codebase-design

Deep modules hide implementation complexity behind a small, clean interface seam. This design approach makes systems easier to understand, test, and change by consolidating scattered logic into high-leverage entry points.

Choosing seam placement involves comparing alternative interface designs to determine what should be internal versus external. You shape better module entry points by analyzing dependency control and testability across modules.

To deepen shallow modules safely, you move logic behind a simpler interface while preserving testability through dependency-driven testing guidance. This ensures adapters and seams maintain clean separation during restructuring.

You need adapters and seams when a feature is spread across many thin functions and callers. Consolidating this logic behind a deeper module interface helps coordinate testing strategy and control dependencies across your codebase.

You can compare alternative interface designs by applying a consistent vocabulary for modules, depth, leverage, and locality. This helps you evaluate different seam placements and choose the highest-leverage module structure for your system.