public bool TryGetValue(string key, out CachedSpanList value)
            {
                bool result = m_spans.TryGetValue(key, out value);

                if (result)
                {
                    value.HitCount++;
                }
                return(result);
            }
 public CachedSpanList this[string key]
 {
     get
     {
         CachedSpanList value = m_spans[key];
         value.HitCount++;
         return(value);
     }
     set
     {
         m_spans[key] = value;
         CleanupCache();
     }
 }