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:wcc62mtav52.fsf@shell01.TheWorld.com...
> "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.

Ugh. There really should be a restriction or something to prevent using <> 
for uninitialized things. We have such a rule for discriminants, it would 
seem easy enough to have it for all types (admittedly, it would be 
complicated by the recursive nature for record types). It can't be very 
common that the program actually wants to write aggregates that fill the 
aggregate with junk.

                                     Randy.