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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: memory management
Date: 31 May 2005 08:04:47 -0400
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2005-05-31T08:04:47-04:00
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Simon Wright <simon@pushface.org> writes:

> Robert A Duff <bobduff@shell01.TheWorld.com> writes:
> 
> > By the way, I believe the fat pointers used by GNAT are an option --
> > there's some way to tell it to use thin pointers for
> > access-to-array.  GNAT uses fat pointers (by default) only when the
> > designated type is an array, or when the designated type is unknown
> > to the compiler.  Access-to-record, which is far more common, uses
> > thin pointers.  I don't know of any Ada implementation besides GNAT
> > that uses fat pointers at all.
> 
> I think that it uses fat pointers when the type concerned is
> indefinite.

I don't think so -- I think it's only for indefinite *arrays*
(or unknown types).  There's really no advantage in fat pointers
for records, unless tags/discrims are separated out, which GNAT
does not do.  (Nor does any other compiler I know of.)

> You can make it use thin pointers by specifying the 'Size of the
> pointer (to be 32) or, I'm pretty sure, by pragma Convention (C); I've
> sent classwide pointers via Xt client_data values using one of these
> techniques.

Yes, I think that's right.

- Bob