AMDG Joel FALCOU wrote:
I started porting over some old codes that used hand-made MPL<->concrete object code to Fusion. I'm currently trying to have the following to work with no results so far :
Strange as it may seem, fusion::transform is not the right tool in this case, mpl::transform is what you want. fusion::transform is lazy. It returns a transform_view. mpl::transform works because fusion sequences /are/ mpl sequences. The default behavior of mpl::transform is to preserve the input sequence type. i.e. transforming an mpl::vector gives an mpl::vector, transforming an mpl::list gives an mpl::list, and transforming a fusion::vector gives a fusion::vector. #include <boost/fusion/include/vector.hpp> #include <boost/fusion/include/mpl.hpp> #include <boost/fusion/include/at.hpp> #include <boost/type_traits/add_reference.hpp> #include <boost/type_traits/add_const.hpp> #include <boost/type_traits/function_traits.hpp> #include <boost/mpl/transform.hpp> #include <boost/mpl/vector.hpp> #include <boost/mpl/back_inserter.hpp> namespace bf = boost::fusion; namespace mpl = boost::mpl; struct make_arg { template<class T> struct apply { typedef typename boost::add_reference< typename boost::add_const<T>::type >::type type; }; }; template<class Args> struct tree { typedef Args children; typedef typename mpl::transform<Args, make_arg>::type contents; template<class T0,class T1> tree( const T0& t0 , const T1& t1 ) : mArgs(t0, t1) {} template<size_t I> typename bf::result_of::at_c<contents,I>::type get() const { return bf::at_c<I>(mArgs); } contents mArgs; }; int main() { int k = 3; float u = 7.2f; tree< bf::vector<int, float> > tree(k, u); } In Christ, Steven Watanabe