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kmp-boundaries

Designs Kotlin Multiplatform boundaries between shared commonMain code and platform-specific implementations.

Updated Jul 1, 2026
Search Tags:#architecture#kmp#compose multiplatform#kotlin multiplatform#source sets#expect actual#swift interop
One-click install
npx skills add https://github.com/w0lzard/Wolzard-s-Marketplace --skill kmp-boundaries-w0lzard
Or copy as Structured Prompt for Agent▼
Please help me install this Agent Skill.
Skill: kmp-boundaries
Source: https://github.com/w0lzard/Wolzard-s-Marketplace/tree/main/plugins/personal-skills/skills/kmp-boundaries
Command: npx skills add https://github.com/w0lzard/Wolzard-s-Marketplace --skill kmp-boundaries-w0lzard

SYSTEM DOCUMENTATION & REQUIREMENTS

💡 This Skill includes references (resource) components.

What problem does it solve? Kotlin Multiplatform projects struggle with deciding how shared code should reach platform APIs — choosing between expect/actual, common interfaces with DI, or separate platform screens — and often end up with monolithic Platform objects, leaky abstractions, and untestable actuals. ## Core Features & Use Cases - Boundary Shape Selection: Decision tables for choosing expect/actual functions, common interfaces with platform bindings, expect leaf composables, or fully separate platform screens based on testability, DI, and lifecycle needs. - Capability Granularity Rules: Guidance for splitting platform services (clipboard, share, haptics, biometrics, notifications) into small fakeable interfaces instead of one giant Platform object, with Activity-ownership rules for Android UI actions. - Source-Set Hierarchy & AGP 9 Constraints: Covers skikoMain/appleMain intermediate source sets, the new com.android.kotlin.multiplatform.library plugin limits (no BuildConfig, no variants, no NDK), and Compose Multiplatform interop patterns. - Use Case: When common code needs to trigger the system share sheet, this Skill guides you to define a semantic ShareSheet interface in commonMain, bind an Activity-scoped AndroidShareSheet via Hilt, and keep business rules in a common ShareUseCase testable with a fake. ## Quick Start Ask the AI to design a Kotlin Multiplatform boundary for accessing the device clipboard and haptics from shared commonMain code.

Frequently Asked Questions about kmp-boundaries

High-intent search queries and answers about installing and using this skill.

FAQPage Schema
How do I choose between expect/actual and a common interface in Kotlin Multiplatform?▼

Use expect/actual for compile-time specialization of a single pure function, value, or leaf composable. Switch to a common interface with platform bindings when you need test fakes, injected dependencies, runtime selection, or lifecycle ownership such as an Activity.

When should I use expect class vs interface in KMP?▼

Prefer a common interface bound per platform in almost all cases, since expect class is hard to fake, hard to extend, and requires a platform runtime in tests. Reserve expect declarations for pure functions, constants, and typealiases.

Does AGP 9 support BuildConfig in Kotlin Multiplatform libraries?▼

No. The com.android.kotlin.multiplatform.library plugin in AGP 9 removes BuildConfig, build variants, and NDK support. Use BuildKonfig or inject an AppConfiguration interface per platform for compile-time constants.

Why is using applicationContext with FLAG_ACTIVITY_NEW_TASK a mistake in KMP?▼

Launching UI from a generic Context hides the fact that the operation requires a foreground Activity and breaks lifecycle correctness. The platform binding should be Activity-owned, constructed in an activity-scoped DI module such as Hilt's ActivityComponent.

How do I expose Kotlin Flow and suspend functions to Swift in KMP?▼

Use SKIE, which automatically bridges suspend functions to Swift async and Flow to AsyncSequence, and converts sealed classes to exhaustive Swift enums via onEnum(of:). KMP-NativeCoroutines is the annotation-based alternative for existing projects.

When should I create an intermediate source set like skikoMain?▼

Create an intermediate source set only when at least two platforms can genuinely share an actual implementation, such as desktop, iOS, and web sharing Skia-based rendering. Do not add hierarchy speculatively for a single platform.

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