3725. reverse_iterator::operator-> should not use prev for non-pointer iterators

Section: [reverse.iter.elem] Status: New Submitter: Hewill Kang Opened: 2022-06-26 Last modified: 2022-07-09 11:01:30 UTC

Priority: 3

View all other issues in [reverse.iter.elem].

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When the underlying iterator is not a pointer type, reverse_iterator::operator-> returns prev(current).operator->(). However, prev only works with Cpp17BidirectionalIterator, given that C++20 bidirectional_iterator may just be Cpp17InputIterator, we shouldn't use prev here.

[2022-07-08; Reflector poll]

Set priority to 3 after reflector poll. Suggested to use ranges::prev instead.

Proposed resolution:

This wording is relative to N4910.

  1. Modify [reverse.iter.elem] as indicated:

    constexpr pointer operator->() const
      requires (is_pointer_v<Iterator> ||
                requires(const Iterator i) { i.operator->(); });

    -2- Effects:

    1. (2.1) — If Iterator is a pointer type, equivalent to: return prev(current);

    2. (2.2) — Otherwise, equivalent to: return prev(current).operator->();

      Iterator tmp = current;
      return tmp.operator->();