Kotlin Multiplatform Intro

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Kotlin Multiplatform Intro Kevin Galligan

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Touchlab

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What is Kotlin Multiplatform?

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kot·lin mul·ti·plat·form /ˌkätˈlin məltiˈplatfôrm,ˌkätˈlin məltīˈplatfôrm/ noun noun: kotlin multiplatform 1.optional, natively-integrated, open-source, code sharing platform, based on the popular, modern language kotlin. facilitates non-ui logic availability on many platforms.

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Optional Sharing Low risk. No Big Decisions.

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Natively Integrated smooth interop

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open source

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Code Sharing not “cross platform”

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popular

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popular

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popular

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modern

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Not UI well, not necessarily UI

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-Kevin Galligan “Shared UI is a history of pain and failure. Shared logic is the history of computers.”

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Many Platforms

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Common JVM JS Native iOS Mac Linux Windows Android/NDK Wasm Others… Java-6 Java-8 Android Browser Node

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IDE and Tooling JetBrains makes it

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Why Kotlin? High Efficiency Low Risk Modern Language/Tools Highly Engaged Community

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mobile is easy

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mobile is easy

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Technically, Though what is it?

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Common JVM JS Native

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Common JVM JS Native iOS Mac Linux Windows Android/NDK Wasm Others… Java-6 Java-8 Android Browser Node

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Common JVM JS Native iOS Mac Linux Windows Android/NDK Wasm Others… Java-6 Java-8 Android Browser Node

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Common JVM JS Native iOS Mac Linux Windows Android/NDK Wasm Others… Java-6 Java-8 Android Browser Node

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Common JVM JS Native iOS Mac Linux Windows Android/NDK Wasm Others… Java-6 Java-8 Android Browser Node

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Common JVM JS Native iOS Mac Linux Windows Android/NDK Wasm Others… Java-6 Java-8 Android Browser Node

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Common JVM Native iOS Mac Linux Windows Android/NDK Wasm Others… Java-6 Java-8 Android

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Common JVM Native

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Common JVM Native

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Common JVM Native iOS

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Common JVM iOS

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Common JVM iOS Framework

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Common JVM iOS Framework Android

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Common Android iOS Framework

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Common Android iOS Framework Android Stuff iOS Stuff

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Status

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Q3 Q2 Q4 Q1 Q2 2018 2019 v0.7 v0.8 v0.8.2 v0.9.3 IDE tooling! Coroutines? K/N 1.0, Kotlin 1.3 Gradle 4.10+ Android Studio Compiler plugins! Other samples/libraries Production deployments Paid license/debugger Reactive Library Big Production Apps Webassembly stuﬀ? MT Coroutines!

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Q3 Q2 Q4 Q1 Q2 2019 2020 v1.3.30 v1.3.40 v1.3.50 v1.3.60? MT Coroutines? Many Threading Libraries Many Threading Blog Posts Increased Production Adoption Improved Tooling Stability Compiler Plugins? Date/Time?

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Q3 Q2 Q4 Q1 Q2 2019 2020 v1.3.30 v1.3.40 v1.3.50 v1.3.60? MT Coroutines? Mainstream Date/Time?

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Is This Ready? that’s more about your team

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Multithreaded Coroutines need to change my slides

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Sharing Code

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Kotlin Embraces “Native” the interop story is really good

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expect/actual

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//In common code expect val isMainThread: Boolean

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//In common code expect val isMainThread: Boolean //In Android/JVM actual val isMainThread: Boolean get() = Looper.getMainLooper() === Looper.myLooper()

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//In common code expect val isMainThread: Boolean //In Android/JVM actual val isMainThread: Boolean get() = Looper.getMainLooper() === Looper.myLooper() //In iOS/native code actual val isMainThread: Boolean get() = NSThread.isMainThread()

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//Value expect val isMainThread: Boolean

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//Value expect val isMainThread: Boolean //Function expect fun myFun():String

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//Value expect val isMainThread: Boolean //Function expect fun myFun():String //Class expect class MyClass { fun heyo(): String }

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//Value expect val isMainThread: Boolean //Function expect fun myFun():String //Class expect class MyClass { fun heyo(): String } //Object expect object MyObject { fun heyo(): String }

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//Value expect val isMainThread: Boolean //Function expect fun myFun():String //Class expect class MyClass { fun heyo(): String } //Object expect object MyObject { fun heyo(): String } //Annotation @Target(AnnotationTarget.FUNCTION, AnnotationTarget.CONSTRUCTOR) @Retention(AnnotationRetention.SOURCE) expect annotation class Throws(vararg val exceptionClasses: KClass)

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expect class Sample() { fun checkMe(): Int } expect object Platform { val name: String } fun hello(): String = "Hello from ${Platform.name}"

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actual class Sample { actual fun checkMe() = 44 } actual object Platform { actual val name: String = "Android" }

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actual class Sample { actual fun checkMe() = 7 } actual object Platform { actual val name: String = "iOS" }

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actual typealias with great power…

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/** * Multiplatform AtomicInt implementation */ expect class AtomicInt(initialValue: Int) { fun get(): Int fun set(newValue: Int) fun incrementAndGet(): Int fun decrementAndGet(): Int fun addAndGet(delta: Int): Int fun compareAndSet(expected: Int, new: Int): Boolean }

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JVM Side?

