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 = '0.79';
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 }
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 $class =~ /^\w+(?:::\w+)*$/;
143 $class = blessed($class) || $class;
145 return get_metaclass_by_name($class);
148 ## ----------------------------------------------------------------------------
149 ## Setting up our environment ...
150 ## ----------------------------------------------------------------------------
151 ## Class::MOP needs to have a few things in the global perl environment so
152 ## that it can operate effectively. Those things are done here.
153 ## ----------------------------------------------------------------------------
155 # ... nothing yet actually ;)
157 ## ----------------------------------------------------------------------------
159 ## ----------------------------------------------------------------------------
160 ## The code below here is to bootstrap our MOP with itself. This is also
161 ## sometimes called "tying the knot". By doing this, we make it much easier
162 ## to extend the MOP through subclassing and such since now you can use the
163 ## MOP itself to extend itself.
165 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
166 ## ----------------------------------------------------------------------------
168 # We need to add in the meta-attributes here so that
169 # any subclass of Class::MOP::* will be able to
170 # inherit them using &construct_instance
172 ## --------------------------------------------------------
173 ## Class::MOP::Package
175 Class::MOP::Package->meta->add_attribute(
176 Class::MOP::Attribute->new('package' => (
178 # NOTE: we need to do this in order
179 # for the instance meta-object to
180 # not fall into meta-circular death
182 # we just alias the original method
183 # rather than re-produce it here
184 'name' => \&Class::MOP::Package::name
189 Class::MOP::Package->meta->add_attribute(
190 Class::MOP::Attribute->new('namespace' => (
193 # we just alias the original method
194 # rather than re-produce it here
195 'namespace' => \&Class::MOP::Package::namespace
198 default => sub { \undef }
202 ## --------------------------------------------------------
203 ## Class::MOP::Module
206 # yeah this is kind of stretching things a bit,
207 # but truthfully the version should be an attribute
208 # of the Module, the weirdness comes from having to
209 # stick to Perl 5 convention and store it in the
210 # $VERSION package variable. Basically if you just
211 # squint at it, it will look how you want it to look.
212 # Either as a package variable, or as a attribute of
213 # the metaclass, isn't abstraction great :)
215 Class::MOP::Module->meta->add_attribute(
216 Class::MOP::Attribute->new('version' => (
219 # we just alias the original method
220 # rather than re-produce it here
221 'version' => \&Class::MOP::Module::version
224 default => sub { \undef }
229 # By following the same conventions as version here,
230 # we are opening up the possibility that people can
231 # use the $AUTHORITY in non-Class::MOP modules as
234 Class::MOP::Module->meta->add_attribute(
235 Class::MOP::Attribute->new('authority' => (
238 # we just alias the original method
239 # rather than re-produce it here
240 'authority' => \&Class::MOP::Module::authority
243 default => sub { \undef }
247 ## --------------------------------------------------------
250 Class::MOP::Class->meta->add_attribute(
251 Class::MOP::Attribute->new('attributes' => (
253 # NOTE: we need to do this in order
254 # for the instance meta-object to
255 # not fall into meta-circular death
257 # we just alias the original method
258 # rather than re-produce it here
259 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
261 default => sub { {} }
265 Class::MOP::Class->meta->add_attribute(
266 Class::MOP::Attribute->new('methods' => (
269 # we just alias the original method
270 # rather than re-produce it here
271 'get_method_map' => \&Class::MOP::Class::get_method_map
273 default => sub { {} }
277 Class::MOP::Class->meta->add_attribute(
278 Class::MOP::Attribute->new('superclasses' => (
281 # we just alias the original method
282 # rather than re-produce it here
283 'superclasses' => \&Class::MOP::Class::superclasses
286 default => sub { \undef }
290 Class::MOP::Class->meta->add_attribute(
291 Class::MOP::Attribute->new('attribute_metaclass' => (
294 # we just alias the original method
295 # rather than re-produce it here
296 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
298 default => 'Class::MOP::Attribute',
302 Class::MOP::Class->meta->add_attribute(
303 Class::MOP::Attribute->new('method_metaclass' => (
306 # we just alias the original method
307 # rather than re-produce it here
308 'method_metaclass' => \&Class::MOP::Class::method_metaclass
310 default => 'Class::MOP::Method',
314 Class::MOP::Class->meta->add_attribute(
315 Class::MOP::Attribute->new('wrapped_method_metaclass' => (
318 # we just alias the original method
319 # rather than re-produce it here
320 'wrapped_method_metaclass' => \&Class::MOP::Class::wrapped_method_metaclass
322 default => 'Class::MOP::Method::Wrapped',
326 Class::MOP::Class->meta->add_attribute(
327 Class::MOP::Attribute->new('instance_metaclass' => (
329 # NOTE: we need to do this in order
330 # for the instance meta-object to
331 # not fall into meta-circular death
333 # we just alias the original method
334 # rather than re-produce it here
335 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
337 default => 'Class::MOP::Instance',
341 Class::MOP::Class->meta->add_attribute(
342 Class::MOP::Attribute->new('immutable_transformer' => (
344 'immutable_transformer' => \&Class::MOP::Class::immutable_transformer
347 '_set_immutable_transformer' => \&Class::MOP::Class::_set_immutable_transformer
353 # we don't actually need to tie the knot with
354 # Class::MOP::Class here, it is actually handled
355 # within Class::MOP::Class itself in the
356 # construct_class_instance method.
