LWG3810 CTAD for std::basic_format_args

[jwakely]

https://cplusplus.github.io/LWG/issue3810

LWG would like design guidance here. Should CTAD work? It's currently sort-of implied it should, but only if you assume that the exposition-only types and constructors are implemented exactly as shown. If the format-arg-store-type is defined as a nested type of basic_format_args (as in libstdc++) then it doesn't work.

There's an example from Tomasz in the issue showing a case where CTAD might be useful, but Victor suggested we should explicitly disable CTAD here, because it makes it easier to create dangling references.

[brycelelbach]

2023-01-10 Library Evolution Telecon

LWG3810: CTAD for basic_format_args

2023-01-10 Library Evolution Telecon Minutes

Chair: Bryce Adelstein Lelbach

Minute Taker: Ben Craig

Start: 2023-01-10 11:58 Eastern

POLL: Send the proposed resolution to LWG3810 (CTAD for basic_format_args) to Library for C++23, to be confirmed by a Library Evolution electronic poll.

Strongly Favor	Weakly Favor	Neutral	Weakly Against	Strongly Against
0	8	0	0	0

Attendance: 13

# of Authors: 0

Author Position: N/A

Outcome: Unanimous consensus in favor.

End: 12:01

Next Steps

Take a Library Evolution electronic poll to send the proposed resolution to LWG3810 (CTAD for basic_format_args) to Library for C++23.

[brycelelbach]

We only have two C++23 papers that need electronic polling, and both were non-controversial. I'm going to send this directly to Library.