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 Carp::cluck("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 = '0.82';
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 return unless defined $_[0];
66 my $class = blessed($_[0]) || $_[0];
67 return $METAS{$class};
71 # We only cache metaclasses, meaning instances of
72 # Class::MOP::Class. We do not cache instance of
73 # Class::MOP::Package or Class::MOP::Module. Mostly
74 # because I don't yet see a good reason to do so.
77 sub _class_to_pmfile {
80 my $file = $class . '.pm';
86 sub load_first_existing_class {
90 foreach my $class (@classes) {
91 unless ( _is_valid_class_name($class) ) {
92 my $display = defined($class) ? $class : 'undef';
93 confess "Invalid class name ($display)";
99 for my $class (@classes) {
100 my $pmfile = _class_to_pmfile($class);
101 my $e = _try_load_one_class($class);
104 $exceptions{$class} = $e;
105 last if $e !~ /^Can't locate \Q$pmfile\E in \@INC/;
113 return $found if $found;
119 "Could not load class (%s) because : %s", $_,
124 exists $exceptions{$_}
129 sub _try_load_one_class {
132 return if is_class_loaded($class);
134 my $file = _class_to_pmfile($class);
138 eval { require($file) };
144 my $class = load_first_existing_class($_[0]);
145 return get_metaclass_by_name($class) || $class;
148 sub _is_valid_class_name {
151 return 0 if ref($class);
152 return 0 unless defined($class);
153 return 0 unless length($class);
155 return 1 if $class =~ /^\w+(?:::\w+)*$/;
160 ## ----------------------------------------------------------------------------
161 ## Setting up our environment ...
162 ## ----------------------------------------------------------------------------
163 ## Class::MOP needs to have a few things in the global perl environment so
164 ## that it can operate effectively. Those things are done here.
165 ## ----------------------------------------------------------------------------
167 # ... nothing yet actually ;)
169 ## ----------------------------------------------------------------------------
171 ## ----------------------------------------------------------------------------
172 ## The code below here is to bootstrap our MOP with itself. This is also
173 ## sometimes called "tying the knot". By doing this, we make it much easier
174 ## to extend the MOP through subclassing and such since now you can use the
175 ## MOP itself to extend itself.
177 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
178 ## ----------------------------------------------------------------------------
180 # We need to add in the meta-attributes here so that
181 # any subclass of Class::MOP::* will be able to
182 # inherit them using _construct_instance
184 ## --------------------------------------------------------
185 ## Class::MOP::Package
187 Class::MOP::Package->meta->add_attribute(
188 Class::MOP::Attribute->new('package' => (
190 # NOTE: we need to do this in order
191 # for the instance meta-object to
192 # not fall into meta-circular death
194 # we just alias the original method
195 # rather than re-produce it here
196 'name' => \&Class::MOP::Package::name
201 Class::MOP::Package->meta->add_attribute(
202 Class::MOP::Attribute->new('namespace' => (
205 # we just alias the original method
206 # rather than re-produce it here
207 'namespace' => \&Class::MOP::Package::namespace
210 default => sub { \undef }
214 ## --------------------------------------------------------
215 ## Class::MOP::Module
218 # yeah this is kind of stretching things a bit,
219 # but truthfully the version should be an attribute
220 # of the Module, the weirdness comes from having to
221 # stick to Perl 5 convention and store it in the
222 # $VERSION package variable. Basically if you just
223 # squint at it, it will look how you want it to look.
