code: public function update(\SplSubject $eventManager) {
          $this->isUpdate = true;
          if ($eventManager->event->function !== NULL) {
              $this->{$eventManager->event->function}($eventManager);
          }
      }
docs: Is the function that Event manager will invoke, when the event subscribe
  for this class will be dispatch.
  
  @param SplSubject $eventManager