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)
27 *HAVE_ISAREV = defined(&mro::get_isarev)
31 # this is either part of core or set up appropriately by MRO::Compat
32 *check_package_cache_flag = \&mro::get_pkg_gen;
35 our $VERSION = '0.79';
36 our $XS_VERSION = $VERSION;
37 $VERSION = eval $VERSION;
38 our $AUTHORITY = 'cpan:STEVAN';
41 XSLoader::load( __PACKAGE__, $XS_VERSION );
45 # Metaclasses are singletons, so we cache them here.
46 # there is no need to worry about destruction though
47 # because they should die only when the program dies.
48 # After all, do package definitions even get reaped?
51 # means of accessing all the metaclasses that have
52 # been initialized thus far (for mugwumps obj browser)
53 sub get_all_metaclasses { %METAS }
54 sub get_all_metaclass_instances { values %METAS }
55 sub get_all_metaclass_names { keys %METAS }
56 sub get_metaclass_by_name { $METAS{$_[0]} }
57 sub store_metaclass_by_name { $METAS{$_[0]} = $_[1] }
58 sub weaken_metaclass { weaken($METAS{$_[0]}) }
59 sub does_metaclass_exist { exists $METAS{$_[0]} && defined $METAS{$_[0]} }
60 sub remove_metaclass_by_name { $METAS{$_[0]} = undef }
62 # This handles instances as well as class names
64 my $class = blessed($_[0]) || $_[0];
65 return $METAS{$class};
69 # We only cache metaclasses, meaning instances of
70 # Class::MOP::Class. We do not cache instance of
71 # Class::MOP::Package or Class::MOP::Module. Mostly
72 # because I don't yet see a good reason to do so.
75 sub _class_to_pmfile {
78 my $file = $class . '.pm';
84 sub load_first_existing_class {
88 foreach my $class (@classes) {
89 unless ( _is_valid_class_name($class) ) {
90 my $display = defined($class) ? $class : 'undef';
91 confess "Invalid class name ($display)";
97 for my $class (@classes) {
98 my $pmfile = _class_to_pmfile($class);
99 my $e = _try_load_one_class($class);
102 $exceptions{$class} = $e;
103 last if $e !~ /^Can't locate \Q$pmfile\E in \@INC/;
111 return $found if $found;
117 "Could not load class (%s) because : %s", $_,
122 exists $exceptions{$_}
127 sub _try_load_one_class {
130 return if is_class_loaded($class);
132 my $file = _class_to_pmfile($class);
136 eval { require($file) };
142 my $class = load_first_existing_class($_[0]);
143 return get_metaclass_by_name($class) || $class;
146 sub _is_valid_class_name {
149 return 0 if ref($class);
150 return 0 unless defined($class);
151 return 0 unless length($class);
153 return 1 if $class =~ /^\w+(?:::\w+)*$/;
158 ## ----------------------------------------------------------------------------
159 ## Setting up our environment ...
160 ## ----------------------------------------------------------------------------
161 ## Class::MOP needs to have a few things in the global perl environment so
162 ## that it can operate effectively. Those things are done here.
163 ## ----------------------------------------------------------------------------
165 # ... nothing yet actually ;)
167 ## ----------------------------------------------------------------------------
169 ## ----------------------------------------------------------------------------
170 ## The code below here is to bootstrap our MOP with itself. This is also
171 ## sometimes called "tying the knot". By doing this, we make it much easier
172 ## to extend the MOP through subclassing and such since now you can use the
173 ## MOP itself to extend itself.
