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From: "Jeffrey R. Carter" <spam.jrcarter.not@spam.not.acm.org>
Newsgroups: comp.lang.ada
Subject: Re: Generic Embedded List Nodes
Date: Sat, 18 Jun 2016 16:40:23 -0700
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Date: 2016-06-18T16:40:23-07:00
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On 06/18/2016 03:52 PM, Warren wrote:
> 
> The idea is that the list node resides within the structure/tagged type,
> and acts as a doubly linked list node when in a list. The Emb_Node can
> be used as a list head when itself (or as part of another structure). This
> kind of thing is done in the Linux kernel, for example.
>    
> The Emb_Node and its operations are trivial. The problem occurs when
> you traverse a linked list of Emb_Nodes (or its derived type). With
> a given node, I need to then access the object that _contains_ it. In
> C/C++ you do some offset calculation from the node address back to
> the owning struct/class.

Let me make sure I understand this. You have type Emb_Node, and you can string
Emb_Nodes together to make a list. You want to make a composite type with an
Emb_Node component:

type Outer is record
   ...
   Node : Emb_Node;
   ...
end record;

and declare objects of this type:

O1 : Outer;
O2 : Outer;

type O_Set is array (Positive range <>) of Outer;

O_List : O_Set (1 .. 10);

type Something is record
   ...
   O : Outer;
   ...
end record;

S : Something;

and then be able to string the Node components of all these Outers together into
a list, and then treat that list as a list of Outers.

Is that correct?

-- 
Jeff Carter
"My legs are gray, my ears are gnarled, my eyes are old and bent."
Monty Python's Life of Brian
81