12 use Scalar::Util 'weaken';
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 = '0.73';
35 our $XS_VERSION = $VERSION;
36 $VERSION = eval $VERSION;
37 our $AUTHORITY = 'cpan:STEVAN';
39 # after that everything is loaded, if we're allowed try to load faster XS
40 # versions of various things
41 _try_load_xs() or _load_pure_perl();
44 return if $ENV{CLASS_MOP_NO_XS};
50 # just doing this - no warnings 'redefine' - doesn't work
53 __PACKAGE__->XSLoader::load($XS_VERSION);
56 Sub::Name->import(qw(subname));
58 require Devel::GlobalDestruction;
59 Devel::GlobalDestruction->import("in_global_destruction");
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 }
79 # Metaclasses are singletons, so we cache them here.
80 # there is no need to worry about destruction though
81 # because they should die only when the program dies.
82 # After all, do package definitions even get reaped?
85 # means of accessing all the metaclasses that have
86 # been initialized thus far (for mugwumps obj browser)
87 sub get_all_metaclasses { %METAS }
88 sub get_all_metaclass_instances { values %METAS }
89 sub get_all_metaclass_names { keys %METAS }
90 sub get_metaclass_by_name { $METAS{$_[0]} }
91 sub store_metaclass_by_name { $METAS{$_[0]} = $_[1] }
92 sub weaken_metaclass { weaken($METAS{$_[0]}) }
93 sub does_metaclass_exist { exists $METAS{$_[0]} && defined $METAS{$_[0]} }
94 sub remove_metaclass_by_name { $METAS{$_[0]} = undef }
97 # We only cache metaclasses, meaning instances of
98 # Class::MOP::Class. We do not cache instance of
99 # Class::MOP::Package or Class::MOP::Module. Mostly
100 # because I don't yet see a good reason to do so.
103 sub load_first_existing_class {
107 foreach my $class (@classes) {
108 unless ( _is_valid_class_name($class) ) {
109 my $display = defined($class) ? $class : 'undef';
110 confess "Invalid class name ($display)";
116 for my $class (@classes) {
117 my $e = _try_load_one_class($class);
120 $exceptions{$class} = $e;
128 return $found if $found;
134 "Could not load class (%s) because : %s", $_,
141 sub _try_load_one_class {
144 return if is_class_loaded($class);
146 my $file = $class . '.pm';
151 eval { require($file) };
157 my $class = load_first_existing_class($_[0]);
158 return get_metaclass_by_name($class) || $class;
161 sub _is_valid_class_name {
164 return 0 if ref($class);
165 return 0 unless defined($class);
166 return 0 unless length($class);
168 return 1 if $class =~ /^\w+(?:::\w+)*$/;
173 sub is_class_loaded {
176 return 0 unless _is_valid_class_name($class);
178 # walk the symbol table tree to avoid autovififying
179 # \*{${main::}{"Foo::"}} == \*main::Foo::
182 foreach my $part (split('::', $class)) {
183 return 0 unless exists ${$$pack}{"${part}::"};
184 $pack = \*{${$$pack}{"${part}::"}};
187 # check for $VERSION or @ISA
188 return 1 if exists ${$$pack}{VERSION}
189 && defined *{${$$pack}{VERSION}}{SCALAR};
190 return 1 if exists ${$$pack}{ISA}
191 && defined *{${$$pack}{ISA}}{ARRAY};
193 # check for any method
194 foreach ( keys %{$$pack} ) {
195 next if substr($_, -2, 2) eq '::';
197 my $glob = ${$$pack}{$_} || next;
200 if ( IS_RUNNING_ON_5_10 ) {
201 return 1 if ref $glob eq 'SCALAR';
204 return 1 if defined *{$glob}{CODE};
212 ## ----------------------------------------------------------------------------
213 ## Setting up our environment ...
214 ## ----------------------------------------------------------------------------
215 ## Class::MOP needs to have a few things in the global perl environment so
216 ## that it can operate effectively. Those things are done here.
