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4.17. Implementing a Circular List

4.17.1. Problem

You
want to create and manipulate a circular list.

4.17.2. Solution

Use
unshift and pop (or
push and shift) on a normal
array.

4.17.3. Procedure

unshift(@circular, pop(@circular));  # the last shall be first
push(@circular, shift(@circular));   # and vice versa

4.17.4. Discussion

Circular lists are commonly used to repeatedly process things in
order; for example, connections to a server. The code shown
previously isn't a true computer science circular list, with pointers
and true circularity. Instead, the operations provide for moving the
last element to the first position, and vice versa.

sub grab_and_rotate ( \@ ) {
my $listref = shift;
my $element = $listref->[0];
push(@$listref, shift @$listref);
return $element;
}
@processes = ( 1, 2, 3, 4, 5 );
while (1) {
$process = grab_and_rotate(@processes);
print "Handling process $process\n";
sleep 1;
}

4.17.5. See Also

The unshift and push functions
in perlfunc(1) and Chapter 29 of
Programming Perl; Recipe 13.13