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+[/
+ / Copyright (c) 2001, 2002 Peter Dimov and Multi Media Ltd.
+ / Copyright (c) 2003-2005 Peter Dimov
+ /
+ / 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:purpose Purpose]
+
+`boost::mem_fn` is a generalization of the standard functions `std::mem_fun`
+and `std::mem_fun_ref`. It supports member function pointers with more than
+one argument, and the returned function object can take a pointer, a
+reference, or a smart pointer to an object instance as its first argument.
+`mem_fn` also supports pointers to data members by treating them as functions
+taking no arguments and returning a (const) reference to the member.
+
+The purpose of `mem_fn` is twofold. First, it allows users to invoke a member
+function on a container with the familiar
+
+ std::for_each(v.begin(), v.end(), boost::mem_fn(&Shape::draw));
+
+syntax, even when the container stores smart pointers.
+
+Second, it can be used as a building block by library developers that want to
+treat a pointer to member function as a function object. A library might
+define an enhanced `for_each` algorithm with an overload of the form:
+
+ template<class It, class R, class T> void for_each(It first, It last, R (T::*pmf) ())
+ {
+ std::for_each(first, last, boost::mem_fn(pmf));
+ }
+
+that will allow the convenient syntax:
+
+ for_each(v.begin(), v.end(), &Shape::draw);
+
+When documenting the feature, the library author will simply state:
+
+ template<class It, class R, class T> void for_each(It first, It last, R (T::*pmf) ());
+
+* /Effects:/ Equivalent to `std::for_each(first, last, boost::mem_fn(pmf))`.
+
+where `boost::mem_fn` can be a link to this page. See the
+[@boost:/libs/bind/bind.html documentation of `bind`] for an example.
+
+`mem_fn` takes one argument, a pointer to a member, and returns a function
+object suitable for use with standard or user-defined algorithms:
+
+ struct X
+ {
+ void f();
+ };
+
+ void g(std::vector<X> & v)
+ {
+ std::for_each(v.begin(), v.end(), boost::mem_fn(&X::f));
+ };
+
+ void h(std::vector<X *> const & v)
+ {
+ std::for_each(v.begin(), v.end(), boost::mem_fn(&X::f));
+ };
+
+ void k(std::vector<boost::shared_ptr<X> > const & v)
+ {
+ std::for_each(v.begin(), v.end(), boost::mem_fn(&X::f));
+ };
+
+The returned function object takes the same arguments as the input member
+function plus a "flexible" first argument that represents the object instance.
+
+When the function object is invoked with a first argument `x` that is neither
+a pointer nor a reference to the appropriate class (`X` in the example above),
+it uses `get_pointer(x)` to obtain a pointer from `x`. Library authors can
+"register" their smart pointer classes by supplying an appropriate
+`get_pointer` overload, allowing `mem_fn` to recognize and support them.
+
+
+/[Note:/ `get_pointer` is not restricted to return a pointer. Any object that
+can be used in a member function call expression `(x->*pmf)(...)` will work./]/
+
+/[Note:/ the library uses an unqualified call to `get_pointer`. Therefore, it
+will find, through argument-dependent lookup, `get_pointer` overloads that are
+defined in the same namespace as the corresponding smart pointer class, in
+addition to any `boost::get_pointer` overloads./]/
+
+All function objects returned by `mem_fn` expose a `result_type` typedef that
+represents the return type of the member function. For data members,
+`result_type` is defined as the type of the member.
+
+[endsect]