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)