12 use Scalar::Util 'weaken', 'reftype', 'blessed';
15 use Class::MOP::HasAttributes;
16 use Class::MOP::HasMethods;
17 use Class::MOP::Class;
18 use Class::MOP::Attribute;
19 use Class::MOP::Method;
22 *IS_RUNNING_ON_5_10 = ($] < 5.009_005)
26 # this is either part of core or set up appropriately by MRO::Compat
27 *check_package_cache_flag = \&mro::get_pkg_gen;
30 our $VERSION = '0.95';
31 our $XS_VERSION = $VERSION;
32 $VERSION = eval $VERSION;
33 our $AUTHORITY = 'cpan:STEVAN';
36 XSLoader::load( __PACKAGE__, $XS_VERSION );
40 # Metaclasses are singletons, so we cache them here.
41 # there is no need to worry about destruction though
42 # because they should die only when the program dies.
43 # After all, do package definitions even get reaped?
44 # Anonymous classes manage their own destruction.
47 sub get_all_metaclasses { %METAS }
48 sub get_all_metaclass_instances { values %METAS }
49 sub get_all_metaclass_names { keys %METAS }
50 sub get_metaclass_by_name { $METAS{$_[0]} }
51 sub store_metaclass_by_name { $METAS{$_[0]} = $_[1] }
52 sub weaken_metaclass { weaken($METAS{$_[0]}) }
53 sub does_metaclass_exist { exists $METAS{$_[0]} && defined $METAS{$_[0]} }
54 sub remove_metaclass_by_name { delete $METAS{$_[0]}; return }
56 # This handles instances as well as class names
58 return unless defined $_[0];
59 my $class = blessed($_[0]) || $_[0];
60 return $METAS{$class};
64 # We only cache metaclasses, meaning instances of
65 # Class::MOP::Class. We do not cache instance of
66 # Class::MOP::Package or Class::MOP::Module. Mostly
67 # because I don't yet see a good reason to do so.
70 sub _class_to_pmfile {
73 my $file = $class . '.pm';
79 sub load_first_existing_class {
83 foreach my $class (@classes) {
84 unless ( _is_valid_class_name($class) ) {
85 my $display = defined($class) ? $class : 'undef';
86 confess "Invalid class name ($display)";
93 for my $class (@classes) {
94 my $file = _class_to_pmfile($class);
96 return $class if is_class_loaded($class);;
98 return $class if try {
104 unless (/^Can't locate \Q$file\E in \@INC/) {
105 confess "Couldn't load class ($class) because: $_";
112 if ( @classes > 1 ) {
113 confess "Can't locate any of @classes in \@INC (\@INC contains: @INC).";
115 confess "Can't locate " . _class_to_pmfile($classes[0]) . " in \@INC (\@INC contains: @INC).";
120 load_first_existing_class($_[0]);
122 # This is done to avoid breaking code which checked the return value. Said
123 # code is dumb. The return value was _always_ true, since it dies on
128 sub _is_valid_class_name {
131 return 0 if ref($class);
132 return 0 unless defined($class);
133 return 0 unless length($class);
135 return 1 if $class =~ /^\w+(?:::\w+)*$/;
140 ## ----------------------------------------------------------------------------
141 ## Setting up our environment ...
142 ## ----------------------------------------------------------------------------
143 ## Class::MOP needs to have a few things in the global perl environment so
144 ## that it can operate effectively. Those things are done here.
145 ## ----------------------------------------------------------------------------
147 # ... nothing yet actually ;)
149 ## ----------------------------------------------------------------------------
151 ## ----------------------------------------------------------------------------
152 ## The code below here is to bootstrap our MOP with itself. This is also
153 ## sometimes called "tying the knot". By doing this, we make it much easier
154 ## to extend the MOP through subclassing and such since now you can use the
155 ## MOP itself to extend itself.
