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### is_copy_assignable

    template <class T>
    struct is_copy_assignable : public true_type-or-false_type {};

Inherits: 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)`.

Compiler Compatibility: If the compiler does not support partial-specialization of class templates, then this template can not be used.

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 specializing the trait.

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