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

Provided by: libalgorithm-c3-perl_0.08-1_all

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.

   What is C3?
       C3 is the name of an algorithm which aims to provide a sane method resolution order under
       multiple inheritance. It was first introduced in the language Dylan (see links in the "SEE
       ALSO" section), and then later adopted as the preferred MRO (Method Resolution Order) for
       the new-style classes in Python 2.3. Most recently it has been adopted as the 'canonical'
       MRO for Perl 6 classes, and the default MRO for Parrot objects as well.

   How does C3 work.
       C3 works by always preserving local precedence ordering. This essentially means that no
       class will appear before any of it's subclasses. Take the classic diamond inheritance
       pattern for instance:

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

       The standard Perl 5 MRO would be (D, B, A, C). The result being that A appears before C,
       even though C is the subclass of A.  The C3 MRO algorithm however, produces the following
       MRO (D, B, C, A), which does not have this same issue.

       This example is fairly trivial, for more complex examples and a deeper explanation, see
       the links in the "SEE ALSO" section.

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
        ------------------------ ------ ------ ------ ------ ------ ------ ------

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.