[AnimalMuppet]

Sorry, I'm not trying to be dense, but:

> No, you have to write their code (concrete implementation for a new type) manually.

Say we're talking about a sort function. Are you saying that I have to write both sort(Foo) and sort(Bar), rather than simply writing sort(SomeInterfaceSharedByFooAndBar)?

I presume you're not just saying that I have to write the code for Foo and Bar; I don't know of anything that will save me from that.