Function types versus arrays

[Neal Gafter]

On Wed, Feb 17, 2010 at 2:39 PM, Joshua Bloch <jjb at google.com> wrote:
> Neal,
> I'm having a bit of trouble understanding this.  I'm not endorsing any
> implementation scheme, but you say that this program necessarily breaks the
> type system:
>
> public void main(String[] args) {
>     #void()[] arrayOfFunction = new #void()[1];
>     Object[] objectArray = arrayOfFunction;
>     objectArray[0] = #(){ throw new IOException(); };  // **
>     arrayOfFunction[0].(); // invoke the function out of the array
> }
>
> It would appear that the starred line should generate an ArrayStoreException
> at runtime, as #void()(throws IOException) isn't a subtype of #void().  I
> understand that it might take a sophisticated implementation to enforce
> this. What am I missing?
>          Josh

Presuming the source were legal, that's exactly right.  We're
exploring how such a "sophisticated implementation" breaks
compatibility with the existing language specification (thus the
"implementation" focus of the discussion), with the consequence that
the source must not be allowed.

Cheers,
Neal