Virtual overloaded operators >> and <<

Question

I need an interface that would require its subclasses to overload << and >>, but I'm not quite sure how since these operators aren't overloaded as member functions:

std::istream& operator>> (std::istream& in, Student& student) {
    in >> student.name >> student.group;
    for (int& i : student.marks) { in >> i; }
    return in;
} 

Maybe there's a way to make it a member function?

Answer 1

You could do something like this:

class StudentInterface
{
public:
    virtual void readSelfFrom(std::istream& in) = 0;
};

std::istream& operator>> (std::istream& in, StudentInteface& student) 
{
    student.readSelfFrom(in);
    return in;
} 

And then let users derive from StudentInterface, eg:

class Student: public StudentInterface
{
public:
    void readSelfFrom(std::istream& in) override
    {
        in >> name >> group;
        for (int& i : marks) { in >> i; }
    }
};