package MyClass;
use strict;

sub new($)
{
    my $invocant = shift;
    my $class = ref($invocant) || $invocant;   # object or class name
    my $self = { };
    bless($self, $class);
    return $self;
}

sub HelloWorld($)
{
    my $self = shift;
    print "Hello, World!\n";
}

1;

##</code><code>##

use MyClass;
use strict;

my $pack = MyClass->new();
my $string = "HelloWorld";

$string = ref($pack) . "::$string";
no strict 'refs';
&$string($pack);

##</code><code>##

package MySubClass;
use strict;

our @ISA = qw(MyClass);
require MyClass;

# All implementation is done by the superclass

1;

##</code><code>##

use MySubClass;
use strict;

my $pack = MySubClass->new();
my $string = "HelloWorld";

$string = ref($pack) . "::$string";
no strict 'refs';
&$string($pack);