Commit | Line | Data |
94b19069 |
1 | |
2 | package Class::MOP; |
3 | |
4 | use strict; |
5 | use warnings; |
6 | |
727919c5 |
7 | use Carp 'confess'; |
aa448b16 |
8 | use Scalar::Util (); |
8b978dd5 |
9 | |
2eb717d5 |
10 | use Class::MOP::Class; |
11 | use Class::MOP::Attribute; |
12 | use Class::MOP::Method; |
13 | |
857f87a7 |
14 | use Class::MOP::Class::Immutable; |
15 | |
1a09d9cc |
16 | our $VERSION = '0.31'; |
94b19069 |
17 | |
aa448b16 |
18 | ## ---------------------------------------------------------------------------- |
19 | ## Setting up our environment ... |
20 | ## ---------------------------------------------------------------------------- |
21 | ## Class::MOP needs to have a few things in the global perl environment so |
22 | ## that it can operate effectively. Those things are done here. |
23 | ## ---------------------------------------------------------------------------- |
24 | |
3bf7644b |
25 | # ... nothing yet actually ;) |
8b978dd5 |
26 | |
b51af7f9 |
27 | ## ---------------------------------------------------------------------------- |
28 | ## Bootstrapping |
29 | ## ---------------------------------------------------------------------------- |
30 | ## The code below here is to bootstrap our MOP with itself. This is also |
31 | ## sometimes called "tying the knot". By doing this, we make it much easier |
32 | ## to extend the MOP through subclassing and such since now you can use the |
33 | ## MOP itself to extend itself. |
34 | ## |
35 | ## Yes, I know, thats weird and insane, but it's a good thing, trust me :) |
36 | ## ---------------------------------------------------------------------------- |
727919c5 |
37 | |
38 | # We need to add in the meta-attributes here so that |
39 | # any subclass of Class::MOP::* will be able to |
40 | # inherit them using &construct_instance |
41 | |
6d5355c3 |
42 | ## Class::MOP::Package |
727919c5 |
43 | |
6d5355c3 |
44 | Class::MOP::Package->meta->add_attribute( |
351bd7d4 |
45 | Class::MOP::Attribute->new('$:package' => ( |
b880e0de |
46 | reader => { |
47 | # NOTE: we need to do this in order |
48 | # for the instance meta-object to |
49 | # not fall into meta-circular death |
50 | 'name' => sub { (shift)->{'$:package'} } |
51 | }, |
7b31baf4 |
52 | init_arg => ':package', |
727919c5 |
53 | )) |
54 | ); |
55 | |
a5e51f0b |
56 | Class::MOP::Package->meta->add_attribute( |
57 | Class::MOP::Attribute->new('%:namespace' => ( |
58 | reader => { |
59 | 'namespace' => sub { (shift)->{'%:namespace'} } |
60 | }, |
61 | default => sub { |
62 | my ($class) = @_; |
63 | no strict 'refs'; |
64 | return \%{$class->name . '::'}; |
65 | }, |
66 | # NOTE: |
67 | # protect this from silliness |
68 | init_arg => '............something no one will guess ...............', |
69 | )) |
70 | ); |
71 | |
9d6dce77 |
72 | # NOTE: |
73 | # use the metaclass to construct the meta-package |
74 | # which is a superclass of the metaclass itself :P |
75 | Class::MOP::Package->meta->add_method('initialize' => sub { |
76 | my $class = shift; |
77 | my $package_name = shift; |
78 | $class->meta->new_object(':package' => $package_name, @_); |
79 | }); |
80 | |
6d5355c3 |
81 | ## Class::MOP::Class |
82 | |
727919c5 |
83 | Class::MOP::Class->meta->add_attribute( |
351bd7d4 |
84 | Class::MOP::Attribute->new('%:attributes' => ( |
f7259199 |
85 | reader => { |
86 | # NOTE: we need to do this in order |
87 | # for the instance meta-object to |
88 | # not fall into meta-circular death |
89 | 'get_attribute_map' => sub { (shift)->{'%:attributes'} } |
90 | }, |
351bd7d4 |
91 | init_arg => ':attributes', |
727919c5 |
92 | default => sub { {} } |
