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 = '0.92';
33 our $XS_VERSION = $VERSION;
34 $VERSION = eval $VERSION;
35 our $AUTHORITY = 'cpan:STEVAN';
39 local *dl_load_flags = sub{ 0x01 };
40 DynaLoader::bootstrap_inherit( __PACKAGE__, $XS_VERSION );
44 # Metaclasses are singletons, so we cache them here.
45 # there is no need to worry about destruction though
46 # because they should die only when the program dies.
47 # After all, do package definitions even get reaped?
48 # Anonymous classes manage their own destruction.
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 { delete $METAS{$_[0]}; return }
60 # This handles instances as well as class names
62 return unless defined $_[0];
63 my $class = blessed($_[0]) || $_[0];
64 return $METAS{$class};
68 # We only cache metaclasses, meaning instances of
69 # Class::MOP::Class. We do not cache instance of
70 # Class::MOP::Package or Class::MOP::Module. Mostly
71 # because I don't yet see a good reason to do so.
74 sub _class_to_pmfile {
77 my $file = $class . '.pm';
83 sub load_first_existing_class {
87 foreach my $class (@classes) {
88 unless ( _is_valid_class_name($class) ) {
89 my $display = defined($class) ? $class : 'undef';
90 confess "Invalid class name ($display)";
96 for my $class (@classes) {
97 my $e = _try_load_one_class($class);
100 my $pmfile = _class_to_pmfile($class);
101 $exceptions{$class} = $e;
102 last if $e !~ /^Can't locate \Q$pmfile\E in \@INC/;
110 return $found if $found;
116 "Could not load class (%s) because : %s", $_,
121 exists $exceptions{$_}
126 sub _try_load_one_class {
129 return if is_class_loaded($class);
131 my $file = _class_to_pmfile($class);
136 eval { require($file) };
142 my $class = load_first_existing_class($_[0]);
143 return get_metaclass_by_name($class) || $class;
146 sub _is_valid_class_name {
149 return 0 if ref($class);
150 return 0 unless defined($class);
151 return 0 unless length($class);
153 return 1 if $class =~ /^\w+(?:::\w+)*$/;
160 Carp::carp("Class::MOP::subname is deprecated. Please use Sub::Name directly.");
161 goto \&Sub::Name::subname;
164 sub in_global_destruction {
165 require Devel::GlobalDestruction;
166 Carp::carp("Class::MOP::in_global_destruction is deprecated. Please use Devel::GlobalDestruction directly.");
167 goto \&Devel::GlobalDestruction::in_global_destruction;
170 ## ----------------------------------------------------------------------------
171 ## Setting up our environment ...
172 ## ----------------------------------------------------------------------------
173 ## Class::MOP needs to have a few things in the global perl environment so
174 ## that it can operate effectively. Those things are done here.
175 ## ----------------------------------------------------------------------------
177 # ... nothing yet actually ;)
179 ## ----------------------------------------------------------------------------
181 ## ----------------------------------------------------------------------------
182 ## The code below here is to bootstrap our MOP with itself. This is also
183 ## sometimes called "tying the knot". By doing this, we make it much easier
184 ## to extend the MOP through subclassing and such since now you can use the
185 ## MOP itself to extend itself.
