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.
99 if (ref($class) || !defined($class) || !length($class)) {
100 my $display = defined($class) ? $class : 'undef';
101 confess "Invalid class name ($display)";
104 # if the class is not already loaded in the symbol table..
105 unless (is_class_loaded($class)) {
107 my $e = do { local $@; eval "require $class"; $@ };
108 confess "Could not load class ($class) because : $e" if $e;
111 # initialize a metaclass if necessary
112 unless (does_metaclass_exist($class)) {
113 my $e = do { local $@; eval { Class::MOP::Class->initialize($class) }; $@ };
114 confess "Could not initialize class ($class) because : $e" if $e;
117 return get_metaclass_by_name($class) if defined wantarray;
120 sub is_class_loaded {
123 return 0 if ref($class) || !defined($class) || !length($class);
125 # walk the symbol table tree to avoid autovififying
126 # \*{${main::}{"Foo::"}} == \*main::Foo::
129 foreach my $part (split('::', $class)) {
130 return 0 unless exists ${$$pack}{"${part}::"};
131 $pack = \*{${$$pack}{"${part}::"}};
134 # check for $VERSION or @ISA
135 return 1 if exists ${$$pack}{VERSION}
136 && defined *{${$$pack}{VERSION}}{SCALAR};
137 return 1 if exists ${$$pack}{ISA}
138 && defined *{${$$pack}{ISA}}{ARRAY};
140 # check for any method
141 foreach ( keys %{$$pack} ) {
142 next if substr($_, -2, 2) eq '::';
144 my $glob = ${$$pack}{$_} || next;
147 if ( IS_RUNNING_ON_5_10 ) {
148 return 1 if ref $glob eq 'SCALAR';
151 return 1 if defined *{$glob}{CODE};
159 ## ----------------------------------------------------------------------------
160 ## Setting up our environment ...
161 ## ----------------------------------------------------------------------------
162 ## Class::MOP needs to have a few things in the global perl environment so
163 ## that it can operate effectively. Those things are done here.
164 ## ----------------------------------------------------------------------------
166 # ... nothing yet actually ;)
168 ## ----------------------------------------------------------------------------
170 ## ----------------------------------------------------------------------------
171 ## The code below here is to bootstrap our MOP with itself. This is also
172 ## sometimes called "tying the knot". By doing this, we make it much easier
173 ## to extend the MOP through subclassing and such since now you can use the
174 ## MOP itself to extend itself.
176 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
177 ## ----------------------------------------------------------------------------
179 # We need to add in the meta-attributes here so that
180 # any subclass of Class::MOP::* will be able to
181 # inherit them using &construct_instance
183 ## --------------------------------------------------------
184 ## Class::MOP::Package
186 Class::MOP::Package->meta->add_attribute(
187 Class::MOP::Attribute->new('package' => (
189 # NOTE: we need to do this in order
190 # for the instance meta-object to
191 # not fall into meta-circular death
193 # we just alias the original method
194 # rather than re-produce it here
195 'name' => \&Class::MOP::Package::name
200 Class::MOP::Package->meta->add_attribute(
201 Class::MOP::Attribute->new('namespace' => (
204 # we just alias the original method
205 # rather than re-produce it here
206 'namespace' => \&Class::MOP::Package::namespace
209 default => sub { \undef }
213 ## --------------------------------------------------------
214 ## Class::MOP::Module
217 # yeah this is kind of stretching things a bit,
218 # but truthfully the version should be an attribute
219 # of the Module, the weirdness comes from having to
220 # stick to Perl 5 convention and store it in the
221 # $VERSION package variable. Basically if you just
222 # squint at it, it will look how you want it to look.
