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; |
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24 | my $current_parents = [ $root->$parent_fetcher ]; |
cf85d7d3 |
25 | my $recurse_mergeout = []; |
26 | my $i = 0; |
27 | |
28 | while(1) { |
29 | if($i < @$current_parents) { |
30 | my $new_root = $current_parents->[$i++]; |
31 | |
aeed4a60 |
32 | unless ($pfetcher_is_coderef or $new_root->can($parent_fetcher)) { |
33 | confess "Could not find method $parent_fetcher in $new_root"; |
34 | } |
35 | |
cf85d7d3 |
36 | push(@STACK, [ |
37 | $current_root, |
38 | $current_parents, |
39 | $recurse_mergeout, |
40 | $i, |
41 | ]); |
42 | |
43 | $current_root = $new_root; |
ca604ce2 |
44 | $current_parents = $cache->{pfetch}->{$current_root} ||= [ $current_root->$parent_fetcher ]; |
cf85d7d3 |
45 | $recurse_mergeout = []; |
46 | $i = 0; |
47 | next; |
48 | } |
49 | |
ca604ce2 |
50 | my $mergeout = $cache->{merge}->{$current_root} ||= do { |
cf85d7d3 |
51 | |
52 | # This do-block is the code formerly known as the function |
53 | # that was a perl-port of the python code at |
54 | # http://www.python.org/2.3/mro.html :) |
55 | |
7946639b |
56 | # Initial set (make sure everything is copied - it will be modded) |
657499e7 |
57 | my (@seqs, %tails); |
58 | for my $d (@$recurse_mergeout, $current_parents){ |
59 | if(@$d){ |
60 | push @seqs, [@$d]; |
61 | # Construct the tail-checking hash |
62 | $tails{$_}++ for (@$d[1..$#$d]); |
63 | } |
cf85d7d3 |
64 | } |
65 | |
7946639b |
66 | my @res = ( $current_root ); |
cf85d7d3 |
67 | while (1) { |
657499e7 |
68 | my ($cand, $winner); |
69 | my $j = 0; |
cf85d7d3 |
70 | foreach (@seqs) { |
657499e7 |
71 | $j++; |
72 | if(!@$_){ |
73 | splice @seqs, $j, 1; |
74 | next; |
75 | } |
76 | |
77 | if(!$winner){ |
78 | next if $tails{ $cand = $_->[0] }; |
79 | push(@res, $winner = $cand); |
cf85d7d3 |
80 | } |
657499e7 |
81 | |
cf85d7d3 |
82 | if($_->[0] eq $winner) { |
83 | shift @$_; # strip off our winner |
657499e7 |
84 | $tails{ $_->[0] }-- if @$_; # keep %tails sane |
cf85d7d3 |
85 | } |
86 | } |
657499e7 |
87 | |
cf85d7d3 |
88 | last if !$cand; |
89 | die q{Inconsistent hierarchy found while merging '} |
90 | . $current_root . qq{':\n\t} |
91 | . qq{current merge results [\n\t\t} |
92 | . (join ",\n\t\t" => @res) |
93 | . qq{\n\t]\n\t} . qq{merging failed on '$cand'\n} |
94 | if !$winner; |
95 | } |
96 | \@res; |
97 | }; |
98 | |
99 | return @$mergeout if !@STACK; |
100 | |
101 | ($current_root, $current_parents, $recurse_mergeout, $i) |
102 | = @{pop @STACK}; |
103 | |
104 | push(@$recurse_mergeout, $mergeout); |
105 | } |
c0b91998 |
106 | } |
107 | |
108 | 1; |
109 | |
110 | __END__ |
111 | |
112 | =pod |
113 | |
114 | =head1 NAME |
115 | |
8fe16bec |
116 | Algorithm::C3 - A module for merging hierarchies using the C3 algorithm |
c0b91998 |
117 | |
118 | =head1 SYNOPSIS |
119 | |
120 | use Algorithm::C3; |
121 | |
122 | # merging a classic diamond |
123 | # inheritence graph like this: |
124 | # |
125 | # <A> |
126 | # / \ |
127 | # <B> <C> |
128 | # \ / |
129 | # <D> |
130 | |
131 | my @merged = Algorithm::C3::merge( |
132 | 'D', |
133 | sub { |
134 | # extract the ISA array |
135 | # from the package |
136 | no strict 'refs'; |
137 | @{$_[0] . '::ISA'}; |
138 | } |
