On Fri, 6 May 2022 10:51:33 GMT, Jan Lahoda <jlah...@openjdk.org> wrote:
>> I now believe that the check is needed to properly classify patterns based
>> on the type of the i-th component. That said, not sure this should be a
>> subtyping check, or a type equality
>
> A good question. Consider code like:
>
> private void test(R r) {
> switch (r) {
> case R(A a, A v) -> {}
> case R(B b, A v) -> {}
> case R(I i, B v) -> {}
> }
> }
> final class A implements I {}
> sealed interface I permits A, B {}
> final class B implements I {}
> record R(I i1, I i2) {}
>
>
> The switch is exhaustive - all the possible combinations are covered. When
> checking the first component, the code will categorize the patterns like:
>
> A -> R(A a, A v), R(I i, B v)
> B -> R(B b, A v), R(I i, B v)
> I -> R(I i, B v)
>
> this categorization is done using the subtype check, so that `R(I i, B v)`
> will appear in the list for `A`. When checking the second component, the
> possibility for `I` is not exhaustive (does not cover `A` in the second
> component), but the possibilities for `A` and `B` are exhaustive, and they
> together cover `I`.
Ah - makes sense of course - I "just" needed a more convoluted example :-)
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PR: https://git.openjdk.java.net/jdk/pull/8516
