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From: Simon Wright <simon.j.wright@mac.com>
Newsgroups: comp.lang.ada
Subject: Re: how to import a package
Date: Mon, 11 Dec 2006 07:00:48 +0000
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Date: 2006-12-11T07:00:48+00:00
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"markww" <markww@gmail.com> writes:

> Ok I still don't understand why this assignment is illegal though -
> here's a test I have:
>
>     generic
>         type T is private;
>     package GenericNode is
>         type Node;
>         type Node_Ptr is access Node;
>         type Node is record
>             Data     : T;           -- the generic data we want to
> store in a node.
>             Prev_Rec : access Node_Ptr; -- points to the next record or
> null if none exists.
>             Next_Rec : access Node_Ptr; -- points to the previous
> record or null if none exists.
>         end record;
>     end GenericNode;
>
> now later...
>
>     package gNode is new GenericNode(T => PERSON_REC);
>     use gNode;
>
>     function Test(whatever : INTEGER) return INTEGER is
>     Temp : gNode.Node_Ptr;
>     begin
>         Temp := Temp.Next_Rec; -- no!!!!!!!!!!!!!!!!
>         return 0;
>     end Test;
>
> Why is the Temp assignment not possible? The compiler says: expected
> type Node_Ptr defined in genericnode.ads. But I have defined it as type
> Node_Ptr.

You've declared Next_Rec as *access* Note_Ptr. I think you meant to
declare it as just Node_Ptr.

   struct node {
      T data;
      node** prev_rec;   /* should be just node* ? */
      node** next_rec;
   };

Also, look at the way you've commented on Prev_Rec and Next_Rec. Aside
from the comments being the wrong way round, you say 'points to the
... record'. As written, it points to *a pointer to* the .. record.