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 advanced 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_interface<D>)
   cend returns a sentinel for the constant iterator of the range.
   (C++23) (public member function of std::ranges::view_interface<D>)
   operator bool returns whether the derived view is not empty. Provided if
   (C++20) ranges::empty is applicable to it.
                     (public member function of std::ranges::view_interface<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_interface<D>)
   front returns the first element in the derived view. Provided if it
   (C++20) satisfies forward_range.
                     (public member function of std::ranges::view_interface<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_interface<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_interface<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 components of a
   (C++20) std::ranges::subrange
                        (class template specialization)
   std::tuple_element<std::ranges::subrange> obtains the type of the iterator or the
   (C++20) sentinel of a std::ranges::subrange
                        (class template specialization)
   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)