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Hi all,

just stumbeled over a strange behaviour of perl: When trying to
retrieve a non-existing value from a perl array, e.g. by saying

my $a = [1,2];
my $b = $$a[3][0];

then $a is modified to [1,2,[]].

Is this a feature I just don't understand or is it really a bug (as I
would suppose)?

Thanx in advance,

thoin

thoin wrote:
> just stumbeled over a strange behaviour of perl: When trying to
> retrieve a non-existing value from a perl array, e.g. by saying
>
> my $a = [1,2];
> my $b = $$a[3][0];
>
> then $a is modified to [1,2,[]].

Suppose you mean [1,2,undef,[]].

> Is this a feature I just don't understand or is it really a bug (as
> I would suppose)?

I think it's called autovivification. One place where it is commented
on is

perldoc -f exists

--
Gunnar Hjalmarsson
Email: http://www.gunnar.cc/cgi-bin/contact.pl

Gunnar Hjalmarsson <> wrote in message news:<mKK0c.50876$>...
> thoin wrote:
> > just stumbeled over a strange behaviour of perl: When trying to
> > retrieve a non-existing value from a perl array, e.g. by saying
> >
> > my $a = [1,2];
> > my $b = $$a[3][0];
> >
> > then $a is modified to [1,2,[]].
>
> Suppose you mean [1,2,undef,[]].

Yes, of course I do mean that

> > Is this a feature I just don't understand or is it really a bug (as
> > I would suppose)?
>
> I think it's called autovivification. One place where it is commented
> on is
>
> perldoc -f exists

Phew, nice to see that it will be fixed in the future. I mean, nice to
see that I was right supposing this behaviour to be kind of wrong.

Thanks a lot for your hint!

Thoin

In article < >, thoin
<> wrote:

> Gunnar Hjalmarsson <> wrote in message
> news:<mKK0c.50876$>...
> > thoin wrote:
> > > just stumbeled over a strange behaviour of perl: When trying to
> > > retrieve a non-existing value from a perl array, e.g. by saying
> > >
> > > my $a = [1,2];
> > > my $b = $$a[3][0];
> > >
> > > then $a is modified to [1,2,[]].
> >
> > Suppose you mean [1,2,undef,[]].
>
> Yes, of course I do mean that
>
> > > Is this a feature I just don't understand or is it really a bug (as
> > > I would suppose)?
> >
> > I think it's called autovivification. One place where it is commented
> > on is
> >
> > perldoc -f exists
>
> Phew, nice to see that it will be fixed in the future. I mean, nice to
> see that I was right supposing this behaviour to be kind of wrong.
>
> Thanks a lot for your hint!
>
> Thoin

The only thing "perldoc -f exists" says might be fixed in the future is
that "exists $$a[3][0]" may not create $$a[3] if it doesn't already
exist. The statement "$b = $$a[3][0]" will definitely create $$a[3] if
it doesn't exist now and forever more in the future.

FYI: this newsgroup is defunct. Please try comp.lang.perl.misc in the
future.