12 use Devel::GlobalDestruction qw( in_global_destruction );
13 use Scalar::Util 'weaken', 'reftype';
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 = '0.78_02';
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 }
63 # We only cache metaclasses, meaning instances of
64 # Class::MOP::Class. We do not cache instance of
65 # Class::MOP::Package or Class::MOP::Module. Mostly
66 # because I don't yet see a good reason to do so.
69 sub load_first_existing_class {
73 foreach my $class (@classes) {
74 unless ( _is_valid_class_name($class) ) {
75 my $display = defined($class) ? $class : 'undef';
76 confess "Invalid class name ($display)";
82 for my $class (@classes) {
83 my $e = _try_load_one_class($class);
86 $exceptions{$class} = $e;
94 return $found if $found;
100 "Could not load class (%s) because : %s", $_,
107 sub _try_load_one_class {
110 return if is_class_loaded($class);
112 my $file = $class . '.pm';
117 eval { require($file) };
123 my $class = load_first_existing_class($_[0]);
124 return get_metaclass_by_name($class) || $class;
127 sub _is_valid_class_name {
130 return 0 if ref($class);
131 return 0 unless defined($class);
132 return 0 unless length($class);
134 return 1 if $class =~ /^\w+(?:::\w+)*$/;
139 ## ----------------------------------------------------------------------------
140 ## Setting up our environment ...
141 ## ----------------------------------------------------------------------------
142 ## Class::MOP needs to have a few things in the global perl environment so
143 ## that it can operate effectively. Those things are done here.
144 ## ----------------------------------------------------------------------------
146 # ... nothing yet actually ;)
148 ## ----------------------------------------------------------------------------
150 ## ----------------------------------------------------------------------------
151 ## The code below here is to bootstrap our MOP with itself. This is also
152 ## sometimes called "tying the knot". By doing this, we make it much easier
153 ## to extend the MOP through subclassing and such since now you can use the
154 ## MOP itself to extend itself.
156 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
157 ## ----------------------------------------------------------------------------
159 # We need to add in the meta-attributes here so that
160 # any subclass of Class::MOP::* will be able to
161 # inherit them using &construct_instance
163 ## --------------------------------------------------------
164 ## Class::MOP::Package
166 Class::MOP::Package->meta->add_attribute(
167 Class::MOP::Attribute->new('package' => (
169 # NOTE: we need to do this in order
170 # for the instance meta-object to
171 # not fall into meta-circular death
173 # we just alias the original method
174 # rather than re-produce it here
175 'name' => \&Class::MOP::Package::name
180 Class::MOP::Package->meta->add_attribute(
181 Class::MOP::Attribute->new('namespace' => (
184 # we just alias the original method
185 # rather than re-produce it here
186 'namespace' => \&Class::MOP::Package::namespace
189 default => sub { \undef }
193 ## --------------------------------------------------------
194 ## Class::MOP::Module
197 # yeah this is kind of stretching things a bit,
198 # but truthfully the version should be an attribute
199 # of the Module, the weirdness comes from having to
200 # stick to Perl 5 convention and store it in the
201 # $VERSION package variable. Basically if you just
202 # squint at it, it will look how you want it to look.