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import java.util.concurrent.atomic.AtomicInteger actual typealias AtomicInt = AtomicInteger

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Actual needs to match because obviously it does

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import kotlin.native.concurrent.AtomicInt actual class AtomicInt actual constructor(initialValue:Int){ private val atom = AtomicInt(initialValue) actual fun get(): Int = atom.value actual fun set(newValue: Int) { atom.value = newValue } actual fun incrementAndGet(): Int = atom.addAndGet(1) actual fun decrementAndGet(): Int = atom.addAndGet(-1) actual fun addAndGet(delta: Int): Int = atom.addAndGet(delta) actual fun compareAndSet(expected: Int, new: Int): Boolean = atom.compareAndSet(expected, new) }

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library talk

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Prefer Interfaces for “service” objects

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public interface Settings { public fun clear() public fun remove(key: String) public fun hasKey(key: String): Boolean public fun putInt(key: String, value: Int) public fun getInt(key: String, defaultValue: Int = 0): Int public fun getIntOrNull(key: String): Int? public fun putLong(key: String, value: Long) public fun getLong(key: String, defaultValue: Long = 0): Long public fun getLongOrNull(key: String): Long? //Etc... } from https://github.com/russhwolf/multiplatform-settings

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expect fun platformSettings():Settings

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object ServiceRegistry { var sessionizeApi:SessionizeApi by ThreadLocalDelegate() var analyticsApi: AnalyticsApi by FrozenDelegate() var notificationsApi:NotificationsApi by FrozenDelegate() var dbDriver: SqlDriver by FrozenDelegate() var cd: CoroutineDispatcher by FrozenDelegate() var appSettings: Settings by FrozenDelegate() var concurrent: Concurrent by FrozenDelegate() var timeZone: String by FrozenDelegate() //Etc… from https://github.com/touchlab/DroidconKotlin/

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Just an Interface no expect/actual required

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class TestSettings:Settings { private val map = frozenHashMap() override fun clear() { map.clear() } override fun getBoolean(key: String, defaultValue: Boolean): Bo return if(map.containsKey(key)){ map[key] as Boolean }else{ defaultValue } } //Etc… from https://github.com/touchlab/DroidconKotlin/

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koin multiplatform

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interface AnalyticsApi { fun logEvent(name: String, params: Map) }

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class AnalyticsApiImpl(val firebaseAnalytics: FirebaseAnalytics) : AnalyticsApi { override fun logEvent(name: String, params: Map) { val bundle = Bundle() params.keys.forEach { key -> when (val obj = params[key]) { is String -> bundle.putString(key, obj) is Int -> bundle.putInt(key, obj) else -> { throw IllegalArgumentException(“…”) } } } firebaseAnalytics.logEvent(name, bundle) } }

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class AnalyticsApiMock : AnalyticsApi { var logCalled = false override fun logEvent(name: String, params: Map) { logCalled = true } }

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class FirebaseAnalyticsApi: AnalyticsApi{ func logEvent(name: String, params: [String : Any]) { Analytics.logEvent(name, parameters: params) } }

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serviceRegistry.doInitLambdas(staticFileLoader: loadAsset, clLogCallback: csLog, softExceptionCallback: softExceptionCallback) serviceRegistry.doInitServiceRegistry(sqlDriver: …, coroutineDispatcher: UI(), settings: FunctionsKt.defaultSettings(), concurrent: MainConcurrent(), sessionizeApi: SessionizeApiImpl(), analyticsApi: …, notificationsApi: NotificationsApiImpl(), timeZone: timeZone) AppContext().doInitAppContext(networkRepo: NetworkRepo(), fileRepo: FileRepo(), serviceRegistry: serviceRegistry, dbHelper: SessionizeDbHelper(), notificationsModel: NotificationsModel())

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Function args! swift friendly

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fun initLambdas( staticFileLoader: (filePrefix: String, fileType: String) -> String?, clLogCallback: (s: String) -> Unit, softExceptionCallback: (e:Throwable, message:String) - >Unit)

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func loadAsset(filePrefix:String, fileType:String) -> String?{ do{ let bundleFile = Bundle.main.path(forResource: filePrefix, ofType: fileType) return try String(contentsOfFile: bundleFile!) } catch { return nil } }

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Hard(er) to test tests are Kotlin exe

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go.touchlab.co/dcktsrc

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go.touchlab.co/dcktsrc

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So no expect/actual? um…

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Minimize expect/actual Droidcon App: 9 functions, 2 classes

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Minimize expect/actual? Firestore SDK: 100+ ‘expect’ instances

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Getting Started

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Droidcon is OK there’s a lot going on, though

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JetBrains Doc kotlinlang.org/docs/reference/building-mpp-with-gradle.html

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“5 minutes” go.touchlab.co/kmp5

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Kotlin Slack https://kotlinlang.org/community/

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KMP evaluation kit

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KaMP-Kit go.touchlab.co/KaMP-Kit

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Concurrency it’s complicated (with native)

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Two Rules mutable = 1 thread/immutable = many threads

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Frozen new state of state

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public fun T.freeze(): T {...}

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public fun T.freeze(): T {...}

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JetBrains Links • https://github.com/JetBrains/kotlin-native/blob/ master/IMMUTABILITY.md • https://github.com/JetBrains/kotlin-native/blob/ master/CONCURRENCY.md • https://www.youtube.com/watch?v=nw6YTfEyfO0