Hidden Columns in Gtk::TreeView

[Nathan Hüsken <gtkmm lonely-star org>]

Hello together,
I want to add some extra information to every row in Gtk::TreeView. The 
tutorial says:

"Hidden" Columns
You might want to associate extra data with each row. If so, just add 
it as a Model
column, but don't add it to the View.

So I want information from the class "may_class" in a hidden column. I had

# Gtk::TreeModelColumn<my_class> data;

To my Model class and put

# add(data);

into its contructor. Compiling this program gives me a linker error:

value_custom.h:267: undefined reference to 
`rythem_pattern::rythem_pattern[in-charge]()'

What do I have to do?
Thanks

Nathan

PS: I accidently sent this message to 
gtkmm-forge lists sourceforge net  I do not know what happened to it. I 
am sorry if I am double-posting.