std::ranges::iter_swap(3)

🌟 std::ranges::iter_swap(3) 🌟

okay bestie, welcome to the std::ranges::iter_swap(3) page from the C++ Standard Libary manual ✨ this one is giving template-wizard energy, and we’re gonna keep every single detail, no cap 💅

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🌸 NAME 🌸

std::ranges::iter_swap — std::ranges::iter_swap

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✨ Synopsis ✨

It’s defined in the header <iterator>, and here’s the synopsis tea exactly as the page serves it — yes, the formatting is a little chaotic, but we keep it 100 😭

Defined in header <iterator>
namespace ranges {

    inline namespace /* unspecified */ {
(since C++20)
        inline constexpr /* unspecified */
(customization
                iter_swap = /* unspecified */;
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 )
(exposition
                                                                      only*)
noexcept(noexcept(std::iter_value_t<X>(std::ranges::iter_move(x)))
&&

             noexcept(*x = std::ranges::iter_move(y)));

It 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

• 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.

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🎀 Example 🎀

This section is incomplete Reason: no example

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🌈 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)

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💀 Category 💀

• Todo no example

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