157 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
158 ## ----------------------------------------------------------------------------
160 # We need to add in the meta-attributes here so that
161 # any subclass of Class::MOP::* will be able to
162 # inherit them using _construct_instance
164 ## --------------------------------------------------------
165 ## Class::MOP::HasMethods
167 Class::MOP::HasMethods->meta->add_attribute(
168 Class::MOP::Attribute->new('_methods' => (
171 # we just alias the original method
172 # rather than re-produce it here
173 '_full_method_map' => \&Class::MOP::HasMethods::_full_method_map
175 default => sub { {} }
179 Class::MOP::HasMethods->meta->add_attribute(
180 Class::MOP::Attribute->new('method_metaclass' => (
183 # we just alias the original method
184 # rather than re-produce it here
185 'method_metaclass' => \&Class::MOP::HasMethods::method_metaclass
187 default => 'Class::MOP::Method',
191 Class::MOP::HasMethods->meta->add_attribute(
192 Class::MOP::Attribute->new('wrapped_method_metaclass' => (
195 # we just alias the original method
196 # rather than re-produce it here
197 'wrapped_method_metaclass' => \&Class::MOP::HasMethods::wrapped_method_metaclass
199 default => 'Class::MOP::Method::Wrapped',
203 ## --------------------------------------------------------
204 ## Class::MOP::HasMethods
206 Class::MOP::HasAttributes->meta->add_attribute(
207 Class::MOP::Attribute->new('attributes' => (
209 # NOTE: we need to do this in order
210 # for the instance meta-object to
211 # not fall into meta-circular death
213 # we just alias the original method
214 # rather than re-produce it here
215 '_attribute_map' => \&Class::MOP::HasAttributes::_attribute_map
217 default => sub { {} }
221 Class::MOP::HasAttributes->meta->add_attribute(
222 Class::MOP::Attribute->new('attribute_metaclass' => (
225 # we just alias the original method
226 # rather than re-produce it here
227 'attribute_metaclass' => \&Class::MOP::HasAttributes::attribute_metaclass
229 default => 'Class::MOP::Attribute',
233 ## --------------------------------------------------------
234 ## Class::MOP::Package
236 Class::MOP::Package->meta->add_attribute(
237 Class::MOP::Attribute->new('package' => (
239 # NOTE: we need to do this in order
240 # for the instance meta-object to
241 # not fall into meta-circular death
243 # we just alias the original method
244 # rather than re-produce it here
245 'name' => \&Class::MOP::Package::name
250 Class::MOP::Package->meta->add_attribute(
251 Class::MOP::Attribute->new('namespace' => (
254 # we just alias the original method
255 # rather than re-produce it here
256 'namespace' => \&Class::MOP::Package::namespace
259 default => sub { \undef }
263 ## --------------------------------------------------------
264 ## Class::MOP::Module
267 # yeah this is kind of stretching things a bit,
268 # but truthfully the version should be an attribute
269 # of the Module, the weirdness comes from having to
270 # stick to Perl 5 convention and store it in the
271 # $VERSION package variable. Basically if you just
272 # squint at it, it will look how you want it to look.
