From: Matthew Heaney <matthew_heaney@acm.org>
Subject: Re: Wanted: Ada STL. Reward: Ada's Future
Date: 1999/02/01
Date: 1999-02-01T00:00:00+00:00 [thread overview]
Message-ID: <m3btje7i1b.fsf@mheaney.ni.net> (raw)
In-Reply-To: 7931ej$qqf@bgtnsc02.worldnet.att.net
"Alexy V Khrabrov" <khrabrov.a@worldnet.att.net> writes:
> Matthew Heaney wrote in message ...
>
> >On the contrary, a set is next-to-useless as a collection abstraction in
> >any real program.
>
>
> On the contrary, set is a useful abstraction. In fact, it's the first
> abstaction in mathematics, used by Euclid to prove that the SET of primes is
> infinite.
I don't care about mathematics or Euclid. I care about writing real
computer programs that have to meet real deadlines.
> Set is a part of C++ STL which is used all the time, and emphasized in all
> STL books.
> I've seen a gazillion programs using lists for mimicing set behavior, and
> will see a bazillion more.
Then the STL has invented an abstraction I'll probably never use.
The STL is not a good model for an Ada components library, anyway.
> >A set is an unordered collection without duplicates.
>
> Not necessarily unordered. A very useful extension of math set is a set of
> ordered items, for which a generic taking an "<" parameter along with the
> Element type and "=" is most suitable form in Ada.
Ah, but there's the rub. From a semantic point of view, a set is
unordered, even if it has an implementation that is ordered.
The reason you have to order the items (internally) is because the set
is being used to ... implement a computer program! Requiring that the
items have a comparison operator is in fact exposing an implementation
detail, a detail that only manifests itself because you have to pay
attention to space & time semantics too.
If you need an unordered collection without duplicates, then by all
means use a set, and import a comparison operator if necessary (always a
good idea, actually).
But if you need just an unordered collection, and duplicates are
acceptable, then do NOT use a set, use a container.
> And I do require sets, as many other people do, too. Real world contains
> sets, and any faithful OOP will need them.
Funny, I've been programming for over 10 years, and I've NEVER needed an
unordered collection without duplicates (i.e. a set). But there have
been MANY times when I needed an unordered collection with duplicates
(i.e. a container).
Most of the time you just want to stuff something into a collection so
you can remember it for a little while, without incurring any insertion
overhead.
When we were using the old Booch Components, I NEVER used the Set
packages, because I never had a use for them.
What happens is that the programmer looks in his components library,
doesn't see what he needs, and instead of writing a high-level
container, uses a low-level linked list to implement his collection.
This is all wrong, because a linked list is at the wrong level of
abstraction.
> I prefer ordered sets whenever I can supply the "<" -- and I almost always
> can. Give me one example where you can't. I can even sort files on their
> last access time, can't I? Tasks on their name, etc. -- even limited
> private types, that is.
I use sets when I need an unordered collection without duplicates
(which almost never need).
I use containers when I need an unordered collection with duplicates
(which I almost always need).
> >In my work on the ACL (which I suspended until gnat 3.11p came out: it
> >wouldn't compile otherwise), I call this kind of abstraction a
> >"container." There is only a minimal set of operations on a Container
> >type:
> >
> >o add an item to the container
> >
> >o iterate over items in the container
> >
> >o remove the item currently designated by an (active) iterator
>
>
> Where is your ACL? Is it public?
It will be made public as soon as some caring person ports gnat 3.11p to
LinuxPPC. If I could only convince Robert Dewar to get himself a nice
Mac...
> >The first thing in the morning you need a Container, not a Set.
>
> Well, and I need sets, buddy!
That, and a big cup of coffee...
