How do you implement the memento pattern?

Question

Accepted Answer

**Memento** — capture and restore state.

**Implementation:**
```csharp
public class Memento
{
    public string State { get; }
    public Memento(string state) => State = state;
}

public class Originator
{
    public string State { get; set; }
    public Memento Save() => new(State);
    public void Restore(Memento m) => State = m.State;
}

public class Caretaker
{
    private readonly Stack<Memento> _history = new();
    public void Save(Originator o) => _history.Push(o.Save());
    public void Undo(Originator o) => o.Restore(_history.Pop());
}
```

**Key:** Memento for undo/redo.

C#: How do you implement the memento pattern?