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 = '0.76';
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('instance_metaclass' => (
393 # NOTE: we need to do this in order
394 # for the instance meta-object to
395 # not fall into meta-circular death
397 # we just alias the original method
398 # rather than re-produce it here
399 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
401 default => 'Class::MOP::Instance',
406 # we don't actually need to tie the knot with
407 # Class::MOP::Class here, it is actually handled
408 # within Class::MOP::Class itself in the
409 # construct_class_instance method.
411 ## --------------------------------------------------------
412 ## Class::MOP::Attribute
414 Class::MOP::Attribute->meta->add_attribute(
415 Class::MOP::Attribute->new('name' => (
417 # NOTE: we need to do this in order
418 # for the instance meta-object to
419 # not fall into meta-circular death
421 # we just alias the original method
422 # rather than re-produce it here
423 'name' => \&Class::MOP::Attribute::name
428 Class::MOP::Attribute->meta->add_attribute(
429 Class::MOP::Attribute->new('associated_class' => (
431 # NOTE: we need to do this in order
432 # for the instance meta-object to
433 # not fall into meta-circular death
435 # we just alias the original method
436 # rather than re-produce it here
437 'associated_class' => \&Class::MOP::Attribute::associated_class
442 Class::MOP::Attribute->meta->add_attribute(
443 Class::MOP::Attribute->new('accessor' => (
444 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
445 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
449 Class::MOP::Attribute->meta->add_attribute(
450 Class::MOP::Attribute->new('reader' => (
451 reader => { 'reader' => \&Class::MOP::Attribute::reader },
452 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
456 Class::MOP::Attribute->meta->add_attribute(
457 Class::MOP::Attribute->new('initializer' => (
458 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
459 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
463 Class::MOP::Attribute->meta->add_attribute(
464 Class::MOP::Attribute->new('definition_context' => (
465 reader => { 'definition_context' => \&Class::MOP::Attribute::definition_context },
469 Class::MOP::Attribute->meta->add_attribute(
470 Class::MOP::Attribute->new('writer' => (
471 reader => { 'writer' => \&Class::MOP::Attribute::writer },
472 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
476 Class::MOP::Attribute->meta->add_attribute(
477 Class::MOP::Attribute->new('predicate' => (
478 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
479 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
483 Class::MOP::Attribute->meta->add_attribute(
484 Class::MOP::Attribute->new('clearer' => (
485 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
486 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
490 Class::MOP::Attribute->meta->add_attribute(
491 Class::MOP::Attribute->new('builder' => (
492 reader => { 'builder' => \&Class::MOP::Attribute::builder },
493 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
497 Class::MOP::Attribute->meta->add_attribute(
498 Class::MOP::Attribute->new('init_arg' => (
499 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
500 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
504 Class::MOP::Attribute->meta->add_attribute(
505 Class::MOP::Attribute->new('default' => (
506 # default has a custom 'reader' method ...
