---
id: wiki-2026-0508-code-smells
title: Code Smells
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [코드 악취, code smell, refactoring catalog, Fowler, bloater, coupler, dispensable]
duplicate_of: none
source_trust_level: A
confidence_score: 0.93
verification_status: applied
tags: [refactoring, code-smell, fowler, software-quality, technical-debt, oop, code-review]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: language-agnostic
  framework: refactoring catalog
---

# Code Smells

## 📌 한 줄 통찰
> **"매 code 의 surface 의 sign 의 deeper problem"**. Martin Fowler 의 catalog. 매 syntax 의 OK 가, 매 design 의 ill. 매 refactoring 의 trigger. 매 modern: 매 SonarQube / Semgrep / AI review 의 자동 detect.

## 📖 핵심

### 매 Fowler 의 6 category

#### 1. Bloater
- **Long Method**: 매 single function 의 거대.
- **Large Class**: 매 god class.
- **Primitive Obsession**: 매 string / int 의 abuse.
- **Long Parameter List**: 매 4+ parameter.
- **Data Clump**: 매 같이 쓰이는 data 의 group X.

#### 2. OO Abuser
- **Switch Statement**: 매 polymorphism 의 missed.
- **Temporary Field**: 매 일부 case 만 의 사용 field.
- **Refused Bequest**: 매 inherit 가, 매 일부 의 X.
- **Alternative Classes with Different Interface**: 매 same job, 매 다른 method name.

#### 3. Change Preventer
- **Divergent Change**: 매 1 class 의 매 다른 reason 의 수정.
- **Shotgun Surgery**: 매 1 변경 의 매 N class 의 수정.
- **Parallel Inheritance Hierarchies**: 매 두 hierarchy 의 동시 의 grow.

#### 4. Dispensable
- **Duplicate Code** (DRY violation).
- **Lazy Class**: 매 도움 X.
- **Data Class**: 매 anaemic (case-by-case).
- **Dead Code**: 매 unused.
- **Speculative Generality**: 매 hypothetical 의 design.
- **Comments**: 매 reason 의 explain 의 X 의 case.

#### 5. Coupler
- **Feature Envy**: 매 method 의 다른 class 의 더 사용.
- **Inappropriate Intimacy**: 매 internal 의 over-share.
- **Message Chain**: `a.b().c().d()` 의 chain.
- **Middle Man**: 매 delegation 만.

#### 6. Other
- **Mysterious Name**: 매 unclear identifier.
- **Magic Number**: 매 unnamed constant.
- **Insider Trading**: 매 inappropriate field access.
- **Incomplete Library Class**.

### 매 modern addition (Fowler 2nd ed)
- **Mutable Data**.
- **Global Data**.
- **Loops** (Stream / functional 의 lieu).
- **Repeated Switches**.

### 매 detection
- **Manual review**.
- **Linter**: ESLint, RuboCop, Pylint.
- **SAST**: SonarQube, CodeClimate.
- **Semgrep**: 매 custom rule.
- **AI review**: CodeRabbit, Greptile.

### 매 refactoring (corresponding)
- **Extract Method**: Long Method.
- **Extract Class**: Large Class.
- **Replace Conditional with Polymorphism**: Switch.
- **Move Method**: Feature Envy.
- **Hide Delegate**: Message Chain.
- **Introduce Parameter Object**: Long Parameter / Data Clump.

### 매 priority
- 매 not all smells 의 fix 의 immediate.
- 매 changing area 의 first.
- 매 boy scout rule (better than found).

## 💻 패턴

### Long Method (extract)
```ts
// ❌ Long Method
function processOrder(order: Order) {
  // 매 50+ lines: validate, calculate, save, notify, log...
}

// ✅ Extract Method
function processOrder(order: Order) {
  validate(order);
  const total = calculateTotal(order);
  save(order, total);
  notify(order);
}

function validate(order: Order) { ... }
function calculateTotal(order: Order) { ... }
```

### Primitive Obsession → Value Object
```ts
// ❌
function transfer(amount: number, currency: string) { ... }

// ✅
class Money {
  constructor(public amount: bigint, public currency: string) {}
  add(other: Money) { 
    if (this.currency !== other.currency) throw new Error();
    return new Money(this.amount + other.amount, this.currency);
  }
}

function transfer(money: Money) { ... }
```

