Kotlin Multiplatform Libraries

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Kotlin Multiplatform Libraries Kevin Galligan

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Touchlab

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Libraries are crucial

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-Kevin Galligan “Shared UI is a history of pain and failure. Shared logic is the history of computers.”

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“The easiest overhead to predict with C++ is the need to build frameworks and libraries” -Eyal Guthmann (Dropbox blog post author)

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KMP is no exception in fact, more so

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KMP is lean

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You don’t get • Concurrency • Locale • Date/Time • File I/O • Networking • (most of JRE)

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Big hill to climb however…

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Kotlin ecosystem is strong lot’s of stuff out there

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decade of android libraries

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Very engaged community you’re here, right?

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Why consider KMP?

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lots of interest

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lots of interest

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Growth in deployment much more in 2020

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Android ecosystem is crowded hard to get focus

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Great time to get in much bigger impact

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What is Kotlin Multiplatform?

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Common JVM JS Native

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Common JVM JS Native iOS Mac Linux Windows Android/NDK Wasm Others… Java-6 Java-8 Android Browser Node

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Common JVM JS Native iOS Mac Linux Windows Android/NDK Wasm Others… Java-6 Java-8 Android Browser Node

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Common JVM JS Native iOS (arm 64) Java-6 Java-8 Android Browser Node

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Common Native iOS (arm 64) Xcode framework

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Common Native iOS (arm 64) klib Xcode framework

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Common JVM Android

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Common JVM Android App

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Common JVM Android App AAR

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Library Patterns

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Just Code not super complicated

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SDK Wrapper Firestore SDK

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Not super clear cut most libraries are a mix

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Published SDK many from one

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Platform Specific Logic

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expect/actual

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//In common code expect val isMainThread: Boolean

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//In common code expect val isMainThread: Boolean //In Android/JVM actual val isMainThread: Boolean get() = Looper.getMainLooper() === Looper.myLooper()

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//In common code expect val isMainThread: Boolean //In Android/JVM actual val isMainThread: Boolean get() = Looper.getMainLooper() === Looper.myLooper() //In iOS/native code actual val isMainThread: Boolean get() = NSThread.isMainThread()

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//Value expect val isMainThread: Boolean

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//Value expect val isMainThread: Boolean //Function expect fun myFun():String

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//Value expect val isMainThread: Boolean //Function expect fun myFun():String //Class expect class MyClass { fun heyo(): String }

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//Value expect val isMainThread: Boolean //Function expect fun myFun():String //Class expect class MyClass { fun heyo(): String } //Object expect object MyObject { fun heyo(): String }

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//Value expect val isMainThread: Boolean //Function expect fun myFun():String //Class expect class MyClass { fun heyo(): String } //Object expect object MyObject { fun heyo(): String } //Annotation @Target(AnnotationTarget.FUNCTION, AnnotationTarget.CONSTRUCTOR) @Retention(AnnotationRetention.SOURCE) expect annotation class Throws(vararg val exceptionClasses: KClass)

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actual typealias with great power…

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/** * Multiplatform AtomicInt implementation */ expect class AtomicInt(initialValue: Int) { fun get(): Int fun set(newValue: Int) fun incrementAndGet(): Int fun decrementAndGet(): Int fun addAndGet(delta: Int): Int fun compareAndSet(expected: Int, new: Int): Boolean }

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JVM Side?

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import java.util.concurrent.atomic.AtomicInteger actual typealias AtomicInt = AtomicInteger

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Actual needs to match because obviously it does

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import kotlin.native.concurrent.AtomicInt actual class AtomicInt actual constructor(initialValue:Int){ private val atom = AtomicInt(initialValue) actual fun get(): Int = atom.value actual fun set(newValue: Int) { atom.value = newValue } actual fun incrementAndGet(): Int = atom.addAndGet(1) actual fun decrementAndGet(): Int = atom.addAndGet(-1) actual fun addAndGet(delta: Int): Int = atom.addAndGet(delta) actual fun compareAndSet(expected: Int, new: Int): Boolean = atom.compareAndSet(expected, new) }

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Platform Affinity android iOS ?

