7 use Scalar::Util 'blessed';
10 use Class::MOP::Attribute;
11 use Class::MOP::Method;
13 our $VERSION = '0.01';
18 if ($_[0] eq ':universal') {
19 *UNIVERSAL::meta = sub {
20 Class::MOP::Class->initialize(blessed($_[0]) || $_[0])
33 Class::MOP - A Meta Object Protocol for Perl 5
37 use Class::MOP ':universal';
41 Foo->meta->add_method('foo' => sub { ... });
45 This module is an attempt to create a meta object protocol for the
46 Perl 5 object system. It makes no attempt to change the behavior or
47 characteristics of the Perl 5 object system, only to create a
48 protocol for its manipulation and introspection.
50 That said, it does attempt to create the tools for building a rich
51 set of extensions to the Perl 5 object system. Every attempt has been
52 made for these tools to keep to the spirit of the Perl 5 object
53 system that we all know and love.
55 =head2 What is a Meta Object Protocol?
57 A meta object protocol is an API to an object system.
59 To be more specific, it is a set of abstractions of the components of
60 an object system (typically things like; classes, object, methods,
61 object attributes, etc.). These abstractions can then be used to both
62 inspect and manipulate the object system which they describe.
64 It can be said that there are two MOPs for any object system; the
65 implicit MOP, and the explicit MOP. The implicit MOP handles things
66 like method dispatch or inheritance, which happen automatically as
67 part of how the object system works. The explicit MOP typically
68 handles the introspection/reflection features of the object system.
69 All object systems have implicit MOPs, without one, they would not
70 work. Explict MOPs however as less common, and depending on the
71 language can vary from restrictive (Reflection in Java or C#) to
72 wide open (CLOS is a perfect example).
74 =head2 Yet Another Class Builder!! Why?
76 This is B<not> a class builder so much as it is a I<class builder
77 B<builder>>. My intent is that an end user does not use this module
78 directly, but instead this module is used by module authors to
79 build extensions and features onto the Perl 5 object system.
81 =head2 Who is this module for?
83 This module is specifically for anyone who has ever created or
84 wanted to create a module for the Class:: namespace. The tools which
85 this module will provide will hopefully make it easier to do more
86 complex things with Perl 5 classes by removing such barriers as
87 the need to hack the symbol tables, or understand the fine details
90 =head2 What changes do I have to make to use this module?
92 This module was designed to be as unintrusive as possible. Many of
93 it's features are accessible without B<any> change to your existsing
94 code at all. It is meant to be a compliment to your existing code and
95 not an intrusion on your code base. Unlike many other B<Class::>
96 modules, this module does require you subclass it, or even that you
97 C<use> it in within your module's package.
99 The only features which requires additions to your code are the
100 attribute handling and instance construction features, and these are
101 both optional features as well. The only reason for this is because
102 Perl 5's object system does not actually have these features built
103 in. More information about this feature can be found below.
105 =head2 A Note about Performance?
107 It is a common misconception that explict MOPs are performance drains.
108 But this is not a universal truth at all, it is an side-effect of
109 specific implementations. For instance, using Java reflection is much
110 slower because the JVM cannot take advantage of any compiler
111 optimizations, and the JVM has to deal with much more runtime type
112 information as well. Reflection in C# is marginally better as it was
113 designed into the language and runtime (the CLR). In contrast, CLOS
114 (the Common Lisp Object System) was built to support an explicit MOP,
115 and so performance is tuned for it.
117 This library in particular does it's absolute best to avoid putting
118 B<any> drain at all upon your code's performance. In fact, by itself
119 it does nothing to affect your existing code. So you only pay for
120 what you actually use.
124 The protocol is divided into 3 main sub-protocols:
128 =item The Class protocol
130 This provides a means of manipulating and introspecting a Perl 5
131 class. It handles all of symbol table hacking for you, and provides
132 a rich set of methods that go beyond simple package introspection.
134 See L<Class::MOP::Class> for more details.
136 =item The Attribute protocol
138 This provides a consistent represenation for an attribute of a
139 Perl 5 class. Since there are so many ways to create and handle
140 atttributes in Perl 5 OO, this attempts to provide as much of a
141 unified approach as possible, while giving the freedom and
142 flexibility to subclass for specialization.
144 See L<Class::MOP::Attribute> for more details.
146 =item The Method protocol
148 This provides a means of manipulating and introspecting methods in
149 the Perl 5 object system. As with attributes, there are many ways to
150 approach this topic, so we try to keep it pretty basic, while still
151 making it possible to extend the system in many ways.
153 See L<Class::MOP::Method> for more details.
163 =item "The Art of the Meta Object Protocol"
165 =item "Advances in Object-Oriented Metalevel Architecture and Reflection"
173 =item The Perl 6 MetaModel work
177 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
179 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
187 Stevan Little E<gt>stevan@iinteractive.comE<lt>
189 Rob Kinyon E<gt>rob@iinteractive.comE<lt>
191 =head1 COPYRIGHT AND LICENSE
193 Copyright 2006 by Infinity Interactive, Inc.
195 L<http://www.iinteractive.com>
197 This library is free software; you can redistribute it and/or modify
198 it under the same terms as Perl itself.