public void Dispose()
 {
     _parent?.Dispose();
     _parent = null;
     _src?.Dispose();
     _src = default;
     Pool <CastExprEnumerator> .Return(this);
 }
 public CastExprEnumerator Init(IPoolingEnumerator src, CastExprEnumerable <T> parent)
 {
     _src    = src;
     _parent = parent;
     return(this);
 }