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 | |
df7b4119 |
16 | our $VERSION = '0.29_02'; |
94b19069 |
17 | |
aa448b16 |
18 | ## ---------------------------------------------------------------------------- |
19 | ## Setting up our environment ... |
20 | ## ---------------------------------------------------------------------------- |
21 | ## Class::MOP needs to have a few things in the global perl environment so |
22 | ## that it can operate effectively. Those things are done here. |
23 | ## ---------------------------------------------------------------------------- |
24 | |
3bf7644b |
25 | # ... nothing yet actually ;) |
8b978dd5 |
26 | |
b51af7f9 |
27 | ## ---------------------------------------------------------------------------- |
28 | ## Bootstrapping |
29 | ## ---------------------------------------------------------------------------- |
30 | ## The code below here is to bootstrap our MOP with itself. This is also |
31 | ## sometimes called "tying the knot". By doing this, we make it much easier |
32 | ## to extend the MOP through subclassing and such since now you can use the |
33 | ## MOP itself to extend itself. |
34 | ## |
35 | ## Yes, I know, thats weird and insane, but it's a good thing, trust me :) |
36 | ## ---------------------------------------------------------------------------- |
727919c5 |
37 | |
38 | # We need to add in the meta-attributes here so that |
39 | # any subclass of Class::MOP::* will be able to |
40 | # inherit them using &construct_instance |
41 | |
42 | ## Class::MOP::Class |
43 | |
44 | Class::MOP::Class->meta->add_attribute( |
351bd7d4 |
45 | Class::MOP::Attribute->new('$: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)->{'$:package'} } |
51 | }, |
7b31baf4 |
52 | init_arg => ':package', |
727919c5 |
53 | )) |
54 | ); |
55 | |
56 | Class::MOP::Class->meta->add_attribute( |
351bd7d4 |
57 | Class::MOP::Attribute->new('%:attributes' => ( |
f7259199 |
58 | reader => { |
59 | # NOTE: we need to do this in order |
60 | # for the instance meta-object to |
61 | # not fall into meta-circular death |
62 | 'get_attribute_map' => sub { (shift)->{'%:attributes'} } |
63 | }, |
351bd7d4 |
64 | init_arg => ':attributes', |
727919c5 |
65 | default => sub { {} } |
66 | )) |
67 | ); |
68 | |
351bd7d4 |
69 | Class::MOP::Class->meta->add_attribute( |
70 | Class::MOP::Attribute->new('$:attribute_metaclass' => ( |
7b31baf4 |
71 | reader => 'attribute_metaclass', |
351bd7d4 |
72 | init_arg => ':attribute_metaclass', |
73 | default => 'Class::MOP::Attribute', |
74 | )) |
75 | ); |
76 | |
77 | Class::MOP::Class->meta->add_attribute( |
78 | Class::MOP::Attribute->new('$:method_metaclass' => ( |
7b31baf4 |
79 | reader => 'method_metaclass', |
351bd7d4 |
80 | init_arg => ':method_metaclass', |
81 | default => 'Class::MOP::Method', |
82 | )) |
83 | ); |
84 | |
2bab2be6 |
85 | Class::MOP::Class->meta->add_attribute( |
86 | Class::MOP::Attribute->new('$:instance_metaclass' => ( |
b880e0de |
87 | reader => { |
88 | # NOTE: we need to do this in order |
89 | # for the instance meta-object to |
90 | # not fall into meta-circular death |
91 | 'instance_metaclass' => sub { (shift)->{'$:instance_metaclass'} } |
92 | }, |
2bab2be6 |
93 | init_arg => ':instance_metaclass', |
94 | default => 'Class::MOP::Instance', |
95 | )) |
96 | ); |
97 | |
727919c5 |
98 | ## Class::MOP::Attribute |
99 | |
7b31baf4 |
100 | Class::MOP::Attribute->meta->add_attribute( |
101 | Class::MOP::Attribute->new('name' => ( |
b880e0de |
102 | reader => { |
103 | # NOTE: we need to do this in order |
104 | # for the instance meta-object to |
105 | # not fall into meta-circular death |
106 | 'name' => sub { (shift)->{name} } |
107 | } |
7b31baf4 |
108 | )) |
109 | ); |
110 | |
111 | Class::MOP::Attribute->meta->add_attribute( |
112 | Class::MOP::Attribute->new('associated_class' => ( |
b880e0de |
113 | reader => { |
