12 use Scalar::Util 'weaken', 'reftype';
15 use Class::MOP::Class;
16 use Class::MOP::Attribute;
17 use Class::MOP::Method;
19 use Class::MOP::Immutable;
22 *IS_RUNNING_ON_5_10 = ($] < 5.009_005)
26 *HAVE_ISAREV = defined(&mro::get_isarev)
30 # this is either part of core or set up appropriately by MRO::Compat
31 *check_package_cache_flag = \&mro::get_pkg_gen;
34 our $VERSION = '0.78';
35 our $XS_VERSION = $VERSION;
36 $VERSION = eval $VERSION;
37 our $AUTHORITY = 'cpan:STEVAN';
39 _try_load_xs() or _load_pure_perl();
42 return if $ENV{CLASS_MOP_NO_XS};
48 # just doing this - no warnings 'redefine' - doesn't work
51 __PACKAGE__->XSLoader::load($XS_VERSION);
54 Sub::Name->import(qw(subname));
56 require Devel::GlobalDestruction;
57 Devel::GlobalDestruction->import("in_global_destruction");
59 *USING_XS = sub () { 1 };
64 die $e if $e && $e !~ /object version|loadable object/;
70 require Sub::Identify;
71 Sub::Identify->import('get_code_info');
73 *subname = sub { $_[1] };
74 *in_global_destruction = sub () { !1 };
76 *USING_XS = sub () { 0 };
81 # Metaclasses are singletons, so we cache them here.
82 # there is no need to worry about destruction though
83 # because they should die only when the program dies.
84 # After all, do package definitions even get reaped?
87 # means of accessing all the metaclasses that have
88 # been initialized thus far (for mugwumps obj browser)
89 sub get_all_metaclasses { %METAS }
90 sub get_all_metaclass_instances { values %METAS }
91 sub get_all_metaclass_names { keys %METAS }
92 sub get_metaclass_by_name { $METAS{$_[0]} }
93 sub store_metaclass_by_name { $METAS{$_[0]} = $_[1] }
94 sub weaken_metaclass { weaken($METAS{$_[0]}) }
95 sub does_metaclass_exist { exists $METAS{$_[0]} && defined $METAS{$_[0]} }
96 sub remove_metaclass_by_name { $METAS{$_[0]} = undef }
99 # We only cache metaclasses, meaning instances of
100 # Class::MOP::Class. We do not cache instance of
101 # Class::MOP::Package or Class::MOP::Module. Mostly
102 # because I don't yet see a good reason to do so.
105 sub load_first_existing_class {
109 foreach my $class (@classes) {
110 unless ( _is_valid_class_name($class) ) {
111 my $display = defined($class) ? $class : 'undef';
112 confess "Invalid class name ($display)";
118 for my $class (@classes) {
119 my $e = _try_load_one_class($class);
122 $exceptions{$class} = $e;
130 return $found if $found;
136 "Could not load class (%s) because : %s", $_,
143 sub _try_load_one_class {
146 return if is_class_loaded($class);
148 my $file = $class . '.pm';
153 eval { require($file) };
159 my $class = load_first_existing_class($_[0]);
160 return get_metaclass_by_name($class) || $class;
163 sub _is_valid_class_name {
166 return 0 if ref($class);
167 return 0 unless defined($class);
168 return 0 unless length($class);
170 return 1 if $class =~ /^\w+(?:::\w+)*$/;
175 sub is_class_loaded {
178 return 0 unless _is_valid_class_name($class);
180 # walk the symbol table tree to avoid autovififying
181 # \*{${main::}{"Foo::"}} == \*main::Foo::
184 foreach my $part (split('::', $class)) {
185 return 0 unless exists ${$$pack}{"${part}::"};
186 $pack = \*{${$$pack}{"${part}::"}};
189 # We used to check in the package stash, but it turns out that
190 # *{${$$package}{VERSION}{SCALAR}} can end up pointing to a
191 # reference to undef. It looks
195 ${$class . '::VERSION'};
198 return 1 if ! ref $version && defined $version;
199 # Sometimes $VERSION ends up as a reference to undef (weird)
200 return 1 if ref $version && reftype $version eq 'SCALAR' && defined ${$version};
202 return 1 if exists ${$$pack}{ISA}
203 && defined *{${$$pack}{ISA}}{ARRAY};
205 # check for any method
206 foreach ( keys %{$$pack} ) {
207 next if substr($_, -2, 2) eq '::';
209 my $glob = ${$$pack}{$_} || next;
212 if ( IS_RUNNING_ON_5_10 ) {
213 return 1 if ref $glob eq 'SCALAR';
216 return 1 if defined *{$glob}{CODE};
224 ## ----------------------------------------------------------------------------
225 ## Setting up our environment ...
