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 | |
667cecf3 |
14 | our $VERSION = '0.29_01'; |
94b19069 |
15 | |
aa448b16 |
16 | ## ---------------------------------------------------------------------------- |
17 | ## Setting up our environment ... |
18 | ## ---------------------------------------------------------------------------- |
19 | ## Class::MOP needs to have a few things in the global perl environment so |
20 | ## that it can operate effectively. Those things are done here. |
21 | ## ---------------------------------------------------------------------------- |
22 | |
3bf7644b |
23 | # ... nothing yet actually ;) |
8b978dd5 |
24 | |
b51af7f9 |
25 | ## ---------------------------------------------------------------------------- |
26 | ## Bootstrapping |
27 | ## ---------------------------------------------------------------------------- |
28 | ## The code below here is to bootstrap our MOP with itself. This is also |
29 | ## sometimes called "tying the knot". By doing this, we make it much easier |
30 | ## to extend the MOP through subclassing and such since now you can use the |
31 | ## MOP itself to extend itself. |
32 | ## |
33 | ## Yes, I know, thats weird and insane, but it's a good thing, trust me :) |
34 | ## ---------------------------------------------------------------------------- |
727919c5 |
35 | |
36 | # We need to add in the meta-attributes here so that |
37 | # any subclass of Class::MOP::* will be able to |
38 | # inherit them using &construct_instance |
39 | |
40 | ## Class::MOP::Class |
41 | |
42 | Class::MOP::Class->meta->add_attribute( |
351bd7d4 |
43 | Class::MOP::Attribute->new('$: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 | |
40483095 |
214 | This documentation is admittedly sparse on details, as time permits |
215 | I will try to improve them. For now, I suggest looking at the items |
216 | listed in the L<SEE ALSO> section for more information. In particular |
217 | the book "The Art of the Meta Object Protocol" was very influential |
218 | in the development of this system. |
219 | |
bfe4d0fc |
220 | =head2 What is a Meta Object Protocol? |
221 | |
222 | A meta object protocol is an API to an object system. |
223 | |
224 | To be more specific, it is a set of abstractions of the components of |
225 | an object system (typically things like; classes, object, methods, |
226 | object attributes, etc.). These abstractions can then be used to both |
227 | inspect and manipulate the object system which they describe. |
228 | |
229 | It can be said that there are two MOPs for any object system; the |
230 | implicit MOP, and the explicit MOP. The implicit MOP handles things |
231 | like method dispatch or inheritance, which happen automatically as |
232 | part of how the object system works. The explicit MOP typically |
233 | handles the introspection/reflection features of the object system. |
234 | All object systems have implicit MOPs, without one, they would not |
235 | work. Explict MOPs however as less common, and depending on the |
236 | language can vary from restrictive (Reflection in Java or C#) to |
237 | wide open (CLOS is a perfect example). |
238 | |
e16da3e6 |
239 | =head2 Yet Another Class Builder!! Why? |
240 | |
241 | This is B<not> a class builder so much as it is a I<class builder |
242 | B<builder>>. My intent is that an end user does not use this module |
243 | directly, but instead this module is used by module authors to |
244 | build extensions and features onto the Perl 5 object system. |
245 | |
94b19069 |
246 | =head2 Who is this module for? |
247 | |
248 | This module is specifically for anyone who has ever created or |
249 | wanted to create a module for the Class:: namespace. The tools which |
250 | this module will provide will hopefully make it easier to do more |
251 | complex things with Perl 5 classes by removing such barriers as |
252 | the need to hack the symbol tables, or understand the fine details |
253 | of method dispatch. |
254 | |
bfe4d0fc |
255 | =head2 What changes do I have to make to use this module? |
256 | |
2eb717d5 |
257 | This module was designed to be as unintrusive as possible. Many of |
343203ee |
258 | its features are accessible without B<any> change to your existsing |
bfe4d0fc |
259 | code at all. It is meant to be a compliment to your existing code and |
2eb717d5 |
260 | not an intrusion on your code base. Unlike many other B<Class::> |
a2e85e6c |
261 | modules, this module B<does not> require you subclass it, or even that |
262 | you C<use> it in within your module's package. |
bfe4d0fc |
263 | |
2eb717d5 |
264 | The only features which requires additions to your code are the |
