iter_swap(s...d_iterator)(3)

✨ NAME ✨

okay so bestie, welcome to iter_swap(s...d_iterator)(3), straight out of the C++ Standard Libary manual (yes, “Libary” is literally how it’s spelled on the page, and honestly? iconic). This is the std::counted_iterator flavor of iter_swap, and it swaps the objects pointed to by two underlying iterators. 💅

🌸 Synopsis 🌸

The page lays the synopsis out all wrapped and chaotic, so here is the exact block, bestie:

          template< std::indirectly_swappable<I> I2 >

              friend constexpr void
                  iter_swap( const counted_iterator& x, const
       (since C++20)
          std::counted_iterator<I2>& y )

                      noexcept(noexcept(ranges::iter_swap(x.base(),
          y.base())));

That (since C++20) marker means this overload is since C++20, and the signature is a friend constexpr void iter_swap( const counted_iterator& x, const std::counted_iterator<I2>& y ) with noexcept(noexcept(ranges::iter_swap(x.base(), y.base()))). The template constraint is template< std::indirectly_swappable<I> I2 >. 🫶

It swaps the objects pointed to by two underlying iterators. 🚨 Undefined behavior alert: the behavior is undefined if either x.count() or y.count() is equal to 0 — like, do not do that, bestie. 😭

The function body is equivalent to: ranges::iter_swap(x.base(), y.base());.

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

🎀 Parameters 🎀

• x, y — iterator adaptors to the elements to swap

💖 Return value 💖

(none)

🦋 Complexity 🦋

Constant. no cap, it’s giving efficiency.

🌈 Example 🌈

The page has the classic // Run this code line, so here’s the code, exactly:

        #include <iostream>
        #include <iterator>
        #include <list>
        #include <vector>

        int main()
        {
            std::vector p{1, 2, 3, 4},
                        q{5, 6, 7, 8};

            std::counted_iterator<std::vector<int>::iterator> ip{p.begin(), 2};
            std::counted_iterator<std::vector<int>::iterator> iq{q.begin(), 3};

            std::cout << *ip << ' ' << *iq << '\n';
            iter_swap(ip, iq); // ADL
            std::cout << *ip << ' ' << *iq << '\n';

            std::list x{0, 1, 3};
            std::counted_iterator<std::list<int>::iterator> ix{x.begin(), 2};
        //  iter_swap(ip, ix); // error: not indirectly swappable
        }

⭐ Output ⭐

        1 5
        5 1

🔥 See also 🔥

• 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_move (C++20) — casts the result of dereferencing the underlying iterator to its associated rvalue reference type (function)

kisses, your fave C++ bestie 💖 signing off with source/version http://cppreference.com and date 2024.06.10 🫶✨