Efficient way to set a `json` object as value into another `json` key

[ibc]

I've a function somewhere that creates and returns a json data object, and I want to use such a json data as value into the "data" key of another json response object.

Currently I'm doing something like this, and just wonder whether there is a way to avoid the data copy:

json response = json::object();

response["id"] = this->id;
response["data"] = this->foo.GetJsonData(); // This produces a `json`.

this->DoSomethingWith(response);

I expect there is no magic here and the json data returned by foo.GetJsonData() is being mem copied into response["data"]. May be I should, instead, do something like this?:

json response = json::object();

response["id"] = this->id;

// Allocate empty object for "data" key:
response["data"] = json::object();

// Get iterator to "data" object:
auto dataIterator = response.find("data"); 

// Pass the iterator to `foo.GetJsonData()` so it adds its keys/values into it.
this->foo.GetJsonData(dataIterator);

this->DoSomethingWith(response);

Then, void Foo::GetJsonData(json::iterator dataIterator) would do something like:

(*dataIterator)["foo"] = "FOO";
(*dataIterator)["bar"] = 1234;

Does it make any sense?

[gregmarr]

Yes, this would definitely be more efficient:

void Foo::GetJsonData(json &storeDataInHere) {
    storeDataInHere["foo"] = "FOO";
    storeDataInHere["bar"] = 1234;
}

this->foo.GetJsonData(response["data"]);

[ibc]

Already using it, thanks :)

[ibc]

Sorry, just a question: Is there any way to optimize this?:

// Allocate empty object for "data" key:
response["data"] = json::object();

// Get iterator to "data" object:
auto dataIterator = response.find("data"); 

Obviously the response.find("data") is internally checking whether "data" exists in the map and so on. Is there something as follows?:

// Allocate empty object for "data" key and get its iterator:
auto dataIterator = response.addKeyValue("data", json::object());

...where addKeyValue() is a method that receives a key and value and returns a iterator to the new created value.

Obviously it does not exist, just wondering if it makes sense :)

[gregmarr]

Read what I posted above again, and I think you'll find your answer. Maybe this will help:

json response = json::object();
response["id"] = this->id;
this->foo.GetJsonData(response["data"]);

[ibc]

Ok, so you are directly passing response["data"] to foo.GetJsonData(), this is, you are creating a "data" key in-place, great!

I have to remove some asserts that check storeDataInHere.is_object() to make it work, but nothing else. Thanks!