Commit | Line | Data |
95bebf8c |
1 | |
2 | package Class::C3; |
3 | |
4 | use strict; |
5 | use warnings; |
6 | |
95bebf8c |
7 | use Scalar::Util 'blessed'; |
2ffffc6d |
8 | use Algorithm::C3; |
95bebf8c |
9 | |
5f01eb5f |
10 | our $VERSION = '0.12'; |
d401eda1 |
11 | |
12 | # this is our global stash of both |
13 | # MRO's and method dispatch tables |
14 | # the structure basically looks like |
15 | # this: |
16 | # |
17 | # $MRO{$class} = { |
18 | # MRO => [ <class precendence list> ], |
19 | # methods => { |
20 | # orig => <original location of method>, |
21 | # code => \&<ref to original method> |
680100b1 |
22 | # }, |
23 | # has_overload_fallback => (1 | 0) |
d401eda1 |
24 | # } |
25 | # |
f7facd7b |
26 | our %MRO; |
95bebf8c |
27 | |
d0e2efe5 |
28 | # use these for debugging ... |
d401eda1 |
29 | sub _dump_MRO_table { %MRO } |
d401eda1 |
30 | our $TURN_OFF_C3 = 0; |
31 | |
95bebf8c |
32 | sub import { |
33 | my $class = caller(); |
d401eda1 |
34 | # skip if the caller is main:: |
35 | # since that is clearly not relevant |
95bebf8c |
36 | return if $class eq 'main'; |
d401eda1 |
37 | return if $TURN_OFF_C3; |
38 | # make a note to calculate $class |
39 | # during INIT phase |
f7facd7b |
40 | $MRO{$class} = undef unless exists $MRO{$class}; |
95bebf8c |
41 | } |
42 | |
d401eda1 |
43 | ## initializers |
44 | |
d401eda1 |
45 | sub initialize { |
46 | # why bother if we don't have anything ... |
47 | return unless keys %MRO; |
48 | _calculate_method_dispatch_tables(); |
49 | _apply_method_dispatch_tables(); |
5d5c86d9 |
50 | %next::METHOD_CACHE = (); |
d401eda1 |
51 | } |
52 | |
d0e2efe5 |
53 | sub uninitialize { |
54 | # why bother if we don't have anything ... |
55 | return unless keys %MRO; |
56 | _remove_method_dispatch_tables(); |
5d5c86d9 |
57 | %next::METHOD_CACHE = (); |
d0e2efe5 |
58 | } |
59 | |
60 | sub reinitialize { |
61 | uninitialize(); |
62 | # clean up the %MRO before we re-initialize |
63 | $MRO{$_} = undef foreach keys %MRO; |
64 | initialize(); |
65 | } |
66 | |
d401eda1 |
67 | ## functions for applying C3 to classes |
68 | |
69 | sub _calculate_method_dispatch_tables { |
95bebf8c |
70 | foreach my $class (keys %MRO) { |
d401eda1 |
71 | _calculate_method_dispatch_table($class); |
95bebf8c |
72 | } |
d401eda1 |
73 | } |
74 | |
75 | sub _calculate_method_dispatch_table { |
76 | my $class = shift; |
77 | no strict 'refs'; |
78 | my @MRO = calculateMRO($class); |
79 | $MRO{$class} = { MRO => \@MRO }; |
680100b1 |
80 | my $has_overload_fallback = 0; |
d401eda1 |
81 | my %methods; |
82 | # NOTE: |
83 | # we do @MRO[1 .. $#MRO] here because it |
84 | # makes no sense to interogate the class |
85 | # which you are calculating for. |
86 | foreach my $local (@MRO[1 .. $#MRO]) { |
680100b1 |
87 | # if overload has tagged this module to |
88 | # have use "fallback", then we want to |
89 | # grab that value |
90 | $has_overload_fallback = ${"${local}::()"} |
91 | if defined ${"${local}::()"}; |
d401eda1 |
92 | foreach my $method (grep { defined &{"${local}::$_"} } keys %{"${local}::"}) { |
93 | # skip if already overriden in local class |
94 | next unless !defined *{"${class}::$method"}{CODE}; |
95 | $methods{$method} = { |
96 | orig => "${local}::$method", |
97 | code => \&{"${local}::$method"} |
98 | } unless exists $methods{$method}; |
95bebf8c |
99 | } |
d401eda1 |
100 | } |
101 | # now stash them in our %MRO table |
680100b1 |
102 | $MRO{$class}->{methods} = \%methods; |
