Commit | Line | Data |
95bebf8c |
1 | |
2 | package Class::C3; |
3 | |
4 | use strict; |
5 | use warnings; |
6 | |
95bebf8c |
7 | use Scalar::Util 'blessed'; |
8 | |
ac6b0914 |
9 | our $VERSION = '0.08'; |
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> |
680100b1 |
21 | # }, |
22 | # has_overload_fallback => (1 | 0) |
d401eda1 |
23 | # } |
24 | # |
f7facd7b |
25 | our %MRO; |
95bebf8c |
26 | |
d0e2efe5 |
27 | # use these for debugging ... |
d401eda1 |
28 | sub _dump_MRO_table { %MRO } |
d401eda1 |
29 | our $TURN_OFF_C3 = 0; |
30 | |
95bebf8c |
31 | sub import { |
32 | my $class = caller(); |
d401eda1 |
33 | # skip if the caller is main:: |
34 | # since that is clearly not relevant |
95bebf8c |
35 | return if $class eq 'main'; |
d401eda1 |
36 | return if $TURN_OFF_C3; |
37 | # make a note to calculate $class |
38 | # during INIT phase |
f7facd7b |
39 | $MRO{$class} = undef unless exists $MRO{$class}; |
95bebf8c |
40 | } |
41 | |
d401eda1 |
42 | ## initializers |
43 | |
44 | # NOTE: |
45 | # this will not run under the following |
46 | # conditions: |
47 | # - mod_perl |
48 | # - require Class::C3; |
49 | # - eval "use Class::C3" |
50 | # in all those cases, you need to call |
51 | # the initialize() function manually |
52 | INIT { initialize() } |
53 | |
54 | sub initialize { |
55 | # why bother if we don't have anything ... |
56 | return unless keys %MRO; |
57 | _calculate_method_dispatch_tables(); |
58 | _apply_method_dispatch_tables(); |
5d5c86d9 |
59 | %next::METHOD_CACHE = (); |
d401eda1 |
60 | } |
61 | |
d0e2efe5 |
62 | sub uninitialize { |
63 | # why bother if we don't have anything ... |
64 | return unless keys %MRO; |
65 | _remove_method_dispatch_tables(); |
5d5c86d9 |
66 | %next::METHOD_CACHE = (); |
d0e2efe5 |
67 | } |
68 | |
69 | sub reinitialize { |
70 | uninitialize(); |
71 | # clean up the %MRO before we re-initialize |
72 | $MRO{$_} = undef foreach keys %MRO; |
73 | initialize(); |
74 | } |
75 | |
d401eda1 |
76 | ## functions for applying C3 to classes |
77 | |
78 | sub _calculate_method_dispatch_tables { |
95bebf8c |
79 | foreach my $class (keys %MRO) { |
d401eda1 |
80 | _calculate_method_dispatch_table($class); |
95bebf8c |
81 | } |
d401eda1 |
82 | } |
83 | |
84 | sub _calculate_method_dispatch_table { |
85 | my $class = shift; |
86 | no strict 'refs'; |
87 | my @MRO = calculateMRO($class); |
88 | $MRO{$class} = { MRO => \@MRO }; |
680100b1 |
89 | my $has_overload_fallback = 0; |
d401eda1 |
90 | my %methods; |
91 | # NOTE: |
92 | # we do @MRO[1 .. $#MRO] here because it |
93 | # makes no sense to interogate the class |
94 | # which you are calculating for. |
95 | foreach my $local (@MRO[1 .. $#MRO]) { |
680100b1 |
96 | # if overload has tagged this module to |
97 | # have use "fallback", then we want to |
98 | # grab that value |
99 | $has_overload_fallback = ${"${local}::()"} |
100 | if defined ${"${local}::()"}; |
d401eda1 |
101 | foreach my $method (grep { defined &{"${local}::$_"} } keys %{"${local}::"}) { |
102 | # skip if already overriden in local class |
103 | next unless !defined *{"${class}::$method"}{CODE}; |
104 | $methods{$method} = { |
105 | orig => "${local}::$method", |
106 | code => \&{"${local}::$method"} |
107 | } unless exists $methods{$method}; |
95bebf8c |
108 | } |
d401eda1 |
109 | } |
110 | # now stash them in our %MRO table |
680100b1 |
111 | $MRO{$class}->{methods} = \%methods; |
112 | $MRO{$class}->{has_overload_fallback} = $has_overload_fallback; |
d401eda1 |
113 | } |
114 | |
115 | sub _apply_method_dispatch_tables { |
116 | foreach my $class (keys %MRO) { |
117 | _apply_method_dispatch_table($class); |
118 | } |
95bebf8c |
119 | } |
120 | |
d401eda1 |
121 | sub _apply_method_dispatch_table { |
122 | my $class = shift; |
123 | no strict 'refs'; |
680100b1 |
124 | ${"${class}::()"} = $MRO{$class}->{has_overload_fallback} |
125 | if $MRO{$class}->{has_overload_fallback}; |
