exercise-7-7.hpp

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// ===-- chapter-7/exercise-7-7.hpp ----------------------- -*- C++ -*- --=== //
#ifndef EXERCISE_7_7
#define EXERCISE_7_7
 
#include <boost/static_assert.hpp>
 
#include <boost/mpl/begin_end.hpp>
#include <boost/mpl/deref.hpp>
#include <boost/mpl/iterator_category.hpp>
#include <boost/mpl/iterator_tags.hpp>
#include <boost/mpl/next_prior.hpp>
#include <boost/mpl/or.hpp>
 
#include <boost/type_traits/is_same.hpp>
 
 
namespace exercise_7_7 {
 
template <typename ForwardIt>
struct reverse_iterator
{
    typedef ForwardIt base;
    typedef typename boost::mpl::iterator_category<ForwardIt>::type category;
 
    typedef reverse_iterator<ForwardIt> type;
};
 
template <typename Iterator>
struct is_valid_reverse_category
    : boost::mpl::or_<
        boost::is_same<
            typename boost::mpl::iterator_category<Iterator>::type,
            boost::mpl::bidirectional_iterator_tag>,
        boost::is_same<
            typename boost::mpl::iterator_category<Iterator>::type,
            boost::mpl::random_access_iterator_tag>
    >
{ };
 
} // namespace exercise_7_7
 
 
namespace boost {
namespace mpl {
 
 
template <typename Sequence>
struct rend
{
    typedef typename prior<typename begin<Sequence>::type>::type end_iterator;
    BOOST_STATIC_ASSERT((
        exercise_7_7::is_valid_reverse_category<end_iterator>::value));
 
    typedef exercise_7_7::reverse_iterator<end_iterator> type;
};
 
template <typename Sequence>
struct rbegin
{
    typedef typename prior<typename end<Sequence>::type>::type first_iterator;
    BOOST_STATIC_ASSERT((
        exercise_7_7::is_valid_reverse_category<first_iterator>::value));
 
    typedef exercise_7_7::reverse_iterator<first_iterator> type;
};
 
template <typename ForwardIt>
struct deref< exercise_7_7::reverse_iterator<ForwardIt> >
    : deref<ForwardIt> { };
 
template <typename ForwardIt>
struct next< exercise_7_7::reverse_iterator<ForwardIt> >
    : exercise_7_7::reverse_iterator<typename prior<ForwardIt>::type> { };
 
template <typename ForwardIt>
struct prior< exercise_7_7::reverse_iterator<ForwardIt> >
    : exercise_7_7::reverse_iterator<typename next<ForwardIt>::type> { };
 
 
} // namespace mpl
} // namespace boost
 
#endif // EXERCISE_7_7