Re: Notes about fixing regexes and UTF-8 (yet again)

On 02/17/2012 09:39 AM, Tom Lane wrote:
> Heikki Linnakangas<heikki(dot)linnakangas(at)enterprisedb(dot)com> writes:
>> Here's a wild idea: keep the class of each codepoint in a hash table.
>> Initialize it with all codepoints up to 0xFFFF. After that, whenever a
>> string contains a character that's not in the hash table yet, query the
>> class of that character, and add it to the hash table. Then recompile
>> the whole regex and restart the matching engine.
>> Recompiling is expensive, but if you cache the results for the session,
>> it would probably be acceptable.
> Dunno ... recompiling is so expensive that I can't see this being a win;
> not to mention that it would require fundamental surgery on the regex
> code.
>
> In the Tcl implementation, no codepoints above U+FFFF have any locale
> properties (alpha/digit/punct/etc), period. Personally I'd not have a
> problem imposing the same limitation, so that dealing with stuff above
> that range isn't really a consideration anyway.

up to U+FFFF is the BMP which is described as containing "characters for
almost all modern languages, and a large number of special characters."
It seems very likely to be acceptable not to bother about the locale of
code points in the supplementary planes.

See <http://en.wikipedia.org/wiki/Plane_%28Unicode%29> for descriptions
of which sets of characters are involved.

cheers

andrew