Decoupling Game Logic: Building Reusable Systems with FCIS

Game developers often struggle with code tightly coupled to their engine, making it impossible to reuse logic across projects. This article presents FCIS (Functional Core, Imperative Shell)—an architectural pattern that separates pure, side-effect-free game logic from engine-specific code. By adopting this approach, developers can build portable game systems and maintain reusable libraries that work across different projects and engines.