Defined in header <ranges>
template< class T >
concept constant_range = 
  ranges::input_range<T> &&
(1) (since C++23)
Helper concepts
template< class T >
concept /*constant-iterator*/ = 
  std::input_iterator<T> &&
  std::same_as<std::iter_const_reference_t<T>, std::iter_reference_t<T>>;
(2) (since C++23)
1) The constant_range concept is a refinement of range for which ranges::begin returns a constant iterator.
2) The exposition-only concept /*constant-iterator*/<T> is satisfied when the result of the indirection operation of the input iterator is its const reference type which implies read-only.


#include <ranges>
#include <vector>
#include <string_view>
#include <span>
int main()
    static_assert(not std::ranges::constant_range<std::vector<int>>
              and std::ranges::constant_range<const std::vector<int>>
              and std::ranges::constant_range<std::string_view>
              and not std::ranges::constant_range<std::span<int>>
              and not std::ranges::constant_range<const std::span<int>>
              and std::ranges::constant_range<std::span<const int>>);

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