203 # Either as a package variable, or as a attribute of
204 # the metaclass, isn't abstraction great :)
206 Class::MOP::Module->meta->add_attribute(
207 Class::MOP::Attribute->new('version' => (
210 # we just alias the original method
211 # rather than re-produce it here
212 'version' => \&Class::MOP::Module::version
215 default => sub { \undef }
220 # By following the same conventions as version here,
221 # we are opening up the possibility that people can
222 # use the $AUTHORITY in non-Class::MOP modules as
225 Class::MOP::Module->meta->add_attribute(
226 Class::MOP::Attribute->new('authority' => (
229 # we just alias the original method
230 # rather than re-produce it here
231 'authority' => \&Class::MOP::Module::authority
234 default => sub { \undef }
238 ## --------------------------------------------------------
241 Class::MOP::Class->meta->add_attribute(
242 Class::MOP::Attribute->new('attributes' => (
244 # NOTE: we need to do this in order
245 # for the instance meta-object to
246 # not fall into meta-circular death
248 # we just alias the original method
249 # rather than re-produce it here
250 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
252 default => sub { {} }
256 Class::MOP::Class->meta->add_attribute(
257 Class::MOP::Attribute->new('methods' => (
260 # we just alias the original method
261 # rather than re-produce it here
262 'get_method_map' => \&Class::MOP::Class::get_method_map
264 default => sub { {} }
268 Class::MOP::Class->meta->add_attribute(
269 Class::MOP::Attribute->new('superclasses' => (
272 # we just alias the original method
273 # rather than re-produce it here
274 'superclasses' => \&Class::MOP::Class::superclasses
277 default => sub { \undef }
281 Class::MOP::Class->meta->add_attribute(
282 Class::MOP::Attribute->new('attribute_metaclass' => (
285 # we just alias the original method
286 # rather than re-produce it here
287 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
289 default => 'Class::MOP::Attribute',
293 Class::MOP::Class->meta->add_attribute(
294 Class::MOP::Attribute->new('method_metaclass' => (
297 # we just alias the original method
298 # rather than re-produce it here
299 'method_metaclass' => \&Class::MOP::Class::method_metaclass
301 default => 'Class::MOP::Method',
305 Class::MOP::Class->meta->add_attribute(
306 Class::MOP::Attribute->new('wrapped_method_metaclass' => (
309 # we just alias the original method
310 # rather than re-produce it here
311 'wrapped_method_metaclass' => \&Class::MOP::Class::wrapped_method_metaclass
313 default => 'Class::MOP::Method::Wrapped',
317 Class::MOP::Class->meta->add_attribute(
318 Class::MOP::Attribute->new('instance_metaclass' => (
320 # NOTE: we need to do this in order
321 # for the instance meta-object to
322 # not fall into meta-circular death
324 # we just alias the original method
325 # rather than re-produce it here
326 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
328 default => 'Class::MOP::Instance',
332 Class::MOP::Class->meta->add_attribute(
333 Class::MOP::Attribute->new('immutable_transformer' => (
335 'immutable_transformer' => \&Class::MOP::Class::immutable_transformer
338 '_set_immutable_transformer' => \&Class::MOP::Class::_set_immutable_transformer
344 # we don't actually need to tie the knot with
345 # Class::MOP::Class here, it is actually handled
346 # within Class::MOP::Class itself in the
347 # construct_class_instance method.
349 ## --------------------------------------------------------
350 ## Class::MOP::Attribute
352 Class::MOP::Attribute->meta->add_attribute(
353 Class::MOP::Attribute->new('name' => (
355 # NOTE: we need to do this in order
356 # for the instance meta-object to
357 # not fall into meta-circular death
359 # we just alias the original method
360 # rather than re-produce it here
361 'name' => \&Class::MOP::Attribute::name
366 Class::MOP::Attribute->meta->add_attribute(
367 Class::MOP::Attribute->new('associated_class' => (
369 # NOTE: we need to do this in order
370 # for the instance meta-object to
371 # not fall into meta-circular death
373 # we just alias the original method
374 # rather than re-produce it here
375 'associated_class' => \&Class::MOP::Attribute::associated_class
380 Class::MOP::Attribute->meta->add_attribute(
381 Class::MOP::Attribute->new('accessor' => (
382 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
383 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
387 Class::MOP::Attribute->meta->add_attribute(
388 Class::MOP::Attribute->new('reader' => (
389 reader => { 'reader' => \&Class::MOP::Attribute::reader },
390 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
394 Class::MOP::Attribute->meta->add_attribute(
395 Class::MOP::Attribute->new('initializer' => (
396 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
397 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
401 Class::MOP::Attribute->meta->add_attribute(
402 Class::MOP::Attribute->new('definition_context' => (
403 reader => { 'definition_context' => \&Class::MOP::Attribute::definition_context },
407 Class::MOP::Attribute->meta->add_attribute(
408 Class::MOP::Attribute->new('writer' => (
409 reader => { 'writer' => \&Class::MOP::Attribute::writer },
410 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
414 Class::MOP::Attribute->meta->add_attribute(
415 Class::MOP::Attribute->new('predicate' => (
416 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
417 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
421 Class::MOP::Attribute->meta->add_attribute(
422 Class::MOP::Attribute->new('clearer' => (
423 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
424 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
428 Class::MOP::Attribute->meta->add_attribute(
429 Class::MOP::Attribute->new('builder' => (
430 reader => { 'builder' => \&Class::MOP::Attribute::builder },
431 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
435 Class::MOP::Attribute->meta->add_attribute(
436 Class::MOP::Attribute->new('init_arg' => (
437 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
438 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
442 Class::MOP::Attribute->meta->add_attribute(
443 Class::MOP::Attribute->new('default' => (
444 # default has a custom 'reader' method ...
