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Code reuse with Kotlin Multiplatform

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Felipe Costa Senior Software engineer @ OLX Brasil Passionate Software Craftsman. I have been developing mobile applications since 2011 and enjoying it mostly in Kotlin since 2016.

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Our purpose We approach Brazilians to turn items into happiness.

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Kotlin @ OLX 0 Python Javascript Java C PHP Kotlin Objective-C Perl

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Kotlin @ OLX 0 Android Authentication Experimentação Insertion Search Recomendation

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Karol & Multiplatform Chat MVP

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Why reuse code between platforms?

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DRY

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Risk mitigation

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Feature parity

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Solutions

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Input Process Output App type Native Language: Kotlin & Swift & JS Outra linguagem Cross-Compile Inclui Runtime (Interpretador, VM, Bibliotecas) Native Code Native Language: Javascript Native Web Native Web

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Input Process Output App type Native Language Other Language: Javascript Cross-Compile Include Runtime (Interpreter, VM, Libraries) Native Code + Bundle JS Native Language Native Web React Native

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Flutter Input Process Output App type Native Language Other Language: Dart Cross-Compile Include Runtime (Interpreter, VM, Libraries) Native Code Native Language Native Web

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Kotlin Multiplatform Input Process Output App Type Native Language: Kotlin Other Language Cross-Compile Include Runtime (Interpreter, VM, Libraries) Native Code Native Language: Javascript Native Web Android iOS Web

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Why Kotlin Multiplatform?

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Optional Sharing Low risk No Big decisions

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100% Native smooth interop

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Code sharing not “cross platform”

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Activity community

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Good tools

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Modern Language

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Not UI not necessarily

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Many Platforms

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Common *.kt

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plugins { id 'kotlin-multiplatform' version '1.3.31' } repositories { mavenCentral() } kotlin { sourceSets { commonMain { dependencies { implementation kotlin('stdlib-common') } } } } Build.gradle

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plugins { id 'kotlin-multiplatform' version '1.3.31' } repositories { mavenCentral() } kotlin { sourceSets { commonMain { dependencies { implementation kotlin('stdlib-common') } } } } Build.gradle

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plugins { id 'kotlin-multiplatform' version '1.3.31' } repositories { mavenCentral() } kotlin { sourceSets { commonMain { dependencies { implementation kotlin('stdlib-common') } } } } Build.gradle

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plugins { id 'kotlin-multiplatform' version '1.3.31' } repositories { mavenCentral() } kotlin { sourceSets { commonMain { dependencies { implementation kotlin('stdlib-common') } } } } Build.gradle

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Common *.kt

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Common *.kt *.class *.jar, *.apk

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kotlin { jvm() sourceSets { commonMain { /* */ } } } Build.gradle

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kotlin { jvm() sourceSets { commonMain { /* */ } } } Build.gradle

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kotlin { jvm() sourceSets { commonMain { /* */ } } } Build.gradle

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Common *.kt *.class *.jar, *.apk

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Common *.kt *.class *.jar, *.apk *.js

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kotlin { jvm() js() sourceSets { commonMain { /* */ } } } Build.gradle

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kotlin { jvm() js() sourceSets { commonMain { /* */ } } } Build.gradle

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kotlin { jvm() js() sourceSets { commonMain { /* */ } } } Build.gradle

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Common *.kt *.class *.jar, *.apk *.js

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Common *.kt *.class *.jar, *.apk *.js binário nativo Android/ NDK iOS Mac Linux Windows Webassembly Outros

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Common *.kt *.class *.jar, *.apk *.js binário nativo Android/ NDK iOS Mac Linux Windows Webassembly Outros

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kotlin { jvm() js() // For ARM, should be changed to iosArm32 or iosArm64 // For Linux, should be changed to e.g. linuxX64 // For MacOS, should be changed to e.g. macosX64 // For Windows, should be changed to e.g. mingwX64 macosX64("macos") sourceSets { commonMain { /* */ } } } Build.gradle

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kotlin { jvm() js() // For ARM, should be changed to iosArm32 or iosArm64 // For Linux, should be changed to e.g. linuxX64 // For MacOS, should be changed to e.g. macosX64 // For Windows, should be changed to e.g. mingwX64 macosX64("macos") sourceSets { commonMain { /* */ } } } Build.gradle

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kotlin { jvm() js() // For ARM, should be changed to iosArm32 or iosArm64 // For Linux, should be changed to e.g. linuxX64 // For MacOS, should be changed to e.g. macosX64 // For Windows, should be changed to e.g. mingwX64 macosX64("macos") sourceSets { commonMain { /* */ } } } Build.gradle

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fun hello(): String = "Hello from Kotlin Multiplatform" Common

