Return JsonDocument from class methods

[Laxilef]

Hi,

Question about optimization when returning JsonDocument from class methods. Let's say there is code:

JsonDocument Bot::getUpdates(long offset, unsigned short limit) {
  JsonDocument payload;
  payload["offset"] = offset;
  payload["limit"] = limit;

  unsigned short timeout = 0;
  if (this->longPollTime > 0) {
    payload["timeout"] = this->longPollTime;
    timeout = this->longPollTime * 1000u + this->timeout;
  }

  auto response = this->sendRequest("POST", "getUpdates", payload, timeout);
  if (!response.isNull() && response.is<JsonArray>()) {
    // some code
  }

  return response;
}

JsonDocument Bot::getUpdates(long offset) {
  return this->getUpdates(offset, this->messagesLimit);
}

JsonDocument Bot::getUpdates() {
  return this->getUpdates(this->offset + 1, this->messagesLimit);
}

In the first Bot::getUpdates() method I create a JsonDocument and the other methods are helpers. If I understand correctly, then every time the JsonDocument will be copied at each nesting level and create an extra load? The problem is that there can be more nesting levels. Would it be more correct to pass JsonDocument by reference to a method or is there a more elegant way? Thank you!

[bblanchon]

Hi @Laxilef,

The second and third getUpdates() overloads won't create copies of the returned JsonDocument because of the copy elision mechanism. Even if copy elision didn't trigger, JsonDocument is move-contructible, so it would not produce a copy.

Passing by reference would work, too, but it would be less elegant.

Best regards, Benoit

[Laxilef]

Thanks!