NAME

List::Rotation - Loop (Cycle, Alternate or Toggle) through a list of values via a singleton object implemented as closure.

SYNOPSIS

use List::Rotation;

my @array = qw( A B C );

my $first_cycle  = List::Rotation::Cycle->new(@array);

print $first_cycle->next;  ## prints A
print $first_cycle->next;  ## prints B
print $first_cycle->next;  ## prints C
print $first_cycle->next;  ## prints A, looping back to beginning
print $first_cycle->next;  ## prints B
print $first_cycle->next;  ## prints C

print $first_cycle->prev;  ## prints B, going back
print $first_cycle->prev;  ## prints A, going back
print $first_cycle->prev;  ## prints C, looping forward to last
print $first_cycle->curr;  ## prints C, at current position

my $second_cycle = List::Rotation::Cycle->new(@array);  ##  the same object is returned as above
$first_cycle->reset;       ## reset position
print $first_cycle->next;  ## prints A
print $second_cycle->next; ## prints B
print $first_cycle->next;  ## prints C
print $second_cycle->next; ## prints A, looping back to beginning

my $alternation  = List::Rotation::Alternate->new( qw( odd even ) );

print $alternation->next;  ## prints odd
print $alternation->next;  ## prints even
print $alternation->next;  ## prints odd
$alternation->reset;       ## reset the alternation to first item
print $alternation->next;  ## prints odd

my $switch  = List::Rotation::Toggle->new;

##  prints even numbers between 2 and 10
foreach ( 2..10 ) {
    print "$_\n" if $switch->next;
}

DESCRIPTION

Use List::Rotation to loop through a list of values. Once you get to the end of the list, you go back to the beginning. Alternatively you can walk backwards through your list of values.

List::Rotation is implemented as a Singleton Pattern. You always just get 1 (the very same) Rotation object if you use the new method several times with the exact same set of parameters. This is done by using Memoize on the new method. It returns the same object for every use of new that comes with the same list of parameters.

The class List::Rotation contains three subclasses:

List::Rotation::Cycle

Loop through a list of arbitrary values. The list must not be empty.

List::Rotation::Alternate

Alternate two values.

List::Rotation::Toggle

Toggle between true and false.

OBJECT METHODS

new

Create a Cycle object for the list of values in the list.

next

Return the next element.

prev

Return the previous element.

curr

Return the element at the current position.

reset

Reset the list to the beginning; the following call of next will return the first item of the list again.

References

There are several similar modules available:

Tie::FlipFlop

by Abigail: Alternate between two values.

List::Cycle

by Andi Lester: Objects for cycling through a list of values

Tie::Cycle

by Brian D. Foy: Cycle through a list of values via a scalar.

Tie::Toggle

by Brian D. Foy: False and true, alternately, ad infinitum.

AUTHOR

Imre Saling, <pelagicatcpandotorg>

COPYRIGHT and LICENSE

Copyright 2010, Imre Saling, All rights reserved.

This software is available under the same terms as perl.