Author: ND Date: To: Pcre-dev Subject: Re: [pcre-dev] Remove some restrictions of lookbehind assertions
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
> > 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
What can you say about this suggestions?
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