Fwd: Re: [boost] Re: cycle_iterator

From: Thomas Witt (witt_at_[hidden])
Date: 2002-02-19 13:02:58

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Oups

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Subject: Re: [boost] Re: cycle_iterator
Date: Tue, 19 Feb 2002 17:25:00 +0100
From: Thomas Witt <witt_at_[hidden]>
To: "David Abrahams" <david.abrahams_at_[hidden]>

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On Tuesday 19 February 2002 14:53, David Abrahams wrote:
> Hi Thomas,
>
> How's it going with Gennadiy?

I am happy.

> I haven't been watching closely, but I just
> want to make sure it's not too frustrating for you.

Not at all.

> Do you feel you're
> making forward progress on this?

There are a few things to sort out, but I am optimistic. After all
it's Gennadiys project and I don't wont to do a hostile takeover.

> Do you think I need to step in?

When it comes to nailing down the interface, comments might be helpfull.

Thanks

Thomas

> Best Regards,
> Dave
>
> ----- Original Message -----
> From: "Thomas Witt" <witt_at_[hidden]>
> To: <boost_at_[hidden]>
> Sent: Tuesday, February 19, 2002 5:44 AM
> Subject: Re: [boost] Re: cycle_iterator
>
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> >
> > On Tuesday 19 February 2002 07:09, rogeeff wrote:
> > > --- In boost_at_y..., Thomas Witt <witt_at_i...> wrote:
> > > > Gennadiy
> > >
> > > [...]
> > >
> > > > The main changes are:
> > > >
> > > > Added a const here and there.
> > >
> > > The only placewhere I would agree to put const in constructor: const&
> > > instead of value. You can't make class data members const.
> > > First of
> > > all it prevent implementing mutable iterators and second you can't
> > > even assign const iterator.
> >
> > I think you misinterpret the const here. Iterators are just values, they
>
> have
>
> > pointer semantic but they are values. As a result const iterator and
> > const_iterator are fundamentally different. A const iterator is the same
>
> as
>
> > *const whereas a const_iterator is the same as const*.
> >
> > Copying a const iterator to an iterator works just as copying a const
>
> double
>
> > to a double. You even can assign to the value pointed to by an const
> > iterator.
> >
> > Making an iterator const means fixing its position and thats exactly what
>
> is
>
> > needed here. The range boundaries should be immutable for an
>
> cycle_iterator.
>
> > > Also I do not see any paractical reasons
> > > in defining local veriables in 2 line inline function const. Do you?
> >
> > I would not see not making them const as a fundamental error but they are
> > const so they should be made const. Removing the const here would be an
> > error.
> >
> > > > Added make_cycle_iterator with iterator position (+ only works for
> > >
> > > random
> > >
> > > > access iterators). What do you think about the interface.
> > >
> > > Specifying three
> > >
> > > > iterators seemed to error prone to me.
> > >
> > > I do not like the idea by itself. Since you can't check that this
> > > iterator position is in a range it could be very dengerous.
> >
> > I do not buy this one. With the same argument std::copy or any other std
> > algorithm should be banned.
> >
> > > For
> > > example, surprisingly the following statement would be an infinite
> > > loop:
> > >
> > > v - some container
> > >
> > > std::copy( boost::make_cycle_iterator( v ),
> > >            boost::make_cycle_iterator( v.end(), v ),
> > >            std::ostream_iterator( std::cout, "" ) );
> >
> > This one could be easisly diagnosed by an implementation. v.end is not a
>
> valid
>
> > base iterator position as it is not in the range. Checking for base ==
> > end
>
> as
>
> > a common error seems like a good idea to me.
> >
> > > I do not think you need this ability in a real life for cycle
> > > iterator.
> >
> > Honestly, I _do_.
> >
> > > > Removed make_cycle with container argument.
> > >
> > > I think creating cycle iterator for container would be the most
> > > frequently used feature. But we can't pass container by value. So we
> > > need to choose between const/mutable reference. After some
> > > consideration I would probably choose const version now.
> >
> > To me make_cycle with container argument is a covenience function. It can
>
> be
>
> > provided in addtion to a pure iterator function but not as a replacement.
> > First all std interfaces use iterators and so should cycle_iterator.
>
> Second
>
> > cycle_iterators should not be reduced to containers. They can be used and
>
> are
>
> > usefull with every valid range.
> >
> > In my oppinion make_cycle with container argument should be removed as
>
> long as
>
> > there is no solution that covers both const and non-const containers.
> > Otherwise we would only confuse the users.
> >
> > Thomas
> >
> > > [...]
> > >
> > > > Thomas
> > >
> > > Gennadiy
> > >
> > >
> > >
> > >
> > > Info: http://www.boost.org  Send unsubscribe requests to:
> > > <mailto:boost-unsubscribe_at_[hidden]>
> > >
> > > Your use of Yahoo! Groups is subject to
>
> http://docs.yahoo.com/info/terms/
>
> > - --
> > Dipl.-Ing. Thomas Witt
> > Institut fuer Verkehrswesen, Eisenbahnbau und -betrieb, Universitaet
>
> Hannover
>
> > voice: [phone] - 4273, fax: [phone]
> > http://www.ive.uni-hannover.de
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>
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>
> > Your use of Yahoo! Groups is subject to http://docs.yahoo.com/info/terms/

- - --
Dipl.-Ing. Thomas Witt
Institut fuer Verkehrswesen, Eisenbahnbau und -betrieb, Universitaet Hannover
voice: [phone] - 4273, fax: [phone]
http://www.ive.uni-hannover.de
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- -------------------------------------------------------
- -- 
Dipl.-Ing. Thomas Witt
Institut fuer Verkehrswesen, Eisenbahnbau und -betrieb, Universitaet Hannover
voice: [phone] - 4273, fax: [phone]
http://www.ive.uni-hannover.de
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