import Dispatch class Loader { var onComplete: (() -> Void)? func load() { // simulate async completion DispatchQueue.main.asyncAfter(deadline: .now() + 0.1) { [weak self] in guard let self = self else { return } print("Finished: \(self)") self.onComplete?() } } deinit { print("Loader deinit") } } do { let loader = Loader() loader.onComplete = { print("done callback") } loader.load() } // loader can be deallocated if nothing else references it