction,
+ assignment, swap and relational operations.
+ </p>
+<p>
+ For the value access operations, which are undefined (w.r.t the type <code class="computeroutput"><span class="identifier">T</span></code>) when the operand is uninitialized,
+ a different interface is chosen (which will be explained next).
+ </p>
+<p>
+ Also, the presence of the possibly uninitialized state requires additional
+ operations not provided by <code class="computeroutput"><span class="identifier">T</span></code>
+ itself which are supported by a special interface.
+ </p>
+<h6>
+<a name="boost_optional.tutorial.design_overview.the_interface.h0"></a>
+ <span class="phrase"><a name="boost_optional.tutorial.design_overview.the_interface.lexically_hinted_value_access_in_the_presence_of_possibly_uninitialized_optional_objects__the_operators___and___gt_"></a></span><a class="link" href="the_interface.html#boost_optional.tutorial.design_overview.the_interface.lexically_hinted_value_access_in_the_presence_of_possibly_uninitialized_optional_objects__the_operators___and___gt_">Lexically-hinted
+ Value Access in the presence of possibly uninitialized optional objects:
+ The operators * and -></a>
+ </h6>
+<p>
+ A relevant feature of a pointer is that it can have a <span class="bold"><strong>null
+ pointer value</strong></span>. This is a <span class="emphasis"><em>special</em></span> value
+ which is used to indicate that the pointer is not referring to any object
+ at all. In other words, null pointer values convey the notion of nonexistent
+ objects.
+ </p>
+<p>
+ This meaning of the null pointer value allowed pointers to became a <span class="emphasis"><em>de
+ facto</em></span> standard for handling optional objects because all you
+ have to do to refer to a value which you don't really have is to use a
+ null pointer value of the appropriate type. Pointers have been used for
+ decades—from the days of C APIs to modern C++ libraries—to <span class="emphasis"><em>refer</em></span>
+ to optional (that is, possibly nonexistent) objects; particularly as optional
+ arguments to a function, but also quite often as optional data members.
+ </p>
+<p>
+ The possible presence of a null pointer value makes the operations that
+ access the pointee's value possibly undefined, therefore, expressions which
+ use dereference and access operators, such as: <code class="computeroutput"><span class="special">(</span>
+ <span class="special">*</span><span class="identifier">p</span>
+ <span class="special">=</span> <span class="number">2</span> <span class="special">)</span></code> and <code class="computeroutput"><span class="special">(</span>
+ <span class="identifier">p</span><span class="special">-></span><span class="identifier">foo</span><span class="special">()</span> <span class="special">)</span></code>, implicitly convey the notion of optionality,
+ and this information is tied to the <span class="emphasis"><em>syntax</em></span> of the
+ expressions. That is, the presence of operators <code class="computeroutput"><span class="special">*</span></code>
+ and <code class="computeroutput"><span class="special">-></span></code> tell by themselves
+ —without any additional context— that the expression will be undefined
+ unless the implied pointee actually exist.
+ </p>
+<p>
+ Such a <span class="emphasis"><em>de facto</em></span> idiom for referring to optional objects
+ can be formalized in the form of a concept: the <a href="../../../../../../utility/OptionalPointee.html" target="_top"><code class="computeroutput"><span class="identifier">OptionalPointee</span></code></a> concept. This
+ concept captures the syntactic usage of operators <code class="computeroutput"><span class="special">*</span></code>,
+ <code class="computeroutput"><span class="special">-></span></code> and contextual conversion
+ to <code class="computeroutput"><span class="keyword">bool</span></code> to convey the notion
+ of optionality.
+ </p>
+<p>
+ However, pointers are good to <span class="underline">refer</span>
+ to optional objects, but not particularly good to handle the optional objects
+ in all other respects, such as initializing or moving/copying them. The
+ problem resides in the shallow-copy of pointer semantics: if you need to
+ effectively move or copy the object, pointers alone are not enough. The
+ problem is that copies of pointers do not imply copies of pointees. For
+ example, as was discussed in the motivation, pointers alone cannot be used
+ to return optional objects from a function because the object must move
+ outside from the function and into the caller's context.
+ </p>
+<p>
+ A solution to the shallow-copy problem that is often used is to resort
+ to dynamic allocation and use a smart pointer to automatically handle the
+ details of this. For example, if a function is to optionally return an
+ object <code class="computeroutput"><span class="identifier">X</span></code>, it can use <code class="computeroutput"><span class="identifier">shared_ptr</span><span class="special"><</span><span class="identifier">X</span><span class="special">></span></code>
+ as the return value. However, this requires dynamic allocation of <code class="computeroutput"><span class="identifier">X</span></code>. If <code class="computeroutput"><span class="identifier">X</span></code>
+ is a built-in or small POD, this technique is very poor in terms of required
+ resources. Optional objects are essentially values so it is very convenient
+ to be able to use automatic storage and deep-copy semantics to manipulate
+ optional values just as we do with ordinary values. Pointers do not have
+ this semantics, so are inappropriate for the initialization and transport
+ of optional values, yet are quite convenient for handling the access to
+ the possible undefined value because of the idiomatic aid present in the
+ <a href="../../../../../../utility/OptionalPointee.html" target="_top"><code class="computeroutput"><span class="identifier">OptionalPointee</span></code></a>
+ concept incarnated by pointers.
+ </p>
+<h6>
+<a name="boost_optional.tutorial.design_overview.the_interface.h1"></a>
+ <span class="phrase"><a name="boost_optional.tutorial.design_overview.the_interface.optional_lt_t_gt__as_a_model_of_optionalpointee"></a></span><a class="link" href="the_interface.html#boost_optional.tutorial.design_overview.the_interface.optional_lt_t_gt__as_a_model_of_optionalpointee">Optional<T>
+ as a model of OptionalPointee</a>
+ </h6>
+<p>
+ For value access operations <code class="computeroutput"><span class="identifier">optional</span><span class="special"><></span></code> uses operators <code class="computeroutput"><span class="special">*</span></code>
+ and <code class="computeroutput"><span class="special">-></span></code> to lexically warn
+ about the possibly uninitialized state appealing to the familiar pointer
+ semantics w.r.t. to null pointers.
+ </p>
+<div class="caution"><table border="0" summary="Caution">
+<tr>
+<td rowspan="2" align="center" valign="top" width="25"><img alt="[Caution]" src="../../../../../../../doc/src/images/caution.png"></td>
+<th align="left">Caution</th>
+</tr>
+<tr><td align="left" valign="top"><p>
+ However, it is particularly important to note that <code class="computeroutput"><span class="identifier">optional</span><span class="special"><></span></code> objects are not pointers. <span class="underline"><code class="computeroutput"><span class="identifier">optional</span><span class="special"><></span></code> is not, and does not model, a
+ pointer</span>.
+ </p></td></tr>
+</table></div>
+<p>
+ For instance, <code class="computeroutput"><span class="identifier">optional</span><span class="special"><></span></code> does not have shallow-copy so does
+ not alias: two different optionals never refer to the <span class="emphasis"><em>same</em></span>
+ value unless <code class="computeroutput"><span class="identifier">T</span></code> itself is
+ a reference (but may have <span class="emphasis"><em>equivalent</em></span> values). The
+ difference between an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> and a pointer must be kept in mind,
+ particularly because the semantics of relational operators are different:
+ since <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ is a value-wrapper, relational operators are deep: they compare optional
+ values; but relational operators for pointers are shallow: they do not
+ compare pointee values. As a result, you might be able to replace <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ by <code class="computeroutput"><span class="identifier">T</span><span class="special">*</span></code>
+ on some situations but not always. Specifically, on generic code written
+ for both, you cannot use relational operators directly, and must use the
+ template functions <a href="../../../../../../utility/OptionalPointee.html#equal" target="_top"><code class="computeroutput"><span class="identifier">equal_pointees</span><span class="special">()</span></code></a>
+ and <a href="../../../../../../utility/OptionalPointee.html#less" target="_top"><code class="computeroutput"><span class="identifier">less_pointees</span><span class="special">()</span></code></a>
+ instead.
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="the_semantics.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../design_overview.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../when_to_use_optional.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/tutorial/design_overview/the_semantics.html b/doc/html/boost_optional/tutorial/design_overview/the_semantics.html
new file mode 100644
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@@ -0,0 +1,121 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>The semantics</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
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+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../design_overview.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../design_overview.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="the_interface.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.tutorial.design_overview.the_semantics"></a><a class="link" href="the_semantics.html" title="The semantics">The
+ semantics</a>
+</h4></div></div></div>
+<p>
+ Objects of type <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> are intended to be used in places where
+ objects of type <code class="computeroutput"><span class="identifier">T</span></code> would
+ but which might be uninitialized. Hence, <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>'s purpose is to formalize the additional
+ possibly uninitialized state. From the perspective of this role, <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ can have the same operational semantics of <code class="computeroutput"><span class="identifier">T</span></code>
+ plus the additional semantics corresponding to this special state. As such,
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ could be thought of as a <span class="emphasis"><em>supertype</em></span> of <code class="computeroutput"><span class="identifier">T</span></code>. Of course, we can't do that in C++,
+ so we need to compose the desired semantics using a different mechanism.
+ Doing it the other way around, that is, making <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> a <span class="emphasis"><em>subtype</em></span> of
+ <code class="computeroutput"><span class="identifier">T</span></code> is not only conceptually
+ wrong but also impractical: it is not allowed to derive from a non-class
+ type, such as a built-in type.
+ </p>
+<p>
+ We can draw from the purpose of <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> the required basic semantics:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="bold"><strong>Default Construction:</strong></span> To introduce
+ a formally uninitialized wrapped object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Direct Value Construction via copy:</strong></span>
+ To introduce a formally initialized wrapped object whose value is obtained
+ as a copy of some object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Deep Copy Construction:</strong></span> To obtain
+ a new yet equivalent wrapped object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Direct Value Assignment (upon initialized):</strong></span>
+ To assign a value to the wrapped object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Direct Value Assignment (upon uninitialized):</strong></span>
+ To initialize the wrapped object with a value obtained as a copy of
+ some object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Assignment (upon initialized):</strong></span> To
+ assign to the wrapped object the value of another wrapped object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Assignment (upon uninitialized):</strong></span> To
+ initialize the wrapped object with value of another wrapped object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Deep Relational Operations (when supported by
+ the type T):</strong></span> To compare wrapped object values taking into
+ account the presence of uninitialized states.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Value access:</strong></span> To unwrap the wrapped
+ object.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Initialization state query:</strong></span> To determine
+ if the object is formally initialized or not.
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>Swap:</strong></span> To exchange wrapped objects.
+ (with whatever exception safety guarantees are provided by <code class="computeroutput"><span class="identifier">T</span></code>'s swap).
+ </li>
+<li class="listitem">
+ <span class="bold"><strong>De-initialization:</strong></span> To release the
+ wrapped object (if any) and leave the wrapper in the uninitialized
+ state.
+ </li>
+</ul></div>
+<p>
+ Additional operations are useful, such as converting constructors and converting
+ assignments, in-place construction and assignment, and safe value access
+ via a pointer to the wrapped object or null.
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
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diff --git a/doc/html/boost_optional/tutorial/exception_safety_guarantees.html b/doc/html/boost_optional/tutorial/exception_safety_guarantees.html
new file mode 100644
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@@ -0,0 +1,175 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Exception Safety Guarantees</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../index.html" title="Boost.Optional">
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+<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="gotchas/false_positive_with__wmaybe_uninitialized.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="type_requirements.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.tutorial.exception_safety_guarantees"></a><a class="link" href="exception_safety_guarantees.html" title="Exception Safety Guarantees">Exception
+ Safety Guarantees</a>
+</h3></div></div></div>
+<p>
+ This library assumes that <code class="computeroutput"><span class="identifier">T</span></code>'s
+ destructor does not throw exceptions. If it does, the behaviour of many operations
+ on <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> is
+ undefined.
+ </p>
+<p>
+ The following mutating operations never throw exceptions:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">none_t</span>
+ <span class="special">)</span> <span class="keyword">noexcept</span></code>
+ </li>
+<li class="listitem">
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">reset</span><span class="special">()</span> <span class="keyword">noexcept</span></code>
+ </li>
+</ul></div>
+<p>
+ In addition, the following constructors and the destructor never throw exceptions:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">()</span>
+ <span class="keyword">noexcept</span></code>
+ </li>
+<li class="listitem">
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">optional</span><span class="special">(</span>
+ <span class="identifier">none_t</span> <span class="special">)</span>
+ <span class="keyword">noexcept</span></code>
+ </li>
+</ul></div>
+<p>
+ Regarding the following assignment functions:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code>
+ </li>
+<li class="listitem">
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code>
+ </li>
+<li class="listitem">
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">U</span><span class="special">></span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code>
+ </li>
+<li class="listitem">
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">InPlaceFactory</span><span class="special">></span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">InPlaceFactory</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span></code>
+ </li>
+<li class="listitem">
+ <code class="computeroutput"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">TypedInPlaceFactory</span><span class="special">></span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="keyword">operator</span><span class="special">=</span> <span class="special">(</span> <span class="identifier">TypedInPlaceFactory</span>
+ <span class="keyword">const</span><span class="special">&</span>
+ <span class="special">)</span> </code>
+ </li>
+<li class="listitem">
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>::</span><span class="identifier">reset</span><span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="special">)</span></code>
+ </li>
+</ul></div>
+<p>
+ They forward calls to the corresponding <code class="computeroutput"><span class="identifier">T</span></code>'s
+ constructors or assignments (depending on whether the optional object is
+ initialized or not); so if both <code class="computeroutput"><span class="identifier">T</span></code>'s
+ constructor and the assignment provide strong exception safety guarantee,
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>'s
+ assignment also provides strong exception safety guarantee; otherwise we
+ only get the basic guarantee. Additionally, if both involved <code class="computeroutput"><span class="identifier">T</span></code>'s constructor and the assignment never
+ throw, <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>'s
+ assignment also never throws.