223 # Either as a package variable, or as a attribute of
224 # the metaclass, isn't abstraction great :)
226 Class::MOP::Module->meta->add_attribute(
227 Class::MOP::Attribute->new('version' => (
230 # we just alias the original method
231 # rather than re-produce it here
232 'version' => \&Class::MOP::Module::version
235 default => sub { \undef }
240 # By following the same conventions as version here,
241 # we are opening up the possibility that people can
242 # use the $AUTHORITY in non-Class::MOP modules as
245 Class::MOP::Module->meta->add_attribute(
246 Class::MOP::Attribute->new('authority' => (
249 # we just alias the original method
250 # rather than re-produce it here
251 'authority' => \&Class::MOP::Module::authority
254 default => sub { \undef }
258 ## --------------------------------------------------------
261 Class::MOP::Class->meta->add_attribute(
262 Class::MOP::Attribute->new('attributes' => (
264 # NOTE: we need to do this in order
265 # for the instance meta-object to
266 # not fall into meta-circular death
268 # we just alias the original method
269 # rather than re-produce it here
270 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
272 default => sub { {} }
276 Class::MOP::Class->meta->add_attribute(
277 Class::MOP::Attribute->new('methods' => (
280 # we just alias the original method
281 # rather than re-produce it here
282 'get_method_map' => \&Class::MOP::Class::get_method_map
284 default => sub { {} }
288 Class::MOP::Class->meta->add_attribute(
289 Class::MOP::Attribute->new('superclasses' => (
292 # we just alias the original method
293 # rather than re-produce it here
294 'superclasses' => \&Class::MOP::Class::superclasses
297 default => sub { \undef }
301 Class::MOP::Class->meta->add_attribute(
302 Class::MOP::Attribute->new('attribute_metaclass' => (
305 # we just alias the original method
306 # rather than re-produce it here
307 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
309 default => 'Class::MOP::Attribute',
313 Class::MOP::Class->meta->add_attribute(
314 Class::MOP::Attribute->new('method_metaclass' => (
317 # we just alias the original method
318 # rather than re-produce it here
319 'method_metaclass' => \&Class::MOP::Class::method_metaclass
321 default => 'Class::MOP::Method',
325 Class::MOP::Class->meta->add_attribute(
326 Class::MOP::Attribute->new('instance_metaclass' => (
328 # NOTE: we need to do this in order
329 # for the instance meta-object to
330 # not fall into meta-circular death
332 # we just alias the original method
333 # rather than re-produce it here
334 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
336 default => 'Class::MOP::Instance',
341 # we don't actually need to tie the knot with
342 # Class::MOP::Class here, it is actually handled
343 # within Class::MOP::Class itself in the
344 # construct_class_instance method.
346 ## --------------------------------------------------------
347 ## Class::MOP::Attribute
349 Class::MOP::Attribute->meta->add_attribute(
350 Class::MOP::Attribute->new('name' => (
352 # NOTE: we need to do this in order
353 # for the instance meta-object to
354 # not fall into meta-circular death
356 # we just alias the original method
357 # rather than re-produce it here
358 'name' => \&Class::MOP::Attribute::name
363 Class::MOP::Attribute->meta->add_attribute(
364 Class::MOP::Attribute->new('associated_class' => (
366 # NOTE: we need to do this in order
367 # for the instance meta-object to
368 # not fall into meta-circular death
370 # we just alias the original method
371 # rather than re-produce it here
372 'associated_class' => \&Class::MOP::Attribute::associated_class
377 Class::MOP::Attribute->meta->add_attribute(
378 Class::MOP::Attribute->new('accessor' => (
379 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
380 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
384 Class::MOP::Attribute->meta->add_attribute(
385 Class::MOP::Attribute->new('reader' => (
386 reader => { 'reader' => \&Class::MOP::Attribute::reader },
387 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
391 Class::MOP::Attribute->meta->add_attribute(
392 Class::MOP::Attribute->new('initializer' => (
393 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
394 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
398 Class::MOP::Attribute->meta->add_attribute(
399 Class::MOP::Attribute->new('writer' => (
400 reader => { 'writer' => \&Class::MOP::Attribute::writer },
401 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
405 Class::MOP::Attribute->meta->add_attribute(
406 Class::MOP::Attribute->new('predicate' => (
407 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
408 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
412 Class::MOP::Attribute->meta->add_attribute(
413 Class::MOP::Attribute->new('clearer' => (
414 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
415 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
419 Class::MOP::Attribute->meta->add_attribute(
420 Class::MOP::Attribute->new('builder' => (
421 reader => { 'builder' => \&Class::MOP::Attribute::builder },
422 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
426 Class::MOP::Attribute->meta->add_attribute(
427 Class::MOP::Attribute->new('init_arg' => (
428 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
429 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
433 Class::MOP::Attribute->meta->add_attribute(
434 Class::MOP::Attribute->new('default' => (
435 # default has a custom 'reader' method ...
