From: kilgallen@eisner.decus.org (Larry Kilgallen)
Subject: Re: Implementing pointers to pointers in Ada
Date: 1996/09/11
Date: 1996-09-11T00:00:00+00:00 [thread overview]
Message-ID: <1996Sep11.091148.1@eisner> (raw)
In-Reply-To: 3235E2C3.636F@itg-sepg.logicon.com
In article <3235E2C3.636F@itg-sepg.logicon.com>, David Shochat <shochat@itg-sepg.logicon.com> writes:
> John Herro wrote:
>
>> Of course, it's not obvious WHY you want to use two levels of indirection.
>
> It was necessary for 68K Mac programming (I don't know about PPC). The
> OS had to be able to move heap objects around whenever memory got tight,
> so the programmer would access most GUI objects through a so-called
> "handle" which was a pointer to a "master" pointer to the actual data.
> In Meridian's Ada for the Mac, this was declared just as the examples in
> this thread show (without the "all" -- it was Ada 83). This scheme was
> crucial to allow the original Mac to run with only 128K. This scheme is
> actually much older than the Mac.
I would _hope_ that Macintosh Ada 95 implementations would make
details of the handle mechanism _private_, since many mistakes
one can make involve saving a copy of the middle pointer when
the handle is not locked.
This is _exactly_ the sort of situation where higher level
languages can help, and Ada has the syntax to do it.
Larry Kilgallen
next prev parent reply other threads:[~1996-09-11 0:00 UTC|newest]
Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top
1996-09-09 0:00 Implementing pointers to pointers in Ada Vasilios Tourloupis
1996-09-09 0:00 ` Samuel Tardieu
1996-09-09 0:00 ` Norman H. Cohen
1996-09-09 0:00 ` Mark A Biggar
1996-09-09 0:00 ` John Herro
1996-09-10 0:00 ` David Shochat
1996-09-11 0:00 ` Larry Kilgallen [this message]
1996-09-12 0:00 ` Dr. John B. Matthews
1996-09-13 0:00 ` Better MacOS Handles through Ada (was: Implementing Pointers to Pointe Larry Kilgallen
1996-09-14 0:00 ` Dr. John B. Matthews
1996-09-15 0:00 ` GUI Generators and Class Libraries (was: Better MacOS Handles Larry Kilgallen
1996-09-15 0:00 ` jim hopper
1996-09-16 0:00 ` Larry Kilgallen
1996-09-17 0:00 ` GUI Generators and Class Libraries (wa David Kristola
1996-09-17 0:00 ` GUI Generators and Class Libraries Dr. John B. Matthews
1996-09-09 0:00 ` Implementing pointers to pointers in Ada Jonas Nygren
1996-09-10 0:00 ` John Demby
1996-09-10 0:00 ` Robert A Duff
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