NAME¶

std::ranges::in_value_result - std::ranges::in_value_result

Synopsis¶

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

ranges::in_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¶

I, T - the types of the objects that the ranges::in_value_result stores.

Data members

Member name Definition
in a value (that is supposed to be an iterator) of type I.
(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::in_value_result::operator in_value_result<I2, T2>

template<class I2, class T2>

requires convertible_to<const I&, I2> && convertible_to<const T&, T2> (1)

constexpr operator in_value_result<I2, T2>() const &;
template<class I2, class T2>

requires convertible_to<I, I2> && convertible_to<T, T2> (2)

constexpr operator in_value_result<I2, T2>() &&;

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

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

Standard library¶

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

Algorithm functions
ranges::fold_left_with_iter left-folds a range of elements, and returns a pair
(C++23) (iterator, value)
(niebloid)
left-folds a range of elements using the first
ranges::fold_left_first_with_iter element as an initial value, and returns a pair
(C++23) (iterator, optional)
(niebloid)

Synopsis¶

namespace std::ranges
{
template<class I, class T>
struct in_value_result
{
[[no_unique_address]] I in;
[[no_unique_address]] T value;

template<class I2, class T2>
requires convertible_to<const I&, I2> && convertible_to<const T&, T2>
constexpr operator in_value_result<I2, T2>() const &
{
return {in, value};
}

template<class I2, class T2>
requires convertible_to<I, I2> && convertible_to<T, T2>
constexpr operator in_value_result<I2, T2>() &&
{
return {std::move(in), 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 <cassert>
#include <functional>

int main()
{
const auto v = {1, 2, 3};
const auto ret = std::ranges::fold_left_with_iter(v, 4, std::plus<>());
assert(ret.in == v.end());
assert(ret.value == 1 + 2 + 3 + 4);
}

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)