d401eda1 |
126 | foreach my $method (keys %{$MRO{$class}->{methods}}) { |
127 | *{"${class}::$method"} = $MRO{$class}->{methods}->{$method}->{code}; |
128 | } |
129 | } |
130 | |
d0e2efe5 |
131 | sub _remove_method_dispatch_tables { |
132 | foreach my $class (keys %MRO) { |
133 | _remove_method_dispatch_table($class); |
134 | } |
135 | } |
136 | |
137 | sub _remove_method_dispatch_table { |
138 | my $class = shift; |
139 | no strict 'refs'; |
680100b1 |
140 | delete ${"${class}::"}{"()"} if $MRO{$class}->{has_overload_fallback}; |
d0e2efe5 |
141 | foreach my $method (keys %{$MRO{$class}->{methods}}) { |
494799c3 |
142 | ${"${class}::"}{$method}{CODE} = undef |
143 | if defined ${"${class}::"}{$method}{CODE} && |
144 | ${"${class}::"}{$method}{CODE} eq $MRO{$class}->{methods}->{$method}->{code}; |
d0e2efe5 |
145 | } |
146 | } |
147 | |
d401eda1 |
148 | ## functions for calculating C3 MRO |
149 | |
150 | # this function is a perl-port of the |
151 | # python code on this page: |
152 | # http://www.python.org/2.3/mro.html |
95bebf8c |
153 | sub _merge { |
154 | my (@seqs) = @_; |
4e47d2a4 |
155 | my $class_being_merged = $seqs[0]->[0]; |
95bebf8c |
156 | my @res; |
157 | while (1) { |
158 | # remove all empty seqences |
159 | my @nonemptyseqs = (map { (@{$_} ? $_ : ()) } @seqs); |
160 | # return the list if we have no more no-empty sequences |
161 | return @res if not @nonemptyseqs; |
4e47d2a4 |
162 | my $reject; |
95bebf8c |
163 | my $cand; # a canidate .. |
164 | foreach my $seq (@nonemptyseqs) { |
165 | $cand = $seq->[0]; # get the head of the list |
166 | my $nothead; |
167 | foreach my $sub_seq (@nonemptyseqs) { |
168 | # XXX - this is instead of the python "in" |
169 | my %in_tail = (map { $_ => 1 } @{$sub_seq}[ 1 .. $#{$sub_seq} ]); |
170 | # NOTE: |
171 | # jump out as soon as we find one matching |
172 | # there is no reason not too. However, if |
173 | # we find one, then just remove the '&& last' |
ac6b0914 |
174 | ++$nothead && last if exists $in_tail{$cand}; |
95bebf8c |
175 | } |
176 | last unless $nothead; # leave the loop with our canidate ... |
4e47d2a4 |
177 | $reject = $cand; |
95bebf8c |
178 | $cand = undef; # otherwise, reject it ... |
179 | } |
4e47d2a4 |
180 | die "Inconsistent hierarchy found while merging '$class_being_merged':\n\t" . |
181 | "current merge results [\n\t\t" . (join ",\n\t\t" => @res) . "\n\t]\n\t" . |
182 | "mergeing failed on '$reject'\n" if not $cand; |
95bebf8c |
183 | push @res => $cand; |
184 | # now loop through our non-empties and pop |
185 | # off the head if it matches our canidate |
186 | foreach my $seq (@nonemptyseqs) { |
187 | shift @{$seq} if $seq->[0] eq $cand; |
188 | } |
189 | } |
190 | } |
191 | |
192 | sub calculateMRO { |
193 | my ($class) = @_; |
194 | no strict 'refs'; |
195 | return _merge( |
196 | [ $class ], # the class we are linearizing |
197 | (map { [ calculateMRO($_) ] } @{"${class}::ISA"}), # the MRO of all the superclasses |
198 | [ @{"${class}::ISA"} ] # a list of all the superclasses |
199 | ); |
200 | } |
201 | |
5d5c86d9 |
202 | package # hide me from PAUSE |
203 | next; |
204 | |
205 | use strict; |
206 | use warnings; |
207 | |
208 | use Scalar::Util 'blessed'; |
209 | |
ac6b0914 |
210 | our $VERSION = '0.05'; |
5d5c86d9 |
211 | |
212 | our %METHOD_CACHE; |
213 | |
214 | sub method { |
ac6b0914 |
215 | my $level = 1; |
216 | my $method_caller; |
217 | while ($method_caller = (caller($level++))[3]) { |
218 | last unless $method_caller eq '(eval)'; |
219 | } |
220 | my @label = (split '::', $method_caller); |
494799c3 |
221 | #my @label = (split '::', (caller(1))[3]); |
5d5c86d9 |
222 | my $label = pop @label; |
223 | my $caller = join '::' => @label; |
224 | my $self = $_[0]; |
225 | my $class = blessed($self) || $self; |
226 | |
227 | goto &{ $METHOD_CACHE{"$class|$caller|$label"} ||= do { |
228 | |
229 | my @MRO = Class::C3::calculateMRO($class); |