226 ## ----------------------------------------------------------------------------
227 ## Class::MOP needs to have a few things in the global perl environment so
228 ## that it can operate effectively. Those things are done here.
229 ## ----------------------------------------------------------------------------
231 # ... nothing yet actually ;)
233 ## ----------------------------------------------------------------------------
235 ## ----------------------------------------------------------------------------
236 ## The code below here is to bootstrap our MOP with itself. This is also
237 ## sometimes called "tying the knot". By doing this, we make it much easier
238 ## to extend the MOP through subclassing and such since now you can use the
239 ## MOP itself to extend itself.
241 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
242 ## ----------------------------------------------------------------------------
244 # We need to add in the meta-attributes here so that
245 # any subclass of Class::MOP::* will be able to
246 # inherit them using &construct_instance
248 ## --------------------------------------------------------
249 ## Class::MOP::Package
251 Class::MOP::Package->meta->add_attribute(
252 Class::MOP::Attribute->new('package' => (
254 # NOTE: we need to do this in order
255 # for the instance meta-object to
256 # not fall into meta-circular death
258 # we just alias the original method
259 # rather than re-produce it here
260 'name' => \&Class::MOP::Package::name
265 Class::MOP::Package->meta->add_attribute(
266 Class::MOP::Attribute->new('namespace' => (
269 # we just alias the original method
270 # rather than re-produce it here
271 'namespace' => \&Class::MOP::Package::namespace
274 default => sub { \undef }
278 ## --------------------------------------------------------
279 ## Class::MOP::Module
282 # yeah this is kind of stretching things a bit,
283 # but truthfully the version should be an attribute
284 # of the Module, the weirdness comes from having to
285 # stick to Perl 5 convention and store it in the
286 # $VERSION package variable. Basically if you just
287 # squint at it, it will look how you want it to look.
288 # Either as a package variable, or as a attribute of
289 # the metaclass, isn't abstraction great :)
291 Class::MOP::Module->meta->add_attribute(
292 Class::MOP::Attribute->new('version' => (
295 # we just alias the original method
296 # rather than re-produce it here
297 'version' => \&Class::MOP::Module::version
300 default => sub { \undef }
305 # By following the same conventions as version here,
306 # we are opening up the possibility that people can
307 # use the $AUTHORITY in non-Class::MOP modules as
310 Class::MOP::Module->meta->add_attribute(
311 Class::MOP::Attribute->new('authority' => (
314 # we just alias the original method
315 # rather than re-produce it here
316 'authority' => \&Class::MOP::Module::authority
319 default => sub { \undef }
323 ## --------------------------------------------------------
326 Class::MOP::Class->meta->add_attribute(
327 Class::MOP::Attribute->new('attributes' => (
329 # NOTE: we need to do this in order
330 # for the instance meta-object to
331 # not fall into meta-circular death
333 # we just alias the original method
334 # rather than re-produce it here
335 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
337 default => sub { {} }
341 Class::MOP::Class->meta->add_attribute(
342 Class::MOP::Attribute->new('methods' => (
345 # we just alias the original method
346 # rather than re-produce it here
347 'get_method_map' => \&Class::MOP::Class::get_method_map
349 default => sub { {} }
353 Class::MOP::Class->meta->add_attribute(
354 Class::MOP::Attribute->new('superclasses' => (
357 # we just alias the original method
358 # rather than re-produce it here
359 'superclasses' => \&Class::MOP::Class::superclasses
362 default => sub { \undef }
366 Class::MOP::Class->meta->add_attribute(
367 Class::MOP::Attribute->new('attribute_metaclass' => (
370 # we just alias the original method
371 # rather than re-produce it here
372 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
374 default => 'Class::MOP::Attribute',
378 Class::MOP::Class->meta->add_attribute(
379 Class::MOP::Attribute->new('method_metaclass' => (
382 # we just alias the original method
383 # rather than re-produce it here
384 'method_metaclass' => \&Class::MOP::Class::method_metaclass
386 default => 'Class::MOP::Method',
390 Class::MOP::Class->meta->add_attribute(
391 Class::MOP::Attribute->new('wrapped_method_metaclass' => (
394 # we just alias the original method
395 # rather than re-produce it here
396 'wrapped_method_metaclass' => \&Class::MOP::Class::wrapped_method_metaclass
398 default => 'Class::MOP::Method::Wrapped',
402 Class::MOP::Class->meta->add_attribute(
403 Class::MOP::Attribute->new('instance_metaclass' => (
405 # NOTE: we need to do this in order
406 # for the instance meta-object to
407 # not fall into meta-circular death
409 # we just alias the original method
410 # rather than re-produce it here
411 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
413 default => 'Class::MOP::Instance',
418 # we don't actually need to tie the knot with
419 # Class::MOP::Class here, it is actually handled
420 # within Class::MOP::Class itself in the
421 # construct_class_instance method.