224 # Either as a package variable, or as a attribute of
225 # the metaclass, isn't abstraction great :)
227 Class::MOP::Module->meta->add_attribute(
228 Class::MOP::Attribute->new('version' => (
231 # we just alias the original method
232 # rather than re-produce it here
233 'version' => \&Class::MOP::Module::version
236 default => sub { \undef }
241 # By following the same conventions as version here,
242 # we are opening up the possibility that people can
243 # use the $AUTHORITY in non-Class::MOP modules as
246 Class::MOP::Module->meta->add_attribute(
247 Class::MOP::Attribute->new('authority' => (
250 # we just alias the original method
251 # rather than re-produce it here
252 'authority' => \&Class::MOP::Module::authority
255 default => sub { \undef }
259 ## --------------------------------------------------------
262 Class::MOP::Class->meta->add_attribute(
263 Class::MOP::Attribute->new('attributes' => (
265 # NOTE: we need to do this in order
266 # for the instance meta-object to
267 # not fall into meta-circular death
269 # we just alias the original method
270 # rather than re-produce it here
271 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
273 default => sub { {} }
277 Class::MOP::Class->meta->add_attribute(
278 Class::MOP::Attribute->new('methods' => (
281 # we just alias the original method
282 # rather than re-produce it here
283 'get_method_map' => \&Class::MOP::Class::get_method_map
285 default => sub { {} }
289 Class::MOP::Class->meta->add_attribute(
290 Class::MOP::Attribute->new('superclasses' => (
293 # we just alias the original method
294 # rather than re-produce it here
295 'superclasses' => \&Class::MOP::Class::superclasses
298 default => sub { \undef }
302 Class::MOP::Class->meta->add_attribute(
303 Class::MOP::Attribute->new('attribute_metaclass' => (
306 # we just alias the original method
307 # rather than re-produce it here
308 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
310 default => 'Class::MOP::Attribute',
314 Class::MOP::Class->meta->add_attribute(
315 Class::MOP::Attribute->new('method_metaclass' => (
318 # we just alias the original method
319 # rather than re-produce it here
320 'method_metaclass' => \&Class::MOP::Class::method_metaclass
322 default => 'Class::MOP::Method',
326 Class::MOP::Class->meta->add_attribute(
327 Class::MOP::Attribute->new('wrapped_method_metaclass' => (
330 # we just alias the original method
331 # rather than re-produce it here
332 'wrapped_method_metaclass' => \&Class::MOP::Class::wrapped_method_metaclass
334 default => 'Class::MOP::Method::Wrapped',
338 Class::MOP::Class->meta->add_attribute(
339 Class::MOP::Attribute->new('instance_metaclass' => (
341 # NOTE: we need to do this in order
342 # for the instance meta-object to
343 # not fall into meta-circular death
345 # we just alias the original method
346 # rather than re-produce it here
347 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
349 default => 'Class::MOP::Instance',
353 Class::MOP::Class->meta->add_attribute(
354 Class::MOP::Attribute->new('immutable_transformer' => (
356 'immutable_transformer' => \&Class::MOP::Class::immutable_transformer
359 '_set_immutable_transformer' => \&Class::MOP::Class::_set_immutable_transformer
365 # we don't actually need to tie the knot with
366 # Class::MOP::Class here, it is actually handled
367 # within Class::MOP::Class itself in the
368 # _construct_class_instance method.
370 ## --------------------------------------------------------
371 ## Class::MOP::Attribute
373 Class::MOP::Attribute->meta->add_attribute(
374 Class::MOP::Attribute->new('name' => (
376 # NOTE: we need to do this in order
377 # for the instance meta-object to
378 # not fall into meta-circular death
380 # we just alias the original method
381 # rather than re-produce it here
382 'name' => \&Class::MOP::Attribute::name
387 Class::MOP::Attribute->meta->add_attribute(
388 Class::MOP::Attribute->new('associated_class' => (
390 # NOTE: we need to do this in order
391 # for the instance meta-object to
392 # not fall into meta-circular death
394 # we just alias the original method
395 # rather than re-produce it here
396 'associated_class' => \&Class::MOP::Attribute::associated_class
401 Class::MOP::Attribute->meta->add_attribute(
402 Class::MOP::Attribute->new('accessor' => (
403 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
404 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
408 Class::MOP::Attribute->meta->add_attribute(
409 Class::MOP::Attribute->new('reader' => (
410 reader => { 'reader' => \&Class::MOP::Attribute::reader },
411 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
415 Class::MOP::Attribute->meta->add_attribute(
416 Class::MOP::Attribute->new('initializer' => (
417 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
418 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
422 Class::MOP::Attribute->meta->add_attribute(
423 Class::MOP::Attribute->new('definition_context' => (
424 reader => { 'definition_context' => \&Class::MOP::Attribute::definition_context },
428 Class::MOP::Attribute->meta->add_attribute(
429 Class::MOP::Attribute->new('writer' => (
430 reader => { 'writer' => \&Class::MOP::Attribute::writer },
431 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
435 Class::MOP::Attribute->meta->add_attribute(
436 Class::MOP::Attribute->new('predicate' => (
437 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
438 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
442 Class::MOP::Attribute->meta->add_attribute(
443 Class::MOP::Attribute->new('clearer' => (
444 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
445 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
449 Class::MOP::Attribute->meta->add_attribute(
450 Class::MOP::Attribute->new('builder' => (
451 reader => { 'builder' => \&Class::MOP::Attribute::builder },
452 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
456 Class::MOP::Attribute->meta->add_attribute(
457 Class::MOP::Attribute->new('init_arg' => (
458 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
459 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
463 Class::MOP::Attribute->meta->add_attribute(
464 Class::MOP::Attribute->new('default' => (
465 # default has a custom 'reader' method ...