139 | ); |
140 | |
141 | print join ", " => @merged; # prints D, B, C, A |
142 | |
143 | =head1 DESCRIPTION |
144 | |
145 | This module implements the C3 algorithm. I have broken this out |
146 | into it's own module because I found myself copying and pasting |
147 | it way too often for various needs. Most of the uses I have for |
148 | C3 revolve around class building and metamodels, but it could |
149 | also be used for things like dependency resolution as well since |
150 | it tends to do such a nice job of preserving local precendence |
151 | orderings. |
152 | |
153 | Below is a brief explanation of C3 taken from the L<Class::C3> |
154 | module. For more detailed information, see the L<SEE ALSO> section |
155 | and the links there. |
156 | |
157 | =head2 What is C3? |
158 | |
159 | C3 is the name of an algorithm which aims to provide a sane method |
160 | resolution order under multiple inheritence. It was first introduced |
161 | in the langauge Dylan (see links in the L<SEE ALSO> section), and |
162 | then later adopted as the prefered MRO (Method Resolution Order) |
163 | for the new-style classes in Python 2.3. Most recently it has been |
164 | adopted as the 'canonical' MRO for Perl 6 classes, and the default |
165 | MRO for Parrot objects as well. |
166 | |
167 | =head2 How does C3 work. |
168 | |
169 | C3 works by always preserving local precendence ordering. This |
170 | essentially means that no class will appear before any of it's |
171 | subclasses. Take the classic diamond inheritence pattern for |
172 | instance: |
173 | |
174 | <A> |
175 | / \ |
176 | <B> <C> |
177 | \ / |
178 | <D> |
179 | |
180 | The standard Perl 5 MRO would be (D, B, A, C). The result being that |
181 | B<A> appears before B<C>, even though B<C> is the subclass of B<A>. |
182 | The C3 MRO algorithm however, produces the following MRO (D, B, C, A), |
183 | which does not have this same issue. |
184 | |
185 | This example is fairly trival, for more complex examples and a deeper |
186 | explaination, see the links in the L<SEE ALSO> section. |
187 | |
188 | =head1 FUNCTION |
189 | |
190 | =over 4 |
191 | |
ca604ce2 |
192 | =item B<merge ($root, $func_to_fetch_parent, $cache)> |
c0b91998 |
193 | |
194 | This takes a C<$root> node, which can be anything really it |
195 | is up to you. Then it takes a C<$func_to_fetch_parent> which |
196 | can be either a CODE reference (see L<SYNOPSIS> above for an |
197 | example), or a string containing a method name to be called |
198 | on all the items being linearized. An example of how this |
199 | might look is below: |
200 | |
201 | { |
202 | package A; |
203 | |
204 | sub supers { |
205 | no strict 'refs'; |
206 | @{$_[0] . '::ISA'}; |
207 | } |
208 | |
209 | package C; |
210 | our @ISA = ('A'); |
211 | package B; |
212 | our @ISA = ('A'); |
213 | package D; |
214 | our @ISA = ('B', 'C'); |
215 | } |
216 | |
217 | print join ", " => Algorithm::C3::merge('D', 'supers'); |
218 | |
219 | The purpose of C<$func_to_fetch_parent> is to provide a way |
220 | for C<merge> to extract the parents of C<$root>. This is |
221 | needed for C3 to be able to do it's work. |
222 | |
ca604ce2 |
223 | The C<$cache> parameter is an entirely optional performance |
224 | measure, and should not change behavior. |
