chapter-6-tree.hpp

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// ===-- chapter-6/chapter-6-tree.hpp --------------------- -*- C++ -*- --=== //
#ifndef CHAPTER_6_TREE
#define CHAPTER_6_TREE
 
#include "chapter-5-tree.hpp"
 
#include <boost/static_assert.hpp>
 
#include <boost/mpl/greater.hpp>
#include <boost/mpl/if.hpp>
#include <boost/mpl/push_back.hpp>
 
#include <boost/type_traits/is_same.hpp>
 
 
namespace boost {
namespace mpl {
 
 
template<>
struct push_back_impl<chapter5::tree_tag>
{
    template <typename S, typename New>
    struct apply
        : boost::mpl::eval_if<
            boost::mpl::greater<S, New>,
            chapter5::tree<S, New, void_>,
            chapter5::tree<S, void_, New> >
    { };
 
    template <typename New, typename Cur, typename L, typename R>
    struct apply<chapter5::tree<Cur, L, R>, New>
        : boost::mpl::eval_if<
            boost::mpl::greater<Cur, New>,
            chapter5::tree<
                Cur,
                typename apply<L, New>::type,
                R>,
            chapter5::tree<
                Cur,
                L,
                typename apply<R, New>::type>
        >
    { };
 
    template <typename New>
    struct apply<chapter5::tree<>, New>
    {
        typedef chapter5::tree<New> type;
    };
 
    template <typename New>
    struct apply<void_, New>
    {
        typedef New type;
    };
};
 
 
} // namespace mpl
} // namespace boost
 
 
typedef chapter5::tree<> t1;
typedef boost::mpl::push_back<t1, boost::mpl::int_<5> >::type t2;
typedef boost::mpl::push_back<t2, boost::mpl::int_<3> >::type t3;
typedef boost::mpl::push_back<t3, boost::mpl::int_<7> >::type t4;
typedef boost::mpl::push_back<t4, boost::mpl::int_<1> >::type t5;
 
typedef chapter5::tree<
    boost::mpl::int_<5>,
    chapter5::tree<boost::mpl::int_<3>, boost::mpl::int_<1>, void_>,
    boost::mpl::int_<7>
> expected_t5;
BOOST_STATIC_ASSERT((boost::is_same<t5, expected_t5>::value));
 
#endif // CHAPTER_6_TREE