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

From: Sebastian Weber (sebastian.weber_at_[hidden])
Date: 2008-04-07 02:51:53

Whow! This looks cool. Could have never thought of this solution.

Thanks a lot for this code snippet.

Sebastian

On Fri, 2008-04-04 at 10:40 -0700, Steven Watanabe wrote:
> 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
> 
> einfaches Textdokument attachment (scratch.cpp)
> #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
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