EWG in Kona

CWG in Cologne: Needs updates.

Reviewed in CWG telecon 2022-01-27: Needs revision.

Advised authors of C++23 timeline and urged them to produce an update.

This has missed C++23.

R3 which was never uploaded in the paper system seems to be there https://wiki.edg.com/pub/Wg21cologne2019/CoreWorkingGroup/d1306r3.pdf

"Removed the ability to expand over parameter packs" seems to be a design change.

Assigning to EWG to confirm.

The history of this paper is a bit tangled, but as far as I can tell:

R3 which was never uploaded in the paper system seems to be there https://wiki.edg.com/pub/Wg21cologne2019/CoreWorkingGroup/d1306r3.pdf

^ This is not the most up-to-date revision of the paper. For anybody that might want to pick this up, the history seems to be:

• R1 revision was reviewed by EWG in Kona 2019. EWG voted to forward to Core.
• CWG reviewed in Cologne 2019. A sequence of two further revisions were reviewed by Core: R2, R3. The R3 cited above by Corentin is this R3 revision.
• Work on the paper stopped until it was picked back up in 2022. A different R2 revision was then reviewed by CWG during the 2022-01-27 telecon. This seems to have been the last revision reviewed by CWG.
• As noted by the telecon notes, this Google Doc contains the most up-to-date revision of the paper, including changes that have not been reviewed by CWG (e.g., adoption of P2320-style reflection syntax).

Through these revisions, the "Revision Notes" do not seem to have been always kept up-to-date. In particular,

"Removed the ability to expand over parameter packs"

^ This note was added in the 2019 R2 revision from Cologne, but CWG continued to review revisions thereafter.

I hadn't noticed this before, but it looks like the decision to remove parameter pack support was discussed and approved in Cologne 2019, before the paper went to CWG.
https://wiki.edg.com/bin/view/Wg21cologne2019/D1306R2-EWG

@jensmaurer As far as I can tell, no significant design changes have taken place since EWG last approved the proposal. I think the next revision (which I'm partnering with the authors to help with) should be reviewed by Core.

Once the next revision is actually available, @jfbastien can determine that no EWG-relevant changes have actually occurred and can forward directly to CWG. (Having a confusing R2 vs. R3 revision history is not helpful.)

@katzdm is correct: Te decision to drop pack support was already approved by EWG during the C++20 cycle.

@jensmaurer As far as I can tell, no significant design changes have taken place since EWG last approved the proposal. I think the next revision (which I'm partnering with the authors to help with) should be reviewed by Core.

As a quick update, we've now submitted a new revision for the upcoming May mailing. Note that we've taken the opportunity to extend the scope of the proposal by re-introducing support for expansion over parameter packs (with a now hopefully unambiguous syntax), so we welcome and look forward to the further review from EWG.

P1306R2 Expansion statements (Dan Katz, Andrew Sutton, Sam Goodrick, Daveed Vandevoorde)

P1306R3 Expansion statements (Dan Katz, Andrew Sutton, Sam Goodrick, Daveed Vandevoorde)

Seen in EWG in Hagenberg on Friday:

Poll: P1306r3 Expansion statements: forward to CWG for inclusion in C++26.

Consensus in favor.