+ </p>
+<p>
+ Unless <code class="computeroutput"><span class="identifier">T</span></code>'s constructor or
+ assignment throws, assignments to <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ do not throw anything else on its own. A throw during assignment never changes
+ the initialization state of any optional object involved:
+ </p>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt1</span><span class="special">(</span><span class="identifier">val1</span><span class="special">);</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">opt2</span><span class="special">(</span><span class="identifier">val2</span><span class="special">);</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">opt1</span><span class="special">);</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">opt2</span><span class="special">);</span>
+
+<span class="keyword">try</span>
+<span class="special">{</span>
+ <span class="identifier">opt1</span> <span class="special">=</span> <span class="identifier">opt2</span><span class="special">;</span> <span class="comment">// throws</span>
+<span class="special">}</span>
+<span class="keyword">catch</span><span class="special">(...)</span>
+<span class="special">{</span>
+ <span class="identifier">assert</span><span class="special">(</span><span class="identifier">opt1</span><span class="special">);</span>
+ <span class="identifier">assert</span><span class="special">(</span><span class="identifier">opt2</span><span class="special">);</span>
+<span class="special">}</span>
+</pre>
+<p>
+ This also applies to move assignments/constructors. However, move operations
+ are made no-throw more often.
+ </p>
+<p>
+ Operation <code class="computeroutput"><span class="identifier">emplace</span></code> provides
+ basic exception safety guarantee. If it throws, the optional object becomes
+ uninitialized regardless of its initial state, and its previous contained
+ value (if any) is destroyed. It doesn't call any assignment or move/copy
+ constructor on <code class="computeroutput"><span class="identifier">T</span></code>.
+ </p>
+<h5>
+<a name="boost_optional.tutorial.exception_safety_guarantees.h0"></a>
+ <span class="phrase"><a name="boost_optional.tutorial.exception_safety_guarantees.swap"></a></span><a class="link" href="exception_safety_guarantees.html#boost_optional.tutorial.exception_safety_guarantees.swap">Swap</a>
+ </h5>
+<p>
+ Unless <code class="computeroutput"><span class="identifier">swap</span></code> on optional is
+ customized, its primary implementation forwards calls to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <code class="computeroutput"><span class="identifier">swap</span></code> or move constructor
+ (depending on the initialization state of the optional objects). Thus, if
+ both <code class="computeroutput"><span class="identifier">T</span></code>'s <code class="computeroutput"><span class="identifier">swap</span></code>
+ and move constructor never throw, <code class="computeroutput"><span class="identifier">swap</span></code>
+ on <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> never
+ throws. similarly, if both <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <code class="computeroutput"><span class="identifier">swap</span></code> and move constructor
+ offer strong guarantee, <code class="computeroutput"><span class="identifier">swap</span></code>
+ on <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> also
+ offers a strong guarantee.
+ </p>
+<p>
+ In case <code class="computeroutput"><span class="identifier">swap</span></code> on optional
+ is customized, the call to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ move constructor are replaced with the calls to <code class="computeroutput"><span class="identifier">T</span></code>'s
+ default constructor followed by <code class="computeroutput"><span class="identifier">swap</span></code>.
+ (This is more useful on older compilers that do not support move semantics,
+ when one wants to acheive stronger exception safety guarantees.) In this
+ case the exception safety guarantees for <code class="computeroutput"><span class="identifier">swap</span></code>
+ are reliant on the guarantees of <code class="computeroutput"><span class="identifier">T</span></code>'s
+ <code class="computeroutput"><span class="identifier">swap</span></code> and default constructor
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="gotchas/false_positive_with__wmaybe_uninitialized.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="type_requirements.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/tutorial/gotchas.html b/doc/html/boost_optional/tutorial/gotchas.html
new file mode 100644
index 0000000..c11cad2
--- /dev/null
+++ b/doc/html/boost_optional/tutorial/gotchas.html
@@ -0,0 +1,112 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Gotchas</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../index.html" title="Boost.Optional">
+<link rel="up" href="../../optional/tutorial.html" title="Tutorial">
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+<link rel="next" href="gotchas/moved_from__optional_.html" title="Moved-from optional">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../index.html">Home</a></td>
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+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="in_place_factories.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="gotchas/moved_from__optional_.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.tutorial.gotchas"></a><a class="link" href="gotchas.html" title="Gotchas">Gotchas</a>
+</h3></div></div></div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.tutorial.gotchas.a_note_about_optional_bool_"></a><a class="link" href="gotchas.html#boost_optional.tutorial.gotchas.a_note_about_optional_bool_" title="A note about optional<bool>">A
+ note about optional<bool></a>
+</h4></div></div></div>
+<p>
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span></code>
+ should be used with special caution and consideration.
+ </p>
+<p>
+ First, it is functionally similar to a tristate boolean (false, maybe,
+ true) —such as <a href="../../../../../../doc/html/tribool.html" target="_top">boost::tribool</a>—
+ except that in a tristate boolean, the maybe state <span class="underline">represents
+ a valid value</span>, unlike the corresponding state of an uninitialized
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span></code>.
+ It should be carefully considered if an <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span></code> instead of a <code class="computeroutput"><span class="identifier">tribool</span></code>
+ is really needed.
+ </p>
+<p>
+ Second, although <code class="computeroutput"><span class="identifier">optional</span><span class="special"><></span></code> provides a contextual conversion
+ to <code class="computeroutput"><span class="keyword">bool</span></code> in C++11, this falls
+ back to an implicit conversion on older compilers. This conversion refers
+ to the initialization state and not to the contained value. Using <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span></code>
+ can lead to subtle errors due to the implicit <code class="computeroutput"><span class="keyword">bool</span></code>
+ conversion:
+ </p>
+<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">foo</span> <span class="special">(</span> <span class="keyword">bool</span> <span class="identifier">v</span> <span class="special">)</span> <span class="special">;</span>
+<span class="keyword">void</span> <span class="identifier">bar</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span> <span class="identifier">v</span> <span class="special">=</span> <span class="keyword">try</span><span class="special">();</span>
+
+ <span class="comment">// The following intended to pass the value of 'v' to foo():</span>
+ <span class="identifier">foo</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+ <span class="comment">// But instead, the initialization state is passed</span>
+ <span class="comment">// due to a typo: it should have been foo(*v).</span>
+<span class="special">}</span>
+</pre>
+<p>
+ The only implicit conversion is to <code class="computeroutput"><span class="keyword">bool</span></code>,
+ and it is safe in the sense that typical integral promotions don't apply
+ (i.e. if <code class="computeroutput"><span class="identifier">foo</span><span class="special">()</span></code>
+ takes an <code class="computeroutput"><span class="keyword">int</span></code> instead, it won't
+ compile).
+ </p>
+<p>
+ Third, mixed comparisons with <code class="computeroutput"><span class="keyword">bool</span></code>
+ work differently than similar mixed comparisons between pointers and <code class="computeroutput"><span class="keyword">bool</span></code>, so the results might surprise you:
+ </p>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">bool</span><span class="special">></span> <span class="identifier">oEmpty</span><span class="special">(</span><span class="identifier">none</span><span class="special">),</span> <span class="identifier">oTrue</span><span class="special">(</span><span class="keyword">true</span><span class="special">),</span> <span class="identifier">oFalse</span><span class="special">(</span><span class="keyword">false</span><span class="special">);</span>
+
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oEmpty</span> <span class="special">==</span> <span class="identifier">none</span><span class="special">);</span> <span class="comment">// renders true</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oEmpty</span> <span class="special">==</span> <span class="keyword">false</span><span class="special">);</span> <span class="comment">// renders false!</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oEmpty</span> <span class="special">==</span> <span class="keyword">true</span><span class="special">);</span> <span class="comment">// renders false!</span>
+
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oFalse</span> <span class="special">==</span> <span class="identifier">none</span><span class="special">);</span> <span class="comment">// renders false</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oFalse</span> <span class="special">==</span> <span class="keyword">false</span><span class="special">);</span> <span class="comment">// renders true!</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oFalse</span> <span class="special">==</span> <span class="keyword">true</span><span class="special">);</span> <span class="comment">// renders false</span>
+
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oTrue</span> <span class="special">==</span> <span class="identifier">none</span><span class="special">);</span> <span class="comment">// renders false</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oTrue</span> <span class="special">==</span> <span class="keyword">false</span><span class="special">);</span> <span class="comment">// renders false</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">oTrue</span> <span class="special">==</span> <span class="keyword">true</span><span class="special">);</span> <span class="comment">// renders true</span>
+</pre>
+<p>
+ In other words, for <code class="computeroutput"><span class="identifier">optional</span><span class="special"><></span></code>, the following assertion does not
+ hold:
+ </p>
+<pre class="programlisting"><span class="identifier">assert</span><span class="special">((</span><span class="identifier">opt</span> <span class="special">==</span> <span class="keyword">false</span><span class="special">)</span> <span class="special">==</span> <span class="special">(!</span><span class="identifier">opt</span><span class="special">));</span>
+</pre>
+</div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="in_place_factories.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="gotchas/moved_from__optional_.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/tutorial/gotchas/false_positive_with__wmaybe_uninitialized.html b/doc/html/boost_optional/tutorial/gotchas/false_positive_with__wmaybe_uninitialized.html
new file mode 100644
index 0000000..240ee0f
--- /dev/null
+++ b/doc/html/boost_optional/tutorial/gotchas/false_positive_with__wmaybe_uninitialized.html
@@ -0,0 +1,77 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>False positive with -Wmaybe-uninitialized</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../gotchas.html" title="Gotchas">
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+<link rel="next" href="../exception_safety_guarantees.html" title="Exception Safety Guarantees">
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+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td>
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+<td align="center"><a href="../../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="mixed_relational_comparisons.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../gotchas.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../exception_safety_guarantees.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.tutorial.gotchas.false_positive_with__wmaybe_uninitialized"></a><a class="link" href="false_positive_with__wmaybe_uninitialized.html" title="False positive with -Wmaybe-uninitialized">False
+ positive with -Wmaybe-uninitialized</a>
+</h4></div></div></div>
+<p>
+ Sometimes on GCC compilers below version 5.1 you may get an -Wmaybe-uninitialized
+ warning when copiling with option -02 on a perfectly valid <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span></code> usage. For instance in this
+ program:
+ </p>
+<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">optional</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
+
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">getitem</span><span class="special">();</span>
+
+<span class="keyword">int</span> <span class="identifier">main</span><span class="special">(</span><span class="keyword">int</span> <span class="identifier">argc</span><span class="special">,</span> <span class="keyword">const</span> <span class="keyword">char</span> <span class="special">*[])</span>
+<span class="special">{</span>
+ <span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">a</span> <span class="special">=</span> <span class="identifier">getitem</span><span class="special">();</span>
+ <span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">b</span><span class="special">;</span>
+
+ <span class="keyword">if</span> <span class="special">(</span><span class="identifier">argc</span> <span class="special">></span> <span class="number">0</span><span class="special">)</span>
+ <span class="identifier">b</span> <span class="special">=</span> <span class="identifier">argc</span><span class="special">;</span>
+
+ <span class="keyword">if</span> <span class="special">(</span><span class="identifier">a</span> <span class="special">!=</span> <span class="identifier">b</span><span class="special">)</span>
+ <span class="keyword">return</span> <span class="number">1</span><span class="special">;</span>
+
+ <span class="keyword">return</span> <span class="number">0</span><span class="special">;</span>
+<span class="special">}</span>
+</pre>
+<p>
+ This is a bug in the compiler. As a workaround (provided in <a href="http://stackoverflow.com/questions/21755206/how-to-get-around-gcc-void-b-4-may-be-used-uninitialized-in-this-funct" target="_top">this
+ Stack Overflow question</a>) use the following way of initializing
+ an optional containing no value:
+ </p>
+<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">b</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">make_optional</span><span class="special">(</span><span class="keyword">false</span><span class="special">,</span> <span class="keyword">int</span><span class="special">());</span>
+</pre>
+<p>
+ This is obviously redundant, but makes the warning disappear.
