+= issue with multiple redirection.

[sreerajchundayil]

Doing += with js2["key"]["num"] is an error while runtime.

Error message is : what(): [json.exception.type_error.308] cannot use push_back() with number

But it works fine with js1["num"].
Why are they different, it's against the intuition I think?

And is the error message relevant with the operation we are doing?

    int main()
    {
      json js1,js2;
    
      js1["num"] = 0;
      js2["key"]["num"] = 0;
    
      js1["num"] += 10;//fine
      js2["key"]["num"] += 10;//error
    }

[nlohmann]

Already the first occurrence of += yields the same exception. The library uses operator+= as synonym of push_back, and it is not usable with numbers.

If you want to use += with the stored integer, you need to make it explicit:

int main()
{
    json js1,js2;
  
    js1["num"] = 0;
    js2["key"]["num"] = 0;
  
    js1["num"].get_ref<json::number_integer_t&>() += 10;
    js2["key"]["num"].get_ref<json::number_integer_t&>() += 10;
 
    std::cout << js1 << '\n' << js2 << std::endl;
}

Output:

{"num":10}
{"key":{"num":10}}