10 use Scalar::Util 'weaken';
12 use Class::MOP::Class;
13 use Class::MOP::Attribute;
14 use Class::MOP::Method;
16 use Class::MOP::Immutable;
19 our $VERSION = '0.56';
20 our $AUTHORITY = 'cpan:STEVAN';
23 XSLoader::load( 'Class::MOP', $VERSION );
25 *IS_RUNNING_ON_5_10 = ($] < 5.009_005)
29 # get it from MRO::Compat now ...
30 *check_package_cache_flag = \&mro::get_pkg_gen;
32 # UNCOMMENT ME TO TEST WITHOUT XS
33 #no warnings 'prototype', 'redefine';
34 #*check_package_cache_flag = \&MRO::Compat::__get_pkg_gen_pp
38 # Metaclasses are singletons, so we cache them here.
39 # there is no need to worry about destruction though
40 # because they should die only when the program dies.
41 # After all, do package definitions even get reaped?
44 # means of accessing all the metaclasses that have
45 # been initialized thus far (for mugwumps obj browser)
46 sub get_all_metaclasses { %METAS }
47 sub get_all_metaclass_instances { values %METAS }
48 sub get_all_metaclass_names { keys %METAS }
49 sub get_metaclass_by_name { $METAS{$_[0]} }
50 sub store_metaclass_by_name { $METAS{$_[0]} = $_[1] }
51 sub weaken_metaclass { weaken($METAS{$_[0]}) }
52 sub does_metaclass_exist { exists $METAS{$_[0]} && defined $METAS{$_[0]} }
53 sub remove_metaclass_by_name { $METAS{$_[0]} = undef }
56 # We only cache metaclasses, meaning instances of
57 # Class::MOP::Class. We do not cache instance of
58 # Class::MOP::Package or Class::MOP::Module. Mostly
59 # because I don't yet see a good reason to do so.
64 # see if this is already
65 # loaded in the symbol table
66 return 1 if is_class_loaded($class);
67 # otherwise require it ...
68 my $file = $class . '.pm';
70 eval { CORE::require($file) };
71 confess "Could not load class ($class) because : $@" if $@;
72 unless (does_metaclass_exist($class)) {
73 eval { Class::MOP::Class->initialize($class) };
74 confess "Could not initialize class ($class) because : $@" if $@;
76 1; # return true if it worked
82 return 1 if defined ${"${class}::VERSION"} || defined @{"${class}::ISA"};
83 foreach my $symbol (keys %{"${class}::"}) {
84 next if substr($symbol, -2, 2) eq '::';
85 return 1 if defined &{"${class}::${symbol}"};
91 ## ----------------------------------------------------------------------------
92 ## Setting up our environment ...
93 ## ----------------------------------------------------------------------------
94 ## Class::MOP needs to have a few things in the global perl environment so
95 ## that it can operate effectively. Those things are done here.
96 ## ----------------------------------------------------------------------------
98 # ... nothing yet actually ;)
100 ## ----------------------------------------------------------------------------
102 ## ----------------------------------------------------------------------------
103 ## The code below here is to bootstrap our MOP with itself. This is also
104 ## sometimes called "tying the knot". By doing this, we make it much easier
105 ## to extend the MOP through subclassing and such since now you can use the
106 ## MOP itself to extend itself.
108 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
109 ## ----------------------------------------------------------------------------
111 # We need to add in the meta-attributes here so that
112 # any subclass of Class::MOP::* will be able to
113 # inherit them using &construct_instance
115 ## --------------------------------------------------------
116 ## Class::MOP::Package
118 Class::MOP::Package->meta->add_attribute(
119 Class::MOP::Attribute->new('$!package' => (
121 # NOTE: we need to do this in order
122 # for the instance meta-object to
123 # not fall into meta-circular death
125 # we just alias the original method
126 # rather than re-produce it here
127 'name' => \&Class::MOP::Package::name
129 init_arg => 'package',
133 Class::MOP::Package->meta->add_attribute(
134 Class::MOP::Attribute->new('%!namespace' => (
137 # we just alias the original method
138 # rather than re-produce it here
139 'namespace' => \&Class::MOP::Package::namespace
142 default => sub { \undef }
147 # use the metaclass to construct the meta-package
148 # which is a superclass of the metaclass itself :P
149 Class::MOP::Package->meta->add_method('initialize' => sub {
151 my $package_name = shift;
152 $class->meta->new_object('package' => $package_name, @_);
155 ## --------------------------------------------------------
156 ## Class::MOP::Module
159 # yeah this is kind of stretching things a bit,
160 # but truthfully the version should be an attribute
161 # of the Module, the weirdness comes from having to
162 # stick to Perl 5 convention and store it in the
163 # $VERSION package variable. Basically if you just
164 # squint at it, it will look how you want it to look.
