As you can read here I like to qr// my patterns. In my case I gained nothing from it (other than not biting myself), but you'd gain a great deal by qr//:ing the @patterns. And while we're talking about qr//, I'd prefer to see a qr// object instead of an o modifier in the if expression.

The o modifier is evil and as of qr//'s introduction we no longer need it. But we'd be fine even without both qr// and the o modifier in this particular case. That is because perl is friendly enough to remember the last pattern used for every match op. If the patterns are identical (stringwise) the last compiled regex for that match op is used. Since you only use $pat once no recompilation is done.

Demonstration: 
my @patterns1 = ('foo') x 2;
my @patterns2 = ('bar') x 2;

use re 'debug';
while (@patterns1) {
    'a' =~ shift @patterns1;
    'b' =~ shift @patterns2;
}

__END__

Compiling REx `foo'
size 3 first at 1
   1: EXACT <foo>(3)
   3: END(0)
anchored `foo' at 0 (checking anchored isall) minlen 3
Compiling REx `bar'
size 3 first at 1
   1: EXACT <bar>(3)
   3: END(0)
anchored `bar' at 0 (checking anchored isall) minlen 3
Freeing REx: `foo'
Freeing REx: `bar'

[download]
As you can see, the foo pattern and the bar pattern are only compiled once. But there's no harm in using qr// here, so I still suggest it.

Cheers,
-Anomo

In reply to Re: Re: Re: First Pattern Matching by Anonymous Monk
in thread First Pattern Matching by artist

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