RFR: 8300543 Compiler Implementation for Pattern Matching for switch [v4]

[Maurizio Cimadamore]

On Fri, 21 Apr 2023 15:16:03 GMT, Maurizio Cimadamore <mcimadamore at openjdk.org> wrote:

>> Jan Lahoda has updated the pull request incrementally with one additional commit since the last revision:
>> 
>>   Replacing use of mutable callsite with a mutable state.
>
> 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?

-------------

PR Review Comment: https://git.openjdk.org/jdk/pull/13074#discussion_r1173898106