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="mixed_relational_comparisons.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../gotchas.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../exception_safety_guarantees.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/tutorial/gotchas/mixed_relational_comparisons.html b/doc/html/boost_optional/tutorial/gotchas/mixed_relational_comparisons.html
new file mode 100644
index 0000000..8d25f0d
--- /dev/null
+++ b/doc/html/boost_optional/tutorial/gotchas/mixed_relational_comparisons.html
@@ -0,0 +1,59 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Mixed relational comparisons</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../gotchas.html" title="Gotchas">
+<link rel="prev" href="moved_from__optional_.html" title="Moved-from optional">
+<link rel="next" href="false_positive_with__wmaybe_uninitialized.html" title="False positive with -Wmaybe-uninitialized">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td>
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+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="moved_from__optional_.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../gotchas.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="false_positive_with__wmaybe_uninitialized.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.tutorial.gotchas.mixed_relational_comparisons"></a><a class="link" href="mixed_relational_comparisons.html" title="Mixed relational comparisons">Mixed
+ relational comparisons</a>
+</h4></div></div></div>
+<p>
+ Because <code class="computeroutput"><span class="identifier">T</span></code> is convertible
+ to <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ and because <code class="computeroutput"><span class="identifier">opiotnal</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ is <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a> when <code class="computeroutput"><span class="identifier">T</span></code> is <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a>, you can sometimes
+ get an unexpected runtime result where you would rather expect a compiler
+ error:
+ </p>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">double</span><span class="special">></span> <span class="identifier">Flight_plan</span><span class="special">::</span><span class="identifier">weight</span><span class="special">();</span> <span class="comment">// sometimes no weight can be returned</span>
+
+<span class="keyword">bool</span> <span class="identifier">is_aircraft_too_heavy</span><span class="special">(</span><span class="identifier">Flight_plan</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">p</span><span class="special">)</span>
+<span class="special">{</span>
+ <span class="keyword">return</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">weight</span><span class="special">()</span> <span class="special">></span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">aircraft</span><span class="special">().</span><span class="identifier">max_weight</span><span class="special">();</span> <span class="comment">// compiles!</span>
+<span class="special">}</span> <span class="comment">// returns false when the optional contains no value </span>
+</pre>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="moved_from__optional_.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../gotchas.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="false_positive_with__wmaybe_uninitialized.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/tutorial/gotchas/moved_from__optional_.html b/doc/html/boost_optional/tutorial/gotchas/moved_from__optional_.html
new file mode 100644
index 0000000..7a4e444
--- /dev/null
+++ b/doc/html/boost_optional/tutorial/gotchas/moved_from__optional_.html
@@ -0,0 +1,63 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Moved-from optional</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../gotchas.html" title="Gotchas">
+<link rel="prev" href="../gotchas.html" title="Gotchas">
+<link rel="next" href="mixed_relational_comparisons.html" title="Mixed relational comparisons">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../gotchas.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../gotchas.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="mixed_relational_comparisons.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.tutorial.gotchas.moved_from__optional_"></a><a class="link" href="moved_from__optional_.html" title="Moved-from optional">Moved-from
+ <code class="computeroutput"><span class="identifier">optional</span></code></a>
+</h4></div></div></div>
+<p>
+ When an optional object that contains a value is moved from (is a source
+ of move constructor or assignment) it still contains a value and its contained
+ value is left in a moved-from state. This can be illustrated with the following
+ example.
+ </p>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="keyword">int</span><span class="special">>></span> <span class="identifier">opi</span> <span class="special">{</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">make_unique</span><span class="special"><</span><span class="keyword">int</span><span class="special">>(</span><span class="number">1</span><span class="special">)};</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">unique_ptr</span><span class="special"><</span><span class="keyword">int</span><span class="special">>></span> <span class="identifier">opj</span> <span class="special">=</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">move</span><span class="special">(</span><span class="identifier">opi</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(</span><span class="identifier">opi</span><span class="special">);</span>
+<span class="identifier">assert</span> <span class="special">(*</span><span class="identifier">opi</span> <span class="special">==</span> <span class="keyword">nullptr</span><span class="special">);</span>
+</pre>
+<p>
+ Quite a lot of people expect that when an object that contains a value
+ is moved from, its contained value should be destroyed. This is not so,
+ for performance reasons. Current semantics allow the implementation of
+ <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">opiotnal</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ to be trivially copyable when <code class="computeroutput"><span class="identifier">T</span></code>
+ is trivial.
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../gotchas.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../gotchas.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="mixed_relational_comparisons.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/tutorial/in_place_factories.html b/doc/html/boost_optional/tutorial/in_place_factories.html
new file mode 100644
index 0000000..5f0c426
--- /dev/null
+++ b/doc/html/boost_optional/tutorial/in_place_factories.html
@@ -0,0 +1,197 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>In-Place Factories</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../index.html" title="Boost.Optional">
+<link rel="up" href="../../optional/tutorial.html" title="Tutorial">
+<link rel="prev" href="optional_references/rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">
+<link rel="next" href="gotchas.html" title="Gotchas">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="optional_references/rebinding_semantics_for_assignment_of_optional_references.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="gotchas.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.tutorial.in_place_factories"></a><a class="link" href="in_place_factories.html" title="In-Place Factories">In-Place
+ Factories</a>
+</h3></div></div></div>
+<p>
+ One of the typical problems with wrappers and containers is that their interfaces
+ usually provide an operation to initialize or assign the contained object
+ as a copy of some other object. This not only requires the underlying type
+ to be <a href="../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a>, but also requires
+ the existence of a fully constructed object, often temporary, just to follow
+ the copy from:
+ </p>
+<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">X</span>
+<span class="special">{</span>
+ <span class="identifier">X</span> <span class="special">(</span> <span class="keyword">int</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">}</span> <span class="special">;</span>
+
+<span class="keyword">class</span> <span class="identifier">W</span>
+<span class="special">{</span>
+ <span class="identifier">X</span> <span class="identifier">wrapped_</span> <span class="special">;</span>
+
+ <span class="keyword">public</span><span class="special">:</span>
+
+ <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">X</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span> <span class="special">)</span> <span class="special">:</span> <span class="identifier">wrapped_</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">{}</span>
+<span class="special">}</span> <span class="special">;</span>
+
+<span class="keyword">void</span> <span class="identifier">foo</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="comment">// Temporary object created.</span>
+ <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">X</span><span class="special">(</span><span class="number">123</span><span class="special">,</span><span class="string">"hello"</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">}</span>
+</pre>
+<p>
+ A solution to this problem is to support direct construction of the contained
+ object right in the container's storage. In this scheme, the user only needs
+ to supply the arguments to the constructor to use in the wrapped object construction.
+ </p>
+<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">W</span>
+<span class="special">{</span>
+ <span class="identifier">X</span> <span class="identifier">wrapped_</span> <span class="special">;</span>
+
+ <span class="keyword">public</span><span class="special">:</span>
+
+ <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">X</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span> <span class="special">)</span> <span class="special">:</span> <span class="identifier">wrapped_</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">{}</span>
+ <span class="identifier">W</span> <span class="special">(</span> <span class="keyword">int</span> <span class="identifier">a0</span><span class="special">,</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span> <span class="identifier">a1</span><span class="special">)</span> <span class="special">:</span> <span class="identifier">wrapped_</span><span class="special">(</span><span class="identifier">a0</span><span class="special">,</span><span class="identifier">a1</span><span class="special">)</span> <span class="special">{}</span>
+<span class="special">}</span> <span class="special">;</span>
+
+<span class="keyword">void</span> <span class="identifier">foo</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="comment">// Wrapped object constructed in-place</span>
+ <span class="comment">// No temporary created.</span>
+ <span class="identifier">W</span> <span class="special">(</span><span class="number">123</span><span class="special">,</span><span class="string">"hello"</span><span class="special">)</span> <span class="special">;</span>
+<span class="special">}</span>
+</pre>
+<p>
+ A limitation of this method is that it doesn't scale well to wrapped objects
+ with multiple constructors nor to generic code were the constructor overloads
+ are unknown.
+ </p>
+<p>
+ The solution presented in this library is the family of <span class="bold"><strong>InPlaceFactories</strong></span>
+ and <span class="bold"><strong>TypedInPlaceFactories</strong></span>. These factories
+ are a family of classes which encapsulate an increasing number of arbitrary
+ constructor parameters and supply a method to construct an object of a given
+ type using those parameters at an address specified by the user via placement
+ new.
+ </p>
+<p>
+ For example, one member of this family looks like:
+ </p>
+<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span><span class="keyword">class</span> <span class="identifier">A0</span><span class="special">,</span> <span class="keyword">class</span> <span class="identifier">A1</span><span class="special">></span>
+<span class="keyword">class</span> <span class="identifier">TypedInPlaceFactory2</span>
+<span class="special">{</span>
+ <span class="identifier">A0</span> <span class="identifier">m_a0</span> <span class="special">;</span> <span class="identifier">A1</span> <span class="identifier">m_a1</span> <span class="special">;</span>
+
+ <span class="keyword">public</span><span class="special">:</span>
+
+ <span class="identifier">TypedInPlaceFactory2</span><span class="special">(</span> <span class="identifier">A0</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">a0</span><span class="special">,</span> <span class="identifier">A1</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">a1</span> <span class="special">)</span> <span class="special">:</span> <span class="identifier">m_a0</span><span class="special">(</span><span class="identifier">a0</span><span class="special">),</span> <span class="identifier">m_a1</span><span class="special">(</span><span class="identifier">a1</span><span class="special">)</span> <span class="special">{}</span>
+
+ <span class="keyword">void</span> <span class="identifier">construct</span> <span class="special">(</span> <span class="keyword">void</span><span class="special">*</span> <span class="identifier">p</span> <span class="special">)</span> <span class="special">{</span> <span class="keyword">new</span> <span class="special">(</span><span class="identifier">p</span><span class="special">)</span> <span class="identifier">T</span><span class="special">(</span><span class="identifier">m_a0</span><span class="special">,</span><span class="identifier">m_a1</span><span class="special">)</span> <span class="special">;</span> <span class="special">}</span>
+ <span class="special">}</span> <span class="special">;</span>
+</pre>
+<p>
+ A wrapper class aware of this can use it as:
+ </p>
+<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">W</span>
+<span class="special">{</span>
+ <span class="identifier">X</span> <span class="identifier">wrapped_</span> <span class="special">;</span>
+
+ <span class="keyword">public</span><span class="special">:</span>
+
+ <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">X</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span> <span class="special">)</span> <span class="special">:</span> <span class="identifier">wrapped_</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">{}</span>
+ <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">TypedInPlaceFactory2</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">fac</span> <span class="special">)</span> <span class="special">{</span> <span class="identifier">fac</span><span class="special">.</span><span class="identifier">construct</span><span class="special">(&</span><span class="identifier">wrapped_</span><span class="special">)</span> <span class="special">;</span> <span class="special">}</span>
+<span class="special">}</span> <span class="special">;</span>
+
+<span class="keyword">void</span> <span class="identifier">foo</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="comment">// Wrapped object constructed in-place via a TypedInPlaceFactory.</span>
+ <span class="comment">// No temporary created.</span>
+ <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">TypedInPlaceFactory2</span><span class="special"><</span><span class="identifier">X</span><span class="special">,</span><span class="keyword">int</span><span class="special">,</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">>(</span><span class="number">123</span><span class="special">,</span><span class="string">"hello"</span><span class="special">))</span> <span class="special">;</span>
+<span class="special">}</span>
+</pre>
+<p>
+ The factories are divided in two groups:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ <span class="underline">TypedInPlaceFactories</span>: those which
+ take the target type as a primary template parameter.
+ </li>
+<li class="listitem">
+ <span class="underline">InPlaceFactories</span>: those with a
+ template <code class="computeroutput"><span class="identifier">construct</span><span class="special">(</span><span class="keyword">void</span><span class="special">*)</span></code>
+ member function taking the target type.
+ </li>
+</ul></div>
+<p>
+ Within each group, all the family members differ only in the number of parameters
+ allowed.
