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Swift Academy · Lesson

Bridging Result to async/await

Converting callback-based Result APIs into async throwing functions.

Bridging Result to async/await is a free Swift Academy lesson on CoddyKit — lesson 4 of 4. You can read the complete lesson below for free — then practise it hands-on in the browser with a built-in code editor and a 24/7 AI tutor. It is part of the Swift Academy learning path, one of 4 lessons in the course, and your progress syncs across the web and the CoddyKit app.

Welcome

Legacy callback-based APIs return `Result`. Modern code uses async/await. Bridging between them is a common task — Swift has clean patterns for both directions.

withCheckedThrowingContinuation

```swift func fetchAsync(url: URL) async throws -> Data { try await withCheckedThrowingContinuation { cont in fetchCallback(url) { result in cont.resume(with: result) } } } ``` `cont.resume(with: result)` accepts a `Result` directly.

withCheckedContinuation (Non-Throwing)

```swift func fetchAsync(url: URL) async -> Result { await withCheckedContinuation { cont in fetchCallback(url) { result in cont.resume(returning: result) } } } ```

Converting async to Result

```swift func asResult(of operation: () async throws -> T) async -> Result { do { return .success(try await operation()) } catch { return .failure(error) } } let r = await asResult { try await fetch(url) } ```

Result.get() in async Context

```swift func process() async { let result: Result = await fetchAsync(url) do { let data = try result.get() handle(data) } catch { handle(error) } } ```

Task { } for Bridging

```swift func load() { Task { let data = try await fetchAsync(url) await MainActor.run { self.render(data) } } } ```

AsyncStream from Callbacks

```swift func events() -> AsyncStream { AsyncStream { cont in let token = subscribe { event in cont.yield(event) } cont.onTermination = { _ in unsubscribe(token) } } } ```

Continuation Safety Rules

• Call `resume` exactly once — calling twice is undefined behaviour • Do not resume after the function has returned • Use `withCheckedContinuation` in debug (detects mistakes); `withUnsafeContinuation` in release if needed for performance

MainActor for UI Updates

```swift await MainActor.run { label.text = data.description } // or: @MainActor func updateUI(_ d: Data) { label.text = ... } await updateUI(data) ```

Testing Async+Result

```swift func testFetch() async throws { let result = await asResult { try await fetchAsync(url) } switch result { case .success(let d): XCTAssertFalse(d.isEmpty) case .failure(let e): XCTFail(e.localizedDescription) } } ```

Quick Check

Which continuation type detects misuse like double-resume in debug builds?

Recap

Key takeaways: • `withCheckedThrowingContinuation` bridges callbacks to async throws • `cont.resume(with: result)` accepts a Result directly • Wrap `async throws` in `Result` with a helper function • Call `resume` exactly once • `MainActor.run { }` for safe UI updates from async context Course complete! Next: SwiftUI basics.

Frequently asked questions

Is the “Bridging Result to async/await” lesson free?

Yes — the full text of “Bridging Result to async/await” is free to read here on the web, and the Swift Academy course includes 4 lessons in total. To practise it interactively (a built-in code editor and a 24/7 AI tutor) and unlock the rest of the Swift Academy course, upgrade to CoddyKit PRO.

What will I learn in “Bridging Result to async/await”?

Converting callback-based Result APIs into async throwing functions. You practise Swift Academy with hands-on code you run directly in the browser, and a 24/7 AI tutor answers your questions as you work through the lesson.

Do I need any experience to start Swift Academy?

No prior experience is required. Swift Academy on CoddyKit is structured for beginners through advanced learners; this is — lesson 4 of 4, so you can start here or from the beginning and move at your own pace.

How long does the “Bridging Result to async/await” lesson take?

Most CoddyKit lessons take about 5–10 minutes. Each one is bite-sized and interactive, so you make steady progress and pick up exactly where you left off across the web and the app.

Can I write and run code in this Swift Academy lesson?

Yes. Every Swift Academy lesson includes a built-in code editor, so you write and run real code right in your browser and get instant AI feedback — no local setup required.

All lessons in this course

  1. Result Fundamentals
  2. map and flatMap on Result
  3. Custom Error Types with LocalizedError
  4. Bridging Result to async/await
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