Or, if not additive, but we end up reusing the `final` keyword in the
way shown at the bottom of this email, then we could at least allow
`permits /<bikeshed>/, TypeA, TypeB` which is maybe nearly as good.
In light of this morning's observation about hyphenated keywords ...
there's a lot in this thread about why it seemed more attractive to
retcon final for sealed-ness rather than create a new conditional
keyword. But it was a bit confusing (because final already has
associations), and we ran into the problem that
final class X { }
already means something, which deprived us of the opportunity to infer a
permits clause. Switching to something derived from `final` (such as
`semi-final`) restores that, while keeping the associations with final:
semi-final class A
permits X, Y, Z { ... }
non-final class X extends A { ... }
class Y extends A { } // implicitly final
semi-final class B
/* inferred permits clause */ { ... }
I think this is the best of both worlds; we clearly connect to finality,
but don't directly overload it.
