package ClientFactory;
    
    sub genericClient {
        my $client = new Client();
        my $calculator = new InvoiceCalculator ($client);
        $client->setCalculator ($calculator);
        
        return ($client);
    }
    
    package main;
    
    my $client = ClientFactory::genericClient();
    my $calculator = $client->getCalculator();

##</code><code>##

    package Storage;
    
    sub new {
        return (bless {
            'key 1' =>  'default 1',
            'key 2' =>  'default 2',
        }, shift);
    }
    
    
    package InvoiceCalculator;
    
    sub new {
        my $O = bless {}, shift;
        $O->{'data'} = shift;
        return ($O);
    }
    
    sub calculate {
        my $O = shift;
        
        for my $k (sort keys %{ $O->{'data'} }) {
            printf ("%s -> %s\n", $k, $O->{'data'}->{ $k });
        }
        return;
    }
    
    
    package Client;
    
    sub new {
        my $O = bless {}, shift;
        $O->{'data'} = new Storage ();
        
        return ($O);
    }
    
    sub getCalculator {
        my $O = shift;
        
        return (new InvoiceCalculator ($O->{'data'}));
    }
    
    
    package main;
    
    my $client = new Client;
    my $calc = $client->getCalculator();
    $calc->calculate();

##</code><code>##

    sub InvoiceCalculator::calculate {
        my $O = shift;
        
        my $data = $O->{'data'};
        
        for my $k (sort keys %$data) {
            printf ("%s -> %s\n", $k, $data->{ $k });
        }
        return;
    }