jacobsapps

// the compiler is happy now
func escapingSendableClosure(_ then: @escaping @Sendable () -> Void) {
    Task {
        then()
    }
}

jacobsapps

// Error: Capture of 'then' with non-sendable type 
// '() -> Void' in a `@Sendable` closure
func escapingClosure(_ then: @escaping () -> Void) {
    Task {
        then()
    }
}

jacobsapps

// safe to pass between arbitrary Tasks, async functions, and Actors
struct UserData: Sendable {
    var id: Int
    var name: String
}

// safe because properties are immutable and we can't subclass
final class User: Sendable {
    let name: String
    let age: Int

jacobsapps

import AuthenticationServices

func signInWithGoogle() async throws -> String {
    try await withCheckedThrowingContinuation { continuation in
        let session = ASWebAuthenticationSession(
            url: URL(string: "https://oauth.example.com/auth")!,
            callbackURLScheme: "myapp"
        ) { callbackURL, error in
            if let error = error {
                continuation.resume(throwing: error)

jacobsapps

public protocol View {
    associatedtype Body : View
    @ViewBuilder @MainActor var body: Self.Body { get }
}

jacobsapps

// All code runs on MainActor
@MainActor
func updateUI(with text: String) {
    label.text = text
}

// properties and functions implicitly marked @MainActor
@MainActor
class ViewModel: ObservableObject {
    // ...

jacobsapps

actor BankAccount { 
    // ... 
} 

let account = BankAccount()

await account.deposit(1000)

// simultaneously attempt to withdraw
async let one = account.withdraw(500)

jacobsapps

class BankAccount {
    enum BankAccountError: Error {
        case insufficientFunds
    }
    
    private(set) var balance: Double = 0
    
    func deposit(_ amount: Double) {
        balance += amount
    }

jacobsapps

// user IDs not known at compile-time
let userIds = getUserIds() // [1, 2, 3, 4, 5]

let users = await withTaskGroup(of: User.self) { group in
    for id in userIds {
        group.addTask {
            await fetchUser(id: id)
        }
    }
    

jacobsapps

async let user = fetchUser(id: 1)
async let posts = fetchPosts(userId: 1)
async let friends = fetchFriends(userId: 1)
// no suspension yet 
// execution kicks off all child tasks immediately 

// suspension only happens at the first await 
self.user = await user            // fetchUser() async 
self.posts = try? await posts     // fetchPosts() async throws 
self.friends = try await friends  // fetchFriends() async throws