187 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
188 ## ----------------------------------------------------------------------------
190 # We need to add in the meta-attributes here so that
191 # any subclass of Class::MOP::* will be able to
192 # inherit them using _construct_instance
194 ## --------------------------------------------------------
195 ## Class::MOP::Package
197 Class::MOP::Package->meta->add_attribute(
198 Class::MOP::Attribute->new('package' => (
200 # NOTE: we need to do this in order
201 # for the instance meta-object to
202 # not fall into meta-circular death
204 # we just alias the original method
205 # rather than re-produce it here
206 'name' => \&Class::MOP::Package::name
211 Class::MOP::Package->meta->add_attribute(
212 Class::MOP::Attribute->new('namespace' => (
215 # we just alias the original method
216 # rather than re-produce it here
217 'namespace' => \&Class::MOP::Package::namespace
220 default => sub { \undef }
224 Class::MOP::Package->meta->add_attribute(
225 Class::MOP::Attribute->new('methods' => (
228 # we just alias the original method
229 # rather than re-produce it here
230 'get_method_map' => \&Class::MOP::Package::get_method_map
232 default => sub { {} }
236 Class::MOP::Package->meta->add_attribute(
237 Class::MOP::Attribute->new('method_metaclass' => (
240 # we just alias the original method
241 # rather than re-produce it here
242 'method_metaclass' => \&Class::MOP::Package::method_metaclass
244 default => 'Class::MOP::Method',
248 Class::MOP::Package->meta->add_attribute(
249 Class::MOP::Attribute->new('wrapped_method_metaclass' => (
252 # we just alias the original method
253 # rather than re-produce it here
254 'wrapped_method_metaclass' => \&Class::MOP::Package::wrapped_method_metaclass
256 default => 'Class::MOP::Method::Wrapped',
260 ## --------------------------------------------------------
261 ## Class::MOP::Module
264 # yeah this is kind of stretching things a bit,
265 # but truthfully the version should be an attribute
266 # of the Module, the weirdness comes from having to
267 # stick to Perl 5 convention and store it in the
268 # $VERSION package variable. Basically if you just
269 # squint at it, it will look how you want it to look.
270 # Either as a package variable, or as a attribute of
271 # the metaclass, isn't abstraction great :)
273 Class::MOP::Module->meta->add_attribute(
274 Class::MOP::Attribute->new('version' => (
277 # we just alias the original method
278 # rather than re-produce it here
279 'version' => \&Class::MOP::Module::version
282 default => sub { \undef }
287 # By following the same conventions as version here,
288 # we are opening up the possibility that people can
289 # use the $AUTHORITY in non-Class::MOP modules as
292 Class::MOP::Module->meta->add_attribute(
293 Class::MOP::Attribute->new('authority' => (
296 # we just alias the original method
297 # rather than re-produce it here
298 'authority' => \&Class::MOP::Module::authority
301 default => sub { \undef }
305 ## --------------------------------------------------------
308 Class::MOP::Class->meta->add_attribute(
309 Class::MOP::Attribute->new('attributes' => (
311 # NOTE: we need to do this in order
312 # for the instance meta-object to
313 # not fall into meta-circular death
315 # we just alias the original method
316 # rather than re-produce it here
317 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
319 default => sub { {} }
323 Class::MOP::Class->meta->add_attribute(
324 Class::MOP::Attribute->new('superclasses' => (
327 # we just alias the original method
328 # rather than re-produce it here
329 'superclasses' => \&Class::MOP::Class::superclasses
332 default => sub { \undef }
336 Class::MOP::Class->meta->add_attribute(
337 Class::MOP::Attribute->new('attribute_metaclass' => (
340 # we just alias the original method
341 # rather than re-produce it here
342 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
344 default => 'Class::MOP::Attribute',
348 Class::MOP::Class->meta->add_attribute(
349 Class::MOP::Attribute->new('instance_metaclass' => (
351 # NOTE: we need to do this in order
352 # for the instance meta-object to
353 # not fall into meta-circular death
355 # we just alias the original method
356 # rather than re-produce it here
357 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
359 default => 'Class::MOP::Instance',
363 Class::MOP::Class->meta->add_attribute(
364 Class::MOP::Attribute->new('immutable_trait' => (
366 'immutable_trait' => \&Class::MOP::Class::immutable_trait
368 default => "Class::MOP::Class::Immutable::Trait",
372 Class::MOP::Class->meta->add_attribute(
373 Class::MOP::Attribute->new('constructor_name' => (
375 'constructor_name' => \&Class::MOP::Class::constructor_name,
381 Class::MOP::Class->meta->add_attribute(
382 Class::MOP::Attribute->new('constructor_class' => (
384 'constructor_class' => \&Class::MOP::Class::constructor_class,
386 default => "Class::MOP::Method::Constructor",
391 Class::MOP::Class->meta->add_attribute(
392 Class::MOP::Attribute->new('destructor_class' => (
394 'destructor_class' => \&Class::MOP::Class::destructor_class,
400 # we don't actually need to tie the knot with
401 # Class::MOP::Class here, it is actually handled
402 # within Class::MOP::Class itself in the
403 # _construct_class_instance method.