175 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
176 ## ----------------------------------------------------------------------------
178 # We need to add in the meta-attributes here so that
179 # any subclass of Class::MOP::* will be able to
180 # inherit them using &construct_instance
182 ## --------------------------------------------------------
183 ## Class::MOP::Package
185 Class::MOP::Package->meta->add_attribute(
186 Class::MOP::Attribute->new('package' => (
188 # NOTE: we need to do this in order
189 # for the instance meta-object to
190 # not fall into meta-circular death
192 # we just alias the original method
193 # rather than re-produce it here
194 'name' => \&Class::MOP::Package::name
199 Class::MOP::Package->meta->add_attribute(
200 Class::MOP::Attribute->new('namespace' => (
203 # we just alias the original method
204 # rather than re-produce it here
205 'namespace' => \&Class::MOP::Package::namespace
208 default => sub { \undef }
212 ## --------------------------------------------------------
213 ## Class::MOP::Module
216 # yeah this is kind of stretching things a bit,
217 # but truthfully the version should be an attribute
218 # of the Module, the weirdness comes from having to
219 # stick to Perl 5 convention and store it in the
220 # $VERSION package variable. Basically if you just
221 # squint at it, it will look how you want it to look.
222 # Either as a package variable, or as a attribute of
223 # the metaclass, isn't abstraction great :)
225 Class::MOP::Module->meta->add_attribute(
226 Class::MOP::Attribute->new('version' => (
229 # we just alias the original method
230 # rather than re-produce it here
231 'version' => \&Class::MOP::Module::version
234 default => sub { \undef }
239 # By following the same conventions as version here,
240 # we are opening up the possibility that people can
241 # use the $AUTHORITY in non-Class::MOP modules as
244 Class::MOP::Module->meta->add_attribute(
245 Class::MOP::Attribute->new('authority' => (
248 # we just alias the original method
249 # rather than re-produce it here
250 'authority' => \&Class::MOP::Module::authority
253 default => sub { \undef }
257 ## --------------------------------------------------------
260 Class::MOP::Class->meta->add_attribute(
261 Class::MOP::Attribute->new('attributes' => (
263 # NOTE: we need to do this in order
264 # for the instance meta-object to
265 # not fall into meta-circular death
267 # we just alias the original method
268 # rather than re-produce it here
269 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
271 default => sub { {} }
275 Class::MOP::Class->meta->add_attribute(
276 Class::MOP::Attribute->new('methods' => (
279 # we just alias the original method
280 # rather than re-produce it here
281 'get_method_map' => \&Class::MOP::Class::get_method_map
283 default => sub { {} }
287 Class::MOP::Class->meta->add_attribute(
288 Class::MOP::Attribute->new('superclasses' => (
291 # we just alias the original method
292 # rather than re-produce it here
293 'superclasses' => \&Class::MOP::Class::superclasses
296 default => sub { \undef }
300 Class::MOP::Class->meta->add_attribute(
301 Class::MOP::Attribute->new('attribute_metaclass' => (
304 # we just alias the original method
305 # rather than re-produce it here
306 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
308 default => 'Class::MOP::Attribute',
312 Class::MOP::Class->meta->add_attribute(
313 Class::MOP::Attribute->new('method_metaclass' => (
316 # we just alias the original method
317 # rather than re-produce it here
318 'method_metaclass' => \&Class::MOP::Class::method_metaclass
320 default => 'Class::MOP::Method',
324 Class::MOP::Class->meta->add_attribute(
325 Class::MOP::Attribute->new('wrapped_method_metaclass' => (
328 # we just alias the original method
329 # rather than re-produce it here
330 'wrapped_method_metaclass' => \&Class::MOP::Class::wrapped_method_metaclass
332 default => 'Class::MOP::Method::Wrapped',
336 Class::MOP::Class->meta->add_attribute(
337 Class::MOP::Attribute->new('instance_metaclass' => (
339 # NOTE: we need to do this in order
340 # for the instance meta-object to
341 # not fall into meta-circular death
343 # we just alias the original method
344 # rather than re-produce it here
345 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
347 default => 'Class::MOP::Instance',
351 Class::MOP::Class->meta->add_attribute(
352 Class::MOP::Attribute->new('immutable_transformer' => (
354 'immutable_transformer' => \&Class::MOP::Class::immutable_transformer
357 '_set_immutable_transformer' => \&Class::MOP::Class::_set_immutable_transformer
363 # we don't actually need to tie the knot with
364 # Class::MOP::Class here, it is actually handled
365 # within Class::MOP::Class itself in the
366 # construct_class_instance method.