445 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
449 Class::MOP::Attribute->meta->add_attribute(
450 Class::MOP::Attribute->new('associated_methods' => (
451 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
452 default => sub { [] }
456 Class::MOP::Attribute->meta->add_method('clone' => sub {
458 $self->meta->clone_object($self, @_);
461 ## --------------------------------------------------------
462 ## Class::MOP::Method
463 Class::MOP::Method->meta->add_attribute(
464 Class::MOP::Attribute->new('body' => (
465 reader => { 'body' => \&Class::MOP::Method::body },
469 Class::MOP::Method->meta->add_attribute(
470 Class::MOP::Attribute->new('associated_metaclass' => (
471 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
475 Class::MOP::Method->meta->add_attribute(
476 Class::MOP::Attribute->new('package_name' => (
477 reader => { 'package_name' => \&Class::MOP::Method::package_name },
481 Class::MOP::Method->meta->add_attribute(
482 Class::MOP::Attribute->new('name' => (
483 reader => { 'name' => \&Class::MOP::Method::name },
487 Class::MOP::Method->meta->add_attribute(
488 Class::MOP::Attribute->new('original_method' => (
489 reader => { 'original_method' => \&Class::MOP::Method::original_method },
490 writer => { '_set_original_method' => \&Class::MOP::Method::_set_original_method },
494 Class::MOP::Method->meta->add_method('clone' => sub {
496 my $clone = $self->meta->clone_object($self, @_);
497 $clone->_set_original_method($self);
501 ## --------------------------------------------------------
502 ## Class::MOP::Method::Wrapped
505 # the way this item is initialized, this
506 # really does not follow the standard
507 # practices of attributes, but we put
508 # it here for completeness
509 Class::MOP::Method::Wrapped->meta->add_attribute(
510 Class::MOP::Attribute->new('modifier_table')
513 ## --------------------------------------------------------
514 ## Class::MOP::Method::Generated
516 Class::MOP::Method::Generated->meta->add_attribute(
517 Class::MOP::Attribute->new('is_inline' => (
518 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
523 Class::MOP::Method::Generated->meta->add_attribute(
524 Class::MOP::Attribute->new('definition_context' => (
525 reader => { 'definition_context' => \&Class::MOP::Method::Generated::definition_context },
529 ## --------------------------------------------------------
530 ## Class::MOP::Method::Accessor
532 Class::MOP::Method::Accessor->meta->add_attribute(
533 Class::MOP::Attribute->new('attribute' => (
535 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
540 Class::MOP::Method::Accessor->meta->add_attribute(
541 Class::MOP::Attribute->new('accessor_type' => (
542 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
546 ## --------------------------------------------------------
547 ## Class::MOP::Method::Constructor
549 Class::MOP::Method::Constructor->meta->add_attribute(
550 Class::MOP::Attribute->new('options' => (
552 'options' => \&Class::MOP::Method::Constructor::options
554 default => sub { +{} }
558 Class::MOP::Method::Constructor->meta->add_attribute(
559 Class::MOP::Attribute->new('associated_metaclass' => (
560 init_arg => "metaclass", # FIXME alias and rename
562 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
567 ## --------------------------------------------------------
568 ## Class::MOP::Instance
571 # these don't yet do much of anything, but are just
572 # included for completeness
574 Class::MOP::Instance->meta->add_attribute(
575 Class::MOP::Attribute->new('associated_metaclass',
576 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
580 Class::MOP::Instance->meta->add_attribute(
581 Class::MOP::Attribute->new('_class_name',
583 reader => { _class_name => \&Class::MOP::Instance::_class_name },
584 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
585 #default => sub { $_[0]->associated_metaclass->name },
589 Class::MOP::Instance->meta->add_attribute(
590 Class::MOP::Attribute->new('attributes',
591 reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
595 Class::MOP::Instance->meta->add_attribute(
596 Class::MOP::Attribute->new('slots',
597 reader => { slots => \&Class::MOP::Instance::slots },
601 Class::MOP::Instance->meta->add_attribute(
602 Class::MOP::Attribute->new('slot_hash',
603 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
608 # we need the meta instance of the meta instance to be created now, in order
609 # for the constructor to be able to use it
610 Class::MOP::Instance->meta->get_meta_instance;
612 # pretend the add_method never happenned. it hasn't yet affected anything
613 undef Class::MOP::Instance->meta->{_package_cache_flag};
615 ## --------------------------------------------------------
616 ## Now close all the Class::MOP::* classes
618 # NOTE: we don't need to inline the the accessors this only lengthens
619 # the compile time of the MOP, and gives us no actual benefits.
