Commit | Line | Data |
95bebf8c |
1 | |
2 | package Class::C3; |
3 | |
4 | use strict; |
5 | use warnings; |
6 | |
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7 | our $VERSION = '0.15_01'; |
8 | |
9 | # Class::C3 defines Class::C3::* in pure perl |
10 | # if mro, it does nothing else |
11 | # elsif Class::C3::XS, do nothing else |
12 | # else load next.pm |
13 | # Class::C3::XS defines the same routines as next.pm, |
14 | # and also redefines (suppress warning) calculateMRO |
15 | # (ditto for anything else in Class::C3::* we want to |
16 | # XS-ize). |
17 | |
18 | our $C3_IN_CORE; |
ecb0388d |
19 | |
20 | BEGIN { |
e86d671c |
21 | eval "require mro"; # XXX in the future, this should be a version check |
ecb0388d |
22 | if($@) { |
e86d671c |
23 | die $@ if $@ !~ /locate/; |
24 | eval "require Class::C3::XS"; |
25 | if($@) { |
26 | die $@ if $@ !~ /locate/; |
27 | eval "require Algorithm::C3; require Class::C3::next"; |
28 | die $@ if $@; |
29 | } |
30 | } |
31 | else { |
32 | $C3_IN_CORE = 1; |
33 | } |
34 | } |
35 | |
36 | # this is our global stash of both |
37 | # MRO's and method dispatch tables |
38 | # the structure basically looks like |
39 | # this: |
40 | # |
41 | # $MRO{$class} = { |
42 | # MRO => [ <class precendence list> ], |
43 | # methods => { |
44 | # orig => <original location of method>, |
45 | # code => \&<ref to original method> |
46 | # }, |
47 | # has_overload_fallback => (1 | 0) |
48 | # } |
49 | # |
50 | our %MRO; |
51 | |
52 | # use these for debugging ... |
53 | sub _dump_MRO_table { %MRO } |
54 | our $TURN_OFF_C3 = 0; |
55 | |
56 | # state tracking for initialize()/uninitialize() |
57 | our $_initialized = 0; |
58 | |
59 | sub import { |
60 | my $class = caller(); |
61 | # skip if the caller is main:: |
62 | # since that is clearly not relevant |
63 | return if $class eq 'main'; |
64 | |
65 | return if $TURN_OFF_C3; |
66 | mro::set_mro($class, 'c3') if $C3_IN_CORE; |
67 | |
68 | # make a note to calculate $class |
69 | # during INIT phase |
70 | $MRO{$class} = undef unless exists $MRO{$class}; |
71 | } |
72 | |
73 | ## initializers |
74 | |
75 | sub initialize { |
76 | %next::METHOD_CACHE = (); |
77 | # why bother if we don't have anything ... |
78 | return unless keys %MRO; |
79 | if($C3_IN_CORE) { |
80 | mro::set_mro($_, 'c3') for keys %MRO; |
ac6b0914 |
81 | } |
e86d671c |
82 | else { |
83 | if($_initialized) { |
84 | uninitialize(); |
85 | $MRO{$_} = undef foreach keys %MRO; |
86 | } |
87 | _calculate_method_dispatch_tables(); |
88 | _apply_method_dispatch_tables(); |
89 | $_initialized = 1; |
90 | } |
91 | } |
92 | |
93 | sub uninitialize { |
94 | # why bother if we don't have anything ... |
95 | %next::METHOD_CACHE = (); |
96 | return unless keys %MRO; |
97 | if($C3_IN_CORE) { |
98 | mro::set_mro($_, 'dfs') for keys %MRO; |
99 | } |
100 | else { |
101 | _remove_method_dispatch_tables(); |
102 | $_initialized = 0; |
103 | } |
104 | } |
105 | |
106 | sub reinitialize { goto &initialize } |
107 | |
108 | ## functions for applying C3 to classes |
109 | |
110 | sub _calculate_method_dispatch_tables { |
111 | return if $C3_IN_CORE; |
112 | my %merge_cache; |
113 | foreach my $class (keys %MRO) { |
114 | _calculate_method_dispatch_table($class, \%merge_cache); |
115 | } |
116 | } |
117 | |
118 | sub _calculate_method_dispatch_table { |
119 | return if $C3_IN_CORE; |
120 | my ($class, $merge_cache) = @_; |
121 | no strict 'refs'; |
122 | my @MRO = calculateMRO($class, $merge_cache); |
123 | $MRO{$class} = { MRO => \@MRO }; |
124 | my $has_overload_fallback = 0; |