93 | )) |
94 | ); |
95 | |
351bd7d4 |
96 | Class::MOP::Class->meta->add_attribute( |
97 | Class::MOP::Attribute->new('$:attribute_metaclass' => ( |
7b31baf4 |
98 | reader => 'attribute_metaclass', |
351bd7d4 |
99 | init_arg => ':attribute_metaclass', |
100 | default => 'Class::MOP::Attribute', |
101 | )) |
102 | ); |
103 | |
104 | Class::MOP::Class->meta->add_attribute( |
105 | Class::MOP::Attribute->new('$:method_metaclass' => ( |
7b31baf4 |
106 | reader => 'method_metaclass', |
351bd7d4 |
107 | init_arg => ':method_metaclass', |
108 | default => 'Class::MOP::Method', |
109 | )) |
110 | ); |
111 | |
2bab2be6 |
112 | Class::MOP::Class->meta->add_attribute( |
113 | Class::MOP::Attribute->new('$:instance_metaclass' => ( |
b880e0de |
114 | reader => { |
115 | # NOTE: we need to do this in order |
116 | # for the instance meta-object to |
117 | # not fall into meta-circular death |
118 | 'instance_metaclass' => sub { (shift)->{'$:instance_metaclass'} } |
119 | }, |
2bab2be6 |
120 | init_arg => ':instance_metaclass', |
121 | default => 'Class::MOP::Instance', |
122 | )) |
123 | ); |
124 | |
9d6dce77 |
125 | # NOTE: |
126 | # we don't actually need to tie the knot with |
127 | # Class::MOP::Class here, it is actually handled |
128 | # within Class::MOP::Class itself in the |
129 | # construct_class_instance method. |
130 | |
727919c5 |
131 | ## Class::MOP::Attribute |
132 | |
7b31baf4 |
133 | Class::MOP::Attribute->meta->add_attribute( |
134 | Class::MOP::Attribute->new('name' => ( |
b880e0de |
135 | reader => { |
136 | # NOTE: we need to do this in order |
137 | # for the instance meta-object to |
138 | # not fall into meta-circular death |
139 | 'name' => sub { (shift)->{name} } |
140 | } |
7b31baf4 |
141 | )) |
142 | ); |
143 | |
144 | Class::MOP::Attribute->meta->add_attribute( |
145 | Class::MOP::Attribute->new('associated_class' => ( |
b880e0de |
146 | reader => { |
147 | # NOTE: we need to do this in order |
148 | # for the instance meta-object to |
149 | # not fall into meta-circular death |
150 | 'associated_class' => sub { (shift)->{associated_class} } |
151 | } |
7b31baf4 |
152 | )) |
153 | ); |
154 | |
155 | Class::MOP::Attribute->meta->add_attribute( |
156 | Class::MOP::Attribute->new('accessor' => ( |
157 | reader => 'accessor', |
158 | predicate => 'has_accessor', |
159 | )) |
160 | ); |
161 | |
162 | Class::MOP::Attribute->meta->add_attribute( |
163 | Class::MOP::Attribute->new('reader' => ( |
164 | reader => 'reader', |
165 | predicate => 'has_reader', |
166 | )) |
167 | ); |
168 | |
169 | Class::MOP::Attribute->meta->add_attribute( |
170 | Class::MOP::Attribute->new('writer' => ( |
171 | reader => 'writer', |
172 | predicate => 'has_writer', |
173 | )) |
174 | ); |
175 | |
176 | Class::MOP::Attribute->meta->add_attribute( |
177 | Class::MOP::Attribute->new('predicate' => ( |
178 | reader => 'predicate', |
179 | predicate => 'has_predicate', |
180 | )) |
181 | ); |
182 | |
183 | Class::MOP::Attribute->meta->add_attribute( |
184 | Class::MOP::Attribute->new('init_arg' => ( |
185 | reader => 'init_arg', |
186 | predicate => 'has_init_arg', |
187 | )) |
188 | ); |
189 | |
190 | Class::MOP::Attribute->meta->add_attribute( |
191 | Class::MOP::Attribute->new('default' => ( |
192 | # default has a custom 'reader' method ... |
193 | predicate => 'has_default', |
194 | )) |
195 | ); |
196 | |
727919c5 |
197 | |
198 | # NOTE: (meta-circularity) |
199 | # This should be one of the last things done |
200 | # it will "tie the knot" with Class::MOP::Attribute |
201 | # so that it uses the attributes meta-objects |
202 | # to construct itself. |
