I fell in the same trap yet again :( Am i the only one that want to throw exceptions in all branches of a switch ?
https://github.com/forax/write_your_own_java_framework/blob/master/interceptor/src/test/java/org/github/forax/framework/interceptor/InterceptorRegistryTest.java#L523 Rémi ----- Original Message ----- > From: "Tagir Valeev" <amae...@gmail.com> > To: "Remi Forax" <fo...@univ-mlv.fr> > Cc: "amber-spec-experts" <amber-spec-experts@openjdk.java.net> > Sent: Lundi 30 Août 2021 04:00:27 > Subject: Re: switch expression with not explicit yield value should work ? > Hello! > > I think this is not related to recent JEPs. This behavior is > standardised since Java 14 when Switch expression was introduced: > > // Compilation error > int x = switch(0) { > default -> throw new IllegalArgumentException(); > }; > > This is explicitly specified (15.28.1) [1]: > >> It is a compile-time error if a switch expression has no result expressions. > > There was some discussion about this rule in March, 2019 [2]. > Basically, the idea is to preserve the possibility of normal > (non-abrupt) execution of every expression. > I believe, preventing unreachable code has always been in the spirit > of Java. In your code sample, the execution of the 'return' statement > itself is unreachable, > so writing 'return' is redundant. In my sample above, the 'x' variable > is never assigned to anything, and the subsequent statements (if any) > are unreachable as well. > > I'd vote to keep the current behavior. While it may complicate code > generation and automatic refactorings, this additional complexity is > only marginal. The benefit is > that this behavior may save us from accidental mistakes. > > Btw, you may deceive the compiler introducing a method like > > static Object fail() { > throw new IllegalArgumentException(); > } > > And use "case Object __ -> fail()" > > With best regards, > Tagir Valeev. > > [1] https://docs.oracle.com/javase/specs/jls/se16/html/jls-15.html#jls-15.28.1 > [2] > https://mail.openjdk.java.net/pipermail/amber-spec-experts/2019-March/001067.html > > On Sun, Aug 29, 2021 at 9:00 PM Remi Forax <fo...@univ-mlv.fr> wrote: >> >> Another case where the spec is weird, >> i've converted a project that generate a visitor from a grammar (something >> like >> yacc) to use a switch on type instead. >> >> Sometimes for a degenerate portion of the grammar i've an empty visitor that >> always throw an exception, >> the equivalent code with a switch is >> >> static Object result(Object o) { >> return switch (o) { >> case Object __ -> throw new AssertionError(); >> }; >> } >> >> >> Obviously i can tweak the code generator to generate >> >> static Object result(Object o) { >> throw new AssertionError(); >> } >> >> but not be able to compile the former code strike me as odd. >> >> An expression switch is a poly-expression, so the result type is >> back-propagated >> from the return type of the method result, so it should be Object. >> >> Moreover, if the switch is not a switch expression but a switch statement, >> the >> code is also valid >> >> static Object result(Object o) { >> switch (o) { >> case Object __ -> throw new AssertionError(); >> } >> } >> >> Not be able to compile a switch expression when there is no explicit result >> type >> but only an implicit type seems arbitrary to me >> (this change is backward compatible because it only makes more codes >> compiling). >> > > Rémi
