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 my $class = load_first_existing_class($_[0]);
136 return get_metaclass_by_name($class) || $class;
139 sub _is_valid_class_name {
142 return 0 if ref($class);
143 return 0 unless defined($class);
144 return 0 unless length($class);
146 return 1 if $class =~ /^\w+(?:::\w+)*$/;
151 ## ----------------------------------------------------------------------------
152 ## Setting up our environment ...
153 ## ----------------------------------------------------------------------------
154 ## Class::MOP needs to have a few things in the global perl environment so
155 ## that it can operate effectively. Those things are done here.
156 ## ----------------------------------------------------------------------------
158 # ... nothing yet actually ;)
160 ## ----------------------------------------------------------------------------
162 ## ----------------------------------------------------------------------------
163 ## The code below here is to bootstrap our MOP with itself. This is also
164 ## sometimes called "tying the knot". By doing this, we make it much easier
165 ## to extend the MOP through subclassing and such since now you can use the
166 ## MOP itself to extend itself.
168 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
169 ## ----------------------------------------------------------------------------
171 # We need to add in the meta-attributes here so that
172 # any subclass of Class::MOP::* will be able to
173 # inherit them using _construct_instance
175 ## --------------------------------------------------------
176 ## Class::MOP::Package
178 Class::MOP::Package->meta->add_attribute(
179 Class::MOP::Attribute->new('package' => (
181 # NOTE: we need to do this in order
182 # for the instance meta-object to
183 # not fall into meta-circular death
185 # we just alias the original method
186 # rather than re-produce it here
187 'name' => \&Class::MOP::Package::name
192 Class::MOP::Package->meta->add_attribute(
193 Class::MOP::Attribute->new('namespace' => (
196 # we just alias the original method
197 # rather than re-produce it here
198 'namespace' => \&Class::MOP::Package::namespace
201 default => sub { \undef }
205 Class::MOP::Package->meta->add_attribute(
206 Class::MOP::Attribute->new('methods' => (
209 # we just alias the original method
210 # rather than re-produce it here
211 'get_method_map' => \&Class::MOP::Package::get_method_map
213 default => sub { {} }
217 Class::MOP::Package->meta->add_attribute(
218 Class::MOP::Attribute->new('method_metaclass' => (
221 # we just alias the original method
222 # rather than re-produce it here
223 'method_metaclass' => \&Class::MOP::Package::method_metaclass
225 default => 'Class::MOP::Method',
229 Class::MOP::Package->meta->add_attribute(
230 Class::MOP::Attribute->new('wrapped_method_metaclass' => (
233 # we just alias the original method
234 # rather than re-produce it here
235 'wrapped_method_metaclass' => \&Class::MOP::Package::wrapped_method_metaclass
237 default => 'Class::MOP::Method::Wrapped',
241 ## --------------------------------------------------------
242 ## Class::MOP::Module
245 # yeah this is kind of stretching things a bit,
246 # but truthfully the version should be an attribute
247 # of the Module, the weirdness comes from having to
248 # stick to Perl 5 convention and store it in the
249 # $VERSION package variable. Basically if you just
250 # squint at it, it will look how you want it to look.