203 | Class::MOP::Attribute->meta->add_method('new' => sub { |
204 | my $class = shift; |
205 | my $name = shift; |
206 | my %options = @_; |
207 | |
208 | (defined $name && $name) |
209 | || confess "You must provide a name for the attribute"; |
5659d76e |
210 | $options{init_arg} = $name |
211 | if not exists $options{init_arg}; |
651955fb |
212 | |
5659d76e |
213 | # return the new object |
214 | $class->meta->new_object(name => $name, %options); |
215 | }); |
216 | |
217 | Class::MOP::Attribute->meta->add_method('clone' => sub { |
a740253a |
218 | my $self = shift; |
a27ae83f |
219 | $self->meta->clone_object($self, @_); |
727919c5 |
220 | }); |
221 | |
4d47b77f |
222 | ## Try and close Class::MOP::* |
223 | |
224 | Class::MOP::Package ->meta->make_immutable(inline_constructor => 0); |
225 | Class::MOP::Module ->meta->make_immutable(inline_constructor => 0); |
226 | Class::MOP::Class ->meta->make_immutable(inline_constructor => 0); |
227 | Class::MOP::Attribute->meta->make_immutable(inline_constructor => 0); |
228 | Class::MOP::Method ->meta->make_immutable(inline_constructor => 0); |
229 | Class::MOP::Instance ->meta->make_immutable(inline_constructor => 0); |
230 | |
231 | |
94b19069 |
232 | 1; |
233 | |
234 | __END__ |
235 | |
236 | =pod |
237 | |
238 | =head1 NAME |
239 | |
240 | Class::MOP - A Meta Object Protocol for Perl 5 |
241 | |
242 | =head1 SYNOPSIS |
243 | |
a2e85e6c |
244 | # ... This will come later, for now see |
245 | # the other SYNOPSIS for more information |
94b19069 |
246 | |
247 | =head1 DESCRIPTON |
248 | |
249 | This module is an attempt to create a meta object protocol for the |
250 | Perl 5 object system. It makes no attempt to change the behavior or |
251 | characteristics of the Perl 5 object system, only to create a |
27e31eaf |
252 | protocol for its manipulation and introspection. |
94b19069 |
253 | |
254 | That said, it does attempt to create the tools for building a rich |
255 | set of extensions to the Perl 5 object system. Every attempt has been |
256 | made for these tools to keep to the spirit of the Perl 5 object |
257 | system that we all know and love. |
258 | |
40483095 |
259 | This documentation is admittedly sparse on details, as time permits |
260 | I will try to improve them. For now, I suggest looking at the items |
261 | listed in the L<SEE ALSO> section for more information. In particular |
262 | the book "The Art of the Meta Object Protocol" was very influential |
263 | in the development of this system. |
264 | |
bfe4d0fc |
265 | =head2 What is a Meta Object Protocol? |
266 | |
267 | A meta object protocol is an API to an object system. |
268 | |
269 | To be more specific, it is a set of abstractions of the components of |
270 | an object system (typically things like; classes, object, methods, |
271 | object attributes, etc.). These abstractions can then be used to both |
272 | inspect and manipulate the object system which they describe. |
273 | |
274 | It can be said that there are two MOPs for any object system; the |
275 | implicit MOP, and the explicit MOP. The implicit MOP handles things |
276 | like method dispatch or inheritance, which happen automatically as |
277 | part of how the object system works. The explicit MOP typically |
278 | handles the introspection/reflection features of the object system. |
279 | All object systems have implicit MOPs, without one, they would not |
280 | work. Explict MOPs however as less common, and depending on the |
281 | language can vary from restrictive (Reflection in Java or C#) to |
282 | wide open (CLOS is a perfect example). |
283 | |
