applying-composition-over-inheritancelisted

# Applying Composition Over Inheritance ## Quick start 1. Identify the variation axis: data variant, algorithm, cross-cutting behavior, or framework constraint. 2. Default to composition unless inheritance is explicitly justified by substitutability and stability. 3. If the variant set is closed and data-shaped, prefer an ADT/sealed type over open inheritance. 4. Produce a concrete migration plan with tests, rollout order, and review checkpoints. ## Reference routing (progressive disclosure) Read only the file needed for the current task: - **Foundations and mechanism choice** → [references/01-foundations-and-decision-making.md](references/01-foundations-and-decision-making.md) - **ADTs, composition patterns, frontend composition** → [references/02-adts-patterns-and-frontend-composition.md](references/02-adts-patterns-and-frontend-composition.md) - **Step-by-step migration and code review checks** → [references/03-refactoring-and-review-checklist.md](references/03-refactoring-and-review-checklist.md) - **CI metrics, custom static checks, team adoption** → [references/04-metrics-and-adoption.md](references/04-metrics-and-adoption.md) ## Default workflow 1. **Assess the current model** - List base classes, subclass count, hierarchy depth, and known pain points. - Mark each variation as one of: data variant, behavior strategy, or infrastructure concern. 2. **Choose mechanism (default-first)** - Choose **composition** for behavior variation, runtime swapping, or