From: Brian Rogoff <bpr@shell5.ba.best.com>
Subject: Re: Wanted: Ada STL. Reward: Ada's Future
Date: 1999/02/04
Date: 1999-02-04T00:00:00+00:00 [thread overview]
Message-ID: <Pine.BSF.4.05.9902041013030.19316-100000@shell5.ba.best.com> (raw)
In-Reply-To: u7lty3wpx.fsf@gsfc.nasa.gov
On 4 Feb 1999, Stephen Leake wrote:
> Brian Rogoff <bpr@shell5.ba.best.com> writes:
> > On Wed, 3 Feb 1999, Matthew Heaney wrote:
> > > ... snip ...
> > >
> > > for Index in Map'Range loop
> > >
> > > <do something with Map (Index)>
> > >
> > > end loop;
> > >
> > > If this looks simpler than my earlier formulation, that's because it's
> > > simpler. Loop iteration in Ada is less error prone than in C.
> > >
> > > This is yet another reason why I think that looking at the STL as a
> > > model for a standard Ada library is dangerous and misleading.
> >
> > Indeed. Just look at how incomprehensible AGL looping looks
> >
> > Os := Copy(Start(Deque'Access), Finish(Deque'Access), Os);
> >
> > or
> >
> > Pos := Find(Start(IVec'Access), Finish(IVec'Access), 42);
> >
> > The horror, the horror ...
> >
> > > The idioms in both languages are completely different. So forget about
> > > the STL as a model for an Ada library.
... snip ...
> >
> > So far, you've said nothing that indicates that you've looked seriously at
> > the STL. Why don't you just get very specific and say exactly why you
> > think it is a bad model for an Ada library, using examples? I think the
> > idea of writing algorithms over collections in terms of their iterators is
> > a good one.
>
> I thought Matthew just did that, but you haven't answered the question
> "why does the STL allow iteration past the end of the array". This
> bugs me too. Is there a real reason here, or is it an accident of the
> implementation?
How do you even know that it points past the end of the array, in an Ada
implementation? We have a constructor for an iterator called "Last" or
"Finish" or whatever. Should it matter how Finish is implemented?
> Perhaps it is the most general way to define an iterator that points
> to nothing?
It is *a* way to define a stopping condition or sentinel value. In the
case of a red-black tree, the null pointer is a sentinel. In the case of
an array, whose iterator conceptually looks like a pointer-offset pair,
an offset one greater than the highest index of the array makes a fine
sentinel, and it just so happens that in C++ you can use this easily.
> Certainly if the underlying implementation of a collection
> is an array, this makes sense. But if the underlying implementation is
> a list, then a null pointer makes more sense. Why not make the
> abstraction resemble a null pointer, rather than an out-of-bounds
> index?
In what way does the value of Finish not resemble a null pointer,indeed,
when iterating over a list and checking for nullness of a pointer, in what
way does that not resemble checking for an out of bounds index?
-- Brian
next prev parent reply other threads:[~1999-02-04 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 ` Stanley R. Allen
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 ` Matthew Heaney
1999-02-01 0:00 ` Alexy V Khrabrov
1999-02-01 0:00 ` Matthew Heaney
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 ` Richard D Riehle
1999-02-03 0:00 ` robert_dewar
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 [this message]
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 ` Brian Rogoff
1999-02-05 0:00 ` Richard D Riehle
1999-02-05 0:00 ` Brian Rogoff
1999-02-06 0:00 ` Matthew Heaney
1999-02-05 0:00 ` Nick Roberts
1999-02-05 0:00 ` John English
1999-02-04 0:00 ` Ehud Lamm
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 ` Larry Kilgallen
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
[not found] ` <36ba730b.35540068@ <79fmg1$fn0$1@nnrp1.dejanews.com>
1999-02-06 0:00 ` Larry Kilgallen
1999-02-05 0:00 ` robert_dewar
1999-02-05 0:00 ` robert_dewar
1999-02-05 0:00 ` Larry Kilgallen
1999-02-05 0:00 ` robert_dewar
1999-02-05 0:00 ` Tucker Taft
1999-02-05 0:00 ` dennison
1999-02-05 0:00 ` robert_dewar
1999-02-05 0:00 ` dennison
1999-02-06 0:00 ` Nick Roberts
[not found] ` <79f24e$t14 <36BB4162.52FC6D9F@averstar.com>
1999-02-05 0:00 ` robert_dewar
1999-02-05 0:00 ` dennison
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
1999-02-05 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 ` robert_dewar
1999-02-03 0:00 ` Nick Roberts
1999-02-03 0:00 ` robert_dewar
1999-02-03 0:00 ` Robert A Duff
1999-02-01 0:00 ` Wanted: Ada STL. Reward: Ada's Future Jeff Carter
1999-02-08 0:00 ` Michael F Brenner
1999-02-05 0:00 ` Corey Minyard
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