405 ## --------------------------------------------------------
406 ## Class::MOP::Attribute
408 Class::MOP::Attribute->meta->add_attribute(
409 Class::MOP::Attribute->new('name' => (
411 # NOTE: we need to do this in order
412 # for the instance meta-object to
413 # not fall into meta-circular death
415 # we just alias the original method
416 # rather than re-produce it here
417 'name' => \&Class::MOP::Attribute::name
422 Class::MOP::Attribute->meta->add_attribute(
423 Class::MOP::Attribute->new('associated_class' => (
425 # NOTE: we need to do this in order
426 # for the instance meta-object to
427 # not fall into meta-circular death
429 # we just alias the original method
430 # rather than re-produce it here
431 'associated_class' => \&Class::MOP::Attribute::associated_class
436 Class::MOP::Attribute->meta->add_attribute(
437 Class::MOP::Attribute->new('accessor' => (
438 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
439 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
443 Class::MOP::Attribute->meta->add_attribute(
444 Class::MOP::Attribute->new('reader' => (
445 reader => { 'reader' => \&Class::MOP::Attribute::reader },
446 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
450 Class::MOP::Attribute->meta->add_attribute(
451 Class::MOP::Attribute->new('initializer' => (
452 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
453 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
457 Class::MOP::Attribute->meta->add_attribute(
458 Class::MOP::Attribute->new('definition_context' => (
459 reader => { 'definition_context' => \&Class::MOP::Attribute::definition_context },
463 Class::MOP::Attribute->meta->add_attribute(
464 Class::MOP::Attribute->new('writer' => (
465 reader => { 'writer' => \&Class::MOP::Attribute::writer },
466 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
470 Class::MOP::Attribute->meta->add_attribute(
471 Class::MOP::Attribute->new('predicate' => (
472 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
473 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
477 Class::MOP::Attribute->meta->add_attribute(
478 Class::MOP::Attribute->new('clearer' => (
479 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
480 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
484 Class::MOP::Attribute->meta->add_attribute(
485 Class::MOP::Attribute->new('builder' => (
486 reader => { 'builder' => \&Class::MOP::Attribute::builder },
487 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
491 Class::MOP::Attribute->meta->add_attribute(
492 Class::MOP::Attribute->new('init_arg' => (
493 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
494 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
498 Class::MOP::Attribute->meta->add_attribute(
499 Class::MOP::Attribute->new('default' => (
500 # default has a custom 'reader' method ...
501 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
505 Class::MOP::Attribute->meta->add_attribute(
506 Class::MOP::Attribute->new('associated_methods' => (
507 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
508 default => sub { [] }
512 Class::MOP::Attribute->meta->add_attribute(
513 Class::MOP::Attribute->new('insertion_order' => (
514 reader => { 'insertion_order' => \&Class::MOP::Attribute::insertion_order },
515 writer => { '_set_insertion_order' => \&Class::MOP::Attribute::_set_insertion_order },
516 predicate => { 'has_insertion_order' => \&Class::MOP::Attribute::has_insertion_order },
520 Class::MOP::Attribute->meta->add_method('clone' => sub {
522 $self->meta->clone_object($self, @_);
525 ## --------------------------------------------------------
526 ## Class::MOP::Method
527 Class::MOP::Method->meta->add_attribute(
528 Class::MOP::Attribute->new('body' => (
529 reader => { 'body' => \&Class::MOP::Method::body },
533 Class::MOP::Method->meta->add_attribute(
534 Class::MOP::Attribute->new('associated_metaclass' => (
535 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
539 Class::MOP::Method->meta->add_attribute(
540 Class::MOP::Attribute->new('package_name' => (
541 reader => { 'package_name' => \&Class::MOP::Method::package_name },
545 Class::MOP::Method->meta->add_attribute(
546 Class::MOP::Attribute->new('name' => (
547 reader => { 'name' => \&Class::MOP::Method::name },
551 Class::MOP::Method->meta->add_attribute(
552 Class::MOP::Attribute->new('original_method' => (
553 reader => { 'original_method' => \&Class::MOP::Method::original_method },
554 writer => { '_set_original_method' => \&Class::MOP::Method::_set_original_method },
