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KOTLIN FOR SWIFT DEVELOPERS SWIFT PARIS | PARIS, FRANCE | OCTOBER 2018 @DESIGNATEDNERD | BAKKENBAECK.COM | JUSTHUM.COM

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KOTLIN POUR SWIFT DEVELOPPEURS SWIFT PARIS ! PARIS, FRANCE OCTOBRE 2018 @DESIGNATEDNERD ! BAKKENBAECK.COM JUSTHUM.COM

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!"

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✨ " ☕

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WHAT IS KOTLIN ?

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WHY SHOULD I CARE?

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A CONSTANT STRING

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SWIFT let greeting = "Hello World"

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SWIFT let greeting = "Hello World" KOTLIN val greeting = "Hello World"

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AN OPTIONAL INTEGER VARIABLE

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SWIFT var something: Int?

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SWIFT var something: Int? KOTLIN var something: Int?

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☠ NullPointerException

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!"

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GENERICS AND FUNCTIONS AS PARAMETERS

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SWIFT func useFunction(on item: T, function: (T) -> U) -> U { return function(item) } func insertExclamationPoint(in string: String) -> String { return string .components(separatedBy: " ") .joined(separator: "! ") } let result = useFunction(on: "try Swift", function: insertExclamationPoint(in:)) // result: "try! Swift"

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KOTLIN fun T.useFunction(action: (T) -> U): U { return action(this) } fun insertExclamationPoint(in: String) : String { return in.split(" ").joinToString("! ") } val result = "try Kotlin".useFunction { insertExclamationPoint(it) } // result: "try! Kotlin"

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map filter reduce

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map filter reduce*

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SWIFT let numbers = [ 1, 2, 3 ] let reduced = numbers.reduce(0, +) // reduced: 6

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SWIFT let numbers = [ 1, 2, 3 ] let reduced = numbers.reduce(0, +) // // reduced: 6

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SWIFT let numbers = [ 1, 2, 3 ] let reduced = numbers.reduce(0) { $0 + $1 } // reduced: 6

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SWIFT let numbers = [ 1, 2, 3 ] let reduced = numbers.reduce(20) { $0 + $1 } // reduced: 26

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SWIFT let numbers = [ 1, 2, 3 ] let reduced = numbers.reduce(20) { $0 + $1 } // reduced: 26 KOTLIN val numbers = arrayOf(1, 2, 3) val reduced = numbers.reduce { total, current -> total + current } // reduced: 6

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SWIFT let numbers = [ 1, 2, 3 ] let reduced = numbers.reduce(20) { $0 + $1 } // reduced: 26 ⬆ KOTLIN val numbers = arrayOf(1, 2, 3) val reduced = numbers.reduce { total, current -> total + current } // reduced: 6

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SWIFT let numbers = [ 1, 2, 3 ] let reduced = numbers.reduce(20) { $0 + $1 } // reduced: 26 KOTLIN val numbers = arrayOf(1, 2, 3) val folded = numbers.fold(20) ⬅ { total, current -> total + current } // folded: 26

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SWIFT let doubled = [ 1, 2, 3 ].map { $0 * 2 }

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SWIFT let doubled = [ 1, 2, 3 ].map { $0 * 2 } KOTLIN arrayOf(1, 2, 3).map { it * 2 }

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SWIFT let doubled = [ 1, 2, 3 ].map { $0 * 2 } KOTLIN arrayOf(1, 2, 3).map { it * 2 }

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SWIFT let numbers = [ 1, 2, 3 ] let reduced = numbers.reduce(20) { $0 + $1 } // reduced: 26

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$0 $1 $2...$∞

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SWIFT let numbers = [ 1, 2, 3 ] let reduced = numbers.reduce(20) { $0 + $1 } // reduced: 26 KOTLIN val numbers = arrayOf(1, 2, 3) val folded = numbers.fold(20) { total, current -> total + current } // folded: 26 ⬆

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!"#

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guard

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NOW (KOTLIN) optionalThing?.let { it.doSomething() }

