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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 }, });
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% --
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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