TF_AttrMetadata metadata;
  const auto* attr = GetAttrValue(oper, attr_name, status);
  if (!status->status.ok()) return metadata;
  switch (attr->value_case()) {
#define SINGLE_CASE(kK, attr_type, size_expr) \
  case tensorflow::AttrValue::kK:             \
    metadata.is_list = 0;                     \
    metadata.list_size = -1;                  \
    metadata.type = attr_type;                \