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)->{'$:package'} } |
49 | }, |
7b31baf4 |
50 | init_arg => ':package', |
727919c5 |
51 | )) |
52 | ); |
53 | |
54 | Class::MOP::Class->meta->add_attribute( |
351bd7d4 |
55 | Class::MOP::Attribute->new('%:attributes' => ( |
7b31baf4 |
56 | reader => 'get_attribute_map', |
351bd7d4 |
57 | init_arg => ':attributes', |
727919c5 |
58 | default => sub { {} } |
59 | )) |
60 | ); |
61 | |
351bd7d4 |
62 | Class::MOP::Class->meta->add_attribute( |
63 | Class::MOP::Attribute->new('$:attribute_metaclass' => ( |
7b31baf4 |
64 | reader => 'attribute_metaclass', |
351bd7d4 |
65 | init_arg => ':attribute_metaclass', |
66 | default => 'Class::MOP::Attribute', |
67 | )) |
68 | ); |
69 | |
70 | Class::MOP::Class->meta->add_attribute( |
71 | Class::MOP::Attribute->new('$:method_metaclass' => ( |
7b31baf4 |
72 | reader => 'method_metaclass', |
351bd7d4 |
73 | init_arg => ':method_metaclass', |
74 | default => 'Class::MOP::Method', |
75 | )) |
76 | ); |
77 | |
2bab2be6 |
78 | Class::MOP::Class->meta->add_attribute( |
79 | Class::MOP::Attribute->new('$:instance_metaclass' => ( |
b880e0de |
80 | reader => { |
81 | # NOTE: we need to do this in order |
82 | # for the instance meta-object to |
83 | # not fall into meta-circular death |
84 | 'instance_metaclass' => sub { (shift)->{'$:instance_metaclass'} } |
85 | }, |
2bab2be6 |
86 | init_arg => ':instance_metaclass', |
87 | default => 'Class::MOP::Instance', |
88 | )) |
89 | ); |
90 | |
727919c5 |
91 | ## Class::MOP::Attribute |
92 | |
7b31baf4 |
93 | Class::MOP::Attribute->meta->add_attribute( |
94 | Class::MOP::Attribute->new('name' => ( |
b880e0de |
95 | reader => { |
96 | # NOTE: we need to do this in order |
97 | # for the instance meta-object to |
98 | # not fall into meta-circular death |
99 | 'name' => sub { (shift)->{name} } |
100 | } |
7b31baf4 |
101 | )) |
102 | ); |
103 | |
104 | Class::MOP::Attribute->meta->add_attribute( |
105 | Class::MOP::Attribute->new('associated_class' => ( |
b880e0de |
106 | reader => { |
107 | # NOTE: we need to do this in order |
108 | # for the instance meta-object to |
109 | # not fall into meta-circular death |
110 | 'associated_class' => sub { (shift)->{associated_class} } |
111 | } |
7b31baf4 |
112 | )) |
113 | ); |
114 | |
115 | Class::MOP::Attribute->meta->add_attribute( |
116 | Class::MOP::Attribute->new('accessor' => ( |
117 | reader => 'accessor', |
118 | predicate => 'has_accessor', |
119 | )) |
120 | ); |
121 | |
122 | Class::MOP::Attribute->meta->add_attribute( |
123 | Class::MOP::Attribute->new('reader' => ( |
124 | reader => 'reader', |
125 | predicate => 'has_reader', |
126 | )) |
127 | ); |
128 | |
129 | Class::MOP::Attribute->meta->add_attribute( |
130 | Class::MOP::Attribute->new('writer' => ( |
131 | reader => 'writer', |
132 | predicate => 'has_writer', |
133 | )) |
134 | ); |
135 | |
136 | Class::MOP::Attribute->meta->add_attribute( |
137 | Class::MOP::Attribute->new('predicate' => ( |
138 | reader => 'predicate', |
139 | predicate => 'has_predicate', |
140 | )) |
141 | ); |
142 | |
143 | Class::MOP::Attribute->meta->add_attribute( |
144 | Class::MOP::Attribute->new('init_arg' => ( |
145 | reader => 'init_arg', |
146 | predicate => 'has_init_arg', |
147 | )) |
148 | ); |
149 | |
150 | Class::MOP::Attribute->meta->add_attribute( |
151 | Class::MOP::Attribute->new('default' => ( |
152 | # default has a custom 'reader' method ... |
153 | predicate => 'has_default', |
154 | )) |
155 | ); |
156 | |
727919c5 |
157 | |
158 | # NOTE: (meta-circularity) |
159 | # This should be one of the last things done |
160 | # it will "tie the knot" with Class::MOP::Attribute |
161 | # so that it uses the attributes meta-objects |
162 | # to construct itself. |
163 | Class::MOP::Attribute->meta->add_method('new' => sub { |
164 | my $class = shift; |
165 | my $name = shift; |
166 | my %options = @_; |
167 | |
168 | (defined $name && $name) |
169 | || confess "You must provide a name for the attribute"; |
5659d76e |
170 | $options{init_arg} = $name |
171 | if not exists $options{init_arg}; |
651955fb |
172 | |
5659d76e |
173 | # return the new object |
174 | $class->meta->new_object(name => $name, %options); |
175 | }); |
176 | |
177 | Class::MOP::Attribute->meta->add_method('clone' => sub { |
