12 use Devel::GlobalDestruction qw( in_global_destruction );
13 use Scalar::Util 'weaken', 'reftype', 'blessed';
14 use Sub::Name qw( subname );
16 use Class::MOP::Class;
17 use Class::MOP::Attribute;
18 use Class::MOP::Method;
20 use Class::MOP::Immutable;
23 *IS_RUNNING_ON_5_10 = ($] < 5.009_005)
28 warn "Class::MOP::HAVE_ISAREV is deprecated and will be removed in a future release. It has always returned 1 anyway.";
32 # this is either part of core or set up appropriately by MRO::Compat
33 *check_package_cache_flag = \&mro::get_pkg_gen;
36 our $VERSION = '0.80';
37 our $XS_VERSION = $VERSION;
38 $VERSION = eval $VERSION;
39 our $AUTHORITY = 'cpan:STEVAN';
42 XSLoader::load( __PACKAGE__, $XS_VERSION );
46 # Metaclasses are singletons, so we cache them here.
47 # there is no need to worry about destruction though
48 # because they should die only when the program dies.
49 # After all, do package definitions even get reaped?
52 # means of accessing all the metaclasses that have
53 # been initialized thus far (for mugwumps obj browser)
54 sub get_all_metaclasses { %METAS }
55 sub get_all_metaclass_instances { values %METAS }
56 sub get_all_metaclass_names { keys %METAS }
57 sub get_metaclass_by_name { $METAS{$_[0]} }
58 sub store_metaclass_by_name { $METAS{$_[0]} = $_[1] }
59 sub weaken_metaclass { weaken($METAS{$_[0]}) }
60 sub does_metaclass_exist { exists $METAS{$_[0]} && defined $METAS{$_[0]} }
61 sub remove_metaclass_by_name { $METAS{$_[0]} = undef }
63 # This handles instances as well as class names
65 my $class = blessed($_[0]) || $_[0];
66 return $METAS{$class};
70 # We only cache metaclasses, meaning instances of
71 # Class::MOP::Class. We do not cache instance of
72 # Class::MOP::Package or Class::MOP::Module. Mostly
73 # because I don't yet see a good reason to do so.
76 sub _class_to_pmfile {
79 my $file = $class . '.pm';
85 sub load_first_existing_class {
89 foreach my $class (@classes) {
90 unless ( _is_valid_class_name($class) ) {
91 my $display = defined($class) ? $class : 'undef';
92 confess "Invalid class name ($display)";
98 for my $class (@classes) {
99 my $pmfile = _class_to_pmfile($class);
100 my $e = _try_load_one_class($class);
103 $exceptions{$class} = $e;
104 last if $e !~ /^Can't locate \Q$pmfile\E in \@INC/;
112 return $found if $found;
118 "Could not load class (%s) because : %s", $_,
123 exists $exceptions{$_}
128 sub _try_load_one_class {
131 return if is_class_loaded($class);
133 my $file = _class_to_pmfile($class);
137 eval { require($file) };
143 my $class = load_first_existing_class($_[0]);
144 return get_metaclass_by_name($class) || $class;
147 sub _is_valid_class_name {
150 return 0 if ref($class);
151 return 0 unless defined($class);
152 return 0 unless length($class);
154 return 1 if $class =~ /^\w+(?:::\w+)*$/;
159 ## ----------------------------------------------------------------------------
160 ## Setting up our environment ...
161 ## ----------------------------------------------------------------------------
162 ## Class::MOP needs to have a few things in the global perl environment so
163 ## that it can operate effectively. Those things are done here.
164 ## ----------------------------------------------------------------------------
166 # ... nothing yet actually ;)
168 ## ----------------------------------------------------------------------------
170 ## ----------------------------------------------------------------------------
171 ## The code below here is to bootstrap our MOP with itself. This is also
172 ## sometimes called "tying the knot". By doing this, we make it much easier
173 ## to extend the MOP through subclassing and such since now you can use the
174 ## MOP itself to extend itself.
