I'm assuming that Net::Server::POP3 inherits from some basic Net::Server module that provides basic server functionality. Even if it doesn't, let's say that it does.

Now, let's say that there is some other server base module, called Net2::Server. It provides a very similar (but not identical) interface, but radically different innards. It's useful for different types of servers.

Now, let's say that I am using five servers, each an object of a class that either inherits from Net::Server or Net2::Server. I don't know which inherits from which. But, I do know that there is one interface difference I need to be aware of - foo() vs. bar(). So, I can do the following:

my $method = $server->can('foo') || $server->can('bar');
$server->$method( @args );
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And I guarantee that my code will work, regardless of which baseclass the server inherits from.