The philosophy of Nothing

[tronicek at fit.cvut.cz]

Yes! Compiler infers the return type to be able to do type checking. And
both of these must be correct:

Integer i = (#() { throw new AssertionError(); }).invoke();
String s = (#() { throw new AssertionError(); }).invoke();

Z.
-- 
Zdenek Tronicek
FIT CTU in Prague


Paul Benedict napsal(a):
> Zdenek,
>
> Is a problem present if the compiler were to infer it as void?
>
> When I put these side-by-side, I don't see any particular issue.
> closure #() { throw new AssertionError(); }
> public void something() { throw new AssertionError(); }
>
> You can write code today that never returns -- my second example.
>
> Paul
>
> On Sun, Nov 29, 2009 at 11:25 PM,  <tronicek at fit.cvut.cz> wrote:
>> Hi Paul,
>>
>> as far as I know, Nothing is used only by compiler. And I do not see any
>> benifits if I was allowed to use it as an ordinary type in my code.
>>
>> What is the primary purpose of Nothing?
>> Look at closure #() { throw new AssertionError(); }
>> Compiler must infer the return type here. But what it should be?
>> It can be anything because the closure never returns normally.
>> So, compiler will use Nothing which is a subclass of any type.
>>
>> Z.
>> --
>> Zdenek Tronicek
>> FIT CTU in Prague
>>
>>
>> Paul Benedict napsal(a):
>>> Thanks Neal. Reiner, your explanation was very good.
>>>
>>> So basically Nothing can be used outside of closures:
>>> public Nothing throwMe(RuntimeException t) {
>>>     throw t;
>>> }
>>>
>>> 1) Does the Java compiler have to prove a method can never return
>>> normally?
>>>
>>> 2) What is the benefit of telling the compiler the method *must* throw
>>> an Exception? Don't say read the spec :-) I did, but it's sparse on
>>> the purpose
>>>
>>> 3) For a method that returns Nothing, if a class transformer alters
>>> the method body and actually issues a return, what happens? is a JVM
>>> Error thrown?
>>>
>>> Paul
>>>
>>>
>>
>>
>