Kotlin != Swift

Two modern languages critical to native mobile development with similar language features and subtle differences. In this talk we’ll quickly refresh the basic syntax structures between Swift and Kotlin, and then explore some of the more important conceptual nuances.

If you find yourself working in two native iOS and Android codebases, then this talk is for you! Guard, swizzle, retain cycles and memory management, struct, argument labels, and whatever else we can fit in between.

1. @jacksoncheek Kotlin != Swift
2. Mobile Engineer
3. Android + iOS
4. Kotlin + Swift Bridging the gap between your two codebases
5. @jacksoncheek 1. The basics Outline
6. @jacksoncheek 1. The basics 2. Language feature differences Outline
7. Kotlin == Swift
8. @jacksoncheek http://nilhcem.com/swift-is-like-kotlin/
9. @jacksoncheek let name: String = "Jackson Cheek" print("My name is \(name)") // My name is Jackson Cheek val name: String = "Jackson Cheek” print("My name is $name”) // My name is Jackson Cheek Swift Kotlin
10. @jacksoncheek enum Language { case kotlin case swift case java case objective_c } enum class Language { KOTLIN, SWIFT, JAVA, OBJECTIVE_C } Swift Kotlin
11. @jacksoncheek enum class Language(name: String) { KOTLIN("kotlin"), SWIFT("swift"), JAVA("java"), OBJECTIVE_C("objective-c") } enum Language: String { case kotlin = "kotlin" case swift = "swift" case java = "java" case objective_c = "objective-c" } Swift Kotlin
12. @jacksoncheek protocol Developer { } interface Developer { } Swift Kotlin
13. @jacksoncheek protocol Developer { func languages() -> Set<Language> } interface Developer { fun languages(): Set<Language> } Swift Kotlin
14. @jacksoncheek class Person { init() { } } class Person( ) { } Swift Kotlin
15. @jacksoncheek class Person { let name: String let languages: Array<Language> init(name: String, _ languages: Language...) { self.name = name self.languages = languages } } class Person( val name: String, vararg val languages: Language ) { } Swift Kotlin
16. @jacksoncheek class Person: Developer { let name: String let languages: Array<Language> init(name: String, _ languages: Language...) { self.name = name self.languages = languages } } class Person( val name: String, vararg val languages: Language ): Developer { } Swift Kotlin
17. @jacksoncheek class Person: Developer { let name: String let languages: Array<Language> init(name: String, _ languages: Language...) { self.name = name self.languages = languages } func languages() -> Set<Language> { } } class Person( val name: String, vararg val languages: Language ): Developer { override fun languages(): Set<Language> { } } Swift Kotlin
18. @jacksoncheek class Person: Developer { let name: String let languages: Array<Language> init(name: String, _ languages: Language...) { self.name = name self.languages = languages } func languages() -> Set<Language> { var unique: Set<Language> = Set() return unique } } class Person( val name: String, vararg val languages: Language ): Developer { override fun languages(): Set<Language> { val unique: Set<Language> = setOf() return unique } } Swift Kotlin
19. @jacksoncheek class Person: Developer { let name: String let languages: Array<Language> init(name: String, _ languages: Language...) { self.name = name self.languages = languages } func languages() -> Set<Language> { var unique: Set<Language> = Set() for language in _languages { } return unique } } class Person( val name: String, vararg val languages: Language ): Developer { override fun languages(): Set<Language> { val unique: Set<Language> = setOf() for (language in languages) { } return unique } } Swift Kotlin
20. @jacksoncheek class Person: Developer { let name: String let languages: Array<Language> init(name: String, _ languages: Language...) { self.name = name self.languages = languages } func languages() -> Set<Language> { var unique: Set<Language> = Set() for language in _languages { unique.insert(language) } return unique } } class Person( val name: String, vararg val languages: Language ): Developer { override fun languages(): Set<Language> { val unique: Set<Language> = setOf() for (language in languages) { unique.plus(language) } return unique } } Swift Kotlin
21. @jacksoncheek let jackson: Person = Person( name: "Jackson Cheek", .kotlin, .java, .swift ) val jackson: Person = Person( "Jackson Cheek", Language.KOTLIN, Language.JAVA, Language.SWIFT ) Swift Kotlin
22. Kotlin != Swift
23. guard Preference for early return and optional unwrapping
24. @jacksoncheek guard [expression|condition] else { [statement] return } Swift
25. @jacksoncheek var optName: String? = "Jackson Cheek" guard let name = optName else { print("Oops") return } print("My name is \(name)") // My name is Jackson Cheek Swift
26. @jacksoncheek var optName: String? = "Jackson Cheek" guard let name = optName else { print("Oops") return } print("My name is \(name)") // My name is Jackson Cheek var optName: String? = "Jackson Cheek" val name = optName?.let { it } if (name != null) { print("My name is $name") } else { print("Oops") } // My name is Jackson Cheek Swift Kotlin
27. @jacksoncheek var optName: String? = "Jackson Cheek" let age = 30 guard let name = optName, age > 21 else { print("Conditions not met") return } print("Conditions met”) // Conditions met Swift
28. @jacksoncheek var optName: String? = "Jackson Cheek" let age = 30 guard let name = optName, age > 21 else { print("Conditions not met") return } print("Conditions met”) // Conditions met var optName: String? = "Jackson Cheek" val age = 30 val name = optName?.let { it } if (name != null && age > 21) { print("Conditions met") } else { print("Conditions not met") } // Conditions met Swift Kotlin
29. swizzle Changing an implementation at runtime (dangerous)
30. @jacksoncheek • onCreate • onStart • onResume • onPause • onStop • onDestroy
31. @jacksoncheek • viewDidLoad • viewWillAppear • viewDidAppear • viewWillDisappear • viewDidDisappear
32. @jacksoncheek • viewDidLoad • viewWillAppear • viewDidAppear • viewWillDisappear • viewDidDisappear Product Manager: “I want to track every time a user lands on a new screen!”
