Gtk::TreeModel::get_value_vfunc() constness

[Dominique Würtz <dwuertz gmx net>]

I'm implementing a custom Gtk::TreeModel for displaying database query
results. In order to avoid storing the entire result in memory, I'm
using a caching mechanism which stores only those rows in the
neighborhood of recently queried rows. In my get_value_vfunc(), if a
requested row is not in the cache, I need to update my cache.
Unfortunately, the get_value_vfunc() is declared const and thus forbids
mutating my TreeModel object which owns the cache. Any idea how to
resolve this?

Thanks!

Dominique