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std::ranges::subrange

From cppreference.com
< cpp‎ | ranges
 
 
 
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
>
  requires (K == ranges::subrange_kind::sized || !std::sized_sentinel_for<S, I>)

class subrange : public ranges::view_interface<subrange<I, S, K>>
(since C++20)

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 sized_sentinel_for<S, I> is satisfied or when size is passed explicitly as a constructor argument)

[edit] Helper templates

template<std::input_or_output_iterator I, std::sentinel_for<I> 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.

[edit] Example

#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 iter_pair = m.equal_range(k);
    for (auto& [_, v] : std::ranges::subrange(iter_pair.first, iter_pair.second)) {
        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,'-'} }