That much is obvious - that inside of (?{}) there is a pos() value which can be manipulated. Now is $_ a copy of the bound string or is it the actual string. See... if $_ is the actual string then stomping on pos() should work. Hmm... maybe I just answered my own question. Maybe instead of aliasing $_ which is what I thought was happening it's copying it instead.

No wait... I included a code fragment that shows that $_ is aliased to $str and that $str's pos value is being altered inside the (?{}). It looks like the regex engine is replacing the pos() value with a saved copy. So again - do you know a way to keep the regex engine from copying pos() back into place?

use Devel::Peek;
$str = 'a string';
print 'x' x 50, "\n";
Dump($str);
$str =~ m/(?:.(?{Dump($_);Dump(pos());pos()+=3;
                 Dump($_);Dump(pos())}))/g;
print STDERR "OUT\n";
Dump($str);

[download]
__SIG__
use B;
printf "You are here %08x\n", unpack "L!", unpack "P4", pack
  "L!", B::svref_2object(sub{})->OUTSIDE;

[download]

In reply to Re^2: immutable pos() inside regex by diotalevi
in thread immutable pos() inside regex by diotalevi

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