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';
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',
333 # we don't actually need to tie the knot with
334 # Class::MOP::Class here, it is actually handled
335 # within Class::MOP::Class itself in the
336 # construct_class_instance method.
338 ## --------------------------------------------------------
339 ## Class::MOP::Attribute
341 Class::MOP::Attribute->meta->add_attribute(
342 Class::MOP::Attribute->new('name' => (
344 # NOTE: we need to do this in order
345 # for the instance meta-object to
346 # not fall into meta-circular death
348 # we just alias the original method
349 # rather than re-produce it here
350 'name' => \&Class::MOP::Attribute::name
355 Class::MOP::Attribute->meta->add_attribute(
356 Class::MOP::Attribute->new('associated_class' => (
358 # NOTE: we need to do this in order
359 # for the instance meta-object to
360 # not fall into meta-circular death
362 # we just alias the original method
363 # rather than re-produce it here
364 'associated_class' => \&Class::MOP::Attribute::associated_class
369 Class::MOP::Attribute->meta->add_attribute(
370 Class::MOP::Attribute->new('accessor' => (
371 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
372 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
376 Class::MOP::Attribute->meta->add_attribute(
377 Class::MOP::Attribute->new('reader' => (
378 reader => { 'reader' => \&Class::MOP::Attribute::reader },
379 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
383 Class::MOP::Attribute->meta->add_attribute(
384 Class::MOP::Attribute->new('initializer' => (
385 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
386 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
390 Class::MOP::Attribute->meta->add_attribute(
391 Class::MOP::Attribute->new('definition_context' => (
392 reader => { 'definition_context' => \&Class::MOP::Attribute::definition_context },
396 Class::MOP::Attribute->meta->add_attribute(
397 Class::MOP::Attribute->new('writer' => (
398 reader => { 'writer' => \&Class::MOP::Attribute::writer },
399 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
403 Class::MOP::Attribute->meta->add_attribute(
404 Class::MOP::Attribute->new('predicate' => (
405 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
406 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
410 Class::MOP::Attribute->meta->add_attribute(
411 Class::MOP::Attribute->new('clearer' => (
412 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
413 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
417 Class::MOP::Attribute->meta->add_attribute(
418 Class::MOP::Attribute->new('builder' => (
419 reader => { 'builder' => \&Class::MOP::Attribute::builder },
420 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
424 Class::MOP::Attribute->meta->add_attribute(
425 Class::MOP::Attribute->new('init_arg' => (
426 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
427 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
431 Class::MOP::Attribute->meta->add_attribute(
432 Class::MOP::Attribute->new('default' => (
433 # default has a custom 'reader' method ...
434 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
438 Class::MOP::Attribute->meta->add_attribute(
439 Class::MOP::Attribute->new('associated_methods' => (
440 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
441 default => sub { [] }
445 Class::MOP::Attribute->meta->add_method('clone' => sub {
447 $self->meta->clone_object($self, @_);
450 ## --------------------------------------------------------
451 ## Class::MOP::Method
452 Class::MOP::Method->meta->add_attribute(
453 Class::MOP::Attribute->new('body' => (
454 reader => { 'body' => \&Class::MOP::Method::body },
458 Class::MOP::Method->meta->add_attribute(
459 Class::MOP::Attribute->new('associated_metaclass' => (
460 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
464 Class::MOP::Method->meta->add_attribute(
465 Class::MOP::Attribute->new('package_name' => (
466 reader => { 'package_name' => \&Class::MOP::Method::package_name },
470 Class::MOP::Method->meta->add_attribute(
471 Class::MOP::Attribute->new('name' => (
472 reader => { 'name' => \&Class::MOP::Method::name },
476 Class::MOP::Method->meta->add_attribute(
477 Class::MOP::Attribute->new('original_method' => (
