While slimming down some code in a parser, I ran across what I thought was a good solution only to create a nasty debugging situation. Here's a code snippet: 
sub dis {
    shift =~ /.?.?(.)/;
}

[download]
With the idea of stripping off the optional first two characters and returning the last character. For instance dis('QNP') returns 'P' and so on. To my surprise, this worked---at least seemed to at first. It turns out that in some cases this works, but in others, there are strange side-effects that that leave you looking at once working code that perl now claims is defective. Lucky for me, I typically change only one thing at a time before regression testing and it was fairly easy to spot this one. Here is the patched code: 
sub dis {
    shift =~ /.?.?(.)/;
    $1;
}

[download]
The reason I labeled this node a puzzle is that I've no clue as to what was wrong or why this fixes it! So I ask the more knowledgeable out there, what is going on here?

--hsm

"Never try to teach a pig to sing...it wastes your time and it annoys the pig."

In reply to Parse Puzzle by hsmyers

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