Refactor Skill

Collaborating skills

• TDD: skill: tdd for guiding through Red-Green-Refactor cycles and ensuring tests are in place before refactoring
• Design Patterns: skill: design-pattern-adopter for guidance on applying design patterns effectively

Quick Reference

Code Smells Reference

Smell	Detection	Refactoring
Long function	>20 lines	Extract Method
Duplicated code	Similar logic	Extract Method, Pull Up
Long parameter list	>3 params	Introduce Parameter Object
Large class	>10 methods	Extract Class
Feature envy	Method uses other class	Move Method
Switch statements	Type checking	Replace with Polymorphism
Speculative generality	Unused abstractions	Inline, Collapse Hierarchy
Message chains	a.b.c.d	Hide Delegate
Middle man	Excessive delegation	Remove Middle Man
Incomplete library class	Missing methods	Introduce Foreign Method

Process

1. VERIFY  - Tests exist and pass
2. ANALYZE - Identify code smells (see references/code-smells.md)
3. SELECT  - Choose appropriate pattern (see references/catalog.md)
4. APPLY   - One small step at a time
5. VERIFY  - Run tests after each change
6. REPEAT  - Until clean

TDD Cycle

For each discrete refactoring:

🔴 RED    - If adding behavior, write failing test first
🟢 GREEN  - Make minimal changes to pass tests
🔵 REFACTOR - Apply pattern while keeping tests green
✅ VERIFY - Run tests, lint, type check

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Prerequisites

1. Tests must exist - If no tests, write them first
2. Tests must pass - Run tests before starting
3. Understand the code - Read and comprehend behavior

Verification Commands

Python:

pytest              # Run tests
ruff check src/     # Lint
mypy src/           # Type check

Ruby:

rspec               # Run tests
rubocop             # Lint
steep check         # Type check (if using Steep)

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Refactoring Checklist

- [ ] Function does one thing only (SRP)
- [ ] Function name clearly describes intent
- [ ] Function is 20 lines or fewer
- [ ] 3 or fewer parameters
- [ ] No duplicate code (DRY)
- [ ] If nesting is 2 levels or fewer
- [ ] No magic numbers
- [ ] Self-documenting code
- [ ] Tests pass
- [ ] Lint passes
- [ ] Type check passes

Constraints

MUST:

• Write/run tests before refactoring
• Change one thing at a time
• Preserve behavior exactly

MUST NOT:

• Refactor + add features simultaneously
• Refactor without tests
• Batch multiple refactorings

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References

• Code Smells Guide - Detection patterns and fixes for all code smells
• Refactoring Catalog - Complete catalog with Ruby/Python examples
• Advanced Patterns - SOLID refactorings, prompt patterns, functional patterns

External Resources

• Refactoring (Martin Fowler)
• Catalog of Refactorings
• Clean Code (Robert C. Martin)