12 use Scalar::Util 'weaken';
14 use Sub::Identify 'get_code_info';
20 Sub::Name->import(qw(subname));
22 } or eval 'sub subname { $_[1] }';
24 # this is either part of core or set up appropriately by MRO::Compat
25 *check_package_cache_flag = \&mro::get_pkg_gen;
28 require Devel::GlobalDestruction;
29 Devel::GlobalDestruction->import("in_global_destruction");
31 } or *in_global_destruction = sub () { !1 };
35 use Class::MOP::Class;
36 use Class::MOP::Attribute;
37 use Class::MOP::Method;
39 use Class::MOP::Immutable;
42 *IS_RUNNING_ON_5_10 = ($] < 5.009_005)
46 *HAVE_ISAREV = defined(&mro::get_isarev)
51 our $VERSION = '0.64_06';
52 our $XS_VERSION = $VERSION;
53 $VERSION = eval $VERSION;
54 our $AUTHORITY = 'cpan:STEVAN';
56 # after that everything is loaded, if we're allowed try to load faster XS
57 # versions of various things
58 unless ($ENV{CLASS_MOP_NO_XS}) {
63 __PACKAGE__->XSLoader::load($XS_VERSION);
68 die $e if $e && $e !~ /object version|loadable object/;
72 # Metaclasses are singletons, so we cache them here.
73 # there is no need to worry about destruction though
74 # because they should die only when the program dies.
75 # After all, do package definitions even get reaped?
78 # means of accessing all the metaclasses that have
79 # been initialized thus far (for mugwumps obj browser)
80 sub get_all_metaclasses { %METAS }
81 sub get_all_metaclass_instances { values %METAS }
82 sub get_all_metaclass_names { keys %METAS }
83 sub get_metaclass_by_name { $METAS{$_[0]} }
84 sub store_metaclass_by_name { $METAS{$_[0]} = $_[1] }
85 sub weaken_metaclass { weaken($METAS{$_[0]}) }
86 sub does_metaclass_exist { exists $METAS{$_[0]} && defined $METAS{$_[0]} }
87 sub remove_metaclass_by_name { $METAS{$_[0]} = undef }
90 # We only cache metaclasses, meaning instances of
91 # Class::MOP::Class. We do not cache instance of
92 # Class::MOP::Package or Class::MOP::Module. Mostly
93 # because I don't yet see a good reason to do so.
102 || $class !~ /^\w+(?::\w+)*$/ ) {
103 my $display = defined($class) ? $class : 'undef';
104 confess "Invalid class name ($display)";
107 # if the class is not already loaded in the symbol table..
108 unless (is_class_loaded($class)) {
110 my $e = do { local $@; eval "require $class"; $@ };
111 confess "Could not load class ($class) because : $e" if $e;
114 # initialize a metaclass if necessary
115 unless (does_metaclass_exist($class)) {
116 my $e = do { local $@; eval { Class::MOP::Class->initialize($class) }; $@ };
117 confess "Could not initialize class ($class) because : $e" if $e;
120 return get_metaclass_by_name($class) if defined wantarray;
123 sub is_class_loaded {
126 return 0 if ref($class) || !defined($class) || !length($class);
128 # walk the symbol table tree to avoid autovififying
129 # \*{${main::}{"Foo::"}} == \*main::Foo::
132 foreach my $part (split('::', $class)) {
133 return 0 unless exists ${$$pack}{"${part}::"};
134 $pack = \*{${$$pack}{"${part}::"}};
137 # check for $VERSION or @ISA
138 return 1 if exists ${$$pack}{VERSION}
139 && defined *{${$$pack}{VERSION}}{SCALAR};
140 return 1 if exists ${$$pack}{ISA}
141 && defined *{${$$pack}{ISA}}{ARRAY};
143 # check for any method
144 foreach ( keys %{$$pack} ) {
145 next if substr($_, -2, 2) eq '::';
147 my $glob = ${$$pack}{$_} || next;
150 if ( IS_RUNNING_ON_5_10 ) {
151 return 1 if ref $glob eq 'SCALAR';
154 return 1 if defined *{$glob}{CODE};
162 ## ----------------------------------------------------------------------------
163 ## Setting up our environment ...
