10 use Scalar::Util 'weaken';
12 use Sub::Identify 'get_code_info';
18 Sub::Name->import(qw(subname));
20 } or eval 'sub subname { $_[1] }';
22 # this is either part of core or set up appropriately by MRO::Compat
23 *check_package_cache_flag = \&mro::get_pkg_gen;
26 require Devel::GlobalDestruction;
27 Devel::GlobalDestruction->import("in_global_destruction");
29 } or *in_global_destruction = sub () { '' };
33 use Class::MOP::Class;
34 use Class::MOP::Attribute;
35 use Class::MOP::Method;
37 use Class::MOP::Immutable;
40 *IS_RUNNING_ON_5_10 = ($] < 5.009_005)
44 *HAVE_ISAREV = defined(&mro::get_isarev)
49 our $VERSION = '0.65';
50 our $AUTHORITY = 'cpan:STEVAN';
52 # after that everything is loaded, if we're allowed try to load faster XS
53 # versions of various things
54 unless ($ENV{CLASS_MOP_NO_XS}) {
59 __PACKAGE__->XSLoader::load($VERSION);
64 die $e if $e && $e !~ /object version|loadable object/;
68 # Metaclasses are singletons, so we cache them here.
69 # there is no need to worry about destruction though
70 # because they should die only when the program dies.
71 # After all, do package definitions even get reaped?
74 # means of accessing all the metaclasses that have
75 # been initialized thus far (for mugwumps obj browser)
76 sub get_all_metaclasses { %METAS }
77 sub get_all_metaclass_instances { values %METAS }
78 sub get_all_metaclass_names { keys %METAS }
79 sub get_metaclass_by_name { $METAS{$_[0]} }
80 sub store_metaclass_by_name { $METAS{$_[0]} = $_[1] }
81 sub weaken_metaclass { weaken($METAS{$_[0]}) }
82 sub does_metaclass_exist { exists $METAS{$_[0]} && defined $METAS{$_[0]} }
83 sub remove_metaclass_by_name { $METAS{$_[0]} = undef }
86 # We only cache metaclasses, meaning instances of
87 # Class::MOP::Class. We do not cache instance of
88 # Class::MOP::Package or Class::MOP::Module. Mostly
89 # because I don't yet see a good reason to do so.
95 if (ref($class) || !defined($class) || !length($class)) {
96 my $display = defined($class) ? $class : 'undef';
97 confess "Invalid class name ($display)";
100 # if the class is not already loaded in the symbol table..
101 unless (is_class_loaded($class)) {
103 my $file = $class . '.pm';
105 my $e = do { local $@; eval { require($file) }; $@ };
106 confess "Could not load class ($class) because : $e" if $e;
109 # initialize a metaclass if necessary
110 unless (does_metaclass_exist($class)) {
111 my $e = do { local $@; eval { Class::MOP::Class->initialize($class) }; $@ };
112 confess "Could not initialize class ($class) because : $e" if $e;
115 return get_metaclass_by_name($class) if defined wantarray;
118 sub is_class_loaded {
121 return 0 if ref($class) || !defined($class) || !length($class);
123 # walk the symbol table tree to avoid autovififying
124 # \*{${main::}{"Foo::"}} == \*main::Foo::
127 foreach my $part (split('::', $class)) {
128 return 0 unless exists ${$$pack}{"${part}::"};
129 $pack = \*{${$$pack}{"${part}::"}};
132 # check for $VERSION or @ISA
133 return 1 if exists ${$$pack}{VERSION}
134 && defined *{${$$pack}{VERSION}}{SCALAR};
135 return 1 if exists ${$$pack}{ISA}
136 && defined *{${$$pack}{ISA}}{ARRAY};
138 # check for any method
139 foreach ( keys %{$$pack} ) {
140 next if substr($_, -2, 2) eq '::';
142 my $glob = ${$$pack}{$_} || next;
145 if ( IS_RUNNING_ON_5_10 ) {
146 return 1 if ref $glob eq 'SCALAR';
149 return 1 if defined *{$glob}{CODE};
157 ## ----------------------------------------------------------------------------
158 ## Setting up our environment ...