507 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
511 Class::MOP::Attribute->meta->add_attribute(
512 Class::MOP::Attribute->new('associated_methods' => (
513 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
514 default => sub { [] }
518 Class::MOP::Attribute->meta->add_method('clone' => sub {
520 $self->meta->clone_object($self, @_);
523 ## --------------------------------------------------------
524 ## Class::MOP::Method
525 Class::MOP::Method->meta->add_attribute(
526 Class::MOP::Attribute->new('body' => (
527 reader => { 'body' => \&Class::MOP::Method::body },
531 Class::MOP::Method->meta->add_attribute(
532 Class::MOP::Attribute->new('associated_metaclass' => (
533 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
537 Class::MOP::Method->meta->add_attribute(
538 Class::MOP::Attribute->new('package_name' => (
539 reader => { 'package_name' => \&Class::MOP::Method::package_name },
543 Class::MOP::Method->meta->add_attribute(
544 Class::MOP::Attribute->new('name' => (
545 reader => { 'name' => \&Class::MOP::Method::name },
549 Class::MOP::Method->meta->add_attribute(
550 Class::MOP::Attribute->new('original_method' => (
551 reader => { 'original_method' => \&Class::MOP::Method::original_method },
552 writer => { '_set_original_method' => \&Class::MOP::Method::_set_original_method },
556 Class::MOP::Method->meta->add_method('clone' => sub {
558 my $clone = $self->meta->clone_object($self, @_);
559 $clone->_set_original_method($self);
563 ## --------------------------------------------------------
564 ## Class::MOP::Method::Wrapped
567 # the way this item is initialized, this
568 # really does not follow the standard
569 # practices of attributes, but we put
570 # it here for completeness
571 Class::MOP::Method::Wrapped->meta->add_attribute(
572 Class::MOP::Attribute->new('modifier_table')
575 ## --------------------------------------------------------
576 ## Class::MOP::Method::Generated
578 Class::MOP::Method::Generated->meta->add_attribute(
579 Class::MOP::Attribute->new('is_inline' => (
580 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
585 Class::MOP::Method::Generated->meta->add_attribute(
586 Class::MOP::Attribute->new('definition_context' => (
587 reader => { 'definition_context' => \&Class::MOP::Method::Generated::definition_context },
591 ## --------------------------------------------------------
592 ## Class::MOP::Method::Accessor
594 Class::MOP::Method::Accessor->meta->add_attribute(
595 Class::MOP::Attribute->new('attribute' => (
597 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
602 Class::MOP::Method::Accessor->meta->add_attribute(
603 Class::MOP::Attribute->new('accessor_type' => (
604 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
608 ## --------------------------------------------------------
609 ## Class::MOP::Method::Constructor
611 Class::MOP::Method::Constructor->meta->add_attribute(
612 Class::MOP::Attribute->new('options' => (
614 'options' => \&Class::MOP::Method::Constructor::options
616 default => sub { +{} }
620 Class::MOP::Method::Constructor->meta->add_attribute(
621 Class::MOP::Attribute->new('associated_metaclass' => (
622 init_arg => "metaclass", # FIXME alias and rename
624 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
629 ## --------------------------------------------------------
630 ## Class::MOP::Instance
633 # these don't yet do much of anything, but are just
634 # included for completeness
636 Class::MOP::Instance->meta->add_attribute(
637 Class::MOP::Attribute->new('associated_metaclass',
638 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
642 Class::MOP::Instance->meta->add_attribute(
643 Class::MOP::Attribute->new('_class_name',
645 reader => { _class_name => \&Class::MOP::Instance::_class_name },
646 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
647 #default => sub { $_[0]->associated_metaclass->name },
651 Class::MOP::Instance->meta->add_attribute(
652 Class::MOP::Attribute->new('attributes',
653 reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
657 Class::MOP::Instance->meta->add_attribute(
658 Class::MOP::Attribute->new('slots',
659 reader => { slots => \&Class::MOP::Instance::slots },
663 Class::MOP::Instance->meta->add_attribute(
664 Class::MOP::Attribute->new('slot_hash',
665 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
670 # we need the meta instance of the meta instance to be created now, in order
671 # for the constructor to be able to use it
672 Class::MOP::Instance->meta->get_meta_instance;
674 # pretend the add_method never happenned. it hasn't yet affected anything
675 undef Class::MOP::Instance->meta->{_package_cache_flag};
677 ## --------------------------------------------------------
678 ## Now close all the Class::MOP::* classes
680 # NOTE: we don't need to inline the the accessors this only lengthens
681 # the compile time of the MOP, and gives us no actual benefits.
683 $_->meta->make_immutable(
684 inline_constructor => 1,
685 replace_constructor => 1,
686 constructor_name => "_new",
687 inline_accessors => 0,
693 Class::MOP::Attribute
699 Class::MOP::Method::Generated
701 Class::MOP::Method::Accessor
702 Class::MOP::Method::Constructor
703 Class::MOP::Method::Wrapped
714 Class::MOP - A Meta Object Protocol for Perl 5
718 This module is a fully functioning meta object protocol for the
719 Perl 5 object system. It makes no attempt to change the behavior or
720 characteristics of the Perl 5 object system, only to create a
721 protocol for its manipulation and introspection.