265 | attribute handling and instance construction features, and these are |
a2e85e6c |
266 | both completely optional features. The only reason for this is because |
2eb717d5 |
267 | Perl 5's object system does not actually have these features built |
268 | in. More information about this feature can be found below. |
bfe4d0fc |
269 | |
270 | =head2 A Note about Performance? |
271 | |
272 | It is a common misconception that explict MOPs are performance drains. |
273 | But this is not a universal truth at all, it is an side-effect of |
274 | specific implementations. For instance, using Java reflection is much |
275 | slower because the JVM cannot take advantage of any compiler |
276 | optimizations, and the JVM has to deal with much more runtime type |
277 | information as well. Reflection in C# is marginally better as it was |
278 | designed into the language and runtime (the CLR). In contrast, CLOS |
279 | (the Common Lisp Object System) was built to support an explicit MOP, |
280 | and so performance is tuned for it. |
281 | |
282 | This library in particular does it's absolute best to avoid putting |
2eb717d5 |
283 | B<any> drain at all upon your code's performance. In fact, by itself |
284 | it does nothing to affect your existing code. So you only pay for |
285 | what you actually use. |
bfe4d0fc |
286 | |
550d56db |
287 | =head2 About Metaclass compatibility |
288 | |
289 | This module makes sure that all metaclasses created are both upwards |
290 | and downwards compatible. The topic of metaclass compatibility is |
291 | highly esoteric and is something only encountered when doing deep and |
292 | involved metaclass hacking. There are two basic kinds of metaclass |
293 | incompatibility; upwards and downwards. |
294 | |
295 | Upwards metaclass compatibility means that the metaclass of a |
296 | given class is either the same as (or a subclass of) all of the |
297 | class's ancestors. |
298 | |
299 | Downward metaclass compatibility means that the metaclasses of a |
300 | given class's anscestors are all either the same as (or a subclass |
301 | of) that metaclass. |
302 | |
303 | Here is a diagram showing a set of two classes (C<A> and C<B>) and |
304 | two metaclasses (C<Meta::A> and C<Meta::B>) which have correct |
305 | metaclass compatibility both upwards and downwards. |
306 | |
307 | +---------+ +---------+ |
308 | | Meta::A |<----| Meta::B | <....... (instance of ) |
309 | +---------+ +---------+ <------- (inherits from) |
310 | ^ ^ |
311 | : : |
312 | +---------+ +---------+ |
313 | | A |<----| B | |
314 | +---------+ +---------+ |
315 | |
316 | As I said this is a highly esoteric topic and one you will only run |
317 | into if you do a lot of subclassing of B<Class::MOP::Class>. If you |
318 | are interested in why this is an issue see the paper |
319 | I<Uniform and safe metaclass composition> linked to in the |
320 | L<SEE ALSO> section of this document. |
321 | |
aa448b16 |
322 | =head2 Using custom metaclasses |
323 | |
324 | Always use the metaclass pragma when using a custom metaclass, this |
325 | will ensure the proper initialization order and not accidentely |
326 | create an incorrect type of metaclass for you. This is a very rare |
327 | problem, and one which can only occur if you are doing deep metaclass |
328 | programming. So in other words, don't worry about it. |
329 | |
94b19069 |
330 | =head1 PROTOCOLS |
331 | |
332 | The protocol is divided into 3 main sub-protocols: |
333 | |
334 | =over 4 |
335 | |
336 | =item The Class protocol |
337 | |
338 | This provides a means of manipulating and introspecting a Perl 5 |
339 | class. It handles all of symbol table hacking for you, and provides |
340 | a rich set of methods that go beyond simple package introspection. |
341 | |
552e3d24 |
342 | See L<Class::MOP::Class> for more details. |
343 | |
94b19069 |
344 | =item The Attribute protocol |
345 | |
346 | This provides a consistent represenation for an attribute of a |
347 | Perl 5 class. Since there are so many ways to create and handle |
348 | atttributes in Perl 5 OO, this attempts to provide as much of a |
349 | unified approach as possible, while giving the freedom and |
350 | flexibility to subclass for specialization. |
351 | |
552e3d24 |
352 | See L<Class::MOP::Attribute> for more details. |
353 | |
94b19069 |
354 | =item The Method protocol |
355 | |
356 | This provides a means of manipulating and introspecting methods in |
357 | the Perl 5 object system. As with attributes, there are many ways to |
358 | approach this topic, so we try to keep it pretty basic, while still |
