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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 $VERSION = '0.01'; |
15 | |
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16 | sub import { |
17 | shift; |
18 | return unless @_; |
19 | if ($_[0] eq ':universal') { |
20 | *UNIVERSAL::meta = sub { |
21 | Class::MOP::Class->initialize(blessed($_[0]) || $_[0]) |
22 | }; |
23 | } |
24 | } |
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25 | |
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26 | ## ---------------------------------------------------------------------------- |
27 | ## Bootstrapping |
28 | ## ---------------------------------------------------------------------------- |
29 | ## The code below here is to bootstrap our MOP with itself. This is also |
30 | ## sometimes called "tying the knot". By doing this, we make it much easier |
31 | ## to extend the MOP through subclassing and such since now you can use the |
32 | ## MOP itself to extend itself. |
33 | ## |
34 | ## Yes, I know, thats weird and insane, but it's a good thing, trust me :) |
35 | ## ---------------------------------------------------------------------------- |
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36 | |
37 | # We need to add in the meta-attributes here so that |
38 | # any subclass of Class::MOP::* will be able to |
39 | # inherit them using &construct_instance |
40 | |
41 | ## Class::MOP::Class |
42 | |
43 | Class::MOP::Class->meta->add_attribute( |
44 | Class::MOP::Attribute->new('$:pkg' => ( |
45 | init_arg => ':pkg' |
46 | )) |
47 | ); |
48 | |
49 | Class::MOP::Class->meta->add_attribute( |
50 | Class::MOP::Attribute->new('%:attrs' => ( |
51 | init_arg => ':attrs', |
52 | default => sub { {} } |
53 | )) |
54 | ); |
55 | |
56 | ## Class::MOP::Attribute |
57 | |
58 | Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('name')); |
59 | Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('accessor')); |
60 | Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('reader')); |
61 | Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('writer')); |
62 | Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('predicate')); |
63 | Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('init_arg')); |
64 | Class::MOP::Attribute->meta->add_attribute(Class::MOP::Attribute->new('default')); |
65 | |
66 | # NOTE: (meta-circularity) |
67 | # This should be one of the last things done |
68 | # it will "tie the knot" with Class::MOP::Attribute |
69 | # so that it uses the attributes meta-objects |
70 | # to construct itself. |
71 | Class::MOP::Attribute->meta->add_method('new' => sub { |
72 | my $class = shift; |
73 | my $name = shift; |
74 | my %options = @_; |
75 | |
76 | (defined $name && $name) |
77 | || confess "You must provide a name for the attribute"; |
78 | (!exists $options{reader} && !exists $options{writer}) |
79 | || confess "You cannot declare an accessor and reader and/or writer functions" |
80 | if exists $options{accessor}; |
81 | |
82 | bless $class->meta->construct_instance(name => $name, %options) => $class; |
83 | }); |
84 | |
85 | # NOTE: (meta-circularity) |
86 | # This is how we "tie the knot" for the class |
87 | # meta-objects. This is used to construct the |
88 | # Class::MOP::Class instances after all the |
89 | # bootstrapping is complete. |
90 | Class::MOP::Class->meta->add_method('construct_class_instance' => sub { |
91 | my ($class, $package_name) = @_; |
92 | (defined $package_name && $package_name) |
93 | || confess "You must pass a package name"; |
94 | bless Class::MOP::Class->meta->construct_instance(':pkg' => $package_name) => blessed($class) || $class |
95 | }); |
96 | |
94b19069 |
97 | 1; |
98 | |
99 | __END__ |
100 | |
101 | =pod |
102 | |
103 | =head1 NAME |
104 | |
105 | Class::MOP - A Meta Object Protocol for Perl 5 |
106 | |
107 | =head1 SYNOPSIS |
108 | |
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109 | use Class::MOP ':universal'; |
110 | |
111 | package Foo; |
112 | |
113 | Foo->meta->add_method('foo' => sub { ... }); |
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114 | |
115 | =head1 DESCRIPTON |
116 | |
117 | This module is an attempt to create a meta object protocol for the |
118 | Perl 5 object system. It makes no attempt to change the behavior or |
119 | characteristics of the Perl 5 object system, only to create a |
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120 | protocol for its manipulation and introspection. |
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121 | |
122 | That said, it does attempt to create the tools for building a rich |
123 | set of extensions to the Perl 5 object system. Every attempt has been |
124 | made for these tools to keep to the spirit of the Perl 5 object |
125 | system that we all know and love. |
126 | |
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127 | =head2 What is a Meta Object Protocol? |
128 | |
129 | A meta object protocol is an API to an object system. |
130 | |
131 | To be more specific, it is a set of abstractions of the components of |
132 | an object system (typically things like; classes, object, methods, |
133 | object attributes, etc.). These abstractions can then be used to both |
134 | inspect and manipulate the object system which they describe. |
135 | |
136 | It can be said that there are two MOPs for any object system; the |
137 | implicit MOP, and the explicit MOP. The implicit MOP handles things |
138 | like method dispatch or inheritance, which happen automatically as |
139 | part of how the object system works. The explicit MOP typically |
140 | handles the introspection/reflection features of the object system. |
141 | All object systems have implicit MOPs, without one, they would not |
142 | work. Explict MOPs however as less common, and depending on the |
143 | language can vary from restrictive (Reflection in Java or C#) to |
144 | wide open (CLOS is a perfect example). |
145 | |
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146 | =head2 Yet Another Class Builder!! Why? |
147 | |
148 | This is B<not> a class builder so much as it is a I<class builder |
149 | B<builder>>. My intent is that an end user does not use this module |
150 | directly, but instead this module is used by module authors to |
151 | build extensions and features onto the Perl 5 object system. |
152 | |
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153 | =head2 Who is this module for? |