217 ## ----------------------------------------------------------------------------
219 # ... nothing yet actually ;)
221 ## ----------------------------------------------------------------------------
223 ## ----------------------------------------------------------------------------
224 ## The code below here is to bootstrap our MOP with itself. This is also
225 ## sometimes called "tying the knot". By doing this, we make it much easier
226 ## to extend the MOP through subclassing and such since now you can use the
227 ## MOP itself to extend itself.
229 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
230 ## ----------------------------------------------------------------------------
232 # We need to add in the meta-attributes here so that
233 # any subclass of Class::MOP::* will be able to
234 # inherit them using &construct_instance
236 ## --------------------------------------------------------
237 ## Class::MOP::Package
239 Class::MOP::Package->meta->add_attribute(
240 Class::MOP::Attribute->new('package' => (
242 # NOTE: we need to do this in order
243 # for the instance meta-object to
244 # not fall into meta-circular death
246 # we just alias the original method
247 # rather than re-produce it here
248 'name' => \&Class::MOP::Package::name
253 Class::MOP::Package->meta->add_attribute(
254 Class::MOP::Attribute->new('namespace' => (
257 # we just alias the original method
258 # rather than re-produce it here
259 'namespace' => \&Class::MOP::Package::namespace
262 default => sub { \undef }
266 ## --------------------------------------------------------
267 ## Class::MOP::Module
270 # yeah this is kind of stretching things a bit,
271 # but truthfully the version should be an attribute
272 # of the Module, the weirdness comes from having to
273 # stick to Perl 5 convention and store it in the
274 # $VERSION package variable. Basically if you just
275 # squint at it, it will look how you want it to look.
276 # Either as a package variable, or as a attribute of
277 # the metaclass, isn't abstraction great :)
279 Class::MOP::Module->meta->add_attribute(
280 Class::MOP::Attribute->new('version' => (
283 # we just alias the original method
284 # rather than re-produce it here
285 'version' => \&Class::MOP::Module::version
288 default => sub { \undef }
293 # By following the same conventions as version here,
294 # we are opening up the possibility that people can
295 # use the $AUTHORITY in non-Class::MOP modules as
298 Class::MOP::Module->meta->add_attribute(
299 Class::MOP::Attribute->new('authority' => (
302 # we just alias the original method
303 # rather than re-produce it here
304 'authority' => \&Class::MOP::Module::authority
307 default => sub { \undef }
311 ## --------------------------------------------------------
314 Class::MOP::Class->meta->add_attribute(
315 Class::MOP::Attribute->new('attributes' => (
317 # NOTE: we need to do this in order
318 # for the instance meta-object to
319 # not fall into meta-circular death
321 # we just alias the original method
322 # rather than re-produce it here
323 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
325 default => sub { {} }
329 Class::MOP::Class->meta->add_attribute(
330 Class::MOP::Attribute->new('methods' => (
333 # we just alias the original method
334 # rather than re-produce it here
335 'get_method_map' => \&Class::MOP::Class::get_method_map
337 default => sub { {} }
341 Class::MOP::Class->meta->add_attribute(
342 Class::MOP::Attribute->new('superclasses' => (
345 # we just alias the original method
346 # rather than re-produce it here
347 'superclasses' => \&Class::MOP::Class::superclasses
350 default => sub { \undef }
354 Class::MOP::Class->meta->add_attribute(
355 Class::MOP::Attribute->new('attribute_metaclass' => (
358 # we just alias the original method
359 # rather than re-produce it here
360 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
362 default => 'Class::MOP::Attribute',
366 Class::MOP::Class->meta->add_attribute(
367 Class::MOP::Attribute->new('method_metaclass' => (
370 # we just alias the original method
371 # rather than re-produce it here
372 'method_metaclass' => \&Class::MOP::Class::method_metaclass
374 default => 'Class::MOP::Method',
378 Class::MOP::Class->meta->add_attribute(
379 Class::MOP::Attribute->new('instance_metaclass' => (
381 # NOTE: we need to do this in order
382 # for the instance meta-object to
383 # not fall into meta-circular death
385 # we just alias the original method
386 # rather than re-produce it here
387 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
389 default => 'Class::MOP::Instance',
394 # we don't actually need to tie the knot with
395 # Class::MOP::Class here, it is actually handled
396 # within Class::MOP::Class itself in the
397 # construct_class_instance method.
