I had to look up anonymous data structures to figure out what you were referring to and it appears that they are just talking about references. THAT I can help you with.

Normally there are two ways of working with a variable, making a copy of it, or using a reference to it. A simplified example would be a sign-in sheet for a writing class. You want everyone to write their name on the sheet so you have to get information from everyone. There are two ways of doing this,

• Make a copy of it.
  1. make a copy of the sign-in sheet.
  2. have the student sign the sheet new copy.
  3. Get the copy back from the student.
  4. Throw away the old sign-in sheet and go back to step 1. Repeat until finished
• Use a reference
1. Take a sign-in sheet.
2. Have the student sign their new on the sign-in sheet
3. Repeat until finished.

The first way sounds stupid, but you will be surprised how often it occurs, especially with beginners. Here is code to show how it works.

#!/usr/bin/perl

use strict;
use warnings;

# Make a copy of a variable

my $counter = 0;
print "Copying and replacing the variable\n";
for (1..10) {
    $counter = increment_number( $counter );
    print "Count is $counter\n";
}

$counter = 0;
print "Passing a reference to the variable\n";
for (1..10) {
    increment_number( \$counter );
    print "Count is $counter\n";
}

sub increment_number {
    my $number = shift;

    if (ref $number eq 'SCALAR') {
        $$number++;
        return;
    }
    return ++$number;
}
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