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std::ranges::move, std::ranges::move_result

Defined in header `<algorithm>`
Call signature
template< std::input_iterator I, std::sentinel_for<I> S, std::weakly_incrementable O > requires std::indirectly_movable<I, O> constexpr move_result<I, O> move( I first, S last, O result );	(1)	(since C++20)
template< ranges::input_range R, std::weakly_incrementable O > requires std::indirectly_movable<ranges::iterator_t<R>, O> constexpr move_result<ranges::borrowed_iterator_t<R>, O> move( R&& r, O result );	(2)	(since C++20)
Helper types
template< class I, class O > using move_result = ranges::in_out_result<I, O>;	(3)	(since C++20)

1) Moves the elements in the range, defined by [first, last), to another range beginning at result. The behavior is undefined if result is within the range [first, last). In such a case, ranges::move_backward may be used instead.

2) Same as (1), but uses r as the source range, as if using ranges::begin(r) as first, and ranges::end(r) as last.

The elements in the moved-from range will still contain valid values of the appropriate type, but not necessarily the same values as before the move.

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

first	-	the beginning of the range of elements to move
last	-	the end of the range of elements to move
r	-	the range of the elements to move
result	-	the beginning of the destination range

Return value

{last, result + N}, where.

1) N = ranges::distance(first, last).

2) N = ranges::distance(r).

Complexity

Exactly N move assignments.

Notes

When moving overlapping ranges, ranges::move is appropriate when moving to the left (beginning of the destination range is outside the source range) while ranges::move_backward is appropriate when moving to the right (end of the destination range is outside the source range).

Possible implementation

struct move_fn
{
    template<std::input_iterator I, std::sentinel_for<I> S, std::weakly_incrementable O>
    requires std::indirectly_movable<I, O>
    constexpr ranges::move_result<I, O>
        operator()(I first, S last, O result) const
    {
        for (; first != last; ++first, ++result)
            *result = ranges::iter_move(first);
        return {std::move(first), std::move(result)};
    }
    template<ranges::input_range R, std::weakly_incrementable O>
    requires std::indirectly_movable<ranges::iterator_t<R>, O>
    constexpr ranges::move_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 move_fn move {};

Example

The following code moves thread objects (which themselves are non copyable) from one container to another.

#include <algorithm>
#include <chrono>
#include <iostream>
#include <iterator>
#include <list>
#include <thread>
#include <vector>
using namespace std::literals::chrono_literals;
 
void f(std::chrono::milliseconds n)
{
    std::this_thread::sleep_for(n);
    std::cout << "thread with n=" << n.count() << "ms ended" << std::endl;
}
 
int main()
{
    std::vector<std::jthread> v;
    v.emplace_back(f, 400ms);
    v.emplace_back(f, 600ms);
    v.emplace_back(f, 800ms);
 
    std::list<std::jthread> l;
 
    // std::ranges::copy() would not compile, because std::jthread is non-copyable
    std::ranges::move(v, std::back_inserter(l));
}

Output:

thread with n=400ms ended
thread with n=600ms ended
thread with n=800ms ended

ranges::move_backward (C++20)	moves a range of elements to a new location in backwards order (niebloid)
ranges::copyranges::copy_if (C++20)(C++20)	copies a range of elements to a new location (niebloid)
ranges::copy_backward (C++20)	copies a range of elements in backwards order (niebloid)
move (C++11)	moves a range of elements to a new location (function template)
move (C++11)	obtains an rvalue reference (function template)