void GraphConstructor::Undo() {
  for (const auto& iter : gdef_nodes_) {
    if (iter.second.node != nullptr) {
      g_->RemoveNode(iter.second.node);
    }
  }
  g_->set_versions(original_versions_);
}
void GraphConstructor::Undo() {
  for (const auto& iter : gdef_nodes_) {
    if (iter.second.node != nullptr) {
      g_->RemoveNode(iter.second.node);
    }
  }
  g_->set_versions(original_versions_);
}