358 ## --------------------------------------------------------
359 ## Class::MOP::Attribute
361 Class::MOP::Attribute->meta->add_attribute(
362 Class::MOP::Attribute->new('name' => (
364 # NOTE: we need to do this in order
365 # for the instance meta-object to
366 # not fall into meta-circular death
368 # we just alias the original method
369 # rather than re-produce it here
370 'name' => \&Class::MOP::Attribute::name
375 Class::MOP::Attribute->meta->add_attribute(
376 Class::MOP::Attribute->new('associated_class' => (
378 # NOTE: we need to do this in order
379 # for the instance meta-object to
380 # not fall into meta-circular death
382 # we just alias the original method
383 # rather than re-produce it here
384 'associated_class' => \&Class::MOP::Attribute::associated_class
389 Class::MOP::Attribute->meta->add_attribute(
390 Class::MOP::Attribute->new('accessor' => (
391 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
392 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
396 Class::MOP::Attribute->meta->add_attribute(
397 Class::MOP::Attribute->new('reader' => (
398 reader => { 'reader' => \&Class::MOP::Attribute::reader },
399 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
403 Class::MOP::Attribute->meta->add_attribute(
404 Class::MOP::Attribute->new('initializer' => (
405 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
406 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
410 Class::MOP::Attribute->meta->add_attribute(
411 Class::MOP::Attribute->new('definition_context' => (
412 reader => { 'definition_context' => \&Class::MOP::Attribute::definition_context },
416 Class::MOP::Attribute->meta->add_attribute(
417 Class::MOP::Attribute->new('writer' => (
418 reader => { 'writer' => \&Class::MOP::Attribute::writer },
419 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
423 Class::MOP::Attribute->meta->add_attribute(
424 Class::MOP::Attribute->new('predicate' => (
425 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
426 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
430 Class::MOP::Attribute->meta->add_attribute(
431 Class::MOP::Attribute->new('clearer' => (
432 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
433 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
437 Class::MOP::Attribute->meta->add_attribute(
438 Class::MOP::Attribute->new('builder' => (
439 reader => { 'builder' => \&Class::MOP::Attribute::builder },
440 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
444 Class::MOP::Attribute->meta->add_attribute(
445 Class::MOP::Attribute->new('init_arg' => (
446 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
447 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
451 Class::MOP::Attribute->meta->add_attribute(
452 Class::MOP::Attribute->new('default' => (
453 # default has a custom 'reader' method ...