399 ## --------------------------------------------------------
400 ## Class::MOP::Attribute
402 Class::MOP::Attribute->meta->add_attribute(
403 Class::MOP::Attribute->new('name' => (
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 'name' => \&Class::MOP::Attribute::name
416 Class::MOP::Attribute->meta->add_attribute(
417 Class::MOP::Attribute->new('associated_class' => (
419 # NOTE: we need to do this in order
420 # for the instance meta-object to
421 # not fall into meta-circular death
423 # we just alias the original method
424 # rather than re-produce it here
425 'associated_class' => \&Class::MOP::Attribute::associated_class
430 Class::MOP::Attribute->meta->add_attribute(
431 Class::MOP::Attribute->new('accessor' => (
432 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
433 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
437 Class::MOP::Attribute->meta->add_attribute(
438 Class::MOP::Attribute->new('reader' => (
439 reader => { 'reader' => \&Class::MOP::Attribute::reader },
440 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
444 Class::MOP::Attribute->meta->add_attribute(
445 Class::MOP::Attribute->new('initializer' => (
446 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
447 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
451 Class::MOP::Attribute->meta->add_attribute(
452 Class::MOP::Attribute->new('writer' => (
453 reader => { 'writer' => \&Class::MOP::Attribute::writer },
454 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
458 Class::MOP::Attribute->meta->add_attribute(
459 Class::MOP::Attribute->new('predicate' => (
460 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
461 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
465 Class::MOP::Attribute->meta->add_attribute(
466 Class::MOP::Attribute->new('clearer' => (
467 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
468 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
472 Class::MOP::Attribute->meta->add_attribute(
473 Class::MOP::Attribute->new('builder' => (
474 reader => { 'builder' => \&Class::MOP::Attribute::builder },
475 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
479 Class::MOP::Attribute->meta->add_attribute(
480 Class::MOP::Attribute->new('init_arg' => (
481 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
482 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
486 Class::MOP::Attribute->meta->add_attribute(
487 Class::MOP::Attribute->new('default' => (
488 # default has a custom 'reader' method ...
489 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
493 Class::MOP::Attribute->meta->add_attribute(
494 Class::MOP::Attribute->new('associated_methods' => (
495 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
496 default => sub { [] }
500 Class::MOP::Attribute->meta->add_method('clone' => sub {
502 $self->meta->clone_object($self, @_);
505 ## --------------------------------------------------------
506 ## Class::MOP::Method
507 Class::MOP::Method->meta->add_attribute(
508 Class::MOP::Attribute->new('body' => (
509 reader => { 'body' => \&Class::MOP::Method::body },
513 Class::MOP::Method->meta->add_attribute(
514 Class::MOP::Attribute->new('associated_metaclass' => (
515 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
519 Class::MOP::Method->meta->add_attribute(
520 Class::MOP::Attribute->new('package_name' => (
521 reader => { 'package_name' => \&Class::MOP::Method::package_name },
525 Class::MOP::Method->meta->add_attribute(
526 Class::MOP::Attribute->new('name' => (
527 reader => { 'name' => \&Class::MOP::Method::name },
531 Class::MOP::Method->meta->add_attribute(
532 Class::MOP::Attribute->new('original_method' => (
533 reader => { 'original_method' => \&Class::MOP::Method::original_method },
534 writer => { '_set_original_method' => \&Class::MOP::Method::_set_original_method },
538 Class::MOP::Method->meta->add_method('clone' => sub {
540 my $clone = $self->meta->clone_object($self, @_);
541 $clone->_set_original_method($self);
545 ## --------------------------------------------------------
