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Perl for Web Site Management
book

Perl for Web Site Management

by John Callender
October 2001
Beginner content levelBeginner
528 pages
15h 20m
English
O'Reilly Media, Inc.
Content preview from Perl for Web Site Management

Creating Anonymous Hashes and Arrays

If we look at Dumper’s output more closely, we can see that something interesting is going on. Here’s a simplified version of it:

$HoH = {
    key1 => {
                key_a => 'value_a',
                key_b => 'value_b',
            },
    key2 => {
                key_a => 'value_a',
                key_b => 'value_b',
            },
};

What’s up with the curly braces? We haven’t seen them used like this before.

What’s up is the fourth and final piece of reference magic we need to know: how to initialize an anonymous hash and return a reference to it at the same time. We do that by putting curly braces around it, where we would normally put the enclosing parentheses:

$hash_ref = { 
              key1 => 'value1',
              key2 => 'value2',
            };

Here we have created an anonymous hash with two keys and two corresponding values, and returned a reference to it that we’ve then stuck in the scalar variable $hash_ref. If we take a bunch of those anonymous hashes and make the references that they return the values in an all-encompassing hash, and if we make that all-encompassing hash an anonymous hash and return a reference to it, we get a reference to a hash of hashes, or HoH. That’s what Data::Dumper’s Dumper routine printed out for us.

We can do similar reference magic with square brackets to create and return an anonymous array reference:

my $ary_ref = [ 'item1', 'item2', 'item3' ];

If we nest those we get a reference to an LoL, or List of Lists:

my $LoL = [ 
            [ 'item1', 'item2', 'item3' ],
            [ 'item1', 'item2', 'item3' ],
            [ 'item1', 'item2', 'item3' ],
          ];

And we can ...

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Publisher Resources

ISBN: 1565926471Catalog PageErrata