Commit | Line | Data |
c0b91998 |
1 | |
2 | package Algorithm::C3; |
3 | |
4 | use strict; |
5 | use warnings; |
6 | |
7 | use Carp 'confess'; |
8 | |
21f53c4c |
9 | our $VERSION = '0.06'; |
c0b91998 |
10 | |
c0b91998 |
11 | sub merge { |
ca604ce2 |
12 | my ($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; |
0f7ef7b1 |
27 | my %seen = ( $root => 1 ); |
cf85d7d3 |
28 | |
29 | while(1) { |
30 | if($i < @$current_parents) { |
31 | my $new_root = $current_parents->[$i++]; |
fa27b316 |
32 | |
33 | if($seen{$new_root}) { |
0f7ef7b1 |
34 | my @isastack = ( |
35 | (map { $_->[0] } @STACK), |
36 | $current_root, |
37 | $new_root |
38 | ); |
39 | shift @isastack while $isastack[0] ne $new_root; |
40 | my $isastack = join(q{ -> }, @isastack); |
41 | die "Infinite loop detected in parents of '$root': $isastack"; |
fa27b316 |
42 | } |
bb0280c5 |
43 | $seen{$new_root} = 1; |
cf85d7d3 |
44 | |
aeed4a60 |
45 | unless ($pfetcher_is_coderef or $new_root->can($parent_fetcher)) { |
46 | confess "Could not find method $parent_fetcher in $new_root"; |
47 | } |
48 | |
cf85d7d3 |
49 | push(@STACK, [ |
50 | $current_root, |
51 | $current_parents, |
52 | $recurse_mergeout, |
53 | $i, |
54 | ]); |
55 | |
56 | $current_root = $new_root; |
ca604ce2 |
57 | $current_parents = $cache->{pfetch}->{$current_root} ||= [ $current_root->$parent_fetcher ]; |
cf85d7d3 |
58 | $recurse_mergeout = []; |
59 | $i = 0; |
60 | next; |
61 | } |
62 | |
bb0280c5 |
63 | $seen{$current_root} = 0; |
64 | |
ca604ce2 |
65 | my $mergeout = $cache->{merge}->{$current_root} ||= do { |
cf85d7d3 |
66 | |
67 | # This do-block is the code formerly known as the function |
68 | # that was a perl-port of the python code at |
69 | # http://www.python.org/2.3/mro.html :) |
70 | |
7946639b |
71 | # Initial set (make sure everything is copied - it will be modded) |
5a07d049 |
72 | my @seqs = map { [@$_] } (@$recurse_mergeout, $current_parents); |
73 | |
74 | # Construct the tail-checking hash |
75 | my %tails; |
76 | foreach my $seq (@seqs) { |
77 | $tails{$_}++ for (@$seq[1..$#$seq]); |
cf85d7d3 |
78 | } |
79 | |
7946639b |
80 | my @res = ( $current_root ); |
cf85d7d3 |
81 | while (1) { |
5a07d049 |
82 | my $cand; |
83 | my $winner; |
cf85d7d3 |
84 | foreach (@seqs) { |
5a07d049 |
85 | next if !@$_; |
86 | if(!$winner) { # looking for a winner |
87 | $cand = $_->[0]; # seq head is candidate |
88 | next if $tails{$cand}; # he loses if in %tails |
fc8171f5 |
89 | |
90 | # Handy warn to give a output like the ones on |
91 | # http://www.python.org/download/releases/2.3/mro/ |
92 | #warn " = " . join(' + ', @res) . " + merge([" . join('] [', map { join(', ', @$_) } grep { @$_ } @seqs) . "])\n"; |
5a07d049 |
93 | push @res => $winner = $cand; |
cf85d7d3 |
94 | } |
95 | if($_->[0] eq $winner) { |
96 | shift @$_; # strip off our winner |
5a07d049 |
97 | $tails{$_->[0]}-- if @$_; # keep %tails sane |
cf85d7d3 |
98 | } |
99 | } |
fc8171f5 |
100 | |
101 | # Handy warn to give a output like the ones on |
102 | # http://www.python.org/download/releases/2.3/mro/ |
103 | #warn " = " . join(' + ', @res) . "\n" if !$cand; |
104 | |
cf85d7d3 |
105 | last if !$cand; |
106 | die q{Inconsistent hierarchy found while merging '} |
107 | . $current_root . qq{':\n\t} |
108 | . qq{current merge results [\n\t\t} |
109 | . (join ",\n\t\t" => @res) |
110 | . qq{\n\t]\n\t} . qq{merging failed on '$cand'\n} |
111 | if !$winner; |
112 | } |
113 | \@res; |
114 | }; |
115 | |
116 | return @$mergeout if !@STACK; |
117 | |
118 | ($current_root, $current_parents, $recurse_mergeout, $i) |
119 | = @{pop @STACK}; |
120 | |