454 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
458 Class::MOP::Attribute->meta->add_attribute(
459 Class::MOP::Attribute->new('associated_methods' => (
460 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
461 default => sub { [] }
465 Class::MOP::Attribute->meta->add_method('clone' => sub {
467 $self->meta->clone_object($self, @_);
470 ## --------------------------------------------------------
471 ## Class::MOP::Method
472 Class::MOP::Method->meta->add_attribute(
473 Class::MOP::Attribute->new('body' => (
474 reader => { 'body' => \&Class::MOP::Method::body },
478 Class::MOP::Method->meta->add_attribute(
479 Class::MOP::Attribute->new('associated_metaclass' => (
480 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
484 Class::MOP::Method->meta->add_attribute(
485 Class::MOP::Attribute->new('package_name' => (
486 reader => { 'package_name' => \&Class::MOP::Method::package_name },
490 Class::MOP::Method->meta->add_attribute(
491 Class::MOP::Attribute->new('name' => (
492 reader => { 'name' => \&Class::MOP::Method::name },
496 Class::MOP::Method->meta->add_attribute(
497 Class::MOP::Attribute->new('original_method' => (
498 reader => { 'original_method' => \&Class::MOP::Method::original_method },
499 writer => { '_set_original_method' => \&Class::MOP::Method::_set_original_method },
503 Class::MOP::Method->meta->add_method('clone' => sub {
505 my $clone = $self->meta->clone_object($self, @_);
506 $clone->_set_original_method($self);
510 ## --------------------------------------------------------
511 ## Class::MOP::Method::Wrapped
514 # the way this item is initialized, this
515 # really does not follow the standard
516 # practices of attributes, but we put
517 # it here for completeness
518 Class::MOP::Method::Wrapped->meta->add_attribute(
519 Class::MOP::Attribute->new('modifier_table')
522 ## --------------------------------------------------------
523 ## Class::MOP::Method::Generated
525 Class::MOP::Method::Generated->meta->add_attribute(
526 Class::MOP::Attribute->new('is_inline' => (
527 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
532 Class::MOP::Method::Generated->meta->add_attribute(
533 Class::MOP::Attribute->new('definition_context' => (
534 reader => { 'definition_context' => \&Class::MOP::Method::Generated::definition_context },
538 ## --------------------------------------------------------
539 ## Class::MOP::Method::Accessor
541 Class::MOP::Method::Accessor->meta->add_attribute(
542 Class::MOP::Attribute->new('attribute' => (
544 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
549 Class::MOP::Method::Accessor->meta->add_attribute(
550 Class::MOP::Attribute->new('accessor_type' => (
551 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
555 ## --------------------------------------------------------
556 ## Class::MOP::Method::Constructor
558 Class::MOP::Method::Constructor->meta->add_attribute(
559 Class::MOP::Attribute->new('options' => (
561 'options' => \&Class::MOP::Method::Constructor::options
563 default => sub { +{} }
567 Class::MOP::Method::Constructor->meta->add_attribute(
568 Class::MOP::Attribute->new('associated_metaclass' => (
569 init_arg => "metaclass", # FIXME alias and rename
571 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
576 ## --------------------------------------------------------
577 ## Class::MOP::Instance
580 # these don't yet do much of anything, but are just
581 # included for completeness
583 Class::MOP::Instance->meta->add_attribute(
584 Class::MOP::Attribute->new('associated_metaclass',
585 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
589 Class::MOP::Instance->meta->add_attribute(
590 Class::MOP::Attribute->new('_class_name',
592 reader => { _class_name => \&Class::MOP::Instance::_class_name },
593 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
594 #default => sub { $_[0]->associated_metaclass->name },
598 Class::MOP::Instance->meta->add_attribute(
599 Class::MOP::Attribute->new('attributes',
600 reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
604 Class::MOP::Instance->meta->add_attribute(
605 Class::MOP::Attribute->new('slots',
606 reader => { slots => \&Class::MOP::Instance::slots },
610 Class::MOP::Instance->meta->add_attribute(
611 Class::MOP::Attribute->new('slot_hash',
612 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
617 # we need the meta instance of the meta instance to be created now, in order
618 # for the constructor to be able to use it
619 Class::MOP::Instance->meta->get_meta_instance;
621 # pretend the add_method never happenned. it hasn't yet affected anything
622 undef Class::MOP::Instance->meta->{_package_cache_flag};
624 ## --------------------------------------------------------
625 ## Now close all the Class::MOP::* classes
627 # NOTE: we don't need to inline the the accessors this only lengthens
628 # the compile time of the MOP, and gives us no actual benefits.
