func processImageData2a(completionBlock: (_ result: Image?, _ error: Error?) -> Void) {    loadWebResource("dataprofile.txt") { dataResource, error in        guard let dataResource = dataResource else {            completionBlock(nil, error)            return        }        loadWebResource("imagedata.dat") { imageResource, error in            guard let imageResource = imageResource else {                completionBlock(nil, error)                return            }            decodeImage(dataResource, imageResource) { imageTmp, error in                guard let imageTmp = imageTmp else {                    completionBlock(nil, error)                    return                }                dewarpAndCleanupImage(imageTmp) { imageResult, error in                    guard let imageResult = imageResult else {                        completionBlock(nil, error)                        return                    }                    completionBlock(imageResult)                }            }        }    }}
processImageData2a { image, error in    guard let image = image else {        display("No image today", error)        return    }    display(image)}

func loadWebResource(_ path: String) async throws -> Resourcefunc decodeImage(_ r1: Resource, _ r2: Resource) async throws -> Imagefunc dewarpAndCleanupImage(_ i : Image) async throws -> Image
func processImageData() async throws -> Image {  let dataResource  = try await loadWebResource("dataprofile.txt")  let imageResource = try await loadWebResource("imagedata.dat")  let imageTmp      = try await decodeImage(dataResource, imageResource)  let imageResult   = try await dewarpAndCleanupImage(imageTmp)  return imageResult}

func chopVegetables() async throws -> [Vegetable] { ... }func marinateMeat() async -> Meat { ... }func preheatOven(temperature: Double) async throws -> Oven { ... }
// ...
func makeDinner() async throws -> Meal {  let veggies = try await chopVegetables()  // 处理蔬菜  let meat = await marinateMeat()           // 腌制肉  let oven = try await preheatOven(temperature: 350) //预热烤箱
  let dish = Dish(ingredients: [veggies, meat])   // 把蔬菜和肉装盘  return try await oven.cook(dish, duration: .hours(3))  // 用烤箱做出晚餐}

func makeDinner() async throws -> Meal {  // Prepare some variables to receive results from our concurrent child tasks  var veggies: [Vegetable]?  var meat: Meat?  var oven: Oven?
  enum CookingStep {     case veggies([Vegetable])    case meat(Meat)    case oven(Oven)  }
  // Create a task group to scope the lifetime of our three child tasks  try await withThrowingTaskGroup(of: CookingStep.self) { group in    group.async {      try await .veggies(chopVegetables())    }    group.async {      await .meat(marinateMeat())    }    group.async {      try await .oven(preheatOven(temperature: 350))    }
    for try await finishedStep in group {      switch finishedStep {        case .veggies(let v): veggies = v        case .meat(let m): meat = m        case .oven(let o): oven = o      }    }  }
  // If execution resumes normally after `withTaskGroup`, then we can assume  // that all child tasks added to the group completed successfully. That means  // we can confidently force-unwrap the variables containing the child task  // results here.  let dish = Dish(ingredients: [veggies!, meat!])  return try await oven!.cook(dish, duration: .hours(3))}

class RiskyCollector {    var deck: Set<String>
    init(deck: Set<String>) {        self.deck = deck    }
    func send(card selected: String, to person: RiskyCollector) -> Bool {        guard deck.contains(selected) else { return false }
        deck.remove(selected)        person.transfer(card: selected)        return true    }
    func transfer(card: String) {        deck.insert(card)    }}