code: func (v *ComboBox) GetActiveIter() (*TreeIter, error) {
  	var cIter C.GtkTreeIter
  	c := C.gtk_combo_box_get_active_iter(v.native(), &cIter)
  	if !gobool(c) {
  		return nil, errors.New("unable to get active iter")
  	}
  	return &TreeIter{cIter}, nil
  }
docs: // GetActiveIter is a wrapper around gtk_combo_box_get_active_iter().