MultiArray

multiarray.cc

#include <assert.h>
#include <array>
#include <functional>
#include <numeric>

template<typename T, int N>
class MultiArrayBase
{
 public:
  MultiArrayBase(T* data, const std::array<int, N>& dim)
    : data_(data), dim_(dim)
  {
    next_ = std::accumulate(dim.begin()+1, dim.end(), 1L, std::multiplies<size_t>());
  }
  
  MultiArrayBase<T, N-1> operator[](unsigned idx)
  {
    assert(idx < static_cast<unsigned>(dim_[0]));
    std::array<int, N-1> dim;
    std::copy(dim_.begin()+1, dim_.end(), dim.begin());
    MultiArrayBase<T, N-1> result(data_ + idx * next_, dim);
    return result;
  }

  T* data_;
  size_t next_;
  const std::array<int, N> dim_;
};

template<typename T>
class MultiArrayBase<T, 1>
{
 public:
  MultiArrayBase(T* data, const std::array<int, 1>& dim)
    : data_(data), next_(1), dim_(dim)
  {
  }
  
  T& operator[](unsigned idx)
  {
    assert(idx < dim_[0]);
    return data_[idx];
  }

  T* const data_;
  const size_t next_;
  const std::array<int, 1> dim_;
};

template<typename T, int N>
class MultiArray : public MultiArrayBase<T, N>
{
 public:
  explicit MultiArray(const std::array<int, N>& dim)
    : MultiArrayBase<T, N>(nullptr, dim)
  {
    size_t sz = this->next_ * dim[0];
    this->data_ = new T[sz]();
  }

  ~MultiArray()
  {
    delete[] this->data_;
  }

 private:
  // FIXME:
  MultiArray(const MultiArray&) = delete;
  void operator=(const MultiArray&) = delete;
};

int main()
{
  std::array<int, 3> dim3{4,5,3};
  MultiArray<double, 3> arr3(dim3);

  int value = 0;
  for (int i = 0; i < dim3[0]; ++i)
    for (int j = 0; j < dim3[1]; ++j)
      for (int k = 0; k < dim3[2]; ++k)
        arr3[i][j][k] = 10.0 * ++value;

  for (int i = 0; i < dim3[0]; ++i)
    for (int j = 0; j < dim3[1]; ++j)
      for (int k = 0; k < dim3[2]; ++k)
        printf("%.1f\n", arr3[i][j][k]);

  arr3[3][5][2];  // fail
}