558 Class::MOP::Method->meta->add_method('clone' => sub {
560 my $clone = $self->meta->clone_object($self, @_);
561 $clone->_set_original_method($self);
565 ## --------------------------------------------------------
566 ## Class::MOP::Method::Wrapped
569 # the way this item is initialized, this
570 # really does not follow the standard
571 # practices of attributes, but we put
572 # it here for completeness
573 Class::MOP::Method::Wrapped->meta->add_attribute(
574 Class::MOP::Attribute->new('modifier_table')
577 ## --------------------------------------------------------
578 ## Class::MOP::Method::Generated
580 Class::MOP::Method::Generated->meta->add_attribute(
581 Class::MOP::Attribute->new('is_inline' => (
582 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
587 Class::MOP::Method::Generated->meta->add_attribute(
588 Class::MOP::Attribute->new('definition_context' => (
589 reader => { 'definition_context' => \&Class::MOP::Method::Generated::definition_context },
594 ## --------------------------------------------------------
595 ## Class::MOP::Method::Inlined
597 Class::MOP::Method::Inlined->meta->add_attribute(
598 Class::MOP::Attribute->new('_expected_method_class' => (
599 reader => { '_expected_method_class' => \&Class::MOP::Method::Inlined::_expected_method_class },
603 ## --------------------------------------------------------
604 ## Class::MOP::Method::Accessor
606 Class::MOP::Method::Accessor->meta->add_attribute(
607 Class::MOP::Attribute->new('attribute' => (
609 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
614 Class::MOP::Method::Accessor->meta->add_attribute(
615 Class::MOP::Attribute->new('accessor_type' => (
616 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
620 ## --------------------------------------------------------
621 ## Class::MOP::Method::Constructor
623 Class::MOP::Method::Constructor->meta->add_attribute(
624 Class::MOP::Attribute->new('options' => (
626 'options' => \&Class::MOP::Method::Constructor::options
628 default => sub { +{} }
632 Class::MOP::Method::Constructor->meta->add_attribute(
633 Class::MOP::Attribute->new('associated_metaclass' => (
634 init_arg => "metaclass", # FIXME alias and rename
636 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
641 ## --------------------------------------------------------
642 ## Class::MOP::Instance
645 # these don't yet do much of anything, but are just
646 # included for completeness
648 Class::MOP::Instance->meta->add_attribute(
649 Class::MOP::Attribute->new('associated_metaclass',
650 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
654 Class::MOP::Instance->meta->add_attribute(
655 Class::MOP::Attribute->new('_class_name',
657 reader => { _class_name => \&Class::MOP::Instance::_class_name },
658 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
659 #default => sub { $_[0]->associated_metaclass->name },
663 Class::MOP::Instance->meta->add_attribute(
664 Class::MOP::Attribute->new('attributes',
665 reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
669 Class::MOP::Instance->meta->add_attribute(
670 Class::MOP::Attribute->new('slots',
671 reader => { slots => \&Class::MOP::Instance::slots },
675 Class::MOP::Instance->meta->add_attribute(
676 Class::MOP::Attribute->new('slot_hash',
677 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
682 # we need the meta instance of the meta instance to be created now, in order
683 # for the constructor to be able to use it
684 Class::MOP::Instance->meta->get_meta_instance;
686 # pretend the add_method never happenned. it hasn't yet affected anything
687 undef Class::MOP::Instance->meta->{_package_cache_flag};
689 ## --------------------------------------------------------
690 ## Now close all the Class::MOP::* classes
692 # NOTE: we don't need to inline the the accessors this only lengthens
693 # the compile time of the MOP, and gives us no actual benefits.
695 $_->meta->make_immutable(
696 inline_constructor => 0,
697 constructor_name => "_new",
698 inline_accessors => 0,
704 Class::MOP::Attribute
710 Class::MOP::Method::Generated
711 Class::MOP::Method::Inlined
713 Class::MOP::Method::Accessor
714 Class::MOP::Method::Constructor
715 Class::MOP::Method::Wrapped
726 Class::MOP - A Meta Object Protocol for Perl 5
730 This module is a fully functioning meta object protocol for the
731 Perl 5 object system. It makes no attempt to change the behavior or
732 characteristics of the Perl 5 object system, only to create a
733 protocol for its manipulation and introspection.
