How-to derive from Gtk::Builder?

[Markus Kolb <markus kolb+gtkmm tower-net de>]

Hi,

how can I derive from Gtk::Builder?
I've problems to cast the Glib::RefPtr<Gtk::Builder> to the 
G::R<Derived>:

/usr/include/glibmm-2.4/glibmm/refptr.h:237:3: error: cannot initialize 
a member
      subobject of type 'Derived *' with an rvalue of type 'Gtk::Builder 
*'
  pCppObject_ (src.operator->())


I need to overwrite
get_widget_derived(const Glib::ustring& name, T_Widget*& widget)
because there seems to be no way to get the widget name in the derived 
widget.

There is a method get_name(), but there I only get something like 
Gtk__Button
and not the unique id set in the glade file and requested with the name 
argument.

So I'd like to store the name argument when calling get_widget_derived 
from
AppBuilder in an instance variable.
The derived widget could then use the derived Builder to have access to 
the
name.

Thanks.