Kotlin in 2019 - Speaker Deck

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Kotlin in 2019 Pietro Maggi @pfmaggi

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Kotlin

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Language design is cast in stone, but this stone is reasonably soft, and with some effort we can reshape it later. Kotlin Design Team

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Pragmatic Ergonomic Constant feedback loop

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Kotlin ● Object Oriented and Functional ● Static typing with type inference ● Safe ● Concise

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package hello; class HelloWorld { public static void main(String args[]) { System.out.println("Hello, World"); } } Kotlin ● Object Oriented and Functional ● Static typing with type inference ● Safe ● Concise

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package hello fun main() { println("Hello World") } Kotlin ● Object Oriented and Functional ● Static typing with type inference ● Safe ● Concise

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History Kotlin is announced Creation of Kotlin by Jetbrains 2011 2012 2013 2014 2015 2016 2017 2018 2019 ?

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History Kotlin is announced Creation of Kotlin by Jetbrains 2011 2012 2013 2014 2015 2016 2017 2018 2019 ? Kotlin is released Development tools are open source

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History Kotlin is announced Creation of Kotlin by Jetbrains 2011 2012 2013 2014 2015 2016 2017 2018 2019 ? Kotlin is released Development tools are open source Kotlin 1.0 First stable

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History Kotlin is announced Creation of Kotlin by Jetbrains Kotlin 1.1 (March) JavaScript support Coroutines introduction 2011 2012 2013 2014 2015 2016 2017 2018 2019 ? Kotlin is released Development tools are open source Kotlin 1.0 First stable

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History Kotlin is announced Creation of Kotlin by Jetbrains Kotlin 1.3 (October) Coroutines stable (JVM) Kotlin/Native beta Kotlin 1.1 (March) JavaScript support Coroutines introduction 2011 2012 2013 2014 2015 2016 2017 2018 2019 ? Kotlin is released Development tools are open source Kotlin 1.0 First stable Kotlin 1.2 (November) Code sharing between platforms

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Android SDK Java application development 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 Android Development

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Android SDK Java application development 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 Android NDK C and C ++ support for games and cross-platform library/applications Android Development

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Android SDK Java application development 2008 2009 2010 2011 2012 2013 2014 2015 2016 2017 2018 2019 2020 Kotlin on Android Official support Android NDK C and C ++ support for games and cross-platform library/applications Android Development

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Kotlin First

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Kotlin First

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Personal Kotlin’s Favorites

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Null Safety Aims to eliminate NullPointerException

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var a: String = "abc" a = null Null Safety Aims to eliminate NullPointerException

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var a: String = "abc" a = null Null Safety Aims to eliminate NullPointerException > Null can not be a value of a non-null type String

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var a: String = "abc" a = null Null Safety Aims to eliminate NullPointerException > Null can not be a value of a non-null type String var b: String? = "abc" b = null print(b)

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var a: String = "abc" a = null Null Safety Aims to eliminate NullPointerException > Null can not be a value of a non-null type String var b: String? = "abc" b = null print(b) > null

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Asynchronous Operations Coroutines are light-weight threads

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import kotlinx.coroutines.* fun main() { GlobalScope.launch { delay(1000L) println("World!") } print("Hello, ") Thread.sleep(2000L) } Asynchronous Operations Coroutines are light-weight threads

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import kotlinx.coroutines.* fun main() { GlobalScope.launch { delay(1000L) println("World!") } print("Hello, ") Thread.sleep(2000L) } Asynchronous Operations Coroutines are light-weight threads

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import kotlinx.coroutines.* fun main() { GlobalScope.launch { delay(1000L) println("World!") } print("Hello, ") Thread.sleep(2000L) } Asynchronous Operations Coroutines are light-weight threads > Hello,

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Extension Functions Add functionality to a type, without directly modifying the type’s definition

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fun Byte.toUnsigned(): Int { return if (this < 0) this + 256 else this.toInt() } Extension Functions Add functionality to a type, without directly modifying the type’s definition

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fun Byte.toUnsigned(): Int { return if (this < 0) this + 256 else this.toInt() } Extension Functions Add functionality to a type, without directly modifying the type’s definition val x: Byte = -1 println(x.toUnsigned()) > 255

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Developer Experience

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Android Studio Kotlin ● Kotlin plugin is part of Android Studio ● Lint checks & refactoring support ● Project templates and samples ● Kotlin-friendly Android SDK (nullability)

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Android Studio Kotlin ● Kotlin plugin is part of Android Studio ● Lint checks & refactoring support ● Project templates and samples ● Kotlin-friendly Android SDK (nullability)

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Kapt is incremental now

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Android Studio Kotlin

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R8 Kotlin

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Kotlin’s Companion Object fun main() { println(Greeter.hello().greet("Olive")) } class Greeter(val greeting: String) { fun greet(name: String) = "$greeting, $name!" companion object { fun hello() = Greeter("Hello") } }

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Companion Object… as seen from Java public final class Greeter { public static final Companion Companion = new Companion(); private final String greeting; public Greeter(String greeting) { this.greeting = greeting; } public String getGreeting() { return greeting; } public String greet(String name) { return greeting + ", " + name; } public static final class Companion { private Companion() {} public Greeter hello() { return new Greeter("Hello"); } } }

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public final class Greeter { - public static final Companion Companion = new Companion(); private final String greeting; - public static final class Companion { - private Companion() {} - - public Greeter hello() { - return new Greeter("Hello"); - } - } + public static Greeter hello() { + return new Greeter("Hello"); + } public String greet(String name) { return greeting + ", " + name; } } Fortunately there’s R8

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Kotlin’s Adoption

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Kotlin’s Adoption

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Google Apps Kotlin

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Android Kotlin

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Android Jetpack Kotlin & Coroutines ● Kotlin-friendly APIs ● Room suspend functions ● WorkManager CoroutineWorker ● Lifecycles & ViewModel coroutine scopes ● + more KTX libraries...

