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 = '0.91';
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?
46 # Anonymous classes manage their own destruction.
49 sub get_all_metaclasses { %METAS }
50 sub get_all_metaclass_instances { values %METAS }
51 sub get_all_metaclass_names { keys %METAS }
52 sub get_metaclass_by_name { $METAS{$_[0]} }
53 sub store_metaclass_by_name { $METAS{$_[0]} = $_[1] }
54 sub weaken_metaclass { weaken($METAS{$_[0]}) }
55 sub does_metaclass_exist { exists $METAS{$_[0]} && defined $METAS{$_[0]} }
56 sub remove_metaclass_by_name { delete $METAS{$_[0]}; return }
58 # This handles instances as well as class names
60 return unless defined $_[0];
61 my $class = blessed($_[0]) || $_[0];
62 return $METAS{$class};
66 # We only cache metaclasses, meaning instances of
67 # Class::MOP::Class. We do not cache instance of
68 # Class::MOP::Package or Class::MOP::Module. Mostly
69 # because I don't yet see a good reason to do so.
72 sub _class_to_pmfile {
75 my $file = $class . '.pm';
81 sub load_first_existing_class {
85 foreach my $class (@classes) {
86 unless ( _is_valid_class_name($class) ) {
87 my $display = defined($class) ? $class : 'undef';
88 confess "Invalid class name ($display)";
94 for my $class (@classes) {
95 my $e = _try_load_one_class($class);
98 my $pmfile = _class_to_pmfile($class);
99 $exceptions{$class} = $e;
100 last if $e !~ /^Can't locate \Q$pmfile\E in \@INC/;
108 return $found if $found;
114 "Could not load class (%s) because : %s", $_,
119 exists $exceptions{$_}
124 sub _try_load_one_class {
127 return if is_class_loaded($class);
129 my $file = _class_to_pmfile($class);
134 eval { require($file) };
140 my $class = load_first_existing_class($_[0]);
141 return get_metaclass_by_name($class) || $class;
144 sub _is_valid_class_name {
147 return 0 if ref($class);
148 return 0 unless defined($class);
149 return 0 unless length($class);
151 return 1 if $class =~ /^\w+(?:::\w+)*$/;
158 Carp::carp("Class::MOP::subname is deprecated. Please use Sub::Name directly.");
159 goto \&Sub::Name::subname;
162 sub in_global_destruction {
163 require Devel::GlobalDestruction;
164 Carp::carp("Class::MOP::in_global_destruction is deprecated. Please use Devel::GlobalDestruction directly.");
165 goto \&Devel::GlobalDestruction::in_global_destruction;
168 ## ----------------------------------------------------------------------------
169 ## Setting up our environment ...
170 ## ----------------------------------------------------------------------------
171 ## Class::MOP needs to have a few things in the global perl environment so
172 ## that it can operate effectively. Those things are done here.
173 ## ----------------------------------------------------------------------------
175 # ... nothing yet actually ;)
177 ## ----------------------------------------------------------------------------
179 ## ----------------------------------------------------------------------------
180 ## The code below here is to bootstrap our MOP with itself. This is also
181 ## sometimes called "tying the knot". By doing this, we make it much easier
182 ## to extend the MOP through subclassing and such since now you can use the
183 ## MOP itself to extend itself.
