std::is_swappable_with, std::is_swappable, std::is_nothrow_swappable_with, std::is_nothrow_swappable
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) |
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.
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
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, 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
See also
swaps the values of two objects (function template) |
|
(C++11)(C++11)(C++11)
|
checks if a type has a move assignment operator (class template) |
(C++20)
|
specifies that a type can be swapped or that two types can be swapped with each other (concept) |
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