From virtual extension methods to mixins

[Yuval Shavit]

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-
> > >
> >
> >
>
>