#!/usr/bin/perl

use strict;
use warnings;

use Benchmark 'cmpthese';

our $string  = "abcd" x 1000;
    $string .= "e";
    $string .= "abcd" x 1000;
our $study   = $string;
our $pass    = "abcde";
our $fail1   = "foo12";
our $fail2   = "abdce";

study $study;

cmpthese(-1, {
    index_pass => 'index($string, $pass)',
    regex_pass => '$string =~ /$pass/',
    study_pass => '$study  =~ /$pass/',
});
print ("\n\n");

cmpthese(-1, {
    index_fail1 => 'index($string, $fail1)',
    index_fail2 => 'index($string, $fail2)',
    regex_fail1 => '$string =~ /$fail1/',
    regex_fail2 => '$string =~ /$fail2/',
    study_fail1 => '$study  =~ /$fail1/',
    study_fail2 => '$study  =~ /$fail2/',
});

__END__
               Rate index_pass study_pass regex_pass
index_pass  38331/s         --        -6%       -69%
study_pass  40960/s         7%         --       -67%
regex_pass 125463/s       227%       206%         --


                 Rate index_fail2 study_fail2 index_fail1 regex_fail2 
+regex_fail1 study_fail1
index_fail2   27306/s          --         -0%        -48%        -56% 
+       -64%        -99%
study_fail2   27307/s          0%          --        -48%        -56% 
+       -64%        -99%
index_fail1   52608/s         93%         93%          --        -15% 
+       -31%        -98%
regex_fail2   61837/s        126%        126%         18%          -- 
+       -19%        -98%
regex_fail1   75918/s        178%        178%         44%         23% 
+         --        -98%
study_fail1 3412032/s      12396%      12395%       6386%       5418% 
+      4394%          --
[download]

Right, except no one ever uses study, and most Perl hackers still pull out m// even if they only need to search for or one or two constant substrings. Also, you didn't quote meta characters in the pattern strings.

Even without using study, the speed advantage of index is almost lost when the match is at the end of a long string.

my $string       = "this is a string" x 300 . "xyz";

cmpthese(500000, {
    'index' => sub {
        my $res;
        $res = index($string, "xyz");
    },
    regex   => sub {
        my $res;
        $res = $string =~ /xyz/;
    },
});
[download]

         Rate regex index
regex 97087/s    --   -2%
index 98619/s    2%    --

most Perl hackers still pull out m//...

Ok, I agree that index is faster in some cases. However, I think there are good reasons for the behavior of most Perl hackers:

1. m// "scales" better in terms of uses. You can use it for the simplest things as well as for very complex things. It is practical and idiomatic. To me, that sounds like a description of Perl itself.
2. If you use it for your constant string to begin with and then you decide you need metacharacters, the change is smaller. Ok, this is a minor advantage, as the change wouldn't be that big anyway.
3. If you are using regular expressions elsewhere in the code, the code looks more consistent, and that makes it more readable.
4. Worring about the speed of index vs m// may be premature optimization. If you wanted the fastest possible solution you might not want to use Perl in the first place. Even if you want the fastest possible Perl implementation it is always better to make the code correct and readable first, and optimize the hot spots later.

I realize that some of this reasons (particularly the last one) agree with your argument for using for and push instead of map. I just wasn't sure that your assertion regarding index was correct, as my benchmarks had shown the opposite in the past. Now I see that it depends on the situation.

Regarding the readability of map vs for, I would say that a distinct advantage of map is that it documents the purpose of the loop right at the top (when used properly). As soon as you see the map keyword you'll know that you are building a list and you'll know where it is being stored; with for, you have to wait until you see the push to see the true purpose of the loop. Which approach is better depends on the intention of the coder, and I agree that the size of the block may be a factor to consider. The problem is that the exact line between map and for is blurry, partly a matter of style and personal preference.

Well, you were the one claiming they shouldn't use m// because that's more work for perl than using index, posting a benchmark to back up your claim. I posted a benchmark using different data which shows index losing. index *isn't* always faster, so Perl hackers aren't "wrong" or even inefficient for using m// over index.

Also, you didn't quote meta characters in the pattern strings.

Yes I did. If you think I'm wrong, please point out an unquated meta character in one of the pattern strings. If there were unquoted meta characters in the pattern strings, the benchmark wouldn't be fair, would it? index doesn't know metacharacters.

Your benchmark seems quite confused and, well, all but useful.

Your distinction between a short and long string is useless and deceptive because there are matches near both ends of the test strings for all of the searches you run, and there are no non-match data sets at all. index( $foo, $bar, 0 ) is no different from index( $foo, $bar ), neither of which does the same as /^$bar/, just like rindex( $foo, $bar ) is something entirely different from /$bar$/. You are comparing apples and meteors.

Note that putting multiple different benchmarks in a single table only serves the purpose of casting further confusion onto the data. You are benchmarking three things; run three benchmarks, look at three tables.

use re 'debug'; and compile a few regexen sometime, you'll see that the regex engine turns the trivial cases into pretty much a plain index. There's more fixed overhead for invoking the engine rather than just calling that function, of course, but on large data sets that's negligible.