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 | |
2bab2be6 |
14 | our $VERSION = '0.30'; |
94b19069 |
15 | |
aa448b16 |
16 | ## ---------------------------------------------------------------------------- |
17 | ## Setting up our environment ... |
18 | ## ---------------------------------------------------------------------------- |
19 | ## Class::MOP needs to have a few things in the global perl environment so |
20 | ## that it can operate effectively. Those things are done here. |
21 | ## ---------------------------------------------------------------------------- |
22 | |
3bf7644b |
23 | # ... nothing yet actually ;) |
8b978dd5 |
24 | |
b51af7f9 |
25 | ## ---------------------------------------------------------------------------- |
26 | ## Bootstrapping |
27 | ## ---------------------------------------------------------------------------- |
28 | ## The code below here is to bootstrap our MOP with itself. This is also |
29 | ## sometimes called "tying the knot". By doing this, we make it much easier |
30 | ## to extend the MOP through subclassing and such since now you can use the |
31 | ## MOP itself to extend itself. |
32 | ## |
33 | ## Yes, I know, thats weird and insane, but it's a good thing, trust me :) |
34 | ## ---------------------------------------------------------------------------- |
727919c5 |
35 | |
36 | # We need to add in the meta-attributes here so that |
37 | # any subclass of Class::MOP::* will be able to |
38 | # inherit them using &construct_instance |
39 | |
40 | ## Class::MOP::Class |
41 | |
42 | Class::MOP::Class->meta->add_attribute( |
351bd7d4 |
43 | Class::MOP::Attribute->new('$:package' => ( |
b880e0de |
44 | reader => { |
45 | # NOTE: we need to do this in order |
46 | # for the instance meta-object to |
47 | # not fall into meta-circular death |
48 | 'name' => sub { (shift)->{'$:package'} } |
49 | }, |
7b31baf4 |
50 | init_arg => ':package', |
727919c5 |
51 | )) |
52 | ); |
53 | |
54 | Class::MOP::Class->meta->add_attribute( |
351bd7d4 |
55 | Class::MOP::Attribute->new('%:attributes' => ( |
f7259199 |
56 | reader => { |
57 | # NOTE: we need to do this in order |
58 | # for the instance meta-object to |
59 | # not fall into meta-circular death |
60 | 'get_attribute_map' => sub { (shift)->{'%:attributes'} } |
61 | }, |
351bd7d4 |
62 | init_arg => ':attributes', |
727919c5 |
63 | default => sub { {} } |
64 | )) |
65 | ); |
66 | |
351bd7d4 |
67 | Class::MOP::Class->meta->add_attribute( |
68 | Class::MOP::Attribute->new('$:attribute_metaclass' => ( |
7b31baf4 |
69 | reader => 'attribute_metaclass', |
351bd7d4 |
70 | init_arg => ':attribute_metaclass', |
71 | default => 'Class::MOP::Attribute', |
72 | )) |
73 | ); |
74 | |
75 | Class::MOP::Class->meta->add_attribute( |
76 | Class::MOP::Attribute->new('$:method_metaclass' => ( |
7b31baf4 |
77 | reader => 'method_metaclass', |
351bd7d4 |
78 | init_arg => ':method_metaclass', |
79 | default => 'Class::MOP::Method', |
80 | )) |
81 | ); |
82 | |
2bab2be6 |
83 | Class::MOP::Class->meta->add_attribute( |
84 | Class::MOP::Attribute->new('$:instance_metaclass' => ( |
b880e0de |
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 | 'instance_metaclass' => sub { (shift)->{'$:instance_metaclass'} } |
90 | }, |
2bab2be6 |
91 | init_arg => ':instance_metaclass', |
92 | default => 'Class::MOP::Instance', |
93 | )) |
94 | ); |
95 | |
727919c5 |
96 | ## Class::MOP::Attribute |
97 | |
7b31baf4 |
98 | Class::MOP::Attribute->meta->add_attribute( |
99 | Class::MOP::Attribute->new('name' => ( |
b880e0de |
100 | reader => { |
101 | # NOTE: we need to do this in order |
102 | # for the instance meta-object to |
103 | # not fall into meta-circular death |
104 | 'name' => sub { (shift)->{name} } |
105 | } |
7b31baf4 |
106 | )) |
107 | ); |
108 | |
109 | Class::MOP::Attribute->meta->add_attribute( |
