Commit | Line | Data |
94b19069 |
1 | |
2 | package Class::MOP; |
3 | |
4 | use strict; |
5 | use warnings; |
6 | |
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7 | use Scalar::Util 'blessed'; |
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8 | use Carp 'confess'; |
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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 $VERSION = '0.06'; |
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15 | |
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16 | sub import { |
17 | shift; |
18 | return unless @_; |
19 | if ($_[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]) || $_[0]) |
29 | }; |
30 | } |
2eb717d5 |
31 | } |
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32 | |
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33 | ## ---------------------------------------------------------------------------- |
34 | ## Bootstrapping |
35 | ## ---------------------------------------------------------------------------- |
36 | ## The code below here is to bootstrap our MOP with itself. This is also |
37 | ## sometimes called "tying the knot". By doing this, we make it much easier |
38 | ## to extend the MOP through subclassing and such since now you can use the |
39 | ## MOP itself to extend itself. |
40 | ## |
41 | ## Yes, I know, thats weird and insane, but it's a good thing, trust me :) |
42 | ## ---------------------------------------------------------------------------- |
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43 | |
44 | # We need to add in the meta-attributes here so that |
45 | # any subclass of Class::MOP::* will be able to |
46 | # inherit them using &construct_instance |
47 | |
48 | ## Class::MOP::Class |
49 | |
50 | Class::MOP::Class->meta->add_attribute( |
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51 | Class::MOP::Attribute->new('$:package' => ( |
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52 | reader => 'name', |
53 | init_arg => ':package', |
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54 | )) |
55 | ); |
56 | |
57 | Class::MOP::Class->meta->add_attribute( |
351bd7d4 |
58 | Class::MOP::Attribute->new('%:attributes' => ( |
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59 | reader => 'get_attribute_map', |
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60 | init_arg => ':attributes', |
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61 | default => sub { {} } |
62 | )) |
63 | ); |
64 | |
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65 | Class::MOP::Class->meta->add_attribute( |
66 | Class::MOP::Attribute->new('$:attribute_metaclass' => ( |
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67 | reader => 'attribute_metaclass', |
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68 | init_arg => ':attribute_metaclass', |
69 | default => 'Class::MOP::Attribute', |
70 | )) |
71 | ); |
72 | |
73 | Class::MOP::Class->meta->add_attribute( |
74 | Class::MOP::Attribute->new('$:method_metaclass' => ( |
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75 | reader => 'method_metaclass', |
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76 | init_arg => ':method_metaclass', |
77 | default => 'Class::MOP::Method', |
78 | )) |
79 | ); |
80 | |
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81 | ## Class::MOP::Attribute |
82 | |
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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 | |
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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"; |
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150 | $options{init_arg} = $name |
151 | if not exists $options{init_arg}; |
651955fb |
152 | |
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153 | # return the new object |
154 | $class->meta->new_object(name => $name, %options); |
155 | }); |
156 | |
157 | Class::MOP::Attribute->meta->add_method('clone' => sub { |
158 | my $self = shift; |
159 | $self->meta->clone_object($self, @_); |
727919c5 |
160 | }); |
161 | |
94b19069 |
162 | 1; |
163 | |
164 | __END__ |
165 | |
166 | =pod |
167 | |
168 | =head1 NAME |
169 | |
170 | Class::MOP - A Meta Object Protocol for Perl 5 |
171 | |
172 | =head1 SYNOPSIS |
173 | |
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174 | # ... This will come later, for now see |
175 | # the other SYNOPSIS for more information |
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176 | |
177 | =head1 DESCRIPTON |
178 | |
179 | This module is an attempt to create a meta object protocol for the |
180 | Perl 5 object system. It makes no attempt to change the behavior or |
181 | characteristics of the Perl 5 object system, only to create a |
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182 | protocol for its manipulation and introspection. |
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183 | |
184 | That said, it does attempt to create the tools for building a rich |
185 | set of extensions to the Perl 5 object system. Every attempt has been |
186 | made for these tools to keep to the spirit of the Perl 5 object |
187 | system that we all know and love. |
188 | |
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189 | =head2 What is a Meta Object Protocol? |
190 | |
191 | A meta object protocol is an API to an object system. |
192 | |
193 | To be more specific, it is a set of abstractions of the components of |