e16da3e6 |
284 | =head2 Yet Another Class Builder!! Why? |
285 | |
286 | This is B<not> a class builder so much as it is a I<class builder |
287 | B<builder>>. My intent is that an end user does not use this module |
288 | directly, but instead this module is used by module authors to |
289 | build extensions and features onto the Perl 5 object system. |
290 | |
94b19069 |
291 | =head2 Who is this module for? |
292 | |
293 | This module is specifically for anyone who has ever created or |
294 | wanted to create a module for the Class:: namespace. The tools which |
295 | this module will provide will hopefully make it easier to do more |
296 | complex things with Perl 5 classes by removing such barriers as |
297 | the need to hack the symbol tables, or understand the fine details |
298 | of method dispatch. |
299 | |
bfe4d0fc |
300 | =head2 What changes do I have to make to use this module? |
301 | |
2eb717d5 |
302 | This module was designed to be as unintrusive as possible. Many of |
343203ee |
303 | its features are accessible without B<any> change to your existsing |
bfe4d0fc |
304 | code at all. It is meant to be a compliment to your existing code and |
2eb717d5 |
305 | not an intrusion on your code base. Unlike many other B<Class::> |
a2e85e6c |
306 | modules, this module B<does not> require you subclass it, or even that |
307 | you C<use> it in within your module's package. |
bfe4d0fc |
308 | |
2eb717d5 |
309 | The only features which requires additions to your code are the |
310 | attribute handling and instance construction features, and these are |
a2e85e6c |
311 | both completely optional features. The only reason for this is because |
2eb717d5 |
312 | Perl 5's object system does not actually have these features built |
313 | in. More information about this feature can be found below. |
bfe4d0fc |
314 | |
315 | =head2 A Note about Performance? |
316 | |
317 | It is a common misconception that explict MOPs are performance drains. |
318 | But this is not a universal truth at all, it is an side-effect of |
319 | specific implementations. For instance, using Java reflection is much |
320 | slower because the JVM cannot take advantage of any compiler |
321 | optimizations, and the JVM has to deal with much more runtime type |
322 | information as well. Reflection in C# is marginally better as it was |
323 | designed into the language and runtime (the CLR). In contrast, CLOS |
324 | (the Common Lisp Object System) was built to support an explicit MOP, |
325 | and so performance is tuned for it. |
326 | |
327 | This library in particular does it's absolute best to avoid putting |
2eb717d5 |
328 | B<any> drain at all upon your code's performance. In fact, by itself |
329 | it does nothing to affect your existing code. So you only pay for |
330 | what you actually use. |
bfe4d0fc |
331 | |
550d56db |
332 | =head2 About Metaclass compatibility |
333 | |
334 | This module makes sure that all metaclasses created are both upwards |
335 | and downwards compatible. The topic of metaclass compatibility is |
336 | highly esoteric and is something only encountered when doing deep and |
337 | involved metaclass hacking. There are two basic kinds of metaclass |
338 | incompatibility; upwards and downwards. |
339 | |
340 | Upwards metaclass compatibility means that the metaclass of a |
341 | given class is either the same as (or a subclass of) all of the |
342 | class's ancestors. |
343 | |
344 | Downward metaclass compatibility means that the metaclasses of a |
345 | given class's anscestors are all either the same as (or a subclass |
346 | of) that metaclass. |