621 $_->meta->make_immutable(
622 inline_constructor => 1,
623 replace_constructor => 1,
624 constructor_name => "_new",
625 inline_accessors => 0,
631 Class::MOP::Attribute
637 Class::MOP::Method::Generated
639 Class::MOP::Method::Accessor
640 Class::MOP::Method::Constructor
641 Class::MOP::Method::Wrapped
652 Class::MOP - A Meta Object Protocol for Perl 5
656 This module is a fully functioning meta object protocol for the
657 Perl 5 object system. It makes no attempt to change the behavior or
658 characteristics of the Perl 5 object system, only to create a
659 protocol for its manipulation and introspection.
661 That said, it does attempt to create the tools for building a rich set
662 of extensions to the Perl 5 object system. Every attempt has been made
663 to abide by the spirit of the Perl 5 object system that we all know
666 This documentation is sparse on conceptual details. We suggest looking
667 at the items listed in the L<SEE ALSO> section for more
668 information. In particular the book "The Art of the Meta Object
669 Protocol" was very influential in the development of this system.
671 =head2 What is a Meta Object Protocol?
673 A meta object protocol is an API to an object system.
675 To be more specific, it abstracts the components of an object system
676 (classes, object, methods, object attributes, etc.). These
677 abstractions can then be used to inspect and manipulate the object
678 system which they describe.
680 It can be said that there are two MOPs for any object system; the
681 implicit MOP and the explicit MOP. The implicit MOP handles things
682 like method dispatch or inheritance, which happen automatically as
683 part of how the object system works. The explicit MOP typically
684 handles the introspection/reflection features of the object system.
686 All object systems have implicit MOPs. Without one, they would not
687 work. Explicit MOPs are much less common, and depending on the
688 language can vary from restrictive (Reflection in Java or C#) to wide
689 open (CLOS is a perfect example).
691 =head2 Yet Another Class Builder! Why?
693 This is B<not> a class builder so much as a I<class builder
694 B<builder>>. The intent is that an end user will not use this module
695 directly, but instead this module is used by module authors to build
696 extensions and features onto the Perl 5 object system.
698 This system is used by L<Moose>, which supplies a powerful class
699 builder system built entirely on top of C<Class::MOP>.
701 =head2 Who is this module for?
703 This module is for anyone who has ever created or wanted to create a
704 module for the Class:: namespace. The tools which this module provides
705 make doing complex Perl 5 wizardry simpler, by removing such barriers
706 as the need to hack symbol tables, or understand the fine details of
709 =head2 What changes do I have to make to use this module?
711 This module was designed to be as unintrusive as possible. Many of its
712 features are accessible without B<any> change to your existing
713 code. It is meant to be a compliment to your existing code and not an
714 intrusion on your code base. Unlike many other B<Class::> modules,
715 this module B<does not> require you subclass it, or even that you
716 C<use> it in within your module's package.
718 The only features which requires additions to your code are the
719 attribute handling and instance construction features, and these are
720 both completely optional features. The only reason for this is because
721 Perl 5's object system does not actually have these features built
722 in. More information about this feature can be found below.
724 =head2 About Performance
726 It is a common misconception that explicit MOPs are a performance hit.
727 This is not a universal truth, it is a side-effect of some specific
728 implementations. For instance, using Java reflection is slow because
729 the JVM cannot take advantage of any compiler optimizations, and the
730 JVM has to deal with much more runtime type information as well.
732 Reflection in C# is marginally better as it was designed into the
733 language and runtime (the CLR). In contrast, CLOS (the Common Lisp
734 Object System) was built to support an explicit MOP, and so
735 performance is tuned for it.
737 This library in particular does its absolute best to avoid putting
738 B<any> drain at all upon your code's performance. In fact, by itself
739 it does nothing to affect your existing code. So you only pay for what
742 =head2 About Metaclass compatibility
744 This module makes sure that all metaclasses created are both upwards
745 and downwards compatible. The topic of metaclass compatibility is
746 highly esoteric and is something only encountered when doing deep and
747 involved metaclass hacking. There are two basic kinds of metaclass
748 incompatibility; upwards and downwards.
