Issue 3432: Missing requirement for comparison_category

Title: Missing requirement for comparison_category
Status: c++23
Section: [string.view.comparison]
Submitter: Jonathan Wakely

Created on 2020-04-19.00:00:00 last changed 5 months ago

Messages

msg11547 (view)

Date: 2020-11-09.20:31:48

Proposed resolution:

This wording is relative to N4861.

Modify [string.view.comparison] by adding a new paragraph after p3:

As result of reflector discussion we decided to make a drive-by fix in p3 below.
```
template<class charT, class traits>
  constexpr see below operator<=>(basic_string_view<charT, traits> lhs,
                                  basic_string_view<charT, traits> rhs) noexcept;
```
-3- Let R denote the type traits::comparison_category if that qualified-id is valid and denotes a type ([temp.deduct])~~it exists~~, otherwise R is weak_ordering.

-?- Mandates: R denotes a comparison category type ([cmp.categories]).

-4- Returns: static_cast<R>(lhs.compare(rhs) <=> 0).

msg11392 (view)

Date: 2020-11-09.00:00:00

[ 2020-11-09 Approved In November virtual meeting. Status changed: Ready → WP. ]

msg11230 (view)

Date: 2020-07-15.00:00:00

[ 2020-07-17; Moved to Ready in telecon ]

msg11229 (view)

Date: 2020-04-19.00:00:00

It's not clear what happens if a program-defined character traits type defines comparison_category as a synonym for void, or some other bogus type.

Discussion on the LWG reflector settled on making it ill-formed at the point of use.

History
Date	User	Action	Args
2023-11-22 15:47:43	admin	set	status: wp -> c++23
2020-11-09 20:31:48	admin	set	messages: + msg11547
2020-11-09 20:31:48	admin	set	status: ready -> wp
2020-07-17 22:37:26	admin	set	messages: + msg11392
2020-07-17 22:37:26	admin	set	status: new -> ready
2020-04-20 13:25:37	admin	set	messages: + msg11230
2020-04-19 00:00:00	admin	create