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std::ranges::in_fun_result(3)  C++ Standard Libary std::ranges::in_fun_result(3)

NAME
     std::ranges::in_fun_result - std::ranges::in_fun_result

Synopsis
	Defined in header <algorithm>
	template< class I, class F >   (since C++20)
	struct in_fun_result;

	ranges::in_fun_result  is  a class template that provides a way to store
     an iterator
	and a function object 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 - the type of the iterator that the ranges::in_fun_result stores.
	F  -  the  type  of  the  function object that the ranges::in_fun_result
     stores.

	Data members

	Member name Definition
	in	    a value (that is supposed to be an iterator) of type I.
		    (public member object)
	fun	    a value (that is supposed to be a function object)	of  type
     F.
		    (public member object)

	All these members are declared with [[no_unique_address]] attribute.

Member functions
     std::ranges::in_fun_result::operator in_fun_result<I2, F2>

	template<class I2, class F2>

	requires  std::convertible_to<const I&, I2> && std::convertible_to<const
     F&, F2> (1)

	constexpr operator in_fun_result<I2, F2>() const &;
	template<class I2, class F2>

	requires  std::convertible_to<I,  I2>  &&   std::convertible_to<F,   F2>
     (2)

	constexpr operator in_fun_result<I2, F2>() &&;

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

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

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

	      Algorithm functions
	ranges::for_each   applies a function to a range of elements
	(C++20) 	   (niebloid)
	ranges::for_each_n  applies a function object to the first N elements of
     a sequence
	(C++20) 	   (niebloid)

Synopsis
      namespace std::ranges
      {
	  template<class I, class F>
	  struct in_fun_result
	  {
	      [[no_unique_address]] I in;
	      [[no_unique_address]] F fun;

	      template<class I2, class F2>
	      requires	std::convertible_to<const  I&,	I2>   &&   std::convert-
     ible_to<const F&, F2>
	      constexpr operator in_fun_result<I2, F2>() const &
	      {
		  return {in, fun};
	      }

	      template<class I2, class F2>
	      requires std::convertible_to<I, I2> && std::convertible_to<F, F2>
	      constexpr operator in_fun_result<I2, F2>() &&
	      {
		  return {std::move(in), std::move(fun)};
	      }
	  };
      }

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

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

	  const std::ranges::in_fun_result res1 = std::ranges::for_each_n(
	      v, std::size(v),
	      [](int& x) { return x = -x; } // negating lambda
	  );
	  assert(res1.in == std::end(v));

	  const std::ranges::in_fun_result res2 = std::ranges::for_each(
	      std::begin(v),
	      res1.in,
	      [](int x) { std::cout << x << ' '; } // printing lambda
	  );

	  std::cout << "a ";

	  std::ranges::for_each(v, res1.fun); // uses negating lambda
	  std::ranges::for_each(v, res2.fun); // uses printing lambda
	  std::cout << '\n';
      }

Output:
      -1 -2 -3 a 1 2 3

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::in_fun_result(3)
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