如何获得n嵌套向量的最内部类型?
我需要获取 n 嵌套向量的内部类型.例如:
I need to get the inner type of a n-nested vector. For Example:
type a; //base_type of a = type
std::vector<type> b; //base_type of b = type
std::vector<std::vector<type>> c;//base_type of c = type
等等.我尝试使用包装器，但这会导致编译器错误.
and so on. I tried using a wrapper, but this results in a compiler error.
template<typename T1>
struct base_type : T1::value_type { };
template<typename T1>
struct base_type<std::vector<T1>> {
using type = typename base_type<T1>::value_type;
};
推荐答案
你的两个案例都错了.
您的基本案例应该是非vector 案例.对于非vector，没有::value_type.你只想要类型:
Your base case should be the non-vector case. For a non-vector, there is no ::value_type. You just want the type:
template <typename T>
struct base_type {
using type = T;
};
对于您的递归情况，base_type 的结果"类型被命名为 type.不是 value_type，所以我们必须在这里使用它:
For your recursive case, base_type's "result" type is named type. Not value_type, so we have to use that here:
template<typename T>
struct base_type<std::vector<T>> {
using type = typename base_type<T>::type;
};
我们可以简化为:
template<typename T>
struct base_type<std::vector<T>>
: base_type<T>
{ };
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