Title
Missing change for element_view::iterator in LWG 3798
Status
new
Section
[range.elements.iterator]
Submitter
Jiang An

Created on 2022-11-23.00:00:00 last changed yesterday

Messages

Date: 2023-01-28.12:16:49

Proposed resolution:

This wording is relative to N4928.

  1. Modify [range.elements.iterator] as indicated:

    -2- The member typedef-name iterator_category is defined if and only if Base models forward_range. In that case, iterator_category is defined as follows: Let C denote the type iterator_traits<iterator_t<Base>>::iterator_category.

    1. (2.1) — If range_reference_t<Base> is a reference type and std::get<N>(*current_) is an prvalue or neither range_reference_t<Base> nor tuple_element_t<N, range_reference_t<Base> is a reference type, iterator_category denotes input_iterator_tag.

    2. (2.2) — Otherwise, if C models derived_from<random_access_iterator_tag>, iterator_category denotes random_access_iterator_tag.

    3. (2.3) — Otherwise, iterator_category denotes C.

Date: 2023-01-15.00:00:00

[ 2023-01-22; Jiang An comments and provides improved wording ]

The old proposed resolution was incorrect. I think the correct criteria could be that determined from the return type of get-element.

Date: 2022-11-15.00:00:00

[ 2022-11-30; Reflector poll ]

Set priority to 3 after reflector poll.

"The proposed resolution is incorrect - just because the get expression is an xvalue doesn't mean operator* returns by reference."

Previous resolution [SUPERSEDED]:

This wording is relative to N4917.

  1. Modify [range.elements.iterator] as indicated:

    -2- The member typedef-name iterator_category is defined if and only if Base models forward_range. In that case, iterator_category is defined as follows: Let C denote the type iterator_traits<iterator_t<Base>>::iterator_category.

    1. (2.1) — If std::get<N>(*current_) is an prvalue, iterator_category denotes input_iterator_tag.

    2. (2.2) — Otherwise, if C models derived_from<random_access_iterator_tag>, iterator_category denotes random_access_iterator_tag.

    3. (2.3) — Otherwise, iterator_category denotes C.

Date: 2022-11-23.00:00:00

In LWG 3798 (voted into WP in November 2022), iterator types of several range adaptors may have forward_iterator_tag or stronger iterator tag types as their iterator_category type when their operator* returns rvalue references. However, the proposed resolution missed the similar change for element_view::iterator.

History
Date User Action Args
2023-01-28 12:16:49adminsetmessages: + msg13217
2022-11-30 10:08:16adminsetmessages: + msg13128
2022-11-26 12:42:02adminsetmessages: + msg13116
2022-11-23 00:00:00admincreate