159 ## ----------------------------------------------------------------------------
160 ## Class::MOP needs to have a few things in the global perl environment so
161 ## that it can operate effectively. Those things are done here.
162 ## ----------------------------------------------------------------------------
164 # ... nothing yet actually ;)
166 ## ----------------------------------------------------------------------------
168 ## ----------------------------------------------------------------------------
169 ## The code below here is to bootstrap our MOP with itself. This is also
170 ## sometimes called "tying the knot". By doing this, we make it much easier
171 ## to extend the MOP through subclassing and such since now you can use the
172 ## MOP itself to extend itself.
174 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
175 ## ----------------------------------------------------------------------------
177 # We need to add in the meta-attributes here so that
178 # any subclass of Class::MOP::* will be able to
179 # inherit them using &construct_instance
181 ## --------------------------------------------------------
182 ## Class::MOP::Package
184 Class::MOP::Package->meta->add_attribute(
185 Class::MOP::Attribute->new('package' => (
187 # NOTE: we need to do this in order
188 # for the instance meta-object to
189 # not fall into meta-circular death
191 # we just alias the original method
192 # rather than re-produce it here
193 'name' => \&Class::MOP::Package::name
198 Class::MOP::Package->meta->add_attribute(
199 Class::MOP::Attribute->new('namespace' => (
202 # we just alias the original method
203 # rather than re-produce it here
204 'namespace' => \&Class::MOP::Package::namespace
207 default => sub { \undef }
212 # use the metaclass to construct the meta-package
213 # which is a superclass of the metaclass itself :P
214 Class::MOP::Package->meta->add_method('initialize' => sub {
216 my $package_name = shift;
217 $class->meta->new_object('package' => $package_name, @_);
220 ## --------------------------------------------------------
221 ## Class::MOP::Module
224 # yeah this is kind of stretching things a bit,
225 # but truthfully the version should be an attribute
226 # of the Module, the weirdness comes from having to
227 # stick to Perl 5 convention and store it in the
228 # $VERSION package variable. Basically if you just
229 # squint at it, it will look how you want it to look.
230 # Either as a package variable, or as a attribute of
231 # the metaclass, isn't abstraction great :)
233 Class::MOP::Module->meta->add_attribute(
234 Class::MOP::Attribute->new('version' => (
237 # we just alias the original method
238 # rather than re-produce it here
239 'version' => \&Class::MOP::Module::version
242 default => sub { \undef }
247 # By following the same conventions as version here,
248 # we are opening up the possibility that people can
249 # use the $AUTHORITY in non-Class::MOP modules as
252 Class::MOP::Module->meta->add_attribute(
253 Class::MOP::Attribute->new('authority' => (
256 # we just alias the original method
257 # rather than re-produce it here
258 'authority' => \&Class::MOP::Module::authority
261 default => sub { \undef }
265 ## --------------------------------------------------------
268 Class::MOP::Class->meta->add_attribute(
269 Class::MOP::Attribute->new('attributes' => (
271 # NOTE: we need to do this in order
272 # for the instance meta-object to
273 # not fall into meta-circular death
275 # we just alias the original method
276 # rather than re-produce it here
277 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
279 default => sub { {} }
283 Class::MOP::Class->meta->add_attribute(
284 Class::MOP::Attribute->new('methods' => (
287 # we just alias the original method
288 # rather than re-produce it here
289 'get_method_map' => \&Class::MOP::Class::get_method_map
291 default => sub { {} }
295 Class::MOP::Class->meta->add_attribute(
296 Class::MOP::Attribute->new('superclasses' => (
299 # we just alias the original method
300 # rather than re-produce it here
301 'superclasses' => \&Class::MOP::Class::superclasses
304 default => sub { \undef }
308 Class::MOP::Class->meta->add_attribute(
309 Class::MOP::Attribute->new('attribute_metaclass' => (
312 # we just alias the original method
313 # rather than re-produce it here
314 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
316 default => 'Class::MOP::Attribute',
320 Class::MOP::Class->meta->add_attribute(
321 Class::MOP::Attribute->new('method_metaclass' => (
324 # we just alias the original method
325 # rather than re-produce it here
326 'method_metaclass' => \&Class::MOP::Class::method_metaclass
328 default => 'Class::MOP::Method',
332 Class::MOP::Class->meta->add_attribute(
333 Class::MOP::Attribute->new('instance_metaclass' => (
335 # NOTE: we need to do this in order
336 # for the instance meta-object to
337 # not fall into meta-circular death
339 # we just alias the original method
340 # rather than re-produce it here
341 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
343 default => 'Class::MOP::Instance',
348 # we don't actually need to tie the knot with
349 # Class::MOP::Class here, it is actually handled
350 # within Class::MOP::Class itself in the
351 # construct_class_instance method.
