public ReverseExprEnumerator Init(PoolingList <T> src, ReverseExprEnumerable <T> parent)
 {
     _position = src.Count;
     _src      = src;
     _parent   = parent;
     return(this);
 }
            public void Dispose()
            {
                _parent?.Dispose();
                _parent   = default;
                _src      = default;
                _position = default;

                Pool <ReverseExprEnumerator> .Return(this);
            }