请解释下面的崩溃..
＃3。NSManagedObjectContext 0x1701c9ab0：xxxxxxxxx 0 libsystem_kernel.dylib 0x1848898e8 __ulock_wait + 8 1 libdispatch.dylib 0x18475977c _dispatch_ulock_wait + 48 2 libdispatch.dylib 0x1847598a4 _dispatch_thread_event_wait_slow + 36 3 libdispatch.dylib 0x1847574f0 _dispatch_barrier_sync_f_slow + 236 4 CoreData 0x187c0703c _perform + 232 5 CoreData 0x187c178b8 -[NSManagedObjectContext(_NestedContextSupport) ）executeRequest：withContext：error：] + 176 6 CoreData 0x187b675e0 -[NSManagedObjectContextexecuteFetchRequest：error：] + 580 7 MyApp 0x1002f596c专门静态RecentItemsController.cleanupItems（inContext：ofType：limitingTo：sortingByAttribute：withPredicate :)（xxxxx.swift：182） 8 MyApp 0x1002f6574 静态 xxx.xxx(inStore:completion:) 中的专用闭包 #1 (xxx.swift:163) 9 MyApp 0x1002f5118 部分申请静态 xxx.xxx(inStore:completion:) 中的闭包 #1 (xxx.swift) 10 CoreData 0x187c0c214开发者提交块到NSManagedObjectContextPerform + 152 11 libdispatch.dylib 0x1847469a0 _dispatch_client_callout + 16 12 libdispatch.dylib 0x184754ad4 …
protocol aView: class { }
extension aView where Self: UIView { }
任何人都可以帮我理解这段代码吗？