What's a good way to handle asynchronous code

Handling asynchronous code in Swift can be effectively managed using the async and await keywords. Here are some key points and techniques discussed in various WWDC sessions:

1. Async/Await Syntax:

   • Swift uses the async keyword to mark functions that may suspend, and the await keyword to indicate suspension points within those functions. This allows the CPU to yield to other tasks while waiting for an asynchronous operation to complete.
   • Example:

     func fetchData() async throws -> Data {
         let data = try await someAsyncFunction()
         return data
     }
     

   • For more details, you can refer to the session A Swift Tour: Explore Swift’s features and design.

2. Handling Completion Handlers:

   • If you have code that uses completion handlers, Swift provides an async overload automatically. If an async overload is not available, you can use withCheckedContinuation or withCheckedThrowingContinuation to convert it to an expression that can be awaited.
   • Example:

     func fetchData() async throws -> Data {
         return try await withCheckedThrowingContinuation { continuation in
             someFunctionWithCompletionHandler { result, error in
                 if let error = error {
                     continuation.resume(throwing: error)
                 } else {
                     continuation.resume(returning: result)
                 }
             }
         }
     }
     

   • For more information, see the session Go further with Swift Testing.

3. Concurrency and Data-Race Safety:

   • Swift 6 introduces complete data-race protection, ensuring that concurrent code is safe and reliable. This includes using actors to manage state and ensuring that access to shared mutable state is properly synchronized.
   • Example:

     actor UserStore {
         var users: [User] = []
         
         func addUser(_ user: User) {
             users.append(user)
         }
     }
     

   • For more details, refer to the session Migrate your app to Swift 6.

4. Testing Asynchronous Code:

   • When writing tests for asynchronous code, you can use the same concurrency features as in your production code. The await keyword will suspend the test, allowing other test code to execute while waiting for the asynchronous operation to complete.
   • Example:

     func testAsyncFunction() async throws {
         let result = try await someAsyncFunction()
         XCTAssertEqual(result, expectedValue)
     }
     

   • For more information, see the session Go further with Swift Testing.

By leveraging these techniques, you can handle asynchronous code in Swift more effectively, ensuring better performance and reliability in your applications.