On 2019-08-08 16:59, ph10 wrote:
On Sat, 3 Aug 2019, ND via Pcre-dev wrote:
May be it can be useful to have ability to set a limits of lookbehind
search
> for performance reasons.
> I can imagine a rule: If nonfixedlength lookbehind immediately
preceded by
> capture group, then it is restricted to start position of this group.
Non-fixed-length lookbehinds are almost certainly never going to be
implemented with the current PCRE2 design. It was originally inventedfor
Perl-4 patterns and is very much left-to-right oriented. Note thatwhen
Perl-5 invented lookarounds, they also restricted lookbehinds tofixed
length, and I presume Perl implements them in the same way: moveback a
fixed number of characters, then run the lookbehind forwards.
Nonfixedlength lookbehinds are implemented in some regex engines. And at
least one of them (alternative Python regex engine) successfully implement
it in left-to-right manner.
I'm sorry. But all previous posts in this topic are a suggestions how
actually nonfixedlength lookbehinds can be implemented in CURRENT PCRE
design.
What can you say about this suggestions?
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