Here is another example with i believe the same issue sealed interface Vehicle {} record Car(String owner, String color) implements Vehicle {} record Bus(String owner) implements Vehicle {}
public static void example2() { var vehicles = List.<Vehicle>of( new Car("Bob", "red"), new Bus("Ana") ); for(var vehicle: vehicles) { switch(vehicle) { case Car car -> System.out.println("car !"); case Bus bus -> System.out.println("bus !"); case Record record -> throw new AssertionError(); } } } This code currently compiles even if the last case is not reachable. RĂ©mi ----- Original Message ----- > From: "daniel smith" <daniel.sm...@oracle.com> > To: "amber-spec-experts" <amber-spec-experts@openjdk.java.net> > Cc: "Gavin Bierman" <gavin.bier...@oracle.com> > Sent: Samedi 24 Juillet 2021 00:28:08 > Subject: Switch coverage with multiple branches > An RFE for JEP 406 (or maybe bug fix? I haven't dug into what the spec says). > Can we make this compile? > > public class SwitchCoverage { > sealed interface A {} > sealed interface B1 extends A {} > sealed interface B2 extends A {} > sealed interface C extends A {} > final class D1 implements B1, C {} > final class D2 implements B2, C {} > > void test(A arg) { > int i = switch (arg) { > case B1 b1 -> 1; > case B2 b2 -> 2; > }; > } > > } > > Output: > > % -> `javahome 17`/bin/javac --enable-preview --release 17 SwitchCoverage.java > SwitchCoverage.java:10: error: the switch expression does not cover all > possible > input values > int i = switch (arg) { > ^ > Note: SwitchCoverage.java uses preview features of Java SE 17. > Note: Recompile with -Xlint:preview for details. > 1 error > > The compiler wants to see a 'case C c', not realizing that the combination of > B1 > and B2 already covers C. > > The use case might seem a impractically complex, but I think it's actually > pretty normal to want to define a universe of values (that's A), provide some > implementations (D1 and D2), and then categorize the implementations in > different dimensions (B1/B2 in one dimension, C in another). When I'm writing > my switch, I might only care about one of these dimensions.