Rx Subscribe where onNext returns a IDisposable

SubscribeWithDisposable.cs

public static IDisposable Subscribe<TSource> (this IObservable<TSource> sequence, Func<TSource, IDisposable> onNext) {
    var disposePreviousValues = sequence.Aggregate (Disposable.Empty,
                                                    (disposable, value) => {
                                                        using (disposable)
                                                            return onNext (value);
                                                    });
    var disposeLastValue = disposePreviousValues.TakeLast (1).Subscribe (last => last.Dispose ());
    return disposeLastValue;
}