Simplifying switch labels

[Brian Goetz]

> Oh, I guess I missed your point here, thinking that P and Q were 
> constants.
>
> Your comment implies that the two rules that restrict usage of 
> patterns—can't fall through past one, and can't combine one (via ',') 
> with most other labels—could be relaxed slightly in the case of 
> patterns that have no bindings. I suppose that's formally true, though 
> I'm not sure it's practically all that useful. (The only non-binding 
> pattern we have right now is a zero-component record, right? And any 
> non-binding patterns in the future could be equivalently expressed 
> with 'when' clauses.)

Here's an example that's not so contrived:

     String kind = switch (o) {
         case Integer _, Long _, Short _, Character _, Byte _ -> "integral";
         case Double _, Float _ -> "floating point";
         case Boolean _ -> "boolean";
         default -> "something else";
     };

Once we have a "don't care" pattern, any pattern can become binding-less.

Looking two steps ahead, we might decide it is not so much that there 
can be _no_ bindings, as much as are the bindings unifiable:

     case Bag(String x), Box(String x) -> "container of string";