std::is_move_assignable,std::is_trivially_move_assignable,(3)

NAME
std::is_move_assignable,std::is_trivially_move_assignable, - std::is_move_assignable,std::is_trivially_move_assignable,

Synopsis
   Defined in header <type_traits>
   template< class T > (1) (since C++11)
   struct is_move_assignable;
   template< class T > (2) (since C++11)
   struct is_trivially_move_assignable;
   template< class T > (3) (since C++11)
   struct is_nothrow_move_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&, T&&>::value.
   2) Same as (1), but uses std::is_trivially_assignable<T&, T&&>
   3) Same as (1), but uses std::is_nothrow_assignable<T&, 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_move_assignable_v = (since C++17)
   is_move_assignable<T>::value;
   template< class T >
   inline constexpr bool is_trivially_move_assignable_v = (since C++17)
   is_trivially_move_assignable<T>::value;
   template< class T >
   inline constexpr bool is_nothrow_move_assignable_v = (since C++17)
   is_nothrow_move_assignable<T>::value; Inherited from std::integral_constant

Member constants
   value true if T is move-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_move_assignable
       : std::is_assignable< typename std::add_lvalue_reference<T>::type,
                        typename std::add_rvalue_reference<T>::type> {};
   template< class T>
   struct is_trivially_move_assignable
       : std::is_trivially_assignable< typename std::add_lvalue_reference<T>::type,
                        typename std::add_rvalue_reference<T>::type> {};
   template< class T>
   struct is_nothrow_move_assignable
       : std::is_nothrow_assignable< typename std::add_lvalue_reference<T>::type,
                        typename std::add_rvalue_reference<T>::type> {};

Notes
   The trait std::is_move_assignable is less strict than MoveAssignable because it does
   not check the type of the result of the assignment (which, for a MoveAssignable
   type, must be T&), nor the semantic requirement that the target's value after the
   assignment is equivalent to the source's value before the assignment.
   The type does not have to implement a move assignment operator in order to satisfy
   this trait; see MoveAssignable for details.

Example
// Run this code
 #include <iostream>
 #include <string>
 #include <type_traits>
 struct Foo { int n; };
 struct NoMove {
     // prevents implicit declaration of default move assignment operator
     // however, the class is still move-assignable because its
     // copy assignment operator can bind to an rvalue argument
     NoMove& operator=(const NoMove&) { return *this; }
 };
 int main() {
     std::cout << std::boolalpha
               << "std::string is nothrow move-assignable? "
               << std::is_nothrow_move_assignable<std::string>::value << '\n'
               << "int[2] is move-assignable? "
               << std::is_move_assignable<int[2]>::value << '\n'
               << "Foo is trivally move-assignable? "
               << std::is_trivially_move_assignable<Foo>::value << '\n';
     std::cout << std::boolalpha
               << "NoMove is move-assignable? "
               << std::is_move_assignable<NoMove>::value << '\n'
               << "NoMove is nothrow move-assignable? "
               << std::is_nothrow_move_assignable<NoMove>::value << '\n';
 }

Output:
 std::string is nothrow move-assignable? true
 int[2] is move-assignable? false
 Foo is trivially move-assignable? true
 NoMove is move-assignable? true
 NoMove is nothrow move-assignable? false

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_copy_assignable
   is_trivially_copy_assignable
   is_nothrow_copy_assignable checks if a type has a copy assignment operator
   (C++11) (class template)
   (C++11)
   (C++11)