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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Array Help?
Date: Wed, 29 Feb 2012 11:09:04 -0500
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Date: 2012-02-29T11:09:04-05:00
List-Id: <comp.lang.ada>

Adam Beneschan <adam@irvine.com> writes:

>   type Integer_Array is array (Integer range <>) of Integer;
>   A : Integer_Array (2 .. 7);

Right, and this is a rich source of bugs.  You usually want
arrays to start at 1, or sometimes 0 (assuming the index type
is a signed integer type, which is almost always the case
for unconstrained arrays).  In Ada 2012, you can say:

    type Integer_Array is array (Positive range <>) of Integer
        with Dynamic_Predicate => Integer_Array'First = 1;

or:

    type Integer_Array is array (Natural range <>) of Integer
        with Dynamic_Predicate => Integer_Array'First = 0;

Now 'Last can be anything you like, but 'First is fixed.

In GNAT, you can write "Predicate" instead of "Dynamic_Predicate".

- Bob