Issue 3555: {transform,elements}_view::iterator::iterator_concept

should consider const-qualification of the underlying range (original) (raw)

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3555. {transform,elements}_view::_iterator_::iterator_conceptshould consider const-qualification of the underlying range

Section: 25.7.9.3 [range.transform.iterator], 25.7.23.3 [range.elements.iterator] Status: C++23 Submitter: Tim Song Opened: 2021-05-23 Last modified: 2023-11-22

Priority: Not Prioritized

View all other issues in [range.transform.iterator].

View all issues with C++23 status.

Discussion:

transform_view::_iterator<true>_::iterator_concept andelements_view::_iterator<true>_::iterator_concept (i.e., the const versions) are currently specified as looking at the properties of V(i.e., the underlying view without const), while the actual iterator operations are all correctly specified as using _Base_ (which includes the const). iterator_concept should do so too.

The proposed resolution has been implemented and tested on top of libstdc++.

[2021-05-26; Reflector poll]

Set status to Tentatively Ready after six votes in favour during reflector poll.

[2021-06-07 Approved at June 2021 virtual plenary. Status changed: Voting → WP.]

Proposed resolution:

This wording is relative to N4885.

1. Modify 25.7.9.3 [range.transform.iterator] as indicated:

   -1- iterator::iterator_concept is defined as follows:

   1. (1.1) — If ~~V~~_Base_ models random_access_range, theniterator_concept denotes random_access_iterator_tag.
   2. (1.2) — Otherwise, if ~~V~~_Base_ models bidirectional_range, then iterator_concept denotes bidirectional_iterator_tag.
   3. (1.3) — Otherwise, if ~~V~~_Base_ models forward_range, then iterator_concept denotes forward_iterator_tag.
   4. (1.4) — Otherwise, iterator_concept denotes input_iterator_tag.

2. Modify 25.7.23.3 [range.elements.iterator] as indicated:

   -1- The member typedef-name iterator_concept is defined as follows:

   1. (1.1) — If ~~V~~_Base_ models random_access_range, theniterator_concept denotes random_access_iterator_tag.
   2. (1.2) — Otherwise, if ~~V~~_Base_ models bidirectional_range, then iterator_concept denotes bidirectional_iterator_tag.
   3. (1.3) — Otherwise, if ~~V~~_Base_ models forward_range, then iterator_concept denotes forward_iterator_tag.
   4. (1.4) — Otherwise, iterator_concept denotes input_iterator_tag.