+ </p>
+<p>
+ This library provides an overloaded set of helper template functions to construct
+ these factories without requiring unnecessary template parameters:
+ </p>
+<pre class="programlisting"><span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">A0</span><span class="special">,...,</span><span class="keyword">class</span> <span class="identifier">AN</span><span class="special">></span>
+<span class="identifier">InPlaceFactoryN</span> <span class="special"><</span><span class="identifier">A0</span><span class="special">,...,</span><span class="identifier">AN</span><span class="special">></span> <span class="identifier">in_place</span> <span class="special">(</span> <span class="identifier">A0</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">a0</span><span class="special">,</span> <span class="special">...,</span> <span class="identifier">AN</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">aN</span><span class="special">)</span> <span class="special">;</span>
+
+<span class="keyword">template</span><span class="special"><</span><span class="keyword">class</span> <span class="identifier">T</span><span class="special">,</span><span class="keyword">class</span> <span class="identifier">A0</span><span class="special">,...,</span><span class="keyword">class</span> <span class="identifier">AN</span><span class="special">></span>
+<span class="identifier">TypedInPlaceFactoryN</span> <span class="special"><</span><span class="identifier">T</span><span class="special">,</span><span class="identifier">A0</span><span class="special">,...,</span><span class="identifier">AN</span><span class="special">></span> <span class="identifier">in_place</span> <span class="special">(</span> <span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">a0</span><span class="special">,</span> <span class="identifier">A0</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">a0</span><span class="special">,</span> <span class="special">...,</span> <span class="identifier">AN</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">aN</span><span class="special">)</span> <span class="special">;</span>
+</pre>
+<p>
+ In-place factories can be used generically by the wrapper and user as follows:
+ </p>
+<pre class="programlisting"><span class="keyword">class</span> <span class="identifier">W</span>
+<span class="special">{</span>
+ <span class="identifier">X</span> <span class="identifier">wrapped_</span> <span class="special">;</span>
+
+ <span class="keyword">public</span><span class="special">:</span>
+
+ <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">X</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">x</span> <span class="special">)</span> <span class="special">:</span> <span class="identifier">wrapped_</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">{}</span>
+
+ <span class="keyword">template</span><span class="special"><</span> <span class="keyword">class</span> <span class="identifier">InPlaceFactory</span> <span class="special">></span>
+ <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">InPlaceFactory</span> <span class="keyword">const</span><span class="special">&</span> <span class="identifier">fac</span> <span class="special">)</span> <span class="special">{</span> <span class="identifier">fac</span><span class="special">.</span><span class="keyword">template</span> <span class="special"><</span><span class="identifier">X</span><span class="special">></span><span class="identifier">construct</span><span class="special">(&</span><span class="identifier">wrapped_</span><span class="special">)</span> <span class="special">;</span> <span class="special">}</span>
+
+<span class="special">}</span> <span class="special">;</span>
+
+<span class="keyword">void</span> <span class="identifier">foo</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="comment">// Wrapped object constructed in-place via a InPlaceFactory.</span>
+ <span class="comment">// No temporary created.</span>
+ <span class="identifier">W</span> <span class="special">(</span> <span class="identifier">in_place</span><span class="special">(</span><span class="number">123</span><span class="special">,</span><span class="string">"hello"</span><span class="special">)</span> <span class="special">)</span> <span class="special">;</span>
+<span class="special">}</span>
+</pre>
+<p>
+ The factories are implemented in the headers: <a href="../../../../../../boost/utility/in_place_factory.hpp" target="_top">in_place_factory.hpp</a>
+ and <a href="../../../../../../boost/utility/typed_in_place_factory.hpp" target="_top">typed_in_place_factory.hpp</a>
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="optional_references/rebinding_semantics_for_assignment_of_optional_references.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="gotchas.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/tutorial/io_operators.html b/doc/html/boost_optional/tutorial/io_operators.html
new file mode 100644
index 0000000..713b283
--- /dev/null
+++ b/doc/html/boost_optional/tutorial/io_operators.html
@@ -0,0 +1,87 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>IO operators</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../index.html" title="Boost.Optional">
+<link rel="up" href="../../optional/tutorial.html" title="Tutorial">
+<link rel="prev" href="relational_operators.html" title="Relational operators">
+<link rel="next" href="optional_references.html" title="Optional references">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="relational_operators.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="optional_references.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.tutorial.io_operators"></a><a class="link" href="io_operators.html" title="IO operators">IO operators</a>
+</h3></div></div></div>
+<p>
+ It is possible to use <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ with IO streams, provided that <code class="computeroutput"><span class="identifier">T</span></code>
+ can be used with streams. IOStream operators are defined in a separate header.
+ </p>
+<p>
+</p>
+<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">iostream</span><span class="special">></span>
+<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">optional</span><span class="special">/</span><span class="identifier">optional_io</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
+
+<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">o1</span> <span class="special">=</span> <span class="number">1</span><span class="special">,</span> <span class="identifier">oN</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span><span class="special">;</span>
+ <span class="identifier">std</span><span class="special">::</span><span class="identifier">cout</span> <span class="special"><<</span> <span class="identifier">o1</span><span class="special">;</span>
+ <span class="identifier">std</span><span class="special">::</span><span class="identifier">cin</span> <span class="special">>></span> <span class="identifier">oN</span><span class="special">;</span>
+<span class="special">}</span>
+</pre>
+<p>
+ </p>
+<p>
+ The current implementation does not guarantee any particular output. What
+ it guarantees is that if streaming out and then back in <code class="computeroutput"><span class="identifier">T</span></code>
+ gives the same value, then streaming out and then back in <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ will also give back the same result:
+ </p>
+<p>
+</p>
+<pre class="programlisting"><span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">cassert</span><span class="special">></span>
+<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">sstream</span><span class="special">></span>
+<span class="preprocessor">#include</span> <span class="special"><</span><span class="identifier">boost</span><span class="special">/</span><span class="identifier">optional</span><span class="special">/</span><span class="identifier">optional_io</span><span class="special">.</span><span class="identifier">hpp</span><span class="special">></span>
+
+<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">o1</span> <span class="special">=</span> <span class="number">1</span><span class="special">,</span> <span class="identifier">oN</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span><span class="special">;</span>
+ <span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">x1</span><span class="special">,</span> <span class="identifier">x2</span><span class="special">;</span>
+ <span class="identifier">std</span><span class="special">::</span><span class="identifier">stringstream</span> <span class="identifier">s</span><span class="special">;</span>
+ <span class="identifier">s</span> <span class="special"><<</span> <span class="identifier">o1</span> <span class="special"><<</span> <span class="identifier">oN</span><span class="special">;</span>
+ <span class="identifier">s</span> <span class="special">>></span> <span class="identifier">x1</span> <span class="special">>></span> <span class="identifier">x2</span><span class="special">;</span>
+ <span class="identifier">assert</span> <span class="special">(</span><span class="identifier">o1</span> <span class="special">==</span> <span class="identifier">x1</span><span class="special">);</span>
+ <span class="identifier">assert</span> <span class="special">(</span><span class="identifier">oN</span> <span class="special">==</span> <span class="identifier">x2</span><span class="special">);</span>
+<span class="special">}</span>
+</pre>
+<p>
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="relational_operators.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="optional_references.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/tutorial/motivation.html b/doc/html/boost_optional/tutorial/motivation.html
new file mode 100644
index 0000000..3b9f43c
--- /dev/null
+++ b/doc/html/boost_optional/tutorial/motivation.html
@@ -0,0 +1,129 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Motivation</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../../index.html" title="Chapter 1. Boost.Optional">
+<link rel="up" href="../../optional/tutorial.html" title="Tutorial">
+<link rel="prev" href="../../optional/tutorial.html" title="Tutorial">
+<link rel="next" href="design_overview.html" title="Design Overview">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="design_overview.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.tutorial.motivation"></a><a class="link" href="motivation.html" title="Motivation">Motivation</a>
+</h3></div></div></div>
+<p>
+ Consider these functions which should return a value but which might not
+ have a value to return:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ (A) <code class="computeroutput"><span class="keyword">double</span> <span class="identifier">sqrt</span><span class="special">(</span><span class="keyword">double</span> <span class="identifier">n</span> <span class="special">);</span></code>
+ </li>
+<li class="listitem">
+ (B) <code class="computeroutput"><span class="keyword">char</span> <span class="identifier">get_async_input</span><span class="special">();</span></code>
+ </li>
+<li class="listitem">
+ (C) <code class="computeroutput"><span class="identifier">point</span> <span class="identifier">polygon</span><span class="special">::</span><span class="identifier">get_any_point_effectively_inside</span><span class="special">();</span></code>
+ </li>
+</ul></div>
+<p>
+ There are different approaches to the issue of not having a value to return.
+ </p>
+<p>
+ A typical approach is to consider the existence of a valid return value as
+ a postcondition, so that if the function cannot compute the value to return,
+ it has either undefined behavior (and can use assert in a debug build) or
+ uses a runtime check and throws an exception if the postcondition is violated.
+ This is a reasonable choice for example, for function (A), because the lack
+ of a proper return value is directly related to an invalid parameter (out
+ of domain argument), so it is appropriate to require the callee to supply
+ only parameters in a valid domain for execution to continue normally.
+ </p>
+<p>
+ However, function (B), because of its asynchronous nature, does not fail
+ just because it can't find a value to return; so it is incorrect to consider
+ such a situation an error and assert or throw an exception. This function
+ must return, and somehow, must tell the callee that it is not returning a
+ meaningful value.
+ </p>
+<p>
+ A similar situation occurs with function (C): it is conceptually an error
+ to ask a <span class="emphasis"><em>null-area</em></span> polygon to return a point inside
+ itself, but in many applications, it is just impractical for performance
+ reasons to treat this as an error (because detecting that the polygon has
+ no area might be too expensive to be required to be tested previously), and
+ either an arbitrary point (typically at infinity) is returned, or some efficient
+ way to tell the callee that there is no such point is used.
+ </p>
+<p>
+ There are various mechanisms to let functions communicate that the returned
+ value is not valid. One such mechanism, which is quite common since it has
+ zero or negligible overhead, is to use a special value which is reserved
+ to communicate this. Classical examples of such special values are <code class="computeroutput"><span class="identifier">EOF</span></code>, <code class="computeroutput"><span class="identifier">string</span><span class="special">::</span><span class="identifier">npos</span></code>,
+ points at infinity, etc...
+ </p>
+<p>
+ When those values exist, i.e. the return type can hold all meaningful values
+ <span class="emphasis"><em>plus</em></span> the <span class="emphasis"><em>signal</em></span> value, this mechanism
+ is quite appropriate and well known. Unfortunately, there are cases when
+ such values do not exist. In these cases, the usual alternative is either
+ to use a wider type, such as <code class="computeroutput"><span class="keyword">int</span></code>
+ in place of <code class="computeroutput"><span class="keyword">char</span></code>; or a compound
+ type, such as <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">point</span><span class="special">,</span><span class="keyword">bool</span><span class="special">></span></code>.
+ </p>
+<p>
+ Returning a <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">T</span><span class="special">,</span><span class="keyword">bool</span><span class="special">></span></code>, thus attaching a boolean flag to the
+ result which indicates if the result is meaningful, has the advantage that
+ can be turned into a consistent idiom since the first element of the pair
+ can be whatever the function would conceptually return. For example, the
+ last two functions could have the following interface:
+ </p>
+<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="keyword">char</span><span class="special">,</span><span class="keyword">bool</span><span class="special">></span> <span class="identifier">get_async_input</span><span class="special">();</span>
+<span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">point</span><span class="special">,</span><span class="keyword">bool</span><span class="special">></span> <span class="identifier">polygon</span><span class="special">::</span><span class="identifier">get_any_point_effectively_inside</span><span class="special">();</span>
+</pre>
+<p>
+ These functions use a consistent interface for dealing with possibly nonexistent
+ results:
+ </p>
+<pre class="programlisting"><span class="identifier">std</span><span class="special">::</span><span class="identifier">pair</span><span class="special"><</span><span class="identifier">point</span><span class="special">,</span><span class="keyword">bool</span><span class="special">></span> <span class="identifier">p</span> <span class="special">=</span> <span class="identifier">poly</span><span class="special">.</span><span class="identifier">get_any_point_effectively_inside</span><span class="special">();</span>
+<span class="keyword">if</span> <span class="special">(</span> <span class="identifier">p</span><span class="special">.</span><span class="identifier">second</span> <span class="special">)</span>
+ <span class="identifier">flood_fill</span><span class="special">(</span><span class="identifier">p</span><span class="special">.</span><span class="identifier">first</span><span class="special">);</span>
+</pre>
+<p>
+ However, not only is this quite a burden syntactically, it is also error
+ prone since the user can easily use the function result (first element of
+ the pair) without ever checking if it has a valid value.
+ </p>
+<p>
+ Clearly, we need a better idiom.
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="design_overview.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/tutorial/optional_references.html b/doc/html/boost_optional/tutorial/optional_references.html
new file mode 100644
index 0000000..fb0fb56
--- /dev/null
+++ b/doc/html/boost_optional/tutorial/optional_references.html
@@ -0,0 +1,117 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Optional references</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../index.html" title="Boost.Optional">
+<link rel="up" href="../../optional/tutorial.html" title="Tutorial">
+<link rel="prev" href="io_operators.html" title="IO operators">
+<link rel="next" href="optional_references/rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="io_operators.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="optional_references/rebinding_semantics_for_assignment_of_optional_references.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.tutorial.optional_references"></a><a class="link" href="optional_references.html" title="Optional references">Optional
+ references</a>
+</h3></div></div></div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.tutorial.optional_references.overview"></a><a class="link" href="optional_references.html#boost_optional.tutorial.optional_references.overview" title="Overview">Overview</a>
+</h4></div></div></div>
+<p>
+ This library allows the template parameter <code class="computeroutput"><span class="identifier">T</span></code>
+ to be of reference type: <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span></code>, and to some extent, <code class="computeroutput"><span class="identifier">T</span> <span class="keyword">const</span><span class="special">&</span></code>.
+ </p>
+<p>
+ However, since references are not real objects some restrictions apply
+ and some operations are not available in this case:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ Converting constructors
+ </li>
+<li class="listitem">
+ Converting assignment
+ </li>
+<li class="listitem">
+ InPlace construction
+ </li>
+<li class="listitem">
+ InPlace assignment
+ </li>
+<li class="listitem">
+ Value-access via pointer
+ </li>
+</ul></div>
+<p>
+ Also, even though <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code> treats it wrapped pseudo-object
+ much as a real value, a true real reference is stored so aliasing will
+ ocurr:
+ </p>
+<div class="itemizedlist"><ul class="itemizedlist" style="list-style-type: disc; ">
+<li class="listitem">
+ Copies of <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code> will copy the references but
+ all these references will nonetheless refer to the same object.
