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)
23 # this is either part of core or set up appropriately by MRO::Compat
24 *check_package_cache_flag = \&mro::get_pkg_gen;
27 our $VERSION = '0.92_01';
28 our $XS_VERSION = $VERSION;
29 $VERSION = eval $VERSION;
30 our $AUTHORITY = 'cpan:STEVAN';
33 XSLoader::load( __PACKAGE__, $XS_VERSION );
37 # Metaclasses are singletons, so we cache them here.
38 # there is no need to worry about destruction though
39 # because they should die only when the program dies.
40 # After all, do package definitions even get reaped?
41 # Anonymous classes manage their own destruction.
44 sub get_all_metaclasses { %METAS }
45 sub get_all_metaclass_instances { values %METAS }
46 sub get_all_metaclass_names { keys %METAS }
47 sub get_metaclass_by_name { $METAS{$_[0]} }
48 sub store_metaclass_by_name { $METAS{$_[0]} = $_[1] }
49 sub weaken_metaclass { weaken($METAS{$_[0]}) }
50 sub does_metaclass_exist { exists $METAS{$_[0]} && defined $METAS{$_[0]} }
51 sub remove_metaclass_by_name { delete $METAS{$_[0]}; return }
53 # This handles instances as well as class names
55 return unless defined $_[0];
56 my $class = blessed($_[0]) || $_[0];
57 return $METAS{$class};
61 # We only cache metaclasses, meaning instances of
62 # Class::MOP::Class. We do not cache instance of
63 # Class::MOP::Package or Class::MOP::Module. Mostly
64 # because I don't yet see a good reason to do so.
67 sub _class_to_pmfile {
70 my $file = $class . '.pm';
76 sub load_first_existing_class {
80 foreach my $class (@classes) {
81 unless ( _is_valid_class_name($class) ) {
82 my $display = defined($class) ? $class : 'undef';
83 confess "Invalid class name ($display)";
89 for my $class (@classes) {
90 my $e = _try_load_one_class($class);
93 my $pmfile = _class_to_pmfile($class);
94 $exceptions{$class} = $e;
95 last if $e !~ /^Can't locate \Q$pmfile\E in \@INC/;
103 return $found if $found;
109 "Could not load class (%s) because : %s", $_,
114 exists $exceptions{$_}
119 sub _try_load_one_class {
122 return if is_class_loaded($class);
124 my $file = _class_to_pmfile($class);
129 eval { require($file) };
135 load_first_existing_class($_[0]);
140 sub _is_valid_class_name {
143 return 0 if ref($class);
144 return 0 unless defined($class);
145 return 0 unless length($class);
147 return 1 if $class =~ /^\w+(?:::\w+)*$/;
152 ## ----------------------------------------------------------------------------
153 ## Setting up our environment ...
154 ## ----------------------------------------------------------------------------
155 ## Class::MOP needs to have a few things in the global perl environment so
156 ## that it can operate effectively. Those things are done here.
157 ## ----------------------------------------------------------------------------
159 # ... nothing yet actually ;)
161 ## ----------------------------------------------------------------------------
163 ## ----------------------------------------------------------------------------
164 ## The code below here is to bootstrap our MOP with itself. This is also
165 ## sometimes called "tying the knot". By doing this, we make it much easier
166 ## to extend the MOP through subclassing and such since now you can use the
167 ## MOP itself to extend itself.
