std::ranges...nges_result(3)

💖 NAME 💖

This is std::ranges...nges_result(3) from the C++ Standard Libary — the manual page for std::ranges::swap_ranges and std::ranges::swap_ranges_result, and the NAME line is literally std::ranges::swap_ranges,std::ranges::swap_ranges_result - std::ranges::swap_ranges,std::ranges::swap_ranges_result. Yes bestie, it said it twice, and honestly? Iconic.

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✨ Synopsis ✨

Defined in header <algorithm>

Call signature

(1) (since C++20)

template< std::input_iterator I1, std::sentinel_for<I1> S1,
          std::input_iterator I2, std::sentinel_for<I2> S2 >
    requires std::indirectly_swappable<I1, I2>
constexpr swap_ranges_result<I1, I2>
    swap_ranges( I1 first1, S1 last1, I2 first2, S2 last2 );

(2) (since C++20)

template< ranges::input_range R1, ranges::input_range R2 >
    requires std::indirectly_swappable<ranges::iterator_t<R1>,
                                        ranges::iterator_t<R2>>
constexpr swap_ranges_result<ranges::borrowed_iterator_t<R1>,
                              ranges::borrowed_iterator_t<R2>>
    swap_ranges( R1&& r1, R2&& r2 );

Helper types

(3) (since C++20)

template< class I1, class I2 >
using swap_ranges_result = ranges::in_in_result<I1, I2>;

Okay so (1) is the iterator-pair version: it exchanges elements between the first range [first1, first1 + M) and the second range [first2, first2 + M) by calling ranges::iter_swap(first1 + i, first2 + i), where

M = ranges::min(ranges::distance(first1, last1), ranges::distance(first2, last2)).

⚠️ The ranges [first1, last1) and [first2, last2) must not overlap. Not a vibe suggestion, bestie — do not overlap them.

(2) is the same as (1), but it uses r1 as the first range and r2 as the second range, as if it were using ranges::begin(r1) as first1, ranges::end(r1) as last1, ranges::begin(r2) as first2, and ranges::end(r2) as last2.

The function-like entities described on this page are niebloids, that is:

• Explicit template argument lists cannot be specified when calling any of them.
• None of them are visible to argument-dependent lookup.
• When any of them are found by normal unqualified lookup as the name to the left of the function-call operator, argument-dependent lookup is inhibited.

In practice, they may be implemented as function objects, or with special compiler extensions.

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🌸 Parameters 🌸

• first1, last1 — the first range of elements to swap.
• first2, last2 — the second range of elements to swap.
• r1 — the first range of elements to swap.
• r2 — the second range of elements to swap.

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🎀 Return value 🎀

{first1 + M, first2 + M}.

That's the return value. Cute, clean, no drama.

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🦋 Complexity 🦋

Exactly M swaps.

Not "around M", not "M-ish", not "vibes-based". Exactly M. Slay.

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💅 Notes 💅

Implementations (e.g. MSVC STL) may enable vectorization when the iterator type models contiguous_iterator and swapping its value type calls neither non-trivial special member function nor ADL-found swap.

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👑 Possible implementation 👑

struct swap_ranges_fn
{
    template<std::input_iterator I1, std::sentinel_for<I1> S1,
             std::input_iterator I2, std::sentinel_for<I2> S2>
    requires std::indirectly_swappable<I1, I2>
    constexpr ranges::swap_ranges_result<I1, I2>
        operator()(I1 first1, S1 last1, I2 first2, S2 last2) const
    {
        for (; !(first1 == last1 or first2 == last2); ++first1, ++first2)
            ranges::iter_swap(first1, first2);
        return {std::move(first1), std::move(first2)};
    }

    template<ranges::input_range R1, ranges::input_range R2>
    requires std::indirectly_swappable<ranges::iterator_t<R1>,
                                       ranges::iterator_t<R2>>
    constexpr
    ranges::swap_ranges_result<ranges::borrowed_iterator_t<R1>,
                               ranges::borrowed_iterator_t<R2>>
        operator()(R1&& r1, R2&& r2) const
    {
        return (*this)(ranges::begin(r1), ranges::end(r1),
                       ranges::begin(r2), ranges::end(r2));
    }
};

inline constexpr swap_ranges_fn swap_ranges {};

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🌈 Example 🌈

// Run this code

#include <algorithm>
#include <iostream>
#include <list>
#include <string_view>
#include <vector>

auto print(std::string_view name, auto const& seq, std::string_view term = "\n")
{
    std::cout << name << " : ";
    for (const auto& elem : seq)
        std::cout << elem << ' ';
    std::cout << term;
}

int main()
{
    std::vector<char> p {'A', 'B', 'C', 'D', 'E'};
    std::list<char> q {'1', '2', '3', '4', '5', '6'};

    print("p", p);
    print("q", q, "\n\n");

    // swap p[0, 2) and q[1, 3):
    std::ranges::swap_ranges(p.begin(),
                             p.begin() + 4,
                             std::ranges::next(q.begin(), 1),
                             std::ranges::next(q.begin(), 3));
    print("p", p);
    print("q", q, "\n\n");

    // swap p[0, 5) and q[0, 5):
    std::ranges::swap_ranges(p, q);

    print("p", p);
    print("q", q);
}

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💖 Output 💖

p : A B C D E
q : 1 2 3 4 5 6

p : 2 3 C D E
q : 1 A B 4 5 6

p : 1 A B 4 5
q : 2 3 C D E 6

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🫶 See also 🫶

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

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Source/version: http://cppreference.com, 2024.06.10; date: 2024.06.10 — big mwah to the source, and that's the page, bestie 💋✨💖