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From: "Nick Roberts" <nick.roberts@acm.org>
Newsgroups: comp.lang.ada
Subject: Re: Rep spec for tagged type
Date: Fri, 13 Aug 2004 18:07:18 +0100
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Date: 2004-08-13T18:07:18+01:00
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On 13 Aug 2004 20:47:59 +0930, Daniel Wild <dan@example.com> wrote:

> I'm trying to create a rep spec for a tagged type and getting errors
> from GNAT that say `compoonent overlaps tag field of ...'.
>
> I gather this means that GNAT stores the tag for the type at the
> beginning of the memory used for the type and I'm trying to overwrite
> that by starting my rep spec at 0.
>
> So, I figure I need to shift my rep spec along by however big the tag
> is. How can I find the size of this? (I'd rather do it properly that
> assume it's 32 bits on my machine).

The expression:

    Ada.Tags.Tag'Size

will probably give you the size of the tag, but for its position you
will have to look in the GNAT documentation (maybe it is 0).

Unfortunately, I think this means your code may not be portable.

-- 
Nick Roberts