436 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
440 Class::MOP::Attribute->meta->add_attribute(
441 Class::MOP::Attribute->new('associated_methods' => (
442 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
443 default => sub { [] }
447 Class::MOP::Attribute->meta->add_method('clone' => sub {
449 $self->meta->clone_object($self, @_);
452 ## --------------------------------------------------------
453 ## Class::MOP::Method
454 Class::MOP::Method->meta->add_attribute(
455 Class::MOP::Attribute->new('body' => (
456 reader => { 'body' => \&Class::MOP::Method::body },
460 Class::MOP::Method->meta->add_attribute(
461 Class::MOP::Attribute->new('associated_metaclass' => (
462 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
466 Class::MOP::Method->meta->add_attribute(
467 Class::MOP::Attribute->new('package_name' => (
468 reader => { 'package_name' => \&Class::MOP::Method::package_name },
472 Class::MOP::Method->meta->add_attribute(
473 Class::MOP::Attribute->new('name' => (
474 reader => { 'name' => \&Class::MOP::Method::name },
478 Class::MOP::Method->meta->add_method('clone' => sub {
480 $self->meta->clone_object($self, @_);
483 ## --------------------------------------------------------
484 ## Class::MOP::Method::Wrapped
487 # the way this item is initialized, this
488 # really does not follow the standard
489 # practices of attributes, but we put
490 # it here for completeness
491 Class::MOP::Method::Wrapped->meta->add_attribute(
492 Class::MOP::Attribute->new('modifier_table')
495 ## --------------------------------------------------------
496 ## Class::MOP::Method::Generated
498 Class::MOP::Method::Generated->meta->add_attribute(
499 Class::MOP::Attribute->new('is_inline' => (
500 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
505 ## --------------------------------------------------------
506 ## Class::MOP::Method::Accessor
508 Class::MOP::Method::Accessor->meta->add_attribute(
509 Class::MOP::Attribute->new('attribute' => (
511 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
516 Class::MOP::Method::Accessor->meta->add_attribute(
517 Class::MOP::Attribute->new('accessor_type' => (
518 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
522 ## --------------------------------------------------------
523 ## Class::MOP::Method::Constructor
525 Class::MOP::Method::Constructor->meta->add_attribute(
526 Class::MOP::Attribute->new('options' => (
528 'options' => \&Class::MOP::Method::Constructor::options
530 default => sub { +{} }
534 Class::MOP::Method::Constructor->meta->add_attribute(
535 Class::MOP::Attribute->new('associated_metaclass' => (
536 init_arg => "metaclass", # FIXME alias and rename
538 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
543 ## --------------------------------------------------------
544 ## Class::MOP::Instance
547 # these don't yet do much of anything, but are just
548 # included for completeness
550 Class::MOP::Instance->meta->add_attribute(
551 Class::MOP::Attribute->new('associated_metaclass',
552 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
556 Class::MOP::Instance->meta->add_attribute(
557 Class::MOP::Attribute->new('_class_name',
559 reader => { _class_name => \&Class::MOP::Instance::_class_name },
560 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
561 #default => sub { $_[0]->associated_metaclass->name },
565 Class::MOP::Instance->meta->add_attribute(
566 Class::MOP::Attribute->new('attributes',
567 reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
571 Class::MOP::Instance->meta->add_attribute(
572 Class::MOP::Attribute->new('slots',
573 reader => { slots => \&Class::MOP::Instance::slots },
577 Class::MOP::Instance->meta->add_attribute(
578 Class::MOP::Attribute->new('slot_hash',
579 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
584 # we need the meta instance of the meta instance to be created now, in order
585 # for the constructor to be able to use it
586 Class::MOP::Instance->meta->get_meta_instance;
588 # pretend the add_method never happenned. it hasn't yet affected anything
589 undef Class::MOP::Instance->meta->{_package_cache_flag};
591 ## --------------------------------------------------------
592 ## Now close all the Class::MOP::* classes
595 # we don't need to inline the
596 # constructors or the accessors
597 # this only lengthens the compile
598 # time of the MOP, and gives us
599 # no actual benefits.
