Re^4: Bug with finding all regexp matches

[Anonymous Monk]

I opened a bug on this, https://rt.perl.org/Ticket/Display.html?id=129886 .

[dave_the_m]

This isn't a bug, it's intended behaviour :-). The superlinear cache kicks in for various types of complex/nested quantifiers (such as (z?)+) to avoid heat-death-of-the-universe time to find failure. It records pattern/string position combos where a match failed, and if it comes across the same combo again it stops and backtracks immediately at that point rather than continuing with the rest of the pattern (which will inevitably fail later).

See the very first paragraph in perlre.pod about re_evals:

B<WARNING>: Using this feature safely requires that you understand its limitations. Code executed that has side effects may not perform identically from version to version due to the effect of future optimisations in the regex engine. For more information on this, see L</Embedded Code Execution Frequency>

Where that link goes to: Embedded Code Execution Frequency

Dave.

[Anonymous Monk]

This isn't a bug, it's intended behaviour :-)

Hmm, I see your point but AFAIU (*FAIL) itself doesn't add to regexp complexity and could be exempted from caching to allow (${ eval })(*FAIL) pattern to work as the doc itself suggests in other place. Still, my bug report landed next to others that are 4 years old, and given your comment I see where it will go...

So, is there a way in Perl to find all regexp matches?

[dave_the_m]

(*FAIL) itself doesn't add to regexp complexity and could be exempted from caching

Well it could (if at the top-level of a pattern), but that doesn't solve the issue - there are other regex optimisations (currrent or future) apart from the superlinear cache, any of which could potentially cause a match to "prematurely" fail.

So, is there a way in Perl to find all regexp matches?

I don't know, but I doubt it could be done reliably,

Dave.