103 | $MRO{$class}->{has_overload_fallback} = $has_overload_fallback; |
d401eda1 |
104 | } |
105 | |
106 | sub _apply_method_dispatch_tables { |
107 | foreach my $class (keys %MRO) { |
108 | _apply_method_dispatch_table($class); |
109 | } |
95bebf8c |
110 | } |
111 | |
d401eda1 |
112 | sub _apply_method_dispatch_table { |
113 | my $class = shift; |
114 | no strict 'refs'; |
680100b1 |
115 | ${"${class}::()"} = $MRO{$class}->{has_overload_fallback} |
116 | if $MRO{$class}->{has_overload_fallback}; |
d401eda1 |
117 | foreach my $method (keys %{$MRO{$class}->{methods}}) { |
118 | *{"${class}::$method"} = $MRO{$class}->{methods}->{$method}->{code}; |
119 | } |
120 | } |
121 | |
d0e2efe5 |
122 | sub _remove_method_dispatch_tables { |
123 | foreach my $class (keys %MRO) { |
124 | _remove_method_dispatch_table($class); |
125 | } |
126 | } |
127 | |
128 | sub _remove_method_dispatch_table { |
129 | my $class = shift; |
130 | no strict 'refs'; |
680100b1 |
131 | delete ${"${class}::"}{"()"} if $MRO{$class}->{has_overload_fallback}; |
d0e2efe5 |
132 | foreach my $method (keys %{$MRO{$class}->{methods}}) { |
5dd9299c |
133 | delete ${"${class}::"}{$method} |
134 | if defined *{"${class}::${method}"}{CODE} && |
135 | (*{"${class}::${method}"}{CODE} eq $MRO{$class}->{methods}->{$method}->{code}); |
d0e2efe5 |
136 | } |
137 | } |
138 | |
d401eda1 |
139 | ## functions for calculating C3 MRO |
140 | |
95bebf8c |
141 | sub calculateMRO { |
142 | my ($class) = @_; |
2ffffc6d |
143 | return Algorithm::C3::merge($class, sub { |
144 | no strict 'refs'; |
145 | @{$_[0] . '::ISA'}; |
146 | }); |
95bebf8c |
147 | } |
148 | |
5d5c86d9 |
149 | package # hide me from PAUSE |
150 | next; |
151 | |
152 | use strict; |
153 | use warnings; |
154 | |
155 | use Scalar::Util 'blessed'; |
156 | |
ac6b0914 |
157 | our $VERSION = '0.05'; |
5d5c86d9 |
158 | |
159 | our %METHOD_CACHE; |
160 | |
fa91a1c7 |
161 | sub method { |
162 | my $indirect = caller() =~ /^(?:next|maybe::next)$/; |
163 | my $level = $indirect ? 2 : 1; |
164 | |
7bb662d7 |
165 | my ($method_caller, $label, @label); |
ac6b0914 |
166 | while ($method_caller = (caller($level++))[3]) { |
7bb662d7 |
167 | @label = (split '::', $method_caller); |
168 | $label = pop @label; |
169 | last unless |
170 | $label eq '(eval)' || |
171 | $label eq '__ANON__'; |
ac6b0914 |
172 | } |
5d5c86d9 |
173 | my $caller = join '::' => @label; |
174 | my $self = $_[0]; |
175 | my $class = blessed($self) || $self; |
176 | |
fa91a1c7 |
177 | my $method = $METHOD_CACHE{"$class|$caller|$label"} ||= do { |
322a5920 |
178 | |
179 | my @MRO = Class::C3::calculateMRO($class); |
180 | |
181 | my $current; |
182 | while ($current = shift @MRO) { |
183 | last if $caller eq $current; |
184 | } |
185 | |
186 | no strict 'refs'; |
187 | my $found; |
188 | foreach my $class (@MRO) { |
189 | next if (defined $Class::C3::MRO{$class} && |
190 | defined $Class::C3::MRO{$class}{methods}{$label}); |
191 | last if (defined ($found = *{$class . '::' . $label}{CODE})); |
192 | } |
193 | |
322a5920 |
194 | $found; |
195 | }; |
fa91a1c7 |
196 | |
197 | return $method if $indirect; |
198 | |
199 | die "No next::method '$label' found for $self" if !$method; |
200 | |
201 | goto &{$method}; |
322a5920 |
202 | } |
5d5c86d9 |
203 | |
fa91a1c7 |
204 | sub can { method($_[0]) } |
5d5c86d9 |
205 | |
fa91a1c7 |
206 | package # hide me from PAUSE |
207 | maybe::next; |
208 | |