185 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
186 ## ----------------------------------------------------------------------------
188 # We need to add in the meta-attributes here so that
189 # any subclass of Class::MOP::* will be able to
190 # inherit them using _construct_instance
192 ## --------------------------------------------------------
193 ## Class::MOP::Package
195 Class::MOP::Package->meta->add_attribute(
196 Class::MOP::Attribute->new('package' => (
198 # NOTE: we need to do this in order
199 # for the instance meta-object to
200 # not fall into meta-circular death
202 # we just alias the original method
203 # rather than re-produce it here
204 'name' => \&Class::MOP::Package::name
209 Class::MOP::Package->meta->add_attribute(
210 Class::MOP::Attribute->new('namespace' => (
213 # we just alias the original method
214 # rather than re-produce it here
215 'namespace' => \&Class::MOP::Package::namespace
218 default => sub { \undef }
222 Class::MOP::Package->meta->add_attribute(
223 Class::MOP::Attribute->new('methods' => (
226 # we just alias the original method
227 # rather than re-produce it here
228 'get_method_map' => \&Class::MOP::Package::get_method_map
230 default => sub { {} }
234 Class::MOP::Package->meta->add_attribute(
235 Class::MOP::Attribute->new('method_metaclass' => (
238 # we just alias the original method
239 # rather than re-produce it here
240 'method_metaclass' => \&Class::MOP::Package::method_metaclass
242 default => 'Class::MOP::Method',
246 Class::MOP::Package->meta->add_attribute(
247 Class::MOP::Attribute->new('wrapped_method_metaclass' => (
250 # we just alias the original method
251 # rather than re-produce it here
252 'wrapped_method_metaclass' => \&Class::MOP::Package::wrapped_method_metaclass
254 default => 'Class::MOP::Method::Wrapped',
258 ## --------------------------------------------------------
259 ## Class::MOP::Module
262 # yeah this is kind of stretching things a bit,
263 # but truthfully the version should be an attribute
264 # of the Module, the weirdness comes from having to
265 # stick to Perl 5 convention and store it in the
266 # $VERSION package variable. Basically if you just
267 # squint at it, it will look how you want it to look.
268 # Either as a package variable, or as a attribute of
269 # the metaclass, isn't abstraction great :)
271 Class::MOP::Module->meta->add_attribute(
272 Class::MOP::Attribute->new('version' => (
275 # we just alias the original method
276 # rather than re-produce it here
277 'version' => \&Class::MOP::Module::version
280 default => sub { \undef }
285 # By following the same conventions as version here,
286 # we are opening up the possibility that people can
287 # use the $AUTHORITY in non-Class::MOP modules as
290 Class::MOP::Module->meta->add_attribute(
291 Class::MOP::Attribute->new('authority' => (
294 # we just alias the original method
295 # rather than re-produce it here
296 'authority' => \&Class::MOP::Module::authority
299 default => sub { \undef }
303 ## --------------------------------------------------------
306 Class::MOP::Class->meta->add_attribute(
307 Class::MOP::Attribute->new('attributes' => (
309 # NOTE: we need to do this in order
310 # for the instance meta-object to
311 # not fall into meta-circular death
313 # we just alias the original method
314 # rather than re-produce it here
315 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
317 default => sub { {} }
321 Class::MOP::Class->meta->add_attribute(
322 Class::MOP::Attribute->new('superclasses' => (
325 # we just alias the original method
326 # rather than re-produce it here
327 'superclasses' => \&Class::MOP::Class::superclasses
330 default => sub { \undef }
334 Class::MOP::Class->meta->add_attribute(
335 Class::MOP::Attribute->new('attribute_metaclass' => (
338 # we just alias the original method
339 # rather than re-produce it here
340 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
342 default => 'Class::MOP::Attribute',
346 Class::MOP::Class->meta->add_attribute(
347 Class::MOP::Attribute->new('instance_metaclass' => (
349 # NOTE: we need to do this in order
350 # for the instance meta-object to
351 # not fall into meta-circular death
353 # we just alias the original method
354 # rather than re-produce it here
355 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
357 default => 'Class::MOP::Instance',
361 Class::MOP::Class->meta->add_attribute(
362 Class::MOP::Attribute->new('immutable_trait' => (
364 'immutable_trait' => \&Class::MOP::Class::immutable_trait
366 default => "Class::MOP::Class::Immutable::Trait",
370 Class::MOP::Class->meta->add_attribute(
371 Class::MOP::Attribute->new('constructor_name' => (
373 'constructor_name' => \&Class::MOP::Class::constructor_name,
379 Class::MOP::Class->meta->add_attribute(
380 Class::MOP::Attribute->new('constructor_class' => (
382 'constructor_class' => \&Class::MOP::Class::constructor_class,
384 default => "Class::MOP::Method::Constructor",
389 Class::MOP::Class->meta->add_attribute(
390 Class::MOP::Attribute->new('destructor_class' => (
392 'destructor_class' => \&Class::MOP::Class::destructor_class,
398 # we don't actually need to tie the knot with
399 # Class::MOP::Class here, it is actually handled
400 # within Class::MOP::Class itself in the
401 # _construct_class_instance method.
