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Newsgroups: comp.lang.ada
Subject: Re: put of access type
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From: Stephen Leake <stephen_leake@stephe-leake.org>
Date: Fri, 21 Aug 2009 04:24:03 -0400
Message-ID: <u63chwp5o.fsf@stephe-leake.org>
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Date: 2009-08-21T04:24:03-04:00
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Adam Beneschan <adam@irvine.com> writes:

> On Aug 20, 1:05�am, Stephen Leake <stephen_le...@stephe-leake.org>
> wrote:
>> Dennis Lee Bieber <wlfr...@ix.netcom.com> writes:
>>
>> > On Tue, 18 Aug 2009 23:36:15 -0400, Rob Solomon
>> > <use...@drrob1-noreply.com> declaimed the following in comp.lang.ada:
>>
>> >> The only way I know to see the results of my playing is to output
>> >> them.
>>
>> > � �And what meaning would some address from either the stack or a heap
>> > have? You can't modify them -- Ada's access types are so heavily
>> > controlled they are basically black boxes with no inherent meaning.
>>
>> Yes, but seeing the actual values helps the learning process.
>
> I don't see how.  

Ok. For you, personally, this style of learning doesn't help. For the
OP, and for me, it does. Let it go at that.

>> A : aliased Interfaces.Unsigned_32;
>> B : aliased Interfaces.Unsigned_32;
>>
>> begin
>> � � Put (To_Integer (A'access));
>> � � Put (To_Integer (B'access));
>>
>> The results should be 4 bytes apart.
>
> Ummm... why?  What rule in Ada says that the compiler has to put A and
> B next to each other?

Ok. To be pedantic, I should have said "in practice, for most compilers
on most targets, the results will be 4 bytes apart".

When focussing on implementations, you do need to be aware that some
targets are significantly different than mainstream ones.

However, learning some implementation details for the mainstream
processors can help in understanding how a language works.

Thinking of an access value as an address helps you understand how it
works. Thinking of it as mysterious magic does not.

-- 
-- Stephe