12 use Scalar::Util 'weaken';
14 use Sub::Identify 'get_code_info';
20 Sub::Name->import(qw(subname));
22 } or eval 'sub subname { $_[1] }';
24 # this is either part of core or set up appropriately by MRO::Compat
25 *check_package_cache_flag = \&mro::get_pkg_gen;
28 require Devel::GlobalDestruction;
29 Devel::GlobalDestruction->import("in_global_destruction");
31 } or *in_global_destruction = sub () { !1 };
35 use Class::MOP::Class;
36 use Class::MOP::Attribute;
37 use Class::MOP::Method;
39 use Class::MOP::Immutable;
42 *IS_RUNNING_ON_5_10 = ($] < 5.009_005)
46 *HAVE_ISAREV = defined(&mro::get_isarev)
51 our $VERSION = '0.64_06';
52 our $XS_VERSION = $VERSION;
53 $VERSION = eval $VERSION;
54 our $AUTHORITY = 'cpan:STEVAN';
56 # after that everything is loaded, if we're allowed try to load faster XS
57 # versions of various things
58 unless ($ENV{CLASS_MOP_NO_XS}) {
63 __PACKAGE__->XSLoader::load($XS_VERSION);
68 die $e if $e && $e !~ /object version|loadable object/;
72 # Metaclasses are singletons, so we cache them here.
73 # there is no need to worry about destruction though
74 # because they should die only when the program dies.
75 # After all, do package definitions even get reaped?
78 # means of accessing all the metaclasses that have
79 # been initialized thus far (for mugwumps obj browser)
80 sub get_all_metaclasses { %METAS }
81 sub get_all_metaclass_instances { values %METAS }
82 sub get_all_metaclass_names { keys %METAS }
83 sub get_metaclass_by_name { $METAS{$_[0]} }
84 sub store_metaclass_by_name { $METAS{$_[0]} = $_[1] }
85 sub weaken_metaclass { weaken($METAS{$_[0]}) }
86 sub does_metaclass_exist { exists $METAS{$_[0]} && defined $METAS{$_[0]} }
87 sub remove_metaclass_by_name { $METAS{$_[0]} = undef }
90 # We only cache metaclasses, meaning instances of
91 # Class::MOP::Class. We do not cache instance of
92 # Class::MOP::Package or Class::MOP::Module. Mostly
93 # because I don't yet see a good reason to do so.
99 unless ( _is_valid_class_name($class) ) {
100 my $display = defined($class) ? $class : 'undef';
101 confess "Invalid class name ($display)";
104 # if the class is not already loaded in the symbol table..
105 unless (is_class_loaded($class)) {
107 my $e = do { local $@; eval "require $class"; $@ };
108 confess "Could not load class ($class) because : $e" if $e;
111 # initialize a metaclass if necessary
112 unless (does_metaclass_exist($class)) {
113 my $e = do { local $@; eval { Class::MOP::Class->initialize($class) }; $@ };
114 confess "Could not initialize class ($class) because : $e" if $e;
117 return get_metaclass_by_name($class) if defined wantarray;
120 sub _is_valid_class_name {
123 return 0 if ref($class);
124 return 0 unless defined($class);
125 return 0 unless length($class);
127 return 1 if $class =~ /^\w+(?:::\w+)*$/;
132 sub is_class_loaded {
135 return 0 if ref($class) || !defined($class) || !length($class);
137 # walk the symbol table tree to avoid autovififying
138 # \*{${main::}{"Foo::"}} == \*main::Foo::
141 foreach my $part (split('::', $class)) {
142 return 0 unless exists ${$$pack}{"${part}::"};
143 $pack = \*{${$$pack}{"${part}::"}};
146 # check for $VERSION or @ISA
147 return 1 if exists ${$$pack}{VERSION}
148 && defined *{${$$pack}{VERSION}}{SCALAR};
149 return 1 if exists ${$$pack}{ISA}
150 && defined *{${$$pack}{ISA}}{ARRAY};
152 # check for any method
153 foreach ( keys %{$$pack} ) {
154 next if substr($_, -2, 2) eq '::';
156 my $glob = ${$$pack}{$_} || next;
159 if ( IS_RUNNING_ON_5_10 ) {
160 return 1 if ref $glob eq 'SCALAR';
163 return 1 if defined *{$glob}{CODE};
171 ## ----------------------------------------------------------------------------
172 ## Setting up our environment ...
