Compose generics without Transformer

[vadims]

No description provided.

[benjchristensen]

The test failure is a known non-deterministic test.

[benjchristensen]

This change forces this code:

public static void main(String[] args) {
        List<Movie> list1 = Arrays.asList(new Movie(), new HorrorMovie(), new ActionMovie());
        List<Movie> list2 = Arrays.asList(new ActionMovie(), new Movie(), new HorrorMovie(), new ActionMovie());
        Observable<List<Movie>> movies = Observable.just(list1, list2);
        Observable<Movie> compose = movies.compose(ComposeExample2::transform);
        compose.subscribe(System.out::println);
    }

    public static Observable<Movie> transform(Observable<List<Movie>> movieList) {
        return movieList
                .startWith(new ArrayList<Movie>())
                .buffer(2, 1)
                .skip(1)
                .flatMap(ComposeExample2::calculateDelta);
    }

    public static Observable<Movie> calculateDelta(List<List<Movie>> listOfLists) {
        if (listOfLists.size() == 1) {
            return Observable.from(listOfLists.get(0));
        } else {
            // diff the two
            List<Movie> newList = listOfLists.get(1);
            List<Movie> oldList = new ArrayList<Movie>(listOfLists.get(0));

            Set<Movie> delta = new LinkedHashSet<Movie>();
            delta.addAll(newList);
            // remove all that match in old
            delta.removeAll(oldList);

            // filter oldList to those that aren't in the newList
            oldList.removeAll(newList);

            // for all left in the oldList we'll create DROP events
            for (Movie old : oldList) {
                delta.add(new Movie());
            }

            return Observable.from(delta);
        }
    };

to something that is awkward enough I gave up after a few minutes to try and make it work:

public static Observable<? extends Movie> transform(Observable<? super List<Movie>> movieList) {
        return movieList
                .startWith(new ArrayList<Movie>())
                .buffer(2, 1)
                .skip(1)
                .flatMap(ComposeExample2::calculateDelta);
    }

    public static Observable<Movie> calculateDelta(List<? super List<Movie>> listOfLists) {
... all breaks here ...
    }

I really don't like when we need signatures like List<? super List<Movie>>.

[vadims]

After playing with it some more, I don't think that Transformer can be removed