Hello, I've just tried to compile a small piece of code using mpl::switch_ starting from an example Aleksey Gurtovoy sent to this list a while ago. I slightly modified the code to use the boost::is_same<T,U> template but I can't make it compile. On the other hand, if I comment out the line in the switch_body containing the is_same template, it compile without any problem. I spent the whole day on this and I'm lost. Any help would be welcome. Thanks, Istvan PS: I'm using boost 1.30.2 and g++ 3.3.3. #include "boost/mpl/vector.hpp" #include "boost/mpl/switch.hpp" #include "boost/mpl/project1st.hpp" #include "boost/mpl/pair.hpp" #include "boost/mpl/always.hpp" #include "boost/mpl/bool.hpp" #include "boost/mpl/assert_is_same.hpp" #include "boost/type_traits/remove_reference.hpp" #include "boost/type_traits/add_const.hpp" #include "boost/type_traits/is_pointer.hpp" #include "boost/type_traits/is_reference.hpp" #include "boost/type_traits/is_same.hpp" using namespace boost::mpl ; using boost::mpl::_ ; struct MyType { typedef int type ; } ; int main() { typedef vector< pair< boost::is_pointer<_1>, _1 > // If the following line is commented out it compile. , pair< boost::is_same<_1, _1 >, boost::add_const<_1> > , pair< boost::is_reference<_1>, boost::remove_reference<_1> > , pair< always<bool_<true > >, boost::add_const<_1> > > switch_body; typedef switch_< switch_body, char& >::type t1; typedef switch_< switch_body, int* >::type t2; typedef switch_< switch_body, int >::type t3; BOOST_MPL_ASSERT_IS_SAME(t1, char); BOOST_MPL_ASSERT_IS_SAME(t2, int*); BOOST_MPL_ASSERT_IS_SAME(t3, int const); }