169 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
170 ## ----------------------------------------------------------------------------
172 # We need to add in the meta-attributes here so that
173 # any subclass of Class::MOP::* will be able to
174 # inherit them using _construct_instance
176 ## --------------------------------------------------------
177 ## Class::MOP::Package
179 Class::MOP::Package->meta->add_attribute(
180 Class::MOP::Attribute->new('package' => (
182 # NOTE: we need to do this in order
183 # for the instance meta-object to
184 # not fall into meta-circular death
186 # we just alias the original method
187 # rather than re-produce it here
188 'name' => \&Class::MOP::Package::name
193 Class::MOP::Package->meta->add_attribute(
194 Class::MOP::Attribute->new('namespace' => (
197 # we just alias the original method
198 # rather than re-produce it here
199 'namespace' => \&Class::MOP::Package::namespace
202 default => sub { \undef }
206 Class::MOP::Package->meta->add_attribute(
207 Class::MOP::Attribute->new('methods' => (
210 # we just alias the original method
211 # rather than re-produce it here
212 'get_method_map' => \&Class::MOP::Package::get_method_map
214 default => sub { {} }
218 Class::MOP::Package->meta->add_attribute(
219 Class::MOP::Attribute->new('method_metaclass' => (
222 # we just alias the original method
223 # rather than re-produce it here
224 'method_metaclass' => \&Class::MOP::Package::method_metaclass
226 default => 'Class::MOP::Method',
230 Class::MOP::Package->meta->add_attribute(
231 Class::MOP::Attribute->new('wrapped_method_metaclass' => (
234 # we just alias the original method
235 # rather than re-produce it here
236 'wrapped_method_metaclass' => \&Class::MOP::Package::wrapped_method_metaclass
238 default => 'Class::MOP::Method::Wrapped',
242 ## --------------------------------------------------------
243 ## Class::MOP::Module
246 # yeah this is kind of stretching things a bit,
247 # but truthfully the version should be an attribute
248 # of the Module, the weirdness comes from having to
249 # stick to Perl 5 convention and store it in the
250 # $VERSION package variable. Basically if you just
251 # squint at it, it will look how you want it to look.
252 # Either as a package variable, or as a attribute of
253 # the metaclass, isn't abstraction great :)
255 Class::MOP::Module->meta->add_attribute(
256 Class::MOP::Attribute->new('version' => (
259 # we just alias the original method
260 # rather than re-produce it here
261 'version' => \&Class::MOP::Module::version
264 default => sub { \undef }
269 # By following the same conventions as version here,
270 # we are opening up the possibility that people can
271 # use the $AUTHORITY in non-Class::MOP modules as
274 Class::MOP::Module->meta->add_attribute(
275 Class::MOP::Attribute->new('authority' => (
278 # we just alias the original method
279 # rather than re-produce it here
280 'authority' => \&Class::MOP::Module::authority
283 default => sub { \undef }
287 ## --------------------------------------------------------
290 Class::MOP::Class->meta->add_attribute(
291 Class::MOP::Attribute->new('attributes' => (
293 # NOTE: we need to do this in order
294 # for the instance meta-object to
295 # not fall into meta-circular death
297 # we just alias the original method
298 # rather than re-produce it here
299 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
301 default => sub { {} }
305 Class::MOP::Class->meta->add_attribute(
306 Class::MOP::Attribute->new('superclasses' => (
309 # we just alias the original method
310 # rather than re-produce it here
311 'superclasses' => \&Class::MOP::Class::superclasses
314 default => sub { \undef }
318 Class::MOP::Class->meta->add_attribute(
319 Class::MOP::Attribute->new('attribute_metaclass' => (
322 # we just alias the original method
323 # rather than re-produce it here
324 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
326 default => 'Class::MOP::Attribute',
330 Class::MOP::Class->meta->add_attribute(
331 Class::MOP::Attribute->new('instance_metaclass' => (
333 # NOTE: we need to do this in order
334 # for the instance meta-object to
335 # not fall into meta-circular death
337 # we just alias the original method
338 # rather than re-produce it here
339 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
341 default => 'Class::MOP::Instance',
345 Class::MOP::Class->meta->add_attribute(
346 Class::MOP::Attribute->new('immutable_trait' => (
348 'immutable_trait' => \&Class::MOP::Class::immutable_trait
350 default => "Class::MOP::Class::Immutable::Trait",
354 Class::MOP::Class->meta->add_attribute(
355 Class::MOP::Attribute->new('constructor_name' => (
357 'constructor_name' => \&Class::MOP::Class::constructor_name,
363 Class::MOP::Class->meta->add_attribute(
364 Class::MOP::Attribute->new('constructor_class' => (
366 'constructor_class' => \&Class::MOP::Class::constructor_class,
368 default => "Class::MOP::Method::Constructor",
373 Class::MOP::Class->meta->add_attribute(
374 Class::MOP::Attribute->new('destructor_class' => (
376 'destructor_class' => \&Class::MOP::Class::destructor_class,
382 # we don't actually need to tie the knot with
383 # Class::MOP::Class here, it is actually handled
384 # within Class::MOP::Class itself in the
385 # _construct_class_instance method.