165 # Either as a package variable, or as a attribute of
166 # the metaclass, isn't abstraction great :)
168 Class::MOP::Module->meta->add_attribute(
169 Class::MOP::Attribute->new('$!version' => (
172 # we just alias the original method
173 # rather than re-produce it here
174 'version' => \&Class::MOP::Module::version
177 default => sub { \undef }
182 # By following the same conventions as version here,
183 # we are opening up the possibility that people can
184 # use the $AUTHORITY in non-Class::MOP modules as
187 Class::MOP::Module->meta->add_attribute(
188 Class::MOP::Attribute->new('$!authority' => (
191 # we just alias the original method
192 # rather than re-produce it here
193 'authority' => \&Class::MOP::Module::authority
196 default => sub { \undef }
200 ## --------------------------------------------------------
203 Class::MOP::Class->meta->add_attribute(
204 Class::MOP::Attribute->new('%!attributes' => (
206 # NOTE: we need to do this in order
207 # for the instance meta-object to
208 # not fall into meta-circular death
210 # we just alias the original method
211 # rather than re-produce it here
212 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
214 init_arg => 'attributes',
215 default => sub { {} }
219 Class::MOP::Class->meta->add_attribute(
220 Class::MOP::Attribute->new('%!methods' => (
221 init_arg => 'methods',
224 # we just alias the original method
225 # rather than re-produce it here
226 'get_method_map' => \&Class::MOP::Class::get_method_map
228 default => sub { {} }
232 Class::MOP::Class->meta->add_attribute(
233 Class::MOP::Attribute->new('@!superclasses' => (
236 # we just alias the original method
237 # rather than re-produce it here
238 'superclasses' => \&Class::MOP::Class::superclasses
241 default => sub { \undef }
245 Class::MOP::Class->meta->add_attribute(
246 Class::MOP::Attribute->new('$!attribute_metaclass' => (
249 # we just alias the original method
250 # rather than re-produce it here
251 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
253 init_arg => 'attribute_metaclass',
254 default => 'Class::MOP::Attribute',
258 Class::MOP::Class->meta->add_attribute(
259 Class::MOP::Attribute->new('$!method_metaclass' => (
262 # we just alias the original method
263 # rather than re-produce it here
264 'method_metaclass' => \&Class::MOP::Class::method_metaclass
266 init_arg => 'method_metaclass',
267 default => 'Class::MOP::Method',
271 Class::MOP::Class->meta->add_attribute(
272 Class::MOP::Attribute->new('$!instance_metaclass' => (
274 # NOTE: we need to do this in order
275 # for the instance meta-object to
276 # not fall into meta-circular death
278 # we just alias the original method
279 # rather than re-produce it here
280 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
282 init_arg => 'instance_metaclass',
283 default => 'Class::MOP::Instance',
288 # we don't actually need to tie the knot with
289 # Class::MOP::Class here, it is actually handled
290 # within Class::MOP::Class itself in the
291 # construct_class_instance method.
