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

NAME
     std::ranges::subrange - std::ranges::subrange

Synopsis
	Defined in header <ranges>
	template<

	    std::input_or_output_iterator I,
	    std::sentinel_for<I> S = I,
	    ranges::subrange_kind K = std::sized_sentinel_for<S, I> ?
		ranges::subrange_kind::sized   :  ranges::subrange_kind::unsized
     (since C++20)
	>
	    requires (K == ranges::subrange_kind::sized ||
	!std::sized_sentinel_for<S, I>)

	class subrange : public ranges::view_interface<subrange<I, S, K>>

	The subrange class template combines together an iterator and a sentinel
     into a
	single view.

	Additionally, the subrange is a sized_range whenever the final	template
     parameter is
	subrange_kind::sized  (which  happens when std::sized_sentinel_for<S, I>
     is satisfied
	or when size is passed explicitly as a constructor argument).  The  size
     record is
	needed	to  be	stored	if  and only if std::sized_sentinel_for<S, I> is
     false and K is
	subrange_kind::sized.

Member functions
	constructor	  creates a new subrange
	(C++20) 	  (public member function)
	operator PairLike converts the subrange to a pair-like type
	(C++20) 	  (public member function)

Observers
	begin		  obtains the iterator
	(C++20) 	  (public member function)
	end		  obtains the sentinel
	(C++20) 	  (public member function)
	empty		  checks whether the subrange is empty
	(C++20) 	  (public member function)
	size		  obtains the size of the subrange
	(C++20) 	  (public member function)

Iterator operations
	advance 	  advances the iterator by given distance
	(C++20) 	  (public member function)
	prev		  obtains a copy  of  the  subrange  with  its	iterator
     decremented by a
	(C++20) 	  given distance
			  (public member function)
	next		   obtains  a copy of the subrange with its iterator ad-
     vanced by a
	(C++20) 	  given distance
			  (public member function)
	      Inherited from std::ranges::view_interface
	cbegin		  returns a constant iterator to the  beginning  of  the
     range.
	(C++23) 	   (public  member  function of std::ranges::view_inter-
     face<D>)
	cend		  returns a sentinel for the constant  iterator  of  the
     range.
	(C++23) 	   (public  member  function of std::ranges::view_inter-
     face<D>)
	operator bool	  returns whether the derived view is  not  empty.  Pro-
     vided if
	(C++20) 	  ranges::empty is applicable to it.
			  (public  member  function  of std::ranges::view_inter-
     face<D>)
	data		  gets the address of derived view's data.  Provided  if
     its iterator
	(C++20) 	  type satisfies contiguous_iterator.
			  (public  member  function  of std::ranges::view_inter-
     face<D>)
	front		  returns the first element in the  derived  view.  Pro-
     vided if it
	(C++20) 	  satisfies forward_range.
			  (public  member  function  of std::ranges::view_inter-
     face<D>)
	back		  returns the last element in the derived view. Provided
     if it
	(C++20) 	  satisfies bidirectional_range and common_range.
			  (public member  function  of	std::ranges::view_inter-
     face<D>)
	operator[]	  returns the n^th element in the derived view. Provided
     if it
	(C++20) 	  satisfies random_access_range.
			  (public  member  function  of std::ranges::view_inter-
     face<D>)

	Deduction guides

Non-member functions
	get(std::ranges::subrange)  obtains  iterator	or   sentinel	from   a
     std::ranges::subrange
	(C++20) 		   (function template)

Helper types
	ranges::subrange_kind			      specifies     whether    a
     std::ranges::subrange
	(C++20) 							  models
     std::ranges::sized_range
						  (enum)
	std::tuple_size<std::ranges::subrange>	   obtains  the number of compo-
     nents of a
	(C++20) 				  std::ranges::subrange
						  (class  template   specializa-
     tion)
	std::tuple_element<std::ranges::subrange> obtains the type of the itera-
     tor or the
	(C++20) 					sentinel       of      a
     std::ranges::subrange
						  (class  template   specializa-
     tion)

	Helper templates

	template< class I, class S, ranges::subrange_kind K >
	inline constexpr bool enable_borrowed_range<ranges::subrange<I, S, K>> =
     true;

	This specialization of std::ranges::enable_borrowed_range makes subrange
     satisfy
	borrowed_range.

Example
     // Run this code

      #include <iostream>
      #include <map>
      #include <ranges>
      #include <string_view>

      template<class V>
      void mutate(V& v)
      {
	  v += 'A' - 'a';
      }

      template<class K, class V>
      void mutate_map_values(std::multimap<K, V>& m, K k)
      {
	  auto [first, last] = m.equal_range(k);
	  for (auto& [_, v] : std::ranges::subrange(first, last))
	      mutate(v);
      }

      int main()
      {
	  auto print = [](std::string_view rem, auto const& mm)
	  {
	      std::cout << rem << "{ ";
	      for (const auto& [k, v] : mm)
		  std::cout << '{' << k << ",'" << v << "'} ";
	      std::cout << "}\n";
	  };

	  std::multimap<int,   char>   mm{{4,'a'},  {3,'-'},  {4,'b'},	{5,'-'},
     {4,'c'}};
	  print("Before: ", mm);
	  mutate_map_values(mm, 4);
	  print("After:  ", mm);
      }

Output:
      Before: { {3,'-'} {4,'a'} {4,'b'} {4,'c'} {5,'-'} }
      After:  { {3,'-'} {4,'A'} {4,'B'} {4,'C'} {5,'-'} }

See also
	ranges::view_interface helper class template for defining a view,  using
     the
	(C++20) 	       curiously recurring template pattern
			       (class template)

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