#include <type_traits>

template <typename...>
struct Pack { };

template <typename, typename>
struct Add_Type;

template <typename T, typename... Ts>
struct Add_Type<T, Pack<Ts...>>
{
    using type = Pack<T, Ts...>;
};

template <typename, typename>
struct Remove_Type;

template <typename T>
struct Remove_Type<T, Pack<>>
{
    using type = Pack<>;
};

template <typename T, typename... Ts>
struct Remove_Type<T, Pack<T, Ts...>>
{
    using type = typename Remove_Type<T, Pack<Ts...>>::type;
};

template <typename T, typename First, typename... Rest>
struct Remove_Type<T, Pack<First, Rest...>>
{
    using type = typename Add_Type<First, typename Remove_Type<T, Pack<Rest...>>::type>::type;
};

int main()
{
    // Testing Add_Type
    {
        using Target = int;
        using Indata = Pack<float, bool>;
        using Answer = Pack<int, float, bool>;
        using Result = typename Add_Type<Target, Indata>::type;
        static_assert( std::is_same_v<Result, Answer> );
    }
    // No types to remove
    {
        using Target = int;
        using Indata = Pack<float, bool>;
        using Answer = Pack<float, bool>;
        using Result = typename Remove_Type<Target, Indata>::type;
        static_assert( std::is_same_v<Result, Answer> );
    }
    // One to remove, in the beginning
    {
        using Target = int;
        using Indata = Pack<int, float, bool>;
        using Answer = Pack<float, bool>;
        using Result = typename Remove_Type<Target, Indata>::type;
        static_assert( std::is_same_v<Result, Answer> );
    }
    // Multiple to remove, not in the beginning, other than int
    {
        using Target = float;
        using Indata = Pack<int, float, bool, float, float, int>;
        using Answer = Pack<int, bool, int>;
        using Result = typename Remove_Type<Target, Indata>::type;
        static_assert( std::is_same_v<Result, Answer> );
    }
}