code: func (r FilteringResourceEventHandler) OnUpdate(oldObj, newObj interface{}) {
  	newer := r.FilterFunc(newObj)
  	older := r.FilterFunc(oldObj)
  	switch {
  	case newer && older:
  		r.Handler.OnUpdate(oldObj, newObj)
  	case newer && !older:
  		r.Handler.OnAdd(newObj)
  	case !newer && older:
  		r.Handler.OnDelete(oldObj)
  	default:
  		// do nothing
  	}
  }
docs: // OnUpdate ensures the proper handler is called depending on whether the filter matches