[jira] [Created] (MESOS-3580) Refactor 'protobuf' to accept project function

["Klaus Ma (JIRA)" <ji...@apache.org>]

Klaus Ma created MESOS-3580:
-------------------------------

             Summary: Refactor 'protobuf' to accept project function
                 Key: MESOS-3580
                 URL: https://issues.apache.org/jira/browse/MESOS-3580
             Project: Mesos
          Issue Type: Bug
          Components: stout
            Reporter: Klaus Ma
            Assignee: Klaus Ma


During the code review of MESOS3405, [~alex-mesos] realized that we use the same pattern again and again, for example:

    JSON::Array array;
    array.values.reserve(status.network_infos().size()); // MESOS-2353.
    foreach (const NetworkInfo& info, status.network_infos()) {
      array.values.push_back(model(info));
    }
    object.values["network_infos"] = std::move(array);

We cannot use newly added JSON::protobuf() here, because a different way for rendering JSON from protobuf is used. Without digging deep inside, I know three ways how we create a JSON out of a proto in our codebase:
- wrap in JSON::Protobuf() for individual messages;
- wrap in one of the model() family functions;
- pass as it is for built-in types.

The proposed conversion function covers one of the possible ways. How about add one more convertion? Something like:

template <typename T>
Array protobuf(const google::protobuf::RepeatedPtrField<T>& repeated,
    const lambda::function<JSON::Object>(const T&)>& converter)
{
  static_assert(std::is_convertible<T*, google::protobuf::Message*>::value,
                "T must be a google::protobuf::Message");
  JSON::Array array;
  array.values.reserve(repeated.size());
  foreach (const T& elem, repeated) {
    array.values.push_back(converter(elem));
  }

  return array;
}


Then the snippet above could be rewritten as:

object.values["network_infos"] = std::move(JSON::protobuf(status.network_infos(), [](const NetworkInfo& info) { return model(info); });




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