std::ranges::swap

 

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Defined in header <concepts>
inline namespace /* unspecified */ {     inline constexpr /* unspecified */ swap = /* unspecified */; }		(since C++20) (customization point object)
Call signature
template< class T, class U >     requires /* see below */ constexpr void swap(T&& t, U&& u) noexcept(/* see below */);

Exchanges the values referenced by t and u.

A call to ranges::swap is equivalent to:

1) (void)swap(std::forward<T>(t), std::forward<U>(u)), if that expression is valid, where the overload resolution is performed with the following candidates:

• template<class T> void swap(T&, T&) = delete;
• template<class T, std::size_t N> void swap(T(&)[N], T(&)[N]) = delete;
• any declarations of swap found by argument-dependent lookup.

If the function selected by overload resolution does not exchange the values referenced by t and u, the program is ill-formed; no diagnostic required.

2) Otherwise, (void)ranges::swap_ranges(t, u), if T and U are lvalue references to array types of equal extent (but possibly different element types) and ranges::swap(*t, *u) is a valid expression;

3) Otherwise, if T and U are both V& for some type V that meets the syntactic requirements of MoveConstructible<V> and Assignable<V&, V>, exchanges the referenced values as if by V v{std::move(t)}; t = std::move(u); u = std::move(v);. If the semantic requirements of either concept are not satisfied, the program is ill-formed; no diagnostic required.

4) In all other cases, a call to ranges::swap is ill-formed.

ranges::swap can be used in a constant expression if every function it calls (as specified above) can be so used.

Customization point objects

The name ranges::swap denotes a customization point object, which is a function object of a literal Semiregular class type (denoted, for exposition purposes, as SwapT). All instances of SwapT are equal. Thus, ranges::swap can be copied freely and its copies can be used interchangeably.

Given a set of types Args..., if std::declval<Args>()... meet the requirements for arguments to ranges::swap above, SwapT will satisfy std::Invocable<const SwapT&, Args...>. Otherwise, no function call operator of SwapT participates in overload resolution.

Exceptions

1)

noexcept specification:  

noexcept(noexcept((void)swap(std::forward<T>(t), std::forward<T>(u))))

, where swap is found as described above.

2)

noexcept specification:  

noexcept(noexcept(ranges::swap(*t, *u)))

3)

noexcept specification:  

noexcept(std::is_nothrow_move_constructible_v<V> &&
         std::is_nothrow_move_assignable_v<V>)

See also

SwappableSwappableWith (C++20)	specifies that a type can be swapped or that two types can be swapped with each other (concept)
swap	swaps the values of two objects (function template)