[Design Pattern] 메멘토 패턴 (Memento Pattern)

메멘토 패턴이란 객체의 정보를 저장하고 사용자가 원하는 시점의 데이터를 복원할 수 있도록 하는 패턴입니다.

클래스 다이어그램

Originator: 현재 상태를 저장하고 Memento 객체의 정보를 얻는 클래스

Memento: 상태를 갖고 있는 클래스

Caretaker: Memento 클래스를 순서대로 저장하는 클래스

예제

public class Memento {
    private final String state;

    public Memento(String state){
        this.state = state;
    }

    public String getState(){
        return state;
    }
}

public class Originator {
    private String state;

    public void setState(String state){
        this.state = state;
    }

    public String getState(){
        return state;
    }

    public Memento saveStateToMemento(){
        return new Memento(state);
    }

    public void getStateFromMemento(Memento memento){
        state = memento.getState();
    }
}

public class CareTaker {
    private final List<Memento> mementoList = new ArrayList<>();

    public void add(Memento state){
        mementoList.add(state);
    }

    public Memento get(int index){
        return mementoList.get(index);
    }
}

Originator originator = new Originator();
CareTaker careTaker = new CareTaker();
originator.setState("State #1");
originator.setState("State #2");
careTaker.add(originator.saveStateToMemento());
originator.setState("State #3");
careTaker.add(originator.saveStateToMemento());
originator.setState("State #4");

System.out.println("Current State: " + originator.getState());
originator.getStateFromMemento(careTaker.get(0));
System.out.println("First saved State: " + originator.getState());
originator.getStateFromMemento(careTaker.get(1));
System.out.println("Second saved State: " + originator.getState());

// Current State: State #4
// First saved State: State #2
// Second saved State: State #3

파이썬

class Memento:
    def __init__(self, state):
        self._state = state

    @property
    def state(self):
        return self._state

class Originator:
    def __init__(self):
        self._state = None

    @property
    def state(self):
        return self._state

    @state.setter
    def state(self, state):
        self._state = state

    def create_memento(self):
        return Memento(self.state)

    def get_memento_state(self, memento):
        self._state = memento.state

class CareTaker(list):
    pass

originator = Originator()
care_taker = CareTaker()

originator.state = "State #1"
originator.state = "State #2"
care_taker.append(originator.create_memento())
originator.state = "State #3"
care_taker.append(originator.create_memento())
originator.state = "State #4"

print(f"Current State: {originator.state}")
originator.get_memento_state(care_taker[0])
print(f"First saved State: {originator.state}")
originator.get_memento_state(care_taker[1])
print(f"Second saved State: {originator.state}")

# Current State: State #4
# First saved State: State #2
# Second saved State: State #3