C++ Generic Initializer List

gistfile1.cpp

// from: http://stackoverflow.com/questions/15848781/constructor-for-nested-initializer-lists

template <int d, typename T>
class ClassA {

  size_t n_[d] = {0};
  T* data_;

  template <int D, typename U>
  struct Initializer_list {

    typedef std::initializer_list<typename Initializer_list<D-1,U>::list_type > list_type;

    Initializer_list(list_type l, ClassA& a, size_t s, size_t idx) {

      a.n_[d-D] = l.size();

      size_t j = 0;
      for (const auto& r : l)
        Initializer_list<D-1, U> pl(r, a, s*l.size(), idx + s*j++);
    }
  };

  template <typename U>
  struct Initializer_list<1,U> {

    typedef std::initializer_list<T> list_type;

    Initializer_list(list_type l, ClassA& a, size_t s, size_t i) {

      a.n_[d-1] = l.size();
      if (!a.data_)
        a.data_ = new T[s*l.size()];

      size_t j = 0;
      for (const auto& r : l)
        a.data_[i + s*j++] = r;
    }
  };

  typedef typename Initializer_list<d,T>::list_type initializer_type;

public:

  // initializer list constructor
  ClassA(initializer_type l) : data_(nullptr) {
    Initializer_list<d, T> r(l, *this, 1, 0);
  }

  size_t size() const {
    size_t n = 1;
    for (size_t i=0; i<4; ++i)
      n *= n_[i];
    return n;
  }

  friend std::ostream& operator<<(std::ostream& os, const ClassA& a) {
    for (int i=0; i<a.size(); ++i)
      os<<" "<<a.data_[i];
    return os<<endl;
  }
};

int main()
{

  ClassA<4, double> TT = { {{{1.}, {7.}, {13.}, {19}}, {{2}, {8}, {14}, {20}}, {{3}, {9}, {15}, {21}}}, {{{4.}, {10}, {16}, {22}}, {{5}, {11}, {17}, {23}}, {{6}, {12}, {18}, {24}}} };
  cout<<"TT -> "<<TT<<endl;

  return 0;
}