If you intend to make boost::iterator_core_access friend the friend declaration is indeed wrong as Dave suggested. There is basically no name lookup for friend declarations. I.e. a non qualified name in a friend declaration either declares a class/function in the current namespace or "refers" to such a thing that is in the current namespace.
of boost you need to say friend class boost::iterator_core_accessIn order to make boost::iterator_core_access friend from a sub namespace.
HTH
Thomas
You basically saying that following is incorrect: namespace out { class A {}; namespace in { class B { friend class A; }; } // namespace in } // namespace out I bit strange. After all at the point of friend statement there is symbol A that fit the bill. Why exactly standard doing that? Gennadiy.