121 | push(@$recurse_mergeout, $mergeout); |
122 | } |
c0b91998 |
123 | } |
124 | |
125 | 1; |
126 | |
127 | __END__ |
128 | |
129 | =pod |
130 | |
131 | =head1 NAME |
132 | |
8fe16bec |
133 | Algorithm::C3 - A module for merging hierarchies using the C3 algorithm |
c0b91998 |
134 | |
135 | =head1 SYNOPSIS |
136 | |
137 | use Algorithm::C3; |
138 | |
139 | # merging a classic diamond |
140 | # inheritence graph like this: |
141 | # |
142 | # <A> |
143 | # / \ |
144 | # <B> <C> |
145 | # \ / |
146 | # <D> |
147 | |
148 | my @merged = Algorithm::C3::merge( |
149 | 'D', |
150 | sub { |
151 | # extract the ISA array |
152 | # from the package |
153 | no strict 'refs'; |
154 | @{$_[0] . '::ISA'}; |
155 | } |
156 | ); |
157 | |
158 | print join ", " => @merged; # prints D, B, C, A |
159 | |
160 | =head1 DESCRIPTION |
161 | |
162 | This module implements the C3 algorithm. I have broken this out |
163 | into it's own module because I found myself copying and pasting |
164 | it way too often for various needs. Most of the uses I have for |
165 | C3 revolve around class building and metamodels, but it could |
166 | also be used for things like dependency resolution as well since |
167 | it tends to do such a nice job of preserving local precendence |
168 | orderings. |
169 | |
170 | Below is a brief explanation of C3 taken from the L<Class::C3> |
171 | module. For more detailed information, see the L<SEE ALSO> section |
172 | and the links there. |
173 | |
174 | =head2 What is C3? |
175 | |
176 | C3 is the name of an algorithm which aims to provide a sane method |
177 | resolution order under multiple inheritence. It was first introduced |
178 | in the langauge Dylan (see links in the L<SEE ALSO> section), and |
179 | then later adopted as the prefered MRO (Method Resolution Order) |
180 | for the new-style classes in Python 2.3. Most recently it has been |
181 | adopted as the 'canonical' MRO for Perl 6 classes, and the default |
182 | MRO for Parrot objects as well. |
183 | |
184 | =head2 How does C3 work. |
185 | |
186 | C3 works by always preserving local precendence ordering. This |
187 | essentially means that no class will appear before any of it's |
188 | subclasses. Take the classic diamond inheritence pattern for |
189 | instance: |
190 | |
191 | <A> |
192 | / \ |
193 | <B> <C> |
194 | \ / |
195 | <D> |
196 | |
197 | The standard Perl 5 MRO would be (D, B, A, C). The result being that |
198 | B<A> appears before B<C>, even though B<C> is the subclass of B<A>. |
199 | The C3 MRO algorithm however, produces the following MRO (D, B, C, A), |
200 | which does not have this same issue. |
201 | |
202 | This example is fairly trival, for more complex examples and a deeper |
203 | explaination, see the links in the L<SEE ALSO> section. |
204 | |
205 | =head1 FUNCTION |
206 | |
207 | =over 4 |
208 | |
ca604ce2 |
209 | =item B<merge ($root, $func_to_fetch_parent, $cache)> |
c0b91998 |
210 | |
211 | This takes a C<$root> node, which can be anything really it |
212 | is up to you. Then it takes a C<$func_to_fetch_parent> which |
213 | can be either a CODE reference (see L<SYNOPSIS> above for an |
214 | example), or a string containing a method name to be called |
215 | on all the items being linearized. An example of how this |
216 | might look is below: |
217 | |
218 | { |
219 | package A; |
220 | |
221 | sub supers { |
222 | no strict 'refs'; |
223 | @{$_[0] . '::ISA'}; |
224 | } |
225 | |
226 | package C; |
227 | our @ISA = ('A'); |
228 | package B; |
229 | our @ISA = ('A'); |
230 | package D; |
231 | our @ISA = ('B', 'C'); |
232 | } |
