NAME
Array::Iterator - A simple class for iterating over Perl arrays
VERSION
version 0.11
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 is
uni-directional and can only be used once. It provides no means of
reverseing or reseting 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 faily 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.
BUGS
None that I am aware of. The code is pretty thoroughly tested (see "CODE
COVERAGE" below) and is based on an (non-publicly released) module which
I had used in production systems for about 2 years without incident. Of
course, if you find a bug, let me know, and I will be sure to fix it.
CODE COVERAGE
I use Devel::Cover to test the code coverage of my tests, below is the
Devel::Cover report on this module's test suite.
------------------------------- ------ ------ ------ ------ ------ ------ ------
File stmt bran cond sub pod time total
------------------------------- ------ ------ ------ ------ ------ ------ ------
Array/Iterator.pm 100.0 100.0 66.7 100.0 100.0 67.6 98.2
Array/Iterator/BiDirectional.pm 100.0 100.0 n/a 100.0 100.0 20.2 100.0
Array/Iterator/Circular.pm 100.0 100.0 n/a 100.0 100.0 7.1 100.0
Array/Iterator/Reusable.pm 100.0 n/a n/a 100.0 100.0 5.0 100.0
------------------------------- ------ ------ ------ ------ ------ ------ ------
Total 100.0 100.0 66.7 100.0 100.0 100.0 99.0
------------------------------- ------ ------ ------ ------ ------ ------ ------
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 recommened 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 iteratation 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 complextity 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.
AUTHOR
Steven Haryanto <stevenharyanto@gmail.com>
COPYRIGHT AND LICENSE
This software is copyright (c) 2013 by Steven Haryanto.
This is free software; you can redistribute it and/or modify it under
the same terms as the Perl 5 programming language system itself.