114 | # NOTE: we need to do this in order |
115 | # for the instance meta-object to |
116 | # not fall into meta-circular death |
117 | 'associated_class' => sub { (shift)->{associated_class} } |
118 | } |
7b31baf4 |
119 | )) |
120 | ); |
121 | |
122 | Class::MOP::Attribute->meta->add_attribute( |
123 | Class::MOP::Attribute->new('accessor' => ( |
124 | reader => 'accessor', |
125 | predicate => 'has_accessor', |
126 | )) |
127 | ); |
128 | |
129 | Class::MOP::Attribute->meta->add_attribute( |
130 | Class::MOP::Attribute->new('reader' => ( |
131 | reader => 'reader', |
132 | predicate => 'has_reader', |
133 | )) |
134 | ); |
135 | |
136 | Class::MOP::Attribute->meta->add_attribute( |
137 | Class::MOP::Attribute->new('writer' => ( |
138 | reader => 'writer', |
139 | predicate => 'has_writer', |
140 | )) |
141 | ); |
142 | |
143 | Class::MOP::Attribute->meta->add_attribute( |
144 | Class::MOP::Attribute->new('predicate' => ( |
145 | reader => 'predicate', |
146 | predicate => 'has_predicate', |
147 | )) |
148 | ); |
149 | |
150 | Class::MOP::Attribute->meta->add_attribute( |
151 | Class::MOP::Attribute->new('init_arg' => ( |
152 | reader => 'init_arg', |
153 | predicate => 'has_init_arg', |
154 | )) |
155 | ); |
156 | |
157 | Class::MOP::Attribute->meta->add_attribute( |
158 | Class::MOP::Attribute->new('default' => ( |
159 | # default has a custom 'reader' method ... |
160 | predicate => 'has_default', |
161 | )) |
162 | ); |
163 | |
727919c5 |
164 | |
165 | # NOTE: (meta-circularity) |
166 | # This should be one of the last things done |
167 | # it will "tie the knot" with Class::MOP::Attribute |
168 | # so that it uses the attributes meta-objects |
169 | # to construct itself. |
170 | Class::MOP::Attribute->meta->add_method('new' => sub { |
171 | my $class = shift; |
172 | my $name = shift; |
173 | my %options = @_; |
174 | |
175 | (defined $name && $name) |
176 | || confess "You must provide a name for the attribute"; |
5659d76e |
177 | $options{init_arg} = $name |
178 | if not exists $options{init_arg}; |
651955fb |
179 | |
5659d76e |
180 | # return the new object |
181 | $class->meta->new_object(name => $name, %options); |
182 | }); |
183 | |
184 | Class::MOP::Attribute->meta->add_method('clone' => sub { |
a740253a |
185 | my $self = shift; |
a27ae83f |
186 | $self->meta->clone_object($self, @_); |
727919c5 |
187 | }); |
188 | |
94b19069 |
189 | 1; |
190 | |
191 | __END__ |
192 | |
193 | =pod |
194 | |
195 | =head1 NAME |
196 | |
197 | Class::MOP - A Meta Object Protocol for Perl 5 |
198 | |
199 | =head1 SYNOPSIS |
200 | |
a2e85e6c |
201 | # ... This will come later, for now see |
202 | # the other SYNOPSIS for more information |
94b19069 |
203 | |
204 | =head1 DESCRIPTON |
205 | |
206 | This module is an attempt to create a meta object protocol for the |
207 | Perl 5 object system. It makes no attempt to change the behavior or |
208 | characteristics of the Perl 5 object system, only to create a |
27e31eaf |
209 | protocol for its manipulation and introspection. |
94b19069 |
210 | |
211 | That said, it does attempt to create the tools for building a rich |
212 | set of extensions to the Perl 5 object system. Every attempt has been |
213 | made for these tools to keep to the spirit of the Perl 5 object |
214 | system that we all know and love. |
215 | |
40483095 |
216 | This documentation is admittedly sparse on details, as time permits |
217 | I will try to improve them. For now, I suggest looking at the items |
218 | listed in the L<SEE ALSO> section for more information. In particular |
219 | the book "The Art of the Meta Object Protocol" was very influential |
220 | in the development of this system. |
221 | |
bfe4d0fc |
222 | =head2 What is a Meta Object Protocol? |
223 | |
224 | A meta object protocol is an API to an object system. |
225 | |
226 | To be more specific, it is a set of abstractions of the components of |
