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, potentiallythrowingness, and constexprness of corresponding operations on data members.
I    the type of the iterator that the ranges::in_found_result stores. 
[[no_unique_address]] I in; 
a value (that is supposed to be an iterator).
bool found; 
a boolean flag (that may show whether an appropriate range can be found).
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
.
return {in, found};
.return {std::move(in), found};
. The following standard library functions use ranges::in_found_result
as the return type:
Algorithm functions 

(C++20)  generates the next greater lexicographic permutation of a range of elements (niebloid) 
(C++20)  generates the next smaller lexicographic permutation of a range of elements (niebloid) 
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}; } }; }
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.
#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
implements binary tuple, i.e. a pair of values (class template) 

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