466 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
470 Class::MOP::Attribute->meta->add_attribute(
471 Class::MOP::Attribute->new('associated_methods' => (
472 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
473 default => sub { [] }
477 Class::MOP::Attribute->meta->add_method('clone' => sub {
479 $self->meta->clone_object($self, @_);
482 ## --------------------------------------------------------
483 ## Class::MOP::Method
484 Class::MOP::Method->meta->add_attribute(
485 Class::MOP::Attribute->new('body' => (
486 reader => { 'body' => \&Class::MOP::Method::body },
490 Class::MOP::Method->meta->add_attribute(
491 Class::MOP::Attribute->new('associated_metaclass' => (
492 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
496 Class::MOP::Method->meta->add_attribute(
497 Class::MOP::Attribute->new('package_name' => (
498 reader => { 'package_name' => \&Class::MOP::Method::package_name },
502 Class::MOP::Method->meta->add_attribute(
503 Class::MOP::Attribute->new('name' => (
504 reader => { 'name' => \&Class::MOP::Method::name },
508 Class::MOP::Method->meta->add_attribute(
509 Class::MOP::Attribute->new('original_method' => (
510 reader => { 'original_method' => \&Class::MOP::Method::original_method },
511 writer => { '_set_original_method' => \&Class::MOP::Method::_set_original_method },
515 Class::MOP::Method->meta->add_method('clone' => sub {
517 my $clone = $self->meta->clone_object($self, @_);
518 $clone->_set_original_method($self);
522 ## --------------------------------------------------------
523 ## Class::MOP::Method::Wrapped
526 # the way this item is initialized, this
527 # really does not follow the standard
528 # practices of attributes, but we put
529 # it here for completeness
530 Class::MOP::Method::Wrapped->meta->add_attribute(
531 Class::MOP::Attribute->new('modifier_table')
534 ## --------------------------------------------------------
535 ## Class::MOP::Method::Generated
537 Class::MOP::Method::Generated->meta->add_attribute(
538 Class::MOP::Attribute->new('is_inline' => (
539 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
544 Class::MOP::Method::Generated->meta->add_attribute(
545 Class::MOP::Attribute->new('definition_context' => (
546 reader => { 'definition_context' => \&Class::MOP::Method::Generated::definition_context },
550 ## --------------------------------------------------------
551 ## Class::MOP::Method::Accessor
553 Class::MOP::Method::Accessor->meta->add_attribute(
554 Class::MOP::Attribute->new('attribute' => (
556 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
561 Class::MOP::Method::Accessor->meta->add_attribute(
562 Class::MOP::Attribute->new('accessor_type' => (
563 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
567 ## --------------------------------------------------------
568 ## Class::MOP::Method::Constructor
570 Class::MOP::Method::Constructor->meta->add_attribute(
571 Class::MOP::Attribute->new('options' => (
573 'options' => \&Class::MOP::Method::Constructor::options
575 default => sub { +{} }
579 Class::MOP::Method::Constructor->meta->add_attribute(
580 Class::MOP::Attribute->new('associated_metaclass' => (
581 init_arg => "metaclass", # FIXME alias and rename
583 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
588 ## --------------------------------------------------------
589 ## Class::MOP::Instance
592 # these don't yet do much of anything, but are just
593 # included for completeness
595 Class::MOP::Instance->meta->add_attribute(
596 Class::MOP::Attribute->new('associated_metaclass',
597 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
601 Class::MOP::Instance->meta->add_attribute(
602 Class::MOP::Attribute->new('_class_name',
604 reader => { _class_name => \&Class::MOP::Instance::_class_name },
605 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
606 #default => sub { $_[0]->associated_metaclass->name },
610 Class::MOP::Instance->meta->add_attribute(
611 Class::MOP::Attribute->new('attributes',
612 reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
616 Class::MOP::Instance->meta->add_attribute(
617 Class::MOP::Attribute->new('slots',
618 reader => { slots => \&Class::MOP::Instance::slots },
622 Class::MOP::Instance->meta->add_attribute(
623 Class::MOP::Attribute->new('slot_hash',
624 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
629 # we need the meta instance of the meta instance to be created now, in order
630 # for the constructor to be able to use it
631 Class::MOP::Instance->meta->get_meta_instance;
633 # pretend the add_method never happenned. it hasn't yet affected anything
634 undef Class::MOP::Instance->meta->{_package_cache_flag};
636 ## --------------------------------------------------------
637 ## Now close all the Class::MOP::* classes
639 # NOTE: we don't need to inline the the accessors this only lengthens
640 # the compile time of the MOP, and gives us no actual benefits.
