On 15 October 2012 16:04, Casper Bang <[email protected]> wrote:
>
> On Monday, October 15, 2012 3:27:20 PM UTC+2, KWright wrote:
>>
>> Void isn't quite right though. It corresponds to "return, but with no
>> useful information", which isn't the same thing as not returning at all.
>
>
> Why the interest in modeling "not returning at all"? Isn't that mostly
> interesting to people studying the halting problem? I'm strictly interested
> in modelling "return with nothing" and "return with something", what else
> is there but blocking the thread or looping indefinitely?
>
Then there's throwing an exception... Where control is NOT returned to the
caller, but instead to the nearest matching catch{} block. From the
perspective of the caller, a method that throws an exception has not
returned in any way, shape or form:
int someMethod(int question) {
final int retval =
question.equals("What is the answer?")
? 42
: throw new Exception("that's not the question");
return retval;
}
So what's the type of throw new Exception(...)?
It HAS to be a subclass of int, or the definition of retval is invalid.
The only possible answer is Nothing (or Bottom, or _|_ if you prefer).
Void is an empty return, it's not a subclass of int.
> A compiler seeing generic capture of Void, could allow an implicit return
> clause (as is the case with the void keyword) and furthermore optimize
> stack push/pop away (rather than boxing null). It seems like the issue is
> going to come up much more, when/if closures are introduced.
>
> Yes, this will become a whole lot more important once folk begin using
lambdas.
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