209 | use strict; |
210 | use warnings; |
211 | |
212 | our $VERSION = '0.01'; |
213 | |
214 | sub method { (next::method($_[0]) || return)->(@_) } |
5d5c86d9 |
215 | |
95bebf8c |
216 | 1; |
217 | |
218 | __END__ |
219 | |
220 | =pod |
221 | |
222 | =head1 NAME |
223 | |
224 | Class::C3 - A pragma to use the C3 method resolution order algortihm |
225 | |
226 | =head1 SYNOPSIS |
227 | |
228 | package A; |
229 | use Class::C3; |
230 | sub hello { 'A::hello' } |
231 | |
232 | package B; |
233 | use base 'A'; |
234 | use Class::C3; |
235 | |
236 | package C; |
237 | use base 'A'; |
238 | use Class::C3; |
239 | |
240 | sub hello { 'C::hello' } |
241 | |
242 | package D; |
243 | use base ('B', 'C'); |
244 | use Class::C3; |
245 | |
246 | # Classic Diamond MI pattern |
d401eda1 |
247 | # <A> |
248 | # / \ |
249 | # <B> <C> |
250 | # \ / |
251 | # <D> |
95bebf8c |
252 | |
253 | package main; |
2ffffc6d |
254 | |
255 | # initializez the C3 module |
256 | # (formerly called in INIT) |
257 | Class::C3::initialize(); |
95bebf8c |
258 | |
259 | print join ', ' => Class::C3::calculateMRO('Diamond_D') # prints D, B, C, A |
260 | |
261 | print D->hello() # prints 'C::hello' instead of the standard p5 'A::hello' |
262 | |
263 | D->can('hello')->(); # can() also works correctly |
264 | UNIVERSAL::can('D', 'hello'); # as does UNIVERSAL::can() |
265 | |
266 | =head1 DESCRIPTION |
267 | |
2ffffc6d |
268 | This is pragma to change Perl 5's standard method resolution order from depth-first left-to-right |
269 | (a.k.a - pre-order) to the more sophisticated C3 method resolution order. |
95bebf8c |
270 | |
271 | =head2 What is C3? |
272 | |
273 | C3 is the name of an algorithm which aims to provide a sane method resolution order under multiple |
274 | inheritence. It was first introduced in the langauge Dylan (see links in the L<SEE ALSO> section), |
275 | and then later adopted as the prefered MRO (Method Resolution Order) for the new-style classes in |
276 | Python 2.3. Most recently it has been adopted as the 'canonical' MRO for Perl 6 classes, and the |
277 | default MRO for Parrot objects as well. |
278 | |
279 | =head2 How does C3 work. |
280 | |
281 | C3 works by always preserving local precendence ordering. This essentially means that no class will |
282 | appear before any of it's subclasses. Take the classic diamond inheritence pattern for instance: |
283 | |
d401eda1 |
284 | <A> |
285 | / \ |
286 | <B> <C> |
287 | \ / |
288 | <D> |
95bebf8c |
289 | |
290 | The standard Perl 5 MRO would be (D, B, A, C). The result being that B<A> appears before B<C>, even |
291 | though B<C> is the subclass of B<A>. The C3 MRO algorithm however, produces the following MRO |
292 | (D, B, C, A), which does not have this same issue. |
293 | |
294 | This example is fairly trival, for more complex examples and a deeper explaination, see the links in |
295 | the L<SEE ALSO> section. |
296 | |
297 | =head2 How does this module work? |
298 | |
2ffffc6d |
299 | This module uses a technique similar to Perl 5's method caching. When C<Class::C3::initialize> is |
300 | called, this module calculates the MRO of all the classes which called C<use Class::C3>. It then |
301 | gathers information from the symbol tables of each of those classes, and builds a set of method |
302 | aliases for the correct dispatch ordering. Once all these C3-based method tables are created, it |
303 | then adds the method aliases into the local classes symbol table. |
