@CheckReturnValue
    @SchedulerSupport(SchedulerSupport.NONE)
    public final Observable<T> distinctUntilChanged(BiPredicate<? super T, ? super T> comparer) {
        ObjectHelper.requireNonNull(comparer, "comparer is null");
        return RxJavaPlugins.onAssembly(new ObservableDistinctUntilChanged<T, T>(this, Functions.<T>identity(), comparer));
    }