public void Dispose()
 {
     _parent?.Dispose();
     _parent = null;
     _src?.Dispose();
     _src = default;
     Pool <AppendExprEnumerator> .Return(this);
 }
 public AppendExprEnumerator Init(IPoolingEnumerator src, AppendExprEnumerable <T> parent, T element)
 {
     _src       = src;
     _parent    = parent;
     _element   = element;
     _overcount = 0;
     return(this);
 }