125 | my %methods; |
126 | # NOTE: |
127 | # we do @MRO[1 .. $#MRO] here because it |
128 | # makes no sense to interogate the class |
129 | # which you are calculating for. |
130 | foreach my $local (@MRO[1 .. $#MRO]) { |
131 | # if overload has tagged this module to |
132 | # have use "fallback", then we want to |
133 | # grab that value |
134 | $has_overload_fallback = ${"${local}::()"} |
135 | if defined ${"${local}::()"}; |
136 | foreach my $method (grep { defined &{"${local}::$_"} } keys %{"${local}::"}) { |
137 | # skip if already overriden in local class |
138 | next unless !defined *{"${class}::$method"}{CODE}; |
139 | $methods{$method} = { |
140 | orig => "${local}::$method", |
141 | code => \&{"${local}::$method"} |
142 | } unless exists $methods{$method}; |
143 | } |
144 | } |
145 | # now stash them in our %MRO table |
146 | $MRO{$class}->{methods} = \%methods; |
147 | $MRO{$class}->{has_overload_fallback} = $has_overload_fallback; |
148 | } |
149 | |
150 | sub _apply_method_dispatch_tables { |
151 | return if $C3_IN_CORE; |
152 | foreach my $class (keys %MRO) { |
153 | _apply_method_dispatch_table($class); |
154 | } |
155 | } |
156 | |
157 | sub _apply_method_dispatch_table { |
158 | return if $C3_IN_CORE; |
159 | my $class = shift; |
160 | no strict 'refs'; |
161 | ${"${class}::()"} = $MRO{$class}->{has_overload_fallback} |
162 | if $MRO{$class}->{has_overload_fallback}; |
163 | foreach my $method (keys %{$MRO{$class}->{methods}}) { |
164 | *{"${class}::$method"} = $MRO{$class}->{methods}->{$method}->{code}; |
165 | } |
166 | } |
167 | |
168 | sub _remove_method_dispatch_tables { |
169 | return if $C3_IN_CORE; |
170 | foreach my $class (keys %MRO) { |
171 | _remove_method_dispatch_table($class); |
172 | } |
173 | } |
174 | |
175 | sub _remove_method_dispatch_table { |
176 | return if $C3_IN_CORE; |
177 | my $class = shift; |
178 | no strict 'refs'; |
179 | delete ${"${class}::"}{"()"} if $MRO{$class}->{has_overload_fallback}; |
180 | foreach my $method (keys %{$MRO{$class}->{methods}}) { |
181 | delete ${"${class}::"}{$method} |
182 | if defined *{"${class}::${method}"}{CODE} && |
183 | (*{"${class}::${method}"}{CODE} eq $MRO{$class}->{methods}->{$method}->{code}); |
184 | } |
185 | } |
186 | |
187 | sub calculateMRO { |
188 | my ($class, $merge_cache) = @_; |
189 | |
190 | return @{mro::get_linear_isa($class)} if $C3_IN_CORE; |
191 | |
192 | return Algorithm::C3::merge($class, sub { |
193 | no strict 'refs'; |
194 | @{$_[0] . '::ISA'}; |
195 | }, $merge_cache); |
322a5920 |
196 | } |
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197 | |
95bebf8c |
198 | 1; |
199 | |
200 | __END__ |
201 | |
202 | =pod |
203 | |
204 | =head1 NAME |
205 | |
206 | Class::C3 - A pragma to use the C3 method resolution order algortihm |
207 | |
208 | =head1 SYNOPSIS |
209 | |
210 | package A; |
211 | use Class::C3; |
212 | sub hello { 'A::hello' } |
213 | |
214 | package B; |
215 | use base 'A'; |
216 | use Class::C3; |
217 | |
218 | package C; |
219 | use base 'A'; |
220 | use Class::C3; |
221 | |
222 | sub hello { 'C::hello' } |
223 | |
224 | package D; |
225 | use base ('B', 'C'); |
226 | use Class::C3; |
227 | |
228 | # Classic Diamond MI pattern |
d401eda1 |
229 | # <A> |
230 | # / \ |
231 | # <B> <C> |
232 | # \ / |
233 | # <D> |
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234 | |
235 | package main; |
2ffffc6d |
236 | |
237 | # initializez the C3 module |
238 | # (formerly called in INIT) |
239 | Class::C3::initialize(); |
95bebf8c |
240 | |
241 | print join ', ' => Class::C3::calculateMRO('Diamond_D') # prints D, B, C, A |
