Pattern matching on Class<T>

[Nathan Reynolds]

I have hit this same idea several times in the past 2 weeks.  I too would
like to switch on Class.

On Sat, Jun 11, 2022 at 6:06 AM Vikram Bakshi <vab2048 at gmail.com> wrote:

> Hello,
>
> Apologies if code formatting does not appear well (I'm not used to mailing
> lists). All code blocks are available to view here:
> https://stackoverflow.com/questions/72545671/pattern-matching-on-classt
>
> I asked a question on stackoverflow about why we cannot match on Class<T>
> in the way I expect. Suppose we have:
>
>     sealed interface Animal permits Dog, Cat, Bear {}
>     record Dog() implements Animal {}
>     record Cat() implements Animal {}
>     record Bear() implements Animal {}
>
> This would work:
>
>     static <T extends Animal> String makeNoise(Class<T> cls) {
>         if(cls.equals(Dog.class)) {
>             return "WOOF";
>         } else if(cls.equals(Cat.class)) {
>             return "MEOW";
>         } else if(cls.equals(Bear.class)) {
>             return "ROAR";
>         } else {
>             throw new IllegalStateException("Unknown state");
>         }
>     }
>
> But this wouldn't:
>
>     static <T extends Animal> String makeNoisePatternMatch(Class<? extends
> Animal> cls) {
>         return switch(cls) {
>             case Dog.class c -> "WOOF";
>             case Cat.class c -> "MEOW";
>             case Bear.class c -> "ROAR";
>         };
>     }
>
> I got the answer on Stack Overflow that this is not allowed by the spec. My
> question to the mailing list is: will the current restriction be lifted in
> the future?
>
> Will we be able to pattern match like the above? And if not - how come it
> is restricted (I'm  not criticising but rather just asking more out of
> curiosity to understand the decision to maintain the restriction)?
>
> Regards,
>