Perfect Forwarding

#include <iostream>
#include <typeinfo>
#include <type_traits>

template <typename Fn, typename T>
void dy_call(Fn call_back, T& t) {
    const std::type_info& info = typeid(call_back);
    if ( info == typeid(void (*)(T&)))
        ((void (*)(T&))call_back)(t);
    else if ( info == typeid(void (*)(const T&)) )
        ((void (*)(const T&))call_back)(t);
    else if ( info == typeid(void (*)(T)) )
        ((void (*)(T))call_back)(t);
    else
        std::cout << "dy_call(Fn call_back, T& t): Failed to match" << std::endl;
}

template <typename Fn, typename T>
void dy_call(Fn call_back, const T& t) {
    const std::type_info& info = typeid(call_back);
    if ( info == typeid(void (*)(const T&)) )
        ((void (*)(const T&))call_back)(t);
    else if ( info == typeid(void (*)(T)) )
        ((void (*)(T))call_back)(t);
    else
        std::cout << "dy_call(Fn call_back, T& t): Failed to match" << std::endl;
}

template <typename Fn, typename T>
void dy_call_Cpp11(Fn call_back, T&& t) {
    const std::type_info& info = typeid(call_back);
    if ( !std::is_const<T>::value && std::is_reference<T>::value && info == typeid(void (*)(T)))    // 尝试普通引用
        return ((void (*)(T&))call_back)(t);
    if ( info == typeid(void (*)(const typename std::remove_reference<T>::type&)) )                 // 尝试const引用
        return ((void (*)(const typename std::remove_reference<T>::type&))call_back)(t);
    if ( info == typeid(void (*)(typename std::remove_reference<T>::type)) )                        // 尝试传值
        return ((void (*)(typename std::remove_reference<T>::type))call_back)(t);
    std::cout << "dy_call(Fn call_back, T& t): Failed to match" << std::endl;                       // 调用失败
}

/////////////////////////////////////////////////////////////////////////////////////

using namespace std;

void fn_int(int arg) { cout << "fn_int is called" << endl; }
void fn_int_r(int& arg) { cout << "fn_int_r is called" << endl; }
void fn_int_cr(const int& arg) { cout << "fn_int_cr is called" << endl; }

inline void fn(int&& a) { cout << a; }

int main() {
    fn(12);

    int a = 10;
    int& r = a;
    const int& cr = a;
    dy_call(fn_int, 10);
    dy_call(fn_int, a);
    dy_call(fn_int, r);
    dy_call(fn_int, cr);
    dy_call(fn_int_r, 10);
    dy_call(fn_int_r, a);
    dy_call(fn_int_r, r);
    dy_call(fn_int_r, cr);
    dy_call(fn_int_cr, 10);
    dy_call(fn_int_cr, a);
    dy_call(fn_int_cr, r);
    dy_call(fn_int_cr, cr);
    cout << endl << endl;
    dy_call_Cpp11(fn_int, 10);
    dy_call_Cpp11(fn_int, a);
    dy_call_Cpp11(fn_int, r);
    dy_call_Cpp11(fn_int, cr);
    dy_call_Cpp11(fn_int_r, 10);
    dy_call_Cpp11(fn_int_r, a);
    dy_call_Cpp11(fn_int_r, r);
    dy_call_Cpp11(fn_int_r, cr);
    dy_call_Cpp11(fn_int_cr, 10);
    dy_call_Cpp11(fn_int_cr, a);
    dy_call_Cpp11(fn_int_cr, r);
    dy_call_Cpp11(fn_int_cr, cr);
}