12 use Devel::GlobalDestruction qw( in_global_destruction );
13 use Scalar::Util 'weaken', 'reftype', 'blessed';
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 sub HAVE_ISAREV () { 1 }
29 # this is either part of core or set up appropriately by MRO::Compat
30 *check_package_cache_flag = \&mro::get_pkg_gen;
33 our $VERSION = '0.79';
34 our $XS_VERSION = $VERSION;
35 $VERSION = eval $VERSION;
36 our $AUTHORITY = 'cpan:STEVAN';
39 XSLoader::load( __PACKAGE__, $XS_VERSION );
43 # Metaclasses are singletons, so we cache them here.
44 # there is no need to worry about destruction though
45 # because they should die only when the program dies.
46 # After all, do package definitions even get reaped?
49 # means of accessing all the metaclasses that have
50 # been initialized thus far (for mugwumps obj browser)
51 sub get_all_metaclasses { %METAS }
52 sub get_all_metaclass_instances { values %METAS }
53 sub get_all_metaclass_names { keys %METAS }
54 sub get_metaclass_by_name { $METAS{$_[0]} }
55 sub store_metaclass_by_name { $METAS{$_[0]} = $_[1] }
56 sub weaken_metaclass { weaken($METAS{$_[0]}) }
57 sub does_metaclass_exist { exists $METAS{$_[0]} && defined $METAS{$_[0]} }
58 sub remove_metaclass_by_name { $METAS{$_[0]} = undef }
60 # This handles instances as well as class names
62 my $class = blessed($_[0]) || $_[0];
63 return $METAS{$class};
67 # We only cache metaclasses, meaning instances of
68 # Class::MOP::Class. We do not cache instance of
69 # Class::MOP::Package or Class::MOP::Module. Mostly
70 # because I don't yet see a good reason to do so.
73 sub _class_to_pmfile {
76 my $file = $class . '.pm';
82 sub load_first_existing_class {
86 foreach my $class (@classes) {
87 unless ( _is_valid_class_name($class) ) {
88 my $display = defined($class) ? $class : 'undef';
89 confess "Invalid class name ($display)";
95 for my $class (@classes) {
96 my $pmfile = _class_to_pmfile($class);
97 my $e = _try_load_one_class($class);
100 $exceptions{$class} = $e;
101 last if $e !~ /^Can't locate \Q$pmfile\E in \@INC/;
109 return $found if $found;
115 "Could not load class (%s) because : %s", $_,
120 exists $exceptions{$_}
125 sub _try_load_one_class {
128 return if is_class_loaded($class);
130 my $file = _class_to_pmfile($class);
134 eval { require($file) };
140 my $class = load_first_existing_class($_[0]);
141 return get_metaclass_by_name($class) || $class;
144 sub _is_valid_class_name {
147 return 0 if ref($class);
148 return 0 unless defined($class);
149 return 0 unless length($class);
151 return 1 if $class =~ /^\w+(?:::\w+)*$/;
156 ## ----------------------------------------------------------------------------
157 ## Setting up our environment ...
158 ## ----------------------------------------------------------------------------
159 ## Class::MOP needs to have a few things in the global perl environment so
160 ## that it can operate effectively. Those things are done here.
161 ## ----------------------------------------------------------------------------
163 # ... nothing yet actually ;)
165 ## ----------------------------------------------------------------------------
167 ## ----------------------------------------------------------------------------
168 ## The code below here is to bootstrap our MOP with itself. This is also
169 ## sometimes called "tying the knot". By doing this, we make it much easier
170 ## to extend the MOP through subclassing and such since now you can use the
171 ## MOP itself to extend itself.