403 ## --------------------------------------------------------
404 ## Class::MOP::Attribute
406 Class::MOP::Attribute->meta->add_attribute(
407 Class::MOP::Attribute->new('name' => (
409 # NOTE: we need to do this in order
410 # for the instance meta-object to
411 # not fall into meta-circular death
413 # we just alias the original method
414 # rather than re-produce it here
415 'name' => \&Class::MOP::Attribute::name
420 Class::MOP::Attribute->meta->add_attribute(
421 Class::MOP::Attribute->new('associated_class' => (
423 # NOTE: we need to do this in order
424 # for the instance meta-object to
425 # not fall into meta-circular death
427 # we just alias the original method
428 # rather than re-produce it here
429 'associated_class' => \&Class::MOP::Attribute::associated_class
434 Class::MOP::Attribute->meta->add_attribute(
435 Class::MOP::Attribute->new('accessor' => (
436 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
437 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
441 Class::MOP::Attribute->meta->add_attribute(
442 Class::MOP::Attribute->new('reader' => (
443 reader => { 'reader' => \&Class::MOP::Attribute::reader },
444 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
448 Class::MOP::Attribute->meta->add_attribute(
449 Class::MOP::Attribute->new('initializer' => (
450 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
451 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
455 Class::MOP::Attribute->meta->add_attribute(
456 Class::MOP::Attribute->new('definition_context' => (
457 reader => { 'definition_context' => \&Class::MOP::Attribute::definition_context },
461 Class::MOP::Attribute->meta->add_attribute(
462 Class::MOP::Attribute->new('writer' => (
463 reader => { 'writer' => \&Class::MOP::Attribute::writer },
464 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
468 Class::MOP::Attribute->meta->add_attribute(
469 Class::MOP::Attribute->new('predicate' => (
470 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
471 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
475 Class::MOP::Attribute->meta->add_attribute(
476 Class::MOP::Attribute->new('clearer' => (
477 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
478 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
482 Class::MOP::Attribute->meta->add_attribute(
483 Class::MOP::Attribute->new('builder' => (
484 reader => { 'builder' => \&Class::MOP::Attribute::builder },
485 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
489 Class::MOP::Attribute->meta->add_attribute(
490 Class::MOP::Attribute->new('init_arg' => (
491 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
492 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
496 Class::MOP::Attribute->meta->add_attribute(
497 Class::MOP::Attribute->new('default' => (
498 # default has a custom 'reader' method ...
499 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
503 Class::MOP::Attribute->meta->add_attribute(
504 Class::MOP::Attribute->new('associated_methods' => (
505 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
506 default => sub { [] }
510 Class::MOP::Attribute->meta->add_attribute(
511 Class::MOP::Attribute->new('insertion_order' => (
512 reader => { 'insertion_order' => \&Class::MOP::Attribute::insertion_order },
513 writer => { '_set_insertion_order' => \&Class::MOP::Attribute::_set_insertion_order },
514 predicate => { 'has_insertion_order' => \&Class::MOP::Attribute::has_insertion_order },
518 Class::MOP::Attribute->meta->add_method('clone' => sub {
520 $self->meta->clone_object($self, @_);
523 ## --------------------------------------------------------
524 ## Class::MOP::Method
525 Class::MOP::Method->meta->add_attribute(
526 Class::MOP::Attribute->new('body' => (
527 reader => { 'body' => \&Class::MOP::Method::body },
531 Class::MOP::Method->meta->add_attribute(
532 Class::MOP::Attribute->new('associated_metaclass' => (
533 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
537 Class::MOP::Method->meta->add_attribute(
538 Class::MOP::Attribute->new('package_name' => (
539 reader => { 'package_name' => \&Class::MOP::Method::package_name },
543 Class::MOP::Method->meta->add_attribute(
544 Class::MOP::Attribute->new('name' => (
545 reader => { 'name' => \&Class::MOP::Method::name },
549 Class::MOP::Method->meta->add_attribute(
550 Class::MOP::Attribute->new('original_method' => (
551 reader => { 'original_method' => \&Class::MOP::Method::original_method },
552 writer => { '_set_original_method' => \&Class::MOP::Method::_set_original_method },
