in reply to Re: multiple values for one key in hash
in thread multiple values for one key in hash

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'
                   ]
        };

[download]

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

Replies are listed 'Best First'.
Re^3: multiple values for one key in hash
by wade (Pilgrim) on May 12, 2008 at 22:46 UTC

    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; ++

    --
    Wade
[reply]
      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.
      My criteria for good software:
      1. Does it work?
      2. Can someone else come in, make a change, and be reasonably certain no bugs were introduced?
[reply]

        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

        [download]

        The cake is a lie.
        The cake is a lie.
        The cake is a lie.

[reply]
[d/l]

In Section Seekers of Perl Wisdom