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;

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, T&&>::value
(2) std::is_trivially_assignable<T, T&&>::value false
(3) std::is_nothrow_assignable<T, 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 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 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';
}

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 an 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)