556 Class::MOP::Method->meta->add_method('clone' => sub {
558 my $clone = $self->meta->clone_object($self, @_);
559 $clone->_set_original_method($self);
563 ## --------------------------------------------------------
564 ## Class::MOP::Method::Wrapped
567 # the way this item is initialized, this
568 # really does not follow the standard
569 # practices of attributes, but we put
570 # it here for completeness
571 Class::MOP::Method::Wrapped->meta->add_attribute(
572 Class::MOP::Attribute->new('modifier_table')
575 ## --------------------------------------------------------
576 ## Class::MOP::Method::Generated
578 Class::MOP::Method::Generated->meta->add_attribute(
579 Class::MOP::Attribute->new('is_inline' => (
580 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
585 Class::MOP::Method::Generated->meta->add_attribute(
586 Class::MOP::Attribute->new('definition_context' => (
587 reader => { 'definition_context' => \&Class::MOP::Method::Generated::definition_context },
592 ## --------------------------------------------------------
593 ## Class::MOP::Method::Inlined
595 Class::MOP::Method::Inlined->meta->add_attribute(
596 Class::MOP::Attribute->new('_expected_method_class' => (
597 reader => { '_expected_method_class' => \&Class::MOP::Method::Inlined::_expected_method_class },
601 ## --------------------------------------------------------
602 ## Class::MOP::Method::Accessor
604 Class::MOP::Method::Accessor->meta->add_attribute(
605 Class::MOP::Attribute->new('attribute' => (
607 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
612 Class::MOP::Method::Accessor->meta->add_attribute(
613 Class::MOP::Attribute->new('accessor_type' => (
614 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
618 ## --------------------------------------------------------
619 ## Class::MOP::Method::Constructor
621 Class::MOP::Method::Constructor->meta->add_attribute(
622 Class::MOP::Attribute->new('options' => (
624 'options' => \&Class::MOP::Method::Constructor::options
626 default => sub { +{} }
630 Class::MOP::Method::Constructor->meta->add_attribute(
631 Class::MOP::Attribute->new('associated_metaclass' => (
632 init_arg => "metaclass", # FIXME alias and rename
634 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
639 ## --------------------------------------------------------
640 ## Class::MOP::Instance
643 # these don't yet do much of anything, but are just
644 # included for completeness
646 Class::MOP::Instance->meta->add_attribute(
647 Class::MOP::Attribute->new('associated_metaclass',
648 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
652 Class::MOP::Instance->meta->add_attribute(
653 Class::MOP::Attribute->new('_class_name',
655 reader => { _class_name => \&Class::MOP::Instance::_class_name },
656 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
657 #default => sub { $_[0]->associated_metaclass->name },
661 Class::MOP::Instance->meta->add_attribute(
662 Class::MOP::Attribute->new('attributes',
663 reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
667 Class::MOP::Instance->meta->add_attribute(
668 Class::MOP::Attribute->new('slots',
669 reader => { slots => \&Class::MOP::Instance::slots },
673 Class::MOP::Instance->meta->add_attribute(
674 Class::MOP::Attribute->new('slot_hash',
675 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
680 # we need the meta instance of the meta instance to be created now, in order
681 # for the constructor to be able to use it
682 Class::MOP::Instance->meta->get_meta_instance;
684 # pretend the add_method never happenned. it hasn't yet affected anything
685 undef Class::MOP::Instance->meta->{_package_cache_flag};
687 ## --------------------------------------------------------
688 ## Now close all the Class::MOP::* classes
690 # NOTE: we don't need to inline the the accessors this only lengthens
691 # the compile time of the MOP, and gives us no actual benefits.
693 $_->meta->make_immutable(
694 inline_constructor => 0,
695 constructor_name => "_new",
696 inline_accessors => 0,
702 Class::MOP::Attribute
708 Class::MOP::Method::Generated
709 Class::MOP::Method::Inlined
711 Class::MOP::Method::Accessor
712 Class::MOP::Method::Constructor
713 Class::MOP::Method::Wrapped
724 Class::MOP - A Meta Object Protocol for Perl 5
728 This module is a fully functioning meta object protocol for the
729 Perl 5 object system. It makes no attempt to change the behavior or
730 characteristics of the Perl 5 object system, only to create a
731 protocol for its manipulation and introspection.