546 ## Class::MOP::Method::Wrapped
549 # the way this item is initialized, this
550 # really does not follow the standard
551 # practices of attributes, but we put
552 # it here for completeness
553 Class::MOP::Method::Wrapped->meta->add_attribute(
554 Class::MOP::Attribute->new('modifier_table')
557 ## --------------------------------------------------------
558 ## Class::MOP::Method::Generated
560 Class::MOP::Method::Generated->meta->add_attribute(
561 Class::MOP::Attribute->new('is_inline' => (
562 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
567 ## --------------------------------------------------------
568 ## Class::MOP::Method::Accessor
570 Class::MOP::Method::Accessor->meta->add_attribute(
571 Class::MOP::Attribute->new('attribute' => (
573 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
578 Class::MOP::Method::Accessor->meta->add_attribute(
579 Class::MOP::Attribute->new('accessor_type' => (
580 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
584 ## --------------------------------------------------------
585 ## Class::MOP::Method::Constructor
587 Class::MOP::Method::Constructor->meta->add_attribute(
588 Class::MOP::Attribute->new('options' => (
590 'options' => \&Class::MOP::Method::Constructor::options
592 default => sub { +{} }
596 Class::MOP::Method::Constructor->meta->add_attribute(
597 Class::MOP::Attribute->new('associated_metaclass' => (
598 init_arg => "metaclass", # FIXME alias and rename
600 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
605 ## --------------------------------------------------------
606 ## Class::MOP::Instance
609 # these don't yet do much of anything, but are just
610 # included for completeness
612 Class::MOP::Instance->meta->add_attribute(
613 Class::MOP::Attribute->new('associated_metaclass',
614 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
618 Class::MOP::Instance->meta->add_attribute(
619 Class::MOP::Attribute->new('_class_name',
621 reader => { _class_name => \&Class::MOP::Instance::_class_name },
622 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
623 #default => sub { $_[0]->associated_metaclass->name },
627 Class::MOP::Instance->meta->add_attribute(
628 Class::MOP::Attribute->new('attributes',
629 reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
633 Class::MOP::Instance->meta->add_attribute(
634 Class::MOP::Attribute->new('slots',
635 reader => { slots => \&Class::MOP::Instance::slots },
639 Class::MOP::Instance->meta->add_attribute(
640 Class::MOP::Attribute->new('slot_hash',
641 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
646 # we need the meta instance of the meta instance to be created now, in order
647 # for the constructor to be able to use it
648 Class::MOP::Instance->meta->get_meta_instance;
650 # pretend the add_method never happenned. it hasn't yet affected anything
651 undef Class::MOP::Instance->meta->{_package_cache_flag};
653 ## --------------------------------------------------------
654 ## Now close all the Class::MOP::* classes
656 # NOTE: we don't need to inline the the accessors this only lengthens
657 # the compile time of the MOP, and gives us no actual benefits.
659 $_->meta->make_immutable(
660 inline_constructor => 1,
661 replace_constructor => 1,
662 constructor_name => "_new",
663 inline_accessors => 0,
669 Class::MOP::Attribute
675 Class::MOP::Method::Generated
677 Class::MOP::Method::Accessor
678 Class::MOP::Method::Constructor
679 Class::MOP::Method::Wrapped
690 Class::MOP - A Meta Object Protocol for Perl 5
694 This module is a fully functioning meta object protocol for the
695 Perl 5 object system. It makes no attempt to change the behavior or
696 characteristics of the Perl 5 object system, only to create a
697 protocol for its manipulation and introspection.
699 That said, it does attempt to create the tools for building a rich
700 set of extensions to the Perl 5 object system. Every attempt has been
701 made for these tools to keep to the spirit of the Perl 5 object
702 system that we all know and love.
