On Monday 27 September 2010 10:17:16 HACKER Nora wrote:
> Hi Shlomi,
>
> > You shouldn't modify an array (@arr1 in this case) while iterating
>
> over it using
>
> > foreach. Otherwise, the results will be unpredictable. One option to
> > overcome it is to do:
> >
> > [code]
> > my @arr1_copy = @arr1;
> >
> > while (defined (my $arr1_elem = shift(@arr1_copy))) {
> >
> > # Do something with $arr1_elem
> >
> > }
> > [/code]
>
> Is the principle you are trying to explain that the foreach loop should
> be changed to a while or that it is advisable to make a copy of the
> original array? (Or just both? :-) )
Well, if you don't care about the array being emptied (forever) by the loop,
then you don't have to the «my @arr1_copy = @arr1;» thing and use the
(while(defined loop on it as it is. Moreover, you shouldn't iterate on an
array using *foreach* while changing the order of its elements (or removing
them) because you'll get unexpected results. The "while shift" loop I've shown
avoids such problems.
> I suppose it's all about the
> 'while' because even if I made a copy of the array but continued with
> the foreach I would have the same problems, wouldn't I? Please confirm.
>
Yes, you would.
> If not answered to the above question, please explain why it is
> advisable to make a copy of the original array?
Well, it is advisable if you want to preserve the original array. If not, you
can use it as it is.
Regards,
Shlomi Fish
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Shlomi Fish http://www.shlomifish.org/
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