735 That said, it does attempt to create the tools for building a rich set
736 of extensions to the Perl 5 object system. Every attempt has been made
737 to abide by the spirit of the Perl 5 object system that we all know
740 This documentation is sparse on conceptual details. We suggest looking
741 at the items listed in the L<SEE ALSO> section for more
742 information. In particular the book "The Art of the Meta Object
743 Protocol" was very influential in the development of this system.
745 =head2 What is a Meta Object Protocol?
747 A meta object protocol is an API to an object system.
749 To be more specific, it abstracts the components of an object system
750 (classes, object, methods, object attributes, etc.). These
751 abstractions can then be used to inspect and manipulate the object
752 system which they describe.
754 It can be said that there are two MOPs for any object system; the
755 implicit MOP and the explicit MOP. The implicit MOP handles things
756 like method dispatch or inheritance, which happen automatically as
757 part of how the object system works. The explicit MOP typically
758 handles the introspection/reflection features of the object system.
760 All object systems have implicit MOPs. Without one, they would not
761 work. Explicit MOPs are much less common, and depending on the
762 language can vary from restrictive (Reflection in Java or C#) to wide
763 open (CLOS is a perfect example).
765 =head2 Yet Another Class Builder! Why?
767 This is B<not> a class builder so much as a I<class builder
768 B<builder>>. The intent is that an end user will not use this module
769 directly, but instead this module is used by module authors to build
770 extensions and features onto the Perl 5 object system.
772 This system is used by L<Moose>, which supplies a powerful class
773 builder system built entirely on top of C<Class::MOP>.
775 =head2 Who is this module for?
777 This module is for anyone who has ever created or wanted to create a
778 module for the Class:: namespace. The tools which this module provides
779 make doing complex Perl 5 wizardry simpler, by removing such barriers
780 as the need to hack symbol tables, or understand the fine details of
783 =head2 What changes do I have to make to use this module?
785 This module was designed to be as unintrusive as possible. Many of its
786 features are accessible without B<any> change to your existing
787 code. It is meant to be a compliment to your existing code and not an
788 intrusion on your code base. Unlike many other B<Class::> modules,
789 this module B<does not> require you subclass it, or even that you
790 C<use> it in within your module's package.
792 The only features which requires additions to your code are the
793 attribute handling and instance construction features, and these are
794 both completely optional features. The only reason for this is because
795 Perl 5's object system does not actually have these features built
796 in. More information about this feature can be found below.
798 =head2 About Performance
800 It is a common misconception that explicit MOPs are a performance hit.
801 This is not a universal truth, it is a side-effect of some specific
802 implementations. For instance, using Java reflection is slow because
803 the JVM cannot take advantage of any compiler optimizations, and the
804 JVM has to deal with much more runtime type information as well.
806 Reflection in C# is marginally better as it was designed into the
807 language and runtime (the CLR). In contrast, CLOS (the Common Lisp
808 Object System) was built to support an explicit MOP, and so
809 performance is tuned for it.
811 This library in particular does its absolute best to avoid putting
812 B<any> drain at all upon your code's performance. In fact, by itself
813 it does nothing to affect your existing code. So you only pay for what
816 =head2 About Metaclass compatibility
818 This module makes sure that all metaclasses created are both upwards
819 and downwards compatible. The topic of metaclass compatibility is
820 highly esoteric and is something only encountered when doing deep and
821 involved metaclass hacking. There are two basic kinds of metaclass
822 incompatibility; upwards and downwards.
824 Upwards metaclass compatibility means that the metaclass of a
825 given class is either the same as (or a subclass of) all of the
828 Downward metaclass compatibility means that the metaclasses of a
829 given class's ancestors are all either the same as (or a subclass
832 Here is a diagram showing a set of two classes (C<A> and C<B>) and
833 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
834 metaclass compatibility both upwards and downwards.
836 +---------+ +---------+
837 | Meta::A |<----| Meta::B | <....... (instance of )
838 +---------+ +---------+ <------- (inherits from)
841 +---------+ +---------+
843 +---------+ +---------+
845 As I said this is a highly esoteric topic and one you will only run
846 into if you do a lot of subclassing of L<Class::MOP::Class>. If you
847 are interested in why this is an issue see the paper I<Uniform and
848 safe metaclass composition> linked to in the L<SEE ALSO> section of
851 =head2 Using custom metaclasses
853 Always use the L<metaclass> pragma when using a custom metaclass, this
854 will ensure the proper initialization order and not accidentally
855 create an incorrect type of metaclass for you. This is a very rare
856 problem, and one which can only occur if you are doing deep metaclass
857 programming. So in other words, don't worry about it.
