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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: Wed, 20 Jul 2011 17:21:55 -0400
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Date: 2011-07-20T17:21:55-04:00
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okellogg <okellogg@users.sourceforge.net> writes:

>> � � � � with Predicate => T.Gap1 = 0 and T.Gap2 = 0;
>
> I'd imagine that a default assignment at Gap1 and Gap2 would suffice?
>          Gap1 : Bits2 := 0;

Yeah, maybe.

>> � �for T1 use
>> � � � record
>> � � � � �pragma Complete_Representation;
>> � � � � �One at 0 range 0..0;
>> � � � � �Tooth at 0 range 3..3;
>> � � � � �Ree at 0 range 15..15;
>> � � � end record;
>>
>> � �for T2 use
>> � � � record
>> � � � � �pragma Complete_Representation;
>> � � � � �Gap1 at 0 range 1..2;
>> � � � � �Gap2 at 0 range 4..14;
>> � � � end record;
>>
>
> I believe the compiler would warn about incomplete representation at
> T1?

I think "pragma Complete_Representation" means "require every component
to be mentioned", not "require every bit from 0 to 'Size-1 to be used up.
Not sure.

> Also I guess an upcast from T2 to T1 should do for converting the
> types but I'm not so sure about the downcast from T1 to T2?

I'm assuming the package would export functions to create T2 objects
and operate on them.  Or maybe it would be more convenient to derive
the other way round (put the gaps in the parent type), so clients
could say (Parent_Type with One | Tooth => True, Ree => False),
assuming Parent_Type defaults the gaps to 0, as you suggested.

- Bob