+ </li>
+<li class="listitem">
+ Value-access will actually provide access to the referenced object
+ rather than the reference itself.
+ </li>
+</ul></div>
+<div class="caution"><table border="0" summary="Caution">
+<tr>
+<td rowspan="2" align="center" valign="top" width="25"><img alt="[Caution]" src="../../../../../../doc/src/images/caution.png"></td>
+<th align="left">Caution</th>
+</tr>
+<tr><td align="left" valign="top"><p>
+ On compilers that do not conform to Standard C++ rules of reference binding,
+ some operations on optional references are disabled in order to prevent
+ subtle bugs. For more details see <a class="link" href="../dependencies_and_portability/optional_reference_binding.html" title="Optional Reference Binding">Dependencies
+ and Portability section</a>.
+ </p></td></tr>
+</table></div>
+<h6>
+<a name="boost_optional.tutorial.optional_references.overview.h0"></a>
+ <span class="phrase"><a name="boost_optional.tutorial.optional_references.overview.rvalue_references"></a></span><a class="link" href="optional_references.html#boost_optional.tutorial.optional_references.overview.rvalue_references">Rvalue
+ references</a>
+ </h6>
+<p>
+ Rvalue references and lvalue references to const have the ability in C++
+ to extend the life time of a temporary they bind to. Optional references
+ do not have this capability, therefore to avoid surprising effects it is
+ not possible to initialize an optional references from a temporary. Optional
+ rvalue references are disabled altogether. Also, the initialization and
+ assignment of an optional reference to const from rvalue reference is disabled.
+ </p>
+<pre class="programlisting"><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&</span> <span class="identifier">i</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span> <span class="comment">// legal</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">const</span> <span class="keyword">int</span><span class="special">&></span> <span class="identifier">oi</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span> <span class="comment">// illegal</span>
+</pre>
+</div>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="io_operators.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="optional_references/rebinding_semantics_for_assignment_of_optional_references.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/tutorial/optional_references/rebinding_semantics_for_assignment_of_optional_references.html b/doc/html/boost_optional/tutorial/optional_references/rebinding_semantics_for_assignment_of_optional_references.html
new file mode 100644
index 0000000..6e827d0
--- /dev/null
+++ b/doc/html/boost_optional/tutorial/optional_references/rebinding_semantics_for_assignment_of_optional_references.html
@@ -0,0 +1,147 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Rebinding semantics for assignment of optional references</title>
+<link rel="stylesheet" href="../../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../../index.html" title="Boost.Optional">
+<link rel="up" href="../optional_references.html" title="Optional references">
+<link rel="prev" href="../optional_references.html" title="Optional references">
+<link rel="next" href="../in_place_factories.html" title="In-Place Factories">
+</head>
+<body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF">
+<table cellpadding="2" width="100%"><tr>
+<td valign="top"><img alt="Boost C++ Libraries" width="277" height="86" src="../../../../../../../boost.png"></td>
+<td align="center"><a href="../../../../../../../index.html">Home</a></td>
+<td align="center"><a href="../../../../../../../libs/libraries.htm">Libraries</a></td>
+<td align="center"><a href="http://www.boost.org/users/people.html">People</a></td>
+<td align="center"><a href="http://www.boost.org/users/faq.html">FAQ</a></td>
+<td align="center"><a href="../../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../optional_references.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../optional_references.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../in_place_factories.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h4 class="title">
+<a name="boost_optional.tutorial.optional_references.rebinding_semantics_for_assignment_of_optional_references"></a><a class="link" href="rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">Rebinding
+ semantics for assignment of optional references</a>
+</h4></div></div></div>
+<p>
+ If you assign to an <span class="emphasis"><em>uninitialized </em></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code> the effect is to bind (for the
+ first time) to the object. Clearly, there is no other choice.
+ </p>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">x</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">rx</span> <span class="special">=</span> <span class="identifier">x</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">ora</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">orb</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">ora</span> <span class="special">=</span> <span class="identifier">orb</span> <span class="special">;</span> <span class="comment">// now 'ora' is bound to 'x' through 'rx'</span>
+<span class="special">*</span><span class="identifier">ora</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span> <span class="comment">// Changes value of 'x' through 'ora'</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">x</span><span class="special">==</span><span class="number">2</span><span class="special">);</span>
+</pre>
+<p>
+ If you assign to a bare C++ reference, the assignment is forwarded to the
+ referenced object; its value changes but the reference is never rebound.
+ </p>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
+<span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">rb</span> <span class="special">;</span> <span class="comment">// Changes the value of 'a' to 'b'</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">a</span><span class="special">==</span><span class="identifier">b</span><span class="special">);</span>
+<span class="identifier">b</span> <span class="special">=</span> <span class="number">3</span> <span class="special">;</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">ra</span><span class="special">!=</span><span class="identifier">b</span><span class="special">);</span> <span class="comment">// 'ra' is not rebound to 'b'</span>
+</pre>
+<p>
+ Now, if you assign to an <span class="emphasis"><em>initialized </em></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code>,
+ the effect is to <span class="bold"><strong>rebind</strong></span> to the new object
+ instead of assigning the referee. This is unlike bare C++ references.
+ </p>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">ora</span><span class="special">(</span><span class="identifier">ra</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">orb</span><span class="special">(</span><span class="identifier">rb</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">ora</span> <span class="special">=</span> <span class="identifier">orb</span> <span class="special">;</span> <span class="comment">// 'ora' is rebound to 'b'</span>
+<span class="special">*</span><span class="identifier">ora</span> <span class="special">=</span> <span class="number">3</span> <span class="special">;</span> <span class="comment">// Changes value of 'b' (not 'a')</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">a</span><span class="special">==</span><span class="number">1</span><span class="special">);</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">b</span><span class="special">==</span><span class="number">3</span><span class="special">);</span>
+</pre>
+<h6>
+<a name="boost_optional.tutorial.optional_references.rebinding_semantics_for_assignment_of_optional_references.h0"></a>
+ <span class="phrase"><a name="boost_optional.tutorial.optional_references.rebinding_semantics_for_assignment_of_optional_references.rationale"></a></span><a class="link" href="rebinding_semantics_for_assignment_of_optional_references.html#boost_optional.tutorial.optional_references.rebinding_semantics_for_assignment_of_optional_references.rationale">Rationale</a>
+ </h6>
+<p>
+ Rebinding semantics for the assignment of <span class="emphasis"><em>initialized </em></span>
+ <code class="computeroutput"><span class="identifier">optional</span></code> references has
+ been chosen to provide <span class="bold"><strong>consistency among initialization
+ states</strong></span> even at the expense of lack of consistency with the semantics
+ of bare C++ references. It is true that <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span></code> strives to behave as much as possible
+ as <code class="computeroutput"><span class="identifier">U</span></code> does whenever it is
+ initialized; but in the case when <code class="computeroutput"><span class="identifier">U</span></code>
+ is <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span></code>,
+ doing so would result in inconsistent behavior w.r.t to the lvalue initialization
+ state.
+ </p>
+<p>
+ Imagine <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code>
+ forwarding assignment to the referenced object (thus changing the referenced
+ object value but not rebinding), and consider the following code:
+ </p>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">a</span> <span class="special">=</span> <span class="identifier">get</span><span class="special">();</span>
+<span class="keyword">int</span> <span class="identifier">x</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">rx</span> <span class="special">=</span> <span class="identifier">x</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">b</span><span class="special">(</span><span class="identifier">rx</span><span class="special">);</span>
+<span class="identifier">a</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
+</pre>
+<p>
+ What does the assignment do?
+ </p>
+<p>
+ If <code class="computeroutput"><span class="identifier">a</span></code> is <span class="emphasis"><em>uninitialized</em></span>,
+ the answer is clear: it binds to <code class="computeroutput"><span class="identifier">x</span></code>
+ (we now have another reference to <code class="computeroutput"><span class="identifier">x</span></code>).
+ But what if <code class="computeroutput"><span class="identifier">a</span></code> is already
+ <span class="emphasis"><em>initialized</em></span>? it would change the value of the referenced
+ object (whatever that is); which is inconsistent with the other possible
+ case.
+ </p>
+<p>
+ If <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code>
+ would assign just like <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span></code> does, you would never be able to use
+ Optional's assignment without explicitly handling the previous initialization
+ state unless your code is capable of functioning whether after the assignment,
+ <code class="computeroutput"><span class="identifier">a</span></code> aliases the same object
+ as <code class="computeroutput"><span class="identifier">b</span></code> or not.
+ </p>
+<p>
+ That is, you would have to discriminate in order to be consistent.
+ </p>
+<p>
+ If in your code rebinding to another object is not an option, then it is
+ very likely that binding for the first time isn't either. In such case,
+ assignment to an <span class="emphasis"><em>uninitialized </em></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code> shall be prohibited. It is quite
+ possible that in such a scenario it is a precondition that the lvalue must
+ be already initialized. If it isn't, then binding for the first time is
+ OK while rebinding is not which is IMO very unlikely. In such a scenario,
+ you can assign the value itself directly, as in:
+ </p>
+<pre class="programlisting"><span class="identifier">assert</span><span class="special">(!!</span><span class="identifier">opt</span><span class="special">);</span>
+<span class="special">*</span><span class="identifier">opt</span><span class="special">=</span><span class="identifier">value</span><span class="special">;</span>
+</pre>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="../optional_references.html"><img src="../../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../optional_references.html"><img src="../../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../../index.html"><img src="../../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../in_place_factories.html"><img src="../../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/tutorial/performance_considerations.html b/doc/html/boost_optional/tutorial/performance_considerations.html
new file mode 100644
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@@ -0,0 +1,265 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Performance considerations</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../index.html" title="Boost.Optional">
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+<hr>
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+<a accesskey="p" href="type_requirements.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.tutorial.performance_considerations"></a><a class="link" href="performance_considerations.html" title="Performance considerations">Performance
+ considerations</a>
+</h3></div></div></div>
+<p>
+ Technical details aside, the memory layout of <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ for a generic <code class="computeroutput"><span class="identifier">T</span></code> is more-less
+ this:
+ </p>
+<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span>
+<span class="keyword">class</span> <span class="identifier">optional</span>
+<span class="special">{</span>
+ <span class="keyword">bool</span> <span class="identifier">_initialized</span><span class="special">;</span>
+ <span class="identifier">std</span><span class="special">::</span><span class="identifier">aligned_storage_t</span><span class="special"><</span><span class="keyword">sizeof</span><span class="special">(</span><span class="identifier">t</span><span class="special">),</span> <span class="keyword">alignof</span><span class="special">(</span><span class="identifier">T</span><span class="special">)></span> <span class="identifier">_storage</span><span class="special">;</span>
+<span class="special">};</span>
+</pre>
+<p>
+ Lifetime of the <code class="computeroutput"><span class="identifier">T</span></code> inside
+ <code class="computeroutput"><span class="identifier">_storage</span></code> is manually controlled
+ with placement-<code class="computeroutput"><span class="keyword">new</span></code>s and pseudo-destructor
+ calls. However, for scalar <code class="computeroutput"><span class="identifier">T</span></code>s
+ we use a different way of storage, by simply holding a <code class="computeroutput"><span class="identifier">T</span></code>:
+ </p>
+<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span>
+<span class="keyword">class</span> <span class="identifier">optional</span>
+<span class="special">{</span>
+ <span class="keyword">bool</span> <span class="identifier">_initialized</span><span class="special">;</span>
+ <span class="identifier">T</span> <span class="identifier">_storage</span><span class="special">;</span>
+<span class="special">};</span>
+</pre>
+<p>
+ We call it a <span class="emphasis"><em>direct</em></span> storage. This makes <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> a
+ trivially-copyable type for scalar <code class="computeroutput"><span class="identifier">T</span></code>s.
+ This only works for compilers that support defaulted functions (including
+ defaulted move assignment and constructor). On compilers without defaulted
+ functions we still use the direct storage, but <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ is no longer recognized as trivially-copyable. Apart from scalar types, we
+ leave the programmer a way of customizing her type, so that it is reconized
+ by <code class="computeroutput"><span class="identifier">optional</span></code> as candidate
+ for optimized storage, by specializing type trait <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">opitonal_config</span><span class="special">::</span><span class="identifier">optional_uses_direct_storage_for</span></code>:
+ </p>
+<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">X</span> <span class="comment">// not trivial</span>
+<span class="special">{</span>
+ <span class="identifier">X</span><span class="special">()</span> <span class="special">{}</span>
+<span class="special">};</span>
+
+<span class="keyword">namespace</span> <span class="identifier">boost</span> <span class="special">{</span> <span class="keyword">namespace</span> <span class="identifier">optional_config</span> <span class="special">{</span>
+
+ <span class="keyword">template</span> <span class="special"><></span> <span class="keyword">struct</span> <span class="identifier">optional_uses_direct_storage_for</span><span class="special"><</span><span class="identifier">X</span><span class="special">></span> <span class="special">:</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">true_type</span> <span class="special">{};</span>
+
+<span class="special">}}</span>
+</pre>
+<h5>
+<a name="boost_optional.tutorial.performance_considerations.h0"></a>
+ <span class="phrase"><a name="boost_optional.tutorial.performance_considerations.controlling_the_size"></a></span><a class="link" href="performance_considerations.html#boost_optional.tutorial.performance_considerations.controlling_the_size">Controlling
+ the size</a>
+ </h5>
+<p>
+ For the purpose of the following analysis, considering memory layouts, we
+ can think of it as:
+ </p>
+<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span>
+<span class="keyword">class</span> <span class="identifier">optional</span>
+<span class="special">{</span>
+ <span class="keyword">bool</span> <span class="identifier">_initialized</span><span class="special">;</span>
+ <span class="identifier">T</span> <span class="identifier">_storage</span><span class="special">;</span>
+<span class="special">};</span>
+</pre>
+<p>
+ Given type <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span></code>, and
+ assuming that <code class="computeroutput"><span class="keyword">sizeof</span><span class="special">(</span><span class="keyword">int</span><span class="special">)</span> <span class="special">==</span>
+ <span class="number">4</span></code>, we will get <code class="computeroutput"><span class="keyword">sizeof</span><span class="special">(</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">>)</span>
+ <span class="special">==</span> <span class="number">8</span></code>.
