Kotlin Multiplatform (KMP) Overview: Concepts, Advantages, Demo, and Ecosystem

Introduction

As Android developers we are familiar with Kotlin and its excellent interoperability with Java, which makes Kotlin the preferred language for Android. While Kotlin/JVM runs on any device that supports the JVM, true cross‑platform support requires Kotlin Multiplatform (KMP), which can target iOS, web, desktop, and server environments.

What is KMP

KMP enables reuse of Kotlin code across Android, iOS, web, desktop, and server while still allowing native code where needed. This dual capability—broad platform coverage and native interop—sets KMP apart from other cross‑platform solutions.

Advantages of KMP

Performance and Flexibility

Shared Kotlin code is compiled into platform‑specific binaries (class files on JVM, JS files on browsers, native executables on Windows, etc.), eliminating the need for a runtime engine or bridge and thus avoiding extra performance overhead.

Because the compiled output is native code, interaction with platform APIs incurs no additional cost, and the binary size is comparable to a regular library rather than a full framework.

Applicability to Any Project

KMP can be introduced incrementally—only for shared business logic such as encryption or data models—or used for an entire codebase, including UI via Compose for Desktop and iOS.

Simple Demo

Project Creation

KMP projects are initialized via the JetBrains website (https://kmp.jetbrains.com/#newProject) which offers three templates: Android‑iOS with UI, Android‑iOS logic‑only, and multi‑platform logic‑only.

Project Structure

The generated library module contains commonMain for shared code and platformMain directories for platform‑specific implementations. The build.gradle file defines supported targets and dependencies.

Code Writing

expect val firstElement: Int
expect val secondElement: Int

fun twoSum(first: Int, second: Int): Int {
    return first + second
}

fun main() {
    val result = twoSum(firstElement, secondElement)
    println(result)
}

The expect declarations are given concrete values in platform‑specific source sets, e.g., for macOS:

actual val firstElement: Int = 7
actual val secondElement: Int = 8

Running the macOS binary yields 15, demonstrating platform‑specific implementations.

Build Artifacts

By default, Kotlin/Native produces a .klib library. To obtain an executable or shared library, the Gradle script must declare binaries { executable { } } for macOS and sharedLib { } for Linux, then run the appropriate Gradle tasks (e.g., ./gradlew :library:runDebugExecutableMacosArm64 or ./gradlew :library:linkDebugSharedLinuxX64 ).

Implementation Principles

Kotlin’s compiler separates front‑end (syntax and semantic analysis) from back‑end (IR generation and machine‑code emission). The front‑end is platform‑agnostic, while each back‑end emits code for a specific target, enabling true cross‑platform compilation.

Compose Cross‑Platform Rendering

Compose relies on Skia for rendering. On Android, Skia is already part of the system; on other platforms JetBrains uses the skiko library to bundle Skia with the native binary.

KMP Ecosystem

JetBrains provides first‑party libraries such as Ktor, kotlinx‑serialization, kotlinx‑datetime, and coroutines. The community contributes projects like Square’s Okio and SQLDelight, and Google is gradually porting Android components to KMP.

Industry Cases

Several overseas companies use KMP, and Chinese firms like Meituan have shared detailed adoption experiences (see linked Bilibili videos).

Conclusion

The article gives a comprehensive overview of Kotlin Multiplatform, covering its definition, benefits, practical setup, compilation details, rendering pipeline, ecosystem, and real‑world usage, helping developers decide whether KMP fits their cross‑platform needs.