Commit | Line | Data |
c0b91998 |
1 | |
2 | package Algorithm::C3; |
3 | |
4 | use strict; |
5 | use warnings; |
6 | |
7 | use Carp 'confess'; |
8 | |
ca604ce2 |
9 | our $VERSION = '0.05'; |
c0b91998 |
10 | |
c0b91998 |
11 | sub merge { |
ca604ce2 |
12 | my ($root, $parent_fetcher, $cache) = @_; |
cf85d7d3 |
13 | |
ca604ce2 |
14 | $cache ||= {}; |
cf85d7d3 |
15 | my @STACK; # stack for simulating recursion |
cf85d7d3 |
16 | |
aeed4a60 |
17 | my $pfetcher_is_coderef = ref($parent_fetcher) eq 'CODE'; |
18 | |
19 | unless ($pfetcher_is_coderef or $root->can($parent_fetcher)) { |
20 | confess "Could not find method $parent_fetcher in $root"; |
21 | } |
22 | |
cf85d7d3 |
23 | my $current_root = $root; |
aeed4a60 |
24 | my $current_parents = [ $root->$parent_fetcher ]; |
cf85d7d3 |
25 | my $recurse_mergeout = []; |
26 | my $i = 0; |
e742c620 |
27 | my %seen; |
cf85d7d3 |
28 | |
29 | while(1) { |
30 | if($i < @$current_parents) { |
31 | my $new_root = $current_parents->[$i++]; |
e742c620 |
32 | die "Infinite loop detected" if $seen{$new_root}++; |
cf85d7d3 |
33 | |
aeed4a60 |
34 | unless ($pfetcher_is_coderef or $new_root->can($parent_fetcher)) { |
35 | confess "Could not find method $parent_fetcher in $new_root"; |
36 | } |
37 | |
cf85d7d3 |
38 | push(@STACK, [ |
39 | $current_root, |
40 | $current_parents, |
41 | $recurse_mergeout, |
42 | $i, |
43 | ]); |
44 | |
45 | $current_root = $new_root; |
ca604ce2 |
46 | $current_parents = $cache->{pfetch}->{$current_root} ||= [ $current_root->$parent_fetcher ]; |
cf85d7d3 |
47 | $recurse_mergeout = []; |
48 | $i = 0; |
49 | next; |
50 | } |
51 | |
ca604ce2 |
52 | my $mergeout = $cache->{merge}->{$current_root} ||= do { |
cf85d7d3 |
53 | |
54 | # This do-block is the code formerly known as the function |
55 | # that was a perl-port of the python code at |
56 | # http://www.python.org/2.3/mro.html :) |
57 | |
7946639b |
58 | # Initial set (make sure everything is copied - it will be modded) |
5a07d049 |
59 | my @seqs = map { [@$_] } (@$recurse_mergeout, $current_parents); |
60 | |
61 | # Construct the tail-checking hash |
62 | my %tails; |
63 | foreach my $seq (@seqs) { |
64 | $tails{$_}++ for (@$seq[1..$#$seq]); |
cf85d7d3 |
65 | } |
66 | |
7946639b |
67 | my @res = ( $current_root ); |
cf85d7d3 |
68 | while (1) { |
5a07d049 |
69 | my $cand; |
70 | my $winner; |
cf85d7d3 |
71 | foreach (@seqs) { |
5a07d049 |
72 | next if !@$_; |
73 | if(!$winner) { # looking for a winner |
74 | $cand = $_->[0]; # seq head is candidate |
75 | next if $tails{$cand}; # he loses if in %tails |
76 | push @res => $winner = $cand; |
cf85d7d3 |
77 | } |
78 | if($_->[0] eq $winner) { |
79 | shift @$_; # strip off our winner |
5a07d049 |
80 | $tails{$_->[0]}-- if @$_; # keep %tails sane |
cf85d7d3 |
81 | } |
82 | } |
83 | last if !$cand; |
84 | die q{Inconsistent hierarchy found while merging '} |
85 | . $current_root . qq{':\n\t} |
86 | . qq{current merge results [\n\t\t} |
87 | . (join ",\n\t\t" => @res) |
88 | . qq{\n\t]\n\t} . qq{merging failed on '$cand'\n} |
89 | if !$winner; |
90 | } |
91 | \@res; |
92 | }; |
93 | |
94 | return @$mergeout if !@STACK; |
95 | |
3d42306b |
96 | $seen{$current_root}--; |
97 | |
cf85d7d3 |
98 | ($current_root, $current_parents, $recurse_mergeout, $i) |
99 | = @{pop @STACK}; |
100 | |
101 | push(@$recurse_mergeout, $mergeout); |
102 | } |
c0b91998 |
103 | } |
104 | |
105 | 1; |
106 | |
107 | __END__ |
108 | |
109 | =pod |
110 | |
111 | =head1 NAME |
112 | |
8fe16bec |
