/// <summary>
        /// Subscribe a consumer to this observable using delegates.
        /// This method is a helper for the IAsyncBatchObservable.SubscribeAsync allowing the subscribing class to inline the
        /// handler methods instead of requiring an instance of IAsyncBatchObserver.
        /// </summary>
        /// <typeparam name="T">The type of object produced by the observable.</typeparam>
        /// <param name="obs">The Observable object.</param>
        /// <param name="onNextAsync">Delegate that is called for IAsyncBatchObserver.OnNextAsync.</param>
        /// <param name="onErrorAsync">Delegate that is called for IAsyncBatchObserver.OnErrorAsync.</param>
        /// <param name="onCompletedAsync">Delegate that is called for IAsyncBatchObserver.OnCompletedAsync.</param>
        /// <returns>A promise for a StreamSubscriptionHandle that represents the subscription.
        /// The consumer may unsubscribe by using this handle.
        /// The subscription remains active for as long as it is not explicitly unsubscribed.</returns>
        public static Task <StreamSubscriptionHandle <T> > SubscribeAsync <T>(this IAsyncBatchObservable <T> obs,
                                                                              Func <IList <SequentialItem <T> >, Task> onNextAsync,
                                                                              Func <Exception, Task> onErrorAsync,
                                                                              Func <Task> onCompletedAsync)
        {
            var genericObserver = new GenericAsyncBatchObserver <T>(onNextAsync, onErrorAsync, onCompletedAsync);

            return(obs.SubscribeAsync(genericObserver));
        }
 /// <summary>
 /// Subscribe a consumer to this observable using delegates.
 /// This method is a helper for the IAsyncBatchObservable.SubscribeAsync allowing the subscribing class to inline the
 /// handler methods instead of requiring an instance of IAsyncBatchObserver.
 /// </summary>
 /// <typeparam name="T">The type of object produced by the observable.</typeparam>
 /// <param name="obs">The Observable object.</param>
 /// <param name="onNextAsync">Delegate that is called for IAsyncBatchObserver.OnNextAsync.</param>
 /// <returns>A promise for a StreamSubscriptionHandle that represents the subscription.
 /// The consumer may unsubscribe by using this handle.
 /// The subscription remains active for as long as it is not explicitly unsubscribed.</returns>
 public static Task <StreamSubscriptionHandle <T> > SubscribeAsync <T>(this IAsyncBatchObservable <T> obs,
                                                                       Func <IList <SequentialItem <T> >, Task> onNextAsync)
 {
     return(obs.SubscribeAsync(onNextAsync, DefaultOnError, DefaultOnCompleted));
 }