a740253a |
178 | my $self = shift; |
a27ae83f |
179 | $self->meta->clone_object($self, @_); |
727919c5 |
180 | }); |
181 | |
94b19069 |
182 | 1; |
183 | |
184 | __END__ |
185 | |
186 | =pod |
187 | |
188 | =head1 NAME |
189 | |
190 | Class::MOP - A Meta Object Protocol for Perl 5 |
191 | |
192 | =head1 SYNOPSIS |
193 | |
a2e85e6c |
194 | # ... This will come later, for now see |
195 | # the other SYNOPSIS for more information |
94b19069 |
196 | |
197 | =head1 DESCRIPTON |
198 | |
199 | This module is an attempt to create a meta object protocol for the |
200 | Perl 5 object system. It makes no attempt to change the behavior or |
201 | characteristics of the Perl 5 object system, only to create a |
27e31eaf |
202 | protocol for its manipulation and introspection. |
94b19069 |
203 | |
204 | That said, it does attempt to create the tools for building a rich |
205 | set of extensions to the Perl 5 object system. Every attempt has been |
206 | made for these tools to keep to the spirit of the Perl 5 object |
207 | system that we all know and love. |
208 | |
bfe4d0fc |
209 | =head2 What is a Meta Object Protocol? |
210 | |
211 | A meta object protocol is an API to an object system. |
212 | |
213 | To be more specific, it is a set of abstractions of the components of |
214 | an object system (typically things like; classes, object, methods, |
215 | object attributes, etc.). These abstractions can then be used to both |
216 | inspect and manipulate the object system which they describe. |
217 | |
218 | It can be said that there are two MOPs for any object system; the |
219 | implicit MOP, and the explicit MOP. The implicit MOP handles things |
220 | like method dispatch or inheritance, which happen automatically as |
221 | part of how the object system works. The explicit MOP typically |
222 | handles the introspection/reflection features of the object system. |
223 | All object systems have implicit MOPs, without one, they would not |
224 | work. Explict MOPs however as less common, and depending on the |
225 | language can vary from restrictive (Reflection in Java or C#) to |
226 | wide open (CLOS is a perfect example). |
227 | |
e16da3e6 |
228 | =head2 Yet Another Class Builder!! Why? |
229 | |
230 | This is B<not> a class builder so much as it is a I<class builder |
231 | B<builder>>. My intent is that an end user does not use this module |
232 | directly, but instead this module is used by module authors to |
233 | build extensions and features onto the Perl 5 object system. |
234 | |
94b19069 |
235 | =head2 Who is this module for? |
236 | |
237 | This module is specifically for anyone who has ever created or |
238 | wanted to create a module for the Class:: namespace. The tools which |
239 | this module will provide will hopefully make it easier to do more |
240 | complex things with Perl 5 classes by removing such barriers as |
241 | the need to hack the symbol tables, or understand the fine details |
242 | of method dispatch. |
243 | |
bfe4d0fc |
244 | =head2 What changes do I have to make to use this module? |
245 | |
2eb717d5 |
246 | This module was designed to be as unintrusive as possible. Many of |
343203ee |
247 | its features are accessible without B<any> change to your existsing |
bfe4d0fc |
248 | code at all. It is meant to be a compliment to your existing code and |
2eb717d5 |
249 | not an intrusion on your code base. Unlike many other B<Class::> |
a2e85e6c |
250 | modules, this module B<does not> require you subclass it, or even that |
251 | you C<use> it in within your module's package. |
bfe4d0fc |
252 | |
2eb717d5 |
253 | The only features which requires additions to your code are the |
254 | attribute handling and instance construction features, and these are |
a2e85e6c |
255 | both completely optional features. The only reason for this is because |
2eb717d5 |
256 | Perl 5's object system does not actually have these features built |
257 | in. More information about this feature can be found below. |
bfe4d0fc |
258 | |
259 | =head2 A Note about Performance? |
260 | |
261 | It is a common misconception that explict MOPs are performance drains. |
262 | But this is not a universal truth at all, it is an side-effect of |
263 | specific implementations. For instance, using Java reflection is much |