368 ## --------------------------------------------------------
369 ## Class::MOP::Attribute
371 Class::MOP::Attribute->meta->add_attribute(
372 Class::MOP::Attribute->new('name' => (
374 # NOTE: we need to do this in order
375 # for the instance meta-object to
376 # not fall into meta-circular death
378 # we just alias the original method
379 # rather than re-produce it here
380 'name' => \&Class::MOP::Attribute::name
385 Class::MOP::Attribute->meta->add_attribute(
386 Class::MOP::Attribute->new('associated_class' => (
388 # NOTE: we need to do this in order
389 # for the instance meta-object to
390 # not fall into meta-circular death
392 # we just alias the original method
393 # rather than re-produce it here
394 'associated_class' => \&Class::MOP::Attribute::associated_class
399 Class::MOP::Attribute->meta->add_attribute(
400 Class::MOP::Attribute->new('accessor' => (
401 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
402 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
406 Class::MOP::Attribute->meta->add_attribute(
407 Class::MOP::Attribute->new('reader' => (
408 reader => { 'reader' => \&Class::MOP::Attribute::reader },
409 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
413 Class::MOP::Attribute->meta->add_attribute(
414 Class::MOP::Attribute->new('initializer' => (
415 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
416 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
420 Class::MOP::Attribute->meta->add_attribute(
421 Class::MOP::Attribute->new('definition_context' => (
422 reader => { 'definition_context' => \&Class::MOP::Attribute::definition_context },
426 Class::MOP::Attribute->meta->add_attribute(
427 Class::MOP::Attribute->new('writer' => (
428 reader => { 'writer' => \&Class::MOP::Attribute::writer },
429 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
433 Class::MOP::Attribute->meta->add_attribute(
434 Class::MOP::Attribute->new('predicate' => (
435 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
436 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
440 Class::MOP::Attribute->meta->add_attribute(
441 Class::MOP::Attribute->new('clearer' => (
442 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
443 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
447 Class::MOP::Attribute->meta->add_attribute(
448 Class::MOP::Attribute->new('builder' => (
449 reader => { 'builder' => \&Class::MOP::Attribute::builder },
450 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
454 Class::MOP::Attribute->meta->add_attribute(
455 Class::MOP::Attribute->new('init_arg' => (
456 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
457 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
461 Class::MOP::Attribute->meta->add_attribute(
462 Class::MOP::Attribute->new('default' => (
463 # default has a custom 'reader' method ...
464 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
468 Class::MOP::Attribute->meta->add_attribute(
469 Class::MOP::Attribute->new('associated_methods' => (
470 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
471 default => sub { [] }
475 Class::MOP::Attribute->meta->add_method('clone' => sub {
477 $self->meta->clone_object($self, @_);
480 ## --------------------------------------------------------
481 ## Class::MOP::Method
482 Class::MOP::Method->meta->add_attribute(
483 Class::MOP::Attribute->new('body' => (
484 reader => { 'body' => \&Class::MOP::Method::body },
488 Class::MOP::Method->meta->add_attribute(
489 Class::MOP::Attribute->new('associated_metaclass' => (
490 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
494 Class::MOP::Method->meta->add_attribute(
495 Class::MOP::Attribute->new('package_name' => (
496 reader => { 'package_name' => \&Class::MOP::Method::package_name },
500 Class::MOP::Method->meta->add_attribute(
501 Class::MOP::Attribute->new('name' => (
502 reader => { 'name' => \&Class::MOP::Method::name },
506 Class::MOP::Method->meta->add_attribute(
507 Class::MOP::Attribute->new('original_method' => (
508 reader => { 'original_method' => \&Class::MOP::Method::original_method },
509 writer => { '_set_original_method' => \&Class::MOP::Method::_set_original_method },
513 Class::MOP::Method->meta->add_method('clone' => sub {
515 my $clone = $self->meta->clone_object($self, @_);
516 $clone->_set_original_method($self);
520 ## --------------------------------------------------------
521 ## Class::MOP::Method::Wrapped
524 # the way this item is initialized, this