194 | an object system (typically things like; classes, object, methods, |
195 | object attributes, etc.). These abstractions can then be used to both |
196 | inspect and manipulate the object system which they describe. |
197 | |
198 | It can be said that there are two MOPs for any object system; the |
199 | implicit MOP, and the explicit MOP. The implicit MOP handles things |
200 | like method dispatch or inheritance, which happen automatically as |
201 | part of how the object system works. The explicit MOP typically |
202 | handles the introspection/reflection features of the object system. |
203 | All object systems have implicit MOPs, without one, they would not |
204 | work. Explict MOPs however as less common, and depending on the |
205 | language can vary from restrictive (Reflection in Java or C#) to |
206 | wide open (CLOS is a perfect example). |
207 | |
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208 | =head2 Yet Another Class Builder!! Why? |
209 | |
210 | This is B<not> a class builder so much as it is a I<class builder |
211 | B<builder>>. My intent is that an end user does not use this module |
212 | directly, but instead this module is used by module authors to |
213 | build extensions and features onto the Perl 5 object system. |
214 | |
94b19069 |
215 | =head2 Who is this module for? |
216 | |
217 | This module is specifically for anyone who has ever created or |
218 | wanted to create a module for the Class:: namespace. The tools which |
219 | this module will provide will hopefully make it easier to do more |
220 | complex things with Perl 5 classes by removing such barriers as |
221 | the need to hack the symbol tables, or understand the fine details |
222 | of method dispatch. |
223 | |
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224 | =head2 What changes do I have to make to use this module? |
225 | |
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226 | This module was designed to be as unintrusive as possible. Many of |
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227 | its features are accessible without B<any> change to your existsing |
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228 | code at all. It is meant to be a compliment to your existing code and |
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229 | not an intrusion on your code base. Unlike many other B<Class::> |
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230 | modules, this module B<does not> require you subclass it, or even that |
231 | you C<use> it in within your module's package. |
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232 | |
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233 | The only features which requires additions to your code are the |
234 | attribute handling and instance construction features, and these are |
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235 | both completely optional features. The only reason for this is because |
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236 | Perl 5's object system does not actually have these features built |
237 | in. More information about this feature can be found below. |
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238 | |
239 | =head2 A Note about Performance? |
240 | |
241 | It is a common misconception that explict MOPs are performance drains. |
242 | But this is not a universal truth at all, it is an side-effect of |
243 | specific implementations. For instance, using Java reflection is much |
244 | slower because the JVM cannot take advantage of any compiler |
245 | optimizations, and the JVM has to deal with much more runtime type |
246 | information as well. Reflection in C# is marginally better as it was |
247 | designed into the language and runtime (the CLR). In contrast, CLOS |
248 | (the Common Lisp Object System) was built to support an explicit MOP, |
249 | and so performance is tuned for it. |
250 | |
251 | This library in particular does it's absolute best to avoid putting |
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252 | B<any> drain at all upon your code's performance. In fact, by itself |
253 | it does nothing to affect your existing code. So you only pay for |
254 | what you actually use. |
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255 | |
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256 | =head1 PROTOCOLS |
257 | |
258 | The protocol is divided into 3 main sub-protocols: |
259 | |
260 | =over 4 |
261 | |
262 | =item The Class protocol |
263 | |
264 | This provides a means of manipulating and introspecting a Perl 5 |
265 | class. It handles all of symbol table hacking for you, and provides |
266 | a rich set of methods that go beyond simple package introspection. |
267 | |
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268 | See L<Class::MOP::Class> for more details. |
269 | |
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270 | =item The Attribute protocol |
271 | |
272 | This provides a consistent represenation for an attribute of a |
273 | Perl 5 class. Since there are so many ways to create and handle |
274 | atttributes in Perl 5 OO, this attempts to provide as much of a |
275 | unified approach as possible, while giving the freedom and |
276 | flexibility to subclass for specialization. |
277 | |
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278 | See L<Class::MOP::Attribute> for more details. |