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Platform Affinity android iOS android-y

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Platform Affinity android iOS iOS-ish

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Platform Affinity android iOS iOS-ish JS

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Parallel Delegates android iOS android-y

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(Maybe) Optimize for JVM (if) most of your users

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Stately has a fair bit of stuff

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Minimal JVM-side impact

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typealias can be brittle

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Prefer Interfaces for “service” objects

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public interface Settings { public fun clear() public fun remove(key: String) public fun hasKey(key: String): Boolean public fun putInt(key: String, value: Int) public fun getInt(key: String, defaultValue: Int = 0): Int public fun getIntOrNull(key: String): Int? public fun putLong(key: String, value: Long) public fun getLong(key: String, defaultValue: Long = 0): Long public fun getLongOrNull(key: String): Long? //Etc... } from https://github.com/russhwolf/multiplatform-settings

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expect fun platformSettings():Settings

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object ServiceRegistry { var sessionizeApi:SessionizeApi by ThreadLocalDelegate() var analyticsApi: AnalyticsApi by FrozenDelegate() var notificationsApi:NotificationsApi by FrozenDelegate() var dbDriver: SqlDriver by FrozenDelegate() var cd: CoroutineDispatcher by FrozenDelegate() var appSettings: Settings by FrozenDelegate() var concurrent: Concurrent by FrozenDelegate() var timeZone: String by FrozenDelegate() //Etc… from https://github.com/touchlab/DroidconKotlin/

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Just an Interface no expect/actual required

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class TestSettings:Settings { private val map = frozenHashMap() override fun clear() { map.clear() } override fun getBoolean(key: String, defaultValue: Boolean): Bo return if(map.containsKey(key)){ map[key] as Boolean }else{ defaultValue } } //Etc… from https://github.com/touchlab/DroidconKotlin/

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Minimize expect/actual Droidcon App: 9 functions, 2 classes

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https://go.touchlab.co/dcrw

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Firestore SDK wrapping multiple clients

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2 (or more) Similar Things but not the same

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Platform Affinity android iOS ?

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Empty Typealias wait, hear me out

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Platform Affinity

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Platform Agnostic

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Empty Typealias everything is extensions

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expect class QuerySnapshot expect val QuerySnapshot.documentChanges_:List expect fun QuerySnapshot.getDocumentChanges_(…):List expect val QuerySnapshot.documents_:List expect val QuerySnapshot.metadata: SnapshotMetadata expect val QuerySnapshot.query: Query expect val QuerySnapshot.empty: Boolean expect val QuerySnapshot.size: Int

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actual typealias QuerySnapshot = FIRQuerySnapshot actual val QuerySnapshot.documentChanges_: List get() = documentChanges as List actual val QuerySnapshot.documents_: List get() = documents as List actual fun QuerySnapshot.getDocumentChanges_(metadataChanges: Metadata documentChangesWithIncludeMetadataChanges(metadataChanges == Metad iOS

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expect open class DocumentSnapshot DocumentSnapshot actual typealias DocumentSnapshot = FIRDocumentSnapshot iOS common actual typealias DocumentSnapshot = com.google.firebase.firestore.DocumentSnapshot Android

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actual typealias QuerySnapshot = com.google.firebase.firestore.QuerySn actual val QuerySnapshot.documentChanges_: List get() = documentChanges actual val QuerySnapshot.documents_: List get() = documents actual fun QuerySnapshot.getDocumentChanges_(metadataChanges: Metadata getDocumentChanges(metadataChanges.toJvm()) Android

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Watch Return Types be careful of matching signatures

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expect fun FirebaseFirestore.disableNetwork_():TaskVoid

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expect fun FirebaseFirestore.disableNetwork_():TaskVoid actual fun FirebaseFirestore.disableNetwork_(): TaskVoid = TaskVoid(disableNetwork())

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expect fun FirebaseFirestore.disableNetwork_():TaskVoid actual fun FirebaseFirestore.disableNetwork_(): TaskVoid = TaskVoid(disableNetwork()) public Task disableNetwork() { this.ensureClientConfigured(); return this.client.disableNetwork(); }

