sub DESTROY {
    my $id = refaddr shift;
    delete $_->{ $id} for \ ( %street, %city, %state, %zip);
}
[download]

I'd like to contrast an implementation of the Address class based on the Alter module. It is itself hash-based and thus closer to the original hash-based implementation than the inside-out variant, while still offering the black-box-inheritance properties. Essentially, the changes are that the ego() function is called on the object before each access to the object data.

#class Address (Alter-based)
package Address;
use strict;
use warnings;

use Alter ego => {}; # alter ego is a hash

#constructor
sub new {
    my ($class) = @_;
    my $self = \ my $o; # the object proper (a scalar ref)
    %{ ego $self } = ( # set up the ego for this class
        _street => undef,
        _city  => undef,
        _state => undef,
        _zip   => undef
    );
    bless $self, $class;
    return $self;
}

sub street {
    my ( $self, $street ) = @_;
    ego( $self)->{_street} = $street if defined($street);
    return ego( $self)->{_street};
}
sub city {
    my ( $self, $city ) = @_;
    ego( $self)->{_city} = $city if defined($city);
    return ego( $self)->{_city};
}
sub state {
    my ( $self, $state ) = @_;
    ego( $self)->{_state} = $state if defined($state);
    return ego( $self)->{_state};
}
sub zip {
    my ( $self, $zip ) = @_;
    ego( $self)->{_zip} = $zip if defined($zip);
    return ego( $self)->{_zip};
}

sub print {
    print "Address: $_->{_street}\n".
                   "$_->{_city}\n"  .
                   "$_->{_state}\n" .
                   "$_->{_zip}\n\n" for ego shift;
}

1;
[download]