Jon Pretty

Is class Foo(x: Int) extends Any okay? If so, does it box? Seems like complex rules between extends AnyVal, extends Any, extends Top

I didn’t see any of this answered. Opaque type is much more contained and lacking most of these consistency questions.

The SIP still doesn't explain what happens here: (x: Unsigned) match { case y: Int => ... } I wouldn't say it "lacks consistency questions".

I thought it did. I thought opaque said that is a compiler error?

Though what about, (x: Any) match { case y: Unsigned => ... } You can do it for `Int` so why not an opaque "Int"?

You can't match against abstract types, and opaque types should have similar semantics (because they're semantically the same, duh).

This seems a piece of evidence that opaque types might seem easy (short) but aren't simple. Good answers exist.

Honestly, scala already has Any, AnyRef and AnyVal. Adding Top to the mix seems like too much.