The Philosophy of Nothing

[Paul Benedict]

Neal,

2) Outside of the whole closure conversation, can java.lang.Nothing be 
used? And is there value in it? For example:
>
>     class Test {
>      public Nothing throw_it() {
>        throw new AssertionError();
>      }
>     }
>
>
> Yes, but the most important use cases arise with closures.

Java existed all this time without caring whether methods complete or 
not. Neither Java reflection, dynamic language support, or JSR-292 has 
had a pressing desire to know this. Are we sure this is a good 
advancement in the language design? Aside from closure support, what is 
the value in saying a method returns Nothing?

>     3) In regards to byte-code manipulation, what would happen at
>     runtime if a class transformer takes the body of method that
>     cannot return normally ("returns" java.lang.Nothing) and actually
>     returns? The opposite case must be considered too. Would a JVM
>     error be thrown?
>
>
> Yes.  It would be a NullPointerException at the call site (that's the 
> only value the verifier would let be returned from a Nothing-returning 
> method).  The opposite case (failing to return from a method) isn't an 
> issue.

I don't think NPE is very descript in this situation or useful in 
helping debugging. I think the error goes beyond bogus pointers and into 
something more deep. Can you consider a new Exception for this?

Paul
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