154 | |
155 | This module is specifically for anyone who has ever created or |
156 | wanted to create a module for the Class:: namespace. The tools which |
157 | this module will provide will hopefully make it easier to do more |
158 | complex things with Perl 5 classes by removing such barriers as |
159 | the need to hack the symbol tables, or understand the fine details |
160 | of method dispatch. |
161 | |
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162 | =head2 What changes do I have to make to use this module? |
163 | |
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164 | This module was designed to be as unintrusive as possible. Many of |
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165 | it's features are accessible without B<any> change to your existsing |
166 | code at all. It is meant to be a compliment to your existing code and |
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167 | not an intrusion on your code base. Unlike many other B<Class::> |
168 | modules, this module does require you subclass it, or even that you |
169 | C<use> it in within your module's package. |
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170 | |
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171 | The only features which requires additions to your code are the |
172 | attribute handling and instance construction features, and these are |
173 | both optional features as well. The only reason for this is because |
174 | Perl 5's object system does not actually have these features built |
175 | in. More information about this feature can be found below. |
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176 | |
177 | =head2 A Note about Performance? |
178 | |
179 | It is a common misconception that explict MOPs are performance drains. |
180 | But this is not a universal truth at all, it is an side-effect of |
181 | specific implementations. For instance, using Java reflection is much |
182 | slower because the JVM cannot take advantage of any compiler |
183 | optimizations, and the JVM has to deal with much more runtime type |
184 | information as well. Reflection in C# is marginally better as it was |
185 | designed into the language and runtime (the CLR). In contrast, CLOS |
186 | (the Common Lisp Object System) was built to support an explicit MOP, |
187 | and so performance is tuned for it. |
188 | |
189 | This library in particular does it's absolute best to avoid putting |
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190 | B<any> drain at all upon your code's performance. In fact, by itself |
191 | it does nothing to affect your existing code. So you only pay for |
192 | what you actually use. |
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193 | |
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194 | =head1 PROTOCOLS |
195 | |
196 | The protocol is divided into 3 main sub-protocols: |
197 | |
198 | =over 4 |
199 | |
200 | =item The Class protocol |
201 | |
202 | This provides a means of manipulating and introspecting a Perl 5 |
203 | class. It handles all of symbol table hacking for you, and provides |
204 | a rich set of methods that go beyond simple package introspection. |
205 | |
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206 | See L<Class::MOP::Class> for more details. |
207 | |
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208 | =item The Attribute protocol |
209 | |
210 | This provides a consistent represenation for an attribute of a |
211 | Perl 5 class. Since there are so many ways to create and handle |
212 | atttributes in Perl 5 OO, this attempts to provide as much of a |
213 | unified approach as possible, while giving the freedom and |
214 | flexibility to subclass for specialization. |
215 | |
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216 | See L<Class::MOP::Attribute> for more details. |
217 | |
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218 | =item The Method protocol |
219 | |
220 | This provides a means of manipulating and introspecting methods in |
221 | the Perl 5 object system. As with attributes, there are many ways to |
222 | approach this topic, so we try to keep it pretty basic, while still |
223 | making it possible to extend the system in many ways. |
224 | |
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225 | See L<Class::MOP::Method> for more details. |
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226 | |
227 | =back |
228 | |
7184ca14 |
229 | head1 BUGS |
230 | |
231 | All complex software has bugs lurking in it, and this module is no |
232 | exception. If you find a bug please either email me, or add the bug |
233 | to cpan-RT. |
234 | |
552e3d24 |
235 | =head1 SEE ALSO |
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236 | |
552e3d24 |
237 | =head2 Books |
8b978dd5 |
238 | |
239 | =over 4 |
240 | |
552e3d24 |
241 | =item "The Art of the Meta Object Protocol" |
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242 | |
552e3d24 |
243 | =item "Advances in Object-Oriented Metalevel Architecture and Reflection" |
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244 | |
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245 | =item "Putting MetaClasses to Work" |
246 | |
94b19069 |
247 | =back |
248 | |
552e3d24 |
249 | =head2 Prior Art |
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250 | |
251 | =over 4 |
252 | |
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253 | =item The Perl 6 MetaModel work in the Pugs project |
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254 | |
255 | =over 4 |
256 | |
552e3d24 |
257 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel> |
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258 | |
552e3d24 |
259 | =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace> |
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260 | |
261 | =back |
262 | |
94b19069 |
263 | =back |
264 | |
265 | =head1 AUTHOR |
266 | |
267 | Stevan Little E<gt>stevan@iinteractive.comE<lt> |
268 | |
552e3d24 |
269 | Rob Kinyon E<gt>rob@iinteractive.comE<lt> |
270 | |
94b19069 |
271 | =head1 COPYRIGHT AND LICENSE |
272 | |
273 | Copyright 2006 by Infinity Interactive, Inc. |
274 | |
275 | L<http://www.iinteractive.com> |
276 | |
277 | This library is free software; you can redistribute it and/or modify |
278 | it under the same terms as Perl itself. |
279 | |
280 | =cut |