353 ## --------------------------------------------------------
354 ## Class::MOP::Attribute
356 Class::MOP::Attribute->meta->add_attribute(
357 Class::MOP::Attribute->new('name' => (
359 # NOTE: we need to do this in order
360 # for the instance meta-object to
361 # not fall into meta-circular death
363 # we just alias the original method
364 # rather than re-produce it here
365 'name' => \&Class::MOP::Attribute::name
370 Class::MOP::Attribute->meta->add_attribute(
371 Class::MOP::Attribute->new('associated_class' => (
373 # NOTE: we need to do this in order
374 # for the instance meta-object to
375 # not fall into meta-circular death
377 # we just alias the original method
378 # rather than re-produce it here
379 'associated_class' => \&Class::MOP::Attribute::associated_class
384 Class::MOP::Attribute->meta->add_attribute(
385 Class::MOP::Attribute->new('accessor' => (
386 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
387 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
391 Class::MOP::Attribute->meta->add_attribute(
392 Class::MOP::Attribute->new('reader' => (
393 reader => { 'reader' => \&Class::MOP::Attribute::reader },
394 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
398 Class::MOP::Attribute->meta->add_attribute(
399 Class::MOP::Attribute->new('initializer' => (
400 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
401 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
405 Class::MOP::Attribute->meta->add_attribute(
406 Class::MOP::Attribute->new('writer' => (
407 reader => { 'writer' => \&Class::MOP::Attribute::writer },
408 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
412 Class::MOP::Attribute->meta->add_attribute(
413 Class::MOP::Attribute->new('predicate' => (
414 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
415 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
419 Class::MOP::Attribute->meta->add_attribute(
420 Class::MOP::Attribute->new('clearer' => (
421 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
422 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
426 Class::MOP::Attribute->meta->add_attribute(
427 Class::MOP::Attribute->new('builder' => (
428 reader => { 'builder' => \&Class::MOP::Attribute::builder },
429 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
433 Class::MOP::Attribute->meta->add_attribute(
434 Class::MOP::Attribute->new('init_arg' => (
435 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
436 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
440 Class::MOP::Attribute->meta->add_attribute(
441 Class::MOP::Attribute->new('default' => (
442 # default has a custom 'reader' method ...