164 ## ----------------------------------------------------------------------------
165 ## Class::MOP needs to have a few things in the global perl environment so
166 ## that it can operate effectively. Those things are done here.
167 ## ----------------------------------------------------------------------------
169 # ... nothing yet actually ;)
171 ## ----------------------------------------------------------------------------
173 ## ----------------------------------------------------------------------------
174 ## The code below here is to bootstrap our MOP with itself. This is also
175 ## sometimes called "tying the knot". By doing this, we make it much easier
176 ## to extend the MOP through subclassing and such since now you can use the
177 ## MOP itself to extend itself.
179 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
180 ## ----------------------------------------------------------------------------
182 # We need to add in the meta-attributes here so that
183 # any subclass of Class::MOP::* will be able to
184 # inherit them using &construct_instance
186 ## --------------------------------------------------------
187 ## Class::MOP::Package
189 Class::MOP::Package->meta->add_attribute(
190 Class::MOP::Attribute->new('package' => (
192 # NOTE: we need to do this in order
193 # for the instance meta-object to
194 # not fall into meta-circular death
196 # we just alias the original method
197 # rather than re-produce it here
198 'name' => \&Class::MOP::Package::name
203 Class::MOP::Package->meta->add_attribute(
204 Class::MOP::Attribute->new('namespace' => (
207 # we just alias the original method
208 # rather than re-produce it here
209 'namespace' => \&Class::MOP::Package::namespace
212 default => sub { \undef }
216 ## --------------------------------------------------------
217 ## Class::MOP::Module
220 # yeah this is kind of stretching things a bit,
221 # but truthfully the version should be an attribute
222 # of the Module, the weirdness comes from having to
223 # stick to Perl 5 convention and store it in the
224 # $VERSION package variable. Basically if you just
225 # squint at it, it will look how you want it to look.
226 # Either as a package variable, or as a attribute of
227 # the metaclass, isn't abstraction great :)
229 Class::MOP::Module->meta->add_attribute(
230 Class::MOP::Attribute->new('version' => (
233 # we just alias the original method
234 # rather than re-produce it here
235 'version' => \&Class::MOP::Module::version
238 default => sub { \undef }
243 # By following the same conventions as version here,
244 # we are opening up the possibility that people can
245 # use the $AUTHORITY in non-Class::MOP modules as
248 Class::MOP::Module->meta->add_attribute(
249 Class::MOP::Attribute->new('authority' => (
252 # we just alias the original method
253 # rather than re-produce it here
254 'authority' => \&Class::MOP::Module::authority
257 default => sub { \undef }
261 ## --------------------------------------------------------
264 Class::MOP::Class->meta->add_attribute(
265 Class::MOP::Attribute->new('attributes' => (
267 # NOTE: we need to do this in order
268 # for the instance meta-object to
269 # not fall into meta-circular death
271 # we just alias the original method
272 # rather than re-produce it here
273 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
275 default => sub { {} }
279 Class::MOP::Class->meta->add_attribute(
280 Class::MOP::Attribute->new('methods' => (
283 # we just alias the original method
284 # rather than re-produce it here
285 'get_method_map' => \&Class::MOP::Class::get_method_map
287 default => sub { {} }
291 Class::MOP::Class->meta->add_attribute(
292 Class::MOP::Attribute->new('superclasses' => (
295 # we just alias the original method
296 # rather than re-produce it here
297 'superclasses' => \&Class::MOP::Class::superclasses
300 default => sub { \undef }
304 Class::MOP::Class->meta->add_attribute(
305 Class::MOP::Attribute->new('attribute_metaclass' => (
308 # we just alias the original method
309 # rather than re-produce it here
310 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
312 default => 'Class::MOP::Attribute',
316 Class::MOP::Class->meta->add_attribute(
317 Class::MOP::Attribute->new('method_metaclass' => (
320 # we just alias the original method
321 # rather than re-produce it here
322 'method_metaclass' => \&Class::MOP::Class::method_metaclass
324 default => 'Class::MOP::Method',
328 Class::MOP::Class->meta->add_attribute(
329 Class::MOP::Attribute->new('instance_metaclass' => (
331 # NOTE: we need to do this in order
332 # for the instance meta-object to
333 # not fall into meta-circular death
335 # we just alias the original method
336 # rather than re-produce it here
337 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
339 default => 'Class::MOP::Instance',
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('writer' => (
403 reader => { 'writer' => \&Class::MOP::Attribute::writer },
404 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
408 Class::MOP::Attribute->meta->add_attribute(
409 Class::MOP::Attribute->new('predicate' => (
410 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
411 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
415 Class::MOP::Attribute->meta->add_attribute(
416 Class::MOP::Attribute->new('clearer' => (
417 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
418 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
422 Class::MOP::Attribute->meta->add_attribute(
423 Class::MOP::Attribute->new('builder' => (
424 reader => { 'builder' => \&Class::MOP::Attribute::builder },
425 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
429 Class::MOP::Attribute->meta->add_attribute(
430 Class::MOP::Attribute->new('init_arg' => (
431 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
432 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
436 Class::MOP::Attribute->meta->add_attribute(
437 Class::MOP::Attribute->new('default' => (
438 # default has a custom 'reader' method ...
