Stupid Enum Tricks in Swift and Kotlin - We Are Developers, Vienna, Austria, May 2018

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PREFACE: A NOTE ON PRONUNCIATION

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"EE-NUMB" VS. "EE-NOOM"

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"EE-NUMB" VS. "EE-NOOM" ⬆ (I PRONOUNCE IT THIS WAY)

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"EE-NUMB" VS. "EE-NOOM" (THIS WAY IS ALSO FINE)

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GIF

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GIF

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WHAT IS AN ENUM?

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A LIST OF VALUES THAT ARE POSSIBLE

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OPTION SET

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OPTION SET

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POSSIBLE IT COULD BE ANY ONE OF THESE THINGS IN THE LIST

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SWIFT enum ColorName: String { case red case orange case yellow case green case blue case violet }

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IT COULD ALSO BE SOMETHING TOTALLY DIFFERENT

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SWIFT func colorForName(_ name: String) -> UIColor? { switch name { case ColorName.red.rawValue: return UIColor.red case ColorName.orange.rawValue: return UIColor.orange // same for other ColorName cases default: return nil }

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EXHAUSTIVE ENUMS

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EXAUSTIVE BUT THESE ARE THE ONLY THINGS WHICH ARE POSSIBLE

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SWIFT enum TrafficLightColor { case red case yellow case green }

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LIMIT YOUR POSSIBILITIES

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LIMIT YOUR RUNTIME ERRORS

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SWIFT STANDARD LIBRARY public enum ComparisonResult : Int { case orderedAscending case orderedSame case orderedDescending }

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KOTLIN STANDARD LIBRARY public enum ClassKind { CLASS, INTERFACE, ENUM_CLASS, ENUM_ENTRY, ANNOTATION_CLASS, OBJECT; }

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HOW DO I CREATE MY OWN ENUM?

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SWIFT enum TrafficLightColor { case red case yellow case green }

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KOTLIN enum class

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KOTLIN enum class TrafficLightColor { Red, Yellow, Green; }

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HOW DO I USE ENUMS?

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switch / when

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SWIFT var currentColor: TrafficLightColor = .red switch currentColor { case .red: print("STOP RIGHT THERE") case .yellow: print("Whoa, slow down there, buddy.") case .green: print("Go, go, go!") }

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SWIFT var currentColor: TrafficLightColor = .red switch currentColor { case .red: print("STOP RIGHT THERE") case .green: print("Go, go, go!") // Error: Unhandled case! }

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SWIFT var currentColor: TrafficLightColor = .red switch currentColor { case .red: print("STOP RIGHT THERE") case .yellow, .green: print("Go, go, go!") }

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KOTLIN var currentColor = TrafficLightColor.Red when (currentColor) { TrafficLightColor.Red -> println("STOP RIGHT THERE") TrafficLightColor.Yellow -> println("Whoa, slow down there, buddy.") TrafficLightColor.Green -> println("Go, go, go!") }

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WHAT DO I GET FOR FREE WITH ENUMS?

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KOTLIN: A LOT!

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KOTLIN Instance Gets You Example instance.name String value of case's written name Days.THURSDAY.name is "THURSDAY", Days.Thursday.name is "Thursday" instance.ordinal Index of case in list of cases

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KOTLIN Type Gets You Type.valueOf(string: String) Enum value of string, or null Type.values() Generated list of all values in the enum class

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SWIFT: IT DEPENDS

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BY DEFAULT: NOT MUCH

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RawRepresentable

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SWIFT enum SettingsSection { case profile case contact case legalese case logout }

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SWIFT enum SettingsSection: Int { case profile case contact case legalese case logout }

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SWIFT enum SettingsSection: Int { case profile // 0 case contact // 1 case legalese // 2 case logout // 3 }

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SWIFT enum SettingsSection: Int { case profile // 0 case legalese // 1 case contact // 2 case logout // 3 }

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SWIFT guard let section = SettingsSection(rawValue: 10) else { assertionFailure("Section 10 does not exist!") }

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SWIFT enum JSONKey: String { case user_name case email_address case latitude case longitude }

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SWIFT enum JSONKey: String { case user_name case email_address case latitude = "lat" case longitude = "long" }

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SWIFT Codable class User: Codable { let userName: String let email: String let latitude: Double let longitude: Double enum CodingKeys: String, CodingKey { case userName = "user_name" case email = "email_address" case latitude = "lat" case longitude = "long" } }

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SWIFT 4.2: CaseIterable

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SWIFT

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SWIFT enum SettingsSection: Int, CaseIterable { case profile case legalese case contact case logout }

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SWIFT enum SettingsSection: Int, CaseIterable { case profile case legalese case contact case logout } // Automatically generated: static var allCases: [SettingsSection]

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SWIFT func numberOfSectionsInTableView(_ tableView: UITableView) -> Int { return SettingsSection.allCases.count } func tableView(_ tableView: UITableView, titleForHeaderInSection section: Int) -> String { let section = SettingsSection.allCases[section] return section.localizedTitle }

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WHAT CAN I ADD TO ENUMS?

