12 use Scalar::Util 'weaken', 'reftype', 'blessed';
14 use Class::MOP::Class;
15 use Class::MOP::Attribute;
16 use Class::MOP::Method;
19 *IS_RUNNING_ON_5_10 = ($] < 5.009_005)
24 Carp::cluck("Class::MOP::HAVE_ISAREV is deprecated and will be removed in a future release. It has always returned 1 anyway.");
28 # this is either part of core or set up appropriately by MRO::Compat
29 *check_package_cache_flag = \&mro::get_pkg_gen;
32 our $VERSION = '0.84';
33 our $XS_VERSION = $VERSION;
34 $VERSION = eval $VERSION;
35 our $AUTHORITY = 'cpan:STEVAN';
38 XSLoader::load( __PACKAGE__, $XS_VERSION );
42 # Metaclasses are singletons, so we cache them here.
43 # there is no need to worry about destruction though
44 # because they should die only when the program dies.
45 # After all, do package definitions even get reaped?
48 # means of accessing all the metaclasses that have
49 # been initialized thus far (for mugwumps obj browser)
50 sub get_all_metaclasses { %METAS }
51 sub get_all_metaclass_instances { values %METAS }
52 sub get_all_metaclass_names { keys %METAS }
53 sub get_metaclass_by_name { $METAS{$_[0]} }
54 sub store_metaclass_by_name { $METAS{$_[0]} = $_[1] }
55 sub weaken_metaclass { weaken($METAS{$_[0]}) }
56 sub does_metaclass_exist { exists $METAS{$_[0]} && defined $METAS{$_[0]} }
57 sub remove_metaclass_by_name { $METAS{$_[0]} = undef }
59 # This handles instances as well as class names
61 return unless defined $_[0];
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 $class =~ /^\w+(?:::\w+)*$/;
158 Carp::carp("Class::MOP::subname is deprecated. Please use Sub::Name directly.");
159 goto \&Sub::Name::subname;
162 sub in_global_destruction {
163 require Devel::GlobalDestruction;
164 Carp::carp("Class::MOP::in_global_destruction is deprecated. Please use Devel::GlobalDestruction directly.");
165 goto \&Devel::GlobalDestruction::in_global_destruction;
168 ## ----------------------------------------------------------------------------
169 ## Setting up our environment ...
170 ## ----------------------------------------------------------------------------
171 ## Class::MOP needs to have a few things in the global perl environment so
172 ## that it can operate effectively. Those things are done here.
173 ## ----------------------------------------------------------------------------
175 # ... nothing yet actually ;)
177 ## ----------------------------------------------------------------------------
179 ## ----------------------------------------------------------------------------
180 ## The code below here is to bootstrap our MOP with itself. This is also
181 ## sometimes called "tying the knot". By doing this, we make it much easier
182 ## to extend the MOP through subclassing and such since now you can use the
183 ## MOP itself to extend itself.
185 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
186 ## ----------------------------------------------------------------------------
188 # We need to add in the meta-attributes here so that
189 # any subclass of Class::MOP::* will be able to
190 # inherit them using _construct_instance
192 ## --------------------------------------------------------
193 ## Class::MOP::Package
195 Class::MOP::Package->meta->add_attribute(
196 Class::MOP::Attribute->new('package' => (
198 # NOTE: we need to do this in order
199 # for the instance meta-object to
200 # not fall into meta-circular death
202 # we just alias the original method
203 # rather than re-produce it here
204 'name' => \&Class::MOP::Package::name
209 Class::MOP::Package->meta->add_attribute(
210 Class::MOP::Attribute->new('namespace' => (
213 # we just alias the original method
214 # rather than re-produce it here
215 'namespace' => \&Class::MOP::Package::namespace
218 default => sub { \undef }
222 ## --------------------------------------------------------
223 ## Class::MOP::Module
226 # yeah this is kind of stretching things a bit,
227 # but truthfully the version should be an attribute
228 # of the Module, the weirdness comes from having to
229 # stick to Perl 5 convention and store it in the
230 # $VERSION package variable. Basically if you just
231 # squint at it, it will look how you want it to look.
