[External] : Re: Consolidating the user model

[John Rose]

On Nov 3, 2021, at 10:23 AM, Kevin Bourrillion <kevinb at google.com<mailto:kevinb at google.com>> wrote:

I think this fits neatly with the current design: `Point` has no supertypes*, not even `Object`, but `Point.ref` does.

(*I mean "supertype" in the polymorphic sense, not the "has a conversion" sense or the "can inherit" sense. I don't know what the word is really supposed to mean. :-))

Slippery terms.  “Type” is hopelessly broad as is “super type”.

For types as value sets, a super type is a value super set.
Again, int <: long in this view, and even in the JLS.

For types as in an object hierarchy, a super type is a parent+
type, an upper limit in the hierarchy lattice.  That view
centers on object polymorphism and virtual methods,
and is suspiciously bound up with pointer polymorphism.
So String <: Object in this view.

To heal the rift we are groping towards int <: Object, but
we don’t fully know which kind of “<:” that is, and how
it breaks down into a value set super, an object hierarchy
super, or perhaps something further.  The best view we
have so far, IMO, is that int <: Object breaks apart into
int <: int.ref (value set) and int.ref <: Object (hierarchy).
In that view, the last link of int <: int.ref requires a
story of how methods “inherit” across value sets,
without the benefit of a pointer-polymorphic hierarchy
to inherit within.  It’s doable, but we are running
into the sub-problems of this task.