public LinkedDictionaryEnumerator(AbstractLinkedDictionary <TKey, TValue> parent, bool forward)
 {
     _parent  = parent;
     _forward = forward;
     _current = null;
     _updates = parent.Updates;
 }
 public DictionaryValues(AbstractLinkedDictionary <TKey, TValue> parent, bool forward)
 {
     _parent  = parent;
     _forward = forward;
 }