NAME¶

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

Synopsis¶

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> (1) (since C++20)
constexpr move_result<I, O>

move( I first, S last, O result );
template< ranges::input_range R, std::weakly_incrementable O >

requires std::indirectly_movable<ranges::iterator_t<R>, O> (2) (since C++20)
constexpr move_result<ranges::borrowed_iterator_t<R>, O>

move( R&& r, O result );

Helper types¶

template< class I, class O > (3) (since C++20)
using move_result = ranges::in_out_result<I, O>;

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.

// Run this code

#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

See also¶

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