173 ## ----------------------------------------------------------------------------
174 ## Class::MOP needs to have a few things in the global perl environment so
175 ## that it can operate effectively. Those things are done here.
176 ## ----------------------------------------------------------------------------
178 # ... nothing yet actually ;)
180 ## ----------------------------------------------------------------------------
182 ## ----------------------------------------------------------------------------
183 ## The code below here is to bootstrap our MOP with itself. This is also
184 ## sometimes called "tying the knot". By doing this, we make it much easier
185 ## to extend the MOP through subclassing and such since now you can use the
186 ## MOP itself to extend itself.
188 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
189 ## ----------------------------------------------------------------------------
191 # We need to add in the meta-attributes here so that
192 # any subclass of Class::MOP::* will be able to
193 # inherit them using &construct_instance
195 ## --------------------------------------------------------
196 ## Class::MOP::Package
198 Class::MOP::Package->meta->add_attribute(
199 Class::MOP::Attribute->new('package' => (
201 # NOTE: we need to do this in order
202 # for the instance meta-object to
203 # not fall into meta-circular death
205 # we just alias the original method
206 # rather than re-produce it here
207 'name' => \&Class::MOP::Package::name
212 Class::MOP::Package->meta->add_attribute(
213 Class::MOP::Attribute->new('namespace' => (
216 # we just alias the original method
217 # rather than re-produce it here
218 'namespace' => \&Class::MOP::Package::namespace
221 default => sub { \undef }
225 ## --------------------------------------------------------
226 ## Class::MOP::Module
229 # yeah this is kind of stretching things a bit,
230 # but truthfully the version should be an attribute
231 # of the Module, the weirdness comes from having to
232 # stick to Perl 5 convention and store it in the
233 # $VERSION package variable. Basically if you just
234 # squint at it, it will look how you want it to look.
235 # Either as a package variable, or as a attribute of
236 # the metaclass, isn't abstraction great :)
238 Class::MOP::Module->meta->add_attribute(
239 Class::MOP::Attribute->new('version' => (
242 # we just alias the original method
243 # rather than re-produce it here
244 'version' => \&Class::MOP::Module::version
247 default => sub { \undef }
252 # By following the same conventions as version here,
253 # we are opening up the possibility that people can
254 # use the $AUTHORITY in non-Class::MOP modules as
257 Class::MOP::Module->meta->add_attribute(
258 Class::MOP::Attribute->new('authority' => (
261 # we just alias the original method
262 # rather than re-produce it here
263 'authority' => \&Class::MOP::Module::authority
266 default => sub { \undef }
270 ## --------------------------------------------------------
273 Class::MOP::Class->meta->add_attribute(
274 Class::MOP::Attribute->new('attributes' => (
276 # NOTE: we need to do this in order
277 # for the instance meta-object to
278 # not fall into meta-circular death
280 # we just alias the original method
281 # rather than re-produce it here
282 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
284 default => sub { {} }
288 Class::MOP::Class->meta->add_attribute(
289 Class::MOP::Attribute->new('methods' => (
292 # we just alias the original method
293 # rather than re-produce it here
294 'get_method_map' => \&Class::MOP::Class::get_method_map
296 default => sub { {} }
300 Class::MOP::Class->meta->add_attribute(
301 Class::MOP::Attribute->new('superclasses' => (
304 # we just alias the original method
305 # rather than re-produce it here
306 'superclasses' => \&Class::MOP::Class::superclasses
309 default => sub { \undef }
313 Class::MOP::Class->meta->add_attribute(
314 Class::MOP::Attribute->new('attribute_metaclass' => (
317 # we just alias the original method
318 # rather than re-produce it here
319 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
321 default => 'Class::MOP::Attribute',
325 Class::MOP::Class->meta->add_attribute(
326 Class::MOP::Attribute->new('method_metaclass' => (
329 # we just alias the original method
330 # rather than re-produce it here
331 'method_metaclass' => \&Class::MOP::Class::method_metaclass
333 default => 'Class::MOP::Method',
337 Class::MOP::Class->meta->add_attribute(
338 Class::MOP::Attribute->new('instance_metaclass' => (
340 # NOTE: we need to do this in order
341 # for the instance meta-object to
342 # not fall into meta-circular death
344 # we just alias the original method
345 # rather than re-produce it here
346 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
348 default => 'Class::MOP::Instance',
353 # we don't actually need to tie the knot with
354 # Class::MOP::Class here, it is actually handled
355 # within Class::MOP::Class itself in the
356 # construct_class_instance method.
