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From: dewar@merv.cs.nyu.edu (Robert Dewar)
Subject: Re: Equality operator overloading in ADA 83
Date: 1997/04/27
Message-ID: <dewar.862141608@merv>#1/1
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References: <01bc4e9b$ac0e7fa0$72041dc2@lightning>
 <335E0B1F.12C9@elca-matrix.ch> <E93v4u.DG1@world.std.com>
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Organization: New York University
Newsgroups: comp.lang.ada
Date: 1997-04-27T00:00:00+00:00
List-Id: <comp.lang.ada>


Mats says

<<And yes, I think that there should be an automatic redefinition in Ada
once "=" and one of "<", ">", ">=", "<=" are defined (but I realize it's
too late now, this should have been done in Ada 83).>>

This would be a terrible idea, since it would build in serious inefficiencies.
A typical way of implementing comparisons for a complex type is to have a
single comparison routine that indicates the compare status (LT, EQ, GT) and
then have the operators be a simple wrapper around this routine.

Your automatically constructed cases would introduce serious inefficiencies,
typically doubling the time of some complex comparisons. FOr instance, you
define "<=" as "<" or "=", but look at the following from the GNAT ureal
package (arbitrary precision reals):

   -----------
   -- UR_Le --
   -----------

   function UR_Le (Left, Right : Ureal) return Boolean is
   begin
      return not (Right < Left);
   end UR_Le;


(and the "<=" operator renames UR_Le)

Your approach would make this important operation take twice as long ...
Yes, I suppose I could get around it with caching, but that is messy
to do in a task safe manner.

I don't like this idea at all, and if it was ever suggested for Ada 83
(I can't remember it having come up, but it must be something the design
team considered), then it was correctly rejected in my view.