242 | |
243 | print D->hello() # prints 'C::hello' instead of the standard p5 'A::hello' |
244 | |
245 | D->can('hello')->(); # can() also works correctly |
246 | UNIVERSAL::can('D', 'hello'); # as does UNIVERSAL::can() |
247 | |
248 | =head1 DESCRIPTION |
249 | |
2ffffc6d |
250 | This is pragma to change Perl 5's standard method resolution order from depth-first left-to-right |
251 | (a.k.a - pre-order) to the more sophisticated C3 method resolution order. |
95bebf8c |
252 | |
253 | =head2 What is C3? |
254 | |
255 | C3 is the name of an algorithm which aims to provide a sane method resolution order under multiple |
256 | inheritence. It was first introduced in the langauge Dylan (see links in the L<SEE ALSO> section), |
257 | and then later adopted as the prefered MRO (Method Resolution Order) for the new-style classes in |
258 | Python 2.3. Most recently it has been adopted as the 'canonical' MRO for Perl 6 classes, and the |
259 | default MRO for Parrot objects as well. |
260 | |
261 | =head2 How does C3 work. |
262 | |
263 | C3 works by always preserving local precendence ordering. This essentially means that no class will |
264 | appear before any of it's subclasses. Take the classic diamond inheritence pattern for instance: |
265 | |
d401eda1 |
266 | <A> |
267 | / \ |
268 | <B> <C> |
269 | \ / |
270 | <D> |
95bebf8c |
271 | |
272 | The standard Perl 5 MRO would be (D, B, A, C). The result being that B<A> appears before B<C>, even |
273 | though B<C> is the subclass of B<A>. The C3 MRO algorithm however, produces the following MRO |
274 | (D, B, C, A), which does not have this same issue. |
275 | |
276 | This example is fairly trival, for more complex examples and a deeper explaination, see the links in |
277 | the L<SEE ALSO> section. |
278 | |
279 | =head2 How does this module work? |
280 | |
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281 | This module uses a technique similar to Perl 5's method caching. When C<Class::C3::initialize> is |
282 | called, this module calculates the MRO of all the classes which called C<use Class::C3>. It then |
283 | gathers information from the symbol tables of each of those classes, and builds a set of method |
284 | aliases for the correct dispatch ordering. Once all these C3-based method tables are created, it |
285 | then adds the method aliases into the local classes symbol table. |
95bebf8c |
286 | |
287 | The end result is actually classes with pre-cached method dispatch. However, this caching does not |
288 | do well if you start changing your C<@ISA> or messing with class symbol tables, so you should consider |
289 | your classes to be effectively closed. See the L<CAVEATS> section for more details. |
290 | |
d401eda1 |
291 | =head1 OPTIONAL LOWERCASE PRAGMA |
292 | |
293 | This release also includes an optional module B<c3> in the F<opt/> folder. I did not include this in |
294 | the regular install since lowercase module names are considered I<"bad"> by some people. However I |
295 | think that code looks much nicer like this: |
296 | |
297 | package MyClass; |
298 | use c3; |
299 | |
300 | The the more clunky: |
301 | |
302 | package MyClass; |
303 | use Class::C3; |
304 | |
305 | But hey, it's your choice, thats why it is optional. |
306 | |
95bebf8c |
307 | =head1 FUNCTIONS |
308 | |
309 | =over 4 |
310 | |
311 | =item B<calculateMRO ($class)> |
312 | |
313 | Given a C<$class> this will return an array of class names in the proper C3 method resolution order. |
314 | |
