C++0 x変長パラメータテンプレートを使用してメタグループを実現

最近,C++0 xに関する問題を検討し,GCC 4.6で変長パラメータテンプレートを用いてメタグループを実現した.
 

template<typename ... AllTypes>
struct MyTuple;

template<> struct MyTuple<> {};

template<int N, class T>
struct ElementType;

template<typename Head, typename ... Tail>
struct MyTuple<Head,Tail...>
{
    MyTuple(Head h, Tail... t)
        : tail(t...)
        , head(h)
    {
    }
    MyTuple(const MyTuple<Head,Tail...>& t)
        : tail(t.tail)
        , head(t.head)
    {
    }
    MyTuple(MyTuple<Head,Tail...>&& t)
        : tail(t.tail)
        , head(t.head)
    {
    }

    MyTuple<Tail...> tail;
    Head head;

    typedef Head HeadType;
    typedef MyTuple<Tail...> TailType;
};

//          
template <int k>
struct get_class {
    template <typename Head, typename ... Tail>
    static typename ElementType<k,MyTuple<Head,Tail...> >::type& get(MyTuple<Head,Tail...>& t )
    {
         return get_class<k-1>::get(t.tail);
    }

    template <typename Head, typename ... Tail>
    static const typename ElementType<k,MyTuple<Head,Tail...> >::type& get(const MyTuple<Head,Tail...>& t )
    {
         return get_class<k-1>::get(t.tail);
    }
};

template <>
struct get_class<0> {

    template <typename Head, typename ... Tail>
    static typename MyTuple<Head,Tail...>::HeadType& get(MyTuple<Head,Tail...>& t )
    {
         return t.head;
    }

    template <typename Head, typename ... Tail>
    static const typename MyTuple<Head,Tail...>::HeadType& get(const MyTuple<Head,Tail...>& t )
    {
         return t.head;
    }
};

//           
template<int N, class T>
struct ElementType
{
private:
  typedef typename T::TailType Next;
public:
  typedef typename ElementType<N-1, Next>::type type;
};


template<class T>
struct ElementType<0, T>
{
  typedef typename T::HeadType type;
};


template < int k,typename Head, typename ... Tail>
typename ElementType<k,MyTuple<Head,Tail...> >::type& get(MyTuple<Head,Tail...>& t)
{
    return get_class<k>::get(t);
}

template < int k,typename Head, typename ... Tail>
const typename ElementType<k,MyTuple<Head,Tail...> >::type& get(const MyTuple<Head,Tail...>& t)
{
    return get_class<k>::get(t);
}

 使用方法:

    MyTuple<double,int,double,int,string,const char*> t(2.1,0,1.11,6666,"helloworld z","world");
    cout << get<0>(t) << get<1>(t) << get<2>(t) << get<3>(t) << get<4>(t) << get<5>(t) << std::endl;
    get<0>(t) = 100;
    get<1>(t) = 10;
    get<4>(t) = "gg world";

    const MyTuple<int,int,double,int,string> tc(0,0,111.1,5555,"helloworld");
    cout << get<0>(tc) << get<1>(tc) << get<2>(tc) << get<3>(tc) << get<4>(tc) << std::endl;

    cout << get<1>( MyTuple<double,char>(3.1415926,'c')) << std::endl;