443 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
447 Class::MOP::Attribute->meta->add_attribute(
448 Class::MOP::Attribute->new('associated_methods' => (
449 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
450 default => sub { [] }
454 Class::MOP::Attribute->meta->add_method('clone' => sub {
456 $self->meta->clone_object($self, @_);
459 ## --------------------------------------------------------
460 ## Class::MOP::Method
461 Class::MOP::Method->meta->add_attribute(
462 Class::MOP::Attribute->new('body' => (
463 reader => { 'body' => \&Class::MOP::Method::body },
467 Class::MOP::Method->meta->add_attribute(
468 Class::MOP::Attribute->new('associated_metaclass' => (
469 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
473 Class::MOP::Method->meta->add_attribute(
474 Class::MOP::Attribute->new('package_name' => (
475 reader => { 'package_name' => \&Class::MOP::Method::package_name },
479 Class::MOP::Method->meta->add_attribute(
480 Class::MOP::Attribute->new('name' => (
481 reader => { 'name' => \&Class::MOP::Method::name },
485 Class::MOP::Method->meta->add_method('clone' => sub {
487 $self->meta->clone_object($self, @_);
490 ## --------------------------------------------------------
491 ## Class::MOP::Method::Wrapped
494 # the way this item is initialized, this
495 # really does not follow the standard
496 # practices of attributes, but we put
497 # it here for completeness
498 Class::MOP::Method::Wrapped->meta->add_attribute(
499 Class::MOP::Attribute->new('modifier_table')
502 ## --------------------------------------------------------
503 ## Class::MOP::Method::Generated
505 Class::MOP::Method::Generated->meta->add_attribute(
506 Class::MOP::Attribute->new('is_inline' => (
507 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
512 Class::MOP::Method::Generated->meta->add_method('new' => sub {
513 my ($class, %options) = @_;
514 ($options{package_name} && $options{name})
515 || confess "You must supply the package_name and name parameters";
516 my $self = $class->meta->new_object(%options);
517 $self->initialize_body;
521 ## --------------------------------------------------------
522 ## Class::MOP::Method::Accessor
524 Class::MOP::Method::Accessor->meta->add_attribute(
525 Class::MOP::Attribute->new('attribute' => (
527 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
532 Class::MOP::Method::Accessor->meta->add_attribute(
533 Class::MOP::Attribute->new('accessor_type' => (
534 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
538 Class::MOP::Method::Accessor->meta->add_method('new' => sub {
542 (exists $options{attribute})
543 || confess "You must supply an attribute to construct with";
545 (exists $options{accessor_type})
546 || confess "You must supply an accessor_type to construct with";
548 (Scalar::Util::blessed($options{attribute}) && $options{attribute}->isa('Class::MOP::Attribute'))
549 || confess "You must supply an attribute which is a 'Class::MOP::Attribute' instance";
551 ($options{package_name} && $options{name})
552 || confess "You must supply the package_name and name parameters";
554 # return the new object
555 my $self = $class->meta->new_object(%options);
557 # we don't want this creating
558 # a cycle in the code, if not
560 Scalar::Util::weaken($self->{'attribute'});
562 $self->initialize_body;
568 ## --------------------------------------------------------
569 ## Class::MOP::Method::Constructor
571 Class::MOP::Method::Constructor->meta->add_attribute(
572 Class::MOP::Attribute->new('options' => (
574 'options' => \&Class::MOP::Method::Constructor::options
576 default => sub { +{} }
580 Class::MOP::Method::Constructor->meta->add_attribute(
581 Class::MOP::Attribute->new('associated_metaclass' => (
582 init_arg => "metaclass", # FIXME alias and rename
584 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
589 Class::MOP::Method::Constructor->meta->add_method('new' => sub {
593 (Scalar::Util::blessed $options{metaclass} && $options{metaclass}->isa('Class::MOP::Class'))
594 || confess "You must pass a metaclass instance if you want to inline"
595 if $options{is_inline};
597 ($options{package_name} && $options{name})
598 || confess "You must supply the package_name and name parameters";
600 # return the new object
601 my $self = $class->meta->new_object(%options);
603 # we don't want this creating
604 # a cycle in the code, if not
606 Scalar::Util::weaken($self->{'associated_metaclass'});
608 $self->initialize_body;
613 ## --------------------------------------------------------
614 ## Class::MOP::Instance
617 # these don't yet do much of anything, but are just
618 # included for completeness
620 Class::MOP::Instance->meta->add_attribute(
621 Class::MOP::Attribute->new('associated_metaclass',
622 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
626 Class::MOP::Instance->meta->add_attribute(
627 Class::MOP::Attribute->new('_class_name',
629 reader => { _class_name => \&Class::MOP::Instance::_class_name },
630 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
631 #default => sub { $_[0]->associated_metaclass->name },
635 Class::MOP::Instance->meta->add_attribute(
636 Class::MOP::Attribute->new('attributes',
637 reader => { attributes => \&Class::MOP::Instance::attributes },
641 Class::MOP::Instance->meta->add_attribute(
642 Class::MOP::Attribute->new('slots',
643 reader => { slots => \&Class::MOP::Instance::slots },
647 Class::MOP::Instance->meta->add_attribute(
648 Class::MOP::Attribute->new('slot_hash',
649 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
654 # we need the meta instance of the meta instance to be created now, in order
655 # for the constructor to be able to use it
656 Class::MOP::Instance->meta->get_meta_instance;
658 Class::MOP::Instance->meta->add_method('new' => sub {
660 my $options = $class->BUILDARGS(@_);
662 my $self = $class->meta->new_object(%$options);
664 Scalar::Util::weaken($self->{'associated_metaclass'});
669 # pretend the add_method never happenned. it hasn't yet affected anything
670 undef Class::MOP::Instance->meta->{_package_cache_flag};
672 ## --------------------------------------------------------
673 ## Now close all the Class::MOP::* classes
676 # we don't need to inline the
677 # constructors or the accessors
678 # this only lengthens the compile
679 # time of the MOP, and gives us
680 # no actual benefits.
