exercise-5-6.hpp

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// ===-- chapter-5/exercise-5-6.hpp ----------------------- -*- C++ -*- --=== //
#ifndef EXERCISE_5_6
#define EXERCISE_5_6
 
#include <boost/mpl/begin_end.hpp>
#include <boost/mpl/deref.hpp>
#include <boost/mpl/iterator_tags.hpp>
#include <boost/mpl/next_prior.hpp>
 
#include <boost/type_traits/is_array.hpp>
#include <boost/type_traits/is_same.hpp>
 
 
namespace exercise_5_6 {
 
struct dimensions_tag {};
 
template <typename T>
struct dimensions : boost::mpl::void_ { };
 
template <typename T, size_t N>
struct dimensions<T[N]>
{
    static size_t const value = N;
 
    typedef dimensions<T[N]> type;
 
    typedef typename boost::mpl::if_<
        boost::is_array<T>,
        dimensions<T>,
        boost::mpl::void_
    >::type tail;
 
    typedef dimensions_tag tag;
};
 
template <typename S>
struct dimensions_iterator
{
    typedef boost::mpl::forward_iterator_tag category;
};
 
} // namespace exercise_5_6
 
 
namespace boost {
namespace mpl {
 
 
template <>
struct begin_impl<exercise_5_6::dimensions_tag>
{
    template <typename S>
    struct apply
    {
        typedef exercise_5_6::dimensions_iterator<S> type;
    };
};
template <>
struct end_impl<exercise_5_6::dimensions_tag>
{
    template <typename S>
    struct apply
    {
        typedef exercise_5_6::dimensions_iterator<boost::mpl::void_> type;
    };
};
 
template <typename S>
struct deref< exercise_5_6::dimensions_iterator<S> >
{
    typedef S type;
};
 
template <typename S>
struct next< exercise_5_6::dimensions_iterator<S> >
{
    typedef typename boost::mpl::if_<
        boost::is_same<boost::mpl::void_, S>,
        exercise_5_6::dimensions_iterator<boost::mpl::void_>,
        exercise_5_6::dimensions_iterator<typename S::tail> >::type type;
};
 
 
} // namespace mpl
} // namespace boost
 
#endif // EXERCISE_5_6