Commit | Line | Data |
94b19069 |
1 | |
2 | package Class::MOP; |
3 | |
4 | use strict; |
5 | use warnings; |
6 | |
8b978dd5 |
7 | use Scalar::Util 'blessed'; |
727919c5 |
8 | use Carp 'confess'; |
8b978dd5 |
9 | |
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10 | use Class::MOP::Class; |
11 | use Class::MOP::Attribute; |
12 | use Class::MOP::Method; |
13 | |
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14 | our $VERSION = '0.06'; |
94b19069 |
15 | |
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16 | sub import { |
17 | shift; |
18 | return unless @_; |
19 | if ($_[0] eq ':universal') { |
20 | *UNIVERSAL::meta = sub { |
21 | Class::MOP::Class->initialize(blessed($_[0]) || $_[0]) |
22 | }; |
23 | } |
1a7ebbb3 |
24 | else { |
25 | my $pkg = caller(); |
26 | no strict 'refs'; |
27 | *{$pkg . '::' . $_[0]} = sub { |
28 | Class::MOP::Class->initialize(blessed($_[0]) || $_[0]) |
29 | }; |
30 | } |
2eb717d5 |
31 | } |
8b978dd5 |
32 | |
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33 | ## ---------------------------------------------------------------------------- |
34 | ## Bootstrapping |
35 | ## ---------------------------------------------------------------------------- |
36 | ## The code below here is to bootstrap our MOP with itself. This is also |
37 | ## sometimes called "tying the knot". By doing this, we make it much easier |
38 | ## to extend the MOP through subclassing and such since now you can use the |
39 | ## MOP itself to extend itself. |
40 | ## |
41 | ## Yes, I know, thats weird and insane, but it's a good thing, trust me :) |
42 | ## ---------------------------------------------------------------------------- |
727919c5 |
43 | |
44 | # We need to add in the meta-attributes here so that |
45 | # any subclass of Class::MOP::* will be able to |
46 | # inherit them using &construct_instance |
47 | |
48 | ## Class::MOP::Class |
49 | |
50 | Class::MOP::Class->meta->add_attribute( |
351bd7d4 |
51 | Class::MOP::Attribute->new('$:package' => ( |
7b31baf4 |
52 | reader => 'name', |
53 | init_arg => ':package', |
727919c5 |
54 | )) |
55 | ); |
56 | |
57 | Class::MOP::Class->meta->add_attribute( |
351bd7d4 |
58 | Class::MOP::Attribute->new('%:attributes' => ( |
7b31baf4 |
59 | reader => 'get_attribute_map', |
351bd7d4 |
60 | init_arg => ':attributes', |
727919c5 |
61 | default => sub { {} } |
62 | )) |
63 | ); |
64 | |
351bd7d4 |
65 | Class::MOP::Class->meta->add_attribute( |
66 | Class::MOP::Attribute->new('$:attribute_metaclass' => ( |
7b31baf4 |
67 | reader => 'attribute_metaclass', |
351bd7d4 |
68 | init_arg => ':attribute_metaclass', |
69 | default => 'Class::MOP::Attribute', |
70 | )) |
71 | ); |
72 | |
73 | Class::MOP::Class->meta->add_attribute( |
74 | Class::MOP::Attribute->new('$:method_metaclass' => ( |
7b31baf4 |
75 | reader => 'method_metaclass', |
351bd7d4 |
76 | init_arg => ':method_metaclass', |
77 | default => 'Class::MOP::Method', |
78 | )) |
79 | ); |
80 | |
727919c5 |
81 | ## Class::MOP::Attribute |
82 | |
7b31baf4 |
83 | Class::MOP::Attribute->meta->add_attribute( |
84 | Class::MOP::Attribute->new('name' => ( |
85 | reader => 'name' |
86 | )) |
87 | ); |
88 | |
89 | Class::MOP::Attribute->meta->add_attribute( |
90 | Class::MOP::Attribute->new('associated_class' => ( |
91 | reader => 'associated_class' |
92 | )) |
93 | ); |
94 | |
95 | Class::MOP::Attribute->meta->add_attribute( |
96 | Class::MOP::Attribute->new('accessor' => ( |
97 | reader => 'accessor', |
98 | predicate => 'has_accessor', |
99 | )) |
100 | ); |
101 | |
102 | Class::MOP::Attribute->meta->add_attribute( |
103 | Class::MOP::Attribute->new('reader' => ( |
104 | reader => 'reader', |
105 | predicate => 'has_reader', |
106 | )) |
107 | ); |
108 | |
109 | Class::MOP::Attribute->meta->add_attribute( |
110 | Class::MOP::Attribute->new('writer' => ( |
111 | reader => 'writer', |
112 | predicate => 'has_writer', |
113 | )) |
114 | ); |
115 | |
116 | Class::MOP::Attribute->meta->add_attribute( |
117 | Class::MOP::Attribute->new('predicate' => ( |
118 | reader => 'predicate', |
119 | predicate => 'has_predicate', |
120 | )) |
121 | ); |
122 | |
123 | Class::MOP::Attribute->meta->add_attribute( |
124 | Class::MOP::Attribute->new('init_arg' => ( |
125 | reader => 'init_arg', |
126 | predicate => 'has_init_arg', |
127 | )) |
128 | ); |
129 | |
130 | Class::MOP::Attribute->meta->add_attribute( |
131 | Class::MOP::Attribute->new('default' => ( |
