From mboxrd@z Thu Jan  1 00:00:00 1970
X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me
X-Spam-Level: 
X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00,FREEMAIL_FROM
	autolearn=ham autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,3f8d8581bfd0fa44,start
X-Google-Attributes: gid103376,public
X-Google-ArrivalTime: 2002-08-17 14:20:40 PST
Path: 
 archiver1.google.com!news1.google.com!newsfeed.stanford.edu!bloom-beacon.mit.edu!nycmny1-snh1.gtei.net!news.gtei.net!newsfeed.mathworks.com!fu-berlin.de!uni-berlin.de!pcp01485549pcs.limstn01.de.comcast.NET!not-for-mail
From: Ryan <rtarpine@hotmail.com>
Newsgroups: comp.lang.ada
Subject: Array-like object indexing
Date: Sat, 17 Aug 2002 17:22:33 -0700
Message-ID: <3D5EE8C9.2080601@hotmail.com>
NNTP-Posting-Host: pcp01485549pcs.limstn01.de.comcast.net (68.82.51.136)
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii; format=flowed
Content-Transfer-Encoding: 7bit
X-Trace: fu-berlin.de 1029619238 45931980 68.82.51.136 (16 [151722])
User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.0.0) Gecko/20020722
X-Accept-Language: en-us, en, eo
Xref: archiver1.google.com comp.lang.ada:28192
Date: 2002-08-17T17:22:33-07:00
List-Id: <comp.lang.ada>

I've recently been playing with making all the standard data structures
in Ada to prepare myself for writing my first major project.  Currently 
I'm writing a resizable-array package.  I am trying to make it as 
similar to built-in arrays as possible, with functions for First, Length 
and other useful operations and attributes.  It is a generic package 
instantiated with a type for the elements to be stored and a type for 
indexing.  I've run into a small problem with respect to the indexing type.

I'm not sure how to represent the boundaries of an empty array without 
raising a constraint error in some cases.  If an array is being indexed 
by Natural, for example, and the first index should be 0 (as makes sense 
in many situations), then what should the First and Last functions 
(intended to work like their analogous attributes) return?  I cannot 
return 0 and -1 because -1 would raise a constraint error.

Should the responsibility for this rest on the package or the user? 
Would it be a better to return 1 and 0, or to force a user of the 
package to instantiate it with an indexing type that starts at -1 
instead even though -1 should never be used to actually look into the 
array?  What are your opinions on this?

Thank you,
Ryan Tarpine