176 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
177 ## ----------------------------------------------------------------------------
179 # We need to add in the meta-attributes here so that
180 # any subclass of Class::MOP::* will be able to
181 # inherit them using &construct_instance
183 ## --------------------------------------------------------
184 ## Class::MOP::Package
186 Class::MOP::Package->meta->add_attribute(
187 Class::MOP::Attribute->new('package' => (
189 # NOTE: we need to do this in order
190 # for the instance meta-object to
191 # not fall into meta-circular death
193 # we just alias the original method
194 # rather than re-produce it here
195 'name' => \&Class::MOP::Package::name
200 Class::MOP::Package->meta->add_attribute(
201 Class::MOP::Attribute->new('namespace' => (
204 # we just alias the original method
205 # rather than re-produce it here
206 'namespace' => \&Class::MOP::Package::namespace
209 default => sub { \undef }
213 ## --------------------------------------------------------
214 ## Class::MOP::Module
217 # yeah this is kind of stretching things a bit,
218 # but truthfully the version should be an attribute
219 # of the Module, the weirdness comes from having to
220 # stick to Perl 5 convention and store it in the
221 # $VERSION package variable. Basically if you just
222 # squint at it, it will look how you want it to look.
223 # Either as a package variable, or as a attribute of
224 # the metaclass, isn't abstraction great :)
226 Class::MOP::Module->meta->add_attribute(
227 Class::MOP::Attribute->new('version' => (
230 # we just alias the original method
231 # rather than re-produce it here
232 'version' => \&Class::MOP::Module::version
235 default => sub { \undef }
240 # By following the same conventions as version here,
241 # we are opening up the possibility that people can
242 # use the $AUTHORITY in non-Class::MOP modules as
245 Class::MOP::Module->meta->add_attribute(
246 Class::MOP::Attribute->new('authority' => (
249 # we just alias the original method
250 # rather than re-produce it here
251 'authority' => \&Class::MOP::Module::authority
254 default => sub { \undef }
258 ## --------------------------------------------------------
261 Class::MOP::Class->meta->add_attribute(
262 Class::MOP::Attribute->new('attributes' => (
264 # NOTE: we need to do this in order
265 # for the instance meta-object to
266 # not fall into meta-circular death
268 # we just alias the original method
269 # rather than re-produce it here
270 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
272 default => sub { {} }
276 Class::MOP::Class->meta->add_attribute(
277 Class::MOP::Attribute->new('methods' => (
280 # we just alias the original method
281 # rather than re-produce it here
282 'get_method_map' => \&Class::MOP::Class::get_method_map
284 default => sub { {} }
288 Class::MOP::Class->meta->add_attribute(
289 Class::MOP::Attribute->new('superclasses' => (
292 # we just alias the original method
293 # rather than re-produce it here
294 'superclasses' => \&Class::MOP::Class::superclasses
297 default => sub { \undef }
301 Class::MOP::Class->meta->add_attribute(
302 Class::MOP::Attribute->new('attribute_metaclass' => (
305 # we just alias the original method
306 # rather than re-produce it here
307 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
309 default => 'Class::MOP::Attribute',
313 Class::MOP::Class->meta->add_attribute(
314 Class::MOP::Attribute->new('method_metaclass' => (
317 # we just alias the original method
318 # rather than re-produce it here
319 'method_metaclass' => \&Class::MOP::Class::method_metaclass
321 default => 'Class::MOP::Method',
325 Class::MOP::Class->meta->add_attribute(
326 Class::MOP::Attribute->new('wrapped_method_metaclass' => (
329 # we just alias the original method
330 # rather than re-produce it here
331 'wrapped_method_metaclass' => \&Class::MOP::Class::wrapped_method_metaclass
333 default => 'Class::MOP::Method::Wrapped',
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',
352 Class::MOP::Class->meta->add_attribute(
353 Class::MOP::Attribute->new('immutable_transformer' => (
355 'immutable_transformer' => \&Class::MOP::Class::immutable_transformer
358 '_set_immutable_transformer' => \&Class::MOP::Class::_set_immutable_transformer
364 # we don't actually need to tie the knot with
365 # Class::MOP::Class here, it is actually handled
366 # within Class::MOP::Class itself in the
367 # construct_class_instance method.
