public function __construct(TickObserver $o, $id)
 {
     parent::__construct($id);
     $this->o = $o;
 }
 public function __construct(NowPlayingObserver $o, $id)
 {
     parent::__construct($id);
     $this->o = $o;
 }
 public function __construct(TrackChangeObserver $o, $id)
 {
     parent::__construct($id);
     $this->o = $o;
 }