12 use Devel::GlobalDestruction qw( in_global_destruction );
13 use Scalar::Util 'weaken', 'reftype', 'blessed';
14 use Sub::Name qw( subname );
16 use Class::MOP::Class;
17 use Class::MOP::Attribute;
18 use Class::MOP::Method;
21 *IS_RUNNING_ON_5_10 = ($] < 5.009_005)
26 Carp::cluck("Class::MOP::HAVE_ISAREV is deprecated and will be removed in a future release. It has always returned 1 anyway.");
30 # this is either part of core or set up appropriately by MRO::Compat
31 *check_package_cache_flag = \&mro::get_pkg_gen;
34 our $VERSION = '0.83';
35 our $XS_VERSION = $VERSION;
36 $VERSION = eval $VERSION;
37 our $AUTHORITY = 'cpan:STEVAN';
40 XSLoader::load( __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?
50 # means of accessing all the metaclasses that have
51 # been initialized thus far (for mugwumps obj browser)
52 sub get_all_metaclasses { %METAS }
53 sub get_all_metaclass_instances { values %METAS }
54 sub get_all_metaclass_names { keys %METAS }
55 sub get_metaclass_by_name { $METAS{$_[0]} }
56 sub store_metaclass_by_name { $METAS{$_[0]} = $_[1] }
57 sub weaken_metaclass { weaken($METAS{$_[0]}) }
58 sub does_metaclass_exist { exists $METAS{$_[0]} && defined $METAS{$_[0]} }
59 sub remove_metaclass_by_name { $METAS{$_[0]} = undef }
61 # This handles instances as well as class names
63 return unless defined $_[0];
64 my $class = blessed($_[0]) || $_[0];
65 return $METAS{$class};
69 # We only cache metaclasses, meaning instances of
70 # Class::MOP::Class. We do not cache instance of
71 # Class::MOP::Package or Class::MOP::Module. Mostly
72 # because I don't yet see a good reason to do so.
75 sub _class_to_pmfile {
78 my $file = $class . '.pm';
84 sub load_first_existing_class {
88 foreach my $class (@classes) {
89 unless ( _is_valid_class_name($class) ) {
90 my $display = defined($class) ? $class : 'undef';
91 confess "Invalid class name ($display)";
97 for my $class (@classes) {
98 my $pmfile = _class_to_pmfile($class);
99 my $e = _try_load_one_class($class);
102 $exceptions{$class} = $e;
103 last if $e !~ /^Can't locate \Q$pmfile\E in \@INC/;
111 return $found if $found;
117 "Could not load class (%s) because : %s", $_,
122 exists $exceptions{$_}
127 sub _try_load_one_class {
130 return if is_class_loaded($class);
132 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 $class =~ /^\w+(?:::\w+)*$/;
158 ## ----------------------------------------------------------------------------
159 ## Setting up our environment ...
160 ## ----------------------------------------------------------------------------
161 ## Class::MOP needs to have a few things in the global perl environment so
162 ## that it can operate effectively. Those things are done here.
163 ## ----------------------------------------------------------------------------
165 # ... nothing yet actually ;)
167 ## ----------------------------------------------------------------------------
169 ## ----------------------------------------------------------------------------
170 ## The code below here is to bootstrap our MOP with itself. This is also
171 ## sometimes called "tying the knot". By doing this, we make it much easier
172 ## to extend the MOP through subclassing and such since now you can use the
173 ## MOP itself to extend itself.
175 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
176 ## ----------------------------------------------------------------------------
178 # We need to add in the meta-attributes here so that
179 # any subclass of Class::MOP::* will be able to
180 # inherit them using _construct_instance
182 ## --------------------------------------------------------
183 ## Class::MOP::Package
185 Class::MOP::Package->meta->add_attribute(
186 Class::MOP::Attribute->new('package' => (
188 # NOTE: we need to do this in order
189 # for the instance meta-object to
190 # not fall into meta-circular death
192 # we just alias the original method
193 # rather than re-produce it here
194 'name' => \&Class::MOP::Package::name
199 Class::MOP::Package->meta->add_attribute(
200 Class::MOP::Attribute->new('namespace' => (
203 # we just alias the original method
204 # rather than re-produce it here
205 'namespace' => \&Class::MOP::Package::namespace
208 default => sub { \undef }
212 ## --------------------------------------------------------
213 ## Class::MOP::Module
216 # yeah this is kind of stretching things a bit,
217 # but truthfully the version should be an attribute
218 # of the Module, the weirdness comes from having to
219 # stick to Perl 5 convention and store it in the
220 # $VERSION package variable. Basically if you just
221 # squint at it, it will look how you want it to look.
