# std::ranges::swap_ranges, std::ranges::swap_ranges_result

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< cpp‎ | algorithm‎ | ranges

Defined in header `<algorithm>` |  |
Call signature |  |
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 ); | (1) | (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 ); | (2) | (since C++20)
Helper types |  |
template< class I1, class I2 > using swap_ranges_result = ranges::in_in_result <I1, I2>; | (3) | (since C++20)

1) Exchanges elements between first range `[`first1`,` first1 + M`)` and second range `[`first2`,` first2 + M`)` via 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.
2) Same as (1), but uses r1 as the first range and r2 as the second range, as if 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 algorithm function objects (informally known as 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.

### 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.

### Return value

{first1 + M, first2 + M}.

### Complexity

Exactly M swaps.

### 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`.

### 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 {};

### 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);
    }

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

### See also

iter_swap (C++20) | swaps the values referenced by two dereferenceable objects (customization point object)
ranges::swap (C++20) | swaps the values of two objects (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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