387 ## --------------------------------------------------------
388 ## Class::MOP::Attribute
390 Class::MOP::Attribute->meta->add_attribute(
391 Class::MOP::Attribute->new('name' => (
393 # NOTE: we need to do this in order
394 # for the instance meta-object to
395 # not fall into meta-circular death
397 # we just alias the original method
398 # rather than re-produce it here
399 'name' => \&Class::MOP::Attribute::name
404 Class::MOP::Attribute->meta->add_attribute(
405 Class::MOP::Attribute->new('associated_class' => (
407 # NOTE: we need to do this in order
408 # for the instance meta-object to
409 # not fall into meta-circular death
411 # we just alias the original method
412 # rather than re-produce it here
413 'associated_class' => \&Class::MOP::Attribute::associated_class
418 Class::MOP::Attribute->meta->add_attribute(
419 Class::MOP::Attribute->new('accessor' => (
420 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
421 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
425 Class::MOP::Attribute->meta->add_attribute(
426 Class::MOP::Attribute->new('reader' => (
427 reader => { 'reader' => \&Class::MOP::Attribute::reader },
428 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
432 Class::MOP::Attribute->meta->add_attribute(
433 Class::MOP::Attribute->new('initializer' => (
434 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
435 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
439 Class::MOP::Attribute->meta->add_attribute(
440 Class::MOP::Attribute->new('definition_context' => (
441 reader => { 'definition_context' => \&Class::MOP::Attribute::definition_context },
445 Class::MOP::Attribute->meta->add_attribute(
446 Class::MOP::Attribute->new('writer' => (
447 reader => { 'writer' => \&Class::MOP::Attribute::writer },
448 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
452 Class::MOP::Attribute->meta->add_attribute(
453 Class::MOP::Attribute->new('predicate' => (
454 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
455 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
459 Class::MOP::Attribute->meta->add_attribute(
460 Class::MOP::Attribute->new('clearer' => (
461 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
462 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
466 Class::MOP::Attribute->meta->add_attribute(
467 Class::MOP::Attribute->new('builder' => (
468 reader => { 'builder' => \&Class::MOP::Attribute::builder },
469 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
473 Class::MOP::Attribute->meta->add_attribute(
474 Class::MOP::Attribute->new('init_arg' => (
475 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
476 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
480 Class::MOP::Attribute->meta->add_attribute(
481 Class::MOP::Attribute->new('default' => (
482 # default has a custom 'reader' method ...
483 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
487 Class::MOP::Attribute->meta->add_attribute(
488 Class::MOP::Attribute->new('associated_methods' => (
489 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
490 default => sub { [] }
494 Class::MOP::Attribute->meta->add_attribute(
495 Class::MOP::Attribute->new('insertion_order' => (
496 reader => { 'insertion_order' => \&Class::MOP::Attribute::insertion_order },
497 writer => { '_set_insertion_order' => \&Class::MOP::Attribute::_set_insertion_order },
498 predicate => { 'has_insertion_order' => \&Class::MOP::Attribute::has_insertion_order },
502 Class::MOP::Attribute->meta->add_method('clone' => sub {
504 $self->meta->clone_object($self, @_);
507 ## --------------------------------------------------------
508 ## Class::MOP::Method
509 Class::MOP::Method->meta->add_attribute(
510 Class::MOP::Attribute->new('body' => (
511 reader => { 'body' => \&Class::MOP::Method::body },
515 Class::MOP::Method->meta->add_attribute(
516 Class::MOP::Attribute->new('associated_metaclass' => (
517 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
521 Class::MOP::Method->meta->add_attribute(
522 Class::MOP::Attribute->new('package_name' => (
523 reader => { 'package_name' => \&Class::MOP::Method::package_name },
527 Class::MOP::Method->meta->add_attribute(
528 Class::MOP::Attribute->new('name' => (
529 reader => { 'name' => \&Class::MOP::Method::name },
533 Class::MOP::Method->meta->add_attribute(
534 Class::MOP::Attribute->new('original_method' => (
535 reader => { 'original_method' => \&Class::MOP::Method::original_method },
536 writer => { '_set_original_method' => \&Class::MOP::Method::_set_original_method },
