Refactoring Patterns

Safe techniques for restructuring code without changing its behavior. Every refactoring follows: test green -> refactor -> test green.

Golden Rule

Never refactor and change behavior in the same commit. Refactoring = same behavior, different structure. Feature work = different behavior. Mixing them makes bugs untraceable.

Pre-Refactoring Checklist

Before any refactoring:

• Tests exist and pass for the code being refactored
• You can describe what the code does WITHOUT reading it line by line
• The refactoring has a clear motivation (not "it could be cleaner")
• The scope is bounded — you know exactly which files/functions change

Core Refactorings

1. Extract Function