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Newsgroups: comp.lang.ada
Date: Mon, 2 Apr 2018 12:46:58 -0700 (PDT)
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Subject: Re: limited agregate and limited components default initialization
From: Jere <jhb.chat@gmail.com>
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Xref: reader02.eternal-september.org comp.lang.ada:51302
Date: 2018-04-02T12:46:58-07:00
List-Id: <comp.lang.ada>

On Monday, April 2, 2018 at 2:51:00 PM UTC-4, Dmitry A. Kazakov wrote:
> On 2018-04-02 20:19, Jere wrote:
> 
> > Something else unrelated to your question, but that I just noticed: Assuming
> > you could have gotten a list definition that you were happy with, there is
> > still a very serious problem with it.  Doubly linked lists (ones that use
> > both Next and Prev/Pred) are susceptible to "circular references" when using
> > reference counting smart pointers.  You would need to use a weak reference
> > based smart pointer for one of the two (either Next or Prev/Pred, whichever
> > you prefer).
> > 
> > -- very simple/silly example
> > type Node is
> >     Value : Item_Type;
> >     Next  : Smart_Pointer_Type;
> >     Prev  : Weak_Smart_Pointer_Type;
> > end Node;
> 
> This is still circular. Weak/strong references work only in hierarchical 
> structures. If a doubly-linked list must deploy them then it should be 
> the head holding references to all nodes. It does not make much sense 
> though.
> 
Nope, not circular at all unless you connect Tail to Head (which isn't
the normal use case). The List type would hold a smart pointer to the
head node.  Been working flawlessly for over a decade now with no
circular references.