273 # Either as a package variable, or as a attribute of
274 # the metaclass, isn't abstraction great :)
276 Class::MOP::Module->meta->add_attribute(
277 Class::MOP::Attribute->new('version' => (
280 # we just alias the original method
281 # rather than re-produce it here
282 'version' => \&Class::MOP::Module::version
285 default => sub { \undef }
290 # By following the same conventions as version here,
291 # we are opening up the possibility that people can
292 # use the $AUTHORITY in non-Class::MOP modules as
295 Class::MOP::Module->meta->add_attribute(
296 Class::MOP::Attribute->new('authority' => (
299 # we just alias the original method
300 # rather than re-produce it here
301 'authority' => \&Class::MOP::Module::authority
304 default => sub { \undef }
308 ## --------------------------------------------------------
311 Class::MOP::Class->meta->add_attribute(
312 Class::MOP::Attribute->new('superclasses' => (
315 # we just alias the original method
316 # rather than re-produce it here
317 'superclasses' => \&Class::MOP::Class::superclasses
320 default => sub { \undef }
324 Class::MOP::Class->meta->add_attribute(
325 Class::MOP::Attribute->new('instance_metaclass' => (
327 # NOTE: we need to do this in order
328 # for the instance meta-object to
329 # not fall into meta-circular death
331 # we just alias the original method
332 # rather than re-produce it here
333 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
335 default => 'Class::MOP::Instance',
339 Class::MOP::Class->meta->add_attribute(
340 Class::MOP::Attribute->new('immutable_trait' => (
342 'immutable_trait' => \&Class::MOP::Class::immutable_trait
344 default => "Class::MOP::Class::Immutable::Trait",
348 Class::MOP::Class->meta->add_attribute(
349 Class::MOP::Attribute->new('constructor_name' => (
351 'constructor_name' => \&Class::MOP::Class::constructor_name,
357 Class::MOP::Class->meta->add_attribute(
358 Class::MOP::Attribute->new('constructor_class' => (
360 'constructor_class' => \&Class::MOP::Class::constructor_class,
362 default => "Class::MOP::Method::Constructor",
367 Class::MOP::Class->meta->add_attribute(
368 Class::MOP::Attribute->new('destructor_class' => (
370 'destructor_class' => \&Class::MOP::Class::destructor_class,
376 # we don't actually need to tie the knot with
377 # Class::MOP::Class here, it is actually handled
378 # within Class::MOP::Class itself in the
379 # _construct_class_instance method.
381 ## --------------------------------------------------------
382 ## Class::MOP::Attribute
384 Class::MOP::Attribute->meta->add_attribute(
385 Class::MOP::Attribute->new('name' => (
387 # NOTE: we need to do this in order
388 # for the instance meta-object to
389 # not fall into meta-circular death
391 # we just alias the original method
392 # rather than re-produce it here
393 'name' => \&Class::MOP::Attribute::name
398 Class::MOP::Attribute->meta->add_attribute(
399 Class::MOP::Attribute->new('associated_class' => (
401 # NOTE: we need to do this in order
402 # for the instance meta-object to
403 # not fall into meta-circular death
405 # we just alias the original method
406 # rather than re-produce it here
407 'associated_class' => \&Class::MOP::Attribute::associated_class
412 Class::MOP::Attribute->meta->add_attribute(
413 Class::MOP::Attribute->new('accessor' => (
414 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
415 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
419 Class::MOP::Attribute->meta->add_attribute(
420 Class::MOP::Attribute->new('reader' => (
421 reader => { 'reader' => \&Class::MOP::Attribute::reader },
422 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
426 Class::MOP::Attribute->meta->add_attribute(
427 Class::MOP::Attribute->new('initializer' => (
428 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
429 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
433 Class::MOP::Attribute->meta->add_attribute(
434 Class::MOP::Attribute->new('definition_context' => (
435 reader => { 'definition_context' => \&Class::MOP::Attribute::definition_context },
439 Class::MOP::Attribute->meta->add_attribute(
440 Class::MOP::Attribute->new('writer' => (
441 reader => { 'writer' => \&Class::MOP::Attribute::writer },
442 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
446 Class::MOP::Attribute->meta->add_attribute(
447 Class::MOP::Attribute->new('predicate' => (
448 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
449 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
453 Class::MOP::Attribute->meta->add_attribute(
454 Class::MOP::Attribute->new('clearer' => (
455 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
456 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
460 Class::MOP::Attribute->meta->add_attribute(
461 Class::MOP::Attribute->new('builder' => (
462 reader => { 'builder' => \&Class::MOP::Attribute::builder },
463 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
467 Class::MOP::Attribute->meta->add_attribute(
468 Class::MOP::Attribute->new('init_arg' => (
469 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
470 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
474 Class::MOP::Attribute->meta->add_attribute(
475 Class::MOP::Attribute->new('default' => (
476 # default has a custom 'reader' method ...