251 # Either as a package variable, or as a attribute of
252 # the metaclass, isn't abstraction great :)
254 Class::MOP::Module->meta->add_attribute(
255 Class::MOP::Attribute->new('version' => (
258 # we just alias the original method
259 # rather than re-produce it here
260 'version' => \&Class::MOP::Module::version
263 default => sub { \undef }
268 # By following the same conventions as version here,
269 # we are opening up the possibility that people can
270 # use the $AUTHORITY in non-Class::MOP modules as
273 Class::MOP::Module->meta->add_attribute(
274 Class::MOP::Attribute->new('authority' => (
277 # we just alias the original method
278 # rather than re-produce it here
279 'authority' => \&Class::MOP::Module::authority
282 default => sub { \undef }
286 ## --------------------------------------------------------
289 Class::MOP::Class->meta->add_attribute(
290 Class::MOP::Attribute->new('attributes' => (
292 # NOTE: we need to do this in order
293 # for the instance meta-object to
294 # not fall into meta-circular death
296 # we just alias the original method
297 # rather than re-produce it here
298 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
300 default => sub { {} }
304 Class::MOP::Class->meta->add_attribute(
305 Class::MOP::Attribute->new('superclasses' => (
308 # we just alias the original method
309 # rather than re-produce it here
310 'superclasses' => \&Class::MOP::Class::superclasses
313 default => sub { \undef }
317 Class::MOP::Class->meta->add_attribute(
318 Class::MOP::Attribute->new('attribute_metaclass' => (
321 # we just alias the original method
322 # rather than re-produce it here
323 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
325 default => 'Class::MOP::Attribute',
329 Class::MOP::Class->meta->add_attribute(
330 Class::MOP::Attribute->new('instance_metaclass' => (
332 # NOTE: we need to do this in order
333 # for the instance meta-object to
334 # not fall into meta-circular death
336 # we just alias the original method
337 # rather than re-produce it here
338 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
340 default => 'Class::MOP::Instance',
344 Class::MOP::Class->meta->add_attribute(
345 Class::MOP::Attribute->new('immutable_trait' => (
347 'immutable_trait' => \&Class::MOP::Class::immutable_trait
349 default => "Class::MOP::Class::Immutable::Trait",
353 Class::MOP::Class->meta->add_attribute(
354 Class::MOP::Attribute->new('constructor_name' => (
356 'constructor_name' => \&Class::MOP::Class::constructor_name,
362 Class::MOP::Class->meta->add_attribute(
363 Class::MOP::Attribute->new('constructor_class' => (
365 'constructor_class' => \&Class::MOP::Class::constructor_class,
367 default => "Class::MOP::Method::Constructor",
372 Class::MOP::Class->meta->add_attribute(
373 Class::MOP::Attribute->new('destructor_class' => (
375 'destructor_class' => \&Class::MOP::Class::destructor_class,
381 # we don't actually need to tie the knot with
382 # Class::MOP::Class here, it is actually handled
383 # within Class::MOP::Class itself in the
384 # _construct_class_instance method.
386 ## --------------------------------------------------------
387 ## Class::MOP::Attribute
389 Class::MOP::Attribute->meta->add_attribute(
390 Class::MOP::Attribute->new('name' => (
392 # NOTE: we need to do this in order
393 # for the instance meta-object to
394 # not fall into meta-circular death
396 # we just alias the original method
397 # rather than re-produce it here
398 'name' => \&Class::MOP::Attribute::name
403 Class::MOP::Attribute->meta->add_attribute(
404 Class::MOP::Attribute->new('associated_class' => (
406 # NOTE: we need to do this in order
407 # for the instance meta-object to
408 # not fall into meta-circular death
410 # we just alias the original method
411 # rather than re-produce it here
412 'associated_class' => \&Class::MOP::Attribute::associated_class
417 Class::MOP::Attribute->meta->add_attribute(
418 Class::MOP::Attribute->new('accessor' => (
419 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
420 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
424 Class::MOP::Attribute->meta->add_attribute(
425 Class::MOP::Attribute->new('reader' => (
426 reader => { 'reader' => \&Class::MOP::Attribute::reader },
427 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
431 Class::MOP::Attribute->meta->add_attribute(
432 Class::MOP::Attribute->new('initializer' => (
433 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
434 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
438 Class::MOP::Attribute->meta->add_attribute(
439 Class::MOP::Attribute->new('definition_context' => (
440 reader => { 'definition_context' => \&Class::MOP::Attribute::definition_context },
444 Class::MOP::Attribute->meta->add_attribute(
445 Class::MOP::Attribute->new('writer' => (
446 reader => { 'writer' => \&Class::MOP::Attribute::writer },
447 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
451 Class::MOP::Attribute->meta->add_attribute(
452 Class::MOP::Attribute->new('predicate' => (
453 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
454 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
458 Class::MOP::Attribute->meta->add_attribute(
459 Class::MOP::Attribute->new('clearer' => (
460 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
461 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
465 Class::MOP::Attribute->meta->add_attribute(
466 Class::MOP::Attribute->new('builder' => (
467 reader => { 'builder' => \&Class::MOP::Attribute::builder },
468 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
472 Class::MOP::Attribute->meta->add_attribute(
473 Class::MOP::Attribute->new('init_arg' => (
474 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
475 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
479 Class::MOP::Attribute->meta->add_attribute(
480 Class::MOP::Attribute->new('default' => (
481 # default has a custom 'reader' method ...