423 ## --------------------------------------------------------
424 ## Class::MOP::Attribute
426 Class::MOP::Attribute->meta->add_attribute(
427 Class::MOP::Attribute->new('name' => (
429 # NOTE: we need to do this in order
430 # for the instance meta-object to
431 # not fall into meta-circular death
433 # we just alias the original method
434 # rather than re-produce it here
435 'name' => \&Class::MOP::Attribute::name
440 Class::MOP::Attribute->meta->add_attribute(
441 Class::MOP::Attribute->new('associated_class' => (
443 # NOTE: we need to do this in order
444 # for the instance meta-object to
445 # not fall into meta-circular death
447 # we just alias the original method
448 # rather than re-produce it here
449 'associated_class' => \&Class::MOP::Attribute::associated_class
454 Class::MOP::Attribute->meta->add_attribute(
455 Class::MOP::Attribute->new('accessor' => (
456 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
457 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
461 Class::MOP::Attribute->meta->add_attribute(
462 Class::MOP::Attribute->new('reader' => (
463 reader => { 'reader' => \&Class::MOP::Attribute::reader },
464 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
468 Class::MOP::Attribute->meta->add_attribute(
469 Class::MOP::Attribute->new('initializer' => (
470 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
471 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
475 Class::MOP::Attribute->meta->add_attribute(
476 Class::MOP::Attribute->new('definition_context' => (
477 reader => { 'definition_context' => \&Class::MOP::Attribute::definition_context },
481 Class::MOP::Attribute->meta->add_attribute(
482 Class::MOP::Attribute->new('writer' => (
483 reader => { 'writer' => \&Class::MOP::Attribute::writer },
484 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
488 Class::MOP::Attribute->meta->add_attribute(
489 Class::MOP::Attribute->new('predicate' => (
490 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
491 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
495 Class::MOP::Attribute->meta->add_attribute(
496 Class::MOP::Attribute->new('clearer' => (
497 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
498 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
502 Class::MOP::Attribute->meta->add_attribute(
503 Class::MOP::Attribute->new('builder' => (
504 reader => { 'builder' => \&Class::MOP::Attribute::builder },
505 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
509 Class::MOP::Attribute->meta->add_attribute(
510 Class::MOP::Attribute->new('init_arg' => (
511 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
512 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
516 Class::MOP::Attribute->meta->add_attribute(
517 Class::MOP::Attribute->new('default' => (
518 # default has a custom 'reader' method ...