227 | an object system (typically things like; classes, object, methods, |
228 | object attributes, etc.). These abstractions can then be used to both |
229 | inspect and manipulate the object system which they describe. |
230 | |
231 | It can be said that there are two MOPs for any object system; the |
232 | implicit MOP, and the explicit MOP. The implicit MOP handles things |
233 | like method dispatch or inheritance, which happen automatically as |
234 | part of how the object system works. The explicit MOP typically |
235 | handles the introspection/reflection features of the object system. |
236 | All object systems have implicit MOPs, without one, they would not |
237 | work. Explict MOPs however as less common, and depending on the |
238 | language can vary from restrictive (Reflection in Java or C#) to |
239 | wide open (CLOS is a perfect example). |
240 | |
e16da3e6 |
241 | =head2 Yet Another Class Builder!! Why? |
242 | |
243 | This is B<not> a class builder so much as it is a I<class builder |
244 | B<builder>>. My intent is that an end user does not use this module |
245 | directly, but instead this module is used by module authors to |
246 | build extensions and features onto the Perl 5 object system. |
247 | |
94b19069 |
248 | =head2 Who is this module for? |
249 | |
250 | This module is specifically for anyone who has ever created or |
251 | wanted to create a module for the Class:: namespace. The tools which |
252 | this module will provide will hopefully make it easier to do more |
253 | complex things with Perl 5 classes by removing such barriers as |
254 | the need to hack the symbol tables, or understand the fine details |
255 | of method dispatch. |
256 | |
bfe4d0fc |
257 | =head2 What changes do I have to make to use this module? |
258 | |
2eb717d5 |
259 | This module was designed to be as unintrusive as possible. Many of |
343203ee |
260 | its features are accessible without B<any> change to your existsing |
bfe4d0fc |
261 | code at all. It is meant to be a compliment to your existing code and |
2eb717d5 |
262 | not an intrusion on your code base. Unlike many other B<Class::> |
a2e85e6c |
263 | modules, this module B<does not> require you subclass it, or even that |
264 | you C<use> it in within your module's package. |
bfe4d0fc |
265 | |
2eb717d5 |
266 | The only features which requires additions to your code are the |
267 | attribute handling and instance construction features, and these are |
a2e85e6c |
268 | both completely optional features. The only reason for this is because |
2eb717d5 |
269 | Perl 5's object system does not actually have these features built |
270 | in. More information about this feature can be found below. |
bfe4d0fc |
271 | |
272 | =head2 A Note about Performance? |
273 | |
274 | It is a common misconception that explict MOPs are performance drains. |
275 | But this is not a universal truth at all, it is an side-effect of |
276 | specific implementations. For instance, using Java reflection is much |
277 | slower because the JVM cannot take advantage of any compiler |
278 | optimizations, and the JVM has to deal with much more runtime type |
279 | information as well. Reflection in C# is marginally better as it was |
280 | designed into the language and runtime (the CLR). In contrast, CLOS |
281 | (the Common Lisp Object System) was built to support an explicit MOP, |
282 | and so performance is tuned for it. |
283 | |
284 | This library in particular does it's absolute best to avoid putting |
2eb717d5 |
285 | B<any> drain at all upon your code's performance. In fact, by itself |
286 | it does nothing to affect your existing code. So you only pay for |
287 | what you actually use. |
bfe4d0fc |
288 | |
550d56db |
289 | =head2 About Metaclass compatibility |
290 | |
291 | This module makes sure that all metaclasses created are both upwards |