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315 | =item B<initialize> |
316 | |
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317 | This B<must be called> to initalize the C3 method dispatch tables, this module B<will not work> if |
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318 | you do not do this. It is advised to do this as soon as possible B<after> loading any classes which |
319 | use C3. Here is a quick code example: |
320 | |
321 | package Foo; |
322 | use Class::C3; |
323 | # ... Foo methods here |
324 | |
325 | package Bar; |
326 | use Class::C3; |
327 | use base 'Foo'; |
328 | # ... Bar methods here |
329 | |
330 | package main; |
331 | |
332 | Class::C3::initialize(); # now it is safe to use Foo and Bar |
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333 | |
334 | This function used to be called automatically for you in the INIT phase of the perl compiler, but |
335 | that lead to warnings if this module was required at runtime. After discussion with my user base |
336 | (the L<DBIx::Class> folks), we decided that calling this in INIT was more of an annoyance than a |
337 | convience. I apologize to anyone this causes problems for (although i would very suprised if I had |
338 | any other users other than the L<DBIx::Class> folks). The simplest solution of course is to define |
339 | your own INIT method which calls this function. |
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340 | |
341 | NOTE: |
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342 | |
343 | If C<initialize> detects that C<initialize> has already been executed, it will L</uninitialize> and |
344 | clear the MRO cache first. |
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345 | |
346 | =item B<uninitialize> |
347 | |
348 | Calling this function results in the removal of all cached methods, and the restoration of the old Perl 5 |
349 | style dispatch order (depth-first, left-to-right). |
350 | |
351 | =item B<reinitialize> |
352 | |
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353 | This is an alias for L</initialize> above. |
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354 | |
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355 | =back |
356 | |
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357 | =head1 METHOD REDISPATCHING |
358 | |
359 | It is always useful to be able to re-dispatch your method call to the "next most applicable method". This |
360 | module provides a pseudo package along the lines of C<SUPER::> or C<NEXT::> which will re-dispatch the |
361 | method along the C3 linearization. This is best show with an examples. |
362 | |
363 | # a classic diamond MI pattern ... |
364 | <A> |
365 | / \ |
366 | <B> <C> |
367 | \ / |
368 | <D> |
369 | |
370 | package A; |
371 | use c3; |
372 | sub foo { 'A::foo' } |
373 | |
374 | package B; |
375 | use base 'A'; |
376 | use c3; |
377 | sub foo { 'B::foo => ' . (shift)->next::method() } |
378 | |
379 | package B; |
380 | use base 'A'; |
381 | use c3; |
382 | sub foo { 'C::foo => ' . (shift)->next::method() } |
383 | |
384 | package D; |
385 | use base ('B', 'C'); |
386 | use c3; |
387 | sub foo { 'D::foo => ' . (shift)->next::method() } |
388 | |
389 | print D->foo; # prints out "D::foo => B::foo => C::foo => A::foo" |
390 | |
391 | A few things to note. First, we do not require you to add on the method name to the C<next::method> |
392 | call (this is unlike C<NEXT::> and C<SUPER::> which do require that). This helps to enforce the rule |
393 | that you cannot dispatch to a method of a different name (this is how C<NEXT::> behaves as well). |