525 # really does not follow the standard
526 # practices of attributes, but we put
527 # it here for completeness
528 Class::MOP::Method::Wrapped->meta->add_attribute(
529 Class::MOP::Attribute->new('modifier_table')
532 ## --------------------------------------------------------
533 ## Class::MOP::Method::Generated
535 Class::MOP::Method::Generated->meta->add_attribute(
536 Class::MOP::Attribute->new('is_inline' => (
537 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
542 Class::MOP::Method::Generated->meta->add_attribute(
543 Class::MOP::Attribute->new('definition_context' => (
544 reader => { 'definition_context' => \&Class::MOP::Method::Generated::definition_context },
548 ## --------------------------------------------------------
549 ## Class::MOP::Method::Accessor
551 Class::MOP::Method::Accessor->meta->add_attribute(
552 Class::MOP::Attribute->new('attribute' => (
554 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
559 Class::MOP::Method::Accessor->meta->add_attribute(
560 Class::MOP::Attribute->new('accessor_type' => (
561 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
565 ## --------------------------------------------------------
566 ## Class::MOP::Method::Constructor
568 Class::MOP::Method::Constructor->meta->add_attribute(
569 Class::MOP::Attribute->new('options' => (
571 'options' => \&Class::MOP::Method::Constructor::options
573 default => sub { +{} }
577 Class::MOP::Method::Constructor->meta->add_attribute(
578 Class::MOP::Attribute->new('associated_metaclass' => (
579 init_arg => "metaclass", # FIXME alias and rename
581 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
586 ## --------------------------------------------------------
587 ## Class::MOP::Instance
590 # these don't yet do much of anything, but are just
591 # included for completeness
593 Class::MOP::Instance->meta->add_attribute(
594 Class::MOP::Attribute->new('associated_metaclass',
595 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
599 Class::MOP::Instance->meta->add_attribute(
600 Class::MOP::Attribute->new('_class_name',
602 reader => { _class_name => \&Class::MOP::Instance::_class_name },
603 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
604 #default => sub { $_[0]->associated_metaclass->name },
608 Class::MOP::Instance->meta->add_attribute(
609 Class::MOP::Attribute->new('attributes',
610 reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
614 Class::MOP::Instance->meta->add_attribute(
615 Class::MOP::Attribute->new('slots',
616 reader => { slots => \&Class::MOP::Instance::slots },
620 Class::MOP::Instance->meta->add_attribute(
621 Class::MOP::Attribute->new('slot_hash',
622 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
627 # we need the meta instance of the meta instance to be created now, in order
628 # for the constructor to be able to use it
629 Class::MOP::Instance->meta->get_meta_instance;
631 # pretend the add_method never happenned. it hasn't yet affected anything
632 undef Class::MOP::Instance->meta->{_package_cache_flag};
634 ## --------------------------------------------------------
635 ## Now close all the Class::MOP::* classes
637 # NOTE: we don't need to inline the the accessors this only lengthens
638 # the compile time of the MOP, and gives us no actual benefits.
640 $_->meta->make_immutable(
641 inline_constructor => 1,
642 replace_constructor => 1,
643 constructor_name => "_new",
644 inline_accessors => 0,
650 Class::MOP::Attribute
656 Class::MOP::Method::Generated
658 Class::MOP::Method::Accessor
659 Class::MOP::Method::Constructor
660 Class::MOP::Method::Wrapped
671 Class::MOP - A Meta Object Protocol for Perl 5
675 This module is a fully functioning meta object protocol for the
676 Perl 5 object system. It makes no attempt to change the behavior or
677 characteristics of the Perl 5 object system, only to create a
678 protocol for its manipulation and introspection.
680 That said, it does attempt to create the tools for building a rich set
681 of extensions to the Perl 5 object system. Every attempt has been made
682 to abide by the spirit of the Perl 5 object system that we all know
685 This documentation is sparse on conceptual details. We suggest looking
686 at the items listed in the L<SEE ALSO> section for more
687 information. In particular the book "The Art of the Meta Object
688 Protocol" was very influential in the development of this system.
690 =head2 What is a Meta Object Protocol?