359 | making it possible to extend the system in many ways. |
360 | |
552e3d24 |
361 | See L<Class::MOP::Method> for more details. |
94b19069 |
362 | |
363 | =back |
364 | |
552e3d24 |
365 | =head1 SEE ALSO |
8b978dd5 |
366 | |
552e3d24 |
367 | =head2 Books |
8b978dd5 |
368 | |
a2e85e6c |
369 | There are very few books out on Meta Object Protocols and Metaclasses |
370 | because it is such an esoteric topic. The following books are really |
371 | the only ones I have found. If you know of any more, B<I<please>> |
372 | email me and let me know, I would love to hear about them. |
373 | |
8b978dd5 |
374 | =over 4 |
375 | |
552e3d24 |
376 | =item "The Art of the Meta Object Protocol" |
8b978dd5 |
377 | |
552e3d24 |
378 | =item "Advances in Object-Oriented Metalevel Architecture and Reflection" |
8b978dd5 |
379 | |
b51af7f9 |
380 | =item "Putting MetaClasses to Work" |
381 | |
a2e85e6c |
382 | =item "Smalltalk: The Language" |
383 | |
94b19069 |
384 | =back |
385 | |
550d56db |
386 | =head2 Papers |
387 | |
388 | =over 4 |
389 | |
390 | =item Uniform and safe metaclass composition |
391 | |
392 | An excellent paper by the people who brought us the original Traits paper. |
393 | This paper is on how Traits can be used to do safe metaclass composition, |
394 | and offers an excellent introduction section which delves into the topic of |
395 | metaclass compatibility. |
396 | |
397 | L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf> |
398 | |
399 | =item Safe Metaclass Programming |
400 | |
401 | This paper seems to precede the above paper, and propose a mix-in based |
402 | approach as opposed to the Traits based approach. Both papers have similar |
403 | information on the metaclass compatibility problem space. |
404 | |
405 | L<http://citeseer.ist.psu.edu/37617.html> |
406 | |
407 | =back |
408 | |
552e3d24 |
409 | =head2 Prior Art |
8b978dd5 |
410 | |
411 | =over 4 |
412 | |
7184ca14 |
413 | =item The Perl 6 MetaModel work in the Pugs project |
8b978dd5 |
414 | |
415 | =over 4 |
416 | |
552e3d24 |
417 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel> |
8b978dd5 |
418 | |
552e3d24 |
419 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace> |
8b978dd5 |
420 | |
421 | =back |
422 | |
94b19069 |
423 | =back |
424 | |
a2e85e6c |
425 | =head1 SIMILAR MODULES |
426 | |
427 | As I have said above, this module is a class-builder-builder, so it is |
428 | not the same thing as modules like L<Class::Accessor> and |
429 | L<Class::MethodMaker>. That being said there are very few modules on CPAN |
430 | with similar goals to this module. The one I have found which is most |
550d56db |
431 | like this module is L<Class::Meta>, although it's philosophy and the MOP it |
432 | creates are very different from this modules. |
94b19069 |
433 | |
a2e85e6c |
434 | =head1 BUGS |
435 | |
436 | All complex software has bugs lurking in it, and this module is no |
437 | exception. If you find a bug please either email me, or add the bug |
438 | to cpan-RT. |
439 | |
22286063 |
440 | =head1 CODE COVERAGE |
441 | |
442 | I use L<Devel::Cover> to test the code coverage of my tests, below is the |
443 | L<Devel::Cover> report on this module's test suite. |
444 | |
445 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
446 | File stmt bran cond sub pod time total |
447 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
40483095 |
448 | Class/MOP.pm 100.0 100.0 100.0 100.0 n/a 24.3 100.0 |
449 | Class/MOP/Attribute.pm 100.0 100.0 91.7 63.6 100.0 9.2 88.8 |
450 | Class/MOP/Class.pm 98.1 91.8 77.3 96.8 100.0 58.3 93.3 |
451 | Class/MOP/Instance.pm 87.5 100.0 0.0 87.5 100.0 5.9 88.0 |
452 | Class/MOP/Method.pm 100.0 64.3 52.9 80.0 100.0 1.4 85.3 |
453 | metaclass.pm 100.0 100.0 83.3 100.0 n/a 0.9 97.7 |
22286063 |
454 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
40483095 |
455 | Total 97.8 90.1 74.8 82.9 100.0 100.0 91.5 |
22286063 |
456 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
457 | |
a2e85e6c |
458 | =head1 ACKNOWLEDGEMENTS |
459 | |
460 | =over 4 |
461 | |
462 | =item Rob Kinyon E<lt>rob@iinteractive.comE<gt> |
463 | |
464 | Thanks to Rob for actually getting the development of this module kick-started. |
465 | |
466 | =back |
467 | |
468 | =head1 AUTHOR |
94b19069 |
469 | |
a2e85e6c |
470 | Stevan Little E<lt>stevan@iinteractive.comE<gt> |
552e3d24 |
471 | |
94b19069 |
472 | =head1 COPYRIGHT AND LICENSE |
473 | |
474 | Copyright 2006 by Infinity Interactive, Inc. |
475 | |
476 | L<http://www.iinteractive.com> |
477 | |
478 | This library is free software; you can redistribute it and/or modify |
479 | it under the same terms as Perl itself. |
480 | |
481 | =cut |