Actually, I tend to shy away from using qr, because they are dead slow when interpolating into larger constructs. Building large regexes from smaller parts is something I do often. Here's a benchmark showing a dramatic difference:

#!/usr/bin/perl

use strict;
use warnings;

use Benchmark qw /cmpthese/;

cmpthese -2 => {
    qq  =>  'my $x = qq "[a]"; $x = qq "[a]$x" for 1 .. 100; "" =~ /$x
+/',
    qr  =>  'my $x = qr "[a]"; $x = qr "[a]$x" for 1 .. 100; "" =~ /$x
+/',
}
__END__

Benchmark: running qq, qr for at least 2 CPU seconds...
  qq:  6 wallclock secs ( 2.11 usr +  0.03 sys =  2.14 CPU) @ 5902.80/
+s (n=12632)
  qr:  4 wallclock secs ( 2.03 usr +  0.00 sys =  2.03 CPU) @ 39.90/s 
+(n=81)
     Rate     qr     qq
qr 39.9/s     --   -99%
qq 5903/s 14693%     --
[download]

Abigail

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