477 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
481 Class::MOP::Attribute->meta->add_attribute(
482 Class::MOP::Attribute->new('associated_methods' => (
483 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
484 default => sub { [] }
488 Class::MOP::Attribute->meta->add_attribute(
489 Class::MOP::Attribute->new('insertion_order' => (
490 reader => { 'insertion_order' => \&Class::MOP::Attribute::insertion_order },
491 writer => { '_set_insertion_order' => \&Class::MOP::Attribute::_set_insertion_order },
492 predicate => { 'has_insertion_order' => \&Class::MOP::Attribute::has_insertion_order },
496 Class::MOP::Attribute->meta->add_method('clone' => sub {
498 $self->meta->clone_object($self, @_);
501 ## --------------------------------------------------------
502 ## Class::MOP::Method
503 Class::MOP::Method->meta->add_attribute(
504 Class::MOP::Attribute->new('body' => (
505 reader => { 'body' => \&Class::MOP::Method::body },
509 Class::MOP::Method->meta->add_attribute(
510 Class::MOP::Attribute->new('associated_metaclass' => (
511 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
515 Class::MOP::Method->meta->add_attribute(
516 Class::MOP::Attribute->new('package_name' => (
517 reader => { 'package_name' => \&Class::MOP::Method::package_name },
521 Class::MOP::Method->meta->add_attribute(
522 Class::MOP::Attribute->new('name' => (
523 reader => { 'name' => \&Class::MOP::Method::name },
527 Class::MOP::Method->meta->add_attribute(
528 Class::MOP::Attribute->new('original_method' => (
529 reader => { 'original_method' => \&Class::MOP::Method::original_method },
530 writer => { '_set_original_method' => \&Class::MOP::Method::_set_original_method },
534 Class::MOP::Method->meta->add_method('clone' => sub {
536 my $clone = $self->meta->clone_object($self, @_);
537 $clone->_set_original_method($self);
541 ## --------------------------------------------------------
542 ## Class::MOP::Method::Wrapped
545 # the way this item is initialized, this
546 # really does not follow the standard
547 # practices of attributes, but we put
548 # it here for completeness
549 Class::MOP::Method::Wrapped->meta->add_attribute(
550 Class::MOP::Attribute->new('modifier_table')
553 ## --------------------------------------------------------
554 ## Class::MOP::Method::Generated
556 Class::MOP::Method::Generated->meta->add_attribute(
557 Class::MOP::Attribute->new('is_inline' => (
558 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
563 Class::MOP::Method::Generated->meta->add_attribute(
564 Class::MOP::Attribute->new('definition_context' => (
565 reader => { 'definition_context' => \&Class::MOP::Method::Generated::definition_context },
570 ## --------------------------------------------------------
571 ## Class::MOP::Method::Inlined
573 Class::MOP::Method::Inlined->meta->add_attribute(
574 Class::MOP::Attribute->new('_expected_method_class' => (
575 reader => { '_expected_method_class' => \&Class::MOP::Method::Inlined::_expected_method_class },
579 ## --------------------------------------------------------
580 ## Class::MOP::Method::Accessor
582 Class::MOP::Method::Accessor->meta->add_attribute(
583 Class::MOP::Attribute->new('attribute' => (
585 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
590 Class::MOP::Method::Accessor->meta->add_attribute(
591 Class::MOP::Attribute->new('accessor_type' => (
592 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
596 ## --------------------------------------------------------
597 ## Class::MOP::Method::Constructor
599 Class::MOP::Method::Constructor->meta->add_attribute(
600 Class::MOP::Attribute->new('options' => (
602 'options' => \&Class::MOP::Method::Constructor::options
604 default => sub { +{} }
608 Class::MOP::Method::Constructor->meta->add_attribute(
609 Class::MOP::Attribute->new('associated_metaclass' => (
610 init_arg => "metaclass", # FIXME alias and rename
612 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
