Local functions

[Alex Buckley]

Neal Gafter wrote:
> On Wed, Feb 10, 2010 at 11:26 AM, Alex Buckley <Alex.Buckley at sun.com> wrote:
>> Method references are in scope for this project, though I tend to think
>> that relying on ordinary methods ignores Doug's plea for clear
>> demarcation of (and restrictions on) code that experiences parallel
>> execution.
> 
> Sounds great, but it seems to me that's orthogonal to lambdas and
> function types.  Are you considering how to distinguish "parallel"
> closures from other closures?  I don't think restricting them to the
> parallel use cases is wise.

I agree demarcation of/restrictions on parallel code are orthogonal to 
lambdas and function types. A glance at the FindBugs bugs for 
multithreaded correctness shows little the language could internalize to 
make the body of a lambda expression correct by construction. (Short of 
horrendous type system "enhancements".)

That said, I am happy to prioritize parallel use cases over non-parallel 
use cases. Sun is not aiming to add lambdas to allow control abstraction 
or DSL building, but rather to support FJ ParallelArray and APIs like 
it. So I'm fine if lambda bodies are restricted along the lines Doug 
suggested. ("Ideally, for the sake of parallel execution, we'd disallow 
automatic sharing of locals and automatic elevation of "this", "return" 
or "break" to enclosing scopes.") The Lambda strawman is at odds with 
some of those restrictions; resolution is forthcoming.

Alex