Commit | Line | Data |
95bebf8c |
1 | |
2 | package Class::C3; |
3 | |
4 | use strict; |
5 | use warnings; |
6 | |
95bebf8c |
7 | use Scalar::Util 'blessed'; |
8 | |
4e47d2a4 |
9 | our $VERSION = '0.06'; |
d401eda1 |
10 | |
11 | # this is our global stash of both |
12 | # MRO's and method dispatch tables |
13 | # the structure basically looks like |
14 | # this: |
15 | # |
16 | # $MRO{$class} = { |
17 | # MRO => [ <class precendence list> ], |
18 | # methods => { |
19 | # orig => <original location of method>, |
20 | # code => \&<ref to original method> |
21 | # } |
22 | # } |
23 | # |
95bebf8c |
24 | my %MRO; |
25 | |
d0e2efe5 |
26 | # use these for debugging ... |
d401eda1 |
27 | sub _dump_MRO_table { %MRO } |
d401eda1 |
28 | our $TURN_OFF_C3 = 0; |
29 | |
95bebf8c |
30 | sub import { |
31 | my $class = caller(); |
d401eda1 |
32 | # skip if the caller is main:: |
33 | # since that is clearly not relevant |
95bebf8c |
34 | return if $class eq 'main'; |
d401eda1 |
35 | return if $TURN_OFF_C3; |
36 | # make a note to calculate $class |
37 | # during INIT phase |
95bebf8c |
38 | $MRO{$class} = undef; |
39 | } |
40 | |
d401eda1 |
41 | ## initializers |
42 | |
43 | # NOTE: |
44 | # this will not run under the following |
45 | # conditions: |
46 | # - mod_perl |
47 | # - require Class::C3; |
48 | # - eval "use Class::C3" |
49 | # in all those cases, you need to call |
50 | # the initialize() function manually |
51 | INIT { initialize() } |
52 | |
53 | sub initialize { |
54 | # why bother if we don't have anything ... |
55 | return unless keys %MRO; |
56 | _calculate_method_dispatch_tables(); |
57 | _apply_method_dispatch_tables(); |
5d5c86d9 |
58 | %next::METHOD_CACHE = (); |
d401eda1 |
59 | } |
60 | |
d0e2efe5 |
61 | sub uninitialize { |
62 | # why bother if we don't have anything ... |
63 | return unless keys %MRO; |
64 | _remove_method_dispatch_tables(); |
5d5c86d9 |
65 | %next::METHOD_CACHE = (); |
d0e2efe5 |
66 | } |
67 | |
68 | sub reinitialize { |
69 | uninitialize(); |
70 | # clean up the %MRO before we re-initialize |
71 | $MRO{$_} = undef foreach keys %MRO; |
72 | initialize(); |
73 | } |
74 | |
d401eda1 |
75 | ## functions for applying C3 to classes |
76 | |
77 | sub _calculate_method_dispatch_tables { |
95bebf8c |
78 | foreach my $class (keys %MRO) { |
d401eda1 |
79 | _calculate_method_dispatch_table($class); |
95bebf8c |
80 | } |
d401eda1 |
81 | } |
82 | |
83 | sub _calculate_method_dispatch_table { |
84 | my $class = shift; |
85 | no strict 'refs'; |
86 | my @MRO = calculateMRO($class); |
87 | $MRO{$class} = { MRO => \@MRO }; |
88 | my %methods; |
89 | # NOTE: |
90 | # we do @MRO[1 .. $#MRO] here because it |
91 | # makes no sense to interogate the class |
92 | # which you are calculating for. |
93 | foreach my $local (@MRO[1 .. $#MRO]) { |
94 | foreach my $method (grep { defined &{"${local}::$_"} } keys %{"${local}::"}) { |
95 | # skip if already overriden in local class |
96 | next unless !defined *{"${class}::$method"}{CODE}; |
97 | $methods{$method} = { |
98 | orig => "${local}::$method", |
99 | code => \&{"${local}::$method"} |
100 | } unless exists $methods{$method}; |
95bebf8c |
101 | } |
d401eda1 |
102 | } |
103 | # now stash them in our %MRO table |
104 | $MRO{$class}->{methods} = \%methods; |
105 | } |
106 | |
107 | sub _apply_method_dispatch_tables { |
108 | foreach my $class (keys %MRO) { |
109 | _apply_method_dispatch_table($class); |
110 | } |
95bebf8c |
111 | } |
112 | |
d401eda1 |
113 | sub _apply_method_dispatch_table { |
114 | my $class = shift; |
115 | no strict 'refs'; |
116 | foreach my $method (keys %{$MRO{$class}->{methods}}) { |
117 | *{"${class}::$method"} = $MRO{$class}->{methods}->{$method}->{code}; |
