NAME¶

Algorithm::C3 - A module for merging hierarchies using the C3 algorithm

SYNOPSIS¶

  use Algorithm::C3;
  # merging a classic diamond
  # inheritance graph like this:
  #
  #    <A>
  #   /   \
  # <B>   <C>
  #   \   /
  #    <D>
  my @merged = Algorithm::C3::merge(
      'D',
      sub {
          # extract the ISA array
          # from the package
          no strict 'refs';
          @{$_[0] . '::ISA'};
      }
  );
  print join ", " => @merged; # prints D, B, C, A

DESCRIPTION¶

This module implements the C3 algorithm. I have broken this out into it's own module because I found myself copying and pasting it way too often for various needs. Most of the uses I have for C3 revolve around class building and metamodels, but it could also be used for things like dependency resolution as well since it tends to do such a nice job of preserving local precedence orderings.

Below is a brief explanation of C3 taken from the Class::C3 module. For more detailed information, see the "SEE ALSO" section and the links there.

     <A>
    /   \
  <B>   <C>
    \   /
     <D>

FUNCTION¶

merge ($root, $func_to_fetch_parent, $cache)

This takes a $root node, which can be anything really it is up to you. Then it takes a $func_to_fetch_parent which can be either a CODE reference (see SYNOPSIS above for an example), or a string containing a method name to be called on all the items being linearized. An example of how this might look is below:

  {
      package A;
      sub supers {
          no strict 'refs';
          @{$_[0] . '::ISA'};
      }
      package C;
      our @ISA = ('A');
      package B;
      our @ISA = ('A');
      package D;
      our @ISA = ('B', 'C');
  }
  print join ", " => Algorithm::C3::merge('D', 'supers');
    

The purpose of $func_to_fetch_parent is to provide a way for "merge" to extract the parents of $root. This is needed for C3 to be able to do it's work.

The $cache parameter is an entirely optional performance measure, and should not change behavior.

If supplied, it should be a hashref that merge can use as a private cache between runs to speed things up. Generally speaking, if you will be calling merge many times on related things, and the parent fetching function will return constant results given the same arguments during all of these calls, you can and should reuse the same shared cache hash for all of the calls. Example:

  sub do_some_merging {
      my %merge_cache;
      my @foo_mro = Algorithm::C3::Merge('Foo', \&get_supers, \%merge_cache);
      my @bar_mro = Algorithm::C3::Merge('Bar', \&get_supers, \%merge_cache);
      my @baz_mro = Algorithm::C3::Merge('Baz', \&get_supers, \%merge_cache);
      my @quux_mro = Algorithm::C3::Merge('Quux', \&get_supers, \%merge_cache);
      # ...
  }
    

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
 ------------------------ ------ ------ ------ ------ ------ ------ ------
 Algorithm/C3.pm           100.0  100.0  100.0  100.0  100.0  100.0  100.0
 ------------------------ ------ ------ ------ ------ ------ ------ ------
 Total                     100.0  100.0  100.0  100.0  100.0  100.0  100.0
 ------------------------ ------ ------ ------ ------ ------ ------ ------

SEE ALSO¶

AUTHORS¶

Stevan Little, <stevan@iinteractive.com>

Brandon L. Black, <blblack@gmail.com>

COPYRIGHT AND LICENSE¶

Copyright 2006 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.