230 | |
231 | my $current; |
232 | while ($current = shift @MRO) { |
233 | last if $caller eq $current; |
234 | } |
235 | |
236 | no strict 'refs'; |
237 | my $found; |
238 | foreach my $class (@MRO) { |
f7facd7b |
239 | next if (defined $Class::C3::MRO{$class} && |
240 | defined $Class::C3::MRO{$class}{methods}{$label}); |
5d5c86d9 |
241 | last if (defined ($found = *{$class . '::' . $label}{CODE})); |
242 | } |
243 | |
244 | die "No next::method '$label' found for $self" unless $found; |
245 | |
246 | $found; |
247 | } }; |
248 | } |
249 | |
95bebf8c |
250 | 1; |
251 | |
252 | __END__ |
253 | |
254 | =pod |
255 | |
256 | =head1 NAME |
257 | |
258 | Class::C3 - A pragma to use the C3 method resolution order algortihm |
259 | |
260 | =head1 SYNOPSIS |
261 | |
262 | package A; |
263 | use Class::C3; |
264 | sub hello { 'A::hello' } |
265 | |
266 | package B; |
267 | use base 'A'; |
268 | use Class::C3; |
269 | |
270 | package C; |
271 | use base 'A'; |
272 | use Class::C3; |
273 | |
274 | sub hello { 'C::hello' } |
275 | |
276 | package D; |
277 | use base ('B', 'C'); |
278 | use Class::C3; |
279 | |
280 | # Classic Diamond MI pattern |
d401eda1 |
281 | # <A> |
282 | # / \ |
283 | # <B> <C> |
284 | # \ / |
285 | # <D> |
95bebf8c |
286 | |
287 | package main; |
288 | |
289 | print join ', ' => Class::C3::calculateMRO('Diamond_D') # prints D, B, C, A |
290 | |
291 | print D->hello() # prints 'C::hello' instead of the standard p5 'A::hello' |
292 | |
293 | D->can('hello')->(); # can() also works correctly |
294 | UNIVERSAL::can('D', 'hello'); # as does UNIVERSAL::can() |
295 | |
296 | =head1 DESCRIPTION |
297 | |
298 | This is currently an experimental pragma to change Perl 5's standard method resolution order |
299 | from depth-first left-to-right (a.k.a - pre-order) to the more sophisticated C3 method resolution |
300 | order. |
301 | |
302 | =head2 What is C3? |
303 | |
304 | C3 is the name of an algorithm which aims to provide a sane method resolution order under multiple |
305 | inheritence. It was first introduced in the langauge Dylan (see links in the L<SEE ALSO> section), |
306 | and then later adopted as the prefered MRO (Method Resolution Order) for the new-style classes in |
307 | Python 2.3. Most recently it has been adopted as the 'canonical' MRO for Perl 6 classes, and the |
308 | default MRO for Parrot objects as well. |
309 | |
310 | =head2 How does C3 work. |
311 | |
312 | C3 works by always preserving local precendence ordering. This essentially means that no class will |
313 | appear before any of it's subclasses. Take the classic diamond inheritence pattern for instance: |
314 | |
d401eda1 |
315 | <A> |
316 | / \ |
317 | <B> <C> |
318 | \ / |
319 | <D> |
95bebf8c |
320 | |
321 | The standard Perl 5 MRO would be (D, B, A, C). The result being that B<A> appears before B<C>, even |
322 | though B<C> is the subclass of B<A>. The C3 MRO algorithm however, produces the following MRO |
323 | (D, B, C, A), which does not have this same issue. |
324 | |
325 | This example is fairly trival, for more complex examples and a deeper explaination, see the links in |
326 | the L<SEE ALSO> section. |
327 | |
328 | =head2 How does this module work? |
329 | |
330 | This module uses a technique similar to Perl 5's method caching. During the INIT phase, this module |
331 | calculates the MRO of all the classes which called C<use Class::C3>. It then gathers information from |
332 | the symbol tables of each of those classes, and builds a set of method aliases for the correct |
333 | dispatch ordering. Once all these C3-based method tables are created, it then adds the method aliases |
334 | into the local classes symbol table. |
335 | |
336 | The end result is actually classes with pre-cached method dispatch. However, this caching does not |
337 | do well if you start changing your C<@ISA> or messing with class symbol tables, so you should consider |
