Re^2: Using a capture in /(?{...})/

I spoke too soon, kinda.

pos works, but gives a weird warning when + is used:

use strict;
use warnings;

my $re0;
my $re1;

our $s_pos;

$re1 = qr/
          (?{ local $s_pos = pos; })
          [A-Z]
          (?{ print("[", substr($_, $s_pos, pos()-$s_pos), "]\n") })
       /x;

$re0 = qr/
          (?:
             (??{ $re1 })
          )+
       /x;

'abcDE' =~ $re0;

__END__
output
======
(?:
             (??{ $re1 })
          )+
        matches null string many times before HERE mark in regex m/
          (?:
             (??{ $re1 })
          )+
        << HERE / at script.pl line 19.
[D]
[E]
[download]

Same with the extra capture:

use strict;
use warnings;

my $re0;
my $re1;

$re1 = qr/
          ([A-Z])
          (?{ print("[$1]\n") })
       /x;

$re0 = qr/
          (?:
             ()
             (??{ $re1 })
          )+
       /x;

'abcDE' =~ $re0;

__END__
(?:
             ()
             (??{ $re1 })
          )+
        matches null string many times before HERE mark in regex m/
          (?:
             ()
             (??{ $re1 })
          )+
        << HERE / at script.pl line 17.
[D]
[E]
[download]

However, the warning seems to be spurious. The warning check is using a variable that's not updated, but the pos truly is changing.

Comment on Re^2: Using a capture in /(?{...})/ Select or Download Code

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Re^3: Using a capture in /(?{...})/ by japhy (Canon) on Jul 25, 2005 at 22:09 UTC
The warning comes from the fact that Perl can't tell if `(?{ ... })` matches any characters or not, so it's possible you're putting a quantifier on a zero-width assertion. Jeff `japhy` Pinyan, P.L., P.M., P.O.D, X.S.: Perl, regex, and `perl` hacker How can we ever be the sold short or the cheated, we who for every service have long ago been overpaid? ~~ Meister Eckhart	[reply] [d/l]
Re^4: Using a capture in /(?{...})/ by ikegami (Patriarch) on Jul 26, 2005 at 00:07 UTC
You mean `(??{ ... })`. (`(?{ ... })` is always zero-width.) Ok, the warning makes sense. There are (at least) two ways of hidding it: 1) Use `no warnings 'regexp'`, or 2) refactor the regexp to hide that particular instance of the warning while leaving others on. For example, `$re0 = qr/ (??{ $re1 })* /x;` [download] can be written as: `$re0 = qr/ (??{ $re1 }) (??{ $re0 }) \| # Nothing /x;` [download] and `$re0 = qr/ (??{ $re1 })+ /x;` [download] can be written as: `$re0 = qr/ (??{ $re1 }) (??{ $re0_ }) /x; $re0_ = qr/ (??{ $re1 }) (??{ $re0_ }) \| # Nothing /x;` [download] and `$re0 = qr/ (??{ $re1 })? /x;` [download] can be written as: `$re0 = qr/ (??{ $re1 }) \| # Nothing /x;` [download]	[reply] [d/l] [select]