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From: Andrew Wall on 10 Dec 2009 11:25

"beemaster" <beemasterz(a)gmail.com> wrote in message
news:c3c6f1f5-d866-47e7-a018-b10b339ce3ad(a)r40g2000yqn.googlegroups.com...
>I have hierarchy, that contains one base interface class -
> IConnection,
> and two derived interfaces: IClientConnection and IServerConnection
>
> =================
>
> class IConnection
> {
> public:
> virtual void Send() = 0;
> };
>
> class IClientConnection : public virtual IConnection
> {
> public:
> virtual void Connect() = 0;
> };
>
> class IServerConnection : public virtual IConnection
> {
> public:
> virtual void Accept() = 0;
> };
>
> =================
>
> I also have a realization for base interface
>
> =================
>
> class Connection : public virtual IConnection
> {
> public:
> virtual void Send()
> {
> //...
> };
> };
>
> =================
>
> For two other interfaces I want to use existing realization of base
> interface.
>
> =================
>
> class ServerConnection : public IServerConnection,
> piblic Connection
> {
> public:
> virtual void Accept();
> };
>
> =================
>
> I inherit Connection, because I don't want to duplicate the code from
> Connection::Send();
>
> When I compile this code with Microsoft compiler, I get following
> errors:
> warning C4250: 'ClientConnection' : inherits
> 'Connection::Connection::Send' via dominance.
> Is there a better way of doing this? How can I avoid multiple
> inheritance and code duplication?
> I really like an idea of such inheritance. Why is it bad?
>

>From the source code you supply, I think you've got the hang of this
multiple inheritance thing.
The Microsoft warning C4250 is only a warning and not even that - its really
just information which you knew anyway. When I've encountered this, I've
just disabled the warning (after a lot of thought about it), and I recommend
you do the same.

IMHO this is exactly the way to use multiple inheritance - it avoids code
duplication, but you have to accept fixed compile time and run time
behaviour.

Andrew Wall


--
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]

From: anand on 16 Dec 2009 20:32
On Dec 10, 11:25 pm, "Andrew Wall" <wallguide-usen...(a)yahoo.com>
wrote:
> "beemaster" <beemast...(a)gmail.com> wrote in message
>
> news:c3c6f1f5-d866-47e7-a018-b10b339ce3ad(a)r40g2000yqn.googlegroups.com...
>
>
>
> >I have hierarchy, that contains one base interface class -
> > IConnection,
> > and two derived interfaces: IClientConnection and IServerConnection
>
> > =================
>
> > class IConnection
> > {
> > public:
> > virtual void Send() = 0;
> > };
>
> > class IClientConnection : public virtual IConnection
> > {
> > public:
> > virtual void Connect() = 0;
> > };
>
> > class IServerConnection : public virtual IConnection
> > {
> > public:
> > virtual void Accept() = 0;
> > };
>
> > =================
>
> > I also have a realization for base interface
>
> > =================
>
> > class Connection : public virtual IConnection
> > {
> > public:
> > virtual void Send()
> > {
> > //...
> > };
> > };
>
> > =================
>
> > For two other interfaces I want to use existing realization of base
> > interface.
>
> > =================
>
> > class ServerConnection : public IServerConnection,
> > piblic Connection
> > {
> > public:
> > virtual void Accept();
> > };
>
> > =================
>
> > I inherit Connection, because I don't want to duplicate the code from
> > Connection::Send();
>
> > When I compile this code with Microsoft compiler, I get following
> > errors:
> > warning C4250: 'ClientConnection' : inherits
> > 'Connection::Connection::Send' via dominance.
> > Is there a better way of doing this? How can I avoid multiple
> > inheritance and code duplication?
> > I really like an idea of such inheritance. Why is it bad?
>
> >From the source code you supply, I think you've got the hang of this
>
> multiple inheritance thing.
> The Microsoft warning C4250 is only a warning and not even that - its really
> just information which you knew anyway. When I've encountered this, I've
> just disabled the warning (after a lot of thought about it), and I recommend
> you do the same.
>
> IMHO this is exactly the way to use multiple inheritance - it avoids code
> duplication, but you have to accept fixed compile time and run time
> behaviour.
>
> Andrew Wall
>


I encountered the same problem today. But I got rid of the warning by
making the base class functions as "virtual". The rationale behind
that was: if the derived class needs to add some more functionality
(in the future) than whats derived from the base, then this should
allow it to do.

But I wonder whether its a good practice or is it the correct way of
doing?

Cheers,
Anand.


--
[ See http://www.gotw.ca/resources/clcm.htm for info about ]
[ comp.lang.c++.moderated. First time posters: Do this! ]

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