Question

I’m wanting to invoke a specialized templated function by using a pointer to it’s base type. I’m not sure if this possible so I’m open to suggestions and/or alternatives. Here is an example of my situation:

class CBase {};
class CDerivedClass : public CBase {};

template<class T>
int func<T>(T &x) { ... };

template<>
int func<CDerivedClass>(CDerivedClass &x) { ... };

I have another function that manages a list of CBase pointers and then calls the func() function.

void doStuff()
{
    CBase *foo[10] = { ...... };

    for (int i = 0; i < 10; ++i)
        func(*foo[i]);
}

Is there a way to get the derived type, so that func(CDerivedClass &) is called?

Answer 1

The “Visitor” pattern comes to the rescue in this case. It enables polymorphic behavior in an algorithm implemented outside the class. Some support code is required inside the class, but new algorithms can later be added, existing algorithms modified, etc., without affecting the class.