Re^2: multiple values for one key in hash

[moritz]

Note: you have to create the anonymous reference -- you can't just push a value if the key doesn't exist.

In perl you can ;-)

use strict;
use warnings;
use Data::Dumper;

my %hash;
push @{$hash{key}}, 'value';
print Dumper \%hash;
__END__
$VAR1 = {
          'key' => [
                     'value'
                   ]
        };

This nice feature is called "autovivification" and is quite useful most of the time.

[wade]

Son of a gun! You can just push the value. I could have sworn that this didn't work when I tried it at my old job (about 2 years ago). Is this a feature that has happened since then or have I been brain dead all this time?

Thanks, moritz; ++

[dragonchild]

It doesn't work if there was an undef explicitly assigned to the value before. A lot of people get tripped up by this because they just assign undef to something they don't use anymore instead of deleting the key.

[Fletch]

How would autovivification know that the undef in lvalue context it's autovivifying wasn't the original undef?

$ perl -MYAML::Syck -le '$h{bar}=1;$h{bar}=undef;push @{$h{bar}}, qw/a
+ b c/;print Dump( \%h )'
--- 
bar: 
  - a
  - b
  - c