682 $_->meta->make_immutable(
683 inline_constructor => 1,
684 replace_constructor => 1,
685 constructor_name => "_new",
686 inline_accessors => 0,
692 Class::MOP::Attribute
698 Class::MOP::Method::Generated
700 Class::MOP::Method::Accessor
701 Class::MOP::Method::Constructor
702 Class::MOP::Method::Wrapped
713 Class::MOP - A Meta Object Protocol for Perl 5
717 This module is a fully functioning meta object protocol for the
718 Perl 5 object system. It makes no attempt to change the behavior or
719 characteristics of the Perl 5 object system, only to create a
720 protocol for its manipulation and introspection.
722 That said, it does attempt to create the tools for building a rich
723 set of extensions to the Perl 5 object system. Every attempt has been
724 made for these tools to keep to the spirit of the Perl 5 object
725 system that we all know and love.
727 This documentation is admittedly sparse on details, as time permits
728 I will try to improve them. For now, I suggest looking at the items
729 listed in the L<SEE ALSO> section for more information. In particular
730 the book "The Art of the Meta Object Protocol" was very influential
731 in the development of this system.
733 =head2 What is a Meta Object Protocol?
735 A meta object protocol is an API to an object system.
737 To be more specific, it is a set of abstractions of the components of
738 an object system (typically things like; classes, object, methods,
739 object attributes, etc.). These abstractions can then be used to both
740 inspect and manipulate the object system which they describe.
742 It can be said that there are two MOPs for any object system; the
743 implicit MOP, and the explicit MOP. The implicit MOP handles things
744 like method dispatch or inheritance, which happen automatically as
745 part of how the object system works. The explicit MOP typically
746 handles the introspection/reflection features of the object system.
747 All object systems have implicit MOPs, without one, they would not
748 work. Explict MOPs however as less common, and depending on the
749 language can vary from restrictive (Reflection in Java or C#) to
750 wide open (CLOS is a perfect example).
752 =head2 Yet Another Class Builder!! Why?
754 This is B<not> a class builder so much as it is a I<class builder
755 B<builder>>. My intent is that an end user does not use this module
756 directly, but instead this module is used by module authors to
757 build extensions and features onto the Perl 5 object system.
759 =head2 Who is this module for?
761 This module is specifically for anyone who has ever created or
762 wanted to create a module for the Class:: namespace. The tools which
763 this module will provide will hopefully make it easier to do more
764 complex things with Perl 5 classes by removing such barriers as
765 the need to hack the symbol tables, or understand the fine details
768 =head2 What changes do I have to make to use this module?
770 This module was designed to be as unintrusive as possible. Many of
771 its features are accessible without B<any> change to your existsing
772 code at all. It is meant to be a compliment to your existing code and
773 not an intrusion on your code base. Unlike many other B<Class::>
774 modules, this module B<does not> require you subclass it, or even that
775 you C<use> it in within your module's package.
777 The only features which requires additions to your code are the
778 attribute handling and instance construction features, and these are
779 both completely optional features. The only reason for this is because
780 Perl 5's object system does not actually have these features built
781 in. More information about this feature can be found below.
783 =head2 A Note about Performance?
