在编译期间如何切换/选择类型？(How do I switch/select types during compile

在编译期间如何切换/选择类型？(How do I switch/select types during compile-time?)

有没有一种标准的方式让我在编译时在c ++ 11的无符号索引中选择一个类型？

例如，像这样的东西：

using type_0 = static_switch<0,T,U>; // yields type T using type_1 = static_switch<1,T,U>; // yields type U

如果有一个可变模板版本，这将是非常有用的。

Is there a standard way for me to select a type at compile-time on an unsigned index in c++11?

For example, something like:

using type_0 = static_switch<0,T,U>; // yields type T using type_1 = static_switch<1,T,U>; // yields type U

If there is a variadic-template version, it would be very useful.

最满意答案

这应该工作：

template<std::size_t N, typename... T> using static_switch = typename std::tuple_element<N, std::tuple<T...> >::type;

另一种方法：

template<std::size_t N, typename T, typename... Ts> struct static_switch { using type = typename static_switch<N - 1, Ts...>::type; }; template<typename T, typename... Ts> struct static_switch<0, T, Ts...> { using type = T; };

This should work:

template<std::size_t N, typename... T> using static_switch = typename std::tuple_element<N, std::tuple<T...> >::type;

Another method:

template<std::size_t N, typename T, typename... Ts> struct static_switch { using type = typename static_switch<N - 1, Ts...>::type; }; template<typename T, typename... Ts> struct static_switch<0, T, Ts...> { using type = T; };