Lifting into a Subject

[abersnaze]

Mildly interesting idea to see if there would be any interest.

public class Subject<T, R> extends Observable<R> implements Observer<T> {
    ...
    public <X> Subject<X, R> liftHead(final Operator<? extends T, ? super X> op) { ... }
    public <X> Subject<T, X> liftTail(final Operator<? extends X, ? super R> op) { ... }

    @Override
    public <X> Subject<T, X> lift(final Operator<? extends X, ? super R> op) { return liftTail(op); }
}

[akarnokd]

What do you want to achieve with this change?

[abersnaze]

Up till now all the APIs that want to delegate part of the observable change chain to another piece of code has had to pass in the head as an argument. With these methods the delegate could return a subject the represents the some segment of the chain without any arguments.

For example retryWhen() takes a notification handler Func1<Observable<Exception>, Observable<?>>. With this it would have been possible for retryWhen to take a notification handler Func0<Subject<Exception, ?>

[akarnokd]

If I understand correctly, a chain of Subject<Integer, String> -> Subject<String, Date> -> Subject<Date, Long>, I can hand out each to different parties and observe them at any point?

[abersnaze]

Yes. The Subject returned could be reused to subscribe() different source observables. The Subject would just be an capsulation of some computation without defining where the data comes from or where it is going to.

[benjchristensen]

The encapsulation of computation sounds like the Transformer with Observable.compose.

[akarnokd]

Do you still want to pursue this?

[benjchristensen]

Punting to 2.0 for bikeshedding.

[akarnokd]

See #3975.