482 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
486 Class::MOP::Attribute->meta->add_attribute(
487 Class::MOP::Attribute->new('associated_methods' => (
488 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
489 default => sub { [] }
493 Class::MOP::Attribute->meta->add_attribute(
494 Class::MOP::Attribute->new('insertion_order' => (
495 reader => { 'insertion_order' => \&Class::MOP::Attribute::insertion_order },
496 writer => { '_set_insertion_order' => \&Class::MOP::Attribute::_set_insertion_order },
497 predicate => { 'has_insertion_order' => \&Class::MOP::Attribute::has_insertion_order },
501 Class::MOP::Attribute->meta->add_method('clone' => sub {
503 $self->meta->clone_object($self, @_);
506 ## --------------------------------------------------------
507 ## Class::MOP::Method
508 Class::MOP::Method->meta->add_attribute(
509 Class::MOP::Attribute->new('body' => (
510 reader => { 'body' => \&Class::MOP::Method::body },
514 Class::MOP::Method->meta->add_attribute(
515 Class::MOP::Attribute->new('associated_metaclass' => (
516 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
520 Class::MOP::Method->meta->add_attribute(
521 Class::MOP::Attribute->new('package_name' => (
522 reader => { 'package_name' => \&Class::MOP::Method::package_name },
526 Class::MOP::Method->meta->add_attribute(
527 Class::MOP::Attribute->new('name' => (
528 reader => { 'name' => \&Class::MOP::Method::name },
532 Class::MOP::Method->meta->add_attribute(
533 Class::MOP::Attribute->new('original_method' => (
534 reader => { 'original_method' => \&Class::MOP::Method::original_method },
535 writer => { '_set_original_method' => \&Class::MOP::Method::_set_original_method },
539 Class::MOP::Method->meta->add_method('clone' => sub {
541 my $clone = $self->meta->clone_object($self, @_);
542 $clone->_set_original_method($self);
546 ## --------------------------------------------------------
547 ## Class::MOP::Method::Wrapped
550 # the way this item is initialized, this
551 # really does not follow the standard
552 # practices of attributes, but we put
553 # it here for completeness
554 Class::MOP::Method::Wrapped->meta->add_attribute(
555 Class::MOP::Attribute->new('modifier_table')
558 ## --------------------------------------------------------
559 ## Class::MOP::Method::Generated
561 Class::MOP::Method::Generated->meta->add_attribute(
562 Class::MOP::Attribute->new('is_inline' => (
563 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
568 Class::MOP::Method::Generated->meta->add_attribute(
569 Class::MOP::Attribute->new('definition_context' => (
570 reader => { 'definition_context' => \&Class::MOP::Method::Generated::definition_context },
575 ## --------------------------------------------------------
576 ## Class::MOP::Method::Inlined
578 Class::MOP::Method::Inlined->meta->add_attribute(
579 Class::MOP::Attribute->new('_expected_method_class' => (
580 reader => { '_expected_method_class' => \&Class::MOP::Method::Inlined::_expected_method_class },
584 ## --------------------------------------------------------
585 ## Class::MOP::Method::Accessor
587 Class::MOP::Method::Accessor->meta->add_attribute(
588 Class::MOP::Attribute->new('attribute' => (
590 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
595 Class::MOP::Method::Accessor->meta->add_attribute(
596 Class::MOP::Attribute->new('accessor_type' => (
597 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
601 ## --------------------------------------------------------
602 ## Class::MOP::Method::Constructor
604 Class::MOP::Method::Constructor->meta->add_attribute(
605 Class::MOP::Attribute->new('options' => (
607 'options' => \&Class::MOP::Method::Constructor::options
609 default => sub { +{} }
613 Class::MOP::Method::Constructor->meta->add_attribute(
614 Class::MOP::Attribute->new('associated_metaclass' => (
615 init_arg => "metaclass", # FIXME alias and rename
617 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
622 ## --------------------------------------------------------
623 ## Class::MOP::Instance
626 # these don't yet do much of anything, but are just
627 # included for completeness
629 Class::MOP::Instance->meta->add_attribute(
630 Class::MOP::Attribute->new('associated_metaclass',
631 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
635 Class::MOP::Instance->meta->add_attribute(
636 Class::MOP::Attribute->new('_class_name',
638 reader => { _class_name => \&Class::MOP::Instance::_class_name },
639 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
640 #default => sub { $_[0]->associated_metaclass->name },
644 Class::MOP::Instance->meta->add_attribute(
645 Class::MOP::Attribute->new('attributes',
646 reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
650 Class::MOP::Instance->meta->add_attribute(
651 Class::MOP::Attribute->new('slots',
652 reader => { slots => \&Class::MOP::Instance::slots },
656 Class::MOP::Instance->meta->add_attribute(
657 Class::MOP::Attribute->new('slot_hash',
658 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
662 require Class::MOP::Deprecated unless our $no_deprecated;
664 # we need the meta instance of the meta instance to be created now, in order
665 # for the constructor to be able to use it
666 Class::MOP::Instance->meta->get_meta_instance;
668 # pretend the add_method never happenned. it hasn't yet affected anything
669 undef Class::MOP::Instance->meta->{_package_cache_flag};
671 ## --------------------------------------------------------
672 ## Now close all the Class::MOP::* classes
674 # NOTE: we don't need to inline the the accessors this only lengthens
675 # the compile time of the MOP, and gives us no actual benefits.