+ This is so because of the alignment rules, for our two members we get the
+ following alignment:
+ </p>
+<p>
+ <span class="inlinemediaobject"><img src="../../images/opt_align1.png" alt="opt_align1"></span>
+ </p>
+<p>
+ This means you can fit twice as many <code class="computeroutput"><span class="keyword">int</span></code>s
+ as <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span></code>s into
+ the same space of memory. Therefore, if the size of the objects is critical
+ for your application (e.g., because you want to utilize your CPU cache in
+ order to gain performance) and you have determined you are willing to trade
+ the code clarity, it is recommended that you simply go with type <code class="computeroutput"><span class="keyword">int</span></code> and use some 'magic value' to represent
+ <span class="emphasis"><em>not-an-int</em></span>, or use something like <a href="https://github.com/akrzemi1/markable" target="_top"><code class="computeroutput"><span class="identifier">markable</span></code></a> library.
+ </p>
+<p>
+ Even if you cannot spare any value of <code class="computeroutput"><span class="keyword">int</span></code>
+ to represent <span class="emphasis"><em>not-an-int</em></span> (e.g., because every value is
+ useful, or you do want to signal <span class="emphasis"><em>not-an-int</em></span> explicitly),
+ at least for <code class="computeroutput"><span class="identifier">Trivial</span></code> types
+ you should consider storing the value and the <code class="computeroutput"><span class="keyword">bool</span></code>
+ flag representing the <span class="emphasis"><em>null-state</em></span> separately. Consider
+ the following class:
+ </p>
+<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">Record</span>
+<span class="special">{</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">_min</span><span class="special">;</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">_max</span><span class="special">;</span>
+<span class="special">};</span>
+</pre>
+<p>
+ Its memory layout can be depicted as follows:
+ </p>
+<p>
+ <span class="inlinemediaobject"><img src="../../images/opt_align2.png" alt="opt_align2"></span>
+ </p>
+<p>
+ This is exactly the same as if we had the following members:
+ </p>
+<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">Record</span>
+<span class="special">{</span>
+ <span class="keyword">bool</span> <span class="identifier">_has_min</span><span class="special">;</span>
+ <span class="keyword">int</span> <span class="identifier">_min</span><span class="special">;</span>
+ <span class="keyword">bool</span> <span class="identifier">_has_max</span><span class="special">;</span>
+ <span class="keyword">int</span> <span class="identifier">_max</span><span class="special">;</span>
+<span class="special">};</span>
+</pre>
+<p>
+ But when they are stored separately, we at least have an option to reorder
+ them like this:
+ </p>
+<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">Record</span>
+<span class="special">{</span>
+ <span class="keyword">bool</span> <span class="identifier">_has_min</span><span class="special">;</span>
+ <span class="keyword">bool</span> <span class="identifier">_has_max</span><span class="special">;</span>
+ <span class="keyword">int</span> <span class="identifier">_min</span><span class="special">;</span>
+ <span class="keyword">int</span> <span class="identifier">_max</span><span class="special">;</span>
+<span class="special">};</span>
+</pre>
+<p>
+ Which gives us the following layout (and smaller total size):
+ </p>
+<p>
+ <span class="inlinemediaobject"><img src="../../images/opt_align3.png" alt="opt_align3"></span>
+ </p>
+<p>
+ Sometimes it requires detailed consideration what data we make optional.
+ In our case above, if we determine that both minimum and maximum value can
+ be provided or not provided together, but one is never provided without the
+ other, we can make only one optional memebr:
+ </p>
+<pre class="programlisting"><span class="keyword">struct</span> <span class="identifier">Limits</span>
+<span class="special">{</span>
+ <span class="keyword">int</span> <span class="identifier">_min</span><span class="special">;</span>
+ <span class="keyword">int</span> <span class="identifier">_max</span><span class="special">;</span>
+<span class="special">};</span>
+
+<span class="keyword">struct</span> <span class="identifier">Record</span>
+<span class="special">{</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">Limits</span><span class="special">></span> <span class="identifier">_limits</span><span class="special">;</span>
+<span class="special">};</span>
+</pre>
+<p>
+ This would give us the following layout:
+ </p>
+<p>
+ <span class="inlinemediaobject"><img src="../../images/opt_align4.png" alt="opt_align4"></span>
+ </p>
+<h5>
+<a name="boost_optional.tutorial.performance_considerations.h1"></a>
+ <span class="phrase"><a name="boost_optional.tutorial.performance_considerations.optional_function_parameters"></a></span><a class="link" href="performance_considerations.html#boost_optional.tutorial.performance_considerations.optional_function_parameters">Optional
+ function parameters</a>
+ </h5>
+<p>
+ Having function parameters of type <code class="computeroutput"><span class="keyword">const</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span></code>
+ may incur certain unexpected run-time cost connected to copy construction
+ of <code class="computeroutput"><span class="identifier">T</span></code>. Consider the following
+ code.
+ </p>
+<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">fun</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">Big</span><span class="special">>&</span> <span class="identifier">v</span><span class="special">)</span>
+<span class="special">{</span>
+ <span class="keyword">if</span> <span class="special">(</span><span class="identifier">v</span><span class="special">)</span> <span class="identifier">doSomethingWith</span><span class="special">(*</span><span class="identifier">v</span><span class="special">);</span>
+ <span class="keyword">else</span> <span class="identifier">doSomethingElse</span><span class="special">();</span>
+<span class="special">}</span>
+
+<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">Big</span><span class="special">></span> <span class="identifier">ov</span><span class="special">;</span>
+ <span class="identifier">Big</span> <span class="identifier">v</span><span class="special">;</span>
+ <span class="identifier">fun</span><span class="special">(</span><span class="identifier">none</span><span class="special">);</span>
+ <span class="identifier">fun</span><span class="special">(</span><span class="identifier">ov</span><span class="special">);</span> <span class="comment">// no copy</span>
+ <span class="identifier">fun</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> <span class="comment">// copy constructor of Big</span>
+<span class="special">}</span>
+</pre>
+<p>
+ No copy elision or move semantics can save us from copying type <code class="computeroutput"><span class="identifier">Big</span></code> here. Not that we need any copy, but
+ this is how <code class="computeroutput"><span class="identifier">optional</span></code> works.
+ In order to avoid copying in this case, one could provide second overload
+ of <code class="computeroutput"><span class="identifier">fun</span></code>:
+ </p>
+<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">fun</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">Big</span><span class="special">&</span> <span class="identifier">v</span><span class="special">)</span>
+<span class="special">{</span>
+ <span class="identifier">doSomethingWith</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span>
+<span class="special">}</span>
+
+<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">Big</span><span class="special">></span> <span class="identifier">ov</span><span class="special">;</span>
+ <span class="identifier">Big</span> <span class="identifier">v</span><span class="special">;</span>
+ <span class="identifier">fun</span><span class="special">(</span><span class="identifier">ov</span><span class="special">);</span> <span class="comment">// no copy</span>
+ <span class="identifier">fun</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> <span class="comment">// no copy: second overload selected</span>
+<span class="special">}</span>
+</pre>
+<p>
+ Alternatively, you could consider using an optional reference instead:
+ </p>
+<pre class="programlisting"><span class="keyword">void</span> <span class="identifier">fun</span><span class="special">(</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">const</span> <span class="identifier">Big</span><span class="special">&></span> <span class="identifier">v</span><span class="special">)</span> <span class="comment">// note where the reference is</span>
+<span class="special">{</span>
+ <span class="keyword">if</span> <span class="special">(</span><span class="identifier">v</span><span class="special">)</span> <span class="identifier">doSomethingWith</span><span class="special">(*</span><span class="identifier">v</span><span class="special">);</span>
+ <span class="keyword">else</span> <span class="identifier">doSomethingElse</span><span class="special">();</span>
+<span class="special">}</span>
+
+<span class="keyword">int</span> <span class="identifier">main</span><span class="special">()</span>
+<span class="special">{</span>
+ <span class="identifier">optional</span><span class="special"><</span><span class="identifier">Big</span><span class="special">></span> <span class="identifier">ov</span><span class="special">;</span>
+ <span class="identifier">Big</span> <span class="identifier">v</span><span class="special">;</span>
+ <span class="identifier">fun</span><span class="special">(</span><span class="identifier">none</span><span class="special">);</span>
+ <span class="identifier">fun</span><span class="special">(</span><span class="identifier">ov</span><span class="special">);</span> <span class="comment">// doesn't compile</span>
+ <span class="identifier">fun</span><span class="special">(</span><span class="identifier">v</span><span class="special">);</span> <span class="comment">// no copy</span>
+<span class="special">}</span>
+</pre>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="type_requirements.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="../../optional/reference.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
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+</html>
diff --git a/doc/html/boost_optional/tutorial/rebinding_semantics_for_assignment_of_optional_references.html b/doc/html/boost_optional/tutorial/rebinding_semantics_for_assignment_of_optional_references.html
new file mode 100644
index 0000000..ee693ee
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@@ -0,0 +1,149 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Rebinding semantics for assignment of optional references</title>
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+<hr>
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+<a accesskey="p" href="optional_references.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="in_place_factories.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.tutorial.rebinding_semantics_for_assignment_of_optional_references"></a><a class="link" href="rebinding_semantics_for_assignment_of_optional_references.html" title="Rebinding semantics for assignment of optional references">Rebinding
+ semantics for assignment of optional references</a>
+</h3></div></div></div>
+<p>
+ If you assign to an <span class="emphasis"><em>uninitialized </em></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code>
+ the effect is to bind (for the first time) to the object. Clearly, there
+ is no other choice.
+ </p>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">x</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">rx</span> <span class="special">=</span> <span class="identifier">x</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">ora</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">orb</span><span class="special">(</span><span class="identifier">x</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">ora</span> <span class="special">=</span> <span class="identifier">orb</span> <span class="special">;</span> <span class="comment">// now 'ora' is bound to 'x' through 'rx'</span>
+<span class="special">*</span><span class="identifier">ora</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span> <span class="comment">// Changes value of 'x' through 'ora'</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">x</span><span class="special">==</span><span class="number">2</span><span class="special">);</span>
+</pre>
+<p>
+ If you assign to a bare C++ reference, the assignment is forwarded to the
+ referenced object; its value changes but the reference is never rebound.
+ </p>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
+<span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">rb</span> <span class="special">;</span> <span class="comment">// Changes the value of 'a' to 'b'</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">a</span><span class="special">==</span><span class="identifier">b</span><span class="special">);</span>
+<span class="identifier">b</span> <span class="special">=</span> <span class="number">3</span> <span class="special">;</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">ra</span><span class="special">!=</span><span class="identifier">b</span><span class="special">);</span> <span class="comment">// 'ra' is not rebound to 'b'</span>
+</pre>
+<p>
+ Now, if you assign to an <span class="emphasis"><em>initialized </em></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code>,
+ the effect is to <span class="bold"><strong>rebind</strong></span> to the new object
+ instead of assigning the referee. This is unlike bare C++ references.
+ </p>
+<pre class="programlisting"><span class="keyword">int</span> <span class="identifier">a</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span> <span class="identifier">b</span> <span class="special">=</span> <span class="number">2</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">ra</span> <span class="special">=</span> <span class="identifier">a</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">rb</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">ora</span><span class="special">(</span><span class="identifier">ra</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">orb</span><span class="special">(</span><span class="identifier">rb</span><span class="special">)</span> <span class="special">;</span>
+<span class="identifier">ora</span> <span class="special">=</span> <span class="identifier">orb</span> <span class="special">;</span> <span class="comment">// 'ora' is rebound to 'b'</span>
+<span class="special">*</span><span class="identifier">ora</span> <span class="special">=</span> <span class="number">3</span> <span class="special">;</span> <span class="comment">// Changes value of 'b' (not 'a')</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">a</span><span class="special">==</span><span class="number">1</span><span class="special">);</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">b</span><span class="special">==</span><span class="number">3</span><span class="special">);</span>
+</pre>
+<h5>
+<a name="boost_optional.tutorial.rebinding_semantics_for_assignment_of_optional_references.h0"></a>
+ <span class="phrase"><a name="boost_optional.tutorial.rebinding_semantics_for_assignment_of_optional_references.rationale"></a></span><a class="link" href="rebinding_semantics_for_assignment_of_optional_references.html#boost_optional.tutorial.rebinding_semantics_for_assignment_of_optional_references.rationale">Rationale</a>
+ </h5>
+<p>
+ Rebinding semantics for the assignment of <span class="emphasis"><em>initialized </em></span>
+ <code class="computeroutput"><span class="identifier">optional</span></code> references has been
+ chosen to provide <span class="bold"><strong>consistency among initialization
+ states</strong></span> even at the expense of lack of consistency with the semantics
+ of bare C++ references. It is true that <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">U</span><span class="special">></span></code>
+ strives to behave as much as possible as <code class="computeroutput"><span class="identifier">U</span></code>
+ does whenever it is initialized; but in the case when <code class="computeroutput"><span class="identifier">U</span></code>
+ is <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span></code>,
+ doing so would result in inconsistent behavior w.r.t to the lvalue initialization
+ state.
