Object Oriented Programming

One skill covering the full OOP review/design lens: whether something should be a class at all, SOLID, GoF patterns, Tell Don't Ask, and Object Calisthenics. Don't recite theory — point at the specific line, name the violation, propose the concrete refactor.

Core rule: Use a class only when it creates multiple instances with their own state. Otherwise prefer functions, object literals, or types. — Dave Thomas

Step 0 — Should this even be a class?

Before applying any other rule, run new or reviewed code through this first: