Syntax for existential type as a box for generic type

[Nickolas_Pohilets (Nickolas Pokhylets)]

And with generic types, it would be something like this, right?

any Dictionary where Key == some KeyWrapper, Value == some ValueWrapper, Key.Wrapped == Value.Wrapped, Key.Wrapped: P

I guess this would work too. The two syntaxes seem to be equivalent in their expressiveness, with first one being bottom-up and second one being top-down, but otherwise describing the same DAG.

Actually, my point is not even about the specific syntax, but rather about the feature parity between generics and existentials.

@Joe_Groff

Existentials are hampered by the lack of three key features in Swift today, but although these features would push the frontier forward of what existentials can do, they won't ever quite reach the full power that generic types have.

The statement above does not need to be true. If we want, it is possible to make existentials as expressive as generics, and keep them in sync in the future as new features are added. But I don't know if we do want it. I don't have yet any motivational real-world examples where this would be needed. If anyone has - please share.