95bebf8c |
304 | |
305 | The end result is actually classes with pre-cached method dispatch. However, this caching does not |
306 | do well if you start changing your C<@ISA> or messing with class symbol tables, so you should consider |
307 | your classes to be effectively closed. See the L<CAVEATS> section for more details. |
308 | |
d401eda1 |
309 | =head1 OPTIONAL LOWERCASE PRAGMA |
310 | |
311 | This release also includes an optional module B<c3> in the F<opt/> folder. I did not include this in |
312 | the regular install since lowercase module names are considered I<"bad"> by some people. However I |
313 | think that code looks much nicer like this: |
314 | |
315 | package MyClass; |
316 | use c3; |
317 | |
318 | The the more clunky: |
319 | |
320 | package MyClass; |
321 | use Class::C3; |
322 | |
323 | But hey, it's your choice, thats why it is optional. |
324 | |
95bebf8c |
325 | =head1 FUNCTIONS |
326 | |
327 | =over 4 |
328 | |
329 | =item B<calculateMRO ($class)> |
330 | |
331 | Given a C<$class> this will return an array of class names in the proper C3 method resolution order. |
332 | |
d401eda1 |
333 | =item B<initialize> |
334 | |
2ffffc6d |
335 | This B<must be called> to initalize the C3 method dispatch tables, this module B<will not work> if |
5f01eb5f |
336 | you do not do this. It is advised to do this as soon as possible B<after> loading any classes which |
337 | use C3. Here is a quick code example: |
338 | |
339 | package Foo; |
340 | use Class::C3; |
341 | # ... Foo methods here |
342 | |
343 | package Bar; |
344 | use Class::C3; |
345 | use base 'Foo'; |
346 | # ... Bar methods here |
347 | |
348 | package main; |
349 | |
350 | Class::C3::initialize(); # now it is safe to use Foo and Bar |
2ffffc6d |
351 | |
352 | This function used to be called automatically for you in the INIT phase of the perl compiler, but |
353 | that lead to warnings if this module was required at runtime. After discussion with my user base |
354 | (the L<DBIx::Class> folks), we decided that calling this in INIT was more of an annoyance than a |
355 | convience. I apologize to anyone this causes problems for (although i would very suprised if I had |
356 | any other users other than the L<DBIx::Class> folks). The simplest solution of course is to define |
357 | your own INIT method which calls this function. |
d401eda1 |
358 | |
359 | NOTE: |
d0e2efe5 |
360 | This can B<not> be used to re-load the dispatch tables for all classes. Use C<reinitialize> for that. |
361 | |
362 | =item B<uninitialize> |
363 | |
364 | Calling this function results in the removal of all cached methods, and the restoration of the old Perl 5 |
365 | style dispatch order (depth-first, left-to-right). |
366 | |
367 | =item B<reinitialize> |
368 | |
369 | This effectively calls C<uninitialize> followed by C<initialize> the result of which is a reloading of |
370 | B<all> the calculated C3 dispatch tables. |
371 | |
372 | It should be noted that if you have a large class library, this could potentially be a rather costly |
373 | operation. |
d401eda1 |
374 | |
95bebf8c |
375 | =back |
376 | |
5d5c86d9 |
377 | =head1 METHOD REDISPATCHING |
378 | |
379 | It is always useful to be able to re-dispatch your method call to the "next most applicable method". This |
380 | module provides a pseudo package along the lines of C<SUPER::> or C<NEXT::> which will re-dispatch the |
