> On Apr 1, 2021, at 9:23 AM, Brian Goetz <brian.go...@oracle.com> wrote:
>
> ...
> Without trying to paint the bikeshed, this is a pretty simple extension to
> sealing:
>
> sealed interface WithCheese __refines Sandwich { }
>
> This says that WithCheese is sealed to either classes that extend Sandwich,
> or other interfaces that __refines Sandwich. As a bonus, default methods in
> WithCheese can refer to methods in Sandwich, since it must always be the case
> that `this instanceof Sandwich`.
>
> Essentially, I want to put the `permits` list on Sandwich, and have
> `WithCheese` and friends delegate their permits to `Sandwich`, rather than
> having each interface enumerate their subtypes.
Maybe “__refines” should be spelled “extend”?
If an interface J extends a class C, it means that it is a compile-time error
if class D implements interface J but class D is not a subclass of C.
Such a constraint might be useful even if C is not sealed.
—Guy
