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=-1.3 required=5.0 tests=BAYES_00,INVALID_MSGID
	autolearn=no autolearn_force=no version=3.4.4
X-Google-Language: ENGLISH,ASCII-7-bit
X-Google-Thread: 103376,751584f55705ddb7
X-Google-Attributes: gid103376,public
From: John G. Volan <John_Volan@ccmail.dayton.saic.com>
Subject: Re: Side-effect arithmetic again [was: Ada ... in embedded systems]
Date: 1996/03/23
Message-ID: <4ivnr9$86o@dayuc.dayton.saic.com>#1/1
X-Deja-AN: 143854400
distribution: world
references: <826571250.140@assen.demon.co.uk> <dewar.827413120@schonberg>
 <EACHUS.96Mar21184540@spectre.mitre.org> <827432438.26126@assen.demon.co.uk>
content-type: text/plain; charset=ISO-8859-1
x-xxmessage-id: <AD78C87640011A68@volanj.dayton.saic.com>
organization: Science Applications International Corp. (SAIC)
mime-version: 1.0
newsgroups: comp.lang.ada
Date: 1996-03-23T00:00:00+00:00
List-Id: <comp.lang.ada>

In article <EACHUS.96Mar21184540@spectre.mitre.org> 
Robert I. Eachus, eachus@spectre.mitre.org writes:
>In article <4iq2ia$lk7@dayuc.dayton.saic.com> 
>John G. Volan ><John_Volan@ccmail.dayton.saic.com> writes:
...
>  (My conclusion was that you really only need one package:)
...
>    --add
>
>    procedure Increment (This : in out Item; By: in Positive);
>    procedure Decrement (This : in out Item; By: in Positive);
...
>    procedure Increment (This : in out Item; By: in Positive) is
                                                     ^^^^^^^^^
>    begin
>      This := Item'Val(Item'Pos(This) + By);
>    end Increment;
>
>    procedure Decrement (This : in out Item; By: in Positive) is
                                                     ^^^^^^^^^
>    begin
>      This := Item'Val(Item'Pos(This) - By);
>    end Decrement;
...

Horrors! This assumes that Standard.Integer subsumes all possible ranges
of 'Pos values for all discrete types (enumeration, integer, modular).
A very dubious assumption!  What about Long_Long_Integer?  The long-term
reusability of this package is problematic.

Also, why limit Increment/Decrement to Positive?  Why not allow any
arbitrary integer?  The C analogs for these procedures, += and -=,
carry no such limitation.

Finally, you're looking too narrowly at the problem:  You seem to be
focussed exclusively on analogs for ++ -- += -= , and are neglecting 
similarly contentious operations such as *= /= %= .  Also, you're
only looking at discrete types.  What about real types?  My inanely
trivial packages covered all the bases.

However, your Cycle operation is a nice touch.

------------------------------------------------------------------------
Internet.Usenet.Put_Signature
( Name => "John G. Volan", E_Mail => "John_Volan@dayton.saic.com",
  Favorite_Slogan => "Ada95: The *FIRST* International-Standard OOPL",
  Humorous_Disclaimer => "These opinions are undefined by SAIC, so" &
    "any use would be erroneous ... or is that a bounded error now?" );
------------------------------------------------------------------------