std::is_move_assignable, std::is_trivially_move_assignable, std::is_nothrow_move_assignable

Since C++11

Header: <type_traits>

If T is not a complete type, (possibly cv-qualified) void, or an array of unknown bound, the behavior is undefined.

# Declarations

template< class T >
struct is_move_assignable;

(since C++11)

template< class T >
struct is_trivially_move_assignable;

(since C++11)

template< class T >
struct is_nothrow_move_assignable;

(since C++11)

# 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

#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 trivially move-assignable? "
              << std::is_trivially_move_assignable<Foo>::value << '\n'
              << "NoMove is move-assignable? "
              << std::is_move_assignable<NoMove>::value << '\n'
              << "NoMove is nothrow move-assignable? "
              << std::is_nothrow_move_assignable<NoMove>::value << '\n';
}

# Defect reports

DRApplied toBehavior as publishedCorrect behavior
LWG 2196C++11the behavior was unclear if T&& cannot be formedthe value produced is false in this case

# See also