It is called auto-vivification, and you can't avoid it.
If you look at a hash of a hash that doesn't exist, perl
creates the lower hash, rather than giving you an error
for trying to access a hash that does not exist. Instead
do
unless exists $apples{$t} && $apples{$t}{weight}
On Thu, Feb 06, 2003 at 10:56:06AM -0500, Joel Gwynn wrote:
> Wow. This is driving me crazy. I'm looking for a value in one of the
> keys in a hash, like so:
>
> my %apples = (macintosh => {weight => '10lb', cost => '5'},
> red_delicious => {weight => '15lb', cost => '2'},
> fuji => {weight => '12lb', cost => '7'});
>
> my @test = qw(granny_smith crabapple);
>
> foreach my $t (@test){ print "$t not found\n" unless $apples{$t}{weight}
> } print "\n-----------------------\n"; foreach my $a (keys %apples){
> print "$a: weight: $apples{$a}{weight}\n";
> }
>
> And what I get output is this:
>
> granny_smith not found
> crabapple not found
>
> -----------------------
> granny_smith: weight:
> fuji: weight: 12lb
> crabapple: weight:
> red_delicious: weight: 15lb
> macintosh: weight: 10lb
>
> Now, what's driving me crazy is that the two test values are being added
> to the hash, simply by looking for $apples{$t}{weight}. If I simply
> look for $apples{$t}, like so:
>
> foreach my $t (@test){ print "$t not found\n" unless $apples{$t} }
>
> new hash members are not created. Why should this be?
>
>
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