Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!swrinde!zaphod.mps.ohio-state.edu!uwm.edu!bionet!arisia!sgi!shinobu!odin!delrey!shap
From: shap@delrey.sgi.com (Jonathan Shapiro)
Newsgroups: comp.lang.c++
Subject: Re: Novice question re: class derivation
Message-ID: <2995@odin.SGI.COM>
Date: 19 Jan 90 18:46:19 GMT
References: <44.UUL1.3#5109@pantor.UUCP>
Sender: news@odin.SGI.COM
Organization: Silicon Graphics, Inc., Mountain View, CA
Lines: 32

In article <44.UUL1.3#5109@pantor.UUCP> richard@pantor.UUCP (Richard Sargent) writes:
>So the bottom line is: How can I set up a hierarchy of device
>classes that will allow me to code (my main application, at least)
>to be independent of the display device?
>
>Richard Sargent                   Internet: richard@pantor.UUCP
>Systems Analyst                   UUCP:     ...!mnetor!becker!pantor!richard

Right idea.  Wrong implementation.  By the time you hit the Device
constructor, you are essentially saying that you already are
constructing the appropriate kind.  What is needed is a single library
routine that determines the device type, allocates the right kind, and
returns a Device *:

Device *
getDevice()
{
   kind = determine_which_graphics_head();
   switch(kind) {
   case Targa:
       return new Targa;
   case Wombat:
       return new Wombat;
   ...
   }

   return 0;
}


Jonathan Shapiro
Silicon Graphics, Inc.