33. @jacksoncheek @objc func swizzledViewDidAppear() { guard let screenName = className else { return } analyticsService.trackScreen(screenName: screenName) } Swift
34. @jacksoncheek @objc func swizzledViewDidAppear() { guard let screenName = className else { return } analyticsService.trackScreen(screenName: screenName) } class func swizzle() { guard self === UIViewController.self else { return } let original = class_getInstanceMethod( self, #selector(viewDidAppear(_:)) ) } Swift
35. @jacksoncheek @objc func swizzledViewDidAppear() { guard let screenName = className else { return } analyticsService.trackScreen(screenName: screenName) } class func swizzle() { guard self === UIViewController.self else { return } let original = class_getInstanceMethod( self, #selector(viewDidAppear(_:)) ) } #selector Reference to method in compiled code Swift
36. @jacksoncheek @objc func swizzledViewDidAppear() { guard let screenName = className else { return } analyticsService.trackScreen(screenName: screenName) } class func swizzle() { guard self === UIViewController.self else { return } let original = class_getInstanceMethod( self, #selector(viewDidAppear(_:)) ) let swizzled = class_getInstanceMethod( self, #selector(swizzledViewDidAppear) ) } Swift
37. @jacksoncheek @objc func swizzledViewDidAppear() { guard let screenName = className else { return } analyticsService.trackScreen(screenName: screenName) } class func swizzle() { guard self === UIViewController.self else { return } let original = class_getInstanceMethod( self, #selector(viewDidAppear(_:)) ) let swizzled = class_getInstanceMethod( self, #selector(swizzledViewDidAppear) ) method_exchangeImplementations(original!, swizzled!) } Swift
38. retain cycle Just a memory leak
39. @jacksoncheek • No garbage collector Memory Management
40. @jacksoncheek • No garbage collector • Automatic Reference Counting Memory Management
41. @jacksoncheek • No garbage collector • Automatic Reference Counting • Memory allocated for an object when initialized Memory Management
42. @jacksoncheek • No garbage collector • Automatic Reference Counting • Memory allocated for an object when initialized • Memory deallocated when there are no more strong references to that object Memory Management
43. @jacksoncheek • No garbage collector • Automatic Reference Counting • Memory allocated for an object when initialized • Memory deallocated when there are no more strong references to that object • Leak when all references aren’t cleaned up Memory Management
44. @jacksoncheek class Person { let name: String var phone: Phone? = nil init(name: String) { self.name = name } } class Phone { let model: String var owner: Person? = nil init(model: String) { self.model = model } } Swift
45. @jacksoncheek class Person { let name: String var phone: Phone? = nil init(name: String) { self.name = name } } class Phone { let model: String var owner: Person? = nil init(model: String) { self.model = model } } var jackson: Person? = Person(name: "Jackson") var pixel3: Phone? = Phone(model: "Pixel 3") Swift
46. @jacksoncheek class Person { let name: String var phone: Phone? = nil init(name: String) { self.name = name } } class Phone { let model: String var owner: Person? = nil init(model: String) { self.model = model } } var jackson: Person? = Person(name: "Jackson") var pixel3: Phone? = Phone(model: "Pixel 3") jackson!.phone = pixel3 pixel3!.owner = jackson Swift
47. @jacksoncheek var jackson var pixel3 <Person Instance> name: “Jackson” phone: nil <Phone Instance> model: “Pixel 3” owner: nil strong strong 1 1 var jackson: Person? = Person(name: "Jackson") var pixel3: Phone? = Phone(model: "Pixel 3") Swift
48. @jacksoncheek var jackson var pixel3 <Person Instance> name: “Jackson” phone: <Phone> <Phone Instance> model: “Pixel 3” owner: <Person> strong strong strong strong 2 2 var jackson: Person? = Person(name: "Jackson") var pixel3: Phone? = Phone(model: "Pixel 3") jackson!.phone = pixel3 pixel3!.owner = jackson Swift
49. @jacksoncheek var jackson var pixel3 strong strong <Person Instance> name: “Jackson” phone: <Phone> <Phone Instance> model: “Pixel 3” owner: <Person> 1 1 var jackson: Person? = Person(name: "Jackson") var pixel3: Phone? = Phone(model: "Pixel 3") jackson!.phone = pixel3 pixel3!.owner = jackson jackson = nil pixel3 = nil Swift