439 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
443 Class::MOP::Attribute->meta->add_attribute(
444 Class::MOP::Attribute->new('associated_methods' => (
445 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
446 default => sub { [] }
450 Class::MOP::Attribute->meta->add_method('clone' => sub {
452 $self->meta->clone_object($self, @_);
455 ## --------------------------------------------------------
456 ## Class::MOP::Method
457 Class::MOP::Method->meta->add_attribute(
458 Class::MOP::Attribute->new('body' => (
459 reader => { 'body' => \&Class::MOP::Method::body },
463 Class::MOP::Method->meta->add_attribute(
464 Class::MOP::Attribute->new('associated_metaclass' => (
465 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
469 Class::MOP::Method->meta->add_attribute(
470 Class::MOP::Attribute->new('package_name' => (
471 reader => { 'package_name' => \&Class::MOP::Method::package_name },
475 Class::MOP::Method->meta->add_attribute(
476 Class::MOP::Attribute->new('name' => (
477 reader => { 'name' => \&Class::MOP::Method::name },
481 Class::MOP::Method->meta->add_method('clone' => sub {
483 $self->meta->clone_object($self, @_);
486 ## --------------------------------------------------------
487 ## Class::MOP::Method::Wrapped
490 # the way this item is initialized, this
491 # really does not follow the standard
492 # practices of attributes, but we put
493 # it here for completeness
494 Class::MOP::Method::Wrapped->meta->add_attribute(
495 Class::MOP::Attribute->new('modifier_table')
498 ## --------------------------------------------------------
499 ## Class::MOP::Method::Generated
501 Class::MOP::Method::Generated->meta->add_attribute(
502 Class::MOP::Attribute->new('is_inline' => (
503 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
508 ## --------------------------------------------------------
509 ## Class::MOP::Method::Accessor
511 Class::MOP::Method::Accessor->meta->add_attribute(
512 Class::MOP::Attribute->new('attribute' => (
514 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
519 Class::MOP::Method::Accessor->meta->add_attribute(
520 Class::MOP::Attribute->new('accessor_type' => (
521 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
525 ## --------------------------------------------------------
526 ## Class::MOP::Method::Constructor
528 Class::MOP::Method::Constructor->meta->add_attribute(
529 Class::MOP::Attribute->new('options' => (
531 'options' => \&Class::MOP::Method::Constructor::options
533 default => sub { +{} }
537 Class::MOP::Method::Constructor->meta->add_attribute(
538 Class::MOP::Attribute->new('associated_metaclass' => (
539 init_arg => "metaclass", # FIXME alias and rename
541 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
546 ## --------------------------------------------------------
547 ## Class::MOP::Instance
550 # these don't yet do much of anything, but are just
551 # included for completeness
553 Class::MOP::Instance->meta->add_attribute(
554 Class::MOP::Attribute->new('associated_metaclass',
555 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
559 Class::MOP::Instance->meta->add_attribute(
560 Class::MOP::Attribute->new('_class_name',
562 reader => { _class_name => \&Class::MOP::Instance::_class_name },
563 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
564 #default => sub { $_[0]->associated_metaclass->name },
568 Class::MOP::Instance->meta->add_attribute(
569 Class::MOP::Attribute->new('attributes',
570 reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
574 Class::MOP::Instance->meta->add_attribute(
575 Class::MOP::Attribute->new('slots',
576 reader => { slots => \&Class::MOP::Instance::slots },
580 Class::MOP::Instance->meta->add_attribute(
581 Class::MOP::Attribute->new('slot_hash',
582 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
587 # we need the meta instance of the meta instance to be created now, in order
588 # for the constructor to be able to use it
589 Class::MOP::Instance->meta->get_meta_instance;
591 # pretend the add_method never happenned. it hasn't yet affected anything
592 undef Class::MOP::Instance->meta->{_package_cache_flag};
594 ## --------------------------------------------------------
595 ## Now close all the Class::MOP::* classes
598 # we don't need to inline the
599 # constructors or the accessors
600 # this only lengthens the compile
601 # time of the MOP, and gives us
602 # no actual benefits.
