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 = '0.86';
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);
135 eval { require($file) };
141 my $class = load_first_existing_class($_[0]);
142 return get_metaclass_by_name($class) || $class;
145 sub _is_valid_class_name {
148 return 0 if ref($class);
149 return 0 unless defined($class);
150 return 0 unless length($class);
152 return 1 if $class =~ /^\w+(?:::\w+)*$/;
159 Carp::carp("Class::MOP::subname is deprecated. Please use Sub::Name directly.");
160 goto \&Sub::Name::subname;
163 sub in_global_destruction {
164 require Devel::GlobalDestruction;
165 Carp::carp("Class::MOP::in_global_destruction is deprecated. Please use Devel::GlobalDestruction directly.");
166 goto \&Devel::GlobalDestruction::in_global_destruction;
169 ## ----------------------------------------------------------------------------
170 ## Setting up our environment ...
171 ## ----------------------------------------------------------------------------
172 ## Class::MOP needs to have a few things in the global perl environment so
173 ## that it can operate effectively. Those things are done here.
174 ## ----------------------------------------------------------------------------
176 # ... nothing yet actually ;)
178 ## ----------------------------------------------------------------------------
180 ## ----------------------------------------------------------------------------
181 ## The code below here is to bootstrap our MOP with itself. This is also
182 ## sometimes called "tying the knot". By doing this, we make it much easier
183 ## to extend the MOP through subclassing and such since now you can use the
184 ## MOP itself to extend itself.
186 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
187 ## ----------------------------------------------------------------------------
189 # We need to add in the meta-attributes here so that
190 # any subclass of Class::MOP::* will be able to
191 # inherit them using _construct_instance
193 ## --------------------------------------------------------
194 ## Class::MOP::Package
196 Class::MOP::Package->meta->add_attribute(
197 Class::MOP::Attribute->new('package' => (
199 # NOTE: we need to do this in order
200 # for the instance meta-object to
201 # not fall into meta-circular death
203 # we just alias the original method
204 # rather than re-produce it here
205 'name' => \&Class::MOP::Package::name
210 Class::MOP::Package->meta->add_attribute(
211 Class::MOP::Attribute->new('namespace' => (
214 # we just alias the original method
215 # rather than re-produce it here
216 'namespace' => \&Class::MOP::Package::namespace
219 default => sub { \undef }
223 ## --------------------------------------------------------
224 ## Class::MOP::Module
227 # yeah this is kind of stretching things a bit,
228 # but truthfully the version should be an attribute
229 # of the Module, the weirdness comes from having to
230 # stick to Perl 5 convention and store it in the
231 # $VERSION package variable. Basically if you just
232 # squint at it, it will look how you want it to look.
233 # Either as a package variable, or as a attribute of
234 # the metaclass, isn't abstraction great :)
236 Class::MOP::Module->meta->add_attribute(
237 Class::MOP::Attribute->new('version' => (
240 # we just alias the original method
241 # rather than re-produce it here
242 'version' => \&Class::MOP::Module::version
245 default => sub { \undef }
250 # By following the same conventions as version here,
251 # we are opening up the possibility that people can
252 # use the $AUTHORITY in non-Class::MOP modules as
255 Class::MOP::Module->meta->add_attribute(
256 Class::MOP::Attribute->new('authority' => (
259 # we just alias the original method
260 # rather than re-produce it here
261 'authority' => \&Class::MOP::Module::authority
264 default => sub { \undef }
268 ## --------------------------------------------------------
271 Class::MOP::Class->meta->add_attribute(
272 Class::MOP::Attribute->new('attributes' => (
274 # NOTE: we need to do this in order
275 # for the instance meta-object to
276 # not fall into meta-circular death
278 # we just alias the original method
279 # rather than re-produce it here
280 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
282 default => sub { {} }
286 Class::MOP::Class->meta->add_attribute(
287 Class::MOP::Attribute->new('methods' => (
290 # we just alias the original method
291 # rather than re-produce it here
292 'get_method_map' => \&Class::MOP::Class::get_method_map
294 default => sub { {} }
298 Class::MOP::Class->meta->add_attribute(
299 Class::MOP::Attribute->new('superclasses' => (
302 # we just alias the original method
303 # rather than re-produce it here
304 'superclasses' => \&Class::MOP::Class::superclasses
307 default => sub { \undef }
311 Class::MOP::Class->meta->add_attribute(
312 Class::MOP::Attribute->new('attribute_metaclass' => (