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Again, Prefer Interfaces for service objects

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expect fun getFirebaseInstance():FirebaseFirestore expect class FirebaseFirestore expect fun FirebaseFirestore.batch(): WriteBatch expect fun FirebaseFirestore.collection(collectionPath:String):Collect expect fun FirebaseFirestore.collectionGroup(collectionId:String):Quer expect fun FirebaseFirestore.disableNetwork_():TaskVoid expect fun FirebaseFirestore.document(documentPath:String):DocumentRef expect fun FirebaseFirestore.enableNetwork_():TaskVoid expect var FirebaseFirestore.settings:FirebaseFirestoreSettings

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expect fun getFirebaseInstance():FirebaseFirestore interface FirebaseFirestore{ fun batch(): WriteBatch fun collection(collectionPath:String):CollectionReference fun collectionGroup(collectionId:String):Query fun disableNetwork():TaskVoid fun document(documentPath:String):DocumentReference fun enableNetwork():TaskVoid var FirebaseFirestore.settings:FirebaseFirestoreSettings }

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Minimize expect/actual? Firestore SDK: 100+ ‘expect’ instances

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Which to use? • Interfaces when reasonable • Singletons and service objects for sure • Easier to test • typealias when you need a bunch of things and don’t want a parallel delegate hierarchy • Data classes and type hierarchies get complicated with interfaces

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Inline Classes the other option

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inline class Name(val s: String) { val length: Int get() = s.length fun greet() { println("Hello, $s") } }

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inline class Name(val s: String) { val length: Int get() = s.length fun greet() { println("Hello, $s") } }

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Experimental had some trouble, but promising (1.3.70?)

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Function args! swift friendly

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fun initLambdas( staticFileLoader: (filePrefix: String, fileType: String) -> String?, clLogCallback: (s: String) -> Unit, softExceptionCallback: (e:Throwable, message:String) - >Unit)

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func loadAsset(filePrefix:String, fileType:String) -> String?{ do{ let bundleFile = Bundle.main.path(forResource: filePrefix, ofType: fileType) return try String(contentsOfFile: bundleFile!) } catch { return nil } }

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Hard(er) to test interfaces and functions are stubs

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Objc Platform Interop? sure, but meh

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configure([targets.iosX64, targets.iosArm64 ]) { compilations.main.source(sourceSets.iosMain) compilations.test.source(sourceSets.iosTest) compilations["main"].cinterops { firebasecore { packageName 'cocoapods.FirebaseCore' defFile = file("$projectDir/src/iosMain/c_interop/FirebaseCore.def") includeDirs ("$projectDir/../iosApp/Pods/FirebaseCore/Firebase/Core/Public") compilerOpts ("-F$projectDir/src/iosMain/c_interop/modules/FirebaseCore-$ {versions.firebaseCoreIos}") } firestore { packageName 'cocoapods.FirebaseFirestore' defFile = file("$projectDir/src/iosMain/c_interop/FirebaseFirestore.def") includeDirs ("$projectDir/../iosApp/Pods/FirebaseFirestore/Firestore/Source/Public", "$projectDir/../iosApp/Pods/FirebaseCore/Firebase/Core/Public") compilerOpts ("-F$projectDir/src/iosMain/c_interop/modules/FirebaseFirestore-$ {versions.firebaseFirestoreIos}") } } }

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@ExternalObjCClass open class FIRAppMeta : NSObjectMeta { val allApps: Map? @ObjCMethod("allApps", "@16@0:8") external get @ObjCMethod("configure", "v16@0:8") external open fun configure(): Unit @ObjCMethod("configureWithOptions:", "v24@0:8@16") external open fun configureWithOptions(options: FIROptions): Unit @ObjCMethod("configureWithName:options:", "v32@0:8@16@24") external open fun configureWithName(name: String, options: FIROptions): Unit @ObjCMethod("defaultApp", "@16@0:8") external open fun defaultApp(): FIRApp? @ObjCMethod("appNamed:", "@24@0:8@16") external open fun appNamed(name: String): FIRApp? @ObjCMethod("allApps", "@16@0:8")

