🚀 go-pugleaf

NEW(p)
~~~~~~

I have problems with this creation of pointers (as I mentioned in
an earlier post, this is because of many errors in the book about
Oberon by M. Reiser and N. Wirth, even if it is a very good book,
I'm disappointed about the chapter "pointers").

But basically, a pointer doesn't exist if it's not created with
a NEW(p) (p:P is declared by VAR or TYPE as a POINTER TO basetype)

Allright, let's start with what I know:

 The declaration of a pointer does not produce the variable it points to. 
 We have to generate the variable explicitly by NEW(p), where the actual
 parameter p is a pointer of type P. NEW(p) creates a variable that is
 an instance of the base type of P. The pointer p is initialized such that
 it points to that instance.

That means we have to create each pointer with NEW(p) before we can
work with it.
For example

TYPE P = POINTER TO PDesc;
     PDesc = RECORD key: Key; next: P END;

VAR p:P;

What about the p.next then? It is a pointer too, does it have to
be created with NEW() as well? I guess not. What is it's value? NIL?

Before we can assign something to p or p.next, we have to create this
with NEW(), right?

Because there is no such thing as a "spontaneous pointer", it doesn't
exist before we create it with NEW().

Therefore we have to produce each node (e.g. of a list) with NEW(node),
before we add it to the list.

My problem seems to be too many NEW instruction (because I think we have to create every pointer). Please help me here:

(Let "first:P" be a pointer that provides a link to the first list node.)

An example of a "removal of the first node of a list" is:

PROCEDURE FirstNode(VAR first: P):P;
VAR n: P;
BEGIN
  n := first;
  IF n # NIL THEN first := n.next END;
  RETURN n
END FirstNode;

My questions now:

* Why can we assign something to n without a NEW(n) statement?
* Why is there no NEW(n) at all?

I assume because we did VAR n:P and first exists as a variable
parameter.

Please mail your suggestions to rmichl@cinenet.ch or post here.

Thanxx,
Robert


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