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From: Mats Weber <Mats.Weber@elca-matrix.ch>
Subject: Re: Pb with use of redefined "=" operator
Date: 1998/11/05
Message-ID: <3641D551.CCA4379C@elca-matrix.ch>#1/1
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References: <363F62F3.3FF7@club-internet.fr> <m3zpa860yd.fsf@mheaney.ni.net>
 <3640B520.D7BEEE72@elca-matrix.ch> <m3iugv70ke.fsf@mheaney.ni.net>
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Newsgroups: comp.lang.ada
Date: 1998-11-05T00:00:00+00:00
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Matthew Heaney wrote:

> I make it a point that when I create a composite type --an abstract data
> type, or "open," as in your example-- that I guarantee equality will
> compose.
> 
> It is for this reason that I always implement (the full view of) ADTs as
> tagged, even if the partial view is not itself tagged.

But if you do that, then you don't need to explicitly import "=" as a
generic formal, because the reemergence problem does not exist with
(visibly or not) tagged types.

This also makes the following trick unnecessary:

> But the solution is trivial: just don't use equality for the composite
> type!  What I do is, always declare the equality for composite types as
> abstract:
> 
> [...]
>    type Pair is
>       record
>          X, Y : Item_Type;
>       end record;
> 
>   function "="
>     (L, R : Pair) return Boolean is abstract;