std::ranges::rotate_copy, std::ranges::rotate_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}, where N = ranges::distance (first, last)

Complexity

Linear: exactly N assignments.

Notes

If the value type is TriviallyCopyable and the iterator types satisfy contiguous_iterator, implementations of ranges::rotate_copy usually avoid multiple assignments by using a "bulk copy" function such as std::memmove

Possible implementation

See also the implementations in libstdc++ and MSVC STL

struct rotate_copy_fn
{
    template<std::forward_iterator I, std::sentinel_for<I> S, std::weakly_incrementable O>
    requires std::indirectly_copyable<I, O>
    constexpr ranges::rotate_copy_result<I, O>
        operator()(I first, I middle, S last, O result) const
    {
        auto c1 {ranges::copy(middle, std::move(last), std::move(result))};
        auto c2 {ranges::copy(std::move(first), std::move(middle), std::move(c1.out))};
        return {std::move(c1.in), std::move(c2.out)};
    }
 
    template<ranges::forward_range R, std::weakly_incrementable O>
    requires std::indirectly_copyable<ranges::iterator_t<R>, O>
    constexpr ranges::rotate_copy_result<ranges::borrowed_iterator_t<R>, O>
        operator()(R&& r, ranges::iterator_t<R> middle, O result) const
    {
        return (*this)(ranges::begin(r), std::move(middle),
                       ranges::end(r), std::move(result));
    }
};
 
inline constexpr rotate_copy_fn rotate_copy {};

Example

#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector>
 
int main()
{
    std::vector<int> src {1, 2, 3, 4, 5};
    std::vector<int> dest(src.size());
    auto pivot = std::ranges::find(src, 3);
 
    std::ranges::rotate_copy(src, pivot, dest.begin());
    for (int i : dest)
        std::cout << i << ' ';
    std::cout << '\n';
 
    // copy the rotation result directly to the std::cout
    pivot = std::ranges::find(dest, 1);
    std::ranges::rotate_copy(dest, pivot, std::ostream_iterator<int>(std::cout, " "));
    std::cout << '\n';
}

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1 2 3 4 5

See also