class AValue : public virtual ValueBase {
public:

    virtual void ShortItem (Short) = 0;
    virtual Short ShortItem () const = 0;

    virtual void LongItem (Long) = 0;
    virtual Long LongItem () const = 0;

    ...

    virtual ... AnOperation (...) = 0;
}

class OBV_AValue : public virtual AValue {
public:

    virtual void ShortItem (Short) { ... };
    virtual Short ShortItem () const { ... };

    virtual void LongItem (Long) { ... };
    virtual Long LongItem () const { ... };

    ...

    virtual ... AnOperation (...) = 0;
}

class ValueFactoryBase {
private:

    virtual ValueBase *create_for_unmarshal () = 0;

    ...
}

class AValue_init : public ValueFactoryBase {
public:

    virtual AValue *AConstructor (...) = 0;

    ...
}