604 $_->meta->make_immutable(
605 inline_constructor => 1,
606 replace_constructor => 1,
607 constructor_name => "_new",
608 inline_accessors => 0,
614 Class::MOP::Attribute
620 Class::MOP::Method::Generated
622 Class::MOP::Method::Accessor
623 Class::MOP::Method::Constructor
624 Class::MOP::Method::Wrapped
635 Class::MOP - A Meta Object Protocol for Perl 5
639 This module is a fully functioning meta object protocol for the
640 Perl 5 object system. It makes no attempt to change the behavior or
641 characteristics of the Perl 5 object system, only to create a
642 protocol for its manipulation and introspection.
644 That said, it does attempt to create the tools for building a rich
645 set of extensions to the Perl 5 object system. Every attempt has been
646 made for these tools to keep to the spirit of the Perl 5 object
647 system that we all know and love.
649 This documentation is admittedly sparse on details, as time permits
650 I will try to improve them. For now, I suggest looking at the items
651 listed in the L<SEE ALSO> section for more information. In particular
652 the book "The Art of the Meta Object Protocol" was very influential
653 in the development of this system.
655 =head2 What is a Meta Object Protocol?
657 A meta object protocol is an API to an object system.
659 To be more specific, it is a set of abstractions of the components of
660 an object system (typically things like; classes, object, methods,
661 object attributes, etc.). These abstractions can then be used to both
662 inspect and manipulate the object system which they describe.
664 It can be said that there are two MOPs for any object system; the
665 implicit MOP, and the explicit MOP. The implicit MOP handles things
666 like method dispatch or inheritance, which happen automatically as
667 part of how the object system works. The explicit MOP typically
668 handles the introspection/reflection features of the object system.
669 All object systems have implicit MOPs, without one, they would not
670 work. Explict MOPs however as less common, and depending on the
671 language can vary from restrictive (Reflection in Java or C#) to
672 wide open (CLOS is a perfect example).
674 =head2 Yet Another Class Builder!! Why?
676 This is B<not> a class builder so much as it is a I<class builder
677 B<builder>>. My intent is that an end user does not use this module
678 directly, but instead this module is used by module authors to
679 build extensions and features onto the Perl 5 object system.
681 =head2 Who is this module for?
683 This module is specifically for anyone who has ever created or
684 wanted to create a module for the Class:: namespace. The tools which
685 this module will provide will hopefully make it easier to do more
686 complex things with Perl 5 classes by removing such barriers as
687 the need to hack the symbol tables, or understand the fine details
690 =head2 What changes do I have to make to use this module?
692 This module was designed to be as unintrusive as possible. Many of
693 its features are accessible without B<any> change to your existsing
694 code at all. It is meant to be a compliment to your existing code and
695 not an intrusion on your code base. Unlike many other B<Class::>
696 modules, this module B<does not> require you subclass it, or even that
697 you C<use> it in within your module's package.
699 The only features which requires additions to your code are the
700 attribute handling and instance construction features, and these are
701 both completely optional features. The only reason for this is because
702 Perl 5's object system does not actually have these features built
703 in. More information about this feature can be found below.
705 =head2 A Note about Performance?
707 It is a common misconception that explict MOPs are performance drains.
708 But this is not a universal truth at all, it is an side-effect of
709 specific implementations. For instance, using Java reflection is much
710 slower because the JVM cannot take advantage of any compiler
711 optimizations, and the JVM has to deal with much more runtime type
712 information as well. Reflection in C# is marginally better as it was
713 designed into the language and runtime (the CLR). In contrast, CLOS
714 (the Common Lisp Object System) was built to support an explicit MOP,
715 and so performance is tuned for it.