704 This documentation is admittedly sparse on details, as time permits
705 I will try to improve them. For now, I suggest looking at the items
706 listed in the L<SEE ALSO> section for more information. In particular
707 the book "The Art of the Meta Object Protocol" was very influential
708 in the development of this system.
710 =head2 What is a Meta Object Protocol?
712 A meta object protocol is an API to an object system.
714 To be more specific, it is a set of abstractions of the components of
715 an object system (typically things like; classes, object, methods,
716 object attributes, etc.). These abstractions can then be used to both
717 inspect and manipulate the object system which they describe.
719 It can be said that there are two MOPs for any object system; the
720 implicit MOP, and the explicit MOP. The implicit MOP handles things
721 like method dispatch or inheritance, which happen automatically as
722 part of how the object system works. The explicit MOP typically
723 handles the introspection/reflection features of the object system.
724 All object systems have implicit MOPs, without one, they would not
725 work. Explict MOPs however as less common, and depending on the
726 language can vary from restrictive (Reflection in Java or C#) to
727 wide open (CLOS is a perfect example).
729 =head2 Yet Another Class Builder!! Why?
731 This is B<not> a class builder so much as it is a I<class builder
732 B<builder>>. My intent is that an end user does not use this module
733 directly, but instead this module is used by module authors to
734 build extensions and features onto the Perl 5 object system.
736 =head2 Who is this module for?
738 This module is specifically for anyone who has ever created or
739 wanted to create a module for the Class:: namespace. The tools which
740 this module will provide will hopefully make it easier to do more
741 complex things with Perl 5 classes by removing such barriers as
742 the need to hack the symbol tables, or understand the fine details
745 =head2 What changes do I have to make to use this module?
747 This module was designed to be as unintrusive as possible. Many of
748 its features are accessible without B<any> change to your existsing
749 code at all. It is meant to be a compliment to your existing code and
750 not an intrusion on your code base. Unlike many other B<Class::>
751 modules, this module B<does not> require you subclass it, or even that
752 you C<use> it in within your module's package.
754 The only features which requires additions to your code are the
755 attribute handling and instance construction features, and these are
756 both completely optional features. The only reason for this is because
757 Perl 5's object system does not actually have these features built
758 in. More information about this feature can be found below.
760 =head2 A Note about Performance?
762 It is a common misconception that explict MOPs are performance drains.
763 But this is not a universal truth at all, it is an side-effect of
764 specific implementations. For instance, using Java reflection is much
765 slower because the JVM cannot take advantage of any compiler
766 optimizations, and the JVM has to deal with much more runtime type
767 information as well. Reflection in C# is marginally better as it was
768 designed into the language and runtime (the CLR). In contrast, CLOS
769 (the Common Lisp Object System) was built to support an explicit MOP,
770 and so performance is tuned for it.
772 This library in particular does it's absolute best to avoid putting
773 B<any> drain at all upon your code's performance. In fact, by itself
774 it does nothing to affect your existing code. So you only pay for
775 what you actually use.
777 =head2 About Metaclass compatibility
779 This module makes sure that all metaclasses created are both upwards
780 and downwards compatible. The topic of metaclass compatibility is
781 highly esoteric and is something only encountered when doing deep and
782 involved metaclass hacking. There are two basic kinds of metaclass
783 incompatibility; upwards and downwards.
785 Upwards metaclass compatibility means that the metaclass of a
786 given class is either the same as (or a subclass of) all of the
789 Downward metaclass compatibility means that the metaclasses of a
790 given class's anscestors are all either the same as (or a subclass
793 Here is a diagram showing a set of two classes (C<A> and C<B>) and
794 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
795 metaclass compatibility both upwards and downwards.
