Array::Iterator(3pm)

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

VERSION
Version 0.136

SYNOPSIS
"Array::Iterator" is a Perl module that provides a simple, uni-directional iterator interface for traversing arrays. It allows users to iterate over arrays, array references, or hash references containing an array, offering methods like next, has_next, peek, and current to facilitate controlled access to elements. The iterator maintains an internal pointer, ensuring elements are accessed sequentially without modifying the underlying array. Tt offers a clean, object-oriented approach to iteration, inspired by Java’s Iterator interface. The module is extendable, allowing subclassing for custom behaviour.

  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
  }

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).

  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 of 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 });

  _current_index
An lvalue-ed subroutine that allows access to the iterator's internal pointer. This can be used in a subclass to access the value.

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

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

  iterated
Access to the _iterated status, for subclasses

  has_next([$n])
This method 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 an 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.

  hasNext
Alternative name for has_next

  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.

  getNext
Alternative name for get_next

  peek([$n])
This method can be used to peek ahead at the next item in the iterator. It is non-destructive, 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: Before 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 is 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".

  currentIndex
Alternative name for current_index

  reset
Reset index to allow iteration from the start

  get_length
This is a basic accessor for getting the length of the array being iterated over, returns the number of elements in the array.

  getLength
Alternative name for get_length

TODO

Improve BiDirectional Test suite
    I want to test the back-and-forth a little more and 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 backward and forward 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 on the Java Iterator interface.

OTHER ITERATOR MODULES
There are several 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 module's 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 that 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) and 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 extension to Class::Template. Array::Iterator is a standalone module that is not associated with others.

Data::Iterator::EasyObj
    Data::Iterator::EasyObj makes your array of arrays into iterator objects. It also can 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.

MAINTAINER
Nigel Horne, "<njh at nigelhorne.com>"

2025-2026

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.

PREVIOUS MAINTAINER
Maintained 2017 to 2025 PERLANCAR

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>

POD ERRORS
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