Architecting a Kotlin multiplatform project

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FELIPE LIMA / OCT 4TH, 2018 / KOTLINCONF Architecting a Kotlin JVM and JS multiplatform project

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FELIPE LIMA / OCT 4TH, 2018 / KOTLINCONF Architecting a Kotlin JVM and JS multiplatform project

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INTRODUCTION

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• Yet another cross platform framework? • Not all of them are created equal • Several options: React Native, Flutter, Xamarin, PhoneGap, Titanium, Cordova, etc. • Quite unlike all other options • Ideal for business logic code sharing How it works

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Kotlin Multiplatform ≠ React Native TO MAKE IT CLEAR

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Kotlin Multiplatform > C/C++ TO MAKE IT CLEAR

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Common JVM Kotlin/Native Javascript Android

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Common Kotlin/Native kotlinc kotlin2js

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Common Kotlin/Native JVM kotlinc Android kotlin2js

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Common Kotlin/Native Dynamic lib iOS Executable JVM kotlinc Android kotlin2js

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A Common Kotlin/Native Dynamic lib iOS Executable JVM kotlinc Android kotlin2js Javascript

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apply plugin: 'kotlin-platform-common' Gradle plugins

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apply plugin: ‘kotlin-platform-android' Gradle plugins

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apply plugin: ‘kotlin-platform-jvm’ Gradle plugins

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apply plugin: ‘kotlin-platform-js’ Gradle plugins

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apply plugin: ‘konan’ Gradle plugins

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apply plugin: ‘org.jetbrains.kotlin.frontend’ Gradle plugins

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dependencies { expectedBy project(':common') } Declaring dependencies

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KEY CONCEPTS

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L expect Shared module actual Platform module

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expect class Order { val id: Int val userId: Int val amount: Decimal val feePercent: Decimal val price: Decimal val coinPair: CoinPair val status: OrderStatus val type: OrderType } Common

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actual data class Order( actual val id: Int, actual val userId: Int, actual val amount: Decimal, actual val feePercent: Decimal, actual val price: Decimal, actual val coinPair: CoinPair, actual val status: OrderStatus, actual val type: OrderType, val createdAt: DateTime = DateTime.now(), val updatedAt: DateTime = DateTime.now() ) JVM

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expect class Decimal Common

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actual typealias Decimal = BigDecimal JVM

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actual typealias Decimal = Double JS

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expect fun currentTimeMs(): Long Common

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actual fun currentTimeMs(): Long { return System.currentTimeMillis() } JVM

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actual fun currentTimeMs(): Long { memScoped { val now = alloc() gettimeofday(now.ptr, null) return (now.tv_sec.toLong() * 1000) + (now.tv_usec.toLong() / 1000) } } Kotlin/Native

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• Simpler implementation (no factory classes or dep. injection) • Interfaces cannot have constructors • All implementations are known at compile time • More flexibility • Top level and extension functions are supported Why not interfaces?

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• Cannot reference any platform specific code • Can only have Kotlin code • Can only depend on other Kotlin common modules or libraries Common module LIMITATIONS AND CAVEATS

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DEEP DIVE

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Story time

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Console APU PPU CPU Mapper Audio buffer Video buffer Audio device Video device

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Console APU PPU CPU Mapper Audio buffer Video buffer Audio device Video device

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PPU Bitmap OpenGL ES GLSurfaceView

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expect class Bitmap constructor( width: Int, height: Int ) { fun setPixel(x: Int, y: Int, value: Int) }

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package android.graphics; public final class Bitmap implements Parcelable { // ... }

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typealias AndroidBitmap = android.graphics.Bitmap actual class Bitmap actual constructor(width: Int, height: Int) { private val delegate: AndroidBitmap = AndroidBitmap.createBitmap(width, height, RGB_565) actual fun setPixel(x: Int, y: Int, value: Int) { delegate.setPixel(x, y, value) } }

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actual typealias Bitmap = android.graphics.Bitmap

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PPU IntArray OpenGL ES GLSurfaceView

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internal class PPU( internal var buffer: IntArray = IntArray(IMG_WIDTH * IMG_HEIGHT) // ... }

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KEY TAKE AWAYS

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• Support is still experimental, expect rough edges and breaking changes • Very exciting technology • Benefits from a large and quickly growing Kotlin community • Expect the usual top notch tooling support by Jetbrains • You can start trying it out using it right now Key take aways

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• Makes no assumptions about your system architecture • Not a framework, just a platform • Has the potential to turn into an entire ecosystem • Probably will require bigger organizational changes Key take aways

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THANK YOU!