fbb_.AddOffset(SignatureDef::VT_SIGNATURE_KEY, signature_key);
  }
  void add_subgraph_index(uint32_t subgraph_index) {
    fbb_.AddElement<uint32_t>(SignatureDef::VT_SUBGRAPH_INDEX, subgraph_index, 0);
  }
  explicit SignatureDefBuilder(::flatbuffers::FlatBufferBuilder &_fbb)
        : fbb_(_fbb) {
    start_ = fbb_.StartTable();
  }