110 | Class::MOP::Attribute->new('associated_class' => ( |
b880e0de |
111 | reader => { |
112 | # NOTE: we need to do this in order |
113 | # for the instance meta-object to |
114 | # not fall into meta-circular death |
115 | 'associated_class' => sub { (shift)->{associated_class} } |
116 | } |
7b31baf4 |
117 | )) |
118 | ); |
119 | |
120 | Class::MOP::Attribute->meta->add_attribute( |
121 | Class::MOP::Attribute->new('accessor' => ( |
122 | reader => 'accessor', |
123 | predicate => 'has_accessor', |
124 | )) |
125 | ); |
126 | |
127 | Class::MOP::Attribute->meta->add_attribute( |
128 | Class::MOP::Attribute->new('reader' => ( |
129 | reader => 'reader', |
130 | predicate => 'has_reader', |
131 | )) |
132 | ); |
133 | |
134 | Class::MOP::Attribute->meta->add_attribute( |
135 | Class::MOP::Attribute->new('writer' => ( |
136 | reader => 'writer', |
137 | predicate => 'has_writer', |
138 | )) |
139 | ); |
140 | |
141 | Class::MOP::Attribute->meta->add_attribute( |
142 | Class::MOP::Attribute->new('predicate' => ( |
143 | reader => 'predicate', |
144 | predicate => 'has_predicate', |
145 | )) |
146 | ); |
147 | |
148 | Class::MOP::Attribute->meta->add_attribute( |
149 | Class::MOP::Attribute->new('init_arg' => ( |
150 | reader => 'init_arg', |
151 | predicate => 'has_init_arg', |
152 | )) |
153 | ); |
154 | |
155 | Class::MOP::Attribute->meta->add_attribute( |
156 | Class::MOP::Attribute->new('default' => ( |
157 | # default has a custom 'reader' method ... |
158 | predicate => 'has_default', |
159 | )) |
160 | ); |
161 | |
727919c5 |
162 | |
163 | # NOTE: (meta-circularity) |
164 | # This should be one of the last things done |
165 | # it will "tie the knot" with Class::MOP::Attribute |
166 | # so that it uses the attributes meta-objects |
167 | # to construct itself. |
168 | Class::MOP::Attribute->meta->add_method('new' => sub { |
169 | my $class = shift; |
170 | my $name = shift; |
171 | my %options = @_; |
172 | |
173 | (defined $name && $name) |
174 | || confess "You must provide a name for the attribute"; |
5659d76e |
175 | $options{init_arg} = $name |
176 | if not exists $options{init_arg}; |
651955fb |
177 | |
5659d76e |
178 | # return the new object |
179 | $class->meta->new_object(name => $name, %options); |
180 | }); |
181 | |
182 | Class::MOP::Attribute->meta->add_method('clone' => sub { |
a740253a |
183 | my $self = shift; |
a27ae83f |
184 | $self->meta->clone_object($self, @_); |
727919c5 |
185 | }); |
186 | |
94b19069 |
187 | 1; |
188 | |
189 | __END__ |
190 | |
191 | =pod |
192 | |
193 | =head1 NAME |
194 | |
195 | Class::MOP - A Meta Object Protocol for Perl 5 |
196 | |
197 | =head1 SYNOPSIS |
198 | |
a2e85e6c |
199 | # ... This will come later, for now see |
200 | # the other SYNOPSIS for more information |
94b19069 |
201 | |
202 | =head1 DESCRIPTON |
203 | |
204 | This module is an attempt to create a meta object protocol for the |
205 | Perl 5 object system. It makes no attempt to change the behavior or |
206 | characteristics of the Perl 5 object system, only to create a |
27e31eaf |
207 | protocol for its manipulation and introspection. |
94b19069 |
208 | |
209 | That said, it does attempt to create the tools for building a rich |
210 | set of extensions to the Perl 5 object system. Every attempt has been |
211 | made for these tools to keep to the spirit of the Perl 5 object |
212 | system that we all know and love. |
213 | |
bfe4d0fc |
214 | =head2 What is a Meta Object Protocol? |
215 | |
216 | A meta object protocol is an API to an object system. |
217 | |
218 | To be more specific, it is a set of abstractions of the components of |
219 | an object system (typically things like; classes, object, methods, |
220 | object attributes, etc.). These abstractions can then be used to both |
