objects.swift

let gifsProvider: AnyObjectsProvider<GIF> = objectsManager.makeGIFsProvider()

protocol ObjectsManager {
    
    var defaultGIFPredicate: NSPredicate { get }
    
    func makeGIFsProvider() -> AnyObjectsProvider<GIF>
    func save(gifs: [GIF]) -> Completable
    func hide(gif: GIF)
    
    static func makeObjectsManager(logger: Logger, completion: @escaping (ObjectsManager) -> Void)
}

protocol ObjectsProvider {
    
    associatedtype Object
    
    var updates: Observable<[Update]> { get }
    
    func numberOfObjects() -> Int
    func object(at indexPath: IndexPath) -> Object
    func set(predicate: NSPredicate)
}

class AnyObjectsProvider<T>: ObjectsProvider {
        
    let updates: Observable<[Update]>    
    
    init<OP: ObjectsProvider>(objectsProvider: OP) where OP.Object == T {
        
        updates = objectsProvider.updates
        _numberOfObjects = objectsProvider.numberOfObjects
        _object = objectsProvider.object
        _set = objectsProvider.set
    }
  
    ... 
}

class CoreDataObjectsProvider<CoreDataObject: Convertible>: NSObject, ObjectsProvider, NSFetchedResultsControllerDelegate where CoreDataObject: NSFetchRequestResult {
    
    let updates: Observable<[Update]>
    
    private let updatesBehaviorRelay = BehaviorRelay<[Update]>(value: [])
    private let fetchedResultsController: NSFetchedResultsController<CoreDataObject>
    
    private var updatesList: [Update] = []
    
    init(fetchedResultsController: NSFetchedResultsController<CoreDataObject>) {
        self.fetchedResultsController = fetchedResultsController
        try! fetchedResultsController.performFetch()
        updates = updatesBehaviorRelay.asObservable()
        
        super.init()
        
        fetchedResultsController.delegate = self
    }
     
    ...
}