Example of reflection in C++

json.cc

#define REFLECT(x) template<class R> void reflect(R& r) { r x; }

#include <string>

struct Person {
  std::string name;
  int age;

  REFLECT(
    ("name", name)
    ("age", age)
  )
};

#include <iostream>

class JSONWriter {
  std::ostream& output;
  bool needsComma;

  public:

  JSONWriter(std::ostream& output) : output(output)
  {}

  template<class T>
  auto write(T& obj) -> decltype(obj.reflect(*this), void()) {
    output << "{";
    needsComma = false;
    obj.reflect(*this);
    output << "}";
  }

  void write(int value) {
    output << value;
  }

  void write(std::string& value) {
    output << '"' << value << '"';
  }

  template<class T>
  JSONWriter& operator()(const char* name, T& field) {
    if (needsComma) {
      output << ",";
    }
    needsComma = true;
    output << name << ":";
    write(field);
    return *this;
  }

};

int main() {
  JSONWriter json(std::cout);
  Person me = { "Magnus Holm", 23 };
  json.write(me);
}

This is pretty cool! I have been looking for a simple solution like this but couldn't find anywhere...
Do you think it would be possible to have the inverse operation, i.e given a well-formed json and a Person reference a method that would populate the correct attributes onto the given object?

You should be able to use the same trick to reflect on fields, but you'd have to plug in a "real" JSON parser, parse the data into a hash-map-like structure and then fill out the data.