Hello, I'm not really sure but isn't there a friend declaration missing in the fixed_mapping class? Given the following code: template< ... > class fixed_mapping { typedef std::pair<Key,Value> elem_type; ... struct p1 : public std::binary_function<elem_type,Key,bool> { bool operator()( elem_type const& x, Key const& y ) const { return Compare()( x.first, y ); } }; ... }; doesn't this require p1 to be a friend of fixed mapping to be able to access elem_type in it's operator()? This would then give: template< ... > class fixed_mapping { typedef std::pair<Key,Value> elem_type; ... struct p1; friend struct p1; ... struct p1 : public std::binary_function<elem_type,Key,bool> { bool operator()( elem_type const& x, Key const& y ) const { return Compare()( x.first, y ); } }; ... }; Markus