interfaces and contracts - new pattern

[Adam D. Ruppe]

On Tuesday, 3 December 2019 at 16:03:18 UTC, Ola Fosheim Grøstad 
wrote:
> But this doesn't work in D.

That's my point - it is unsound in the static type system and D 
correctly rejects it. Might work in a dynamic language, but not 
in static.

> Yes, but when do you need to do it? So it is typesafe, but what 
> would the use case be?

You could conceivably write a child class that wraps or converts. 
For example, perhaps:

class Serializer {
     void serialize(Serializable s) {}
}

class ExtendedSerializer: Serializer {
     override void serialize(Object o) {
         super.serialize(reflectToSerializable(o));
     }
}

I probably wouldn't do it that way... and I can't think of a time 
I actually used this myself which is why I had to make something 
up. But still, it conceivably makes sense.

> I've got a feeling that one could do something interesting with 
> such semantics that would make all this variance-stuff 
> cleaner... somehow. But I haven't given it a lot of thought. 
> Just a feeling. :)

Maybe, I haven't thought a lot of it.