Re: Should representation clauses be complete for each bit?

["Randy Brukardt" <randy@rrsoftware.com>]

"Robert A Duff" <bobduff@shell01.TheWorld.com> wrote in message 
news:wcczkk9ngxy.fsf@shell01.TheWorld.com...
...
> I think the unused bits should be explicitly declared.

I agree.

...
> How about the following?
>
> package P is
>   type Bits2 is mod 2**2;
>   pragma Assert (Bits2'Size = 2);
>   type Bits11 is mod 2**11;
>   pragma Assert (Bits11'Size = 11);
>
>   type T is
>      record
>         One : Boolean;
>         Gap1 : Bits2; -- must be zero
>         Tooth : Boolean;
>         Gap2 : Bits11; -- must be zero
>         Ree : Boolean;
>      end record
>        with Predicate => T.Gap1 = 0 and T.Gap2 = 0;

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

                             Randy.