692 A meta object protocol is an API to an object system.
694 To be more specific, it abstracts the components of an object system
695 (classes, object, methods, object attributes, etc.). These
696 abstractions can then be used to inspect and manipulate the object
697 system which they describe.
699 It can be said that there are two MOPs for any object system; the
700 implicit MOP and the explicit MOP. The implicit MOP handles things
701 like method dispatch or inheritance, which happen automatically as
702 part of how the object system works. The explicit MOP typically
703 handles the introspection/reflection features of the object system.
705 All object systems have implicit MOPs. Without one, they would not
706 work. Explicit MOPs are much less common, and depending on the
707 language can vary from restrictive (Reflection in Java or C#) to wide
708 open (CLOS is a perfect example).
710 =head2 Yet Another Class Builder! Why?
712 This is B<not> a class builder so much as a I<class builder
713 B<builder>>. The intent is that an end user will not use this module
714 directly, but instead this module is used by module authors to build
715 extensions and features onto the Perl 5 object system.
717 This system is used by L<Moose>, which supplies a powerful class
718 builder system built entirely on top of C<Class::MOP>.
720 =head2 Who is this module for?
722 This module is for anyone who has ever created or wanted to create a
723 module for the Class:: namespace. The tools which this module provides
724 make doing complex Perl 5 wizardry simpler, by removing such barriers
725 as the need to hack symbol tables, or understand the fine details of
728 =head2 What changes do I have to make to use this module?
730 This module was designed to be as unintrusive as possible. Many of its
731 features are accessible without B<any> change to your existing
732 code. It is meant to be a compliment to your existing code and not an
733 intrusion on your code base. Unlike many other B<Class::> modules,
734 this module B<does not> require you subclass it, or even that you
735 C<use> it in within your module's package.
737 The only features which requires additions to your code are the
738 attribute handling and instance construction features, and these are
739 both completely optional features. The only reason for this is because
740 Perl 5's object system does not actually have these features built
741 in. More information about this feature can be found below.
743 =head2 About Performance
745 It is a common misconception that explicit MOPs are a performance hit.
746 This is not a universal truth, it is a side-effect of some specific
747 implementations. For instance, using Java reflection is slow because
748 the JVM cannot take advantage of any compiler optimizations, and the
749 JVM has to deal with much more runtime type information as well.
751 Reflection in C# is marginally better as it was designed into the
752 language and runtime (the CLR). In contrast, CLOS (the Common Lisp
753 Object System) was built to support an explicit MOP, and so
754 performance is tuned for it.
756 This library in particular does its absolute best to avoid putting
757 B<any> drain at all upon your code's performance. In fact, by itself
758 it does nothing to affect your existing code. So you only pay for what
761 =head2 About Metaclass compatibility
763 This module makes sure that all metaclasses created are both upwards
764 and downwards compatible. The topic of metaclass compatibility is
765 highly esoteric and is something only encountered when doing deep and
766 involved metaclass hacking. There are two basic kinds of metaclass
767 incompatibility; upwards and downwards.
769 Upwards metaclass compatibility means that the metaclass of a
770 given class is either the same as (or a subclass of) all of the
773 Downward metaclass compatibility means that the metaclasses of a
774 given class's ancestors are all either the same as (or a subclass
777 Here is a diagram showing a set of two classes (C<A> and C<B>) and
778 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
779 metaclass compatibility both upwards and downwards.
781 +---------+ +---------+
782 | Meta::A |<----| Meta::B | <....... (instance of )
783 +---------+ +---------+ <------- (inherits from)
786 +---------+ +---------+
788 +---------+ +---------+
790 As I said this is a highly esoteric topic and one you will only run
791 into if you do a lot of subclassing of L<Class::MOP::Class>. If you
792 are interested in why this is an issue see the paper I<Uniform and
793 safe metaclass composition> linked to in the L<SEE ALSO> section of
796 =head2 Using custom metaclasses
798 Always use the L<metaclass> pragma when using a custom metaclass, this
799 will ensure the proper initialization order and not accidentally
800 create an incorrect type of metaclass for you. This is a very rare
801 problem, and one which can only occur if you are doing deep metaclass
802 programming. So in other words, don't worry about it.
