exercise-6-1.hpp

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// ===-- chapter-6/exercise-6-1.hpp ----------------------- -*- C++ -*- --=== //
#ifndef EXERCISE_6_1
#define EXERCISE_6_1
 
#include <boost/static_assert.hpp>
 
#include <boost/mpl/accumulate.hpp>
#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/mpl/placeholders.hpp>
#include <boost/mpl/plus.hpp>
#include <boost/mpl/times.hpp>
using namespace boost::mpl::placeholders;
 
 
namespace exercise_6_1 {
 
struct binary_tag { };
 
// Forward declaration for the benefit of the MPL sequence algorithms...
template <unsigned long N> struct binary;
 
} // namespace exercise_6_1
 
 
namespace boost {
namespace mpl {
 
 
template <unsigned long N>
struct next< exercise_6_1::binary<N> >
{
    typedef exercise_6_1::binary<N/10> type;
};
 
template <unsigned long N>
struct deref< exercise_6_1::binary<N> >
{
    typedef exercise_6_1::binary<N> type;
};
 
template <>
struct begin_impl<exercise_6_1::binary_tag>
{
    template <typename T> struct apply { };
 
    template <unsigned long N>
    struct apply< exercise_6_1::binary<N> >
    {
        typedef exercise_6_1::binary<N> type;
    };
};
 
template <>
struct end_impl<exercise_6_1::binary_tag>
{
    template <typename T> struct apply { };
 
    template <unsigned long N>
    struct apply< exercise_6_1::binary<N> >
    {
        typedef exercise_6_1::binary<0> type;
    };
};
 
 
} // namespace mpl
} // namespace boost
 
 
namespace exercise_6_1 {
 
template <unsigned long N>
struct binary
{
    typedef binary_tag tag;
 
    // Reverse iteration is trivial, but not useful at the moment.
    typedef boost::mpl::forward_iterator_tag category;
 
    template <typename T1, typename T2> struct apply_binary_digit { };
 
    template <typename T1, unsigned long N2>
    struct apply_binary_digit< T1, binary<N2> >
    {
        BOOST_STATIC_ASSERT((N2 % 10 < 2));
        typedef boost::mpl::plus<
            boost::mpl::times< T1, boost::mpl::int_<2> >,
            boost::mpl::int_<N2 % 10>
        > type;
    };
 
    typedef typename boost::mpl::accumulate<
        binary<N>,
        boost::mpl::int_<0>,
        apply_binary_digit<_,_> >::type type;
 
    static int const value = type::value;
};
 
} // namespace exercise_6_1
 
#endif // EXERCISE_6_1