519 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
523 Class::MOP::Attribute->meta->add_attribute(
524 Class::MOP::Attribute->new('associated_methods' => (
525 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
526 default => sub { [] }
530 Class::MOP::Attribute->meta->add_method('clone' => sub {
532 $self->meta->clone_object($self, @_);
535 ## --------------------------------------------------------
536 ## Class::MOP::Method
537 Class::MOP::Method->meta->add_attribute(
538 Class::MOP::Attribute->new('body' => (
539 reader => { 'body' => \&Class::MOP::Method::body },
543 Class::MOP::Method->meta->add_attribute(
544 Class::MOP::Attribute->new('associated_metaclass' => (
545 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
549 Class::MOP::Method->meta->add_attribute(
550 Class::MOP::Attribute->new('package_name' => (
551 reader => { 'package_name' => \&Class::MOP::Method::package_name },
555 Class::MOP::Method->meta->add_attribute(
556 Class::MOP::Attribute->new('name' => (
557 reader => { 'name' => \&Class::MOP::Method::name },
561 Class::MOP::Method->meta->add_attribute(
562 Class::MOP::Attribute->new('original_method' => (
563 reader => { 'original_method' => \&Class::MOP::Method::original_method },
564 writer => { '_set_original_method' => \&Class::MOP::Method::_set_original_method },
568 Class::MOP::Method->meta->add_method('clone' => sub {
570 my $clone = $self->meta->clone_object($self, @_);
571 $clone->_set_original_method($self);
575 ## --------------------------------------------------------
576 ## Class::MOP::Method::Wrapped
579 # the way this item is initialized, this
580 # really does not follow the standard
581 # practices of attributes, but we put
582 # it here for completeness
583 Class::MOP::Method::Wrapped->meta->add_attribute(
584 Class::MOP::Attribute->new('modifier_table')
587 ## --------------------------------------------------------
588 ## Class::MOP::Method::Generated
590 Class::MOP::Method::Generated->meta->add_attribute(
591 Class::MOP::Attribute->new('is_inline' => (
592 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
597 Class::MOP::Method::Generated->meta->add_attribute(
598 Class::MOP::Attribute->new('definition_context' => (
599 reader => { 'definition_context' => \&Class::MOP::Method::Generated::definition_context },
603 ## --------------------------------------------------------
604 ## Class::MOP::Method::Accessor
606 Class::MOP::Method::Accessor->meta->add_attribute(
607 Class::MOP::Attribute->new('attribute' => (
609 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
614 Class::MOP::Method::Accessor->meta->add_attribute(
615 Class::MOP::Attribute->new('accessor_type' => (
616 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
620 ## --------------------------------------------------------
621 ## Class::MOP::Method::Constructor
623 Class::MOP::Method::Constructor->meta->add_attribute(
624 Class::MOP::Attribute->new('options' => (
626 'options' => \&Class::MOP::Method::Constructor::options
628 default => sub { +{} }
632 Class::MOP::Method::Constructor->meta->add_attribute(
633 Class::MOP::Attribute->new('associated_metaclass' => (
634 init_arg => "metaclass", # FIXME alias and rename
636 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
641 ## --------------------------------------------------------
642 ## Class::MOP::Instance
645 # these don't yet do much of anything, but are just
646 # included for completeness
648 Class::MOP::Instance->meta->add_attribute(
649 Class::MOP::Attribute->new('associated_metaclass',
650 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
654 Class::MOP::Instance->meta->add_attribute(
655 Class::MOP::Attribute->new('_class_name',
657 reader => { _class_name => \&Class::MOP::Instance::_class_name },
658 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
659 #default => sub { $_[0]->associated_metaclass->name },
663 Class::MOP::Instance->meta->add_attribute(
664 Class::MOP::Attribute->new('attributes',
665 reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
669 Class::MOP::Instance->meta->add_attribute(
670 Class::MOP::Attribute->new('slots',
671 reader => { slots => \&Class::MOP::Instance::slots },
675 Class::MOP::Instance->meta->add_attribute(
676 Class::MOP::Attribute->new('slot_hash',
677 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
682 # we need the meta instance of the meta instance to be created now, in order
683 # for the constructor to be able to use it
684 Class::MOP::Instance->meta->get_meta_instance;
686 # pretend the add_method never happenned. it hasn't yet affected anything
687 undef Class::MOP::Instance->meta->{_package_cache_flag};
689 ## --------------------------------------------------------
690 ## Now close all the Class::MOP::* classes
692 # NOTE: we don't need to inline the the accessors this only lengthens
693 # the compile time of the MOP, and gives us no actual benefits.