222 # Either as a package variable, or as a attribute of
223 # the metaclass, isn't abstraction great :)
225 Class::MOP::Module->meta->add_attribute(
226 Class::MOP::Attribute->new('version' => (
229 # we just alias the original method
230 # rather than re-produce it here
231 'version' => \&Class::MOP::Module::version
234 default => sub { \undef }
239 # By following the same conventions as version here,
240 # we are opening up the possibility that people can
241 # use the $AUTHORITY in non-Class::MOP modules as
244 Class::MOP::Module->meta->add_attribute(
245 Class::MOP::Attribute->new('authority' => (
248 # we just alias the original method
249 # rather than re-produce it here
250 'authority' => \&Class::MOP::Module::authority
253 default => sub { \undef }
257 ## --------------------------------------------------------
260 Class::MOP::Class->meta->add_attribute(
261 Class::MOP::Attribute->new('attributes' => (
263 # NOTE: we need to do this in order
264 # for the instance meta-object to
265 # not fall into meta-circular death
267 # we just alias the original method
268 # rather than re-produce it here
269 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
271 default => sub { {} }
275 Class::MOP::Class->meta->add_attribute(
276 Class::MOP::Attribute->new('methods' => (
279 # we just alias the original method
280 # rather than re-produce it here
281 'get_method_map' => \&Class::MOP::Class::get_method_map
283 default => sub { {} }
287 Class::MOP::Class->meta->add_attribute(
288 Class::MOP::Attribute->new('superclasses' => (
291 # we just alias the original method
292 # rather than re-produce it here
293 'superclasses' => \&Class::MOP::Class::superclasses
296 default => sub { \undef }
300 Class::MOP::Class->meta->add_attribute(
301 Class::MOP::Attribute->new('attribute_metaclass' => (
304 # we just alias the original method
305 # rather than re-produce it here
306 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
308 default => 'Class::MOP::Attribute',
312 Class::MOP::Class->meta->add_attribute(
313 Class::MOP::Attribute->new('method_metaclass' => (
316 # we just alias the original method
317 # rather than re-produce it here
318 'method_metaclass' => \&Class::MOP::Class::method_metaclass
320 default => 'Class::MOP::Method',
324 Class::MOP::Class->meta->add_attribute(
325 Class::MOP::Attribute->new('wrapped_method_metaclass' => (
328 # we just alias the original method
329 # rather than re-produce it here
330 'wrapped_method_metaclass' => \&Class::MOP::Class::wrapped_method_metaclass
332 default => 'Class::MOP::Method::Wrapped',
336 Class::MOP::Class->meta->add_attribute(
337 Class::MOP::Attribute->new('instance_metaclass' => (
339 # NOTE: we need to do this in order
340 # for the instance meta-object to
341 # not fall into meta-circular death
343 # we just alias the original method
344 # rather than re-produce it here
345 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
347 default => 'Class::MOP::Instance',
351 Class::MOP::Class->meta->add_attribute(
352 Class::MOP::Attribute->new('immutable_trait' => (
354 'immutable_trait' => \&Class::MOP::Class::immutable_trait
356 default => "Class::MOP::Class::Immutable::Trait",
360 Class::MOP::Class->meta->add_attribute(
361 Class::MOP::Attribute->new('constructor_name' => (
363 'constructor_name' => \&Class::MOP::Class::constructor_name,
369 Class::MOP::Class->meta->add_attribute(
370 Class::MOP::Attribute->new('constructor_class' => (
372 'constructor_class' => \&Class::MOP::Class::constructor_class,
374 default => "Class::MOP::Method::Constructor",
379 Class::MOP::Class->meta->add_attribute(
380 Class::MOP::Attribute->new('destructor_class' => (
382 'destructor_class' => \&Class::MOP::Class::destructor_class,
388 # we don't actually need to tie the knot with
389 # Class::MOP::Class here, it is actually handled
390 # within Class::MOP::Class itself in the
391 # _construct_class_instance method.