+ </p>
+<p>
+ Imagine <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code>
+ forwarding assignment to the referenced object (thus changing the referenced
+ object value but not rebinding), and consider the following code:
+ </p>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">a</span> <span class="special">=</span> <span class="identifier">get</span><span class="special">();</span>
+<span class="keyword">int</span> <span class="identifier">x</span> <span class="special">=</span> <span class="number">1</span> <span class="special">;</span>
+<span class="keyword">int</span><span class="special">&</span> <span class="identifier">rx</span> <span class="special">=</span> <span class="identifier">x</span> <span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">&></span> <span class="identifier">b</span><span class="special">(</span><span class="identifier">rx</span><span class="special">);</span>
+<span class="identifier">a</span> <span class="special">=</span> <span class="identifier">b</span> <span class="special">;</span>
+</pre>
+<p>
+ What does the assignment do?
+ </p>
+<p>
+ If <code class="computeroutput"><span class="identifier">a</span></code> is <span class="emphasis"><em>uninitialized</em></span>,
+ the answer is clear: it binds to <code class="computeroutput"><span class="identifier">x</span></code>
+ (we now have another reference to <code class="computeroutput"><span class="identifier">x</span></code>).
+ But what if <code class="computeroutput"><span class="identifier">a</span></code> is already
+ <span class="emphasis"><em>initialized</em></span>? it would change the value of the referenced
+ object (whatever that is); which is inconsistent with the other possible
+ case.
+ </p>
+<p>
+ If <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code>
+ would assign just like <code class="computeroutput"><span class="identifier">T</span><span class="special">&</span></code> does, you would never be able to use
+ Optional's assignment without explicitly handling the previous initialization
+ state unless your code is capable of functioning whether after the assignment,
+ <code class="computeroutput"><span class="identifier">a</span></code> aliases the same object
+ as <code class="computeroutput"><span class="identifier">b</span></code> or not.
+ </p>
+<p>
+ That is, you would have to discriminate in order to be consistent.
+ </p>
+<p>
+ If in your code rebinding to another object is not an option, then it is
+ very likely that binding for the first time isn't either. In such case, assignment
+ to an <span class="emphasis"><em>uninitialized </em></span> <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">&></span></code>
+ shall be prohibited. It is quite possible that in such a scenario it is a
+ precondition that the lvalue must be already initialized. If it isn't, then
+ binding for the first time is OK while rebinding is not which is IMO very
+ unlikely. In such a scenario, you can assign the value itself directly, as
+ in:
+ </p>
+<pre class="programlisting"><span class="identifier">assert</span><span class="special">(!!</span><span class="identifier">opt</span><span class="special">);</span>
+<span class="special">*</span><span class="identifier">opt</span><span class="special">=</span><span class="identifier">value</span><span class="special">;</span>
+</pre>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2016 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="optional_references.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="in_place_factories.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/tutorial/relational_operators.html b/doc/html/boost_optional/tutorial/relational_operators.html
new file mode 100644
index 0000000..376bdcc
--- /dev/null
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@@ -0,0 +1,113 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Relational operators</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
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+<link rel="home" href="../../index.html" title="Boost.Optional">
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+<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="when_to_use_optional.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="io_operators.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.tutorial.relational_operators"></a><a class="link" href="relational_operators.html" title="Relational operators">Relational
+ operators</a>
+</h3></div></div></div>
+<p>
+ Type <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> is
+ <a href="http://www.sgi.com/tech/stl/EqualityComparable.html" target="_top"><code class="computeroutput"><span class="identifier">EqualityComparable</span></code></a> whenever <code class="computeroutput"><span class="identifier">T</span></code> is <a href="http://www.sgi.com/tech/stl/EqualityComparable.html" target="_top"><code class="computeroutput"><span class="identifier">EqualityComparable</span></code></a>. Two optional
+ objects containing a value compare in the same way as their contained values.
+ The uninitialized state of <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ is treated as a distinct value, equal to itself, and unequal to any value
+ of type <code class="computeroutput"><span class="identifier">T</span></code>:
+ </p>
+<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">oN</span> <span class="special">=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span><span class="special">;</span>
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">o0</span> <span class="special">=</span> <span class="number">0</span><span class="special">;</span>
+<span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">o1</span> <span class="special">=</span> <span class="number">1</span><span class="special">;</span>
+
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">oN</span> <span class="special">!=</span> <span class="identifier">o0</span><span class="special">);</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">o1</span> <span class="special">!=</span> <span class="identifier">oN</span><span class="special">);</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">o0</span> <span class="special">!=</span> <span class="identifier">o1</span><span class="special">);</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">oN</span> <span class="special">==</span> <span class="identifier">oN</span><span class="special">);</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">o0</span> <span class="special">==</span> <span class="identifier">o0</span><span class="special">);</span>
+</pre>
+<p>
+ The converting constructor from <code class="computeroutput"><span class="identifier">T</span></code>
+ as well as from <code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code> implies the existence and semantics
+ of the mixed comparison between <code class="computeroutput"><span class="identifier">T</span></code>
+ and <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> as
+ well as between <code class="computeroutput"><span class="identifier">none_t</span></code> and
+ <code class="computeroutput"><span class="identifier">optionl</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>:
+ </p>
+<pre class="programlisting"><span class="identifier">assert</span><span class="special">(</span><span class="identifier">oN</span> <span class="special">!=</span> <span class="number">0</span><span class="special">);</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">o1</span> <span class="special">!=</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span><span class="special">);</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">o0</span> <span class="special">!=</span> <span class="number">1</span><span class="special">);</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">oN</span> <span class="special">==</span> <span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span><span class="special">);</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">o0</span> <span class="special">==</span> <span class="number">0</span><span class="special">);</span>
+</pre>
+<p>
+ This mixed comparison has a practical interpretation, which is occasionally
+ useful:
+ </p>
+<pre class="programlisting"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">choice</span> <span class="special">=</span> <span class="identifier">ask_user</span><span class="special">();</span>
+<span class="keyword">if</span> <span class="special">(</span><span class="identifier">choice</span> <span class="special">==</span> <span class="number">2</span><span class="special">)</span>
+ <span class="identifier">start_procedure_2</span><span class="special">();</span>
+</pre>
+<p>
+ In the above example, the meaning of the comparison is 'user chose number
+ 2'. If user chose nothing, he didn't choose number 2.
+ </p>
+<p>
+ In case where <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> is
+ compared to <code class="computeroutput"><span class="identifier">none</span></code>, it is not
+ required that <code class="computeroutput"><span class="identifier">T</span></code> be <a href="http://www.sgi.com/tech/stl/EqualityComparable.html" target="_top"><code class="computeroutput"><span class="identifier">EqualityComparable</span></code></a>.
+ </p>
+<p>
+ In a similar manner, type <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ is <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a> whenever <code class="computeroutput"><span class="identifier">T</span></code> is <a href="http://www.sgi.com/tech/stl/LessThanComparable.html" target="_top"><code class="computeroutput"><span class="identifier">LessThanComparable</span></code></a>. The optional
+ object containing no value is compared less than any value of <code class="computeroutput"><span class="identifier">T</span></code>. To illustrate this, if the default ordering
+ of <code class="computeroutput"><span class="identifier">size_t</span></code> is {<code class="computeroutput"><span class="number">0</span></code>, <code class="computeroutput"><span class="number">1</span></code>,
+ <code class="computeroutput"><span class="number">2</span></code>, ...}, the default ordering
+ of <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">size_t</span><span class="special">></span></code>
+ is {<code class="computeroutput"><span class="identifier">boost</span><span class="special">::</span><span class="identifier">none</span></code>, <code class="computeroutput"><span class="number">0</span></code>,
+ <code class="computeroutput"><span class="number">1</span></code>, <code class="computeroutput"><span class="number">2</span></code>,
+ ...}. This order does not have a practical interpretation. The goal is to
+ have any semantically correct default ordering in order for <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> to
+ be usable in ordered associative containers (wherever <code class="computeroutput"><span class="identifier">T</span></code>
+ is usable).
+ </p>
+<p>
+ Mixed relational operators are the only case where the contained value of
+ an optional object can be inspected without the usage of value accessing
+ function (<code class="computeroutput"><span class="keyword">operator</span><span class="special">*</span></code>,
+ <code class="computeroutput"><span class="identifier">value</span></code>, <code class="computeroutput"><span class="identifier">value_or</span></code>).
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="when_to_use_optional.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="io_operators.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/tutorial/type_requirements.html b/doc/html/boost_optional/tutorial/type_requirements.html
new file mode 100644
index 0000000..d213a4f
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+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Type requirements</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
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+<link rel="home" href="../../index.html" title="Boost.Optional">
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+<td align="center"><a href="../../../../../../more/index.htm">More</a></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="exception_safety_guarantees.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="performance_considerations.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.tutorial.type_requirements"></a><a class="link" href="type_requirements.html" title="Type requirements">Type requirements</a>
+</h3></div></div></div>
+<p>
+ The very minimum requirement of <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ is that <code class="computeroutput"><span class="identifier">T</span></code> is a complete type
+ and that it has a publicly accessible destructor. <code class="computeroutput"><span class="identifier">T</span></code>
+ doesn't even need to be constructible. You can use a very minimum interface:
+ </p>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o</span><span class="special">;</span> <span class="comment">// uninitialized</span>
+<span class="identifier">assert</span><span class="special">(</span><span class="identifier">o</span> <span class="special">==</span> <span class="identifier">none</span><span class="special">);</span> <span class="comment">// check if initialized</span>
+<span class="identifier">assert</span><span class="special">(!</span><span class="identifier">o</span><span class="special">);</span> <span class="comment">//</span>
+<span class="identifier">o</span><span class="special">.</span><span class="identifier">value</span><span class="special">();</span> <span class="comment">// always throws</span>
+</pre>
+<p>
+ But this is practically useless. In order for <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ to be able to do anything useful and offer all the spectrum of ways of accessing
+ the contained value, <code class="computeroutput"><span class="identifier">T</span></code> needs
+ to have at least one accessible constructor. In that case you need to initialize
+ the optional object with function <code class="computeroutput"><span class="identifier">emplace</span><span class="special">()</span></code>, or if your compiler does not support it,
+ resort to <a class="link" href="in_place_factories.html" title="In-Place Factories">In-Place
+ Factories</a>:
+ </p>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o</span><span class="special">;</span>
+<span class="identifier">o</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">(</span><span class="string">"T"</span><span class="special">,</span> <span class="string">"ctor"</span><span class="special">,</span> <span class="string">"params"</span><span class="special">);</span>
+</pre>
+<p>
+ If <code class="computeroutput"><span class="identifier">T</span></code> is <code class="computeroutput"><span class="identifier">MoveConstructible</span></code>,
+ <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> is
+ also <code class="computeroutput"><span class="identifier">MoveConstructible</span></code> and
+ can be easily initialized from an rvalue of type <code class="computeroutput"><span class="identifier">T</span></code>
+ and be passed by value:
+ </p>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o</span> <span class="special">=</span> <span class="identifier">make_T</span><span class="special">();</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">p</span> <span class="special">=</span> <span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">>();</span>
+</pre>
+<p>
+ If <code class="computeroutput"><span class="identifier">T</span></code> is <a href="../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a>, <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> is
+ also <a href="../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a>
+ and can be easily initialized from an lvalue of type <code class="computeroutput"><span class="identifier">T</span></code>:
+ </p>
+<pre class="programlisting"><span class="identifier">T</span> <span class="identifier">v</span> <span class="special">=</span> <span class="identifier">make_T</span><span class="special">();</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">o</span> <span class="special">=</span> <span class="identifier">v</span><span class="special">;</span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span> <span class="identifier">p</span> <span class="special">=</span> <span class="identifier">o</span><span class="special">;</span>
+</pre>
+<p>
+ If <code class="computeroutput"><span class="identifier">T</span></code> is not <code class="computeroutput"><span class="identifier">MoveAssignable</span></code>, it is still possible to
+ reset the value of <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ using function <code class="computeroutput"><span class="identifier">emplace</span><span class="special">()</span></code>:
+ </p>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">const</span> <span class="identifier">T</span><span class="special">></span> <span class="identifier">o</span> <span class="special">=</span> <span class="identifier">make_T</span><span class="special">();</span>
+<span class="identifier">o</span><span class="special">.</span><span class="identifier">emplace</span><span class="special">(</span><span class="identifier">make_another_T</span><span class="special">());</span>
+</pre>
+<p>
+ If <code class="computeroutput"><span class="identifier">T</span></code> is <code class="computeroutput"><span class="identifier">Moveable</span></code>
+ (both <code class="computeroutput"><span class="identifier">MoveConstructible</span></code> and
+ <code class="computeroutput"><span class="identifier">MoveAssignable</span></code>) then <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> is
+ also <code class="computeroutput"><span class="identifier">Moveable</span></code> and additionally
+ can be constructed and assigned from an rvalue of type <code class="computeroutput"><span class="identifier">T</span></code>.