695 $_->meta->make_immutable(
696 inline_constructor => 1,
697 replace_constructor => 1,
698 constructor_name => "_new",
699 inline_accessors => 0,
705 Class::MOP::Attribute
711 Class::MOP::Method::Generated
713 Class::MOP::Method::Accessor
714 Class::MOP::Method::Constructor
715 Class::MOP::Method::Wrapped
726 Class::MOP - A Meta Object Protocol for Perl 5
730 This module is a fully functioning meta object protocol for the
731 Perl 5 object system. It makes no attempt to change the behavior or
732 characteristics of the Perl 5 object system, only to create a
733 protocol for its manipulation and introspection.
735 That said, it does attempt to create the tools for building a rich
736 set of extensions to the Perl 5 object system. Every attempt has been
737 made for these tools to keep to the spirit of the Perl 5 object
738 system that we all know and love.
740 This documentation is admittedly sparse on details, as time permits
741 I will try to improve them. For now, I suggest looking at the items
742 listed in the L<SEE ALSO> section for more information. In particular
743 the book "The Art of the Meta Object Protocol" was very influential
744 in the development of this system.
746 =head2 What is a Meta Object Protocol?
748 A meta object protocol is an API to an object system.
750 To be more specific, it is a set of abstractions of the components of
751 an object system (typically things like; classes, object, methods,
752 object attributes, etc.). These abstractions can then be used to both
753 inspect and manipulate the object system which they describe.
755 It can be said that there are two MOPs for any object system; the
756 implicit MOP, and the explicit MOP. The implicit MOP handles things
757 like method dispatch or inheritance, which happen automatically as
758 part of how the object system works. The explicit MOP typically
759 handles the introspection/reflection features of the object system.
760 All object systems have implicit MOPs, without one, they would not
761 work. Explict MOPs however as less common, and depending on the
762 language can vary from restrictive (Reflection in Java or C#) to
763 wide open (CLOS is a perfect example).
765 =head2 Yet Another Class Builder!! Why?
767 This is B<not> a class builder so much as it is a I<class builder
768 B<builder>>. My intent is that an end user does not use this module
769 directly, but instead this module is used by module authors to
770 build extensions and features onto the Perl 5 object system.
772 =head2 Who is this module for?
774 This module is specifically for anyone who has ever created or
775 wanted to create a module for the Class:: namespace. The tools which
776 this module will provide will hopefully make it easier to do more
777 complex things with Perl 5 classes by removing such barriers as
778 the need to hack the symbol tables, or understand the fine details
781 =head2 What changes do I have to make to use this module?
783 This module was designed to be as unintrusive as possible. Many of
784 its features are accessible without B<any> change to your existsing
785 code at all. It is meant to be a compliment to your existing code and
786 not an intrusion on your code base. Unlike many other B<Class::>
787 modules, this module B<does not> require you subclass it, or even that
788 you C<use> it in within your module's package.
790 The only features which requires additions to your code are the
791 attribute handling and instance construction features, and these are
792 both completely optional features. The only reason for this is because
793 Perl 5's object system does not actually have these features built
794 in. More information about this feature can be found below.
796 =head2 A Note about Performance?
798 It is a common misconception that explict MOPs are performance drains.
799 But this is not a universal truth at all, it is an side-effect of
800 specific implementations. For instance, using Java reflection is much
801 slower because the JVM cannot take advantage of any compiler
802 optimizations, and the JVM has to deal with much more runtime type
803 information as well. Reflection in C# is marginally better as it was
804 designed into the language and runtime (the CLR). In contrast, CLOS
805 (the Common Lisp Object System) was built to support an explicit MOP,
806 and so performance is tuned for it.
808 This library in particular does it's absolute best to avoid putting
809 B<any> drain at all upon your code's performance. In fact, by itself
810 it does nothing to affect your existing code. So you only pay for
811 what you actually use.
813 =head2 About Metaclass compatibility
815 This module makes sure that all metaclasses created are both upwards
816 and downwards compatible. The topic of metaclass compatibility is
817 highly esoteric and is something only encountered when doing deep and
818 involved metaclass hacking. There are two basic kinds of metaclass
819 incompatibility; upwards and downwards.
