7 use Scalar::Util 'blessed';
10 use Class::MOP::Class;
11 use Class::MOP::Attribute;
12 use Class::MOP::Method;
14 our $VERSION = '0.06';
19 if ($_[0] eq ':universal') {
20 *UNIVERSAL::meta = sub {
21 Class::MOP::Class->initialize(blessed($_[0]) || $_[0])
27 *{$pkg . '::' . $_[0]} = sub {
28 Class::MOP::Class->initialize(blessed($_[0]) || $_[0])
33 ## ----------------------------------------------------------------------------
35 ## ----------------------------------------------------------------------------
36 ## The code below here is to bootstrap our MOP with itself. This is also
37 ## sometimes called "tying the knot". By doing this, we make it much easier
38 ## to extend the MOP through subclassing and such since now you can use the
39 ## MOP itself to extend itself.
41 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
42 ## ----------------------------------------------------------------------------
44 # We need to add in the meta-attributes here so that
45 # any subclass of Class::MOP::* will be able to
46 # inherit them using &construct_instance
50 Class::MOP::Class->meta->add_attribute(
51 Class::MOP::Attribute->new('$:package' => (
53 init_arg => ':package',
57 Class::MOP::Class->meta->add_attribute(
58 Class::MOP::Attribute->new('%:attributes' => (
59 reader => 'get_attribute_map',
60 init_arg => ':attributes',
65 Class::MOP::Class->meta->add_attribute(
66 Class::MOP::Attribute->new('$:attribute_metaclass' => (
67 reader => 'attribute_metaclass',
68 init_arg => ':attribute_metaclass',
69 default => 'Class::MOP::Attribute',
73 Class::MOP::Class->meta->add_attribute(
74 Class::MOP::Attribute->new('$:method_metaclass' => (
75 reader => 'method_metaclass',
76 init_arg => ':method_metaclass',
77 default => 'Class::MOP::Method',
81 ## Class::MOP::Attribute
83 Class::MOP::Attribute->meta->add_attribute(
84 Class::MOP::Attribute->new('name' => (
89 Class::MOP::Attribute->meta->add_attribute(
90 Class::MOP::Attribute->new('associated_class' => (
91 reader => 'associated_class'
95 Class::MOP::Attribute->meta->add_attribute(
96 Class::MOP::Attribute->new('accessor' => (
98 predicate => 'has_accessor',
102 Class::MOP::Attribute->meta->add_attribute(
103 Class::MOP::Attribute->new('reader' => (
105 predicate => 'has_reader',
109 Class::MOP::Attribute->meta->add_attribute(
110 Class::MOP::Attribute->new('writer' => (
112 predicate => 'has_writer',
116 Class::MOP::Attribute->meta->add_attribute(
117 Class::MOP::Attribute->new('predicate' => (
118 reader => 'predicate',
119 predicate => 'has_predicate',
123 Class::MOP::Attribute->meta->add_attribute(
124 Class::MOP::Attribute->new('init_arg' => (
125 reader => 'init_arg',
126 predicate => 'has_init_arg',
130 Class::MOP::Attribute->meta->add_attribute(
131 Class::MOP::Attribute->new('default' => (
132 # default has a custom 'reader' method ...
133 predicate => 'has_default',
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 {
148 (defined $name && $name)
149 || confess "You must provide a name for the attribute";
150 (!exists $options{reader} && !exists $options{writer})
151 || confess "You cannot declare an accessor and reader and/or writer functions"
152 if exists $options{accessor};
153 $options{init_arg} = $name if not exists $options{init_arg};
155 bless $class->meta->construct_instance(name => $name, %options) => blessed($class) || $class;
166 Class::MOP - A Meta Object Protocol for Perl 5
170 # ... This will come later, for now see
171 # the other SYNOPSIS for more information
175 This module is an attempt to create a meta object protocol for the
176 Perl 5 object system. It makes no attempt to change the behavior or
177 characteristics of the Perl 5 object system, only to create a
178 protocol for its manipulation and introspection.
180 That said, it does attempt to create the tools for building a rich
181 set of extensions to the Perl 5 object system. Every attempt has been
182 made for these tools to keep to the spirit of the Perl 5 object
183 system that we all know and love.
185 =head2 What is a Meta Object Protocol?
187 A meta object protocol is an API to an object system.
189 To be more specific, it is a set of abstractions of the components of
190 an object system (typically things like; classes, object, methods,
191 object attributes, etc.). These abstractions can then be used to both
192 inspect and manipulate the object system which they describe.
194 It can be said that there are two MOPs for any object system; the
195 implicit MOP, and the explicit MOP. The implicit MOP handles things
196 like method dispatch or inheritance, which happen automatically as
197 part of how the object system works. The explicit MOP typically
198 handles the introspection/reflection features of the object system.
199 All object systems have implicit MOPs, without one, they would not
200 work. Explict MOPs however as less common, and depending on the
201 language can vary from restrictive (Reflection in Java or C#) to
202 wide open (CLOS is a perfect example).
204 =head2 Yet Another Class Builder!! Why?
206 This is B<not> a class builder so much as it is a I<class builder
207 B<builder>>. My intent is that an end user does not use this module
208 directly, but instead this module is used by module authors to
209 build extensions and features onto the Perl 5 object system.
