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std::ranges...alue_result(3)   C++ Standard Libary  std::ranges...alue_result(3)

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  de-
     clared, which
	makes specializations be aggregate classes, and propagate triviality,
	potentially-throwing-ness,  and  constexpr-ness  of corresponding opera-
     tions 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  re-
     turns 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 possi-
     bly different
	(C++11) types
		(class template)

http://cppreference.com 	   2024.06.10	    std::ranges...alue_result(3)
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