gistfile1.cpp

namespace detail {
    template<typename T>
    bool constexpr contains(T) {
        return false;
    }

    template<typename T, typename... U>
    bool constexpr contains(T needle, T head, U... tail) {
        return needle == head || contains(needle, tail...);
    }
}

template<typename T, T Needle, T... Haystack>
struct contains : std::integral_constant<bool, detail::contains(Needle, Haystack...)> { };