601 $_->meta->make_immutable(
602 inline_constructor => 1,
603 replace_constructor => 1,
604 constructor_name => "_new",
605 inline_accessors => 0,
611 Class::MOP::Attribute
617 Class::MOP::Method::Generated
619 Class::MOP::Method::Accessor
620 Class::MOP::Method::Constructor
621 Class::MOP::Method::Wrapped
632 Class::MOP - A Meta Object Protocol for Perl 5
636 This module is a fully functioning meta object protocol for the
637 Perl 5 object system. It makes no attempt to change the behavior or
638 characteristics of the Perl 5 object system, only to create a
639 protocol for its manipulation and introspection.
641 That said, it does attempt to create the tools for building a rich
642 set of extensions to the Perl 5 object system. Every attempt has been
643 made for these tools to keep to the spirit of the Perl 5 object
644 system that we all know and love.
646 This documentation is admittedly sparse on details, as time permits
647 I will try to improve them. For now, I suggest looking at the items
648 listed in the L<SEE ALSO> section for more information. In particular
649 the book "The Art of the Meta Object Protocol" was very influential
650 in the development of this system.
652 =head2 What is a Meta Object Protocol?
654 A meta object protocol is an API to an object system.
656 To be more specific, it is a set of abstractions of the components of
657 an object system (typically things like; classes, object, methods,
658 object attributes, etc.). These abstractions can then be used to both
659 inspect and manipulate the object system which they describe.
661 It can be said that there are two MOPs for any object system; the
662 implicit MOP, and the explicit MOP. The implicit MOP handles things
663 like method dispatch or inheritance, which happen automatically as
664 part of how the object system works. The explicit MOP typically
665 handles the introspection/reflection features of the object system.
666 All object systems have implicit MOPs, without one, they would not
667 work. Explict MOPs however as less common, and depending on the
668 language can vary from restrictive (Reflection in Java or C#) to
669 wide open (CLOS is a perfect example).
671 =head2 Yet Another Class Builder!! Why?
673 This is B<not> a class builder so much as it is a I<class builder
674 B<builder>>. My intent is that an end user does not use this module
675 directly, but instead this module is used by module authors to
676 build extensions and features onto the Perl 5 object system.
678 =head2 Who is this module for?
680 This module is specifically for anyone who has ever created or
681 wanted to create a module for the Class:: namespace. The tools which
682 this module will provide will hopefully make it easier to do more
683 complex things with Perl 5 classes by removing such barriers as
684 the need to hack the symbol tables, or understand the fine details
687 =head2 What changes do I have to make to use this module?
689 This module was designed to be as unintrusive as possible. Many of
690 its features are accessible without B<any> change to your existsing
691 code at all. It is meant to be a compliment to your existing code and
692 not an intrusion on your code base. Unlike many other B<Class::>
693 modules, this module B<does not> require you subclass it, or even that
694 you C<use> it in within your module's package.
696 The only features which requires additions to your code are the
697 attribute handling and instance construction features, and these are
698 both completely optional features. The only reason for this is because
699 Perl 5's object system does not actually have these features built
700 in. More information about this feature can be found below.
702 =head2 A Note about Performance?
704 It is a common misconception that explict MOPs are performance drains.
705 But this is not a universal truth at all, it is an side-effect of
706 specific implementations. For instance, using Java reflection is much
707 slower because the JVM cannot take advantage of any compiler
708 optimizations, and the JVM has to deal with much more runtime type
709 information as well. Reflection in C# is marginally better as it was
710 designed into the language and runtime (the CLR). In contrast, CLOS
711 (the Common Lisp Object System) was built to support an explicit MOP,
712 and so performance is tuned for it.
714 This library in particular does it's absolute best to avoid putting
715 B<any> drain at all upon your code's performance. In fact, by itself
716 it does nothing to affect your existing code. So you only pay for
717 what you actually use.
