UPDATE: typo inflates the results here, study does not produce the improvement shown here. But it does do something, not nothing, so I'm pretty sure it's not a no-op.

C:\perl>perl -v

This is perl 5, version 20, subversion 1 (v5.20.1) built for MSWin32-x
+86-multi-thread-64int
[download]

#!/usr/bin/perl
use strict;
use warnings;
use 5.010;
use Benchmark qw(cmpthese);

my @messages = <DATA>;

cmpthese(1000000, {
    'mca_func' => sub {
        my $out = mca_substitute($_) foreach (@messages);
    },
    'toolic_func' => sub {
        my $out = toolic_substitute($_) foreach (@messages);
    },
    'study_func' => sub {
    my $out = study_substitute($_) for each (@messages);
    },
});


sub toolic_substitute {
    my $message = shift;
    $message =~ s/\{\\d(\d+)\}/sprintf "%0${1}d", int(rand(10**$1))/ge
+;
    return $message;
}

sub study_substitute {
    my $message = shift; study $message;
    $message =~ s/\{\\d(\d+)\}/sprintf "%0${1}d", int(rand(10**$1))/ge
+;
    return $message;
}

sub mca_substitute {
    my $message = shift;
    $message =~ s/\{\\d(\d+)\}/myreplace($1)/ge;
    return $message;
}

sub myreplace {
    return '' unless $_[0];

    my $string = '';
    $string .= int(rand 10) for (1..$_[0]);
    return $string;
}


__DATA__
This is a message! {\d3} --- {\d2}
Another {\d3} Message with {\d5}
A {\d1} little {\d6} longer string {\d3}
[download]

C:\perl>perl testpm.pl
                Rate    mca_func toolic_func  study_func
mca_func     34744/s          --        -32%        -78%
toolic_func  50795/s         46%          --        -68%
study_func  157505/s        353%        210%          --

C:\perl>
[download]

Not bad for a no-op.

I think you may be being fooled by an error:

    my $out = study_substitute($_) for each (@messages);
#..................................^^^?^^^^
[download]

FWIW: I don't see any improvement (actually a 2% drop) in the performance of the study version (using 5.10/win).

---

With the rise and rise of 'Social' network sites: 'Computers are making people easier to use everyday'

Examine what is said, not who speaks -- Silence betokens consent -- Love the truth but pardon error.

"Science is about questioning the status quo. Questioning authority".

In the absence of evidence, opinion is indistinguishable from prejudice.

I got the same results once I fixed the typo: yours and McA's algorithms performed slightly worse, toolic's only marginally better when study was added. So something happened, definitely not a no-op, but nothing useful either! With such short strings, I shouldn't be surprised.

1 Peter 4:10

I stop working now in the hope that my no-op will result in such a gain in performance... :-)

Thank you for that addition.

McA