I'm guessing the optimization of using qr// over a plain string (ie: "Since Perl may compile the pattern at the moment of execution of the qr() operator, using qr() may have speed advantages in some situations ...")

From your previous post I would say that this happens when there is a big compilation overhead, so I thought about this, and used this list of words for testing: 

use strict;
use warnings;
use Benchmark qw( cmpthese timethese );

open my $words, "<", "linuxwords.txt" or die "$!";
my @words = <$words>;
chomp @words;

my @search = @words[0..10];

$" = "|";

my $re = qr/^(?:@words)$/;
my $str = "^(?:@words)\$";

my $r = timethese
(
    -5,
    {
        use_qr  => sub { map /$re/, @search },
        use_str => sub { map /$str/, @search },
        use_re  => sub { map /^(?:@words)$/, @search },
    }
);
cmpthese $r;

[download]
Benchmark: running use_qr, use_re, use_str for at least 5 CPU seconds.
+..
    use_qr:  5 wallclock secs ( 5.23 usr +  0.00 sys =  5.23 CPU) @ 98
+736.51/s (n=515997)
    use_re:  5 wallclock secs ( 5.33 usr +  0.00 sys =  5.33 CPU) @ 23
+.99/s (n=128)
   use_str:  5 wallclock secs ( 5.23 usr +  0.00 sys =  5.23 CPU) @ 22
+68.47/s (n=11855)
           Rate  use_re use_str  use_qr
use_re   24.0/s      --    -99%   -100%
use_str  2268/s   9355%      --    -98%
use_qr  98737/s 411431%   4253%      --

[download]
The re case is pretty bad because of the systematic interpolation, but I can't help but feel like I might be missing something because of how absurd the difference between qr and str is? But if this is correct, then qr is a clear winner for dictionary search.

In reply to Re^4: Performance penalty of using qr// by Eily
in thread Performance penalty of using qr// by Athanasius

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