Updated State of the Lambda

[Maurizio Cimadamore]

On 19/10/10 12:48, Gernot Neppert wrote:
> 2010/10/19 Maurizio Cimadamore<maurizio.cimadamore at oracle.com>:
>    
>> Hi Gernot,
>>
>>      
>>> Merely prefixing 'cancel' with 'this' will now cause the TimerTask to
>>> cancel the entire timer instead:
>>>
>>>        
>> not quite, this.cancel() and cancel() [unqualified] both refers to
>> MyClass.cancel - in the latter case the reference to the 'right' this will
>> simply be inferred by the compiler, as already happens with Java. But, from
>> the compiler perspective, there's no TimerTask.cancel() available inside the
>> lambda body - in order to call that you should use the DA/DU trick discussed
>> yesterday:
>>
>>      
> I see what you mean, thanks for the clarification!
> (which will also interest Reinier Zwitserloot whom I cited in my first post).
>
> However, I see another problem with the approach:
> If the only way to access members of the SAM itself from a within
> lambda is via the reference that it will get assigned to,
> we'll run into trouble with visibility rules!
> See the following example. Provided that the rules for final
> assignment will have been updated, the following should compile.
> The lambda expression wants to make use of the protected
> 'totallyUsefulHelperMethod()' defined in the abstract base class
> 'Sam'.
> However, it can't, because it does not have access to protected
> methods of other instances (even though we know that it's supposed to
> be the same instance in this case).
> This would mean that we could never make use of protected methods of
> abstract base classes in lambdas.
>
> What do we do?
>    
I'm tempted to say that whenever you feel you need to access 'this' then 
you probably need an anonymous inner class, not a lambda - however we 
will look into this and try to assess how frequent this pattern would be.

Thanks
Maurizio
>
> package net.lambdas;
>
> public abstract class Sam implements Runnable
> {
>      protected final void totallyUsefulHelperMethod()
>     {
>     }
> }
>
> package net.lambdas.test;
>
> public class TestSam
> {
>     public void testSam()
>     {
>        final Sam s = #{  s.totallyUsefulHelperMethod(); };
>     }
> }
>