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Postings from February 2009
Citeren David Nicol <davidnicol@gmail.com>:
> Does the following qualify as a "sane" workaround? It is still
> clearly inferior to the limit going away.
>
>
> $ perl -lwe '$a="xyzt"x10000; utf8::upgrade($a);print $a =~
> /\A(?>[a-z])*\z/ ? "ok" : "bug"'
> bug
It doesn't look like a sane regex to me...
Why use (?>[a-z])* ? Is it any different than ([a-z])* ?
Or did you mean to write (?>[a-z]*) ?
>
> $ perl -lwe '$a="xyzt"x10000; utf8::upgrade($a);print $a =~
> /\A(?>(?>[a-z])*)*\z/ ? "ok" : "bug"'
> ok
In a small regex/a smaller string this might be a work around but if
the re becomes bigger and bigger then it can seriously slow the re
down (in case of a non successful match).
Some counts:
First re:
$ perl -wle '$a="xyzt"x5000; utf8::upgrade($a);$a =~ /\A(?>[a-z])*(?{
$count++})(?!)/;print $count;'
20001
=> 20001 different combinations were tried (lots of backtracking)
(modified first re)
$ perl -wle '$a="xyzt"x5000; utf8::upgrade($a);$a =~ /\A(?>[a-z]*)(?{
$count++})(?!)/;print $count;'
1
=> Only 1 combination tried (good)
Second re:
$ perl -wle '$a="xyzt"x5000; utf8::upgrade($a);$a =~
/\A(?>(?>[a-z])*)*(?{ $count++})(?!)/;print $count;'
3
While this may look sane see what happens when we increase the length
of the string:
$ perl -wle '$a="xyzt"x5_000_000; utf8::upgrade($a);$a =~
/\A(?>(?>[a-z])*)*(?{ $count++})(?!)/;print $count;'
613
Modified re:
$ perl -wle '$a="xyzt"x5_000_000; utf8::upgrade($a);$a =~
/\A(?>(?>[a-z]*)*)(?{ $count++})(?!)/;print $count;'
1
Kind regards,
Bram
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