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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 $VERSION = '0.02'; |
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15 | |
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16 | sub import { |
17 | shift; |
18 | return unless @_; |
19 | if ($_[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]) || $_[0]) |
29 | }; |
30 | } |
2eb717d5 |
31 | } |
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32 | |
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33 | ## ---------------------------------------------------------------------------- |
34 | ## Bootstrapping |
35 | ## ---------------------------------------------------------------------------- |
36 | ## The code below here is to bootstrap our MOP with itself. This is also |
37 | ## sometimes called "tying the knot". By doing this, we make it much easier |
38 | ## to extend the MOP through subclassing and such since now you can use the |
39 | ## MOP itself to extend itself. |
40 | ## |
41 | ## Yes, I know, thats weird and insane, but it's a good thing, trust me :) |
42 | ## ---------------------------------------------------------------------------- |
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43 | |
44 | # We need to add in the meta-attributes here so that |
45 | # any subclass of Class::MOP::* will be able to |
46 | # inherit them using &construct_instance |
47 | |
48 | ## Class::MOP::Class |
49 | |
50 | Class::MOP::Class->meta->add_attribute( |
51 | Class::MOP::Attribute->new('$:pkg' => ( |
52 | init_arg => ':pkg' |
53 | )) |
54 | ); |
55 | |
56 | Class::MOP::Class->meta->add_attribute( |
57 | Class::MOP::Attribute->new('%:attrs' => ( |
58 | init_arg => ':attrs', |
59 | default => sub { {} } |
60 | )) |
61 | ); |
62 | |
63 | ## Class::MOP::Attribute |
64 | |
65 | Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('name')); |
66 | Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('accessor')); |
67 | Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('reader')); |
68 | Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('writer')); |
69 | Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('predicate')); |
70 | Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('init_arg')); |
71 | Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('default')); |
72 | |
73 | # NOTE: (meta-circularity) |
74 | # This should be one of the last things done |
75 | # it will "tie the knot" with Class::MOP::Attribute |
76 | # so that it uses the attributes meta-objects |
77 | # to construct itself. |
78 | Class::MOP::Attribute->meta->add_method('new' => sub { |
79 | my $class = shift; |
80 | my $name = shift; |
81 | my %options = @_; |
82 | |
83 | (defined $name && $name) |
84 | || confess "You must provide a name for the attribute"; |
85 | (!exists $options{reader} && !exists $options{writer}) |
86 | || confess "You cannot declare an accessor and reader and/or writer functions" |
87 | if exists $options{accessor}; |
88 | |
89 | bless $class->meta->construct_instance(name => $name, %options) => $class; |
90 | }); |
91 | |
94b19069 |
92 | 1; |
93 | |
94 | __END__ |
95 | |
96 | =pod |
97 | |
98 | =head1 NAME |
99 | |
100 | Class::MOP - A Meta Object Protocol for Perl 5 |
101 | |
102 | =head1 SYNOPSIS |
103 | |
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104 | # ... This will come later, for now see |
105 | # the other SYNOPSIS for more information |
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106 | |
107 | =head1 DESCRIPTON |
108 | |
109 | This module is an attempt to create a meta object protocol for the |
110 | Perl 5 object system. It makes no attempt to change the behavior or |
111 | characteristics of the Perl 5 object system, only to create a |
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112 | protocol for its manipulation and introspection. |
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113 | |
114 | That said, it does attempt to create the tools for building a rich |
115 | set of extensions to the Perl 5 object system. Every attempt has been |
116 | made for these tools to keep to the spirit of the Perl 5 object |
117 | system that we all know and love. |
118 | |
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119 | =head2 What is a Meta Object Protocol? |
120 | |
121 | A meta object protocol is an API to an object system. |
122 | |
123 | To be more specific, it is a set of abstractions of the components of |
124 | an object system (typically things like; classes, object, methods, |
125 | object attributes, etc.). These abstractions can then be used to both |
126 | inspect and manipulate the object system which they describe. |
127 | |
128 | It can be said that there are two MOPs for any object system; the |
129 | implicit MOP, and the explicit MOP. The implicit MOP handles things |
130 | like method dispatch or inheritance, which happen automatically as |
131 | part of how the object system works. The explicit MOP typically |
132 | handles the introspection/reflection features of the object system. |
133 | All object systems have implicit MOPs, without one, they would not |