733 That said, it does attempt to create the tools for building a rich set
734 of extensions to the Perl 5 object system. Every attempt has been made
735 to abide by the spirit of the Perl 5 object system that we all know
738 This documentation is sparse on conceptual details. We suggest looking
739 at the items listed in the L<SEE ALSO> section for more
740 information. In particular the book "The Art of the Meta Object
741 Protocol" was very influential in the development of this system.
743 =head2 What is a Meta Object Protocol?
745 A meta object protocol is an API to an object system.
747 To be more specific, it abstracts the components of an object system
748 (classes, object, methods, object attributes, etc.). These
749 abstractions can then be used to inspect and manipulate the object
750 system which they describe.
752 It can be said that there are two MOPs for any object system; the
753 implicit MOP and the explicit MOP. The implicit MOP handles things
754 like method dispatch or inheritance, which happen automatically as
755 part of how the object system works. The explicit MOP typically
756 handles the introspection/reflection features of the object system.
758 All object systems have implicit MOPs. Without one, they would not
759 work. Explicit MOPs are much less common, and depending on the
760 language can vary from restrictive (Reflection in Java or C#) to wide
761 open (CLOS is a perfect example).
763 =head2 Yet Another Class Builder! Why?
765 This is B<not> a class builder so much as a I<class builder
766 B<builder>>. The intent is that an end user will not use this module
767 directly, but instead this module is used by module authors to build
768 extensions and features onto the Perl 5 object system.
770 This system is used by L<Moose>, which supplies a powerful class
771 builder system built entirely on top of C<Class::MOP>.
773 =head2 Who is this module for?
775 This module is for anyone who has ever created or wanted to create a
776 module for the Class:: namespace. The tools which this module provides
777 make doing complex Perl 5 wizardry simpler, by removing such barriers
778 as the need to hack symbol tables, or understand the fine details of
781 =head2 What changes do I have to make to use this module?
783 This module was designed to be as unintrusive as possible. Many of its
784 features are accessible without B<any> change to your existing
785 code. It is meant to be a compliment to your existing code and not an
786 intrusion on your code base. Unlike many other B<Class::> modules,
787 this module B<does not> require you subclass it, or even that you
788 C<use> it in within your module's package.
790 The only features which requires additions to your code are the
791 attribute handling and instance construction features, and these are
792 both completely optional features. The only reason for this is because
793 Perl 5's object system does not actually have these features built
794 in. More information about this feature can be found below.
796 =head2 About Performance
798 It is a common misconception that explicit MOPs are a performance hit.
799 This is not a universal truth, it is a side-effect of some specific
800 implementations. For instance, using Java reflection is slow because
801 the JVM cannot take advantage of any compiler optimizations, and the
802 JVM has to deal with much more runtime type information as well.
804 Reflection in C# is marginally better as it was designed into the
805 language and runtime (the CLR). In contrast, CLOS (the Common Lisp
806 Object System) was built to support an explicit MOP, and so
807 performance is tuned for it.
809 This library in particular does its absolute best to avoid putting
810 B<any> drain at all upon your code's performance. In fact, by itself
811 it does nothing to affect your existing code. So you only pay for what
814 =head2 About Metaclass compatibility
816 This module makes sure that all metaclasses created are both upwards
817 and downwards compatible. The topic of metaclass compatibility is
818 highly esoteric and is something only encountered when doing deep and
819 involved metaclass hacking. There are two basic kinds of metaclass
820 incompatibility; upwards and downwards.
822 Upwards metaclass compatibility means that the metaclass of a
823 given class is either the same as (or a subclass of) all of the
826 Downward metaclass compatibility means that the metaclasses of a
827 given class's ancestors are all either the same as (or a subclass
830 Here is a diagram showing a set of two classes (C<A> and C<B>) and
831 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
832 metaclass compatibility both upwards and downwards.
834 +---------+ +---------+
835 | Meta::A |<----| Meta::B | <....... (instance of )
836 +---------+ +---------+ <------- (inherits from)
839 +---------+ +---------+
841 +---------+ +---------+
843 As I said this is a highly esoteric topic and one you will only run
844 into if you do a lot of subclassing of L<Class::MOP::Class>. If you
845 are interested in why this is an issue see the paper I<Uniform and
846 safe metaclass composition> linked to in the L<SEE ALSO> section of
849 =head2 Using custom metaclasses
851 Always use the L<metaclass> pragma when using a custom metaclass, this
852 will ensure the proper initialization order and not accidentally
853 create an incorrect type of metaclass for you. This is a very rare
854 problem, and one which can only occur if you are doing deep metaclass
855 programming. So in other words, don't worry about it.