617 ## --------------------------------------------------------
618 ## Class::MOP::Instance
621 # these don't yet do much of anything, but are just
622 # included for completeness
624 Class::MOP::Instance->meta->add_attribute(
625 Class::MOP::Attribute->new('associated_metaclass',
626 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
630 Class::MOP::Instance->meta->add_attribute(
631 Class::MOP::Attribute->new('_class_name',
633 reader => { _class_name => \&Class::MOP::Instance::_class_name },
634 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
635 #default => sub { $_[0]->associated_metaclass->name },
639 Class::MOP::Instance->meta->add_attribute(
640 Class::MOP::Attribute->new('attributes',
641 reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
645 Class::MOP::Instance->meta->add_attribute(
646 Class::MOP::Attribute->new('slots',
647 reader => { slots => \&Class::MOP::Instance::slots },
651 Class::MOP::Instance->meta->add_attribute(
652 Class::MOP::Attribute->new('slot_hash',
653 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
657 require Class::MOP::Deprecated unless our $no_deprecated;
659 # we need the meta instance of the meta instance to be created now, in order
660 # for the constructor to be able to use it
661 Class::MOP::Instance->meta->get_meta_instance;
663 # pretend the add_method never happenned. it hasn't yet affected anything
664 undef Class::MOP::Instance->meta->{_package_cache_flag};
666 ## --------------------------------------------------------
667 ## Now close all the Class::MOP::* classes
669 # NOTE: we don't need to inline the the accessors this only lengthens
670 # the compile time of the MOP, and gives us no actual benefits.
672 $_->meta->make_immutable(
673 inline_constructor => 0,
674 constructor_name => "_new",
675 inline_accessors => 0,
681 Class::MOP::Attribute
687 Class::MOP::Method::Generated
688 Class::MOP::Method::Inlined
690 Class::MOP::Method::Accessor
691 Class::MOP::Method::Constructor
692 Class::MOP::Method::Wrapped
695 $_->meta->make_immutable(
696 inline_constructor => 0,
697 constructor_name => undef,
698 inline_accessors => 0,
700 Class::MOP::HasAttributes
701 Class::MOP::HasMethods
712 Class::MOP - A Meta Object Protocol for Perl 5
716 This module is a fully functioning meta object protocol for the
717 Perl 5 object system. It makes no attempt to change the behavior or
718 characteristics of the Perl 5 object system, only to create a
719 protocol for its manipulation and introspection.
721 That said, it does attempt to create the tools for building a rich set
722 of extensions to the Perl 5 object system. Every attempt has been made
723 to abide by the spirit of the Perl 5 object system that we all know
726 This documentation is sparse on conceptual details. We suggest looking
727 at the items listed in the L<SEE ALSO> section for more
728 information. In particular the book "The Art of the Meta Object
729 Protocol" was very influential in the development of this system.
731 =head2 What is a Meta Object Protocol?
733 A meta object protocol is an API to an object system.
735 To be more specific, it abstracts the components of an object system
736 (classes, object, methods, object attributes, etc.). These
737 abstractions can then be used to inspect and manipulate the object
738 system which they describe.
740 It can be said that there are two MOPs for any object system; the
741 implicit MOP and the explicit MOP. The implicit MOP handles things
742 like method dispatch or inheritance, which happen automatically as
743 part of how the object system works. The explicit MOP typically
744 handles the introspection/reflection features of the object system.
746 All object systems have implicit MOPs. Without one, they would not
747 work. Explicit MOPs are much less common, and depending on the
748 language can vary from restrictive (Reflection in Java or C#) to wide
749 open (CLOS is a perfect example).
751 =head2 Yet Another Class Builder! Why?