264 | slower because the JVM cannot take advantage of any compiler |
265 | optimizations, and the JVM has to deal with much more runtime type |
266 | information as well. Reflection in C# is marginally better as it was |
267 | designed into the language and runtime (the CLR). In contrast, CLOS |
268 | (the Common Lisp Object System) was built to support an explicit MOP, |
269 | and so performance is tuned for it. |
270 | |
271 | This library in particular does it's absolute best to avoid putting |
2eb717d5 |
272 | B<any> drain at all upon your code's performance. In fact, by itself |
273 | it does nothing to affect your existing code. So you only pay for |
274 | what you actually use. |
bfe4d0fc |
275 | |
550d56db |
276 | =head2 About Metaclass compatibility |
277 | |
278 | This module makes sure that all metaclasses created are both upwards |
279 | and downwards compatible. The topic of metaclass compatibility is |
280 | highly esoteric and is something only encountered when doing deep and |
281 | involved metaclass hacking. There are two basic kinds of metaclass |
282 | incompatibility; upwards and downwards. |
283 | |
284 | Upwards metaclass compatibility means that the metaclass of a |
285 | given class is either the same as (or a subclass of) all of the |
286 | class's ancestors. |
287 | |
288 | Downward metaclass compatibility means that the metaclasses of a |
289 | given class's anscestors are all either the same as (or a subclass |
290 | of) that metaclass. |
291 | |
292 | Here is a diagram showing a set of two classes (C<A> and C<B>) and |
293 | two metaclasses (C<Meta::A> and C<Meta::B>) which have correct |
294 | metaclass compatibility both upwards and downwards. |
295 | |
296 | +---------+ +---------+ |
297 | | Meta::A |<----| Meta::B | <....... (instance of ) |
298 | +---------+ +---------+ <------- (inherits from) |
299 | ^ ^ |
300 | : : |
301 | +---------+ +---------+ |
302 | | A |<----| B | |
303 | +---------+ +---------+ |
304 | |
305 | As I said this is a highly esoteric topic and one you will only run |
306 | into if you do a lot of subclassing of B<Class::MOP::Class>. If you |
307 | are interested in why this is an issue see the paper |
308 | I<Uniform and safe metaclass composition> linked to in the |
309 | L<SEE ALSO> section of this document. |
310 | |
aa448b16 |
311 | =head2 Using custom metaclasses |
312 | |
313 | Always use the metaclass pragma when using a custom metaclass, this |
314 | will ensure the proper initialization order and not accidentely |
315 | create an incorrect type of metaclass for you. This is a very rare |
316 | problem, and one which can only occur if you are doing deep metaclass |
317 | programming. So in other words, don't worry about it. |
318 | |
94b19069 |
319 | =head1 PROTOCOLS |
320 | |
321 | The protocol is divided into 3 main sub-protocols: |
322 | |
323 | =over 4 |
324 | |
325 | =item The Class protocol |
326 | |
327 | This provides a means of manipulating and introspecting a Perl 5 |
328 | class. It handles all of symbol table hacking for you, and provides |
329 | a rich set of methods that go beyond simple package introspection. |
330 | |
552e3d24 |
331 | See L<Class::MOP::Class> for more details. |
332 | |
94b19069 |
333 | =item The Attribute protocol |
334 | |
335 | This provides a consistent represenation for an attribute of a |
336 | Perl 5 class. Since there are so many ways to create and handle |
337 | atttributes in Perl 5 OO, this attempts to provide as much of a |
338 | unified approach as possible, while giving the freedom and |
339 | flexibility to subclass for specialization. |
340 | |
552e3d24 |
341 | See L<Class::MOP::Attribute> for more details. |
342 | |
94b19069 |
343 | =item The Method protocol |
344 | |
345 | This provides a means of manipulating and introspecting methods in |
346 | the Perl 5 object system. As with attributes, there are many ways to |
347 | approach this topic, so we try to keep it pretty basic, while still |
348 | making it possible to extend the system in many ways. |
349 | |
552e3d24 |
350 | See L<Class::MOP::Method> for more details. |
94b19069 |
351 | |
352 | =back |
353 | |
552e3d24 |
354 | =head1 SEE ALSO |
8b978dd5 |
355 | |
552e3d24 |
356 | =head2 Books |
8b978dd5 |
357 | |
a2e85e6c |
