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.

---

---

• Are you posting in the right place? Check out Where do I post X? to know for sure.
• Posts may use any of the Perl Monks Approved HTML tags. Currently these include the following:

  <code> <a> <b> <big> <blockquote> <br /> <dd> <dl> <dt> <em> <font> <h1> <h2> <h3> <h4> <h5> <h6> <hr /> <i> <li> <nbsp> <ol> <p> <small> <strike> <strong> <sub> <sup> <table> <td> <th> <tr> <tt> <u> <ul>

• Snippets of code should be wrapped in <code> tags not <pre> tags. In fact, <pre> tags should generally be avoided. If they must be used, extreme care should be taken to ensure that their contents do not have long lines (<70 chars), in order to prevent horizontal scrolling (and possible janitor intervention).
• Want more info? How to link or How to display code and escape characters are good places to start.