switch expression with not explicit yield value should work ?

[forax at univ-mlv.fr]

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" <amaembo at gmail.com>
> To: "Remi Forax" <forax at univ-mlv.fr>
> Cc: "amber-spec-experts" <amber-spec-experts at 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 <forax at 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