+ </p>
+<p>
+ Similarly, if <code class="computeroutput"><span class="identifier">T</span></code> is <code class="computeroutput"><span class="identifier">Copyable</span></code> (both <a href="../../../../../utility/CopyConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">CopyConstructible</span></code></a> and <code class="computeroutput"><span class="identifier">CopyAssignable</span></code>) then <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ is also <code class="computeroutput"><span class="identifier">Copyable</span></code> and additionally
+ can be constructed and assigned from an lvalue of type <code class="computeroutput"><span class="identifier">T</span></code>.
+ </p>
+<p>
+ <code class="computeroutput"><span class="identifier">T</span></code> <span class="emphasis"><em>is not</em></span>
+ required to be <a href="http://www.sgi.com/tech/stl/DefaultConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">DefaultConstructible</span></code></a>.
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="exception_safety_guarantees.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="performance_considerations.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/tutorial/when_to_use_optional.html b/doc/html/boost_optional/tutorial/when_to_use_optional.html
new file mode 100644
index 0000000..3caec24
--- /dev/null
+++ b/doc/html/boost_optional/tutorial/when_to_use_optional.html
@@ -0,0 +1,142 @@
+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>When to use Optional</title>
+<link rel="stylesheet" href="../../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets Vsnapshot">
+<link rel="home" href="../../index.html" title="Boost.Optional">
+<link rel="up" href="../../optional/tutorial.html" title="Tutorial">
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+</tr></table>
+<hr>
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+<a accesskey="p" href="design_overview/the_interface.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="relational_operators.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h3 class="title">
+<a name="boost_optional.tutorial.when_to_use_optional"></a><a class="link" href="when_to_use_optional.html" title="When to use Optional">When to
+ use Optional</a>
+</h3></div></div></div>
+<p>
+ It is recommended to use <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ in situations where there is exactly one, clear (to all parties) reason for
+ having no value of type <code class="computeroutput"><span class="identifier">T</span></code>,
+ and where the lack of value is as natural as having any regular value of
+ <code class="computeroutput"><span class="identifier">T</span></code>. One example of such situation
+ is asking the user in some GUI form to optionally specify some limit on an
+ <code class="computeroutput"><span class="keyword">int</span></code> value, but the user is allowed
+ to say 'I want the number not to be constrained by the maximum'. For another
+ example, consider a config parameter specifying how many threads the application
+ should launch. Leaving this parameter unspecified means that the application
+ should decide itself. For yet another example, consider a function returning
+ the index of the smallest element in a <code class="computeroutput"><span class="identifier">vector</span></code>.
+ We need to be prepared for the situation, where the <code class="computeroutput"><span class="identifier">vector</span></code>
+ is empty. Therefore a natural signature for such function would be:
+ </p>
+<pre class="programlisting"><span class="keyword">template</span> <span class="special"><</span><span class="keyword">typename</span> <span class="identifier">T</span><span class="special">></span>
+<span class="identifier">optional</span><span class="special"><</span><span class="identifier">size_t</span><span class="special">></span> <span class="identifier">find_smallest_elem</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">std</span><span class="special">::</span><span class="identifier">vector</span><span class="special"><</span><span class="identifier">T</span><span class="special">>&</span> <span class="identifier">vec</span><span class="special">);</span>
+</pre>
+<p>
+ Here, having received an empty <code class="computeroutput"><span class="identifier">vec</span></code>
+ and having no <code class="computeroutput"><span class="identifier">size_t</span></code> to return
+ is not a <span class="emphasis"><em>failure</em></span> but a <span class="emphasis"><em>normal</em></span>,
+ albeit irregular, situation.
+ </p>
+<p>
+ Another typical situation is to indicate that we do not have a value yet,
+ but we expect to have it later. This notion can be used in implementing solutions
+ like lazy initialization or a two-phase initialization.
+ </p>
+<p>
+ <code class="computeroutput"><span class="identifier">optional</span></code> can be used to take
+ a non-<a href="http://www.sgi.com/tech/stl/DefaultConstructible.html" target="_top"><code class="computeroutput"><span class="identifier">DefaultConstructible</span></code></a> type <code class="computeroutput"><span class="identifier">T</span></code> and create a sibling type with a default
+ constructor. This is a way to add a <span class="emphasis"><em>null-state</em></span> to any
+ type that doesn't have it already.
+ </p>
+<p>
+ Sometimes type <code class="computeroutput"><span class="identifier">T</span></code> already
+ provides a built-in null-state, but it may still be useful to wrap it into
+ <code class="computeroutput"><span class="identifier">optional</span></code>. Consider <code class="computeroutput"><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span></code>.
+ When you read a piece of text from a GUI form or a DB table, it is hardly
+ ever that the empty string indicates anything else but a missing text. And
+ some data bases do not even distinguish between a null string entry and a
+ non-null string of length 0. Still, it may be practical to use <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">string</span><span class="special">></span></code>
+ to indicate in the returned type that we want to treat the empty string in
+ a special dedicated program path:
+ </p>
+<pre class="programlisting"><span class="keyword">if</span><span class="special">(</span><span class="identifier">boost</span><span class="special">::</span><span class="identifier">optional</span><span class="special"><</span><span class="identifier">std</span><span class="special">::</span><span class="identifier">string</span><span class="special">></span> <span class="identifier">name</span> <span class="special">=</span> <span class="identifier">ask_user_name</span><span class="special">())</span> <span class="special">{</span>
+ <span class="identifier">assert</span><span class="special">(*</span><span class="identifier">name</span> <span class="special">!=</span> <span class="string">""</span><span class="special">);</span>
+ <span class="identifier">logon_as</span><span class="special">(*</span><span class="identifier">name</span><span class="special">);</span>
+<span class="special">}</span>
+<span class="keyword">else</span> <span class="special">{</span>
+ <span class="identifier">skip_logon</span><span class="special">();</span>
+<span class="special">}</span>
+</pre>
+<p>
+ In the example above, the assertion indicates that if we choose to use this
+ technique, we must translate the empty string state to an optional object
+ with no contained value (inside function <code class="computeroutput"><span class="identifier">ask_user_name</span></code>).
+ </p>
+<h5>
+<a name="boost_optional.tutorial.when_to_use_optional.h0"></a>
+ <span class="phrase"><a name="boost_optional.tutorial.when_to_use_optional.not_recommended_usages"></a></span><a class="link" href="when_to_use_optional.html#boost_optional.tutorial.when_to_use_optional.not_recommended_usages">Not
+ recommended usages</a>
+ </h5>
+<p>
+ It is not recommended to use <code class="computeroutput"><span class="identifier">optional</span></code>
+ to indicate that we were not able to compute a value because of a <span class="emphasis"><em>failure</em></span>.
+ It is difficult to define what a failure is, but it usually has one common
+ characteristic: an associated information on the cause of the failure. This
+ can be the type and member data of an exception object, or an error code.
+ It is a bad design to signal a failure and not inform about the cause. If
+ you do not want to use exceptions, and do not like the fact that by returning
+ error codes you cannot return the computed value, you can use <a href="https://github.com/ptal/Boost.Expected" target="_top">Expected</a>
+ library. It is sort of <a href="../../../../../variant/index.html" target="_top">Boost.Variant</a>
+ that contains either a computed value or a reason why the computation failed.
+ </p>
+<p>
+ Sometimes the distinction into what is a failure and what is a valid but
+ irregular result is blurry and depends on a particular usage and personal
+ preference. Consider a function that converts a <code class="computeroutput"><span class="identifier">string</span></code>
+ to an <code class="computeroutput"><span class="keyword">int</span></code>. Is it a failure that
+ you cannot convert? It might in some cases, but in other you may call it
+ exactly for the purpose of figuring out if a given <code class="computeroutput"><span class="identifier">string</span></code>
+ is convertible, and you are not even interested in the resulting value. Sometimes
+ when a conversion fails you may not consider it a failure, but you need to
+ know why it cannot be converted; for instance at which character it is determined
+ that the conversion is impossible. In this case returning <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ will not suffice. Finally, there is a use case where an input string that
+ does not represent an <code class="computeroutput"><span class="keyword">int</span></code> is
+ not a failure condition, but during the conversion we use resources whose
+ acquisition may fail. In that case the natural representation is to both
+ return <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span></code> and
+ signal failure:
+ </p>
+<pre class="programlisting"><span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">></span> <span class="identifier">convert1</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">string</span><span class="special">&</span> <span class="identifier">str</span><span class="special">);</span> <span class="comment">// throws</span>
+<span class="identifier">expected</span><span class="special"><</span><span class="identifier">ErrorT</span><span class="special">,</span> <span class="identifier">optional</span><span class="special"><</span><span class="keyword">int</span><span class="special">>></span> <span class="identifier">convert2</span><span class="special">(</span><span class="keyword">const</span> <span class="identifier">string</span><span class="special">&</span> <span class="identifier">str</span><span class="special">);</span> <span class="comment">// return either optional or error</span>
+</pre>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014-2018 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
+<div class="spirit-nav">
+<a accesskey="p" href="design_overview/the_interface.html"><img src="../../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../../optional/tutorial.html"><img src="../../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../../index.html"><img src="../../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="relational_operators.html"><img src="../../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+</body>
+</html>
diff --git a/doc/html/boost_optional/type_requirements.html b/doc/html/boost_optional/type_requirements.html
new file mode 100644
index 0000000..e1ee777
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+<html>
+<head>
+<meta http-equiv="Content-Type" content="text/html; charset=US-ASCII">
+<title>Type requirements</title>
+<link rel="stylesheet" href="../../../../../doc/src/boostbook.css" type="text/css">
+<meta name="generator" content="DocBook XSL Stylesheets V1.78.1">
+<link rel="home" href="../index.html" title="Chapter 1. Boost.Optional">
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+<hr>
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+<a accesskey="p" href="exception_safety_guarantees.html"><img src="../../../../../doc/src/images/prev.png" alt="Prev"></a><a accesskey="u" href="../index.html"><img src="../../../../../doc/src/images/up.png" alt="Up"></a><a accesskey="h" href="../index.html"><img src="../../../../../doc/src/images/home.png" alt="Home"></a><a accesskey="n" href="dependencies_and_portability.html"><img src="../../../../../doc/src/images/next.png" alt="Next"></a>
+</div>
+<div class="section">
+<div class="titlepage"><div><div><h2 class="title" style="clear: both">
+<a name="boost_optional.type_requirements"></a><a class="link" href="type_requirements.html" title="Type requirements">Type requirements</a>
+</h2></div></div></div>
+<p>
+ At the very minimum for <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ to work with a minimum interface it is required that <code class="computeroutput"><span class="identifier">T</span></code>
+ has a publicly accessible no-throw destructor. In that case you need to initialize
+ the optional object with function <code class="computeroutput"><span class="identifier">emplace</span><span class="special">()</span></code> or use <span class="bold"><strong>InPlaceFactories</strong></span>.
+ Additionally, if <code class="computeroutput"><span class="identifier">T</span></code> is <code class="computeroutput"><span class="identifier">Moveable</span></code>, <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code>
+ is also <code class="computeroutput"><span class="identifier">Moveable</span></code> and can be
+ easily initialized from an rvalue of type <code class="computeroutput"><span class="identifier">T</span></code>
+ and be passed by value. Additionally, if <code class="computeroutput"><span class="identifier">T</span></code>
+ is <code class="computeroutput"><span class="identifier">Copyable</span></code>, <code class="computeroutput"><span class="identifier">optional</span><span class="special"><</span><span class="identifier">T</span><span class="special">></span></code> is
+ also <code class="computeroutput"><span class="identifier">Copyable</span></code> and can be easily
+ initialized from an lvalue of type <code class="computeroutput"><span class="identifier">T</span></code>.
+ </p>
+<p>
+ <code class="computeroutput"><span class="identifier">T</span></code> <span class="underline">is
+ not</span> required to be <a href="http://www.sgi.com/tech/stl/DefaultConstructible.html" target="_top">Default
+ Constructible</a>.
+ </p>
+</div>
+<table xmlns:rev="http://www.cs.rpi.edu/~gregod/boost/tools/doc/revision" width="100%"><tr>
+<td align="left"></td>
+<td align="right"><div class="copyright-footer">Copyright © 2003-2007 Fernando Luis Cacciola Carballal<br>Copyright © 2014 Andrzej Krzemieński<p>
+ Distributed under the Boost Software License, Version 1.0. (See accompanying
+ file LICENSE_1_0.txt or copy at <a href="http://www.boost.org/LICENSE_1_0.txt" target="_top">http://www.boost.org/LICENSE_1_0.txt</a>)
+ </p>
+</div></td>
+</tr></table>
+<hr>
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