---

name: Kotlin Multiplatform Architecture description: This skill should be used when implementing KMP features, creating shared modules, using expect/actual, setting up Koin/SQLDelight/Ktor, or implementing Compose Multiplatform. references:

• path: ../../references/common/clean-architecture.md
• path: ../../references/common/testing-strategy.md
• path: ../../references/languages/kotlin/coroutines.md
• path: ../../references/languages/kotlin/kmp-architecture.md external:
• id: kmp-docs
• id: compose-multiplatform
• id: kotlin-coroutines

---

Kotlin Multiplatform Architecture

Multiplatform development patterns based on Kotlin official documentation and Google's KMP recommendations.

Core Principles

1. Share Business Logic - Place Domain/Data Layer in shared module
2. Minimize Platform-Specific Code - Abstract with expect/actual
3. Single Source of Truth (SSOT) - Repository in shared module is the SSOT for data
4. Unidirectional Data Flow (UDF) - Events flow upstream, state flows downstream
5. Dependency Direction - Shared module does not depend on platform

CopyPlatform UI → Shared (Presentation → Domain → Data)

Layer Structure

Module Structure

Directory Structure

Copyshared/
├── commonMain/kotlin/      # Common to all platforms
│   ├── presentation/
│   ├── domain/
│   └── data/
├── androidMain/kotlin/     # Android-specific (expect/actual)
├── iosMain/kotlin/         # iOS-specific (expect/actual)
└── commonTest/kotlin/      # Common tests

expect/actual Pattern

Copy// commonMain
expect class PlatformContext

// androidMain
actual typealias PlatformContext = android.content.Context

// iosMain
actual class PlatformContext(val nsObject: platform.darwin.NSObject? = null)

Platform-Specific Implementation Example

Copy// commonMain
expect fun getPlatformName(): String

// androidMain
actual fun getPlatformName(): String = "Android ${android.os.Build.VERSION.SDK_INT}"

// iosMain
actual fun getPlatformName(): String = platform.UIKit.UIDevice.currentDevice.systemName()

Naming Conventions

Compose Multiplatform

Copy// commonMain - Shared UI
@Composable
fun UserListScreen(viewModel: UserListViewModel) {
    val state by viewModel.uiState.collectAsState()
    // Shared composable implementation
}

• Use @Composable functions in commonMain for shared UI
• Platform-specific styling via expect/actual for resources
• Navigation handled per-platform or via shared navigation library

DI with Koin

Copy// commonMain
val commonModule = module {
    single { UserRepository(get()) }
    factory { GetUsersUseCase(get()) }
}

// androidMain
val androidModule = module {
    single<DatabaseDriver> { AndroidSqliteDriver(Database.Schema, get(), "app.db") }
}

// iosMain
val iosModule = module {
    single<DatabaseDriver> { NativeSqliteDriver(Database.Schema, "app.db") }
}

Testing Strategy

Detailed References

• Clean Architecture Guide
• Testing Strategy Guide
• Kotlin Coroutines Guide
• KMP Architecture Details