540 Class::MOP::Method->meta->add_method('clone' => sub {
542 my $clone = $self->meta->clone_object($self, @_);
543 $clone->_set_original_method($self);
547 ## --------------------------------------------------------
548 ## Class::MOP::Method::Wrapped
551 # the way this item is initialized, this
552 # really does not follow the standard
553 # practices of attributes, but we put
554 # it here for completeness
555 Class::MOP::Method::Wrapped->meta->add_attribute(
556 Class::MOP::Attribute->new('modifier_table')
559 ## --------------------------------------------------------
560 ## Class::MOP::Method::Generated
562 Class::MOP::Method::Generated->meta->add_attribute(
563 Class::MOP::Attribute->new('is_inline' => (
564 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
569 Class::MOP::Method::Generated->meta->add_attribute(
570 Class::MOP::Attribute->new('definition_context' => (
571 reader => { 'definition_context' => \&Class::MOP::Method::Generated::definition_context },
576 ## --------------------------------------------------------
577 ## Class::MOP::Method::Inlined
579 Class::MOP::Method::Inlined->meta->add_attribute(
580 Class::MOP::Attribute->new('_expected_method_class' => (
581 reader => { '_expected_method_class' => \&Class::MOP::Method::Inlined::_expected_method_class },
585 ## --------------------------------------------------------
586 ## Class::MOP::Method::Accessor
588 Class::MOP::Method::Accessor->meta->add_attribute(
589 Class::MOP::Attribute->new('attribute' => (
591 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
596 Class::MOP::Method::Accessor->meta->add_attribute(
597 Class::MOP::Attribute->new('accessor_type' => (
598 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
602 ## --------------------------------------------------------
603 ## Class::MOP::Method::Constructor
605 Class::MOP::Method::Constructor->meta->add_attribute(
606 Class::MOP::Attribute->new('options' => (
608 'options' => \&Class::MOP::Method::Constructor::options
610 default => sub { +{} }
614 Class::MOP::Method::Constructor->meta->add_attribute(
615 Class::MOP::Attribute->new('associated_metaclass' => (
616 init_arg => "metaclass", # FIXME alias and rename
618 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
623 ## --------------------------------------------------------
624 ## Class::MOP::Instance
627 # these don't yet do much of anything, but are just
628 # included for completeness
630 Class::MOP::Instance->meta->add_attribute(
631 Class::MOP::Attribute->new('associated_metaclass',
632 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
636 Class::MOP::Instance->meta->add_attribute(
637 Class::MOP::Attribute->new('_class_name',
639 reader => { _class_name => \&Class::MOP::Instance::_class_name },
640 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
641 #default => sub { $_[0]->associated_metaclass->name },
645 Class::MOP::Instance->meta->add_attribute(
646 Class::MOP::Attribute->new('attributes',
647 reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
651 Class::MOP::Instance->meta->add_attribute(
652 Class::MOP::Attribute->new('slots',
653 reader => { slots => \&Class::MOP::Instance::slots },
657 Class::MOP::Instance->meta->add_attribute(
658 Class::MOP::Attribute->new('slot_hash',
659 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
663 require Class::MOP::Deprecated unless our $no_deprecated;
665 # we need the meta instance of the meta instance to be created now, in order
666 # for the constructor to be able to use it
667 Class::MOP::Instance->meta->get_meta_instance;
669 # pretend the add_method never happenned. it hasn't yet affected anything
670 undef Class::MOP::Instance->meta->{_package_cache_flag};
672 ## --------------------------------------------------------
673 ## Now close all the Class::MOP::* classes
675 # NOTE: we don't need to inline the the accessors this only lengthens
676 # the compile time of the MOP, and gives us no actual benefits.
678 $_->meta->make_immutable(
679 inline_constructor => 0,
680 constructor_name => "_new",
681 inline_accessors => 0,
687 Class::MOP::Attribute
693 Class::MOP::Method::Generated
694 Class::MOP::Method::Inlined
696 Class::MOP::Method::Accessor
697 Class::MOP::Method::Constructor
698 Class::MOP::Method::Wrapped
709 Class::MOP - A Meta Object Protocol for Perl 5
713 This module is a fully functioning meta object protocol for the
714 Perl 5 object system. It makes no attempt to change the behavior or
715 characteristics of the Perl 5 object system, only to create a
716 protocol for its manipulation and introspection.