358 ## --------------------------------------------------------
359 ## Class::MOP::Attribute
361 Class::MOP::Attribute->meta->add_attribute(
362 Class::MOP::Attribute->new('name' => (
364 # NOTE: we need to do this in order
365 # for the instance meta-object to
366 # not fall into meta-circular death
368 # we just alias the original method
369 # rather than re-produce it here
370 'name' => \&Class::MOP::Attribute::name
375 Class::MOP::Attribute->meta->add_attribute(
376 Class::MOP::Attribute->new('associated_class' => (
378 # NOTE: we need to do this in order
379 # for the instance meta-object to
380 # not fall into meta-circular death
382 # we just alias the original method
383 # rather than re-produce it here
384 'associated_class' => \&Class::MOP::Attribute::associated_class
389 Class::MOP::Attribute->meta->add_attribute(
390 Class::MOP::Attribute->new('accessor' => (
391 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
392 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
396 Class::MOP::Attribute->meta->add_attribute(
397 Class::MOP::Attribute->new('reader' => (
398 reader => { 'reader' => \&Class::MOP::Attribute::reader },
399 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
403 Class::MOP::Attribute->meta->add_attribute(
404 Class::MOP::Attribute->new('initializer' => (
405 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
406 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
410 Class::MOP::Attribute->meta->add_attribute(
411 Class::MOP::Attribute->new('writer' => (
412 reader => { 'writer' => \&Class::MOP::Attribute::writer },
413 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
417 Class::MOP::Attribute->meta->add_attribute(
418 Class::MOP::Attribute->new('predicate' => (
419 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
420 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
424 Class::MOP::Attribute->meta->add_attribute(
425 Class::MOP::Attribute->new('clearer' => (
426 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
427 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
431 Class::MOP::Attribute->meta->add_attribute(
432 Class::MOP::Attribute->new('builder' => (
433 reader => { 'builder' => \&Class::MOP::Attribute::builder },
434 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
438 Class::MOP::Attribute->meta->add_attribute(
439 Class::MOP::Attribute->new('init_arg' => (
440 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
441 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
445 Class::MOP::Attribute->meta->add_attribute(
446 Class::MOP::Attribute->new('default' => (
447 # default has a custom 'reader' method ...
