JetBrains announced a new default project structure for KMP. Two shared modules — sharedLogic and sharedUI — plus separate application modules for each platform. Clean. Simple. Obvious.
It's also a trap.
The problem with sharedLogic and sharedUI
A fresh sharedLogic module looks innocent. Business logic, models, repositories. sharedUI holds your Composables. What could go wrong?
Three months later sharedLogic contains:
- Business logic
- Network clients
- Database models
- Constants
- Utility functions
- Something called
CommonUtils.kt that nobody understands but everyone is afraid to delete
sharedLogic has no internal boundaries. Everything depends on everything. You can import a database model from a use case and nobody stops you. The compiler certainly won't.
JetBrains tells you where to start. They don't tell you what happens when two modules become 50,000 lines.
What actually happens
You try to split sharedLogic into more modules. But there are no rules. So you end up with:
:sharedLogic:core — the new dumping ground:sharedLogic:data — which also contains business logic somehow
The dependencies look like spaghetti. Changing one module breaks three others. You didn't enforce boundaries early, and now every refactoring is a gamble.
FLIP: the next step after sharedLogic
FLIP is an architectural pattern that gives you rules for splitting sharedLogic before it becomes a problem.
Five layers. One direction. Zero horizontal dependencies.
| Layer | Purpose | Depends on |
|---|
| :common:core | Foundation | Nothing |
| :service | Domain logic without UI | :common:core |
| :feature | UI features | :service, :common:core |
| :entrypoint | DI assembly + slot composition | Everything above |
| :platform | Platform entry point | :entrypoint |
The rule is simple: features don't know about other features. services don't know about other services. Dependencies only flow down.
Your IDE enforces this. You literally cannot import a feature from another feature — Gradle won't compile. The structure prevents the dumpster fire before it starts.
Start with JetBrains. Grow with FLIP.
The new KMP structure is a great starting point. Two modules is better than one. But when sharedLogic starts feeling like a junk drawer, you know what to do.
FLIP is at github.com/numq/flip. Template included. Konsist tests included. Rules over conventions.