class BaseIntf {
public:
    virtual ~BaseIntf() {}
    virtual void foo() = 0;
};

class BaseImpl: public virtual BaseIntf {
public:
    virtual void foo() {}
};

class ListenerBaseInft: public virtual BaseIntf {
};

class Listener: public ListenerBaseInft, public BaseImpl {
};

int main(int argc, char *argv[]) {
    // The type 'Listener' must implement the inherited pure virtual method 'BaseIntf::foo'
    Listener* listener = new Listener();
    listener->foo();
    return 0;
}