Trip report: Autumn ISO C++ standards meeting (Belfast)

A few minutes ago, the ISO C++ committee completed its autumn meeting in Belfast, Northern Ireland, hosted with thanks by clearpool.io, Archer-Yates, Microsoft, C++ Alliance, MCS Group, Instil, and the Standard C++ Foundation. As usual, we met for six days Monday through Saturday, and we had about 200 attendees. We now have 23 active subgroups, most of which met in nine parallel tracks all week long; some groups ran all week, and others ran for a few days or a part of a day, depending on their workloads.

See also the Reddit trip report, which was collaboratively edited by many committee members and has lots of excellent detail. You can find a brief summary of ISO procedures here.

C++20 is on schedule to be finalized in February

Per our official
C++20 schedule, at our previous meeting in July
we reached feature-freeze for C++20 and sent out the C++20 draft for its
international comment ballot (Committee Draft, or CD) which ran over the summer
and generated 378 comments from national bodies.

At this meeting and the next one (February in Prague), our main job was to work through these comments as well as other fit-and-finish work for C++20. To make sure we were in good shape to finish in Prague, our goal was to make sure we resolved at least half the national body comments at this meeting. Thanks to a lot of hard work across all the subgroups, and especially the subgroup chairs who leveraged our ability to do work in parallel in our nine tracks and domain-specific subgroups, this week we resolved 73% of the national body comments, and made good progress on most of the rest. Here’s a snapshot of national body comment status, breaking out the number that we were able to close even before the end of the week, and the number of CWG (core language) and LWG (standard library) comments whose final resolutions we adopted today:

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This means we are
in good shape to ship the final text of the C++20 standard at high quality and on
time, at the end of the next meeting in February in Prague.

Because we are in
feature freeze for C++20, no new major proposals were added into C++20 at this
meeting, though we did adopt a few minor design fixes. Most of the changes made
at this meeting were bug-fix level improvements, mostly to the “wording implementation
details” to make sure features were specified correctly and clearly in the
formal specification wording to implement the approved design.

Other progress

In addition to C++20 work, we also had time to make progress
on a number of post-C++20 proposals, including:

the new SG21 (Contracts) study group’s
first meeting;the newly reopened SG4 (Networking) study
group including an evening session on networking security;an evening session on executors;further progress on reflection and compile-time
programming proposals;progress on pattern matching in the main language
evolution design group;and much more.

Thank you again to the approximately 200 experts who
attended this meeting, and the many more who participate in standardization
through their national bodies! Our next step is to finish the final text of C++20
three months from now in February (Prague, Czech Republic) and then send final
C++20 out for its approval ballot.