### Switch → Polymorphism
```ts
// ❌
function area(shape: Shape) {
  switch (shape.type) {
    case 'circle': return Math.PI * shape.r ** 2;
    case 'square': return shape.side ** 2;
    case 'rectangle': return shape.w * shape.h;
  }
}

// ✅
abstract class Shape { abstract area(): number; }
class Circle extends Shape { constructor(public r: number) {} area() { return Math.PI * this.r ** 2; } }
class Square extends Shape { constructor(public side: number) {} area() { return this.side ** 2; } }
```

### Feature Envy → Move Method
```ts
// ❌
class Order {
  total(customer: Customer) {
    // 매 모든 logic 의 customer 의 사용
    return customer.discount * customer.tax * ...;
  }
}

// ✅ Move to Customer
class Customer {
  applyDiscount(amount: number) { return amount * this.discountRate; }
}
```

### Message Chain → Hide Delegate
```ts
// ❌ Chain
order.getCustomer().getAddress().getCountry().getName();

// ✅ Hide
class Order {
  customerCountry() {
    return this.customer.address.country.name;
  }
}
```

### Detection (Semgrep)
```yaml
# 매 long parameter list detection
rules:
  - id: long-parameter-list
    pattern-either:
      - pattern: function $F($A, $B, $C, $D, $E, ...) { ... }
    message: "Function has 5+ parameters — consider Parameter Object"
    severity: WARNING
    languages: [typescript, javascript]
```

### SonarQube quality gate
```properties
# 매 cognitive complexity
sonar.javascript.cognitive-complexity-threshold=15

# 매 duplicate threshold
sonar.cpd.minimumLines=20
sonar.duplicatedLines.maximum=3.0
```

### AI review (CodeRabbit)
```yaml
# .coderabbit.yaml
language: en
reviews:
  profile: chill
  high_level_summary: true
  poem: false
  auto_review:
    enabled: true
    drafts: false

# 매 auto-detect: long methods, missing tests, complexity, etc.
```

### Refactor metric (cyclomatic complexity)
```bash
# 매 radon (Python)
radon cc src/ -a -nb

# 매 ESLint complexity rule
echo '{ "rules": { "complexity": ["error", 10] } }' > .eslintrc.json
```

### Bobby tables (refactor cadence)
```python
# 매 boy scout rule
def visit(file):
    if needs_change(file):
        # 매 main change
        do_main_change()
        # 매 small refactor (touching area)
        if has_smell(file):
            small_refactor()
```

## 🤔 결정 기준
| Smell | Refactor |
|---|---|
| Long Method | Extract Method |
| Large Class | Extract Class |
| Primitive Obsession | Value Object |
| Long Parameter | Parameter Object |
| Duplicate | DRY (Extract) |
| Switch | Polymorphism |
| Feature Envy | Move Method |
| Data Clump | Class |
| Comments (bad) | Rename / Restructure |
| Magic Number | Named Constant |

**기본값**: 매 fix-as-you-touch + 매 priority queue (changing area).

## 🔗 Graph
- 부모: [[Refactoring]] · [[Code-Quality]] · [[Software-Engineering]]
- 변형: [[Bloater]] · [[Coupler]] · [[Dispensable]] · [[Change-Preventer]]
- 응용: [[Extract-Method]] · [[Replace-Conditional-with-Polymorphism]] · [[Move-Method]]
- 비판: [[Anaemic-Domain-Model]] (Data Class)
- Adjacent: [[Architecture-Anti-Patterns]] · [[Quality_Code_Review_Modern]] · [[Clean-Code-Principles]] · [[SOLID]]

## 🤖 LLM 활용
**언제**: 매 code review. 매 refactor planning. 매 onboarding (smell 의 catalog 인지).
**언제 X**: 매 prototype (premature). 매 throwaway script.

## ❌ 안티패턴
- **모든 smell 의 fix 의 obsession**: 매 productivity ↓.
- **No measure**: 매 better 의 prove 의 X.
- **Smell 의 ignore**: 매 technical debt 의 accumulate.
- **Refactor without test**: 매 regression.
- **Big bang refactor**: 매 risky.
- **Clean Code 의 dogma**: 매 sometimes wrong.

## 🧪 검증 / 중복
- Verified (Fowler "Refactoring", Beck "Implementation Patterns", SonarQube rules).
- 신뢰도 A.
- Related: [[Architecture-Anti-Patterns]] · [[Anaemic-Domain-Model]] · [[Quality_Code_Review_Modern]] · [[Clean-Code-Principles]].

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — 6 category + refactor + 매 TS / Semgrep / SonarQube code |
