7 use Scalar::Util 'blessed';
12 # sub UNIVERSAL::meta {
13 # my $class = blessed($_[0]) || $_[0];
14 # $METAS{$class} ||= Class::MOP::Class->initialize($class)
25 Class::MOP - A Meta Object Protocol for Perl 5
33 This module is an attempt to create a meta object protocol for the
34 Perl 5 object system. It makes no attempt to change the behavior or
35 characteristics of the Perl 5 object system, only to create a
36 protocol for its manipulation and introspection.
38 That said, it does attempt to create the tools for building a rich
39 set of extensions to the Perl 5 object system. Every attempt has been
40 made for these tools to keep to the spirit of the Perl 5 object
41 system that we all know and love.
43 =head2 What is a Meta Object Protocol?
45 A meta object protocol is an API to an object system.
47 To be more specific, it is a set of abstractions of the components of
48 an object system (typically things like; classes, object, methods,
49 object attributes, etc.). These abstractions can then be used to both
50 inspect and manipulate the object system which they describe.
52 It can be said that there are two MOPs for any object system; the
53 implicit MOP, and the explicit MOP. The implicit MOP handles things
54 like method dispatch or inheritance, which happen automatically as
55 part of how the object system works. The explicit MOP typically
56 handles the introspection/reflection features of the object system.
57 All object systems have implicit MOPs, without one, they would not
58 work. Explict MOPs however as less common, and depending on the
59 language can vary from restrictive (Reflection in Java or C#) to
60 wide open (CLOS is a perfect example).
62 =head2 Yet Another Class Builder!! Why?
64 This is B<not> a class builder so much as it is a I<class builder
65 B<builder>>. My intent is that an end user does not use this module
66 directly, but instead this module is used by module authors to
67 build extensions and features onto the Perl 5 object system.
69 =head2 Who is this module for?
71 This module is specifically for anyone who has ever created or
72 wanted to create a module for the Class:: namespace. The tools which
73 this module will provide will hopefully make it easier to do more
74 complex things with Perl 5 classes by removing such barriers as
75 the need to hack the symbol tables, or understand the fine details
78 =head2 What changes do I have to make to use this module?
80 This module was designed to be as unintrusive as possible. So many of
81 it's features are accessible without B<any> change to your existsing
82 code at all. It is meant to be a compliment to your existing code and
83 not an intrusion on your code base.
85 The only feature which requires additions to your code are the
86 attribute handling and instance construction features. The only reason
87 for this is because Perl 5's object system does not actually have
88 these features built in. More information about this feature can be
91 =head2 A Note about Performance?
93 It is a common misconception that explict MOPs are performance drains.
94 But this is not a universal truth at all, it is an side-effect of
95 specific implementations. For instance, using Java reflection is much
96 slower because the JVM cannot take advantage of any compiler
97 optimizations, and the JVM has to deal with much more runtime type
98 information as well. Reflection in C# is marginally better as it was
99 designed into the language and runtime (the CLR). In contrast, CLOS
100 (the Common Lisp Object System) was built to support an explicit MOP,
101 and so performance is tuned for it.
103 This library in particular does it's absolute best to avoid putting
104 B<any> drain at all upon your code's performance, while still trying
105 to make sure it is fast as well (although only as a secondary
110 The protocol is divided into 3 main sub-protocols:
114 =item The Class protocol
116 This provides a means of manipulating and introspecting a Perl 5
117 class. It handles all of symbol table hacking for you, and provides
118 a rich set of methods that go beyond simple package introspection.
120 See L<Class::MOP::Class> for more details.
122 =item The Attribute protocol
124 This provides a consistent represenation for an attribute of a
125 Perl 5 class. Since there are so many ways to create and handle
126 atttributes in Perl 5 OO, this attempts to provide as much of a
127 unified approach as possible, while giving the freedom and
128 flexibility to subclass for specialization.
130 See L<Class::MOP::Attribute> for more details.
132 =item The Method protocol
134 This provides a means of manipulating and introspecting methods in
135 the Perl 5 object system. As with attributes, there are many ways to
136 approach this topic, so we try to keep it pretty basic, while still
137 making it possible to extend the system in many ways.
139 See L<Class::MOP::Method> for more details.
149 =item "The Art of the Meta Object Protocol"
151 =item "Advances in Object-Oriented Metalevel Architecture and Reflection"
159 =item The Perl 6 MetaModel work
163 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
165 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
173 Stevan Little E<gt>stevan@iinteractive.comE<lt>
175 Rob Kinyon E<gt>rob@iinteractive.comE<lt>
177 =head1 COPYRIGHT AND LICENSE
179 Copyright 2006 by Infinity Interactive, Inc.
181 L<http://www.iinteractive.com>
183 This library is free software; you can redistribute it and/or modify
184 it under the same terms as Perl itself.