How does these 2 functions act as getters and setters?

Question

I'm studying matrix operations, and out teacher provided us this 3 next functions:

//methods used as GETTERS and SETTERS - to access the matrix elements
    float& mat3::at(int i, int j) {
        return matrixData[i + 3 * j];
    }

    const float& mat3::at(int i, int j) const {
        return matrixData[i + 3 * j];
    }

    mat3& mat3::operator =(const mat3& srcMatrix) {
        //usage example for the "at" getter/setter methods
        for (int i = 0; i < 3; i++) {
            for (int j = 0; j < 3; j++) {
                //at(i,j) acts as a setter
                //srcMatrix.at(i, j) is used as a getter
                at(i, j) = srcMatrix.at(i, j);
            }   
        }

        return (*this);
    }

I get that 'srcMatrix.at(i,j)' acts as a getter, that's pretty obvious, because the fucntions returns the value at that location. But I can't understand why it acts as a setter as well, there is no assignment. And which one of the 'at' functions is a getter and which is a setter?

Answer 1

The first member function float& mat3::at(int i, int j) can be used as a setter. Because it returns a non-const reference you can assign to it's result to change the matrix's elements.

For example srcMatrix.at(i,j) = 4.2; will set the element that position to 4.2.

The second overload const float& mat3::at(int i, int j) const can only act as a getter. The result is a const reference so it's not possible to assign to the result. Its provided so that it's still possible to get the value of an element if you have a const mat3.