deduction guides for matrix

Question

I'm looking for deduction guide for initialize matrix.

I've tried to use pack in pack and sizeof..., initializer_list<initializer_list<T>>, custom classes for arrays for construct, but nothing is works...

so, i'm looking for initialize

template <class T, size_t s1, size_t s2>
class matrix
{
T matr[s1][s2]; //maybe with custom array class, if this problem need this
public:
//constructor
};
//deductor

like

matrix m{{1, 2}, {1, 2}};

or

matrix m({1, 2}, {1, 2});

Answer 1

I've found the way to avoid the additional brackets.

This time is required also an explicit deduction guides, SFINAE and an additional method to initialize the matr member but should works.

The following is a full complete example

#include <iostream>

template <typename T, std::size_t s1, std::size_t s2>
class matrix
 {
   private:
      T matr[s1][s2];

      void init_row (std::size_t i, T const (&arr)[s2])
       {
         for ( auto j = 0u ; j < s2 ; ++j )
            matr[i][j] = arr[j];
       }

   public:
      template <std::size_t ... Dims,
                std::enable_if_t<sizeof...(Dims) == s1, bool> = true,
                std::enable_if_t<((Dims == s2) && ...), bool> = true>
      matrix (T const (&...arrs)[Dims])
       { std::size_t i = -1; (init_row(++i, arrs), ...); }
 };

template <typename T, std::size_t Dim0, std::size_t ... Dims,
          std::enable_if_t<((Dim0 == Dims) && ...), bool> = true>
matrix (T const (&)[Dim0], T const (&...arrs)[Dims])
   -> matrix<T, 1u+sizeof...(Dims), Dim0>;


int main()
{
   matrix m{{1, 2}, {1, 2}, {1, 2}};

   static_assert( std::is_same_v<decltype(m), matrix<int, 3u, 2u>> );
}