292 | and downwards compatible. The topic of metaclass compatibility is |
293 | highly esoteric and is something only encountered when doing deep and |
294 | involved metaclass hacking. There are two basic kinds of metaclass |
295 | incompatibility; upwards and downwards. |
296 | |
297 | Upwards metaclass compatibility means that the metaclass of a |
298 | given class is either the same as (or a subclass of) all of the |
299 | class's ancestors. |
300 | |
301 | Downward metaclass compatibility means that the metaclasses of a |
302 | given class's anscestors are all either the same as (or a subclass |
303 | of) that metaclass. |
304 | |
305 | Here is a diagram showing a set of two classes (C<A> and C<B>) and |
306 | two metaclasses (C<Meta::A> and C<Meta::B>) which have correct |
307 | metaclass compatibility both upwards and downwards. |
308 | |
309 | +---------+ +---------+ |
310 | | Meta::A |<----| Meta::B | <....... (instance of ) |
311 | +---------+ +---------+ <------- (inherits from) |
312 | ^ ^ |
313 | : : |
314 | +---------+ +---------+ |
315 | | A |<----| B | |
316 | +---------+ +---------+ |
317 | |
318 | As I said this is a highly esoteric topic and one you will only run |
319 | into if you do a lot of subclassing of B<Class::MOP::Class>. If you |
320 | are interested in why this is an issue see the paper |
321 | I<Uniform and safe metaclass composition> linked to in the |
322 | L<SEE ALSO> section of this document. |
323 | |
aa448b16 |
324 | =head2 Using custom metaclasses |
325 | |
326 | Always use the metaclass pragma when using a custom metaclass, this |
327 | will ensure the proper initialization order and not accidentely |
328 | create an incorrect type of metaclass for you. This is a very rare |
329 | problem, and one which can only occur if you are doing deep metaclass |
330 | programming. So in other words, don't worry about it. |
331 | |
94b19069 |
332 | =head1 PROTOCOLS |
333 | |
334 | The protocol is divided into 3 main sub-protocols: |
335 | |
336 | =over 4 |
337 | |
338 | =item The Class protocol |
339 | |
340 | This provides a means of manipulating and introspecting a Perl 5 |
341 | class. It handles all of symbol table hacking for you, and provides |
342 | a rich set of methods that go beyond simple package introspection. |
343 | |
552e3d24 |
344 | See L<Class::MOP::Class> for more details. |
345 | |
94b19069 |
346 | =item The Attribute protocol |
347 | |
348 | This provides a consistent represenation for an attribute of a |
349 | Perl 5 class. Since there are so many ways to create and handle |
350 | atttributes in Perl 5 OO, this attempts to provide as much of a |
351 | unified approach as possible, while giving the freedom and |
352 | flexibility to subclass for specialization. |
353 | |
552e3d24 |
354 | See L<Class::MOP::Attribute> for more details. |
355 | |
94b19069 |
356 | =item The Method protocol |
357 | |
358 | This provides a means of manipulating and introspecting methods in |
359 | the Perl 5 object system. As with attributes, there are many ways to |
360 | approach this topic, so we try to keep it pretty basic, while still |
361 | making it possible to extend the system in many ways. |
362 | |
552e3d24 |
363 | See L<Class::MOP::Method> for more details. |
94b19069 |
364 | |
365 | =back |
366 | |
552e3d24 |
367 | =head1 SEE ALSO |
8b978dd5 |
368 | |
552e3d24 |
369 | =head2 Books |
8b978dd5 |
370 | |
a2e85e6c |
371 | There are very few books out on Meta Object Protocols and Metaclasses |
372 | because it is such an esoteric topic. The following books are really |
373 | the only ones I have found. If you know of any more, B<I<please>> |
374 | email me and let me know, I would love to hear about them. |
375 | |
8b978dd5 |
376 | =over 4 |
377 | |
552e3d24 |
378 | =item "The Art of the Meta Object Protocol" |
8b978dd5 |
379 | |
552e3d24 |
380 | =item "Advances in Object-Oriented Metalevel Architecture and Reflection" |