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COMPUTED PROPERTIES

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SWIFT enum LandingScreenButton { case signIn case signUp case viewTerms }

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SWIFT enum LandingScreenButton { case signIn case signUp case viewTerms var localizedTitle: String { switch self { case .signIn: return NSLocalizedString("Sign In", "Sign in button title") case .signUp: return NSLocalizedString("Sign Up", "Sign up button title") case .viewTerms: return NSLocalizedString("View Terms & Conditions", "Title for button to view legalese") } }

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SWIFT public enum LandingScreenButton { case signIn case signUp case viewTerms public var localizedTitle: String { switch self { case .signIn: return NSLocalizedString("Sign In", "Sign in button title") case .signUp: return NSLocalizedString("Sign Up", "Sign up button title") case .viewTerms: return NSLocalizedString("View Terms & Conditions", "Title for button to view legalese") } }

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UI TESTING

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SWIFT / XCUI

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KOTLIN / ESPRESSO

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ASSET HANDLING [IOS]

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ASSET CATALOGS

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SWIFT / IOS: BEFORE guard let image = UIImage(named: "cinnamon_rolls") else { return }

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SWIFT / IOS: BEFORE guard let image = UIImage(named: "cinnamon_rolls") else { return }

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SWIFT / IOS: BEFORE guard let image = UIImage(named: "cinamon_rolls") else { return }

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SWIFT / IOS: BEFORE guard let image = UIImage(named: "cinamon_rolls") else { return }

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SWIFT / IOS: AFTER public enum Asset: String { case cinnamon_rolls case innocent case no case snack case window var image: UIImage { return UIImage(named: self.rawValue)! } }

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SWIFT / IOS: TESTS! func testAllAssetsAreThere() { XCTAssertNotNil(UIImage(named: Asset.cinnamon_rolls.rawValue)) XCTAssertNotNil(UIImage(named: Asset.cinnamon_rolls.rawValue)) XCTAssertNotNil(UIImage(named: Asset.cinnamon_rolls.rawValue)) XCTAssertNotNil(UIImage(named: Asset.cinnamon_rolls.rawValue)) XCTAssertNotNil(UIImage(named: Asset.cinnamon_rolls.rawValue)) }

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SWIFT / IOS: TESTS! func testAllAssetsAreThere() { for asset in Asset.allCases { XCTassertNotNil(UIImage(named: asset.rawValue), "Image for \(asset.rawValue) was nil!") } }

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SWIFT / IOS: TESTS! func testAllAssetsAreThere() { for asset in Asset.allCases { XCTassertNotNil(UIImage(named: asset.rawValue), "Image for \(asset.rawValue) was nil!") } } !!!!!!!

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USE CODE GENERATION

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USE CODE GENERATION (OR THIS CAN GET SUPER-TEDIOUS ON BIG PROJECTS)

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SWIFT CODE GENERATION > https://github.com/SwiftGen/SwiftGen > https://github.com/krzysztofzablocki/Sourcery > https://github.com/stencilproject/Stencil

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BENDING ENUMS TO YOUR WILL

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COMBINING ENUMS + PROTOCOLS / INTERFACES

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SWIFT: BEFORE @IBAction private func signIn() { guard self.validates() else { return } performSegue(withIdentifier: "toCatsLoggedIn", sender: nil) }

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SWIFT: THE ENUM enum MainStoryboardSegue: String { case toSignIn case toSignUp case toTerms case toCats case toCatsLoggedIn }

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SWIFT: THE PROTOCOL protocol SeguePerforming { var rawValue: String { get } }

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SIDE NOTE: LEARN TO CHEAT

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SWIFT: THE PROTOCOL WITH A GENERIC EXTENSION FUNCTION protocol SeguePerforming { var rawValue: String { get } } extension UIViewController { func perform(segue: T, sender: Any? = nil) { performSegue(withIdentifier: segue.rawValue, sender: sender) } }

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SWIFT: THE ENUM, REVISED enum MainStoryboardSegue: String, SeguePerforming { case toSignIn case toSignUp case toTerms case toCats case toCatsLoggedIn }

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SWIFT: AFTER @IBAction private func signIn() { guard self.validates() else { return } self.perform(MainStoryboardSegue.toCats) }

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ASSOCIATED OBJECTS

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SWIFT enum DownloadState { case notStarted, case downloading(let progress: Float) case success(let data: Data) case error(let error: Error?) }

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KOTLIN enum class CreditCard(val prefix: String) { Visa("4"), Mastercard("5"), Amex("3"); }