394 | |
395 | The next thing to keep in mind is that you will need to pass all arguments to C<next::method> it can |
396 | not automatically use the current C<@_>. |
397 | |
322a5920 |
398 | If C<next::method> cannot find a next method to re-dispatch the call to, it will throw an exception. |
399 | You can use C<next::can> to see if C<next::method> will succeed before you call it like so: |
400 | |
401 | $self->next::method(@_) if $self->next::can; |
402 | |
fa91a1c7 |
403 | Additionally, you can use C<maybe::next::method> as a shortcut to only call the next method if it exists. |
404 | The previous example could be simply written as: |
405 | |
406 | $self->maybe::next::method(@_); |
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407 | |
2ffffc6d |
408 | There are some caveats about using C<next::method>, see below for those. |
95bebf8c |
409 | |
2ffffc6d |
410 | =head1 CAVEATS |
95bebf8c |
411 | |
2ffffc6d |
412 | This module used to be labeled as I<experimental>, however it has now been pretty heavily tested by |
413 | the good folks over at L<DBIx::Class> and I am confident this module is perfectly usable for |
414 | whatever your needs might be. |
95bebf8c |
415 | |
2ffffc6d |
416 | But there are still caveats, so here goes ... |
95bebf8c |
417 | |
418 | =over 4 |
419 | |
420 | =item Use of C<SUPER::>. |
421 | |
422 | The idea of C<SUPER::> under multiple inheritence is ambigious, and generally not recomended anyway. |
423 | However, it's use in conjuntion with this module is very much not recommended, and in fact very |
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424 | discouraged. The recommended approach is to instead use the supplied C<next::method> feature, see |
425 | more details on it's usage above. |
95bebf8c |
426 | |
427 | =item Changing C<@ISA>. |
428 | |
429 | It is the author's opinion that changing C<@ISA> at runtime is pure insanity anyway. However, people |
430 | do it, so I must caveat. Any changes to the C<@ISA> will not be reflected in the MRO calculated by this |
d0e2efe5 |
431 | module, and therefor probably won't even show up. If you do this, you will need to call C<reinitialize> |
432 | in order to recalulate B<all> method dispatch tables. See the C<reinitialize> documentation and an example |
433 | in F<t/20_reinitialize.t> for more information. |
95bebf8c |
434 | |
435 | =item Adding/deleting methods from class symbol tables. |
436 | |
2ffffc6d |
437 | This module calculates the MRO for each requested class by interogatting the symbol tables of said classes. |
438 | So any symbol table manipulation which takes place after our INIT phase is run will not be reflected in |
439 | the calculated MRO. Just as with changing the C<@ISA>, you will need to call C<reinitialize> for any |
440 | changes you make to take effect. |
95bebf8c |
441 | |
2ffffc6d |
442 | =item Calling C<next::method> from methods defined outside the class |
95bebf8c |
443 | |
2ffffc6d |
444 | There is an edge case when using C<next::method> from within a subroutine which was created in a different |
445 | module than the one it is called from. It sounds complicated, but it really isn't. Here is an example which |
446 | will not work correctly: |
15eeb546 |
447 | |
2ffffc6d |
448 | *Foo::foo = sub { (shift)->next::method(@_) }; |
449 | |
450 | The problem exists because the anonymous subroutine being assigned to the glob C<*Foo::foo> will show up |
451 | in the call stack as being called C<__ANON__> and not C<foo> as you might expect. Since C<next::method> |
