Thanks, the other node you're referring to was an answer to my previous question :)

Are you saying that Server and Client each want a different derived class of the Connection, but the Connection may already be different concrete classes?

I'm not sure if I understand you here correctly: The basic idea is to have 2 interchangeable ways of providing "remote access" functionality to the Server and Client objects. The application will then do something like:

my $server = Server->new(type => "ssh"); # to create an SSH connection
$server->run("ifconfig");
my $server2 = Server->new(type => "socket"); # to create a socket conn
+ection
$server2->run("ifconfig");
my $client = Client->new(type => "ssh");
$client->run("ls");
[download]

Where in this example "run" is defined in the Role and implemented by SSH and Socket.