642 $_->meta->make_immutable(
643 inline_constructor => 1,
644 replace_constructor => 1,
645 constructor_name => "_new",
646 inline_accessors => 0,
652 Class::MOP::Attribute
658 Class::MOP::Method::Generated
660 Class::MOP::Method::Accessor
661 Class::MOP::Method::Constructor
662 Class::MOP::Method::Wrapped
673 Class::MOP - A Meta Object Protocol for Perl 5
677 This module is a fully functioning meta object protocol for the
678 Perl 5 object system. It makes no attempt to change the behavior or
679 characteristics of the Perl 5 object system, only to create a
680 protocol for its manipulation and introspection.
682 That said, it does attempt to create the tools for building a rich set
683 of extensions to the Perl 5 object system. Every attempt has been made
684 to abide by the spirit of the Perl 5 object system that we all know
687 This documentation is sparse on conceptual details. We suggest looking
688 at the items listed in the L<SEE ALSO> section for more
689 information. In particular the book "The Art of the Meta Object
690 Protocol" was very influential in the development of this system.
692 =head2 What is a Meta Object Protocol?
694 A meta object protocol is an API to an object system.
696 To be more specific, it abstracts the components of an object system
697 (classes, object, methods, object attributes, etc.). These
698 abstractions can then be used to inspect and manipulate the object
699 system which they describe.
701 It can be said that there are two MOPs for any object system; the
702 implicit MOP and the explicit MOP. The implicit MOP handles things
703 like method dispatch or inheritance, which happen automatically as
704 part of how the object system works. The explicit MOP typically
705 handles the introspection/reflection features of the object system.
707 All object systems have implicit MOPs. Without one, they would not
708 work. Explicit MOPs are much less common, and depending on the
709 language can vary from restrictive (Reflection in Java or C#) to wide
710 open (CLOS is a perfect example).
712 =head2 Yet Another Class Builder! Why?
714 This is B<not> a class builder so much as a I<class builder
715 B<builder>>. The intent is that an end user will not use this module
716 directly, but instead this module is used by module authors to build
717 extensions and features onto the Perl 5 object system.
719 This system is used by L<Moose>, which supplies a powerful class
720 builder system built entirely on top of C<Class::MOP>.
722 =head2 Who is this module for?
724 This module is for anyone who has ever created or wanted to create a
725 module for the Class:: namespace. The tools which this module provides
726 make doing complex Perl 5 wizardry simpler, by removing such barriers
727 as the need to hack symbol tables, or understand the fine details of
730 =head2 What changes do I have to make to use this module?
732 This module was designed to be as unintrusive as possible. Many of its
733 features are accessible without B<any> change to your existing
734 code. It is meant to be a compliment to your existing code and not an
735 intrusion on your code base. Unlike many other B<Class::> modules,
736 this module B<does not> require you subclass it, or even that you
737 C<use> it in within your module's package.
739 The only features which requires additions to your code are the
740 attribute handling and instance construction features, and these are
741 both completely optional features. The only reason for this is because
742 Perl 5's object system does not actually have these features built
743 in. More information about this feature can be found below.
745 =head2 About Performance
747 It is a common misconception that explicit MOPs are a performance hit.
748 This is not a universal truth, it is a side-effect of some specific
749 implementations. For instance, using Java reflection is slow because
750 the JVM cannot take advantage of any compiler optimizations, and the
751 JVM has to deal with much more runtime type information as well.
753 Reflection in C# is marginally better as it was designed into the
754 language and runtime (the CLR). In contrast, CLOS (the Common Lisp
755 Object System) was built to support an explicit MOP, and so
756 performance is tuned for it.
758 This library in particular does its absolute best to avoid putting
759 B<any> drain at all upon your code's performance. In fact, by itself
760 it does nothing to affect your existing code. So you only pay for what
763 =head2 About Metaclass compatibility
765 This module makes sure that all metaclasses created are both upwards
766 and downwards compatible. The topic of metaclass compatibility is
767 highly esoteric and is something only encountered when doing deep and
768 involved metaclass hacking. There are two basic kinds of metaclass
769 incompatibility; upwards and downwards.
