Swift 6 cheatsheet

Swift 6: Errors and concurrency

6 common Swift 6 tasks.

Throw and catch errors

Mark functions that can fail with throws, call them with try, and handle errors in do/catch.

enum ValidationError: Error { case empty }

func validate(_ text: String) throws {
    if text.isEmpty { throw ValidationError.empty }
}

do {
    try validate("")
} catch {
    print("failed: \(error)")
}

Async functions

async functions can suspend. Call them with await.

func fetchUser() async throws -> User {
    let (data, _) = try await URLSession.shared.data(from: url)
    return try JSONDecoder().decode(User.self, from: data)
}

Run work in parallel

async let starts child tasks that run concurrently.

async let first = fetchUser()
async let second = fetchPosts()
let (user, posts) = try await (first, second)

Start a task

Task starts asynchronous work from synchronous code.

Task {
    let user = try await fetchUser()
    print(user.name)
}

Protect shared state with an actor

An actor processes one call at a time, which prevents data races. Call its methods with await.

actor Counter {
    private var value = 0
    func increment() -> Int {
        value += 1
        return value
    }
}

let count = await counter.increment()

Update the UI on the main actor

Mark UI code @MainActor so it always runs on the main thread.

@MainActor
final class ViewModel: ObservableObject {
    @Published var items: [String] = []
}