# 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>)

### Example

| This section is incomplete Reason: no example

### 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)

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