132 | # default has a custom 'reader' method ... |
133 | predicate => 'has_default', |
134 | )) |
135 | ); |
136 | |
727919c5 |
137 | |
138 | # NOTE: (meta-circularity) |
139 | # This should be one of the last things done |
140 | # it will "tie the knot" with Class::MOP::Attribute |
141 | # so that it uses the attributes meta-objects |
142 | # to construct itself. |
143 | Class::MOP::Attribute->meta->add_method('new' => sub { |
144 | my $class = shift; |
145 | my $name = shift; |
146 | my %options = @_; |
147 | |
148 | (defined $name && $name) |
149 | || confess "You must provide a name for the attribute"; |
5659d76e |
150 | $options{init_arg} = $name |
151 | if not exists $options{init_arg}; |
651955fb |
152 | |
5659d76e |
153 | # return the new object |
154 | $class->meta->new_object(name => $name, %options); |
155 | }); |
156 | |
157 | Class::MOP::Attribute->meta->add_method('clone' => sub { |
a740253a |
158 | my $self = shift; |
159 | my $class = $self->associated_class; |
160 | $self->detach_from_class() if defined $class; |
161 | my $clone = $self->meta->clone_object($self, @_); |
162 | if (defined $class) { |
163 | $self->attach_to_class($class); |
164 | $clone->attach_to_class($class); |
165 | } |
166 | return $clone; |
727919c5 |
167 | }); |
168 | |
94b19069 |
169 | 1; |
170 | |
171 | __END__ |
172 | |
173 | =pod |
174 | |
175 | =head1 NAME |
176 | |
177 | Class::MOP - A Meta Object Protocol for Perl 5 |
178 | |
179 | =head1 SYNOPSIS |
180 | |
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181 | # ... This will come later, for now see |
182 | # the other SYNOPSIS for more information |
94b19069 |
183 | |
184 | =head1 DESCRIPTON |
185 | |
186 | This module is an attempt to create a meta object protocol for the |
187 | Perl 5 object system. It makes no attempt to change the behavior or |
188 | characteristics of the Perl 5 object system, only to create a |
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189 | protocol for its manipulation and introspection. |
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190 | |
191 | That said, it does attempt to create the tools for building a rich |
192 | set of extensions to the Perl 5 object system. Every attempt has been |
193 | made for these tools to keep to the spirit of the Perl 5 object |
194 | system that we all know and love. |
195 | |
bfe4d0fc |
196 | =head2 What is a Meta Object Protocol? |
197 | |
198 | A meta object protocol is an API to an object system. |
199 | |
200 | To be more specific, it is a set of abstractions of the components of |
201 | an object system (typically things like; classes, object, methods, |
202 | object attributes, etc.). These abstractions can then be used to both |
203 | inspect and manipulate the object system which they describe. |
204 | |
205 | It can be said that there are two MOPs for any object system; the |
206 | implicit MOP, and the explicit MOP. The implicit MOP handles things |
207 | like method dispatch or inheritance, which happen automatically as |
208 | part of how the object system works. The explicit MOP typically |
209 | handles the introspection/reflection features of the object system. |
210 | All object systems have implicit MOPs, without one, they would not |
211 | work. Explict MOPs however as less common, and depending on the |
212 | language can vary from restrictive (Reflection in Java or C#) to |
213 | wide open (CLOS is a perfect example). |
214 | |
e16da3e6 |
215 | =head2 Yet Another Class Builder!! Why? |
216 | |
217 | This is B<not> a class builder so much as it is a I<class builder |
218 | B<builder>>. My intent is that an end user does not use this module |
219 | directly, but instead this module is used by module authors to |
220 | build extensions and features onto the Perl 5 object system. |
221 | |
94b19069 |
222 | =head2 Who is this module for? |
223 | |
224 | This module is specifically for anyone who has ever created or |
225 | wanted to create a module for the Class:: namespace. The tools which |
226 | this module will provide will hopefully make it easier to do more |
227 | complex things with Perl 5 classes by removing such barriers as |
228 | the need to hack the symbol tables, or understand the fine details |
229 | of method dispatch. |
230 | |
bfe4d0fc |
231 | =head2 What changes do I have to make to use this module? |
232 | |
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233 | This module was designed to be as unintrusive as possible. Many of |
