특정한 시점으로 rollback 할 수 있음

Memento

class Memento
{
    let balance : Int
    init(_ balance: Int)
    {
        self.balance = balance
    }
}


class BanckAccount: CustomStringConvertible
{
    private var balance : Int
    
    init(_ balance: Int)
    {
        self.balance = balance
    }
    
    func deposit(_ amount: Int) -> Memento
    {
        balance += amount
        return Memento(balance)
    }
    
    func restore(_ m: Memento)
    {
        balance = m.balance
    }
    
    var description: String
    {
        return "Balance = \(balance)"
    }
}


func main()
{
    var ba = BanckAccount(400)
    let m1 = ba.deposit(50) // 450
    let m2 = ba.deposit(100) // 550
    print(ba)
    
    // restore to m1
    ba.restore(m1)
    print(ba)
    
    // restore to m2
    ba.restore(m2)
    print(ba)
}

Undo and Redo

class BanckAccount: CustomStringConvertible
{
    private var balance : Int
    private var changes = [Memento]()
    private var current = 0
    
    init(_ balance: Int)
    {
        self.balance = balance
        changes.append(Memento(balance))
    }
    
    func deposit(_ amount: Int) -> Memento
    {
        balance += amount
        let m = Memento(balance)
        changes.append(m)
        current += 1
        return m
    }
    
    func restore(_ m: Memento?)
    {
        if let mm = m
        {
            balance = mm.balance
            changes.append(mm)
            current = changes.count - 1
        }
        
    }
    
    func undo() -> Memento?
    {
        
        if current > 0
        {
            current -= 1
            let m = changes[current]
            balance = m.balance
            return m
        }
        return nil
        
    }
    
    func redo() -> Memento?
    {
        if (current+1) < changes.count
        {
            current += 1
            let m = changes[current]
            balance = m.balance
            return m
        }
        return nil
    }
    
    var description: String
    {
        return "Balance = \(balance)"
    }
}


func main()
{
    var ba = BanckAccount(400)
    let m1 = ba.deposit(50) // 450
    let m2 = ba.deposit(100) // 550
    print(ba)

    ba.undo()
    print("Undo 1 : \(ba)")
    ba.undo()
    print("Undo 2 : \(ba)")

    ba.redo()
    print("Redo 1 : \(ba)")
}