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 = '0.76';
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 # check for $VERSION or @ISA
190 return 1 if exists ${$$pack}{VERSION}
191 && defined *{${$$pack}{VERSION}}{SCALAR};
192 return 1 if exists ${$$pack}{ISA}
193 && defined *{${$$pack}{ISA}}{ARRAY};
195 # check for any method
196 foreach ( keys %{$$pack} ) {
197 next if substr($_, -2, 2) eq '::';
199 my $glob = ${$$pack}{$_} || next;
202 if ( IS_RUNNING_ON_5_10 ) {
203 return 1 if ref $glob eq 'SCALAR';
206 return 1 if defined *{$glob}{CODE};
214 ## ----------------------------------------------------------------------------
215 ## Setting up our environment ...
216 ## ----------------------------------------------------------------------------
217 ## Class::MOP needs to have a few things in the global perl environment so
218 ## that it can operate effectively. Those things are done here.
219 ## ----------------------------------------------------------------------------
221 # ... nothing yet actually ;)
223 ## ----------------------------------------------------------------------------
225 ## ----------------------------------------------------------------------------
226 ## The code below here is to bootstrap our MOP with itself. This is also
227 ## sometimes called "tying the knot". By doing this, we make it much easier
228 ## to extend the MOP through subclassing and such since now you can use the
229 ## MOP itself to extend itself.
231 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
232 ## ----------------------------------------------------------------------------
234 # We need to add in the meta-attributes here so that
235 # any subclass of Class::MOP::* will be able to
236 # inherit them using &construct_instance
238 ## --------------------------------------------------------
239 ## Class::MOP::Package
241 Class::MOP::Package->meta->add_attribute(
242 Class::MOP::Attribute->new('package' => (
244 # NOTE: we need to do this in order
245 # for the instance meta-object to
246 # not fall into meta-circular death
248 # we just alias the original method
249 # rather than re-produce it here
250 'name' => \&Class::MOP::Package::name
255 Class::MOP::Package->meta->add_attribute(
256 Class::MOP::Attribute->new('namespace' => (
259 # we just alias the original method
260 # rather than re-produce it here
261 'namespace' => \&Class::MOP::Package::namespace
264 default => sub { \undef }
268 ## --------------------------------------------------------
269 ## Class::MOP::Module
272 # yeah this is kind of stretching things a bit,
273 # but truthfully the version should be an attribute
274 # of the Module, the weirdness comes from having to
275 # stick to Perl 5 convention and store it in the
276 # $VERSION package variable. Basically if you just
277 # squint at it, it will look how you want it to look.
278 # Either as a package variable, or as a attribute of
279 # the metaclass, isn't abstraction great :)
281 Class::MOP::Module->meta->add_attribute(
282 Class::MOP::Attribute->new('version' => (
285 # we just alias the original method
286 # rather than re-produce it here
287 'version' => \&Class::MOP::Module::version
290 default => sub { \undef }
295 # By following the same conventions as version here,
296 # we are opening up the possibility that people can
297 # use the $AUTHORITY in non-Class::MOP modules as
300 Class::MOP::Module->meta->add_attribute(
301 Class::MOP::Attribute->new('authority' => (
304 # we just alias the original method
305 # rather than re-produce it here
306 'authority' => \&Class::MOP::Module::authority
309 default => sub { \undef }
313 ## --------------------------------------------------------
316 Class::MOP::Class->meta->add_attribute(
317 Class::MOP::Attribute->new('attributes' => (
319 # NOTE: we need to do this in order
320 # for the instance meta-object to
321 # not fall into meta-circular death
323 # we just alias the original method
324 # rather than re-produce it here
325 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
327 default => sub { {} }
331 Class::MOP::Class->meta->add_attribute(
332 Class::MOP::Attribute->new('methods' => (
335 # we just alias the original method
336 # rather than re-produce it here
337 'get_method_map' => \&Class::MOP::Class::get_method_map
339 default => sub { {} }
343 Class::MOP::Class->meta->add_attribute(
344 Class::MOP::Attribute->new('superclasses' => (
347 # we just alias the original method
348 # rather than re-produce it here
349 'superclasses' => \&Class::MOP::Class::superclasses
352 default => sub { \undef }
356 Class::MOP::Class->meta->add_attribute(
357 Class::MOP::Attribute->new('attribute_metaclass' => (
360 # we just alias the original method
361 # rather than re-produce it here
362 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
364 default => 'Class::MOP::Attribute',
368 Class::MOP::Class->meta->add_attribute(
369 Class::MOP::Attribute->new('method_metaclass' => (
372 # we just alias the original method
373 # rather than re-produce it here
374 'method_metaclass' => \&Class::MOP::Class::method_metaclass
376 default => 'Class::MOP::Method',
380 Class::MOP::Class->meta->add_attribute(
381 Class::MOP::Attribute->new('instance_metaclass' => (
383 # NOTE: we need to do this in order
384 # for the instance meta-object to
385 # not fall into meta-circular death
387 # we just alias the original method
388 # rather than re-produce it here
389 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
391 default => 'Class::MOP::Instance',
396 # we don't actually need to tie the knot with
397 # Class::MOP::Class here, it is actually handled
398 # within Class::MOP::Class itself in the
399 # construct_class_instance method.