118 | } |
119 | } |
120 | |
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121 | sub _remove_method_dispatch_tables { |
122 | foreach my $class (keys %MRO) { |
123 | _remove_method_dispatch_table($class); |
124 | } |
125 | } |
126 | |
127 | sub _remove_method_dispatch_table { |
128 | my $class = shift; |
129 | no strict 'refs'; |
130 | foreach my $method (keys %{$MRO{$class}->{methods}}) { |
131 | delete ${"${class}::"}{$method}; |
132 | } |
133 | } |
134 | |
d401eda1 |
135 | ## functions for calculating C3 MRO |
136 | |
137 | # this function is a perl-port of the |
138 | # python code on this page: |
139 | # http://www.python.org/2.3/mro.html |
95bebf8c |
140 | sub _merge { |
141 | my (@seqs) = @_; |
4e47d2a4 |
142 | my $class_being_merged = $seqs[0]->[0]; |
95bebf8c |
143 | my @res; |
144 | while (1) { |
145 | # remove all empty seqences |
146 | my @nonemptyseqs = (map { (@{$_} ? $_ : ()) } @seqs); |
147 | # return the list if we have no more no-empty sequences |
148 | return @res if not @nonemptyseqs; |
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149 | my $reject; |
95bebf8c |
150 | my $cand; # a canidate .. |
151 | foreach my $seq (@nonemptyseqs) { |
152 | $cand = $seq->[0]; # get the head of the list |
153 | my $nothead; |
154 | foreach my $sub_seq (@nonemptyseqs) { |
155 | # XXX - this is instead of the python "in" |
156 | my %in_tail = (map { $_ => 1 } @{$sub_seq}[ 1 .. $#{$sub_seq} ]); |
157 | # NOTE: |
158 | # jump out as soon as we find one matching |
159 | # there is no reason not too. However, if |
160 | # we find one, then just remove the '&& last' |
161 | $nothead++ && last if exists $in_tail{$cand}; |
162 | } |
163 | last unless $nothead; # leave the loop with our canidate ... |
4e47d2a4 |
164 | $reject = $cand; |
95bebf8c |
165 | $cand = undef; # otherwise, reject it ... |
166 | } |
4e47d2a4 |
167 | die "Inconsistent hierarchy found while merging '$class_being_merged':\n\t" . |
168 | "current merge results [\n\t\t" . (join ",\n\t\t" => @res) . "\n\t]\n\t" . |
169 | "mergeing failed on '$reject'\n" if not $cand; |
95bebf8c |
170 | push @res => $cand; |
171 | # now loop through our non-empties and pop |
172 | # off the head if it matches our canidate |
173 | foreach my $seq (@nonemptyseqs) { |
174 | shift @{$seq} if $seq->[0] eq $cand; |
175 | } |
176 | } |
177 | } |
178 | |
179 | sub calculateMRO { |
180 | my ($class) = @_; |
181 | no strict 'refs'; |
182 | return _merge( |
183 | [ $class ], # the class we are linearizing |
184 | (map { [ calculateMRO($_) ] } @{"${class}::ISA"}), # the MRO of all the superclasses |
185 | [ @{"${class}::ISA"} ] # a list of all the superclasses |
186 | ); |
187 | } |
188 | |
5d5c86d9 |
189 | package # hide me from PAUSE |
190 | next; |
191 | |
192 | use strict; |
193 | use warnings; |
194 | |
195 | use Scalar::Util 'blessed'; |
196 | |
197 | our $VERSION = '0.03'; |
198 | |
199 | our %METHOD_CACHE; |
200 | |
201 | sub method { |
202 | my @label = (split '::', (caller(1))[3]); |
203 | my $label = pop @label; |
204 | my $caller = join '::' => @label; |
205 | my $self = $_[0]; |
206 | my $class = blessed($self) || $self; |
207 | |
208 | goto &{ $METHOD_CACHE{"$class|$caller|$label"} ||= do { |
209 | |
210 | my @MRO = Class::C3::calculateMRO($class); |
211 | |
212 | my $current; |
213 | while ($current = shift @MRO) { |
214 | last if $caller eq $current; |
215 | } |
216 | |
217 | no strict 'refs'; |
218 | my $found; |
219 | foreach my $class (@MRO) { |
220 | last if (defined ($found = *{$class . '::' . $label}{CODE})); |
221 | } |
222 | |
223 | die "No next::method '$label' found for $self" unless $found; |
224 | |
225 | $found; |
226 | } }; |