753 This is B<not> a class builder so much as a I<class builder
754 B<builder>>. The intent is that an end user will not use this module
755 directly, but instead this module is used by module authors to build
756 extensions and features onto the Perl 5 object system.
758 This system is used by L<Moose>, which supplies a powerful class
759 builder system built entirely on top of C<Class::MOP>.
761 =head2 Who is this module for?
763 This module is for anyone who has ever created or wanted to create a
764 module for the Class:: namespace. The tools which this module provides
765 make doing complex Perl 5 wizardry simpler, by removing such barriers
766 as the need to hack symbol tables, or understand the fine details of
769 =head2 What changes do I have to make to use this module?
771 This module was designed to be as unintrusive as possible. Many of its
772 features are accessible without B<any> change to your existing
773 code. It is meant to be a compliment to your existing code and not an
774 intrusion on your code base. Unlike many other B<Class::> modules,
775 this module B<does not> require you subclass it, or even that you
776 C<use> it in within your module's package.
778 The only features which requires additions to your code are the
779 attribute handling and instance construction features, and these are
780 both completely optional features. The only reason for this is because
781 Perl 5's object system does not actually have these features built
782 in. More information about this feature can be found below.
784 =head2 About Performance
786 It is a common misconception that explicit MOPs are a performance hit.
787 This is not a universal truth, it is a side-effect of some specific
788 implementations. For instance, using Java reflection is slow because
789 the JVM cannot take advantage of any compiler optimizations, and the
790 JVM has to deal with much more runtime type information as well.
792 Reflection in C# is marginally better as it was designed into the
793 language and runtime (the CLR). In contrast, CLOS (the Common Lisp
794 Object System) was built to support an explicit MOP, and so
795 performance is tuned for it.
797 This library in particular does its absolute best to avoid putting
798 B<any> drain at all upon your code's performance. In fact, by itself
799 it does nothing to affect your existing code. So you only pay for what
802 =head2 About Metaclass compatibility
804 This module makes sure that all metaclasses created are both upwards
805 and downwards compatible. The topic of metaclass compatibility is
806 highly esoteric and is something only encountered when doing deep and
807 involved metaclass hacking. There are two basic kinds of metaclass
808 incompatibility; upwards and downwards.
810 Upwards metaclass compatibility means that the metaclass of a
811 given class is either the same as (or a subclass of) all of the
814 Downward metaclass compatibility means that the metaclasses of a
815 given class's ancestors are all either the same as (or a subclass
818 Here is a diagram showing a set of two classes (C<A> and C<B>) and
819 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
820 metaclass compatibility both upwards and downwards.
822 +---------+ +---------+
823 | Meta::A |<----| Meta::B | <....... (instance of )
824 +---------+ +---------+ <------- (inherits from)
827 +---------+ +---------+
829 +---------+ +---------+
831 As I said this is a highly esoteric topic and one you will only run
832 into if you do a lot of subclassing of L<Class::MOP::Class>. If you
833 are interested in why this is an issue see the paper I<Uniform and
834 safe metaclass composition> linked to in the L<SEE ALSO> section of
837 =head2 Using custom metaclasses
839 Always use the L<metaclass> pragma when using a custom metaclass, this
840 will ensure the proper initialization order and not accidentally
841 create an incorrect type of metaclass for you. This is a very rare
842 problem, and one which can only occur if you are doing deep metaclass
843 programming. So in other words, don't worry about it.
845 Note that if you're using L<Moose> we encourage you to I<not> use
846 L<metaclass> pragma, and instead use L<Moose::Util::MetaRole> to apply
847 roles to a class's metaclasses. This topic is covered at length in
848 various L<Moose::Cookbook> recipes.
852 The meta-object protocol is divided into 4 main sub-protocols:
854 =head2 The Class protocol
856 This provides a means of manipulating and introspecting a Perl 5
857 class. It handles symbol table hacking for you, and provides a rich
858 set of methods that go beyond simple package introspection.
