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From: mitchalsup@aol.com (MitchAlsup1)
Newsgroups: comp.arch
Subject: Re: is Vax addressing sane today
Date: Wed, 25 Sep 2024 17:30:46 +0000
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On Wed, 25 Sep 2024 17:07:45 +0000, Michael S wrote:

> On Wed, 25 Sep 2024 09:54:17 -0700
> Stephen Fuld <sfuld@alumni.cmu.edu.invalid> wrote:
>
>> On 9/10/2024 1:13 AM, Niklas Holsti wrote:
>>
>>> In the Ada case, the ability to declare array types with
>>> programmer- chosen index types with bounded range, such as
>>> range-bounded integers or enumerations, means that the compiler can
>>> avoid indexing checks when the (sub)type of the index is known at
>>> compile time to fit within the index range of the array.
>>
>> I have always liked the idea of variable ranges able to be specified
>> in the language.  Besides the advantages you mentioned, it provides
>> more human "comprehensibility" (if the ranges are reasonably named)
>> i.e. better internal documentation, and it makes responding to
>> specification changes required later in the program life cycle easier
>> and less error prone, i.e. if the range has to change, you change it
>> in one place and don't risk missing making the change in some obscure
>> part of the program you forgot about.
>>
>>
>
> The problem here is that arrays with fixed bounds were common when
> Ada was conceived back in the mid 1970s. On general-purpose (as opposed
> to embedded) computers they were already much rarer when Ada was shipped
> in 1983. By late 1990s arrays with fixed bounds were rare exception
> rather than rule.

It sounds like variable ranges (array indexes) would be becoming more
common, also.

Where "variable range" is a variable that is defined to have a
specified range, but from run to run the upper and lower bounds
can be modified without re-compilation.

> Except, of course, for many types of embedded computers. But even that
> is gradually changing. Very gradually.