Recognising code smells before refactoring

What it is

A code smell is a recognisable pattern in code that is not a bug but often indicates a design weakness. Common catalogues group them: bloaters (long method, large class, long parameter list, primitive obsession), object-orientation abusers (switch statements on type, refused bequest), change preventers (divergent change, shotgun surgery), dispensables (duplicate code, dead code, speculative generality) and couplers (feature envy, inappropriate intimacy, message chains).

Why it matters

Smells give reviewers and authors a shared, neutral vocabulary. "This method has feature envy for Order" is more actionable than "this feels wrong", and each smell maps to a small set of known refactorings.

How to apply

• Name the smell in review comments and link the refactoring you would apply.
• Prioritise smells in code that changes often; stable code with smells costs little.
• Fix one smell per refactoring commit with tests green before and after.
• Watch for smells introduced by a change rather than auditing the whole codebase at once.

Pitfalls

Not every smell is a problem: a long method that reads like a checklist may be clearer than five tiny ones. Refactoring without tests turns smells into bugs. Catalogues differ in naming; agree on one.