857 Note that if you're using L<Moose> we encourage you to I<not> use
858 L<metaclass> pragma, and instead use L<Moose::Util::MetaRole> to apply
859 roles to a class's metaclasses. This topic is covered at length in
860 various L<Moose::Cookbook> recipes.
864 The meta-object protocol is divided into 4 main sub-protocols:
866 =head2 The Class protocol
868 This provides a means of manipulating and introspecting a Perl 5
869 class. It handles symbol table hacking for you, and provides a rich
870 set of methods that go beyond simple package introspection.
872 See L<Class::MOP::Class> for more details.
874 =head2 The Attribute protocol
876 This provides a consistent representation for an attribute of a Perl 5
877 class. Since there are so many ways to create and handle attributes in
878 Perl 5 OO, the Attribute protocol provide as much of a unified
879 approach as possible. Of course, you are always free to extend this
880 protocol by subclassing the appropriate classes.
882 See L<Class::MOP::Attribute> for more details.
884 =head2 The Method protocol
886 This provides a means of manipulating and introspecting methods in the
887 Perl 5 object system. As with attributes, there are many ways to
888 approach this topic, so we try to keep it pretty basic, while still
889 making it possible to extend the system in many ways.
891 See L<Class::MOP::Method> for more details.
893 =head2 The Instance protocol
895 This provides a layer of abstraction for creating object instances.
896 Since the other layers use this protocol, it is relatively easy to
897 change the type of your instances from the default hash reference to
898 some other type of reference. Several examples are provided in the
899 F<examples/> directory included in this distribution.
901 See L<Class::MOP::Instance> for more details.
905 Note that this module does not export any constants or functions.
911 =item I<Class::MOP::IS_RUNNING_ON_5_10>
913 We set this constant depending on what version perl we are on, this
914 allows us to take advantage of new 5.10 features and stay backwards
919 =head2 Utility functions
921 Note that these are all called as B<functions, not methods>.
925 =item B<Class::MOP::load_class($class_name)>
927 This will load the specified C<$class_name>, if it is not already
928 loaded (as reported by C<is_class_loaded>). This function can be used
929 in place of tricks like C<eval "use $module"> or using C<require>
930 unconditionally. This will return the metaclass of C<$class_name> if
931 one exists, otherwise it will return C<$class_name>.
933 =item B<Class::MOP::is_class_loaded($class_name)>
935 Returns a boolean indicating whether or not C<$class_name> has been
938 This does a basic check of the symbol table to try and determine as
939 best it can if the C<$class_name> is loaded, it is probably correct
940 about 99% of the time, but it can be fooled into reporting false
941 positives. In particular, loading any of the core L<IO> modules will
942 cause most of the rest of the core L<IO> modules to falsely report
943 having been loaded, due to the way the base L<IO> module works.
945 =item B<Class::MOP::get_code_info($code)>
947 This function returns two values, the name of the package the C<$code>
948 is from and the name of the C<$code> itself. This is used by several
949 elements of the MOP to determine where a given C<$code> reference is
952 =item B<Class::MOP::class_of($instance_or_class_name)>
954 This will return the metaclass of the given instance or class name. If the
955 class lacks a metaclass, no metaclass will be initialized, and C<undef> will be
958 =item B<Class::MOP::check_package_cache_flag($pkg)>
960 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
962 This will return an integer that is managed by L<Class::MOP::Class> to
963 determine if a module's symbol table has been altered.
965 In Perl 5.10 or greater, this flag is package specific. However in
966 versions prior to 5.10, this will use the C<PL_sub_generation>
967 variable which is not package specific.
969 =item B<Class::MOP::load_first_existing_class(@class_names)>
971 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
973 Given a list of class names, this function will attempt to load each
976 If it finds a class it can load, it will return that class' name. If
977 none of the classes can be loaded, it will throw an exception.