719 =head2 About Metaclass compatibility
721 This module makes sure that all metaclasses created are both upwards
722 and downwards compatible. The topic of metaclass compatibility is
723 highly esoteric and is something only encountered when doing deep and
724 involved metaclass hacking. There are two basic kinds of metaclass
725 incompatibility; upwards and downwards.
727 Upwards metaclass compatibility means that the metaclass of a
728 given class is either the same as (or a subclass of) all of the
731 Downward metaclass compatibility means that the metaclasses of a
732 given class's anscestors are all either the same as (or a subclass
735 Here is a diagram showing a set of two classes (C<A> and C<B>) and
736 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
737 metaclass compatibility both upwards and downwards.
739 +---------+ +---------+
740 | Meta::A |<----| Meta::B | <....... (instance of )
741 +---------+ +---------+ <------- (inherits from)
744 +---------+ +---------+
746 +---------+ +---------+
748 As I said this is a highly esoteric topic and one you will only run
749 into if you do a lot of subclassing of B<Class::MOP::Class>. If you
750 are interested in why this is an issue see the paper
751 I<Uniform and safe metaclass composition> linked to in the
752 L<SEE ALSO> section of this document.
754 =head2 Using custom metaclasses
756 Always use the metaclass pragma when using a custom metaclass, this
757 will ensure the proper initialization order and not accidentely
758 create an incorrect type of metaclass for you. This is a very rare
759 problem, and one which can only occur if you are doing deep metaclass
760 programming. So in other words, don't worry about it.
764 The protocol is divided into 4 main sub-protocols:
768 =item The Class protocol
770 This provides a means of manipulating and introspecting a Perl 5
771 class. It handles all of symbol table hacking for you, and provides
772 a rich set of methods that go beyond simple package introspection.
774 See L<Class::MOP::Class> for more details.
776 =item The Attribute protocol
778 This provides a consistent represenation for an attribute of a
779 Perl 5 class. Since there are so many ways to create and handle
780 attributes in Perl 5 OO, this attempts to provide as much of a
781 unified approach as possible, while giving the freedom and
782 flexibility to subclass for specialization.
784 See L<Class::MOP::Attribute> for more details.
786 =item The Method protocol
788 This provides a means of manipulating and introspecting methods in
789 the Perl 5 object system. As with attributes, there are many ways to
790 approach this topic, so we try to keep it pretty basic, while still
791 making it possible to extend the system in many ways.
793 See L<Class::MOP::Method> for more details.
795 =item The Instance protocol
797 This provides a layer of abstraction for creating object instances.
798 Since the other layers use this protocol, it is relatively easy to
799 change the type of your instances from the default HASH ref to other
800 types of references. Several examples are provided in the F<examples/>
801 directory included in this distribution.
803 See L<Class::MOP::Instance> for more details.
813 =item I<IS_RUNNING_ON_5_10>
815 We set this constant depending on what version perl we are on, this
816 allows us to take advantage of new 5.10 features and stay backwards
821 Whether or not C<mro> provides C<get_isarev>, a much faster way to get all the
822 subclasses of a certain class.
826 =head2 Utility functions
830 =item B<load_class ($class_name)>
832 This will load a given C<$class_name> and if it does not have an
833 already initialized metaclass, then it will intialize one for it.
834 This function can be used in place of tricks like
835 C<eval "use $module"> or using C<require>.
837 =item B<is_class_loaded ($class_name)>
839 This will return a boolean depending on if the C<$class_name> has
842 NOTE: This does a basic check of the symbol table to try and
843 determine as best it can if the C<$class_name> is loaded, it
844 is probably correct about 99% of the time.
846 =item B<check_package_cache_flag ($pkg)>
848 This will return an integer that is managed by C<Class::MOP::Class>
849 to determine if a module's symbol table has been altered.
851 In Perl 5.10 or greater, this flag is package specific. However in
852 versions prior to 5.10, this will use the C<PL_sub_generation> variable
853 which is not package specific.
855 =item B<get_code_info ($code)>
857 This function returns two values, the name of the package the C<$code>
858 is from and the name of the C<$code> itself. This is used by several
859 elements of the MOP to detemine where a given C<$code> reference is from.
