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From: mab@dst1.wdl.loral.com (Mark A Biggar)
Subject: Re: Equality operator overloading in ADA 83
Date: 1997/04/22
Message-ID: <5jiq7t$o35@wdl1.wdl.lmco.com>#1/1
X-Deja-AN: 236617713
References: <01bc4e9b$ac0e7fa0$72041dc2@lightning>
 <33602040.3178674@news.airmail.net>
Organization: Loral Western Development Labs
Newsgroups: comp.lang.ada
Date: 1997-04-22T00:00:00+00:00
List-Id: <comp.lang.ada>


In article <33602040.3178674@news.airmail.net> clines@delete_this.airmail.net (Kevin Cline) writes:
>"Manuel Wenger" <manuel@thunder.ch*> wrote:
>>I've started doing some DecADA 83 programming at a technical engineering
>>school ... and I've run into a problem that I was unable to solve (and my
>>teacher didn't know any better either :-))
>>I've tried to overload the "=" operator for fractions in a package. It
>>obviously doesn't work if the type isn't defined as "limited private", and
>>I don't want that. As an alternative, I found out that I might as well do a
>>renaming declaration, just by defining the type as "private" - so I've
>>tried doing that as well, and then using the following to rename the equal
>>sign:
>>In other words, how do I tell my "equal" function to be an equality
>>operator, authorized to be renamed into "="? HELP! :)
>You can't.  Period.  Why?  I don't know.  Drove me crazy once.
>Maybe some Ada-83 committee member will volunteer why it was 
>considered reasonable to redefine '<' and '>' but not '=' .

Actually you can by cheating and using generics.  define a genreics package
looking something like:

generic
	type FOO is limited private;
	with function EQ(L,R: FOO) return Boolean is <>;
package MAKE_EQUALS is
	function "="(L,R: FOO) return Boolean;
end MAKE_EQUALS;

package body MAKE_EQUALS is
	function "="(L,R: FOO) return Boolean is
	body
		return EQ(L,R);
	end "=';
end MAKE_EQUALS;

now you can instantiate it as:

package FAKE_IT is new MAKE_EQUALS(FOO => Your_Type, EQ => Your_Equals);

Now FAKE_IT."=" is an equality operator of your type and can be freely
renamed into what ever scope you want.

--
Mark Biggar
mab@wdl.lmco.com