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

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 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.

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

#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

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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