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import kotlin.Metadata; import org.jetbrains.annotations.NotNull; @Metadata( mv = {1, 1, 15}, bv = {1, 0, 3}, k = 2, d1 = {"\u0000\b\n\u0000\n\u0002\u0010\u000e\n\u0000\u001a\u0006\u0010\u0000\u001a\u00020\u0001¨\u0006\u0002"}, d2 = {"hello", "", "Platform module com.example.hello-world-multiplatform.jvmMain including [com.example.hello-world-multiplatform.commonMain]"} ) public final class SampleKt { @NotNull public static final String hello() { return "Hello from Kotlin Multiplatform"; } } JVM

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if (typeof kotlin === 'undefined') { throw new Error("Error loading module 'hello-world-multiplatform'. Its dependency 'kotlin' was not found. Please, check whether 'kotlin' is loaded prior to 'hello-world-multiplatform'."); } this['hello-world-multiplatform'] = function (_, Kotlin) { 'use strict'; function hello() { return 'Hello from Kotlin Multiplatform'; } var package$sample = _.sample || (_.sample = {}); package$sample.hello = hello; Kotlin.defineModule('hello-world-multiplatform', _); return _; }(typeof this['hello-world-multiplatform'] === 'undefined' ? {} : this['hello-world-multiplatform'], kotlin); JS

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MacOS Binary .kexe

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kotlin { jvm() js() macosX64("macos") { binaries { sharedLib("sharedLib") } } sourceSets { commonMain { /* */ } } } Build.gradle

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kotlin { jvm() js() macosX64("macos") { binaries { sharedLib("sharedLib") } } sourceSets { commonMain { /* */ } } } Build.gradle

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kotlin { jvm() js() macosX64("macos") { binaries { sharedLib("sharedLib") } } sourceSets { commonMain { /* */ } } } Build.gradle

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MacOS Dynamic Library #ifndef KONAN_LIBSHAREDLIB_H #define KONAN_LIBSHAREDLIB_H #ifdef __cplusplus extern "C" { #endif /* typedefes */ typedef struct { /* Service functions. */ /* ... */ /* User functions. */ struct { struct { struct { const char* (*hello)(); } sample; } root; } kotlin; } libsharedLib_ExportedSymbols; extern libsharedLib_ExportedSymbols* libsharedLib_symbols(void); #ifdef __cplusplus } /* extern "C" */ #endif #endif /* KONAN_LIBSHAREDLIB_H */

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kotlin { jvm() js() macosX64("macos") { binaries { framework("framework") } } sourceSets { commonMain { /* */ } } } Build.gradle

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kotlin { jvm() js() macosX64("macos") { binaries { framework("framework") } } sourceSets { commonMain { /* */ } } } Build.gradle

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kotlin { jvm() js() macosX64("macos") { binaries { framework("framework") } } sourceSets { commonMain { /* */ } } } Build.gradle

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MacOS Framework #import NS_ASSUME_NONNULL_BEGIN @interface KotlinBase : NSObject - (instancetype)init __attribute__((unavailable)); + (instancetype)new __attribute__((unavailable)); + (void)initialize __attribute__((objc_requires_super)); @end; @interface KotlinBase (KotlinBaseCopying) @end; /* More types */ __attribute__((objc_subclassing_restricted)) __attribute__((swift_name("SampleKt"))) @interface FrameworkSampleKt : KotlinBase + (NSString *)hello __attribute__((swift_name("hello()"))); @end; NS_ASSUME_NONNULL_END

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fun hello(): String = "Hello from Kotlin Multiplatform" Common

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object Platform { val name: String } fun hello(): String = "Hello from ${Platform.name}" Common

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object Platform { val name: String = "JVM" } fun hello(): String = "Hello from ${Platform.name}" JVM

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object Platform { val name: String = "JS" } fun hello(): String = "Hello from ${Platform.name}" JS

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object Platform { val name: String = "Native" } fun hello(): String = "Hello from ${Platform.name}" Native

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Common *.kt Kotlin/JVM *.kt, *.java Kotlin/JS *.kt, *.js Kotlin/Native *.kt *.class *.jar, *.apk *.js binário nativo Android/ NDK iOS Mac Linux Windows Webassembly Others

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Libraries

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expect object Platform { val name: String } fun hello(): String = "Hello from ${Platform.name}" Common

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expect object Platform { val name: String } fun hello(): String = "Hello from ${Platform.name}" Common

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expect object Platform { val name: String } fun hello(): String = "Hello from ${Platform.name}" Common

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kotlin { jvm() macosX64("macos") sourceSets { commonMain { /* */ } jvmMain { dependencies { implementation kotlin('stdlib-jdk8') } } } } build.gradle

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kotlin { jvm() macosX64("macos") sourceSets { commonMain { /* */ } jvmMain { dependencies { implementation kotlin('stdlib-jdk8') } } } } build.gradle