718 That said, it does attempt to create the tools for building a rich set
719 of extensions to the Perl 5 object system. Every attempt has been made
720 to abide by the spirit of the Perl 5 object system that we all know
723 This documentation is sparse on conceptual details. We suggest looking
724 at the items listed in the L<SEE ALSO> section for more
725 information. In particular the book "The Art of the Meta Object
726 Protocol" was very influential in the development of this system.
728 =head2 What is a Meta Object Protocol?
730 A meta object protocol is an API to an object system.
732 To be more specific, it abstracts the components of an object system
733 (classes, object, methods, object attributes, etc.). These
734 abstractions can then be used to inspect and manipulate the object
735 system which they describe.
737 It can be said that there are two MOPs for any object system; the
738 implicit MOP and the explicit MOP. The implicit MOP handles things
739 like method dispatch or inheritance, which happen automatically as
740 part of how the object system works. The explicit MOP typically
741 handles the introspection/reflection features of the object system.
743 All object systems have implicit MOPs. Without one, they would not
744 work. Explicit MOPs are much less common, and depending on the
745 language can vary from restrictive (Reflection in Java or C#) to wide
746 open (CLOS is a perfect example).
748 =head2 Yet Another Class Builder! Why?
750 This is B<not> a class builder so much as a I<class builder
751 B<builder>>. The intent is that an end user will not use this module
752 directly, but instead this module is used by module authors to build
753 extensions and features onto the Perl 5 object system.
755 This system is used by L<Moose>, which supplies a powerful class
756 builder system built entirely on top of C<Class::MOP>.
758 =head2 Who is this module for?
760 This module is for anyone who has ever created or wanted to create a
761 module for the Class:: namespace. The tools which this module provides
762 make doing complex Perl 5 wizardry simpler, by removing such barriers
763 as the need to hack symbol tables, or understand the fine details of
766 =head2 What changes do I have to make to use this module?
768 This module was designed to be as unintrusive as possible. Many of its
769 features are accessible without B<any> change to your existing
770 code. It is meant to be a compliment to your existing code and not an
771 intrusion on your code base. Unlike many other B<Class::> modules,
772 this module B<does not> require you subclass it, or even that you
773 C<use> it in within your module's package.
775 The only features which requires additions to your code are the
776 attribute handling and instance construction features, and these are
777 both completely optional features. The only reason for this is because
778 Perl 5's object system does not actually have these features built
779 in. More information about this feature can be found below.
781 =head2 About Performance
783 It is a common misconception that explicit MOPs are a performance hit.
784 This is not a universal truth, it is a side-effect of some specific
785 implementations. For instance, using Java reflection is slow because
786 the JVM cannot take advantage of any compiler optimizations, and the
787 JVM has to deal with much more runtime type information as well.
789 Reflection in C# is marginally better as it was designed into the
790 language and runtime (the CLR). In contrast, CLOS (the Common Lisp
791 Object System) was built to support an explicit MOP, and so
792 performance is tuned for it.
794 This library in particular does its absolute best to avoid putting
795 B<any> drain at all upon your code's performance. In fact, by itself
796 it does nothing to affect your existing code. So you only pay for what
799 =head2 About Metaclass compatibility
801 This module makes sure that all metaclasses created are both upwards
802 and downwards compatible. The topic of metaclass compatibility is
803 highly esoteric and is something only encountered when doing deep and
804 involved metaclass hacking. There are two basic kinds of metaclass
805 incompatibility; upwards and downwards.
807 Upwards metaclass compatibility means that the metaclass of a
808 given class is either the same as (or a subclass of) all of the
811 Downward metaclass compatibility means that the metaclasses of a
812 given class's ancestors are all either the same as (or a subclass
815 Here is a diagram showing a set of two classes (C<A> and C<B>) and
816 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
817 metaclass compatibility both upwards and downwards.
