# std::is_swappable_with, std::is_swappable, std::is_nothrow_swappable_with, std::is_nothrow_swappable

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Defined in header `<type_traits>` |  |
template< class T, class U > struct is_swappable_with; | (1) | (since C++17)
template< class T > struct is_swappable; | (2) | (since C++17)
template< class T, class U > struct is_nothrow_swappable_with; | (3) | (since C++17)
template< class T > struct is_nothrow_swappable; | (4) | (since C++17)

1) If the expressions swap(std::declval<T>(), std::declval<U>()) and swap(std::declval<U>(), std::declval<T>()) are both well-formed in unevaluated context after using std::swap; (see Swappable), provides the member constant `value` equal true. Otherwise, `value` is false. Access checks are performed as if from a context unrelated to either type.
2) 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_swappable_with<T&, T&>::value
3) Same as (1), but evaluations of both expressions from (1) are known not to throw exceptions
4) Same as (2), but uses is_nothrow_swappable_with.

`T` and `U` shall each 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.

### Helper variable templates

template <class T, class U> inline constexpr bool is_swappable_with_v = is_swappable_with<T, U>::value; |  | (since C++17)
template <class T> inline constexpr bool is_swappable_v = is_swappable<T>::value; |  | (since C++17)
template <class T, class U> inline constexpr bool is_nothrow_swappable_with_v = is_nothrow_swappable_with<T, U>::value; |  | (since C++17)
template <class T> inline constexpr bool is_nothrow_swappable_v = is_nothrow_swappable<T>::value; |  | (since C++17)

## Inherited from std::integral_constant

### Member constants

value [static] | true if `T` is swappable with `U` , 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>

### Notes

This trait does not check anything outside the immediate context of the swap expressions: if the use of `T` or `U` would trigger template specializations, generation of implicitly-defined special member functions etc, and those have errors, the actual swap may not compile even if `std::is_swappable_with<T,U>::value` compiles and evaluates to `true`.

### Example

| This section is incomplete Reason: no example

### See also

swap | swaps the values of two objects (function template)
is_move_assignable is_trivially_move_assignable is_nothrow_move_assignable (C++11)(C++11)(C++11) | checks if a type has a move assignment operator (class template)

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