std::ranges::swap

 

C++

Language

Standard Library Headers

Freestanding and hosted implementations

Named requirements

Language support library

Concepts library (C++20)

Diagnostics library

Utilities library

Strings library

Containers library

Iterators library

Ranges library (C++20)

Algorithms library

Numerics library

Input/output library

Localizations library

Regular expressions library (C++11)

Atomic operations library (C++11)

Thread support library (C++11)

Filesystem library (C++17)

Technical Specifications

 

Utilities library

Type support (basic types, RTTI, type traits)
Dynamic memory management
Error handling
Program utilities
Variadic functions
Library feature-test macros
Date and time
Function objects
Formatting library (C++20)
initializer_list (C++11)
source_location (C++20)
bitset
hash (C++11)
integer_sequence (C++14)
Relational operators (deprecated in C++20)
rel_ops::operator!=rel_ops::operator>rel_ops::operator<=rel_ops::operator>=
Comparisons (C++20)
three_way_comparablethree_way_comparable_with
strong_ordering weak_ordering partial_ordering common_comparison_category compare_three_way_result compare_three_way	strong_order weak_order partial_order compare_strong_order_fallback compare_weak_order_fallback compare_partial_order_fallback	is_eqis_neqis_ltis_lteqis_gtis_gteq
Common vocabulary types
pair tuple (C++11) apply (C++17) make_from_tuple (C++17)	optional (C++17) any (C++17) variant (C++17)
Swap, forward and move
swap
exchange (C++14)
forward (C++11)
move (C++11)
move_if_noexcept (C++11)
Elementary string conversions
to_chars (C++17)
from_chars (C++17)
chars_format (C++17)
Type operations
declval (C++11)
as_const (C++17)
launder (C++17)

 

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 expression-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 std::move_constructible<V> and std::assignable_from<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, which can result in substitution failure when ranges::swap(t, u) appears in the immediate context of a template instantiation.

Expression-equivalent

Expression e is expression-equivalent to expression f, if e and f have the same effects, either are both potentially-throwing or are both not potentially-throwing (i.e. noexcept(e) == noexcept(f)), and either are both constant subexpressions or are both not constant subexpressions.

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 swap_ftor). All instances of swap_ftor 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, swap_ftor will satisfy std::invocable<const swap_ftor&, Args...>. Otherwise, no function call operator of swap_ftor participates in overload resolution.

See also

swappableswappable_with (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)