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From: "Mattias" <mpedv98@student.vxu.se>
Subject: Problem with dynamic dispatching (Polymorphism)
Date: 1999/04/25
Message-ID: <7fvfcm$cfi$1@news.lth.se>#1/1
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Organization: Lund Institute of Technology, Sweden
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Newsgroups: comp.lang.ada
Date: 1999-04-25T00:00:00+00:00
List-Id: <comp.lang.ada>

Hi!

I�m developing a simple linked list to hold different data types..
I have to one superclass , with two derived classes..

I have declared a 'Class type which I use to access all of my structures,

I have no trouble adding data to the list. The error occures when I wan't to
extract the data and Print it to the screen..

look at the following code example:

program.ads:
type T�cken is tagged null record;
type Siffra is new Tecken with
  Record
      Element : Integer;
  end record;
procedure Print(S : Siffra);

type Bokstav is new T�cken with
  record
         Element : Character;
   end record;
  procedure Print(B : Bokstav);

type pTecken is access all Tecken'Class;


program.adb
-- I have to simple procedures which Print the values of Class bokstav,
'' notice .. pekare is of type pTecken ..

procedure Print(B : Bokstav) is
   begin
      Put(B.Element);
   end Print;

   procedure Print(S : Siffra)  is
   package Iio is new Integer_Io(Integer);
      use Iio;
   begin
      put(S.Element);
   end Print;

-- Then I have this procedure to extract the elements from the list. Pekare
is
Pocedure Display is
   begin
      while Lista /= null loop

         Print(Lista.Pekare);
         Lista := Lista.Next;
      end loop;
   end Display;

Really need help on this one

thx
Mattias