860 See L<Class::MOP::Class> for more details.
862 =head2 The Attribute protocol
864 This provides a consistent representation for an attribute of a Perl 5
865 class. Since there are so many ways to create and handle attributes in
866 Perl 5 OO, the Attribute protocol provide as much of a unified
867 approach as possible. Of course, you are always free to extend this
868 protocol by subclassing the appropriate classes.
870 See L<Class::MOP::Attribute> for more details.
872 =head2 The Method protocol
874 This provides a means of manipulating and introspecting methods in the
875 Perl 5 object system. As with attributes, there are many ways to
876 approach this topic, so we try to keep it pretty basic, while still
877 making it possible to extend the system in many ways.
879 See L<Class::MOP::Method> for more details.
881 =head2 The Instance protocol
883 This provides a layer of abstraction for creating object instances.
884 Since the other layers use this protocol, it is relatively easy to
885 change the type of your instances from the default hash reference to
886 some other type of reference. Several examples are provided in the
887 F<examples/> directory included in this distribution.
889 See L<Class::MOP::Instance> for more details.
893 Note that this module does not export any constants or functions.
899 =item I<Class::MOP::IS_RUNNING_ON_5_10>
901 We set this constant depending on what version perl we are on, this
902 allows us to take advantage of new 5.10 features and stay backwards
907 =head2 Utility functions
909 Note that these are all called as B<functions, not methods>.
913 =item B<Class::MOP::load_class($class_name)>
915 This will load the specified C<$class_name>, if it is not already
916 loaded (as reported by C<is_class_loaded>). This function can be used
917 in place of tricks like C<eval "use $module"> or using C<require>
920 If the module cannot be loaded, an exception is thrown.
922 For historical reasons, this function explicitly returns a true value.
924 =item B<Class::MOP::is_class_loaded($class_name)>
926 Returns a boolean indicating whether or not C<$class_name> has been
929 This does a basic check of the symbol table to try and determine as
930 best it can if the C<$class_name> is loaded, it is probably correct
931 about 99% of the time, but it can be fooled into reporting false
932 positives. In particular, loading any of the core L<IO> modules will
933 cause most of the rest of the core L<IO> modules to falsely report
934 having been loaded, due to the way the base L<IO> module works.
936 =item B<Class::MOP::get_code_info($code)>
938 This function returns two values, the name of the package the C<$code>
939 is from and the name of the C<$code> itself. This is used by several
940 elements of the MOP to determine where a given C<$code> reference is
943 =item B<Class::MOP::class_of($instance_or_class_name)>
945 This will return the metaclass of the given instance or class name. If the
946 class lacks a metaclass, no metaclass will be initialized, and C<undef> will be
949 =item B<Class::MOP::check_package_cache_flag($pkg)>
951 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
953 This will return an integer that is managed by L<Class::MOP::Class> to
954 determine if a module's symbol table has been altered.
956 In Perl 5.10 or greater, this flag is package specific. However in
957 versions prior to 5.10, this will use the C<PL_sub_generation>
958 variable which is not package specific.
960 =item B<Class::MOP::load_first_existing_class(@class_names)>
962 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
964 Given a list of class names, this function will attempt to load each
967 If it finds a class it can load, it will return that class' name. If
968 none of the classes can be loaded, it will throw an exception.
972 =head2 Metaclass cache functions
974 Class::MOP holds a cache of metaclasses. The following are functions
975 (B<not methods>) which can be used to access that cache. It is not
976 recommended that you mess with these. Bad things could happen, but if
977 you are brave and willing to risk it: go for it!
981 =item B<Class::MOP::get_all_metaclasses>
983 This will return a hash of all the metaclass instances that have
984 been cached by L<Class::MOP::Class>, keyed by the package name.
