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

Enums in Swift and enum classes in Kotlin are extremely powerful ways to deal with a known set of possible values. Learn how to use these tools to help you cleaner, safer code, and how to push the boundaries of what's possible with enums.

Transcript

1. STUPID ENUM TRICKS IN SWIFT AND KOTLIN WE ARE DEVELOPERS | VIENNA, AUSTRIA | MAY 2018 BAKKENBAECK.COM | JUSTHUM.COM | DESIGNATEDNERD.COM BY ELLEN SHAPIRO | @DESIGNATEDNERD
2. PREFACE: A NOTE ON PRONUNCIATION
3. "EE-NUMB" VS. "EE-NOOM"
4. "EE-NUMB" VS. "EE-NOOM" ⬆ (I PRONOUNCE IT THIS WAY)
5. "EE-NUMB" VS. "EE-NOOM" (THIS WAY IS ALSO FINE)
6. GIF
7. GIF
8. WHAT IS AN ENUM?
9. A LIST OF VALUES THAT ARE POSSIBLE
10. OPTION SET
11. OPTION SET
12. POSSIBLE IT COULD BE ANY ONE OF THESE THINGS IN THE LIST
13. SWIFT enum ColorName: String { case red case orange case yellow case green case blue case violet }
14. IT COULD ALSO BE SOMETHING TOTALLY DIFFERENT
15. 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 }
16. EXHAUSTIVE ENUMS
17. EXAUSTIVE BUT THESE ARE THE ONLY THINGS WHICH ARE POSSIBLE
18. SWIFT enum TrafficLightColor { case red case yellow case green }
19. LIMIT YOUR POSSIBILITIES
20. LIMIT YOUR RUNTIME ERRORS
21. SWIFT STANDARD LIBRARY public enum ComparisonResult : Int { case orderedAscending case orderedSame case orderedDescending }
22. KOTLIN STANDARD LIBRARY public enum ClassKind { CLASS, INTERFACE, ENUM_CLASS, ENUM_ENTRY, ANNOTATION_CLASS, OBJECT; }
23. HOW DO I CREATE MY OWN ENUM?
24. SWIFT enum TrafficLightColor { case red case yellow case green }
25. KOTLIN enum class
26. KOTLIN enum class TrafficLightColor { Red, Yellow, Green; }
27. HOW DO I USE ENUMS?
28. switch / when
29. 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!") }
30. SWIFT var currentColor: TrafficLightColor = .red switch currentColor { case .red: print("STOP RIGHT THERE") case .green: print("Go, go, go!") // Error: Unhandled case! }
31. SWIFT var currentColor: TrafficLightColor = .red switch currentColor { case .red: print("STOP RIGHT THERE") case .yellow, .green: print("Go, go, go!") }
32. 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!") }
33. WHAT DO I GET FOR FREE WITH ENUMS?
34. KOTLIN: A LOT!
35. 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
36. 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
37. SWIFT: IT DEPENDS
38. BY DEFAULT: NOT MUCH
39. RawRepresentable
40. SWIFT enum SettingsSection { case profile case contact case legalese case logout }
41. SWIFT enum SettingsSection: Int { case profile case contact case legalese case logout }
42. SWIFT enum SettingsSection: Int { case profile // 0 case contact // 1 case legalese // 2 case logout // 3 }
43. SWIFT enum SettingsSection: Int { case profile // 0 case legalese // 1 case contact // 2 case logout // 3 }
44. SWIFT guard let section = SettingsSection(rawValue: 10) else { assertionFailure("Section 10 does not exist!") }
45. SWIFT enum JSONKey: String { case user_name case email_address case latitude case longitude }
46. SWIFT enum JSONKey: String { case user_name case email_address case latitude = "lat" case longitude = "long" }
47. 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" } }
48. SWIFT 4.2: CaseIterable
49. SWIFT
50. SWIFT enum SettingsSection: Int, CaseIterable { case profile case legalese case contact case logout }
51. SWIFT enum SettingsSection: Int, CaseIterable { case profile case legalese case contact case logout } // Automatically generated: static var allCases: [SettingsSection]
52. 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 }
53. WHAT CAN I ADD TO ENUMS?
54. COMPUTED PROPERTIES
55. SWIFT enum LandingScreenButton { case signIn case signUp case viewTerms }
56. 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") } }
57. 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") } }
58. UI TESTING
59. SWIFT / XCUI
60. KOTLIN / ESPRESSO
61. ASSET HANDLING [IOS]
62. ASSET CATALOGS
63. SWIFT / IOS: BEFORE guard let image = UIImage(named: "cinnamon_rolls") else { return }
64. SWIFT / IOS: BEFORE guard let image = UIImage(named: "cinnamon_rolls") else { return }
65. SWIFT / IOS: BEFORE guard let image = UIImage(named: "cinamon_rolls") else { return }
66. SWIFT / IOS: BEFORE guard let image = UIImage(named: "cinamon_rolls") else { return }
67. 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)! } }
68. 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)) }
69. 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)) } !
70. SWIFT / IOS: TESTS! func testAllAssetsAreThere() { for asset in Asset.allCases { XCTassertNotNil(UIImage(named: asset.rawValue), "Image for \(asset.rawValue) was nil!") } }
71. SWIFT / IOS: TESTS! func testAllAssetsAreThere() { for asset in Asset.allCases { XCTassertNotNil(UIImage(named: asset.rawValue), "Image for \(asset.rawValue) was nil!") } } !!!!!!!
72. USE CODE GENERATION
73. USE CODE GENERATION (OR THIS CAN GET SUPER-TEDIOUS ON BIG PROJECTS)
