gistfile1.cs

    //     Provides a mechanism for receiving push-based notifications.
    public interface IObserver<in T>
    {
        // Summary:
        //     Notifies the observer that the provider has finished sending push-based notifications.
        void OnCompleted();

        //     Notifies the observer that the provider has experienced an error condition.
        void OnError(Exception error);
        
        //     Provides the observer with new data.
        void OnNext(T value);
    }