johnnystefan/pattern-factory-method

Skill: Implement Factory Method Pattern

Purpose

Provides an interface for creating objects in a superclass but allows subclasses to alter the type of objects that will be created. It decouples the business logic from the concrete classes it needs to instantiate.

Procedural Instructions

1. Identify Direct Instantiation: Look for new ConcreteClass() calls that make the code rigid.
2. Define Product Interface: Ensure all products follow a common interface.
3. Create Creator Class: Declare the factory method. It should return the product interface.
4. Implement Subclasses: Create concrete creators that override the factory method to return specific instances of products.

TypeScript Example

// Product Interface
interface Transport {
  deliver(): string;
}

// Concrete Products
class Truck implements Transport {
  deliver() {
    return 'Delivering by land in a box.';
  }
}

class Ship implements Transport {
  deliver() {
    return 'Delivering by sea in a container.';
  }
}

// Creator Class
abstract class Logistics {
  public abstract createTransport(): Transport;

  public planDelivery(): string {
    const transport = this.createTransport();
    return transport.deliver();
  }
}

// Concrete Creators
class RoadLogistics extends Logistics {
  public createTransport(): Transport {
    return new Truck();
  }
}

class SeaLogistics extends Logistics {
  public createTransport(): Transport {
    return new Ship();
  }
}

Payoff

• OCP Compliance: You can introduce new types of products without breaking existing client code.
• SRP Compliance: Product creation code is localized in one place.