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From: Mark & Zurima McKinney <mckmark@us.net>
Subject: Re: passing pointer of different type to one procedure
Date: 1997/04/18
Message-ID: <3357BA42.654F@us.net>#1/1
X-Deja-AN: 235730272
References: <01bc4a80$713ca380$52bd0c26@cat>
To: Boaz <boaz@pipeline.com>
Organization: US Net - MD,DC,VA ISP - info@us.net
Newsgroups: comp.lang.ada
Date: 1997-04-18T00:00:00+00:00
List-Id: <comp.lang.ada>


Boaz wrote:
> 
> Hi there,
> 
> I am trying to write a sort procedure for a data base project.  I have 2
> different records.  Instead of having 2 instances for that sort procedure,
> I am thinking to use just one that take a pointer of either one of the
> records type.
> 
> this is my test program but I don't quite sure how to set it up :
> 
> with text_io; use text_io;
> with ada.float_text_io; use ada.float_text_io;
> 
> procedure test is
> 
> type record_pointer is access all record;  <-- error
> 
> type a is record
>         key : float;
>         d : integer;
> end record;
> 
> type b is record
>         key : float;
>         e : float;
> end record;
> 

--You can make then the same type with a discriminant record ...
--Link so ...

type record_types is (A, B);

type Keyed_Record(Record_Type : Record_Types) is 
   record
      Key : Float;
      case Record_Type is
         when A =>
            I : Integer;
         when B =>
            F : Float;
      end case;
   end record;    

--Now the ponter will bee of one type and can point to 2 or more
different types of 
--discriminant records.

type Keyed_Record_Pointer is access Keyed_Record;

--It is likely that you would want to sort an array particularly if
there 
--will be more than two items to sort.

type Keyed_Record_Pointer_Arrays is array(natural range <>) of
Keyed_Record_Pointer;

--this might also be useful
function "<"(Left, Right : in Keyed_Record) return Boolean is
begin
    return Left.Key < Right.Key;
end;

In Ada95 you can also use inheritance.

type keyed_class is tagged 
   record
      Key : Float; 
   end record;

type key_record_pointer is access all keyed_Class;

function "<"(Left, Right : Keyed_Class'Class) return boolean is ......


--perhaps in a child package
type integer_keyed_class is new keyed_class with 
   record
      I : integer;
   end record;

--perhaps in a another child package
type float_keyed_class is new keyed_class with 
   record
      F : float;
   end record;


Enough said this should point you in the right direction.

MArk McKinney