797 +---------+ +---------+
798 | Meta::A |<----| Meta::B | <....... (instance of )
799 +---------+ +---------+ <------- (inherits from)
802 +---------+ +---------+
804 +---------+ +---------+
806 As I said this is a highly esoteric topic and one you will only run
807 into if you do a lot of subclassing of B<Class::MOP::Class>. If you
808 are interested in why this is an issue see the paper
809 I<Uniform and safe metaclass composition> linked to in the
810 L<SEE ALSO> section of this document.
812 =head2 Using custom metaclasses
814 Always use the metaclass pragma when using a custom metaclass, this
815 will ensure the proper initialization order and not accidentely
816 create an incorrect type of metaclass for you. This is a very rare
817 problem, and one which can only occur if you are doing deep metaclass
818 programming. So in other words, don't worry about it.
822 The protocol is divided into 4 main sub-protocols:
826 =item The Class protocol
828 This provides a means of manipulating and introspecting a Perl 5
829 class. It handles all of symbol table hacking for you, and provides
830 a rich set of methods that go beyond simple package introspection.
832 See L<Class::MOP::Class> for more details.
834 =item The Attribute protocol
836 This provides a consistent represenation for an attribute of a
837 Perl 5 class. Since there are so many ways to create and handle
838 attributes in Perl 5 OO, this attempts to provide as much of a
839 unified approach as possible, while giving the freedom and
840 flexibility to subclass for specialization.
842 See L<Class::MOP::Attribute> for more details.
844 =item The Method protocol
846 This provides a means of manipulating and introspecting methods in
847 the Perl 5 object system. As with attributes, there are many ways to
848 approach this topic, so we try to keep it pretty basic, while still
849 making it possible to extend the system in many ways.
851 See L<Class::MOP::Method> for more details.
853 =item The Instance protocol
855 This provides a layer of abstraction for creating object instances.
856 Since the other layers use this protocol, it is relatively easy to
857 change the type of your instances from the default HASH ref to other
858 types of references. Several examples are provided in the F<examples/>
859 directory included in this distribution.
861 See L<Class::MOP::Instance> for more details.
871 =item I<IS_RUNNING_ON_5_10>
873 We set this constant depending on what version perl we are on, this
874 allows us to take advantage of new 5.10 features and stay backwards
879 Whether or not C<mro> provides C<get_isarev>, a much faster way to get all the
880 subclasses of a certain class.
884 =head2 Utility functions
886 Note that these are all called as B<functions, not methods>.
890 =item B<load_class ($class_name)>
892 This will load a given C<$class_name> and if it does not have an
893 already initialized metaclass, then it will intialize one for it.
894 This function can be used in place of tricks like
895 C<eval "use $module"> or using C<require>.
897 =item B<is_class_loaded ($class_name)>
899 This will return a boolean depending on if the C<$class_name> has
902 NOTE: This does a basic check of the symbol table to try and
903 determine as best it can if the C<$class_name> is loaded, it
904 is probably correct about 99% of the time.
906 =item B<check_package_cache_flag ($pkg)>
908 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
910 This will return an integer that is managed by C<Class::MOP::Class>
911 to determine if a module's symbol table has been altered.
913 In Perl 5.10 or greater, this flag is package specific. However in
914 versions prior to 5.10, this will use the C<PL_sub_generation> variable
915 which is not package specific.
917 =item B<get_code_info ($code)>
919 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
921 This function returns two values, the name of the package the C<$code>
922 is from and the name of the C<$code> itself. This is used by several
923 elements of the MOP to detemine where a given C<$code> reference is from.
925 =item B<subname ($name, $code)>
927 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
929 If possible, we will load the L<Sub::Name> module and this will function
930 as C<Sub::Name::subname> does, otherwise it will just return the C<$code>
933 =item B<in_global_destruction>
935 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
937 If L<Devel::GlobalDestruction> is available, this returns true under global
940 Otherwise it's a constant returning false.
942 =item B<load_first_existing_class ($class_name, [$class_name, ...])>
944 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
946 Given a list of class names, this function will attempt to load each
949 If it finds a class it can load, it will return that class' name.
950 If none of the classes can be loaded, it will throw an exception.
954 =head2 Metaclass cache functions
956 Class::MOP holds a cache of metaclasses, the following are functions
957 (B<not methods>) which can be used to access that cache. It is not
958 recommended that you mess with this, bad things could happen. But if
959 you are brave and willing to risk it, go for it.
