The document discusses protocol-oriented programming in Swift, highlighting the use of protocols with associated types and their applications in model design, storyboards, and networking. It provides code examples demonstrating how to implement and utilize protocols, including mixins and traits, and discusses dependency injection in view controllers. Additionally, it touches on testing strategies for networking services in Swift applications.

1. PATs IRL
@NatashaTheRobot

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

4. –- Professor of Blowing-Your-Mind
"Swift is a Protocol-Oriented Programming Language"

5. Protocols with Associated Types
🤔

11. Protocols with Associated Types
🤗

12. • Models
• Storyboards
• Networking

13. PATs 💖 Models

16. protocol HasInit {
init()
}
class Pokemon<Power: HasInit> {
func attack() -> Power {
return Power()
}
}

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

18. class Pikachu: Pokemon<🌩> {}
class Vaporeon: Pokemon<🌧> {}
let pikachu = Pikachu()
pikachu.attack() // 🌩
let vaporeon = Vaporeon()
vaporeon.attack() // 🌧

20. Mixins and Traits in Swift 2.0
by Matthijs Hollemans

21. Mixins and Traits in Swift 2.0
by Matthijs Hollemans

22. protocol PowerTrait {
associatedtype Power: HasInit
func attack() -> Power
}
extension PowerTrait {
func attack() -> Power {
return Power()
}
}

23. struct Pikachu: PowerTrait {
associatedtype Power = 🌩
}
struct Vaporeon: PowerTrait {
// 🌧 is inferred as the associated type
func attack() -> 🌧 {
// custom attack logic
return 🌧()
}
}

25. PATs 💖 Storyboards

28. 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]

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

30. 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)
}
}

31. 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])

33. PATs 💖 Networking

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

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

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

38. // 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)
}
}
}

39. View Controller Tests?!!! 😱

40. // 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)
}
}
}

41. // NYCFoodViewController
func getFood(fromService service: FoodService) {
service.getFood() { [weak self] result in
// handle result
}
}

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

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

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

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

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

47. // 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)
}
}
}

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

49. // 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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