859 Note that if you're using L<Moose> we encourage you to I<not> use
860 L<metaclass> pragma, and instead use L<Moose::Util::MetaRole> to apply
861 roles to a class's metaclasses. This topic is covered at length in
862 various L<Moose::Cookbook> recipes.
866 The meta-object protocol is divided into 4 main sub-protocols:
868 =head2 The Class protocol
870 This provides a means of manipulating and introspecting a Perl 5
871 class. It handles symbol table hacking for you, and provides a rich
872 set of methods that go beyond simple package introspection.
874 See L<Class::MOP::Class> for more details.
876 =head2 The Attribute protocol
878 This provides a consistent representation for an attribute of a Perl 5
879 class. Since there are so many ways to create and handle attributes in
880 Perl 5 OO, the Attribute protocol provide as much of a unified
881 approach as possible. Of course, you are always free to extend this
882 protocol by subclassing the appropriate classes.
884 See L<Class::MOP::Attribute> for more details.
886 =head2 The Method protocol
888 This provides a means of manipulating and introspecting methods in the
889 Perl 5 object system. As with attributes, there are many ways to
890 approach this topic, so we try to keep it pretty basic, while still
891 making it possible to extend the system in many ways.
893 See L<Class::MOP::Method> for more details.
895 =head2 The Instance protocol
897 This provides a layer of abstraction for creating object instances.
898 Since the other layers use this protocol, it is relatively easy to
899 change the type of your instances from the default hash reference to
900 some other type of reference. Several examples are provided in the
901 F<examples/> directory included in this distribution.
903 See L<Class::MOP::Instance> for more details.
907 Note that this module does not export any constants or functions.
913 =item I<Class::MOP::IS_RUNNING_ON_5_10>
915 We set this constant depending on what version perl we are on, this
916 allows us to take advantage of new 5.10 features and stay backwards
921 =head2 Utility functions
923 Note that these are all called as B<functions, not methods>.
927 =item B<Class::MOP::load_class($class_name)>
929 This will load the specified C<$class_name>, if it is not already
930 loaded (as reported by C<is_class_loaded>). This function can be used
931 in place of tricks like C<eval "use $module"> or using C<require>
932 unconditionally. This will return the metaclass of C<$class_name> if
933 one exists, otherwise it will return C<$class_name>.
935 =item B<Class::MOP::is_class_loaded($class_name)>
937 Returns a boolean indicating whether or not C<$class_name> has been
940 This does a basic check of the symbol table to try and determine as
941 best it can if the C<$class_name> is loaded, it is probably correct
942 about 99% of the time, but it can be fooled into reporting false
943 positives. In particular, loading any of the core L<IO> modules will
944 cause most of the rest of the core L<IO> modules to falsely report
945 having been loaded, due to the way the base L<IO> module works.
947 =item B<Class::MOP::get_code_info($code)>
949 This function returns two values, the name of the package the C<$code>
950 is from and the name of the C<$code> itself. This is used by several
951 elements of the MOP to determine where a given C<$code> reference is
954 =item B<Class::MOP::class_of($instance_or_class_name)>
956 This will return the metaclass of the given instance or class name. If the
957 class lacks a metaclass, no metaclass will be initialized, and C<undef> will be
960 =item B<Class::MOP::check_package_cache_flag($pkg)>
962 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
964 This will return an integer that is managed by L<Class::MOP::Class> to
965 determine if a module's symbol table has been altered.
967 In Perl 5.10 or greater, this flag is package specific. However in
968 versions prior to 5.10, this will use the C<PL_sub_generation>
969 variable which is not package specific.
971 =item B<Class::MOP::load_first_existing_class(@class_names)>
973 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
975 Given a list of class names, this function will attempt to load each
978 If it finds a class it can load, it will return that class' name. If
979 none of the classes can be loaded, it will throw an exception.
983 =head2 Metaclass cache functions
985 Class::MOP holds a cache of metaclasses. The following are functions
986 (B<not methods>) which can be used to access that cache. It is not
987 recommended that you mess with these. Bad things could happen, but if
988 you are brave and willing to risk it: go for it!
