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### is_assignable

    template <class T, class U>
    struct is_assignable : public true_type-or-false_type {};

Inherits: If `std::declval<T>() = std::declval<U>()` then inherits from true_type, otherwise from false_type. Type `T` must be a complete type.

Note that this trait is somewhat tricky to use correctly: for example:

    is_assignable<int, int>::value

is `false` since `std::declval<int>()` is an xvalue which can not be assigned to!

If you're intention is to check for copy-assignment from some type U then use:

    is_assignable<T&, const U&>::value

If you're intention is to check for move-assignment then use:

    is_assignable<T&, U&&>::value

or simply:

    is_assignable<T&, U>::value

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

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