723 That said, it does attempt to create the tools for building a rich
724 set of extensions to the Perl 5 object system. Every attempt has been
725 made for these tools to keep to the spirit of the Perl 5 object
726 system that we all know and love.
728 This documentation is admittedly sparse on details, as time permits
729 I will try to improve them. For now, I suggest looking at the items
730 listed in the L<SEE ALSO> section for more information. In particular
731 the book "The Art of the Meta Object Protocol" was very influential
732 in the development of this system.
734 =head2 What is a Meta Object Protocol?
736 A meta object protocol is an API to an object system.
738 To be more specific, it is a set of abstractions of the components of
739 an object system (typically things like; classes, object, methods,
740 object attributes, etc.). These abstractions can then be used to both
741 inspect and manipulate the object system which they describe.
743 It can be said that there are two MOPs for any object system; the
744 implicit MOP, and the explicit MOP. The implicit MOP handles things
745 like method dispatch or inheritance, which happen automatically as
746 part of how the object system works. The explicit MOP typically
747 handles the introspection/reflection features of the object system.
748 All object systems have implicit MOPs, without one, they would not
749 work. Explict MOPs however as less common, and depending on the
750 language can vary from restrictive (Reflection in Java or C#) to
751 wide open (CLOS is a perfect example).
753 =head2 Yet Another Class Builder!! Why?
755 This is B<not> a class builder so much as it is a I<class builder
756 B<builder>>. My intent is that an end user does not use this module
757 directly, but instead this module is used by module authors to
758 build extensions and features onto the Perl 5 object system.
760 =head2 Who is this module for?
762 This module is specifically for anyone who has ever created or
763 wanted to create a module for the Class:: namespace. The tools which
764 this module will provide will hopefully make it easier to do more
765 complex things with Perl 5 classes by removing such barriers as
766 the need to hack the symbol tables, or understand the fine details
769 =head2 What changes do I have to make to use this module?
771 This module was designed to be as unintrusive as possible. Many of
772 its features are accessible without B<any> change to your existsing
773 code at all. It is meant to be a compliment to your existing code and
774 not an intrusion on your code base. Unlike many other B<Class::>
775 modules, this module B<does not> require you subclass it, or even that
776 you C<use> it in within your module's package.
778 The only features which requires additions to your code are the
779 attribute handling and instance construction features, and these are
780 both completely optional features. The only reason for this is because
781 Perl 5's object system does not actually have these features built
782 in. More information about this feature can be found below.
784 =head2 A Note about Performance?
786 It is a common misconception that explict MOPs are performance drains.
787 But this is not a universal truth at all, it is an side-effect of
788 specific implementations. For instance, using Java reflection is much
789 slower because the JVM cannot take advantage of any compiler
790 optimizations, and the JVM has to deal with much more runtime type
791 information as well. Reflection in C# is marginally better as it was
792 designed into the language and runtime (the CLR). In contrast, CLOS
793 (the Common Lisp Object System) was built to support an explicit MOP,
794 and so performance is tuned for it.
796 This library in particular does it's absolute best to avoid putting
797 B<any> drain at all upon your code's performance. In fact, by itself
798 it does nothing to affect your existing code. So you only pay for
799 what you actually use.
801 =head2 About Metaclass compatibility
803 This module makes sure that all metaclasses created are both upwards
804 and downwards compatible. The topic of metaclass compatibility is
805 highly esoteric and is something only encountered when doing deep and
806 involved metaclass hacking. There are two basic kinds of metaclass
807 incompatibility; upwards and downwards.
809 Upwards metaclass compatibility means that the metaclass of a
810 given class is either the same as (or a subclass of) all of the
813 Downward metaclass compatibility means that the metaclasses of a
814 given class's anscestors are all either the same as (or a subclass
817 Here is a diagram showing a set of two classes (C<A> and C<B>) and
818 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
819 metaclass compatibility both upwards and downwards.
