From: Warren <ve3wwg@gmail.com>
Subject: Re: Generic Embedded List Nodes
Date: Sat, 18 Jun 2016 19:50:32 -0700 (PDT)
Date: 2016-06-18T19:50:32-07:00 [thread overview]
Message-ID: <037df2b8-b9c4-4447-87ee-cc89d7072b30@googlegroups.com> (raw)
In-Reply-To: <431af616-7df3-4e4d-9262-26ed68cb74c7@googlegroups.com>
On Saturday, 18 June 2016 22:21:18 UTC-4, Warren wrote:
> On Saturday, 18 June 2016 22:14:22 UTC-4, Jeremiah wrote:
> > On Saturday, June 18, 2016 at 6:52:06 PM UTC-4, 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;
> >
> > Change Node_Type to:
> > type Node_Type(Obj: access Object_Type) is new Emb_Node with null record;
> >
> > You need an extension, even if it is a null record.
>
> I had clearly forgotten about "with null record". I will try that.
>
> Warren
generic
type Object_Type is tagged private;
package Emb_List.Nodes is
type Node_Type(Obj: access Object_Type := Obj'Access) is new Emb_Node
with null record;
function Object(Node: Node_Type) return Object_Type;
end Emb_List.Nodes;
The problem with this now is "discriminant "Obj" cannot be used before end of discriminant part".
This is intended to allow extension of My_Recd with a Node that knows My_Recd'Access.
declare
type My_Recd is tagged
record
Id: Natural := 99;
end record;
package EMB is new Emb_List.Nodes(Object_Type => My_Recd);
Is there another way that I could do this: i.e. determine My_Recd'Access from some list node object, embedded in My_Recd?
Warren
next prev parent reply other threads:[~2016-06-19 2:50 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-06-18 22:52 Generic Embedded List Nodes Warren
2016-06-18 23:40 ` Jeffrey R. Carter
2016-06-19 2:15 ` Warren
2016-06-19 3:04 ` Jeffrey R. Carter
2016-06-19 2:14 ` Jeremiah
2016-06-19 2:21 ` Warren
2016-06-19 2:50 ` Warren [this message]
2016-06-19 4:45 ` Simon Wright
2016-06-19 18:27 ` Warren
2016-06-19 19:04 ` Dmitry A. Kazakov
2016-06-19 20:13 ` Warren
2016-06-19 20:35 ` Dmitry A. Kazakov
2016-06-20 2:42 ` Warren
2016-06-20 7:25 ` Dmitry A. Kazakov
2016-06-20 12:26 ` Warren
2016-06-20 19:33 ` Niklas Holsti
2016-06-21 2:20 ` Warren
2016-06-21 5:52 ` Niklas Holsti
2016-06-21 7:15 ` Dmitry A. Kazakov
2016-06-21 18:54 ` Niklas Holsti
2016-06-21 19:54 ` Dmitry A. Kazakov
2016-06-21 10:31 ` Warren
2016-06-21 17:13 ` Jeffrey R. Carter
2016-06-21 18:56 ` Niklas Holsti
2016-06-21 20:13 ` Warren
2016-06-21 21:38 ` Niklas Holsti
2016-06-23 2:12 ` Warren
2016-06-23 8:19 ` Niklas Holsti
2016-06-23 12:37 ` Warren
2016-06-23 15:36 ` Niklas Holsti
2016-06-24 1:55 ` Warren
2016-06-24 12:49 ` Warren
2016-06-25 5:50 ` Niklas Holsti
2016-06-26 1:36 ` Warren
2016-07-01 13:49 ` Warren
2016-07-01 16:28 ` Warren
2016-06-24 20:25 ` Warren
2016-06-22 13:01 ` G.B.
2016-06-23 2:30 ` Warren
2016-06-20 6:08 ` Niklas Holsti
2016-06-20 12:20 ` Warren
2016-06-20 19:47 ` Shark8
2016-06-21 2:28 ` Warren
2016-06-21 7:21 ` Dmitry A. Kazakov
2016-06-21 10:32 ` Warren
2016-06-21 11:56 ` Dmitry A. Kazakov
2016-06-21 13:39 ` Warren
2016-06-21 14:04 ` Dmitry A. Kazakov
2016-06-23 0:37 ` Randy Brukardt
2016-06-23 2:25 ` Warren
2016-07-01 19:50 ` brbarkstrom
2016-07-02 1:55 ` Warren
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