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 = '0.69';
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 if ref($class) || !defined($class) || !length($class);
178 # walk the symbol table tree to avoid autovififying
179 # \*{${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
657 # we don't need to inline the
658 # constructors or the accessors
659 # this only lengthens the compile
660 # time of the MOP, and gives us
661 # no actual benefits.
663 $_->meta->make_immutable(
664 inline_constructor => 1,
665 replace_constructor => 1,
666 constructor_name => "_new",
667 inline_accessors => 0,
673 Class::MOP::Attribute
679 Class::MOP::Method::Generated
681 Class::MOP::Method::Accessor
682 Class::MOP::Method::Constructor
683 Class::MOP::Method::Wrapped
694 Class::MOP - A Meta Object Protocol for Perl 5
698 This module is a fully functioning meta object protocol for the
699 Perl 5 object system. It makes no attempt to change the behavior or
700 characteristics of the Perl 5 object system, only to create a
701 protocol for its manipulation and introspection.
703 That said, it does attempt to create the tools for building a rich
704 set of extensions to the Perl 5 object system. Every attempt has been
705 made for these tools to keep to the spirit of the Perl 5 object
706 system that we all know and love.
708 This documentation is admittedly sparse on details, as time permits
709 I will try to improve them. For now, I suggest looking at the items
710 listed in the L<SEE ALSO> section for more information. In particular
711 the book "The Art of the Meta Object Protocol" was very influential
712 in the development of this system.
714 =head2 What is a Meta Object Protocol?
716 A meta object protocol is an API to an object system.
718 To be more specific, it is a set of abstractions of the components of
719 an object system (typically things like; classes, object, methods,
720 object attributes, etc.). These abstractions can then be used to both
721 inspect and manipulate the object system which they describe.
723 It can be said that there are two MOPs for any object system; the
724 implicit MOP, and the explicit MOP. The implicit MOP handles things
725 like method dispatch or inheritance, which happen automatically as
726 part of how the object system works. The explicit MOP typically
727 handles the introspection/reflection features of the object system.
728 All object systems have implicit MOPs, without one, they would not
729 work. Explict MOPs however as less common, and depending on the
730 language can vary from restrictive (Reflection in Java or C#) to
731 wide open (CLOS is a perfect example).
733 =head2 Yet Another Class Builder!! Why?
735 This is B<not> a class builder so much as it is a I<class builder
736 B<builder>>. My intent is that an end user does not use this module
737 directly, but instead this module is used by module authors to
738 build extensions and features onto the Perl 5 object system.
740 =head2 Who is this module for?
742 This module is specifically for anyone who has ever created or
743 wanted to create a module for the Class:: namespace. The tools which
744 this module will provide will hopefully make it easier to do more
745 complex things with Perl 5 classes by removing such barriers as
746 the need to hack the symbol tables, or understand the fine details
749 =head2 What changes do I have to make to use this module?
751 This module was designed to be as unintrusive as possible. Many of
752 its features are accessible without B<any> change to your existsing
753 code at all. It is meant to be a compliment to your existing code and
754 not an intrusion on your code base. Unlike many other B<Class::>
755 modules, this module B<does not> require you subclass it, or even that
756 you C<use> it in within your module's package.
758 The only features which requires additions to your code are the
759 attribute handling and instance construction features, and these are
760 both completely optional features. The only reason for this is because
761 Perl 5's object system does not actually have these features built
762 in. More information about this feature can be found below.
764 =head2 A Note about Performance?
766 It is a common misconception that explict MOPs are performance drains.
767 But this is not a universal truth at all, it is an side-effect of
768 specific implementations. For instance, using Java reflection is much
769 slower because the JVM cannot take advantage of any compiler
770 optimizations, and the JVM has to deal with much more runtime type
771 information as well. Reflection in C# is marginally better as it was
772 designed into the language and runtime (the CLR). In contrast, CLOS
773 (the Common Lisp Object System) was built to support an explicit MOP,
774 and so performance is tuned for it.
776 This library in particular does it's absolute best to avoid putting
777 B<any> drain at all upon your code's performance. In fact, by itself
778 it does nothing to affect your existing code. So you only pay for
779 what you actually use.
