---
id: wiki-2026-0508-factory-pattern
title: Factory Pattern
category: 10_Wiki/Topics
status: verified
canonical_id: self
aliases: [factory, factory method, abstract factory, simple factory, GoF factory]
duplicate_of: none
source_trust_level: A
confidence_score: 0.97
verification_status: applied
tags: [design-pattern, gof, factory, oop, creational, abstract-factory]
raw_sources: []
last_reinforced: 2026-05-10
github_commit: pending
tech_stack:
  language: TypeScript / Python / Java
  applicable_to: [OOP, Plugin System, DI]
---

# Factory Pattern

## 매 한 줄
> **"매 object creation 의 의 의 encapsulate"**. GoF creational. 매 simple factory (function), 매 factory method (method), 매 abstract factory (factory of factories). 매 modern: 매 DI / DI container 의 partly 의 replace.

## 매 핵심

### 매 variant
- **Simple factory**: 매 단순 function.
- **Factory method**: 매 polymorphic creation.
- **Abstract factory**: 매 family of factories.

### 매 motivation
- 매 client 의 concrete class 의 의 know X.
- 매 creation logic 의 encapsulate.
- 매 family of related objects.
- 매 testability (mock).

### 매 modern alternative
- **DI container** (Inversify, NestJS).
- **Builder** (complex creation).
- **Static factory method** (named).
- **Functional factory**.

## 💻 패턴

### Simple factory
```typescript
function createButton(theme: 'light' | 'dark'): Button {
  if (theme === 'light') return new LightButton();
  return new DarkButton();
}
```

### Factory method
```typescript
abstract class Dialog {
  protected abstract createButton(): Button;
  
  render() {
    const btn = this.createButton();
    btn.render();
  }
}

class WindowsDialog extends Dialog {
  protected createButton(): Button {
    return new WindowsButton();
  }
}

class MacDialog extends Dialog {
  protected createButton(): Button {
    return new MacButton();
  }
}
```

### Abstract factory
```typescript
interface UIFactory {
  createButton(): Button;
  createCheckbox(): Checkbox;
}

class WindowsFactory implements UIFactory {
  createButton() { return new WindowsButton(); }
  createCheckbox() { return new WindowsCheckbox(); }
}

class MacFactory implements UIFactory {
  createButton() { return new MacButton(); }
  createCheckbox() { return new MacCheckbox(); }
}

function getFactory(): UIFactory {
  return process.platform === 'darwin' ? new MacFactory() : new WindowsFactory();
}
```

### Static factory method (Effective Java)
```typescript
class User {
  private constructor(public id: string, public role: string) {}
  
  static guest() { return new User('guest', 'guest'); }
  static admin(id: string) { return new User(id, 'admin'); }
  static fromJSON(json: any) { return new User(json.id, json.role); }
}
```

### Functional (Python)
```python
from typing import Callable

def make_logger(level: str) -> Callable:
    if level == 'debug':
        return lambda msg: print(f'[DEBUG] {msg}')
    if level == 'error':
        return lambda msg: sys.stderr.write(f'[ERROR] {msg}\n')
    return lambda msg: print(msg)
```

### Registry-based factory
```python
class ShapeRegistry:
    _registry: dict = {}
    
    @classmethod
    def register(cls, name: str):
        def decorator(klass):
            cls._registry[name] = klass
            return klass
        return decorator
    
    @classmethod
    def create(cls, name: str, *args, **kwargs):
        return cls._registry[name](*args, **kwargs)

@ShapeRegistry.register('circle')
class Circle:
    def __init__(self, r): self.r = r

shape = ShapeRegistry.create('circle', 5)
```

### DI container alternative (NestJS)
```typescript
@Injectable()
class UserService {
  constructor(
    @Inject('UserRepo') private repo: UserRepo,
    private logger: Logger,
  ) {}
}

@Module({
  providers: [
    UserService,
    Logger,
    { provide: 'UserRepo', useClass: PostgresUserRepo },
  ],
})
class AppModule {}
```

### Plugin / strategy factory
```python
PARSERS = {
    'json': JSONParser,
    'yaml': YAMLParser,
    'toml': TOMLParser,
}

def parse(content, format):
    return PARSERS[format]().parse(content)
```

### Conditional with extensibility
```python
class ModelFactory:
    def __init__(self):
        self.providers = {}
    
    def register(self, name, provider_cls):
        self.providers[name] = provider_cls
    
    def create(self, name, **config):
        if name not in self.providers:
            raise ValueError(f'Unknown provider: {name}')
        return self.providers[name](**config)

factory = ModelFactory()
factory.register('openai', OpenAIProvider)
factory.register('anthropic', AnthropicProvider)
```

### Async factory
```python
class DBConnectionFactory:
    @classmethod
    async def create(cls, url):
        conn = AsyncConnection(url)
        await conn.connect()
        return conn

db = await DBConnectionFactory.create('postgres://...')
```

## 매 결정 기준
| 상황 | Pattern |
|---|---|
| Simple variant | Simple factory function |
| Polymorphic creation | Factory method |
| Family of objects | Abstract factory |
| Many params | Builder |
| Plugin system | Registry |
| DI heavy | DI container |
| Functional | Closure factory |

**기본값**: 매 simple = 매 plain function. 매 plugin = registry. 매 DI = container. 매 family = abstract factory.

## 🔗 Graph
- 변형: [[Prototype]]
- 응용: [[Dependency_Injection_(DI)|Dependency-Injection]]
- Adjacent: [[Encapsulation-and-Information-Hiding]]

## 🤖 LLM 활용
**언제**: 매 plugin / multiple impl. 매 testability. 매 family of objects.
**언제 X**: 매 single concrete (just `new`).

## ❌ 안티패턴
- **Factory for factory's sake**: 매 single impl.
- **God factory**: 매 too many responsibilities.
- **Hidden global state**: 매 testability lose.
- **Switch explosion**: 매 registry 의 prefer.
- **Reinventing DI**: 매 use container.

## 🧪 검증 / 중복
- Verified (GoF Design Patterns, Effective Java).
- 신뢰도 A.

## 🕓 Changelog
| 날짜 | 변경 |
|---|---|
| 2026-04-20 | Auto-reinforced |
| 2026-05-08 | Phase 1 |
| 2026-05-10 | Manual cleanup — variants + 매 simple / method / abstract / registry / DI code |