232 # Either as a package variable, or as a attribute of
233 # the metaclass, isn't abstraction great :)
235 Class::MOP::Module->meta->add_attribute(
236 Class::MOP::Attribute->new('version' => (
239 # we just alias the original method
240 # rather than re-produce it here
241 'version' => \&Class::MOP::Module::version
244 default => sub { \undef }
249 # By following the same conventions as version here,
250 # we are opening up the possibility that people can
251 # use the $AUTHORITY in non-Class::MOP modules as
254 Class::MOP::Module->meta->add_attribute(
255 Class::MOP::Attribute->new('authority' => (
258 # we just alias the original method
259 # rather than re-produce it here
260 'authority' => \&Class::MOP::Module::authority
263 default => sub { \undef }
267 ## --------------------------------------------------------
270 Class::MOP::Class->meta->add_attribute(
271 Class::MOP::Attribute->new('attributes' => (
273 # NOTE: we need to do this in order
274 # for the instance meta-object to
275 # not fall into meta-circular death
277 # we just alias the original method
278 # rather than re-produce it here
279 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
281 default => sub { {} }
285 Class::MOP::Class->meta->add_attribute(
286 Class::MOP::Attribute->new('methods' => (
289 # we just alias the original method
290 # rather than re-produce it here
291 'get_method_map' => \&Class::MOP::Class::get_method_map
293 default => sub { {} }
297 Class::MOP::Class->meta->add_attribute(
298 Class::MOP::Attribute->new('superclasses' => (
301 # we just alias the original method
302 # rather than re-produce it here
303 'superclasses' => \&Class::MOP::Class::superclasses
306 default => sub { \undef }
310 Class::MOP::Class->meta->add_attribute(
311 Class::MOP::Attribute->new('attribute_metaclass' => (
314 # we just alias the original method
315 # rather than re-produce it here
316 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
318 default => 'Class::MOP::Attribute',
322 Class::MOP::Class->meta->add_attribute(
323 Class::MOP::Attribute->new('method_metaclass' => (
326 # we just alias the original method
327 # rather than re-produce it here
328 'method_metaclass' => \&Class::MOP::Class::method_metaclass
330 default => 'Class::MOP::Method',
334 Class::MOP::Class->meta->add_attribute(
335 Class::MOP::Attribute->new('wrapped_method_metaclass' => (
338 # we just alias the original method
339 # rather than re-produce it here
340 'wrapped_method_metaclass' => \&Class::MOP::Class::wrapped_method_metaclass
342 default => 'Class::MOP::Method::Wrapped',
346 Class::MOP::Class->meta->add_attribute(
347 Class::MOP::Attribute->new('instance_metaclass' => (
349 # NOTE: we need to do this in order
350 # for the instance meta-object to
351 # not fall into meta-circular death
353 # we just alias the original method
354 # rather than re-produce it here
355 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
357 default => 'Class::MOP::Instance',
361 Class::MOP::Class->meta->add_attribute(
362 Class::MOP::Attribute->new('immutable_trait' => (
364 'immutable_trait' => \&Class::MOP::Class::immutable_trait
366 default => "Class::MOP::Class::Immutable::Trait",
370 Class::MOP::Class->meta->add_attribute(
371 Class::MOP::Attribute->new('constructor_name' => (
373 'constructor_name' => \&Class::MOP::Class::constructor_name,
379 Class::MOP::Class->meta->add_attribute(
380 Class::MOP::Attribute->new('constructor_class' => (
382 'constructor_class' => \&Class::MOP::Class::constructor_class,
384 default => "Class::MOP::Method::Constructor",
389 Class::MOP::Class->meta->add_attribute(
390 Class::MOP::Attribute->new('destructor_class' => (
392 'destructor_class' => \&Class::MOP::Class::destructor_class,
398 # we don't actually need to tie the knot with
399 # Class::MOP::Class here, it is actually handled
400 # within Class::MOP::Class itself in the
401 # _construct_class_instance method.