393 ## --------------------------------------------------------
394 ## Class::MOP::Attribute
396 Class::MOP::Attribute->meta->add_attribute(
397 Class::MOP::Attribute->new('name' => (
399 # NOTE: we need to do this in order
400 # for the instance meta-object to
401 # not fall into meta-circular death
403 # we just alias the original method
404 # rather than re-produce it here
405 'name' => \&Class::MOP::Attribute::name
410 Class::MOP::Attribute->meta->add_attribute(
411 Class::MOP::Attribute->new('associated_class' => (
413 # NOTE: we need to do this in order
414 # for the instance meta-object to
415 # not fall into meta-circular death
417 # we just alias the original method
418 # rather than re-produce it here
419 'associated_class' => \&Class::MOP::Attribute::associated_class
424 Class::MOP::Attribute->meta->add_attribute(
425 Class::MOP::Attribute->new('accessor' => (
426 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
427 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
431 Class::MOP::Attribute->meta->add_attribute(
432 Class::MOP::Attribute->new('reader' => (
433 reader => { 'reader' => \&Class::MOP::Attribute::reader },
434 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
438 Class::MOP::Attribute->meta->add_attribute(
439 Class::MOP::Attribute->new('initializer' => (
440 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
441 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
445 Class::MOP::Attribute->meta->add_attribute(
446 Class::MOP::Attribute->new('definition_context' => (
447 reader => { 'definition_context' => \&Class::MOP::Attribute::definition_context },
451 Class::MOP::Attribute->meta->add_attribute(
452 Class::MOP::Attribute->new('writer' => (
453 reader => { 'writer' => \&Class::MOP::Attribute::writer },
454 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
458 Class::MOP::Attribute->meta->add_attribute(
459 Class::MOP::Attribute->new('predicate' => (
460 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
461 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
465 Class::MOP::Attribute->meta->add_attribute(
466 Class::MOP::Attribute->new('clearer' => (
467 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
468 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
472 Class::MOP::Attribute->meta->add_attribute(
473 Class::MOP::Attribute->new('builder' => (
474 reader => { 'builder' => \&Class::MOP::Attribute::builder },
475 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
479 Class::MOP::Attribute->meta->add_attribute(
480 Class::MOP::Attribute->new('init_arg' => (
481 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
482 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
486 Class::MOP::Attribute->meta->add_attribute(
487 Class::MOP::Attribute->new('default' => (
488 # default has a custom 'reader' method ...
489 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
493 Class::MOP::Attribute->meta->add_attribute(
494 Class::MOP::Attribute->new('associated_methods' => (
495 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
496 default => sub { [] }
500 Class::MOP::Attribute->meta->add_method('clone' => sub {
502 $self->meta->clone_object($self, @_);
505 ## --------------------------------------------------------
506 ## Class::MOP::Method
507 Class::MOP::Method->meta->add_attribute(
508 Class::MOP::Attribute->new('body' => (
509 reader => { 'body' => \&Class::MOP::Method::body },
513 Class::MOP::Method->meta->add_attribute(
514 Class::MOP::Attribute->new('associated_metaclass' => (
515 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
519 Class::MOP::Method->meta->add_attribute(
520 Class::MOP::Attribute->new('package_name' => (
521 reader => { 'package_name' => \&Class::MOP::Method::package_name },
525 Class::MOP::Method->meta->add_attribute(
526 Class::MOP::Attribute->new('name' => (
527 reader => { 'name' => \&Class::MOP::Method::name },
531 Class::MOP::Method->meta->add_attribute(
532 Class::MOP::Attribute->new('original_method' => (
533 reader => { 'original_method' => \&Class::MOP::Method::original_method },
534 writer => { '_set_original_method' => \&Class::MOP::Method::_set_original_method },
538 Class::MOP::Method->meta->add_method('clone' => sub {
540 my $clone = $self->meta->clone_object($self, @_);
541 $clone->_set_original_method($self);
545 ## --------------------------------------------------------
546 ## Class::MOP::Method::Wrapped
549 # the way this item is initialized, this
550 # really does not follow the standard
551 # practices of attributes, but we put
