AMDG Istvan Buki wrote:
Dear Boost experts,
I'm trying to copy data between different types of fusion sequences with limited success. The example below shows what I'm trying to achieve.
<snip> Does fusion provide a way to achieve what I'm trying to do?
The elements of the map are fusion pair. You need to extract the second element. #include <boost/fusion/include/vector.hpp> #include <boost/fusion/include/map.hpp> #include <boost/fusion/include/pair.hpp> #include <boost/fusion/include/transform.hpp> namespace fields { struct i; struct l; struct d; } template<class F> struct result_of_second; template<class Self, class Arg1> struct result_of_second<Self(Arg1)> { typedef const typename Arg1::second_type& type; }; template<class Self, class Arg1> struct result_of_second<Self(Arg1&)> { typedef typename Arg1::second_type& type; }; template<class Self, class Arg1> struct result_of_second<Self(const Arg1&)> { typedef const typename Arg1::second_type& type; }; struct second { template<class F> struct result { typedef typename result_of_second<F>::type type; }; template<class T> typename T::second_type& operator()(T& t) const { return(t.second); } template<class T> const typename T::second_type& operator()(const T& t) const { return(t.second); } }; int main() { using namespace boost::fusion ; typedef map< pair<fields::i, int>, pair<fields::l, long>, pair<fields::d, double> > map_type; typedef vector<int, long, double> vect_t; vect_t tup1(1, 2, 3.0); map_type m = tup1; vect_t tup2 = transform(m, second()); // expected result: tup1 == tup2 }
As a side question, I was wondering whether it is possible to synthetize the vect_t type from map_type (with MPL?)
Indeed it is possible, typedef result_of::as_vector< mpl::transform< map_type, result_of::second<mpl::_1>, mpl::back_inserter<mpl::vector0<> > >::type
::type vect_t;
In Christ, Steven Watanabe