It appears that the combination of repetition, alternation and captures can cause the captures to "leak".

Seen on 5.10 and 5.8: 
use strict;
#use warnings;  #printing lots of undefs

print "Enter your test strings:\n";
while (<main::DATA>)
{
    chomp;
    print "\tTesting '$_':\n";
    /^(?:(?:(\d+)\s*c\s*)|(?:(\d+)\s*w\s*)|(?:(\d+)\s*r\s*))+/i;
    print "Capturing \\d+ only:             1='$1', 2='$2', 3='$3'\n";
        /^(?:(?:(\d+\s*c)\s*)|(?:(\d+\s*w)\s*)|(?:(\d+\s*r)\s*))+/i;
    print "Capturing \\d+ plus the letter:  1='$1', 2='$2', 3='$3'\n";
}

__DATA__
1c
2w
2c3w
1w1w
1w2r
2r1c

[download]

Note that the only difference in the regexes is the placement of the capture's closing bracket.

The above prints: 
Enter your test strings:
        Testing '1c':
Capturing \d+ only:             1='1', 2='', 3=''
Capturing \d+ plus the letter:  1='1c', 2='', 3=''
        Testing '2w':
Capturing \d+ only:             1='', 2='2', 3=''
Capturing \d+ plus the letter:  1='', 2='2w', 3=''
        Testing '2c3w':
Capturing \d+ only:             1='3', 2='3', 3=''
Capturing \d+ plus the letter:  1='2c', 2='3w', 3=''
        Testing '1w1w':
Capturing \d+ only:             1='1', 2='1', 3=''
Capturing \d+ plus the letter:  1='', 2='1w', 3=''
        Testing '1w2r':
Capturing \d+ only:             1='2', 2='2', 3='2'
Capturing \d+ plus the letter:  1='', 2='1w', 3='2r'
        Testing '2r1c':
Capturing \d+ only:             1='1', 2='', 3='2'
Capturing \d+ plus the letter:  1='1c', 2='', 3='2r'

[download]

The second regex does what I expect. I can't fathom why the first regex would do what it does, however. I expected it would be the same as the second regex, minus the letters. Instead, after the first repetition, it seems that a match for $2 spills a copy into $1, and a match for $3 spills copies into $2 and $1... but only if the captures contain the same regex pattern (\d+ in this case).

Would I be correct to suspect that this is a bug or mis-optimization of some kind in perl?

The monks can fry your fish, and they can give you some tips and some bait, but you still need to wake up in the morning and climb onto the boat.

In reply to Leaking Regex Captures by SuicideJunkie

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