981 =head2 Metaclass cache functions
983 Class::MOP holds a cache of metaclasses. The following are functions
984 (B<not methods>) which can be used to access that cache. It is not
985 recommended that you mess with these. Bad things could happen, but if
986 you are brave and willing to risk it: go for it!
990 =item B<Class::MOP::get_all_metaclasses>
992 This will return a hash of all the metaclass instances that have
993 been cached by L<Class::MOP::Class>, keyed by the package name.
995 =item B<Class::MOP::get_all_metaclass_instances>
997 This will return a list of all the metaclass instances that have
998 been cached by L<Class::MOP::Class>.
1000 =item B<Class::MOP::get_all_metaclass_names>
1002 This will return a list of all the metaclass names that have
1003 been cached by L<Class::MOP::Class>.
1005 =item B<Class::MOP::get_metaclass_by_name($name)>
1007 This will return a cached L<Class::MOP::Class> instance, or nothing
1008 if no metaclass exists with that C<$name>.
1010 =item B<Class::MOP::store_metaclass_by_name($name, $meta)>
1012 This will store a metaclass in the cache at the supplied C<$key>.
1014 =item B<Class::MOP::weaken_metaclass($name)>
1016 In rare cases (e.g. anonymous metaclasses) it is desirable to
1017 store a weakened reference in the metaclass cache. This
1018 function will weaken the reference to the metaclass stored
1021 =item B<Class::MOP::does_metaclass_exist($name)>
1023 This will return true of there exists a metaclass stored in the
1024 C<$name> key, and return false otherwise.
1026 =item B<Class::MOP::remove_metaclass_by_name($name)>
1028 This will remove the metaclass stored in the C<$name> key.
1036 There are very few books out on Meta Object Protocols and Metaclasses
1037 because it is such an esoteric topic. The following books are really
1038 the only ones I have found. If you know of any more, B<I<please>>
1039 email me and let me know, I would love to hear about them.
1043 =item I<The Art of the Meta Object Protocol>
1045 =item I<Advances in Object-Oriented Metalevel Architecture and Reflection>
1047 =item I<Putting MetaClasses to Work>
1049 =item I<Smalltalk: The Language>
1057 =item "Uniform and safe metaclass composition"
1059 An excellent paper by the people who brought us the original Traits paper.
1060 This paper is on how Traits can be used to do safe metaclass composition,
1061 and offers an excellent introduction section which delves into the topic of
1062 metaclass compatibility.
1064 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
1066 =item "Safe Metaclass Programming"
1068 This paper seems to precede the above paper, and propose a mix-in based
1069 approach as opposed to the Traits based approach. Both papers have similar
1070 information on the metaclass compatibility problem space.
1072 L<http://citeseer.ist.psu.edu/37617.html>
1080 =item The Perl 6 MetaModel work in the Pugs project
1084 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
1086 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1096 =item CPAN Module Review of Class::MOP
1098 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1102 =head1 SIMILAR MODULES
1104 As I have said above, this module is a class-builder-builder, so it is
1105 not the same thing as modules like L<Class::Accessor> and
1106 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1107 with similar goals to this module. The one I have found which is most
1108 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1109 creates are very different from this modules.
1113 All complex software has bugs lurking in it, and this module is no
1116 Please report any bugs to C<bug-class-mop@rt.cpan.org>, or through the
1117 web interface at L<http://rt.cpan.org>.
1119 You can also discuss feature requests or possible bugs on the Moose
1120 mailing list (moose@perl.org) or on IRC at
1121 L<irc://irc.perl.org/#moose>.
1123 =head1 ACKNOWLEDGEMENTS
1129 Thanks to Rob for actually getting the development of this module kick-started.
1135 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1137 B<with contributions from:>
1139 Brandon (blblack) Black
1141 Florian (rafl) Ragwitz
1143 Guillermo (groditi) Roditi
1145 Dave (autarch) Rolsky
1149 Rob (robkinyon) Kinyon
1151 Yuval (nothingmuch) Kogman
1153 Scott (konobi) McWhirter
1157 =head1 COPYRIGHT AND LICENSE
1159 Copyright 2006-2009 by Infinity Interactive, Inc.
1161 L<http://www.iinteractive.com>
1163 This library is free software; you can redistribute it and/or modify
1164 it under the same terms as Perl itself.