50. @jacksoncheek class Phone { let model: String weak var owner: Person? = nil init(model: String) { self.model = model } } Swift var jackson var pixel3 <Person Instance> name: “Jackson” phone: <Phone> <Phone Instance> model: “Pixel 3” owner: <Person> strong strong strong strong 2 2
51. @jacksoncheek var jackson var pixel3 <Person Instance> name: “Jackson” phone: <Phone> <Phone Instance> model: “Pixel 3” owner: <Person> strong strong strong weak 1 2 class Phone { let model: String weak var owner: Person? = nil init(model: String) { self.model = model } } Swift
52. @jacksoncheek var jackson var pixel3 <Person Instance> name: “Jackson” phone: <Phone> <Phone Instance> model: “Pixel 3” owner: <Person> strong strong weak 0 2 jackson = nil Swift
53. @jacksoncheek jackson = nil Swift var jackson var pixel3 strong <Phone Instance> model: “Pixel 3” owner: nil 1
54. @jacksoncheek var jackson var pixel3 <Phone Instance> model: “Pixel 3” owner: nil 0 jackson = nil pixel3 = nil Swift
55. @jacksoncheek var jackson var pixel3 jackson = nil pixel3 = nil Swift
56. struct Basically an object reference-less data class
57. @jacksoncheek struct State { var isLoading: Bool } data class State( var isLoading: Boolean ) Swift Kotlin
58. @jacksoncheek struct State { var isLoading: Bool } var initial = State(isLoading: false) data class State( var isLoading: Boolean ) var initial = State(isLoading = false) Swift Kotlin
59. @jacksoncheek struct State { var isLoading: Bool } var initial = State(isLoading: false) var copy = initial data class State( var isLoading: Boolean ) var initial = State(isLoading = false) var copy = initial Swift Kotlin
60. @jacksoncheek struct State { var isLoading: Bool } var initial = State(isLoading: false) var copy = initial initial.isLoading = true data class State( var isLoading: Boolean ) var initial = State(isLoading = false) var copy = initial initial.isLoading = true Swift Kotlin
61. @jacksoncheek struct State { var isLoading: Bool } var initial = State(isLoading: false) var copy = initial initial.isLoading = true print("Loading state: \(copy.isLoading)") // Loading state: false data class State( var isLoading: Boolean ) var initial = State(isLoading = false) var copy = initial initial.isLoading = true print("Loading state: ${copy.isLoading}") // Loading state: true Swift Kotlin
62. argument labels Syntactic sugar
63. @jacksoncheek enum AccountType { case credit case debit } class Shopper { func payBill(accountType: AccountType) { print("Thank you!") } } enum class AccountType { CREDIT, DEBIT } class Shopper { fun payBill(accountType: AccountType) { print("Thank you!") } } Swift Kotlin
64. @jacksoncheek enum AccountType { case credit case debit } class Shopper { func payBill(accountType: AccountType) { print("Thank you!") } } let shopper: Shopper = Shopper() shopper.payBill(accountType: .credit) // Thank you! enum class AccountType { CREDIT, DEBIT } class Shopper { fun payBill(accountType: AccountType) { print("Thank you!") } } val shopper: Shopper = Shopper() shopper.payBill(accountType = CREDIT) // Thank you! Swift Kotlin
65. @jacksoncheek enum AccountType { case credit case debit } class Shopper { func payBill(_ accountType: AccountType) { print("Thank you!") } } let shopper: Shopper = Shopper() shopper.payBill(.credit) // Thank you! enum class AccountType { CREDIT, DEBIT } class Shopper { fun payBill(accountType: AccountType) { print("Thank you!") } } val shopper: Shopper = Shopper() shopper.payBill(CREDIT) // Thank you! Swift Kotlin
66. @jacksoncheek enum AccountType { case credit case debit } class Shopper { func payBill(with accountType: AccountType) { print("Thank you!”) } } let shopper: Shopper = Shopper() shopper.payBill(with: .credit) // Thank you! enum class AccountType { CREDIT, DEBIT } class Shopper { fun payBill(with accountType: AccountType) { print("Thank you!") } } val shopper: Shopper = Shopper() shopper.payBill(with = CREDIT) // Not possible! ❌ Swift Kotlin
67. @jacksoncheek Questions?