369 ## --------------------------------------------------------
370 ## Class::MOP::Attribute
372 Class::MOP::Attribute->meta->add_attribute(
373 Class::MOP::Attribute->new('name' => (
375 # NOTE: we need to do this in order
376 # for the instance meta-object to
377 # not fall into meta-circular death
379 # we just alias the original method
380 # rather than re-produce it here
381 'name' => \&Class::MOP::Attribute::name
386 Class::MOP::Attribute->meta->add_attribute(
387 Class::MOP::Attribute->new('associated_class' => (
389 # NOTE: we need to do this in order
390 # for the instance meta-object to
391 # not fall into meta-circular death
393 # we just alias the original method
394 # rather than re-produce it here
395 'associated_class' => \&Class::MOP::Attribute::associated_class
400 Class::MOP::Attribute->meta->add_attribute(
401 Class::MOP::Attribute->new('accessor' => (
402 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
403 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
407 Class::MOP::Attribute->meta->add_attribute(
408 Class::MOP::Attribute->new('reader' => (
409 reader => { 'reader' => \&Class::MOP::Attribute::reader },
410 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
414 Class::MOP::Attribute->meta->add_attribute(
415 Class::MOP::Attribute->new('initializer' => (
416 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
417 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
421 Class::MOP::Attribute->meta->add_attribute(
422 Class::MOP::Attribute->new('definition_context' => (
423 reader => { 'definition_context' => \&Class::MOP::Attribute::definition_context },
427 Class::MOP::Attribute->meta->add_attribute(
428 Class::MOP::Attribute->new('writer' => (
429 reader => { 'writer' => \&Class::MOP::Attribute::writer },
430 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
434 Class::MOP::Attribute->meta->add_attribute(
435 Class::MOP::Attribute->new('predicate' => (
436 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
437 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
441 Class::MOP::Attribute->meta->add_attribute(
442 Class::MOP::Attribute->new('clearer' => (
443 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
444 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
448 Class::MOP::Attribute->meta->add_attribute(
449 Class::MOP::Attribute->new('builder' => (
450 reader => { 'builder' => \&Class::MOP::Attribute::builder },
451 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
455 Class::MOP::Attribute->meta->add_attribute(
456 Class::MOP::Attribute->new('init_arg' => (
457 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
458 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
462 Class::MOP::Attribute->meta->add_attribute(
463 Class::MOP::Attribute->new('default' => (
464 # default has a custom 'reader' method ...
465 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
469 Class::MOP::Attribute->meta->add_attribute(
470 Class::MOP::Attribute->new('associated_methods' => (
471 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
472 default => sub { [] }
476 Class::MOP::Attribute->meta->add_method('clone' => sub {
478 $self->meta->clone_object($self, @_);
481 ## --------------------------------------------------------
482 ## Class::MOP::Method
483 Class::MOP::Method->meta->add_attribute(
484 Class::MOP::Attribute->new('body' => (
485 reader => { 'body' => \&Class::MOP::Method::body },
489 Class::MOP::Method->meta->add_attribute(
490 Class::MOP::Attribute->new('associated_metaclass' => (
491 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
495 Class::MOP::Method->meta->add_attribute(
496 Class::MOP::Attribute->new('package_name' => (
497 reader => { 'package_name' => \&Class::MOP::Method::package_name },
501 Class::MOP::Method->meta->add_attribute(
502 Class::MOP::Attribute->new('name' => (
503 reader => { 'name' => \&Class::MOP::Method::name },
507 Class::MOP::Method->meta->add_attribute(
508 Class::MOP::Attribute->new('original_method' => (
509 reader => { 'original_method' => \&Class::MOP::Method::original_method },
510 writer => { '_set_original_method' => \&Class::MOP::Method::_set_original_method },
