Re: [Boost-users] fusion tuple to pod object

4 Apr 2008


      AMDG

Ovanes Markarian wrote:
...
The fusion library seems to be the choice for handling tuple-like data
    in C++. However, for some reasons I would like to be able to
    transform a
    fusion vector into a pod object. Something like:
fusion::vector<int, double, float> myVec;
SOME_MAGIC_ADAPTER_MACRO(myVec)
The macro or whatever should then turn the vector into
struct myVec_pod {
    int v1;
    double v2;
    float v3;
    };
or similar. Is this possible?
Try the attached.

In Christ,
Steven Watanabe


#ifndef BOOST_PP_IS_ITERATING

    #include <boost/fusion/sequence/intrinsic/at.hpp>
    #include <boost/fusion/sequence/intrinsic/value_at.hpp>
    #include <boost/fusion/sequence/intrinsic/size.hpp>
    #include <boost/fusion/container/vector.hpp>
    #include <boost/preprocessor/repetition/repeat.hpp>
    #include <boost/preprocessor/repetition/enum.hpp>
    #include <boost/preprocessor/cat.hpp>

    #include <iostream>

    struct pod_vector_tag {};

    template<int N>
    struct make_pod_vector_impl;

    template<class Vector>
    struct make_pod_vector : make_pod_vector_impl<(boost::fusion::result_of::size<Vector>::value)>::template apply<Vector> {};

#define BOOST_PP_FILENAME_1 "scratch.cpp"
#define BOOST_PP_ITERATION_LIMITS (0, 50)
#include BOOST_PP_ITERATE()

    int main() {
        boost::fusion::vector2<int, char> vec(3, 'd');
        make_pod_vector<boost::fusion::vector2<int, char> >::type pod_vec =
            make_pod_vector<boost::fusion::vector2<int, char> >::call(vec);
        std::cout << pod_vec.value0 << ' ' << pod_vec.value1 << std::endl;
    }

#else

#define n BOOST_PP_ITERATION()

#define POD_VECTOR_ELEMENT(z, n, data)                                                          \
    typedef typename boost::fusion::result_of::value_at_c<data, n>::type BOOST_PP_CAT(type, n);   \
    BOOST_PP_CAT(type, n) BOOST_PP_CAT(value, n);

#define AT(z, n, data)                                                           \
    boost::fusion::at_c<n>(data)

template<class Vector>
struct BOOST_PP_CAT(pod_vector, n) {
    typedef pod_vector_tag fusion_tag;
    BOOST_PP_REPEAT_1(n, POD_VECTOR_ELEMENT, Vector)
};

template<>
struct make_pod_vector_impl<n> {
    template<class Vector>
    struct apply {
        typedef BOOST_PP_CAT(pod_vector, n)<Vector> type;
        static type call(const Vector& vec) {
            type result = { BOOST_PP_ENUM(n, AT, vec) };
            return(result);
        }
    };
};

#undef n

#endif