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std::iter_swap(std::reverse_iterator)

template< std::indirectly_swappable<Iter> Iter2 >
  friend constexpr void
    iter_swap( const reverse_iterator& x,
               const std::reverse_iterator<Iter2>& y ) noexcept(/*see below*/);

(since C++20)

Swaps the objects pointed to by two adjusted underlying iterators. The function body is equivalent to:

auto tmp_x = x.base();
auto tmp_y = y.base();
ranges::iter_swap(--tmp_x, --tmp_y);

This function template is not visible to ordinary unqualified or qualified lookup, and can only be found by argument-dependent lookup when std::reverse_iterator<Iter> is an associated class of the arguments.

Parameters

x, y

reverse iterators to the elements to swap

Return value

(none).

Complexity

Constant.

Exceptions

noexcept specification:

noexcept(
 std::is_nothrow_copy_constructible_v<Iter> &&
 std::is_nothrow_copy_constructible_v<Iter2> &&
 noexcept(ranges::iter_swap(--std::declval<Iter&>(), --std::declval<Iter2&>()))
.
)

Example

#include <iostream>
#include <iterator>
#include <list>
#include <vector>
 
int main()
{
    std::vector v {1, 2, 3};
    std::list   l {4, 5, 6};
 
    std::reverse_iterator<std::vector<int>::iterator> r1 { v.rbegin() };
    std::reverse_iterator<std::list<int>::iterator>   r2 { l.rbegin() };
 
    std::cout << *r1 << ' ' << *r2 << '\n';
 
    iter_swap(r1, r2); // ADL
 
    std::cout << *r1 << ' ' << *r2 << '\n';
}

Output:

3 6
6 3

swap	swaps the values of two objects (function template)
swap_ranges	swaps two ranges of elements (function template)
iter_swap	swaps the elements pointed to by two iterators (function template)
iter_swap (C++20)	swaps the values referenced by two dereferenceable objects (customization point object)
iter_swap (C++20)	swaps the objects pointed to by two underlying iterators (function template)