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Android KTX (core) sharedPreferences .edit() // create an Editor .putBoolean("key", value) .apply() // write to disk asynchronously Default APIs

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Android KTX (core) sharedPreferences .edit() // create an Editor .putBoolean("key", value) .apply() // write to disk asynchronously sharedPreferences.edit { putBoolean("key", value) } Default APIs with core-ktx, syntactic sugar on top of the same APIs

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youtu.be/BOHK_w09pVA

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Jetpack Compose ● Reactive UI toolkit ● Unbundled from Android Framework ● Developer Preview ● Android Studio v4.0

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@Composable fun Greeting(name: String) { Text("Hello $name") } Jetpack Compose ● Reactive UI toolkit ● Unbundled from Android Framework ● Developer Preview ● Android Studio v4.0

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Jetpack Compose ● Reactive UI toolkit ● Unbundled from Android Framework ● Developer Preview ● Android Studio v4.0 github.com/android/compose-samples/tree/master/JetNews

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youtu.be/dtm2h-_sNDQ

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Documentation Kotlin ● Migration to Kotlin pages ● Code snippets in Kotlin ● Switch between Java and Kotlin

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● Kotlin Koans: kotlinlang.org/docs/tutorials/koans.html ● Kotlin Playground play.kotlinlang.org ● Udacity ○ Kotlin Bootcamp for Programmers ○ Developing Android Apps with Kotlin ○ Advanced Android with Kotlin Learning Kotlin

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● Google I/O and ADS apps: github.com/google/iosched ● Sunflower: github.com/android/sunflower ● Plaid: github.com/android/plaid ● More Samples: developer.android.com/samples?language=kotlin Samples Kotlin

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Community Kotlin

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OkHttp ● Client HTTP ● Created by Square ● 100% Kotlin since version 4 fun post(url: String, json: String): String { val mediaType = MediaType.parse("application/json;charset=utf-8") val client = OkHttpClient() val body = RequestBody.create(mediaType, json) val request = Request.Builder().url(url).post(body).build() val response = client.newCall(request).execute() return response.body().string() }

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SQLDelight ● Generates typesafe Kotlin APIs from SQL ● Created by Square ● 100% Kotlin ● Multi-platform (supported SQLite drivers on Android, JVM and iOS) selectAll: SELECT * FROM hockeyPlayer; insert: INSERT INTO hockeyPlayer(player_number, full_name) VALUES (?, ?); insertFullPlayerObject: INSERT INTO hockeyPlayer(player_number, full_name) VALUES ?; Player.sq

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SQLDelight ● Generates typesafe Kotlin APIs from SQL ● Created by Square ● 100% Kotlin ● Multi-platform (supported SQLite drivers on Android, JVM and iOS) val database = Database(driver) val playerQueries: PlayerQueries = database.playerQueries println(playerQueries.selectAll().executeAsList()) // Prints [HockeyPlayer.Impl(15, "Ryan Getzlaf")] playerQueries.insert(player_number = 10, full_name = "Corey Perry") println(playerQueries.selectAll().executeAsList()) // Prints [HockeyPlayer.Impl(15, "Ryan Getzlaf"), ...] val player = HockeyPlayer(10, "Ronald McDonald") playerQueries.insertFullPlayerObject(player) PlayerQueries.kt

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Kotlin multiplatform

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Component Status entered at Mode for Sources Mode for Binaries Kotlin/JVM v1.0 Fully Stable Fully Stable Kotlin/JS v1.1 AIR* Moving Fast Kotlin/Native v1.3 AIR* Moving Fast Kotlin Scripts (*.kts) v1.2 AIR* Moving Fast Multi-Platform Projects v1.2 Moving Fast Moving Fast Coroutines v1.3 Fully Stable Fully Stable Stability of Different Components * Additions in Incremental Releases

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Libraries ● SQLDelight: SQLite model facilitation library ● SQLiter: SQLite access driver. Powering the SQLDelight native driver ● Multiplatform Settings: Save simple key-value data ● Kotlinx.Serialization: cross-platform / multi-format reectionless serialization ● Kotlinx.Coroutines: Support library for coroutines ● Stately: State utility library Kotlin Multiplatform Samples ● Kotlinconf App: Kotlinconf schedule app, iOS/Android/Backend ● DroidconKotlin: Droidcon NY/SF schedule app, iOS/Android/Web ● Sudoku: iOS/Android sample game

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Is Kotlin mobile only

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● Framework Web ● Client/Server ● 100% Kotlin ● Multi-platform fun main(args: Array) { val server = embeddedServer(Netty, port = 8080) { routing { get("/") { call.respondText( "Hello World!", ContentType.Text.Plain ) } get("/demo") { call.respondText("HELLO WORLD!") } } } server.start(wait = true) }

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Spring boot and Kotlin spring.io/guides/tutorials/spring-boot-kotlin/

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KOTLIN ON GOOGLE CLOUD PLATFORM A community-supported project codelabs.developers.google.com/codelabs/cloud-kotlin-emojify/

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Kotlin future?

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● More Coroutines! ● More Multi-Platform ● Even better developer experience

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Thanks Pietro Maggi @pfmaggi