Swift Eye for the Stringly Typed API

This was the talk I gave at try! Swift NYC on September 2nd, 2016.

Transcript

1. SWIFT EYE FOR THE STRINGLY TYPED API Medium: Andyy Hope Twitter: @andyyhope
2. Stringly Typed? "A riff on "strongly typed". Used to describe an implementation that needlessly relies on strings when programmer & refactor friendly options are available." — Internet
3. Stringly Typed? "A riff on "strongly typed". Used to describe an implementation that needlessly relies on strings when programmer & refactor friendly options are available." — Internet // Stringly typed let image = UIImage(named: "PalletTown") // Strongly typed let tableView = UITableView(style: .Plain)
4. Are there downsides to stringly typed APIs?
5. Are there downsides to stringly typed APIs Yep
6. Stringly typed • Typos let notification = "userAlertNotificaton" • Side effects let image = UIImage(named: "Charmandr") • Collisions let keyA = "isUserLoggedIn" let keyB = "isUserLoggedIn" keyA == keyB
7. Stringly typed • Runtime crashes tableView.registerClass(UITableViewCell.self, forCellReuseIdentifier: "CellIdentifer") ... let cell: UITableViewCell = tableView .dequeueReusableCellWithIdentifier("CelIdentifer")
8. Stringly typed • Unicode artifacts "Account.!isUserLoggedIn"
9. Stringly typed • Disorderly • Title cased "IsUserLoggedIn" • Camel cased "isUserLoggedIn"
10. Stringly typed • Disorderly • Prefixes "isUserLoggedIn" "Account.isUserLoggedIn" "com.andyyhope.Account.isUserLoggedIn"
11. Stringly typed • Disorderly • Naming "isUserBlocked" "userBlocked" "hasUserBeenBlocked"
12. They're everywhere... UIImage UITableView UICollectionView UIStoryboard UISegue URL DateFormatter NotificationCenter UserDefaults ...
13. UserDefaults
14. UserDefaults • Used to store small persistent pieces of information: • Settings • Arrays • Booleans
16. UserDefaults • Used to store small persistent pieces of information: • Settings • Arrays • Booleans • (AKA) Diet CoreData
17. UserDefaults • Used to store small persistent pieces of information: • Settings • Arrays • Booleans • (AKA) Diet CoreData • Stringly typed APIs
19. Swift Eye for UserDefaults API
20. Swift 3 UserDefaults Recap Xcode 8 Beta 6. August 15, 2016
21. Swift 3: Rename Old NSUserDefaults New UserDefaults
22. Swift 3: Instance Old NSUserDefaults.standardUserDefaults() New UserDefaults.standard
23. Swift 3: Set API Old .setBool(true, forKey: "isUserLoggedIn") .setInt(1, forKey: "pokeballCount") .setObject(pikachu, forKey: "pikachu") New .set(true, forKey: "isUserLoggedIn") .set(1, forKey: "pokeballCount") .set(pikachu, forKey: "pikachu")
24. Swift 3: Get API Old .boolForKey("isUserLoggedIn") .integerForKey("pokeballCount") .objectForKey("pikachu") New .bool(forKey: "isUserLoggedIn") .integer(forKey: "pokeballCount") .object(forKey: "pikachu")