478 reader => { 'original_method' => \&Class::MOP::Method::original_method },
479 writer => { '_set_original_method' => \&Class::MOP::Method::_set_original_method },
483 Class::MOP::Method->meta->add_method('clone' => sub {
485 my $clone = $self->meta->clone_object($self, @_);
486 $clone->_set_original_method($self);
490 ## --------------------------------------------------------
491 ## Class::MOP::Method::Wrapped
494 # the way this item is initialized, this
495 # really does not follow the standard
496 # practices of attributes, but we put
497 # it here for completeness
498 Class::MOP::Method::Wrapped->meta->add_attribute(
499 Class::MOP::Attribute->new('modifier_table')
502 ## --------------------------------------------------------
503 ## Class::MOP::Method::Generated
505 Class::MOP::Method::Generated->meta->add_attribute(
506 Class::MOP::Attribute->new('is_inline' => (
507 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
512 Class::MOP::Method::Generated->meta->add_attribute(
513 Class::MOP::Attribute->new('definition_context' => (
514 reader => { 'definition_context' => \&Class::MOP::Method::Generated::definition_context },
518 ## --------------------------------------------------------
519 ## Class::MOP::Method::Accessor
521 Class::MOP::Method::Accessor->meta->add_attribute(
522 Class::MOP::Attribute->new('attribute' => (
524 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
529 Class::MOP::Method::Accessor->meta->add_attribute(
530 Class::MOP::Attribute->new('accessor_type' => (
531 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
535 ## --------------------------------------------------------
536 ## Class::MOP::Method::Constructor
538 Class::MOP::Method::Constructor->meta->add_attribute(
539 Class::MOP::Attribute->new('options' => (
541 'options' => \&Class::MOP::Method::Constructor::options
543 default => sub { +{} }
547 Class::MOP::Method::Constructor->meta->add_attribute(
548 Class::MOP::Attribute->new('associated_metaclass' => (
549 init_arg => "metaclass", # FIXME alias and rename
551 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
556 ## --------------------------------------------------------
557 ## Class::MOP::Instance
560 # these don't yet do much of anything, but are just
561 # included for completeness
563 Class::MOP::Instance->meta->add_attribute(
564 Class::MOP::Attribute->new('associated_metaclass',
565 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
569 Class::MOP::Instance->meta->add_attribute(
570 Class::MOP::Attribute->new('_class_name',
572 reader => { _class_name => \&Class::MOP::Instance::_class_name },
573 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
574 #default => sub { $_[0]->associated_metaclass->name },
578 Class::MOP::Instance->meta->add_attribute(
579 Class::MOP::Attribute->new('attributes',
580 reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
584 Class::MOP::Instance->meta->add_attribute(
585 Class::MOP::Attribute->new('slots',
586 reader => { slots => \&Class::MOP::Instance::slots },
590 Class::MOP::Instance->meta->add_attribute(
591 Class::MOP::Attribute->new('slot_hash',
592 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
597 # we need the meta instance of the meta instance to be created now, in order
598 # for the constructor to be able to use it
599 Class::MOP::Instance->meta->get_meta_instance;
601 # pretend the add_method never happenned. it hasn't yet affected anything
602 undef Class::MOP::Instance->meta->{_package_cache_flag};
604 ## --------------------------------------------------------
605 ## Now close all the Class::MOP::* classes
607 # NOTE: we don't need to inline the the accessors this only lengthens
608 # the compile time of the MOP, and gives us no actual benefits.
610 $_->meta->make_immutable(
611 inline_constructor => 1,
612 replace_constructor => 1,
613 constructor_name => "_new",
614 inline_accessors => 0,
620 Class::MOP::Attribute
626 Class::MOP::Method::Generated
628 Class::MOP::Method::Accessor
629 Class::MOP::Method::Constructor
630 Class::MOP::Method::Wrapped
641 Class::MOP - A Meta Object Protocol for Perl 5
645 This module is a fully functioning meta object protocol for the
646 Perl 5 object system. It makes no attempt to change the behavior or
647 characteristics of the Perl 5 object system, only to create a
648 protocol for its manipulation and introspection.
650 That said, it does attempt to create the tools for building a rich
651 set of extensions to the Perl 5 object system. Every attempt has been
652 made for these tools to keep to the spirit of the Perl 5 object
653 system that we all know and love.
655 This documentation is admittedly sparse on details, as time permits
656 I will try to improve them. For now, I suggest looking at the items
657 listed in the L<SEE ALSO> section for more information. In particular
658 the book "The Art of the Meta Object Protocol" was very influential
659 in the development of this system.
661 =head2 What is a Meta Object Protocol?
663 A meta object protocol is an API to an object system.
665 To be more specific, it is a set of abstractions of the components of
666 an object system (typically things like; classes, object, methods,
667 object attributes, etc.). These abstractions can then be used to both
668 inspect and manipulate the object system which they describe.
670 It can be said that there are two MOPs for any object system; the
671 implicit MOP, and the explicit MOP. The implicit MOP handles things
672 like method dispatch or inheritance, which happen automatically as
673 part of how the object system works. The explicit MOP typically
674 handles the introspection/reflection features of the object system.
675 All object systems have implicit MOPs, without one, they would not
676 work. Explict MOPs however as less common, and depending on the
677 language can vary from restrictive (Reflection in Java or C#) to
678 wide open (CLOS is a perfect example).
680 =head2 Yet Another Class Builder!! Why?
682 This is B<not> a class builder so much as it is a I<class builder
683 B<builder>>. My intent is that an end user does not use this module
684 directly, but instead this module is used by module authors to
685 build extensions and features onto the Perl 5 object system.
687 =head2 Who is this module for?
689 This module is specifically for anyone who has ever created or
690 wanted to create a module for the Class:: namespace. The tools which
691 this module will provide will hopefully make it easier to do more
692 complex things with Perl 5 classes by removing such barriers as
693 the need to hack the symbol tables, or understand the fine details
696 =head2 What changes do I have to make to use this module?
698 This module was designed to be as unintrusive as possible. Many of
699 its features are accessible without B<any> change to your existsing
700 code at all. It is meant to be a compliment to your existing code and
701 not an intrusion on your code base. Unlike many other B<Class::>
702 modules, this module B<does not> require you subclass it, or even that
703 you C<use> it in within your module's package.
705 The only features which requires additions to your code are the
706 attribute handling and instance construction features, and these are
707 both completely optional features. The only reason for this is because
708 Perl 5's object system does not actually have these features built
709 in. More information about this feature can be found below.
711 =head2 A Note about Performance?
713 It is a common misconception that explict MOPs are performance drains.
714 But this is not a universal truth at all, it is an side-effect of
715 specific implementations. For instance, using Java reflection is much
716 slower because the JVM cannot take advantage of any compiler
717 optimizations, and the JVM has to deal with much more runtime type
718 information as well. Reflection in C# is marginally better as it was
719 designed into the language and runtime (the CLR). In contrast, CLOS
720 (the Common Lisp Object System) was built to support an explicit MOP,
721 and so performance is tuned for it.
723 This library in particular does it's absolute best to avoid putting
724 B<any> drain at all upon your code's performance. In fact, by itself
725 it does nothing to affect your existing code. So you only pay for
726 what you actually use.
728 =head2 About Metaclass compatibility
730 This module makes sure that all metaclasses created are both upwards
731 and downwards compatible. The topic of metaclass compatibility is
732 highly esoteric and is something only encountered when doing deep and
733 involved metaclass hacking. There are two basic kinds of metaclass
734 incompatibility; upwards and downwards.
736 Upwards metaclass compatibility means that the metaclass of a
737 given class is either the same as (or a subclass of) all of the
740 Downward metaclass compatibility means that the metaclasses of a
741 given class's anscestors are all either the same as (or a subclass
744 Here is a diagram showing a set of two classes (C<A> and C<B>) and
745 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
746 metaclass compatibility both upwards and downwards.
748 +---------+ +---------+
749 | Meta::A |<----| Meta::B | <....... (instance of )
750 +---------+ +---------+ <------- (inherits from)
753 +---------+ +---------+
755 +---------+ +---------+
757 As I said this is a highly esoteric topic and one you will only run
758 into if you do a lot of subclassing of B<Class::MOP::Class>. If you
759 are interested in why this is an issue see the paper
760 I<Uniform and safe metaclass composition> linked to in the
761 L<SEE ALSO> section of this document.
763 =head2 Using custom metaclasses
765 Always use the metaclass pragma when using a custom metaclass, this
766 will ensure the proper initialization order and not accidentely
767 create an incorrect type of metaclass for you. This is a very rare
768 problem, and one which can only occur if you are doing deep metaclass
769 programming. So in other words, don't worry about it.
773 The protocol is divided into 4 main sub-protocols:
777 =item The Class protocol
779 This provides a means of manipulating and introspecting a Perl 5
780 class. It handles all of symbol table hacking for you, and provides
781 a rich set of methods that go beyond simple package introspection.
783 See L<Class::MOP::Class> for more details.
785 =item The Attribute protocol
787 This provides a consistent represenation for an attribute of a
788 Perl 5 class. Since there are so many ways to create and handle
789 attributes in Perl 5 OO, this attempts to provide as much of a
790 unified approach as possible, while giving the freedom and
791 flexibility to subclass for specialization.
793 See L<Class::MOP::Attribute> for more details.
795 =item The Method protocol
797 This provides a means of manipulating and introspecting methods in
798 the Perl 5 object system. As with attributes, there are many ways to
799 approach this topic, so we try to keep it pretty basic, while still
800 making it possible to extend the system in many ways.
802 See L<Class::MOP::Method> for more details.
804 =item The Instance protocol
806 This provides a layer of abstraction for creating object instances.
807 Since the other layers use this protocol, it is relatively easy to
808 change the type of your instances from the default HASH ref to other
809 types of references. Several examples are provided in the F<examples/>
810 directory included in this distribution.
812 See L<Class::MOP::Instance> for more details.
822 =item I<IS_RUNNING_ON_5_10>
824 We set this constant depending on what version perl we are on, this
825 allows us to take advantage of new 5.10 features and stay backwards
830 Whether or not C<mro> provides C<get_isarev>, a much faster way to get all the
831 subclasses of a certain class.
835 =head2 Utility functions
837 Note that these are all called as B<functions, not methods>.
841 =item B<load_class ($class_name)>
843 This will load a given C<$class_name> and if it does not have an
844 already initialized metaclass, then it will intialize one for it.
845 This function can be used in place of tricks like
846 C<eval "use $module"> or using C<require>.
848 =item B<is_class_loaded ($class_name)>
850 This will return a boolean depending on if the C<$class_name> has
853 NOTE: This does a basic check of the symbol table to try and
854 determine as best it can if the C<$class_name> is loaded, it
855 is probably correct about 99% of the time.
857 =item B<check_package_cache_flag ($pkg)>
859 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
861 This will return an integer that is managed by C<Class::MOP::Class>
862 to determine if a module's symbol table has been altered.
864 In Perl 5.10 or greater, this flag is package specific. However in
865 versions prior to 5.10, this will use the C<PL_sub_generation> variable
866 which is not package specific.
868 =item B<get_code_info ($code)>
870 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
872 This function returns two values, the name of the package the C<$code>
873 is from and the name of the C<$code> itself. This is used by several
874 elements of the MOP to detemine where a given C<$code> reference is from.
