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From: Simon Wright <simon@pushface.org>
Newsgroups: 
 comp.lang.java.advocacy,comp.object,comp.lang.ada,comp.software-eng
Subject: Re: Logic Errors and Ada (Was: A big hairy thread on Ada, Quality,
 and Drivers)
Date: 19 May 2003 20:42:42 +0100
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Date: 2003-05-19T20:42:42+01:00
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martin.dowie@btopenworld.com (Martin Dowie) writes:

> softeng3456@netscape.net (soft-eng) wrote in message news:<9fa75d42.0305181502.53703035@posting.google.com>...
> > 
> > That sounds to me an unrealistic level of discipline: subtyping
> > to the extent that all lattitudes and longitudes (and things
> > along that line) are separate types.  More common usage is that both
> > will be just real numbers (floats), whatever the language chosen.  So
> 
> NO! That's just plain wrong - I've spent the last 15 years working in
> aerospace and this is EXACTLY the level of typing that is used
> EVERYDAY.

My project is using 'subtype Radians is Long_Float' or equivalent,
with constraints occasionally (though personally I don't now think
that Radians can sensibly be constrained without a lot of work). Of
course Latitude could be. The trouble is that the constraints won't
catch that may errors (in UK waters, anyway).

I've always thought that the pain of introducing full dimensional
handling (without language support) is unjustifiable, and that if
necessary one should rather go for records in this context:

  type Position is record
     Lat  : Latitude;
     Long : Longitude;
  end record;

and inspect the low-level support subprograms.