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kotlin { jvm() macosX64("macos") sourceSets { commonMain { /* */ } jvmMain { dependencies { implementation kotlin('stdlib-jdk8') } } } } build.gradle

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actual object Platform { actual val name: String = "JVM" } fun hello(): String = "Hello from JVM" JVM

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actual object Platform { actual val name: String = "JVM" } fun hello(): String = "Hello from JVM" JVM

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actual object Platform { actual val name: String = "JVM" } fun hello(): String = "Hello from JVM" JVM

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kotlin { jvm() js() macosX64("macos") sourceSets { commonMain { /* */ } jvmMain { /* */ } jsMain { dependencies { implementation kotlin('stdlib-js') } } } } build.gradle

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kotlin { jvm() js() macosX64("macos") sourceSets { commonMain { /* */ } jvmMain { /* */ } jsMain { dependencies { implementation kotlin('stdlib-js') } } } } build.gradle

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kotlin { jvm() js() macosX64("macos") sourceSets { commonMain { /* */ } jvmMain { /* */ } jsMain { dependencies { implementation kotlin('stdlib-js') } } } } build.gradle

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actual object Platform { actual val name: String = "JS" } fun hello(): String = "Hello from JS" JS

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actual object Platform { actual val name: String = "JS" } fun hello(): String = "Hello from JS" JS

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actual object Platform { actual val name: String = "JS" } fun hello(): String = "Hello from JS" JS

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kotlin { jvm() js() macosX64("macos") sourceSets { commonMain { /* */ } jvmMain { /* */ } jsMain { /* */ } macosMain { } } } build.gradle

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kotlin { jvm() js() macosX64("macos") sourceSets { commonMain { /* */ } jvmMain { /* */ } jsMain { /* */ } macosMain { } } } build.gradle

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kotlin { jvm() js() macosX64("macos") sourceSets { commonMain { /* */ } jvmMain { /* */ } jsMain { /* */ } macosMain { } } } build.gradle

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actual object Platform { actual val name: String = "Native" } fun hello(): String = "Hello from Native” Native

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actual object Platform { actual val name: String = "Native" } fun hello(): String = "Hello from Native” Native

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actual object Platform { actual val name: String = "Native" } fun hello(): String = "Hello from Native” Native

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kotlin { jvm() js() macosX64("macos") sourceSets { commonMain { /* */ } commonTest { /* */ } jvmMain { /* */ } jvmTest { /* */ } jsMain { /* */ } jsTest { /* */ } macosMain { /* */ } macosTest { /* */ } } } build.gradle

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kotlin { jvm() js() macosX64("macos") sourceSets { commonMain { /* */ } commonTest { /* */ } jvmMain { /* */ } jvmTest { /* */ } jsMain { /* */ } jsTest { /* */ } macosMain { /* */ } macosTest { /* */ } } } build.gradle

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kotlin { jvm() js() macosX64("macos") sourceSets { commonMain { /* */ } commonTest { /* */ } jvmMain { /* */ } jvmTest { /* */ } jsMain { /* */ } jsTest { /* */ } macosMain { /* */ } macosTest { /* */ } } } build.gradle

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kotlin { /* */ sourceSets { /* */ commonTest { dependencies { implementation kotlin('test-common') implementation kotlin('test-annotations-common') } } jvmTest { dependencies { implementation kotlin('test') implementation kotlin('test-junit') } } jsTest { dependencies { implementation kotlin('test-js') } } macosTest { } } } build.gradle

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import kotlin.test.Test import kotlin.test.assertTrue class SampleTestsJVM { @Test fun testHello() { assertTrue("JVM" in hello()) } } JVM

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import kotlin.test.Test import kotlin.test.assertTrue class SampleTestsJS { @Test fun testHello() { assertTrue("JS" in hello()) } } JS

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import kotlin.test.Test import kotlin.test.assertTrue class SampleTestsNative { @Test fun testHello() { assertTrue("Native" in hello()) } } Native

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

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import kotlin.test.Test import kotlin.test.assertTrue class SampleTests { @Test fun testMe() { assertTrue(Sample().checkMe() > 0) } } Common

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Ktor Kotlinx.Coroutines kotlinx.io kotlinx.serialization sqldelight MPSettings Stately KorLibs File Access Better test support Date UI state

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Multiplatform Chat MVP

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Architecture Common Client Android iOS Web Server

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Architecture Android iOS Web Server Main Common Message Client ChatViewModel ChatClient

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Common ChatClient.kt Kotlin/JVM ChatClient.kt Kotlin/JS ChatClient.kt Kotlin/Native ChatClient.kt ChatClient.class ChatClient.js binário nativo Android/ NDK iOS Mac Linux Windows Webassembly Outros

