2021-08-31 Library Evolution Telecon

P2418R0: Add support for std::generator-like types to std::format

2021-08-31 Library Evolution Telecon Minutes

Chair: Inbal Levi

Champion: Victor Zverovich

Minute Taker: Ben Craig

Summary

The paper proposes a fix to std::format, which will allow formatting a wider range of facilities (and will align std::format with {fmt}'s current behavior)

The topic of accepting this as a DR to C++20 was broadly discussed (and in particular, with the affected parties), as well as the consequences for not doing so.

The general notion was in favor of having the proposed fix as a DR to C++20 (as well as ship it to C++23)

POLL: Send P2418R0 (Adding support for std::generator to std::format) to LWG for C++23 and as a DR for C++20, treated as an urgent matter.

Neutral: Concerned with format implementation. Not pleased with retroactive changes (But don't want to give off the impression that it will be vetoed)

Attendance: 22

# of Authors: 1

Author Position: SF

Outcome: Consensus in favor

Outcome

Taking library implementers' request to finalize C++20's API & ABI under consideration, the paper will be voted on in a special library evolution electronic poll (starting on the 2021-09-10).

LWG reviewed this change on 2021-09-17 and requested updates. Updated review scheduled for 2021-09-24.

https://wiki.edg.com/bin/view/Wg21telecons2021/P2418-20210917

P2418R1 Add support for std::generator-like types to std::format (Victor Zverovich)

LWG reviewed and approved for C++20 as DR and C++23 in telecom on 2021-09-24 pending completion of electronic polling.

https://wiki.edg.com/bin/view/Wg21telecons2021/P2418-20210924

poll: put P2418r2 into C++23 as a DR against C++20 assuming LEWG approval

2021 September Library Evolution Polls

P2451: 2021 September Library Evolution Poll Outcomes

Poll 1: Send P2418R0 (Add Support For std::generator-like Types To std::format) to Library Working Group for C++23, classified as an improvement of an existing feature (P0592R4 bucket 2 item), with the recommendation that implementations retroactively apply it to C++20.

Outcome: Consensus in favor.

Selected Comments

This fixes cooperation between major C++20 features (ranges and format). Without out, some ranges will be inherently not printable.

— Strongly Favor

Without this change it will be impossible to format std::generator and other types that are neither const-iterable nor copyable.

— Strongly Favor

An improvement, but yet another one that is not really suitable for a DR at this stage.

— Weakly Favor

I'll all for fixes to C++20 (and I think this is one). In my mind, C++20 isn't set in stone until C++23 is close to release.

Also, I am quite fine to throw bitfields under the bus. Always.

— Weakly Favor

I support the general direction of the paper, but I think it's too late for us to continue retroactively changing C++20. I would prefer we instead make a breaking change in C++23. We need to have clear deadlines and releases, but we shouldn't be afraid to fix our mistakes. The more changes we make to C++20, the slower C++20 adoption will be.

— Weakly Against

P2418R2 Add support for std::generator-like types to std::format (Victor Zverovich)

Adopted 2021-10.