Ever since I read in Mastering Regular Expressions that perl makes a copy of the base string when doing a case-insensitive match, I've tried to use character classes instead of /i.

... Before submitting this post, though, I decided to actually benchmark some variations to see whether character classes were faster. To my surprise, it turns out that /i is about 50% faster in the test I used: 

use strict;
use Benchmark qw(cmpthese);

my $foo = "abcdefghijklmnopqrstuvwxyz"x500;
my $re = "[Aa][Bb][Cc]";

cmpthese(1000000, {
  'i'       => sub { $foo =~ /abc/ig },
  'chars'   => sub { $foo =~ /[Aa][Bb][Cc]/og },
  'charvar' => sub { $foo =~ /$re/og },
});

[download]
yielding these results on my machine: 
Benchmark: timing 1000000 iterations of chars, charvar, i...
     chars:  2 wallclock secs ( 1.97 usr +  0.00 sys =  1.97 CPU) @ 50
+7614.21/s (n=1000000)
   charvar:  3 wallclock secs ( 2.04 usr + -0.01 sys =  2.03 CPU) @ 49
+2610.84/s (n=1000000)
         i:  1 wallclock secs ( 1.31 usr +  0.00 sys =  1.31 CPU) @ 76
+3358.78/s (n=1000000)
            Rate charvar   chars       i
charvar 492611/s      --     -3%    -35%
chars   507614/s      3%      --    -34%
i       763359/s     55%     50%      --

[download]
Results are similar for strings of various lengths. So was Mastering Regular Expressions incorrect, or has the problem just been fixed since it was written?

In reply to Re: Idiomatic optimizations by thelenm
in thread Idiomatic optimizations by Juerd

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