Program.cs

Originator<int> originator = new Originator<int>();
originator.SetState(1);

CareTaker<int> careTaker = new CareTaker<int>();
careTaker.SetMemento(originator.Redo());

Console.WriteLine(originator.GetState());

originator.SetState(2);
Console.WriteLine(originator.GetState());


originator.Undo(careTaker.GetMemento());
Console.WriteLine(originator.GetState());


record Memento<T>(T state)
{
}

class Originator<T>
{
    private T _state { get; set; }

    public T GetState() => _state;

    public void SetState(T state) => _state = state;

    public Memento<T> Redo() => new(_state);

    public void Undo(Memento<T> memento) => _state = memento.state;
}

class CareTaker<T>
{
    private Memento<T> _memento;

    public Memento<T> GetMemento() => _memento;

    public void SetMemento(Memento<T> memento) => _memento = memento;
}