401 ## --------------------------------------------------------
402 ## Class::MOP::Attribute
404 Class::MOP::Attribute->meta->add_attribute(
405 Class::MOP::Attribute->new('name' => (
407 # NOTE: we need to do this in order
408 # for the instance meta-object to
409 # not fall into meta-circular death
411 # we just alias the original method
412 # rather than re-produce it here
413 'name' => \&Class::MOP::Attribute::name
418 Class::MOP::Attribute->meta->add_attribute(
419 Class::MOP::Attribute->new('associated_class' => (
421 # NOTE: we need to do this in order
422 # for the instance meta-object to
423 # not fall into meta-circular death
425 # we just alias the original method
426 # rather than re-produce it here
427 'associated_class' => \&Class::MOP::Attribute::associated_class
432 Class::MOP::Attribute->meta->add_attribute(
433 Class::MOP::Attribute->new('accessor' => (
434 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
435 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
439 Class::MOP::Attribute->meta->add_attribute(
440 Class::MOP::Attribute->new('reader' => (
441 reader => { 'reader' => \&Class::MOP::Attribute::reader },
442 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
446 Class::MOP::Attribute->meta->add_attribute(
447 Class::MOP::Attribute->new('initializer' => (
448 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
449 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
453 Class::MOP::Attribute->meta->add_attribute(
454 Class::MOP::Attribute->new('definition_context' => (
455 reader => { 'definition_context' => \&Class::MOP::Attribute::definition_context },
459 Class::MOP::Attribute->meta->add_attribute(
460 Class::MOP::Attribute->new('writer' => (
461 reader => { 'writer' => \&Class::MOP::Attribute::writer },
462 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
466 Class::MOP::Attribute->meta->add_attribute(
467 Class::MOP::Attribute->new('predicate' => (
468 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
469 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
473 Class::MOP::Attribute->meta->add_attribute(
474 Class::MOP::Attribute->new('clearer' => (
475 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
476 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
480 Class::MOP::Attribute->meta->add_attribute(
481 Class::MOP::Attribute->new('builder' => (
482 reader => { 'builder' => \&Class::MOP::Attribute::builder },
483 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
487 Class::MOP::Attribute->meta->add_attribute(
488 Class::MOP::Attribute->new('init_arg' => (
489 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
490 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
494 Class::MOP::Attribute->meta->add_attribute(
495 Class::MOP::Attribute->new('default' => (
496 # default has a custom 'reader' method ...
