2nd/10_Wiki/Topics/AI_and_ML/Code_Smells.md

id, title, category, status, canonical_id, aliases, duplicate_of, source_trust_level, confidence_score, verification_status, tags, raw_sources, last_reinforced, github_commit, tech_stack

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

// ❌ 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

// ❌
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

// ❌
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

// ❌
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

// ❌ Chain
order.getCustomer().getAddress().getCountry().getName();

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

Detection (Semgrep)

# 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

# 매 cognitive complexity
sonar.javascript.cognitive-complexity-threshold=15

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

AI review (CodeRabbit)

# .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)

# 매 radon (Python)
radon cc src/ -a -nb

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

Bobby tables (refactor cadence)

# 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_Best_Practices · Code-Quality
• 변형: Bloater · Coupler · Dispensable
• 응용: Replace-Conditional-with-Polymorphism
• 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