173 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
174 ## ----------------------------------------------------------------------------
176 # We need to add in the meta-attributes here so that
177 # any subclass of Class::MOP::* will be able to
178 # inherit them using &construct_instance
180 ## --------------------------------------------------------
181 ## Class::MOP::Package
183 Class::MOP::Package->meta->add_attribute(
184 Class::MOP::Attribute->new('package' => (
186 # NOTE: we need to do this in order
187 # for the instance meta-object to
188 # not fall into meta-circular death
190 # we just alias the original method
191 # rather than re-produce it here
192 'name' => \&Class::MOP::Package::name
197 Class::MOP::Package->meta->add_attribute(
198 Class::MOP::Attribute->new('namespace' => (
201 # we just alias the original method
202 # rather than re-produce it here
203 'namespace' => \&Class::MOP::Package::namespace
206 default => sub { \undef }
210 ## --------------------------------------------------------
211 ## Class::MOP::Module
214 # yeah this is kind of stretching things a bit,
215 # but truthfully the version should be an attribute
216 # of the Module, the weirdness comes from having to
217 # stick to Perl 5 convention and store it in the
218 # $VERSION package variable. Basically if you just
219 # squint at it, it will look how you want it to look.
220 # Either as a package variable, or as a attribute of
221 # the metaclass, isn't abstraction great :)
223 Class::MOP::Module->meta->add_attribute(
224 Class::MOP::Attribute->new('version' => (
227 # we just alias the original method
228 # rather than re-produce it here
229 'version' => \&Class::MOP::Module::version
232 default => sub { \undef }
237 # By following the same conventions as version here,
238 # we are opening up the possibility that people can
239 # use the $AUTHORITY in non-Class::MOP modules as
242 Class::MOP::Module->meta->add_attribute(
243 Class::MOP::Attribute->new('authority' => (
246 # we just alias the original method
247 # rather than re-produce it here
248 'authority' => \&Class::MOP::Module::authority
251 default => sub { \undef }
255 ## --------------------------------------------------------
258 Class::MOP::Class->meta->add_attribute(
259 Class::MOP::Attribute->new('attributes' => (
261 # NOTE: we need to do this in order
262 # for the instance meta-object to
263 # not fall into meta-circular death
265 # we just alias the original method
266 # rather than re-produce it here
267 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
269 default => sub { {} }
273 Class::MOP::Class->meta->add_attribute(
274 Class::MOP::Attribute->new('methods' => (
277 # we just alias the original method
278 # rather than re-produce it here
279 'get_method_map' => \&Class::MOP::Class::get_method_map
281 default => sub { {} }
285 Class::MOP::Class->meta->add_attribute(
286 Class::MOP::Attribute->new('superclasses' => (
289 # we just alias the original method
290 # rather than re-produce it here
291 'superclasses' => \&Class::MOP::Class::superclasses
294 default => sub { \undef }
298 Class::MOP::Class->meta->add_attribute(
299 Class::MOP::Attribute->new('attribute_metaclass' => (
302 # we just alias the original method
303 # rather than re-produce it here
304 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
306 default => 'Class::MOP::Attribute',
310 Class::MOP::Class->meta->add_attribute(
311 Class::MOP::Attribute->new('method_metaclass' => (
314 # we just alias the original method
315 # rather than re-produce it here
316 'method_metaclass' => \&Class::MOP::Class::method_metaclass
318 default => 'Class::MOP::Method',
322 Class::MOP::Class->meta->add_attribute(
323 Class::MOP::Attribute->new('wrapped_method_metaclass' => (
326 # we just alias the original method
327 # rather than re-produce it here
328 'wrapped_method_metaclass' => \&Class::MOP::Class::wrapped_method_metaclass
330 default => 'Class::MOP::Method::Wrapped',
334 Class::MOP::Class->meta->add_attribute(
335 Class::MOP::Attribute->new('instance_metaclass' => (
337 # NOTE: we need to do this in order
338 # for the instance meta-object to
339 # not fall into meta-circular death
341 # we just alias the original method
342 # rather than re-produce it here
343 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
345 default => 'Class::MOP::Instance',
349 Class::MOP::Class->meta->add_attribute(
350 Class::MOP::Attribute->new('immutable_transformer' => (
352 'immutable_transformer' => \&Class::MOP::Class::immutable_transformer
355 '_set_immutable_transformer' => \&Class::MOP::Class::_set_immutable_transformer
361 # we don't actually need to tie the knot with
362 # Class::MOP::Class here, it is actually handled
363 # within Class::MOP::Class itself in the
364 # construct_class_instance method.
