Re: Pointer compatibility question

From: [at]} <Gérard>
Date: Fri, 20 Jun 2003 00:51:21 +0200

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Hello Wojtek,

Extract from CP language reference:

Parameter compatible
An actual parameter a of type Ta is parameter compatible with a formal
parameter f of type Tf if
1. Tf and Ta are equal types, or
2. f is a value parameter and Ta is assignment compatible with Tf, or
3. f is an IN or VAR parameter and Tf and Ta are record types and Ta is an
extension of Tf.

The only rule that matches your case is the first one, because your formal
parameter is not a value parameter nor a record. What I understand here is
that you cannot consider you make an assignment, since, with a VAR
parameter, you can pass values in both directions.

My solution is this one (if somebody has a better one, tell me please):

MODULE WorkTest;
TYPE
Node = POINTER TO EXTENSIBLE RECORD
next: Node;
END;

HistNode = POINTER TO RECORD (Node)
hist: INTEGER
END;

VAR
anchor: HistNode;
last: HistNode;

PROCEDURE InsertLast (VAR first:Node; new:Node);
BEGIN
END InsertLast;

PROCEDURE AddNew;
VAR
n: Node;
BEGIN
NEW(anchor);
NEW(last);
n := anchor; (* Unless you make anchor a simple Node *)
InsertLast (n, last);
anchor := n(HistNode);
END AddNew;

END WorkTest.

Regards.

Gérard


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Received on Fri Jun 20 2003 - 00:51:21 UTC