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From: Mats Weber <Mats.Weber@elca-matrix.ch>
Subject: Re: Equality operator overloading in ADA 83
Date: 1997/04/22
Message-ID: <335D2B6F.2AA9@elca-matrix.ch>#1/1
X-Deja-AN: 236773784
References: <01bc4e9b$ac0e7fa0$72041dc2@lightning>
 <mheaney-ya023680002204970006190001@news.ni.net>
 <335CAEFE.35DC@elca-matrix.ch> <E91zFw.KDE@world.std.com>
Organization: ELCA Matrix SA
Reply-To: Mats.Weber@elca-matrix.ch
Newsgroups: comp.lang.ada
Date: 1997-04-22T00:00:00+00:00
List-Id: <comp.lang.ada>


>     - Ada.Strings.Bounded.Generic_Bounded_Length.Bounded_String: Two
>       reasonable implementations are: (1) Nul-out the unused
>       characters, and use bit-wise equality, and (2) use a tagged type
>       with a user-defined equality.  Either way, equality will compose.
>       This is, admittedly, a slight implementation burden, because it
>       rules out an untagged record with user-defined equality.

I think there is a third possibility that solves the "=" problem
(predefined equality works just fine so that it does not need
redeclaration):

   subtype Index is Natural range 0 .. Max_Length;

   type Bounded_String_Aux (Length : Index := 0) is
      record
         Value : String(1 .. Length);
      end record;

   type Bounded_String is
      record
         Value : Bounded_String_Aux;
      end record;

(I don't know if two types are still necessary in Ada 95, i.e. can a
full type declaration have discriminants with defaults if the visible
type has none).

We're lucky that all these operators have (Left, Right) as their
parameter names, or we would have had another funny problem.