template<typename T, size_t n, size_t m>
class Matrix
{
public:
  Matrix(){}
  
  Matrix(const Matrix& rhs) { 
    for(int i=0; i<n; ++i)
      for(int j=0; j<m; ++j)
        ElementAt(i,j) = rhs.ElementAt(i,j);
  }
  
  Matrix& operator=(const Matrix& rhs) {
    if( this != &rhs )
      for(int i=0; i<n; ++i)
        for(int j=0; j<m; ++j)
          ElementAt(i,j) = rhs.ElementAt(i,j);
    return *this;
  }
  
  virtual ~Matrix() {}

  const T& ElementAt(size_t n, size_t m) const 
  { return arrData[n][m]; }
  T& ElementAt(size_t n, size_t m)
  { return arrData[n][m]; }

private:
  // C-style array for efficiency and locality of reference
  T arrData[n][m];
};

template<typename T, size_t n, size_t m>
Matrix<T, n, m> operator+(
  const Matrix<T, n, m>& lhs, 
  const Matrix<T, n, m>& rhs
  ) {
  Matrix<T, n, m> matSum;
  for(int i=0; i<n; ++i)
    for(int j=0; j<m; ++j)
      matSum.ElementAt(i,j) = 
        lhs.ElementAt(i,j) + rhs.ElementAt(i,j);
  return matSum;
}