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From: Niklas Holsti <niklas.holsti@tidorum.invalid>
Newsgroups: comp.lang.ada
Subject: Re: Generic Embedded List Nodes
Date: Sat, 25 Jun 2016 08:50:39 +0300
Organization: Tidorum Ltd
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Xref: news.eternal-september.org comp.lang.ada:30918
Date: 2016-06-25T08:50:39+03:00
List-Id: <comp.lang.ada>

On 16-06-24 15:49 , Warren wrote:
> On Thursday, 23 June 2016 11:36:25 UTC-4, Niklas Holsti  wrote:
>> My example had two embedded list nodes in the object, so the object
>> could be a member of two lists. You can define as many nodes as you
>> like, in the same record type, at the same time.
>
> Sorry, yes I see it now.
>
>>  type Integer_Object_T;
>>
>>    type Integer_Emb_Node_T (Obj : access Integer_Object_T)
>  >   is new Emb_Node_T with null record;
>
> I think when I had tried to do this, I had the chicken and egg problem.
> But I see you used the forward undefined type mechanism. I may explore
> this further at some point-- it certainly seems to solve the problem
> as I laid it out.  I just need to find some quiet time. Thanks for the help.

You are very welcome, Warren.

By the way, for record (so to speak), the procedures "Insert_At_Head" 
and "Delete" shown in my example each has an error: a possible use of a 
null reference. The versions below should be better, but they are still 
not tested.

    procedure Insert_At_Head (
       List : access List_T;
       Node : in     Emb_Node_Ref_T)
    is
    begin
       if List.Next /= null then
          List.Next.Prev := Node;
       end if;
       Node.Next := List.Next;
       List.Next := Node;
       Node.Prev := Emb_Node_Ref_T (List);
    end Insert_At_Head;

    procedure Delete (Node : in Emb_Node_Ref_T)
    is
    begin
       Node.Prev.Next := Node.Next;
       if Node.Next /= null then
          Node.Next.Prev := Node.Prev;
       end if;
       Node.Prev := null;
       Node.Next := null;
    end Delete;

-- 
Niklas Holsti
Tidorum Ltd
niklas holsti tidorum fi
       .      @       .