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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: ADA compilers can reject types arbitrarily?
Date: 14 Nov 2005 22:12:59 -0500
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2005-11-14T22:12:59-05:00
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Anonymous Coward <nospam@nospam.com> writes:

> In article <wcchdafhxo5.fsf@shell01.TheWorld.com>, 
> Robert A Duff wrote:
> > 
> > But surely it makes no sense for the size of an object to always be
> > the same as the type's size.  Boolean'Size = 1, but you want to
> > allocate Boolean variables in 32-bit registers, quite often.
> 
> Ah, yes.. I had forgotten that a types size is the same as the value
> size, since I was dealing with records.  It didn't occur to me that
> record type size specs should really be treated the same as they would
> be w/ integers; so that makes sense.

Well, records can be small, too.  E.g a packed record containing 
three booleans could have 'Size = 3, but you want to allocate objects in
a 32-bit register.

>...Considering type sizes are
> really value sizes, it's more clear to me now why T'size would only
> specify a minimum.  I assume I can expect an O'size spec to be
> absolute (O being an object).

Yes.

> No way!  So an ADA compiler can arbitrarily decide whether to accept a
> rep spec?

No, there are all kinds of rules and regulations about what a compiler
has to support, and what it is allowed to support.  See section C.2,
which applies if the SP annex is supported.  I think you can safely
count on SP annex support in all Ada compilers of interest.

My example was T'Size = 0 -- there aren't many types that fit in 0 bits.

- Bob