338 | your classes to be effectively closed. See the L<CAVEATS> section for more details. |
339 | |
d401eda1 |
340 | =head1 OPTIONAL LOWERCASE PRAGMA |
341 | |
342 | This release also includes an optional module B<c3> in the F<opt/> folder. I did not include this in |
343 | the regular install since lowercase module names are considered I<"bad"> by some people. However I |
344 | think that code looks much nicer like this: |
345 | |
346 | package MyClass; |
347 | use c3; |
348 | |
349 | The the more clunky: |
350 | |
351 | package MyClass; |
352 | use Class::C3; |
353 | |
354 | But hey, it's your choice, thats why it is optional. |
355 | |
95bebf8c |
356 | =head1 FUNCTIONS |
357 | |
358 | =over 4 |
359 | |
360 | =item B<calculateMRO ($class)> |
361 | |
362 | Given a C<$class> this will return an array of class names in the proper C3 method resolution order. |
363 | |
d401eda1 |
364 | =item B<initialize> |
365 | |
366 | This can be used to initalize the C3 method dispatch tables. You need to call this if you are running |
367 | under mod_perl, or in any other environment which does not run the INIT phase of the perl compiler. |
368 | |
369 | NOTE: |
d0e2efe5 |
370 | This can B<not> be used to re-load the dispatch tables for all classes. Use C<reinitialize> for that. |
371 | |
372 | =item B<uninitialize> |
373 | |
374 | Calling this function results in the removal of all cached methods, and the restoration of the old Perl 5 |
375 | style dispatch order (depth-first, left-to-right). |
376 | |
377 | =item B<reinitialize> |
378 | |
379 | This effectively calls C<uninitialize> followed by C<initialize> the result of which is a reloading of |
380 | B<all> the calculated C3 dispatch tables. |
381 | |
382 | It should be noted that if you have a large class library, this could potentially be a rather costly |
383 | operation. |
d401eda1 |
384 | |
95bebf8c |
385 | =back |
386 | |
5d5c86d9 |
387 | =head1 METHOD REDISPATCHING |
388 | |
389 | It is always useful to be able to re-dispatch your method call to the "next most applicable method". This |
390 | module provides a pseudo package along the lines of C<SUPER::> or C<NEXT::> which will re-dispatch the |
391 | method along the C3 linearization. This is best show with an examples. |
392 | |
393 | # a classic diamond MI pattern ... |
394 | <A> |
395 | / \ |
396 | <B> <C> |
397 | \ / |
398 | <D> |
399 | |
400 | package A; |
401 | use c3; |
402 | sub foo { 'A::foo' } |
403 | |
404 | package B; |
405 | use base 'A'; |
406 | use c3; |
407 | sub foo { 'B::foo => ' . (shift)->next::method() } |
408 | |
409 | package B; |
410 | use base 'A'; |
411 | use c3; |
412 | sub foo { 'C::foo => ' . (shift)->next::method() } |
413 | |
414 | package D; |
415 | use base ('B', 'C'); |
416 | use c3; |
417 | sub foo { 'D::foo => ' . (shift)->next::method() } |
418 | |
419 | print D->foo; # prints out "D::foo => B::foo => C::foo => A::foo" |
420 | |
421 | A few things to note. First, we do not require you to add on the method name to the C<next::method> |
422 | call (this is unlike C<NEXT::> and C<SUPER::> which do require that). This helps to enforce the rule |
423 | that you cannot dispatch to a method of a different name (this is how C<NEXT::> behaves as well). |
424 | |
425 | The next thing to keep in mind is that you will need to pass all arguments to C<next::method> it can |
426 | not automatically use the current C<@_>. |
427 | |
95bebf8c |
428 | =head1 CAVEATS |
429 | |
430 | Let me first say, this is an experimental module, and so it should not be used for anything other |
431 | then other experimentation for the time being. |
432 | |
433 | That said, it is the authors intention to make this into a completely usable and production stable |
434 | module if possible. Time will tell. |
435 | |
436 | And now, onto the caveats. |
437 | |
438 | =over 4 |
