Swift5.5、DocC、Notifications，WWDC21 带来的最大技术变化

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) }}