I have the following code:

enum type_kind{unkown=-1,carray, multi_carray};

template<class T>
struct detect_carray{
   constexpr static int kind=unkown;
};
template<class T, std::size_t N>
struct detect_carray<T[N]>{
   constexpr static int kind=carray;
};

Now, I want to add another specialization for detecting multidimensional arrays in C-style, that is, T[a][b]....

What is the syntax to achieve this? Can I use Variadic templates?

I expect the following behavior:

int main()
{
std::cout<<detect_carray<std::vector<int>>::kind;//-1
std::cout<<detect_carray<int[3]>::kind;//0
std::cout<<detect_carray<double[3][5]>::kind;//1
std::cout<<detect_carray<std::complex<double>[3][5][8][16]>::kind;//1
//Correct out: -1011
}

CodePudding user response：

There's already a trait called std::rank in the standard library so the solution is quite simple:

template <class T>
struct detect_carray {
  enum type_kind { unknown = -1, carray, multi_carray };

  static constexpr int kind = [] {
    switch (std::rank_v<T>) {
      case 0: return unknown;
      case 1: return carray;
      default: return multi_carray;
    }
  }();
};

CodePudding user response：

Just add a specialization for multidimensional arrays:

template<class T, std::size_t N1, std::size_t N2>
struct detect_carray<T[N1][N2]>{
   constexpr static int kind=multi_carray;
};

then

std::cout<<detect_carray<std::vector<int>>::kind;//-1
std::cout<<detect_carray<int[3]>::kind;//0
std::cout<<detect_carray<double[3][5]>::kind;//1
std::cout<<detect_carray<std::complex<double>[3][5][8][16]>::kind;//1

LIVE

BTW: For double[3][5], T will be double (and N1 will be 3 and N2 will be 5). For std::complex<double>[3][5][8][16], T will be std::complex<double> [8][16] (and N1 will be 3 and N2 will be 5).