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Re: [SG16] SG16 meeting summary for March 24th, 2021

From: Corentin Jabot <corentinjabot_at_[hidden]>
Date: Sun, 28 Mar 2021 23:24:42 +0200
On Sun, Mar 28, 2021 at 11:13 PM Corentin Jabot <corentinjabot_at_[hidden]>

> On Sun, Mar 28, 2021 at 11:01 PM Jens Maurer <Jens.Maurer_at_[hidden]> wrote:
>> On 28/03/2021 22.56, Alisdair Meredith wrote:
>> > Thanks - that was exactly my thoughts, and I missed it when Corentin
>> tried to correct me. All clear now, although is the reference to Raw
>> string literals still useful, or more likely to lead to folks like me mid
>> reading too quickly, and getting confused?
>> >
>> > I believe there would be no cha he of behavior if we strike the
>> “except” that can no longer occur.
>> No. If we strike the "except", we give the impression that a spliced
>> character
>> sequence in a raw string literal that looks like a UCN is somehow special,
>> and would cause undefined behavior. It doesn't.
> We should strike
> > if a splice results in a character sequence that matches the syntax of a
> *universal-character-name*
> <http://eel.is/c++draft/lex#nt:universal-character-name>, the behavior is
> undefined.
> Both because it matches existing practices (except msvc) and because it
> follows the flow of the wording. (ucn are replaced in the next phase)
> What should happen when a ucn is formed by a preprocessor in phase 4 is
> less clear to me.
> Given that no compiler do the right thing, it would be sensible that it
> would be ill-formed https://godbolt.org/z/of4W9dG8h
> > If a ' or a " character matches the last category, the behavior is
> undefined
> That should be ill-formed, which is what all compilers do. I suspect this
> specific undefined behavior is an artifact of C wording

Ultimately, I hope SG-16 can decide when UCNs are formed, and I hope we can
all also agree that ill-formed / implementation-defined are the only
reasonable tools we should use during lexing
(I will gladly let someone else deal with [cpp] though :D)

>> (Note that it says "that matches the syntax". Although UCNs are never
>> formed in raw string literals, the phrasing could be read to actually
>> care for UCNs in raw string literals. Not good.)
>> Jens

Received on 2021-03-28 16:24:54