next prev parent reply other threads:[~1999-02-01 0:00 UTC|newest]
Thread overview: 102+ messages / expand[flat|nested] mbox.gz Atom feed top
1999-01-31 0:00 Wanted: Ada STL. Reward: Ada's Future Alexy V Khrabrov
1999-01-31 0:00 ` Simon Wright
1999-02-01 0:00 ` Jerry van Dijk
1999-02-01 0:00 ` Marin David Condic
1999-02-01 0:00 ` dennison
1999-02-01 0:00 ` Stanley R. Allen
1999-02-01 0:00 ` Matthew Heaney
1999-02-01 0:00 ` Alexy V Khrabrov
1999-02-01 0:00 ` Matthew Heaney [this message]
1999-02-01 0:00 ` Jeff Carter
1999-02-01 0:00 ` Brian Rogoff
1999-02-01 0:00 ` Ehud Lamm
1999-02-02 0:00 ` Brian Rogoff
1999-02-02 0:00 ` robert_dewar
1999-02-04 0:00 ` Ehud Lamm
1999-02-03 0:00 ` John English
1999-02-03 0:00 ` Matthew Heaney
1999-02-03 0:00 ` Brian Rogoff
1999-02-04 0:00 ` Stephen Leake
1999-02-04 0:00 ` Hyman Rosen
1999-02-05 0:00 ` Stephen Leake
1999-02-05 0:00 ` Hyman Rosen
1999-02-04 0:00 ` Matthew Heaney
1999-02-04 0:00 ` Brian Rogoff
1999-02-05 0:00 ` Stephen Leake
1999-02-05 0:00 ` Brian Rogoff
1999-02-05 0:00 ` John English
1999-02-05 0:00 ` Tucker Taft
1999-02-05 0:00 ` Richard D Riehle
1999-02-05 0:00 ` Brian Rogoff
1999-02-05 0:00 ` Brian Rogoff
1999-02-06 0:00 ` Matthew Heaney
1999-02-05 0:00 ` John English
1999-02-05 0:00 ` Nick Roberts
1999-02-04 0:00 ` Ehud Lamm
1999-02-04 0:00 ` Brian Rogoff
1999-02-05 0:00 ` Matthew Heaney
1999-02-05 0:00 ` Brian Rogoff
1999-02-08 0:00 ` John English
1999-02-04 0:00 ` Al Christians
1999-02-04 0:00 ` Pat Rogers
1999-02-04 0:00 ` Larry Kilgallen
1999-02-04 0:00 ` Pat Rogers
1999-02-04 0:00 ` Larry Kilgallen
1999-02-05 0:00 ` robert_dewar
1999-02-05 0:00 ` Tom Moran
1999-02-05 0:00 ` dewar
1999-02-05 0:00 ` Tom Moran
1999-02-05 0:00 ` dewar
1999-02-05 0:00 ` dennison
1999-02-06 0:00 ` dewar
1999-02-08 0:00 ` dennison
1999-02-08 0:00 ` robert_dewar
1999-02-08 0:00 ` dennison
1999-02-09 0:00 ` robert_dewar
1999-02-09 0:00 ` dennison
1999-02-09 0:00 ` Nick Roberts
1999-02-07 0:00 ` Simon Wright
1999-02-08 0:00 ` Corey Minyard
1999-02-08 0:00 ` Open Source Licensing (was: Wanted: Ada STL. Reward: Ada's Future) dennison
1999-02-08 0:00 ` Corey Minyard
1999-02-09 0:00 ` robert_dewar
1999-02-09 0:00 ` Corey Minyard
1999-02-09 0:00 ` dennison
1999-02-09 0:00 ` Corey Minyard
1999-02-09 0:00 ` Wanted: Ada STL. Reward: Ada's Future robert_dewar
1999-02-09 0:00 ` dennison
1999-02-10 0:00 ` robert_dewar
1999-02-07 0:00 ` Simon Wright
1999-02-05 0:00 ` Larry Kilgallen
[not found] ` <36ba730b.35540068@ <79fmg1$fn0$1@nnrp1.dejanews.com>
1999-02-06 0:00 ` Larry Kilgallen
1999-02-05 0:00 ` robert_dewar
1999-02-05 0:00 ` robert_dewar
1999-02-05 0:00 ` Larry Kilgallen
1999-02-05 0:00 ` robert_dewar
[not found] ` <79f24e$t14 <36BB4162.52FC6D9F@averstar.com>
1999-02-05 0:00 ` robert_dewar
1999-02-05 0:00 ` dennison
1999-02-05 0:00 ` dennison
1999-02-05 0:00 ` robert_dewar
1999-02-05 0:00 ` dennison
1999-02-06 0:00 ` Nick Roberts
1999-02-05 0:00 ` Tucker Taft
1999-02-05 0:00 ` John English
1999-02-09 0:00 ` micro_ada
1999-02-05 0:00 ` Nick Roberts
1999-02-08 0:00 ` John English
1999-02-02 0:00 ` Pointer Arithmetic (was: Wanted: Ada STL....) adam
1999-02-02 0:00 ` William Clodius
1999-02-03 0:00 ` adam
1999-02-03 0:00 ` robert_dewar
1999-02-03 0:00 ` Jean-Pierre Rosen
1999-02-03 0:00 ` William Clodius
1999-02-03 0:00 ` Nick Roberts
1999-02-03 0:00 ` Nick Roberts
1999-02-03 0:00 ` robert_dewar
1999-02-03 0:00 ` Robert A Duff
1999-02-03 0:00 ` robert_dewar
1999-02-02 0:00 ` Wanted: Ada STL. Reward: Ada's Future Richard D Riehle
1999-02-03 0:00 ` robert_dewar
1999-02-01 0:00 ` Jeff Carter
1999-02-08 0:00 ` Michael F Brenner
1999-02-05 0:00 ` Corey Minyard
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