NAME¶

std::ranges::in_found_result - std::ranges::in_found_result

Synopsis¶

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

ranges::in_found_result is a class template that provides a way to store an iterator
and a boolean flag 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 - the type of the iterator that the ranges::in_found_result stores.

Data members

Member name Definition
a value (that is supposed to be an iterator) of type I. It is declared
in with [[no_unique_address]] attribute.
(public member object)
a boolean flag (that may show whether an appropriate range can be found)
found of type bool.
(public member object)

Member functions¶

std::ranges::in_found_result::operator in_found_result<I2>

template<class I2>

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

constexpr operator in_found_result<I2>() const &;
template<class I2>

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

constexpr operator in_found_result<I2>() &&;

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

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

Standard library¶

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

Algorithm functions
ranges::next_permutation generates the next greater lexicographic permutation of a
(C++20) range of elements
(niebloid)
ranges::prev_permutation generates the next smaller lexicographic permutation of a
(C++20) range of elements
(niebloid)

Synopsis¶

namespace std::ranges
{
template<class I>
struct in_found_result
{
[[no_unique_address]] I in;
bool found;

template<class I2>
requires std::convertible_to<const I&, I2>
constexpr operator in_found_result<I2>() const &
{
return {in, found};
}

template<class I2>
requires std::convertible_to<I, I2>
constexpr operator in_found_result<I2>() &&
{
return {std::move(in), found};
}
};
}

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 <iostream>
#include <iterator>
#include <ranges>

int main()
{
int v[] {1, 2, 3};

const auto result = std::ranges::next_permutation(v);

std::ranges::for_each(std::cbegin(v), result.in, [](int e) {std::cout << e << ' ';});

std::cout << std::boolalpha << "\n" "result.found: " << result.found << '\n';
}

Output:¶

1 3 2
result.found = true

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)