403 ## --------------------------------------------------------
404 ## Class::MOP::Attribute
406 Class::MOP::Attribute->meta->add_attribute(
407 Class::MOP::Attribute->new('name' => (
409 # NOTE: we need to do this in order
410 # for the instance meta-object to
411 # not fall into meta-circular death
413 # we just alias the original method
414 # rather than re-produce it here
415 'name' => \&Class::MOP::Attribute::name
420 Class::MOP::Attribute->meta->add_attribute(
421 Class::MOP::Attribute->new('associated_class' => (
423 # NOTE: we need to do this in order
424 # for the instance meta-object to
425 # not fall into meta-circular death
427 # we just alias the original method
428 # rather than re-produce it here
429 'associated_class' => \&Class::MOP::Attribute::associated_class
434 Class::MOP::Attribute->meta->add_attribute(
435 Class::MOP::Attribute->new('accessor' => (
436 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
437 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
441 Class::MOP::Attribute->meta->add_attribute(
442 Class::MOP::Attribute->new('reader' => (
443 reader => { 'reader' => \&Class::MOP::Attribute::reader },
444 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
448 Class::MOP::Attribute->meta->add_attribute(
449 Class::MOP::Attribute->new('initializer' => (
450 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
451 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
455 Class::MOP::Attribute->meta->add_attribute(
456 Class::MOP::Attribute->new('definition_context' => (
457 reader => { 'definition_context' => \&Class::MOP::Attribute::definition_context },
461 Class::MOP::Attribute->meta->add_attribute(
462 Class::MOP::Attribute->new('writer' => (
463 reader => { 'writer' => \&Class::MOP::Attribute::writer },
464 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
468 Class::MOP::Attribute->meta->add_attribute(
469 Class::MOP::Attribute->new('predicate' => (
470 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
471 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
475 Class::MOP::Attribute->meta->add_attribute(
476 Class::MOP::Attribute->new('clearer' => (
477 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
478 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
482 Class::MOP::Attribute->meta->add_attribute(
483 Class::MOP::Attribute->new('builder' => (
484 reader => { 'builder' => \&Class::MOP::Attribute::builder },
485 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
489 Class::MOP::Attribute->meta->add_attribute(
490 Class::MOP::Attribute->new('init_arg' => (
491 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
492 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
496 Class::MOP::Attribute->meta->add_attribute(
497 Class::MOP::Attribute->new('default' => (
498 # default has a custom 'reader' method ...
499 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
503 Class::MOP::Attribute->meta->add_attribute(
504 Class::MOP::Attribute->new('associated_methods' => (
505 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
506 default => sub { [] }
510 Class::MOP::Attribute->meta->add_attribute(
511 Class::MOP::Attribute->new('insertion_order' => (
512 reader => { 'insertion_order' => \&Class::MOP::Attribute::insertion_order },
513 writer => { '_set_insertion_order' => \&Class::MOP::Attribute::_set_insertion_order },
514 predicate => { 'has_insertion_order' => \&Class::MOP::Attribute::has_insertion_order },
518 Class::MOP::Attribute->meta->add_method('clone' => sub {
520 $self->meta->clone_object($self, @_);
523 ## --------------------------------------------------------
524 ## Class::MOP::Method
525 Class::MOP::Method->meta->add_attribute(
526 Class::MOP::Attribute->new('body' => (
527 reader => { 'body' => \&Class::MOP::Method::body },
531 Class::MOP::Method->meta->add_attribute(
532 Class::MOP::Attribute->new('associated_metaclass' => (
533 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
537 Class::MOP::Method->meta->add_attribute(
538 Class::MOP::Attribute->new('package_name' => (
539 reader => { 'package_name' => \&Class::MOP::Method::package_name },
543 Class::MOP::Method->meta->add_attribute(
544 Class::MOP::Attribute->new('name' => (
545 reader => { 'name' => \&Class::MOP::Method::name },
549 Class::MOP::Method->meta->add_attribute(
550 Class::MOP::Attribute->new('original_method' => (
551 reader => { 'original_method' => \&Class::MOP::Method::original_method },
552 writer => { '_set_original_method' => \&Class::MOP::Method::_set_original_method },
556 Class::MOP::Method->meta->add_method('clone' => sub {
558 my $clone = $self->meta->clone_object($self, @_);
559 $clone->_set_original_method($self);
563 ## --------------------------------------------------------
