| Defined in header <type_traits> | ||||
|---|---|---|---|---|
| (1) | (since C++11) | ||
| (2) | (since C++11) | ||
| (3) | (since C++11) |
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&&> 2) 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.
Helper variable templates
| (since C++17) | |||
| (since C++17) | |||
| (since C++17) |
Inherited from std::integral_constant
Member constants
| value [static] | true if T is move-assignable, false otherwise (public static member constant) |
Member functions
| operator bool | converts the object to bool, returns value (public member function) |
| operator() (C++14) | returns value (public member function) |
Member types
| Type | Definition |
|---|---|
value_type | bool |
type | std::integral_constant<bool, value> |
Possible implementation
|
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, in 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
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 | #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:
1 2 3 4 5 | std::string is nothrow move-assignable? trueint[2] is move-assignable? falseFoo is trivially move-assignable? trueNoMove is move-assignable? trueNoMove is nothrow move-assignable? false |
See also
| (C++11)(C++11)(C++11) | checks if a type has a assignment operator for a specific argument (class template) |
| (C++11)(C++11)(C++11) | checks if a type has a copy assignment operator (class template) |
| std::experimental::is_move_assignable_v
(library fundamentals TS) | variable template alias of std::is_move_assignable::value (variable template) |
| std::experimental::is_trivially_move_assignable_v
(library fundamentals TS) | variable template alias of std::is_trivially_move_assignable::value (variable template) |
| std::experimental::is_nothrow_move_assignable_v
(library fundamentals TS) | variable template alias of std::is_nothrow_move_assignable::value (variable template) |
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