74. SWIFT CODE GENERATION > https://github.com/SwiftGen/SwiftGen > https://github.com/krzysztofzablocki/Sourcery > https://github.com/stencilproject/Stencil
75. BENDING ENUMS TO YOUR WILL
76. COMBINING ENUMS + PROTOCOLS / INTERFACES
77. SWIFT: BEFORE @IBAction private func signIn() { guard self.validates() else { return } performSegue(withIdentifier: "toCatsLoggedIn", sender: nil) }
78. SWIFT: THE ENUM enum MainStoryboardSegue: String { case toSignIn case toSignUp case toTerms case toCats case toCatsLoggedIn }
79. SWIFT: THE PROTOCOL protocol SeguePerforming { var rawValue: String { get } }
80. SIDE NOTE: LEARN TO CHEAT
81. SWIFT: THE PROTOCOL WITH A GENERIC EXTENSION FUNCTION protocol SeguePerforming { var rawValue: String { get } } extension UIViewController { func perform<T: SeguePerforming>(segue: T, sender: Any? = nil) { performSegue(withIdentifier: segue.rawValue, sender: sender) } }
82. SWIFT: THE ENUM, REVISED enum MainStoryboardSegue: String, SeguePerforming { case toSignIn case toSignUp case toTerms case toCats case toCatsLoggedIn }
83. SWIFT: AFTER @IBAction private func signIn() { guard self.validates() else { return } self.perform(MainStoryboardSegue.toCats) }
84. ASSOCIATED OBJECTS
85. SWIFT enum DownloadState { case notStarted, case downloading(let progress: Float) case success(let data: Data) case error(let error: Error?) }
86. KOTLIN enum class CreditCard(val prefix: String) { Visa("4"), Mastercard("5"), Amex("3"); }
87. KOTLIN sealed class
88. KOTLIN sealed class DownloadStateWithInfo { }
89. KOTLIN sealed class DownloadStateWithInfo { class NotStarted: DownloadStateWithInfo() }
90. KOTLIN sealed class DownloadStateWithInfo { class NotStarted: DownloadStateWithInfo() class Downloading(val progress: Float): DownloadStateWithInfo() }
91. KOTLIN sealed class DownloadStateWithInfo { class NotStarted: DownloadStateWithInfo() class Downloading(val progress: Float): DownloadStateWithInfo() class Succeeded(val data: ByteArray): DownloadStateWithInfo() }
92. KOTLIN sealed class DownloadStateWithInfo { class NotStarted: DownloadStateWithInfo() class Downloading(val progress: Float): DownloadStateWithInfo() class Succeeded(val data: ByteArray): DownloadStateWithInfo() class Failed(val error: Error): DownloadStateWithInfo() }
93. BLACK MAGIC WITH ✨ GENERICS
94. KOTLIN enum class KeyboardType { QWERTY, ABCDEF, QWERTZ, AZERTY; }
95. KOTLIN inline fun <reified T: Enum<T>> T.next(): T { val currentIndex = this.ordinal val nextIndex = currentIndex + 1 val allValues = enumValues<T>() return if (nextIndex >= allValues.size) { allValues[0] } else { allValues[nextIndex] } }
96. KOTLIN inline fun <reified T: Enum<T>> T.next(): T { // val currentIndex = this.ordinal // val nextIndex = currentIndex + 1 // val allValues = enumValues<T>() // return if (nextIndex >= allValues.size) { // allValues[0] // } else { // allValues[nextIndex] // } }
97. KOTLIN inline fun <reified T: Enum<T>> T.next(): T { // val currentIndex = this.ordinal // val nextIndex = currentIndex + 1 val allValues = enumValues<T>() // return if (nextIndex >= allValues.size) { // allValues[0] // } else { // allValues[nextIndex] // } }
98. KOTLIN inline fun <reified T: Enum<T>> T.next(): T { // val currentIndex = this.ordinal // val nextIndex = currentIndex + 1 // val allValues = enumValues<T>() return if (nextIndex >= allValues.size) { allValues[0] } else { allValues[nextIndex] } }
99. 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
100. KOTLIN KeyboardType.QWERTY.next() KeyboardType.ABCDEF.next() KeyboardType.QWERTZ.next() KeyboardType.AZERTY.next()
101. THE LIMITS OF ENUM AWESOMESAUCE
102. ASSOCIATED OBJECTS = AWESOME LISTABILITY = AWESOME LISTABILITY + ASSOCIATED OBJECTS =
103. KOTLIN sealed class DownloadStateWithInfo { class NotStarted: DownloadStateWithInfo() class Downloading(val progress: Float): DownloadStateWithInfo() class Succeeded(val data: ByteArray): DownloadStateWithInfo() class Failed(val error: Error): DownloadStateWithInfo() }
104. KOTLIN DownloadStateWithInfo.NotStarted().next()
105. KOTLIN DownloadStateWithInfo.NotStarted().next() !"!
106. A LITTLE EASY TO GET CARRIED AWAY
107. 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") } }
108. 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) } } }
109. IS THIS FUNCTIONALITY INHERENTLY RELATED TO THE THING I'M REPRESENTING?
110. SEPERATION OF CONCERNS STILL APPLIES!
111. OBLIGATORY SUMMARY SLIDE
112. OBLIGATORY SUMMARY SLIDE > Enums are a great way to represent distinct state
113. OBLIGATORY SUMMARY SLIDE > Enums are a great way to represent distinct state > Limit your cases, limit your bugs
114. 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
115. 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
116. 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 > Don't forget about separation of concerns
117. CODE EXAMPLES IN SWIFT AND KOTLIN! https://github.com/designatednerd/ StupidEnumTricks
118. 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