NAME

Array::Iterator - A simple class for iterating over Perl arrays

VERSION

Version 0.133

SYNOPSIS

use Array::Iterator;

# create an iterator with an array
my $i = Array::Iterator->new(1 .. 100);

# create an iterator with an array reference
my $i = Array::Iterator->new(\@array);

# create an iterator with a hash reference
my $i = Array::Iterator->new({ __array__ => \@array });

# a base iterator example
while ($i->has_next()) {
    if ($i->peek() < 50) {
        # ... do something because
        # the next element is over 50
    }
    my $current = $i->next();
    # ... do something with current
}

# shortcut style
my @accumulation;
push @accumulation => { item => $iterator->next() } while $iterator->has_next();

# C++ ish style iterator
for (my $i = Array::Iterator->new(@array); $i->has_next(); $i->next()) {
  my $current = $i->current();
  # .. do something with current
}

# common perl iterator idiom
my $current;
while ($current = $i->get_next()) {
  # ... do something with $current
}

DESCRIPTION

This class provides a very simple iterator interface. It is uni-directional and can only be used once. It provides no means of reversing or resetting the iterator. It is not recommended to alter the array during iteration, however no attempt is made to enforce this (although I will if I can find an efficient means of doing so). This class only intends to provide a clear and simple means of generic iteration, nothing more (yet).

METHODS

Public Methods

• new (@array | $array_ref | $hash_ref)

  The constructor can be passed either a plain perl array, an array reference, or a hash reference (with the array specified as a single key off the hash, __array__). Single element arrays are not supported by either of the first two calling conventions, since it is not possible to distinguish between an array of a single element which happens to be an array reference, and an array reference of a single element, thus previous versions of the constructor would raise an exception. If you expect to pass arrays to the constructor which may have only a single element, then the array can be passed as the element of a HASH reference, with the key, __array__:

    my $i = Array::Iterator->new({ __array__ => \@array });
  

• has_next([$n])

  This methods returns a boolean. True (1) if there are still more elements in the iterator, false (0) if there are not.

  Takes an optional positive integer (> 0) that specifies the position you want to check. This allows you to check if there an element at arbitrary position. Think of it as an ordinal number you want to check:

    $i->has_next(2);  # 2nd next element
    $i->has_next(10); # 10th next element
  

  Note that has_next(1) is the same as has_next().

  Throws an exception if $n <= 0.

• next

  This method returns the next item in the iterator, be sure to only call this once per iteration as it will advance the index pointer to the next item. If this method is called after all elements have been exhausted, an exception will be thrown.

• get_next

  This method returns the next item in the iterator, be sure to only call this once per iteration as it will advance the index pointer to the next item. If this method is called after all elements have been exhausted, it will return undef.

  This method was added to allow for a fairly common perl iterator idiom of:

    my $current;
    while ($current = $i->get_next()) {
        ...
    }
  

  In this the loop terminates once $current is assigned to a false value. The only problem with this idiom for me is that it does not allow for undefined or false values in the iterator. Of course, if this fits your data, then there is no problem. Otherwise I would recommend the has_next/next idiom instead.

• peek([$n])

  This method can be used to peek ahead at the next item in the iterator. It is non-destructuve, meaning it does not advance the internal pointer. If this method is called and attempts to reach beyond the bounds of the iterator, it will return undef.

  Takes an optional positive integer (> 0) that specifies how far ahead you want to peek:

    $i->peek(2);  # gives you 2nd next element
    $i->peek(10); # gives you 10th next element
  

  Note that peek(1) is the same as peek().

  Throws an exception if $n <= 0.

  NOTE: Prior to version 0.03 this method would throw an exception if called out of bounds. I decided this was not a good practice, as it made it difficult to be able to peek ahead effectively. This not the case when calling with an argument that is <= 0 though, as it's clearly a sign of incorrect usage.

• current

  This method can be used to get the current item in the iterator. It is non-destructive, meaning that it does not advance the internal pointer. This value will match the last value dispensed by next or get_next.

• current_index

  This method can be used to get the current index in the iterator. It is non-destructive, meaning that it does not advance the internal pointer. This value will match the index of the last value dispensed by next or get_next.

• get_length

  This is a basic accessor for getting the length of the array being iterated over.

Protected Methods

These methods are protected, in the Java/C++ sense of the word. They can only be called internally by subclasses of Array::Iterator, an exception is thrown if that condition is violated. They are documented here only for people interested in subclassing Array::Iterator.

