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,FREEMAIL_FROM autolearn=unavailable autolearn_force=no version=3.4.4 X-Received: by 10.25.80.7 with SMTP id e7mr2209276lfb.7.1466452031423; Mon, 20 Jun 2016 12:47:11 -0700 (PDT) X-Received: by 10.157.34.202 with SMTP id y68mr539645ota.4.1466452021016; Mon, 20 Jun 2016 12:47:01 -0700 (PDT) Path: eternal-september.org!reader01.eternal-september.org!reader02.eternal-september.org!news.eternal-september.org!mx02.eternal-september.org!feeder.eternal-september.org!goblin1!goblin.stu.neva.ru!oe3no6338211lbb.1!news-out.google.com!f5ni20747lbb.0!nntp.google.com!oe3no6338210lbb.1!postnews.google.com!glegroupsg2000goo.googlegroups.com!not-for-mail Newsgroups: comp.lang.ada Date: Mon, 20 Jun 2016 12:47:00 -0700 (PDT) In-Reply-To: <66c14298-c62d-4f4b-b0c0-e969454f9334@googlegroups.com> Complaints-To: groups-abuse@google.com Injection-Info: glegroupsg2000goo.googlegroups.com; posting-host=67.0.53.185; posting-account=lJ3JNwoAAAAQfH3VV9vttJLkThaxtTfC NNTP-Posting-Host: 67.0.53.185 References: <66c14298-c62d-4f4b-b0c0-e969454f9334@googlegroups.com> User-Agent: G2/1.0 MIME-Version: 1.0 Message-ID: <4da8ad8e-f6b4-46b3-b81d-b255c030a45c@googlegroups.com> Subject: Re: Generic Embedded List Nodes From: Shark8 Injection-Date: Mon, 20 Jun 2016 19:47:11 +0000 Content-Type: text/plain; charset=UTF-8 Xref: news.eternal-september.org comp.lang.ada:30845 Date: 2016-06-20T12:47:00-07:00 List-Id: On Saturday, June 18, 2016 at 4:52:06 PM UTC-6, Warren wrote: > Getting back to Ada after a hiatus, I currently have a need to build a > generic package to implement "embedded list node" lists. The advantage > is high performance in a server setting to avoid underlying malloc/free > calls. > > 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. > > My idea (in Ada) was to save some kind of access value in a type > derived from Emb_List. But that is where the trouble starts. > > package Emb_List is > > type Emb_Node is tagged private; > > procedure Insert_Head(Head: access Emb_Node; Node: access Emb_Node); > procedure Unlink(Node: access Emb_Node); > > private > > type Emb_Node is tagged > record > Next: access Emb_Node; -- Ptr to next node in list (if any) > Prev: access Emb_Node; -- Ptr to prev node in list (if any) > end record; > > end Emb_List; > > The generic extension (below) was intended to hold the reference to the > containing object, which is where the trouble starts. I was hoping this > would work, but running into "missing full declaration for private > extension". > > generic > type Object_Type is tagged private; > package Emb_List.Nodes is > > type Node_Type(Obj: access Object_Type) is new Emb_Node; > > function Object(Node: Node_Type) return Object_Type; > > end Emb_List.Nodes; > > > The other end of the challenge will be to have the Node_Type save the > owning object access value at the time it is created: > > type Something_New_Type is tagged > record > Stuff: Natural; > Timeout_Node: Node_Type(some access to this record); > ... > end record; > > I am trying to avoid using 'Address for this, since there is likely a > way to do this "right". > > Warren. Hm, have you tried seeing if any Ada.Containers.* fits your needs? You could perhaps use Indefinite_Holder to hold your item or Indefinite_Vector to hold the entire list.