227 | } |
228 | |
95bebf8c |
229 | 1; |
230 | |
231 | __END__ |
232 | |
233 | =pod |
234 | |
235 | =head1 NAME |
236 | |
237 | Class::C3 - A pragma to use the C3 method resolution order algortihm |
238 | |
239 | =head1 SYNOPSIS |
240 | |
241 | package A; |
242 | use Class::C3; |
243 | sub hello { 'A::hello' } |
244 | |
245 | package B; |
246 | use base 'A'; |
247 | use Class::C3; |
248 | |
249 | package C; |
250 | use base 'A'; |
251 | use Class::C3; |
252 | |
253 | sub hello { 'C::hello' } |
254 | |
255 | package D; |
256 | use base ('B', 'C'); |
257 | use Class::C3; |
258 | |
259 | # Classic Diamond MI pattern |
d401eda1 |
260 | # <A> |
261 | # / \ |
262 | # <B> <C> |
263 | # \ / |
264 | # <D> |
95bebf8c |
265 | |
266 | package main; |
267 | |
268 | print join ', ' => Class::C3::calculateMRO('Diamond_D') # prints D, B, C, A |
269 | |
270 | print D->hello() # prints 'C::hello' instead of the standard p5 'A::hello' |
271 | |
272 | D->can('hello')->(); # can() also works correctly |
273 | UNIVERSAL::can('D', 'hello'); # as does UNIVERSAL::can() |
274 | |
275 | =head1 DESCRIPTION |
276 | |
277 | This is currently an experimental pragma to change Perl 5's standard method resolution order |
278 | from depth-first left-to-right (a.k.a - pre-order) to the more sophisticated C3 method resolution |
279 | order. |
280 | |
281 | =head2 What is C3? |
282 | |
283 | C3 is the name of an algorithm which aims to provide a sane method resolution order under multiple |
284 | inheritence. It was first introduced in the langauge Dylan (see links in the L<SEE ALSO> section), |
285 | and then later adopted as the prefered MRO (Method Resolution Order) for the new-style classes in |
286 | Python 2.3. Most recently it has been adopted as the 'canonical' MRO for Perl 6 classes, and the |
287 | default MRO for Parrot objects as well. |
288 | |
289 | =head2 How does C3 work. |
290 | |
291 | C3 works by always preserving local precendence ordering. This essentially means that no class will |
292 | appear before any of it's subclasses. Take the classic diamond inheritence pattern for instance: |
293 | |
d401eda1 |
294 | <A> |
295 | / \ |
296 | <B> <C> |
297 | \ / |
298 | <D> |
95bebf8c |
299 | |
300 | The standard Perl 5 MRO would be (D, B, A, C). The result being that B<A> appears before B<C>, even |
301 | though B<C> is the subclass of B<A>. The C3 MRO algorithm however, produces the following MRO |
302 | (D, B, C, A), which does not have this same issue. |
303 | |
304 | This example is fairly trival, for more complex examples and a deeper explaination, see the links in |
305 | the L<SEE ALSO> section. |
306 | |
307 | =head2 How does this module work? |
308 | |
309 | This module uses a technique similar to Perl 5's method caching. During the INIT phase, this module |
310 | calculates the MRO of all the classes which called C<use Class::C3>. It then gathers information from |
311 | the symbol tables of each of those classes, and builds a set of method aliases for the correct |
312 | dispatch ordering. Once all these C3-based method tables are created, it then adds the method aliases |
313 | into the local classes symbol table. |
314 | |
315 | The end result is actually classes with pre-cached method dispatch. However, this caching does not |
316 | do well if you start changing your C<@ISA> or messing with class symbol tables, so you should consider |
317 | your classes to be effectively closed. See the L<CAVEATS> section for more details. |
318 | |
d401eda1 |
319 | =head1 OPTIONAL LOWERCASE PRAGMA |
320 | |
321 | This release also includes an optional module B<c3> in the F<opt/> folder. I did not include this in |
