Why should you care?

ShopNest seller “product editor” needs undo after a bad edit.

See it live — copy this example

Paste into a C# console or class library project and run dotnet run.

public sealed class ProductEditor
{
    public string Title { get; set; } = "";
    public decimal Price { get; set; }
    public ProductMemento Save() => new(Title, Price);
    public void Restore(ProductMemento m) { Title = m.Title; Price = m.Price; }
}
public sealed record ProductMemento(string Title, decimal Price);
public sealed class EditorHistory
{
    private readonly Stack<ProductMemento> _undo = new();
    public void Push(ProductMemento m) => _undo.Push(m);
    public ProductMemento Pop() => _undo.Pop();
}

var ed = new ProductEditor { Title = "Tee", Price = 499 };
var hist = new EditorHistory();
hist.Push(ed.Save());
ed.Title = "Tee Broken";
ed.Restore(hist.Pop());
Console.WriteLine(ed.Title);

Run Example »

Edit the code below and click Run to see the result in Toolliyo’s live editor.

What happened?

• Save captures state; Restore applies it.
• History holds mementos.
• Keep mementos immutable snapshots.

Practice next

1. Undo the bad title change.
2. Push two snapshots and undo twice.
3. Do not let UI mutate memento fields.
4. Add redo stack.
5. Include Tags in the memento.

Remember

Snapshot + restore. Opaque to outsiders. Great for undo.

ShopNest product editor undo

Seller hits Undo after a typo.

Outcome: Previous title/price restored instantly.