The Triumphs and Tribulations of Kotlin/Native In Practice - GOTO Copenhagen, Denmark - November 2019

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THE TRIUMPHS AND TRIBULATIONS OF KOTLIN/NATIVE IN PRACTICE GOTO COPENHAGEN | NOVEMBER 2019 ELLEN SHAPIRO | @DESIGNATEDNERD | APOLLOGRAPHQL.COM

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THE VIRTUAL MACHINE

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SHAMELESS PLUG! HTTPS://STORE.RAYWENDERLICH.COM PRODUCTS/KOTLIN-APPRENTICE

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PACKAGE THIEF VS. GLITTER BOMB TRAP HTTPS://WWW.YOUTUBE.COM/WATCH?V=XOXHDK-HWUO

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PACKAGE THIEF VS. GLITTER BOMB TRAP HTTPS://WWW.YOUTUBE.COM/WATCH?V=XOXHDK-HWUO

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! "

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WITH WHAT SYSTEMS SHALL I BUILD IT?

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Raspberry pi

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Raspberry pi Server

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Raspberry pi Server iOS app

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Raspberry pi Server iOS app Android App

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Works with Kotlin? Raspberry pi Server iOS app Android App

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Works With Kotlin? Raspberry pi ✅ Server ✅ iOS app ✅ Android App ✅

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HTTP://BAKKENBAECK.NO

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HTTPS://GITHUB.COM/BAKKENBAECK/ PORCH PIRATE PROTECTOR

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NATIVE VS. MULTI-PLATFORM

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apply plugin: 'kotlin-multiplatform'

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apply plugin: 'kotlin-native-platform' apply plugin: 'kotlin-multiplatform'

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// For Native ONLY projects apply plugin: 'kotlin-native-platform' apply plugin: 'kotlin-multiplatform'

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// For Native ONLY projects apply plugin: 'kotlin-native-platform' // For projects targeting multiple platforms, // for example JVM + Native + JS apply plugin: 'kotlin-multiplatform'

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PROTIP: USE GRADLE 5.4.1* enableFeaturePreview('GRADLE_METADATA')

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PROTIP: USE GRADLE 5.4.1* enableFeaturePreview('GRADLE_METADATA') *as of November 18th, 2019

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By Jorje Lascar, https://www.flickr.com/photos/jlascar/4503951595

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FUNCTIONS WITH PER-PLATFORM IMPLEMENTATIONS expect fun

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commonMain

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commonMain

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iosMain

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androidMain

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commonMain

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CALLING CODE FROM BOTH APPS!

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ANDROID: EASY MODE build.gradle SomeFragment.kt

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IOS: MODE

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! OBJECTIVE-C

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IOS/OBJC GOTCHAS

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SWIFT Array != KOTLIN Array

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SWIFT Array == KOTLIN List

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SWIFT enum != KOTLIN enum class IN OBJC

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KOTLIN enum class DayOfWeek { Monday, Tuesday, Wednesday, Thursday, Friday, Saturday, Sunday; }

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KOTLIN fun printForDay(day: DayOfWeek) { when (day) { DayOfWeek.Monday -> println("You can fall apart") DayOfWeek.Tuesday, DayOfWeek.Wednesday -> println("Break my heart") DayOfWeek.Thursday -> println("Doesn't even start") DayOfWeek.Friday -> println("I'm in love") DayOfWeek.Saturday -> println("Wait") DayOfWeek.Sunday -> println("Always comes too late") } }

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SWIFT (THEORETICALLY) func printForDay(day: DayOfWeek) { switch day { case .monday: print("You can fall apart") case .tuesday, .wednesday: print("Break my heart") case .thursday: print("Doesn't even start") case .friday: print("I'm in love") case .saturday: print("Wait") case .sunday: print("Always comes too late") } }

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SWIFT (ACTUALLY) func printForDay(_ day: DayOfWeek) { switch day { case .monday: print("You can fall apart") case .tuesday, .wednesday: print("Break my heart") case .thursday: print("Doesn't even start") case .friday: print("I'm in love") case .saturday: print("Wait") case .sunday: print("Always comes too late") default: fatalError("Not a day") }

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DECIDING WHAT TO CENTRALIZE

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WHAT DO I REALLY HATE BUILDING TWICE?