322 | the regular install since lowercase module names are considered I<"bad"> by some people. However I |
323 | think that code looks much nicer like this: |
324 | |
325 | package MyClass; |
326 | use c3; |
327 | |
328 | The the more clunky: |
329 | |
330 | package MyClass; |
331 | use Class::C3; |
332 | |
333 | But hey, it's your choice, thats why it is optional. |
334 | |
95bebf8c |
335 | =head1 FUNCTIONS |
336 | |
337 | =over 4 |
338 | |
339 | =item B<calculateMRO ($class)> |
340 | |
341 | Given a C<$class> this will return an array of class names in the proper C3 method resolution order. |
342 | |
d401eda1 |
343 | =item B<initialize> |
344 | |
345 | This can be used to initalize the C3 method dispatch tables. You need to call this if you are running |
346 | under mod_perl, or in any other environment which does not run the INIT phase of the perl compiler. |
347 | |
348 | NOTE: |
d0e2efe5 |
349 | This can B<not> be used to re-load the dispatch tables for all classes. Use C<reinitialize> for that. |
350 | |
351 | =item B<uninitialize> |
352 | |
353 | Calling this function results in the removal of all cached methods, and the restoration of the old Perl 5 |
354 | style dispatch order (depth-first, left-to-right). |
355 | |
356 | =item B<reinitialize> |
357 | |
358 | This effectively calls C<uninitialize> followed by C<initialize> the result of which is a reloading of |
359 | B<all> the calculated C3 dispatch tables. |
360 | |
361 | It should be noted that if you have a large class library, this could potentially be a rather costly |
362 | operation. |
d401eda1 |
363 | |
95bebf8c |
364 | =back |
365 | |
5d5c86d9 |
366 | =head1 METHOD REDISPATCHING |
367 | |
368 | It is always useful to be able to re-dispatch your method call to the "next most applicable method". This |
369 | module provides a pseudo package along the lines of C<SUPER::> or C<NEXT::> which will re-dispatch the |
370 | method along the C3 linearization. This is best show with an examples. |
371 | |
372 | # a classic diamond MI pattern ... |
373 | <A> |
374 | / \ |
375 | <B> <C> |
376 | \ / |
377 | <D> |
378 | |
379 | package A; |
380 | use c3; |
381 | sub foo { 'A::foo' } |
382 | |
383 | package B; |
384 | use base 'A'; |
385 | use c3; |
386 | sub foo { 'B::foo => ' . (shift)->next::method() } |
387 | |
388 | package B; |
389 | use base 'A'; |
390 | use c3; |
391 | sub foo { 'C::foo => ' . (shift)->next::method() } |
392 | |
393 | package D; |
394 | use base ('B', 'C'); |
395 | use c3; |
396 | sub foo { 'D::foo => ' . (shift)->next::method() } |
397 | |
398 | print D->foo; # prints out "D::foo => B::foo => C::foo => A::foo" |
399 | |
400 | A few things to note. First, we do not require you to add on the method name to the C<next::method> |
401 | call (this is unlike C<NEXT::> and C<SUPER::> which do require that). This helps to enforce the rule |
402 | that you cannot dispatch to a method of a different name (this is how C<NEXT::> behaves as well). |
403 | |
404 | The next thing to keep in mind is that you will need to pass all arguments to C<next::method> it can |
405 | not automatically use the current C<@_>. |
406 | |
95bebf8c |
407 | =head1 CAVEATS |
408 | |
409 | Let me first say, this is an experimental module, and so it should not be used for anything other |
410 | then other experimentation for the time being. |
411 | |
412 | That said, it is the authors intention to make this into a completely usable and production stable |
413 | module if possible. Time will tell. |
414 | |
415 | And now, onto the caveats. |
416 | |
417 | =over 4 |
418 | |
419 | =item Use of C<SUPER::>. |
420 | |
421 | The idea of C<SUPER::> under multiple inheritence is ambigious, and generally not recomended anyway. |