552 # it here for completeness
553 Class::MOP::Method::Wrapped->meta->add_attribute(
554 Class::MOP::Attribute->new('modifier_table')
557 ## --------------------------------------------------------
558 ## Class::MOP::Method::Generated
560 Class::MOP::Method::Generated->meta->add_attribute(
561 Class::MOP::Attribute->new('is_inline' => (
562 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
567 Class::MOP::Method::Generated->meta->add_attribute(
568 Class::MOP::Attribute->new('definition_context' => (
569 reader => { 'definition_context' => \&Class::MOP::Method::Generated::definition_context },
574 ## --------------------------------------------------------
575 ## Class::MOP::Method::Inlined
577 Class::MOP::Method::Inlined->meta->add_attribute(
578 Class::MOP::Attribute->new('_expected_method_class' => (
579 reader => { '_expected_method_class' => \&Class::MOP::Method::Inlined::_expected_method_class },
583 ## --------------------------------------------------------
584 ## Class::MOP::Method::Accessor
586 Class::MOP::Method::Accessor->meta->add_attribute(
587 Class::MOP::Attribute->new('attribute' => (
589 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
594 Class::MOP::Method::Accessor->meta->add_attribute(
595 Class::MOP::Attribute->new('accessor_type' => (
596 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
600 ## --------------------------------------------------------
601 ## Class::MOP::Method::Constructor
603 Class::MOP::Method::Constructor->meta->add_attribute(
604 Class::MOP::Attribute->new('options' => (
606 'options' => \&Class::MOP::Method::Constructor::options
608 default => sub { +{} }
612 Class::MOP::Method::Constructor->meta->add_attribute(
613 Class::MOP::Attribute->new('associated_metaclass' => (
614 init_arg => "metaclass", # FIXME alias and rename
616 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
621 ## --------------------------------------------------------
622 ## Class::MOP::Instance
625 # these don't yet do much of anything, but are just
626 # included for completeness
628 Class::MOP::Instance->meta->add_attribute(
629 Class::MOP::Attribute->new('associated_metaclass',
630 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
634 Class::MOP::Instance->meta->add_attribute(
635 Class::MOP::Attribute->new('_class_name',
637 reader => { _class_name => \&Class::MOP::Instance::_class_name },
638 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
639 #default => sub { $_[0]->associated_metaclass->name },
643 Class::MOP::Instance->meta->add_attribute(
644 Class::MOP::Attribute->new('attributes',
645 reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
649 Class::MOP::Instance->meta->add_attribute(
650 Class::MOP::Attribute->new('slots',
651 reader => { slots => \&Class::MOP::Instance::slots },
655 Class::MOP::Instance->meta->add_attribute(
656 Class::MOP::Attribute->new('slot_hash',
657 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
662 # we need the meta instance of the meta instance to be created now, in order
663 # for the constructor to be able to use it
664 Class::MOP::Instance->meta->get_meta_instance;
666 # pretend the add_method never happenned. it hasn't yet affected anything
667 undef Class::MOP::Instance->meta->{_package_cache_flag};
669 ## --------------------------------------------------------
670 ## Now close all the Class::MOP::* classes
672 # NOTE: we don't need to inline the the accessors this only lengthens
673 # the compile time of the MOP, and gives us no actual benefits.
675 # this is just nitpicking to ensure Class::MOP::Class->meta == ->meta->meta
676 Class::MOP::Class->meta->_immutable_metaclass;
677 $Class::MOP::Class::immutable_metaclass_cache{"Class::MOP::Class"}{"Class::MOP::Class::Immutable::Trait"} = Class::MOP::Class::Immutable::Class::MOP::Class->meta;
679 $_->meta->make_immutable(
680 inline_constructor => 1,
681 replace_constructor => 1,
682 constructor_name => "_new",
683 inline_accessors => 0,
688 Class::MOP::Class::Immutable::Trait
689 Class::MOP::Class::Immutable::Class::MOP::Class
691 Class::MOP::Attribute
697 Class::MOP::Method::Generated
698 Class::MOP::Method::Inlined
700 Class::MOP::Method::Accessor
701 Class::MOP::Method::Constructor
702 Class::MOP::Method::Wrapped
713 Class::MOP - A Meta Object Protocol for Perl 5
717 This module is a fully functioning meta object protocol for the
718 Perl 5 object system. It makes no attempt to change the behavior or
719 characteristics of the Perl 5 object system, only to create a
720 protocol for its manipulation and introspection.