992 =item B<Class::MOP::get_all_metaclasses>
994 This will return a hash of all the metaclass instances that have
995 been cached by L<Class::MOP::Class>, keyed by the package name.
997 =item B<Class::MOP::get_all_metaclass_instances>
999 This will return a list of all the metaclass instances that have
1000 been cached by L<Class::MOP::Class>.
1002 =item B<Class::MOP::get_all_metaclass_names>
1004 This will return a list of all the metaclass names that have
1005 been cached by L<Class::MOP::Class>.
1007 =item B<Class::MOP::get_metaclass_by_name($name)>
1009 This will return a cached L<Class::MOP::Class> instance, or nothing
1010 if no metaclass exists with that C<$name>.
1012 =item B<Class::MOP::store_metaclass_by_name($name, $meta)>
1014 This will store a metaclass in the cache at the supplied C<$key>.
1016 =item B<Class::MOP::weaken_metaclass($name)>
1018 In rare cases (e.g. anonymous metaclasses) it is desirable to
1019 store a weakened reference in the metaclass cache. This
1020 function will weaken the reference to the metaclass stored
1023 =item B<Class::MOP::does_metaclass_exist($name)>
1025 This will return true of there exists a metaclass stored in the
1026 C<$name> key, and return false otherwise.
1028 =item B<Class::MOP::remove_metaclass_by_name($name)>
1030 This will remove the metaclass stored in the C<$name> key.
1038 There are very few books out on Meta Object Protocols and Metaclasses
1039 because it is such an esoteric topic. The following books are really
1040 the only ones I have found. If you know of any more, B<I<please>>
1041 email me and let me know, I would love to hear about them.
1045 =item I<The Art of the Meta Object Protocol>
1047 =item I<Advances in Object-Oriented Metalevel Architecture and Reflection>
1049 =item I<Putting MetaClasses to Work>
1051 =item I<Smalltalk: The Language>
1059 =item "Uniform and safe metaclass composition"
1061 An excellent paper by the people who brought us the original Traits paper.
1062 This paper is on how Traits can be used to do safe metaclass composition,
1063 and offers an excellent introduction section which delves into the topic of
1064 metaclass compatibility.
1066 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
1068 =item "Safe Metaclass Programming"
1070 This paper seems to precede the above paper, and propose a mix-in based
1071 approach as opposed to the Traits based approach. Both papers have similar
1072 information on the metaclass compatibility problem space.
1074 L<http://citeseer.ist.psu.edu/37617.html>
1082 =item The Perl 6 MetaModel work in the Pugs project
1086 =item L<http://svn.openfoundry.org/pugs/misc/Perl-MetaModel/>
1088 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1098 =item CPAN Module Review of Class::MOP
1100 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1104 =head1 SIMILAR MODULES
1106 As I have said above, this module is a class-builder-builder, so it is
1107 not the same thing as modules like L<Class::Accessor> and
1108 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1109 with similar goals to this module. The one I have found which is most
1110 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1111 creates are very different from this modules.
1115 All complex software has bugs lurking in it, and this module is no
1118 Please report any bugs to C<bug-class-mop@rt.cpan.org>, or through the
1119 web interface at L<http://rt.cpan.org>.
1121 You can also discuss feature requests or possible bugs on the Moose
1122 mailing list (moose@perl.org) or on IRC at
1123 L<irc://irc.perl.org/#moose>.
1125 =head1 ACKNOWLEDGEMENTS
1131 Thanks to Rob for actually getting the development of this module kick-started.
1137 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1139 B<with contributions from:>
1141 Brandon (blblack) Black
1143 Florian (rafl) Ragwitz
1145 Guillermo (groditi) Roditi
1147 Dave (autarch) Rolsky
1151 Rob (robkinyon) Kinyon
1153 Yuval (nothingmuch) Kogman
1155 Scott (konobi) McWhirter
1159 =head1 COPYRIGHT AND LICENSE
1161 Copyright 2006-2009 by Infinity Interactive, Inc.
1163 L<http://www.iinteractive.com>
1165 This library is free software; you can redistribute it and/or modify
1166 it under the same terms as Perl itself.