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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: index check failure - constraint error
Date: Fri, 01 Apr 2011 19:29:31 -0400
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Date: 2011-04-01T19:29:31-04:00
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Adam Beneschan <adam@irvine.com> writes:

> On Apr 1, 3:49�pm, Robert A Duff <bobd...@shell01.TheWorld.com> wrote:
>> Jeffrey Carter <spam.jrcarter....@spam.not.acm.org> writes:
>> > The idea that Strings always have a lower bound of 1 is quite common
>> > among beginners.
>>
>> Whereas experts understand that it OUGHT to be true that
>> "Strings always have a lower bound of 1", but it isn't true.
>> It's a design flaw in the Ada language.
>>
>> > In SPARK all Strings do have a lower bound of 1.
>>
>> As they should. �It really makes things simpler.
>> And (could be) more efficient.
>
> I dunno.  I kind of like it that if I'm parsing a string, and I call
>
>      Next_Item := Ada.Strings.Fixed.Index_Non_Blank (S
> (Current_Index .. S'Last));
>
> then Next_Item is the index of the actual character in S that I need,
> and I don't need to add Current_Index to it and then think about
> whether I need to add 1 or subtract 1 from the sum, as I'd have to do
> something like that if Index_Non_Blank saw its Source parameter as a
> string with a lower bound of 1.

Good point.  But I think that's what cursors are for.
I still think indices into Strings ought to be 1-based.

- Bob