986 =item B<Class::MOP::get_all_metaclass_instances>
988 This will return a list of all the metaclass instances that have
989 been cached by L<Class::MOP::Class>.
991 =item B<Class::MOP::get_all_metaclass_names>
993 This will return a list of all the metaclass names that have
994 been cached by L<Class::MOP::Class>.
996 =item B<Class::MOP::get_metaclass_by_name($name)>
998 This will return a cached L<Class::MOP::Class> instance, or nothing
999 if no metaclass exists with that C<$name>.
1001 =item B<Class::MOP::store_metaclass_by_name($name, $meta)>
1003 This will store a metaclass in the cache at the supplied C<$key>.
1005 =item B<Class::MOP::weaken_metaclass($name)>
1007 In rare cases (e.g. anonymous metaclasses) it is desirable to
1008 store a weakened reference in the metaclass cache. This
1009 function will weaken the reference to the metaclass stored
1012 =item B<Class::MOP::does_metaclass_exist($name)>
1014 This will return true of there exists a metaclass stored in the
1015 C<$name> key, and return false otherwise.
1017 =item B<Class::MOP::remove_metaclass_by_name($name)>
1019 This will remove the metaclass stored in the C<$name> key.
1027 There are very few books out on Meta Object Protocols and Metaclasses
1028 because it is such an esoteric topic. The following books are really
1029 the only ones I have found. If you know of any more, B<I<please>>
1030 email me and let me know, I would love to hear about them.
1034 =item I<The Art of the Meta Object Protocol>
1036 =item I<Advances in Object-Oriented Metalevel Architecture and Reflection>
1038 =item I<Putting MetaClasses to Work>
1040 =item I<Smalltalk: The Language>
1048 =item "Uniform and safe metaclass composition"
1050 An excellent paper by the people who brought us the original Traits paper.
1051 This paper is on how Traits can be used to do safe metaclass composition,
1052 and offers an excellent introduction section which delves into the topic of
1053 metaclass compatibility.
1055 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
1057 =item "Safe Metaclass Programming"
1059 This paper seems to precede the above paper, and propose a mix-in based
1060 approach as opposed to the Traits based approach. Both papers have similar
1061 information on the metaclass compatibility problem space.
1063 L<http://citeseer.ist.psu.edu/37617.html>
1071 =item The Perl 6 MetaModel work in the Pugs project
1075 =item L<http://svn.openfoundry.org/pugs/misc/Perl-MetaModel/>
1077 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1087 =item CPAN Module Review of Class::MOP
1089 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1093 =head1 SIMILAR MODULES
1095 As I have said above, this module is a class-builder-builder, so it is
1096 not the same thing as modules like L<Class::Accessor> and
1097 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1098 with similar goals to this module. The one I have found which is most
1099 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1100 creates are very different from this modules.
1104 All complex software has bugs lurking in it, and this module is no
1107 Please report any bugs to C<bug-class-mop@rt.cpan.org>, or through the
1108 web interface at L<http://rt.cpan.org>.
1110 You can also discuss feature requests or possible bugs on the Moose
1111 mailing list (moose@perl.org) or on IRC at
1112 L<irc://irc.perl.org/#moose>.
1114 =head1 ACKNOWLEDGEMENTS
1120 Thanks to Rob for actually getting the development of this module kick-started.
1126 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1128 B<with contributions from:>
1130 Brandon (blblack) Black
1132 Florian (rafl) Ragwitz
1134 Guillermo (groditi) Roditi
1136 Dave (autarch) Rolsky
1140 Rob (robkinyon) Kinyon
1142 Yuval (nothingmuch) Kogman
1144 Scott (konobi) McWhirter
1148 =head1 COPYRIGHT AND LICENSE
1150 Copyright 2006-2009 by Infinity Interactive, Inc.
1152 L<http://www.iinteractive.com>
1154 This library is free software; you can redistribute it and/or modify
1155 it under the same terms as Perl itself.