Accessing pair in Gtk::TreeModelColumn

[Kamalpreet Grewal <grewalkamal005 gmail com>]

I am making a pair as data type of Gtk::TreeModelColumn.
Gtk::TreeModelColumn<std::pair<Glib::ustring, Glib::ustring> > col;

At some places I wish to get only first string of this pair. So I did
something like row[columns.col].first to access it. But I get an
error.

error: 'class Gtk::TreeValueProxy<std::pair<Glib::ustring,
Glib::ustring> >' has no member named 'first'

I am accessing it just like one will do with another std::pair. How
can this be achieved?

-- 
Kamalpreet Kaur Grewal
Blog: http://kamalpreetgrewal.com/