366 ## --------------------------------------------------------
367 ## Class::MOP::Attribute
369 Class::MOP::Attribute->meta->add_attribute(
370 Class::MOP::Attribute->new('name' => (
372 # NOTE: we need to do this in order
373 # for the instance meta-object to
374 # not fall into meta-circular death
376 # we just alias the original method
377 # rather than re-produce it here
378 'name' => \&Class::MOP::Attribute::name
383 Class::MOP::Attribute->meta->add_attribute(
384 Class::MOP::Attribute->new('associated_class' => (
386 # NOTE: we need to do this in order
387 # for the instance meta-object to
388 # not fall into meta-circular death
390 # we just alias the original method
391 # rather than re-produce it here
392 'associated_class' => \&Class::MOP::Attribute::associated_class
397 Class::MOP::Attribute->meta->add_attribute(
398 Class::MOP::Attribute->new('accessor' => (
399 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
400 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
404 Class::MOP::Attribute->meta->add_attribute(
405 Class::MOP::Attribute->new('reader' => (
406 reader => { 'reader' => \&Class::MOP::Attribute::reader },
407 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
411 Class::MOP::Attribute->meta->add_attribute(
412 Class::MOP::Attribute->new('initializer' => (
413 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
414 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
418 Class::MOP::Attribute->meta->add_attribute(
419 Class::MOP::Attribute->new('definition_context' => (
420 reader => { 'definition_context' => \&Class::MOP::Attribute::definition_context },
424 Class::MOP::Attribute->meta->add_attribute(
425 Class::MOP::Attribute->new('writer' => (
426 reader => { 'writer' => \&Class::MOP::Attribute::writer },
427 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
431 Class::MOP::Attribute->meta->add_attribute(
432 Class::MOP::Attribute->new('predicate' => (
433 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
434 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
438 Class::MOP::Attribute->meta->add_attribute(
439 Class::MOP::Attribute->new('clearer' => (
440 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
441 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
445 Class::MOP::Attribute->meta->add_attribute(
446 Class::MOP::Attribute->new('builder' => (
447 reader => { 'builder' => \&Class::MOP::Attribute::builder },
448 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
452 Class::MOP::Attribute->meta->add_attribute(
453 Class::MOP::Attribute->new('init_arg' => (
454 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
455 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
459 Class::MOP::Attribute->meta->add_attribute(
460 Class::MOP::Attribute->new('default' => (
461 # default has a custom 'reader' method ...
462 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
466 Class::MOP::Attribute->meta->add_attribute(
467 Class::MOP::Attribute->new('associated_methods' => (
468 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
469 default => sub { [] }
473 Class::MOP::Attribute->meta->add_method('clone' => sub {
475 $self->meta->clone_object($self, @_);
478 ## --------------------------------------------------------
479 ## Class::MOP::Method
480 Class::MOP::Method->meta->add_attribute(
481 Class::MOP::Attribute->new('body' => (
482 reader => { 'body' => \&Class::MOP::Method::body },
486 Class::MOP::Method->meta->add_attribute(
487 Class::MOP::Attribute->new('associated_metaclass' => (
488 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
492 Class::MOP::Method->meta->add_attribute(
493 Class::MOP::Attribute->new('package_name' => (
494 reader => { 'package_name' => \&Class::MOP::Method::package_name },
498 Class::MOP::Method->meta->add_attribute(
499 Class::MOP::Attribute->new('name' => (
500 reader => { 'name' => \&Class::MOP::Method::name },
504 Class::MOP::Method->meta->add_attribute(
505 Class::MOP::Attribute->new('original_method' => (
506 reader => { 'original_method' => \&Class::MOP::Method::original_method },
507 writer => { '_set_original_method' => \&Class::MOP::Method::_set_original_method },
