uksza has asked for the wisdom of the Perl Monks concerning the following question:

Hello wise monks,

please, look at this sample code.
#!/usr/bin/perl
use strict;
use warnings;
my %pets;
my $color;

$color="black";
$pets{$color}=\[];
push @${$pets{$color}},"cat";
push @${$pets{$color}},"dog";

$color="while";
$pets{$color}=\[];
push @${$pets{$color}},"rat";
push @${$pets{$color}},"bat";

foreach my $p (values %pets) {
        print "$p\n";
        #^^^this is ref to ref to array?

        print "$$p\n";
        #^^^this is ref to array

        print "@$$p\n\n";
        #^^^this is array
}

[download]
and output: 
push @${$pets{$color}},"rat";
REF(0x815c4d0)
ARRAY(0x815c4e8)
rat bat

REF(0x812ed0c)
ARRAY(0x812ed48)
cat dog

[download]
@$$p looks very strange.
why I can't use @$p.
why $p is ref to ref to array (or maybe is not?) not just ref to array?
I don't understand this. Could anybody help me?

stay in peace
Lukasz

Replies are listed 'Best First'.
Re: Cruel references
by japhy (Canon) on Mar 06, 2005 at 00:27 UTC
    It's because you have \[] instead of just []. [] is a reference to an anonymous array, and \[] is a reference TO a reference to an anonymous array.
    _____________________________________________________
    Jeff japhy Pinyan, P.L., P.M., P.O.D, X.S.: Perl, regex, and perl hacker
    How can we ever be the sold short or the cheated, we who for every service have long ago been overpaid? ~~ Meister Eckhart
[reply]
[d/l]
[select]
      of course!!
      Thanks a lot!
      This is right way: 
      $pets{$color}=[];
push @{$pets{$color}},"cat";

      [download]
[reply]
[d/l]
Re: Cruel references
by trammell (Priest) on Mar 06, 2005 at 00:53 UTC
    You probably mean (or want): 
    ...
my %pets;
my $color = 'black';
# $pets{$color} = [];   # this line is unnecessary
push @{ $pets{$color} }, 'cat';
push @{ $pets{$color} }, 'dog';
foreach my $p (values %pets) {
    print "@$p\n";
}

    [download]
[reply]
[d/l]

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