225 | |
226 | If supplied, it should be a hashref that merge can use as a |
227 | private cache between runs to speed things up. Generally |
228 | speaking, if you will be calling merge many times on related |
229 | things, and the parent fetching function will return constant |
230 | results given the same arguments during all of these calls, |
231 | you can and should reuse the same shared cache hash for all |
232 | of the calls. Example: |
233 | |
234 | sub do_some_merging { |
235 | my %merge_cache; |
236 | my @foo_mro = Algorithm::C3::Merge('Foo', \&get_supers, \%merge_cache); |
237 | my @bar_mro = Algorithm::C3::Merge('Bar', \&get_supers, \%merge_cache); |
238 | my @baz_mro = Algorithm::C3::Merge('Baz', \&get_supers, \%merge_cache); |
239 | my @quux_mro = Algorithm::C3::Merge('Quux', \&get_supers, \%merge_cache); |
240 | # ... |
241 | } |
242 | |
c0b91998 |
243 | =back |
244 | |
245 | =head1 CODE COVERAGE |
246 | |
247 | I use B<Devel::Cover> to test the code coverage of my tests, below |
248 | is the B<Devel::Cover> report on this module's test suite. |
249 | |
250 | ------------------------ ------ ------ ------ ------ ------ ------ ------ |
251 | File stmt bran cond sub pod time total |
252 | ------------------------ ------ ------ ------ ------ ------ ------ ------ |
6d8a26f9 |
253 | Algorithm/C3.pm 100.0 100.0 100.0 100.0 100.0 100.0 100.0 |
c0b91998 |
254 | ------------------------ ------ ------ ------ ------ ------ ------ ------ |
6d8a26f9 |
255 | Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 |
c0b91998 |
256 | ------------------------ ------ ------ ------ ------ ------ ------ ------ |
257 | |
258 | =head1 SEE ALSO |
259 | |
260 | =head2 The original Dylan paper |
261 | |
262 | =over 4 |
263 | |
264 | =item L<http://www.webcom.com/haahr/dylan/linearization-oopsla96.html> |
265 | |
266 | =back |
267 | |
268 | =head2 The prototype Perl 6 Object Model uses C3 |
269 | |
270 | =over 4 |
271 | |
272 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel/> |
273 | |
274 | =back |
275 | |
276 | =head2 Parrot now uses C3 |
277 | |
278 | =over 4 |
279 | |
280 | =item L<http://aspn.activestate.com/ASPN/Mail/Message/perl6-internals/2746631> |
281 | |
282 | =item L<http://use.perl.org/~autrijus/journal/25768> |
283 | |
284 | =back |
285 | |
286 | =head2 Python 2.3 MRO related links |
287 | |
288 | =over 4 |
289 | |
290 | =item L<http://www.python.org/2.3/mro.html> |
291 | |
292 | =item L<http://www.python.org/2.2.2/descrintro.html#mro> |
293 | |
294 | =back |
295 | |
296 | =head2 C3 for TinyCLOS |
297 | |
298 | =over 4 |
299 | |
300 | =item L<http://www.call-with-current-continuation.org/eggs/c3.html> |
301 | |
302 | =back |
303 | |
934d071b |
304 | =head1 AUTHORS |
c0b91998 |
305 | |
306 | Stevan Little, E<lt>stevan@iinteractive.comE<gt> |
307 | |
f4e5601f |
308 | Brandon L. Black, E<lt>blblack@gmail.comE<gt> |
934d071b |
309 | |
c0b91998 |
310 | =head1 COPYRIGHT AND LICENSE |
311 | |
312 | Copyright 2006 by Infinity Interactive, Inc. |
313 | |
314 | L<http://www.iinteractive.com> |
315 | |
316 | This library is free software; you can redistribute it and/or modify |
317 | it under the same terms as Perl itself. |
318 | |
319 | =cut |
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320 | |