sclass PersistentManagedObjects_v1<A extends AbstractManagedObject> {
  replace Addr with int.
  replace BoxedAddr with Int.
  
  ManagedIntObjects_v1 mem;
  IF1<BoxedAddr, A> makeUserObject; // user needs to fill this
  Root root;
  
  final static int
    TYPE_STRING = -1,
    TYPE_INTARRAY = -2,
    TYPE_ROOT = -3;
  
  class Root extends AbstractManagedObject {
    final static int
      ofs_type = 0,
      ofs_version = 1,
      ofs_freeListPtr = 2,
      ofs_userDataPtr = 3;
    final static int objectSize = ofs_userDataPtr+1;
    
    // initialize as wrapper for existing object
    // or create new when addr == 0
    *(Addr addr) {
      if (addr != 0)
        setAddr(addr);  
      else
        create();
    }
    
    // initialize as new object
    *() { create(); }
    
    void create { setAddr(mem.alloc(objectSize)); init(); }
    
    void init { type(TYPE_ROOT); version(1); }
    
    // getters + setters
    int type() { ret mem.get(addr+ofs_type); }
    void type(int x) { mem.set(addr+ofs_type, x); }
    int version() { ret mem.get(addr+ofs_version); }
    void version(int x) { mem.set(addr+ofs_version, x); }
    Addr freeListPtr() { ret mem.get(addr+ofs_freeListPtr); }
    void freeListPtr(Addr x) { mem.set(addr+ofs_freeListPtr, x); }
    Addr userDataPtr() { ret mem.get(addr+ofs_userDataPtr); }
    void userDataPtr(Addr x) { mem.set(addr+ofs_userDataPtr, x); }
    A userData() {
      ret makeUserObject.get(userDataPtr());
    }
    void userData(A userData) { userDataPtr(userData == null ? 0 : userData.addr); }
    
    void setAddr(Addr newAddr) {
      addr = newAddr; mem.setRootField(addr);
    }

    // GC handling
    public void scanForCollection(IManagedObjectCollector gc) {
      gc.noteObject(addr, objectSize, lambda1 setAddr);
      gc.notePointer(addr+ofs_freeListPtr);
      gc.notePointer(addr+ofs_userDataPtr);
      gc.noteIntArray(freeListPtr());
      var userData = userData();
      userData?.scanForCollection(gc);
    }
  }
  
  *(ManagedIntObjects_v1 *mem, IF1<BoxedAddr, A> *makeUserObject) {
    Addr rootPtr = mem.getRootField();
    print(+rootPtr);
    root = new Root(rootPtr);
    mem.freeList = FreeList.fromIntArray(mem.readIntArray(root.freeListPtr()));
  }
  
  void persist {
    mem.freeIntArray(root.freeListPtr());
    root.freeListPtr(mem.newIntArray(mem.freeList.toIntArray()));
  }
  
  A get aka getUserData() {
    ret root.userData();
  }
  
  void set aka setUserData(A userData) {
    root.userData(userData);
  }
}