async/await in Swi! Photo by Stephen H on Unsplash Peter Friese | Firebase Developer Advocate | @pete!riese

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

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

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… !

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

This is just the toolchain, really

Select toolchain here Toolchain is active

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) } }

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

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

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)") } } }

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) { !!% }

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

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

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

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

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await: only from within async context

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

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auth!$signInAnonymously() let user = auth!$currentUser print("User signed in with user ID: \(user!$uid)") This might be nil

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

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

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

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

Here is how much work it was to implement for Firebase: . (yep - it came almost for free)

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Learn more h!ps://pete"riese.dev/async-await-in-swi# h!ps://www.youtube.com/watch?v=sEKw2BMcQtQ

Thanks! Peter Friese h!p://pete"riese.dev @pete"riese youtube.com/c/PeterFriese/ Follow me