Re: private types

[Justin Gombos <rpbkbq.xax.gld@uluv.kbq>]

On 2006-03-25, Robert A Duff <bobduff@shell01.TheWorld.com> wrote:
> Justin Gombos <rpbkbq.xax.gld@uluv.kbq> writes:
>
> So you rarely create trees, linked list, etc?

That's right.  In fact, a few months ago was the first time I
implemented a dynamic container in Ada since I studied it in school.
I haven't had a need for them in any of the avionics systems that I've
worked.

>> Integers, and other non-access scalars are different in this case
>> because you cannot expect zero to have the same meaning.  Zero has
>> a universal meaning with access types,
>
> No, zero has no meaning with access types!
>
>>... but it could be in range or out of range for any other type.
>>The ARM selects access types specifically to get a default
>>initialization of zero for this reason.
>
> There is no "default initialization of zero".  There is a
> default-init to null, which has nothing to do with zero (according
> to the Ada standard).

You're forgetting why we got side tracked on this discussion.  Your
comment was:

  I'm not sure what the right answer is, but surely all the arguments
  for and against dummy values apply equally to access types.

Access types are special, and get different treatment than other
scalars because they include in their set a representation for a null
value.  Integers do not; so the same arguements for implicit
initialization of access values do not necessarily apply.  

Whether null values are actually represented as zeros is irrelevant to
this matter.  Even if null values are nonzero, integers still do not
have a null object.

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