2nd/10_Wiki/Topics/Architecture/Extract Class (클래스 추출하기).md

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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-extract-class-클래스-추출하기	Extract Class (클래스 추출하기)	10_Wiki/Topics	verified	self	Extract Class 클래스 추출 Refactoring	none	A	0.9	applied	refactoring fowler srp oop		2026-05-10	pending	language framework typescript none

Extract Class (클래스 추출하기)

매 한 줄

"매 too-much-doing class 의 cohesive subset 의 split". Extract Class 매 Fowler refactoring catalog 의 core move — 매 single class 매 multiple responsibilities 의 carry, 매 data + methods 의 cohesive cluster 의 new class 의 extract. SRP 의 enforcement.

매 핵심

매 Smell signals

• 매 class 매 200+ lines 의 grow.
• 매 fields 의 subset 매 always 의 used together (e.g., street/city/zip 의 always together).
• 매 methods 매 disjoint groups 의 form — 매 group A methods 매 group A fields only 의 use.
• 매 class name 매 vague — Manager, Helper, Util.

매 Mechanics (Fowler)

1. 매 responsibility 의 identify — 매 split point.
2. 매 new child class 의 create.
3. 매 parent → child reference 의 establish.
4. 매 fields 의 move (Move Field).
5. 매 methods 의 move (Move Method) — 매 leaves first.
6. 매 child interface 의 review — 매 internal exposure 의 minimize.
7. 매 expose: 매 child 의 public 의 또는 parent-only 의 decision.

매 응용

1. Person → Person + TelephoneNumber.
2. Order → Order + ShippingAddress + BillingAddress.
3. UserService → UserService + AuthService + ProfileService.
4. GameEntity → Position + Velocity + Health (ECS).

💻 패턴

Before — God class

class Person {
  name: string;
  officeAreaCode: string;
  officeNumber: string;

  getTelephoneNumber(): string {
    return `(${this.officeAreaCode}) ${this.officeNumber}`;
  }
}

After — Extract Class

class TelephoneNumber {
  constructor(public areaCode: string, public number: string) {}
  toString(): string { return `(${this.areaCode}) ${this.number}`; }
}

class Person {
  constructor(
    public name: string,
    private officeTelephone: TelephoneNumber,
  ) {}
  get telephoneNumber(): string { return this.officeTelephone.toString(); }
  // delegate accessors during transition
  get officeAreaCode() { return this.officeTelephone.areaCode; }
  set officeAreaCode(v: string) { this.officeTelephone.areaCode = v; }
}

Address extraction

// Before
class Order {
  customerName: string;
  street: string; city: string; zipCode: string; country: string;
  shippingCost: number;
}

// After
class Address {
  constructor(
    public street: string,
    public city: string,
    public zipCode: string,
    public country: string,
  ) {}
  format(): string { return `${this.street}, ${this.city} ${this.zipCode}, ${this.country}`; }
  isInternational(home: string) { return this.country !== home; }
}

class Order {
  constructor(
    public customerName: string,
    public shippingAddress: Address,
    public shippingCost: number,
  ) {}
}

Service split (SRP)

// Before — 600 LOC
class UserService {
  signup() { /* ... */ }
  login() { /* ... */ }
  resetPassword() { /* ... */ }
  updateProfile() { /* ... */ }
  uploadAvatar() { /* ... */ }
  getPreferences() { /* ... */ }
}

// After
class AuthService {
  signup() {} login() {} resetPassword() {}
}
class ProfileService {
  updateProfile() {} uploadAvatar() {} getPreferences() {}
}
// UserService 의 orchestration only 의 keep

ECS-style field group extraction

// Before — game entity 의 carries everything
class Enemy {
  x: number; y: number; vx: number; vy: number;
  hp: number; maxHp: number; armor: number;
  spriteId: string; animFrame: number;
}

// After — components
class Position { constructor(public x: number, public y: number) {} }
class Velocity { constructor(public vx: number, public vy: number) {} }
class Health { constructor(public hp: number, public maxHp: number, public armor = 0) {} }
class Sprite { constructor(public id: string, public frame = 0) {} }

class Enemy {
  constructor(
    public position: Position,
    public velocity: Velocity,
    public health: Health,
    public sprite: Sprite,
  ) {}
}

Incremental migration via delegation

class Person {
  private _phone = new TelephoneNumber('', '');
  // Old API 의 keep working
  get officeNumber() { return this._phone.number; }
  set officeNumber(v: string) { this._phone.number = v; }
  // New API 의 prefer
  get phone() { return this._phone; }
}
// Phase 1: delegate. Phase 2: callers migrate to .phone. Phase 3: remove old getters.

매 결정 기준

상황	Approach
Class < 100 LOC, single concept	매 extract 매 X — 매 premature
Field subset always 의 together	매 Extract Class
Two distinct responsibilities	매 Extract Class + Move Method
Component reuse 의 needed (game)	매 ECS-style components 의 extract
Public API 의 break 의 dangerous	매 delegating accessors 의 transition

기본값: 매 class 매 2 의 distinct responsibility 의 carry 의 extract — 매 cohesion > 1 class.

🔗 Graph

• 부모: Refactoring_Best_Practices · SOLID
• 응용: Single Responsibility Principle (SRP) · Entity-Component-System

🤖 LLM 활용

언제: 매 class 매 200+ LOC, 매 multiple distinct concerns. Field cluster 의 always 의 co-occur. Test setup 매 unrelated mocks 의 require. 언제 X: 매 small DTO. 매 abstraction 의 cost > readability gain (매 over-extraction).

❌ 안티패턴

• Anemic extraction: 매 fields only 의 move, 매 methods 매 parent 의 stay — 매 just data bag 의 result. Methods 의 follow 의 must.
• Reverse coupling: 매 child 매 parent 의 reference back — 매 cyclic dependency. One-way reference 의 keep.
• Premature extract: 매 50 LOC class 의 split — 매 navigation overhead > clarity.
• Public sprawl: 매 child 의 immediately public — 매 hide 매 first, 매 expose 의 demand 의 occur 시.

🧪 검증 / 중복

• Verified (Fowler "Refactoring" 2nd ed., Ch. 7).
• 신뢰도 A.

🕓 Changelog

날짜	변경
2026-05-08	Phase 1
2026-05-10	Manual cleanup — Extract Class refactoring 의 mechanics + 5 patterns