std::ranges::reverse_copy, std::ranges::reverse_copy_result

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

Parameters

Return value

{last, result + N}.

Complexity

Exactly N assignments.

Notes

Implementations (e.g. MSVC STL) may enable vectorization when the both iterator types model contiguous_iterator and have the same value type, and the value type is TriviallyCopyable

Possible implementation

See also the implementations in MSVC STL and libstdc++

struct reverse_copy_fn
{
    template<std::bidirectional_iterator I, std::sentinel_for<I> S,
             std::weakly_incrementable O>
    requires std::indirectly_copyable<I, O>
    constexpr ranges::reverse_copy_result<I, O>
        operator()(I first, S last, O result) const
    {
        auto ret = ranges::next(first, last);
        for (; last != first; *result = *--last, ++result);
        return {std::move(ret), std::move(result)};
    }
 
    template<ranges::bidirectional_range R, std::weakly_incrementable O>
    requires std::indirectly_copyable<ranges::iterator_t<R>, O>
    constexpr ranges::reverse_copy_result<ranges::borrowed_iterator_t<R>, O>
        operator()(R&& r, O result) const
    {
        return (*this)(ranges::begin(r), ranges::end(r), std::move(result));
    }
};
 
inline constexpr reverse_copy_fn reverse_copy {};

Example

#include <algorithm>
#include <iostream>
#include <string>
 
int main()
{
    std::string x {"12345"}, y(x.size(), ' ');
    std::cout << x << " → ";
    std::ranges::reverse_copy(x.begin(), x.end(), y.begin());
    std::cout << y << " → ";
    std::ranges::reverse_copy(y, x.begin());
    std::cout << x << '\n';
}

12345 → 54321 → 12345

See also