NAME¶

std::ranges::out_value_result - std::ranges::out_value_result

Synopsis¶

Defined in header <algorithm>
template< class O, class T > (since C++23)
struct out_value_result;

ranges::out_value_result is a class template that provides a way to store an
iterator and a value 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¶

O, T - the types of the objects that the ranges::out_value_result stores.

Data members

Member name Definition
out a value (that is supposed to be an iterator) of type O.
(public member object)
value a value (that is supposed to be a stored value) of type T.
(public member object)

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

Member functions¶

std::ranges::out_value_result::operator out_value_result<O2, T2>

template<class O2, class T2>

requires convertible_to<const O&, O2> && convertible_to<const T&, T2> (1)

constexpr operator out_value_result<O2, T2>() const &;
template<class O2, class T2>

requires convertible_to<O, O2> && convertible_to<T, T2> (2)

constexpr operator out_value_result<O2, T2>() &&;

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

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

Standard library¶

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

Algorithm functions
ranges::iota fills a range with successive increments of the starting value
(C++23) (niebloid)

Synopsis¶

namespace std::ranges
{
template<class O, class T>
struct out_value_result
{
[[no_unique_address]] O out;
[[no_unique_address]] T value;

template<class O2, class T2>
requires convertible_to<const O&, O2> && convertible_to<const T&, T2>
constexpr operator out_value_result<O2, T2>() const &
{
return {out, value};
}

template<class O2, class T2>
requires convertible_to<O, O2> && convertible_to<T, T2>
constexpr operator out_value_result<O2, T2>() &&
{
return {std::move(out), std::move(value)};
}
};
}

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 <cassert>
#include <numeric>
#include <ranges>

int main()
{
std::array<int, 4> a{};
constexpr std::array expected{2, 3, 4, 5};
const auto result = std::ranges::iota(a, 2);
assert(std::ranges::distance(a.cbegin(), result.out) == 4);
assert(result.value == 6);
assert(a == expected);
}

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
(C++11) types
(class template)