630 $_->meta->make_immutable(
631 inline_constructor => 1,
632 replace_constructor => 1,
633 constructor_name => "_new",
634 inline_accessors => 0,
640 Class::MOP::Attribute
646 Class::MOP::Method::Generated
648 Class::MOP::Method::Accessor
649 Class::MOP::Method::Constructor
650 Class::MOP::Method::Wrapped
661 Class::MOP - A Meta Object Protocol for Perl 5
665 This module is a fully functioning meta object protocol for the
666 Perl 5 object system. It makes no attempt to change the behavior or
667 characteristics of the Perl 5 object system, only to create a
668 protocol for its manipulation and introspection.
670 That said, it does attempt to create the tools for building a rich set
671 of extensions to the Perl 5 object system. Every attempt has been made
672 to abide by the spirit of the Perl 5 object system that we all know
675 This documentation is sparse on conceptual details. We suggest looking
676 at the items listed in the L<SEE ALSO> section for more
677 information. In particular the book "The Art of the Meta Object
678 Protocol" was very influential in the development of this system.
680 =head2 What is a Meta Object Protocol?
682 A meta object protocol is an API to an object system.
684 To be more specific, it abstracts the components of an object system
685 (classes, object, methods, object attributes, etc.). These
686 abstractions can then be used to inspect and manipulate the object
687 system which they describe.
689 It can be said that there are two MOPs for any object system; the
690 implicit MOP and the explicit MOP. The implicit MOP handles things
691 like method dispatch or inheritance, which happen automatically as
692 part of how the object system works. The explicit MOP typically
693 handles the introspection/reflection features of the object system.
695 All object systems have implicit MOPs. Without one, they would not
696 work. Explicit MOPs are much less common, and depending on the
697 language can vary from restrictive (Reflection in Java or C#) to wide
698 open (CLOS is a perfect example).
700 =head2 Yet Another Class Builder! Why?
702 This is B<not> a class builder so much as a I<class builder
703 B<builder>>. The intent is that an end user will not use this module
704 directly, but instead this module is used by module authors to build
705 extensions and features onto the Perl 5 object system.
707 This system is used by L<Moose>, which supplies a powerful class
708 builder system built entirely on top of C<Class::MOP>.
710 =head2 Who is this module for?
712 This module is for anyone who has ever created or wanted to create a
713 module for the Class:: namespace. The tools which this module provides
714 make doing complex Perl 5 wizardry simpler, by removing such barriers
715 as the need to hack symbol tables, or understand the fine details of
718 =head2 What changes do I have to make to use this module?
720 This module was designed to be as unintrusive as possible. Many of its
721 features are accessible without B<any> change to your existing
722 code. It is meant to be a compliment to your existing code and not an
723 intrusion on your code base. Unlike many other B<Class::> modules,
724 this module B<does not> require you subclass it, or even that you
725 C<use> it in within your module's package.
727 The only features which requires additions to your code are the
728 attribute handling and instance construction features, and these are
729 both completely optional features. The only reason for this is because
730 Perl 5's object system does not actually have these features built
731 in. More information about this feature can be found below.
733 =head2 About Performance
735 It is a common misconception that explicit MOPs are a performance hit.
736 This is not a universal truth, it is a side-effect of some specific
737 implementations. For instance, using Java reflection is slow because
738 the JVM cannot take advantage of any compiler optimizations, and the
739 JVM has to deal with much more runtime type information as well.
741 Reflection in C# is marginally better as it was designed into the
742 language and runtime (the CLR). In contrast, CLOS (the Common Lisp
743 Object System) was built to support an explicit MOP, and so
744 performance is tuned for it.
746 This library in particular does its absolute best to avoid putting
747 B<any> drain at all upon your code's performance. In fact, by itself
748 it does nothing to affect your existing code. So you only pay for what
751 =head2 About Metaclass compatibility
753 This module makes sure that all metaclasses created are both upwards
754 and downwards compatible. The topic of metaclass compatibility is
755 highly esoteric and is something only encountered when doing deep and
756 involved metaclass hacking. There are two basic kinds of metaclass
757 incompatibility; upwards and downwards.
