What’s up next for Kotlin? Nicola Corti @cortinico 

HH 

A bit of history 

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Speakers • Gesh Markov • Christophe Beyls • Niklas Baudy • Cord Jastram • Yahya Bayramoglu • Jossi Wolf • Jendrik Johannes • Ivan Morgillo • Jule Lehmann • Dmitry Zaytsev Lovis Möller - Nicola Corti 

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Stats • 7 Meetups organized in the last year • ~280 total attendees • 333 Meetup Members • 128 Twitter Followers • Basically always booked out! 

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pusher.com/state-of-kotlin 

Kotlin Adoption 

Migrating Java to Kotlin 

Reasons for returning to Java Over a quarter of respondents who migrated Java to Kotlin needed to revert. 

Favorite Features 

Reasons to use coroutines (or not) 

1.3 

1.3-M1 EAP 

1.3-M1 EAP plugins { kotlin("jvm") version "1.2.60" } repositories { mavenCentral() } dependencies { compile(kotlin("stdlib-jdk8", "1.2.60")) } 

1.3-M1 EAP plugins { kotlin("jvm") version "1.2.60" } repositories { mavenCentral() maven("http://dl.bintray.com/kotlin/kotlin-eap") } dependencies { compile(kotlin("stdlib-jdk8", "1.2.60")) } 

1.3-M1 EAP plugins { kotlin("jvm") version "1.3-M1" } repositories { mavenCentral() maven("http://dl.bintray.com/kotlin/kotlin-eap") } dependencies { compile(kotlin("stdlib-jdk8", "1.3-M1")) } 

1.3-M1 EAP plugins { kotlin("jvm") version "1.3-M1" } repositories { mavenCentral() maven("http://dl.bintray.com/kotlin/kotlin-eap") } dependencies { compile(kotlin("stdlib-jdk8", “1.3-M1")) compile(“org.jetbrains.kotlinx:kotlinx-coroutines-core:0.24.0") } 

1.3-M1 EAP plugins { kotlin("jvm") version "1.3-M1" } repositories { mavenCentral() maven("http://dl.bintray.com/kotlin/kotlin-eap") } dependencies { compile(kotlin("stdlib-jdk8", “1.3-M1")) compile(“org.jetbrains.kotlinx:kotlinx-coroutines-core:0.24.0-eap13") } 

Coroutines 

Coroutines kotlin { experimental.coroutines = Coroutines.ENABLE } 

Coroutines import kotlinx.coroutines.experimental.delay import kotlinx.coroutines.experimental.launch fun justACoroutine() { launch { delay(1000) println("Hello world!") } } 

Coroutines import kotlinx.coroutines.delay import kotlinx.coroutines.launch fun justACoroutine() { launch { delay(1000) println("Hello world!") } } 

Capturing When 

Capturing When fun Request.getBody() : ResponseBody { val response = executeRequest() when (response) { is Authenticator.Success -> response.body is HttpError -> throw HttpException(response.status) } } 

Capturing When fun Request.getBody() : ResponseBody { when (val response = executeRequest()) { is Authenticator.Success -> response.body is HttpError -> throw HttpException(response.status) } } 

Capturing When fun Request.getBody() = when (val response = executeRequest()) { is Authenticator.Success -> response.body is HttpError -> throw HttpException(response.status) } 

Capturing When 

Interfaces interface MyPublicApi { } 

Interfaces interface MyPublicApi { companion object { val baseUrl = "http://..." fun create(): MyPublicApi = ... } } 

Interfaces interface MyPublicApi { companion object { @JvmField val baseUrl = "http://..." @JvmStatic fun create(): MyPublicApi = ... } } Java 1.8 

Annotations annotation class MyAnnotation(val value: Int) 

Annotations annotation class MyAnnotation(val value: Int) { annotation class SubAnnotation } 

Annotations annotation class MyAnnotation(val value: Int) { annotation class SubAnnotation companion object { val timestamp = System.currentTimeMillis() } } 

