How to simplify the task of write to_json function for derived class ?

[gzliudan]

If I have many derived classes which inherits the same parent class, how to simplify tasks of write to_json code for parent class?

class Base {};
void to_json(json& j, const Base& obj);

class Derived1 : public Base {}
void to_json(json& j, const Derived1& obj);

class Derived2 : public Base {}
void to_json(json& j, const Derived2& obj);

[nlohmann]

If some of the classes share code, you can call to_json of the base class explicitly, e.g. by

nlohmann::to_json(j, static_cast<Base&>(obj));

Further note there is an update function to merge/update objects.

A related issue: #2199

[gzliudan]

Thank you very much!