821 +---------+ +---------+
822 | Meta::A |<----| Meta::B | <....... (instance of )
823 +---------+ +---------+ <------- (inherits from)
826 +---------+ +---------+
828 +---------+ +---------+
830 As I said this is a highly esoteric topic and one you will only run
831 into if you do a lot of subclassing of B<Class::MOP::Class>. If you
832 are interested in why this is an issue see the paper
833 I<Uniform and safe metaclass composition> linked to in the
834 L<SEE ALSO> section of this document.
836 =head2 Using custom metaclasses
838 Always use the metaclass pragma when using a custom metaclass, this
839 will ensure the proper initialization order and not accidentely
840 create an incorrect type of metaclass for you. This is a very rare
841 problem, and one which can only occur if you are doing deep metaclass
842 programming. So in other words, don't worry about it.
846 The protocol is divided into 4 main sub-protocols:
850 =item The Class protocol
852 This provides a means of manipulating and introspecting a Perl 5
853 class. It handles all of symbol table hacking for you, and provides
854 a rich set of methods that go beyond simple package introspection.
856 See L<Class::MOP::Class> for more details.
858 =item The Attribute protocol
860 This provides a consistent represenation for an attribute of a
861 Perl 5 class. Since there are so many ways to create and handle
862 attributes in Perl 5 OO, this attempts to provide as much of a
863 unified approach as possible, while giving the freedom and
864 flexibility to subclass for specialization.
866 See L<Class::MOP::Attribute> for more details.
868 =item The Method protocol
870 This provides a means of manipulating and introspecting methods in
871 the Perl 5 object system. As with attributes, there are many ways to
872 approach this topic, so we try to keep it pretty basic, while still
873 making it possible to extend the system in many ways.
875 See L<Class::MOP::Method> for more details.
877 =item The Instance protocol
879 This provides a layer of abstraction for creating object instances.
880 Since the other layers use this protocol, it is relatively easy to
881 change the type of your instances from the default HASH ref to other
882 types of references. Several examples are provided in the F<examples/>
883 directory included in this distribution.
885 See L<Class::MOP::Instance> for more details.
895 =item I<IS_RUNNING_ON_5_10>
897 We set this constant depending on what version perl we are on, this
898 allows us to take advantage of new 5.10 features and stay backwards
903 Whether or not C<mro> provides C<get_isarev>, a much faster way to get all the
904 subclasses of a certain class.
908 Whether or not the running C<Class::MOP> is using its XS version.
912 =head2 Utility functions
914 Note that these are all called as B<functions, not methods>.
918 =item B<load_class ($class_name)>
920 This will load a given C<$class_name> and if it does not have an
921 already initialized metaclass, then it will intialize one for it.
922 This function can be used in place of tricks like
923 C<eval "use $module"> or using C<require>.
925 =item B<is_class_loaded ($class_name)>
927 This will return a boolean depending on if the C<$class_name> has
930 NOTE: This does a basic check of the symbol table to try and
931 determine as best it can if the C<$class_name> is loaded, it
932 is probably correct about 99% of the time.
934 =item B<check_package_cache_flag ($pkg)>
936 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
938 This will return an integer that is managed by C<Class::MOP::Class>
939 to determine if a module's symbol table has been altered.
941 In Perl 5.10 or greater, this flag is package specific. However in
942 versions prior to 5.10, this will use the C<PL_sub_generation> variable
943 which is not package specific.
945 =item B<get_code_info ($code)>
947 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
949 This function returns two values, the name of the package the C<$code>
950 is from and the name of the C<$code> itself. This is used by several
951 elements of the MOP to detemine where a given C<$code> reference is from.
