Updated State of the Lambda

[Brian Goetz]

On Oct 19, 2010, at 4:48 AM, 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?

Use inner classes when you hit the limit of what lambdas can do.  This is a corner case of a corner case; it seems silly to distort the semantics of lambda to accomodate given that there's already a way to do that.  

> 
> 
> 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(); };
>   }
> }
>