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From: Robert A Duff <bobduff@shell01.TheWorld.com>
Newsgroups: comp.lang.ada
Subject: Re: Should representation clauses be complete for each bit?
Date: Sat, 23 Jul 2011 11:12:25 -0400
Organization: The World Public Access UNIX, Brookline, MA
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Date: 2011-07-23T11:12:25-04:00
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"Randy Brukardt" <randy@rrsoftware.com> writes:

> I would do this slightly differently (in fact we did, in Claw where we had 
> this exact problem):
>
>    type T is
>       record
>          One : Boolean;
>          Gap1 : Bits2 := 0; -- must be zero
>          Tooth : Boolean;
>          Gap2 : Bits11 := 0; -- must be zero
>          Ree : Boolean;
>       end record
>        with Predicate => T.Gap1 = 0 and T.Gap2 = 0;
>
> with the same record rep clause.
> Then the (correct) aggregates don't need to mention the gaps explicitly:
>
> with Ada.Assertions; use Ada.Assertions;
> procedure P.Main is
> --   X : T := (One | Tooth | Ree => True, Gap1 => 0, Gap2 => 0); -- OK
>     X : T := (One | Tooth | Ree => True, others =>  <>); -- OK

Hmm.  That seems reasonable, although it makes me nervous that
you might accidentally say:

    X : T := (One | Tooth => True, others =>  <>);

which evilly leaves junk in Ree.  That sort of bug is likely if you add
new components to a record.

- Bob