221 | inspect and manipulate the object system which they describe. |
222 | |
223 | It can be said that there are two MOPs for any object system; the |
224 | implicit MOP, and the explicit MOP. The implicit MOP handles things |
225 | like method dispatch or inheritance, which happen automatically as |
226 | part of how the object system works. The explicit MOP typically |
227 | handles the introspection/reflection features of the object system. |
228 | All object systems have implicit MOPs, without one, they would not |
229 | work. Explict MOPs however as less common, and depending on the |
230 | language can vary from restrictive (Reflection in Java or C#) to |
231 | wide open (CLOS is a perfect example). |
232 | |
e16da3e6 |
233 | =head2 Yet Another Class Builder!! Why? |
234 | |
235 | This is B<not> a class builder so much as it is a I<class builder |
236 | B<builder>>. My intent is that an end user does not use this module |
237 | directly, but instead this module is used by module authors to |
238 | build extensions and features onto the Perl 5 object system. |
239 | |
94b19069 |
240 | =head2 Who is this module for? |
241 | |
242 | This module is specifically for anyone who has ever created or |
243 | wanted to create a module for the Class:: namespace. The tools which |
244 | this module will provide will hopefully make it easier to do more |
245 | complex things with Perl 5 classes by removing such barriers as |
246 | the need to hack the symbol tables, or understand the fine details |
247 | of method dispatch. |
248 | |
bfe4d0fc |
249 | =head2 What changes do I have to make to use this module? |
250 | |
2eb717d5 |
251 | This module was designed to be as unintrusive as possible. Many of |
343203ee |
252 | its features are accessible without B<any> change to your existsing |
bfe4d0fc |
253 | code at all. It is meant to be a compliment to your existing code and |
2eb717d5 |
254 | not an intrusion on your code base. Unlike many other B<Class::> |
a2e85e6c |
255 | modules, this module B<does not> require you subclass it, or even that |
256 | you C<use> it in within your module's package. |
bfe4d0fc |
257 | |
2eb717d5 |
258 | The only features which requires additions to your code are the |
259 | attribute handling and instance construction features, and these are |
a2e85e6c |
260 | both completely optional features. The only reason for this is because |
2eb717d5 |
261 | Perl 5's object system does not actually have these features built |
262 | in. More information about this feature can be found below. |
bfe4d0fc |
263 | |
264 | =head2 A Note about Performance? |
265 | |
266 | It is a common misconception that explict MOPs are performance drains. |
267 | But this is not a universal truth at all, it is an side-effect of |
268 | specific implementations. For instance, using Java reflection is much |
269 | slower because the JVM cannot take advantage of any compiler |
270 | optimizations, and the JVM has to deal with much more runtime type |
271 | information as well. Reflection in C# is marginally better as it was |
272 | designed into the language and runtime (the CLR). In contrast, CLOS |
273 | (the Common Lisp Object System) was built to support an explicit MOP, |
274 | and so performance is tuned for it. |
275 | |
276 | This library in particular does it's absolute best to avoid putting |
2eb717d5 |
277 | B<any> drain at all upon your code's performance. In fact, by itself |
278 | it does nothing to affect your existing code. So you only pay for |
279 | what you actually use. |
bfe4d0fc |
280 | |
550d56db |
281 | =head2 About Metaclass compatibility |
282 | |
283 | This module makes sure that all metaclasses created are both upwards |
284 | and downwards compatible. The topic of metaclass compatibility is |