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TALKING TO THE SERVER

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JSON FROM NETWORK IN MODELS ⬅ JSON OUT TO NETWORK

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IosClientEngine.kt https://github.com/ktorio/ktor/blob/master/ ktor-client/ktor-client-ios/darwin/src/io/ ktor/client/engine/ios/IosClientEngine.kt

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HttpClientJvmEngine.kt https://github.com/ktorio/ktor/blob/master/ ktor-client/ktor-client-core/jvm/src/io/ ktor/client/engine/HttpClientJvmEngine.kt

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androidMain import kotlinx.coroutines.CoroutineDispatcher import kotlinx.coroutines.Dispatchers internal actual val ApplicationDispatcher: CoroutineDispatcher = Dispatchers.Main

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iosMain import kotlinx.coroutines.CoroutineDispatcher import kotlinx.coroutines.Dispatchers import platform.darwin.dispatch_async import platform.darwin.dispatch_get_main_queue import kotlin.coroutines.Runnable internal actual val ApplicationDispatcher: CoroutineDispatcher = NsQueueDispatcher() internal class NsQueueDispatcher: CoroutineDispatcher() { override fun dispatch(context: CoroutineContext, block: Runnable) { val queue = dispatch_get_main_queue() dispatch_async(queue) { block.run() } } }

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iosMain import kotlinx.coroutines.CoroutineDispatcher import kotlinx.coroutines.Dispatchers import platform.darwin.dispatch_async import platform.darwin.dispatch_get_main_queue import kotlin.coroutines.Runnable internal actual val ApplicationDispatcher: CoroutineDispatcher = NsQueueDispatcher() internal class NSQueueDispatcher: CoroutineDispatcher() { override fun dispatch(context: CoroutineContext, block: Runnable) { val queue = dispatch_get_main_queue() dispatch_async(queue) { block.run() } } }

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! FREEZING

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MUTATING VARIABLES RETURNING A NEW OBJECT

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AVOID object FROM IOS

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USE INTERFACES TO MUTATE THINGS IN IOS INSTEAD OF K/N

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commonMain interface SecureStorage { fun storeTokenString(token: String) fun clearTokenString() fun fetchTokenString(): String? }

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iOS App @objc class Keychain: NSObject, SecureStorage { static let shared = Keychain() private override init() { super.init() } //TODO: Actually use keychain private var token: String? func storeTokenString(token: String) { self.token = token } func clearTokenString() { self.token = nil } func fetchTokenString() -> String? { return self.token } }

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commonMain object TokenManager { fun currentToken(storage: SecureStorage): UserToken? { storage.fetchTokenString()?.let { return UserToken(it) } ?: return null } fun storeToken(token: UserToken, storage: SecureStorage) { storage.storeTokenString(token.token) } fun clearToken(storage: SecureStorage) { storage.clearTokenString() } }

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KotlinX Serialization

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commonMain data class UserCredentials( val username: String, val password: String )

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commonMain apply plugin: 'kotlinx-serialization' @Serializable data class UserCredentials( val username: String, val password: String )

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commonMain val creds = UserCredentials("lol@ha.no", "guessme") val string = Json.stringify(UserCredentials.serializer(), creds) // String is '{"username":"lol@ha.no","password":"guessme"}' val updatedCreds = Json.parse(UserCredentials.serializer(), string) // updatedCreds.username is "lol@ha.no" // updatedCreds.password is "guessme"

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FROM CLIENT TO SERVER AND BACK!

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LOGIC

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MVC!

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MVVM!

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MVA!*

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MVA!* * - ANYTHING OTHER THAN A MODEL OR A VIEW FOR THE LOVE OF GOD

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MVP!

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HTTPS://GITHUB.COM/JETBRAINS/ KOTLINCONF-APP

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MODEL: VIEW: PRESENTER:

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MODEL: data class VIEW: PRESENTER:

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MODEL: data class VIEW: interface PRESENTER:

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MODEL: data class VIEW: interface PRESENTER: class

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VIEW: interface

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IOS VIEW: ANDROID VIEW: TESTING VIEW:

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IOS VIEW: UIViewController ANDROID VIEW: TESTING VIEW:

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IOS VIEW: UIViewController ANDROID VIEW: Fragment* TESTING VIEW:

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IOS VIEW: UIViewController ANDROID VIEW: Fragment* TESTING VIEW: *May not apply if your name is jake wharton

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IOS VIEW: UIViewController ANDROID VIEW: Fragment* TESTING VIEW: ¯\_(ϑ)_/¯ *May not apply if your name is jake wharton

