Re: Self-referential types

["Matthew Heaney" <matthew_heaney@acm.org>]

In article <7tvjav$se6$1@nnrp1.deja.com> , Ted Dennison 
<dennison@telepath.com>  wrote:

>> This is the basis for programming with access discriminants, which is
>> how you do MI in Ada95.
>
> Is there somewhere I can go to see an example of this kind of MI? The
> Rationale says pretty much the same thing, but Cohen's tome doesn't go
> over it at all.

You can read my posts in the Ada95 design patterns archive.  The
observer and mediator patterns feature the access discriminant
technique.  (Last month (sep 99) I did a whole series on observer
variations.)

<http://www.acm.org/archives/patterns.html>

Let me know if you have trouble finding or understanding the material.

I also recently wrote Indexed_IO (B tree) and Indexed_Sequential_IO (B+
tree) packages.  The File_Type is implemented using the Rosen Trick,
which uses self-reference to get a variable view of an otherwise
constant object.

<http://www.adapower.com/reuse/indexed_io.html>

Matt

--
If we let the Creationists have their way, we may as well go whole hog.
Let us reintroduce the flat-earth theory, the chemistry of the four
elements, and mediaeval astrology.  For these outworn doctrines have
just as much claim to rival current scientific views as Creationism does
to challenge evolutionary biology.

Abusing Science: The Case Against Creationism
Philip Kitcher