template<std::same_as<int>...T> int sum(T...args){auto s = (args+...+0);return s; }template<typename... Ts> auto make_tuple(Ts ...args) -> decltype(std::tuple<Ts...> t(args...)) //c11 写法 auto make_tuple(Ts ...args) //c14 自动推导 {std::tuple<Ts...> t(args...);return t; }template<std::convertible_to<double>... Ts> //可转成double void f(Ts ...args){std::vector<double>t{1.0+(args)*{args}...};for(auto v:t){cout<<v<<endl;}cout<<"sizeof...(args)"<<endl; } int main(){f(1,2.0f,3,4,1);return 0; }template<typename ...Base> class Myclass:public Base...{public:Myclass():Base()...{} }; int main(){Myclass<BaseClass1,BaseClass2>mc; }template<typename ...Ts> void print_fold(Ts...args){((cout<<args<<endl), ...); }void print_recursion(const auto &first, const auto & ...rest){cout<<first<<endl;if constexpr(sizeof...(rest)>0) {print_recursion(rest...);}}//使用常量n进行索引 auto f(auto ...args){const int n=sizeof...(args);cout<<args...[n]<<endl; }template<std::size_t I,typename...Args> auto element_at(const Args &...args){static_assert(I<sizeof...(args),"Index out of bounds");return std::get<I>(std::forward_as_tuple(args...)); }//递归方式获取。 template<std::size_t I,typename T, typename...Args> auto element_at(T arg0, const Args&... args){static_assert(I<1+sizeof...(args),"Index out of bounds");if constexpr (I==0)return arg0;elsereturn element_at<I-1>(args...); } //c++26 template<std::size_t I, typename ... Args> auto element_at_1(const Args&...args){return args...[I]; }int main(){cout<<element_at<3>(1,2.0,'c',"string")<<endl;return 0; }