Pattern matching, not informative error message when the binding name is missing

[Jan Lahoda]

Hi Remi,


Thanks. I've filled:
https://bugs.openjdk.java.net/browse/JDK-8268320


FWIW, I think compiler-dev is a better place for reports like this.


Jan


On 07. 06. 21 11:03, Remi Forax wrote:
> Hi all,
> with this code
>
>    sealed interface Vehicle {}
>    record Car(String owner, String color) implements Vehicle {}
>    record Bus(String owner) implements Vehicle {}
>
>    public static void example3() {
>      var vehicles = List.of(
>          new Car("Bob", "red"),
>          new Bus("Ana")
>      );
>      var tax = vehicles.stream()
>          .mapToInt(v -> switch(v) {
>              case Car -> 100;
>              case Bus -> 200;
>              default -> throw new AssertionError();
>          }).sum();
>      System.out.println("tax " + tax);
>    }
>
> If there is no binding name in the case,
>    case Car
> instead of
>    case Car car
> the error message is not very explicit
>
> PatternMatching101.java:40: error: cannot find symbol
>                   case Car -> 100;
>                        ^
>    symbol:   variable Car
>    location: class PatternMatching101
>
> I believe that in this case, it's possible to know that this is a switch on types, so provide a better error message.
>
> regards,
> Rémi