514 Class::MOP::Method->meta->add_method('clone' => sub {
516 my $clone = $self->meta->clone_object($self, @_);
517 $clone->_set_original_method($self);
521 ## --------------------------------------------------------
522 ## Class::MOP::Method::Wrapped
525 # the way this item is initialized, this
526 # really does not follow the standard
527 # practices of attributes, but we put
528 # it here for completeness
529 Class::MOP::Method::Wrapped->meta->add_attribute(
530 Class::MOP::Attribute->new('modifier_table')
533 ## --------------------------------------------------------
534 ## Class::MOP::Method::Generated
536 Class::MOP::Method::Generated->meta->add_attribute(
537 Class::MOP::Attribute->new('is_inline' => (
538 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
543 Class::MOP::Method::Generated->meta->add_attribute(
544 Class::MOP::Attribute->new('definition_context' => (
545 reader => { 'definition_context' => \&Class::MOP::Method::Generated::definition_context },
549 ## --------------------------------------------------------
550 ## Class::MOP::Method::Accessor
552 Class::MOP::Method::Accessor->meta->add_attribute(
553 Class::MOP::Attribute->new('attribute' => (
555 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
560 Class::MOP::Method::Accessor->meta->add_attribute(
561 Class::MOP::Attribute->new('accessor_type' => (
562 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
566 ## --------------------------------------------------------
567 ## Class::MOP::Method::Constructor
569 Class::MOP::Method::Constructor->meta->add_attribute(
570 Class::MOP::Attribute->new('options' => (
572 'options' => \&Class::MOP::Method::Constructor::options
574 default => sub { +{} }
578 Class::MOP::Method::Constructor->meta->add_attribute(
579 Class::MOP::Attribute->new('associated_metaclass' => (
580 init_arg => "metaclass", # FIXME alias and rename
582 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
587 ## --------------------------------------------------------
588 ## Class::MOP::Instance
591 # these don't yet do much of anything, but are just
592 # included for completeness
594 Class::MOP::Instance->meta->add_attribute(
595 Class::MOP::Attribute->new('associated_metaclass',
596 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
600 Class::MOP::Instance->meta->add_attribute(
601 Class::MOP::Attribute->new('_class_name',
603 reader => { _class_name => \&Class::MOP::Instance::_class_name },
604 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
605 #default => sub { $_[0]->associated_metaclass->name },
609 Class::MOP::Instance->meta->add_attribute(
610 Class::MOP::Attribute->new('attributes',
611 reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
615 Class::MOP::Instance->meta->add_attribute(
616 Class::MOP::Attribute->new('slots',
617 reader => { slots => \&Class::MOP::Instance::slots },
621 Class::MOP::Instance->meta->add_attribute(
622 Class::MOP::Attribute->new('slot_hash',
623 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
628 # we need the meta instance of the meta instance to be created now, in order
629 # for the constructor to be able to use it
630 Class::MOP::Instance->meta->get_meta_instance;
632 # pretend the add_method never happenned. it hasn't yet affected anything
633 undef Class::MOP::Instance->meta->{_package_cache_flag};
635 ## --------------------------------------------------------
636 ## Now close all the Class::MOP::* classes
638 # NOTE: we don't need to inline the the accessors this only lengthens
639 # the compile time of the MOP, and gives us no actual benefits.
641 $_->meta->make_immutable(
642 inline_constructor => 1,
643 replace_constructor => 1,
644 constructor_name => "_new",
645 inline_accessors => 0,
651 Class::MOP::Attribute
657 Class::MOP::Method::Generated
659 Class::MOP::Method::Accessor
660 Class::MOP::Method::Constructor
661 Class::MOP::Method::Wrapped
672 Class::MOP - A Meta Object Protocol for Perl 5
676 This module is a fully functioning meta object protocol for the
677 Perl 5 object system. It makes no attempt to change the behavior or
678 characteristics of the Perl 5 object system, only to create a
679 protocol for its manipulation and introspection.
