c++参数包展开和折叠表达式

template<typename T>
void fun2(T t)
{

    cout << t << endl;
}

//利用逗号表达式和初始化列表展开
template<typename ...Arg6>
void fun1(Arg6... args)
{
    int arr[] = { (fun2(args),0)... };
}

template<typename T>
int func3Imp(T&& t)
{
    static int c = 0;
    std::cout << t << endl;
    return ++c;
}

template<typename... Ts>
void func3(Ts&&... args)
{
    const int size = sizeof...(args) + 2;
    int res[size] = { 1, args..., 2 };

    //初始化列表展开
    int dummy[sizeof...(Ts)] = { func3Imp(std::forward<Ts>(args))...};
}

template<class... Args>
void fLambda(Args... args)
{
    //注意这里调用func3(args...),属于参数包直接展开为func3的参数
    auto lm = [&, args...] { return func3(args...); };
    lm();
}

template<typename... Ts, int... N>
void print_tuple(const std::tuple<Ts...>& t, std::index_sequence<N...>) {
    int dummy[sizeof...(Ts)] = { func3Imp(std::get<N>(t))... }; // 初始化列表展开,和index_sequence配合使用
    //fLambda(std::get<N>(t)...); //参数包在函数形参中的展开 fLambda(std::get<1>(t),std::get<2>(t),std::get<3>(t))
    //fLambda(func3Imp(std::get<N>(t))...); //fLambda(func3Imp(std::get<1>(t)),func3Imp(std::get<2>(t)),func3Imp(std::get<3>(t)))
   
}
template<typename... Ts, int... N>
void print_tuple2(const std::tuple<Ts...>& t, std::index_sequence<N...>) {
    int dummy[sizeof...(Ts)] = { (func3Imp(std::get<N>(t)),0)... };//利用逗号表达式和初始化列表展开
}

template<typename... Ts, int... N>
void print_tuple3(const std::tuple<Ts...>& t, std::index_sequence<N...>) {
   // ((std::cout << std::get<N>(t) << ' '), ...);      //c++17的折叠表达式
}

//使用
    {
        //auto tuple = std::make_tuple(1, 2.3, "hello");
        auto tuple = std::make_tuple(1, 2, 333);
        print_tuple(tuple, std::make_index_sequence<std::tuple_size_v<decltype(tuple)>>{}); //make_index_sequence的参数必须<=tuple元素数量
        print_tuple2(tuple, std::make_index_sequence<std::tuple_size_v<decltype(tuple)>>{});
        print_tuple3(tuple, std::make_index_sequence<std::tuple_size_v<decltype(tuple)>>{});
    }
    fun1(12, 3, 4);
    func3(12, 13);
    fLambda(11, 12);

参考：https://zh.cppreference.com/w/cpp/language/parameter_pack