Andrej van der Zee <mavdzee@yahoo.co.uk> writes:
Than you for the quick reply :) Now I reimplemented intersect by converting the type sequences to mpl::set and do a mpl::has_key instead of mpl::contains:
template <typename seq1, typename seq2> struct intersect { typedef typename copy<seq2 , inserter< set<>, insert< _1, _2 > > >::type set_seq2;
typedef typename copy_if<seq1 , has_key <set_seq2, _1> , back_inserter < vector<> > >::type type; };
Now I would like to optimize this and only convert to a set if the type sequence does not support mpl::has_key. How should I do this?
Ideally, we should have a metafunction that would allow you to query whether the sequence (or any other library entity) supports a particular concept (Associative Sequence in your case). In absence of that, something like the following should work: template< typename Sequence, typename Dummy = boost::mpl::false_ > struct is_Associative_Sequence : boost::mpl::false_ { }; template< typename S > struct is_Associative_Sequence< S , typename boost::mpl::has_key_impl< typename boost::mpl::sequence_tag<S>::type >::template apply<S,S>::type > : boost::mpl::true_ { }; int main(int argc, char *argv[]) { BOOST_MPL_ASSERT_NOT(( is_Associative_Sequence< boost::mpl::vector0<> > )); BOOST_MPL_ASSERT(( is_Associative_Sequence< boost::mpl::map0<> > )); } HTH, -- Aleksey Gurtovoy MetaCommunications Engineering