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Interop can be tricky with library brittle config (imho)

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Or…

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interface AnalyticsApi { fun logEvent(name: String, params: Map) }

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class FirebaseAnalyticsApi: AnalyticsApi{ func logEvent(name: String, params: [String : Any]) { Analytics.logEvent(name, parameters: params) } }

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Firestore SDK needs objc maybe your library doesn’t

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Firestore SDK https://github.com/touchlab/FirestoreKMP

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Soft Launch: Crash Reporting

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Symbolicated Kotlin Crashes Crashlytics & Bugsnag

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The Problem different platforms

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Kotlin has Exceptions iOS mostly just crashes

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konan::abort()

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Throwable stack

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iOS Needs Interop Crashlytics & Bugsnag libraries

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class CrashNSException: NSException { init(callStack:[NSNumber], exceptionType: String, message: String) { super.init(name: NSExceptionName(rawValue: exceptionType), reason: message, userInfo: nil) self._callStackReturnAddresses = callStack } required init?(coder: NSCoder) { fatalError("init(coder:) has not been implemented") } private lazy var _callStackReturnAddresses: [NSNumber] = [] override var callStackReturnAddresses: [NSNumber] { get { return _callStackReturnAddresses } set { _callStackReturnAddresses = newValue } } } class BugsnagCrashHandler: CrashkiosCrashHandler { override func crashParts(addresses: [KotlinLong], exceptionType: String, message: String) { Bugsnag.notify(CrashNSException(callStack: addresses, exceptionType: exceptionType, message: message)) } }

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class CrashlyticsCrashHandler: CrashkiosCrashHandler { override func crashParts( addresses: [KotlinLong], exceptionType: String, message: String) { let clsStackTrace = addresses.map { CLSStackFrame(address: UInt(truncating: $0)) } Crashlytics.sharedInstance().recordCustomExceptionName( exceptionType, reason: message, frameArray: clsStackTrace ) } }

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CrashKiOS https://github.com/touchlab/CrashKiOS

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CrashKiOS https://github.com/touchlab/CrashKiOS

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Publishing/CI

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Publishing • Maven Central • Bintray (jcenter) • Jitpack does not work

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Maven Central • https://central.sonatype.org/pages/ossrh-guide.html • https://github.com/cashapp/sqldelight • https://github.com/touchlab/FirestoreKMP

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Bintray natanfudge.github.io/fudgedocs/publish-kotlin-mpp-lib.html

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CI • Travis by a lot of the Square stuff • We’ve had some luck with “App Center” • Moving to Azure Pipelines as it makes Windows easier

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Getting Started go.touchlab.co/kmplib

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take a break!

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General Thoughts

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Big Blockers stuff we’re waiting on

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Compiler Plugins no kapt

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Multithreaded Coroutines cascading issue

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What does that mean?

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go.touchlab.co/dcktsrc

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Institutional Libraries the usual stuff

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Institutional Libraries •Date/Time •Locale •Files •I/O

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date libraries

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date libraries

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date libraries

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date libraries

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date libraries

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What to work on? be a little careful

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Skip date/time libraries that’s covered

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Mocking no reflection or compiler plugins

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Mockk wants help

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What about Swift? no reflection, no surrender

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interface HeyStuff { fun myFun(): String val myVal: Int }

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interface HeyStuff { fun myFun(): String val myVal: Int } class MockStuff:HeyStuff{ }

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interface HeyStuff { fun myFun(): String val myVal: Int } class MockStuff:HeyStuff{ }

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File I/O probably OK

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Server Contract swagger, graphql, grpc

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Architecture big word

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Reactive Border LiveData analog? RxSwift?

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Logging waiting on timber

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UI? wait, I thought…

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Join the Slack let’s work together

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Avoid Library Bikeshedding!

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Touchlab Stuff

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Some Stuff • Kotlin Xcode Plugin • Xcode Sync (get you Kotlin in Xcode) • Stately • Sqliter (Sqlite Driver under Sqldelight on native)