717 This library in particular does it's absolute best to avoid putting
718 B<any> drain at all upon your code's performance. In fact, by itself
719 it does nothing to affect your existing code. So you only pay for
720 what you actually use.
722 =head2 About Metaclass compatibility
724 This module makes sure that all metaclasses created are both upwards
725 and downwards compatible. The topic of metaclass compatibility is
726 highly esoteric and is something only encountered when doing deep and
727 involved metaclass hacking. There are two basic kinds of metaclass
728 incompatibility; upwards and downwards.
730 Upwards metaclass compatibility means that the metaclass of a
731 given class is either the same as (or a subclass of) all of the
734 Downward metaclass compatibility means that the metaclasses of a
735 given class's anscestors are all either the same as (or a subclass
738 Here is a diagram showing a set of two classes (C<A> and C<B>) and
739 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
740 metaclass compatibility both upwards and downwards.
742 +---------+ +---------+
743 | Meta::A |<----| Meta::B | <....... (instance of )
744 +---------+ +---------+ <------- (inherits from)
747 +---------+ +---------+
749 +---------+ +---------+
751 As I said this is a highly esoteric topic and one you will only run
752 into if you do a lot of subclassing of B<Class::MOP::Class>. If you
753 are interested in why this is an issue see the paper
754 I<Uniform and safe metaclass composition> linked to in the
755 L<SEE ALSO> section of this document.
757 =head2 Using custom metaclasses
759 Always use the metaclass pragma when using a custom metaclass, this
760 will ensure the proper initialization order and not accidentely
761 create an incorrect type of metaclass for you. This is a very rare
762 problem, and one which can only occur if you are doing deep metaclass
763 programming. So in other words, don't worry about it.
767 The protocol is divided into 4 main sub-protocols:
771 =item The Class protocol
773 This provides a means of manipulating and introspecting a Perl 5
774 class. It handles all of symbol table hacking for you, and provides
775 a rich set of methods that go beyond simple package introspection.
777 See L<Class::MOP::Class> for more details.
779 =item The Attribute protocol
781 This provides a consistent represenation for an attribute of a
782 Perl 5 class. Since there are so many ways to create and handle
783 attributes in Perl 5 OO, this attempts to provide as much of a
784 unified approach as possible, while giving the freedom and
785 flexibility to subclass for specialization.
787 See L<Class::MOP::Attribute> for more details.
789 =item The Method protocol
791 This provides a means of manipulating and introspecting methods in
792 the Perl 5 object system. As with attributes, there are many ways to
793 approach this topic, so we try to keep it pretty basic, while still
794 making it possible to extend the system in many ways.
796 See L<Class::MOP::Method> for more details.
798 =item The Instance protocol
800 This provides a layer of abstraction for creating object instances.
801 Since the other layers use this protocol, it is relatively easy to
802 change the type of your instances from the default HASH ref to other
803 types of references. Several examples are provided in the F<examples/>
804 directory included in this distribution.
806 See L<Class::MOP::Instance> for more details.
816 =item I<IS_RUNNING_ON_5_10>
818 We set this constant depending on what version perl we are on, this
819 allows us to take advantage of new 5.10 features and stay backwards
824 Whether or not C<mro> provides C<get_isarev>, a much faster way to get all the
825 subclasses of a certain class.
829 =head2 Utility functions
833 =item B<load_class ($class_name)>
835 This will load a given C<$class_name> and if it does not have an
836 already initialized metaclass, then it will intialize one for it.
837 This function can be used in place of tricks like
838 C<eval "use $module"> or using C<require>.
840 =item B<is_class_loaded ($class_name)>
842 This will return a boolean depending on if the C<$class_name> has
845 NOTE: This does a basic check of the symbol table to try and
846 determine as best it can if the C<$class_name> is loaded, it
847 is probably correct about 99% of the time.
849 =item B<check_package_cache_flag ($pkg)>
851 This will return an integer that is managed by C<Class::MOP::Class>
852 to determine if a module's symbol table has been altered.
854 In Perl 5.10 or greater, this flag is package specific. However in
855 versions prior to 5.10, this will use the C<PL_sub_generation> variable
856 which is not package specific.
