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
   

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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
   

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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)
   

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4. Are there downsides to
   stringly typed APIs?
   

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5. Are there downsides to
   stringly typed APIs
   Yep
   

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6. Stringly typed
   • Typos
   let notification = "userAlertNotificaton"
   • Side effects
   let image = UIImage(named: "Charmandr")
   • Collisions
   let keyA = "isUserLoggedIn"
   let keyB = "isUserLoggedIn"
   keyA == keyB
   

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7. Stringly typed
   • Runtime crashes
   tableView.registerClass(UITableViewCell.self,
   forCellReuseIdentifier: "CellIdentifer")
   ...
   let cell: UITableViewCell = tableView
   .dequeueReusableCellWithIdentifier("CelIdentifer")
   

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8. Stringly typed
   • Unicode artifacts
   "Account.!isUserLoggedIn"
   

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9. Stringly typed
   • Disorderly
   • Title cased
   "IsUserLoggedIn"
   • Camel cased
   "isUserLoggedIn"
   

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10. Stringly typed
    • Disorderly
    • Prefixes
    "isUserLoggedIn"
    "Account.isUserLoggedIn"
    "com.andyyhope.Account.isUserLoggedIn"
    

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11. Stringly typed
    • Disorderly
    • Naming
    "isUserBlocked"
    "userBlocked"
    "hasUserBeenBlocked"
    

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12. They're
    everywhere...
    UIImage
    UITableView
    UICollectionView
    UIStoryboard
    UISegue
    URL
    DateFormatter
    NotificationCenter
    UserDefaults
    ...
    

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13. UserDefaults
    

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14. UserDefaults
    • Used to store small persistent pieces of information:
    • Settings
    • Arrays
    • Booleans
    

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16. UserDefaults
    • Used to store small persistent pieces of
    information:
    • Settings
    • Arrays
    • Booleans
    • (AKA) Diet CoreData
    

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17. UserDefaults
    • Used to store small persistent pieces of
    information:
    • Settings
    • Arrays
    • Booleans
    • (AKA) Diet CoreData
    • Stringly typed APIs
    

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19. Swift Eye for
    UserDefaults API
    

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20. Swift 3
    UserDefaults Recap
    Xcode 8 Beta 6. August 15, 2016
    

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21. Swift 3: Rename
    Old
    NSUserDefaults
    New
    UserDefaults
    

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22. Swift 3: Instance
    Old
    NSUserDefaults.standardUserDefaults()
    New
    UserDefaults.standard
    

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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")
    

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24. Swift 3: Get API
    Old
    .boolForKey("isUserLoggedIn")
    .integerForKey("pokeballCount")
    .objectForKey("pikachu")
    New
    .bool(forKey: "isUserLoggedIn")
    .integer(forKey: "pokeballCount")
    .object(forKey: "pikachu")
    

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25. Swift 3: Synchronize
    Old
    NSUserDefaults.standardUserDefaults().synchronize()
    New
    // deprecated !
    

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26. UserDefaults
    Stringly typed API
    // Setter
    UserDefaults.standard.set(true, forKey: "isUserLoggedIn")
    // Getter
    UserDefaults.standard.bool(forKey: "isUserLoggedIn")
    

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27. Fix: Constants
    UserDefaults.standard.set(true, forKey: "isUserLoggedIn")
    UserDefaults.standard.bool(forKey: "isUserLoggedIn")
    

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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)
    

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29. Fix: Unify
    struct Constants {
    struct Keys {
    // Account
    static let isUserLoggedIn = "isUserLoggedIn"
    // Onboarding
    ...
    }
    }
    

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30. // Set
    UserDefaults.standard
    .set(true, forKey: Constants.Keys.isUserLoggedIn)
    // Get
    UserDefaults.standard
    .bool(forKey: Constants.Keys.isUserLoggedIn)
    

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31. Fix: Unify with context
    struct Constants {
    struct Keys {
    struct Account {
    static let isUserLoggedIn = "isUserLoggedIn"
    }
    }
    }
    

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32. // Set
    UserDefaults.standard
    .set(true, forKey: Constants.Keys.Account.isUserLoggedIn)
    // Get
    UserDefaults.standard
    .bool(forKey: Constants.Keys.Account.isUserLoggedIn)
    

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33. Fix: Unify
    Constants.swift
    struct Account {
    static let isUserLoggedIn = "isUserLoggedIn"
    }
    

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34. Fix: Unify with enums
    Constants.swift
    enum Account : String {
    case isUserLoggedIn
    }
    

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35. struct Constants {
    struct Keys {
    enum Account : String {
    case isUserLoggedIn
    }
    }
    }
    

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36. // Set
    UserDefaults.standard
    .set(true, forKey: Constants.Keys.Account.isUserLoggedIn.rawValue)
    // Get
    UserDefaults.standard
    .bool(forKey: Constants.Keys.Account.isUserLoggedIn.rawValue)
    

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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
    

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38. // Set
    UserDefaults.standard
    .set(true, forKey: Constants.Keys.Account.isUserLoggedIn.rawValue)
    // Get
    UserDefaults.standard
    .bool(forKey: Constants.Keys.Account.isUserLoggedIn.rawValue)
    