8b978dd5 |
381 | |
b51af7f9 |
382 | =item "Putting MetaClasses to Work" |
383 | |
a2e85e6c |
384 | =item "Smalltalk: The Language" |
385 | |
94b19069 |
386 | =back |
387 | |
550d56db |
388 | =head2 Papers |
389 | |
390 | =over 4 |
391 | |
392 | =item Uniform and safe metaclass composition |
393 | |
394 | An excellent paper by the people who brought us the original Traits paper. |
395 | This paper is on how Traits can be used to do safe metaclass composition, |
396 | and offers an excellent introduction section which delves into the topic of |
397 | metaclass compatibility. |
398 | |
399 | L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf> |
400 | |
401 | =item Safe Metaclass Programming |
402 | |
403 | This paper seems to precede the above paper, and propose a mix-in based |
404 | approach as opposed to the Traits based approach. Both papers have similar |
405 | information on the metaclass compatibility problem space. |
406 | |
407 | L<http://citeseer.ist.psu.edu/37617.html> |
408 | |
409 | =back |
410 | |
552e3d24 |
411 | =head2 Prior Art |
8b978dd5 |
412 | |
413 | =over 4 |
414 | |
7184ca14 |
415 | =item The Perl 6 MetaModel work in the Pugs project |
8b978dd5 |
416 | |
417 | =over 4 |
418 | |
552e3d24 |
419 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel> |
8b978dd5 |
420 | |
552e3d24 |
421 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace> |
8b978dd5 |
422 | |
423 | =back |
424 | |
94b19069 |
425 | =back |
426 | |
a2e85e6c |
427 | =head1 SIMILAR MODULES |
428 | |
429 | As I have said above, this module is a class-builder-builder, so it is |
430 | not the same thing as modules like L<Class::Accessor> and |
431 | L<Class::MethodMaker>. That being said there are very few modules on CPAN |
432 | with similar goals to this module. The one I have found which is most |
550d56db |
433 | like this module is L<Class::Meta>, although it's philosophy and the MOP it |
434 | creates are very different from this modules. |
94b19069 |
435 | |
a2e85e6c |
436 | =head1 BUGS |
437 | |
438 | All complex software has bugs lurking in it, and this module is no |
439 | exception. If you find a bug please either email me, or add the bug |
440 | to cpan-RT. |
441 | |
22286063 |
442 | =head1 CODE COVERAGE |
443 | |
444 | I use L<Devel::Cover> to test the code coverage of my tests, below is the |
445 | L<Devel::Cover> report on this module's test suite. |
446 | |
447 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
448 | File stmt bran cond sub pod time total |
449 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
cdfaa4cc |
450 | Class/MOP.pm 100.0 100.0 100.0 100.0 n/a 19.8 100.0 |
451 | Class/MOP/Attribute.pm 100.0 100.0 91.7 61.2 100.0 14.3 87.9 |
452 | Class/MOP/Class.pm 97.6 91.3 77.3 98.4 100.0 56.4 93.2 |
453 | Class/MOP/Instance.pm 91.1 75.0 33.3 91.7 100.0 6.8 90.7 |
454 | Class/MOP/Method.pm 97.6 60.0 52.9 76.9 100.0 1.6 82.6 |
455 | metaclass.pm 100.0 100.0 83.3 100.0 n/a 1.0 97.7 |
22286063 |
456 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
cdfaa4cc |
457 | Total 97.5 88.5 75.5 82.8 100.0 100.0 91.2 |
22286063 |
458 | ---------------------------- ------ ------ ------ ------ ------ ------ ------ |
459 | |
a2e85e6c |
460 | =head1 ACKNOWLEDGEMENTS |
461 | |
462 | =over 4 |
463 | |
464 | =item Rob Kinyon E<lt>rob@iinteractive.comE<gt> |
465 | |
466 | Thanks to Rob for actually getting the development of this module kick-started. |
467 | |
468 | =back |
469 | |
470 | =head1 AUTHOR |
94b19069 |
471 | |
a2e85e6c |
472 | Stevan Little E<lt>stevan@iinteractive.comE<gt> |
552e3d24 |
473 | |
94b19069 |
474 | =head1 COPYRIGHT AND LICENSE |
475 | |
476 | Copyright 2006 by Infinity Interactive, Inc. |
477 | |
478 | L<http://www.iinteractive.com> |
479 | |
480 | This library is free software; you can redistribute it and/or modify |
481 | it under the same terms as Perl itself. |
482 | |
483 | =cut |