std::ranges::iter_swap(3)

NAME
std::ranges::iter_swap - std::ranges::iter_swap

Synopsis
   Defined in header <iterator>
   namespace ranges {
   inline namespace /*unspecified*/ {
   inline constexpr /*unspecified*/ iter_swap = (since C++20)
   /*unspecified*/; (customization point object)
   }
   }
   Call signature
   template< class I1, class I2 >
   constexpr void iter_swap( I1&& i1, I2&& i2 ) (since C++20)
   noexcept(/* see below */);
   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 swaps the objects pointed to by two adjusted underlying iterators
   (C++20) (function template)
   iter_swap swaps the objects pointed to by two underlying iterators
   (C++20) (function template)
   iter_swap swaps the elements pointed to by two iterators
             (function template)