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234 | its features are accessible without B<any> change to your existsing |
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235 | code at all. It is meant to be a compliment to your existing code and |
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236 | not an intrusion on your code base. Unlike many other B<Class::> |
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237 | modules, this module B<does not> require you subclass it, or even that |
238 | you C<use> it in within your module's package. |
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239 | |
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240 | The only features which requires additions to your code are the |
241 | attribute handling and instance construction features, and these are |
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242 | both completely optional features. The only reason for this is because |
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243 | Perl 5's object system does not actually have these features built |
244 | in. More information about this feature can be found below. |
bfe4d0fc |
245 | |
246 | =head2 A Note about Performance? |
247 | |
248 | It is a common misconception that explict MOPs are performance drains. |
249 | But this is not a universal truth at all, it is an side-effect of |
250 | specific implementations. For instance, using Java reflection is much |
251 | slower because the JVM cannot take advantage of any compiler |
252 | optimizations, and the JVM has to deal with much more runtime type |
253 | information as well. Reflection in C# is marginally better as it was |
254 | designed into the language and runtime (the CLR). In contrast, CLOS |
255 | (the Common Lisp Object System) was built to support an explicit MOP, |
256 | and so performance is tuned for it. |
257 | |
258 | This library in particular does it's absolute best to avoid putting |
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259 | B<any> drain at all upon your code's performance. In fact, by itself |
260 | it does nothing to affect your existing code. So you only pay for |
261 | what you actually use. |
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262 | |
550d56db |
263 | =head2 About Metaclass compatibility |
264 | |
265 | This module makes sure that all metaclasses created are both upwards |
266 | and downwards compatible. The topic of metaclass compatibility is |
267 | highly esoteric and is something only encountered when doing deep and |
268 | involved metaclass hacking. There are two basic kinds of metaclass |
269 | incompatibility; upwards and downwards. |
270 | |
271 | Upwards metaclass compatibility means that the metaclass of a |
272 | given class is either the same as (or a subclass of) all of the |
273 | class's ancestors. |
274 | |
275 | Downward metaclass compatibility means that the metaclasses of a |
276 | given class's anscestors are all either the same as (or a subclass |
277 | of) that metaclass. |
278 | |
279 | Here is a diagram showing a set of two classes (C<A> and C<B>) and |
280 | two metaclasses (C<Meta::A> and C<Meta::B>) which have correct |
281 | metaclass compatibility both upwards and downwards. |
282 | |
283 | +---------+ +---------+ |
284 | | Meta::A |<----| Meta::B | <....... (instance of ) |
285 | +---------+ +---------+ <------- (inherits from) |
286 | ^ ^ |
287 | : : |
288 | +---------+ +---------+ |
289 | | A |<----| B | |
290 | +---------+ +---------+ |
291 | |
292 | As I said this is a highly esoteric topic and one you will only run |
293 | into if you do a lot of subclassing of B<Class::MOP::Class>. If you |
294 | are interested in why this is an issue see the paper |
295 | I<Uniform and safe metaclass composition> linked to in the |
296 | L<SEE ALSO> section of this document. |
297 | |
94b19069 |
298 | =head1 PROTOCOLS |
299 | |
300 | The protocol is divided into 3 main sub-protocols: |
301 | |
302 | =over 4 |
303 | |
304 | =item The Class protocol |
305 | |
306 | This provides a means of manipulating and introspecting a Perl 5 |
307 | class. It handles all of symbol table hacking for you, and provides |
308 | a rich set of methods that go beyond simple package introspection. |
309 | |
552e3d24 |
310 | See L<Class::MOP::Class> for more details. |
311 | |
94b19069 |