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commonMain interface LoginView: IndefiniteLoadingIndicating { /// The text the user has input as their email address. var email: String? /// The text the user has input as their password. var password: String? fun emailErrorUpdated(toString: String?) fun passwordErrorUpdated(toString: String?) fun apiErrorUpdated(toString: String?) fun setSubmitButtonEnabled(enabled: Boolean) /// Called when login completes successfully. fun loginSucceeded() }

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commonMain class LoginPresenter( val view: LoginView, storage: SecureStorage ): BaseCoroutinePresenter(storage) { // rest of presenter class }

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suspend fun loginAsync(): Boolean { if (!isCurrentInputValid()) { return false } // If input is valid, these will not be null. val creds = UserCredentials(view.email!!, view.password!!) view.startLoadingIndicator() view.setSubmitButtonEnabled(false) apiError = null var success = false try { val token = api.login(creds) secureStorage.storeTokenString(token.token) view.loginSucceeded() success = true } catch (exception: Exception) { apiError = exception.message } view.stopLoadingIndicator() view.setSubmitButtonEnabled(true) return success } fun login() { launch { loginAsync() } }

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Android App

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Android App

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iOS App class LoginViewController: UIViewController { @IBOutlet private var emailTextInput: TextInputContainer! @IBOutlet private var passwordTextInput: TextInputContainer! @IBOutlet private var loginButton: UIButton! @IBOutlet private var apiErrorLabel: UILabel! @IBOutlet private var activityIndicator: UIActivityIndicatorView! private lazy var presenter = LoginPresenter(view: self, storage: Keychain.shared) @IBAction private func login() { self.presenter.login() } }

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extension LoginViewController: LoginView { func setSubmitButtonEnabled(enabled: Bool) { self.loginButton.isEnabled = enabled } func emailErrorUpdated(toString: String?) { self.emailTextInput.errorText = toString } func passwordErrorUpdated(toString: String?) { self.passwordTextInput.errorText = toString } func apiErrorUpdated(toString: String?) { self.apiErrorLabel.text = toString self.apiErrorLabel.isHidden = (toString == nil) } func loginSucceeded() { self.perform(segue: LoginSegue.loginSucceeded) } var email: String? { get { return self.emailTextInput.text } set(email) { self.emailTextInput.text = email } } var password: String? { get { return self.passwordTextInput.text } set(password) { self.passwordTextInput.text = password } } }

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TESTING YOUR COMMON CODE

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commonTest WORKS IF COROUTINES AREN'T INVOLVED!

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class TestLoginView: LoginView { override var email: String? = null override var password: String? = null var submitEnabled = true var submitWasDisabled = false override fun setSubmitButtonEnabled(enabled: Boolean) { submitEnabled = enabled if (!submitEnabled) { submitWasDisabled = true } } var emailError: String? = null override fun emailErrorUpdated(toString: String?) { emailError = toString } var passwordError: String? = null override fun passwordErrorUpdated(toString: String?) { passwordError = toString } var apiError: String? = null override fun apiErrorUpdated(toString: String?) { apiError = toString } var loginHasSucceeded = false override fun loginSucceeded() { loginHasSucceeded = true } }

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@Test fun validationSetsProperErrorsThenClearsThemAfterChangesMade() { val view = TestLoginView() val presenter = LoginPresenter(view, MockStorage()) view.password = "aaaaaa" presenter.validatePassword() assertFalse(presenter.isCurrentInputValid()) assertEquals(expectedEmailError.reason, view.emailError) assertNull(view.passwordError) view.email = "not@real.biz" presenter.validateEmail() assertTrue(presenter.isCurrentInputValid()) assertNull(view.emailError) assertNull(view.passwordError) }

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@Test fun attemptingToLoginWithoutChangesTriggersErrorsAndFails() = runBlocking { val view = TestLoginView() val presenter = LoginPresenter(view, MockStorage()) val expectedEmailError = ValidationResult.Invalid.WasNull("email") val expectedPasswordError = ValidationResult.Invalid.WasNull("password") val result = presenter.loginAsync() assertFalse(result) assertFalse(presenter.isCurrentInputValid()) // Actual attempt to login should never have been made since // the input was invalid assertFalse(view.submitWasDisabled) assertTrue(view.submitEnabled) assertNull(view.apiError) assertFalse(view.loginHasSucceeded) assertEquals(expectedEmailError.reason, view.emailError) assertEquals(expectedPasswordError.reason, view.passwordError) }

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runBlocking DOESN'T EXIST FOR ALL PLATFORMS

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JAVASCRIIIIIIIIPT!