448 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
452 Class::MOP::Attribute->meta->add_attribute(
453 Class::MOP::Attribute->new('associated_methods' => (
454 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
455 default => sub { [] }
459 Class::MOP::Attribute->meta->add_method('clone' => sub {
461 $self->meta->clone_object($self, @_);
464 ## --------------------------------------------------------
465 ## Class::MOP::Method
466 Class::MOP::Method->meta->add_attribute(
467 Class::MOP::Attribute->new('body' => (
468 reader => { 'body' => \&Class::MOP::Method::body },
472 Class::MOP::Method->meta->add_attribute(
473 Class::MOP::Attribute->new('associated_metaclass' => (
474 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
478 Class::MOP::Method->meta->add_attribute(
479 Class::MOP::Attribute->new('package_name' => (
480 reader => { 'package_name' => \&Class::MOP::Method::package_name },
484 Class::MOP::Method->meta->add_attribute(
485 Class::MOP::Attribute->new('name' => (
486 reader => { 'name' => \&Class::MOP::Method::name },
490 Class::MOP::Method->meta->add_method('clone' => sub {
492 $self->meta->clone_object($self, @_);
495 ## --------------------------------------------------------
496 ## Class::MOP::Method::Wrapped
499 # the way this item is initialized, this
500 # really does not follow the standard
501 # practices of attributes, but we put
502 # it here for completeness
503 Class::MOP::Method::Wrapped->meta->add_attribute(
504 Class::MOP::Attribute->new('modifier_table')
507 ## --------------------------------------------------------
508 ## Class::MOP::Method::Generated
510 Class::MOP::Method::Generated->meta->add_attribute(
511 Class::MOP::Attribute->new('is_inline' => (
512 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
517 ## --------------------------------------------------------
518 ## Class::MOP::Method::Accessor
520 Class::MOP::Method::Accessor->meta->add_attribute(
521 Class::MOP::Attribute->new('attribute' => (
523 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
528 Class::MOP::Method::Accessor->meta->add_attribute(
529 Class::MOP::Attribute->new('accessor_type' => (
530 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
534 ## --------------------------------------------------------
535 ## Class::MOP::Method::Constructor
537 Class::MOP::Method::Constructor->meta->add_attribute(
538 Class::MOP::Attribute->new('options' => (
540 'options' => \&Class::MOP::Method::Constructor::options
542 default => sub { +{} }
546 Class::MOP::Method::Constructor->meta->add_attribute(
547 Class::MOP::Attribute->new('associated_metaclass' => (
548 init_arg => "metaclass", # FIXME alias and rename
550 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
555 ## --------------------------------------------------------
556 ## Class::MOP::Instance
559 # these don't yet do much of anything, but are just
560 # included for completeness
562 Class::MOP::Instance->meta->add_attribute(
563 Class::MOP::Attribute->new('associated_metaclass',
564 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
568 Class::MOP::Instance->meta->add_attribute(
569 Class::MOP::Attribute->new('_class_name',
571 reader => { _class_name => \&Class::MOP::Instance::_class_name },
572 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
573 #default => sub { $_[0]->associated_metaclass->name },
577 Class::MOP::Instance->meta->add_attribute(
578 Class::MOP::Attribute->new('attributes',
579 reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
583 Class::MOP::Instance->meta->add_attribute(
584 Class::MOP::Attribute->new('slots',
585 reader => { slots => \&Class::MOP::Instance::slots },
589 Class::MOP::Instance->meta->add_attribute(
590 Class::MOP::Attribute->new('slot_hash',
591 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
596 # we need the meta instance of the meta instance to be created now, in order
597 # for the constructor to be able to use it
598 Class::MOP::Instance->meta->get_meta_instance;
600 # pretend the add_method never happenned. it hasn't yet affected anything
601 undef Class::MOP::Instance->meta->{_package_cache_flag};
603 ## --------------------------------------------------------
604 ## Now close all the Class::MOP::* classes
607 # we don't need to inline the
608 # constructors or the accessors
609 # this only lengthens the compile
610 # time of the MOP, and gives us
611 # no actual benefits.
613 $_->meta->make_immutable(
614 inline_constructor => 1,
615 replace_constructor => 1,
616 constructor_name => "_new",
617 inline_accessors => 0,
623 Class::MOP::Attribute
629 Class::MOP::Method::Generated
631 Class::MOP::Method::Accessor
632 Class::MOP::Method::Constructor
633 Class::MOP::Method::Wrapped
644 Class::MOP - A Meta Object Protocol for Perl 5
648 This module is a fully functioning meta object protocol for the
649 Perl 5 object system. It makes no attempt to change the behavior or
650 characteristics of the Perl 5 object system, only to create a
651 protocol for its manipulation and introspection.
