假设我们想要创建一个帮助类来反转模板包,例如如下:
#include <tuple>
#include <utility>
#include <typeinfo>
#include <iostream>
template <class>
struct sizer;
template <template<class...> class Pack, class... Args>
struct sizer<Pack<Args...>> {
static constexpr size_t value = sizeof...(Args);
};
template <class Pack, class Indices = std::make_index_sequence<sizer<Pack>::value>>
struct reverse_pack;
template <class... Args, size_t... I>
struct reverse_pack<std::tuple<Args...>, std::integer_sequence<std::size_t, I...>> {
using type = typename std::tuple<typename std::tuple_element<(sizeof...(Args) - I - 1), std::tuple<Args...>>::type...>;
};
int main() {
std::cout << typeid(reverse_pack<std::tuple<int, float, double>>::type).name() << std::endl;
}
我们可以使用例如函数签名作为模板参数成功完成相同的事情:
#include <utility>
#include <typeinfo>
#include <iostream>
template <class> …