804 Note that if you're using L<Moose> we encourage you to I<not> use
805 L<metaclass> pragma, and instead use L<Moose::Util::MetaRole> to apply
806 roles to a class's metaclasses. This topic is covered at length in
807 various L<Moose::Cookbook> recipes.
811 The meta-object protocol is divided into 4 main sub-protocols:
813 =head2 The Class protocol
815 This provides a means of manipulating and introspecting a Perl 5
816 class. It handles symbol table hacking for you, and provides a rich
817 set of methods that go beyond simple package introspection.
819 See L<Class::MOP::Class> for more details.
821 =head2 The Attribute protocol
823 This provides a consistent representation for an attribute of a Perl 5
824 class. Since there are so many ways to create and handle attributes in
825 Perl 5 OO, the Attribute protocol provide as much of a unified
826 approach as possible. Of course, you are always free to extend this
827 protocol by subclassing the appropriate classes.
829 See L<Class::MOP::Attribute> for more details.
831 =head2 The Method protocol
833 This provides a means of manipulating and introspecting methods in the
834 Perl 5 object system. As with attributes, there are many ways to
835 approach this topic, so we try to keep it pretty basic, while still
836 making it possible to extend the system in many ways.
838 See L<Class::MOP::Method> for more details.
840 =head2 The Instance protocol
842 This provides a layer of abstraction for creating object instances.
843 Since the other layers use this protocol, it is relatively easy to
844 change the type of your instances from the default hash reference to
845 some other type of reference. Several examples are provided in the
846 F<examples/> directory included in this distribution.
848 See L<Class::MOP::Instance> for more details.
852 Note that this module does not export any constants or functions.
858 =item I<Class::MOP::IS_RUNNING_ON_5_10>
860 We set this constant depending on what version perl we are on, this
861 allows us to take advantage of new 5.10 features and stay backwards
864 =item I<Class::MOP::HAVE_ISAREV>
866 Whether or not the L<mro> pragma provides C<get_isarev>, a much faster
867 way to get all the subclasses of a certain class.
871 =head2 Utility functions
873 Note that these are all called as B<functions, not methods>.
877 =item B<Class::MOP::load_class($class_name)>
879 This will load the specified C<$class_name>. This function can be used
880 in place of tricks like C<eval "use $module"> or using C<require>
881 unconditionally. This will return the metaclass of C<$class_name>.
883 =item B<Class::MOP::is_class_loaded($class_name)>
885 Returns a boolean indicating whether or not C<$class_name> has been
888 This does a basic check of the symbol table to try and determine as
889 best it can if the C<$class_name> is loaded, it is probably correct
890 about 99% of the time, but it can be fooled into reporting false
893 =item B<Class::MOP::get_code_info($code)>
895 This function returns two values, the name of the package the C<$code>
896 is from and the name of the C<$code> itself. This is used by several
897 elements of the MOP to determine where a given C<$code> reference is
900 =item B<Class::MOP::class_of($instance_or_class_name)>
902 This will return the metaclass of the given instance or class name.
903 Even if the class lacks a metaclass, no metaclass will be initialized
904 and C<undef> will be returned.
906 =item B<Class::MOP::check_package_cache_flag($pkg)>
908 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
910 This will return an integer that is managed by L<Class::MOP::Class> to
911 determine if a module's symbol table has been altered.
913 In Perl 5.10 or greater, this flag is package specific. However in
914 versions prior to 5.10, this will use the C<PL_sub_generation>
915 variable which is not package specific.
917 =item B<Class::MOP::load_first_existing_class(@class_names)>
919 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
921 Given a list of class names, this function will attempt to load each
924 If it finds a class it can load, it will return that class' name. If
925 none of the classes can be loaded, it will throw an exception.
