std::ranges::iter_swap

 

C++

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Concepts library (C++20)

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Ranges library (C++20)

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Technical Specifications

 

Iterator library

Iterator concepts
indirectly_readable (C++20) indirectly_writable (C++20) weakly_incrementable (C++20) incrementable (C++20) input_or_output_iterator (C++20) sentinel_for (C++20) sized_sentinel_for (C++20)	input_iterator (C++20) output_iterator (C++20) forward_iterator (C++20) bidirectional_iterator (C++20) random_access_iterator (C++20) contiguous_iterator (C++20)
Iterator primitives
iterator_traits input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag (C++20) iterator (deprecated in C++17)	incrementable_traits (C++20) indirectly_readable_traits (C++20) iter_value_titer_difference_titer_reference_titer_rvalue_reference_titer_common_reference_t (C++20)(C++20)(C++20)(C++20)(C++20)
Algorithm concepts and utilities
Indirect callable concepts
indirectly_unary_invocableindirectly_regular_unary_invocable (C++20)(C++20) indirect_unary_predicate (C++20)	indirect_binary_predicate (C++20) indirect_equivalence_relation (C++20) indirect_strict_weak_order (C++20)
Common algorithm requirements
indirectly_movable (C++20) indirectly_movable_storable (C++20) indirectly_copyable (C++20) indirectly_copyable_storable (C++20)	indirectly_swappable (C++20) indirectly_comparable (C++20) permutable (C++20) mergeable (C++20) sortable (C++20)
Utilities
indirect_result_t	projected
Iterator adaptors
reverse_iterator move_iterator (C++11) move_sentinel (C++20) common_iterator (C++20) counted_iterator (C++20) back_insert_iterator front_insert_iterator insert_iterator	make_reverse_iterator (C++14) make_move_iterator (C++11) default_sentinel_tdefault_sentinel (C++20)(C++20) unreachable_sentinel_tunreachable_sentinel (C++20)(C++20) back_inserter front_inserter inserter
Stream iterators
istream_iterator ostream_iterator	istreambuf_iterator ostreambuf_iterator
Iterator customization points
ranges::iter_move (C++20)
ranges::iter_swap (C++20)
Iterator operations
advance distance prev (C++11) next (C++11)	ranges::advance (C++20) ranges::distance (C++20) ranges::prev (C++20) ranges::next (C++20)
Range access
begincbegin (C++11)(C++14) endcend (C++11)(C++14) sizessize (C++17)(C++20)	rbegincrbegin (C++14)(C++14) rendcrend (C++14)(C++14) empty (C++17) data (C++17)

 

Defined in header <iterator>
inline namespace /*unspecified*/ {     inline constexpr /*unspecified*/ iter_swap = /*unspecified*/; }		(since C++20) (customization point object)
Call signature
template< class I1, class I2 >     requires /* see below */ constexpr void iter_swap(I1&& i1, I2&& i2) noexcept(/* see below */);

Swaps values denoted by two iterators.

A call to ranges::iter_swap is expression-equivalent to:

1. (void)iter_swap(std::forward<I1>(i1), std::forward<I2>(i2)), if either std::remove_cvref_t<I1> or std::remove_cvref_t<I2> is a class or enumeration type and the expression is well-formed in unevaluated context, where the overload resolution is performed with the following candidates:
   • void iter_swap(auto, auto) = delete;
   • any declarations of iter_swap found by argument-dependent lookup.

   If the selected overload does not exchange the value denoted by i1 and i2, the program is ill-formed, no diagnostic required.

2. otherwise, ranges::swap(*std::forward<I1>(i1), *std::forward<I2>(i2)) if both I1 and I2 model indirectly_readable and if std::iter_reference_t<I1> and std::iter_reference_t<I2> model swappable_with.
3. otherwise, (void)(*std::forward<I1>(i1) = /*iter_exchange_move*/(std::forward<I2>(i2), std::forward<I1>(i1))), if I1 and I2 model std::indirectly_move_storable<I1, I2> and std::indirectly_move_storable<I2, I1>, where iter_exchange_move is an expositon-only function template described below.

In all other cases, a call to ranges::iter_swap is ill-formed, which can result in substitution failure when ranges::iter_swap(e1, e2) appears in the immediate context of a template instantiation.

The exposition-only function template iter_exchange_move is equivalently defined as:

template<class X, class Y>
constexpr std::iter_value_t<X> /*iter_exchange_move*/(X&& x, Y&& y)
    noexcept(noexcept(std::iter_value_t<X>(std::move(x)) &&
             noexcept(*x = std::ranges::iter_move(y))))
{
    std::iter_value_t<X> old(std::ranges::iter_move(x));
    *x = std::ranges::iter_move(y);
    return old;
}

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::iter_swap denotes a customization point object, which is a const function object of a literal semiregular class type (denoted, for exposition purposes, as iter_swap_ftor). All instances of iter_swap_ftor are equal. Thus, ranges::iter_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::iter_swap above, iter_swap_ftor will satisfy std::invocable<const iter_swap_ftor&, Args...>. Otherwise, no function call operator of iter_swap_ftor participates in overload resolution.

See also

iter_swap (C++20)	swap the objects pointed to by two adjusted underlying iterators (function template)
iter_swap (C++20)	swap the objects pointed to by two underlying iterators (function template)
iter_swap	swaps the elements pointed to by two iterators (function template)