Re: Inheritance: Implementing pure virtual functions by inheriting from an object providing an implementation

From:
"Alf P. Steinbach" <alfps@start.no>
Newsgroups:
comp.lang.c++
Date:
Tue, 31 Mar 2009 10:57:02 +0200
Message-ID:
<gqslp4$2gu$2@news.motzarella.org>
* Jaco Naude:

Hi

I'm wondering if an idea that I have should work. Well the compiler
(mingw) does not seem to allow it, but I'm not sure why it does not
work.

I have an interface class:

class IManagable {
public:
    virtual void setID(int new_id) = 0;
    virtual int getID() = 0;
}

And an object implementing this interface:

class ManagableObject {
public:
    ManagableObject () { id = -1; }
    ~ManagableObject ();

   // Implement functions
    inline void setID(int new_id) { id = new_id; }
    inline int getID() { return id; }

private:
   int id;
}

I've read in the FAQ that inheritance should not be used for code
reuse in general. But in my case I think it is a good idea. I want to
be able to assign unique IDs to objects implementing the interface. If
all of these objects can use the interface as well as the
ManagableObject implementation of the interface, it will reduce my
workload quite a lot I believe.

Now the problem. I have an object that I want to be able to manage
that looks like this:

class ManageMe : virtual public IManagable, public ManagableObject {
    ManageMe () {}
    ~ManageMe () {}
}

This complains that the IManagable pure virtual public functions
aren't implemented by ManageMe. So my approach to accomplish this is
not working. Is there a different way that I can do this without
having to implement the IManagable interface in ManageMe (where the
implementation calls the ManagableObject functions).

Thanks in advance for any advice


class ManagableObject: public virtual IManagable

Cheers & hth.,

- Alf

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