C#

public class Cache
{
  private List<IMemento> _cache = new List<IMemento>
  public void AddToCache<T>(T cacheItem)
  {
    _cache.Add(new MementoCache(cacheItem));
  }

  public T CancelChanges<T>(T cacheItem)
  {
    // Get the original item out of the cache and remove it.
    T item = _cache[...];
    _cache.Remove(...);
    return item;
  }

  internal class CacheMemento : IMemento
  {
    public void AddToCache<T>(T cacheItem)
    {
      // Save this item.
    }
  }
}