722 That said, it does attempt to create the tools for building a rich set
723 of extensions to the Perl 5 object system. Every attempt has been made
724 to abide by the spirit of the Perl 5 object system that we all know
727 This documentation is sparse on conceptual details. We suggest looking
728 at the items listed in the L<SEE ALSO> section for more
729 information. In particular the book "The Art of the Meta Object
730 Protocol" was very influential in the development of this system.
732 =head2 What is a Meta Object Protocol?
734 A meta object protocol is an API to an object system.
736 To be more specific, it abstracts the components of an object system
737 (classes, object, methods, object attributes, etc.). These
738 abstractions can then be used to inspect and manipulate the object
739 system which they describe.
741 It can be said that there are two MOPs for any object system; the
742 implicit MOP and the explicit MOP. The implicit MOP handles things
743 like method dispatch or inheritance, which happen automatically as
744 part of how the object system works. The explicit MOP typically
745 handles the introspection/reflection features of the object system.
747 All object systems have implicit MOPs. Without one, they would not
748 work. Explicit MOPs are much less common, and depending on the
749 language can vary from restrictive (Reflection in Java or C#) to wide
750 open (CLOS is a perfect example).
752 =head2 Yet Another Class Builder! Why?
754 This is B<not> a class builder so much as a I<class builder
755 B<builder>>. The intent is that an end user will not use this module
756 directly, but instead this module is used by module authors to build
757 extensions and features onto the Perl 5 object system.
759 This system is used by L<Moose>, which supplies a powerful class
760 builder system built entirely on top of C<Class::MOP>.
762 =head2 Who is this module for?
764 This module is for anyone who has ever created or wanted to create a
765 module for the Class:: namespace. The tools which this module provides
766 make doing complex Perl 5 wizardry simpler, by removing such barriers
767 as the need to hack symbol tables, or understand the fine details of
770 =head2 What changes do I have to make to use this module?
772 This module was designed to be as unintrusive as possible. Many of its
773 features are accessible without B<any> change to your existing
774 code. It is meant to be a compliment to your existing code and not an
775 intrusion on your code base. Unlike many other B<Class::> modules,
776 this module B<does not> require you subclass it, or even that you
777 C<use> it in within your module's package.
779 The only features which requires additions to your code are the
780 attribute handling and instance construction features, and these are
781 both completely optional features. The only reason for this is because
782 Perl 5's object system does not actually have these features built
783 in. More information about this feature can be found below.
785 =head2 About Performance
787 It is a common misconception that explicit MOPs are a performance hit.
788 This is not a universal truth, it is a side-effect of some specific
789 implementations. For instance, using Java reflection is slow because
790 the JVM cannot take advantage of any compiler optimizations, and the
791 JVM has to deal with much more runtime type information as well.
793 Reflection in C# is marginally better as it was designed into the
794 language and runtime (the CLR). In contrast, CLOS (the Common Lisp
795 Object System) was built to support an explicit MOP, and so
796 performance is tuned for it.
798 This library in particular does its absolute best to avoid putting
799 B<any> drain at all upon your code's performance. In fact, by itself
800 it does nothing to affect your existing code. So you only pay for what
803 =head2 About Metaclass compatibility
805 This module makes sure that all metaclasses created are both upwards
806 and downwards compatible. The topic of metaclass compatibility is
807 highly esoteric and is something only encountered when doing deep and
808 involved metaclass hacking. There are two basic kinds of metaclass
809 incompatibility; upwards and downwards.
811 Upwards metaclass compatibility means that the metaclass of a
812 given class is either the same as (or a subclass of) all of the
815 Downward metaclass compatibility means that the metaclasses of a
816 given class's ancestors are all either the same as (or a subclass
819 Here is a diagram showing a set of two classes (C<A> and C<B>) and
820 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
821 metaclass compatibility both upwards and downwards.
