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Re^3: Perl Complains of Nested Quantifiers

by AnomalousMonk (Canon)
on May 22, 2012 at 23:14 UTC ( #971908=note: print w/ replies, xml ) Need Help??

in reply to Re^2: Perl Complains of Nested Quantifiers
in thread Perl Complains of Nested Quantifiers

A concern was expressed about "catastrophic backtracking." I'm curious about ... whether your solution would satisfactorily avert it.

It would not. AFAIU, possessive quantifiers like  ++ *+ ?+ {n,m}+ are just special, limited cases of the general  (?>...) atomic grouping. See example below.

>perl -wMstrict -le "my $s = 'foobazbazbaz foobazbazbaz'; print 'match 1' if $s =~ m{ foo (?> (?:baz)+) baz }xms; print 'match 2' if $s =~ m{ foo (?> .* baz) baz }xms; "
(no output)

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