extension NSPersistentContainer {

    func modify<T: NSManagedObject>(object: T,
                                    in closure: @escaping ((T) -> Void),
                                    completed: (() -> Void)? = nil) {
        let objectID = object.objectID
        let managedObjectContext = object.managedObjectContext
        performBackgroundTask { context in
            if let objectInContext = context.object(with: objectID) as? T {
                closure(objectInContext)
                try? context.save()
            }

            if let managedObjectContext = managedObjectContext {
                managedObjectContext.perform {
                    completed?()
                }
            } else {
                DispatchQueue.main.async {
                    completed?()
                }
            }
        }
    }

}