Algorithm::C3(3pm)

1Algorithm::C3(3)      User Contributed Perl Documentation     Algorithm::C3(3)
2
3
4

NAME

6       Algorithm::C3 - A module for merging hierarchies using the C3 algorithm
7

SYNOPSIS

9         use Algorithm::C3;
10
11         # merging a classic diamond
12         # inheritence graph like this:
13         #
14         #    <A>
15         #   /   \
16         # <B>   <C>
17         #   \   /
18         #    <D>
19
20         my @merged = Algorithm::C3::merge(
21             'D',
22             sub {
23                 # extract the ISA array
24                 # from the package
25                 no strict 'refs';
26                 @{$_[0] . '::ISA'};
27             }
28         );
29
30         print join ", " => @merged; # prints D, B, C, A
31

DESCRIPTION

33       This module implements the C3 algorithm. I have broken this out into
34       it's own module because I found myself copying and pasting it way too
35       often for various needs. Most of the uses I have for C3 revolve around
36       class building and metamodels, but it could also be used for things
37       like dependency resolution as well since it tends to do such a nice job
38       of preserving local precendence orderings.
39
40       Below is a brief explanation of C3 taken from the Class::C3 module. For
41       more detailed information, see the "SEE ALSO" section and the links
42       there.
43
44       What is C3?
45
46       C3 is the name of an algorithm which aims to provide a sane method res‐
47       olution order under multiple inheritence. It was first introduced in
48       the langauge Dylan (see links in the "SEE ALSO" section), and then
49       later adopted as the prefered MRO (Method Resolution Order) for the
50       new-style classes in Python 2.3. Most recently it has been adopted as
51       the 'canonical' MRO for Perl 6 classes, and the default MRO for Parrot
52       objects as well.
53
54       How does C3 work.
55
56       C3 works by always preserving local precendence ordering. This essen‐
57       tially means that no class will appear before any of it's subclasses.
58       Take the classic diamond inheritence pattern for instance:
59
60            <A>
61           /   \
62         <B>   <C>
63           \   /
64            <D>
65
66       The standard Perl 5 MRO would be (D, B, A, C). The result being that A
67       appears before C, even though C is the subclass of A.  The C3 MRO algo‐
68       rithm however, produces the following MRO (D, B, C, A), which does not
69       have this same issue.
70
71       This example is fairly trival, for more complex examples and a deeper
72       explaination, see the links in the "SEE ALSO" section.
73

FUNCTION

75       merge ($root, $func_to_fetch_parent, $cache)
76           This takes a $root node, which can be anything really it is up to
77           you. Then it takes a $func_to_fetch_parent which can be either a
78           CODE reference (see SYNOPSIS above for an example), or a string
79           containing a method name to be called on all the items being lin‐
80           earized. An example of how this might look is below:
81
82             {
83                 package A;
84
85                 sub supers {
86                     no strict 'refs';
87                     @{$_[0] . '::ISA'};
88                 }
89
90                 package C;
91                 our @ISA = ('A');
92                 package B;
93                 our @ISA = ('A');
94                 package D;
95                 our @ISA = ('B', 'C');
96             }
97
98             print join ", " => Algorithm::C3::merge('D', 'supers');
99
100           The purpose of $func_to_fetch_parent is to provide a way for
101           "merge" to extract the parents of $root. This is needed for C3 to
102           be able to do it's work.
103
104           The $cache parameter is an entirely optional performance measure,
105           and should not change behavior.
106
107           If supplied, it should be a hashref that merge can use as a private
108           cache between runs to speed things up.  Generally speaking, if you
109           will be calling merge many times on related things, and the parent
110           fetching function will return constant results given the same argu‐
111           ments during all of these calls, you can and should reuse the same
112           shared cache hash for all of the calls.  Example:
113
114             sub do_some_merging {
115                 my %merge_cache;
116                 my @foo_mro = Algorithm::C3::Merge('Foo', \&get_supers, \%merge_cache);
117                 my @bar_mro = Algorithm::C3::Merge('Bar', \&get_supers, \%merge_cache);
118                 my @baz_mro = Algorithm::C3::Merge('Baz', \&get_supers, \%merge_cache);
119                 my @quux_mro = Algorithm::C3::Merge('Quux', \&get_supers, \%merge_cache);
120                 # ...
121             }
122

CODE COVERAGE

124       I use Devel::Cover to test the code coverage of my tests, below is the
125       Devel::Cover report on this module's test suite.
126
127        ------------------------ ------ ------ ------ ------ ------ ------ ------
128        File                       stmt   bran   cond    sub    pod   time  total
129        ------------------------ ------ ------ ------ ------ ------ ------ ------
130        Algorithm/C3.pm           100.0  100.0  100.0  100.0  100.0  100.0  100.0
131        ------------------------ ------ ------ ------ ------ ------ ------ ------
132        Total                     100.0  100.0  100.0  100.0  100.0  100.0  100.0
133        ------------------------ ------ ------ ------ ------ ------ ------ ------
134

AUTHORS

159       Stevan Little, <stevan@iinteractive.com>
160
161       Brandon L. Black, <blblack@gmail.com>
162

COPYRIGHT AND LICENSE

164       Copyright 2006 by Infinity Interactive, Inc.
165
166       <http://www.iinteractive.com>
167
168       This library is free software; you can redistribute it and/or modify it
169       under the same terms as Perl itself.
170
171
172
173perl v5.8.8                       2007-05-31                  Algorithm::C3(3)