#!/usr/bin/perl
        
use strict;
use warnings;
    
package HashBased;
        
sub new {
    my $class = shift;
    return bless {@_}, $class;
}

sub noise {
    my $self = shift;
    printf "The %s goes %s!\n", $self->{name}, $self->{sound}
}
sub name {     
    my $self = shift;
    return $self->{name};
}
 
package InsideOut; {
    use Scalar::Util 'refaddr';
    my %legs;
    our @ISA = 'HashBased';
    sub new {
        my $class = shift;
        my $legs  = pop;
        my $obj   = bless $class->SUPER::new(@_), $class;
        $legs{refaddr $obj} = $legs;
        return $obj;
    }
    sub show_legs {
        my $self = shift;
        printf "The %s has %d legs\n", $self->name, $legs{refaddr $self};
    }
    sub DESTROY {
        my $self = shift;
        delete $legs{$self}
    }
}
    
package main;
my $dog  = InsideOut->new(name => 'dog',  sound => 'bark', 4);
my $bird = InsideOut->new(name => 'bird', sound => 'peep', 2);
    
$dog->noise;
$dog->show_legs;
$bird->noise;  
$bird->show_legs;
__END__
The dog goes bark!
The dog has 4 legs
The bird goes peep!
The bird has 2 legs