KMP_for_Swift.pdf - Speaker Deck

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KMP for Mobile Developers Enrique López Mañas

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Ego Slide • Google Developer Expert • 🇻🇳 🇩🇪 🇪🇸 • Kotlin Weekly publisher • @eenriquelopez • Mainly Android Kotlin, Backend Kotlin, iOS (mostly Swift)

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expect fun

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Motivation < Costs Sharing code within the company Feature teams > Quality One tech-stack

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Multiplatform development Platform Proprietary Hybrid HTML & JavaScript Frameworks Cross-platform Native

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Kotlin Modern language

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Kotlin

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Kotlin

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Kotlin Interop

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Kotlin Community support

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Kotlin Top-notch tooling

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Kotlin Sharing is optional! No life or death commitment

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Kotlin/Anywhere Android Browser Server

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Kotlin/Native Common JVM Native iOS framework Your iOS dev Your Android Dev JS

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Kotlin/Native or KMP or KMM

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KMP Sharing architecture (not UI) Shared UI is a mess

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Kotlin/Native - Uses LLVM (5.0) - Provides runtime guarantees - Exceptions, memory management - Interop with C/Objective-C (Swift) - Platform libraries (POSIX, Apple Frameworks, Win32, DOM, etc)

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Kotlin/Native Kotlin Compiler LLVM Kotlin Source Code (.kt) Platform Binary IR

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The compiler -Shares Front-end with Kotlin/JVM and Kotlin/JS - Written in Java and Kotlin - Produces bitcode via LLVM API

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Memory Management - ARC with Cycle Collector - When working pure Kotlin,don’t worry about memory management - Weak references supported - Memory sharing model - Different threads have disjoint object graphs - Object subgraphs can be transferred between threads - Immutable objects can be shared

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Interoperatibility - Interoperatibility with C, Objective-C and Swift - Kotlin can call C/Objective-C and vice-versa - Kotlin can extend Objective-C classes and vice-versa - Memory management aware of Objective-C runtime

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Mapping - Numbers are kept - Strings converted - Kotlin declarations wrapping C entities (functions, struct, unions, etc.) are auto- generated - Objective-C OO concepts (classes, protocols, blocks) are represented as matching Kotlin entities (classes, interfaces, lambdas) - For Objective-C, Kotlin code can be compiled to a framework

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Mapping

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Kotlin Library - Hold collection of code for reusability and sharing - Own format: ‘klib’ extension, which holds metadata and bitcode - Tool for creating and storing libraries in repositories

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expect/actual

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expect/actual

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expect/actual

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expect/actual JVM

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expect/actual JS

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expect/actual

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expect/actual // Common expect fun randomUUID(): String // Android import java.util.* actual fun randomUUID() = UUID.randomUUID().toString()     // iOS import platform.Foundation.NSUUID actual fun randomUUID(): String = NSUUID().UUIDString()

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Square JetBrains TouchLab Others

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Community projects - Sqldelight - SQLiter - Multiplatform settings - Stately - OKIO2

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Existing native libraries - Ktor - Kotlinx.Coroutines - Kotlinx.io - Atomic-fu

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ktor - Web application framework   -Domain Specific Language (DSL) syntax for web apps-Kotlin coroutines for asynchronous programming   -Can be used on web, iOS and Android   -Provides a unified toolset with a single language, like Node.js but with type-safety and build-concurrency.  

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ktor

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ktor

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ktor

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ktor

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ktor

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ktor

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Coroutines JetBrains async library

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Coroutines

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Coroutines

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kotlinx.io Library for I/O primitives building and manipulations Experimental

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kotlinx.io

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kotlinx.io

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kotlinx.io

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AtomicFU Library for atomic operations in Kotlin

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Considerations in state No threading primitives: synchronized, volatile Use atomic-fu instead

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AtomicFU

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AtomicFU

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SQLiter •Evoution of knarch.db   •From Touchlab   •SQLiter -> SQL Driver    

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SQLiter . DatabaseInstance.

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SQLiter

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Multiplatform settings SharedPreferences on Android and NSUserDefaults on iOS.

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Multiplatform settings

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kotlinx.serialization

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Considerations in state An object belongs to one thread

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Considerations in state Frozen objects can be shared by threads

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Concurrency - frozen objects Everything you have written until now is not frozen

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Considerations in state Runtime safety: KMP can verify safe mutability

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Considerations in state - Generics

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Considerations in state - Generics

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Considerations in state - Generics

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Considerations in state

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Considerations in state Exhaustive enums

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Considerations in state Default arguments

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Considerations in state // Kotlin enum class LogLevel { ERROR, WARNING, INFO, DEBUG } class Logger { companion object default { fun log(level: LogLevel = LogLevel.ERROR, message: String, completion: (Boolean) -> Unit) { } } }

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Considerations in state // Swift Logger.default.log(.error, "An error ocurred") { // Closure }

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Considerations in state

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Considerations in state iOS devs?

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Architecture https://proandroiddev.com/kotlin-multiplatform-mvvm-clean-architecture-f20b99f90b95 Javier Arroyo

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KMM Survey Q1-Q2 2021

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KMM Survey Q1-Q2 2021

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KMM Survey Q1-Q2 2021

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Case studies? https://kotlinlang.org/lp/mobile/case-studies/

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The future Hard to make predictions, easier to bet safe “I don’t know what will happen in 10 years, but there will be people asking in SO about regular expressions, and there will be another JS framework ”

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The future @lehtimaeki

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Recommendations - Use it with caution - Shared components - Keep versioning in mind - Do not compromise 100% of a project

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Further resources Kotlin Slack (kotlinlang.slack.com) Touchlab resources (https://github.com/touchlab) Kotlin Weekly (http://kotlinweekly.net) K/N documentation (https://kotlinlang.org/docs/ native-overview.html)

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Thanks!