511 Class::MOP::Method->meta->add_method('clone' => sub {
513 my $clone = $self->meta->clone_object($self, @_);
514 $clone->_set_original_method($self);
518 ## --------------------------------------------------------
519 ## Class::MOP::Method::Wrapped
522 # the way this item is initialized, this
523 # really does not follow the standard
524 # practices of attributes, but we put
525 # it here for completeness
526 Class::MOP::Method::Wrapped->meta->add_attribute(
527 Class::MOP::Attribute->new('modifier_table')
530 ## --------------------------------------------------------
531 ## Class::MOP::Method::Generated
533 Class::MOP::Method::Generated->meta->add_attribute(
534 Class::MOP::Attribute->new('is_inline' => (
535 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
540 Class::MOP::Method::Generated->meta->add_attribute(
541 Class::MOP::Attribute->new('definition_context' => (
542 reader => { 'definition_context' => \&Class::MOP::Method::Generated::definition_context },
546 ## --------------------------------------------------------
547 ## Class::MOP::Method::Accessor
549 Class::MOP::Method::Accessor->meta->add_attribute(
550 Class::MOP::Attribute->new('attribute' => (
552 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
557 Class::MOP::Method::Accessor->meta->add_attribute(
558 Class::MOP::Attribute->new('accessor_type' => (
559 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
563 ## --------------------------------------------------------
564 ## Class::MOP::Method::Constructor
566 Class::MOP::Method::Constructor->meta->add_attribute(
567 Class::MOP::Attribute->new('options' => (
569 'options' => \&Class::MOP::Method::Constructor::options
571 default => sub { +{} }
575 Class::MOP::Method::Constructor->meta->add_attribute(
576 Class::MOP::Attribute->new('associated_metaclass' => (
577 init_arg => "metaclass", # FIXME alias and rename
579 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
584 ## --------------------------------------------------------
585 ## Class::MOP::Instance
588 # these don't yet do much of anything, but are just
589 # included for completeness
591 Class::MOP::Instance->meta->add_attribute(
592 Class::MOP::Attribute->new('associated_metaclass',
593 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
597 Class::MOP::Instance->meta->add_attribute(
598 Class::MOP::Attribute->new('_class_name',
600 reader => { _class_name => \&Class::MOP::Instance::_class_name },
601 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
602 #default => sub { $_[0]->associated_metaclass->name },
606 Class::MOP::Instance->meta->add_attribute(
607 Class::MOP::Attribute->new('attributes',
608 reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
612 Class::MOP::Instance->meta->add_attribute(
613 Class::MOP::Attribute->new('slots',
614 reader => { slots => \&Class::MOP::Instance::slots },
618 Class::MOP::Instance->meta->add_attribute(
619 Class::MOP::Attribute->new('slot_hash',
620 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
625 # we need the meta instance of the meta instance to be created now, in order
626 # for the constructor to be able to use it
627 Class::MOP::Instance->meta->get_meta_instance;
629 # pretend the add_method never happenned. it hasn't yet affected anything
630 undef Class::MOP::Instance->meta->{_package_cache_flag};
632 ## --------------------------------------------------------
633 ## Now close all the Class::MOP::* classes
635 # NOTE: we don't need to inline the the accessors this only lengthens
636 # the compile time of the MOP, and gives us no actual benefits.
638 $_->meta->make_immutable(
639 inline_constructor => 1,
640 replace_constructor => 1,
641 constructor_name => "_new",
642 inline_accessors => 0,
648 Class::MOP::Attribute
654 Class::MOP::Method::Generated
656 Class::MOP::Method::Accessor
657 Class::MOP::Method::Constructor
658 Class::MOP::Method::Wrapped
669 Class::MOP - A Meta Object Protocol for Perl 5
673 This module is a fully functioning meta object protocol for the
674 Perl 5 object system. It makes no attempt to change the behavior or
675 characteristics of the Perl 5 object system, only to create a
676 protocol for its manipulation and introspection.
