[MESOS-3580] Refactor 'protobuf' to accept project function

• Type: Bug
• Status: Resolved
• Priority: Major
• Resolution: Won't Fix
• Component/s: stout
• Labels: refactor stout
• Assignee: Unassigned
• Reporter: Klaus Ma
• Created: 05/Oct/15 02:05
• Updated: 02/Nov/19 22:12
• Resolved: 02/Nov/19 22:12

Description

During the code review of MESOS-3405, 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); });