315 # we just alias the original method
316 # rather than re-produce it here
317 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
319 default => 'Class::MOP::Attribute',
323 Class::MOP::Class->meta->add_attribute(
324 Class::MOP::Attribute->new('method_metaclass' => (
327 # we just alias the original method
328 # rather than re-produce it here
329 'method_metaclass' => \&Class::MOP::Class::method_metaclass
331 default => 'Class::MOP::Method',
335 Class::MOP::Class->meta->add_attribute(
336 Class::MOP::Attribute->new('wrapped_method_metaclass' => (
339 # we just alias the original method
340 # rather than re-produce it here
341 'wrapped_method_metaclass' => \&Class::MOP::Class::wrapped_method_metaclass
343 default => 'Class::MOP::Method::Wrapped',
347 Class::MOP::Class->meta->add_attribute(
348 Class::MOP::Attribute->new('instance_metaclass' => (
350 # NOTE: we need to do this in order
351 # for the instance meta-object to
352 # not fall into meta-circular death
354 # we just alias the original method
355 # rather than re-produce it here
356 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
358 default => 'Class::MOP::Instance',
362 Class::MOP::Class->meta->add_attribute(
363 Class::MOP::Attribute->new('immutable_trait' => (
365 'immutable_trait' => \&Class::MOP::Class::immutable_trait
367 default => "Class::MOP::Class::Immutable::Trait",
371 Class::MOP::Class->meta->add_attribute(
372 Class::MOP::Attribute->new('constructor_name' => (
374 'constructor_name' => \&Class::MOP::Class::constructor_name,
380 Class::MOP::Class->meta->add_attribute(
381 Class::MOP::Attribute->new('constructor_class' => (
383 'constructor_class' => \&Class::MOP::Class::constructor_class,
385 default => "Class::MOP::Method::Constructor",
390 Class::MOP::Class->meta->add_attribute(
391 Class::MOP::Attribute->new('destructor_class' => (
393 'destructor_class' => \&Class::MOP::Class::destructor_class,
399 # we don't actually need to tie the knot with
400 # Class::MOP::Class here, it is actually handled
401 # within Class::MOP::Class itself in the
402 # _construct_class_instance method.
404 ## --------------------------------------------------------
405 ## Class::MOP::Attribute
407 Class::MOP::Attribute->meta->add_attribute(
408 Class::MOP::Attribute->new('name' => (
410 # NOTE: we need to do this in order
411 # for the instance meta-object to
412 # not fall into meta-circular death
414 # we just alias the original method
415 # rather than re-produce it here
416 'name' => \&Class::MOP::Attribute::name
421 Class::MOP::Attribute->meta->add_attribute(
422 Class::MOP::Attribute->new('associated_class' => (
424 # NOTE: we need to do this in order
425 # for the instance meta-object to
426 # not fall into meta-circular death
428 # we just alias the original method
429 # rather than re-produce it here
430 'associated_class' => \&Class::MOP::Attribute::associated_class
435 Class::MOP::Attribute->meta->add_attribute(
436 Class::MOP::Attribute->new('accessor' => (
437 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
438 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
442 Class::MOP::Attribute->meta->add_attribute(
443 Class::MOP::Attribute->new('reader' => (
444 reader => { 'reader' => \&Class::MOP::Attribute::reader },
445 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
449 Class::MOP::Attribute->meta->add_attribute(
450 Class::MOP::Attribute->new('initializer' => (
451 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
452 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
456 Class::MOP::Attribute->meta->add_attribute(
457 Class::MOP::Attribute->new('definition_context' => (
458 reader => { 'definition_context' => \&Class::MOP::Attribute::definition_context },
462 Class::MOP::Attribute->meta->add_attribute(
463 Class::MOP::Attribute->new('writer' => (
464 reader => { 'writer' => \&Class::MOP::Attribute::writer },
465 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
469 Class::MOP::Attribute->meta->add_attribute(
470 Class::MOP::Attribute->new('predicate' => (
471 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
472 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
476 Class::MOP::Attribute->meta->add_attribute(
477 Class::MOP::Attribute->new('clearer' => (
478 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
479 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
483 Class::MOP::Attribute->meta->add_attribute(
484 Class::MOP::Attribute->new('builder' => (
485 reader => { 'builder' => \&Class::MOP::Attribute::builder },
486 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
490 Class::MOP::Attribute->meta->add_attribute(
491 Class::MOP::Attribute->new('init_arg' => (
492 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
493 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
497 Class::MOP::Attribute->meta->add_attribute(
498 Class::MOP::Attribute->new('default' => (
499 # default has a custom 'reader' method ...
