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Sergey Leschev
Sergey Leschev

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πŸ’Ύ Memento Pattern

Memento Pattern


The memento pattern is used to capture the current state of an object and store it in such a manner that it can be restored at a later time without breaking the rules of encapsulation.

Github https://github.com/sergeyleschev/design-patterns

Example

typealias Memento = [String: String]
Originator
protocol MementoConvertible {
    var memento: Memento { get }
    init?(memento: Memento)
}

struct GameState: MementoConvertible {

    private enum Keys {
        static let chapter = "com.valve.halflife.chapter"
        static let weapon = "com.valve.halflife.weapon"
    }

    var chapter: String
    var weapon: String

    init(chapter: String, weapon: String) {
        self.chapter = chapter
        self.weapon = weapon
    }

    init?(memento: Memento) {
        guard let mementoChapter = memento[Keys.chapter],
              let mementoWeapon = memento[Keys.weapon] else {
            return nil
        }

        chapter = mementoChapter
        weapon = mementoWeapon
    }

    var memento: Memento {
        return [ Keys.chapter: chapter, Keys.weapon: weapon ]
    }
}
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Caretaker

enum CheckPoint {

    private static let defaults = UserDefaults.standard

    static func save(_ state: MementoConvertible, saveName: String) {
        defaults.set(state.memento, forKey: saveName)
        defaults.synchronize()
    }

    static func restore(saveName: String) -> Any? {
        return defaults.object(forKey: saveName)
    }
}
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Usage

var gameState = GameState(chapter: "Black Mesa Inbound", weapon: "Crowbar")

gameState.chapter = "Anomalous Materials"
gameState.weapon = "Glock 17"
CheckPoint.save(gameState, saveName: "gameState1")

gameState.chapter = "Unforeseen Consequences"
gameState.weapon = "MP5"
CheckPoint.save(gameState, saveName: "gameState2")

gameState.chapter = "Office Complex"
gameState.weapon = "Crossbow"
CheckPoint.save(gameState, saveName: "gameState3")

if let memento = CheckPoint.restore(saveName: "gameState1") as? Memento {
    let finalState = GameState(memento: memento)
    dump(finalState)
}
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Sources: Github

Behavioral
In software engineering, behavioral design patterns are design patterns that identify common communication patterns between objects and realize these patterns. By doing so, these patterns increase flexibility in carrying out this communication.
Source: wikipedia.org


🐝 Chain Of Responsibility
πŸ‘« Command Pattern
🎢 Interpreter Pattern
🍫 Iterator Pattern
πŸ’ Mediator Pattern
πŸ’Ύ Memento Pattern
πŸ‘“ Observer Pattern
πŸ‰ State Pattern
πŸ’‘ Strategy Pattern
πŸ“ Template Method
πŸƒ Visitor Pattern
🌰 Abstract Factory
πŸ‘· Builder Pattern
🏭 Factory Method
πŸ”‚ Monostate Pattern
πŸƒ Prototype Pattern
πŸ’ Singleton
πŸ”Œ Adapter Pattern
πŸŒ‰ Bridge Pattern
🌿 Composite Pattern
🍧 Decorator Pattern
🎁 Facade Pattern
πŸƒ Flyweight Pattern
β˜” Protection Proxy
🍬 Virtual Proxy


Contacts
I have a clear focus on time-to-market and don't prioritize technical debt. And I took part in the Pre-Sale/RFX activity as a System Architect, assessment efforts for Mobile (iOS-Swift, Android-Kotlin), Frontend (React-TypeScript) and Backend (NodeJS-.NET-PHP-Kafka-SQL-NoSQL). And I also formed the work of Pre-Sale as a CTO from Opportunity to Proposal via knowledge transfer to Successful Delivery.

πŸ›©οΈ #startups #management #cto #swift #typescript #database
πŸ“§ Email: sergey.leschev@gmail.com
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πŸ‘‹ Github: https://github.com/sergeyleschev
🌎 Website: https://sergeyleschev.github.io
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🌎 Quora: https://quora.com/sergey-leschev
🌎 Medium: https://medium.com/@sergeyleschev
πŸ–¨οΈ PDF Design Patterns: Download

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