681 That said, it does attempt to create the tools for building a rich set
682 of extensions to the Perl 5 object system. Every attempt has been made
683 to abide by the spirit of the Perl 5 object system that we all know
686 This documentation is sparse on conceptual details. We suggest looking
687 at the items listed in the L<SEE ALSO> section for more
688 information. In particular the book "The Art of the Meta Object
689 Protocol" was very influential in the development of this system.
691 =head2 What is a Meta Object Protocol?
693 A meta object protocol is an API to an object system.
695 To be more specific, it abstracts the components of an object system
696 (classes, object, methods, object attributes, etc.). These
697 abstractions can then be used to inspect and manipulate the object
698 system which they describe.
700 It can be said that there are two MOPs for any object system; the
701 implicit MOP and the explicit MOP. The implicit MOP handles things
702 like method dispatch or inheritance, which happen automatically as
703 part of how the object system works. The explicit MOP typically
704 handles the introspection/reflection features of the object system.
706 All object systems have implicit MOPs. Without one, they would not
707 work. Explicit MOPs are much less common, and depending on the
708 language can vary from restrictive (Reflection in Java or C#) to wide
709 open (CLOS is a perfect example).
711 =head2 Yet Another Class Builder! Why?
713 This is B<not> a class builder so much as a I<class builder
714 B<builder>>. The intent is that an end user will not use this module
715 directly, but instead this module is used by module authors to build
716 extensions and features onto the Perl 5 object system.
718 This system is used by L<Moose>, which supplies a powerful class
719 builder system built entirely on top of C<Class::MOP>.
721 =head2 Who is this module for?
723 This module is for anyone who has ever created or wanted to create a
724 module for the Class:: namespace. The tools which this module provides
725 make doing complex Perl 5 wizardry simpler, by removing such barriers
726 as the need to hack symbol tables, or understand the fine details of
729 =head2 What changes do I have to make to use this module?
731 This module was designed to be as unintrusive as possible. Many of its
732 features are accessible without B<any> change to your existing
733 code. It is meant to be a compliment to your existing code and not an
734 intrusion on your code base. Unlike many other B<Class::> modules,
735 this module B<does not> require you subclass it, or even that you
736 C<use> it in within your module's package.
738 The only features which requires additions to your code are the
739 attribute handling and instance construction features, and these are
740 both completely optional features. The only reason for this is because
741 Perl 5's object system does not actually have these features built
742 in. More information about this feature can be found below.
744 =head2 About Performance
746 It is a common misconception that explicit MOPs are a performance hit.
747 This is not a universal truth, it is a side-effect of some specific
748 implementations. For instance, using Java reflection is slow because
749 the JVM cannot take advantage of any compiler optimizations, and the
750 JVM has to deal with much more runtime type information as well.
752 Reflection in C# is marginally better as it was designed into the
753 language and runtime (the CLR). In contrast, CLOS (the Common Lisp
754 Object System) was built to support an explicit MOP, and so
755 performance is tuned for it.
757 This library in particular does its absolute best to avoid putting
758 B<any> drain at all upon your code's performance. In fact, by itself
759 it does nothing to affect your existing code. So you only pay for what
762 =head2 About Metaclass compatibility
764 This module makes sure that all metaclasses created are both upwards
765 and downwards compatible. The topic of metaclass compatibility is
766 highly esoteric and is something only encountered when doing deep and
767 involved metaclass hacking. There are two basic kinds of metaclass
768 incompatibility; upwards and downwards.
770 Upwards metaclass compatibility means that the metaclass of a
771 given class is either the same as (or a subclass of) all of the
774 Downward metaclass compatibility means that the metaclasses of a
775 given class's ancestors are all either the same as (or a subclass
778 Here is a diagram showing a set of two classes (C<A> and C<B>) and
779 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
780 metaclass compatibility both upwards and downwards.