500 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
504 Class::MOP::Attribute->meta->add_attribute(
505 Class::MOP::Attribute->new('associated_methods' => (
506 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
507 default => sub { [] }
511 Class::MOP::Attribute->meta->add_attribute(
512 Class::MOP::Attribute->new('insertion_order' => (
513 reader => { 'insertion_order' => \&Class::MOP::Attribute::insertion_order },
514 writer => { '_set_insertion_order' => \&Class::MOP::Attribute::_set_insertion_order },
515 predicate => { 'has_insertion_order' => \&Class::MOP::Attribute::has_insertion_order },
519 Class::MOP::Attribute->meta->add_method('clone' => sub {
521 $self->meta->clone_object($self, @_);
524 ## --------------------------------------------------------
525 ## Class::MOP::Method
526 Class::MOP::Method->meta->add_attribute(
527 Class::MOP::Attribute->new('body' => (
528 reader => { 'body' => \&Class::MOP::Method::body },
532 Class::MOP::Method->meta->add_attribute(
533 Class::MOP::Attribute->new('associated_metaclass' => (
534 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
538 Class::MOP::Method->meta->add_attribute(
539 Class::MOP::Attribute->new('package_name' => (
540 reader => { 'package_name' => \&Class::MOP::Method::package_name },
544 Class::MOP::Method->meta->add_attribute(
545 Class::MOP::Attribute->new('name' => (
546 reader => { 'name' => \&Class::MOP::Method::name },
550 Class::MOP::Method->meta->add_attribute(
551 Class::MOP::Attribute->new('original_method' => (
552 reader => { 'original_method' => \&Class::MOP::Method::original_method },
553 writer => { '_set_original_method' => \&Class::MOP::Method::_set_original_method },
557 Class::MOP::Method->meta->add_method('clone' => sub {
559 my $clone = $self->meta->clone_object($self, @_);
560 $clone->_set_original_method($self);
564 ## --------------------------------------------------------
565 ## Class::MOP::Method::Wrapped
568 # the way this item is initialized, this
569 # really does not follow the standard
570 # practices of attributes, but we put
571 # it here for completeness
572 Class::MOP::Method::Wrapped->meta->add_attribute(
573 Class::MOP::Attribute->new('modifier_table')
576 ## --------------------------------------------------------
577 ## Class::MOP::Method::Generated
579 Class::MOP::Method::Generated->meta->add_attribute(
580 Class::MOP::Attribute->new('is_inline' => (
581 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
586 Class::MOP::Method::Generated->meta->add_attribute(
587 Class::MOP::Attribute->new('definition_context' => (
588 reader => { 'definition_context' => \&Class::MOP::Method::Generated::definition_context },
593 ## --------------------------------------------------------
594 ## Class::MOP::Method::Inlined
596 Class::MOP::Method::Inlined->meta->add_attribute(
597 Class::MOP::Attribute->new('_expected_method_class' => (
598 reader => { '_expected_method_class' => \&Class::MOP::Method::Inlined::_expected_method_class },
602 ## --------------------------------------------------------
603 ## Class::MOP::Method::Accessor
605 Class::MOP::Method::Accessor->meta->add_attribute(
606 Class::MOP::Attribute->new('attribute' => (
608 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
613 Class::MOP::Method::Accessor->meta->add_attribute(
614 Class::MOP::Attribute->new('accessor_type' => (
615 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
619 ## --------------------------------------------------------
620 ## Class::MOP::Method::Constructor
622 Class::MOP::Method::Constructor->meta->add_attribute(
623 Class::MOP::Attribute->new('options' => (
625 'options' => \&Class::MOP::Method::Constructor::options
627 default => sub { +{} }
