9.1.2 الگو Factory Method

package main

import "fmt"

// Product Interface
type Vehicle interface {
    Drive() string
    GetType() string
}

// Concrete Products
type Car struct{}

func (c *Car) Drive() string {
    return "Driving a car on the road"
}

func (c *Car) GetType() string {
    return "Car"
}

type Motorcycle struct{}

func (m *Motorcycle) Drive() string {
    return "Riding a motorcycle on the road"
}

func (m *Motorcycle) GetType() string {
    return "Motorcycle"
}

type Truck struct{}

func (t *Truck) Drive() string {
    return "Driving a truck carrying heavy load"
}

func (t *Truck) GetType() string {
    return "Truck"
}

// Factory
type VehicleFactory struct{}

func (vf *VehicleFactory) CreateVehicle(vehicleType string) (Vehicle, error) {
    switch vehicleType {
    case "car":
        return &Car{}, nil
    case "motorcycle":
        return &Motorcycle{}, nil
    case "truck":
        return &Truck{}, nil
    default:
        return nil, fmt.Errorf("unknown vehicle type: %s", vehicleType)
    }
}

// Alternatively, we can use factory functions instead of a struct
func CreateVehicle(vehicleType string) (Vehicle, error) {
    switch vehicleType {
    case "car":
        return &Car{}, nil
    case "motorcycle":
        return &Motorcycle{}, nil
    case "truck":
        return &Truck{}, nil
    default:
        return nil, fmt.Errorf("unknown vehicle type: %s", vehicleType)
    }
}

func main() {
    // Using the factory struct
    factory := &VehicleFactory{}
    
    fmt.Println("Using VehicleFactory struct:")
    car, _ := factory.CreateVehicle("car")
    fmt.Printf("%s: %s\n", car.GetType(), car.Drive())
    
    motorcycle, _ := factory.CreateVehicle("motorcycle")
    fmt.Printf("%s: %s\n", motorcycle.GetType(), motorcycle.Drive())
    
    truck, _ := factory.CreateVehicle("truck")
    fmt.Printf("%s: %s\n", truck.GetType(), truck.Drive())
    
    // Using the factory function
    fmt.Println("\nUsing factory function:")
    vehicle1, _ := CreateVehicle("car")
    fmt.Printf("%s: %s\n", vehicle1.GetType(), vehicle1.Drive())
    
    vehicle2, _ := CreateVehicle("motorcycle")
    fmt.Printf("%s: %s\n", vehicle2.GetType(), vehicle2.Drive())
    
    // Error handling
    fmt.Println("\nTesting error handling:")
    unknown, err := CreateVehicle("bicycle")
    if err != nil {
        fmt.Printf("Error: %s\n", err)
    } else {
        fmt.Printf("%s: %s\n", unknown.GetType(), unknown.Drive())
    }
    
    // Demonstrating polymorphism
    fmt.Println("\nDemonstrating polymorphism:")
    vehicles := []Vehicle{car, motorcycle, truck}
    for _, vehicle := range vehicles {
        fmt.Printf("- %s\n", vehicle.Drive())
    }
}

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