Adam Kennedy


Algorithm::Dependency::Weight - Calculate dependency 'weights'


  # Create a source from a file
  my $Source = Algorithm::Dependency::Source->new( 'file.txt' );
  # Create a Weight algorithm object
  my $alg = Algorithm::Dependency::Weight->new( source => $Source );
  # Find the weight for a single item
  my $weight = $alg->weight('foo');
  print "The weight of 'foo' is $weight\n";
  # Or a group
  my $hash = $alg->weight_hash('foo', 'bar', 'baz');
  print "The weight of 'foo', 'bar', and 'bar' are $hash->{foo},"
      . " $hash->{bar} and $hash->{baz} respectively\n";
  # Or all of the items
  my $all = $alg->weight_all;
  print "The following is a list from heaviest to lightest:\n";
  foreach ( sort { $all->{$b} <=> $all->{$a} } keys %$all ) {
      print "$_: $all->{$_}\n";


In dependency systems, it can often be very useful to calculate an aggregate or sum for one or all items. For example, to find the "naive install weight" of a Perl distribution (where "naive" means you treat each distribution equally), you would want the distribtion (1) + all its dependencies (n) + all their dependencies (n2) recursively downwards.

If calculated using a normal Algorithm::Dependency object, the result would be (in a simple systems) equal to:

  # Create your normal (non-ordered alg:dep)
  my $dependency = Algorithm::Dependency->new( ... );
  # Find the naive weight for an item
  my $weight = scalar($dependency->schedule('itemname'));

Algorithm::Dependency::Weight provides a way of doing this with a little more sophistication, and in a way that should work reasonable well across all the Algorithm::Dependency family.

Please note that the this might be a little (or more than a little) slower than it could be for the limited case of generating weights for all of the items at once in a dependency system with no selected items and no circular dependencies. BUT you can at least rely on this class to do the job properly regardless of the particulars of the situation, which is probably more important.


new @params

The new constructor creates a new Algorithm::Dependency::Weight object. It takes a number of key/value pairs as parameters (although at the present time only one).

source => $Source

The source param is mostly the same as for Algorithm::Dependency. The one addition is that as a source you can provide an Algorithm::Dependency object, and the Algorithm::Dependency::Source for that will be used.

Returns a new Algorithm::Dependency::Weight object, or undef on error.


The source accessor returns the source used for the weight calculations.

This will be either the one passed to the constructor, or the source from inside the Algorithm::Dependency object passed as the source param (not the object itself, its source).

weight $name

The weight method takes the name of a single item and calculates its weight based on the configuration of the Algorithm::Dependency::Weight object.

Returns the weight as a scalar (which in the naive case will be an integer, but in more complex uses may be any real number), or undef on error.

weight_hash @names

The weight_hash method takes a list of item names, and calculates their weights.

Returns a reference to a HASH with the item names as keys and weights as values, or undef on error.


The weight_all method provides the one-shot method for getting the weights of all items at once. Please note that this does not do anything different or special, but is slightly faster than iterating yourself.



- Add support for non-naive weights via either custom code or method name


Bugs should be submitted via the CPAN bug tracker, located at

For general comments, contact the author.


Adam Kennedy <>,


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


Copyright (c) 2003 - 2005 Adam Kennedy.

