package Foo;
                                                                                
sub new
{
   my ( $class ) = @_;
   return bless {}, $class;
}
                                                                                
package main;
                                                                                
use strict;
                                                                                
my $foo = Foo->new();
                                                                                
*Foo::zub = sub { print "I'm zub!\n"; };
                                                                                
$foo->zub();