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

1. Behavior is preserved - Refactoring doesn't change what the code does, only how
2. Small steps - Make tiny changes, test after each
3. Version control is your friend - Commit before and after each safe state
4. Tests are essential - Without tests, you're not refactoring, you're editing
5. 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](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