279 | |
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280 | =item The Method protocol |
281 | |
282 | This provides a means of manipulating and introspecting methods in |
283 | the Perl 5 object system. As with attributes, there are many ways to |
284 | approach this topic, so we try to keep it pretty basic, while still |
285 | making it possible to extend the system in many ways. |
286 | |
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287 | See L<Class::MOP::Method> for more details. |
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288 | |
289 | =back |
290 | |
552e3d24 |
291 | =head1 SEE ALSO |
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292 | |
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293 | =head2 Books |
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294 | |
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295 | There are very few books out on Meta Object Protocols and Metaclasses |
296 | because it is such an esoteric topic. The following books are really |
297 | the only ones I have found. If you know of any more, B<I<please>> |
298 | email me and let me know, I would love to hear about them. |
299 | |
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300 | =over 4 |
301 | |
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302 | =item "The Art of the Meta Object Protocol" |
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303 | |
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304 | =item "Advances in Object-Oriented Metalevel Architecture and Reflection" |
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305 | |
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306 | =item "Putting MetaClasses to Work" |
307 | |
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308 | =item "Smalltalk: The Language" |
309 | |
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310 | =back |
311 | |
552e3d24 |
312 | =head2 Prior Art |
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313 | |
314 | =over 4 |
315 | |
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316 | =item The Perl 6 MetaModel work in the Pugs project |
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317 | |
318 | =over 4 |
319 | |
552e3d24 |
320 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel> |
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321 | |
552e3d24 |
322 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace> |
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323 | |
324 | =back |
325 | |
94b19069 |
326 | =back |
327 | |
a2e85e6c |
328 | =head1 SIMILAR MODULES |
329 | |
330 | As I have said above, this module is a class-builder-builder, so it is |
331 | not the same thing as modules like L<Class::Accessor> and |
332 | L<Class::MethodMaker>. That being said there are very few modules on CPAN |
333 | with similar goals to this module. The one I have found which is most |
334 | like this module is L<Class::Meta>, although it's philosophy is very |
335 | different from this module. |
336 | |
337 | To start with, it provides wrappers around common Perl data types, and even |
338 | extends those types with more specific subtypes. This module does not |
339 | go into that area at all. |
340 | |
341 | L<Class::Meta> also seems to create it's own custom meta-object protocol, |
342 | which is both more restrictive and more featureful than the vanilla |
343 | Perl 5 one. This module attempts to model the existing Perl 5 MOP as it is. |
344 | |
345 | It's introspection capabilities also seem to be heavily rooted in this |
346 | custom MOP, so that you can only introspect classes which are already |
347 | created with L<Class::Meta>. This module does not make such restictions. |
348 | |
349 | Now, all this said, L<Class::Meta> is much more featureful than B<Class::MOP> |
350 | would ever try to be. But B<Class::MOP> has some features which L<Class::Meta> |
351 | could not easily implement. It would be very possible to completely re-implement |
352 | L<Class::Meta> using B<Class::MOP> and bring some of these features to |
353 | L<Class::Meta> though. |
354 | |
355 | But in the end, this module's admitedly ambitious goals have no direct equal |
356 | on CPAN since surely no one has been crazy enough to try something as silly |
357 | as this ;) until now. |
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358 | |
a2e85e6c |
359 | =head1 BUGS |
360 | |
361 | All complex software has bugs lurking in it, and this module is no |
362 | exception. If you find a bug please either email me, or add the bug |
363 | to cpan-RT. |
364 | |
365 | =head1 ACKNOWLEDGEMENTS |
366 | |
367 | =over 4 |
368 | |
369 | =item Rob Kinyon E<lt>rob@iinteractive.comE<gt> |
370 | |
371 | Thanks to Rob for actually getting the development of this module kick-started. |
372 | |
373 | =back |
374 | |
375 | =head1 AUTHOR |
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376 | |
a2e85e6c |
377 | Stevan Little E<lt>stevan@iinteractive.comE<gt> |
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378 | |
94b19069 |
379 | =head1 COPYRIGHT AND LICENSE |
380 | |
381 | Copyright 2006 by Infinity Interactive, Inc. |
382 | |
383 | L<http://www.iinteractive.com> |
384 | |
385 | This library is free software; you can redistribute it and/or modify |
386 | it under the same terms as Perl itself. |
387 | |
388 | =cut |