677 $_->meta->make_immutable(
678 inline_constructor => 0,
679 constructor_name => "_new",
680 inline_accessors => 0,
686 Class::MOP::Attribute
692 Class::MOP::Method::Generated
693 Class::MOP::Method::Inlined
695 Class::MOP::Method::Accessor
696 Class::MOP::Method::Constructor
697 Class::MOP::Method::Wrapped
708 Class::MOP - A Meta Object Protocol for Perl 5
712 This module is a fully functioning meta object protocol for the
713 Perl 5 object system. It makes no attempt to change the behavior or
714 characteristics of the Perl 5 object system, only to create a
715 protocol for its manipulation and introspection.
717 That said, it does attempt to create the tools for building a rich set
718 of extensions to the Perl 5 object system. Every attempt has been made
719 to abide by the spirit of the Perl 5 object system that we all know
722 This documentation is sparse on conceptual details. We suggest looking
723 at the items listed in the L<SEE ALSO> section for more
724 information. In particular the book "The Art of the Meta Object
725 Protocol" was very influential in the development of this system.
727 =head2 What is a Meta Object Protocol?
729 A meta object protocol is an API to an object system.
731 To be more specific, it abstracts the components of an object system
732 (classes, object, methods, object attributes, etc.). These
733 abstractions can then be used to inspect and manipulate the object
734 system which they describe.
736 It can be said that there are two MOPs for any object system; the
737 implicit MOP and the explicit MOP. The implicit MOP handles things
738 like method dispatch or inheritance, which happen automatically as
739 part of how the object system works. The explicit MOP typically
740 handles the introspection/reflection features of the object system.
742 All object systems have implicit MOPs. Without one, they would not
743 work. Explicit MOPs are much less common, and depending on the
744 language can vary from restrictive (Reflection in Java or C#) to wide
745 open (CLOS is a perfect example).
747 =head2 Yet Another Class Builder! Why?
749 This is B<not> a class builder so much as a I<class builder
750 B<builder>>. The intent is that an end user will not use this module
751 directly, but instead this module is used by module authors to build
752 extensions and features onto the Perl 5 object system.
754 This system is used by L<Moose>, which supplies a powerful class
755 builder system built entirely on top of C<Class::MOP>.
757 =head2 Who is this module for?
759 This module is for anyone who has ever created or wanted to create a
760 module for the Class:: namespace. The tools which this module provides
761 make doing complex Perl 5 wizardry simpler, by removing such barriers
762 as the need to hack symbol tables, or understand the fine details of
765 =head2 What changes do I have to make to use this module?
767 This module was designed to be as unintrusive as possible. Many of its
768 features are accessible without B<any> change to your existing
769 code. It is meant to be a compliment to your existing code and not an
770 intrusion on your code base. Unlike many other B<Class::> modules,
771 this module B<does not> require you subclass it, or even that you
772 C<use> it in within your module's package.
774 The only features which requires additions to your code are the
775 attribute handling and instance construction features, and these are
776 both completely optional features. The only reason for this is because
777 Perl 5's object system does not actually have these features built
778 in. More information about this feature can be found below.
