ExpirationCache outline.

ExpirationCache.Outline.cs

/// <summary>
/// Simple LRU cache with expiring elements.
/// </summary>
public class ExpirationCache<TKey, TValue> where TValue : class
{
  private readonly Dictionary<TKey, LinkedListNode<KeyValuePair<TKey, TimeStamped<TValue>>>> _dict 
    = new Dictionary<TKey, LinkedListNode<KeyValuePair<TKey, TimeStamped<TValue>>>>();
  private readonly LinkedList<KeyValuePair<TKey, TimeStamped<TValue>>> _list 
    = new LinkedList<KeyValuePair<TKey, TimeStamped<TValue>>>();
  private readonly TimeSpan _lifetime;

  ...
}