retrieving data from array changes it???

[thoin]

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

 

[Gunnar Hjalmarsson]

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

 

[thoin]

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

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

 

[Jim Gibson]

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

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.