759 Upwards metaclass compatibility means that the metaclass of a
760 given class is either the same as (or a subclass of) all of the
763 Downward metaclass compatibility means that the metaclasses of a
764 given class's ancestors are all either the same as (or a subclass
767 Here is a diagram showing a set of two classes (C<A> and C<B>) and
768 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
769 metaclass compatibility both upwards and downwards.
771 +---------+ +---------+
772 | Meta::A |<----| Meta::B | <....... (instance of )
773 +---------+ +---------+ <------- (inherits from)
776 +---------+ +---------+
778 +---------+ +---------+
780 As I said this is a highly esoteric topic and one you will only run
781 into if you do a lot of subclassing of L<Class::MOP::Class>. If you
782 are interested in why this is an issue see the paper I<Uniform and
783 safe metaclass composition> linked to in the L<SEE ALSO> section of
786 =head2 Using custom metaclasses
788 Always use the L<metaclass> pragma when using a custom metaclass, this
789 will ensure the proper initialization order and not accidentally
790 create an incorrect type of metaclass for you. This is a very rare
791 problem, and one which can only occur if you are doing deep metaclass
792 programming. So in other words, don't worry about it.
794 Note that if you're using L<Moose> we encourage you to I<not> use
795 L<metaclass> pragma, and instead use L<Moose::Util::MetaRole> to apply
796 roles to a class's metaclasses. This topic is covered at length in
797 various L<Moose::Cookbook> recipes.
801 The meta-object protocol is divided into 4 main sub-protocols:
803 =head2 The Class protocol
805 This provides a means of manipulating and introspecting a Perl 5
806 class. It handles symbol table hacking for you, and provides a rich
807 set of methods that go beyond simple package introspection.
809 See L<Class::MOP::Class> for more details.
811 =head2 The Attribute protocol
813 This provides a consistent representation for an attribute of a Perl 5
814 class. Since there are so many ways to create and handle attributes in
815 Perl 5 OO, the Attribute protocol provide as much of a unified
816 approach as possible. Of course, you are always free to extend this
817 protocol by subclassing the appropriate classes.
819 See L<Class::MOP::Attribute> for more details.
821 =head2 The Method protocol
823 This provides a means of manipulating and introspecting methods in the
824 Perl 5 object system. As with attributes, there are many ways to
825 approach this topic, so we try to keep it pretty basic, while still
826 making it possible to extend the system in many ways.
828 See L<Class::MOP::Method> for more details.
830 =head2 The Instance protocol
832 This provides a layer of abstraction for creating object instances.
833 Since the other layers use this protocol, it is relatively easy to
834 change the type of your instances from the default hash reference to
835 some other type of reference. Several examples are provided in the
836 F<examples/> directory included in this distribution.
838 See L<Class::MOP::Instance> for more details.
842 Note that this module does not export any constants or functions.
848 =item I<Class::MOP::IS_RUNNING_ON_5_10>
850 We set this constant depending on what version perl we are on, this
851 allows us to take advantage of new 5.10 features and stay backwards
854 =item I<Class::MOP::HAVE_ISAREV>
856 Whether or not the L<mro> pragma provides C<get_isarev>, a much faster
857 way to get all the subclasses of a certain class.
861 =head2 Utility functions
863 Note that these are all called as B<functions, not methods>.
867 =item B<Class::MOP::load_class($class_name)>
869 This will load the specified C<$class_name>. This function can be used
870 in place of tricks like C<eval "use $module"> or using C<require>
873 =item B<Class::MOP::is_class_loaded($class_name)>
875 Returns a boolean indicating whether or not C<$class_name> has been
878 This does a basic check of the symbol table to try and determine as
879 best it can if the C<$class_name> is loaded, it is probably correct
880 about 99% of the time, but it can be fooled into reporting false
883 =item B<Class::MOP::get_code_info($code)>
885 This function returns two values, the name of the package the C<$code>
886 is from and the name of the C<$code> itself. This is used by several
887 elements of the MOP to determine where a given C<$code> reference is
890 =item B<Class::MOP::check_package_cache_flag($pkg)>
892 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
894 This will return an integer that is managed by L<Class::MOP::Class> to
895 determine if a module's symbol table has been altered.
897 In Perl 5.10 or greater, this flag is package specific. However in
898 versions prior to 5.10, this will use the C<PL_sub_generation>
899 variable which is not package specific.
