如何重载下标运算符 [] 以引用 2d STL 数组？

Question

I am trying to create an overloaded operator for my class, my class contains a 2d array container. I want use the operator as follows: fooClass a; a[i][j] = 4; i don't want to use it like a[i, j], a(i, j) or call a function to input or output an element. Is is possible?

Chaining the call wont work since the first returns pointer to array, and the second should return an element in an array ie a float.

my class looks something like this:

class foo
{
    public:
    foo();
    ~foo();

    foo& operator=(const foo&rhs);
    foo& operator=(const foo&&rhs);
    foo& operator=(std::initializer_list<std::initializer_list<float>> il); 
    friend std::ostream& operator<<( std::ostream& os, const foo&rhs);
    std::array<float, 3>& operator[](const int & rhs); <<<<HERE<<<< What should it return?

    private:
    std::array<std::array<float, 3>, 3> matrix;
};


int main()
{
    foo a;
    a = {{1,2,3},{4,5,6},{7,8,9}};
    a[1][2] = 13;
    cout << a[1][2] << endl;


    return(0);
}

My question is, how to do this, and what should the function ..... operator[](const int & rhs); return?

FYI I am not using the array container directly because I am implementing other functions also I am doing the matrix column major.

Answer 1

Doesn't this work?

  std::array<float, 3>& operator[](const int & rhs) {
    return matrix[rhs];
  }