public override IBillTypeCollectionEnumerator GetEnumerator()
            {
                IBillTypeCollectionEnumerator enumerator = null;

                rwLock.AcquireReaderLock(timeout);

                try
                {
                    enumerator = collection.GetEnumerator();
                }
                finally
                {
                    rwLock.ReleaseReaderLock();
                }

                return(enumerator);
            }
 public override IBillTypeCollectionEnumerator GetEnumerator()
 {
     return(m_collection.GetEnumerator());
 }