# std::ranges::in_out_result

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< cpp‎ | algorithm‎ | ranges

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

`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

Member name | Definition
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> constexpr operator in_out_result<I2, O2>() const &; | (1) |
template<class I2, class O2> requires std::convertible_to <I, I2> && std::convertible_to <O, O2> constexpr operator in_out_result<I2, O2>() &&; | (2) |

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

##### Memory functions

ranges::uninitialized_copy (C++20) | copies a range of objects to an uninitialized area of memory (algorithm function object)
ranges::uninitialized_copy_n (C++20) | copies a number of objects to an uninitialized area of memory (algorithm function object)
ranges::uninitialized_move (C++20) | moves a range of objects to an uninitialized area of memory (algorithm function object)
ranges::uninitialized_move_n (C++20) | moves a number of objects to an uninitialized area of memory (algorithm function object)

### Synopsis

    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 (C++11) | implements fixed size container, which holds elements of possibly different types (class template)

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