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KOTLIN sealed class

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KOTLIN sealed class DownloadStateWithInfo { }

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KOTLIN sealed class DownloadStateWithInfo { class NotStarted: DownloadStateWithInfo() }

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KOTLIN sealed class DownloadStateWithInfo { class NotStarted: DownloadStateWithInfo() class Downloading(val progress: Float): DownloadStateWithInfo() }

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KOTLIN sealed class DownloadStateWithInfo { class NotStarted: DownloadStateWithInfo() class Downloading(val progress: Float): DownloadStateWithInfo() class Succeeded(val data: ByteArray): DownloadStateWithInfo() }

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BLACK MAGIC WITH ✨ GENERICS

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KOTLIN enum class KeyboardType { QWERTY, ABCDEF, QWERTZ, AZERTY; }

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KOTLIN inline fun > T.next(): T { val currentIndex = this.ordinal val nextIndex = currentIndex + 1 val allValues = enumValues() return if (nextIndex >= allValues.size) { allValues[0] } else { allValues[nextIndex] } }

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KOTLIN inline fun > T.next(): T { // val currentIndex = this.ordinal // val nextIndex = currentIndex + 1 // val allValues = enumValues() // return if (nextIndex >= allValues.size) { // allValues[0] // } else { // allValues[nextIndex] // } }

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KOTLIN inline fun > T.next(): T { // val currentIndex = this.ordinal // val nextIndex = currentIndex + 1 val allValues = enumValues() // return if (nextIndex >= allValues.size) { // allValues[0] // } else { // allValues[nextIndex] // } }

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KOTLIN inline fun > T.next(): T { // val currentIndex = this.ordinal // val nextIndex = currentIndex + 1 // val allValues = enumValues() return if (nextIndex >= allValues.size) { allValues[0] } else { allValues[nextIndex] } }

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KOTLIN KeyboardType.QWERTY.next() // returns KeyboardType.ABCDEF KeyboardType.ABCDEF.next() // returns KeyboardType.QWERTZ KeyboardType.QWERTZ.next() // returns KeyboardType.AZERTY KeyboardType.AZERTY.next() // returns KeyboardType.QWERTY

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KOTLIN KeyboardType.QWERTY.next() KeyboardType.ABCDEF.next() KeyboardType.QWERTZ.next() KeyboardType.AZERTY.next()

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THE LIMITS OF ENUM AWESOMESAUCE

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ASSOCIATED OBJECTS = AWESOME LISTABILITY = AWESOME LISTABILITY + ASSOCIATED OBJECTS =

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KOTLIN DownloadStateWithInfo.NotStarted().next()

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KOTLIN DownloadStateWithInfo.NotStarted().next() !"!

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A LITTLE EASY TO GET CARRIED AWAY

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SWIFT: GOOD enum LandingScreenButton { // Stuff we saw before var localizedTitle: String { switch self { case .signIn: return NSLocalizedString("Sign In", "Sign in button title") case .signUp: return NSLocalizedString("Sign Up", "Sign up button title") case .viewTerms: return NSLocalizedString("View Terms & Conditions", "Title for button to view legalese") } }

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SWIFT: OVER THE TOP enum LandingScreenButton { // Stuff we saw before func handleClick(in viewController: UIViewController) { switch self { case .signIn: viewController.navigationController? .pushViewController(SignInViewController(), animated: true) case .signUp: viewController.navigationController? .pushViewController(RegistrationViewController(), animated: true) case .viewTerms: viewController.present(LegaleseViewController(), animated: true) } } }

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IS THIS FUNCTIONALITY INHERENTLY RELATED TO THE THING I'M REPRESENTING?

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SEPERATION OF CONCERNS STILL APPLIES!

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OBLIGATORY SUMMARY SLIDE

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OBLIGATORY SUMMARY SLIDE > Enums are a great way to represent distinct state

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OBLIGATORY SUMMARY SLIDE > Enums are a great way to represent distinct state > Limit your cases, limit your bugs

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OBLIGATORY SUMMARY SLIDE > Enums are a great way to represent distinct state > Limit your cases, limit your bugs > Value determined by the current case -> computed var

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OBLIGATORY SUMMARY SLIDE > Enums are a great way to represent distinct state > Limit your cases, limit your bugs > Value determined by the current case -> computed var > Generated enums help reduce stringly-typed code

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CODE EXAMPLES IN SWIFT AND KOTLIN! https://github.com/designatednerd/ StupidEnumTricks

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LINKS! > The Swift book's section on Enums: https://developer.apple.com/library/ content/documentation/Swift/Conceptual/ Swift_Programming_Language/ Enumerations.html > Kotlin Enum Class documentation: https://kotlinlang.org/docs/reference/ enum-classes.html