782 +---------+ +---------+
783 | Meta::A |<----| Meta::B | <....... (instance of )
784 +---------+ +---------+ <------- (inherits from)
787 +---------+ +---------+
789 +---------+ +---------+
791 As I said this is a highly esoteric topic and one you will only run
792 into if you do a lot of subclassing of L<Class::MOP::Class>. If you
793 are interested in why this is an issue see the paper I<Uniform and
794 safe metaclass composition> linked to in the L<SEE ALSO> section of
797 =head2 Using custom metaclasses
799 Always use the L<metaclass> pragma when using a custom metaclass, this
800 will ensure the proper initialization order and not accidentally
801 create an incorrect type of metaclass for you. This is a very rare
802 problem, and one which can only occur if you are doing deep metaclass
803 programming. So in other words, don't worry about it.
805 Note that if you're using L<Moose> we encourage you to I<not> use
806 L<metaclass> pragma, and instead use L<Moose::Util::MetaRole> to apply
807 roles to a class's metaclasses. This topic is covered at length in
808 various L<Moose::Cookbook> recipes.
812 The meta-object protocol is divided into 4 main sub-protocols:
814 =head2 The Class protocol
816 This provides a means of manipulating and introspecting a Perl 5
817 class. It handles symbol table hacking for you, and provides a rich
818 set of methods that go beyond simple package introspection.
820 See L<Class::MOP::Class> for more details.
822 =head2 The Attribute protocol
824 This provides a consistent representation for an attribute of a Perl 5
825 class. Since there are so many ways to create and handle attributes in
826 Perl 5 OO, the Attribute protocol provide as much of a unified
827 approach as possible. Of course, you are always free to extend this
828 protocol by subclassing the appropriate classes.
830 See L<Class::MOP::Attribute> for more details.
832 =head2 The Method protocol
834 This provides a means of manipulating and introspecting methods in the
835 Perl 5 object system. As with attributes, there are many ways to
836 approach this topic, so we try to keep it pretty basic, while still
837 making it possible to extend the system in many ways.
839 See L<Class::MOP::Method> for more details.
841 =head2 The Instance protocol
843 This provides a layer of abstraction for creating object instances.
844 Since the other layers use this protocol, it is relatively easy to
845 change the type of your instances from the default hash reference to
846 some other type of reference. Several examples are provided in the
847 F<examples/> directory included in this distribution.
849 See L<Class::MOP::Instance> for more details.
853 Note that this module does not export any constants or functions.
859 =item I<Class::MOP::IS_RUNNING_ON_5_10>
861 We set this constant depending on what version perl we are on, this
862 allows us to take advantage of new 5.10 features and stay backwards
867 =head2 Utility functions
869 Note that these are all called as B<functions, not methods>.
873 =item B<Class::MOP::load_class($class_name)>
875 This will load the specified C<$class_name>. This function can be used
876 in place of tricks like C<eval "use $module"> or using C<require>
877 unconditionally. This will return the metaclass of C<$class_name>.
879 =item B<Class::MOP::is_class_loaded($class_name)>
881 Returns a boolean indicating whether or not C<$class_name> has been
884 This does a basic check of the symbol table to try and determine as
885 best it can if the C<$class_name> is loaded, it is probably correct
886 about 99% of the time, but it can be fooled into reporting false
889 =item B<Class::MOP::get_code_info($code)>
891 This function returns two values, the name of the package the C<$code>
892 is from and the name of the C<$code> itself. This is used by several
893 elements of the MOP to determine where a given C<$code> reference is
896 =item B<Class::MOP::class_of($instance_or_class_name)>
898 This will return the metaclass of the given instance or class name.
899 Even if the class lacks a metaclass, no metaclass will be initialized
900 and C<undef> will be returned.
902 =item B<Class::MOP::check_package_cache_flag($pkg)>
904 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
906 This will return an integer that is managed by L<Class::MOP::Class> to
907 determine if a module's symbol table has been altered.
909 In Perl 5.10 or greater, this flag is package specific. However in
910 versions prior to 5.10, this will use the C<PL_sub_generation>
911 variable which is not package specific.
913 =item B<Class::MOP::load_first_existing_class(@class_names)>
915 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
917 Given a list of class names, this function will attempt to load each
920 If it finds a class it can load, it will return that class' name. If
921 none of the classes can be loaded, it will throw an exception.
