virtual public void CopyTo(VirtualCollection <T> target)
 {
     Flush();
     GZipHelper.CopyStream(StoreStream, target.StoreStream);
     IndexBlock[] indexList = new IndexBlock[Index.Count];
     Index.CopyTo(indexList);
     target.Index    = new List <IndexBlock>(indexList);
     target.Transfer = Transfer;
 }
        override public void CopyTo(VirtualCollection <T> target)
        {
            if (!this.GetType().IsAssignableFrom(target.GetType()))
            {
                base.CopyTo(target);
                return;
            }
            PersistenList <T> targetPersisten = (PersistenList <T>)target;

            GZipHelper.CopyStream(indexStream, targetPersisten.indexStream);
            base.CopyTo(target);
        }