819 +---------+ +---------+
820 | Meta::A |<----| Meta::B | <....... (instance of )
821 +---------+ +---------+ <------- (inherits from)
824 +---------+ +---------+
826 +---------+ +---------+
828 As I said this is a highly esoteric topic and one you will only run
829 into if you do a lot of subclassing of L<Class::MOP::Class>. If you
830 are interested in why this is an issue see the paper I<Uniform and
831 safe metaclass composition> linked to in the L<SEE ALSO> section of
834 =head2 Using custom metaclasses
836 Always use the L<metaclass> pragma when using a custom metaclass, this
837 will ensure the proper initialization order and not accidentally
838 create an incorrect type of metaclass for you. This is a very rare
839 problem, and one which can only occur if you are doing deep metaclass
840 programming. So in other words, don't worry about it.
842 Note that if you're using L<Moose> we encourage you to I<not> use
843 L<metaclass> pragma, and instead use L<Moose::Util::MetaRole> to apply
844 roles to a class's metaclasses. This topic is covered at length in
845 various L<Moose::Cookbook> recipes.
849 The meta-object protocol is divided into 4 main sub-protocols:
851 =head2 The Class protocol
853 This provides a means of manipulating and introspecting a Perl 5
854 class. It handles symbol table hacking for you, and provides a rich
855 set of methods that go beyond simple package introspection.
857 See L<Class::MOP::Class> for more details.
859 =head2 The Attribute protocol
861 This provides a consistent representation for an attribute of a Perl 5
862 class. Since there are so many ways to create and handle attributes in
863 Perl 5 OO, the Attribute protocol provide as much of a unified
864 approach as possible. Of course, you are always free to extend this
865 protocol by subclassing the appropriate classes.
867 See L<Class::MOP::Attribute> for more details.
869 =head2 The Method protocol
871 This provides a means of manipulating and introspecting methods in the
872 Perl 5 object system. As with attributes, there are many ways to
873 approach this topic, so we try to keep it pretty basic, while still
874 making it possible to extend the system in many ways.
876 See L<Class::MOP::Method> for more details.
878 =head2 The Instance protocol
880 This provides a layer of abstraction for creating object instances.
881 Since the other layers use this protocol, it is relatively easy to
882 change the type of your instances from the default hash reference to
883 some other type of reference. Several examples are provided in the
884 F<examples/> directory included in this distribution.
886 See L<Class::MOP::Instance> for more details.
890 Note that this module does not export any constants or functions.
896 =item I<Class::MOP::IS_RUNNING_ON_5_10>
898 We set this constant depending on what version perl we are on, this
899 allows us to take advantage of new 5.10 features and stay backwards
904 =head2 Utility functions
906 Note that these are all called as B<functions, not methods>.
910 =item B<Class::MOP::load_class($class_name)>
912 This will load the specified C<$class_name>, if it is not already
913 loaded (as reported by C<is_class_loaded>). This function can be used
914 in place of tricks like C<eval "use $module"> or using C<require>
917 =item B<Class::MOP::is_class_loaded($class_name)>
919 Returns a boolean indicating whether or not C<$class_name> has been
922 This does a basic check of the symbol table to try and determine as
923 best it can if the C<$class_name> is loaded, it is probably correct
924 about 99% of the time, but it can be fooled into reporting false
925 positives. In particular, loading any of the core L<IO> modules will
926 cause most of the rest of the core L<IO> modules to falsely report
927 having been loaded, due to the way the base L<IO> module works.
929 =item B<Class::MOP::get_code_info($code)>
931 This function returns two values, the name of the package the C<$code>
932 is from and the name of the C<$code> itself. This is used by several
933 elements of the MOP to determine where a given C<$code> reference is
936 =item B<Class::MOP::class_of($instance_or_class_name)>
938 This will return the metaclass of the given instance or class name. If the
939 class lacks a metaclass, no metaclass will be initialized, and C<undef> will be
942 =item B<Class::MOP::check_package_cache_flag($pkg)>
944 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
946 This will return an integer that is managed by L<Class::MOP::Class> to
947 determine if a module's symbol table has been altered.
949 In Perl 5.10 or greater, this flag is package specific. However in
950 versions prior to 5.10, this will use the C<PL_sub_generation>
951 variable which is not package specific.
953 =item B<Class::MOP::load_first_existing_class(@class_names)>
955 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
957 Given a list of class names, this function will attempt to load each
960 If it finds a class it can load, it will return that class' name. If
961 none of the classes can be loaded, it will throw an exception.