• _current_index

  An lvalue-ed subroutine which allows access to the iterator's internal pointer.

• _iteratee

  This returns the item being iteratated over, in our case an array.

• _get_item ($iteratee, $index)

  This method is used by all other routines to access items with. Given the iteratee and an index, it will return the item being stored in the $iteratee at the index of $index.

TO DO

• Improve BiDirectional Test suite

  I want to test the back and forth a little more, make sure they work well with one another.

• Other Iterators

  Array::Iterator::BiDirectional::Circular, Array::Iterator::Skipable and Array::Iterator::BiDirectional::Skipable are just a few ideas I have had. I am going to hold off for now until I am sure they are actually useful.

SEE ALSO

This module now includes several subclasses of Array::Iterator which add certain behaviors to Array::Iterator, they are:

• Array::Iterator::BiDirectional

  Adds the ability to move backwards and forwards through the array.

• Array::Iterator::Circular

  When this iterator reaches the end of its list, it will loop back to the start again.

• Array::Iterator::Reusable

  This iterator can be reset to its beginning and used again.

The Design Patterns book by the Gang of Four, specifically the Iterator pattern.

Some of the interface for this class is based upon the Java Iterator interface.

OTHER ITERATOR MODULES

There are a number of modules on CPAN with the word Iterator in them. Most of them are actually iterators included inside other modules, and only really useful within that parent modules context. There are however some other modules out there that are just for pure iteration. I have provided a list below of the ones I have found, if perhaps you don't happen to like the way I do it.

• Tie::Array::Iterable

  This module ties the array, something we do not do. But it also makes an attempt to account for, and allow the array to be changed during iteration. It accomplishes this control because the underlying array is tied. As we all know, tie-ing things can be a performance issue, but if you need what this module provides, then it will likely be an acceptable compromise. Array::Iterator makes no attempt to deal with this mid-iteration manipulation problem. In fact it is recommended to not alter your array with Array::Iterator, and if possible we will enforce this in later versions.

• Data::Iter

  This module allows for simple iteration over both hashes and arrays. It does it by importing several functions which can be used to loop over either type (hash or array) in the same way. It is an interesting module, it differs from Array::Iterator in paradigm (Array::Iterator is more OO) as well as in intent.

• Class::Iterator

  This is essentially a wrapper around a closure based iterator. This method can be very flexible, but at times is difficult to manage due to the inherent complexity of using closures. I actually was a closure-as-iterator fan for a while, but eventually moved away from it in favor of the more plain vanilla means of iteration, like that found Array::Iterator.

• Class::Iter

  This is part of the Class::Visitor module, and is a Visitor and Iterator extensions to Class::Template. Array::Iterator is a standalone module not associated with others.

• Data::Iterator::EasyObj

  Data::Iterator::EasyObj makes your array of arrays into iterator objects. It also has the ability to further nest additional data structures including Data::Iterator::EasyObj objects. Array::Iterator is one dimensional only, and does not attempt to do many of the more advanced features of this module.

ACKNOWLEDGEMENTS

• Thanks to Hugo Cornelis for pointing out a bug in peek()
• Thanks to Phillip Moore for providing the patch to allow single element iteration through the hash-ref constructor parameter.

ORIGINAL AUTHOR

stevan little, stevan@iinteractive.com

ORIGINAL COPYRIGHT AND LICENSE

Copyright 2004, 2005 by Infinity Interactive, Inc.

http://www.iinteractive.com

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

SUPPORT

This module is provided as-is without any warranty.

Please report any bugs or feature requests to bug-array-iterator at rt.cpan.org, or through the web interface at http://rt.cpan.org/NoAuth/ReportBug.html?Queue=Array-Iterator. I will be notified, and then you'll automatically be notified of progress on your bug as I make changes.

You can find documentation for this module with the perldoc command.

perldoc Array::Iterator

You can also look for information at:

• MetaCPAN

  https://metacpan.org/dist/Array-Iterator

• RT: CPAN's request tracker

  https://rt.cpan.org/NoAuth/Bugs.html?Dist=Array-Iterator

• CPAN Testers' Matrix

  http://matrix.cpantesters.org/?dist=Array-Iterator

• CPAN Testers Dependencies

  http://deps.cpantesters.org/?module=Array::Iterator