subscriber_constructor

protected destination: Observer<any> | Subscriber<any>;

constructor(destinationOrNext?: PartialObserver<any> | ((value: T) => void) | null,
              error?: ((e?: any) => void) | null,
              complete?: (() => void) | null) {
    super();

    switch (arguments.length) {
      case A:
        this.destination = emptyObserver;
      case B:
        this.destination = destinationOrNext;
      case C:
        this.destination = new SafeSubscriber<T>(this, <((value: T) => void)> destinationOrNext, error, complete);
    }
  }