Brian Braatz wrote:
HAHAHAHA
Nevermind.
Just when I was about to post? Anyways, concerning your original message:
template <class type_t, class sequence_t> struct copy_col_if_in_dest : public if_< typename is_same< typename deref<typename boost::mpl::find<sequence_t, type_t>::type >::type, type_t>,
do_copy_col,
do_not_copy_col>::type { };
This code has a problem when type_t is not in sequence_t: the past-the-end iterator gets dereferenced. I wrote a short program to do what you want (it's more explicit, it uses mpl::contains<>): #include <boost/mpl/vector.hpp> #include <boost/mpl/if.hpp> #include <boost/mpl/contains.hpp> namespace mpl = boost::mpl; struct do_copy_col {}; struct dont_copy_col {}; template<typename T, typename Seq> struct copy_col_if_in_dest : mpl::if_< mpl::contains<Seq, T>, do_copy_col, dont_copy_col >::type { }; int main() { typedef mpl::vector<char, short, int, long> v; do_copy_col do_copy = copy_col_if_in_dest<int, v>(); dont_copy_col dont_copy = copy_col_if_in_dest<bool, v>(); return 0; }