771 Upwards metaclass compatibility means that the metaclass of a
772 given class is either the same as (or a subclass of) all of the
775 Downward metaclass compatibility means that the metaclasses of a
776 given class's ancestors are all either the same as (or a subclass
779 Here is a diagram showing a set of two classes (C<A> and C<B>) and
780 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
781 metaclass compatibility both upwards and downwards.
783 +---------+ +---------+
784 | Meta::A |<----| Meta::B | <....... (instance of )
785 +---------+ +---------+ <------- (inherits from)
788 +---------+ +---------+
790 +---------+ +---------+
792 As I said this is a highly esoteric topic and one you will only run
793 into if you do a lot of subclassing of L<Class::MOP::Class>. If you
794 are interested in why this is an issue see the paper I<Uniform and
795 safe metaclass composition> linked to in the L<SEE ALSO> section of
798 =head2 Using custom metaclasses
800 Always use the L<metaclass> pragma when using a custom metaclass, this
801 will ensure the proper initialization order and not accidentally
802 create an incorrect type of metaclass for you. This is a very rare
803 problem, and one which can only occur if you are doing deep metaclass
804 programming. So in other words, don't worry about it.
806 Note that if you're using L<Moose> we encourage you to I<not> use
807 L<metaclass> pragma, and instead use L<Moose::Util::MetaRole> to apply
808 roles to a class's metaclasses. This topic is covered at length in
809 various L<Moose::Cookbook> recipes.
813 The meta-object protocol is divided into 4 main sub-protocols:
815 =head2 The Class protocol
817 This provides a means of manipulating and introspecting a Perl 5
818 class. It handles symbol table hacking for you, and provides a rich
819 set of methods that go beyond simple package introspection.
821 See L<Class::MOP::Class> for more details.
823 =head2 The Attribute protocol
825 This provides a consistent representation for an attribute of a Perl 5
826 class. Since there are so many ways to create and handle attributes in
827 Perl 5 OO, the Attribute protocol provide as much of a unified
828 approach as possible. Of course, you are always free to extend this
829 protocol by subclassing the appropriate classes.
831 See L<Class::MOP::Attribute> for more details.
833 =head2 The Method protocol
835 This provides a means of manipulating and introspecting methods in the
836 Perl 5 object system. As with attributes, there are many ways to
837 approach this topic, so we try to keep it pretty basic, while still
838 making it possible to extend the system in many ways.
840 See L<Class::MOP::Method> for more details.
842 =head2 The Instance protocol
844 This provides a layer of abstraction for creating object instances.
845 Since the other layers use this protocol, it is relatively easy to
846 change the type of your instances from the default hash reference to
847 some other type of reference. Several examples are provided in the
848 F<examples/> directory included in this distribution.
850 See L<Class::MOP::Instance> for more details.
854 Note that this module does not export any constants or functions.
860 =item I<Class::MOP::IS_RUNNING_ON_5_10>
862 We set this constant depending on what version perl we are on, this
863 allows us to take advantage of new 5.10 features and stay backwards
868 =head2 Utility functions
870 Note that these are all called as B<functions, not methods>.
874 =item B<Class::MOP::load_class($class_name)>
876 This will load the specified C<$class_name>. This function can be used
877 in place of tricks like C<eval "use $module"> or using C<require>
878 unconditionally. This will return the metaclass of C<$class_name>.
880 =item B<Class::MOP::is_class_loaded($class_name)>
882 Returns a boolean indicating whether or not C<$class_name> has been
885 This does a basic check of the symbol table to try and determine as
886 best it can if the C<$class_name> is loaded, it is probably correct
887 about 99% of the time, but it can be fooled into reporting false
890 =item B<Class::MOP::get_code_info($code)>
892 This function returns two values, the name of the package the C<$code>
893 is from and the name of the C<$code> itself. This is used by several
894 elements of the MOP to determine where a given C<$code> reference is
897 =item B<Class::MOP::class_of($instance_or_class_name)>
899 This will return the metaclass of the given instance or class name.
900 Even if the class lacks a metaclass, no metaclass will be initialized
901 and C<undef> will be returned.
903 =item B<Class::MOP::check_package_cache_flag($pkg)>
905 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
907 This will return an integer that is managed by L<Class::MOP::Class> to
908 determine if a module's symbol table has been altered.
