code: func (v *RadioButton) JoinGroup(groupSource *RadioButton) {
  	var cgroup *C.GtkRadioButton
  	if groupSource != nil {
  		cgroup = groupSource.native()
  	}
  	C.gtk_radio_button_join_group(v.native(), cgroup)
  }
docs: // JoinGroup is a wrapper around gtk_radio_button_join_group().