std::ranges::iter_swap

 

C++

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Feature test macros (C++20)

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Ranges library (C++20)

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Iterator library

Iterator concepts
indirectly_readable (C++20) indirectly_writable (C++20) weakly_incrementable (C++20) incrementable (C++20) is-integer-like is-signed-integer-like (C++20)(C++20)	sentinel_for (C++20) sized_sentinel_for (C++20) input_iterator (C++20) output_iterator (C++20) input_or_output_iterator (C++20)	forward_iterator (C++20) bidirectional_iterator (C++20) random_access_iterator (C++20) contiguous_iterator (C++20)
Iterator primitives
input_iterator_tagoutput_iterator_tagforward_iterator_tagbidirectional_iterator_tagrandom_access_iterator_tagcontiguous_iterator_tag (C++20)	iter_value_titer_difference_titer_reference_titer_const_reference_titer_rvalue_reference_titer_common_reference_t (C++20)(C++20)(C++20)(C++23)(C++20)(C++20)	iterator (deprecated in C++17) iterator_traits incrementable_traits (C++20) indirectly_readable_traits (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 (C++20)	projected (C++20)	projected_value_t (C++26)
Iterator adaptors
reverse_iterator make_reverse_iterator (C++14) move_iterator (C++11) make_move_iterator (C++11) default_sentinel_tdefault_sentinel (C++20)(C++20) unreachable_sentinel_tunreachable_sentinel (C++20)(C++20)	front_insert_iterator back_insert_iterator inserter insert_iterator front_inserter back_inserter move_sentinel (C++20)	common_iterator (C++20) counted_iterator (C++20) basic_const_iterator (C++23) const_iterator (C++23) const_sentinel (C++23) make_const_iterator (C++23) make_const_sentinel (C++23)
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) rbegincrbegin (C++14)(C++14)   endcend (C++11)(C++14) rendcrend (C++14)(C++14)   sizessize (C++17)(C++20) empty (C++17) data (C++17)

 

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

Swaps values denoted by two iterators.

ranges::iter_swap(i1, i2) is expression-equivalent to:

1. (void)iter_swap(i1, i2), if std::remove_cvref_t<I1> or std::remove_cvref_t<I2> is a class or enumeration type and the expression is well-formed, where the overload resolution is performed within namespace std::ranges with the additional candidate:
   • void iter_swap(auto, auto) = delete;

   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(*i1, *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)(*i1 = /*iter_exchange_move*/(i2, i1)), if std::indirectly_movable_storable<I1, I2> and std::indirectly_movable_storable<I2, I1>, where iter_exchange_move is an exposition-only function template described below (and i1 is only evaluated once).
4. Otherwise, ranges::iter_swap(i1, i2) 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 defined the equivalent of:

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::ranges::iter_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, and
• either both are constant subexpressions or else neither is a constant subexpression, and
• either both are potentially-throwing or else neither is potentially-throwing (i.e. noexcept(e) == noexcept(f)).

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. For exposition purposes, the cv-unqualified version of its type is denoted as __iter_swap_fn.

All instances of __iter_swap_fn are equal. The effects of invoking different instances of type __iter_swap_fn on the same arguments are equivalent, regardless of whether the expression denoting the instance is an lvalue or rvalue, and is const-qualified or not (however, a volatile-qualified instance is not required to be invocable). 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_fn models

• std::invocable<__iter_swap_fn, Args...>,
• std::invocable<const __iter_swap_fn, Args...>,
• std::invocable<__iter_swap_fn&, Args...>, and
• std::invocable<const __iter_swap_fn&, Args...>.
  

Otherwise, no function call operator of __iter_swap_fn participates in overload resolution.

See also

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