678 That said, it does attempt to create the tools for building a rich set
679 of extensions to the Perl 5 object system. Every attempt has been made
680 to abide by the spirit of the Perl 5 object system that we all know
683 This documentation is sparse on conceptual details. We suggest looking
684 at the items listed in the L<SEE ALSO> section for more
685 information. In particular the book "The Art of the Meta Object
686 Protocol" was very influential in the development of this system.
688 =head2 What is a Meta Object Protocol?
690 A meta object protocol is an API to an object system.
692 To be more specific, it abstracts the components of an object system
693 (classes, object, methods, object attributes, etc.). These
694 abstractions can then be used to inspect and manipulate the object
695 system which they describe.
697 It can be said that there are two MOPs for any object system; the
698 implicit MOP and the explicit MOP. The implicit MOP handles things
699 like method dispatch or inheritance, which happen automatically as
700 part of how the object system works. The explicit MOP typically
701 handles the introspection/reflection features of the object system.
703 All object systems have implicit MOPs. Without one, they would not
704 work. Explicit MOPs are much less common, and depending on the
705 language can vary from restrictive (Reflection in Java or C#) to wide
706 open (CLOS is a perfect example).
708 =head2 Yet Another Class Builder! Why?
710 This is B<not> a class builder so much as a I<class builder
711 B<builder>>. The intent is that an end user will not use this module
712 directly, but instead this module is used by module authors to build
713 extensions and features onto the Perl 5 object system.
715 This system is used by L<Moose>, which supplies a powerful class
716 builder system built entirely on top of C<Class::MOP>.
718 =head2 Who is this module for?
720 This module is for anyone who has ever created or wanted to create a
721 module for the Class:: namespace. The tools which this module provides
722 make doing complex Perl 5 wizardry simpler, by removing such barriers
723 as the need to hack symbol tables, or understand the fine details of
726 =head2 What changes do I have to make to use this module?
728 This module was designed to be as unintrusive as possible. Many of its
729 features are accessible without B<any> change to your existing
730 code. It is meant to be a compliment to your existing code and not an
731 intrusion on your code base. Unlike many other B<Class::> modules,
732 this module B<does not> require you subclass it, or even that you
733 C<use> it in within your module's package.
735 The only features which requires additions to your code are the
736 attribute handling and instance construction features, and these are
737 both completely optional features. The only reason for this is because
738 Perl 5's object system does not actually have these features built
739 in. More information about this feature can be found below.
741 =head2 About Performance
743 It is a common misconception that explicit MOPs are a performance hit.
744 This is not a universal truth, it is a side-effect of some specific
745 implementations. For instance, using Java reflection is slow because
746 the JVM cannot take advantage of any compiler optimizations, and the
747 JVM has to deal with much more runtime type information as well.
749 Reflection in C# is marginally better as it was designed into the
750 language and runtime (the CLR). In contrast, CLOS (the Common Lisp
751 Object System) was built to support an explicit MOP, and so
752 performance is tuned for it.
754 This library in particular does its absolute best to avoid putting
755 B<any> drain at all upon your code's performance. In fact, by itself
756 it does nothing to affect your existing code. So you only pay for what
759 =head2 About Metaclass compatibility
761 This module makes sure that all metaclasses created are both upwards
762 and downwards compatible. The topic of metaclass compatibility is
763 highly esoteric and is something only encountered when doing deep and
764 involved metaclass hacking. There are two basic kinds of metaclass
765 incompatibility; upwards and downwards.
767 Upwards metaclass compatibility means that the metaclass of a
768 given class is either the same as (or a subclass of) all of the
771 Downward metaclass compatibility means that the metaclasses of a
772 given class's ancestors are all either the same as (or a subclass
775 Here is a diagram showing a set of two classes (C<A> and C<B>) and
776 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
777 metaclass compatibility both upwards and downwards.
779 +---------+ +---------+
780 | Meta::A |<----| Meta::B | <....... (instance of )
781 +---------+ +---------+ <------- (inherits from)
784 +---------+ +---------+
786 +---------+ +---------+
788 As I said this is a highly esoteric topic and one you will only run
789 into if you do a lot of subclassing of L<Class::MOP::Class>. If you
790 are interested in why this is an issue see the paper I<Uniform and
791 safe metaclass composition> linked to in the L<SEE ALSO> section of
794 =head2 Using custom metaclasses
796 Always use the L<metaclass> pragma when using a custom metaclass, this
797 will ensure the proper initialization order and not accidentally
798 create an incorrect type of metaclass for you. This is a very rare
799 problem, and one which can only occur if you are doing deep metaclass
800 programming. So in other words, don't worry about it.
