sclass RecursiveObjectSize {
  long size;
  new SimpleStack stack;
  Set seen = new CompactIdentityHashSet; // add objects here to ignore them
  Set<Field> fieldsToIgnore;
  Set<S> realmsToIgnore;
  
  swappable void onNewObject(O o) {}
  swappable void onSizeChanged() {}
  
  void incSize(long n) {
    size += n;
    onSizeChanged();
  }
  
  void recurse(O o) {
    if (o == null) ret;
    stack.add(o);
    
    while ping (nempty(stack))
      step(popLast(stack));
  }
  
  void step(O o) {
    if (!seen.add(o)) ret;
    if (guessDeepObjectSize_shouldIgnoreObject(o)) ret;
    onNewObject(o);
  
    if (realmsToIgnore != null && contains(realmsToIgnore, getRealm(o))) ret;
  
    ifdef guessDeepObjectSize_recursive_debug
      print("gos: " + getClassName(o));
    endifdef
    if (o instanceof Class) ret;
  
    if (isArray(o)) {
      int len;
      if (o instanceof O[]) {
        // len is computed correctly by unsafe_sizeOf
        len = unsafe_sizeOf(o);
        for (O x : (O[]) o)
          if (x != null && !seen.contains(x)) stack.add(x);
      } else
        len = inMemorySizeOfPrimitiveArray(o);
      size += len;
      ret;
    }
    
    incSize(unsafe_sizeOf(o));
    
    if (sizeCalculation_shouldSkipObject(o)) ret;
    
    for (Field f : nonStaticNonPrimitiveFieldObjects(o)) {
      if (contains(fieldsToIgnore, f)) continue;
      O x;
      try {
        x = f.get(o);
      } catch e {
        print("Error trying to access " + f + ": " + e);
        continue;
      }
      if (x != null && !seen.contains(x)) {
        stack.add(x);
        ifdef guessDeepObjectSize_recursive_debug
          print("gos field " + f + ": " + getClassName(x));
        endifdef
      }
    }
  
    //fail("can't handle object type: " + className(o));
  }
}