泛型编程

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;
}