August 1998
Intermediate to advanced
800 pages
39h 20m
English
You want to create and manipulate a circular list.
Use unshift and pop (or
push and shift) on a normal
array.
unshift(@circular, pop(@circular)); # the last shall be first push(@circular, shift(@circular)); # and vice versa
Circular lists are commonly used to repeatedly process things in order; for example, connections to a server. The code shown above 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;
}The unshift and push functions
in perlfunc(1) and Chapter 3 of
Programming Perl; Section 13.13