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std::is_swappable_with, std::is_swappable, std::is_nothrow_swappable_with, std::is_nothrow_swappable - cppreference.com

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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.

3) Same as (1), but evaluations of both expressions from (1) are known not to throw exceptions.

 Type trait  The value of the member constant value
T is a referenceable type  T is not a referenceable type 
(2) std::is_swappable_with<T&, T&>::value false
(4) std::is_nothrow_swappable_with<T&, T&>::value

If T or U 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.

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

true if T is swappable with U, false otherwise
(public static member constant)

Member functions

converts the object to bool, returns value
(public member function)
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

See also