On Fri, 21 Apr 2023 15:17:37 GMT, Maurizio Cimadamore <mcimadam...@openjdk.org>
wrote:
>> src/jdk.compiler/share/classes/com/sun/tools/javac/comp/Flow.java line 915:
>>
>>> 913: */
>>> 914: private List<PatternDescription> reduceBindingPatterns(Type
>>> selectorType, List<PatternDescription> patterns) {
>>> 915: Set<Symbol> existingBindings = patterns.stream()
>>
>> Playing some more - I found this example:
>>
>>
>> class Test {
>> sealed interface I permits C, D { }
>> non-sealed interface C extends I { }
>> non-sealed interface D extends I { }
>>
>> interface F { }
>>
>> <Z extends I & F> int test(Z o) {
>> return switch (o) {
>> case C c -> 1;
>> case D d -> 2;
>> };
>> }
>> }
>>
>>
>> Which compiles correctly, but it doesn't look exhaustive to me (because of
>> F) ?
>
> Also, surprisingly, if I make C and D classes (instead of interfaces):
>
> class Test {
> sealed interface I permits C, D { }
> final class C implements I { }
> final class D implements I { }
>
> interface F { }
>
> <Z extends I & F> int test(Z o) {
> return switch (o) {
> case C c -> 1;
> case D d -> 2;
> };
> }
> }
>
> I get errors like:
>
>
> Foo.java:10: error: incompatible types: Z cannot be converted to Test.C
> case C c -> 1;
> ^
> where Z is a type-variable:
> Z extends I,F declared in method <Z>test(Z)
>
>
> Which seems odd?
Nevermind - these issues are due to a misunderstanding of the rules with
intersection types - e.g. given A & B, if a pattern covers _any_ of A, B, then
it covers A & B.
Similarly, the second issue I reported is in reality caused by the fact that in
the snippet with `class`, I also added `final` which then makes I & F a type
with no concrete witnesses (so cast will always fail from there to either C/D).
-------------
PR Review Comment: https://git.openjdk.org/jdk/pull/13074#discussion_r1173912165
