Paolo Gianrossi wrote:
Here's my problem (well, a shortened example=)
#hashes.pl
use strict;
use warnings;
use Data::Dumper;
my %a=(a=>1, b=>2, c=>3);
print Dumper \%a;
print "\n".("-" x 10)."\n";
my $c=$a{d}->[0];
print Dumper \%a;
$ perl hashes.pl
$VAR1 = {
'c' => 3,
'a' => 1,
'b' => 2
};
----------
$VAR1 = {
'c' => 3,
'a' => 1,
'b' => 2,
'd' => []
};
Now, while I'd expect a warning on the line of my $c=$a{d}->[0]; (like,
dunno, you're trying to dereference undef?) I'd never think a field is
added to the hash...
I'm confused.. Is this expected behaviour? Changing a right-hand operand
(without calling a sub)?
It is called 'autovivication'. If you try to use the value of a
non-existent hash or array element as if it was a reference to a hash or
array then an anonymous hash or array will be created for you. Take a
look at
perldoc perlglossary
and look at 'autovivification'.
Your example is not a very useful one. It is most often seen as
push @{$a{d}}, $newdata;
or something similar.
HTH,
Rob
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