823 +---------+ +---------+
824 | Meta::A |<----| Meta::B | <....... (instance of )
825 +---------+ +---------+ <------- (inherits from)
828 +---------+ +---------+
830 +---------+ +---------+
832 As I said this is a highly esoteric topic and one you will only run
833 into if you do a lot of subclassing of L<Class::MOP::Class>. If you
834 are interested in why this is an issue see the paper I<Uniform and
835 safe metaclass composition> linked to in the L<SEE ALSO> section of
838 =head2 Using custom metaclasses
840 Always use the L<metaclass> pragma when using a custom metaclass, this
841 will ensure the proper initialization order and not accidentally
842 create an incorrect type of metaclass for you. This is a very rare
843 problem, and one which can only occur if you are doing deep metaclass
844 programming. So in other words, don't worry about it.
846 Note that if you're using L<Moose> we encourage you to I<not> use
847 L<metaclass> pragma, and instead use L<Moose::Util::MetaRole> to apply
848 roles to a class's metaclasses. This topic is covered at length in
849 various L<Moose::Cookbook> recipes.
853 The meta-object protocol is divided into 4 main sub-protocols:
855 =head2 The Class protocol
857 This provides a means of manipulating and introspecting a Perl 5
858 class. It handles symbol table hacking for you, and provides a rich
859 set of methods that go beyond simple package introspection.
861 See L<Class::MOP::Class> for more details.
863 =head2 The Attribute protocol
865 This provides a consistent representation for an attribute of a Perl 5
866 class. Since there are so many ways to create and handle attributes in
867 Perl 5 OO, the Attribute protocol provide as much of a unified
868 approach as possible. Of course, you are always free to extend this
869 protocol by subclassing the appropriate classes.
871 See L<Class::MOP::Attribute> for more details.
873 =head2 The Method protocol
875 This provides a means of manipulating and introspecting methods in the
876 Perl 5 object system. As with attributes, there are many ways to
877 approach this topic, so we try to keep it pretty basic, while still
878 making it possible to extend the system in many ways.
880 See L<Class::MOP::Method> for more details.
882 =head2 The Instance protocol
884 This provides a layer of abstraction for creating object instances.
885 Since the other layers use this protocol, it is relatively easy to
886 change the type of your instances from the default hash reference to
887 some other type of reference. Several examples are provided in the
888 F<examples/> directory included in this distribution.
890 See L<Class::MOP::Instance> for more details.
894 Note that this module does not export any constants or functions.
900 =item I<Class::MOP::IS_RUNNING_ON_5_10>
902 We set this constant depending on what version perl we are on, this
903 allows us to take advantage of new 5.10 features and stay backwards
908 =head2 Utility functions
910 Note that these are all called as B<functions, not methods>.
914 =item B<Class::MOP::load_class($class_name)>
916 This will load the specified C<$class_name>. This function can be used
917 in place of tricks like C<eval "use $module"> or using C<require>
918 unconditionally. This will return the metaclass of C<$class_name>.
920 =item B<Class::MOP::is_class_loaded($class_name)>
922 Returns a boolean indicating whether or not C<$class_name> has been
925 This does a basic check of the symbol table to try and determine as
926 best it can if the C<$class_name> is loaded, it is probably correct
927 about 99% of the time, but it can be fooled into reporting false
930 =item B<Class::MOP::get_code_info($code)>
932 This function returns two values, the name of the package the C<$code>
933 is from and the name of the C<$code> itself. This is used by several
934 elements of the MOP to determine where a given C<$code> reference is
937 =item B<Class::MOP::class_of($instance_or_class_name)>
939 This will return the metaclass of the given instance or class name.
940 Even if the class lacks a metaclass, no metaclass will be initialized
941 and C<undef> will be returned.
943 =item B<Class::MOP::check_package_cache_flag($pkg)>
945 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
947 This will return an integer that is managed by L<Class::MOP::Class> to
948 determine if a module's symbol table has been altered.
950 In Perl 5.10 or greater, this flag is package specific. However in
951 versions prior to 5.10, this will use the C<PL_sub_generation>
952 variable which is not package specific.
954 =item B<Class::MOP::load_first_existing_class(@class_names)>
956 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
958 Given a list of class names, this function will attempt to load each
961 If it finds a class it can load, it will return that class' name. If
962 none of the classes can be loaded, it will throw an exception.
