c++高手请进

template <class TList, template <class> class Unit>
    class GenScatterHierarchy;
     
    template <class T1, class T2, template <class> class Unit>
    class GenScatterHierarchy<Typelist<T1, T2>, Unit>
        : public GenScatterHierarchy<T1, Unit>
        , public GenScatterHierarchy<T2, Unit>
    {
    public:
        typedef Typelist<T1, T2> TList;
        typedef GenScatterHierarchy<T1, Unit> LeftBase;
        typedef GenScatterHierarchy<T2, Unit> RightBase;
        template <typename T> struct Rebind
        {
            typedef Unit<T> Result;
        };
    };
     
    template <class AtomicType, template <class> class Unit>
    class GenScatterHierarchy : public Unit<AtomicType>
    {
        typedef Unit<AtomicType> LeftBase;
        template <typename T> struct Rebind
        {
            typedef Unit<T> Result;
        };
    };
    
    template <template <class> class Unit>
    class GenScatterHierarchy<NullType, Unit>
    {
        template <typename T> struct Rebind
        {
            typedef Unit<T> Result;
        };
    };