452 | uses C<caller> to find the name of the method it was called in, it will fail in this case. |
15eeb546 |
453 | |
2ffffc6d |
454 | But fear not, there is a simple solution. The module C<Sub::Name> will reach into the perl internals and |
455 | assign a name to an anonymous subroutine for you. Simply do this: |
456 | |
457 | use Sub::Name 'subname'; |
458 | *Foo::foo = subname 'Foo::foo' => sub { (shift)->next::method(@_) }; |
15eeb546 |
459 | |
2ffffc6d |
460 | and things will Just Work. Of course this is not always possible to do, but to be honest, I just can't |
461 | manage to find a workaround for it, so until someone gives me a working patch this will be a known |
462 | limitation of this module. |
15eeb546 |
463 | |
5d5c86d9 |
464 | =back |
15eeb546 |
465 | |
5d5c86d9 |
466 | =head1 CODE COVERAGE |
15eeb546 |
467 | |
ac6b0914 |
468 | I use B<Devel::Cover> to test the code coverage of my tests, below is the B<Devel::Cover> report on this |
469 | module's test suite. |
5d5c86d9 |
470 | |
471 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
472 | File stmt bran cond sub pod time total |
473 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
58f0eafe |
474 | Class/C3.pm 98.3 84.4 80.0 96.2 100.0 98.4 94.4 |
5d5c86d9 |
475 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
58f0eafe |
476 | Total 98.3 84.4 80.0 96.2 100.0 98.4 94.4 |
5d5c86d9 |
477 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
15eeb546 |
478 | |
95bebf8c |
479 | =head1 SEE ALSO |
480 | |
481 | =head2 The original Dylan paper |
482 | |
483 | =over 4 |
484 | |
485 | =item L<http://www.webcom.com/haahr/dylan/linearization-oopsla96.html> |
486 | |
487 | =back |
488 | |
489 | =head2 The prototype Perl 6 Object Model uses C3 |
490 | |
491 | =over 4 |
492 | |
493 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel/> |
494 | |
495 | =back |
496 | |
497 | =head2 Parrot now uses C3 |
498 | |
499 | =over 4 |
500 | |
501 | =item L<http://aspn.activestate.com/ASPN/Mail/Message/perl6-internals/2746631> |
502 | |
503 | =item L<http://use.perl.org/~autrijus/journal/25768> |
504 | |
505 | =back |
506 | |
507 | =head2 Python 2.3 MRO related links |
508 | |
509 | =over 4 |
510 | |
511 | =item L<http://www.python.org/2.3/mro.html> |
512 | |
513 | =item L<http://www.python.org/2.2.2/descrintro.html#mro> |
514 | |
515 | =back |
516 | |
517 | =head2 C3 for TinyCLOS |
518 | |
519 | =over 4 |
520 | |
521 | =item L<http://www.call-with-current-continuation.org/eggs/c3.html> |
522 | |
523 | =back |
524 | |
bad9dc59 |
525 | =head1 ACKNOWLEGEMENTS |
526 | |
527 | =over 4 |
528 | |
529 | =item Thanks to Matt S. Trout for using this module in his module L<DBIx::Class> |
530 | and finding many bugs and providing fixes. |
531 | |
532 | =item Thanks to Justin Guenther for making C<next::method> more robust by handling |
533 | calls inside C<eval> and anon-subs. |
534 | |
f480cda1 |
535 | =item Thanks to Robert Norris for adding support for C<next::can> and |
536 | C<maybe::next::method>. |
537 | |
bad9dc59 |
538 | =back |
539 | |
95bebf8c |
540 | =head1 AUTHOR |
541 | |
d401eda1 |
542 | Stevan Little, E<lt>stevan@iinteractive.comE<gt> |
95bebf8c |
543 | |
6262b4cf |
544 | Brandon L. Black, E<lt>blblack@gmail.comE<gt> |
545 | |
95bebf8c |
546 | =head1 COPYRIGHT AND LICENSE |
547 | |
08c29211 |
548 | Copyright 2005, 2006 by Infinity Interactive, Inc. |
95bebf8c |
549 | |
550 | L<http://www.iinteractive.com> |
551 | |
552 | This library is free software; you can redistribute it and/or modify |
553 | it under the same terms as Perl itself. |
554 | |
f4a893b2 |
555 | =cut |