381 | method along the C3 linearization. This is best show with an examples. |
382 | |
383 | # a classic diamond MI pattern ... |
384 | <A> |
385 | / \ |
386 | <B> <C> |
387 | \ / |
388 | <D> |
389 | |
390 | package A; |
391 | use c3; |
392 | sub foo { 'A::foo' } |
393 | |
394 | package B; |
395 | use base 'A'; |
396 | use c3; |
397 | sub foo { 'B::foo => ' . (shift)->next::method() } |
398 | |
399 | package B; |
400 | use base 'A'; |
401 | use c3; |
402 | sub foo { 'C::foo => ' . (shift)->next::method() } |
403 | |
404 | package D; |
405 | use base ('B', 'C'); |
406 | use c3; |
407 | sub foo { 'D::foo => ' . (shift)->next::method() } |
408 | |
409 | print D->foo; # prints out "D::foo => B::foo => C::foo => A::foo" |
410 | |
411 | A few things to note. First, we do not require you to add on the method name to the C<next::method> |
412 | call (this is unlike C<NEXT::> and C<SUPER::> which do require that). This helps to enforce the rule |
413 | that you cannot dispatch to a method of a different name (this is how C<NEXT::> behaves as well). |
414 | |
415 | The next thing to keep in mind is that you will need to pass all arguments to C<next::method> it can |
416 | not automatically use the current C<@_>. |
417 | |
322a5920 |
418 | If C<next::method> cannot find a next method to re-dispatch the call to, it will throw an exception. |
419 | You can use C<next::can> to see if C<next::method> will succeed before you call it like so: |
420 | |
421 | $self->next::method(@_) if $self->next::can; |
422 | |
fa91a1c7 |
423 | Additionally, you can use C<maybe::next::method> as a shortcut to only call the next method if it exists. |
424 | The previous example could be simply written as: |
425 | |
426 | $self->maybe::next::method(@_); |
322a5920 |
427 | |
2ffffc6d |
428 | There are some caveats about using C<next::method>, see below for those. |
95bebf8c |
429 | |
2ffffc6d |
430 | =head1 CAVEATS |
95bebf8c |
431 | |
2ffffc6d |
432 | This module used to be labeled as I<experimental>, however it has now been pretty heavily tested by |
433 | the good folks over at L<DBIx::Class> and I am confident this module is perfectly usable for |
434 | whatever your needs might be. |
95bebf8c |
435 | |
2ffffc6d |
436 | But there are still caveats, so here goes ... |
95bebf8c |
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 | |
2ffffc6d |
457 | This module calculates the MRO for each requested class by interogatting the symbol tables of said classes. |
458 | So any symbol table manipulation which takes place after our INIT phase is run will not be reflected in |
459 | the calculated MRO. Just as with changing the C<@ISA>, you will need to call C<reinitialize> for any |
460 | changes you make to take effect. |
95bebf8c |
461 | |
2ffffc6d |
462 | =item Calling C<next::method> from methods defined outside the class |
95bebf8c |
463 | |
2ffffc6d |
464 | There is an edge case when using C<next::method> from within a subroutine which was created in a different |
465 | module than the one it is called from. It sounds complicated, but it really isn't. Here is an example which |
466 | will not work correctly: |
15eeb546 |
467 | |
2ffffc6d |
468 | *Foo::foo = sub { (shift)->next::method(@_) }; |
469 | |
470 | The problem exists because the anonymous subroutine being assigned to the glob C<*Foo::foo> will show up |
471 | in the call stack as being called C<__ANON__> and not C<foo> as you might expect. Since C<next::method> |
