std::ranges...move_result(3)

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

Okay bestie, welcome to the C++ Standard Library page for std::ranges...move_result(3) — yes, the title is a whole vibe, and yes, we're about to understand it. 🫶

🌸 NAME 🌸

std::ranges::move,std::ranges::move_result — std::ranges::move,std::ranges::move_result, exactly as the page says. No cap.

🦋 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. Not N+1, not a mystery number — exactly N. ✨

🌈 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). Overlap tea, served correctly. 🍵

🧚 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)
• 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)

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Source http://cppreference.com, version/date 2024.06.10, page std::ranges...move_result(3) — bye bestie, go move those elements with main character energy! 💖✨💅