211 =head2 Who is this module for?
213 This module is specifically for anyone who has ever created or
214 wanted to create a module for the Class:: namespace. The tools which
215 this module will provide will hopefully make it easier to do more
216 complex things with Perl 5 classes by removing such barriers as
217 the need to hack the symbol tables, or understand the fine details
220 =head2 What changes do I have to make to use this module?
222 This module was designed to be as unintrusive as possible. Many of
223 its features are accessible without B<any> change to your existsing
224 code at all. It is meant to be a compliment to your existing code and
225 not an intrusion on your code base. Unlike many other B<Class::>
226 modules, this module B<does not> require you subclass it, or even that
227 you C<use> it in within your module's package.
229 The only features which requires additions to your code are the
230 attribute handling and instance construction features, and these are
231 both completely optional features. The only reason for this is because
232 Perl 5's object system does not actually have these features built
233 in. More information about this feature can be found below.
235 =head2 A Note about Performance?
237 It is a common misconception that explict MOPs are performance drains.
238 But this is not a universal truth at all, it is an side-effect of
239 specific implementations. For instance, using Java reflection is much
240 slower because the JVM cannot take advantage of any compiler
241 optimizations, and the JVM has to deal with much more runtime type
242 information as well. Reflection in C# is marginally better as it was
243 designed into the language and runtime (the CLR). In contrast, CLOS
244 (the Common Lisp Object System) was built to support an explicit MOP,
245 and so performance is tuned for it.
247 This library in particular does it's absolute best to avoid putting
248 B<any> drain at all upon your code's performance. In fact, by itself
249 it does nothing to affect your existing code. So you only pay for
250 what you actually use.
254 The protocol is divided into 3 main sub-protocols:
258 =item The Class protocol
260 This provides a means of manipulating and introspecting a Perl 5
261 class. It handles all of symbol table hacking for you, and provides
262 a rich set of methods that go beyond simple package introspection.
264 See L<Class::MOP::Class> for more details.
266 =item The Attribute protocol
268 This provides a consistent represenation for an attribute of a
269 Perl 5 class. Since there are so many ways to create and handle
270 atttributes in Perl 5 OO, this attempts to provide as much of a
271 unified approach as possible, while giving the freedom and
272 flexibility to subclass for specialization.
274 See L<Class::MOP::Attribute> for more details.
276 =item The Method protocol
278 This provides a means of manipulating and introspecting methods in
279 the Perl 5 object system. As with attributes, there are many ways to
280 approach this topic, so we try to keep it pretty basic, while still
281 making it possible to extend the system in many ways.
283 See L<Class::MOP::Method> for more details.
291 There are very few books out on Meta Object Protocols and Metaclasses
292 because it is such an esoteric topic. The following books are really
293 the only ones I have found. If you know of any more, B<I<please>>
294 email me and let me know, I would love to hear about them.
298 =item "The Art of the Meta Object Protocol"
300 =item "Advances in Object-Oriented Metalevel Architecture and Reflection"
302 =item "Putting MetaClasses to Work"
304 =item "Smalltalk: The Language"
312 =item The Perl 6 MetaModel work in the Pugs project
316 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
318 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
324 =head1 SIMILAR MODULES
326 As I have said above, this module is a class-builder-builder, so it is
327 not the same thing as modules like L<Class::Accessor> and
328 L<Class::MethodMaker>. That being said there are very few modules on CPAN
329 with similar goals to this module. The one I have found which is most
330 like this module is L<Class::Meta>, although it's philosophy is very
331 different from this module.
333 To start with, it provides wrappers around common Perl data types, and even
334 extends those types with more specific subtypes. This module does not
335 go into that area at all.
337 L<Class::Meta> also seems to create it's own custom meta-object protocol,
338 which is both more restrictive and more featureful than the vanilla
339 Perl 5 one. This module attempts to model the existing Perl 5 MOP as it is.
341 It's introspection capabilities also seem to be heavily rooted in this
342 custom MOP, so that you can only introspect classes which are already
343 created with L<Class::Meta>. This module does not make such restictions.
345 Now, all this said, L<Class::Meta> is much more featureful than B<Class::MOP>
346 would ever try to be. But B<Class::MOP> has some features which L<Class::Meta>
347 could not easily implement. It would be very possible to completely re-implement
348 L<Class::Meta> using B<Class::MOP> and bring some of these features to
349 L<Class::Meta> though.
351 But in the end, this module's admitedly ambitious goals have no direct equal
352 on CPAN since surely no one has been crazy enough to try something as silly
353 as this ;) until now.
357 All complex software has bugs lurking in it, and this module is no
358 exception. If you find a bug please either email me, or add the bug
361 =head1 ACKNOWLEDGEMENTS
365 =item Rob Kinyon E<lt>rob@iinteractive.comE<gt>
367 Thanks to Rob for actually getting the development of this module kick-started.
373 Stevan Little E<lt>stevan@iinteractive.comE<gt>
375 =head1 COPYRIGHT AND LICENSE
377 Copyright 2006 by Infinity Interactive, Inc.
379 L<http://www.iinteractive.com>
381 This library is free software; you can redistribute it and/or modify
382 it under the same terms as Perl itself.