Re: [boost] Re: filter_iterator not bidirectional ?

From: Sylvain Pion (Sylvain.Pion_at_[hidden])
Date: 2003-05-07 02:32:21

On Tue, May 06, 2003 at 08:48:51PM -0400, David Abrahams wrote:
> > I was wondering why the filter_iterator could not be made
> > bidirectional when the base iterator is as well.
> 
> It could, for a (rather high) price.
> 
> > Is it because it would have to store the "begin" iterator ?
> > Actually I am wondering whether it should have to store the begin iterator
> > even in this case.
> 
> Yes, it would.
> 
> > Would it be possible to make filter_iterator support operator-- ?
> 
> Yes it would.  It seems like a fun project for someone so inclined ;-)
> Do you need this functionality for something, or are you just curious?

I need it.  I have independently implemented a version of it in CGAL
quite some time ago, and I'm comparing it to Boost's version now.
Mine has to be bidirectional, so I store the "begin" base iterator.

But I was wondering if I could do without, because the only reason for storing
the begin base iterator is just to detect when the user calls operator-- on the
begin() of the resulting filter iterator.
But is this something which really has to be guarded against, or is this just
something which can be left unspecified (i.e. it's a user bug) ?

-- 
Sylvain