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Perl Cookbook
book

Perl Cookbook

by Tom Christiansen, Nathan Torkington
August 1998
Intermediate to advanced content levelIntermediate to advanced
800 pages
39h 20m
English
O'Reilly Media, Inc.
Content preview from Perl Cookbook

Implementing a Circular List

Problem

You want to create and manipulate a circular list.

Solution

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

Procedure

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

Discussion

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;
}

See Also

The unshift and push functions in perlfunc(1) and Chapter 3 of Programming Perl; Section 13.13

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Publisher Resources

ISBN: 1565922433Supplemental ContentCatalog PageErrata