I have nothing more to say on this topic. But I cannot refuse a reasonable request to publish my method of obtaining results.

Code follows. I ran the script on my MPC TransPort X3100, an obsolete laptop upgraded with a Pentium (R) M, with 2 Gb memory. Continued operation at top speed quickly overheats the chip, so I fixed the CPU frequency during these tests to 1.60 GHz. Interpreter version is 'v5.10.1 (*) built for i686-linux-thread-multi'. OS is Ubuntu 9.10, Linux 2.6.31-19-generic. I did my best to idle other tasks while benchmarking but I did not shut down X.

In the script, I bypass the ::XS enhancement with declarations of the form:

Readonly         my $n_true => 1;
[download]

... instead of the correct:

Readonly::Scalar my $r_true => 1;
[download]

While I admit to some doubt as to why ::XS applies to one set of declarations and not the other; and have some small feeling that I would prefer to compare performance with ::XS loaded against that when it is completely not loaded; I'm confident that the usingNo_XS() routine reasonably reflects performance when ::XS is not available.

I noted earlier that you obtained the performance expected without ::XS even using the correct syntax; and therefore, you likely did not have Readonly::XS installed. You replied with, among other stuff, what looked very much like an effort to install it, whereupon your performance improved significantly, as expected. I don't understand why you're not pleased.

I cannot imagine personally fighting a pitched, cross-thread battle over a 2x difference in performance. I can imagine someone else doing so over a 40x difference, which results you showed previously (and which I preserve below). I do not, Sir, call you a liar. I merely fail to replicate your results.

You are /msg-ed.

#! /run/bin/perl
#~ use strict;
use warnings;

use Benchmark qw[ cmpthese ];

use constant {
    C_TRUE => 1,
    C_FALSE => 0,
    C_VALUE => 12345,
};

use Readonly;

# Correct...
Readonly::Scalar my $r_true => 1;
Readonly::Scalar my $r_false => 0;
Readonly::Scalar my $r_value => 12345;

# Much slower...
Readonly my $n_true => 1;
Readonly my $n_false => 0;
Readonly my $n_value => 12345;

# My...
my $m_true = 1;
my $m_false = 0;
my $m_value = 12345;

# Package variables...
$p_true = 1;
$p_false = 0;
$p_value = 12345;


sub usingConstant {
    for( 1 .. 1e6 ) {
        if( C_TRUE ) {
            my $sum = C_VALUE * C_VALUE;
        }
        elsif( C_FALSE ) {
            ;## Never called
        }
    }
}

sub usingReadonly {
    for( 1 .. 1e6 ) {
        if( $r_true ) {
            my $sum = $r_value * $r_value;
        }
        elsif( $r_false ) {
            ;## Never called
        }
    }
}

sub usingNo_XS {
    for( 1 .. 1e6 ) {
        if( $n_true ) {
            my $sum = $n_value * $n_value;
        }
        elsif( $n_false ) {
            ;## Never called
        }
    }
}

sub usingPackage {
    for( 1 .. 1e6 ) {
        if( $p_true ) {
            my $sum = $p_value * $p_value;
        }
        elsif( $p_false ) {
            ;## Never called
        }
    }
}

sub usingMy {
    for( 1 .. 1e6 ) {
        if( $m_true ) {
            my $sum = $m_value * $m_value;
        }
        elsif( $m_false ) {
            ;## Never called
        }
    }
}

sub usingLiterals {
    for( 1 .. 1e6 ) {
        if( 1 ) {
            my $sum = 12345 * 12345;
        }
        if( 0 ) {
            ;## Never called
        }
    }
}

cmpthese -20, {
    const       => sub{ usingConstant() },
    Readonly    => sub{ usingReadonly() },
    My          => sub{ usingMy() },
    literals    => sub{ usingLiterals() },
    package     => sub{ usingPackage() },
    No_XS       => sub{ usingNo_XS() },
};

__END__
c:\test>ROvCONST.pl

         s/iter Readonly    const
Readonly   5.66       --     -98%
const     0.141    3931%       --


(including No_XS; 1.60 GHz fixed)
No_XS    0.159/s       --     -94%     -94%     -94%     -96%     -97%
My        2.76/s    1638%       --      -1%      -3%     -36%     -40%
Readonly  2.79/s    1661%       1%       --      -2%     -35%     -39%
package   2.86/s    1700%       4%       2%       --     -34%     -38%
literals  4.33/s    2630%      57%      55%      52%       --      -6%
const     4.60/s    2796%      67%      64%      61%       6%       --

            Rate    No_XS Readonly       My  package literals    const
No_XS    0.161/s       --     -94%     -94%     -95%     -96%     -97%
Readonly  2.76/s    1619%       --      -2%      -8%     -37%     -42%
My        2.82/s    1659%       2%       --      -6%     -35%     -40%
package   2.99/s    1764%       8%       6%       --     -31%     -37%
literals  4.36/s    2618%      58%      55%      46%       --      -8%
const     4.73/s    2847%      71%      68%      58%       8%       --

            Rate    No_XS Readonly       My  package literals    const
No_XS    0.158/s       --     -94%     -94%     -95%     -96%     -97%
Readonly  2.80/s    1666%       --      -2%      -6%     -37%     -41%
My        2.85/s    1697%       2%       --      -5%     -36%     -40%
package   2.99/s    1785%       7%       5%       --     -33%     -37%
literals  4.47/s    2723%      60%      57%      50%       --      -5%
const     4.73/s    2885%      69%      66%      58%       6%       --
[download]