564 ## Class::MOP::Method::Wrapped
567 # the way this item is initialized, this
568 # really does not follow the standard
569 # practices of attributes, but we put
570 # it here for completeness
571 Class::MOP::Method::Wrapped->meta->add_attribute(
572 Class::MOP::Attribute->new('modifier_table')
575 ## --------------------------------------------------------
576 ## Class::MOP::Method::Generated
578 Class::MOP::Method::Generated->meta->add_attribute(
579 Class::MOP::Attribute->new('is_inline' => (
580 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
585 Class::MOP::Method::Generated->meta->add_attribute(
586 Class::MOP::Attribute->new('definition_context' => (
587 reader => { 'definition_context' => \&Class::MOP::Method::Generated::definition_context },
592 ## --------------------------------------------------------
593 ## Class::MOP::Method::Inlined
595 Class::MOP::Method::Inlined->meta->add_attribute(
596 Class::MOP::Attribute->new('_expected_method_class' => (
597 reader => { '_expected_method_class' => \&Class::MOP::Method::Inlined::_expected_method_class },
601 ## --------------------------------------------------------
602 ## Class::MOP::Method::Accessor
604 Class::MOP::Method::Accessor->meta->add_attribute(
605 Class::MOP::Attribute->new('attribute' => (
607 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
612 Class::MOP::Method::Accessor->meta->add_attribute(
613 Class::MOP::Attribute->new('accessor_type' => (
614 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
618 ## --------------------------------------------------------
619 ## Class::MOP::Method::Constructor
621 Class::MOP::Method::Constructor->meta->add_attribute(
622 Class::MOP::Attribute->new('options' => (
624 'options' => \&Class::MOP::Method::Constructor::options
626 default => sub { +{} }
630 Class::MOP::Method::Constructor->meta->add_attribute(
631 Class::MOP::Attribute->new('associated_metaclass' => (
632 init_arg => "metaclass", # FIXME alias and rename
634 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
639 ## --------------------------------------------------------
640 ## Class::MOP::Instance
643 # these don't yet do much of anything, but are just
644 # included for completeness
646 Class::MOP::Instance->meta->add_attribute(
647 Class::MOP::Attribute->new('associated_metaclass',
648 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
652 Class::MOP::Instance->meta->add_attribute(
653 Class::MOP::Attribute->new('_class_name',
655 reader => { _class_name => \&Class::MOP::Instance::_class_name },
656 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
657 #default => sub { $_[0]->associated_metaclass->name },
661 Class::MOP::Instance->meta->add_attribute(
662 Class::MOP::Attribute->new('attributes',
663 reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
667 Class::MOP::Instance->meta->add_attribute(
668 Class::MOP::Attribute->new('slots',
669 reader => { slots => \&Class::MOP::Instance::slots },
673 Class::MOP::Instance->meta->add_attribute(
674 Class::MOP::Attribute->new('slot_hash',
675 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
680 # we need the meta instance of the meta instance to be created now, in order
681 # for the constructor to be able to use it
682 Class::MOP::Instance->meta->get_meta_instance;
684 # pretend the add_method never happenned. it hasn't yet affected anything
685 undef Class::MOP::Instance->meta->{_package_cache_flag};
687 ## --------------------------------------------------------
688 ## Now close all the Class::MOP::* classes
690 # NOTE: we don't need to inline the the accessors this only lengthens
691 # the compile time of the MOP, and gives us no actual benefits.
693 # this is just nitpicking to ensure Class::MOP::Class->meta == ->meta->meta
694 Class::MOP::Class->meta->_immutable_metaclass;
695 $Class::MOP::Class::immutable_metaclass_cache{"Class::MOP::Class"}{"Class::MOP::Class::Immutable::Trait"} = Class::MOP::Class::Immutable::Class::MOP::Class->meta;
697 $_->meta->make_immutable(
698 inline_constructor => 1,
699 replace_constructor => 1,
700 constructor_name => "_new",
701 inline_accessors => 0,
706 Class::MOP::Class::Immutable::Trait
707 Class::MOP::Class::Immutable::Class::MOP::Class
709 Class::MOP::Attribute
715 Class::MOP::Method::Generated
716 Class::MOP::Method::Inlined
718 Class::MOP::Method::Accessor
719 Class::MOP::Method::Constructor
720 Class::MOP::Method::Wrapped
731 Class::MOP - A Meta Object Protocol for Perl 5
735 This module is a fully functioning meta object protocol for the
736 Perl 5 object system. It makes no attempt to change the behavior or
737 characteristics of the Perl 5 object system, only to create a
738 protocol for its manipulation and introspection.
