> On Jun 2, 2022, at 2:59 PM, Brian Goetz <brian.go...@oracle.com> wrote:
>
>
>> 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";
Okay, those are helpful illustrations, thanks.
So an argument against a syntactic prohibition on things like 'Pattern,
Pattern:' is that we may support those, subject to certain semantic
restrictions, in the future.
I wonder how we would try to explain 'case Integer x, null, Double x'... (Does
'x' get bound to 'null'? How?)