422 | However, it's use in conjuntion with this module is very much not recommended, and in fact very |
5d5c86d9 |
423 | discouraged. The recommended approach is to instead use the supplied C<next::method> feature, see |
424 | more details on it's usage above. |
95bebf8c |
425 | |
426 | =item Changing C<@ISA>. |
427 | |
428 | It is the author's opinion that changing C<@ISA> at runtime is pure insanity anyway. However, people |
429 | do it, so I must caveat. Any changes to the C<@ISA> will not be reflected in the MRO calculated by this |
d0e2efe5 |
430 | module, and therefor probably won't even show up. If you do this, you will need to call C<reinitialize> |
431 | in order to recalulate B<all> method dispatch tables. See the C<reinitialize> documentation and an example |
432 | in F<t/20_reinitialize.t> for more information. |
95bebf8c |
433 | |
434 | =item Adding/deleting methods from class symbol tables. |
435 | |
436 | This module calculates the MRO for each requested class during the INIT phase by interogatting the symbol |
437 | tables of said classes. So any symbol table manipulation which takes place after our INIT phase is run will |
d0e2efe5 |
438 | not be reflected in the calculated MRO. Just as with changing the C<@ISA>, you will need to call |
439 | C<reinitialize> for any changes you make to take effect. |
95bebf8c |
440 | |
95bebf8c |
441 | =back |
442 | |
15eeb546 |
443 | =head1 TODO |
444 | |
445 | =over 4 |
446 | |
447 | =item More tests |
448 | |
449 | You can never have enough tests :) |
450 | |
5d5c86d9 |
451 | =back |
15eeb546 |
452 | |
5d5c86d9 |
453 | =head1 CODE COVERAGE |
15eeb546 |
454 | |
5d5c86d9 |
455 | I use B<Devel::Cover> to test the code coverage of my tests, below is the B<Devel::Cover> report on this module's test suite. |
456 | |
457 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
458 | File stmt bran cond sub pod time total |
459 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
460 | Class/C3.pm 99.2 93.3 66.7 96.0 100.0 92.8 96.3 |
461 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
462 | Total 99.2 93.3 66.7 96.0 100.0 92.8 96.3 |
463 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
15eeb546 |
464 | |
95bebf8c |
465 | =head1 SEE ALSO |
466 | |
467 | =head2 The original Dylan paper |
468 | |
469 | =over 4 |
470 | |
471 | =item L<http://www.webcom.com/haahr/dylan/linearization-oopsla96.html> |
472 | |
473 | =back |
474 | |
475 | =head2 The prototype Perl 6 Object Model uses C3 |
476 | |
477 | =over 4 |
478 | |
479 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel/> |
480 | |
481 | =back |
482 | |
483 | =head2 Parrot now uses C3 |
484 | |
485 | =over 4 |
486 | |
487 | =item L<http://aspn.activestate.com/ASPN/Mail/Message/perl6-internals/2746631> |
488 | |
489 | =item L<http://use.perl.org/~autrijus/journal/25768> |
490 | |
491 | =back |
492 | |
493 | =head2 Python 2.3 MRO related links |
494 | |
495 | =over 4 |
496 | |
497 | =item L<http://www.python.org/2.3/mro.html> |
498 | |
499 | =item L<http://www.python.org/2.2.2/descrintro.html#mro> |
500 | |
501 | =back |
502 | |
503 | =head2 C3 for TinyCLOS |
504 | |
505 | =over 4 |
506 | |
507 | =item L<http://www.call-with-current-continuation.org/eggs/c3.html> |
508 | |
509 | =back |
510 | |
511 | =head1 AUTHOR |
512 | |
d401eda1 |
513 | Stevan Little, E<lt>stevan@iinteractive.comE<gt> |
95bebf8c |
514 | |
515 | =head1 COPYRIGHT AND LICENSE |
516 | |
517 | Copyright 2005 by Infinity Interactive, Inc. |
518 | |
519 | L<http://www.iinteractive.com> |
520 | |
521 | This library is free software; you can redistribute it and/or modify |
522 | it under the same terms as Perl itself. |
523 | |
524 | =cut |