PATs IRL@NatashaTheRobot

Protocol-Oriented Programming in Swift Dave Abrahams Professor of Blowing-Your-Mind

–- Professor of Blowing-Your-Mind

"Swift is a Protocol-Oriented Programming Language"

Protocols with Associated Types 🤔

Protocols with Associated Types 🤗

• Models

• Storyboards

• Networking

PATs 💖 Models

protocol HasInit { init() }

class Pokemon<Power: HasInit> { func attack() -> Power { return Power() } }

// power types struct 🌧: HasInit { } struct 🌩: HasInit { } struct 🔥: HasInit { }

class Pikachu: Pokemon<🌩> {} class Vaporeon: Pokemon<🌧> {}

let pikachu = Pikachu() pikachu.attack() // 🌩

let vaporeon = Vaporeon() vaporeon.attack() // 🌧

Mixins and Traits in Swift 2.0 by Matthijs Hollemans

Mixins and Traits in Swift 2.0 by Matthijs Hollemans

protocol PowerTrait { associatedtype Power: HasInit func attack() -> Power }

extension PowerTrait { func attack() -> Power { return Power() } }

struct Pikachu: PowerTrait { associatedtype Power = 🌩 }

struct Vaporeon: PowerTrait { // 🌧 is inferred as the associated type func attack() -> 🌧 { // custom attack logic return 🌧() } }

PATs 💖 Storyboards

override func prepare(for segue: UIStoryboardSegue, sender: AnyObject?) { switch segueIdentifier(forSegue: segue) { case .StatueOfLibertyAdventure: let statueOfLibertyVC = segue.destinationViewController as? StatueOfLiberityViewController statueOfLibertyVC?.user = user case .EmpireStateAdventure: let empireStateVC = segue.destinationViewController as? EmpireStateViewController

empireStateVC?.friends = [friend1, friend2]

protocol Injectable { associatedtype Item func inject(item: Item) func assertDependencies() }

class AdventureDetailViewController: UIViewController, Injectable {

private var user: User! override func viewDidLoad() { super.viewDidLoad()

assertDependencies() // Do any additional setup after loading the view. } func inject(item: User) { user = item } func assertDependencies() { assert(user != nil) }

}

override func prepare(for segue: UIStoryboardSegue, sender: AnyObject?) { switch segueIdentifier(forSegue: segue) { case .StatueOfLibertyAdventure: let statueOfLibertyVC = segue.destinationViewController as? StatueOfLiberityViewController statueOfLibertyVC?.inject(item: user) case .EmpireStateAdventure: let empireStateVC = segue.destinationViewController as? EmpireStateViewController

empireStateVC?.inject(item: [friend1, friend2])

PATs 💖 Networking

struct FoodService { func get(completionHandler: Result<[Food]> -> Void) { // make asynchronous API call // and return appropriate result } }

enum Result<T> { case Success(T) case Failure(ErrorType) }

struct FoodService { func get(completionHandler: Result<[Food]> -> Void) { // make asynchronous API call // and return appropriate result } }

// NYCFoodViewController

var dataSource = [Food]() { didSet { tableView.reloadData() } }

override func viewDidLoad() { super.viewDidLoad() getFood() }

private func getFood() { FoodService().get() { [weak self] result in switch result { case .Success(let food): self?.dataSource = food case .Failure(let error): self?.showError(error) } } }

View Controller Tests?!!! 😱

// NYCFoodViewController

private func getFood() { FoodService().get() { [weak self] result in switch result { case .Success(let food): self?.dataSource = food case .Failure(let error): self?.showError(error) } } }

// NYCFoodViewController

func getFood(fromService service: FoodService) {

service.getFood() { [weak self] result in // handle result } }

// NYCFoodViewControllerTests

func testFetchFood() { viewController.getFood(fromService: FoodService()) // 🤔 now what? }

struct FoodService { func get(completionHandler: Result<[Food]> -> Void) { // make asynchronous API call // and return appropriate result } }

protocol Gettable { func get(completionHandler: Result<[Food]> -> Void) }

protocol Gettable { associatedtype T func get(completionHandler: Result<T> -> Void) }

struct FoodService: Gettable { func get(completionHandler: Result<[Food]> -> Void) { // make asynchronous API call // and return appropriate result } }

// NYCFoodViewController

override func viewDidLoad() { super.viewDidLoad() getFood(fromService: FoodService()) }

func getFood<S: Gettable where S.T == [Food]>(fromService service: S) { service.get() { [weak self] result in switch result { case .Success(let food): self?.dataSource = food case .Failure(let error): self?.showError(error) } } }

// NYCFoodViewControllerTests

class Fake_FoodService: Gettable { var getWasCalled = false func get(completionHandler: Result<[Food]> -> Void) { getWasCalled = true completionHandler(Result.Success(food)) } }

// NYCFoodViewControllerTests

func testFetchFood() { let fakeFoodService = Fake_FoodService() viewController.getFood(fromService: fakeFoodService) XCTAssertTrue(fakeFoodService.getWasCalled) XCTAssertEqual(viewController.dataSource.count, food.count) XCTAssertEqual(viewController.dataSource, food) }

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