Annotations annotation class MyAnnotation(val value: Int) { annotation class SubAnnotation companion object { @JvmField val timestamp = System.currentTimeMillis() } } 

KEEP 

KEEP 

Arity 

Arity fun arity22Function(lambda : ( Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int) -> Unit) { } 

Arity fun arity22Function(lambda : ( Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int) -> Unit) { } public final void arity22Function(@NotNull Function22 lambda) { Intrinsics.checkParameterIsNotNull(lambda, "lambda"); } 

Arity package kotlin.jvm.functions /** A function that takes 0 arguments. */ public interface Function0 : Function { /** Invokes the function. */ public operator fun invoke(): R } /** A function that takes 1 argument. */ public interface Function1 : Function { /** Invokes the function with the specified argument. */ public operator fun invoke(p1: P1): R } /** A function that takes 2 arguments. */ public interface Function2 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2): R } /** A function that takes 3 arguments. */ public interface Function3 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3): R } /** A function that takes 4 arguments. */ public interface Function4 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4): R } /** A function that takes 5 arguments. */ public interface Function5 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5): R } /** A function that takes 6 arguments. */ public interface Function6 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6): R } /** A function that takes 7 arguments. */ public interface Function7 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7): R } /** A function that takes 8 arguments. */ public interface Function8 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8): R } /** A function that takes 9 arguments. */ public interface Function9 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9): R } /** A function that takes 10 arguments. */ public interface Function10 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10): R } /** A function that takes 11 arguments. */ public interface Function11 : Function { 

Arity /** A function that takes 8 arguments. */ public interface Function8 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8): R } /** A function that takes 9 arguments. */ public interface Function9 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9): R } /** A function that takes 10 arguments. */ public interface Function10 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10): R } /** A function that takes 11 arguments. */ public interface Function11 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11): R } /** A function that takes 12 arguments. */ public interface Function12 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12): R } /** A function that takes 13 arguments. */ public interface Function13 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13): R } /** A function that takes 14 arguments. */ public interface Function14 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14): R } /** A function that takes 15 arguments. */ public interface Function15 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15): R } /** A function that takes 16 arguments. */ public interface Function16 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16): R } /** A function that takes 17 arguments. */ public interface Function17 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17): R } /** A function that takes 18 arguments. */ public interface Function18 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17, p18: P18): R } /** A function that takes 19 arguments. */ public interface Function19 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17, p18: P18, p19: P19): R } /** A function that takes 20 arguments. */ public interface Function20 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17, p18: P18, p19: P19, p20: P20): R } /** A function that takes 21 arguments. */ public interface Function21 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17, p18: P18, p19: P19, p20: P20, p21: P21): R } /** A function that takes 22 arguments. */ public interface Function22 : Function { /** Invokes the function with the specified arguments. */ public operator fun invoke(p1: P1, p2: P2, p3: P3, p4: P4, p5: P5, p6: P6, p7: P7, p8: P8, p9: P9, p10: P10, p11: P11, p12: P12, p13: P13, p14: P14, p15: P15, p16: P16, p17: P17, p18: P18, p19: P19, p20: P20, p21: P21, p22: P22): R } 

Arity fun arity22Function(lambda : ( Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int) -> Unit) { } 

Arity fun arity23Function(lambda : ( Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int) -> Unit) { } 

Arity fun arity23Function(lambda : ( Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int) -> Unit) { } public final void arity23Function(@NotNull FunctionN lambda) { Intrinsics.checkParameterIsNotNull(lambda, "lambda"); } 

Arity fun arity23Function(lambda : ( Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int, Int) -> Unit) { } public final void arity23Function(@NotNull FunctionN lambda) { Intrinsics.checkParameterIsNotNull(lambda, "lambda"); } 

Arity @SinceKotlin("1.3") interface FunctionN : Function, FunctionBase { /** * Invokes the function with the specified arguments. * * Must **throw exception** if the length of passed [args] * is not equal to the parameter count returned by [arity]. * * @param args arguments to the function */ operator fun invoke(vararg args: Any?): R /** * Returns the number of arguments that must be passed to * this function. */ override val arity: Int } http://bit.ly/keep-bigarity 

