Kotlin Multiplatform (KMP): The Future of Cross Platform Development

Introduction

Kotlin Multiplatform (KMP) is a powerful technology from JetBrains that enables code sharing across multiple platforms including Android, iOS, desktop, web, and backend. It solves one of the biggest pain points in cross-platform development: maintaining multiple codebases.

In this Story, we’ll walk through:

•  
• - What is Kotlin Multiplatform
• - How it works under the hood
• - Recommended architecture
• - Tools and libraries
• - Real-world use cases
• - Best practices
• - Full project structure overview

What is Kotlin Multiplatform?

Kotlin Multiplatform is not a framework but a code-sharing strategy. You write common code in Kotlin that is compiled to native code for each platform, and platform-specific code (like UI) can still be written in native languages.

Key Benefits

• - Single source of truth for business logic
• - Native performance
• - Faster time to market
• - Better developer experience with JetBrains tooling

How Does KMP Work?

KMP uses expect/actual declarations to provide platform-specific implementations. The shared code is compiled using the Kotlin compiler to:

• - JVM bytecode (Android)
• - JavaScript (Web)
• - Native binaries (iOS/macOS/Linux/Windows)

// Shared code
expect fun getPlatformName(): String

// Android
actual fun getPlatformName(): String = "Android"

// iOS
actual fun getPlatformName(): String = "iOS"

Recommended Architecture

Clean Architecture Layers

- Presentation Layer: Jetpack Compose Multiplatform (Compose UI)

- Domain Layer: Use cases, business rules

- Data Layer: Repositories, DataSources

- Network/Storage Layer: Ktor, SQLDelight, Realm

MVVM Pattern (Recommended)

• - ViewModel handles logic and state
• - UI observes state
• - Shared ViewModel can be reused across platforms

UI <--> ViewModel <--> UseCase <--> Repository <--> API/DB

Tools and Libraries

Real-World Use Cases

• - Netflix uses KMP for business logic sharing
• - VMware shares authentication modules using KMP
• - Philips builds KMP-based health solutions

Best Practices

• - Don’t over-share UI code. Share business logic instead
• - Use interfaces and dependency injection for testability
• - Write platform-specific code for platform-specific UX
• - Monitor memory usage on iOS (due to Kotlin/Native GC)

Full Project Structure

my-kmp-project/
├── androidApp/            # Android app
├── iosApp/                # iOS app (SwiftUI or UIKit)
├── shared/                # Shared KMP module
│   ├── commonMain/        # Common Kotlin code
│   ├── androidMain/       # Android-specific code
│   ├── iosMain/           # iOS-specific code
│   └── commonTest/        # Common tests

Final Thoughts

Kotlin Multiplatform is maturing rapidly and is now production-ready for many use cases. It strikes the right balance between code reuse and native UX. With Compose Multiplatform and official iOS support improving, the future of cross-platform apps lies in KMP.

Start simple, think clean, and architect for reuse.