966 =head2 Metaclass cache functions
968 Class::MOP holds a cache of metaclasses. The following are functions
969 (B<not methods>) which can be used to access that cache. It is not
970 recommended that you mess with these. Bad things could happen, but if
971 you are brave and willing to risk it: go for it!
975 =item B<Class::MOP::get_all_metaclasses>
977 This will return a hash of all the metaclass instances that have
978 been cached by L<Class::MOP::Class>, keyed by the package name.
980 =item B<Class::MOP::get_all_metaclass_instances>
982 This will return a list of all the metaclass instances that have
983 been cached by L<Class::MOP::Class>.
985 =item B<Class::MOP::get_all_metaclass_names>
987 This will return a list of all the metaclass names that have
988 been cached by L<Class::MOP::Class>.
990 =item B<Class::MOP::get_metaclass_by_name($name)>
992 This will return a cached L<Class::MOP::Class> instance, or nothing
993 if no metaclass exists with that C<$name>.
995 =item B<Class::MOP::store_metaclass_by_name($name, $meta)>
997 This will store a metaclass in the cache at the supplied C<$key>.
999 =item B<Class::MOP::weaken_metaclass($name)>
1001 In rare cases (e.g. anonymous metaclasses) it is desirable to
1002 store a weakened reference in the metaclass cache. This
1003 function will weaken the reference to the metaclass stored
1006 =item B<Class::MOP::does_metaclass_exist($name)>
1008 This will return true of there exists a metaclass stored in the
1009 C<$name> key, and return false otherwise.
1011 =item B<Class::MOP::remove_metaclass_by_name($name)>
1013 This will remove the metaclass stored in the C<$name> key.
1021 There are very few books out on Meta Object Protocols and Metaclasses
1022 because it is such an esoteric topic. The following books are really
1023 the only ones I have found. If you know of any more, B<I<please>>
1024 email me and let me know, I would love to hear about them.
1028 =item I<The Art of the Meta Object Protocol>
1030 =item I<Advances in Object-Oriented Metalevel Architecture and Reflection>
1032 =item I<Putting MetaClasses to Work>
1034 =item I<Smalltalk: The Language>
1042 =item "Uniform and safe metaclass composition"
1044 An excellent paper by the people who brought us the original Traits paper.
1045 This paper is on how Traits can be used to do safe metaclass composition,
1046 and offers an excellent introduction section which delves into the topic of
1047 metaclass compatibility.
1049 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
1051 =item "Safe Metaclass Programming"
1053 This paper seems to precede the above paper, and propose a mix-in based
1054 approach as opposed to the Traits based approach. Both papers have similar
1055 information on the metaclass compatibility problem space.
1057 L<http://citeseer.ist.psu.edu/37617.html>
1065 =item The Perl 6 MetaModel work in the Pugs project
1069 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
1071 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1081 =item CPAN Module Review of Class::MOP
1083 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1087 =head1 SIMILAR MODULES
1089 As I have said above, this module is a class-builder-builder, so it is
1090 not the same thing as modules like L<Class::Accessor> and
1091 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1092 with similar goals to this module. The one I have found which is most
1093 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1094 creates are very different from this modules.
1098 All complex software has bugs lurking in it, and this module is no
1101 Please report any bugs to C<bug-class-mop@rt.cpan.org>, or through the
1102 web interface at L<http://rt.cpan.org>.
1104 You can also discuss feature requests or possible bugs on the Moose
1105 mailing list (moose@perl.org) or on IRC at
1106 L<irc://irc.perl.org/#moose>.
1108 =head1 ACKNOWLEDGEMENTS
1114 Thanks to Rob for actually getting the development of this module kick-started.
1120 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1122 B<with contributions from:>
1124 Brandon (blblack) Black
1126 Florian (rafl) Ragwitz
1128 Guillermo (groditi) Roditi
1130 Dave (autarch) Rolsky
1134 Rob (robkinyon) Kinyon
1136 Yuval (nothingmuch) Kogman
1138 Scott (konobi) McWhirter
1140 =head1 COPYRIGHT AND LICENSE
1142 Copyright 2006-2009 by Infinity Interactive, Inc.
1144 L<http://www.iinteractive.com>
1146 This library is free software; you can redistribute it and/or modify
1147 it under the same terms as Perl itself.