NAME¶

std::is_swappable_with,std::is_swappable,std::is_nothrow_swappable_with, - std::is_swappable_with,std::is_swappable,std::is_nothrow_swappable_with,

Synopsis¶

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

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.

The behavior of a program that adds specializations for any of the templates
described on this page is undefined.

Helper variable templates

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

Inherited from std::integral_constant

Member constants¶

value true if T is swappable with U , 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>

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 checks if a type has a move assignment operator
(C++11) (class template)
(C++11)
(C++11)
swappable specifies that a type can be swapped or that two types
swappable_with can be swapped with each other
(C++20) (concept)