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std::ranges::in_found_result

From cppreference.com
< cpp‎ | algorithm‎ | ranges
 
 
Constrained algorithms
Non-modifying sequence operations
Modifying sequence operations
Operations on uninitialized storage
Partitioning operations
Sorting operations
Binary search operations
Set operations (on sorted ranges)
Heap operations
Minimum/maximum operations
Permutations
 
 
Defined in header <algorithm>
template <class I>
struct in_found_result;
(since C++20)

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.

Contents

[edit] Template parameters

I - the type of the element that the ranges::in_found_result stores.

[edit] Data members

std::ranges::in_found_result::in

[[no_unique_address]] I in;

a value (that is supposed to be an iterator)

std::ranges::in_found_result::found

bool found;

a boolean flag (that may show whether an appropriate range can be found)

[edit] Member functions

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

template<class I2>

requires std::convertible_to<const I&, I2>

constexpr operator in_found_result<I2>() const &;
(1)
template<class I2>

requires std::convertible_to<I, I2>

constexpr operator in_found_result<I2>() &&;
(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, found};.
2) Equivalent to return {std::move(in), found};.

[edit] Standard library

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

Algorithm functions
generates the next greater lexicographic permutation of a range of elements
(niebloid) [edit]
generates the next smaller lexicographic permutation of a range of elements
(niebloid) [edit]

[edit] 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};
        }
    };
}

[edit] 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.

[edit] Example

#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

[edit] See also

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