821 Upwards metaclass compatibility means that the metaclass of a
822 given class is either the same as (or a subclass of) all of the
825 Downward metaclass compatibility means that the metaclasses of a
826 given class's anscestors are all either the same as (or a subclass
829 Here is a diagram showing a set of two classes (C<A> and C<B>) and
830 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
831 metaclass compatibility both upwards and downwards.
833 +---------+ +---------+
834 | Meta::A |<----| Meta::B | <....... (instance of )
835 +---------+ +---------+ <------- (inherits from)
838 +---------+ +---------+
840 +---------+ +---------+
842 As I said this is a highly esoteric topic and one you will only run
843 into if you do a lot of subclassing of B<Class::MOP::Class>. If you
844 are interested in why this is an issue see the paper
845 I<Uniform and safe metaclass composition> linked to in the
846 L<SEE ALSO> section of this document.
848 =head2 Using custom metaclasses
850 Always use the metaclass pragma when using a custom metaclass, this
851 will ensure the proper initialization order and not accidentely
852 create an incorrect type of metaclass for you. This is a very rare
853 problem, and one which can only occur if you are doing deep metaclass
854 programming. So in other words, don't worry about it.
858 The protocol is divided into 4 main sub-protocols:
862 =item The Class protocol
864 This provides a means of manipulating and introspecting a Perl 5
865 class. It handles all of symbol table hacking for you, and provides
866 a rich set of methods that go beyond simple package introspection.
868 See L<Class::MOP::Class> for more details.
870 =item The Attribute protocol
872 This provides a consistent represenation for an attribute of a
873 Perl 5 class. Since there are so many ways to create and handle
874 attributes in Perl 5 OO, this attempts to provide as much of a
875 unified approach as possible, while giving the freedom and
876 flexibility to subclass for specialization.
878 See L<Class::MOP::Attribute> for more details.
880 =item The Method protocol
882 This provides a means of manipulating and introspecting methods in
883 the Perl 5 object system. As with attributes, there are many ways to
884 approach this topic, so we try to keep it pretty basic, while still
885 making it possible to extend the system in many ways.
887 See L<Class::MOP::Method> for more details.
889 =item The Instance protocol
891 This provides a layer of abstraction for creating object instances.
892 Since the other layers use this protocol, it is relatively easy to
893 change the type of your instances from the default HASH ref to other
894 types of references. Several examples are provided in the F<examples/>
895 directory included in this distribution.
897 See L<Class::MOP::Instance> for more details.
907 =item I<IS_RUNNING_ON_5_10>
909 We set this constant depending on what version perl we are on, this
910 allows us to take advantage of new 5.10 features and stay backwards
915 Whether or not C<mro> provides C<get_isarev>, a much faster way to get all the
916 subclasses of a certain class.
920 Whether or not the running C<Class::MOP> is using its XS version.
924 =head2 Utility functions
926 Note that these are all called as B<functions, not methods>.
930 =item B<load_class ($class_name)>
932 This will load a given C<$class_name> and if it does not have an
933 already initialized metaclass, then it will intialize one for it.
934 This function can be used in place of tricks like
935 C<eval "use $module"> or using C<require>.
937 =item B<is_class_loaded ($class_name)>
939 This will return a boolean depending on if the C<$class_name> has
942 NOTE: This does a basic check of the symbol table to try and
943 determine as best it can if the C<$class_name> is loaded, it
944 is probably correct about 99% of the time.
946 =item B<check_package_cache_flag ($pkg)>
948 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
950 This will return an integer that is managed by C<Class::MOP::Class>
951 to determine if a module's symbol table has been altered.
953 In Perl 5.10 or greater, this flag is package specific. However in
954 versions prior to 5.10, this will use the C<PL_sub_generation> variable
955 which is not package specific.
957 =item B<get_code_info ($code)>
959 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
961 This function returns two values, the name of the package the C<$code>
962 is from and the name of the C<$code> itself. This is used by several
963 elements of the MOP to detemine where a given C<$code> reference is from.
