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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Problem with Position of the enumeration Type
Date: Thu, 24 Jan 2019 21:39:00 +0200
Organization: Tidorum Ltd
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Xref: reader01.eternal-september.org comp.lang.ada:55362
Date: 2019-01-24T21:39:00+02:00
List-Id: <comp.lang.ada>

On 19-01-24 18:43 , Jeffrey R. Carter wrote:
> On 1/23/19 11:35 PM, Simon Wright wrote:
>> Niklas Holsti <niklas.holsti@tidorum.invalid> writes:
>>
>>> Such rules also commonly say that such types should not be used as
>>> array index types, because of the possible introduction of gaps in the
>>> array representations.
>>
>> Not, it seems, with GNAT:
>
> This is not a language rule. I can find nothing in the ARM about
> disallowing such types as array indices. So naturally GNAT and all other
> compilers must support it.

All compliant compilers, yes. But the question was: if the enumerated 
index type has gaps in its representation, can there be corresponding 
gaps (unused intervals of storage units) between the elements of the 
array, as represented in memory? Or must the elements still be 
contiguous, except for alignment padding?

In other words, can the compiled code compute the offset of an array 
element directly from the representation of the enumerated index value 
(causing gaps in the array), or must it always first compute the 
position number of that value, and then compute the offset from the 
position number (suppressing gaps)?

This discussion has not yet pointed to an ARM rule that forbids gaps in 
the array's representation.

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .