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+[/
+ (C) Copyright 2009-2011 Frederic Bron.
+ 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:has_plus_assign has_plus_assign]
+ template <class Lhs, class Rhs=Lhs, class Ret=dont_care>
+ struct has_plus_assign : public __tof {};
+
+__inherit
+If (i) `lhs` of type `Lhs` and `rhs` of type `Rhs` can be used in expression `lhs+=rhs`,
+and (ii) `Ret=dont_care` or the result of expression `lhs+=rhs` is convertible to `Ret`
+then inherits from __true_type,
+otherwise inherits from __false_type.
+
+The default behaviour (`Ret=dont_care`) is to not check for the return value of binary `operator+=`.
+If `Ret` is different from the default `dont_care` type, the return value is checked to be convertible to `Ret`.
+Convertible to `Ret` means that the return value of the operator can be used as argument to a function expecting `Ret`:
+``
+void f(Ret);
+Lhs lhs;
+Rhs rhs;
+f(lhs+=rhs); // is valid if has_plus_assign<Lhs, Rhs, Ret>::value==true
+``
+If `Ret=void`, the return type is checked to be exactly `void`.
+
+__header `#include <boost/type_traits/has_plus_assign.hpp>` or `#include <boost/type_traits/has_operator.hpp>` or `#include <boost/type_traits.hpp>`
+
+[has_binary_operator_compat]
+
+__examples
+
+[:`has_plus_assign<Lhs, Rhs, Ret>::value_type` is the type `bool`.]
+[:`has_plus_assign<Lhs, Rhs, Ret>::value` is a `bool` integral constant expression.]
+[:`has_plus_assign<int>::value` is a `bool` integral constant expression that evaluates to `true`.]
+[:`has_plus_assign<long>` inherits from `__true_type`.]
+
+[:`has_plus_assign<int, int, int>` inherits from `__true_type`.]
+[:`has_plus_assign<int, int, long>` inherits from `__true_type`.]
+[:`has_plus_assign<int, double, double>` inherits from `__true_type`.]
+[:`has_plus_assign<int, double, int>` inherits from `__true_type`.]
+
+[:`has_plus_assign<const int, int>::value` inherits from `__false_type`.]
+[:`has_plus_assign<int, int, std::string>` inherits from `__false_type`.]
+
+
+[*See also:] [link boost_typetraits.category.value_traits.operators Operator Type Traits]
+
+[binary_operator_known_issues has_plus_assign..+=..A&..contains<T>&..const ]
+
+[endsect]
+