c++ - 整数参数特殊值的模板特化

Question

我正在为整数参数的模板特化而苦苦挣扎，也许这根本不可能？

我尝试了什么:

template< int COUNT, typename REMOVE, typename ...T>
struct RemoveFirstElementsImpl
{
    using Type= typename RemoveFirstElementsImpl<COUNT-1, T...>::Type;
};

template< typename ...T>
struct RemoveFirstElementsImpl<0, T...>
{
    using Type= TypeContainer<T...>;
};


template < int COUNT, typename ... T >
struct RemoveFirstElements
{
    using Type = typename RemoveFirstElementsImpl< COUNT, T...>::Type;
};

结果

error: partial specialization is not more specialized than the primary template because it replaces multiple parameters with a pack expansion

然后我想到了 SFINAE，比如:

template < int COUNT, typename = typename std::enable_if<COUNT==0>::type, typename HEAD, typename ... T >
struct RemoveFirstElements
{
    using Type= TypeContainer<T...>;
};
template < int COUNT, typename = void, typename HEAD, typename ... T >
struct RemoveFirstElements
{
    using Type= RemoveFirstElements<COUNT-1, T...>
};

但我不知道如何让参数包和默认参数的组合运行。

也许我走错了路。我想要实现的是获取一个参数列表，其中前 n 个参数从我的 TypeContainer 中删除，它只是一个扩展的 std::tuple。我只需要类型本身而不需要任何参数，我只需要类型而不需要任何对象。

Answer 1

我想你想要:

template<int COUNT, typename ...Ts> struct RemoveFirstElementsImpl;

template<>
struct RemoveFirstElementsImpl<0>
{
    using type = std::tuple<>;
};

template<typename T, typename ...Ts>
struct RemoveFirstElementsImpl<0, T, Ts...>
{
    using type = std::tuple<T, Ts...>;
};

template<int N, typename T, typename ...Ts>
struct RemoveFirstElementsImpl<N, T, Ts...>
{
    using type = typename RemoveFirstElementsImpl<N - 1, Ts...>::type;
};

Live Demo