497 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
501 Class::MOP::Attribute->meta->add_attribute(
502 Class::MOP::Attribute->new('associated_methods' => (
503 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
504 default => sub { [] }
508 Class::MOP::Attribute->meta->add_method('clone' => sub {
510 $self->meta->clone_object($self, @_);
513 ## --------------------------------------------------------
514 ## Class::MOP::Method
515 Class::MOP::Method->meta->add_attribute(
516 Class::MOP::Attribute->new('body' => (
517 reader => { 'body' => \&Class::MOP::Method::body },
521 Class::MOP::Method->meta->add_attribute(
522 Class::MOP::Attribute->new('associated_metaclass' => (
523 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
527 Class::MOP::Method->meta->add_attribute(
528 Class::MOP::Attribute->new('package_name' => (
529 reader => { 'package_name' => \&Class::MOP::Method::package_name },
533 Class::MOP::Method->meta->add_attribute(
534 Class::MOP::Attribute->new('name' => (
535 reader => { 'name' => \&Class::MOP::Method::name },
539 Class::MOP::Method->meta->add_attribute(
540 Class::MOP::Attribute->new('original_method' => (
541 reader => { 'original_method' => \&Class::MOP::Method::original_method },
542 writer => { '_set_original_method' => \&Class::MOP::Method::_set_original_method },
546 Class::MOP::Method->meta->add_method('clone' => sub {
548 my $clone = $self->meta->clone_object($self, @_);
549 $clone->_set_original_method($self);
553 ## --------------------------------------------------------
554 ## Class::MOP::Method::Wrapped
557 # the way this item is initialized, this
558 # really does not follow the standard
559 # practices of attributes, but we put
560 # it here for completeness
561 Class::MOP::Method::Wrapped->meta->add_attribute(
562 Class::MOP::Attribute->new('modifier_table')
565 ## --------------------------------------------------------
566 ## Class::MOP::Method::Generated
568 Class::MOP::Method::Generated->meta->add_attribute(
569 Class::MOP::Attribute->new('is_inline' => (
570 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
575 Class::MOP::Method::Generated->meta->add_attribute(
576 Class::MOP::Attribute->new('definition_context' => (
577 reader => { 'definition_context' => \&Class::MOP::Method::Generated::definition_context },
581 ## --------------------------------------------------------
582 ## Class::MOP::Method::Accessor
584 Class::MOP::Method::Accessor->meta->add_attribute(
585 Class::MOP::Attribute->new('attribute' => (
587 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
592 Class::MOP::Method::Accessor->meta->add_attribute(
593 Class::MOP::Attribute->new('accessor_type' => (
594 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
598 ## --------------------------------------------------------
599 ## Class::MOP::Method::Constructor
601 Class::MOP::Method::Constructor->meta->add_attribute(
602 Class::MOP::Attribute->new('options' => (
604 'options' => \&Class::MOP::Method::Constructor::options
606 default => sub { +{} }
610 Class::MOP::Method::Constructor->meta->add_attribute(
611 Class::MOP::Attribute->new('associated_metaclass' => (
612 init_arg => "metaclass", # FIXME alias and rename
614 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
619 ## --------------------------------------------------------
620 ## Class::MOP::Instance
623 # these don't yet do much of anything, but are just
624 # included for completeness
626 Class::MOP::Instance->meta->add_attribute(
627 Class::MOP::Attribute->new('associated_metaclass',
628 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
632 Class::MOP::Instance->meta->add_attribute(
633 Class::MOP::Attribute->new('_class_name',
635 reader => { _class_name => \&Class::MOP::Instance::_class_name },
636 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
637 #default => sub { $_[0]->associated_metaclass->name },
641 Class::MOP::Instance->meta->add_attribute(
642 Class::MOP::Attribute->new('attributes',
643 reader => { attributes => \&Class::MOP::Instance::get_all_attributes },
647 Class::MOP::Instance->meta->add_attribute(
648 Class::MOP::Attribute->new('slots',
649 reader => { slots => \&Class::MOP::Instance::slots },
653 Class::MOP::Instance->meta->add_attribute(
654 Class::MOP::Attribute->new('slot_hash',
655 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
660 # we need the meta instance of the meta instance to be created now, in order
661 # for the constructor to be able to use it
662 Class::MOP::Instance->meta->get_meta_instance;
664 # pretend the add_method never happenned. it hasn't yet affected anything
665 undef Class::MOP::Instance->meta->{_package_cache_flag};
667 ## --------------------------------------------------------
668 ## Now close all the Class::MOP::* classes
670 # NOTE: we don't need to inline the the accessors this only lengthens
671 # the compile time of the MOP, and gives us no actual benefits.
