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From: "Ayende Rahien" <Dont@spam.me>
Newsgroups: comp.lang.ada
Subject: Re: Problem trying to implement generics.
Date: Fri, 13 Apr 2001 13:54:52 +0200
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Date: 2001-04-13T13:54:52+02:00
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"chris.danx" <chris.danx@ntlworld.com> wrote in message
news:PDAB6.10174$FD1.1166748@news6-win.server.ntlworld.com...
> Hi,
>
> > The error from Object Ada is:
> > bintree.adb: Error: line 9 col 28 LRM:4.1(3), Direct name, root, is not
> > visible, Ignoring future references
> >
> > The error from GNAT is:
> >
> > bintree.adb:9:42: "root" is undefined (more references follow)
> >
> > With nothing more to follow this.
>
> Ok, this means it's not found a definition for it.  It doesn't know what
or
> where it is.  You probably know that.
>
> [SNIP]
>
> >  private
> >   type Binary_Tree is new Ada.Finalization.controlled with record
> >    root: Node_access := null;
> >   end record;
>
> the error comes because
>
> > package body binTree is
> [snip]
> >  procedure insert(insert_this : in data_type; Sort : in sort_by) is
> >   New_node : Node_Access := new node;
> >   current : Node_access := root; -- This is the line it compline about!!
>
> you've forgot to that Root is in Binary_Tree.

Okay, so how do I fix it? And what is wrong, anyway?

> I have a question.  From your code it doesn't look like an ADT.  Is this
> what you intended?  I can't remember the term for what this looks like,
but
> I think it's to do with storing the Tree as a global variable in the
package
> not as an ADT.

Okay, major cocept problem here.
I'm coming here with C/C++ background, and I understand that Ada has a
different OO paradigm.
I assumed that for each Binary_Tree spesific type that I create, there would
be its own Root.
I mean:
package Int_BinTree is new Binary_Tree(data_type=>
Integer,Sort_by=>Integer);

Bin_Tree_First, Bin_Tree_Second : Int_BinTree;

Does Bin_Tree_First.Root = Bin_Tree_Second.Root ?


> If you want an ADT you need to pass in a Binary_Tree type as necessary.  I
> didn't see it any where in your code so i'm assuming it's based on a
global
> variable.

I think that you are talking about ADO vs ADT , right?
generic abstract data type & generic abstract data object

> There's nothing wrong doing it this way!

Then why doesn't it compile?