[gecode-users] Questions about the range iterators

[Christian Schulte]

Hi,

I think as you rightly observed, iterators are nothing but temporary
objects. If you need them twice, create them twice. The likes of NaryUnion
and NaryInter are special in that constructing them is expensive and hence
they feature a reset method. For the other iterators, there would be not
benefit in having reset methods (as you observed correctly) as reiterating
is the same efficiencywise as reseting them (actually, redoing is cheaper as
one does need to track pointers etc).

Cheers
Christian

--
Christian Schulte, www.ict.kth.se/~cschulte/


> -----Original Message-----
> From: users-bounces at gecode.org [mailto:users-bounces at gecode.org] On
> Behalf Of Jean-Noël Monette
> Sent: Friday, March 23, 2012 6:05 PM
> To: users at gecode.org
> Subject: [gecode-users] Questions about the range iterators
> 
> Hello,
> 
> I have a few questions about range iterators. Those questions are maybe
more
> reflexions that I hope you will confirm or correct if I misunderstood
something.
> Thank you in advance.
> 
> * Some iterators (those that are not templated), like NaryUnion or Minus,
> maintain their own data structure for the ranges, while the other ones
(most of
> them) rely on the information provided by other iterators.
> 
> * A very few iterators (based on RangeListIter) have a reset() method
allowing
> one to restart the iteration from scratch. The other ones do not have this
> functionality. What is the rational behind this choice? I was thinking
about the
> way/cost of adding a reset method to all iterators and it looks to me that
it
> might be easy enough. But maybe you have no interest in doing this (as it
> typically requires some more pointers (e.g. in classes such as
IntVarImpFwd) for
> only an occasional use), or there are some hidden difficulties (I'm
certainly not
> expert in the implementation of Gecode).
> 
> * From the previous point, most iterators are "one-use" only and are
unusable
> once consumed. If one wants to use twice the same iterator for some
reason,
> he has to recreate it from scratch. Is it right? Or is there some other
way to do it
> (e.g. with a copy constructor)?
> 
> Thank you for your help,
> 
> Jean-Noël Monette
> 
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