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internal expect open class ChatClient(url: String) { open fun start() open fun send(message: Message) open fun receive(receiveBlock: (Message) -> Unit) open fun onFailure(throwableBlock: (Throwable) -> Unit) } Common

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internal expect open class ChatClient(url: String) { open fun start() open fun send(message: Message) open fun receive(receiveBlock: (Message) -> Unit) open fun onFailure(throwableBlock: (Throwable) -> Unit) } Common

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internal expect open class ChatClient(url: String) { open fun start() open fun send(message: Message) open fun receive(receiveBlock: (Message) -> Unit) open fun onFailure(throwableBlock: (Throwable) -> Unit) } Common

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internal actual open class ChatClient actual constructor(val url: String) : WebSocketListener() { actual open fun start() { /* */ } actual open fun send(message: Message) { /* */ } actual open fun receive(receiveBlock: (Message) -> Unit) { /* */ } actual open fun onFailure(throwableBlock: (Throwable) -> Unit) { /* */ } override fun onMessage(webSocket: WebSocket, text: String) { /* */ } override fun onFailure(webSocket: WebSocket, t: Throwable, response: Response?) { /* */ } } Android

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internal actual open class ChatClient actual constructor(val url: String) : WebSocketListener() { actual open fun start() { /* */ } actual open fun send(message: Message) { /* */ } actual open fun receive(receiveBlock: (Message) -> Unit) { /* */ } actual open fun onFailure(throwableBlock: (Throwable) -> Unit) { /* */ } override fun onMessage(webSocket: WebSocket, text: String) { /* */ } override fun onFailure(webSocket: WebSocket, t: Throwable, response: Response?) { /* */ } } Android

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internal actual open class ChatClient actual constructor(val url: String) : WebSocketListener() { actual open fun start() { /* */ } actual open fun send(message: Message) { /* */ } actual open fun receive(receiveBlock: (Message) -> Unit) { /* */ } actual open fun onFailure(throwableBlock: (Throwable) -> Unit) { /* */ } override fun onMessage(webSocket: WebSocket, text: String) { /* */ } override fun onFailure(webSocket: WebSocket, t: Throwable, response: Response?) { /* */ } } Android

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internal actual open class ChatClient actual constructor(val url: String) { actual open fun start() { /* */ } actual open fun send(message: Message) { /* */ } actual open fun receive(receiveBlock: (Message) -> Unit) { /* */ } actual open fun onFailure(throwableBlock: (Throwable) -> Unit) { /* */ } } JS

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internal actual open class ChatClient actual constructor(val url: String) { actual open fun start() { /* */ } actual open fun send(message: Message) { /* */ } actual open fun receive(receiveBlock: (Message) -> Unit) { /* */ } actual open fun onFailure(throwableBlock: (Throwable) -> Unit) { /* */ } } JS

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internal actual open class ChatClient actual constructor(val url: String) { actual open fun start() { /* */ } actual open fun send(message: Message) { /* */ } actual open fun receive(receiveBlock: (Message) -> Unit) { /* */ } actual open fun onFailure(throwableBlock: (Throwable) -> Unit) { /* */ } } JS

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internal actual open class ChatClient actual constructor(val url: String) { actual open fun start() { /* */ } actual open fun send(message: Message) { /* */ } actual open fun receive(receiveBlock: (Message) -> Unit) { /* */ } actual open fun onFailure(throwableBlock: (Throwable) -> Unit) { /* */ } inner class WebSocketDelegate : NSObject(), SRWebSocketDelegateProtocol { override fun webSocket(webSocket: SRWebSocket?, didReceiveMessage: Any?) { /* */ } } } iOS

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internal actual open class ChatClient actual constructor(val url: String) { actual open fun start() { /* */ } actual open fun send(message: Message) { /* */ } actual open fun receive(receiveBlock: (Message) -> Unit) { /* */ } actual open fun onFailure(throwableBlock: (Throwable) -> Unit) { /* */ } inner class WebSocketDelegate : NSObject(), SRWebSocketDelegateProtocol { override fun webSocket(webSocket: SRWebSocket?, didReceiveMessage: Any?) { /* */ } } } iOS

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internal actual open class ChatClient actual constructor(val url: String) { actual open fun start() { /* */ } actual open fun send(message: Message) { /* */ } actual open fun receive(receiveBlock: (Message) -> Unit) { /* */ } actual open fun onFailure(throwableBlock: (Throwable) -> Unit) { /* */ } inner class WebSocketDelegate : NSObject(), SRWebSocketDelegateProtocol { override fun webSocket(webSocket: SRWebSocket?, didReceiveMessage: Any?) { /* */ } } } iOS

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Demo

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Challenges

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Experimental

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Threads

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Debug

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Compile Time

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Chat MVP delivered

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felipehjcosta [email protected]