858 =item B<get_code_info ($code)>
860 This function returns two values, the name of the package the C<$code>
861 is from and the name of the C<$code> itself. This is used by several
862 elements of the MOP to detemine where a given C<$code> reference is from.
864 =item B<subname ($name, $code)>
866 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
868 If possible, we will load the L<Sub::Name> module and this will function
869 as C<Sub::Name::subname> does, otherwise it will just return the C<$code>
872 =item B<in_global_destruction>
874 If L<Devel::GlobalDestruction> is available, this returns true under global
877 Otherwise it's a constant returning false.
881 =head2 Metaclass cache functions
883 Class::MOP holds a cache of metaclasses, the following are functions
884 (B<not methods>) which can be used to access that cache. It is not
885 recommended that you mess with this, bad things could happen. But if
886 you are brave and willing to risk it, go for it.
890 =item B<get_all_metaclasses>
892 This will return an hash of all the metaclass instances that have
893 been cached by B<Class::MOP::Class> keyed by the package name.
895 =item B<get_all_metaclass_instances>
897 This will return an array of all the metaclass instances that have
898 been cached by B<Class::MOP::Class>.
900 =item B<get_all_metaclass_names>
902 This will return an array of all the metaclass names that have
903 been cached by B<Class::MOP::Class>.
905 =item B<get_metaclass_by_name ($name)>
907 This will return a cached B<Class::MOP::Class> instance of nothing
908 if no metaclass exist by that C<$name>.
910 =item B<store_metaclass_by_name ($name, $meta)>
912 This will store a metaclass in the cache at the supplied C<$key>.
914 =item B<weaken_metaclass ($name)>
916 In rare cases it is desireable to store a weakened reference in
917 the metaclass cache. This function will weaken the reference to
918 the metaclass stored in C<$name>.
920 =item B<does_metaclass_exist ($name)>
922 This will return true of there exists a metaclass stored in the
923 C<$name> key and return false otherwise.
925 =item B<remove_metaclass_by_name ($name)>
927 This will remove a the metaclass stored in the C<$name> key.
935 There are very few books out on Meta Object Protocols and Metaclasses
936 because it is such an esoteric topic. The following books are really
937 the only ones I have found. If you know of any more, B<I<please>>
938 email me and let me know, I would love to hear about them.
942 =item "The Art of the Meta Object Protocol"
944 =item "Advances in Object-Oriented Metalevel Architecture and Reflection"
946 =item "Putting MetaClasses to Work"
948 =item "Smalltalk: The Language"
956 =item Uniform and safe metaclass composition
958 An excellent paper by the people who brought us the original Traits paper.
959 This paper is on how Traits can be used to do safe metaclass composition,
960 and offers an excellent introduction section which delves into the topic of
961 metaclass compatibility.
963 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
965 =item Safe Metaclass Programming
967 This paper seems to precede the above paper, and propose a mix-in based
968 approach as opposed to the Traits based approach. Both papers have similar
969 information on the metaclass compatibility problem space.
971 L<http://citeseer.ist.psu.edu/37617.html>
979 =item The Perl 6 MetaModel work in the Pugs project
983 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
985 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
995 =item CPAN Module Review of Class::MOP
997 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1001 =head1 SIMILAR MODULES
1003 As I have said above, this module is a class-builder-builder, so it is
1004 not the same thing as modules like L<Class::Accessor> and
1005 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1006 with similar goals to this module. The one I have found which is most
1007 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1008 creates are very different from this modules.
1012 All complex software has bugs lurking in it, and this module is no
1013 exception. If you find a bug please either email me, or add the bug
1016 =head1 ACKNOWLEDGEMENTS
1022 Thanks to Rob for actually getting the development of this module kick-started.
1028 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1030 B<with contributions from:>
1032 Brandon (blblack) Black
1034 Guillermo (groditi) Roditi
1038 Rob (robkinyon) Kinyon
1040 Yuval (nothingmuch) Kogman
1042 Scott (konobi) McWhirter
1044 =head1 COPYRIGHT AND LICENSE
1046 Copyright 2006-2008 by Infinity Interactive, Inc.
1048 L<http://www.iinteractive.com>
1050 This library is free software; you can redistribute it and/or modify
1051 it under the same terms as Perl itself.