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From: Simon Wright <simon@pushface.org>
Newsgroups: comp.lang.ada
Subject: Re: A few questions
Date: Sat, 14 Nov 2015 20:09:56 +0000
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Date: 2015-11-14T20:09:56+00:00
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Shark8 <onewingedshark@gmail.com> writes:

> On Saturday, November 14, 2015 at 5:37:32 AM UTC-7, Simon Wright wrote:
>> 
>> It's a pity that Next takes the iterator object as an 'in'
>> parameter. This means that, in general, the cursor needs to hold the
>> state. It certainly needs some way of indicating end-of-iteration;
>> perhaps a sentinel value.
>
> Sentinel values, or exceptions?  C-style strings use ASCII.NUL as a
> sentinel value, and look at the trouble that causes. (Of course part
> of that is due to the anemic idea of arrays that C has.)

Next (Iterator, Cursor) return Cursor is the operation that would detect
End_Of_File or whatever and indicate in the result Cursor that the
iteration had ended. Although it would indeed quit the loop, I don't
think using an exception would be good (especially in a restricted
runtime without exception propagation).

If no sentinel value is possible, you're stuck (I think) with

   type Cursor (Running : Boolean := True) is record
      case Running is
         when True  => Element : Whatever;
         when False => null;
      end case;
   end record;