Path: utzoo!utgpu!news-server.csri.toronto.edu!rutgers!apple!usc!cs.utexas.edu!yale!mintaka!bloom-beacon!eru!hagbard!sunic!mcsun!ukc!edcastle!cs.ed.ac.uk!cs.edinburgh.ac.uk!nick
From: nick@cs.edinburgh.ac.uk (Nick Rothwell)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Casting in Think C
Keywords: Casts ThinkC
Message-ID: <3028@skye.cs.ed.ac.uk>
Date: 5 Dec 90 12:30:46 GMT
References: <6167@munnari.oz.au>
Sender: nnews@cs.ed.ac.uk
Reply-To: nick@lfcs.ed.ac.uk
Organization: Wavetables 'R' Us
Lines: 35

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;
> 
> void main()
> 
> {
> 	gApplication = new(CEditApp);
> 	((CEditApp *)  gApplication)->IEditApp();
> 	gApplication->Run();
> 	gApplication->Exit();
> }
> 
> if you remove the cast and try gApplication -> iEditApp(), the compiler
> complains.

As it should. I'm not sure what the argument to new() actually is/does, but
my guess is that it just provides a size (a la "sizeof") to determine how
much store to claim.

gApplication is still a CApplication, and hence doesn't have an IEditApp()
method unless you cast it.

> new is meant to "automatically assign a class to the newly created object"

Now, I've never understood what this kind of thing means, ditto for Bless()
and all the rest. Presumably it does something automagical to the method
dispatcher. Anybody care to comment what "the class of an object" actually
means (as opposed to the static type of the object pointer)?

-- 
Nick Rothwell,  Laboratory for Foundations of Computer Science, Edinburgh.
                nick@lfcs.ed.ac.uk    <Atlantic Ocean>!mcsun!ukc!lfcs!nick
~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~ ~~
 "You ain't seen nothing yet. I can take this floor out too, no trouble."