113 | Algorithm::C3 - A module for merging hierarchies using the C3 algorithm |
c0b91998 |
114 | |
115 | =head1 SYNOPSIS |
116 | |
117 | use Algorithm::C3; |
118 | |
119 | # merging a classic diamond |
120 | # inheritence graph like this: |
121 | # |
122 | # <A> |
123 | # / \ |
124 | # <B> <C> |
125 | # \ / |
126 | # <D> |
127 | |
128 | my @merged = Algorithm::C3::merge( |
129 | 'D', |
130 | sub { |
131 | # extract the ISA array |
132 | # from the package |
133 | no strict 'refs'; |
134 | @{$_[0] . '::ISA'}; |
135 | } |
136 | ); |
137 | |
138 | print join ", " => @merged; # prints D, B, C, A |
139 | |
140 | =head1 DESCRIPTION |
141 | |
142 | This module implements the C3 algorithm. I have broken this out |
143 | into it's own module because I found myself copying and pasting |
144 | it way too often for various needs. Most of the uses I have for |
145 | C3 revolve around class building and metamodels, but it could |
146 | also be used for things like dependency resolution as well since |
147 | it tends to do such a nice job of preserving local precendence |
148 | orderings. |
149 | |
150 | Below is a brief explanation of C3 taken from the L<Class::C3> |
151 | module. For more detailed information, see the L<SEE ALSO> section |
152 | and the links there. |
153 | |
154 | =head2 What is C3? |
155 | |
156 | C3 is the name of an algorithm which aims to provide a sane method |
157 | resolution order under multiple inheritence. It was first introduced |
158 | in the langauge Dylan (see links in the L<SEE ALSO> section), and |
159 | then later adopted as the prefered MRO (Method Resolution Order) |
160 | for the new-style classes in Python 2.3. Most recently it has been |
161 | adopted as the 'canonical' MRO for Perl 6 classes, and the default |
162 | MRO for Parrot objects as well. |
163 | |
164 | =head2 How does C3 work. |
165 | |
166 | C3 works by always preserving local precendence ordering. This |
167 | essentially means that no class will appear before any of it's |
168 | subclasses. Take the classic diamond inheritence pattern for |
169 | instance: |
170 | |
171 | <A> |
172 | / \ |
173 | <B> <C> |
174 | \ / |
175 | <D> |
176 | |
177 | The standard Perl 5 MRO would be (D, B, A, C). The result being that |
178 | B<A> appears before B<C>, even though B<C> is the subclass of B<A>. |
179 | The C3 MRO algorithm however, produces the following MRO (D, B, C, A), |
180 | which does not have this same issue. |
181 | |
182 | This example is fairly trival, for more complex examples and a deeper |
183 | explaination, see the links in the L<SEE ALSO> section. |
184 | |
185 | =head1 FUNCTION |
186 | |
187 | =over 4 |
188 | |
ca604ce2 |
189 | =item B<merge ($root, $func_to_fetch_parent, $cache)> |
c0b91998 |
190 | |
191 | This takes a C<$root> node, which can be anything really it |
192 | is up to you. Then it takes a C<$func_to_fetch_parent> which |
193 | can be either a CODE reference (see L<SYNOPSIS> above for an |
194 | example), or a string containing a method name to be called |
195 | on all the items being linearized. An example of how this |
196 | might look is below: |
197 | |
198 | { |
199 | package A; |
200 | |
201 | sub supers { |
202 | no strict 'refs'; |
203 | @{$_[0] . '::ISA'}; |
204 | } |
205 | |
206 | package C; |
207 | our @ISA = ('A'); |
208 | package B; |
209 | our @ISA = ('A'); |
210 | package D; |
211 | our @ISA = ('B', 'C'); |
212 | } |
213 | |
214 | print join ", " => Algorithm::C3::merge('D', 'supers'); |
215 | |