631 Class::MOP::Method::Constructor->meta->add_attribute(
632 Class::MOP::Attribute->new('associated_metaclass' => (
633 init_arg => "metaclass", # FIXME alias and rename
635 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
640 ## --------------------------------------------------------
641 ## Class::MOP::Instance
644 # these don't yet do much of anything, but are just
645 # included for completeness
647 Class::MOP::Instance->meta->add_attribute(
648 Class::MOP::Attribute->new('associated_metaclass',
649 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
653 Class::MOP::Instance->meta->add_attribute(
654 Class::MOP::Attribute->new('_class_name',
656 reader => { _class_name => \&Class::MOP::Instance::_class_name },
657 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
658 #default => sub { $_[0]->associated_metaclass->name },
662 Class::MOP::Instance->meta->add_attribute(
663 Class::MOP::Attribute->new('attributes',
664 reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
668 Class::MOP::Instance->meta->add_attribute(
669 Class::MOP::Attribute->new('slots',
670 reader => { slots => \&Class::MOP::Instance::slots },
674 Class::MOP::Instance->meta->add_attribute(
675 Class::MOP::Attribute->new('slot_hash',
676 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
681 # we need the meta instance of the meta instance to be created now, in order
682 # for the constructor to be able to use it
683 Class::MOP::Instance->meta->get_meta_instance;
685 # pretend the add_method never happenned. it hasn't yet affected anything
686 undef Class::MOP::Instance->meta->{_package_cache_flag};
688 ## --------------------------------------------------------
689 ## Now close all the Class::MOP::* classes
691 # NOTE: we don't need to inline the the accessors this only lengthens
692 # the compile time of the MOP, and gives us no actual benefits.
694 # this is just nitpicking to ensure Class::MOP::Class->meta == ->meta->meta
695 Class::MOP::Class->meta->_immutable_metaclass;
696 $Class::MOP::Class::immutable_metaclass_cache{"Class::MOP::Class"}{"Class::MOP::Class::Immutable::Trait"} = Class::MOP::Class::Immutable::Class::MOP::Class->meta;
698 $_->meta->make_immutable(
699 inline_constructor => 1,
700 replace_constructor => 1,
701 constructor_name => "_new",
702 inline_accessors => 0,
707 Class::MOP::Class::Immutable::Trait
708 Class::MOP::Class::Immutable::Class::MOP::Class
710 Class::MOP::Attribute
716 Class::MOP::Method::Generated
717 Class::MOP::Method::Inlined
719 Class::MOP::Method::Accessor
720 Class::MOP::Method::Constructor
721 Class::MOP::Method::Wrapped
732 Class::MOP - A Meta Object Protocol for Perl 5
736 This module is a fully functioning meta object protocol for the
737 Perl 5 object system. It makes no attempt to change the behavior or
738 characteristics of the Perl 5 object system, only to create a
739 protocol for its manipulation and introspection.
741 That said, it does attempt to create the tools for building a rich set
742 of extensions to the Perl 5 object system. Every attempt has been made
743 to abide by the spirit of the Perl 5 object system that we all know
746 This documentation is sparse on conceptual details. We suggest looking
747 at the items listed in the L<SEE ALSO> section for more
748 information. In particular the book "The Art of the Meta Object
749 Protocol" was very influential in the development of this system.
751 =head2 What is a Meta Object Protocol?
753 A meta object protocol is an API to an object system.
755 To be more specific, it abstracts the components of an object system
756 (classes, object, methods, object attributes, etc.). These
757 abstractions can then be used to inspect and manipulate the object
758 system which they describe.
