[Boost-users] C++ Template Metaprogramming - Exercise 3-6

Hi, I'm stuck at exercise 3-6 of the book. I have to write twice (see below) as a lambda expression. I don't understand why the same transformation that works for quasi fails for twice. Any help, please? #include #include #include #include #include #include #include #include #include using namespace boost; using namespace boost::mpl; using namespace boost::mpl::placeholders; template struct twice : apply::type > {}; BOOST_MPL_ASSERT(( is_same,int>::type, int**> )); template struct quasi : plus::type > {}; BOOST_MPL_ASSERT(( equal_to,int_<3> >, int_<7> > )); template struct quasi2 : apply >, F, A >::type {}; BOOST_MPL_ASSERT(( equal_to,int_<3> >, int_<7> > )); template struct twice2 : apply >, F, A >::type {}; BOOST_MPL_ASSERT(( is_same,int>::type, int**> )); - Bruno