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39. Hurts
    our brains
    

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40. Extend
    UserDefaults
    

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44. Extend
    UserDefaults
    

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45. tl;dw
    // Set
    UserDefaults.standard
    .set(true, forKey: Constants.Keys.Account.isUserLoggedIn.rawValue)
    // Get
    UserDefaults.standard
    .bool(forKey: Constants.Keys.Account.isUserLoggedIn.rawValue)
    

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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)
    

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47. Protocols
    

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48. Protocol: BoolDefaultSettable
    protocol BoolDefaultSettable {
    associatedtype BoolKey : RawRepresentable
    }
    

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50. "For every protocol, there is an
    equal and corresponding protocol
    extension"
    — Crusty's Third Law
    

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51. Protocol: BoolDefaultSettable
    protocol BoolDefaultSettable {
    associatedtype BoolKey : RawRepresentable
    }
    extension BoolDefaultSettable where BoolKey.RawValue == String {
    }
    

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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)
    }
    }
    

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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)
    }
    }
    

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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)
    }
    }
    

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55. Protocol: DefaultSettable Family
    protocol IntegerDefaultSettable { ... }
    protocol DoubleDefaultSettable { ... }
    protocol FloatDefaultSettable { ... }
    protocol ObjectDefaultSettable { ... }
    protocol URLDefaultSettable { ... }
    

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56. UserDefaults extension
    extension UserDefaults : BoolDefaultSettable {
    enum BoolKey : String {
    case isUserLoggedIn
    }
    }
    

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57. UserDefaults extension
    extension UserDefaults : BoolDefaultSettable {
    enum BoolKey : String {
    case isUserLoggedIn
    }
    }
    ...
    UserDefaults.standard.set(true, forKey: .isUserLoggedIn)
    UserDefaults.standard.bool(forKey: .isUserLoggedIn)
    

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58. Account extension
    extension Account : BoolDefaultSettable {
    enum BoolKey : String {
    case isUserLoggedIn
    }
    }
    ...
    Account.set(true, forKey: .isUserLoggedIn)
    Account.bool(forKey: .isUserLoggedIn)
    

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59. Problem: Collisions
    Account.BoolKey.isUserLoggedIn.rawValue
    // key: "isUserLoggedIn"
    UserDefaults.BoolKey.isUserLoggedIn.rawValue
    // key: "isUserLoggedIn"
    

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60. Protocol: KeyNamespaceable
    protocol KeyNamespaceable {
    func namespaced(_ key: T) -> String
    }
    

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61. Protocol: KeyNamespaceable
    protocol KeyNamespaceable {
    func namespaced(_ key: T) -> String
    }
    extension KeyNamespaceable {
    func namespaced(_ key: T) -> String {
    return "\(Self.self).\(key.rawValue)"
    }
    }
    

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62. protocol KeyNamespaceable {
    func namespaced(_ key: T) -> String
    }
    extension KeyNamespaceable {
    func namespaced(_ key: T) -> String {
    return "\(Self.self).\(key.rawValue)"
    }
    }
    // key: "UserDefaults.isUserLoggedIn"
    

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63. Protocol: BoolDefaultSettable
    protocol BoolDefaultSettable {
    associatedtype BoolKey : RawRepresentable
    }
    

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64. Protocol: BoolDefaultSettable
    protocol BoolDefaultSettable : KeyNamespaceable {
    associatedtype BoolKey : RawRepresentable
    }
    

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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)
    }
    }
    

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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)
    }
    }
    

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67. Collision free
    UserDefaults.set(true, forKey: .isUserLoggedIn)
    // key: "UserDefaults.isUserLoggedIn"
    Account.set(true, forKey: .isUserLoggedIn)
    // key: "Account.isUserLoggedIn"
    

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68. What about
    Uniformity?
    

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69. Constants.swift
    extension Account : BoolDefaultSettable { ... }
    extension Onboarding : BoolDefaultSettable { ... }
    struct Constants { ... }
    

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70. Constants.swift
    extension Account : BoolDefaultSettable { ... }
    extension Onboarding : BoolDefaultSettable { ... }
    struct Constants { ... }
    ...
    Account.set(true, forKey: .isUserLoggedIn)
    Account.bool(forKey: .isUserLoggedIn)
    

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71. What about
    Context?
    

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72. Defaults.swift
    struct Defaults {
    struct Account : BoolDefaultSettable { ... }
    struct Onboarding : BoolDefaultSettable { ... }
    }
    

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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)
    

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75. So what have we
    learned?
    

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76. So what have we learned?
    • Stringly typed API's are bad
    

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77. So what have we learned?
    • Stringly typed API's are bad
    • Plenty of room for improvement
    

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78. So what have we learned?
    • Stringly typed API's are bad
    • Plenty of room for improvement
    • Grouping constants can assist uniformity
    

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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
    

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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
    

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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
    

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82. SWIFT EYE
    FOR THE STRINGLY TYPED API
    Thank You
    Medium: Andyy Hope
    Twitter: @andyyhope
    

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