965 =head2 Metaclass cache functions
967 Class::MOP holds a cache of metaclasses. The following are functions
968 (B<not methods>) which can be used to access that cache. It is not
969 recommended that you mess with these. Bad things could happen, but if
970 you are brave and willing to risk it: go for it!
974 =item B<Class::MOP::get_all_metaclasses>
976 This will return a hash of all the metaclass instances that have
977 been cached by L<Class::MOP::Class>, keyed by the package name.
979 =item B<Class::MOP::get_all_metaclass_instances>
981 This will return a list of all the metaclass instances that have
982 been cached by L<Class::MOP::Class>.
984 =item B<Class::MOP::get_all_metaclass_names>
986 This will return a list of all the metaclass names that have
987 been cached by L<Class::MOP::Class>.
989 =item B<Class::MOP::get_metaclass_by_name($name)>
991 This will return a cached L<Class::MOP::Class> instance, or nothing
992 if no metaclass exists with that C<$name>.
994 =item B<Class::MOP::store_metaclass_by_name($name, $meta)>
996 This will store a metaclass in the cache at the supplied C<$key>.
998 =item B<Class::MOP::weaken_metaclass($name)>
1000 In rare cases (e.g. anonymous metaclasses) it is desirable to
1001 store a weakened reference in the metaclass cache. This
1002 function will weaken the reference to the metaclass stored
1005 =item B<Class::MOP::does_metaclass_exist($name)>
1007 This will return true of there exists a metaclass stored in the
1008 C<$name> key, and return false otherwise.
1010 =item B<Class::MOP::remove_metaclass_by_name($name)>
1012 This will remove the metaclass stored in the C<$name> key.
1020 There are very few books out on Meta Object Protocols and Metaclasses
1021 because it is such an esoteric topic. The following books are really
1022 the only ones I have found. If you know of any more, B<I<please>>
1023 email me and let me know, I would love to hear about them.
1027 =item I<The Art of the Meta Object Protocol>
1029 =item I<Advances in Object-Oriented Metalevel Architecture and Reflection>
1031 =item I<Putting MetaClasses to Work>
1033 =item I<Smalltalk: The Language>
1041 =item "Uniform and safe metaclass composition"
1043 An excellent paper by the people who brought us the original Traits paper.
1044 This paper is on how Traits can be used to do safe metaclass composition,
1045 and offers an excellent introduction section which delves into the topic of
1046 metaclass compatibility.
1048 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
1050 =item "Safe Metaclass Programming"
1052 This paper seems to precede the above paper, and propose a mix-in based
1053 approach as opposed to the Traits based approach. Both papers have similar
1054 information on the metaclass compatibility problem space.
1056 L<http://citeseer.ist.psu.edu/37617.html>
1064 =item The Perl 6 MetaModel work in the Pugs project
1068 =item L<http://svn.openfoundry.org/pugs/misc/Perl-MetaModel/>
1070 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1080 =item CPAN Module Review of Class::MOP
1082 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1086 =head1 SIMILAR MODULES
1088 As I have said above, this module is a class-builder-builder, so it is
1089 not the same thing as modules like L<Class::Accessor> and
1090 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1091 with similar goals to this module. The one I have found which is most
1092 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1093 creates are very different from this modules.
1097 All complex software has bugs lurking in it, and this module is no
1100 Please report any bugs to C<bug-class-mop@rt.cpan.org>, or through the
1101 web interface at L<http://rt.cpan.org>.
1103 You can also discuss feature requests or possible bugs on the Moose
1104 mailing list (moose@perl.org) or on IRC at
1105 L<irc://irc.perl.org/#moose>.
1107 =head1 ACKNOWLEDGEMENTS
1113 Thanks to Rob for actually getting the development of this module kick-started.
1119 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1121 B<with contributions from:>
1123 Brandon (blblack) Black
1125 Florian (rafl) Ragwitz
1127 Guillermo (groditi) Roditi
1129 Dave (autarch) Rolsky
1133 Rob (robkinyon) Kinyon
1135 Yuval (nothingmuch) Kogman
1137 Scott (konobi) McWhirter
1141 =head1 COPYRIGHT AND LICENSE
1143 Copyright 2006-2009 by Infinity Interactive, Inc.
1145 L<http://www.iinteractive.com>
1147 This library is free software; you can redistribute it and/or modify
1148 it under the same terms as Perl itself.