Experimental features 

Inline Classes 

Inline Classes inline class Username(val value: String) 

Inline Classes inline class Username(val value: String) typealias Username = String 

Inline Classes inline class Username(val value: String) inline class Password(val value: String) 

Inline Classes inline class Username(val value: String) inline class Password(val value: String) val myName = Username("nicola") val myPassword = Password("p4ssw0rd") 

Inline Classes inline class Username(val value: String) inline class Password(val value: String) val myName = Username("nicola") val myPassword = Password("p4ssw0rd") myName = myPassword 

Inline Classes inline class Username(val value: String) inline class Password(val value: String) val myName = Username("nicola") val myPassword = Password("p4ssw0rd") myName = myPassword myPassword = myName 

Inline Classes inline class Username(val value: String) inline class Password(val value: String) val myName = Username("nicola") val myPassword = Password("p4ssw0rd") myName = myPassword myPassword = myName myName = "MyNewName" bit.ly/keep-inlineclasses 

Unsigned Types 

Unsigned Types val anUnsignedInteger : UInt val anUnsignedLong : ULong val anUnsignedByte : UByte val anUnsignedShort : UShort 

Unsigned Types val anUnsignedInteger : UInt = 0xFFFF_FFFFu val anUnsignedLong : ULong = 10uL val anUnsignedByte : UByte = 0xFFu val anUnsignedShort : UShort = 0xFFFFu 

Unsigned Types @SinceKotlin("1.3") @ExperimentalUnsignedTypes public inline class UInt internal constructor(private val data: Int) : Comparable { bit.ly/keep-utype 

Experimental Annotations 

Experimental Annotations @Experimental(Experimental.Level.WARNING) annotation class MyCoolFeatureExperimental 

Experimental Annotations @Experimental(Experimental.Level.WARNING) annotation class MyCoolFeatureExperimental @MyCoolFeatureExperimental fun myExperimentalFunction() { // ... } 

Experimental Annotations @Experimental(Experimental.Level.WARNING) annotation class MyCoolFeatureExperimental @MyCoolFeatureExperimental fun myExperimentalFunction() { // ... } @UseExperimental(MyCoolFeatureExperimental::class) fun myClientCode() { myExperimentalFunction() } 

Experimental Annotations @Experimental(Experimental.Level.WARNING) annotation class MyCoolFeatureExperimental @MyCoolFeatureExperimental fun myExperimentalFunction() { // ... } @UseExperimental(MyCoolFeatureExperimental::class) fun myClientCode() { myExperimentalFunction() } bit.ly/keep-experimental 

SuccessOrFailure 

SuccessOrFailure /** * A discriminated union that encapsulates successful outcome * with a value of type [T] or a failure with an arbitrary * [Throwable] exception. */ inline class SuccessOrFailure internal constructor( internal val value: Any? // internal value -- either T or Failure ) { internal class Failure(val exception: Throwable) //... } 

SuccessOrFailure /** * A discriminated union that encapsulates successful outcome * with a value of type [T] or a failure with an arbitrary * [Throwable] exception. */ inline class SuccessOrFailure internal constructor( internal val value: Any? // internal value -- either T or Failure ) { internal class Failure(val exception: Throwable) //... } 

SuccessOrFailure /** * A discriminated union that encapsulates successful outcome * with a value of type [T] or a failure with an arbitrary * [Throwable] exception. */ inline class SuccessOrFailure internal constructor( internal val value: Any? // internal value -- either T or Failure ) { internal class Failure(val exception: Throwable) //... } 

SuccessOrFailure /** * A discriminated union that encapsulates successful outcome * with a value of type [T] or a failure with an arbitrary * [Throwable] exception. */ inline class SuccessOrFailure internal constructor( internal val value: Any? // internal value -- either T or Failure ) { internal class Failure(val exception: Throwable) //... } inline fun runCatching(block: () -> R): SuccessOrFailure 

SuccessOrFailure /** * A discriminated union that encapsulates successful outcome * with a value of type [T] or a failure with an arbitrary * [Throwable] exception. */ inline class SuccessOrFailure internal constructor( internal val value: Any? // internal value -- either T or Failure ) { internal class Failure(val exception: Throwable) //... } inline fun runCatching(block: () -> R): SuccessOrFailure 

SuccessOrFailure inline fun runCatching(block: () -> R): SuccessOrFailure { return try { SuccessOrFailure.success(block()) } catch (e: Throwable) { SuccessOrFailure.failure(e) } } 

SuccessOrFailure fun findUserByName(name: String): ? 

