std::ranges::in_out_result(3)

🌸 std::ranges::in_out_result(3) 🌸

okay so bestie, this page is from the C++ Standard Libary manual — yes, that's the spelling in the header, don't come for me 💅 — and it's literally all about std::ranges::in_out_result. it's giving "tiny struct with main character energy" and we're obsessed. let's get into it 🫶

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✨ NAME ✨

std::ranges::in_out_result — std::ranges::in_out_result (yep, the name line is just the name twice, iconic)

✨ Synopsis ✨

Defined in header <algorithm>
template< class I, class O >   (since C++20)
struct in_out_result;

ranges::in_out_result is a class template that provides a way to store two iterators as a single unit.

This class template has no base classes or declared members other than those shown below. Thus it is suitable for use with structured bindings.

All special member functions of this class template are implicitly declared, which makes specializations be aggregate classes, and propagate triviality, potentially-throwing-ness, and constexpr-ness of corresponding operations on data members.

🎀 Template parameters 🎀

• I, O — the types of the objects that the ranges::in_out_result stores.

🎀 Data members 🎀

• in — a value (that is supposed to be an iterator) of type I. (public member object)
• out — a value (that is supposed to be an iterator) of type O. (public member object)

All these members are declared with [[no_unique_address]] attribute.

💅 Member functions 💅

std::ranges::in_out_result::operator in_out_result<I2, O2>

template<class I2, class O2>

requires std::convertible_to<const I&, I2> &&
       std::convertible_to<const O&, O2> (1)

constexpr operator in_out_result<I2, O2>() const &;

template<class I2, class O2>

requires std::convertible_to<I, I2> && std::convertible_to<O, O2>
(2)

constexpr operator in_out_result<I2, O2>() &&;

Converts *this to the result by constructing every data member of the result from the corresponding member of *this.

1. Equivalent to return {in, out};.
2. Equivalent to return {std::move(in), std::move(out)};.

👑 Standard library 👑

The following standard library functions use ranges::in_out_result as the return type:

Algorithm functions

• ranges::copy — copies a range of elements to a new location. (C++20) (niebloid)
• ranges::copy_if — copies a range of elements to a new location. (C++20) (niebloid)
• ranges::copy_n — copies a number of elements to a new location. (C++20) (niebloid)
• ranges::copy_backward — copies a range of elements in backwards order. (C++20) (niebloid)
• ranges::move — moves a range of elements to a new location. (C++20) (niebloid)
• ranges::move_backward — moves a range of elements to a new location in backwards order. (C++20) (niebloid)
• ranges::transform — applies a function to a range of elements. (C++20) (niebloid)
• ranges::replace_copy — copies a range, replacing elements satisfying specific criteria with another value. (C++20) (niebloid)
• ranges::replace_copy_if — copies a range, replacing elements satisfying specific criteria with another value. (C++20) (niebloid)
• ranges::remove_copy — copies a range of elements omitting those that satisfy specific criteria. (C++20) (niebloid)
• ranges::remove_copy_if — copies a range of elements omitting those that satisfy specific criteria. (C++20) (niebloid)
• ranges::unique_copy — creates a copy of some range of elements that contains no consecutive duplicates. (C++20) (niebloid)
• ranges::reverse_copy — creates a copy of a range that is reversed. (C++20) (niebloid)
• ranges::rotate_copy — copies and rotate a range of elements. (C++20) (niebloid)
• ranges::partial_sort_copy — copies and partially sorts a range of elements. (C++20) (niebloid)
• ranges::set_difference — computes the difference between two sets. (C++20) (niebloid)

Memory functions

• ranges::uninitialized_copy — copies a range of objects to an uninitialized area of memory. (C++20) (niebloid)
• ranges::uninitialized_copy_n — copies a number of objects to an uninitialized area of memory. (C++20) (niebloid)
• ranges::uninitialized_move — moves a range of objects to an uninitialized area of memory. (C++20) (niebloid)
• ranges::uninitialized_move_n — moves a number of objects to an uninitialized area of memory. (C++20) (niebloid)

🌈 Synopsis (the full code moment) 🌈

namespace std::ranges
{
    template<class I, class O>
    struct in_out_result
    {
        [[no_unique_address]] I in;
        [[no_unique_address]] O out;

        template<class I2, class O2>
        requires std::convertible_to<const I&, I2> &&
       std::convertible_to<const O&, O2>
        constexpr operator in_out_result<I2, O2>() const &
        {
            return {in, out};
        }

        template<class I2, class O2>
        requires std::convertible_to<I, I2> && std::convertible_to<O,
       O2>
        constexpr operator in_out_result<I2, O2>() &&
        {
            return {std::move(in), std::move(out)};
        }
    };
}

🦋 Notes 🦋

Each standard library algorithm that uses this family of return types declares a new alias type, e.g. using merge_result = in_in_out_result<I1, I2, O>;.

The names for such aliases are formed by adding the suffix "_result" to the algorithm's name. So, the return type of std::ranges::merge can be named as std::ranges::merge_result.

Unlike std::pair and std::tuple, this class template has data members of meaningful names.

🍓 Example 🍓

// Run this code

#include <algorithm>
#include <array>
#include <cctype>
#include <iostream>
#include <ranges>

int main()
{
    constexpr char in[] = "transform" "\n";
    std::array<char, sizeof(in)> out;

    const auto result = std::ranges::transform(in, out.begin(),
        [](char c) { return std::toupper(c); });

    auto print = [](char c) { std::cout << c; };
    std::ranges::for_each(std::cbegin(in), result.in, print);
    std::ranges::for_each(out.cbegin(), result.out, print);
}

Output

transform
TRANSFORM

🌟 See also 🌟

• pair — implements binary tuple, i.e. a pair of values. (class template)
• tuple — implements fixed size container, which holds elements of possibly different types. (C++11) (class template)

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that's the whole page, bestie 🫶 — source/version: http://cppreference.com, dated 2024.06.10. now go slay some ranges 💅✨