LWG Chair post-meeting report

Overview

This is meant to be an ongoing paper, with a series of reports, capturing the information provided by the LWG chair during the plenary session at the previous meeting.

R2: Batavia, August 20-24, 2014

General

In August, LWG met in Batavia, IL to try to reduce the backlog of work that was facing us for C++20. There were about 18 people in attendance.

Since this was not an official WG21 meeting, we could not approve any motions for incorporation into C++20. However, we approved a bunch of papers (and issues) to be put on the motions page in San Diego.

Notable Accomplishments

We reviewed a large chunk of the Ranges proposal (about 150 pages of the 220 page paper). Casey will revise the paper, and we have continued the review on the reflector. (See postings titled "Paper working review: D0896").

There were two fairly large new papers at this meeting. These were both clarification/cleanup papers, rather than proposing new features, and they were both reviewed favorably. Tim Song's paper is titled "Cleaning up Clause 20". Nevin Liber's paper is titled "Explicitly Implicifying explicit Constructors".

Tentatively Approved for C++20 (to be moved in San Diego)

• Many issues (see P1224 in the pre-meeting mailing)
• P0487 - Fixing operator>> (basic_istream&, CharT*) (LWG 2499)
• P0602 - variant and optional should propagate copy/move triviality
• P0655 - visit<R>: Explicit Return Type for visit
• P0972 - <chrono> zero(), min(), and max() should be noexcept
• P1004 - Making std::vector constexpr
• P1006 - Constexpr in std::pointer_traits
• P1032 - Misc constexpr bits
• D1148 - Cleaning up Clause 20
• D1163 - Explicitly Implicifying explicit Constructors

Discussed, but did not approve

• P0052 - Generic Scope Guard and RAII Wrapper for the Standard Library
• P0290 - apply() for synchronized_value<T>
• P0318 - unwrap_ref_decay and unwrap_reference
• P0407 - Efficient Access to basic_stringbuf’s Buffer (now combined with P0407)
• P0429 - Standard flat_map
• P0466 - Layout-compatibility and Pointer-interconvertibility Traits
• P0553 - Bit operations (needs a bit of LEWG review)
• P0608 - A sane variant converting constructor
• P0790 - Effect of operator<=> on the C++ Standard Library
• P0881 - A Proposal to add stack trace library
• P0883 - Fixing Atomic Initialization, Rev1
• P1007 - std::assume_aligned

R1: Rapperswil, June 6-11, 2018

General

LWG (again) entered the week with a large backlog of papers; somewhere around 55. We have dealt with more papers than we accumulated this week, but we still have a large backlog. We reviewed 39 papers, adopting 26 of them. (Five of those are being moved by CWG).

To deal with this backlog of work, we will be holding an additional, LWG-only meeting in Battavia, IL the week of August 20-24. Thanks to Walter Brown for organizing this.

Notable Accomplishments

• The Parallelism TS 2 is now ready for publishing.
• The Reflection TS is now ready for PDTS balloting, after adding the contents of P0670R4 (Function Reflection).
• We are moving the paper "Concepts for the Standard Library".
• We are moving "Atomic Ref".
• Moar Constexpr (array, algorithms)
• We removed a bunch of deprecated features from the standard library.
• We adopted a pair of papers that improve the interface of the standard containers.
• We have 15 issue resolutions to propose as well.

Discussed, but did not move

• P0009 - mdspan
• P0805 - Comparing Containers
• P0811 - Well-behaved interpolation for numbers and pointers
• P0942 - Introducing a <smart_ptr> header

R0: Jacksonville, March 6-11, 2018

General

LWG entered the week with a large backlog of papers; somewhere around 55. We may have exited the week with a larger backlog than we started, since other groups have sent us many papers during the week. Our throughput was limited this week because we spent the first two days of the meeting on two (very large) papers; P0214 (Data-parallelism) and P0355 (calendar support). Fortunately, we completed our review, the authors turned the changes around, and we moved both of them.

Notable Accomplishments

• The Parallelism TS 2 is now ready for PDTS balloting, after adding the contents of P0214.
• The Reflection TS has been created, and initial content has been added.
• The Library Fundamentals 3 TS has been created, with all the parts of LFTS 2 that weren't added into C++17. More will be added here in future meetings.
• We added calendar and time zone support into <chrono> for C++20.
• We added <span> to C++20.
• We added <version> to C++20; a place to put implementation-specific configuration and versioning.
• We have added "Moar constexpr" to the standard library.
• Some issue processing was done

Discussed, but did not move

• expected<T>
• polymorphic_value

Future work

In plenary, I asked for a show of hands for people who would be willing to attend an extra "LWG-only" weeklong session in the late summer. About 14 people raised their hands. Assuming that we can find a venue (and a sufficient number commit to attend), we will have an extra meeting this summer.

We have been processing issues on the reflector; mostly with prioritization, but more and more, we're trying to solve them there. I expect this to continue. Of course, all resolutions will be proposed and voted on in formal meetings.