293 ## --------------------------------------------------------
294 ## Class::MOP::Attribute
296 Class::MOP::Attribute->meta->add_attribute(
297 Class::MOP::Attribute->new('$!name' => (
300 # NOTE: we need to do this in order
301 # for the instance meta-object to
302 # not fall into meta-circular death
304 # we just alias the original method
305 # rather than re-produce it here
306 'name' => \&Class::MOP::Attribute::name
311 Class::MOP::Attribute->meta->add_attribute(
312 Class::MOP::Attribute->new('$!associated_class' => (
313 init_arg => 'associated_class',
315 # NOTE: we need to do this in order
316 # for the instance meta-object to
317 # not fall into meta-circular death
319 # we just alias the original method
320 # rather than re-produce it here
321 'associated_class' => \&Class::MOP::Attribute::associated_class
326 Class::MOP::Attribute->meta->add_attribute(
327 Class::MOP::Attribute->new('$!accessor' => (
328 init_arg => 'accessor',
329 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
330 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
334 Class::MOP::Attribute->meta->add_attribute(
335 Class::MOP::Attribute->new('$!reader' => (
336 init_arg => 'reader',
337 reader => { 'reader' => \&Class::MOP::Attribute::reader },
338 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
342 Class::MOP::Attribute->meta->add_attribute(
343 Class::MOP::Attribute->new('$!initializer' => (
344 init_arg => 'initializer',
345 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
346 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
350 Class::MOP::Attribute->meta->add_attribute(
351 Class::MOP::Attribute->new('$!writer' => (
352 init_arg => 'writer',
353 reader => { 'writer' => \&Class::MOP::Attribute::writer },
354 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
358 Class::MOP::Attribute->meta->add_attribute(
359 Class::MOP::Attribute->new('$!predicate' => (
360 init_arg => 'predicate',
361 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
362 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
366 Class::MOP::Attribute->meta->add_attribute(
367 Class::MOP::Attribute->new('$!clearer' => (
368 init_arg => 'clearer',
369 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
370 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
374 Class::MOP::Attribute->meta->add_attribute(
375 Class::MOP::Attribute->new('$!builder' => (
376 init_arg => 'builder',
377 reader => { 'builder' => \&Class::MOP::Attribute::builder },
378 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
382 Class::MOP::Attribute->meta->add_attribute(
383 Class::MOP::Attribute->new('$!init_arg' => (
384 init_arg => 'init_arg',
385 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
386 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
390 Class::MOP::Attribute->meta->add_attribute(
391 Class::MOP::Attribute->new('$!default' => (
392 init_arg => 'default',
393 # default has a custom 'reader' method ...
394 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
398 Class::MOP::Attribute->meta->add_attribute(
399 Class::MOP::Attribute->new('@!associated_methods' => (
400 init_arg => 'associated_methods',
401 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
402 default => sub { [] }
406 # NOTE: (meta-circularity)
407 # This should be one of the last things done
408 # it will "tie the knot" with Class::MOP::Attribute
409 # so that it uses the attributes meta-objects
410 # to construct itself.
411 Class::MOP::Attribute->meta->add_method('new' => sub {
416 (defined $name && $name)
417 || confess "You must provide a name for the attribute";
418 $options{init_arg} = $name
419 if not exists $options{init_arg};
421 if(exists $options{builder}){
422 confess("builder must be a defined scalar value which is a method name")
423 if ref $options{builder} || !(defined $options{builder});
424 confess("Setting both default and builder is not allowed.")
425 if exists $options{default};
427 (Class::MOP::Attribute::is_default_a_coderef(\%options))
428 || confess("References are not allowed as default values, you must ".
429 "wrap then in a CODE reference (ex: sub { [] } and not [])")
430 if exists $options{default} && ref $options{default};
432 # return the new object
433 $class->meta->new_object(name => $name, %options);
436 Class::MOP::Attribute->meta->add_method('clone' => sub {
438 $self->meta->clone_object($self, @_);
441 ## --------------------------------------------------------
442 ## Class::MOP::Method
444 Class::MOP::Method->meta->add_attribute(
445 Class::MOP::Attribute->new('&!body' => (
447 reader => { 'body' => \&Class::MOP::Method::body },
451 ## --------------------------------------------------------
452 ## Class::MOP::Method::Wrapped
455 # the way this item is initialized, this
456 # really does not follow the standard
457 # practices of attributes, but we put
458 # it here for completeness
459 Class::MOP::Method::Wrapped->meta->add_attribute(
460 Class::MOP::Attribute->new('%!modifier_table')
463 ## --------------------------------------------------------
464 ## Class::MOP::Method::Generated
466 Class::MOP::Method::Generated->meta->add_attribute(
467 Class::MOP::Attribute->new('$!is_inline' => (
468 init_arg => 'is_inline',
469 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
473 ## --------------------------------------------------------
474 ## Class::MOP::Method::Accessor
476 Class::MOP::Method::Accessor->meta->add_attribute(
477 Class::MOP::Attribute->new('$!attribute' => (
478 init_arg => 'attribute',
480 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
485 Class::MOP::Method::Accessor->meta->add_attribute(
486 Class::MOP::Attribute->new('$!accessor_type' => (
487 init_arg => 'accessor_type',
488 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
493 ## --------------------------------------------------------
494 ## Class::MOP::Method::Constructor
496 Class::MOP::Method::Constructor->meta->add_attribute(
497 Class::MOP::Attribute->new('%!options' => (
498 init_arg => 'options',
500 'options' => \&Class::MOP::Method::Constructor::options
505 Class::MOP::Method::Constructor->meta->add_attribute(
506 Class::MOP::Attribute->new('$!associated_metaclass' => (
507 init_arg => 'metaclass',
509 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
514 ## --------------------------------------------------------
515 ## Class::MOP::Instance
518 # these don't yet do much of anything, but are just
519 # included for completeness
521 Class::MOP::Instance->meta->add_attribute(
522 Class::MOP::Attribute->new('$!meta')
525 Class::MOP::Instance->meta->add_attribute(
526 Class::MOP::Attribute->new('@!slots')
529 ## --------------------------------------------------------
530 ## Now close all the Class::MOP::* classes
533 # we don't need to inline the
534 # constructors or the accessors
535 # this only lengthens the compile
536 # time of the MOP, and gives us
537 # no actual benefits.