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NOW (KOTLIN) optionalThing?.let { it.doSomething() } else { doSomethingElse() }

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NOW (KOTLIN) optionalThing?.let { it.doSomething() } else { // ! Not possible doSomethingElse() }

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NOW (KOTLIN) if (optionalThing != nil) { optionalThing.doSomething() } else { doSomethingElse() }

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NOW (KOTLIN) if (optionalThing != nil) { optionalThing.doSomething() //<- magic unwrap!! } else { doSomethingElse() }

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PROPOSED (KOTLIN) guard val thing = optionalThing else { return } thing.doSomething()

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apply

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NOW (SWIFT) UserDefaults.standard.set(true, forKey: "DefaultOne") UserDefaults.standard.set(false, forKey: "DefaultTwo)

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NOW (BETTER SWIFT) let defaults = UserDefaults.standard defaults.set(true, forKey: "DefaultOne") defaults.set(false, forKey: "DefaultTwo)

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PROPOSED (SWIFT) UserDefaults.standard.apply { "DefaultOne" = true, "DefaultTwo" = false, }

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PROTOCOLS WITH DEFAULT IMPLEMENTATIONS

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PROPOSED (KOTLIN) interface SomeInterface { fun doAThing() }

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PROPOSED (KOTLIN) interface SomeInterface { fun doAThing() } @DefaultImpl SomeInterface { fun doAThing() { println("Hi, I'm the default implementation!") } }

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@JVMDefault + DefaultImpl (SORT OF)

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SEALED CLASSES

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KOTLIN sealed class ViewState { class Empty(val placeholder: View): ViewState() class HasContent(val items: List): ViewState() }

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KOTLIN sealed class ViewState { class Empty(val placeholder: View): ViewState() class HasContent(val items: List): ViewState() } when (state) { is ViewState.Empty --> display(it.placeholder) is ViewState.HasContent --> adapter.reloadWith(it.items) }

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SWIFT enum TableViewState { case empty(placeholderView: UIView) case loaded(items: [Item]) } switch state { case .empty(let placeholder): display(placeholder) case .hasContent(let items): dataSource.reloadWith(items) }

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KOTLIN sealed class ViewState { class Empty(val placeholder: View): ViewState() class HasContent(val items: List): ViewState() }

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KOTLIN sealed class ViewState { class Empty(val placeholder: View): ViewState() class HasContent(val items: List): ViewState() { val adapter = RecyclerViewAdapter(items) fun selectedItem(item: Item) { // Do something ith the selected item } } }

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KOTLIN / NATIVE

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PLUS ÇA CHANGE

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LLVM

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LLVM

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LLVM

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SUPPORTED PLATFORMS ▸ x86_64 (macOS, iOS Sim, Linux, Windows) ▸ arm64 (iOS, Android) ▸ arm32 (iOS, Android, Linux) ▸ arm32 hardfp (Raspberry Pi) ▸ MIPS (Linux) ▸ wasm32 (Web Assembly)

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expect fun

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KOTLIN IOS LIBRARY ! WRAPPERS

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KOTLIN IOS LIBRARY ! WRAPPERS* *(WHICH USUALLY WORK)

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KOTLIN / NATIVE val decoded = NSString.create( data = data, encoding = NSUTF8StringEncoding )

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KOTLIN / NATIVE val decoded = NSString.create( data = data, encoding = NSUTF8StringEncoding ) // `decoded` type: NSString

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BUSINESS LOGIC

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KOTLIN / NATIVE GOTCHAS

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!

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+ =

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MEMORY MANAGEMENT AND CONCURRENCY !!!!!!!

