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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
       declared, which
	  makes	specializations	be aggregate classes, and  propagate  trivial-
       ity,
	  potentially-throwing-ness, and constexpr-ness	of corresponding oper-
       ations 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 us-
       ing 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 mem-
       bers 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)

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

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