673 $_->meta->make_immutable(
674 inline_constructor => 1,
675 replace_constructor => 1,
676 constructor_name => "_new",
677 inline_accessors => 0,
683 Class::MOP::Attribute
689 Class::MOP::Method::Generated
691 Class::MOP::Method::Accessor
692 Class::MOP::Method::Constructor
693 Class::MOP::Method::Wrapped
704 Class::MOP - A Meta Object Protocol for Perl 5
708 This module is a fully functioning meta object protocol for the
709 Perl 5 object system. It makes no attempt to change the behavior or
710 characteristics of the Perl 5 object system, only to create a
711 protocol for its manipulation and introspection.
713 That said, it does attempt to create the tools for building a rich
714 set of extensions to the Perl 5 object system. Every attempt has been
715 made for these tools to keep to the spirit of the Perl 5 object
716 system that we all know and love.
718 This documentation is admittedly sparse on details, as time permits
719 I will try to improve them. For now, I suggest looking at the items
720 listed in the L<SEE ALSO> section for more information. In particular
721 the book "The Art of the Meta Object Protocol" was very influential
722 in the development of this system.
724 =head2 What is a Meta Object Protocol?
726 A meta object protocol is an API to an object system.
728 To be more specific, it is a set of abstractions of the components of
729 an object system (typically things like; classes, object, methods,
730 object attributes, etc.). These abstractions can then be used to both
731 inspect and manipulate the object system which they describe.
733 It can be said that there are two MOPs for any object system; the
734 implicit MOP, and the explicit MOP. The implicit MOP handles things
735 like method dispatch or inheritance, which happen automatically as
736 part of how the object system works. The explicit MOP typically
737 handles the introspection/reflection features of the object system.
738 All object systems have implicit MOPs, without one, they would not
739 work. Explict MOPs however as less common, and depending on the
740 language can vary from restrictive (Reflection in Java or C#) to
741 wide open (CLOS is a perfect example).
743 =head2 Yet Another Class Builder!! Why?
745 This is B<not> a class builder so much as it is a I<class builder
746 B<builder>>. My intent is that an end user does not use this module
747 directly, but instead this module is used by module authors to
748 build extensions and features onto the Perl 5 object system.
750 =head2 Who is this module for?
752 This module is specifically for anyone who has ever created or
753 wanted to create a module for the Class:: namespace. The tools which
754 this module will provide will hopefully make it easier to do more
755 complex things with Perl 5 classes by removing such barriers as
756 the need to hack the symbol tables, or understand the fine details
759 =head2 What changes do I have to make to use this module?
761 This module was designed to be as unintrusive as possible. Many of
762 its features are accessible without B<any> change to your existsing
763 code at all. It is meant to be a compliment to your existing code and
764 not an intrusion on your code base. Unlike many other B<Class::>
765 modules, this module B<does not> require you subclass it, or even that
766 you C<use> it in within your module's package.
768 The only features which requires additions to your code are the
769 attribute handling and instance construction features, and these are
770 both completely optional features. The only reason for this is because
771 Perl 5's object system does not actually have these features built
772 in. More information about this feature can be found below.
774 =head2 A Note about Performance?
776 It is a common misconception that explict MOPs are performance drains.
777 But this is not a universal truth at all, it is an side-effect of
778 specific implementations. For instance, using Java reflection is much
779 slower because the JVM cannot take advantage of any compiler
780 optimizations, and the JVM has to deal with much more runtime type
781 information as well. Reflection in C# is marginally better as it was
782 designed into the language and runtime (the CLR). In contrast, CLOS
783 (the Common Lisp Object System) was built to support an explicit MOP,
784 and so performance is tuned for it.
786 This library in particular does it's absolute best to avoid putting
787 B<any> drain at all upon your code's performance. In fact, by itself
788 it does nothing to affect your existing code. So you only pay for
789 what you actually use.
791 =head2 About Metaclass compatibility
793 This module makes sure that all metaclasses created are both upwards
794 and downwards compatible. The topic of metaclass compatibility is
795 highly esoteric and is something only encountered when doing deep and
796 involved metaclass hacking. There are two basic kinds of metaclass
797 incompatibility; upwards and downwards.
