[gtkmm] Radiobutton get_group

[jlm <jsado attbi com>]

I'm converting a library from gtkmm 1.2 to 1.3. I've got some radio
buttons, and I thought that I simply have to change my use of group() to
be get_group(), but on this line:

blue_radio.set_group(red_radio.get_group());

I get this error:

./src/color_dialog_impl.cpp:426: initialization of non-const reference
type `class Gtk::RadioButton_Helpers::Group &'
./src/color_dialog_impl.cpp:426: from rvalue of type
`Gtk::RadioButton_Helpers::Group'
/usr/include/gtkmm-2.0/gtkmm/radiobutton.h:158: in passing argument 1 of
`Gtk::RadioButton::set_group(Gtk::RadioButton_Helpers::Group &)'

I have also tried

blue_radio.set_group(*red_radio.get_group());

blue_radio.set_group(&red_radio.get_group());

I've looked at the tutorial, but it appears to still be focused on gtkmm
1.2, as it continues to use group(), which doesn't exist in 1.3.

Any help would be appreciated.

Thanks.
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