Hi,

Currently, collect in Flowable, Observable accepts a Collector<T, A, R> collector. If that were to be Collector<? super T, A, R> collector, less casting would be needed in some instances. For example, when using java.util.stream.Collectors.joining():

Observable .just("foo", "bar", "baz") .cast(CharSequence.class) .collect(joining(", "));

The .cast(CharSequence.class) would then no longer be needed.

Should also be binary compatible?