799 Upwards metaclass compatibility means that the metaclass of a
800 given class is either the same as (or a subclass of) all of the
803 Downward metaclass compatibility means that the metaclasses of a
804 given class's anscestors are all either the same as (or a subclass
807 Here is a diagram showing a set of two classes (C<A> and C<B>) and
808 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
809 metaclass compatibility both upwards and downwards.
811 +---------+ +---------+
812 | Meta::A |<----| Meta::B | <....... (instance of )
813 +---------+ +---------+ <------- (inherits from)
816 +---------+ +---------+
818 +---------+ +---------+
820 As I said this is a highly esoteric topic and one you will only run
821 into if you do a lot of subclassing of B<Class::MOP::Class>. If you
822 are interested in why this is an issue see the paper
823 I<Uniform and safe metaclass composition> linked to in the
824 L<SEE ALSO> section of this document.
826 =head2 Using custom metaclasses
828 Always use the metaclass pragma when using a custom metaclass, this
829 will ensure the proper initialization order and not accidentely
830 create an incorrect type of metaclass for you. This is a very rare
831 problem, and one which can only occur if you are doing deep metaclass
832 programming. So in other words, don't worry about it.
836 The protocol is divided into 4 main sub-protocols:
840 =item The Class protocol
842 This provides a means of manipulating and introspecting a Perl 5
843 class. It handles all of symbol table hacking for you, and provides
844 a rich set of methods that go beyond simple package introspection.
846 See L<Class::MOP::Class> for more details.
848 =item The Attribute protocol
850 This provides a consistent represenation for an attribute of a
851 Perl 5 class. Since there are so many ways to create and handle
852 attributes in Perl 5 OO, this attempts to provide as much of a
853 unified approach as possible, while giving the freedom and
854 flexibility to subclass for specialization.
856 See L<Class::MOP::Attribute> for more details.
858 =item The Method protocol
860 This provides a means of manipulating and introspecting methods in
861 the Perl 5 object system. As with attributes, there are many ways to
862 approach this topic, so we try to keep it pretty basic, while still
863 making it possible to extend the system in many ways.
865 See L<Class::MOP::Method> for more details.
867 =item The Instance protocol
869 This provides a layer of abstraction for creating object instances.
870 Since the other layers use this protocol, it is relatively easy to
871 change the type of your instances from the default HASH ref to other
872 types of references. Several examples are provided in the F<examples/>
873 directory included in this distribution.
875 See L<Class::MOP::Instance> for more details.
885 =item I<IS_RUNNING_ON_5_10>
887 We set this constant depending on what version perl we are on, this
888 allows us to take advantage of new 5.10 features and stay backwards
893 Whether or not C<mro> provides C<get_isarev>, a much faster way to get all the
894 subclasses of a certain class.
898 Whether or not the running C<Class::MOP> is using its XS version.
902 =head2 Utility functions
904 Note that these are all called as B<functions, not methods>.
908 =item B<load_class ($class_name)>
910 This will load a given C<$class_name> and if it does not have an
911 already initialized metaclass, then it will intialize one for it.
912 This function can be used in place of tricks like
913 C<eval "use $module"> or using C<require>.
915 =item B<is_class_loaded ($class_name)>
917 This will return a boolean depending on if the C<$class_name> has
920 NOTE: This does a basic check of the symbol table to try and
921 determine as best it can if the C<$class_name> is loaded, it
922 is probably correct about 99% of the time.
924 =item B<check_package_cache_flag ($pkg)>
926 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
928 This will return an integer that is managed by C<Class::MOP::Class>
929 to determine if a module's symbol table has been altered.
931 In Perl 5.10 or greater, this flag is package specific. However in
932 versions prior to 5.10, this will use the C<PL_sub_generation> variable
933 which is not package specific.
935 =item B<get_code_info ($code)>
937 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
939 This function returns two values, the name of the package the C<$code>
940 is from and the name of the C<$code> itself. This is used by several
941 elements of the MOP to detemine where a given C<$code> reference is from.
