From mboxrd@z Thu Jan 1 00:00:00 1970 X-Spam-Checker-Version: SpamAssassin 3.4.4 (2020-01-24) on polar.synack.me X-Spam-Level: X-Spam-Status: No, score=-1.9 required=5.0 tests=BAYES_00 autolearn=unavailable autolearn_force=no version=3.4.4 Path: eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!mx02.eternal-september.org!feeder.eternal-september.org!aioe.org!.POSTED!not-for-mail From: "Dmitry A. Kazakov" Newsgroups: comp.lang.ada Subject: Re: Generic Embedded List Nodes Date: Mon, 20 Jun 2016 09:25:16 +0200 Organization: Aioe.org NNTP Server Message-ID: References: <66c14298-c62d-4f4b-b0c0-e969454f9334@googlegroups.com> <2e39857a-7121-476b-807a-d2bff1e598f4@googlegroups.com> <431af616-7df3-4e4d-9262-26ed68cb74c7@googlegroups.com> <037df2b8-b9c4-4447-87ee-cc89d7072b30@googlegroups.com> <15914c54-191c-4f37-b754-282855d1aeaf@googlegroups.com> NNTP-Posting-Host: vFKDMXWEWKqnQQwESBoFfw.user.gioia.aioe.org Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit X-Complaints-To: abuse@aioe.org User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:45.0) Gecko/20100101 Thunderbird/45.1.1 X-Notice: Filtered by postfilter v. 0.8.2 Xref: news.eternal-september.org comp.lang.ada:30825 Date: 2016-06-20T09:25:16+02:00 List-Id: On 20/06/2016 04:42, Warren wrote: > On Sunday, 19 June 2016 16:35:32 UTC-4, Dmitry A. Kazakov wrote: >> No, doubly-linked list deletion is O(1). > > Ok you're tracking the link in Element, which is fine. However, your > Element also needs a reference to the separately allocated object (which > is a problem for me). This requires two allocations instead of one. No, that is the point. The object and the element (links) are in one continuous chunk of memory. I believe this is what you meant under being "embedded" nodes. When an object is allocated, element + object is instead and the address to the object's part is returned back from Allocate. Deallocate takes the object's address, subtracts the offset and deallocates the whole chunk. > I only need to insert head, traversal and delete. That's it! Yes, and the schema above is as effective as it can be. >>> In the embedded node case, I already have direct access to the >>> affected link node. To remove the node from a list I simply say: >>> >>> R.Link_Node.Unlink; >> >> The operation Delete has the list head parameter (Container) not for >> traversing the list, but for modifying the list head if the first >> element is deleted from the list. > >> If you don't have it, you must maintain a dedicated list head element >> with no object attached. That is a less safe and clean because it >> ultimately leads to run-time type checks in the client code. > > I agree with the dedicated list head statement, but not the "less > safe" part. You either have container or you have a list head (each > represents one list, though yours potentially several). > > There is nothing to check about a list head- you simply begin there. > If you have no "head.next", you have an empty list. Not with doubly-linked lists. There is always Next, because the list is circular. When you delete an element from the list you always get two lists. Deletion of a single element is an idempotent operation unless you have a dedicated head or else have the list head pointer corrected. List traversal when the list head is a pointer is performed like this: if Head /= null then This := Head; loop ... -- Do something This := This.Next; exit when This = Head; end loop; end if; -- Regards, Dmitry A. Kazakov http://www.dmitry-kazakov.de