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));
}

template <typename T>
using Unqualified = typename std::remove_cv<typename std::remove_reference<T>::type>::type;

/*!
 * \struct HasCallOperator
 * http://stackoverflow.com/a/5117641
 */
template <typename T>
struct HasCallOperator {
    template <typename U>
    static char check(decltype(&U::operator(), char(0)));

    template <typename U>
    static char (&check(...))[2];

    static const bool value = (sizeof(check<T>(0)) == 1);
};

/*!
 * \struct ArgsOf
 * http://stackoverflow.com/a/7943765
 * http://stackoverflow.com/a/27885283
 */
template <typename... Args>
struct ArgsTraits {
    using types = std::tuple<Args...>;
    using first = typename std::tuple_element<0, types>::type;
    static const size_t count = std::tuple_size<types>::value;
};

template <>
struct ArgsTraits<> {
    using types = std::tuple<>;
    using first = void;
    static const size_t count = 0;
};

// Fallback implementation, including types (T) which are not functions but
// also lambda with `auto` arguments, which are not covered but still valid
// callbacks (see the QPromiseBase<T> template constructor).
template <typename T, typename Enabled = void>
struct ArgsOf : public ArgsTraits<> {};

// Partial specialization for null function.
template <>
struct ArgsOf<std::nullptr_t> : public ArgsTraits<> {};

// Partial specialization for type with a non-overloaded operator().
// This applies to lambda, std::function but not to std::bind result.
template <typename T>
struct ArgsOf<T, typename std::enable_if<HasCallOperator<T>::value>::type> : public ArgsOf<decltype(&T::operator())> {};

// Partial specialization to remove reference and rvalue (e.g. lambda, std::function, etc.).
template <typename T>
struct ArgsOf<T &> : public ArgsOf<T> {};

template <typename T>
struct ArgsOf<T &&> : public ArgsOf<T> {};

// Partial specialization for function type.
template <typename R, typename... Args>
struct ArgsOf<R(Args...)> : public ArgsTraits<Args...> {};

// Partial specialization for function pointer.
template <typename R, typename... Args>
struct ArgsOf<R (*)(Args...)> : public ArgsTraits<Args...> {};

// Partial specialization for pointer-to-member-function (i.e. operator()'s).
template <typename R, typename T, typename... Args>
struct ArgsOf<R (T::*)(Args...)> : public ArgsTraits<Args...> {};

template <typename R, typename T, typename... Args>
struct ArgsOf<R (T::*)(Args...) const> : public ArgsTraits<Args...> {};

template <typename R, typename T, typename... Args>
struct ArgsOf<R (T::*)(Args...) volatile> : public ArgsTraits<Args...> {};

template <typename R, typename T, typename... Args>
struct ArgsOf<R (T::*)(Args...) const volatile> : public ArgsTraits<Args...> {};

#endif // FUNCTIONTRAITS_H