[bsaul]

You may not be familiar with swift but a protocol isn’t necessarily a class. Structs ( so, value type) can also implements a protocol, and so in effect you can not tell a lot about what you’re manipulating, beyond what’s declared at the protocol level.

[mpweiher]

From TFA:

   class BaseGreeter: Greeter {}

   class LazyGreeter: BaseGreeter {