What problem does it solve? Developers often write new helpers, classes, or add dependencies for functionality that already exists in the language, standard library, current package, or ecosystem, creating unnecessary duplication and maintenance burden. This Skill enforces a deliberate reuse check before any new implementation. ## Core Features & Use Cases - Structured Reuse Hierarchy: Guides investigation through language/standard library, current package, existing dependencies, domain ecosystem, and upstream implementations before writing new code. - Reuse Decision Procedure: Provides a five-step process covering behavior definition, domain-vs-integration separation, capability search, conceptual cost comparison, and narrowest-interface selection. - Public API Enforcement: Prohibits reliance on private APIs, undocumented internals, and hidden slots, with an ordered fallback plan when only private interfaces exist. - Use Case: Before adding a constrained ordination feature to an R package, the Skill directs you to extract and align matrices locally, then delegate the statistical computation to an established package like vegan and return its standard result class. ## Quick Start Before implementing the new feature, apply the reuse-before-implementing checklist to document existing capabilities in the language, package, dependencies, and ecosystem, then state whether to reuse, adapt, or implement locally.
