The coding guidelines document (boost/more/int_const_guidelines.htm), states the following... Always use a fully qualified name to refer to an integral constant expression. For example: typedef myclass< ::boost::is_integral<some_type>::value> mytypedef; Rationale: at least one compiler (Borland's), doesn't recognise the name of a constant as an integral constant expression unless the name is fully qualified (which is to say it starts with ::). However, it appears that the same compiler (BCB6) has problems if the '::' is left in. For example... template <class T> struct Foo { typedef typename ::boost::remove_reference< T >::type type; typedef typename ::boost::add_reference< typename ::boost::add_const< type >::type >::type ref_to_const_type; }; fails to compile. Initially I thought it had something to do with typename (e.g., another BOOST_DEDUCED_TYPENAME) because, the first, simpler line compiles if I remove the "typename" keyword. Unfortunately, the following does not compile either template <class T> struct Foo { typedef ::boost::remove_reference< T >::type type; typedef ::boost::add_reference< ::boost::add_const< type >::type >::type ref_to_const_type; }; After seeing a notice on this list a few minutes ago, I decided to remove the '::' and whaddya know... template <class T> struct Foo { typedef typename boost::remove_reference< T >::type type; typedef typename boost::add_reference< typename boost::add_const< type >::type >::type ref_to_const_type; }; this compiles correctly. So, I am left scratching my head, wondering what to do if I want to use TypeTraits in a portbale manner. Thanks!