943 =item B<subname ($name, $code)>
945 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
947 If possible, we will load the L<Sub::Name> module and this will function
948 as C<Sub::Name::subname> does, otherwise it will just return the C<$code>
951 =item B<in_global_destruction>
953 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
955 If L<Devel::GlobalDestruction> is available, this returns true under global
958 Otherwise it's a constant returning false.
960 =item B<load_first_existing_class ($class_name, [$class_name, ...])>
962 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
964 Given a list of class names, this function will attempt to load each
967 If it finds a class it can load, it will return that class' name.
968 If none of the classes can be loaded, it will throw an exception.
972 =head2 Metaclass cache functions
974 Class::MOP holds a cache of metaclasses. The following are functions
975 (B<not methods>) which can be used to access that cache. It is not
976 recommended that you mess with these. Bad things could happen, but if
977 you are brave and willing to risk it: go for it!
981 =item B<get_all_metaclasses>
983 This will return a hash of all the metaclass instances that have
984 been cached by B<Class::MOP::Class>, keyed by the package name.
986 =item B<get_all_metaclass_instances>
988 This will return a list of all the metaclass instances that have
989 been cached by B<Class::MOP::Class>.
991 =item B<get_all_metaclass_names>
993 This will return a list of all the metaclass names that have
994 been cached by B<Class::MOP::Class>.
996 =item B<get_metaclass_by_name ($name)>
998 This will return a cached B<Class::MOP::Class> instance, or nothing
999 if no metaclass exists with that C<$name>.
1001 =item B<store_metaclass_by_name ($name, $meta)>
1003 This will store a metaclass in the cache at the supplied C<$key>.
1005 =item B<weaken_metaclass ($name)>
1007 In rare cases (e.g. anonymous metaclasses) it is desirable to
1008 store a weakened reference in the metaclass cache. This
1009 function will weaken the reference to the metaclass stored
1012 =item B<does_metaclass_exist ($name)>
1014 This will return true of there exists a metaclass stored in the
1015 C<$name> key, and return false otherwise.
1017 =item B<remove_metaclass_by_name ($name)>
1019 This will remove the metaclass stored in the C<$name> key.
1027 There are very few books out on Meta Object Protocols and Metaclasses
1028 because it is such an esoteric topic. The following books are really
1029 the only ones I have found. If you know of any more, B<I<please>>
1030 email me and let me know, I would love to hear about them.
1034 =item "The Art of the Meta Object Protocol"
1036 =item "Advances in Object-Oriented Metalevel Architecture and Reflection"
1038 =item "Putting MetaClasses to Work"
1040 =item "Smalltalk: The Language"
1048 =item Uniform and safe metaclass composition
1050 An excellent paper by the people who brought us the original Traits paper.
1051 This paper is on how Traits can be used to do safe metaclass composition,
1052 and offers an excellent introduction section which delves into the topic of
1053 metaclass compatibility.
1055 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
1057 =item Safe Metaclass Programming
1059 This paper seems to precede the above paper, and propose a mix-in based
1060 approach as opposed to the Traits based approach. Both papers have similar
1061 information on the metaclass compatibility problem space.
1063 L<http://citeseer.ist.psu.edu/37617.html>
1071 =item The Perl 6 MetaModel work in the Pugs project
1075 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
1077 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1087 =item CPAN Module Review of Class::MOP
1089 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1093 =head1 SIMILAR MODULES
1095 As I have said above, this module is a class-builder-builder, so it is
1096 not the same thing as modules like L<Class::Accessor> and
1097 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1098 with similar goals to this module. The one I have found which is most
1099 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1100 creates are very different from this modules.
1104 All complex software has bugs lurking in it, and this module is no
1105 exception. If you find a bug please either email me, or add the bug
1108 =head1 ACKNOWLEDGEMENTS
1114 Thanks to Rob for actually getting the development of this module kick-started.
1120 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1122 B<with contributions from:>
1124 Brandon (blblack) Black
1126 Florian (rafl) Ragwitz
1128 Guillermo (groditi) Roditi
1132 Rob (robkinyon) Kinyon
1134 Yuval (nothingmuch) Kogman
1136 Scott (konobi) McWhirter
1138 =head1 COPYRIGHT AND LICENSE
1140 Copyright 2006-2008 by Infinity Interactive, Inc.
1142 L<http://www.iinteractive.com>
1144 This library is free software; you can redistribute it and/or modify
1145 it under the same terms as Perl itself.