doc/is_copy_assignable.qbk

[/ 
  Copyright 2007 John Maddock.
  Copyright 2014 Ion Gaztanaga.
  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:is_copy_assignable is_copy_assignable]

   template <class T>
   struct is_copy_assignable : public __tof {};
    
__inherit If `T` is `CopyAssignable` (i.e. has an accessible explicit or implicit copy assignment operator),
then inherits from __true_type, otherwise inherits from __false_type.  Type `T`
must be a complete type.

In other words, inherits from __true_type only if copy assignment of `T` from `const T &` is not 
marked with `= delete`, `T` does not derives from `boost::noncopyable` and 
is not marked with `BOOST_MOVABLE_BUT_NOT_COPYABLE(T)`.

__compat Requires the C++11 features `decltype` and SFINAE-expressions for full support.

If your compiler does not support C++11 deleted functions (`= delete`) or does not support  
SFINAE for the deleted assignments, then derive your classes from `boost::noncopyable` or 
mark them with `BOOST_MOVABLE_BUT_NOT_COPYABLE(T)` to show that class is non-assignable.

Trait does not care about access modifiers, so if you see errors like this:

      'T::operator=(const T&)' is private
      boost/type_traits/is_copy_assignable.hpp:68:5: error: within this context

then you are trying to call that macro for a structure with private assignment:

      struct T {
          // ...
      private:
          T &operator=(const T &);
          // ...
      };

To fix that you must modify your structure, explicitly marking it as noncopyable (`= delete`, 
`boost::noncopyable` or `BOOST_MOVABLE_BUT_NOT_COPYABLE(T)`) or explicitly 
[link boost_typetraits.user_defined specializing the trait].


__header ` #include <boost/type_traits/is_copy_assignable.hpp>` or ` #include <boost/type_traits.hpp>`

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