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From: geert@gonzo.sun3.iaf.nl (Geert Bosch)
Subject: Re: Equality operator overloading in ADA 83
Date: 1997/04/27
Message-ID: <5jvpom$smj$1@gonzo.sun3.iaf.nl>#1/1
X-Deja-AN: 237757382
References: <01bc4e9b$ac0e7fa0$72041dc2@lightning>
 <335E0B1F.12C9@elca-matrix.ch> <E93v4u.DG1@world.std.com>
 <335F5971.6375@elca-matrix.ch> <E95y9L.AK1@world.std.com>
Organization: La Calandre Infortunee
Newsgroups: comp.lang.ada
Date: 1997-04-27T00:00:00+00:00
List-Id: <comp.lang.ada>


Robert A Duff (bobduff@world.std.com) wrote:
 ``OK, but then if I redefine "<" on a scalar type, should ">="
   change? After all, ">=" is (or could be) defined as "not <". ''

No, I don't think you can do that. For a program that finds all
anagrams of some text, I defined a "Signature" type. A signature
of a string is an (long) integer sized hash-value, that makes it 
possible to efficiently implement the following partial ordering:

Given strings A and B with signatures SA and SB:  when SA > SB,
then A is not a partial anagram of B; ie. A cannot be made with
the characters of B. 

In this case SA > SB does not imply that SB < SA.  Of course you
might argue that redefining comparison operators to implement a
type with partial ordering is a "bad thing". I think it makes the
program much more readable.

Regards,
   Geert