910 In Perl 5.10 or greater, this flag is package specific. However in
911 versions prior to 5.10, this will use the C<PL_sub_generation>
912 variable which is not package specific.
914 =item B<Class::MOP::load_first_existing_class(@class_names)>
916 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
918 Given a list of class names, this function will attempt to load each
921 If it finds a class it can load, it will return that class' name. If
922 none of the classes can be loaded, it will throw an exception.
926 =head2 Metaclass cache functions
928 Class::MOP holds a cache of metaclasses. The following are functions
929 (B<not methods>) which can be used to access that cache. It is not
930 recommended that you mess with these. Bad things could happen, but if
931 you are brave and willing to risk it: go for it!
935 =item B<Class::MOP::get_all_metaclasses>
937 This will return a hash of all the metaclass instances that have
938 been cached by L<Class::MOP::Class>, keyed by the package name.
940 =item B<Class::MOP::get_all_metaclass_instances>
942 This will return a list of all the metaclass instances that have
943 been cached by L<Class::MOP::Class>.
945 =item B<Class::MOP::get_all_metaclass_names>
947 This will return a list of all the metaclass names that have
948 been cached by L<Class::MOP::Class>.
950 =item B<Class::MOP::get_metaclass_by_name($name)>
952 This will return a cached L<Class::MOP::Class> instance, or nothing
953 if no metaclass exists with that C<$name>.
955 =item B<Class::MOP::store_metaclass_by_name($name, $meta)>
957 This will store a metaclass in the cache at the supplied C<$key>.
959 =item B<Class::MOP::weaken_metaclass($name)>
961 In rare cases (e.g. anonymous metaclasses) it is desirable to
962 store a weakened reference in the metaclass cache. This
963 function will weaken the reference to the metaclass stored
966 =item B<Class::MOP::does_metaclass_exist($name)>
968 This will return true of there exists a metaclass stored in the
969 C<$name> key, and return false otherwise.
971 =item B<Class::MOP::remove_metaclass_by_name($name)>
973 This will remove the metaclass stored in the C<$name> key.
981 There are very few books out on Meta Object Protocols and Metaclasses
982 because it is such an esoteric topic. The following books are really
983 the only ones I have found. If you know of any more, B<I<please>>
984 email me and let me know, I would love to hear about them.
988 =item I<The Art of the Meta Object Protocol>
990 =item I<Advances in Object-Oriented Metalevel Architecture and Reflection>
992 =item I<Putting MetaClasses to Work>
994 =item I<Smalltalk: The Language>
1002 =item "Uniform and safe metaclass composition"
1004 An excellent paper by the people who brought us the original Traits paper.
1005 This paper is on how Traits can be used to do safe metaclass composition,
1006 and offers an excellent introduction section which delves into the topic of
1007 metaclass compatibility.
1009 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
1011 =item "Safe Metaclass Programming"
1013 This paper seems to precede the above paper, and propose a mix-in based
1014 approach as opposed to the Traits based approach. Both papers have similar
1015 information on the metaclass compatibility problem space.
1017 L<http://citeseer.ist.psu.edu/37617.html>
1025 =item The Perl 6 MetaModel work in the Pugs project
1029 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
1031 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1041 =item CPAN Module Review of Class::MOP
1043 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1047 =head1 SIMILAR MODULES
1049 As I have said above, this module is a class-builder-builder, so it is
1050 not the same thing as modules like L<Class::Accessor> and
1051 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1052 with similar goals to this module. The one I have found which is most
1053 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1054 creates are very different from this modules.
1058 All complex software has bugs lurking in it, and this module is no
1059 exception. If you find a bug please either email me, or add the bug
1062 =head1 ACKNOWLEDGEMENTS
1068 Thanks to Rob for actually getting the development of this module kick-started.
1074 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1076 B<with contributions from:>
1078 Brandon (blblack) Black
1080 Florian (rafl) Ragwitz
1082 Guillermo (groditi) Roditi
1086 Rob (robkinyon) Kinyon
1088 Yuval (nothingmuch) Kogman
1090 Scott (konobi) McWhirter
1092 =head1 COPYRIGHT AND LICENSE
1094 Copyright 2006-2009 by Infinity Interactive, Inc.
1096 L<http://www.iinteractive.com>
1098 This library is free software; you can redistribute it and/or modify
1099 it under the same terms as Perl itself.