285 | highly esoteric and is something only encountered when doing deep and |
286 | involved metaclass hacking. There are two basic kinds of metaclass |
287 | incompatibility; upwards and downwards. |
288 | |
289 | Upwards metaclass compatibility means that the metaclass of a |
290 | given class is either the same as (or a subclass of) all of the |
291 | class's ancestors. |
292 | |
293 | Downward metaclass compatibility means that the metaclasses of a |
294 | given class's anscestors are all either the same as (or a subclass |
295 | of) that metaclass. |
296 | |
297 | Here is a diagram showing a set of two classes (C<A> and C<B>) and |
298 | two metaclasses (C<Meta::A> and C<Meta::B>) which have correct |
299 | metaclass compatibility both upwards and downwards. |
300 | |
301 | +---------+ +---------+ |
302 | | Meta::A |<----| Meta::B | <....... (instance of ) |
303 | +---------+ +---------+ <------- (inherits from) |
304 | ^ ^ |
305 | : : |
306 | +---------+ +---------+ |
307 | | A |<----| B | |
308 | +---------+ +---------+ |
309 | |
310 | As I said this is a highly esoteric topic and one you will only run |
311 | into if you do a lot of subclassing of B<Class::MOP::Class>. If you |
312 | are interested in why this is an issue see the paper |
313 | I<Uniform and safe metaclass composition> linked to in the |
314 | L<SEE ALSO> section of this document. |
315 | |
aa448b16 |
316 | =head2 Using custom metaclasses |
317 | |
318 | Always use the metaclass pragma when using a custom metaclass, this |
319 | will ensure the proper initialization order and not accidentely |
320 | create an incorrect type of metaclass for you. This is a very rare |
321 | problem, and one which can only occur if you are doing deep metaclass |
322 | programming. So in other words, don't worry about it. |
323 | |
94b19069 |
324 | =head1 PROTOCOLS |
325 | |
326 | The protocol is divided into 3 main sub-protocols: |
327 | |
328 | =over 4 |
329 | |
330 | =item The Class protocol |
331 | |
332 | This provides a means of manipulating and introspecting a Perl 5 |
333 | class. It handles all of symbol table hacking for you, and provides |
334 | a rich set of methods that go beyond simple package introspection. |
335 | |
552e3d24 |
336 | See L<Class::MOP::Class> for more details. |
337 | |
94b19069 |
338 | =item The Attribute protocol |
339 | |
340 | This provides a consistent represenation for an attribute of a |
341 | Perl 5 class. Since there are so many ways to create and handle |
342 | atttributes in Perl 5 OO, this attempts to provide as much of a |
343 | unified approach as possible, while giving the freedom and |
344 | flexibility to subclass for specialization. |
345 | |
552e3d24 |
346 | See L<Class::MOP::Attribute> for more details. |
347 | |
94b19069 |
348 | =item The Method protocol |
349 | |
350 | This provides a means of manipulating and introspecting methods in |
351 | the Perl 5 object system. As with attributes, there are many ways to |
352 | approach this topic, so we try to keep it pretty basic, while still |
353 | making it possible to extend the system in many ways. |
354 | |
552e3d24 |
355 | See L<Class::MOP::Method> for more details. |
94b19069 |
356 | |
357 | =back |
358 | |
552e3d24 |
359 | =head1 SEE ALSO |
8b978dd5 |
360 | |
552e3d24 |
361 | =head2 Books |
8b978dd5 |
362 | |
a2e85e6c |
363 | There are very few books out on Meta Object Protocols and Metaclasses |
364 | because it is such an esoteric topic. The following books are really |
365 | the only ones I have found. If you know of any more, B<I<please>> |
366 | email me and let me know, I would love to hear about them. |
367 | |
8b978dd5 |
368 | =over 4 |
369 | |
552e3d24 |
370 | =item "The Art of the Meta Object Protocol" |
8b978dd5 |
371 | |
552e3d24 |
372 | =item "Advances in Object-Oriented Metalevel Architecture and Reflection" |