653 That said, it does attempt to create the tools for building a rich
654 set of extensions to the Perl 5 object system. Every attempt has been
655 made for these tools to keep to the spirit of the Perl 5 object
656 system that we all know and love.
658 This documentation is admittedly sparse on details, as time permits
659 I will try to improve them. For now, I suggest looking at the items
660 listed in the L<SEE ALSO> section for more information. In particular
661 the book "The Art of the Meta Object Protocol" was very influential
662 in the development of this system.
664 =head2 What is a Meta Object Protocol?
666 A meta object protocol is an API to an object system.
668 To be more specific, it is a set of abstractions of the components of
669 an object system (typically things like; classes, object, methods,
670 object attributes, etc.). These abstractions can then be used to both
671 inspect and manipulate the object system which they describe.
673 It can be said that there are two MOPs for any object system; the
674 implicit MOP, and the explicit MOP. The implicit MOP handles things
675 like method dispatch or inheritance, which happen automatically as
676 part of how the object system works. The explicit MOP typically
677 handles the introspection/reflection features of the object system.
678 All object systems have implicit MOPs, without one, they would not
679 work. Explict MOPs however as less common, and depending on the
680 language can vary from restrictive (Reflection in Java or C#) to
681 wide open (CLOS is a perfect example).
683 =head2 Yet Another Class Builder!! Why?
685 This is B<not> a class builder so much as it is a I<class builder
686 B<builder>>. My intent is that an end user does not use this module
687 directly, but instead this module is used by module authors to
688 build extensions and features onto the Perl 5 object system.
690 =head2 Who is this module for?
692 This module is specifically for anyone who has ever created or
693 wanted to create a module for the Class:: namespace. The tools which
694 this module will provide will hopefully make it easier to do more
695 complex things with Perl 5 classes by removing such barriers as
696 the need to hack the symbol tables, or understand the fine details
699 =head2 What changes do I have to make to use this module?
701 This module was designed to be as unintrusive as possible. Many of
702 its features are accessible without B<any> change to your existsing
703 code at all. It is meant to be a compliment to your existing code and
704 not an intrusion on your code base. Unlike many other B<Class::>
705 modules, this module B<does not> require you subclass it, or even that
706 you C<use> it in within your module's package.
708 The only features which requires additions to your code are the
709 attribute handling and instance construction features, and these are
710 both completely optional features. The only reason for this is because
711 Perl 5's object system does not actually have these features built
712 in. More information about this feature can be found below.
714 =head2 A Note about Performance?
716 It is a common misconception that explict MOPs are performance drains.
717 But this is not a universal truth at all, it is an side-effect of
718 specific implementations. For instance, using Java reflection is much
719 slower because the JVM cannot take advantage of any compiler
720 optimizations, and the JVM has to deal with much more runtime type
721 information as well. Reflection in C# is marginally better as it was
722 designed into the language and runtime (the CLR). In contrast, CLOS
723 (the Common Lisp Object System) was built to support an explicit MOP,
724 and so performance is tuned for it.
726 This library in particular does it's absolute best to avoid putting
727 B<any> drain at all upon your code's performance. In fact, by itself
728 it does nothing to affect your existing code. So you only pay for
729 what you actually use.
731 =head2 About Metaclass compatibility
733 This module makes sure that all metaclasses created are both upwards
734 and downwards compatible. The topic of metaclass compatibility is
735 highly esoteric and is something only encountered when doing deep and
736 involved metaclass hacking. There are two basic kinds of metaclass
737 incompatibility; upwards and downwards.
