async/await in Swift

Async/await is a new language feature that will ship with Swift 5.5 this year. There’s no doubt it will have a significant impact on how we write asynchronous code.

In this talk, we’re going to look at some use cases for async/await, how we can call existing Swift APIs using this new feature, and why your decision to write your SDK in Objective-C might turn out to have been a very clever move.

We’ll also have a look at the refactoring support Apple is adding to Xcode and how it will help you migrate your existing code base.

Transcript

1. async/await in Swi! Photo by Stephen H on Unsplash Peter Friese | Firebase Developer Advocate | @pete!riese
2. let req = URLRequest(url: URL(string: “https:!"yourapi/path“)!) let task = URLSession.shared.dataTask(with: req) { data, response, error in !" do stuff once data arrives } task.resume() Asynchronous code is everywhere completion handler
3. func process(url: String, completion: @escaping (Article) !# Void) { self.fetchArticle(from: url) { html in self.extractTitle(from: html) { title in self.extractText(from: html) { text in self.extractImage(from: url) { imageUrl in self.inferTags(from: text) { tags in let article = Article(url: url, title: title, tags: tags, imageUrlString: imageUrl) completion(article) } } } } } } A more complex example
4. extension ArticleAnalyser { func process(url: String, completion: @escaping (Article) !# Void) { self.fetchArticle(from: url) { result in switch result { case .failure(let error): print(error.localizedDescription) case .success(let html): self.extractTitle(from: html) { result in switch result { case .failure(let error): print(error.localizedDescription) case .success(let title): self.extractText(from: html) { result in switch result { case .failure(let error): print(error.localizedDescription) case .success(let text): Let’s add some error handling… !
5. extension AsyncArticleAnalyser { func process(url: String) async throws !# Article { let htmlText = try await fetchArticle(from: url) let text = try await extractText(from: htmlText) let title = try await extractTitle(from: htmlText) let imageUrl = try await extractImage(from: url) let tags = await inferTags(from: text) return Article(url: url, title: title, tags: tags, imageUrlString: imageUrl) } } How about this? Swift 5.5
6. This is just the toolchain, really
7. Select toolchain here Toolchain is active
8. func helloWorld(name: String, completion: (String) !# Void) { completion("Hello, \(name)") } Let’s convert a callback-based function! func greeting() { helloWorld(name: "Peter") { result in print(result) } }
9. func helloWorld(name: String, completion: (String) !# Void) { completion("Hello, \(name)") } Let’s convert a callback-based function! func helloWorld(name: String) async !# String { return "Hello, \(name)" } Before After
10. func helloWorld(name: String, completion: (String) !# Void) { completion("Hello, \(name)") } Let’s convert a callback-based function! let result = await helloWorld(name: "Peter") func helloWorld(name: String) async !# String { return "Hello, \(name)" } Before After Call site
11. Sometimes, it’s more complicated, though func getUser(id: Int, _ completion: @escaping (User?) !# Void) { let req = URLRequest(url: URL(string: "https:!"jsonplaceholder./users/\(id)")!) URLSession.shared.dataTask(with: req) { data, response, error in guard let data = data else { return } do { let user = try JSONDecoder().decode(User.self, from: data) completion(user) } catch { completion(nil) } }.resume() } func greeting() { getUser(id: 1) { result in if let userName = result!$name { print("Hello, \(userName)") } } }
12. Sometimes, it’s more complicated, though func getUser(id: Int, _ completion: @escaping (User?) !# Void) { let req = URLRequest(url: URL(string: "https:!"jsonplaceholder./users/\(id)")!) URLSession.shared.dataTask(with: req) { data, response, error in guard let data = data else { return } do { let user = try JSONDecoder().decode(User.self, from: data) completion(user) } catch { completion(nil) } }.resume() } Let’s keep this entire function func getUser(id: Int, _ completion: @escaping (User?) !# Void) { !!% }
13. func getUser(id: Int, _ completion: @escaping (User?) !# Void) { let req = URLRequest(url: URL(string: "https:!"jsonplaceholder./users/\(id)")!) URLSession.shared.dataTask(with: req) { data, response, error in guard let data = data else { return } do { let user = try JSONDecoder().decode(User.self, from: data) completion(user) } catch { completion(nil) } }.resume() } Sometimes, it’s more complicated, though func getUser(id: Int, _ completion: @escaping (User?) !# Void) { !!% } func getUser(id: Int) async !# User? { return await withCheckedContinuation { cont in getUser(id: id) { result in cont.resume(returning: result) } } } Introduce this wrapper