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commonTest expect fun platformRunBlocking( block: suspend CoroutineScope.() -> T ) : T

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commonTest expect fun platformRunBlocking( block: suspend CoroutineScope.() -> T ) : T androidTest actual fun platformRunBlocking( block: suspend CoroutineScope.() -> T ): T { return runBlocking { block() } }

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commonTest expect fun platformRunBlocking( block: suspend CoroutineScope.() -> T ) : T androidTest + iosTest actual fun platformRunBlocking( block: suspend CoroutineScope.() -> T ): T { return runBlocking { block() } }

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@Test fun attemptingToLoginWithoutChangesTriggersErrorsAndFails() = platformRunBlocking { val view = TestLoginView() val presenter = LoginPresenter(view, MockStorage()) val expectedEmailError = ValidationResult.Invalid.WasNull("email") val expectedPasswordError = ValidationResult.Invalid.WasNull("password") val result = presenter.loginAsync() assertFalse(result) assertFalse(presenter.isCurrentInputValid()) // Actual attempt to login should never have been made since // the input was invalid assertFalse(view.submitWasDisabled) assertTrue(view.submitEnabled) assertNull(view.apiError) assertFalse(view.loginHasSucceeded) assertEquals(expectedEmailError.reason, view.emailError) assertEquals(expectedPasswordError.reason, view.passwordError) }

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androidTest WILL ALSO RUN YOUR commonTest TESTS!

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THINGS YOU'LL LEARN DOING SERVER DEVELOPMENT

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THINGS YOU'LL LEARN DOING SERVER DEVELOPMENT (WHICH HAVE LITTLE TO NOTHING TO DO WITH KOTLIN)

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THINGS YOU'LL LEARN DOING SERVER DEVELOPMENT > Docker

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THINGS YOU'LL LEARN DOING SERVER DEVELOPMENT > Docker > MySQL

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THINGS YOU'LL LEARN DOING SERVER DEVELOPMENT > Docker > MySQL > ORMs for MySQL

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THINGS YOU'LL LEARN DOING SERVER DEVELOPMENT > Docker > MySQL > ORMs for MySQL > One-way hashing for secure password storage

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THINGS YOU'LL LEARN DOING SERVER DEVELOPMENT > Docker > MySQL > ORMs for MySQL > One-way hashing for secure password storage > Your computer's exact melting point

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DO WE HAVE TIME FOR A TERRIBLE IDEA?

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AND NOW, A TERRIBLE IDEA: A LIVE DEMO!

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!"# NEXT STEPS

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!"# NEXT STEPS > Build the prototype box

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!"# NEXT STEPS > Build the prototype box > Get the Raspberry pi software working

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!"# NEXT STEPS > Build the prototype box > Get the Raspberry pi software working > Get the raspberry pi actually unlocking the box

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!"# NEXT STEPS > Build the prototype box > Get the Raspberry pi software working > Get the raspberry pi actually unlocking the box > Work on sharing design elements

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!"# NEXT STEPS > Build the prototype box > Get the Raspberry pi software working > Get the raspberry pi actually unlocking the box > Work on sharing design elements > Work on sharing localized strings

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OBLIGATORY SUMMARY SLIDE!

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OBLIGATORY SUMMARY SLIDE! > Kotlin/Native has made great strides in the last year

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OBLIGATORY SUMMARY SLIDE! > Kotlin/Native has made great strides in the last year > Share logic across iOS, android, and server without killing performance or sacrificing type/null safety

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OBLIGATORY SUMMARY SLIDE! > Kotlin/Native has made great strides in the last year > Share logic across iOS, android, and server without killing performance or sacrificing type/null safety > it's still beta, You will run into a lot of brick walls > Ktor and kotlinX serialization are a huge help, if you can get around what a mess coroutines can be on iOS

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LINKS! > Kotlin MPP for iOS + Android tutorial https://kotlinlang.org/docs/tutorials/ native/mpp-ios-android.html > KotlinConf App https://github.com/JetBrains/kotlinconf- app > KotlinLang Slack https://slack.kotlinlang.org

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LINKS! > My original Kotlin Native sandbox https://github.com/designatednerd/ KotlinNativeTest > Package Thief vs. Glitter Bomb Trap https://youtube.com/watch?v=xoxhDk-hwuo