Kylin/Universal/FunctionTraits.h

#ifndef FUNCTIONTRAITS_H
#define FUNCTIONTRAITS_H

#include <functional>
#include <tuple>
#include <type_traits>

template <typename T>
class FunctionTraits;

template <typename>
struct IsTuple : std::false_type {
    enum {
        num = 1,
    };
};

template <typename... T>
struct IsTuple<std::tuple<T...>> : std::true_type {
    enum {
        num = std::tuple_size<std::tuple<T...>>::value,
    };
};

template <typename... T>
struct IsTuple<std::pair<T...>> : std::true_type {
    enum {
        num = std::tuple_size<std::pair<T...>>::value,
    };
};

template <typename Ret, typename... Args>
class FunctionTraits<Ret(Args...)> {
public:
    enum { arity = sizeof...(Args), Results = IsTuple<Ret>::num };
    using FunctionType = Ret(Args...);
    using FunctionPointerType = FunctionType *;
    using ReturnType = Ret;
    using StlFunctionType = std::function<FunctionType>;
    using Arguments = std::tuple<Args...>;

    template <size_t I>
    class Argument {
    public:
        static_assert(I < arity, "index is out of range, index must less than sizeof Args...");
        using Type = std::tuple_element_t<I, Arguments>;
    };

    using FirstArgumentType = typename Argument<0>::Type;
};

template <typename Ret>
class FunctionTraits<Ret()> {
public:
    enum { arity = 0, Results = IsTuple<Ret>::num };
    using FunctionType = Ret();
    using FunctionPointerType = FunctionType *;
    using ReturnType = Ret;
    using StlFunctionType = std::function<FunctionType>;
    using Arguments = std::tuple<>;
    using FirstArgumentType = void;
    template <size_t I>
    class Argument {
    public:
        using Type = void;
    };
};

template <>
class FunctionTraits<std::nullptr_t> {
public:
    using Arguments = std::tuple<>;
    using FirstArgumentType = void;
    template <size_t I>
    class Argument {
    public:
        using Type = void;
    };
};

template <typename Ret, typename... Args>
class FunctionTraits<Ret (*)(Args...)> : public FunctionTraits<Ret(Args...)> {};

template <typename Ret, typename... Args>
class FunctionTraits<std::function<Ret(Args...)>> : public FunctionTraits<Ret(Args...)> {};

template <typename Ret, typename ClassType, typename... Args>
class FunctionTraits<Ret (ClassType::*)(Args...)> : public FunctionTraits<Ret(Args...)> {};

template <typename Ret, typename ClassType, typename... Args>
class FunctionTraits<Ret (ClassType::*)(Args...) volatile> : public FunctionTraits<Ret(Args...)> {};

template <typename Ret, typename ClassType, typename... Args>
class FunctionTraits<Ret (ClassType::*)(Args...) const> : public FunctionTraits<Ret(Args...)> {};

template <typename Ret, typename ClassType, typename... Args>
class FunctionTraits<Ret (ClassType::*)(Args...) const volatile> : public FunctionTraits<Ret(Args...)> {};

// std::bind for object methods   rclcpp/rclcpp/include/rclcpp/function_traits.hpp
template <typename ClassT, typename ReturnTypeT, typename... Args, typename... FArgs>
#if defined _GLIBCXX_RELEASE // glibc++ (GNU C++ >= 7.1)
struct FunctionTraits<std::_Bind<ReturnTypeT (ClassT::*(FArgs...))(Args...)>>
#elif defined __GLIBCXX__ // glibc++ (GNU C++)
struct FunctionTraits<std::_Bind<std::_Mem_fn<ReturnTypeT (ClassT::*)(Args...)>(FArgs...)>>
#elif defined _MSC_VER    // MS Visual Studio
struct FunctionTraits<std::_Binder<std::_Unforced, ReturnTypeT (ClassT::*)(Args...), FArgs...>>
#elif defined __clang__
struct FunctionTraits<std::__bind<ReturnTypeT (ClassT::*(FArgs...))(Args...)>>
#else
#error "Unsupported C++ compiler / standard library"
#endif
    : FunctionTraits<ReturnTypeT(Args...)> {
};

// template <typename ClassT, typename ReturnTypeT, typename... Args, typename... FArgs>
// class FunctionTraits<std::_Bind<ReturnTypeT (ClassT::*(FArgs...))(Args...)>>
//     : public FunctionTraits<decltype(std::_Bind<ReturnTypeT (ClassT::*(FArgs...))(Args...)>::operator())> {};

template <typename Callable>
class FunctionTraits : public FunctionTraits<decltype(&Callable::operator())> {};

template <typename Function>
typename FunctionTraits<std::decay_t<Function>>::StlFunctionType makeStlFunction(Function &&lambda) {
    return static_cast<typename FunctionTraits<std::decay_t<Function>>::StlFunctionType>(
        std::forward<Function>(lambda));
}

#endif // FUNCTIONTRAITS_H