How to Serialize derived class to JSON object? #2199

class A {
 double Aa;
 double Ab;
class B : public A{
  int Ba;
  int Bb;
What have you tried?
I'm trying to create a JSON object like this:
B = {
 "Aa": 1.0,
 "Ab": 2.0,
 "Ba": 3,
 "Bb": 4
Can you provide a small code example?
inline void to_json( nlohmann::json& JSON, const A& a ) {
  JSON = { "Aa", a.Aa, "Ab", a.Ab };
inline void to_json( nlohmann::json& JSON, const B& b ) {
 // how to call the base class(A)'s to_json and from_json function?
  JSON = { "Ba", b.Ba, "Bb", b.Bb };
Please help me know how to call the base class's to_json and from_json function.
Describe which system (OS, compiler) you are using.

LLVM 3.8.1
Describe which version of the library you are using (release version, develop branch).

Fairly recent from master branch.