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Re: Agenda for the 2022-07-13 SG16 telecon; no official meeting

From: Jens Maurer <Jens.Maurer_at_[hidden]>
Date: Sun, 10 Jul 2022 08:37:04 +0200
On 10/07/2022 00.03, Corentin Jabot wrote:
> On Sat, Jul 9, 2022 at 9:03 PM Jens Maurer <Jens.Maurer_at_[hidden] <mailto:Jens.Maurer_at_[hidden]>> wrote:

> Are there places other than identifiers where we can have UCNs
> outside of char/string literals? If not, maybe we should massage
> the grammar definition of _identifier_ instead of persisting
> the handwaving in lex.phases p4.
> The idea of doing it there, as we form preprocessor tokens, is that we don't want to
> int i\N{SEMICOLON} to do something (I don't think implementers would like that).

I don't understand. What does "do something" want to say?
If we specify _identifier_ to accept any well-formed UCN
and we then say that an _identifier_ containing a UCN
for a basic character is ill-formed, that would seem
to work.

> andi\N{SEMICOLON} doesn't match the grammar of an identifier, so I think an eager replacement makes sense.
> We should avoid having to carry these things around through phase 3.
> > https://isocpp.org/files/papers/P2621R0.pdf <https://isocpp.org/files/papers/P2621R0.pdf> <https://isocpp.org/files/papers/P2621R0.pdf <https://isocpp.org/files/papers/P2621R0.pdf>>
> Should this go to SG12, because it discusses undefined behavior?
> I'm hoping that removing UB from a context in which no UB can meaningfully exist doesn't require
> to visit all the groups

Nobody was suggesting "all the groups"; the suggestion was to visit the
specific group that deals with UB. I expect a rubber stamp, given the
nature of UB and the implementation consensus.

> > * Some unicode algorithms are unbounded, and may require allocation. A small_vector would help specification,
> Why would it help with the specification?
> I guess we could say "does not allocate if some variable is smaller than X" but implementers will have to have a small vector as an implementation detail so if
> people have the idea that such a thing should be standardized anyway, it's something that could be useful.

If something needs allocation for extreme cases, we already have to
deal with the consequences (e.g. throwing std::bad_alloc) in the
specification. It feels entirely an implementation-internal
optimization to avoid the allocation for some cases.
"Recommended practice" is the tool to guide implementations the
right way here. I'm still not seeing a need for small_vector
for the specification.


Received on 2022-07-10 06:37:11