876 =item B<subname ($name, $code)>
878 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
880 If possible, we will load the L<Sub::Name> module and this will function
881 as C<Sub::Name::subname> does, otherwise it will just return the C<$code>
884 =item B<in_global_destruction>
886 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
888 If L<Devel::GlobalDestruction> is available, this returns true under global
891 Otherwise it's a constant returning false.
893 =item B<load_first_existing_class ($class_name, [$class_name, ...])>
895 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
897 Given a list of class names, this function will attempt to load each
900 If it finds a class it can load, it will return that class' name.
901 If none of the classes can be loaded, it will throw an exception.
905 =head2 Metaclass cache functions
907 Class::MOP holds a cache of metaclasses. The following are functions
908 (B<not methods>) which can be used to access that cache. It is not
909 recommended that you mess with these. Bad things could happen, but if
910 you are brave and willing to risk it: go for it!
914 =item B<get_all_metaclasses>
916 This will return a hash of all the metaclass instances that have
917 been cached by B<Class::MOP::Class>, keyed by the package name.
919 =item B<get_all_metaclass_instances>
921 This will return a list of all the metaclass instances that have
922 been cached by B<Class::MOP::Class>.
924 =item B<get_all_metaclass_names>
926 This will return a list of all the metaclass names that have
927 been cached by B<Class::MOP::Class>.
929 =item B<get_metaclass_by_name ($name)>
931 This will return a cached B<Class::MOP::Class> instance, or nothing
932 if no metaclass exists with that C<$name>.
934 =item B<store_metaclass_by_name ($name, $meta)>
936 This will store a metaclass in the cache at the supplied C<$key>.
938 =item B<weaken_metaclass ($name)>
940 In rare cases (e.g. anonymous metaclasses) it is desirable to
941 store a weakened reference in the metaclass cache. This
942 function will weaken the reference to the metaclass stored
945 =item B<does_metaclass_exist ($name)>
947 This will return true of there exists a metaclass stored in the
948 C<$name> key, and return false otherwise.
950 =item B<remove_metaclass_by_name ($name)>
952 This will remove the metaclass stored in the C<$name> key.
960 There are very few books out on Meta Object Protocols and Metaclasses
961 because it is such an esoteric topic. The following books are really
962 the only ones I have found. If you know of any more, B<I<please>>
963 email me and let me know, I would love to hear about them.
967 =item "The Art of the Meta Object Protocol"
969 =item "Advances in Object-Oriented Metalevel Architecture and Reflection"
971 =item "Putting MetaClasses to Work"
973 =item "Smalltalk: The Language"
981 =item Uniform and safe metaclass composition
983 An excellent paper by the people who brought us the original Traits paper.
984 This paper is on how Traits can be used to do safe metaclass composition,
985 and offers an excellent introduction section which delves into the topic of
986 metaclass compatibility.
988 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
990 =item Safe Metaclass Programming
992 This paper seems to precede the above paper, and propose a mix-in based
993 approach as opposed to the Traits based approach. Both papers have similar
994 information on the metaclass compatibility problem space.
996 L<http://citeseer.ist.psu.edu/37617.html>
1004 =item The Perl 6 MetaModel work in the Pugs project
1008 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
1010 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1020 =item CPAN Module Review of Class::MOP
1022 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1026 =head1 SIMILAR MODULES
1028 As I have said above, this module is a class-builder-builder, so it is
1029 not the same thing as modules like L<Class::Accessor> and
1030 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1031 with similar goals to this module. The one I have found which is most
1032 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1033 creates are very different from this modules.
1037 All complex software has bugs lurking in it, and this module is no
1038 exception. If you find a bug please either email me, or add the bug
1041 =head1 ACKNOWLEDGEMENTS
1047 Thanks to Rob for actually getting the development of this module kick-started.
1053 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1055 B<with contributions from:>
1057 Brandon (blblack) Black
1059 Florian (rafl) Ragwitz
1061 Guillermo (groditi) Roditi
1065 Rob (robkinyon) Kinyon
1067 Yuval (nothingmuch) Kogman
1069 Scott (konobi) McWhirter
1071 =head1 COPYRIGHT AND LICENSE
1073 Copyright 2006-2008 by Infinity Interactive, Inc.
1075 L<http://www.iinteractive.com>
1077 This library is free software; you can redistribute it and/or modify
1078 it under the same terms as Perl itself.