134 | work. Explict MOPs however as less common, and depending on the |
135 | language can vary from restrictive (Reflection in Java or C#) to |
136 | wide open (CLOS is a perfect example). |
137 | |
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138 | =head2 Yet Another Class Builder!! Why? |
139 | |
140 | This is B<not> a class builder so much as it is a I<class builder |
141 | B<builder>>. My intent is that an end user does not use this module |
142 | directly, but instead this module is used by module authors to |
143 | build extensions and features onto the Perl 5 object system. |
144 | |
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145 | =head2 Who is this module for? |
146 | |
147 | This module is specifically for anyone who has ever created or |
148 | wanted to create a module for the Class:: namespace. The tools which |
149 | this module will provide will hopefully make it easier to do more |
150 | complex things with Perl 5 classes by removing such barriers as |
151 | the need to hack the symbol tables, or understand the fine details |
152 | of method dispatch. |
153 | |
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154 | =head2 What changes do I have to make to use this module? |
155 | |
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156 | This module was designed to be as unintrusive as possible. Many of |
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157 | it's features are accessible without B<any> change to your existsing |
158 | code at all. It is meant to be a compliment to your existing code and |
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159 | not an intrusion on your code base. Unlike many other B<Class::> |
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160 | modules, this module B<does not> require you subclass it, or even that |
161 | you C<use> it in within your module's package. |
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162 | |
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163 | The only features which requires additions to your code are the |
164 | attribute handling and instance construction features, and these are |
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165 | both completely optional features. The only reason for this is because |
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166 | Perl 5's object system does not actually have these features built |
167 | in. More information about this feature can be found below. |
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168 | |
169 | =head2 A Note about Performance? |
170 | |
171 | It is a common misconception that explict MOPs are performance drains. |
172 | But this is not a universal truth at all, it is an side-effect of |
173 | specific implementations. For instance, using Java reflection is much |
174 | slower because the JVM cannot take advantage of any compiler |
175 | optimizations, and the JVM has to deal with much more runtime type |
176 | information as well. Reflection in C# is marginally better as it was |
177 | designed into the language and runtime (the CLR). In contrast, CLOS |
178 | (the Common Lisp Object System) was built to support an explicit MOP, |
179 | and so performance is tuned for it. |
180 | |
181 | This library in particular does it's absolute best to avoid putting |
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182 | B<any> drain at all upon your code's performance. In fact, by itself |
183 | it does nothing to affect your existing code. So you only pay for |
184 | what you actually use. |
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185 | |
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186 | =head1 PROTOCOLS |
187 | |
188 | The protocol is divided into 3 main sub-protocols: |
189 | |
190 | =over 4 |
191 | |
192 | =item The Class protocol |
193 | |
194 | This provides a means of manipulating and introspecting a Perl 5 |
195 | class. It handles all of symbol table hacking for you, and provides |
196 | a rich set of methods that go beyond simple package introspection. |
197 | |
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198 | See L<Class::MOP::Class> for more details. |
199 | |
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200 | =item The Attribute protocol |
201 | |
202 | This provides a consistent represenation for an attribute of a |
203 | Perl 5 class. Since there are so many ways to create and handle |
204 | atttributes in Perl 5 OO, this attempts to provide as much of a |
205 | unified approach as possible, while giving the freedom and |
206 | flexibility to subclass for specialization. |
207 | |
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208 | See L<Class::MOP::Attribute> for more details. |
209 | |
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210 | =item The Method protocol |
211 | |
212 | This provides a means of manipulating and introspecting methods in |
213 | the Perl 5 object system. As with attributes, there are many ways to |
214 | approach this topic, so we try to keep it pretty basic, while still |