539 $_->meta->make_immutable(
540 inline_constructor => 0,
541 inline_accessors => 0,
547 Class::MOP::Attribute
553 Class::MOP::Method::Generated
555 Class::MOP::Method::Accessor
556 Class::MOP::Method::Constructor
557 Class::MOP::Method::Wrapped
568 Class::MOP - A Meta Object Protocol for Perl 5
572 This module is a fully functioning meta object protocol for the
573 Perl 5 object system. It makes no attempt to change the behavior or
574 characteristics of the Perl 5 object system, only to create a
575 protocol for its manipulation and introspection.
577 That said, it does attempt to create the tools for building a rich
578 set of extensions to the Perl 5 object system. Every attempt has been
579 made for these tools to keep to the spirit of the Perl 5 object
580 system that we all know and love.
582 This documentation is admittedly sparse on details, as time permits
583 I will try to improve them. For now, I suggest looking at the items
584 listed in the L<SEE ALSO> section for more information. In particular
585 the book "The Art of the Meta Object Protocol" was very influential
586 in the development of this system.
588 =head2 What is a Meta Object Protocol?
590 A meta object protocol is an API to an object system.
592 To be more specific, it is a set of abstractions of the components of
593 an object system (typically things like; classes, object, methods,
594 object attributes, etc.). These abstractions can then be used to both
595 inspect and manipulate the object system which they describe.
597 It can be said that there are two MOPs for any object system; the
598 implicit MOP, and the explicit MOP. The implicit MOP handles things
599 like method dispatch or inheritance, which happen automatically as
600 part of how the object system works. The explicit MOP typically
601 handles the introspection/reflection features of the object system.
602 All object systems have implicit MOPs, without one, they would not
603 work. Explict MOPs however as less common, and depending on the
604 language can vary from restrictive (Reflection in Java or C#) to
605 wide open (CLOS is a perfect example).
607 =head2 Yet Another Class Builder!! Why?
609 This is B<not> a class builder so much as it is a I<class builder
610 B<builder>>. My intent is that an end user does not use this module
611 directly, but instead this module is used by module authors to
612 build extensions and features onto the Perl 5 object system.
614 =head2 Who is this module for?
616 This module is specifically for anyone who has ever created or
617 wanted to create a module for the Class:: namespace. The tools which
618 this module will provide will hopefully make it easier to do more
619 complex things with Perl 5 classes by removing such barriers as
620 the need to hack the symbol tables, or understand the fine details
623 =head2 What changes do I have to make to use this module?
625 This module was designed to be as unintrusive as possible. Many of
626 its features are accessible without B<any> change to your existsing
627 code at all. It is meant to be a compliment to your existing code and
628 not an intrusion on your code base. Unlike many other B<Class::>
629 modules, this module B<does not> require you subclass it, or even that
630 you C<use> it in within your module's package.
632 The only features which requires additions to your code are the
633 attribute handling and instance construction features, and these are
634 both completely optional features. The only reason for this is because
635 Perl 5's object system does not actually have these features built
636 in. More information about this feature can be found below.
638 =head2 A Note about Performance?