750 Upwards metaclass compatibility means that the metaclass of a
751 given class is either the same as (or a subclass of) all of the
754 Downward metaclass compatibility means that the metaclasses of a
755 given class's ancestors are all either the same as (or a subclass
758 Here is a diagram showing a set of two classes (C<A> and C<B>) and
759 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
760 metaclass compatibility both upwards and downwards.
762 +---------+ +---------+
763 | Meta::A |<----| Meta::B | <....... (instance of )
764 +---------+ +---------+ <------- (inherits from)
767 +---------+ +---------+
769 +---------+ +---------+
771 As I said this is a highly esoteric topic and one you will only run
772 into if you do a lot of subclassing of L<Class::MOP::Class>. If you
773 are interested in why this is an issue see the paper I<Uniform and
774 safe metaclass composition> linked to in the L<SEE ALSO> section of
777 =head2 Using custom metaclasses
779 Always use the L<metaclass> pragma when using a custom metaclass, this
780 will ensure the proper initialization order and not accidentally
781 create an incorrect type of metaclass for you. This is a very rare
782 problem, and one which can only occur if you are doing deep metaclass
783 programming. So in other words, don't worry about it.
785 Note that if you're using L<Moose> we encourage you to I<not> use
786 L<metaclass> pragma, and instead use L<Moose::Util::MetaRole> to apply
787 roles to a class's metaclasses. This topic is covered at length in
788 various L<Moose::Cookbook> recipes.
792 The meta-object protocol is divided into 4 main sub-protocols:
794 =head2 The Class protocol
796 This provides a means of manipulating and introspecting a Perl 5
797 class. It handles symbol table hacking for you, and provides a rich
798 set of methods that go beyond simple package introspection.
800 See L<Class::MOP::Class> for more details.
802 =head2 The Attribute protocol
804 This provides a consistent representation for an attribute of a Perl 5
805 class. Since there are so many ways to create and handle attributes in
806 Perl 5 OO, the Attribute protocol provide as much of a unified
807 approach as possible. Of course, you are always free to extend this
808 protocol by subclassing the appropriate classes.
810 See L<Class::MOP::Attribute> for more details.
812 =head2 The Method protocol
814 This provides a means of manipulating and introspecting methods in the
815 Perl 5 object system. As with attributes, there are many ways to
816 approach this topic, so we try to keep it pretty basic, while still
817 making it possible to extend the system in many ways.
819 See L<Class::MOP::Method> for more details.
821 =head2 The Instance protocol
823 This provides a layer of abstraction for creating object instances.
824 Since the other layers use this protocol, it is relatively easy to
825 change the type of your instances from the default hash reference to
826 some other type of reference. Several examples are provided in the
827 F<examples/> directory included in this distribution.
829 See L<Class::MOP::Instance> for more details.
833 Note that this module does not export any constants or functions.
839 =item I<Class::MOP::IS_RUNNING_ON_5_10>
841 We set this constant depending on what version perl we are on, this
842 allows us to take advantage of new 5.10 features and stay backwards
845 =item I<Class::MOP::HAVE_ISAREV>
847 Whether or not the L<mro> pragma provides C<get_isarev>, a much faster
848 way to get all the subclasses of a certain class.
852 =head2 Utility functions
854 Note that these are all called as B<functions, not methods>.
858 =item B<Class::MOP::load_class($class_name)>
860 This will load the specified C<$class_name>. This function can be used
861 in place of tricks like C<eval "use $module"> or using C<require>
864 =item B<Class::MOP::is_class_loaded($class_name)>
866 Returns a boolean indicating whether or not C<$class_name> has been
869 This does a basic check of the symbol table to try and determine as
870 best it can if the C<$class_name> is loaded, it is probably correct
871 about 99% of the time, but it can be fooled into reporting false
874 =item B<Class::MOP::get_code_info($code)>
876 This function returns two values, the name of the package the C<$code>
877 is from and the name of the C<$code> itself. This is used by several
878 elements of the MOP to determine where a given C<$code> reference is
881 =item B<Class::MOP::check_package_cache_flag($pkg)>
883 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
885 This will return an integer that is managed by L<Class::MOP::Class> to
886 determine if a module's symbol table has been altered.
