Re: Default rep specs for record types - documented??

[Anonymous Coward <spam@spam.com>]

In article <wcc64qw821y.fsf@shell01.TheWorld.com>, Robert A Duff wrote:
> "Steve" <nospam_steved94@comcast.net> writes:
> 
>> But if you add a representation clause:
>> 
>>   for Color'size use 8;
>> 
>> All compilers will use the same number of bits to represent an instance of 
>> color?
> 
> No (unfortunately).  It means "use at least 8 bits for objects".
> A compiler is free to allocate 32.  To control the size of objects,
> you have to use 'Size on the object, or, if it's a component,
> a record rep clause or a 'Component_Size on an array.

I keep getting to a point where I think I've mastered these rep specs,
and yet more gotchas emerge.  I had no idea I could control the
representation of objects independant of the representation of their
types.

I'm shocked to hear that size specs on types are merely a *minimum*.
Can I at least rely on pragma convention to guarantee an absolute size
on enums/integers?

As for records, I've imposed sizes on all my rep spec'd record types.
It would normally be needless, but to protect the maintainer from
accidentally defining a partial rep spec as the operational spec
grows, I've added a size spec so an error will be thrown at compile
time.  

It seems your statement about size specs on types only being a minimum
does not apply to record types, correct?  Here is some code that fails
to compile because the operational spec forces growth beyond that of
the size spec:

   procedure Record_Experiment is

      type Cuban_Aid_In_USD is range 0..50_000;

      type Bushs_Record is record
         Iraq_WoMD_Count         : Natural;
         Dead_Americans          : Positive;
         Dead_Civilians          : Positive;
         Deficit_In_Thousands    : Integer;
         Aid_Offered_To_Cuba     : Cuban_Aid_In_USD;
      end record;

      for Bushs_Record use record
         Iraq_WoMD_Count      at  0 range 0..31;
         Dead_Americans       at  4 range 0..31;
         Dead_Civilians       at  8 range 0..31;
         Deficit_In_Thousands at 12 range 0..31;
      end record;

      --The following line breaks the compile,
      --which is expected and desirable.
      --
      for Bushs_Record'Size use 128;

      President : Bushs_Record;

      --The following line just illustrates that
      --the object size spec can differ from the
      --type size spec.
      --
      for President'Size use 160;

   begin
      null;
   end Record_Experiment;

In this case, I added "Aid_Offered_To_Cuba" to the operational spec,
forcing the record to exceed 128 bytes, which causes an error.  This
seems like the best protection, but it's still inadequite because a
neglectful maintainer can still increase the size spec without
completing the layout.