640 It is a common misconception that explict MOPs are performance drains.
641 But this is not a universal truth at all, it is an side-effect of
642 specific implementations. For instance, using Java reflection is much
643 slower because the JVM cannot take advantage of any compiler
644 optimizations, and the JVM has to deal with much more runtime type
645 information as well. Reflection in C# is marginally better as it was
646 designed into the language and runtime (the CLR). In contrast, CLOS
647 (the Common Lisp Object System) was built to support an explicit MOP,
648 and so performance is tuned for it.
650 This library in particular does it's absolute best to avoid putting
651 B<any> drain at all upon your code's performance. In fact, by itself
652 it does nothing to affect your existing code. So you only pay for
653 what you actually use.
655 =head2 About Metaclass compatibility
657 This module makes sure that all metaclasses created are both upwards
658 and downwards compatible. The topic of metaclass compatibility is
659 highly esoteric and is something only encountered when doing deep and
660 involved metaclass hacking. There are two basic kinds of metaclass
661 incompatibility; upwards and downwards.
663 Upwards metaclass compatibility means that the metaclass of a
664 given class is either the same as (or a subclass of) all of the
667 Downward metaclass compatibility means that the metaclasses of a
668 given class's anscestors are all either the same as (or a subclass
671 Here is a diagram showing a set of two classes (C<A> and C<B>) and
672 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
673 metaclass compatibility both upwards and downwards.
675 +---------+ +---------+
676 | Meta::A |<----| Meta::B | <....... (instance of )
677 +---------+ +---------+ <------- (inherits from)
680 +---------+ +---------+
682 +---------+ +---------+
684 As I said this is a highly esoteric topic and one you will only run
685 into if you do a lot of subclassing of B<Class::MOP::Class>. If you
686 are interested in why this is an issue see the paper
687 I<Uniform and safe metaclass composition> linked to in the
688 L<SEE ALSO> section of this document.
690 =head2 Using custom metaclasses
692 Always use the metaclass pragma when using a custom metaclass, this
693 will ensure the proper initialization order and not accidentely
694 create an incorrect type of metaclass for you. This is a very rare
695 problem, and one which can only occur if you are doing deep metaclass
696 programming. So in other words, don't worry about it.
700 The protocol is divided into 4 main sub-protocols:
704 =item The Class protocol
706 This provides a means of manipulating and introspecting a Perl 5
707 class. It handles all of symbol table hacking for you, and provides
708 a rich set of methods that go beyond simple package introspection.
710 See L<Class::MOP::Class> for more details.
712 =item The Attribute protocol
714 This provides a consistent represenation for an attribute of a
715 Perl 5 class. Since there are so many ways to create and handle
716 attributes in Perl 5 OO, this attempts to provide as much of a
717 unified approach as possible, while giving the freedom and
718 flexibility to subclass for specialization.
720 See L<Class::MOP::Attribute> for more details.
722 =item The Method protocol
724 This provides a means of manipulating and introspecting methods in
725 the Perl 5 object system. As with attributes, there are many ways to
726 approach this topic, so we try to keep it pretty basic, while still
727 making it possible to extend the system in many ways.
729 See L<Class::MOP::Method> for more details.
731 =item The Instance protocol
733 This provides a layer of abstraction for creating object instances.
734 Since the other layers use this protocol, it is relatively easy to
735 change the type of your instances from the default HASH ref to other
736 types of references. Several examples are provided in the F<examples/>
737 directory included in this distribution.
739 See L<Class::MOP::Instance> for more details.
749 =item I<IS_RUNNING_ON_5_10>
751 We set this constant depending on what version perl we are on, this
752 allows us to take advantage of new 5.10 features and stay backwards
757 =head2 Utility functions
761 =item B<load_class ($class_name)>
763 This will load a given C<$class_name> and if it does not have an
764 already initialized metaclass, then it will intialize one for it.
765 This function can be used in place of tricks like
766 C<eval "use $module"> or using C<require>.
768 =item B<is_class_loaded ($class_name)>
770 This will return a boolean depending on if the C<$class_name> has
773 NOTE: This does a basic check of the symbol table to try and
774 determine as best it can if the C<$class_name> is loaded, it
775 is probably correct about 99% of the time.
