如何为NSFetchedResultsController定义具有通用类型的协议？

Question

这就是我现在的定义方式：

protocol FetchedResultsControlable {
    var fetchedResultsController: NSFetchedResultsController<NSManagedObject>? { get set }
}

为了遵循该协议，我需要做些什么：

var fetchedResultsController: NSFetchedResultsController<Thread>?
var fetchedResultsController: NSFetchedResultsController<Task>?
var fetchedResultsController: NSFetchedResultsController<Notification>?

我该如何实现？

这就是我要使用的方式。只需扩展其他协议即可：

protocol NotificationsViewModelable: FetchedResultsControlable {
    var notifications: [Notificationable] { get }
}
class NotificationsViewModel: NotificationsViewModelable {
    var notifications: [Notificationable] {
        return fetchedResultsController?.fetchedObjects ?? []
    }
    var fetchedResultsController: NSFetchedResultsController<Notification>?
}