Swift Eye for the Stringly Typed API

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SWIFT EYE FOR THE STRINGLY TYPED API Medium: Andyy Hope Twitter: @andyyhope

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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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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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Are there downsides to stringly typed APIs?

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Are there downsides to stringly typed APIs Yep

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

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Stringly typed • Unicode artifacts "Account.!isUserLoggedIn"

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

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

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

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

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UserDefaults

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

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

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

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Swift Eye for UserDefaults API

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

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Swift 3: Rename Old NSUserDefaults New UserDefaults

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

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

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

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

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

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

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

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

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

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

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

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// 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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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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// 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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Hurts our brains

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Extend UserDefaults

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Extend UserDefaults

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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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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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Protocols

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Protocol: BoolDefaultSettable protocol BoolDefaultSettable { associatedtype BoolKey : RawRepresentable }

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

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

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

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

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

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

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

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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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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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Protocol: BoolDefaultSettable protocol BoolDefaultSettable { associatedtype BoolKey : RawRepresentable }

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

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

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What about Uniformity?

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

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

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What about Context?

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

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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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So what have we learned?

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

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

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