From virtual extension methods to mixins

[Zhong Yu]

My problem with Yuval's example is that the object belongs to too many
types, it gets very confusing. It's much better to
    obj.asList().get(0);
than to
    obj.get(0); // uh?

A similar bad example from JDK

    interface java.nio.file.Path extends Iterable<Path>
        Iterator<Path> iterator(); // of elements

    for(Path element : path) ...

I don't think it makes sense. A simpler and clearer API:

    interface Path
        Iterable<Path> elements();

    for(Path element : path.elements) ...

Zhong Yu

On Mon, Jul 9, 2012 at 7:00 PM, Yuval Shavit <yshavit at akiban.com> 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-
>> > >
>> >
>> >
>>
>>
>