factory method pattern

팩토리 메서드 패턴은
팩토리 패턴을 확장시킨 것으로

팩토리에 다른 함수(메서드)들을 추가할 수 있게 하는 패턴이다(팩토리함수의 상태관리, 생성한 객체의 개수 리턴)

class Animal():
  def speak(self):
    pass

class Cat(Animal):
  def speak(self):
    print("meow")

class Dog(Animal):
  def speak(self):
    print("bark")

class AnimalFactory():
  def createAnimal(self):
    pass

class CatFactory(AnimalFactory):
  def __init__(self):
    self.cat_count = 0
  def createAnimal(self):
    self.cat_count += 1
    return Cat()
  def catCount(self):
    return self.cat_count


class DogManager(AnimalFactory):
  def haveDog(self):
    self.dog = self.createAnimal()
  def createAnimal(self):
    return Dog()
  def makeWings(self,dog:Dog):
    print("dog wings added")
    return dog


cat_factory = CatFactory()
cat = cat_factory.createAnimal()
print(f"{cat_factory.catCount()} cats are created")

dog_manager = DogManager()
dog = dog_manager.haveDog()
wing_dog = dog_manager.makeWings(dog)

위와 같이 CatFactory 클래스 안에 catCount(self) 메서드를 넣거나
DogManger 클래스에 makeWings(self,dog:Dog) 메서드를 넣는 것 같이 메서드를 추가하는 것이다.

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JS코드를 예로 들면

var Factory = function () {
    this.createEmployee = function (type) {
        var employee;

        if (type === "fulltime") {
            employee = new FullTime();
        } else if (type === "parttime") {
            employee = new PartTime();
        } else if (type === "temporary") {
            employee = new Temporary();
        } else if (type === "contractor") {
            employee = new Contractor();
        }

        employee.type = type;

        employee.say = function () {
            console.log(this.type + ": rate " + this.hourly + "/hour");
        }

        return employee;
    }
}

var FullTime = function () {
    this.hourly = "$12";
};

var PartTime = function () {
    this.hourly = "$11";
};

var Temporary = function () {
    this.hourly = "$10";
};

var Contractor = function () {
    this.hourly = "$15";
};

function run() {

    var employees = [];
    var factory = new Factory();

    employees.push(factory.createEmployee("fulltime"));
    employees.push(factory.createEmployee("parttime"));
    employees.push(factory.createEmployee("temporary"));
    employees.push(factory.createEmployee("contractor"));

    for (var i = 0, len = employees.length; i < len; i++) {
        employees[i].say();
    }
}

팩토리 함수안에

employee.say = function () {
            console.log(this.type + ": rate " + this.hourly + "/hour");
        }

say메서드를 생성한 것을 볼 수 있다.