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From: Brian Drummond <brian@shapes.demon.co.uk>
Newsgroups: comp.lang.ada
Subject: Re: Should representation clauses be complete for each bit?
Date: Thu, 21 Jul 2011 21:11:28 +0000 (UTC)
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Date: 2011-07-21T21:11:28+00:00
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On Thu, 21 Jul 2011 11:43:22 +0200, Georg Bauhaus wrote:

> On 21.07.11 09:37, Martin wrote:
>> On Jul 20, 6:28 pm, Robert A Duff <bobd...@shell01.TheWorld.com> wrote:
>>> Georg Bauhaus <rm.dash-bauh...@futureapps.de> writes:
>>>> On 20.07.11 16:51, Robert A Duff wrote:
>>>
>>>>> By the way, I find Ada's representation clauses to be at the wrong
>>>>> level of abstraction.  Why can't I just write a single line of code
>>>>> that means "put all the components in declaration order with no gaps
>>>>> in between"?
>>>
>>>> Is this a frequent use case?
>>>
>>> Yes, I think so.
>>>
>>> - Bob
>> 
>> I think you're right, Bob. In fact, I'd go so far as to say it's very,
>> very common.
>> -- Martin
> 
> More specifically, if the original example of "not all bits used and
> some gaps between them" is unusual, is it so
> 
> - when mapping to a set of hardware pins, say?

Not common. But one common case is a hardware register in a peripheral, 
or even something as basic as a mode register in DDR memory ... "these 
fields are reserved, so undefined (probably bad) things will happen if 
you do anything other than set them to 0"

- Brian