[Swift] Memento

SWIFT
Memento
Bill Kim(김정훈) | ibillkim@gmail.com

목차
•Memento
•Structure
•Implementation
•References

Memento
Memento(메멘토) 패턴은 객체의 상태를 저장하고 복원할 수 있는
행동 디자인 패턴입니다.
기본 오리지날 객체는 본래의 기능에만 충실하고 상태 정보에 대한
관리를 메멘토 객체에게 전담하여 상태를 저장하고 복원할 수 있게
한다.

Structure
Memento 패턴을 UML로 도식화하면 아래와 같습니다.

Structure
Originator : 상태값을 가지고 있고 객체의 본연의 기능만을 수행
하며 저장 및 복원에 대한 작업은 Memento 객체에게 넘기는 객체
Memento : Originator 객체의 스냅샷 역할을 하는 값 객체이다.
메멘토 데이터는 생성장를 통해서 한번만 전달하는 것이 일반적입
니다.
ConcreteMemento : Memento 객체를 상속받아 메멘토 객체가
가진 데이터에 대한 초기화를 진행하는 클래스 객체
Caretaker(Client) : Originator 객체에 대한 상태가 언제 바뀌
고 저장되었는지를 알고 있는 객체, 또한 스냅샷 리스트를 가지고 있
고 복원을 할 경우 가장 최상위의 Originator 상태로 복원을 진행
하는 객체

Implementation
구체적인 구현에 대해서 소스 코드를 통하여 살펴봅니다.
class Originator {
private var state: String
init(state: String) {
self.state = state
print("Originator: My initial state is: (state)")
}
func doSomething() {
print("Originator: I'm doing something important.")
state = generateRandomString()
print("Originator: and my state has changed to: (state)")
}
private func generateRandomString() -> String {
return String(UUID().uuidString.suffix(4))
}
func save() -> Memento {
return ConcreteMemento(state: state)
}
func restore(memento: Memento) {
guard let memento = memento as? ConcreteMemento else { return }
self.state = memento.state
print("Originator: My state has changed to: (state)")
}
}

Implementation
protocol Memento {
var name: String { get }
var date: Date { get }
}
class ConcreteMemento: Memento {
private(set) var state: String
private(set) var date: Date
init(state: String) {
self.state = state
self.date = Date()
}
var name:String { return state + " " + date.description.suffix(14).prefix(8) }
}

Implementation
class Caretaker {
private lazy var mementos = [Memento]()
private var originator: Originator
init(originator: Originator) {
self.originator = originator
}
func backup() {
print("nSaving Originator's state...n")
mementos.append(originator.save())
}
func undo() {
guard !mementos.isEmpty else { return }
let removedMemento = mementos.removeLast()
print("Restoring state to: " + removedMemento.name)
originator.restore(memento: removedMemento)
}
func showHistory() {
print("Here's the list of mementos:n")
mementos.forEach({ print($0.name) })
}
}

Implementation
let originator = Originator(state: "Super-duper-super-puper-super.")
// Originator: My initial state is: Super-duper-super-puper-super.
let caretaker = Caretaker(originator: originator)
caretaker.backup()
// Saving Originator's state...
originator.doSomething()
// Originator: I'm doing something important.
// Originator: and my state has changed to: B147
caretaker.backup()
originator.doSomething()
// Originator: I'm doing something important.
// Originator: and my state has changed to: 20B2
caretaker.backup()

Implementation
caretaker.showHistory()
// Super-duper-super-puper-super. 08:22:02
// B147 08:22:02
// 20B2 08:22:02
caretaker.undo()
// Restoring state to: 20B2 08:22:31
// Originator: My state has changed to: 20B2
caretaker.undo()
// Restoring state to: B147 08:22:31
// Originator: My state has changed to: B147
caretaker.undo()
// Caretaker: Restoring state to: Super-duper-super-puper-super. 08:22:31
// Originator: My state has changed to: Super-duper-super-puper-super.

References
[1] Memento in Swift : https://refactoring.guru/design-
patterns/memento/swift/example
[2] 메멘토 패턴 (Memento Pattern in Swift) : https://
jerome.kr/entry/memento-pattern
[3] Design Patterns in Swift #2: Observer and Memento :
https://www.appcoda.com/design-pattern-behavorial/
[4] A Design Pattern Story in Swift – Chapter 17: Memento
: http://audreyli.me/2015/07/15/a-design-pattern-story-in-
swift-chapter-17-memento/
[5] How to Use the Memento Pattern : https://
aruniphoneapplication.blogspot.com/2016/12/the-memento-
pattern.html

References
[6] [Design Pattern] 메멘토(Memento) 패턴 - 디자인 패턴 :
https://palpit.tistory.com/205
[7] Design Patterns - Memento Pattern : https://
www.tutorialspoint.com/design_pattern/
memento_pattern.htm
[8] Design Pattern: Memento Pattern : https://viblo.asia/
p/design-pattern-memento-pattern-eW65GDPOKDO
[9] 메멘토 패턴 : https://ko.wikipedia.org/wiki/메멘토_패턴
[10] Memento Design Pattern : https://
sourcemaking.com/design_patterns/memento

[Swift] Memento

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