[gtkmm] gtkmm api design question

["Serge S. Fukanchik" <fuxx mail ru>]

Hi there,
throughout gtkmm API here and there scattered methods which accept
references to objects, but frequently they require zero value to be
passed.

For instance
Gtk::TreeView::set_cursor (const TreeModel::Path& path,	TreeViewColumn&
focus_column, bool start_editing = false);

takes reference to focus column, and documentation tells that if focus_column
is not 0 (!!!how c++ reference can be zero?) and start_editing = true we start
to edit this column. I'm wandering how one can pass focus column = 0 to this 
function? Is there some NULL gtkmm object, whith gobj() method returning 0,
which i can pass instead of "zero" reference or it is completely impossible
with gtkmm?

I do not wanna start editing here, and do not know current_focus column to
pass it. Gtk::TreeView::set_cursor(const TreeModel::Path& path) can help
me, but there is no such function.

I'm use gtk_tree_view_set_cursor with focus_column = 0 now. So is there
really some way to pass zero to such a function in gtkmm?

--
fuxx