Beginners question: Abstract record extension

From: Wijck, Bart van <"Wijck,>
Date: Mon, 23 Sep 2002 15:25:30 +0200

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Hi BlackBoxers,

I'm trying to create an generic linked list along the lines of the generic
tree in Mossenbock's Object Oriented Programming i n Oberon-2 (page 77). The
abstract base class with its methods (with NEW, ABSTRACT added) compiles
fine.

TYPE
  Node* = POINTER TO NodeDesc;
  NodeDesc* = ABSTRACT RECORD
                      next* : Node;
                  END;

  List* = RECORD
                head* : Node;
            END;

PROCEDURE (x : Node) EqualTo* (y : Node) : BOOLEAN, NEW, ABSTRACT;

etc


However as soon as I try to extend the abstract base class as follows
(following the Oberon-2 example)


  StringNode = POINTER TO StringNodeDesc;
  StringNodeDesc = RECORD (NodeDesc)
                            key : ARRAY 11 OF CHAR;
                     END;

It refuses to compile with the error message 'unimplemented abstract
procedures in base types', marking NodeDesc. What is happening here?

> ____________________________________
> Bart van Wijck
> Senior Business Development Consultant
> Compuware BV
> Telefoon: 020 311 88 57
> Fax : 020 311 88 01
> Mobiel : 06 54 35 23 76
>
>
>
>

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Received on Mon Sep 23 2002 - 15:25:30 UTC