NetNews Usenet Archive 1993 #3/NN_1993_3.iso/spool/comp/lang/cplus/19770

Text File | 1993-01-23 | 3.4 KB | 101 lines

Path: sparky!uunet!pipex!doc.ic.ac.uk!uknet!axion!gssec.bt.co.uk!mjackson
From: [e-mail] (Mark Jackson)
Newsgroups: comp.lang.c++
Subject: Mixins (was Re: C++ Multiple inheritance)
Keywords: multiple inheritance
Message-ID: <[e-mail]>
Date: 22 Jan 93 14:18:45 GMT
References: <[e-mail]> <[e-mail]> <[e-mail]> <[e-mail]>
Sender: [e-mail]
Organization: BT, Software Engineering Centre, Glasgow, Scotland
Lines: 88

In article <[e-mail]>, [e-mail] (John MAX Skaller) writes:
|> In article <[e-mail]> [e-mail] (Mark Jackson) writes:
|> >In reply to Dennis Marer and SR Heintz (sorry, my email doesn't
|> >recognise your mail address), I think I have a 'real world' example
|> >for you...
|> >
|> >The system is Client-Server based, communicating via common IPC
|> >service classes.
|> >
|> >class IPCEventHandler : public IPCClient, public EventHandler
|> >{
|> >  public:
|> >    ......
|> >    // Virtual method Inherited from EventHandler
|> >    void HandleEvent( Event& theEvent )
|> >    {
|> >        // Build an IPC Message from the Event data
|> >        IPCMessage theMessage( theEvent.getData() );
|> >
|> >        // Send the resulting message over the IPC
|> >        // using method inherited from IPCClient
|> >        SendMessage( theMessage );
|> >    }
|> >    ......
|> >};
|> >
|> >Unfortunately, at this point, I was supposed to come up with the reason why
|> >I couldn't just inherit from the EventHandler class, and have the IPCClient
|> >as a data member, but try as I might, I can't remember....................
|>
|>     I'll remind you: you override a method from Event handler,
|> thus you cant have it as a member.

BULL, as you say below. If you'd read what I wrote, you'd see
I'm talking about having an IPC object as a member,
NOT the EventHandler. This would look like

class IPCEventHandler : public EventHandler
{
  private:
    IPCClient *ipc;

  public:
    ......
    // Virtual method Inherited from EventHandler
    void HandleEvent( Event& theEvent )
    {
        // Build an IPC Message from the Event data
        IPCMessage theMessage( theEvent.getData() );

        // Send the resulting message over the IPC
        // using IPCClient object
        ipc->SendMessage( theMessage );
    }
    ......
};

Still can't remember why I couldn't do this, though, which is really beginning
to bug me #$^@!&

|>
|> >P.S. I still think using MI with more than 2 parent classes is decidedly
|> >dodgy. 4 is right out. (Book of Armaments: Ch. 4 v. 5)
|> >
|>     Bull. Use as many as is appropriate.
|>     With mixins, that could be quite a few.

I've seen you championing mixins in other articles. Could you give
us a few wee, but not Noddy, examples.
Then you may be able to twist my arm...

|>
|>
|> --
|> ;----------------------------------------------------------------------
|>         JOHN (MAX) SKALLER,         [e-mail]
|>     Maxtal Pty Ltd, 6 MacKay St ASHFIELD, NSW 2131, AUSTRALIA
|> ;------ SCIENTIFIC AND ENGINEERING SOFTWARE ---ph:  2 799 8223 --------

--

   !!!!!!!     __________________________
   +(.)(.)    (                          )
   C   > )    |  I, and only I, said it. |
    \ V / ----(__________________________)
     ---

Mark Jackson