Why don't we use single member function for set and get the data member value instead of separate accessor/getter and mutator/setter function?

Question

I just have a really quick question as I am trying to grasp C++ class concept. Why don't we use a single member function for set and get the data member value instead of separate accessor/getter and mutator/setter function?

Example Shown Below:

class Student
{
    private: 
            int rollno;
    public:     
            int setGetRollNo(int rn) {
                rollno = rn;
                return rollno;
            }
        
};


int main()
{   
    Student s1;
    cout << s1.setGetRollNo(123);

    
}

It works the same as when we try to do that we sperate the accessor and mutator function.

Answer 1

There is nothing wrong with having a function that can both access and mutate a member. However, the way you are doing is definitely incorrect. With the code you have right now, you cannot get the current value without setting it to a new value first.

Instead, a better way to do this is to do this is to return the reference of the member object:

class Student
{
    int rollno;
public:
    int& rollno_ref()
    {
        return rollno;
    }
};

Now you can use the same function both access and mutate the member like:

std::cout << student.rollno_ref();       // access
student.rollno_ref() = 10;               // mutate

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One thing to note is that this function really doesn't do much beside exposing a reference to an existing member. To add more functionalities to it, you should look up proxy class.

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Another thing to note is this function will not work on const Student. To make it work, you should supply its const version as well.