Refactoring Surgeon
Expert code refactoring specialist focused on improving code quality without changing behavior.
Quick Start
- Ensure tests exist - Never refactor without a safety net
- Identify the smell - Name the specific code smell you're addressing
- Make small changes - One refactoring at a time, commit frequently
- Run tests after each change - Behavior must remain identical
- Don't add features - Refactoring ≠ enhancement
- Document significant changes - Explain the "why" for future maintainers
Core Capabilities
| Category | Techniques |
|---|---|
| Extraction | Extract Method, Extract Class, Extract Interface |
| Movement | Move Method, Move Field, Inline Method |
| Simplification | Replace Conditional with Polymorphism, Decompose Conditional |
| Organization | Introduce Parameter Object, Replace Magic Numbers |
| Legacy Migration | Strangler Fig, Branch by Abstraction, Parallel Change |
Code Smells Reference
Bloaters
┌─────────────────────┐ ┌─────────────────────┐ ┌─────────────────────┐
│ Long Method │ │ Large Class │ │ Long Parameter │
│ > 20 lines? │ │ > 200 lines? │ │ List │
│ → Extract Method │ │ → Extract Class │ │ → Parameter Object │
└─────────────────────┘ └─────────────────────┘ └─────────────────────┘
OO Abusers
┌─────────────────────┐ ┌─────────────────────┐ ┌─────────────────────┐
│ Switch Statements │ │ Refused Bequest │ │ Parallel │
│ Type-checking? │ │ Unused inheritance?│ │ Hierarchies │
│ → Polymorphism │ │ → Delegation │ │ → Move Method │
└─────────────────────┘ └─────────────────────┘ └─────────────────────┘
Change Preventers
┌─────────────────────┐ ┌─────────────────────┐
│ Divergent Change │ │ Shotgun Surgery │
│ One class, many │ │ One change, many │
│ reasons to change? │ │ classes affected? │
│ → Extract Class │ │ → Move/Inline │
└─────────────────────┘ └─────────────────────┘
Reference Examples
Complete refactoring examples in ./references/:
| File | Pattern | Use Case |
|---|---|---|
extract-method.ts |
Extract Method | Long methods → focused functions |
replace-conditional-polymorphism.ts |
Replace Conditional | switch/if → polymorphic classes |
introduce-parameter-object.ts |
Parameter Object | Long params → structured objects |
strangler-fig-pattern.ts |
Strangler Fig | Legacy code → gradual migration |
Anti-Patterns (10 Critical Mistakes)
1. Big Bang Refactoring
Symptom: Rewriting entire modules in one massive change Fix: Strangler fig pattern, small incremental changes with tests
2. Refactoring Without Tests
Symptom: Changing structure without test coverage Fix: Write characterization tests first, add coverage for affected areas
3. Premature Abstraction
Symptom: Creating generic frameworks "for future flexibility" Fix: Wait for three concrete examples before abstracting (Rule of Three)
4. Renaming Without IDE Support
Symptom: Find-and-replace that misses occurrences Fix: Use IDE refactoring tools, search for usages first
5. Mixing Refactoring and Features
Symptom: Adding new functionality while restructuring Fix: Separate commits - refactor first, then add features
6. Ignoring Code Reviews
Symptom: Large refactoring PRs that are hard to review Fix: Small, focused PRs with clear commit messages
7. Over-Abstracting
Symptom: Three layers of abstraction for a simple operation Fix: YAGNI - start concrete, abstract when patterns emerge
8. Incomplete Refactoring
Symptom: Starting Extract Method but leaving partial duplication Fix: Complete the refactoring or revert - no half-measures
9. Refactoring Production During Incidents
Symptom: "I'll just clean this up while I'm here..." Fix: Never refactor during incidents - fix the bug, create a ticket
10. Not Measuring Improvement
Symptom: Refactoring without knowing if it helped Fix: Track metrics: complexity, test coverage, build time
Safety Checklist
Before Refactoring:
- Code compiles/runs successfully
- All tests pass
- Test coverage is adequate for area being refactored
- Commit current state (can rollback)
During Refactoring:
- Make small, incremental changes
- Run tests after each change
- Keep behavior identical
- Don't add features while refactoring
After Refactoring:
- All tests still pass
- No new warnings/errors
- Code is more readable
- Complexity metrics improved
- Document significant changes
Quality Checklist
- No behavior changes (tests prove this)
- Improved readability
- Reduced complexity (cyclomatic, cognitive)
- Better adherence to SOLID principles
- Removed duplication (DRY)
- More testable code
- Clear naming
- Appropriate abstractions (not over-engineered)
Validation Script
Run ./scripts/validate-refactoring.sh to check:
- Test coverage presence
- Code smell indicators
- Duplication patterns
- Complexity metrics
- SOLID violations
- Refactoring safety (git, uncommitted changes)
External Resources
Converted and distributed by TomeVault — claim your Tome and manage your conversions.