439 | |
440 | =item Use of C<SUPER::>. |
441 | |
442 | The idea of C<SUPER::> under multiple inheritence is ambigious, and generally not recomended anyway. |
443 | However, it's use in conjuntion with this module is very much not recommended, and in fact very |
5d5c86d9 |
444 | discouraged. The recommended approach is to instead use the supplied C<next::method> feature, see |
445 | more details on it's usage above. |
95bebf8c |
446 | |
447 | =item Changing C<@ISA>. |
448 | |
449 | It is the author's opinion that changing C<@ISA> at runtime is pure insanity anyway. However, people |
450 | do it, so I must caveat. Any changes to the C<@ISA> will not be reflected in the MRO calculated by this |
d0e2efe5 |
451 | module, and therefor probably won't even show up. If you do this, you will need to call C<reinitialize> |
452 | in order to recalulate B<all> method dispatch tables. See the C<reinitialize> documentation and an example |
453 | in F<t/20_reinitialize.t> for more information. |
95bebf8c |
454 | |
455 | =item Adding/deleting methods from class symbol tables. |
456 | |
457 | This module calculates the MRO for each requested class during the INIT phase by interogatting the symbol |
458 | tables of said classes. So any symbol table manipulation which takes place after our INIT phase is run will |
d0e2efe5 |
459 | not be reflected in the calculated MRO. Just as with changing the C<@ISA>, you will need to call |
460 | C<reinitialize> for any changes you make to take effect. |
95bebf8c |
461 | |
95bebf8c |
462 | =back |
463 | |
15eeb546 |
464 | =head1 TODO |
465 | |
466 | =over 4 |
467 | |
468 | =item More tests |
469 | |
470 | You can never have enough tests :) |
471 | |
5d5c86d9 |
472 | =back |
15eeb546 |
473 | |
5d5c86d9 |
474 | =head1 CODE COVERAGE |
15eeb546 |
475 | |
ac6b0914 |
476 | I use B<Devel::Cover> to test the code coverage of my tests, below is the B<Devel::Cover> report on this |
477 | module's test suite. |
5d5c86d9 |
478 | |
479 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
480 | File stmt bran cond sub pod time total |
481 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
ac6b0914 |
482 | Class/C3.pm 98.6 88.6 75.0 96.0 100.0 70.4 95.2 |
5d5c86d9 |
483 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
ac6b0914 |
484 | Total 98.6 88.6 75.0 96.0 100.0 70.4 95.2 |
5d5c86d9 |
485 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
15eeb546 |
486 | |
95bebf8c |
487 | =head1 SEE ALSO |
488 | |
489 | =head2 The original Dylan paper |
490 | |
491 | =over 4 |
492 | |
493 | =item L<http://www.webcom.com/haahr/dylan/linearization-oopsla96.html> |
494 | |
495 | =back |
496 | |
497 | =head2 The prototype Perl 6 Object Model uses C3 |
498 | |
499 | =over 4 |
500 | |
501 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel/> |
502 | |
503 | =back |
504 | |
505 | =head2 Parrot now uses C3 |
506 | |
507 | =over 4 |
508 | |
509 | =item L<http://aspn.activestate.com/ASPN/Mail/Message/perl6-internals/2746631> |
510 | |
511 | =item L<http://use.perl.org/~autrijus/journal/25768> |
512 | |
513 | =back |
514 | |
515 | =head2 Python 2.3 MRO related links |
516 | |
517 | =over 4 |
518 | |
519 | =item L<http://www.python.org/2.3/mro.html> |
520 | |
521 | =item L<http://www.python.org/2.2.2/descrintro.html#mro> |
522 | |
523 | =back |
524 | |
525 | =head2 C3 for TinyCLOS |
526 | |
527 | =over 4 |
528 | |
529 | =item L<http://www.call-with-current-continuation.org/eggs/c3.html> |
530 | |
531 | =back |
532 | |
533 | =head1 AUTHOR |
534 | |
d401eda1 |
535 | Stevan Little, E<lt>stevan@iinteractive.comE<gt> |
95bebf8c |
536 | |
537 | =head1 COPYRIGHT AND LICENSE |
538 | |
539 | Copyright 2005 by Infinity Interactive, Inc. |
540 | |
541 | L<http://www.iinteractive.com> |
542 | |
543 | This library is free software; you can redistribute it and/or modify |
544 | it under the same terms as Perl itself. |
545 | |
546 | =cut |