215 | making it possible to extend the system in many ways. |
216 | |
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217 | See L<Class::MOP::Method> for more details. |
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218 | |
219 | =back |
220 | |
552e3d24 |
221 | =head1 SEE ALSO |
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222 | |
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223 | =head2 Books |
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224 | |
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225 | There are very few books out on Meta Object Protocols and Metaclasses |
226 | because it is such an esoteric topic. The following books are really |
227 | the only ones I have found. If you know of any more, B<I<please>> |
228 | email me and let me know, I would love to hear about them. |
229 | |
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230 | =over 4 |
231 | |
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232 | =item "The Art of the Meta Object Protocol" |
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233 | |
552e3d24 |
234 | =item "Advances in Object-Oriented Metalevel Architecture and Reflection" |
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235 | |
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236 | =item "Putting MetaClasses to Work" |
237 | |
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238 | =item "Smalltalk: The Language" |
239 | |
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240 | =back |
241 | |
552e3d24 |
242 | =head2 Prior Art |
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243 | |
244 | =over 4 |
245 | |
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246 | =item The Perl 6 MetaModel work in the Pugs project |
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247 | |
248 | =over 4 |
249 | |
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250 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel> |
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251 | |
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252 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace> |
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253 | |
254 | =back |
255 | |
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256 | =back |
257 | |
a2e85e6c |
258 | =head1 SIMILAR MODULES |
259 | |
260 | As I have said above, this module is a class-builder-builder, so it is |
261 | not the same thing as modules like L<Class::Accessor> and |
262 | L<Class::MethodMaker>. That being said there are very few modules on CPAN |
263 | with similar goals to this module. The one I have found which is most |
264 | like this module is L<Class::Meta>, although it's philosophy is very |
265 | different from this module. |
266 | |
267 | To start with, it provides wrappers around common Perl data types, and even |
268 | extends those types with more specific subtypes. This module does not |
269 | go into that area at all. |
270 | |
271 | L<Class::Meta> also seems to create it's own custom meta-object protocol, |
272 | which is both more restrictive and more featureful than the vanilla |
273 | Perl 5 one. This module attempts to model the existing Perl 5 MOP as it is. |
274 | |
275 | It's introspection capabilities also seem to be heavily rooted in this |
276 | custom MOP, so that you can only introspect classes which are already |
277 | created with L<Class::Meta>. This module does not make such restictions. |
278 | |
279 | Now, all this said, L<Class::Meta> is much more featureful than B<Class::MOP> |
280 | would ever try to be. But B<Class::MOP> has some features which L<Class::Meta> |
281 | could not easily implement. It would be very possible to completely re-implement |
282 | L<Class::Meta> using B<Class::MOP> and bring some of these features to |
283 | L<Class::Meta> though. |
284 | |
285 | But in the end, this module's admitedly ambitious goals have no direct equal |
286 | on CPAN since surely no one has been crazy enough to try something as silly |
287 | as this ;) until now. |
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288 | |
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289 | =head1 BUGS |
290 | |
291 | All complex software has bugs lurking in it, and this module is no |
292 | exception. If you find a bug please either email me, or add the bug |
293 | to cpan-RT. |
294 | |
295 | =head1 ACKNOWLEDGEMENTS |
296 | |
297 | =over 4 |
298 | |
299 | =item Rob Kinyon E<lt>rob@iinteractive.comE<gt> |
300 | |
301 | Thanks to Rob for actually getting the development of this module kick-started. |
302 | |
303 | =back |
304 | |
305 | =head1 AUTHOR |
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306 | |
a2e85e6c |
307 | Stevan Little E<lt>stevan@iinteractive.comE<gt> |
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308 | |
94b19069 |
309 | =head1 COPYRIGHT AND LICENSE |
310 | |
311 | Copyright 2006 by Infinity Interactive, Inc. |
312 | |
313 | L<http://www.iinteractive.com> |
314 | |
315 | This library is free software; you can redistribute it and/or modify |
316 | it under the same terms as Perl itself. |
317 | |
318 | =cut |