code: func ControllerToSelectableFields(controller *api.ReplicationController) fields.Set {
  	objectMetaFieldsSet := generic.ObjectMetaFieldsSet(&controller.ObjectMeta, true)
  	controllerSpecificFieldsSet := fields.Set{
  		"status.replicas": strconv.Itoa(int(controller.Status.Replicas)),
  	}
  	return generic.MergeFieldsSets(objectMetaFieldsSet, controllerSpecificFieldsSet)
  }
docs: // ControllerToSelectableFields returns a field set that represents the object.