861 =item B<subname ($name, $code)>
863 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
865 If possible, we will load the L<Sub::Name> module and this will function
866 as C<Sub::Name::subname> does, otherwise it will just return the C<$code>
869 =item B<in_global_destruction>
871 If L<Devel::GlobalDestruction> is available, this returns true under global
874 Otherwise it's a constant returning false.
878 =head2 Metaclass cache functions
880 Class::MOP holds a cache of metaclasses, the following are functions
881 (B<not methods>) which can be used to access that cache. It is not
882 recommended that you mess with this, bad things could happen. But if
883 you are brave and willing to risk it, go for it.
887 =item B<get_all_metaclasses>
889 This will return an hash of all the metaclass instances that have
890 been cached by B<Class::MOP::Class> keyed by the package name.
892 =item B<get_all_metaclass_instances>
894 This will return an array of all the metaclass instances that have
895 been cached by B<Class::MOP::Class>.
897 =item B<get_all_metaclass_names>
899 This will return an array of all the metaclass names that have
900 been cached by B<Class::MOP::Class>.
902 =item B<get_metaclass_by_name ($name)>
904 This will return a cached B<Class::MOP::Class> instance of nothing
905 if no metaclass exist by that C<$name>.
907 =item B<store_metaclass_by_name ($name, $meta)>
909 This will store a metaclass in the cache at the supplied C<$key>.
911 =item B<weaken_metaclass ($name)>
913 In rare cases it is desireable to store a weakened reference in
914 the metaclass cache. This function will weaken the reference to
915 the metaclass stored in C<$name>.
917 =item B<does_metaclass_exist ($name)>
919 This will return true of there exists a metaclass stored in the
920 C<$name> key and return false otherwise.
922 =item B<remove_metaclass_by_name ($name)>
924 This will remove a the metaclass stored in the C<$name> key.
932 There are very few books out on Meta Object Protocols and Metaclasses
933 because it is such an esoteric topic. The following books are really
934 the only ones I have found. If you know of any more, B<I<please>>
935 email me and let me know, I would love to hear about them.
939 =item "The Art of the Meta Object Protocol"
941 =item "Advances in Object-Oriented Metalevel Architecture and Reflection"
943 =item "Putting MetaClasses to Work"
945 =item "Smalltalk: The Language"
953 =item Uniform and safe metaclass composition
955 An excellent paper by the people who brought us the original Traits paper.
956 This paper is on how Traits can be used to do safe metaclass composition,
957 and offers an excellent introduction section which delves into the topic of
958 metaclass compatibility.
960 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
962 =item Safe Metaclass Programming
964 This paper seems to precede the above paper, and propose a mix-in based
965 approach as opposed to the Traits based approach. Both papers have similar
966 information on the metaclass compatibility problem space.
968 L<http://citeseer.ist.psu.edu/37617.html>
976 =item The Perl 6 MetaModel work in the Pugs project
980 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
982 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
992 =item CPAN Module Review of Class::MOP
994 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
998 =head1 SIMILAR MODULES
1000 As I have said above, this module is a class-builder-builder, so it is
1001 not the same thing as modules like L<Class::Accessor> and
1002 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1003 with similar goals to this module. The one I have found which is most
1004 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1005 creates are very different from this modules.
1009 All complex software has bugs lurking in it, and this module is no
1010 exception. If you find a bug please either email me, or add the bug
1013 =head1 ACKNOWLEDGEMENTS
1019 Thanks to Rob for actually getting the development of this module kick-started.
1025 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1027 B<with contributions from:>
1029 Brandon (blblack) Black
1031 Guillermo (groditi) Roditi
1035 Rob (robkinyon) Kinyon
1037 Yuval (nothingmuch) Kogman
1039 Scott (konobi) McWhirter
1041 =head1 COPYRIGHT AND LICENSE
1043 Copyright 2006-2008 by Infinity Interactive, Inc.
1045 L<http://www.iinteractive.com>
1047 This library is free software; you can redistribute it and/or modify
1048 it under the same terms as Perl itself.