740 That said, it does attempt to create the tools for building a rich set
741 of extensions to the Perl 5 object system. Every attempt has been made
742 to abide by the spirit of the Perl 5 object system that we all know
745 This documentation is sparse on conceptual details. We suggest looking
746 at the items listed in the L<SEE ALSO> section for more
747 information. In particular the book "The Art of the Meta Object
748 Protocol" was very influential in the development of this system.
750 =head2 What is a Meta Object Protocol?
752 A meta object protocol is an API to an object system.
754 To be more specific, it abstracts the components of an object system
755 (classes, object, methods, object attributes, etc.). These
756 abstractions can then be used to inspect and manipulate the object
757 system which they describe.
759 It can be said that there are two MOPs for any object system; the
760 implicit MOP and the explicit MOP. The implicit MOP handles things
761 like method dispatch or inheritance, which happen automatically as
762 part of how the object system works. The explicit MOP typically
763 handles the introspection/reflection features of the object system.
765 All object systems have implicit MOPs. Without one, they would not
766 work. Explicit MOPs are much less common, and depending on the
767 language can vary from restrictive (Reflection in Java or C#) to wide
768 open (CLOS is a perfect example).
770 =head2 Yet Another Class Builder! Why?
772 This is B<not> a class builder so much as a I<class builder
773 B<builder>>. The intent is that an end user will not use this module
774 directly, but instead this module is used by module authors to build
775 extensions and features onto the Perl 5 object system.
777 This system is used by L<Moose>, which supplies a powerful class
778 builder system built entirely on top of C<Class::MOP>.
780 =head2 Who is this module for?
782 This module is for anyone who has ever created or wanted to create a
783 module for the Class:: namespace. The tools which this module provides
784 make doing complex Perl 5 wizardry simpler, by removing such barriers
785 as the need to hack symbol tables, or understand the fine details of
788 =head2 What changes do I have to make to use this module?
790 This module was designed to be as unintrusive as possible. Many of its
791 features are accessible without B<any> change to your existing
792 code. It is meant to be a compliment to your existing code and not an
793 intrusion on your code base. Unlike many other B<Class::> modules,
794 this module B<does not> require you subclass it, or even that you
795 C<use> it in within your module's package.
797 The only features which requires additions to your code are the
798 attribute handling and instance construction features, and these are
799 both completely optional features. The only reason for this is because
800 Perl 5's object system does not actually have these features built
801 in. More information about this feature can be found below.
803 =head2 About Performance
805 It is a common misconception that explicit MOPs are a performance hit.
806 This is not a universal truth, it is a side-effect of some specific
807 implementations. For instance, using Java reflection is slow because
808 the JVM cannot take advantage of any compiler optimizations, and the
809 JVM has to deal with much more runtime type information as well.
811 Reflection in C# is marginally better as it was designed into the
812 language and runtime (the CLR). In contrast, CLOS (the Common Lisp
813 Object System) was built to support an explicit MOP, and so
814 performance is tuned for it.
816 This library in particular does its absolute best to avoid putting
817 B<any> drain at all upon your code's performance. In fact, by itself
818 it does nothing to affect your existing code. So you only pay for what
821 =head2 About Metaclass compatibility
823 This module makes sure that all metaclasses created are both upwards
824 and downwards compatible. The topic of metaclass compatibility is
825 highly esoteric and is something only encountered when doing deep and
826 involved metaclass hacking. There are two basic kinds of metaclass
827 incompatibility; upwards and downwards.
829 Upwards metaclass compatibility means that the metaclass of a
830 given class is either the same as (or a subclass of) all of the
833 Downward metaclass compatibility means that the metaclasses of a
834 given class's ancestors are all either the same as (or a subclass
837 Here is a diagram showing a set of two classes (C<A> and C<B>) and
838 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
839 metaclass compatibility both upwards and downwards.
841 +---------+ +---------+
842 | Meta::A |<----| Meta::B | <....... (instance of )
843 +---------+ +---------+ <------- (inherits from)
846 +---------+ +---------+
848 +---------+ +---------+
850 As I said this is a highly esoteric topic and one you will only run
851 into if you do a lot of subclassing of L<Class::MOP::Class>. If you
852 are interested in why this is an issue see the paper I<Uniform and
853 safe metaclass composition> linked to in the L<SEE ALSO> section of
856 =head2 Using custom metaclasses
858 Always use the L<metaclass> pragma when using a custom metaclass, this
859 will ensure the proper initialization order and not accidentally
860 create an incorrect type of metaclass for you. This is a very rare
861 problem, and one which can only occur if you are doing deep metaclass
862 programming. So in other words, don't worry about it.