888 In Perl 5.10 or greater, this flag is package specific. However in
889 versions prior to 5.10, this will use the C<PL_sub_generation>
890 variable which is not package specific.
892 =item B<Class::MOP::load_first_existing_class(@class_names)>
894 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
896 Given a list of class names, this function will attempt to load each
899 If it finds a class it can load, it will return that class' name. If
900 none of the classes can be loaded, it will throw an exception.
904 =head2 Metaclass cache functions
906 Class::MOP holds a cache of metaclasses. The following are functions
907 (B<not methods>) which can be used to access that cache. It is not
908 recommended that you mess with these. Bad things could happen, but if
909 you are brave and willing to risk it: go for it!
913 =item B<Class::MOP::get_all_metaclasses>
915 This will return a hash of all the metaclass instances that have
916 been cached by L<Class::MOP::Class>, keyed by the package name.
918 =item B<Class::MOP::get_all_metaclass_instances>
920 This will return a list of all the metaclass instances that have
921 been cached by L<Class::MOP::Class>.
923 =item B<Class::MOP::get_all_metaclass_names>
925 This will return a list of all the metaclass names that have
926 been cached by L<Class::MOP::Class>.
928 =item B<Class::MOP::get_metaclass_by_name($name)>
930 This will return a cached L<Class::MOP::Class> instance, or nothing
931 if no metaclass exists with that C<$name>.
933 =item B<Class::MOP::store_metaclass_by_name($name, $meta)>
935 This will store a metaclass in the cache at the supplied C<$key>.
937 =item B<Class::MOP::weaken_metaclass($name)>
939 In rare cases (e.g. anonymous metaclasses) it is desirable to
940 store a weakened reference in the metaclass cache. This
941 function will weaken the reference to the metaclass stored
944 =item B<Class::MOP::does_metaclass_exist($name)>
946 This will return true of there exists a metaclass stored in the
947 C<$name> key, and return false otherwise.
949 =item B<Class::MOP::remove_metaclass_by_name($name)>
951 This will remove the metaclass stored in the C<$name> key.
959 There are very few books out on Meta Object Protocols and Metaclasses
960 because it is such an esoteric topic. The following books are really
961 the only ones I have found. If you know of any more, B<I<please>>
962 email me and let me know, I would love to hear about them.
966 =item I<The Art of the Meta Object Protocol>
968 =item I<Advances in Object-Oriented Metalevel Architecture and Reflection>
970 =item I<Putting MetaClasses to Work>
972 =item I<Smalltalk: The Language>
980 =item "Uniform and safe metaclass composition"
982 An excellent paper by the people who brought us the original Traits paper.
983 This paper is on how Traits can be used to do safe metaclass composition,
984 and offers an excellent introduction section which delves into the topic of
985 metaclass compatibility.
987 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
989 =item "Safe Metaclass Programming"
991 This paper seems to precede the above paper, and propose a mix-in based
992 approach as opposed to the Traits based approach. Both papers have similar
993 information on the metaclass compatibility problem space.
995 L<http://citeseer.ist.psu.edu/37617.html>
1003 =item The Perl 6 MetaModel work in the Pugs project
1007 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
1009 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1019 =item CPAN Module Review of Class::MOP
1021 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1025 =head1 SIMILAR MODULES
1027 As I have said above, this module is a class-builder-builder, so it is
1028 not the same thing as modules like L<Class::Accessor> and
1029 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1030 with similar goals to this module. The one I have found which is most
1031 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1032 creates are very different from this modules.
1036 All complex software has bugs lurking in it, and this module is no
1037 exception. If you find a bug please either email me, or add the bug
1040 =head1 ACKNOWLEDGEMENTS
1046 Thanks to Rob for actually getting the development of this module kick-started.
1052 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1054 B<with contributions from:>
1056 Brandon (blblack) Black
1058 Florian (rafl) Ragwitz
1060 Guillermo (groditi) Roditi
1064 Rob (robkinyon) Kinyon
1066 Yuval (nothingmuch) Kogman
1068 Scott (konobi) McWhirter
1070 =head1 COPYRIGHT AND LICENSE
1072 Copyright 2006-2009 by Infinity Interactive, Inc.
1074 L<http://www.iinteractive.com>
1076 This library is free software; you can redistribute it and/or modify
1077 it under the same terms as Perl itself.