No no no, this won't compile. Write the complete code, with all the includes, main function, etc. And write it correctly, iterating over the data, accessing the object fields.
#include <fstream>
#include <json.hpp>
int main()
{
std::ifstream input_file("data.json");
nlohmann::json data;
data << input_file;
for (auto obj : data)
std::cout << obj["x"] << ',' << obj["y"] << '\n';
}If we were talking about language constructs/semantics or flow-control abilities, I'd have a very different opinion - but not having a json decoder builtin, is no reason to use or not use a language.