template virtual function

Question

Here is some code:

class IWorker {
public:
    virtual void Do(int x) const = 0;
};

class TSomeWorker : public IWorker {
    void Do(int x) const {
        // ...
    }
};

Now, imagine that we need to refactor it in such way that function Do should become template (int changes into some T). I know that C++ does not allow to create template virtual functions. Is there any alternative?

Similar question: http://stackoverflow.com/questions/7648430/designing-hiearchical-classes-with-template-function/7648621#7648621 — jpalecek, Jul 02 '12 at 18:40
and another: http://stackoverflow.com/questions/7968023/c-virtual-template-method — jpalecek, Jul 02 '12 at 18:41

score 2 · Answer 1 · answered Jul 02 '12 at 18:38

2

It depends on your specific needs. But according to what you posted I would suggest:

template<typename T>
class IWorker {
public:
    virtual void Do(T x) const = 0;
};

template<typename T>
class TSomeWorker : public IWorker<T> {
    void Do(T x) const {
        // ...
    }
};

answered Jul 02 '12 at 18:38

tenfour

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The problem here is that when I use class IWorker in some other classes I have to make them to be templates too. But they're not. The nature of the class says that only the funciton Do is templated :) – typedef Jul 02 '12 at 18:45
A generalized solution to this is described in the answers @jpalecek linked to. If you want a more specific solution to your problem, you have to give more context. – tenfour Jul 02 '12 at 18:49

score 0 · Answer 2 · answered Jul 02 '12 at 18:56

So, you want to mix static polymorphism (templates) and run-time polymorphism (virtual functions), but those are orthogonal. In such case, you need to cast :

class IWorker {
public:
    virtual void Do(void* x) const = 0;
};

template< typename T >
class TSomeWorker : public IWorker {
    void Do(void* x) const {
        T* realX = reinterpret_cast< T* >( x );
        // ...
    }
};

template virtual function

2 Answers2