802 Note that if you're using L<Moose> we encourage you to I<not> use
803 L<metaclass> pragma, and instead use L<Moose::Util::MetaRole> to apply
804 roles to a class's metaclasses. This topic is covered at length in
805 various L<Moose::Cookbook> recipes.
809 The meta-object protocol is divided into 4 main sub-protocols:
811 =head2 The Class protocol
813 This provides a means of manipulating and introspecting a Perl 5
814 class. It handles symbol table hacking for you, and provides a rich
815 set of methods that go beyond simple package introspection.
817 See L<Class::MOP::Class> for more details.
819 =head2 The Attribute protocol
821 This provides a consistent representation for an attribute of a Perl 5
822 class. Since there are so many ways to create and handle attributes in
823 Perl 5 OO, the Attribute protocol provide as much of a unified
824 approach as possible. Of course, you are always free to extend this
825 protocol by subclassing the appropriate classes.
827 See L<Class::MOP::Attribute> for more details.
829 =head2 The Method protocol
831 This provides a means of manipulating and introspecting methods in the
832 Perl 5 object system. As with attributes, there are many ways to
833 approach this topic, so we try to keep it pretty basic, while still
834 making it possible to extend the system in many ways.
836 See L<Class::MOP::Method> for more details.
838 =head2 The Instance protocol
840 This provides a layer of abstraction for creating object instances.
841 Since the other layers use this protocol, it is relatively easy to
842 change the type of your instances from the default hash reference to
843 some other type of reference. Several examples are provided in the
844 F<examples/> directory included in this distribution.
846 See L<Class::MOP::Instance> for more details.
850 Note that this module does not export any constants or functions.
856 =item I<Class::MOP::IS_RUNNING_ON_5_10>
858 We set this constant depending on what version perl we are on, this
859 allows us to take advantage of new 5.10 features and stay backwards
862 =item I<Class::MOP::HAVE_ISAREV>
864 Whether or not the L<mro> pragma provides C<get_isarev>, a much faster
865 way to get all the subclasses of a certain class.
869 =head2 Utility functions
871 Note that these are all called as B<functions, not methods>.
875 =item B<Class::MOP::load_class($class_name)>
877 This will load the specified C<$class_name>. This function can be used
878 in place of tricks like C<eval "use $module"> or using C<require>
879 unconditionally. This will return the metaclass of C<$class_name>.
881 =item B<Class::MOP::is_class_loaded($class_name)>
883 Returns a boolean indicating whether or not C<$class_name> has been
886 This does a basic check of the symbol table to try and determine as
887 best it can if the C<$class_name> is loaded, it is probably correct
888 about 99% of the time, but it can be fooled into reporting false
891 =item B<Class::MOP::get_code_info($code)>
893 This function returns two values, the name of the package the C<$code>
894 is from and the name of the C<$code> itself. This is used by several
895 elements of the MOP to determine where a given C<$code> reference is
898 =item B<Class::MOP::class_of($instance_or_class_name)>
900 This will return the metaclass of the given instance or class name.
901 Even if the class lacks a metaclass, no metaclass will be initialized
902 and C<undef> will be returned.
904 =item B<Class::MOP::check_package_cache_flag($pkg)>
906 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
908 This will return an integer that is managed by L<Class::MOP::Class> to
909 determine if a module's symbol table has been altered.
911 In Perl 5.10 or greater, this flag is package specific. However in
912 versions prior to 5.10, this will use the C<PL_sub_generation>
913 variable which is not package specific.
915 =item B<Class::MOP::load_first_existing_class(@class_names)>
917 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
919 Given a list of class names, this function will attempt to load each
922 If it finds a class it can load, it will return that class' name. If
923 none of the classes can be loaded, it will throw an exception.