472 | uses C<caller> to find the name of the method it was called in, it will fail in this case. |
15eeb546 |
473 | |
2ffffc6d |
474 | But fear not, there is a simple solution. The module C<Sub::Name> will reach into the perl internals and |
475 | assign a name to an anonymous subroutine for you. Simply do this: |
476 | |
477 | use Sub::Name 'subname'; |
478 | *Foo::foo = subname 'Foo::foo' => sub { (shift)->next::method(@_) }; |
15eeb546 |
479 | |
2ffffc6d |
480 | and things will Just Work. Of course this is not always possible to do, but to be honest, I just can't |
481 | manage to find a workaround for it, so until someone gives me a working patch this will be a known |
482 | limitation of this module. |
15eeb546 |
483 | |
5d5c86d9 |
484 | =back |
15eeb546 |
485 | |
5d5c86d9 |
486 | =head1 CODE COVERAGE |
15eeb546 |
487 | |
ac6b0914 |
488 | I use B<Devel::Cover> to test the code coverage of my tests, below is the B<Devel::Cover> report on this |
489 | module's test suite. |
5d5c86d9 |
490 | |
491 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
492 | File stmt bran cond sub pod time total |
493 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
58f0eafe |
494 | Class/C3.pm 98.3 84.4 80.0 96.2 100.0 98.4 94.4 |
5d5c86d9 |
495 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
58f0eafe |
496 | Total 98.3 84.4 80.0 96.2 100.0 98.4 94.4 |
5d5c86d9 |
497 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
15eeb546 |
498 | |
95bebf8c |
499 | =head1 SEE ALSO |
500 | |
501 | =head2 The original Dylan paper |
502 | |
503 | =over 4 |
504 | |
505 | =item L<http://www.webcom.com/haahr/dylan/linearization-oopsla96.html> |
506 | |
507 | =back |
508 | |
509 | =head2 The prototype Perl 6 Object Model uses C3 |
510 | |
511 | =over 4 |
512 | |
513 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel/> |
514 | |
515 | =back |
516 | |
517 | =head2 Parrot now uses C3 |
518 | |
519 | =over 4 |
520 | |
521 | =item L<http://aspn.activestate.com/ASPN/Mail/Message/perl6-internals/2746631> |
522 | |
523 | =item L<http://use.perl.org/~autrijus/journal/25768> |
524 | |
525 | =back |
526 | |
527 | =head2 Python 2.3 MRO related links |
528 | |
529 | =over 4 |
530 | |
531 | =item L<http://www.python.org/2.3/mro.html> |
532 | |
533 | =item L<http://www.python.org/2.2.2/descrintro.html#mro> |
534 | |
535 | =back |
536 | |
537 | =head2 C3 for TinyCLOS |
538 | |
539 | =over 4 |
540 | |
541 | =item L<http://www.call-with-current-continuation.org/eggs/c3.html> |
542 | |
543 | =back |
544 | |
bad9dc59 |
545 | =head1 ACKNOWLEGEMENTS |
546 | |
547 | =over 4 |
548 | |
549 | =item Thanks to Matt S. Trout for using this module in his module L<DBIx::Class> |
550 | and finding many bugs and providing fixes. |
551 | |
552 | =item Thanks to Justin Guenther for making C<next::method> more robust by handling |
553 | calls inside C<eval> and anon-subs. |
554 | |
555 | =back |
556 | |
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557 | =head1 AUTHOR |
558 | |
d401eda1 |
559 | Stevan Little, E<lt>stevan@iinteractive.comE<gt> |
95bebf8c |
560 | |
561 | =head1 COPYRIGHT AND LICENSE |
562 | |
08c29211 |
563 | Copyright 2005, 2006 by Infinity Interactive, Inc. |
95bebf8c |
564 | |
565 | L<http://www.iinteractive.com> |
566 | |
567 | This library is free software; you can redistribute it and/or modify |
568 | it under the same terms as Perl itself. |
569 | |
570 | =cut |