347 | |
348 | Here is a diagram showing a set of two classes (C<A> and C<B>) and |
349 | two metaclasses (C<Meta::A> and C<Meta::B>) which have correct |
350 | metaclass compatibility both upwards and downwards. |
351 | |
352 | +---------+ +---------+ |
353 | | Meta::A |<----| Meta::B | <....... (instance of ) |
354 | +---------+ +---------+ <------- (inherits from) |
355 | ^ ^ |
356 | : : |
357 | +---------+ +---------+ |
358 | | A |<----| B | |
359 | +---------+ +---------+ |
360 | |
361 | As I said this is a highly esoteric topic and one you will only run |
362 | into if you do a lot of subclassing of B<Class::MOP::Class>. If you |
363 | are interested in why this is an issue see the paper |
364 | I<Uniform and safe metaclass composition> linked to in the |
365 | L<SEE ALSO> section of this document. |
366 | |
aa448b16 |
367 | =head2 Using custom metaclasses |
368 | |
369 | Always use the metaclass pragma when using a custom metaclass, this |
370 | will ensure the proper initialization order and not accidentely |
371 | create an incorrect type of metaclass for you. This is a very rare |
372 | problem, and one which can only occur if you are doing deep metaclass |
373 | programming. So in other words, don't worry about it. |
374 | |
94b19069 |
375 | =head1 PROTOCOLS |
376 | |
377 | The protocol is divided into 3 main sub-protocols: |
378 | |
379 | =over 4 |
380 | |
381 | =item The Class protocol |
382 | |
383 | This provides a means of manipulating and introspecting a Perl 5 |
384 | class. It handles all of symbol table hacking for you, and provides |
385 | a rich set of methods that go beyond simple package introspection. |
386 | |
552e3d24 |
387 | See L<Class::MOP::Class> for more details. |
388 | |
94b19069 |
389 | =item The Attribute protocol |
390 | |
391 | This provides a consistent represenation for an attribute of a |
392 | Perl 5 class. Since there are so many ways to create and handle |
393 | atttributes in Perl 5 OO, this attempts to provide as much of a |
394 | unified approach as possible, while giving the freedom and |
395 | flexibility to subclass for specialization. |
396 | |
552e3d24 |
397 | See L<Class::MOP::Attribute> for more details. |
398 | |
94b19069 |
399 | =item The Method protocol |
400 | |
401 | This provides a means of manipulating and introspecting methods in |
402 | the Perl 5 object system. As with attributes, there are many ways to |
403 | approach this topic, so we try to keep it pretty basic, while still |
404 | making it possible to extend the system in many ways. |
405 | |
552e3d24 |
406 | See L<Class::MOP::Method> for more details. |
94b19069 |
407 | |
408 | =back |
409 | |
552e3d24 |
410 | =head1 SEE ALSO |
8b978dd5 |
411 | |
552e3d24 |
412 | =head2 Books |
8b978dd5 |
413 | |
a2e85e6c |
414 | There are very few books out on Meta Object Protocols and Metaclasses |
415 | because it is such an esoteric topic. The following books are really |
416 | the only ones I have found. If you know of any more, B<I<please>> |
417 | email me and let me know, I would love to hear about them. |
418 | |
8b978dd5 |
419 | =over 4 |
420 | |
552e3d24 |
421 | =item "The Art of the Meta Object Protocol" |
8b978dd5 |
422 | |
552e3d24 |
423 | =item "Advances in Object-Oriented Metalevel Architecture and Reflection" |
8b978dd5 |
424 | |
b51af7f9 |
425 | =item "Putting MetaClasses to Work" |
426 | |
a2e85e6c |
427 | =item "Smalltalk: The Language" |
428 | |
94b19069 |
429 | =back |
430 | |
550d56db |
431 | =head2 Papers |
432 | |
433 | =over 4 |
434 | |
435 | =item Uniform and safe metaclass composition |
436 | |
