From virtual extension methods to mixins

[Brian Goetz]

Yes, this is what I call the "virtual field pattern."  It seems perfectly reasonable to me, because the classes that mix you in have to consent by providing the {get,set}Peeker methods.  (Also, by the nature of interface method merging, it addresses the diamond problem as if all base classes were "virtual".)  

On Jul 9, 2012, at 8:00 PM, Yuval Shavit wrote:

> Stateful mixins like this do indeed seem like a sketchy idea to me -- but is there any official stance on other mixin-like ideas? For instance, it seems to me you could use defender methods to implement delegation. For instance:
> 
> interface Peeker<T> {
>     T peek();
>     T take();
>     // maybe some other methods...
> }
> 
> interface PeekerView<T> extends Peeker<T> {
>     Peeker<T> getPeeker();
>     
>     T peek() default { return getPeeker().peek(); }
>     T take() default { return getPeeker().take(); }
> }
> 
> Now you can become a Peeker just by having one. All of a sudden, it's very easy to be a Peeker, a List and any number of other things.
> 
> public class BagOTricks<T> implements PeekerView<T>, ListView<T>, SupplierView<T> {
>     private List<T> underlying = ...
>     private Peeker<T> peeker = new ListPeeker<T>(underlying);
>     private Supplier<Optional<T>> supplier = new ListSupplier<T>(underlying);
> 
>     @Override
>     public Peeker<T> getPeeker() {
>         return peeker;
>     }
> 
>     @Override
>     public List<T> getList() {
>         return underlying;
>     }
> 
>     @Override
>     public Supplier<Optional<T>> getOptionalSupplier() {
>         return supplier;
>     }
> }
> 
> On Mon, Jul 9, 2012 at 4:38 PM, François Sarradin <fsarradin at gmail.com> wrote:
> Brian,
> 
> Thank you to share your advice. I think that my article provides a bad use
> of Java too. I don't really encourage this. I am just saying it is possible
> and let the reader decides if it is good or bad.
> 
> It is a good thing to share best practices, in a view to build "well craft"
> software. I have done this with small demonstrations of Java's lambda at
> Devoxx France this year. Moreover, I think you know that you can also find
> more and more articles about such best practices in Java 8 (even in French
> ;) ). But I really think that we also have to share worst practices. This
> is motivated by the wish to identify them and prevent them. That is why I
> wanted to share such an article, even if it is unpleasant.
> 
> François-
> Le 9 juil. 2012 13:50, "Brian Goetz" <brian.goetz at oracle.com> a écrit :
> 
> > Please don't encourage techniques like this.  There are a zillion "clever"
> > things you can do in Java, but shouldn't.  We knew it wouldn't be long
> > before someone suggested this, and we can't stop you.  But please, use your
> > power for good, and not for evil.  Teach people to do it right, not to
> > abuse it.
> >
> >
> > On Jul 9, 2012, at 1:12 AM, François Sarradin wrote:
> >
> > > Hi,
> > >
> > > I would like to share a blog post. It explains how to get multiple
> > > inheritance of the state from the virtual extension methods.
> > >
> > > "Java 8: Now You Have Mixins!" =>
> > > http://kerflyn.wordpress.com/2012/07/09/java-8-now-you-have-mixins/
> > >
> > > François-
> > >
> >
> >
> 
>