781 =head2 About Metaclass compatibility
783 This module makes sure that all metaclasses created are both upwards
784 and downwards compatible. The topic of metaclass compatibility is
785 highly esoteric and is something only encountered when doing deep and
786 involved metaclass hacking. There are two basic kinds of metaclass
787 incompatibility; upwards and downwards.
789 Upwards metaclass compatibility means that the metaclass of a
790 given class is either the same as (or a subclass of) all of the
793 Downward metaclass compatibility means that the metaclasses of a
794 given class's anscestors are all either the same as (or a subclass
797 Here is a diagram showing a set of two classes (C<A> and C<B>) and
798 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
799 metaclass compatibility both upwards and downwards.
801 +---------+ +---------+
802 | Meta::A |<----| Meta::B | <....... (instance of )
803 +---------+ +---------+ <------- (inherits from)
806 +---------+ +---------+
808 +---------+ +---------+
810 As I said this is a highly esoteric topic and one you will only run
811 into if you do a lot of subclassing of B<Class::MOP::Class>. If you
812 are interested in why this is an issue see the paper
813 I<Uniform and safe metaclass composition> linked to in the
814 L<SEE ALSO> section of this document.
816 =head2 Using custom metaclasses
818 Always use the metaclass pragma when using a custom metaclass, this
819 will ensure the proper initialization order and not accidentely
820 create an incorrect type of metaclass for you. This is a very rare
821 problem, and one which can only occur if you are doing deep metaclass
822 programming. So in other words, don't worry about it.
826 The protocol is divided into 4 main sub-protocols:
830 =item The Class protocol
832 This provides a means of manipulating and introspecting a Perl 5
833 class. It handles all of symbol table hacking for you, and provides
834 a rich set of methods that go beyond simple package introspection.
836 See L<Class::MOP::Class> for more details.
838 =item The Attribute protocol
840 This provides a consistent represenation for an attribute of a
841 Perl 5 class. Since there are so many ways to create and handle
842 attributes in Perl 5 OO, this attempts to provide as much of a
843 unified approach as possible, while giving the freedom and
844 flexibility to subclass for specialization.
846 See L<Class::MOP::Attribute> for more details.
848 =item The Method protocol
850 This provides a means of manipulating and introspecting methods in
851 the Perl 5 object system. As with attributes, there are many ways to
852 approach this topic, so we try to keep it pretty basic, while still
853 making it possible to extend the system in many ways.
855 See L<Class::MOP::Method> for more details.
857 =item The Instance protocol
859 This provides a layer of abstraction for creating object instances.
860 Since the other layers use this protocol, it is relatively easy to
861 change the type of your instances from the default HASH ref to other
862 types of references. Several examples are provided in the F<examples/>
863 directory included in this distribution.
865 See L<Class::MOP::Instance> for more details.
875 =item I<IS_RUNNING_ON_5_10>
877 We set this constant depending on what version perl we are on, this
878 allows us to take advantage of new 5.10 features and stay backwards
883 Whether or not C<mro> provides C<get_isarev>, a much faster way to get all the
884 subclasses of a certain class.
888 =head2 Utility functions
890 Note that these are all called as B<functions, not methods>.
894 =item B<load_class ($class_name)>
896 This will load a given C<$class_name> and if it does not have an
897 already initialized metaclass, then it will intialize one for it.
898 This function can be used in place of tricks like
899 C<eval "use $module"> or using C<require>.
901 =item B<is_class_loaded ($class_name)>
903 This will return a boolean depending on if the C<$class_name> has
906 NOTE: This does a basic check of the symbol table to try and
907 determine as best it can if the C<$class_name> is loaded, it
908 is probably correct about 99% of the time.
910 =item B<check_package_cache_flag ($pkg)>
912 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
914 This will return an integer that is managed by C<Class::MOP::Class>
915 to determine if a module's symbol table has been altered.
917 In Perl 5.10 or greater, this flag is package specific. However in
918 versions prior to 5.10, this will use the C<PL_sub_generation> variable
919 which is not package specific.
921 =item B<get_code_info ($code)>
923 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
925 This function returns two values, the name of the package the C<$code>
926 is from and the name of the C<$code> itself. This is used by several
927 elements of the MOP to detemine where a given C<$code> reference is from.