780 =head2 About Performance
782 It is a common misconception that explicit MOPs are a performance hit.
783 This is not a universal truth, it is a side-effect of some specific
784 implementations. For instance, using Java reflection is slow because
785 the JVM cannot take advantage of any compiler optimizations, and the
786 JVM has to deal with much more runtime type information as well.
788 Reflection in C# is marginally better as it was designed into the
789 language and runtime (the CLR). In contrast, CLOS (the Common Lisp
790 Object System) was built to support an explicit MOP, and so
791 performance is tuned for it.
793 This library in particular does its absolute best to avoid putting
794 B<any> drain at all upon your code's performance. In fact, by itself
795 it does nothing to affect your existing code. So you only pay for what
798 =head2 About Metaclass compatibility
800 This module makes sure that all metaclasses created are both upwards
801 and downwards compatible. The topic of metaclass compatibility is
802 highly esoteric and is something only encountered when doing deep and
803 involved metaclass hacking. There are two basic kinds of metaclass
804 incompatibility; upwards and downwards.
806 Upwards metaclass compatibility means that the metaclass of a
807 given class is either the same as (or a subclass of) all of the
810 Downward metaclass compatibility means that the metaclasses of a
811 given class's ancestors are all either the same as (or a subclass
814 Here is a diagram showing a set of two classes (C<A> and C<B>) and
815 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
816 metaclass compatibility both upwards and downwards.
818 +---------+ +---------+
819 | Meta::A |<----| Meta::B | <....... (instance of )
820 +---------+ +---------+ <------- (inherits from)
823 +---------+ +---------+
825 +---------+ +---------+
827 As I said this is a highly esoteric topic and one you will only run
828 into if you do a lot of subclassing of L<Class::MOP::Class>. If you
829 are interested in why this is an issue see the paper I<Uniform and
830 safe metaclass composition> linked to in the L<SEE ALSO> section of
833 =head2 Using custom metaclasses
835 Always use the L<metaclass> pragma when using a custom metaclass, this
836 will ensure the proper initialization order and not accidentally
837 create an incorrect type of metaclass for you. This is a very rare
838 problem, and one which can only occur if you are doing deep metaclass
839 programming. So in other words, don't worry about it.
841 Note that if you're using L<Moose> we encourage you to I<not> use
842 L<metaclass> pragma, and instead use L<Moose::Util::MetaRole> to apply
843 roles to a class's metaclasses. This topic is covered at length in
844 various L<Moose::Cookbook> recipes.
848 The meta-object protocol is divided into 4 main sub-protocols:
850 =head2 The Class protocol
852 This provides a means of manipulating and introspecting a Perl 5
853 class. It handles symbol table hacking for you, and provides a rich
854 set of methods that go beyond simple package introspection.
856 See L<Class::MOP::Class> for more details.
858 =head2 The Attribute protocol
860 This provides a consistent representation for an attribute of a Perl 5
861 class. Since there are so many ways to create and handle attributes in
862 Perl 5 OO, the Attribute protocol provide as much of a unified
863 approach as possible. Of course, you are always free to extend this
864 protocol by subclassing the appropriate classes.
866 See L<Class::MOP::Attribute> for more details.
868 =head2 The Method protocol
870 This provides a means of manipulating and introspecting methods in the
871 Perl 5 object system. As with attributes, there are many ways to
872 approach this topic, so we try to keep it pretty basic, while still
873 making it possible to extend the system in many ways.
875 See L<Class::MOP::Method> for more details.
877 =head2 The Instance protocol
879 This provides a layer of abstraction for creating object instances.
880 Since the other layers use this protocol, it is relatively easy to
881 change the type of your instances from the default hash reference to
882 some other type of reference. Several examples are provided in the
883 F<examples/> directory included in this distribution.
885 See L<Class::MOP::Instance> for more details.
889 Note that this module does not export any constants or functions.
895 =item I<Class::MOP::IS_RUNNING_ON_5_10>
897 We set this constant depending on what version perl we are on, this
898 allows us to take advantage of new 5.10 features and stay backwards
903 =head2 Utility functions
905 Note that these are all called as B<functions, not methods>.
909 =item B<Class::MOP::load_class($class_name)>
911 This will load the specified C<$class_name>, if it is not already
912 loaded (as reported by C<is_class_loaded>). This function can be used
913 in place of tricks like C<eval "use $module"> or using C<require>
914 unconditionally. This will return the metaclass of C<$class_name> if
915 one exists, otherwise it will return C<$class_name>.
917 =item B<Class::MOP::is_class_loaded($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.