refactor

Refactor

Overview

Improve code structure and readability without changing external behavior. Refactoring is gradual evolution, not revolution. Use this for improving existing code, not rewriting from scratch.

When to Use

Use this skill when:

Code is hard to understand or maintain
Functions/classes are too large
Code smells need addressing
Adding features is difficult due to code structure
User asks "clean up this code", "refactor this", "improve this"

Refactoring Principles

The Golden Rules

Behavior is preserved - Refactoring doesn't change what the code does, only how
Small steps - Make tiny changes, test after each
Version control is your friend - Commit before and after each safe state
Tests are essential - Without tests, you're not refactoring, you're editing
One thing at a time - Don't mix refactoring with feature changes

When NOT to Refactor

- Code that works and won't change again (if it ain't broke...)
- Critical production code without tests (add tests first)
- When you're under a tight deadline
- "Just because" - need a clear purpose

Catalog & worked examples

The smell-by-smell BAD/GOOD catalog, extract-method / type-safety / design-pattern examples, and the refactoring-operations lookup table live in references/catalog.md. Open it when you hit a specific smell — it covers: Long Method, Duplicated Code, Large Class, Long Parameter List, Feature Envy, Primitive Obsession, Magic Numbers/Strings, Nested Conditionals, Dead Code, Inappropriate Intimacy, plus Strategy / Chain-of-Responsibility patterns.

Refactoring Steps

Safe Refactoring Process

1. PREPARE
   - Ensure tests exist (write them if missing)
   - Commit current state
   - Create feature branch

2. IDENTIFY
   - Find the code smell to address
   - Understand what the code does
   - Plan the refactoring

3. REFACTOR (small steps)
   - Make one small change
   - Run tests
   - Commit if tests pass
   - Repeat

4. VERIFY
   - All tests pass
   - Manual testing if needed
   - Performance unchanged or improved

5. CLEAN UP
   - Update comments
   - Update documentation
   - Final commit

Refactoring Checklist

Code Quality

Functions are small (< 50 lines)
Functions do one thing
No duplicated code
Descriptive names (variables, functions, classes)
No magic numbers/strings
Dead code removed

Structure

Related code is together
Clear module boundaries
Dependencies flow in one direction
No circular dependencies

Type Safety

Types defined for all public APIs
No any types without justification
Nullable types explicitly marked

Testing

Refactored code is tested
Tests cover edge cases
All tests pass