chapter-7-permutation_view.hpp

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// ===-- chapter-7/chapter-7-permutation_view.hpp --------- -*- C++ -*- --=== //
#ifndef CHAPTER_7_PERMUTATION_VIEW
#define CHAPTER_7_PERMUTATION_VIEW
 
#include <boost/mpl/advance.hpp>
#include <boost/mpl/begin_end.hpp>
#include <boost/mpl/deref.hpp>
#include <boost/mpl/iterator_tags.hpp>
#include <boost/mpl/iterator_category.hpp>
#include <boost/mpl/next_prior.hpp>
 
 
namespace chapter7 {
 
template <typename CurIdxIter, typename SeqBegin>
struct permutation_iterator
{
    typedef CurIdxIter current_index_iter;
    typedef SeqBegin   sequence_begin;
 
    typedef typename boost::mpl::iterator_category<CurIdxIter>::type category;
    typedef permutation_iterator<CurIdxIter, SeqBegin> type;
};
 
struct permutation_view_tag { };
 
template <typename Indices, typename Sequence>
struct permutation_view
{
    typedef Indices  indices;
    typedef Sequence orig_sequence;
 
    typedef permutation_view_tag tag;
};
 
} // namespace chapter7
 
 
namespace boost {
namespace mpl {
 
 
template <>
struct begin_impl<chapter7::permutation_view_tag>
{
    // Maybe I should just use duck typing instead of disallowing anything but
    // permutation_view (i.e., use Sequence::indices, etc.)
    template <typename Sequence> struct apply { };
 
    template <typename Indices, typename Sequence>
    struct apply< chapter7::permutation_view<Indices, Sequence> >
        : chapter7::permutation_iterator<
            typename begin<Indices>::type, typename begin<Sequence>::type>
    { };
};
 
template <>
struct end_impl<chapter7::permutation_view_tag>
{
    // Maybe I should only really allow permutation_view here...
    template <typename Sequence>
    struct apply
        : chapter7::permutation_iterator<
            typename end<typename Sequence::indices>::type,
            typename begin<typename Sequence::orig_sequence>::type>
    { };
};
 
template <typename CurIdxIter, typename SeqBegin>
struct deref< chapter7::permutation_iterator<CurIdxIter, SeqBegin> >
    : deref<typename advance<SeqBegin, typename deref<CurIdxIter>::type>::type>
{ };
 
template <typename CurIdxIter, typename SeqBegin>
struct next< chapter7::permutation_iterator<CurIdxIter, SeqBegin> >
    : chapter7::permutation_iterator<typename next<CurIdxIter>::type, SeqBegin>
{ };
 
template <typename CurIdxIter, typename SeqBegin>
struct prior< chapter7::permutation_iterator<CurIdxIter, SeqBegin> >
    : chapter7::permutation_iterator<typename prior<CurIdxIter>::type, SeqBegin>
{ };
 
 
} // namespace mpl
} // namespace boost
 
#endif // CHAPTER_7_PERMUTATION_VIEW