FetchedResultsObserver.swift

private final class FetchedResultsObserver<Result: NSManagedObject>: NSObject, NSFetchedResultsControllerDelegate {
  var willChange: () -> Void = {}
  var didChange: () -> Void = {}
        
  init(controller: NSFetchedResultsController<Result>) {
    super.init()
    controller.delegate = self
  }
        
  func controllerWillChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
    willChange()
  }
        
  func controllerDidChangeContent(_ controller: NSFetchedResultsController<NSFetchRequestResult>) {
    didChange()
  }
}