---
id: wiki-2026-0508-리팩토링-원칙
title: 리팩토링 원칙
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [Refactoring Principles, 리팩토링 가이드라인]
duplicate_of: none
source_trust_level: A
confidence_score: 0.9
verification_status: applied
tags: [refactoring, code-quality, principles]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: polyglot
  framework: ide-tooling
---

# 리팩토링 원칙

## 매 한 줄
> **"매 small step, green test, no behavior change"**. Fowler 의 1999 정의 그대로 — 매 외부 동작 보존, 내부 구조 개선. 2026 에 LLM-assisted refactor 가 boilerplate-level change 를 자동화하지만, 매 design intent 의 보존은 여전히 사람의 책임.

## 매 핵심

### 매 3대 원칙
- **Behavior preservation**: 매 test suite green 유지. Red 면 commit X.
- **Small steps**: 매 1 commit = 1 transformation. revert 가능해야.
- **Refactor ≠ Rewrite**: 매 새 feature 추가 X. 매 bug fix X. 매 oranges-to-oranges.

### 매 Two Hats (Kent Beck)
- "Adding feature" hat 또는 "Refactoring" hat — 매 동시 X.
- Hat 전환 시 commit boundary.

### 매 응용
1. Pre-feature refactor: 매 새 기능 추가 전에 매 ground 정리.
2. Code smell 감지 시 즉시 처리 (Boy Scout Rule).
3. PR review 에서 매 reviewer-suggested refactor 는 별도 PR.

## 💻 패턴

### Extract Function
```python
# Before
def process_order(order):
    if order.total > 100 and order.customer.tier == "gold":
        order.discount = order.total * 0.1
    # ... more logic

# After
def process_order(order):
    if _is_eligible_for_gold_discount(order):
        order.discount = order.total * 0.1

def _is_eligible_for_gold_discount(order):
    return order.total > 100 and order.customer.tier == "gold"
```

### Replace Magic Number
```typescript
// Before
if (user.age >= 18) { ... }

// After
const LEGAL_ADULT_AGE = 18;
if (user.age >= LEGAL_ADULT_AGE) { ... }
```

### Replace Conditional with Polymorphism
```python
# Before
def calculate_pay(employee):
    if employee.type == "salaried":
        return employee.monthly_salary
    elif employee.type == "hourly":
        return employee.hours * employee.rate

# After
class SalariedEmployee:
    def pay(self): return self.monthly_salary

class HourlyEmployee:
    def pay(self): return self.hours * self.rate
```

### Introduce Parameter Object
```typescript
// Before
function createUser(name, email, phone, address, city, country) { ... }

// After
interface UserProfile {
  name: string; email: string; phone: string;
  address: string; city: string; country: string;
}
function createUser(profile: UserProfile) { ... }
```

### Inline Variable
```python
# Before
price_basis = order.quantity * order.item_price
return price_basis > 1000

# After
return order.quantity * order.item_price > 1000
```

### LLM-Assisted Rename (Claude Opus 4.7)
```bash
# claude code refactor --rename "calc" --to "calculateTotal" \
#   --scope src/ --dry-run
# Reviews semantic usages, not just textual replace.
```

## 매 결정 기준
| 상황 | Approach |
|---|---|
| Test 없음 | 매 먼저 characterization test 작성 |
| Behavior change 필요 | 매 refactor 아님 — feature work 으로 분리 |
| Large class (1000+ lines) | Extract Class 점진적 적용 |
| Duplicated code (3+ sites) | Rule of Three — extract |
| Legacy code, no tests | Sprout Method / Sprout Class (Feathers) |

**기본값**: small commit + green test + IDE refactoring tool 사용.

## 🔗 Graph
- 부모: [[Refactoring_Best_Practices|Refactoring]] · [[Code_Quality]]
- 변형: [[Red-Green Refactoring]] · [[Scratch Refactoring (스크래치 리팩토링)]]
- 응용: [[Code Refactoring]] · [[Predictive_Refactoring]]
- Adjacent: [[Boy Scout Rule]] · [[Technical_Debt]]

## 🤖 LLM 활용
**언제**: 매 boilerplate transformation (rename, extract, format), 매 unfamiliar legacy code 의 의도 파악, 매 test scaffolding 자동 생성.
**언제 X**: 매 design decision 이 필요한 architectural refactor — 매 LLM 은 local view 만 봄.

## ❌ 안티패턴
- **Refactoring + Feature mix**: 매 PR 비대 + review 불가능.
- **Big bang refactor**: 매 2주 stop-the-world refactor — merge conflict 폭탄.
- **Test-less refactor**: 매 behavior preservation 증명 불가.
- **Cosmetic-only**: 매 readability 개선 없는 style change 만 — review 시간 낭비.

## 🧪 검증 / 중복
- Verified (Fowler, *Refactoring* 2nd ed., 2018; Beck, *Tidy First?* 2024).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — Fowler/Beck 원칙 + 6 patterns + LLM-assisted refactor 추가 |