zentara++. Perl's magic is one of the things that got me hooked on Perl, so I decided to give it a try. Using "Hello, world!", I tried a peek at a tie that I did, and then I used an example from Variable::Magic. Interesting...

#!/usr/bin/perl

use strict;
use warnings;
use Devel::Peek;
use Variable::Magic qw( wizard cast getdata );

my $b = 'Hello, world!';
my $a = bless(
    do {
        \$b;
    },
    'main'
);
print Dump($a);

print "===========================================\n";

package Magical::UserData;

sub BEGIN {
    require Variable::Magic;
    do {
        'Variable::Magic'->import( 'wizard', 'cast', 'getdata' );
    };
}

package main;
{

    package Magical::UserData;
    my $wiz = wizard(
        'data',
        sub {
            \$_[1];
        }
    );

    sub ud (\[$@%*&]) : lvalue {
        my ($var) = @_;
        my $data = &getdata( $var, $wiz );
        unless ( defined $data ) {
            $data = \my ($slot);
            die q[Couldn't cast UserData magic onto the variable]
              unless &cast( $var, $wiz, $slot );
        }
        $$data;
    }
}

sub BEGIN {
    *ud = \&Magical::UserData::ud;
}
{
    my $cb;
    $cb = sub {
        print 'Hello, ', &ud( \&$cb ), "!\n";
    };
    &ud( \&$cb ) = 'world';
    print Dump( &$cb() );
}
[download]

Update: Fixed line 5. Thanks, ikegami.