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+[/
+ / Copyright (c) 2013 Andrey Semashev
+ /
+ / 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:explicit_operator_bool explicit_operator_bool]
+
+[/=================]
+[simplesect Authors]
+[/=================]
+
+* Andrey Semashev
+
+[endsimplesect]
+
+[/===============]
+[section Overview]
+[/===============]
+
+Header `<boost/core/explicit_operator_bool.hpp>` provides
+`BOOST_EXPLICIT_OPERATOR_BOOL()`, `BOOST_EXPLICIT_OPERATOR_BOOL_NOEXCEPT()`
+and `BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL()` compatibility helper macros
+that expand to an explicit conversion operator to `bool`. For compilers not
+supporting explicit conversion operators introduced in C++11 the macros expand
+to a conversion operator that implements the
+[@http://en.wikibooks.org/wiki/More_C%2B%2B_Idioms/Safe_bool safe bool idiom].
+In case if the compiler is not able to handle safe bool idiom well the macros
+expand to a regular conversion operator to `bool`.
+
+[endsect]
+
+[/===============]
+[section Examples]
+[/===============]
+
+Both macros are intended to be placed within a user's class definition. The
+generated conversion operators will be implemented in terms of `operator!()`
+that should be defined by user in this class. In case of
+`BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL()` the generated conversion operator
+will be declared `constexpr` which requires the corresponding `operator!()`
+to also be `constexpr`.
+
+``
+template< typename T >
+class my_ptr
+{
+ T* m_p;
+
+public:
+ BOOST_EXPLICIT_OPERATOR_BOOL()
+
+ bool operator!() const
+ {
+ return !m_p;
+ }
+};
+``
+
+Now `my_ptr` can be used in conditional expressions, similarly to a regular pointer:
+
+``
+my_ptr< int > p;
+if (p)
+ std::cout << "true" << std::endl;
+``
+
+[endsect]
+
+[/==============]
+[section History]
+[/==============]
+
+[heading boost 1.56]
+
+* Added new macros `BOOST_EXPLICIT_OPERATOR_BOOL_NOEXCEPT` and `BOOST_CONSTEXPR_EXPLICIT_OPERATOR_BOOL` to define `noexcept` and `constexpr` operators.
+* The header moved to Boost.Core.
+
+[heading boost 1.55]
+
+* The macro was extracted from Boost.Log.
+
+[endsect]
+
+[endsect]