8b978dd5 |
373 | |
b51af7f9 |
374 | =item "Putting MetaClasses to Work" |
375 | |
a2e85e6c |
376 | =item "Smalltalk: The Language" |
377 | |
94b19069 |
378 | =back |
379 | |
550d56db |
380 | =head2 Papers |
381 | |
382 | =over 4 |
383 | |
384 | =item Uniform and safe metaclass composition |
385 | |
386 | An excellent paper by the people who brought us the original Traits paper. |
387 | This paper is on how Traits can be used to do safe metaclass composition, |
388 | and offers an excellent introduction section which delves into the topic of |
389 | metaclass compatibility. |
390 | |
391 | L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf> |
392 | |
393 | =item Safe Metaclass Programming |
394 | |
395 | This paper seems to precede the above paper, and propose a mix-in based |
396 | approach as opposed to the Traits based approach. Both papers have similar |
397 | information on the metaclass compatibility problem space. |
398 | |
399 | L<http://citeseer.ist.psu.edu/37617.html> |
400 | |
401 | =back |
402 | |
552e3d24 |
403 | =head2 Prior Art |
8b978dd5 |
404 | |
405 | =over 4 |
406 | |
7184ca14 |
407 | =item The Perl 6 MetaModel work in the Pugs project |
8b978dd5 |
408 | |
409 | =over 4 |
410 | |
552e3d24 |
411 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel> |
8b978dd5 |
412 | |
552e3d24 |
413 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace> |
8b978dd5 |
414 | |
415 | =back |
416 | |
94b19069 |
417 | =back |
418 | |
a2e85e6c |
419 | =head1 SIMILAR MODULES |
420 | |
421 | As I have said above, this module is a class-builder-builder, so it is |
422 | not the same thing as modules like L<Class::Accessor> and |
423 | L<Class::MethodMaker>. That being said there are very few modules on CPAN |
424 | with similar goals to this module. The one I have found which is most |
550d56db |
425 | like this module is L<Class::Meta>, although it's philosophy and the MOP it |
426 | creates are very different from this modules. |
94b19069 |
427 | |
a2e85e6c |
428 | =head1 BUGS |
429 | |
430 | All complex software has bugs lurking in it, and this module is no |
431 | exception. If you find a bug please either email me, or add the bug |
432 | to cpan-RT. |
433 | |
22286063 |
434 | =head1 CODE COVERAGE |
435 | |
436 | I use L<Devel::Cover> to test the code coverage of my tests, below is the |
437 | L<Devel::Cover> report on this module's test suite. |
438 | |
439 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
440 | File stmt bran cond sub pod time total |
441 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
8048fe76 |
442 | Class/MOP.pm 100.0 100.0 100.0 100.0 n/a 9.6 100.0 |
443 | Class/MOP/Attribute.pm 100.0 100.0 91.7 73.8 100.0 28.4 92.1 |
444 | Class/MOP/Class.pm 100.0 93.5 82.3 98.2 100.0 56.6 95.7 |
445 | Class/MOP/Method.pm 100.0 64.3 52.9 80.0 100.0 3.5 85.3 |
446 | metaclass.pm 100.0 100.0 80.0 100.0 n/a 1.9 97.4 |
22286063 |
447 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
8048fe76 |
448 | Total 100.0 90.8 79.7 86.2 100.0 100.0 93.6 |
22286063 |
449 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
450 | |
a2e85e6c |
451 | =head1 ACKNOWLEDGEMENTS |
452 | |
453 | =over 4 |
454 | |
455 | =item Rob Kinyon E<lt>rob@iinteractive.comE<gt> |
456 | |
457 | Thanks to Rob for actually getting the development of this module kick-started. |
458 | |
459 | =back |
460 | |
461 | =head1 AUTHOR |
94b19069 |
462 | |
a2e85e6c |
463 | Stevan Little E<lt>stevan@iinteractive.comE<gt> |
552e3d24 |
464 | |
94b19069 |
465 | =head1 COPYRIGHT AND LICENSE |
466 | |
467 | Copyright 2006 by Infinity Interactive, Inc. |
468 | |
469 | L<http://www.iinteractive.com> |
470 | |
471 | This library is free software; you can redistribute it and/or modify |
472 | it under the same terms as Perl itself. |
473 | |
474 | =cut |