901 =item B<Class::MOP::load_first_existing_class(@class_names)>
903 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
905 Given a list of class names, this function will attempt to load each
908 If it finds a class it can load, it will return that class' name. If
909 none of the classes can be loaded, it will throw an exception.
913 =head2 Metaclass cache functions
915 Class::MOP holds a cache of metaclasses. The following are functions
916 (B<not methods>) which can be used to access that cache. It is not
917 recommended that you mess with these. Bad things could happen, but if
918 you are brave and willing to risk it: go for it!
922 =item B<Class::MOP::get_all_metaclasses>
924 This will return a hash of all the metaclass instances that have
925 been cached by L<Class::MOP::Class>, keyed by the package name.
927 =item B<Class::MOP::get_all_metaclass_instances>
929 This will return a list of all the metaclass instances that have
930 been cached by L<Class::MOP::Class>.
932 =item B<Class::MOP::get_all_metaclass_names>
934 This will return a list of all the metaclass names that have
935 been cached by L<Class::MOP::Class>.
937 =item B<Class::MOP::get_metaclass_by_name($name)>
939 This will return a cached L<Class::MOP::Class> instance, or nothing
940 if no metaclass exists with that C<$name>.
942 =item B<Class::MOP::store_metaclass_by_name($name, $meta)>
944 This will store a metaclass in the cache at the supplied C<$key>.
946 =item B<Class::MOP::weaken_metaclass($name)>
948 In rare cases (e.g. anonymous metaclasses) it is desirable to
949 store a weakened reference in the metaclass cache. This
950 function will weaken the reference to the metaclass stored
953 =item B<Class::MOP::does_metaclass_exist($name)>
955 This will return true of there exists a metaclass stored in the
956 C<$name> key, and return false otherwise.
958 =item B<Class::MOP::remove_metaclass_by_name($name)>
960 This will remove the metaclass stored in the C<$name> key.
968 There are very few books out on Meta Object Protocols and Metaclasses
969 because it is such an esoteric topic. The following books are really
970 the only ones I have found. If you know of any more, B<I<please>>
971 email me and let me know, I would love to hear about them.
975 =item I<The Art of the Meta Object Protocol>
977 =item I<Advances in Object-Oriented Metalevel Architecture and Reflection>
979 =item I<Putting MetaClasses to Work>
981 =item I<Smalltalk: The Language>
989 =item "Uniform and safe metaclass composition"
991 An excellent paper by the people who brought us the original Traits paper.
992 This paper is on how Traits can be used to do safe metaclass composition,
993 and offers an excellent introduction section which delves into the topic of
994 metaclass compatibility.
996 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
998 =item "Safe Metaclass Programming"
1000 This paper seems to precede the above paper, and propose a mix-in based
1001 approach as opposed to the Traits based approach. Both papers have similar
1002 information on the metaclass compatibility problem space.
1004 L<http://citeseer.ist.psu.edu/37617.html>
1012 =item The Perl 6 MetaModel work in the Pugs project
1016 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
1018 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1028 =item CPAN Module Review of Class::MOP
1030 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1034 =head1 SIMILAR MODULES
1036 As I have said above, this module is a class-builder-builder, so it is
1037 not the same thing as modules like L<Class::Accessor> and
1038 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1039 with similar goals to this module. The one I have found which is most
1040 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1041 creates are very different from this modules.
1045 All complex software has bugs lurking in it, and this module is no
1046 exception. If you find a bug please either email me, or add the bug
1049 =head1 ACKNOWLEDGEMENTS
1055 Thanks to Rob for actually getting the development of this module kick-started.
1061 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1063 B<with contributions from:>
1065 Brandon (blblack) Black
1067 Florian (rafl) Ragwitz
1069 Guillermo (groditi) Roditi
1073 Rob (robkinyon) Kinyon
1075 Yuval (nothingmuch) Kogman
1077 Scott (konobi) McWhirter
1079 =head1 COPYRIGHT AND LICENSE
1081 Copyright 2006-2009 by Infinity Interactive, Inc.
1083 L<http://www.iinteractive.com>
1085 This library is free software; you can redistribute it and/or modify
1086 it under the same terms as Perl itself.