How to use gcc __is_class with preprocessor if in C++

I want to send a var to a function if is it a class. I try with std::is_class but this gave me an erros because std::is_class is run time and not a preprocessor. I can't make the preprocessor if to work. any suggestions? in the function 'toJson' in the loop I am adding the types to the json object. I need to check if the type is class, for recursive adding the classes fields to the json object.

source code: https://stackoverflow.com/a/34165367/13277578

template<typename Class, typename T>struct PropertyImpl {    constexpr PropertyImpl(T Class::* aMember, const char* aName) : member{ aMember }, name{ aName } {}    using Type = T;    T Class::* member;    const char* name;};template<typename Class, typename T>constexpr auto property(T Class::* member, const char* name) {    return PropertyImpl<Class, T>{member, name};}template <typename T, T... S, typename F>constexpr void for_sequence(std::integer_sequence<T, S...>, F&& f) {    (static_cast<void>(f(std::integral_constant<T, S>{})), ...);}// the error in this functiontemplate<typename T>json toJson(const T& object){    json data;    // We first get the number of properties    constexpr auto nbProperties = std::tuple_size<decltype(T::properties)>::value;    // We iterate on the index sequence of size `nbProperties`    for_sequence(std::make_index_sequence<nbProperties>{}, [&](auto i) {        // get the property        constexpr auto property = std::get<i>(T::properties);        using Type = typename decltype(property)::Type;        #if __is_class(Type) // C1017        // data[property.name] = toJson(object.*(property.member))  // recursive add the object fields        #else        // addFind(data, object.*(property.member), property.name)) // add the object field (WORK)        #endif        });    return data;}

example of using toJson:

#define PROPERTY(CLASS, MEMBER) property(&CLASS::MEMBER, #MEMBER)    struct GetRooms    {        unsigned int status = 0;        RoomData roomData;        string name;        constexpr static auto properties = std::make_tuple(            PROPERTY(GetRooms, status),            PROPERTY(GetRooms, roomData),            PROPERTY(GetRooms, name)        );    };    GetRooms var;    json varAsJson = toJson(var);