927 =head2 Metaclass cache functions
929 Class::MOP holds a cache of metaclasses. The following are functions
930 (B<not methods>) which can be used to access that cache. It is not
931 recommended that you mess with these. Bad things could happen, but if
932 you are brave and willing to risk it: go for it!
936 =item B<Class::MOP::get_all_metaclasses>
938 This will return a hash of all the metaclass instances that have
939 been cached by L<Class::MOP::Class>, keyed by the package name.
941 =item B<Class::MOP::get_all_metaclass_instances>
943 This will return a list of all the metaclass instances that have
944 been cached by L<Class::MOP::Class>.
946 =item B<Class::MOP::get_all_metaclass_names>
948 This will return a list of all the metaclass names that have
949 been cached by L<Class::MOP::Class>.
951 =item B<Class::MOP::get_metaclass_by_name($name)>
953 This will return a cached L<Class::MOP::Class> instance, or nothing
954 if no metaclass exists with that C<$name>.
956 =item B<Class::MOP::store_metaclass_by_name($name, $meta)>
958 This will store a metaclass in the cache at the supplied C<$key>.
960 =item B<Class::MOP::weaken_metaclass($name)>
962 In rare cases (e.g. anonymous metaclasses) it is desirable to
963 store a weakened reference in the metaclass cache. This
964 function will weaken the reference to the metaclass stored
967 =item B<Class::MOP::does_metaclass_exist($name)>
969 This will return true of there exists a metaclass stored in the
970 C<$name> key, and return false otherwise.
972 =item B<Class::MOP::remove_metaclass_by_name($name)>
974 This will remove the metaclass stored in the C<$name> key.
982 There are very few books out on Meta Object Protocols and Metaclasses
983 because it is such an esoteric topic. The following books are really
984 the only ones I have found. If you know of any more, B<I<please>>
985 email me and let me know, I would love to hear about them.
989 =item I<The Art of the Meta Object Protocol>
991 =item I<Advances in Object-Oriented Metalevel Architecture and Reflection>
993 =item I<Putting MetaClasses to Work>
995 =item I<Smalltalk: The Language>
1003 =item "Uniform and safe metaclass composition"
1005 An excellent paper by the people who brought us the original Traits paper.
1006 This paper is on how Traits can be used to do safe metaclass composition,
1007 and offers an excellent introduction section which delves into the topic of
1008 metaclass compatibility.
1010 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
1012 =item "Safe Metaclass Programming"
1014 This paper seems to precede the above paper, and propose a mix-in based
1015 approach as opposed to the Traits based approach. Both papers have similar
1016 information on the metaclass compatibility problem space.
1018 L<http://citeseer.ist.psu.edu/37617.html>
1026 =item The Perl 6 MetaModel work in the Pugs project
1030 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
1032 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1042 =item CPAN Module Review of Class::MOP
1044 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1048 =head1 SIMILAR MODULES
1050 As I have said above, this module is a class-builder-builder, so it is
1051 not the same thing as modules like L<Class::Accessor> and
1052 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1053 with similar goals to this module. The one I have found which is most
1054 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1055 creates are very different from this modules.
1059 All complex software has bugs lurking in it, and this module is no
1060 exception. If you find a bug please either email me, or add the bug
1063 =head1 ACKNOWLEDGEMENTS
1069 Thanks to Rob for actually getting the development of this module kick-started.
1075 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1077 B<with contributions from:>
1079 Brandon (blblack) Black
1081 Florian (rafl) Ragwitz
1083 Guillermo (groditi) Roditi
1087 Rob (robkinyon) Kinyon
1089 Yuval (nothingmuch) Kogman
1091 Scott (konobi) McWhirter
1093 =head1 COPYRIGHT AND LICENSE
1095 Copyright 2006-2009 by Infinity Interactive, Inc.
1097 L<http://www.iinteractive.com>
1099 This library is free software; you can redistribute it and/or modify
1100 it under the same terms as Perl itself.