437 | An excellent paper by the people who brought us the original Traits paper. |
438 | This paper is on how Traits can be used to do safe metaclass composition, |
439 | and offers an excellent introduction section which delves into the topic of |
440 | metaclass compatibility. |
441 | |
442 | L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf> |
443 | |
444 | =item Safe Metaclass Programming |
445 | |
446 | This paper seems to precede the above paper, and propose a mix-in based |
447 | approach as opposed to the Traits based approach. Both papers have similar |
448 | information on the metaclass compatibility problem space. |
449 | |
450 | L<http://citeseer.ist.psu.edu/37617.html> |
451 | |
452 | =back |
453 | |
552e3d24 |
454 | =head2 Prior Art |
8b978dd5 |
455 | |
456 | =over 4 |
457 | |
7184ca14 |
458 | =item The Perl 6 MetaModel work in the Pugs project |
8b978dd5 |
459 | |
460 | =over 4 |
461 | |
552e3d24 |
462 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel> |
8b978dd5 |
463 | |
552e3d24 |
464 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace> |
8b978dd5 |
465 | |
466 | =back |
467 | |
94b19069 |
468 | =back |
469 | |
a2e85e6c |
470 | =head1 SIMILAR MODULES |
471 | |
472 | As I have said above, this module is a class-builder-builder, so it is |
473 | not the same thing as modules like L<Class::Accessor> and |
474 | L<Class::MethodMaker>. That being said there are very few modules on CPAN |
475 | with similar goals to this module. The one I have found which is most |
550d56db |
476 | like this module is L<Class::Meta>, although it's philosophy and the MOP it |
477 | creates are very different from this modules. |
94b19069 |
478 | |
a2e85e6c |
479 | =head1 BUGS |
480 | |
481 | All complex software has bugs lurking in it, and this module is no |
482 | exception. If you find a bug please either email me, or add the bug |
483 | to cpan-RT. |
484 | |
22286063 |
485 | =head1 CODE COVERAGE |
486 | |
487 | I use L<Devel::Cover> to test the code coverage of my tests, below is the |
488 | L<Devel::Cover> report on this module's test suite. |
489 | |
490 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
491 | File stmt bran cond sub pod time total |
492 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
cdfaa4cc |
493 | Class/MOP.pm 100.0 100.0 100.0 100.0 n/a 19.8 100.0 |
494 | Class/MOP/Attribute.pm 100.0 100.0 91.7 61.2 100.0 14.3 87.9 |
495 | Class/MOP/Class.pm 97.6 91.3 77.3 98.4 100.0 56.4 93.2 |
496 | Class/MOP/Instance.pm 91.1 75.0 33.3 91.7 100.0 6.8 90.7 |
497 | Class/MOP/Method.pm 97.6 60.0 52.9 76.9 100.0 1.6 82.6 |
498 | metaclass.pm 100.0 100.0 83.3 100.0 n/a 1.0 97.7 |
22286063 |
499 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
cdfaa4cc |
500 | Total 97.5 88.5 75.5 82.8 100.0 100.0 91.2 |
22286063 |
501 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
502 | |
a2e85e6c |
503 | =head1 ACKNOWLEDGEMENTS |
504 | |
505 | =over 4 |
506 | |
507 | =item Rob Kinyon E<lt>rob@iinteractive.comE<gt> |
508 | |
509 | Thanks to Rob for actually getting the development of this module kick-started. |
510 | |
511 | =back |
512 | |
1a09d9cc |
513 | =head1 AUTHORS |
94b19069 |
514 | |
a2e85e6c |
515 | Stevan Little E<lt>stevan@iinteractive.comE<gt> |
552e3d24 |
516 | |
1a09d9cc |
517 | Yuval Kogman E<lt>nothingmuch@woobling.comE<gt> |
518 | |
94b19069 |
519 | =head1 COPYRIGHT AND LICENSE |
520 | |
521 | Copyright 2006 by Infinity Interactive, Inc. |
522 | |
523 | L<http://www.iinteractive.com> |
524 | |
525 | This library is free software; you can redistribute it and/or modify |
526 | it under the same terms as Perl itself. |
527 | |
528 | =cut |