Gcc also already has a warning for identifiers not in NFC, so there is an
existence proof that at least one vendor did not find the cost to be
burdensome.

On Thu, Apr 9, 2020, 04:20 Corentin Jabot via SG16 <sg16_at_[hidden]>
wrote:

>
>
> On Thu, 9 Apr 2020 at 08:15, Jens Maurer via SG16 <sg16_at_[hidden]>
> wrote:
>
>>
>> See attached.
>>
>> Note that a universal-character-name never
>> represents a member of the basic source
>> character set, so we don't have to call out
>> underscores specifically.
>>
>> This makes any sequence involving a universal-character-name
>> a pp-identifier (and thus a preprocessing-token), so that
>>
>> #define accent(x) x ## \u0300
>>
>> does the right thing.
>>
>> Did someone check that UAX #31 really is part of ISO 10646?
>> There should be a cross-reference to the Annex somewhere in [lex.name].
>>
>> Further concerns:
>>
>> We have a generic reference to ISO 10646 in the front matter
>> of the standard. That means the most recent version applies,
>> implicitly. That's a bit of a moving target, though: Does
>> an implementation lose conformance if a new version of ISO 10646
>> is issued (because more characters are allowed in identifiers in
>> later versions, maybe)?
>>
>> Should we maybe require an implementation to document which
>> revision of ISO 10646 was used for XID_Start and XID_Continue?
>> This way, programmers can at least find out about a
>> portability pitfall.
>>
>
>
> C++23 programs should remain portable across compilers, therefore, in
> this case, it seems
> necessary to specify a specific version, (and compilers can support newer
> versions as an extensions)
>
>
>> The paper should spend a section on explaining how expensive
>> (code size; maybe performance) a check for NFC is for the compiler.
>> Does the compiler need the entire Unicode tables, or are there
>> shortcuts (e.g. a few ranges of "bad" code points)?
>>
>
> I think both Zach and me should be able to provide data for that
>
>
>>
>> Jens
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