233 | |
234 | print join ", " => Algorithm::C3::merge('D', 'supers'); |
235 | |
236 | The purpose of C<$func_to_fetch_parent> is to provide a way |
237 | for C<merge> to extract the parents of C<$root>. This is |
238 | needed for C3 to be able to do it's work. |
239 | |
ca604ce2 |
240 | The C<$cache> parameter is an entirely optional performance |
241 | measure, and should not change behavior. |
242 | |
243 | If supplied, it should be a hashref that merge can use as a |
244 | private cache between runs to speed things up. Generally |
245 | speaking, if you will be calling merge many times on related |
246 | things, and the parent fetching function will return constant |
247 | results given the same arguments during all of these calls, |
248 | you can and should reuse the same shared cache hash for all |
249 | of the calls. Example: |
250 | |
251 | sub do_some_merging { |
252 | my %merge_cache; |
253 | my @foo_mro = Algorithm::C3::Merge('Foo', \&get_supers, \%merge_cache); |
254 | my @bar_mro = Algorithm::C3::Merge('Bar', \&get_supers, \%merge_cache); |
255 | my @baz_mro = Algorithm::C3::Merge('Baz', \&get_supers, \%merge_cache); |
256 | my @quux_mro = Algorithm::C3::Merge('Quux', \&get_supers, \%merge_cache); |
257 | # ... |
258 | } |
259 | |
c0b91998 |
260 | =back |
261 | |
262 | =head1 CODE COVERAGE |
263 | |
264 | I use B<Devel::Cover> to test the code coverage of my tests, below |
265 | is the B<Devel::Cover> report on this module's test suite. |
266 | |
267 | ------------------------ ------ ------ ------ ------ ------ ------ ------ |
268 | File stmt bran cond sub pod time total |
269 | ------------------------ ------ ------ ------ ------ ------ ------ ------ |
6d8a26f9 |
270 | Algorithm/C3.pm 100.0 100.0 100.0 100.0 100.0 100.0 100.0 |
c0b91998 |
271 | ------------------------ ------ ------ ------ ------ ------ ------ ------ |
6d8a26f9 |
272 | Total 100.0 100.0 100.0 100.0 100.0 100.0 100.0 |
c0b91998 |
273 | ------------------------ ------ ------ ------ ------ ------ ------ ------ |
274 | |
275 | =head1 SEE ALSO |
276 | |
277 | =head2 The original Dylan paper |
278 | |
279 | =over 4 |
280 | |
281 | =item L<http://www.webcom.com/haahr/dylan/linearization-oopsla96.html> |
282 | |
283 | =back |
284 | |
285 | =head2 The prototype Perl 6 Object Model uses C3 |
286 | |
287 | =over 4 |
288 | |
289 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel/> |
290 | |
291 | =back |
292 | |
293 | =head2 Parrot now uses C3 |
294 | |
295 | =over 4 |
296 | |
297 | =item L<http://aspn.activestate.com/ASPN/Mail/Message/perl6-internals/2746631> |
298 | |
299 | =item L<http://use.perl.org/~autrijus/journal/25768> |
300 | |
301 | =back |
302 | |
303 | =head2 Python 2.3 MRO related links |
304 | |
305 | =over 4 |
306 | |
307 | =item L<http://www.python.org/2.3/mro.html> |
308 | |
309 | =item L<http://www.python.org/2.2.2/descrintro.html#mro> |
310 | |
311 | =back |
312 | |
313 | =head2 C3 for TinyCLOS |
314 | |
315 | =over 4 |
316 | |
317 | =item L<http://www.call-with-current-continuation.org/eggs/c3.html> |
318 | |
319 | =back |
320 | |
934d071b |
321 | =head1 AUTHORS |
c0b91998 |
322 | |
323 | Stevan Little, E<lt>stevan@iinteractive.comE<gt> |
324 | |
f4e5601f |
325 | Brandon L. Black, E<lt>blblack@gmail.comE<gt> |
934d071b |
326 | |
c0b91998 |
327 | =head1 COPYRIGHT AND LICENSE |
328 | |
329 | Copyright 2006 by Infinity Interactive, Inc. |
330 | |
331 | L<http://www.iinteractive.com> |
332 | |
333 | This library is free software; you can redistribute it and/or modify |
334 | it under the same terms as Perl itself. |
335 | |
336 | =cut |