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;
   1) If T is not a referenceable type (i.e., possibly cv-qualified void or a function
   type with a cv-qualifier-seq or a ref-qualifier), provides a member constant value
   equal to false. Otherwise, provides a member constant value equal to
   std::is_assignable<T&, const T&>::value.
   2) Same as (1), but uses std::is_trivially_assignable<T&, const T&>
   3) Same as (1), but uses std::is_nothrow_assignable<T&, const T&>
   T shall be a complete type, (possibly cv-qualified) void, or an array of unknown
   bound. Otherwise, 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.
   The behavior of a program that adds specializations for any of the templates
   described on this page is undefined.
  Helper variable templates
   template< class T >
   inline constexpr bool is_copy_assignable_v = (since C++17)
   is_copy_assignable<T>::value;
   template< class T >
   inline constexpr bool is_trivially_copy_assignable_v = (since C++17)
   is_trivially_copy_assignable<T>::value;
   template< class T >
   inline constexpr bool is_nothrow_copy_assignable_v = (since C++17)
   is_nothrow_copy_assignable<T>::value; Inherited from std::integral_constant

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 <utility>
 #include <type_traits>
 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 a 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)