std::is_copy_assignable,std::is_trivially_copy_assignable,(3)

NAME
std::is_copy_assignable,std::is_trivially_copy_assignable, - std::is_copy_assignable,std::is_trivially_copy_assignable,

Synopsis
   Defined in header <type_traits>
   template< class T > (1) (since C++11)
   struct is_copy_assignable;
   template< class T > (2) (since C++11)
   struct is_trivially_copy_assignable;
   template< class T > (3) (since C++11)
   struct is_nothrow_copy_assignable;
                        The value of the member constant value
    Type trait T is a referenceable type T is not a
                        referenceable type
   (1) std::is_assignable<T, const T&>::value
   (2) std::is_trivially_assignable<T, const false
                T&>::value
   (3) std::is_nothrow_assignable<T, const T&>::value
   If T is not a complete type, (possibly cv-qualified) void, or an array of unknown
   bound, the behavior is undefined.
   If an instantiation of a template above depends, directly or indirectly, on an
   incomplete type, and that instantiation could yield a different result if that type
   were hypothetically completed, the behavior is undefined.
   If the program adds specializations for any of the templates described on this page,
   the behavior is undefined.

Member constants
   value true if T is copy-assignable, false otherwise
   [static] (public static member constant)

Member functions
   operator bool converts the object to bool, returns value
                 (public member function)
   operator() returns value
   (C++14) (public member function)

Member types
   Type Definition
   value_type bool
   type std::integral_constant<bool, value>

Possible implementation
 template<class T>
 struct is_copy_assignable
     : std::is_assignable<typename std::add_lvalue_reference<T>::type,
                        typename std::add_lvalue_reference<const T>::type> {};
 template<class T>
 struct is_trivially_copy_assignable
     : std::is_trivially_assignable<typename std::add_lvalue_reference<T>::type,
                        typename std::add_lvalue_reference<const T>::type> {};
 template<class T>
 struct is_nothrow_copy_assignable
     : std::is_nothrow_assignable<typename std::add_lvalue_reference<T>::type,
                        typename std::add_lvalue_reference<const T>::type> {};

Notes
   The trait std::is_copy_assignable is less strict than CopyAssignable because it does
   not check the type of the result of the assignment (which, for a CopyAssignable
   type, must be an lvalue of type T) and does not check the semantic requirement that
   the argument expression remains unchanged. It also does not check that T satisfies
   MoveAssignable, which is required of all CopyAssignable types.

Example
// Run this code
 #include <iostream>
 #include <type_traits>
 #include <utility>
 struct Foo { int n; };
 int main()
 {
     std::cout << std::boolalpha
               << "Foo is trivially copy-assignable? "
               << std::is_trivially_copy_assignable<Foo>::value << '\n'
               << "int[2] is copy-assignable? "
               << std::is_copy_assignable<int[2]>::value << '\n'
               << "int is nothrow copy-assignable? "
               << std::is_nothrow_copy_assignable<int>::value << '\n';
 }

Output:
 Foo is trivially copy-assignable? true
 int[2] is copy-assignable? false
 int is nothrow copy-assignable? true

See also
   is_assignable
   is_trivially_assignable checks if a type has an assignment operator for a
   is_nothrow_assignable specific argument
   (C++11) (class template)
   (C++11)
   (C++11)
   is_move_assignable
   is_trivially_move_assignable
   is_nothrow_move_assignable checks if a type has a move assignment operator
   (C++11) (class template)
   (C++11)
   (C++11)