760 It can be said that there are two MOPs for any object system; the
761 implicit MOP and the explicit MOP. The implicit MOP handles things
762 like method dispatch or inheritance, which happen automatically as
763 part of how the object system works. The explicit MOP typically
764 handles the introspection/reflection features of the object system.
766 All object systems have implicit MOPs. Without one, they would not
767 work. Explicit MOPs are much less common, and depending on the
768 language can vary from restrictive (Reflection in Java or C#) to wide
769 open (CLOS is a perfect example).
771 =head2 Yet Another Class Builder! Why?
773 This is B<not> a class builder so much as a I<class builder
774 B<builder>>. The intent is that an end user will not use this module
775 directly, but instead this module is used by module authors to build
776 extensions and features onto the Perl 5 object system.
778 This system is used by L<Moose>, which supplies a powerful class
779 builder system built entirely on top of C<Class::MOP>.
781 =head2 Who is this module for?
783 This module is for anyone who has ever created or wanted to create a
784 module for the Class:: namespace. The tools which this module provides
785 make doing complex Perl 5 wizardry simpler, by removing such barriers
786 as the need to hack symbol tables, or understand the fine details of
789 =head2 What changes do I have to make to use this module?
791 This module was designed to be as unintrusive as possible. Many of its
792 features are accessible without B<any> change to your existing
793 code. It is meant to be a compliment to your existing code and not an
794 intrusion on your code base. Unlike many other B<Class::> modules,
795 this module B<does not> require you subclass it, or even that you
796 C<use> it in within your module's package.
798 The only features which requires additions to your code are the
799 attribute handling and instance construction features, and these are
800 both completely optional features. The only reason for this is because
801 Perl 5's object system does not actually have these features built
802 in. More information about this feature can be found below.
804 =head2 About Performance
806 It is a common misconception that explicit MOPs are a performance hit.
807 This is not a universal truth, it is a side-effect of some specific
808 implementations. For instance, using Java reflection is slow because
809 the JVM cannot take advantage of any compiler optimizations, and the
810 JVM has to deal with much more runtime type information as well.
812 Reflection in C# is marginally better as it was designed into the
813 language and runtime (the CLR). In contrast, CLOS (the Common Lisp
814 Object System) was built to support an explicit MOP, and so
815 performance is tuned for it.
817 This library in particular does its absolute best to avoid putting
818 B<any> drain at all upon your code's performance. In fact, by itself
819 it does nothing to affect your existing code. So you only pay for what
822 =head2 About Metaclass compatibility
824 This module makes sure that all metaclasses created are both upwards
825 and downwards compatible. The topic of metaclass compatibility is
826 highly esoteric and is something only encountered when doing deep and
827 involved metaclass hacking. There are two basic kinds of metaclass
828 incompatibility; upwards and downwards.
830 Upwards metaclass compatibility means that the metaclass of a
831 given class is either the same as (or a subclass of) all of the
834 Downward metaclass compatibility means that the metaclasses of a
835 given class's ancestors are all either the same as (or a subclass
838 Here is a diagram showing a set of two classes (C<A> and C<B>) and
839 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
840 metaclass compatibility both upwards and downwards.
842 +---------+ +---------+
843 | Meta::A |<----| Meta::B | <....... (instance of )
844 +---------+ +---------+ <------- (inherits from)
847 +---------+ +---------+
849 +---------+ +---------+
851 As I said this is a highly esoteric topic and one you will only run
852 into if you do a lot of subclassing of L<Class::MOP::Class>. If you
853 are interested in why this is an issue see the paper I<Uniform and
854 safe metaclass composition> linked to in the L<SEE ALSO> section of
857 =head2 Using custom metaclasses
859 Always use the L<metaclass> pragma when using a custom metaclass, this
860 will ensure the proper initialization order and not accidentally
861 create an incorrect type of metaclass for you. This is a very rare
862 problem, and one which can only occur if you are doing deep metaclass
863 programming. So in other words, don't worry about it.
