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.
Although you cannot directly use the "new" constructor for
"Algorithm::Dependency::Source", it will work the same in all
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
Returns true if the items are loaded successfully, or "undef" on
The "item" method fetches and returns the item object specified by the
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
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
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 <firstname.lastname@example.org>
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