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From: "Stuart" <stuart@0.0>
Newsgroups: comp.lang.ada
References: 
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 <sa4veko5ndy.fsf@margay.local>
Subject: Re: how to import a package
Date: Thu, 7 Dec 2006 09:32:11 -0000
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Date: 2006-12-07T09:32:11+00:00
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"Brian May" <bam@snoopy.apana.org.au> wrote in message 
news:sa4veko5ndy.fsf@margay.local...
>>>>>> "markww" == markww  <markww@gmail.com> writes:
> Going back in time, you said you defined Next_Rec as:
>
> type Node;
> type Node_Ptr is access Node;
> type Node is record
>            Data     : T;
>            Prev_Rec : access Node;
>            Next_Rec : access Node;
> end record;
>
> Note that "access Node" is not the same thing as "Node_Ptr".
>
> From memory the first is an "anonymous access type", but my memory is
> a bit rusty on this topic right now (Ada 2005 feature when used in a
> record?).

Ada is very particular about type matching and this can lead to some 
consequences that, at first, appear very odd.
If you look at this example:
   package P is
      pragma Elaborate_Body(P);  -- Allow a package body to exist!
   end P;

   package body P is
      type T is array(0..5) of integer;
      A, B : array(0..5) of integer;
      C, D : T;
   begin
      A := B;
      -- Not allowed because types don't match!
      C := D;
      -- Types match!
   end P;

Even though A and B appear in the same statement, they are of different 
anonymous types.  This is because
      A, B : array(0..5) of integer;
is equivalent to

      A : array(0..5) of integer;
      B : array(0..5) of integer;
and, as you may already have realized, homographs are not treated as being 
the same in Ada.

However, both C and D are of the same named type - even though the type T 
has an anonymous type as an index range.  I think it is better to avoid 
anonymous types - so the declaration of T might be better written as:
      type T_index is range 0..5;
      type T is array(T_index) of integer;

-- 
Stuart