865 Note that if you're using L<Moose> we encourage you to I<not> use
866 L<metaclass> pragma, and instead use L<Moose::Util::MetaRole> to apply
867 roles to a class's metaclasses. This topic is covered at length in
868 various L<Moose::Cookbook> recipes.
872 The meta-object protocol is divided into 4 main sub-protocols:
874 =head2 The Class protocol
876 This provides a means of manipulating and introspecting a Perl 5
877 class. It handles symbol table hacking for you, and provides a rich
878 set of methods that go beyond simple package introspection.
880 See L<Class::MOP::Class> for more details.
882 =head2 The Attribute protocol
884 This provides a consistent representation for an attribute of a Perl 5
885 class. Since there are so many ways to create and handle attributes in
886 Perl 5 OO, the Attribute protocol provide as much of a unified
887 approach as possible. Of course, you are always free to extend this
888 protocol by subclassing the appropriate classes.
890 See L<Class::MOP::Attribute> for more details.
892 =head2 The Method protocol
894 This provides a means of manipulating and introspecting methods in the
895 Perl 5 object system. As with attributes, there are many ways to
896 approach this topic, so we try to keep it pretty basic, while still
897 making it possible to extend the system in many ways.
899 See L<Class::MOP::Method> for more details.
901 =head2 The Instance protocol
903 This provides a layer of abstraction for creating object instances.
904 Since the other layers use this protocol, it is relatively easy to
905 change the type of your instances from the default hash reference to
906 some other type of reference. Several examples are provided in the
907 F<examples/> directory included in this distribution.
909 See L<Class::MOP::Instance> for more details.
913 Note that this module does not export any constants or functions.
919 =item I<Class::MOP::IS_RUNNING_ON_5_10>
921 We set this constant depending on what version perl we are on, this
922 allows us to take advantage of new 5.10 features and stay backwards
927 =head2 Utility functions
929 Note that these are all called as B<functions, not methods>.
933 =item B<Class::MOP::load_class($class_name)>
935 This will load the specified C<$class_name>, if it is not already
936 loaded (as reported by C<is_class_loaded>). This function can be used
937 in place of tricks like C<eval "use $module"> or using C<require>
938 unconditionally. This will return the metaclass of C<$class_name> if
939 one exists, otherwise it will return C<$class_name>.
941 =item B<Class::MOP::is_class_loaded($class_name)>
943 Returns a boolean indicating whether or not C<$class_name> has been
946 This does a basic check of the symbol table to try and determine as
947 best it can if the C<$class_name> is loaded, it is probably correct
948 about 99% of the time, but it can be fooled into reporting false
949 positives. In particular, loading any of the core L<IO> modules will
950 cause most of the rest of the core L<IO> modules to falsely report
951 having been loaded, due to the way the base L<IO> module works.
953 =item B<Class::MOP::get_code_info($code)>
955 This function returns two values, the name of the package the C<$code>
956 is from and the name of the C<$code> itself. This is used by several
957 elements of the MOP to determine where a given C<$code> reference is
960 =item B<Class::MOP::class_of($instance_or_class_name)>
962 This will return the metaclass of the given instance or class name. If the
963 class lacks a metaclass, no metaclass will be initialized, and C<undef> will be
966 =item B<Class::MOP::check_package_cache_flag($pkg)>
968 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
970 This will return an integer that is managed by L<Class::MOP::Class> to
971 determine if a module's symbol table has been altered.
973 In Perl 5.10 or greater, this flag is package specific. However in
974 versions prior to 5.10, this will use the C<PL_sub_generation>
975 variable which is not package specific.
977 =item B<Class::MOP::load_first_existing_class(@class_names)>
979 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
981 Given a list of class names, this function will attempt to load each
984 If it finds a class it can load, it will return that class' name. If
985 none of the classes can be loaded, it will throw an exception.
989 =head2 Metaclass cache functions
991 Class::MOP holds a cache of metaclasses. The following are functions
992 (B<not methods>) which can be used to access that cache. It is not
993 recommended that you mess with these. Bad things could happen, but if
994 you are brave and willing to risk it: go for it!