953 =item B<subname ($name, $code)>
955 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
957 If possible, we will load the L<Sub::Name> module and this will function
958 as C<Sub::Name::subname> does, otherwise it will just return the C<$code>
961 =item B<in_global_destruction>
963 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
965 If L<Devel::GlobalDestruction> is available, this returns true under global
968 Otherwise it's a constant returning false.
970 =item B<load_first_existing_class ($class_name, [$class_name, ...])>
972 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
974 Given a list of class names, this function will attempt to load each
977 If it finds a class it can load, it will return that class' name.
978 If none of the classes can be loaded, it will throw an exception.
982 =head2 Metaclass cache functions
984 Class::MOP holds a cache of metaclasses. The following are functions
985 (B<not methods>) which can be used to access that cache. It is not
986 recommended that you mess with these. Bad things could happen, but if
987 you are brave and willing to risk it: go for it!
991 =item B<get_all_metaclasses>
993 This will return a hash of all the metaclass instances that have
994 been cached by B<Class::MOP::Class>, keyed by the package name.
996 =item B<get_all_metaclass_instances>
998 This will return a list of all the metaclass instances that have
999 been cached by B<Class::MOP::Class>.
1001 =item B<get_all_metaclass_names>
1003 This will return a list of all the metaclass names that have
1004 been cached by B<Class::MOP::Class>.
1006 =item B<get_metaclass_by_name ($name)>
1008 This will return a cached B<Class::MOP::Class> instance, or nothing
1009 if no metaclass exists with that C<$name>.
1011 =item B<store_metaclass_by_name ($name, $meta)>
1013 This will store a metaclass in the cache at the supplied C<$key>.
1015 =item B<weaken_metaclass ($name)>
1017 In rare cases (e.g. anonymous metaclasses) it is desirable to
1018 store a weakened reference in the metaclass cache. This
1019 function will weaken the reference to the metaclass stored
1022 =item B<does_metaclass_exist ($name)>
1024 This will return true of there exists a metaclass stored in the
1025 C<$name> key, and return false otherwise.
1027 =item B<remove_metaclass_by_name ($name)>
1029 This will remove the metaclass stored in the C<$name> key.
1037 There are very few books out on Meta Object Protocols and Metaclasses
1038 because it is such an esoteric topic. The following books are really
1039 the only ones I have found. If you know of any more, B<I<please>>
1040 email me and let me know, I would love to hear about them.
1044 =item "The Art of the Meta Object Protocol"
1046 =item "Advances in Object-Oriented Metalevel Architecture and Reflection"
1048 =item "Putting MetaClasses to Work"
1050 =item "Smalltalk: The Language"
1058 =item Uniform and safe metaclass composition
1060 An excellent paper by the people who brought us the original Traits paper.
1061 This paper is on how Traits can be used to do safe metaclass composition,
1062 and offers an excellent introduction section which delves into the topic of
1063 metaclass compatibility.
1065 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
1067 =item Safe Metaclass Programming
1069 This paper seems to precede the above paper, and propose a mix-in based
1070 approach as opposed to the Traits based approach. Both papers have similar
1071 information on the metaclass compatibility problem space.
1073 L<http://citeseer.ist.psu.edu/37617.html>
1081 =item The Perl 6 MetaModel work in the Pugs project
1085 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
1087 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1097 =item CPAN Module Review of Class::MOP
1099 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1103 =head1 SIMILAR MODULES
1105 As I have said above, this module is a class-builder-builder, so it is
1106 not the same thing as modules like L<Class::Accessor> and
1107 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1108 with similar goals to this module. The one I have found which is most
1109 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1110 creates are very different from this modules.
1114 All complex software has bugs lurking in it, and this module is no
1115 exception. If you find a bug please either email me, or add the bug
1118 =head1 ACKNOWLEDGEMENTS
1124 Thanks to Rob for actually getting the development of this module kick-started.
1130 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1132 B<with contributions from:>
1134 Brandon (blblack) Black
1136 Florian (rafl) Ragwitz
1138 Guillermo (groditi) Roditi
1142 Rob (robkinyon) Kinyon
1144 Yuval (nothingmuch) Kogman
1146 Scott (konobi) McWhirter
1148 =head1 COPYRIGHT AND LICENSE
1150 Copyright 2006-2008 by Infinity Interactive, Inc.
1152 L<http://www.iinteractive.com>
1154 This library is free software; you can redistribute it and/or modify
1155 it under the same terms as Perl itself.