25. Swift 3: Synchronize Old NSUserDefaults.standardUserDefaults().synchronize() New // deprecated !
26. UserDefaults Stringly typed API // Setter UserDefaults.standard.set(true, forKey: "isUserLoggedIn") // Getter UserDefaults.standard.bool(forKey: "isUserLoggedIn")
27. Fix: Constants UserDefaults.standard.set(true, forKey: "isUserLoggedIn") UserDefaults.standard.bool(forKey: "isUserLoggedIn")
28. Fix: Constants // UserDefaults.standard.set(true, forKey: "isUserLoggedIn") // UserDefaults.standard.bool(forKey: "isUserLoggedIn") ... let isUserLoggedInKey = "isUserLoggedIn" UserDefaults.standard.set(true, forKey: isUserLoggedInKey) UserDefaults.standard.bool(forKey: isUserLoggedInKey)
29. Fix: Unify struct Constants { struct Keys { // Account static let isUserLoggedIn = "isUserLoggedIn" // Onboarding ... } }
30. // Set UserDefaults.standard .set(true, forKey: Constants.Keys.isUserLoggedIn) // Get UserDefaults.standard .bool(forKey: Constants.Keys.isUserLoggedIn)
31. Fix: Unify with context struct Constants { struct Keys { struct Account { static let isUserLoggedIn = "isUserLoggedIn" } } }
32. // Set UserDefaults.standard .set(true, forKey: Constants.Keys.Account.isUserLoggedIn) // Get UserDefaults.standard .bool(forKey: Constants.Keys.Account.isUserLoggedIn)
33. Fix: Unify Constants.swift struct Account { static let isUserLoggedIn = "isUserLoggedIn" }
34. Fix: Unify with enums Constants.swift enum Account : String { case isUserLoggedIn }
35. struct Constants { struct Keys { enum Account : String { case isUserLoggedIn } } }
36. // Set UserDefaults.standard .set(true, forKey: Constants.Keys.Account.isUserLoggedIn.rawValue) // Get UserDefaults.standard .bool(forKey: Constants.Keys.Account.isUserLoggedIn.rawValue)
37. Recap // Strings let key = "isUserLoggedIn" // Constant & Grouped let key = Constants.isUserLoggedIn // Context let key = Constants.Keys.Account.isUserLoggedIn // Safety let key = Constants.Keys.Account.isUserLoggedIn.rawValue
38. // Set UserDefaults.standard .set(true, forKey: Constants.Keys.Account.isUserLoggedIn.rawValue) // Get UserDefaults.standard .bool(forKey: Constants.Keys.Account.isUserLoggedIn.rawValue)
39. Hurts our brains
40. Extend UserDefaults
44. Extend UserDefaults
45. tl;dw // Set UserDefaults.standard .set(true, forKey: Constants.Keys.Account.isUserLoggedIn.rawValue) // Get UserDefaults.standard .bool(forKey: Constants.Keys.Account.isUserLoggedIn.rawValue)
46. tl;dw // Set // UserDefaults.standard // .set(true, forKey: Constants.Keys.Account.isUserLoggedIn.rawValue) UserDefaults.standard.set(true, forKey: .isUserLoggedIn) // Get // UserDefaults.standard // .bool(forKey: Constants.Keys.Account.isUserLoggedIn.rawValue) UserDefaults.standard.bool(forKey: .isUserLoggedIn)
47. Protocols
48. Protocol: BoolDefaultSettable protocol BoolDefaultSettable { associatedtype BoolKey : RawRepresentable }
50. "For every protocol, there is an equal and corresponding protocol extension" — Crusty's Third Law
51. Protocol: BoolDefaultSettable protocol BoolDefaultSettable { associatedtype BoolKey : RawRepresentable } extension BoolDefaultSettable where BoolKey.RawValue == String { }
52. Protocol: BoolDefaultSettable extension BoolDefaultSettable where BoolKey.RawValue == String { // Setter func set(_ value: Bool, forKey key: BoolKey) { let key = key.rawValue UserDefaults.standard.set(value, forKey: key) } }
53. Protocol: BoolDefaultSettable extension BoolDefaultSettable where BoolKey.RawValue == String { // Getter func bool(forKey key: BoolKey) -> Bool { let key = key.rawValue return UserDefaults.standard.bool(forKey: key) } }
54. protocol BoolDefaultSettable { associatedtype BoolKey : RawRepresentable } extension BoolDefaultSettable where BoolKey.RawValue == String { func set(_ value: Bool, forKey key: BoolKey) { let key = key.rawValue UserDefaults.standard.set(value, forKey: key) } func bool(forKey key: BoolKey) -> Bool { let key = key.rawValue return UserDefaults.standard.bool(forKey: key) } }
55. Protocol: DefaultSettable Family protocol IntegerDefaultSettable { ... } protocol DoubleDefaultSettable { ... } protocol FloatDefaultSettable { ... } protocol ObjectDefaultSettable { ... } protocol URLDefaultSettable { ... }
