Making a class abstract without any pure virtual methods

Question

I have a class which is to listen to mouse events. However, I do not want to force the user to implement any specific one, but I do want to make it clear that they must inhe

Answer 1

Specify the constructor of the base as protected. This does mean that you cannot construct it directly, but forces inheritance. There is nothing that makes a developer inherit from that class aside from good documentation though!

Example:

struct Abstract {
protected:
    Abstract() {}
};

struct Valid: public Abstract {
    // No need to override anything.
};


int main() {
    // Abstract a;  // This line fails constructor is protected
    Valid v;  // This compiles fine.
}