Question

I’ve got a question concerning handling of virtual function in C++ programming. I have something like this:

template<class T>
class baseClass
{
    virtual void doSomething(T& t) {
        // some baseClass specific code
    }

    void doSomethingElse(T& t) {
        // some baseClass specific code

        this->doSomething(t);
    }
}

template<class T>
class subClass
{
    virtual void doSomething(T&) {
        // some subclass related code
    }
}

Now, if I construct an object of type subClass….

int main(int argc, char *argv[])
{
    subClass<anyType> * subClassObject = new subClass<anyType>();
    subClassObject->doSomethingElse(anyTypeObject);
}

…. and call the doSomethingElse method of the base class, this method will call the doSomething method of the base class and not of the sub class.

What I want to have, is calling the doSomething method of the subclass (not of the baseClass).

Can anybody tell me how to accomplish that?

Answer 1

You could accomplish it with CRTP:

template<class T, class Derived>
class baseClass
{    
    void doSomethingElse(T& t) {
        // some baseClass specific code
        static_cast<Derived*>(this)->doSomething(t);
    }
}

template<class T>
class subClass : public baseClass<T, subClass>
{
    void doSomething(T&) {
        // some subclass related code
    }
}

See this for discussion about virtual template methods