56. UserDefaults extension extension UserDefaults : BoolDefaultSettable { enum BoolKey : String { case isUserLoggedIn } }
57. UserDefaults extension extension UserDefaults : BoolDefaultSettable { enum BoolKey : String { case isUserLoggedIn } } ... UserDefaults.standard.set(true, forKey: .isUserLoggedIn) UserDefaults.standard.bool(forKey: .isUserLoggedIn)
58. Account extension extension Account : BoolDefaultSettable { enum BoolKey : String { case isUserLoggedIn } } ... Account.set(true, forKey: .isUserLoggedIn) Account.bool(forKey: .isUserLoggedIn)
59. Problem: Collisions Account.BoolKey.isUserLoggedIn.rawValue // key: "isUserLoggedIn" UserDefaults.BoolKey.isUserLoggedIn.rawValue // key: "isUserLoggedIn"
60. Protocol: KeyNamespaceable protocol KeyNamespaceable { func namespaced<T: RawRepresentable>(_ key: T) -> String }
61. Protocol: KeyNamespaceable protocol KeyNamespaceable { func namespaced<T: RawRepresentable>(_ key: T) -> String } extension KeyNamespaceable { func namespaced<T: RawRepresentable>(_ key: T) -> String { return "\(Self.self).\(key.rawValue)" } }
62. protocol KeyNamespaceable { func namespaced<T: RawRepresentable>(_ key: T) -> String } extension KeyNamespaceable { func namespaced<T: RawRepresentable>(_ key: T) -> String { return "\(Self.self).\(key.rawValue)" } } // key: "UserDefaults.isUserLoggedIn"
63. Protocol: BoolDefaultSettable protocol BoolDefaultSettable { associatedtype BoolKey : RawRepresentable }
64. Protocol: BoolDefaultSettable protocol BoolDefaultSettable : KeyNamespaceable { associatedtype BoolKey : RawRepresentable }
65. extension BoolDefaultSettable where BoolKey.RawValue == String { func set(_ value: Bool, forKey key: BoolKey) { let key = key.rawValue UserDefaults.standard.set(value, forKey: key) } func bool(forKey key: BoolKey) -> Bool { let key = key.rawValue return UserDefaults.standard.bool(forKey: key) } }
66. extension BoolDefaultSettable where BoolKey.RawValue == String { func set(_ value: Bool, forKey key: BoolKey) { let key = namespaced(key) UserDefaults.standard.set(value, forKey: key) } func bool(forKey key: BoolKey) -> Bool { let key = namespaced(key) return UserDefaults.standard.bool(forKey: key) } }
67. Collision free UserDefaults.set(true, forKey: .isUserLoggedIn) // key: "UserDefaults.isUserLoggedIn" Account.set(true, forKey: .isUserLoggedIn) // key: "Account.isUserLoggedIn"
68. What about Uniformity?
69. Constants.swift extension Account : BoolDefaultSettable { ... } extension Onboarding : BoolDefaultSettable { ... } struct Constants { ... }
70. Constants.swift extension Account : BoolDefaultSettable { ... } extension Onboarding : BoolDefaultSettable { ... } struct Constants { ... } ... Account.set(true, forKey: .isUserLoggedIn) Account.bool(forKey: .isUserLoggedIn)
71. What about Context?
72. Defaults.swift struct Defaults { struct Account : BoolDefaultSettable { ... } struct Onboarding : BoolDefaultSettable { ... } }
73. Defaults.swift struct Defaults { struct Account : BoolDefaultSettable { ... } struct Onboarding : BoolDefaultSettable { ... } } ... Defaults.Account.set(true, forKey: .isUserLoggedIn) Defaults.Onboarding.set(true, forKey: .isUserOnboarded) Defaults.Account.bool(forKey: .isUserLoggedIn) Defaults.Onboarding.bool(forKey: .isUserOnboarded)
75. So what have we learned?
76. So what have we learned? • Stringly typed API's are bad
77. So what have we learned? • Stringly typed API's are bad • Plenty of room for improvement
78. So what have we learned? • Stringly typed API's are bad • Plenty of room for improvement • Grouping constants can assist uniformity
79. So what have we learned? • Stringly typed API's are bad • Plenty of room for improvement • Grouping constants can assist uniformity • Namespacing gives context
80. So what have we learned? • Stringly typed API's are bad • Plenty of room for improvement • Grouping constants can assist uniformity • Namespacing gives context • Protocols are (so) hot right now
81. So what have we learned? • Stringly typed API's are bad • Plenty of room for improvement • Grouping constants can assist uniformity • Namespacing gives context • Protocols are (so) hot right now • Rethink how we interact with APIs
82. SWIFT EYE FOR THE STRINGLY TYPED API Thank You Medium: Andyy Hope Twitter: @andyyhope