< cpp‎ | iterator
Iterator library
Iterator concepts
Iterator primitives
Algorithm concepts and utilities
Indirect callable concepts
Common algorithm requirements
Iterator adaptors
Iterator customization points
Range access
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)
Helper function
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)));
(exposition only*)

Swaps values denoted by two iterators.

The effect of the exposition-only helper function iter-exchange-move is equivalent to

std::iter_value_t<X> old(std::ranges::iter_move(x));
*x = std::ranges::iter_move(y);
return old;

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

  1. (void)iter_swap(i1, i2), if i1 or i2 has a class or enumeration type and the expression is well-formed, where the overload resolution of iter_swap is performed with the additional candidate void iter_swap(auto, auto) = delete;[1], excluding std::ranges::iter_swap itself.
    • 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> are both modeled, except that 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(i1, i2) appears in the immediate context of a template instantiation.
  1. This precludes calling unconstrained std::iter_swap.

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

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

[edit] Example

[edit] See also

swaps the objects pointed to by two adjusted underlying iterators
(function template) [edit]
swaps the objects pointed to by two underlying iterators
(function template) [edit]
swaps the elements pointed to by two iterators
(function template) [edit]