925 =head2 Metaclass cache functions
927 Class::MOP holds a cache of metaclasses. The following are functions
928 (B<not methods>) which can be used to access that cache. It is not
929 recommended that you mess with these. Bad things could happen, but if
930 you are brave and willing to risk it: go for it!
934 =item B<Class::MOP::get_all_metaclasses>
936 This will return a hash of all the metaclass instances that have
937 been cached by L<Class::MOP::Class>, keyed by the package name.
939 =item B<Class::MOP::get_all_metaclass_instances>
941 This will return a list of all the metaclass instances that have
942 been cached by L<Class::MOP::Class>.
944 =item B<Class::MOP::get_all_metaclass_names>
946 This will return a list of all the metaclass names that have
947 been cached by L<Class::MOP::Class>.
949 =item B<Class::MOP::get_metaclass_by_name($name)>
951 This will return a cached L<Class::MOP::Class> instance, or nothing
952 if no metaclass exists with that C<$name>.
954 =item B<Class::MOP::store_metaclass_by_name($name, $meta)>
956 This will store a metaclass in the cache at the supplied C<$key>.
958 =item B<Class::MOP::weaken_metaclass($name)>
960 In rare cases (e.g. anonymous metaclasses) it is desirable to
961 store a weakened reference in the metaclass cache. This
962 function will weaken the reference to the metaclass stored
965 =item B<Class::MOP::does_metaclass_exist($name)>
967 This will return true of there exists a metaclass stored in the
968 C<$name> key, and return false otherwise.
970 =item B<Class::MOP::remove_metaclass_by_name($name)>
972 This will remove the metaclass stored in the C<$name> key.
980 There are very few books out on Meta Object Protocols and Metaclasses
981 because it is such an esoteric topic. The following books are really
982 the only ones I have found. If you know of any more, B<I<please>>
983 email me and let me know, I would love to hear about them.
987 =item I<The Art of the Meta Object Protocol>
989 =item I<Advances in Object-Oriented Metalevel Architecture and Reflection>
991 =item I<Putting MetaClasses to Work>
993 =item I<Smalltalk: The Language>
1001 =item "Uniform and safe metaclass composition"
1003 An excellent paper by the people who brought us the original Traits paper.
1004 This paper is on how Traits can be used to do safe metaclass composition,
1005 and offers an excellent introduction section which delves into the topic of
1006 metaclass compatibility.
1008 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
1010 =item "Safe Metaclass Programming"
1012 This paper seems to precede the above paper, and propose a mix-in based
1013 approach as opposed to the Traits based approach. Both papers have similar
1014 information on the metaclass compatibility problem space.
1016 L<http://citeseer.ist.psu.edu/37617.html>
1024 =item The Perl 6 MetaModel work in the Pugs project
1028 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
1030 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1040 =item CPAN Module Review of Class::MOP
1042 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1046 =head1 SIMILAR MODULES
1048 As I have said above, this module is a class-builder-builder, so it is
1049 not the same thing as modules like L<Class::Accessor> and
1050 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1051 with similar goals to this module. The one I have found which is most
1052 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1053 creates are very different from this modules.
1057 All complex software has bugs lurking in it, and this module is no
1058 exception. If you find a bug please either email me, or add the bug
1061 =head1 ACKNOWLEDGEMENTS
1067 Thanks to Rob for actually getting the development of this module kick-started.
1073 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1075 B<with contributions from:>
1077 Brandon (blblack) Black
1079 Florian (rafl) Ragwitz
1081 Guillermo (groditi) Roditi
1085 Rob (robkinyon) Kinyon
1087 Yuval (nothingmuch) Kogman
1089 Scott (konobi) McWhirter
1091 =head1 COPYRIGHT AND LICENSE
1093 Copyright 2006-2009 by Infinity Interactive, Inc.
1095 L<http://www.iinteractive.com>
1097 This library is free software; you can redistribute it and/or modify
1098 it under the same terms as Perl itself.