864 Note that if you're using L<Moose> we encourage you to I<not> use
865 L<metaclass> pragma, and instead use L<Moose::Util::MetaRole> to apply
866 roles to a class's metaclasses. This topic is covered at length in
867 various L<Moose::Cookbook> recipes.
871 The meta-object protocol is divided into 4 main sub-protocols:
873 =head2 The Class protocol
875 This provides a means of manipulating and introspecting a Perl 5
876 class. It handles symbol table hacking for you, and provides a rich
877 set of methods that go beyond simple package introspection.
879 See L<Class::MOP::Class> for more details.
881 =head2 The Attribute protocol
883 This provides a consistent representation for an attribute of a Perl 5
884 class. Since there are so many ways to create and handle attributes in
885 Perl 5 OO, the Attribute protocol provide as much of a unified
886 approach as possible. Of course, you are always free to extend this
887 protocol by subclassing the appropriate classes.
889 See L<Class::MOP::Attribute> for more details.
891 =head2 The Method protocol
893 This provides a means of manipulating and introspecting methods in the
894 Perl 5 object system. As with attributes, there are many ways to
895 approach this topic, so we try to keep it pretty basic, while still
896 making it possible to extend the system in many ways.
898 See L<Class::MOP::Method> for more details.
900 =head2 The Instance protocol
902 This provides a layer of abstraction for creating object instances.
903 Since the other layers use this protocol, it is relatively easy to
904 change the type of your instances from the default hash reference to
905 some other type of reference. Several examples are provided in the
906 F<examples/> directory included in this distribution.
908 See L<Class::MOP::Instance> for more details.
912 Note that this module does not export any constants or functions.
918 =item I<Class::MOP::IS_RUNNING_ON_5_10>
920 We set this constant depending on what version perl we are on, this
921 allows us to take advantage of new 5.10 features and stay backwards
926 =head2 Utility functions
928 Note that these are all called as B<functions, not methods>.
932 =item B<Class::MOP::load_class($class_name)>
934 This will load the specified C<$class_name>, if it is not already
935 loaded (as reported by C<is_class_loaded>). This function can be used
936 in place of tricks like C<eval "use $module"> or using C<require>
937 unconditionally. This will return the metaclass of C<$class_name> if
938 one exists, otherwise it will return C<$class_name>.
940 =item B<Class::MOP::is_class_loaded($class_name)>
942 Returns a boolean indicating whether or not C<$class_name> has been
945 This does a basic check of the symbol table to try and determine as
946 best it can if the C<$class_name> is loaded, it is probably correct
947 about 99% of the time, but it can be fooled into reporting false
948 positives. In particular, loading any of the core L<IO> modules will
949 cause most of the rest of the core L<IO> modules to falsely report
950 having been loaded, due to the way the base L<IO> module works.
952 =item B<Class::MOP::get_code_info($code)>
954 This function returns two values, the name of the package the C<$code>
955 is from and the name of the C<$code> itself. This is used by several
956 elements of the MOP to determine where a given C<$code> reference is
959 =item B<Class::MOP::class_of($instance_or_class_name)>
961 This will return the metaclass of the given instance or class name. If the
962 class lacks a metaclass, no metaclass will be initialized, and C<undef> will be
965 =item B<Class::MOP::check_package_cache_flag($pkg)>
967 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
969 This will return an integer that is managed by L<Class::MOP::Class> to
970 determine if a module's symbol table has been altered.
972 In Perl 5.10 or greater, this flag is package specific. However in
973 versions prior to 5.10, this will use the C<PL_sub_generation>
974 variable which is not package specific.
976 =item B<Class::MOP::load_first_existing_class(@class_names)>
978 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
980 Given a list of class names, this function will attempt to load each
983 If it finds a class it can load, it will return that class' name. If
984 none of the classes can be loaded, it will throw an exception.
