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Date: 17 Dec 92 13:28:50 GMT
From: agate!spool.mu.edu!sdd.hp.com!saimiri.primate.wisc.edu!aplcen.apl.jhu.edu
!ddsdx2.jhuapl.edu!dlc@ucbvax.Berkeley.EDU  (Dave Collard x7468)
Subject: Re: Novice Question on Record Representation
Message-ID: <1992Dec17.132850.2305@aplcen.apl.jhu.edu>
List-Id: <comp.lang.ada>

>Josh Lam
>Honeywell Inc
>lam@saifr00.cfsat.honeywell.com

-- OOH, OOH, OOH!!! Something technical on comp.lang.ada!  Wow!
-- Today should become a federal holiday! :-)

package Some_Package is

 type Some_Int is new short_integer;
 for Some_Int'size use 16;

 type Some_Type is private;

 private

  type Some_Type is new integer;
  for Some_Type'size use 32;

end Some_Package;


with Some_Package;
package My_Package is

 XX : constant Integer := Integer(Some_Package.Some_Type'Size);

 type My_Rec (Choice: Boolean := True) is record
   case Choice is
     when True =>
       A : Some_Package.Some_Int;
       B : Some_Package.Some_Int;
       C : Some_Package.Some_Type;
     when False =>
       D : Some_Package.Some_Int;
   end case;
 end record;
   
-- for My_Rec use record
--    A      at 0 range 0..15;
--    B      at 0 range 16..31;
--    C      at 1 range 0..31;     -- of course there is an error here!
--    Choice at 2 range 0..31;
--    D      at 0 range 0..15;
-- end record;

 -- Is the storage unit on your machine really 32 bits?  the '0' in "A at 0" 
 -- refers to which storage unit to start the component at.  But the answer
 -- to your question is that you CAN use rep specs with private types.  The
 -- attributes of private types are also available (such as 'SIZE).  The 
 -- problem in your example is overlapping components of your record.  Try:

 for My_Rec use record
    A      at 0 range 0..15;
    B      at 2 range 0..15;
    C      at 4 range 0..31;     -- of course there is an error here! NOT!
    Choice at 8 range 0..31;
    D      at 0 range 0..15;
 end record;

 -- This works for me.  Yes I actually compiled it.

-- etc etc

end My_Package;

--I know that I cannot do the above cos C is of Some_Package.Some_Type which
--is a private type.
--
--So, other than yelling at the person and getting him to change his type
--to public, what are my alternatives given that I need to use record
--representation. Please also let me know some pros and cons (if any) to any
--alternative.
--
--Thanks in advance!
--

--Thor
--dlc@ddsdx2.jhuapl.edu
--collard@capsrv.jhuapl.edu