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

%hash = (name => foo,
         list => (1, 2, 3));
@array = $hash{list};
foreach(@array){print "$_\n";}

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Perl seems to ignore the inner parens, 1 is printed and $hash{'2'} is assigned to 3. I'm trying to get a list inside a hash without requiring any extra variables. Is this possible? I tried 
%hash = (name => foo,
         list => \(1, 2, 3));
$ref = $hash{list}
@array = @$ref;
foreach(@array) { print }

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but Perl dies on "Not an ARRAY reference". So, is there any way to put a nameless array inside a hash element without any extra variables? Any help is appreciated.

Replies are listed 'Best First'.
Re: Array inside hashes
by perlmonkey (Hermit) on Jul 22, 2000 at 11:48 UTC
    For an array reference use '[]' instead of '()'
    %hash = (name => foo,
         list => [1, 2, 3]);
$ref = $hash{list};
@array = @$ref;
foreach(@array) { print }

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    See perldoc perlref
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Re: Array inside hashes
by atl (Pilgrim) on Jul 22, 2000 at 11:50 UTC
    Good morning! :-)

    Here's a working script: 

    atl@companion:~/perl > cat aih.pl 
#!/usr/bin/perl -w

%hash = (name => foo,
         list => [1, 2, 3]);
foreach( keys %hash ){
  print "key: $_, value: $hash{$_}\n";
}
$ref = $hash{list};
@array = @$ref;
foreach(@array){print "array: $_\n";}

atl@companion:~/perl > aih.pl 
Unquoted string "foo" may clash with future reserved word at ./aih.pl 
+line 3.
key: name, value: foo
key: list, value: ARRAY(0x80cf9a4)
array: 1
array: 2
array: 3
atl@companion:~/perl >

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    Since I didn't have my cup of tea yet (another sign of PM addiction: checking PM before making tea/coffee) I'll just let the code speak. ;-))

    Ok, one comment. From the perlop manpage: 

    The => digraph is mostly just a synonym for the comma operator.

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    So your code means in essence 
    %hash = (name, foo, list, 1, 2, 4);

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    Have fun ...

    Andreas

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RE: Array inside hashes
by athomason (Curate) on Jul 22, 2000 at 14:03 UTC
    Just a note, \(1, 2, 3) was a good try, but it's actually interpreted as (\1, \2, \3). From perldoc perlref:

    Taking a reference to an enumerated list is not the same as using
square brackets--instead it's the same as creating a list of
references!

    @list = (\$a, \@b, \%c);
    @list = \($a, @b, %c);      # same thing!

As a special case, `\(@foo)' returns a list of references to the
contents of `@foo', not a reference to `@foo' itself. Likewise for
`%foo', except that the key references are to copies (since the keys
are just strings rather than full-fledged scalars).

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    So, as the previous posters mentioned, the solution is to use [1, 2, 3] instead of \(1, 2, 3).

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      (Offer your reply needs a preview button :) Thanks everyone for their help! I knew I was missing something obvious. athomason mentioned \($a, @b, %c) is the same as (\$a, \@b, \%c). But is \[$a, $b, $c) the same as [\$a, \$b, \$c]? All the array elements are references, so I believe the first method would be cleaner. 
      $a = "foo";
$b = "bar";
$c = "baz";
@list = \[$a, $b, $c];
foreach(@list) { print $$_ . "\n"; }

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      Perl appears to set $list[0] to a reference to [$a, $b, $c]. Is there a less redundant way to say [\$a, \$b, \$c]?
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      Thanks everyone for their help! I knew I was missing something obvious. athomason mentioned \($a, @b, %c) is the same as (\$a, \@b, \%c). But is \[$a, $b, $c) the same as \$a, \$b, \$c? All the array elements are references, so I believe the first method would be cleaner. 
      $a = "foo";
$b = "bar";
$c = "baz";
@list = \[$a, $b, $c];
foreach(@list) { print $$_ . "\n"; }

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      Perl appears to set $list[0] to a reference to $a, $b, $c. Is there a less redundant way to say \$a, \$b, \$c?
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(kudra) RE: Array inside hashes
by kudra (Vicar) on Jul 22, 2000 at 11:55 UTC
    How do I make a hash of arrays in the Q&A section might have answered your question. But here's an example: 
    %hash = (name => foo,
         list => [1, 2, 3]);
print join "\n", (@{$hash{list}});
print "\n${$hash{list}}[1]\n"; # Print 2

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    Update: Ignore this. I really need to keep another window open to see who else has answered before hitting submit.
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