Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!mips!apple!keith
From: keith@Apple.COM (Keith Rollin)
Newsgroups: comp.sys.mac.programmer
Subject: Re: Gestalt - new and improved methods
Message-ID: <54051@apple.Apple.COM>
Date: 16 Jun 91 21:51:29 GMT
References: <1991Jun14.160733.14793@terminator.cc.umich.edu>
Organization: Apple Computer Inc., Cupertino, CA
Lines: 40

In article <1991Jun14.160733.14793@terminator.cc.umich.edu> potts@itl.itd.umich.edu (Paul Potts) writes:
>I've been putting together some code to use Gestalt in its new and
>improved form.  Since it has taken me a while to get it going, I thought
>I would post it to save someone else time.
>
>This uses the new method for checking trap availability described in IM-6,
>chapter 3.  I've translated some of that code directly into THINK C.
>
>If anyone finds an error, please post a correction. It seems to work fine.

In the code that you posted, you check for the existance of the
_Gestalt trap. I don't think this is a good idea. Gestalt is both glue
and a trap.  When you compile a program with a version of MPW or THINK
that supports Gestalt, you end up calling the glue. The glue checks to
see if the trap is implemented. If so, the trap is called. If not, the
rest of the glue provides some emulated behavior. If you check for the
trap yourself, you loose out on this emulated behavior.

Actually, the above is just a little shy of the truth. It is possible
for you to specify that you want your program to be built for 7.0 or
later, in which case you end up calling the trap directly. However, in
that case, you can safely assume the existance of _Gestalt and not
check for it.

By the way, in testAttribute(), why do you use:

	return (BitTst((void*)&feature, 31 - attribute));

instead of

	return (feature & (1 << attribute));

?

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"But where the senses fail us, reason must step in."  - Galileo