988 =head2 Metaclass cache functions
990 Class::MOP holds a cache of metaclasses. The following are functions
991 (B<not methods>) which can be used to access that cache. It is not
992 recommended that you mess with these. Bad things could happen, but if
993 you are brave and willing to risk it: go for it!
997 =item B<Class::MOP::get_all_metaclasses>
999 This will return a hash of all the metaclass instances that have
1000 been cached by L<Class::MOP::Class>, keyed by the package name.
1002 =item B<Class::MOP::get_all_metaclass_instances>
1004 This will return a list of all the metaclass instances that have
1005 been cached by L<Class::MOP::Class>.
1007 =item B<Class::MOP::get_all_metaclass_names>
1009 This will return a list of all the metaclass names that have
1010 been cached by L<Class::MOP::Class>.
1012 =item B<Class::MOP::get_metaclass_by_name($name)>
1014 This will return a cached L<Class::MOP::Class> instance, or nothing
1015 if no metaclass exists with that C<$name>.
1017 =item B<Class::MOP::store_metaclass_by_name($name, $meta)>
1019 This will store a metaclass in the cache at the supplied C<$key>.
1021 =item B<Class::MOP::weaken_metaclass($name)>
1023 In rare cases (e.g. anonymous metaclasses) it is desirable to
1024 store a weakened reference in the metaclass cache. This
1025 function will weaken the reference to the metaclass stored
1028 =item B<Class::MOP::does_metaclass_exist($name)>
1030 This will return true of there exists a metaclass stored in the
1031 C<$name> key, and return false otherwise.
1033 =item B<Class::MOP::remove_metaclass_by_name($name)>
1035 This will remove the metaclass stored in the C<$name> key.
1043 There are very few books out on Meta Object Protocols and Metaclasses
1044 because it is such an esoteric topic. The following books are really
1045 the only ones I have found. If you know of any more, B<I<please>>
1046 email me and let me know, I would love to hear about them.
1050 =item I<The Art of the Meta Object Protocol>
1052 =item I<Advances in Object-Oriented Metalevel Architecture and Reflection>
1054 =item I<Putting MetaClasses to Work>
1056 =item I<Smalltalk: The Language>
1064 =item "Uniform and safe metaclass composition"
1066 An excellent paper by the people who brought us the original Traits paper.
1067 This paper is on how Traits can be used to do safe metaclass composition,
1068 and offers an excellent introduction section which delves into the topic of
1069 metaclass compatibility.
1071 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
1073 =item "Safe Metaclass Programming"
1075 This paper seems to precede the above paper, and propose a mix-in based
1076 approach as opposed to the Traits based approach. Both papers have similar
1077 information on the metaclass compatibility problem space.
1079 L<http://citeseer.ist.psu.edu/37617.html>
1087 =item The Perl 6 MetaModel work in the Pugs project
1091 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
1093 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1103 =item CPAN Module Review of Class::MOP
1105 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1109 =head1 SIMILAR MODULES
1111 As I have said above, this module is a class-builder-builder, so it is
1112 not the same thing as modules like L<Class::Accessor> and
1113 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1114 with similar goals to this module. The one I have found which is most
1115 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1116 creates are very different from this modules.
1120 All complex software has bugs lurking in it, and this module is no
1123 Please report any bugs to C<bug-class-mop@rt.cpan.org>, or through the
1124 web interface at L<http://rt.cpan.org>.
1126 You can also discuss feature requests or possible bugs on the Moose
1127 mailing list (moose@perl.org) or on IRC at
1128 L<irc://irc.perl.org/#moose>.
1130 =head1 ACKNOWLEDGEMENTS
1136 Thanks to Rob for actually getting the development of this module kick-started.
1142 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1144 B<with contributions from:>
1146 Brandon (blblack) Black
1148 Florian (rafl) Ragwitz
1150 Guillermo (groditi) Roditi
1152 Dave (autarch) Rolsky
1156 Rob (robkinyon) Kinyon
1158 Yuval (nothingmuch) Kogman
1160 Scott (konobi) McWhirter
1162 =head1 COPYRIGHT AND LICENSE
1164 Copyright 2006-2009 by Infinity Interactive, Inc.
1166 L<http://www.iinteractive.com>
1168 This library is free software; you can redistribute it and/or modify
1169 it under the same terms as Perl itself.