The Young Rappel

Futures and Promises on Swift

Transcript

1. The Young Rappel Futures & Promises
2. Hi! I'm Sergio @fdzsergio
3. Agenda Working with asynchronous tasks Deferred computations Back to the Future
4. Async is hard
5. Request Image login(with: credentials) { (result: JSONResponse) in if case .success(let json) = result, let user = User(with: json) { fetch(avatar: user.avatarURL) { (result: DataResponse) in if case .success(let data) = result { let image = UIImage(data: data) self.imageView = UIImageView(image: image) } } } }
6. then
7. Request Image login(with: credentials) .then(User.init) .then { user in return fetch(avatar: user.avatarURL) }.then { data in self.imageView.image = UIImage(data: data) }.catch { error in // handle error } }
8. Futures & Promises It is the way to handle complex asynchronous operations in a simple way
9. What the heck is a Future?
10. Future is an object that represents that you will get something in the future.
11. Future let login: Promise<User> = login(with: credentials) login.then { user in self.storage.save(user) }
12. What is a Promise?
13. A promise is an object that may produce a single value some time in the future
14. Promise func login(with credentials: Credentials) -> Promise<User> { return Promise { fulfill, reject in self.client.request(task: .login(credentials)) { result in switch result { case .success(let json): fulfill(User(with: json)) case .failure(let error): reject(error) } } } }
15. Common Functions → then → catch → always → when → all
16. Limitations of Futures → Promises can only produce one value → Can nwot encapsulate streams of values → Only consumer driven
17. Back to the Future → Abstraction for async/sync operations → Encapsulate a deferred computation → Centralized error handling → Easily composable
18. DeLorean
19. B-Sides → https://promisesaplus.com → http://khanlou.com/2016/08/promises-in-swift → https://speakerdeck.com/javisoto/back-to-the- futures → https://medium.com/compileswift/hydra- promises-swift-c6319f6a6209
20. The Future is Today. — William Osler
21. Thank You!
22. Questions? @fdzsergio