929 =head2 Metaclass cache functions
931 Class::MOP holds a cache of metaclasses. The following are functions
932 (B<not methods>) which can be used to access that cache. It is not
933 recommended that you mess with these. Bad things could happen, but if
934 you are brave and willing to risk it: go for it!
938 =item B<Class::MOP::get_all_metaclasses>
940 This will return a hash of all the metaclass instances that have
941 been cached by L<Class::MOP::Class>, keyed by the package name.
943 =item B<Class::MOP::get_all_metaclass_instances>
945 This will return a list of all the metaclass instances that have
946 been cached by L<Class::MOP::Class>.
948 =item B<Class::MOP::get_all_metaclass_names>
950 This will return a list of all the metaclass names that have
951 been cached by L<Class::MOP::Class>.
953 =item B<Class::MOP::get_metaclass_by_name($name)>
955 This will return a cached L<Class::MOP::Class> instance, or nothing
956 if no metaclass exists with that C<$name>.
958 =item B<Class::MOP::store_metaclass_by_name($name, $meta)>
960 This will store a metaclass in the cache at the supplied C<$key>.
962 =item B<Class::MOP::weaken_metaclass($name)>
964 In rare cases (e.g. anonymous metaclasses) it is desirable to
965 store a weakened reference in the metaclass cache. This
966 function will weaken the reference to the metaclass stored
969 =item B<Class::MOP::does_metaclass_exist($name)>
971 This will return true of there exists a metaclass stored in the
972 C<$name> key, and return false otherwise.
974 =item B<Class::MOP::remove_metaclass_by_name($name)>
976 This will remove the metaclass stored in the C<$name> key.
984 There are very few books out on Meta Object Protocols and Metaclasses
985 because it is such an esoteric topic. The following books are really
986 the only ones I have found. If you know of any more, B<I<please>>
987 email me and let me know, I would love to hear about them.
991 =item I<The Art of the Meta Object Protocol>
993 =item I<Advances in Object-Oriented Metalevel Architecture and Reflection>
995 =item I<Putting MetaClasses to Work>
997 =item I<Smalltalk: The Language>
1005 =item "Uniform and safe metaclass composition"
1007 An excellent paper by the people who brought us the original Traits paper.
1008 This paper is on how Traits can be used to do safe metaclass composition,
1009 and offers an excellent introduction section which delves into the topic of
1010 metaclass compatibility.
1012 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
1014 =item "Safe Metaclass Programming"
1016 This paper seems to precede the above paper, and propose a mix-in based
1017 approach as opposed to the Traits based approach. Both papers have similar
1018 information on the metaclass compatibility problem space.
1020 L<http://citeseer.ist.psu.edu/37617.html>
1028 =item The Perl 6 MetaModel work in the Pugs project
1032 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
1034 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1044 =item CPAN Module Review of Class::MOP
1046 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1050 =head1 SIMILAR MODULES
1052 As I have said above, this module is a class-builder-builder, so it is
1053 not the same thing as modules like L<Class::Accessor> and
1054 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1055 with similar goals to this module. The one I have found which is most
1056 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1057 creates are very different from this modules.
1061 All complex software has bugs lurking in it, and this module is no
1062 exception. If you find a bug please either email me, or add the bug
1065 =head1 ACKNOWLEDGEMENTS
1071 Thanks to Rob for actually getting the development of this module kick-started.
1077 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1079 B<with contributions from:>
1081 Brandon (blblack) Black
1083 Florian (rafl) Ragwitz
1085 Guillermo (groditi) Roditi
1089 Rob (robkinyon) Kinyon
1091 Yuval (nothingmuch) Kogman
1093 Scott (konobi) McWhirter
1095 =head1 COPYRIGHT AND LICENSE
1097 Copyright 2006-2009 by Infinity Interactive, Inc.
1099 L<http://www.iinteractive.com>
1101 This library is free software; you can redistribute it and/or modify
1102 it under the same terms as Perl itself.