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COROUTINES

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COROUTINES* * ONLY WORK ON THE MAIN THREAD IN KOTLIN / NATIVE

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(˽s̕s҂˽Ɨ ˍʓˍ

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Worker

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! MONOREPO

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https://github.com/designatednerd/ KotlinNativeTest

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OBJ-C INTEROP HILARITY

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SWIFT: ENUMS enum Things { case monday case tuesday case wednesday case thursday case friday case saturday case sunday }

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KOTLIN: ENUM CLASSES enum class DayOfWeek { Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday; }

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A KOTLIN ENUM CLASS IN A KOTLIN / NATIVE FRAMEWORK

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A KOTLIN ENUM CLASS IN A KOTLIN / NATIVE FRAMEWORK

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A KOTLIN ENUM CLASS IN A KOTLIN / NATIVE FRAMEWORK

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SWIFT SWITCHING ON A KOTLIN ENUM switch day { case .monday: print("You can fall apart") case .tuesday, .wednesday: print("Break my heart") case .thursday: print("Doesn't even start") case .friday: print("I'm in love") case .saturday: print("Wait") case .sunday: print("Always comes too late") } // ! Seems legit...

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SWIFT SWITCHING ON A KOTLIN ENUM switch day { case .monday: print("You can fall apart") case .tuesday, .wednesday: print("Break my heart") case .thursday: print("Doesn't even start") case .friday: print("I'm in love") case .saturday: print("Wait") case .sunday: print("Always comes too late") } // ! ERROR: ! Switch must be exhaustive

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SWIFT SWITCHING ON A KOTLIN ENUM switch day { case .monday: print("You can fall apart") case .tuesday, .wednesday: print("Break my heart") case .thursday: print("Doesn't even start") case .friday: print("I'm in love") case .saturday: print("Wait") case .sunday: print("Always comes too late") default: fatalError("Not a day") // ! }

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DOCUMENTATION

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DOCUMENTATION? ¯\_(ϑ)_/¯

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PRODUCTION?!

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KOTLIN: ☕ OR " =

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try? kotlin

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https://try.kotlinlang.org

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EDU TOOLS PLUGIN FOR INTELLIJ OR ANDROID STUDIO

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OBLIGATORY SUMMARY SLIDE

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OBLIGATORY SUMMARY SLIDE ▸ Literally put the fun in functional programming

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OBLIGATORY SUMMARY SLIDE ▸ Literally put the fun in functional programming ▸ Make Friends With Android

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OBLIGATORY SUMMARY SLIDE ▸ Literally put the fun in functional programming ▸ Make Friends With Android ▸ Kotlin Native Could Be A Whole New World

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OBLIGATORY SUMMARY SLIDE ▸ Literally put the fun in functional programming ▸ Make Friends With Android ▸ Kotlin Native Could Be A Whole New World ▸ try! Kotlin

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ONE MORE THING

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ONE MORE THING: (A SHAMELESS PLUG!)

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! MERÇI!

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LINKS! ▸ Kotlin Home & Documentation: https://kotlinlang.org ▸ Kotlin Native MultiplatformApp tutorial https://kotlinlang.org/docs/tutorials/ native/mpp-ios-android.html ▸ KotlinConf iOS App in Kotlin/Native: https://github.com/JetBrains/kotlinconf- app/tree/master/konfios

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MORE LINKS! ▸ The Edu Tools Plugin for IntelliJ or Android Studio https://kotlinlang.org/docs/tutorials/ edu-tools-learner.html ▸ Representing State (KotlinConf talk on Sealed Classes) https://www.youtube.com/watch?v=- lVVfxsRjcY ▸ Sealed Classes Opened My Mind (KotlinConf Talk) https://www.youtube.com/watch? v=uGMm3StjqLI

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SHAMELESS SELF-PROMOTION! ▸ My talk on Protocol-Oriented Programming from Dot Swift https://www.dotconferences.com/2018/01/ ellen-shapiro-protocols-all-the-way-down ▸ Kotlin Apprentice https://store.raywenderlich.com/products/ kotlin-apprentice ▸ Android Apprentice https://store.raywenderlich.com/products/ android-apprentice

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ILLUSTRATION CREDITS ▸ Monica Komperda, Native Code Forever (Hire her! She's awesome!) http://mokomperda.com/design