312 | =item The Attribute protocol |
313 | |
314 | This provides a consistent represenation for an attribute of a |
315 | Perl 5 class. Since there are so many ways to create and handle |
316 | atttributes in Perl 5 OO, this attempts to provide as much of a |
317 | unified approach as possible, while giving the freedom and |
318 | flexibility to subclass for specialization. |
319 | |
552e3d24 |
320 | See L<Class::MOP::Attribute> for more details. |
321 | |
94b19069 |
322 | =item The Method protocol |
323 | |
324 | This provides a means of manipulating and introspecting methods in |
325 | the Perl 5 object system. As with attributes, there are many ways to |
326 | approach this topic, so we try to keep it pretty basic, while still |
327 | making it possible to extend the system in many ways. |
328 | |
552e3d24 |
329 | See L<Class::MOP::Method> for more details. |
94b19069 |
330 | |
331 | =back |
332 | |
552e3d24 |
333 | =head1 SEE ALSO |
8b978dd5 |
334 | |
552e3d24 |
335 | =head2 Books |
8b978dd5 |
336 | |
a2e85e6c |
337 | There are very few books out on Meta Object Protocols and Metaclasses |
338 | because it is such an esoteric topic. The following books are really |
339 | the only ones I have found. If you know of any more, B<I<please>> |
340 | email me and let me know, I would love to hear about them. |
341 | |
8b978dd5 |
342 | =over 4 |
343 | |
552e3d24 |
344 | =item "The Art of the Meta Object Protocol" |
8b978dd5 |
345 | |
552e3d24 |
346 | =item "Advances in Object-Oriented Metalevel Architecture and Reflection" |
8b978dd5 |
347 | |
b51af7f9 |
348 | =item "Putting MetaClasses to Work" |
349 | |
a2e85e6c |
350 | =item "Smalltalk: The Language" |
351 | |
94b19069 |
352 | =back |
353 | |
550d56db |
354 | =head2 Papers |
355 | |
356 | =over 4 |
357 | |
358 | =item Uniform and safe metaclass composition |
359 | |
360 | An excellent paper by the people who brought us the original Traits paper. |
361 | This paper is on how Traits can be used to do safe metaclass composition, |
362 | and offers an excellent introduction section which delves into the topic of |
363 | metaclass compatibility. |
364 | |
365 | L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf> |
366 | |
367 | =item Safe Metaclass Programming |
368 | |
369 | This paper seems to precede the above paper, and propose a mix-in based |
370 | approach as opposed to the Traits based approach. Both papers have similar |
371 | information on the metaclass compatibility problem space. |
372 | |
373 | L<http://citeseer.ist.psu.edu/37617.html> |
374 | |
375 | =back |
376 | |
552e3d24 |
377 | =head2 Prior Art |
8b978dd5 |
378 | |
379 | =over 4 |
380 | |
7184ca14 |
381 | =item The Perl 6 MetaModel work in the Pugs project |
8b978dd5 |
382 | |
383 | =over 4 |
384 | |
552e3d24 |
385 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel> |
8b978dd5 |
386 | |
552e3d24 |
387 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace> |
8b978dd5 |
388 | |
389 | =back |
390 | |
94b19069 |
391 | =back |
392 | |
a2e85e6c |
393 | =head1 SIMILAR MODULES |
394 | |
395 | As I have said above, this module is a class-builder-builder, so it is |
396 | not the same thing as modules like L<Class::Accessor> and |
397 | L<Class::MethodMaker>. That being said there are very few modules on CPAN |
398 | with similar goals to this module. The one I have found which is most |
550d56db |
399 | like this module is L<Class::Meta>, although it's philosophy and the MOP it |
400 | creates are very different from this modules. |
94b19069 |
401 | |
a2e85e6c |
402 | =head1 BUGS |
403 | |
404 | All complex software has bugs lurking in it, and this module is no |
405 | exception. If you find a bug please either email me, or add the bug |
406 | to cpan-RT. |
407 | |
408 | =head1 ACKNOWLEDGEMENTS |
409 | |
410 | =over 4 |
411 | |
412 | =item Rob Kinyon E<lt>rob@iinteractive.comE<gt> |
413 | |
414 | Thanks to Rob for actually getting the development of this module kick-started. |
415 | |
416 | =back |
417 | |
418 | =head1 AUTHOR |
94b19069 |
419 | |
a2e85e6c |
420 | Stevan Little E<lt>stevan@iinteractive.comE<gt> |
552e3d24 |
421 | |
94b19069 |
422 | =head1 COPYRIGHT AND LICENSE |
423 | |
424 | Copyright 2006 by Infinity Interactive, Inc. |
425 | |
426 | L<http://www.iinteractive.com> |
427 | |
428 | This library is free software; you can redistribute it and/or modify |
429 | it under the same terms as Perl itself. |
430 | |
431 | =cut |