739 Upwards metaclass compatibility means that the metaclass of a
740 given class is either the same as (or a subclass of) all of the
743 Downward metaclass compatibility means that the metaclasses of a
744 given class's anscestors are all either the same as (or a subclass
747 Here is a diagram showing a set of two classes (C<A> and C<B>) and
748 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
749 metaclass compatibility both upwards and downwards.
751 +---------+ +---------+
752 | Meta::A |<----| Meta::B | <....... (instance of )
753 +---------+ +---------+ <------- (inherits from)
756 +---------+ +---------+
758 +---------+ +---------+
760 As I said this is a highly esoteric topic and one you will only run
761 into if you do a lot of subclassing of B<Class::MOP::Class>. If you
762 are interested in why this is an issue see the paper
763 I<Uniform and safe metaclass composition> linked to in the
764 L<SEE ALSO> section of this document.
766 =head2 Using custom metaclasses
768 Always use the metaclass pragma when using a custom metaclass, this
769 will ensure the proper initialization order and not accidentely
770 create an incorrect type of metaclass for you. This is a very rare
771 problem, and one which can only occur if you are doing deep metaclass
772 programming. So in other words, don't worry about it.
776 The protocol is divided into 4 main sub-protocols:
780 =item The Class protocol
782 This provides a means of manipulating and introspecting a Perl 5
783 class. It handles all of symbol table hacking for you, and provides
784 a rich set of methods that go beyond simple package introspection.
786 See L<Class::MOP::Class> for more details.
788 =item The Attribute protocol
790 This provides a consistent represenation for an attribute of a
791 Perl 5 class. Since there are so many ways to create and handle
792 attributes in Perl 5 OO, this attempts to provide as much of a
793 unified approach as possible, while giving the freedom and
794 flexibility to subclass for specialization.
796 See L<Class::MOP::Attribute> for more details.
798 =item The Method protocol
800 This provides a means of manipulating and introspecting methods in
801 the Perl 5 object system. As with attributes, there are many ways to
802 approach this topic, so we try to keep it pretty basic, while still
803 making it possible to extend the system in many ways.
805 See L<Class::MOP::Method> for more details.
807 =item The Instance protocol
809 This provides a layer of abstraction for creating object instances.
810 Since the other layers use this protocol, it is relatively easy to
811 change the type of your instances from the default HASH ref to other
812 types of references. Several examples are provided in the F<examples/>
813 directory included in this distribution.
815 See L<Class::MOP::Instance> for more details.
825 =item I<IS_RUNNING_ON_5_10>
827 We set this constant depending on what version perl we are on, this
828 allows us to take advantage of new 5.10 features and stay backwards
833 Whether or not C<mro> provides C<get_isarev>, a much faster way to get all the
834 subclasses of a certain class.
838 =head2 Utility functions
842 =item B<load_class ($class_name)>
844 This will load a given C<$class_name> and if it does not have an
845 already initialized metaclass, then it will intialize one for it.
846 This function can be used in place of tricks like
847 C<eval "use $module"> or using C<require>.
849 =item B<is_class_loaded ($class_name)>
851 This will return a boolean depending on if the C<$class_name> has
854 NOTE: This does a basic check of the symbol table to try and
855 determine as best it can if the C<$class_name> is loaded, it
856 is probably correct about 99% of the time.
858 =item B<check_package_cache_flag ($pkg)>
860 This will return an integer that is managed by C<Class::MOP::Class>
861 to determine if a module's symbol table has been altered.
863 In Perl 5.10 or greater, this flag is package specific. However in
864 versions prior to 5.10, this will use the C<PL_sub_generation> variable
865 which is not package specific.
867 =item B<get_code_info ($code)>
869 This function returns two values, the name of the package the C<$code>
870 is from and the name of the C<$code> itself. This is used by several
871 elements of the MOP to detemine where a given C<$code> reference is from.