SuccessOrFailure fun findUserByName(name: String): SuccessOrFailure You can do better… 

SuccessOrFailure fun findUserByName(name: String): User 

SuccessOrFailure sealed class FindUserResult { data class Found(val user: User) : FindUserResult() data class NotFound(val name: String) : FindUserResult() data class MalformedName(val name: String) : FindUserResult() // other cases that need different business-specific handling code } fun findUserByName(name: String): FindUserResult 

SuccessOrFailure fun findUserByName(name: String): User 

SuccessOrFailure fun findUserByName(name: String): User val result = runCatching { findUserByName("...") } 

SuccessOrFailure fun findUserByName(name: String): User fun findUserByNameCatching(name: String): SuccessOrFailure val result = runCatching { findUserByName("...") } 

SuccessOrFailure - Use Cases 

SuccessOrFailure - Use Cases fun readFilesCatching(files: List): List> = files.map { } 

SuccessOrFailure - Use Cases fun readFilesCatching(files: List): List> = files.map { runCatching { readFile(it) } } 

SuccessOrFailure - Use Cases fun readFilesCatching(files: List): List> = files.map { runCatching { readFile(it) } } readFilesCatching(listOf("...")).map { } 

SuccessOrFailure - Use Cases fun readFilesCatching(files: List): List> = files.map { runCatching { readFile(it) } } readFilesCatching(listOf("...")).map { result -> } 

SuccessOrFailure - Use Cases fun readFilesCatching(files: List): List> = files.map { runCatching { readFile(it) } } readFilesCatching(listOf("...")).map { result : SuccessOrFailure -> } 

SuccessOrFailure - Use Cases fun readFilesCatching(files: List): List> = files.map { runCatching { readFile(it) } } readFilesCatching(listOf("...")).map { result -> result.mapCatching { formatFile(it) } } 

SuccessOrFailure - Use Cases fun readFilesCatching(files: List): List> = files.map { runCatching { readFile(it) } } readFilesCatching(listOf("...")).map { result -> result.mapCatching { formatFile(it) } } 

SuccessOrFailure - Use Cases 

SuccessOrFailure - Use Cases try { val data = doSomething() processData(data) } catch(e: Throwable) { showErrorDialog(e) } 

SuccessOrFailure - Use Cases try { val data = doSomething() processData(data) } catch(e: Throwable) { showErrorDialog(e) } runCatching { doSomething() } .onFailure { showErrorDialog(it) } .onSuccess { processData(it) } 

SuccessOrFailure - Use Cases 

SuccessOrFailure - Use Cases /** * Interface representing a continuation after a suspension point that * returns value of type `T`. */ @SinceKotlin("1.3") public interface Continuation { /** * Context of the coroutine that corresponds to this continuation. */ public val context: CoroutineContext /** * Resumes the execution of the corresponding coroutine passing successful or failed [result] as the * return value of the last suspension point. */ public fun resumeWith(result: SuccessOrFailure) } bit.ly/keep-successorfailure 

To infinity… • Collections Literals • SAM Conversion • Truly Immutability val list = listOf("1", "2", "3") val list = ["1", "2", "3"] val map = mapOf("1" to 1, "2" to 2, "3" to 3) val map = ["1" = 1, "2" = 2, "3" = 3] interface Function { fun run(data: T) } val myFunction: Function = { println ("data $it”) } class Foo(var v: Int) immutable class Bar(val foo: Foo) // This should fail bit.ly/kotlin-feature-survey 

Thanks! Nicola Corti @cortinico