Private overriden virtual functions in derived class

Question

Is there any point to making virtual member functions, overridden from a base class private, if those are public in the base class?

struct base {
    virtual void a();
};

struct derived : base {
// ...
private:
    void a() override;
};

Answer 1

If you are forced to do a 2-phase construction on the implementation class (i.e. have an init() method as well as or instead of a constructor that has to be called (I know, but there are reasons), then this stops you calling any /other/ methods directly on the instance pointer before you pass it back as an interface pointer. Go the extra mile, make the inheritance private, and have your one public init function return the interface pointer!

Another reason is you just don't /need/ to write public: in a final implementation class declaration, so then by default everything is private. But why you would do that and use struct instead of class I don't know. Perhaps this was converted from class at some point due to a style war?