Hi folks, The following code compiles fine against Boost 1.34.1 and 1.35.0, but apparently not anything later. I've tried 1.36.0 and 1.39.0. I'm compiling with Microsoft's Visual C++ 2005 and 2009 compilers (the express editions if it matters). #include <boost/mpl/remove.hpp> #include <boost/mpl/vector.hpp> #include <boost/preprocessor/repetition/enum_params.hpp> #include <boost/preprocessor/repetition/enum_params_with_a_default.hpp> template<BOOST_PP_ENUM_PARAMS_WITH_A_DEFAULT(BOOST_MPL_LIMIT_VECTOR_SIZE, typename T, void)> struct X { typedef typename boost::mpl::vector<BOOST_PP_ENUM_PARAMS(BOOST_MPL_LIMIT_VECTOR_SIZE, T)>::type template_parameters; // mpl::vector of template parameters typedef typename boost::mpl::remove < template_parameters, void > ::type template_parameters_no_voids; // voids removed }; int main() { X<int> x; return 0; } The error messages using Boost 1.39.0 and Visual C++ 2005: mpl_regression.cpp M:\libs\boost\1.39.0\boost/mpl/aux_/push_back_impl.hpp(45) : error C2664: 'boost::mpl::assertion_failed' : cannot convert parameter 1 from 'boost::mpl::failed ************(__thiscall boost::mpl::push_back_impl<Tag>::apply<Sequence,T>::REQUESTED_PUSH_BACK_SPECIALIZATION_FOR_SEQUENCE_DOES_NOT_EXIST::* ***********)(Sequence)' to 'boost::mpl::assert<false>::type' with [ Tag=boost::mpl::aux::vector_tag<20>, Sequence=boost::mpl::vector20<int,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void>, T=boost::mpl::has_push_back_impl<boost::mpl::aux::vector_tag<20>> ] No constructor could take the source type, or constructor overload resolution was ambiguous M:\libs\boost\1.39.0\boost/mpl/push_back.hpp(32) : see reference to class template instantiation 'boost::mpl::push_back_impl<Tag>::apply<Sequence,T>' being compiled with [ Tag=boost::mpl::aux::vector_tag<20>, Sequence=boost::mpl::vector20<int,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void>, T=boost::mpl::has_push_back_impl<boost::mpl::aux::vector_tag<20>> ] M:\libs\boost\1.39.0\boost/mpl/aux_/has_type.hpp(20) : see reference to class template instantiation 'boost::mpl::push_back<Sequence,T>' being compiled with [ Sequence=boost::mpl::vector20<int,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void>, T=boost::mpl::has_push_back_impl<boost::mpl::aux::vector_tag<20>> ] M:\libs\boost\1.39.0\boost/mpl/aux_/push_back_impl.hpp(55) : see reference to class template instantiation 'boost::mpl::aux::has_type<T>' being compiled with [ T=boost::mpl::push_back<boost::mpl::vector20<int,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void>,boost::mpl::has_push_back_impl<boost::mpl::aux::vector_tag<20>>> ] M:\libs\boost\1.39.0\boost/mpl/push_back.hpp(43) : see reference to class template instantiation 'boost::mpl::has_push_back_impl<Tag>::apply<Seq>' being compiled with [ Tag=boost::mpl::aux::vector_tag<20>, Seq=boost::mpl::vector20<int,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void> ] M:\libs\boost\1.39.0\boost/mpl/if.hpp(63) : see reference to class template instantiation 'boost::mpl::has_push_back<Sequence>' being compiled with [ Sequence=boost::mpl::vector20<int,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void> ] M:\libs\boost\1.39.0\boost/mpl/remove.hpp(48) : see reference to class template instantiation 'boost::mpl::if_<T1,T2,T3>' being compiled with [ T1=boost::mpl::has_push_back<boost::mpl::vector20<int,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void>>, T2=boost::mpl::aux::remove_impl<boost::mpl::vector20<int,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void>,void,boost::mpl::back_inserter<boost::mpl::clear_impl<boost::mpl::aux::vector_tag<20>>::apply<boost::mpl::vector20<int,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void>>::type>>, T3=boost::mpl::aux::reverse_remove_impl<boost::mpl::vector20<int,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void>,void,boost::mpl::front_inserter<boost::mpl::clear_impl<boost::mpl::aux::vector_tag<20>>::apply<boost::mpl::vector20<int,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void>>::type>> ] mpl_regression.cpp(18) : see reference to class template instantiation 'boost::mpl::remove<P1,P2>' being compiled with [ P1=boost::mpl::vector20<int,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void>, P2=void ] mpl_regression.cpp(23) : see reference to class template instantiation 'X<T0>' being compiled with [ T0=int ] M:\libs\boost\1.39.0\boost/mpl/aux_/push_back_impl.hpp(45) : error C2866: 'boost::mpl::push_back_impl<Tag>::apply<Sequence,T>::mpl_assertion_in_line_6' : a const static data member of a managed type must be initialized at the point of declaration with [ Tag=boost::mpl::aux::vector_tag<20>, Sequence=boost::mpl::vector20<int,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void,void>, T=boost::mpl::has_push_back_impl<boost::mpl::aux::vector_tag<20>> ] Is this a problem with more recent versions of Boost, or am I doing something wrong? It looks like it's complaining because an mpl::vector of maximal static size doesn't implement push_back, but it surely shouldn't need to for a remove operation? Kind regards, Edd