Drop CLR type on void * and vice versa

Question

How to correctly convert a CLR type, say Foo^, to void*and back after a while?

---

The script has some unmanaged code in a DLL that can be summarized as

class Handler {
  void* _obj;
  void (*_call)(void* obj, int detail);

  void handle_event() { _call(_obj, 1234); }
public:
  void set_object(void* obj) { _obj = obj; }
  void set_callback(void(*callback)(void*,int)) { _call = callback; }
};

I want to save a CLR object in a field Handler _obj. How to implement it, taking into account that the GC can move the CLR object? ( pin_ptr? gcroot?)

static void event_callback(void* obj, int detail) {
   Foo^ clr_obj = undo_magic(obj);
//                ^^^^^^^^^^ how?
   clr_obj->DoStuff(detail);
}

public ref class Foo {
   Handle* h;
public:
   void Start() {
     h = new Handler;
     void* obj = do_magic(this);
//               ^^^^^^^^ how?
     h->set_object(obj);
     h->set_callback(event_callback);
   }
   ...
}

Answer 1

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