std::sentinel_for(3)

NAME
std::sentinel_for - std::sentinel_for

Synopsis
   Defined in header <iterator>
   template<class S, class I>
   concept sentinel_for =
   std::semiregular<S> && (since C++20)
   std::input_or_output_iterator<I> &&
   __WeaklyEqualityComparableWith<S, I>;
   The sentinel_for concept specifies the relationship between an
   input_or_output_iterator type and a semiregular type whose values denote a range.
   The exposition-only concept __WeaklyEqualityComparableWith is described in
   equality_comparable.
  Semantic requirements
   Let s and i be values of type S and I, respectively, such that [i, s) denotes a
   range. sentinel_for<S, I> is modeled only if:
     * i == s is well-defined.
     * If bool(i != s) then i is dereferenceable and [++i, s) denotes a range.
     * std::assignable_from<I&, S> is either modeled or not satisfied.
   The domain of == can change over time. Given an iterator i and sentinel s such that
   [i, s) denotes a range and i != s, [i, s) is not required to continue to denote a
   range after incrementing any iterator equal to i (and so i == s is no longer
   required to be well-defined after such an increment).

Notes
   A sentinel type and its corresponding iterator type are not required to model
   equality_comparable_with, because the sentinel type may not be comparable with
   itself, and they are not required to have a common reference type.
   It has been permitted to use a sentinel type different from the iterator type in the
   range-based for loop since C++17.
  Defect reports
   The following behavior-changing defect reports were applied retroactively to
   previously published C++ standards.
      DR Applied to Behavior as published Correct behavior
   LWG 3453 C++20 semantic requirements for sentinel_for were too strengthened
                       loose for ranges::advance