216 | The purpose of C<$func_to_fetch_parent> is to provide a way |
217 | for C<merge> to extract the parents of C<$root>. This is |
218 | needed for C3 to be able to do it's work. |
219 | |
ca604ce2 |
220 | The C<$cache> parameter is an entirely optional performance |
221 | measure, and should not change behavior. |
222 | |
223 | If supplied, it should be a hashref that merge can use as a |
224 | private cache between runs to speed things up. Generally |
225 | speaking, if you will be calling merge many times on related |
226 | things, and the parent fetching function will return constant |
227 | results given the same arguments during all of these calls, |
228 | you can and should reuse the same shared cache hash for all |
229 | of the calls. Example: |
230 | |
231 | sub do_some_merging { |
232 | my %merge_cache; |
233 | my @foo_mro = Algorithm::C3::Merge('Foo', \&get_supers, \%merge_cache); |
234 | my @bar_mro = Algorithm::C3::Merge('Bar', \&get_supers, \%merge_cache); |
235 | my @baz_mro = Algorithm::C3::Merge('Baz', \&get_supers, \%merge_cache); |
236 | my @quux_mro = Algorithm::C3::Merge('Quux', \&get_supers, \%merge_cache); |
237 | # ... |
238 | } |
239 | |
c0b91998 |
240 | =back |
241 | |
242 | =head1 CODE COVERAGE |
243 | |
244 | I use B<Devel::Cover> to test the code coverage of my tests, below |
245 | is the B<Devel::Cover> report on this module's test suite. |
246 | |
247 | ------------------------ ------ ------ ------ ------ ------ ------ ------ |
248 | File stmt bran cond sub pod time total |
249 | ------------------------ ------ ------ ------ ------ ------ ------ ------ |
6d8a26f9 |
250 | Algorithm/C3.pm 100.0 100.0 100.0 100.0 100.0 100.0 100.0 |
c0b91998 |
251 | ------------------------ ------ ------ ------ ------ ------ ------ ------ |
6d8a26f9 |
252 | Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 |
c0b91998 |
253 | ------------------------ ------ ------ ------ ------ ------ ------ ------ |
254 | |
255 | =head1 SEE ALSO |
256 | |
257 | =head2 The original Dylan paper |
258 | |
259 | =over 4 |
260 | |
261 | =item L<http://www.webcom.com/haahr/dylan/linearization-oopsla96.html> |
262 | |
263 | =back |
264 | |
265 | =head2 The prototype Perl 6 Object Model uses C3 |
266 | |
267 | =over 4 |
268 | |
269 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel/> |
270 | |
271 | =back |
272 | |
273 | =head2 Parrot now uses C3 |
274 | |
275 | =over 4 |
276 | |
277 | =item L<http://aspn.activestate.com/ASPN/Mail/Message/perl6-internals/2746631> |
278 | |
279 | =item L<http://use.perl.org/~autrijus/journal/25768> |
280 | |
281 | =back |
282 | |
283 | =head2 Python 2.3 MRO related links |
284 | |
285 | =over 4 |
286 | |
287 | =item L<http://www.python.org/2.3/mro.html> |
288 | |
289 | =item L<http://www.python.org/2.2.2/descrintro.html#mro> |
290 | |
291 | =back |
292 | |
293 | =head2 C3 for TinyCLOS |
294 | |
295 | =over 4 |
296 | |
297 | =item L<http://www.call-with-current-continuation.org/eggs/c3.html> |
298 | |
299 | =back |
300 | |
934d071b |
301 | =head1 AUTHORS |
c0b91998 |
302 | |
303 | Stevan Little, E<lt>stevan@iinteractive.comE<gt> |
304 | |
f4e5601f |
305 | Brandon L. Black, E<lt>blblack@gmail.comE<gt> |
934d071b |
306 | |
c0b91998 |
307 | =head1 COPYRIGHT AND LICENSE |
308 | |
309 | Copyright 2006 by Infinity Interactive, Inc. |
310 | |
311 | L<http://www.iinteractive.com> |
312 | |
313 | This library is free software; you can redistribute it and/or modify |
314 | it under the same terms as Perl itself. |
315 | |
316 | =cut |