This uber-conservative approach seems a pretty reasonable approach to
me; after all, enums are a language feature, and Enum<T> is a
constrained class (can't implement it directly), so it is not
unreasonable to define its typing wrt its supertypes specially.
So, let's get back to Maurizio's original question, which is: At one
point, we thought this feature was pretty cool, and invested some work
in it. Then we ran into a roadblock, and wrote it off. Now, we've got
a reasonable way to clear the roadblock. Which brings us back to:
- Do we still like the features described in JEP 301?
And, if we're not sure about that, what can we do to get more sure?
There’s an even more conservative option: restrict this only to the
type variable of Enum<T extends Enum<T>>, not just to the type
variables of all supertypes of an enum. Then, the asymmetry is
undetectable, in that it is illegal for a non-enum class to extend
Enum, right?
Yes, that would be the most conservative. If we took that path, I
think a more direct way to describe/specify it, is to say that a raw
enum reference (e.g. Foo) has a special direct supertype Enum<Foo> and
leave all other rules untouched.
Maurizio
