func_traits

func_traits.cpp

template <typename>
struct func_traits;

// function
template <typename R, typename... Args>
struct func_traits<R (*)(Args...)>
{
    using return_type = R;
    using args_type   = std::tuple<Args...>;
    template <int I>
    using arg_type = std::tuple_element_t<I, args_type>;
};

// member function
template <typename R, typename C, typename... Args>
struct func_traits<R (C::*)(Args...)>
{
    using return_type = R;
    using callee_type = C;
    using args_type   = std::tuple<Args...>;
    template <int I>
    using arg_type = std::tuple_element_t<I, args_type>;
};

// const member function
template <typename R, typename C, typename... Args>
struct func_traits<R (C::*)(Args...) const>
{
    using return_type = R;
    using callee_type = const C;
    using args_type   = std::tuple<Args...>;
    template <int I>
    using arg_type = std::tuple_element_t<I, args_type>;
};

// functor
template <typename C>
struct func_traits
{
    using _traits = func_traits<decltype(&C::operator())>;

    using return_type = typename _traits::return_type;
    using callee_type = typename _traits::callee_type;
    using args_type   = typename _traits::args_type;
    template <int I>
    using arg_type = std::tuple_element_t<I, args_type>;
};