Nice to @Share?

[Alex Buckley]

You are right. I did not ask a good question, but you (and David and 
Gernot and Peter) have provided good answers.

Alex

Fredrik Öhrström wrote:
> I cannot see that "start" is different from any other local variable
> that is expected to be mutable when accessed from within a closure. I.e.
> the bytecode will use getfield/putfield instead of aload/astore and the
> object that it will do getfield/putfield on must potentially be an
> environment object separate from the closure object. The initialization
> of the field must be a copy from the argument of course.
> 
> This BGGA example shows that the environment object that contains start
> must exist separately from any closures created using that environment.
> (There are simpler situations where the closure object can serve as the
> env object.) When v == false, then the env will not be live after gen
> has exited. When v == true it will stay alive as long as the closure
> stays alive since the closure holds on to it.
> 
> public class Test
> {
>    public static void main(String... args)
>    {
>       {==>int} f = gen(42);
>       System.err.println(""+f.invoke());
>       System.err.println(""+f.invoke());
>    }
> 
>    static volatile boolean v = false;
>   
>    static {==>int} gen(int start) {
>      
>       if (v) {
>          return {==> start++; start };
>       } else {
>          start++;
>          System.err.println("start="+start);
>          return null;
>       }
>    }
> }
> 
> When v=true, it prints 43, 44 and when v=false it print 43 and throws NPE.
> 
> I am not sure that I really warned about this, my point is that the
> environmental object is inevitable because closures == objects and vice
> versa. This is not necessarily a bad thing.
> 
> //Fredrik
> 
> Alex Buckley skrev:
>> I think the use of 'start' was rather what Fredrik warned about in 
>> http://blogs.oracle.com/ohrstrom/2009/08/using_methodhandles_to_reconci.html
>>
>> What possible effect can mutating 'start' have?
>>
>> Alex
>>
>> David.Moss at ubs.com wrote:
>>   
>>>> By the way, I am very happy with final (or implicit final).
>>>> When I code and find that I need a non-final local variable,
>>>> I first try to rewrite the code to avoid to use non-final
>>>> before trying to use a mutable object.
>>>>       
>>> Where des this leave closures?
>>>
>>> i.e.: what would we need to make the following code do what it is meant to:
>>>
>>> public class C {
>>>     public #int() getSequenceGenerator(int start, int increment) {
>>>         return #int() {
>>>             int ret = start;
>>>             start += increment;
>>>             return ret;
>>>         };
>>>     }
>>> }
>>>
>>>
>>> Kind Regards,
>>>
>>> David.
>>>
>>> --
>