On Sat, Sep 10, 2022 at 3:47 PM Tom Honermann via SG16 <
sg16_at_[hidden]> wrote:

> SG16 will hold a telecon on Wednesday, September 14th, at 19:30 UTC (timezone
> conversion
> <https://www.timeanddate.com/worldclock/converter.html?iso=20220914T193000&p1=1440&p2=tz_pdt&p3=tz_mdt&p4=tz_cdt&p5=tz_edt&p6=tz_cest>
> ).
>
> The agenda is:
>
> - Report on the on-going interactions between WG21 and the Unicode
> Consortium.
> - Report on the backward compatibility impact of P1949 (C++ Identifier
> Syntax using Unicode Standard Annex 31) <https://wg21.link/p1949>.
> - Continued discussion of P2626R0: charN_t incremental adoption:
> Casting pointers of UTF character types <https://wg21.link/p2626r0>.
>
> SG16 has previously engaged with the Unicode Message Format Working Group
> (MFWG) <https://github.com/unicode-org/message-format-wg> (in our March
> 11th, 2020 telecon
> <https://github.com/sg16-unicode/sg16-meetings/blob/master/README-2020.md#march-11th-2020>)
> and the Unicode Source Code Ad Hoc Group (SCAHG) (in our May 25th, 2022
> telecon <https://github.com/sg16-unicode/sg16-meetings#may-25th-2022>
> with Robin Leroy). Peter and Tom have continued engaging with these groups.
> Tom will report on their activities (Peter is not expected to be available
> for this meeting).
>
> Implementation of P1949 in Clang (as a DR unconditionally applied to older
> language modes) prompted some users to report substantial impact to
> projects that previously enjoyed use of mathematical symbols in
> identifiers. Tom will report on some specifics of the impact, discussion
> between Clang implementors, and on-going work by the SCAHG that may provide
> a solution in the future. Further discussion should focus on guidance that
> we may want to offer to implementors.
>
To clarify, it impacted substantially a very small number of users.
The DR status is somewhat beside the point as these users have communicated
that it is not desirable for them to be stuck on C++20 forever.


> Pending Corentin's availability, we'll continue discussion of P2626R0 from
> our August 24th, 2022 telecon
> <https://github.com/sg16-unicode/sg16-meetings#august-24th-2022>.
>
I do believe there are core level concerns to be resolved, the main ones
being

* Can we specify that destroying a range of charX through a pointer of
range of charY is well defined - as we have established that the interface
is not usable in common cases if there needs to be a restoring conversion
prior to destruction. This is the main issue
* Can we control the effect on parent objects (it would be reasonable that
any access to an object be undefined while one of the subobjects is casted
to a different type, but once the cast is reverted, the object needs to be
usable again).





> Tom.
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