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Re: [SG16-Unicode] [isocpp-core] Fwd: New Core Issue: [lex.name]/3.2 under-specifies "uppercase letter"

From: Richard Smith <richardsmith_at_[hidden]>
Date: Mon, 28 Oct 2019 09:58:23 -0700
On Mon, Oct 28, 2019 at 9:39 AM Mathias Stearn via Core <
core_at_[hidden]> wrote:

> Is it just uppercase letters in the basic source character set, or
> anything considered an uppercase letter in the universal character set
> after phase 1 transcoding and universal-character-name resolution? Or is
> there some other definition of uppercase?

My interpretation:

* We don't resolve universal-character-names; rather, we *form* them. (Eg,
int façade; is converted into int fa\u00e7ade;) So for example _Ç becomes
_\u00c7, which doesn't start with an underscore followed by an uppercase
letter (it's an underscore followed by a slash).
* Unicode (to which we have a normative reference) defines uppercase, and
we follow that, but we happen to only ever apply it to the basic source
character set because of the above rewriting.

> I have a slight preference for restricting to just A-Z so that it doesn't
> require humans or tools to consult the unicode data tables to decide if an
> identifier is safe to use.

Regardless of how we express the rule, I agree with this direction.

Proposed resolution:
> Replace [lex.names]/3.2 with:
> Each identifier that contains a double underscore __ or begins with an
> underscore followed by an uppercase <del>letter</del><ins>*nondigit*</ins>
> is reserved to the implementation for any use.

... and I think this is a fine wording improvement, whether or not we think
it's formally necessary.

> Alternatively we could either create a new grammar production for
> uppercase *nondigit*s, or just say something like "one of the universal
> characters in the range 0041-005A (A-Z)"
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Received on 2019-10-28 17:58:37