Hi, (I keep struggling with Boos.Fusion.) How do I deduce the type of the vector resulting from the transformation of another vector? I have a source vector of different types, e.g. vector<quantity<si::length>, quantity<si::mass>, quantity<si::time>
and I have a transformation that is well defined and returns another type depending on the original type. The question is how do I generate a vector type that is the result of the given transformation. I though that result_of::transform was the function to obtain the result but it turns not because it returns a type transform_view instead of a vector. vector< ... > v1; T? v2(transform(v1, transformation())); i.e. what is the type of T as a fusion::vector as deduced from the type of v1 and the transformation type? -- Thank you, Alfredo-- Below is the illustrative code: #include<boost/array.hpp> #include <boost/fusion/container.hpp> #include <boost/fusion/algorithm/transformation/zip.hpp> #include <boost/units/systems/si.hpp> #include<iostream> using std::clog; using std::endl; using namespace boost::fusion; using namespace boost::units; // this is the transformation struct divide{ template <typename SignatureT> struct result; template<class Q> struct result<divide(Q const&)>{ typedef typename divide_typeof_helper<Q, quantity<si::time> >::type type; }; template<typename Q> typename result<divide(Q const&)>::type operator()(Q const& q) const { return q/quantity<si::time>(1.*si::second); } }; int main(){ typedef vector< quantity<si::length>, quantity<si::mass>, quantity<si::time> > source_type ; source_type v1(1.*si::meter, 2.*si::kilogram, 3.*si::second); clog << "v1: " << at_c<0>(v1) << ", "<< at_c<1>(v1) << ", " << at_c<2>(v1) << endl; // how can I deduce the result_type from the type "divide"? // here manually defined typedef vector< divide_typeof_helper<quantity<si::length>, quantity<si::time>
::type, divide_typeof_helper<quantity<si::mass>, quantity<si::time> ::type, divide_typeof_helper<quantity<si::time>, quantity<si::time> >::type > result_type ;
result_type v2( boost::fusion::transform(v1, divide() ) ); clog << "v2: " << at_c<0>(v2) << ", "<< at_c<1>(v2) << ", " << at_c<2>(v2) << endl; return 0; }