963 =item B<get_all_metaclasses>
965 This will return an hash of all the metaclass instances that have
966 been cached by B<Class::MOP::Class> keyed by the package name.
968 =item B<get_all_metaclass_instances>
970 This will return an array of all the metaclass instances that have
971 been cached by B<Class::MOP::Class>.
973 =item B<get_all_metaclass_names>
975 This will return an array of all the metaclass names that have
976 been cached by B<Class::MOP::Class>.
978 =item B<get_metaclass_by_name ($name)>
980 This will return a cached B<Class::MOP::Class> instance of nothing
981 if no metaclass exist by that C<$name>.
983 =item B<store_metaclass_by_name ($name, $meta)>
985 This will store a metaclass in the cache at the supplied C<$key>.
987 =item B<weaken_metaclass ($name)>
989 In rare cases it is desireable to store a weakened reference in
990 the metaclass cache. This function will weaken the reference to
991 the metaclass stored in C<$name>.
993 =item B<does_metaclass_exist ($name)>
995 This will return true of there exists a metaclass stored in the
996 C<$name> key and return false otherwise.
998 =item B<remove_metaclass_by_name ($name)>
1000 This will remove a the metaclass stored in the C<$name> key.
1008 There are very few books out on Meta Object Protocols and Metaclasses
1009 because it is such an esoteric topic. The following books are really
1010 the only ones I have found. If you know of any more, B<I<please>>
1011 email me and let me know, I would love to hear about them.
1015 =item "The Art of the Meta Object Protocol"
1017 =item "Advances in Object-Oriented Metalevel Architecture and Reflection"
1019 =item "Putting MetaClasses to Work"
1021 =item "Smalltalk: The Language"
1029 =item Uniform and safe metaclass composition
1031 An excellent paper by the people who brought us the original Traits paper.
1032 This paper is on how Traits can be used to do safe metaclass composition,
1033 and offers an excellent introduction section which delves into the topic of
1034 metaclass compatibility.
1036 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
1038 =item Safe Metaclass Programming
1040 This paper seems to precede the above paper, and propose a mix-in based
1041 approach as opposed to the Traits based approach. Both papers have similar
1042 information on the metaclass compatibility problem space.
1044 L<http://citeseer.ist.psu.edu/37617.html>
1052 =item The Perl 6 MetaModel work in the Pugs project
1056 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
1058 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1068 =item CPAN Module Review of Class::MOP
1070 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1074 =head1 SIMILAR MODULES
1076 As I have said above, this module is a class-builder-builder, so it is
1077 not the same thing as modules like L<Class::Accessor> and
1078 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1079 with similar goals to this module. The one I have found which is most
1080 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1081 creates are very different from this modules.
1085 All complex software has bugs lurking in it, and this module is no
1086 exception. If you find a bug please either email me, or add the bug
1089 =head1 ACKNOWLEDGEMENTS
1095 Thanks to Rob for actually getting the development of this module kick-started.
1101 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1103 B<with contributions from:>
1105 Brandon (blblack) Black
1107 Florian (rafl) Ragwitz
1109 Guillermo (groditi) Roditi
1113 Rob (robkinyon) Kinyon
1115 Yuval (nothingmuch) Kogman
1117 Scott (konobi) McWhirter
1119 =head1 COPYRIGHT AND LICENSE
1121 Copyright 2006-2008 by Infinity Interactive, Inc.
1123 L<http://www.iinteractive.com>
1125 This library is free software; you can redistribute it and/or modify
1126 it under the same terms as Perl itself.