873 =item B<subname ($name, $code)>
875 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
877 If possible, we will load the L<Sub::Name> module and this will function
878 as C<Sub::Name::subname> does, otherwise it will just return the C<$code>
881 =item B<in_global_destruction>
883 If L<Devel::GlobalDestruction> is available, this returns true under global
886 Otherwise it's a constant returning false.
890 =head2 Metaclass cache functions
892 Class::MOP holds a cache of metaclasses, the following are functions
893 (B<not methods>) which can be used to access that cache. It is not
894 recommended that you mess with this, bad things could happen. But if
895 you are brave and willing to risk it, go for it.
899 =item B<get_all_metaclasses>
901 This will return an hash of all the metaclass instances that have
902 been cached by B<Class::MOP::Class> keyed by the package name.
904 =item B<get_all_metaclass_instances>
906 This will return an array of all the metaclass instances that have
907 been cached by B<Class::MOP::Class>.
909 =item B<get_all_metaclass_names>
911 This will return an array of all the metaclass names that have
912 been cached by B<Class::MOP::Class>.
914 =item B<get_metaclass_by_name ($name)>
916 This will return a cached B<Class::MOP::Class> instance of nothing
917 if no metaclass exist by that C<$name>.
919 =item B<store_metaclass_by_name ($name, $meta)>
921 This will store a metaclass in the cache at the supplied C<$key>.
923 =item B<weaken_metaclass ($name)>
925 In rare cases it is desireable to store a weakened reference in
926 the metaclass cache. This function will weaken the reference to
927 the metaclass stored in C<$name>.
929 =item B<does_metaclass_exist ($name)>
931 This will return true of there exists a metaclass stored in the
932 C<$name> key and return false otherwise.
934 =item B<remove_metaclass_by_name ($name)>
936 This will remove a the metaclass stored in the C<$name> key.
944 There are very few books out on Meta Object Protocols and Metaclasses
945 because it is such an esoteric topic. The following books are really
946 the only ones I have found. If you know of any more, B<I<please>>
947 email me and let me know, I would love to hear about them.
951 =item "The Art of the Meta Object Protocol"
953 =item "Advances in Object-Oriented Metalevel Architecture and Reflection"
955 =item "Putting MetaClasses to Work"
957 =item "Smalltalk: The Language"
965 =item Uniform and safe metaclass composition
967 An excellent paper by the people who brought us the original Traits paper.
968 This paper is on how Traits can be used to do safe metaclass composition,
969 and offers an excellent introduction section which delves into the topic of
970 metaclass compatibility.
972 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
974 =item Safe Metaclass Programming
976 This paper seems to precede the above paper, and propose a mix-in based
977 approach as opposed to the Traits based approach. Both papers have similar
978 information on the metaclass compatibility problem space.
980 L<http://citeseer.ist.psu.edu/37617.html>
988 =item The Perl 6 MetaModel work in the Pugs project
992 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
994 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1004 =item CPAN Module Review of Class::MOP
1006 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1010 =head1 SIMILAR MODULES
1012 As I have said above, this module is a class-builder-builder, so it is
1013 not the same thing as modules like L<Class::Accessor> and
1014 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1015 with similar goals to this module. The one I have found which is most
1016 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1017 creates are very different from this modules.
1021 All complex software has bugs lurking in it, and this module is no
1022 exception. If you find a bug please either email me, or add the bug
1025 =head1 ACKNOWLEDGEMENTS
1031 Thanks to Rob for actually getting the development of this module kick-started.
1037 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1039 B<with contributions from:>
1041 Brandon (blblack) Black
1043 Guillermo (groditi) Roditi
1047 Rob (robkinyon) Kinyon
1049 Yuval (nothingmuch) Kogman
1051 Scott (konobi) McWhirter
1053 =head1 COPYRIGHT AND LICENSE
1055 Copyright 2006-2008 by Infinity Interactive, Inc.
1057 L<http://www.iinteractive.com>
1059 This library is free software; you can redistribute it and/or modify
1060 it under the same terms as Perl itself.