meta_util.hpp

#ifndef REST_RPC_META_UTIL_HPP
#define REST_RPC_META_UTIL_HPP

#include "cplusplus_14.h"

namespace rest_rpc{

    template <typename... Args, typename Func, std::size_t... Idx>
    void for_each(const std::tuple<Args...>& t, Func&& f, std::index_sequence<Idx...>) {
        (void)std::initializer_list<int> { (f(std::get<Idx>(t)), void(), 0)...};
    }

    template <typename... Args, typename Func, std::size_t... Idx>
    void for_each_i(const std::tuple<Args...>& t, Func&& f, std::index_sequence<Idx...>) {
        (void)std::initializer_list<int> { (f(std::get<Idx>(t), std::integral_constant<size_t, Idx>{}), void(), 0)...};
    }

    template<typename T>
    struct function_traits;

    template<typename Ret, typename Arg, typename... Args>
    struct function_traits<Ret(Arg, Args...)>
    {
    public:
        enum { arity = sizeof...(Args)+1 };
        typedef Ret function_type(Arg, Args...);
        typedef Ret return_type;
        using stl_function_type = std::function<function_type>;
        typedef Ret(*pointer)(Arg, Args...);

        typedef std::tuple<Arg, Args...> tuple_type;
        typedef std::tuple<Arg, std::remove_const_t<std::remove_reference_t<Args>>...> bare_tuple_type;
        using args_tuple = std::tuple<std::string, Arg, std::remove_const_t<std::remove_reference_t<Args>>...>;
        using args_tuple_2nd = std::tuple<std::string, std::remove_const_t<std::remove_reference_t<Args>>...>;
    };

    template<typename Ret, typename... Args>
    struct function_traits<Ret(*)(Args...)> : function_traits<Ret(Args...)>{};

    template <typename Ret, typename... Args>
    struct function_traits<std::function<Ret(Args...)>> : function_traits<Ret(Args...)>{};

    template <typename ReturnType, typename ClassType, typename... Args>
    struct function_traits<ReturnType(ClassType::*)(Args...)> : function_traits<ReturnType(Args...)>{};

    template <typename ReturnType, typename ClassType, typename... Args>
    struct function_traits<ReturnType(ClassType::*)(Args...) const> : function_traits<ReturnType(Args...)>{};

    template<typename Callable>
    struct function_traits : function_traits<decltype(&Callable::operator())>{};

    template<typename T>
    using remove_const_reference_t = std::remove_const_t<std::remove_reference_t<T>>;

    template<size_t... Is>
    auto make_tuple_from_sequence(std::index_sequence<Is...>)->decltype(std::make_tuple(Is...)) {
        std::make_tuple(Is...);
    }

    template<size_t N>
    constexpr auto make_tuple_from_sequence()->decltype(make_tuple_from_sequence(std::make_index_sequence<N>{})) {
        return make_tuple_from_sequence(std::make_index_sequence<N>{});
    }

    namespace detail {
        template <class Tuple, class F, std::size_t...Is>
        void tuple_switch(const std::size_t i, Tuple&& t, F&& f, std::index_sequence<Is...>) {
            (void)std::initializer_list<int> {
                    (i == Is && (
                            (void)std::forward<F>(f)(std::integral_constant<size_t, Is>{}), 0))...
            };
        }
    } // namespace detail

    template <class Tuple, class F>
    inline void tuple_switch(const std::size_t i, Tuple&& t, F&& f) {
        constexpr auto N =
                std::tuple_size<std::remove_reference_t<Tuple>>::value;

        detail::tuple_switch(i, std::forward<Tuple>(t), std::forward<F>(f),
                             std::make_index_sequence<N>{});
    }
}

#endif //REST_RPC_META_UTIL_HPP