14. func getUser(id: Int, _ completion: @escaping (User?) !# Void) { let req = URLRequest(url: URL(string: "https:!"jsonplaceholder./users/\(id)")!) URLSession.shared.dataTask(with: req) { data, response, error in guard let data = data else { return } do { let user = try JSONDecoder().decode(User.self, from: data) completion(user) } catch { completion(nil) } }.resume() } Sometimes, it’s more complicated, though func getUser(id: Int, _ completion: @escaping (User?) !# Void) { !!% } func getUser(id: Int) async !# User? { return await withCheckedContinuation { cont in getUser(id: id) { result in cont.resume(returning: result) } } } Call the original here
15. func getUser(id: Int, _ completion: @escaping (User?) !# Void) { let req = URLRequest(url: URL(string: "https:!"jsonplaceholder./users/\(id)")!) URLSession.shared.dataTask(with: req) { data, response, error in guard let data = data else { return } do { let user = try JSONDecoder().decode(User.self, from: data) completion(user) } catch { completion(nil) } }.resume() } Sometimes, it’s more complicated, though func getUser(id: Int, _ completion: @escaping (User?) !# Void) { !!% } func getUser(id: Int) async !# User? { return await withCheckedContinuation { cont in getUser(id: id) { result in cont.resume(returning: result) } } } Create a continuation Resume once we receive a result
16. func getUser(id: Int, _ completion: @escaping (User?) !# Void) { let req = URLRequest(url: URL(string: "https:!"jsonplaceholder./users/\(id)")!) URLSession.shared.dataTask(with: req) { data, response, error in guard let data = data else { return } do { let user = try JSONDecoder().decode(User.self, from: data) completion(user) } catch { completion(nil) } }.resume() } Sometimes, it’s more complicated, though func getUser(id: Int, _ completion: @escaping (User?) !# Void) { !!% } func getUser(id: Int) async !# User? { return await withCheckedContinuation { cont in getUser(id: id) { result in cont.resume(returning: result) } } } let result = await getUser(id: 1) Call site
18. await: only from within async context
19. func getUser(id: Int, _ completion: @escaping (User?) !# Void) { let req = URLRequest(url: URL(string: "https:!"jsonplaceholder./users/\(id)")!) URLSession.shared.dataTask(with: req) { data, response, error in guard let data = data else { return } do { let user = try JSONDecoder().decode(User.self, from: data) completion(user) } catch { completion(nil) } }.resume() } await: only from within async context struct AddArticleView: View { @ObservedObject var viewModel: ArticlesViewModel @State var newUrl: String = "" func addUrl(url: String) { Task.detached { await viewModel.addNewArticle(from: url) } presentationMode.wrappedValue.dismiss() } var body: some View { } } Previously: @asyncHandler
21. Run with confidence Engage users Develop apps faster
22. Run with confidence Crashlytics Performance Monitoring Test Lab App Distribution Engage users Analytics Predictions Cloud Messaging Remote Config A/B Testing Dynamic Links In-app Messaging Develop apps faster Auth Cloud Functions Cloud Firestore Hosting ML Kit Realtime Database Cloud Storage bit.ly/what-is-firebase Extensions Machine Learning
23. auth!$signInAnonymously() let user = auth!$currentUser print("User signed in with user ID: \(user!$uid)") This might be nil
24. auth!$signInAnonymously() let user = auth!$currentUser print("User signed in with user ID: \(user!$uid)") auth!$signInAnonymously { result, error in guard let result = result else { return } print("User signed in with user ID: \(result.user.uid)") } Use callbacks instead
25. auth!$signInAnonymously() let user = auth!$currentUser print("User signed in with user ID: \(user!$uid)") auth!$signInAnonymously { result, error in guard let result = result else { return } print("User signed in with user ID: \(result.user.uid)") } @Published var user: User? !!% auth!$signInAnonymously() .map { $0.user } .replaceError(with: nil) .assign(to: &$user) Combine
26. auth!$signInAnonymously { result, error in guard let result = result else { return } print("User signed in with user ID: \(result.user.uid)") } Firebase and async/await
27. auth!$signInAnonymously { result, error in guard let result = result else { return } print("User signed in with user ID: \(result.user.uid)") } Firebase and async/await do { let result = try await auth!$signInAnonymously() print("User signed in with user ID: \(result.user.uid)") } catch { print(error) } Callback-style Async/await
28. Here is how much work it was to implement for Firebase: . (yep - it came almost for free)
31. Learn more h!ps://pete"riese.dev/async-await-in-swi# h!ps://www.youtube.com/watch?v=sEKw2BMcQtQ
32. Thanks! Peter Friese h!p://pete"riese.dev @pete"riese youtube.com/c/PeterFriese/ Follow me