777 =item B<check_package_cache_flag ($pkg)>
779 This will return an integer that is managed by C<Class::MOP::Class>
780 to determine if a module's symbol table has been altered.
782 In Perl 5.10 or greater, this flag is package specific. However in
783 versions prior to 5.10, this will use the C<PL_sub_generation> variable
784 which is not package specific.
786 =item B<get_code_info ($code)>
788 This function returns two values, the name of the package the C<$code>
789 is from and the name of the C<$code> itself. This is used by several
790 elements of the MOP to detemine where a given C<$code> reference is from.
794 =head2 Metaclass cache functions
796 Class::MOP holds a cache of metaclasses, the following are functions
797 (B<not methods>) which can be used to access that cache. It is not
798 recommended that you mess with this, bad things could happen. But if
799 you are brave and willing to risk it, go for it.
803 =item B<get_all_metaclasses>
805 This will return an hash of all the metaclass instances that have
806 been cached by B<Class::MOP::Class> keyed by the package name.
808 =item B<get_all_metaclass_instances>
810 This will return an array of all the metaclass instances that have
811 been cached by B<Class::MOP::Class>.
813 =item B<get_all_metaclass_names>
815 This will return an array of all the metaclass names that have
816 been cached by B<Class::MOP::Class>.
818 =item B<get_metaclass_by_name ($name)>
820 This will return a cached B<Class::MOP::Class> instance of nothing
821 if no metaclass exist by that C<$name>.
823 =item B<store_metaclass_by_name ($name, $meta)>
825 This will store a metaclass in the cache at the supplied C<$key>.
827 =item B<weaken_metaclass ($name)>
829 In rare cases it is desireable to store a weakened reference in
830 the metaclass cache. This function will weaken the reference to
831 the metaclass stored in C<$name>.
833 =item B<does_metaclass_exist ($name)>
835 This will return true of there exists a metaclass stored in the
836 C<$name> key and return false otherwise.
838 =item B<remove_metaclass_by_name ($name)>
840 This will remove a the metaclass stored in the C<$name> key.
848 There are very few books out on Meta Object Protocols and Metaclasses
849 because it is such an esoteric topic. The following books are really
850 the only ones I have found. If you know of any more, B<I<please>>
851 email me and let me know, I would love to hear about them.
855 =item "The Art of the Meta Object Protocol"
857 =item "Advances in Object-Oriented Metalevel Architecture and Reflection"
859 =item "Putting MetaClasses to Work"
861 =item "Smalltalk: The Language"
869 =item Uniform and safe metaclass composition
871 An excellent paper by the people who brought us the original Traits paper.
872 This paper is on how Traits can be used to do safe metaclass composition,
873 and offers an excellent introduction section which delves into the topic of
874 metaclass compatibility.
876 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
878 =item Safe Metaclass Programming
880 This paper seems to precede the above paper, and propose a mix-in based
881 approach as opposed to the Traits based approach. Both papers have similar
882 information on the metaclass compatibility problem space.
884 L<http://citeseer.ist.psu.edu/37617.html>
892 =item The Perl 6 MetaModel work in the Pugs project
896 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
898 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
908 =item CPAN Module Review of Class::MOP
910 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
914 =head1 SIMILAR MODULES
916 As I have said above, this module is a class-builder-builder, so it is
917 not the same thing as modules like L<Class::Accessor> and
918 L<Class::MethodMaker>. That being said there are very few modules on CPAN
919 with similar goals to this module. The one I have found which is most
920 like this module is L<Class::Meta>, although it's philosophy and the MOP it
921 creates are very different from this modules.
925 All complex software has bugs lurking in it, and this module is no
926 exception. If you find a bug please either email me, or add the bug
929 =head1 ACKNOWLEDGEMENTS
935 Thanks to Rob for actually getting the development of this module kick-started.
941 Stevan Little E<lt>stevan@iinteractive.comE<gt>
943 B<with contributions from:>
945 Brandon (blblack) Black
947 Guillermo (groditi) Roditi
951 Rob (robkinyon) Kinyon
953 Yuval (nothingmuch) Kogman
955 Scott (konobi) McWhirter
957 =head1 COPYRIGHT AND LICENSE
959 Copyright 2006-2008 by Infinity Interactive, Inc.
961 L<http://www.iinteractive.com>
963 This library is free software; you can redistribute it and/or modify
964 it under the same terms as Perl itself.