Kmp Architecture Best Practices

KMP Architecture Rules

Activate only if commonMain exists.

Hard Rules

• No android.* imports in commonMain — use expect/actual for platform APIs.
• No java.time in commonMain — use kotlinx-datetime.
• No Android ViewModel in shared code — use StateHolder pattern.
• No Dispatchers.Main hardcoded in commonMain — inject dispatchers.
• Use KSP for annotation processing — KAPT does not support multiplatform.
• No freeze() calls — the new Kotlin/Native memory model (default since 1.7.20) makes them unnecessary.
• Shared code must compile for all declared targets — never skip a target in CI.

Core Patterns

State Management

• commonMain: StateHolder class exposes StateFlow<UiState>.
• androidMain: ViewModel wraps StateHolder, bridges to Android lifecycle.
• iosMain: Swift class holds StateHolder, collects flows via CancellableContinuation or SKIE/KMP-NativeCoroutines.

Dependency Injection

• Use Koin Multiplatform or manual factory pattern in commonMain.
• Platform modules provide platform-specific implementations via actual declarations or Koin modules.

Source Set Hierarchy

• Use hierarchical source sets (appleMain, nativeMain, jvmMain) to share platform-adjacent code.
• commonMain → jvmMain → androidMain / desktopMain.
• commonMain → nativeMain → appleMain → iosMain / macosMain.

Kotlin 2.0+ Considerations

• K2 compiler is default since Kotlin 2.0 — ensure libraries are K2-compatible.
• Compose Compiler is now a Gradle plugin (org.jetbrains.kotlin.plugin.compose) — not a separate compiler artifact.

References

• references/project_structure.md
• references/common_libraries.md
• references/platform_apis.md
• references/testing_kmp.md
• references/dependency_injection.md

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