358 | There are very few books out on Meta Object Protocols and Metaclasses |
359 | because it is such an esoteric topic. The following books are really |
360 | the only ones I have found. If you know of any more, B<I<please>> |
361 | email me and let me know, I would love to hear about them. |
362 | |
8b978dd5 |
363 | =over 4 |
364 | |
552e3d24 |
365 | =item "The Art of the Meta Object Protocol" |
8b978dd5 |
366 | |
552e3d24 |
367 | =item "Advances in Object-Oriented Metalevel Architecture and Reflection" |
8b978dd5 |
368 | |
b51af7f9 |
369 | =item "Putting MetaClasses to Work" |
370 | |
a2e85e6c |
371 | =item "Smalltalk: The Language" |
372 | |
94b19069 |
373 | =back |
374 | |
550d56db |
375 | =head2 Papers |
376 | |
377 | =over 4 |
378 | |
379 | =item Uniform and safe metaclass composition |
380 | |
381 | An excellent paper by the people who brought us the original Traits paper. |
382 | This paper is on how Traits can be used to do safe metaclass composition, |
383 | and offers an excellent introduction section which delves into the topic of |
384 | metaclass compatibility. |
385 | |
386 | L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf> |
387 | |
388 | =item Safe Metaclass Programming |
389 | |
390 | This paper seems to precede the above paper, and propose a mix-in based |
391 | approach as opposed to the Traits based approach. Both papers have similar |
392 | information on the metaclass compatibility problem space. |
393 | |
394 | L<http://citeseer.ist.psu.edu/37617.html> |
395 | |
396 | =back |
397 | |
552e3d24 |
398 | =head2 Prior Art |
8b978dd5 |
399 | |
400 | =over 4 |
401 | |
7184ca14 |
402 | =item The Perl 6 MetaModel work in the Pugs project |
8b978dd5 |
403 | |
404 | =over 4 |
405 | |
552e3d24 |
406 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel> |
8b978dd5 |
407 | |
552e3d24 |
408 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace> |
8b978dd5 |
409 | |
410 | =back |
411 | |
94b19069 |
412 | =back |
413 | |
a2e85e6c |
414 | =head1 SIMILAR MODULES |
415 | |
416 | As I have said above, this module is a class-builder-builder, so it is |
417 | not the same thing as modules like L<Class::Accessor> and |
418 | L<Class::MethodMaker>. That being said there are very few modules on CPAN |
419 | with similar goals to this module. The one I have found which is most |
550d56db |
420 | like this module is L<Class::Meta>, although it's philosophy and the MOP it |
421 | creates are very different from this modules. |
94b19069 |
422 | |
a2e85e6c |
423 | =head1 BUGS |
424 | |
425 | All complex software has bugs lurking in it, and this module is no |
426 | exception. If you find a bug please either email me, or add the bug |
427 | to cpan-RT. |
428 | |
22286063 |
429 | =head1 CODE COVERAGE |
430 | |
431 | I use L<Devel::Cover> to test the code coverage of my tests, below is the |
432 | L<Devel::Cover> report on this module's test suite. |
433 | |
434 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
435 | File stmt bran cond sub pod time total |
436 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
8048fe76 |
437 | Class/MOP.pm 100.0 100.0 100.0 100.0 n/a 9.6 100.0 |
438 | Class/MOP/Attribute.pm 100.0 100.0 91.7 73.8 100.0 28.4 92.1 |
439 | Class/MOP/Class.pm 100.0 93.5 82.3 98.2 100.0 56.6 95.7 |
440 | Class/MOP/Method.pm 100.0 64.3 52.9 80.0 100.0 3.5 85.3 |
441 | metaclass.pm 100.0 100.0 80.0 100.0 n/a 1.9 97.4 |
22286063 |
442 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
8048fe76 |
443 | Total 100.0 90.8 79.7 86.2 100.0 100.0 93.6 |
22286063 |
444 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
445 | |
a2e85e6c |
446 | =head1 ACKNOWLEDGEMENTS |
447 | |
448 | =over 4 |
449 | |
450 | =item Rob Kinyon E<lt>rob@iinteractive.comE<gt> |
451 | |
452 | Thanks to Rob for actually getting the development of this module kick-started. |
453 | |
454 | =back |
455 | |
456 | =head1 AUTHOR |
94b19069 |
457 | |
a2e85e6c |
458 | Stevan Little E<lt>stevan@iinteractive.comE<gt> |
552e3d24 |
459 | |
94b19069 |
460 | =head1 COPYRIGHT AND LICENSE |
461 | |
462 | Copyright 2006 by Infinity Interactive, Inc. |
463 | |
464 | L<http://www.iinteractive.com> |
465 | |
466 | This library is free software; you can redistribute it and/or modify |
467 | it under the same terms as Perl itself. |
468 | |
469 | =cut |