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Algorithm::Dependency::Source - Implements a source of heirachy items


The Algorithm::Dependency::Source class provides an abstract parent class for implementing sources for the heirachy data the algorithm will use. For an example of an implementation of this, see Algorithm::Dependency::Source::File, which is bundled with the main Algorithm::Dependency package.


new @arguments

Although you cannot directly use the new constructor for Algorithm::Dependency::Source, it will work the same in all subclasses.

The constructor takes zero or more subclass specific arguments to define the location of the source of the items, and returns a new object. Alrough it may check that the arguments you passed are valid, the source will usually NOT actually load the items from the source, instead defering the loading until you need to use the items.

Returns a new object on success, or undef on error.


The load method is the public method used to actually load the items from their storage location into the the source object. The method will automatically called, as needed, in most circumstances. You would generally only want to use load manually if you think there may be some uncertainty that the source will load correctly, and want to check it will work.

Returns true if the items are loaded successfully, or undef on error.

item $name

The item method fetches and returns the item object specified by the name argument.

Returns an Algorithm::Dependency::Item object on success, or undef if the named item does not exist in the source.


The items method returns, as a list of objects, all of the items contained in the source. The item objects will be returned in the same order as that in the storage location.

Returns a list of Algorithm::Dependency::Item objects on success, or undef on error.


By default, we are leniant with missing dependencies if the item is neved used. For systems where having a missing dependency can be very bad, the missing_dependencies method checks all Items to make sure their dependencies exist.

If there are any missing dependencies, returns a reference to an array of their ids. If there are no missing dependencies, returns 0. Returns undef on error.


Algorithm::Dependency::Source itself is a fairly thin module, and it is intended that you will probably need to extend it to be able to extract item data from whatever location you have stored them.

This is usually a fairly simple two step process.

Overload the new method.

Assuming your subclass takes some form or argument on creation, you will need to overload the new method to accept the arguments, validate them, and store them in the source object.

Define the method _load_item_list.

Leaving our parent's load method to take care of conflict, errors, and whatever, the _load_item_list method is used to simply create a list of Algorithm::Dependency::Item objects from wherever you store the item, and return them as a list.

Having completed these two things, your subclass should be completed. For an example of the code, have a look at the source for the simple subclass Algorithm::Dependency::Source::File.


For general comments, contact the author.

To file a bug against this module, in a way you can keep track of, see the CPAN bug tracking system.


Adam Kennedy <>


Algorithm::Dependency, Algorithm::Dependency::Source::File


Copyright 2003 - 2009 Adam Kennedy.

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

The full text of the license can be found in the LICENSE file included with this module.

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