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Arrays with References, Dereferences

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Question

How to create an array of arrays? How to process such a data structure? Can you give me some examples?

Answer

Note: in this example, under class I mean a normal school class.

Example 1

my @school;   # a school is a list of classes

# Say we have two classes. Class 1 with 2 students:
my @class1 = ('A1', 'A2');
push(@school, \@class1);

# Class 2 with 3 students:
my @class2 = ('B1', 'B2', 'B3');
push(@school, \@class2);

print "@school\n";

ARRAY(0x81546d8) ARRAY(0x817c06c)

Now we have two array references in @school.

Example 2

How to traverse @school?

my $array_ref;                  # an array reference
my @class;
foreach $array_ref (@school)
{
   @class = @$array_ref;        # check out the '@' in front of @$array_ref (dereference)
   print "@class\n";
}

A1 A2
B1 B2 B3

Example 3

How to access the first class in the school?

print "@{$school[0]}\n";

A1 A2

That is, $school[0] is an array reference that we need to dereference.

More info

• http://www.perl.com/doc/manual/html/pod/perlref.html
• http://www.perlmeme.org/howtos/using_perl/dereferencing.html