[cfe-dev] UCNs/extended characters revisitted
ned at panic.com
Sat Jul 11 13:40:16 PDT 2009
On Jul 10, 2009, at 2:01 PM, AlisdairM(public) wrote:
> i/ The extended characters must form a valid UTF-8 code point
> ii/ Not all code points in the basic character plane are valid for
> use in identifiers. While C++ might not act on punctuation in
> different alphabets, it should still not allow it in identifiers.
> (i) is easily and efficiently checked.
> (ii) requires a large database of valid/invalid code points to look
> up against - and frankly this part ought to be written by a Unicode
> specialist who can validate all the corner cases. At the moment
> that database is around 2.5Mb, although that contains more info than
> we need for simple validation of identifiers. We will still need a
> reasonable sized lookup though, ideally encoded into some kind of
> sparse bit-vector. I recommend doing this validation in parse or
> sema, and for performance simply allowing lex to pass along tokens
> without splitting on the invalid characters.
As for (ii), I assume you simply want to disallow characters having
general category P* (ie: Pd, Ps, etc.), no? The full list of such
characters for Unicode 5.1 can be found in <http://www.unicode.org/Public/UNIDATA/extracted/DerivedGeneralCategory.txt
>. Do you want to embed data from a particular version of Unicode, or
would you rather track whatever version of Unicode is supported by the
host environment? If the former, for a simple binary test such as this
you could always use a simple inversion list; if the latter, you could
either call directly into a host API to classify each character or you
could preprocess these data to avoid calling the API repeatedly. I'm
happy to assist with any of this.
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