965 =item B<subname ($name, $code)>
967 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
969 If possible, we will load the L<Sub::Name> module and this will function
970 as C<Sub::Name::subname> does, otherwise it will just return the C<$code>
973 =item B<in_global_destruction>
975 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
977 If L<Devel::GlobalDestruction> is available, this returns true under global
980 Otherwise it's a constant returning false.
982 =item B<load_first_existing_class ($class_name, [$class_name, ...])>
984 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
986 Given a list of class names, this function will attempt to load each
989 If it finds a class it can load, it will return that class' name.
990 If none of the classes can be loaded, it will throw an exception.
994 =head2 Metaclass cache functions
996 Class::MOP holds a cache of metaclasses. The following are functions
997 (B<not methods>) which can be used to access that cache. It is not
998 recommended that you mess with these. Bad things could happen, but if
999 you are brave and willing to risk it: go for it!
1003 =item B<get_all_metaclasses>
1005 This will return a hash of all the metaclass instances that have
1006 been cached by B<Class::MOP::Class>, keyed by the package name.
1008 =item B<get_all_metaclass_instances>
1010 This will return a list of all the metaclass instances that have
1011 been cached by B<Class::MOP::Class>.
1013 =item B<get_all_metaclass_names>
1015 This will return a list of all the metaclass names that have
1016 been cached by B<Class::MOP::Class>.
1018 =item B<get_metaclass_by_name ($name)>
1020 This will return a cached B<Class::MOP::Class> instance, or nothing
1021 if no metaclass exists with that C<$name>.
1023 =item B<store_metaclass_by_name ($name, $meta)>
1025 This will store a metaclass in the cache at the supplied C<$key>.
1027 =item B<weaken_metaclass ($name)>
1029 In rare cases (e.g. anonymous metaclasses) it is desirable to
1030 store a weakened reference in the metaclass cache. This
1031 function will weaken the reference to the metaclass stored
1034 =item B<does_metaclass_exist ($name)>
1036 This will return true of there exists a metaclass stored in the
1037 C<$name> key, and return false otherwise.
1039 =item B<remove_metaclass_by_name ($name)>
1041 This will remove the metaclass stored in the C<$name> key.
1049 There are very few books out on Meta Object Protocols and Metaclasses
1050 because it is such an esoteric topic. The following books are really
1051 the only ones I have found. If you know of any more, B<I<please>>
1052 email me and let me know, I would love to hear about them.
1056 =item "The Art of the Meta Object Protocol"
1058 =item "Advances in Object-Oriented Metalevel Architecture and Reflection"
1060 =item "Putting MetaClasses to Work"
1062 =item "Smalltalk: The Language"
1070 =item Uniform and safe metaclass composition
1072 An excellent paper by the people who brought us the original Traits paper.
1073 This paper is on how Traits can be used to do safe metaclass composition,
1074 and offers an excellent introduction section which delves into the topic of
1075 metaclass compatibility.
1077 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
1079 =item Safe Metaclass Programming
1081 This paper seems to precede the above paper, and propose a mix-in based
1082 approach as opposed to the Traits based approach. Both papers have similar
1083 information on the metaclass compatibility problem space.
1085 L<http://citeseer.ist.psu.edu/37617.html>
1093 =item The Perl 6 MetaModel work in the Pugs project
1097 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
1099 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1109 =item CPAN Module Review of Class::MOP
1111 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1115 =head1 SIMILAR MODULES
1117 As I have said above, this module is a class-builder-builder, so it is
1118 not the same thing as modules like L<Class::Accessor> and
1119 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1120 with similar goals to this module. The one I have found which is most
1121 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1122 creates are very different from this modules.
1126 All complex software has bugs lurking in it, and this module is no
1127 exception. If you find a bug please either email me, or add the bug
1130 =head1 ACKNOWLEDGEMENTS
1136 Thanks to Rob for actually getting the development of this module kick-started.
1142 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1144 B<with contributions from:>
1146 Brandon (blblack) Black
1148 Florian (rafl) Ragwitz
1150 Guillermo (groditi) Roditi
1154 Rob (robkinyon) Kinyon
1156 Yuval (nothingmuch) Kogman
1158 Scott (konobi) McWhirter
1160 =head1 COPYRIGHT AND LICENSE
1162 Copyright 2006-2008 by Infinity Interactive, Inc.
1164 L<http://www.iinteractive.com>
1166 This library is free software; you can redistribute it and/or modify
1167 it under the same terms as Perl itself.