929 =item B<subname ($name, $code)>
931 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
933 If possible, we will load the L<Sub::Name> module and this will function
934 as C<Sub::Name::subname> does, otherwise it will just return the C<$code>
937 =item B<in_global_destruction>
939 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
941 If L<Devel::GlobalDestruction> is available, this returns true under global
944 Otherwise it's a constant returning false.
946 =item B<load_first_existing_class ($class_name, [$class_name, ...])>
948 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
950 Given a list of class names, this function will attempt to load each
953 If it finds a class it can load, it will return that class' name.
954 If none of the classes can be loaded, it will throw an exception.
958 =head2 Metaclass cache functions
960 Class::MOP holds a cache of metaclasses, the following are functions
961 (B<not methods>) which can be used to access that cache. It is not
962 recommended that you mess with this, bad things could happen. But if
963 you are brave and willing to risk it, go for it.
967 =item B<get_all_metaclasses>
969 This will return an hash of all the metaclass instances that have
970 been cached by B<Class::MOP::Class> keyed by the package name.
972 =item B<get_all_metaclass_instances>
974 This will return an array of all the metaclass instances that have
975 been cached by B<Class::MOP::Class>.
977 =item B<get_all_metaclass_names>
979 This will return an array of all the metaclass names that have
980 been cached by B<Class::MOP::Class>.
982 =item B<get_metaclass_by_name ($name)>
984 This will return a cached B<Class::MOP::Class> instance of nothing
985 if no metaclass exist by that C<$name>.
987 =item B<store_metaclass_by_name ($name, $meta)>
989 This will store a metaclass in the cache at the supplied C<$key>.
991 =item B<weaken_metaclass ($name)>
993 In rare cases it is desireable to store a weakened reference in
994 the metaclass cache. This function will weaken the reference to
995 the metaclass stored in C<$name>.
997 =item B<does_metaclass_exist ($name)>
999 This will return true of there exists a metaclass stored in the
1000 C<$name> key and return false otherwise.
1002 =item B<remove_metaclass_by_name ($name)>
1004 This will remove a the metaclass stored in the C<$name> key.
1012 There are very few books out on Meta Object Protocols and Metaclasses
1013 because it is such an esoteric topic. The following books are really
1014 the only ones I have found. If you know of any more, B<I<please>>
1015 email me and let me know, I would love to hear about them.
1019 =item "The Art of the Meta Object Protocol"
1021 =item "Advances in Object-Oriented Metalevel Architecture and Reflection"
1023 =item "Putting MetaClasses to Work"
1025 =item "Smalltalk: The Language"
1033 =item Uniform and safe metaclass composition
1035 An excellent paper by the people who brought us the original Traits paper.
1036 This paper is on how Traits can be used to do safe metaclass composition,
1037 and offers an excellent introduction section which delves into the topic of
1038 metaclass compatibility.
1040 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
1042 =item Safe Metaclass Programming
1044 This paper seems to precede the above paper, and propose a mix-in based
1045 approach as opposed to the Traits based approach. Both papers have similar
1046 information on the metaclass compatibility problem space.
1048 L<http://citeseer.ist.psu.edu/37617.html>
1056 =item The Perl 6 MetaModel work in the Pugs project
1060 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
1062 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1072 =item CPAN Module Review of Class::MOP
1074 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1078 =head1 SIMILAR MODULES
1080 As I have said above, this module is a class-builder-builder, so it is
1081 not the same thing as modules like L<Class::Accessor> and
1082 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1083 with similar goals to this module. The one I have found which is most
1084 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1085 creates are very different from this modules.
1089 All complex software has bugs lurking in it, and this module is no
1090 exception. If you find a bug please either email me, or add the bug
1093 =head1 ACKNOWLEDGEMENTS
1099 Thanks to Rob for actually getting the development of this module kick-started.
1105 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1107 B<with contributions from:>
1109 Brandon (blblack) Black
1111 Florian (rafl) Ragwitz
1113 Guillermo (groditi) Roditi
1117 Rob (robkinyon) Kinyon
1119 Yuval (nothingmuch) Kogman
1121 Scott (konobi) McWhirter
1123 =head1 COPYRIGHT AND LICENSE
1125 Copyright 2006-2008 by Infinity Interactive, Inc.
1127 L<http://www.iinteractive.com>
1129 This library is free software; you can redistribute it and/or modify
1130 it under the same terms as Perl itself.