Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!elroy.jpl.nasa.gov!lll-winken!cert!netnews.upenn.edu!tandem.physics.upenn.edu!claytor
From: claytor@tandem.physics.upenn.edu (Nelson Claytor)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Casting in Think C
Message-ID: <34174@netnews.upenn.edu>
Date: 6 Dec 90 15:12:47 GMT
Sender: news@netnews.upenn.edu
Organization: University of Pennsylvania Physics Dept.
Lines: 28
References:<6167@munnari.oz.au> <3028@skye.cs.ed.ac.uk> <6194@munnari.oz.au>

In article <6194@munnari.oz.au> caw@munnari.oz.au (Chris Wright) writes:
> In article <3028@skye.cs.ed.ac.uk>, nick@cs.edinburgh.ac.uk (Nick 
Rothwell) writes:
> > In article <6167@munnari.oz.au>, caw@munnari.oz.au (Chris Wright) 
writes:
> > > Why do you have to cast gApplication in ThinkC e.g.:
> > > extern      CApplication    *gApplication;
>  
> 
> > gApplication is still a CApplication, and hence doesn't have an 
IEditApp()
> > method unless you cast it.
> 
>         If my memory serves me correctly, gApplication is now a 
>         CEditApp. This can be checked with the member function.
>         So it SHOULD have an IEditApp(). And the compiler 
>         shouldn't complain.

At runtime, yes, gApplication is a CEditApp, and therefore it 
does have the IEditApp() method. However, at compile time, all 
the compiler knows is that you declared it as a CApplication. 
Therefore, *as far as the compiler is concerned*, there is 
no IEditApp.

Nelson

Nelson Claytor
claytor@tandem.physics.upenn.edu