998 =item B<Class::MOP::get_all_metaclasses>
1000 This will return a hash of all the metaclass instances that have
1001 been cached by L<Class::MOP::Class>, keyed by the package name.
1003 =item B<Class::MOP::get_all_metaclass_instances>
1005 This will return a list of all the metaclass instances that have
1006 been cached by L<Class::MOP::Class>.
1008 =item B<Class::MOP::get_all_metaclass_names>
1010 This will return a list of all the metaclass names that have
1011 been cached by L<Class::MOP::Class>.
1013 =item B<Class::MOP::get_metaclass_by_name($name)>
1015 This will return a cached L<Class::MOP::Class> instance, or nothing
1016 if no metaclass exists with that C<$name>.
1018 =item B<Class::MOP::store_metaclass_by_name($name, $meta)>
1020 This will store a metaclass in the cache at the supplied C<$key>.
1022 =item B<Class::MOP::weaken_metaclass($name)>
1024 In rare cases (e.g. anonymous metaclasses) it is desirable to
1025 store a weakened reference in the metaclass cache. This
1026 function will weaken the reference to the metaclass stored
1029 =item B<Class::MOP::does_metaclass_exist($name)>
1031 This will return true of there exists a metaclass stored in the
1032 C<$name> key, and return false otherwise.
1034 =item B<Class::MOP::remove_metaclass_by_name($name)>
1036 This will remove the metaclass stored in the C<$name> key.
1044 There are very few books out on Meta Object Protocols and Metaclasses
1045 because it is such an esoteric topic. The following books are really
1046 the only ones I have found. If you know of any more, B<I<please>>
1047 email me and let me know, I would love to hear about them.
1051 =item I<The Art of the Meta Object Protocol>
1053 =item I<Advances in Object-Oriented Metalevel Architecture and Reflection>
1055 =item I<Putting MetaClasses to Work>
1057 =item I<Smalltalk: The Language>
1065 =item "Uniform and safe metaclass composition"
1067 An excellent paper by the people who brought us the original Traits paper.
1068 This paper is on how Traits can be used to do safe metaclass composition,
1069 and offers an excellent introduction section which delves into the topic of
1070 metaclass compatibility.
1072 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
1074 =item "Safe Metaclass Programming"
1076 This paper seems to precede the above paper, and propose a mix-in based
1077 approach as opposed to the Traits based approach. Both papers have similar
1078 information on the metaclass compatibility problem space.
1080 L<http://citeseer.ist.psu.edu/37617.html>
1088 =item The Perl 6 MetaModel work in the Pugs project
1092 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
1094 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1104 =item CPAN Module Review of Class::MOP
1106 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1110 =head1 SIMILAR MODULES
1112 As I have said above, this module is a class-builder-builder, so it is
1113 not the same thing as modules like L<Class::Accessor> and
1114 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1115 with similar goals to this module. The one I have found which is most
1116 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1117 creates are very different from this modules.
1121 All complex software has bugs lurking in it, and this module is no
1124 Please report any bugs to C<bug-class-mop@rt.cpan.org>, or through the
1125 web interface at L<http://rt.cpan.org>.
1127 You can also discuss feature requests or possible bugs on the Moose
1128 mailing list (moose@perl.org) or on IRC at
1129 L<irc://irc.perl.org/#moose>.
1131 =head1 ACKNOWLEDGEMENTS
1137 Thanks to Rob for actually getting the development of this module kick-started.
1143 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1145 B<with contributions from:>
1147 Brandon (blblack) Black
1149 Florian (rafl) Ragwitz
1151 Guillermo (groditi) Roditi
1153 Dave (autarch) Rolsky
1157 Rob (robkinyon) Kinyon
1159 Yuval (nothingmuch) Kogman
1161 Scott (konobi) McWhirter
1165 =head1 COPYRIGHT AND LICENSE
1167 Copyright 2006-2009 by Infinity Interactive, Inc.
1169 L<http://www.iinteractive.com>
1171 This library is free software; you can redistribute it and/or modify
1172 it under the same terms as Perl itself.