785 It is a common misconception that explict MOPs are performance drains.
786 But this is not a universal truth at all, it is an side-effect of
787 specific implementations. For instance, using Java reflection is much
788 slower because the JVM cannot take advantage of any compiler
789 optimizations, and the JVM has to deal with much more runtime type
790 information as well. Reflection in C# is marginally better as it was
791 designed into the language and runtime (the CLR). In contrast, CLOS
792 (the Common Lisp Object System) was built to support an explicit MOP,
793 and so performance is tuned for it.
795 This library in particular does it's absolute best to avoid putting
796 B<any> drain at all upon your code's performance. In fact, by itself
797 it does nothing to affect your existing code. So you only pay for
798 what you actually use.
800 =head2 About Metaclass compatibility
802 This module makes sure that all metaclasses created are both upwards
803 and downwards compatible. The topic of metaclass compatibility is
804 highly esoteric and is something only encountered when doing deep and
805 involved metaclass hacking. There are two basic kinds of metaclass
806 incompatibility; upwards and downwards.
808 Upwards metaclass compatibility means that the metaclass of a
809 given class is either the same as (or a subclass of) all of the
812 Downward metaclass compatibility means that the metaclasses of a
813 given class's anscestors are all either the same as (or a subclass
816 Here is a diagram showing a set of two classes (C<A> and C<B>) and
817 two metaclasses (C<Meta::A> and C<Meta::B>) which have correct
818 metaclass compatibility both upwards and downwards.
820 +---------+ +---------+
821 | Meta::A |<----| Meta::B | <....... (instance of )
822 +---------+ +---------+ <------- (inherits from)
825 +---------+ +---------+
827 +---------+ +---------+
829 As I said this is a highly esoteric topic and one you will only run
830 into if you do a lot of subclassing of B<Class::MOP::Class>. If you
831 are interested in why this is an issue see the paper
832 I<Uniform and safe metaclass composition> linked to in the
833 L<SEE ALSO> section of this document.
835 =head2 Using custom metaclasses
837 Always use the metaclass pragma when using a custom metaclass, this
838 will ensure the proper initialization order and not accidentely
839 create an incorrect type of metaclass for you. This is a very rare
840 problem, and one which can only occur if you are doing deep metaclass
841 programming. So in other words, don't worry about it.
845 The protocol is divided into 4 main sub-protocols:
849 =item The Class protocol
851 This provides a means of manipulating and introspecting a Perl 5
852 class. It handles all of symbol table hacking for you, and provides
853 a rich set of methods that go beyond simple package introspection.
855 See L<Class::MOP::Class> for more details.
857 =item The Attribute protocol
859 This provides a consistent represenation for an attribute of a
860 Perl 5 class. Since there are so many ways to create and handle
861 attributes in Perl 5 OO, this attempts to provide as much of a
862 unified approach as possible, while giving the freedom and
863 flexibility to subclass for specialization.
865 See L<Class::MOP::Attribute> for more details.
867 =item The Method protocol
869 This provides a means of manipulating and introspecting methods in
870 the Perl 5 object system. As with attributes, there are many ways to
871 approach this topic, so we try to keep it pretty basic, while still
872 making it possible to extend the system in many ways.
874 See L<Class::MOP::Method> for more details.
876 =item The Instance protocol
878 This provides a layer of abstraction for creating object instances.
879 Since the other layers use this protocol, it is relatively easy to
880 change the type of your instances from the default HASH ref to other
881 types of references. Several examples are provided in the F<examples/>
882 directory included in this distribution.
884 See L<Class::MOP::Instance> for more details.
894 =item I<IS_RUNNING_ON_5_10>
896 We set this constant depending on what version perl we are on, this
897 allows us to take advantage of new 5.10 features and stay backwards
902 Whether or not C<mro> provides C<get_isarev>, a much faster way to get all the
903 subclasses of a certain class.
907 =head2 Utility functions
911 =item B<load_class ($class_name)>
913 This will load a given C<$class_name> and if it does not have an
914 already initialized metaclass, then it will intialize one for it.
915 This function can be used in place of tricks like
916 C<eval "use $module"> or using C<require>.
918 =item B<is_class_loaded ($class_name)>
920 This will return a boolean depending on if the C<$class_name> has
923 NOTE: This does a basic check of the symbol table to try and
924 determine as best it can if the C<$class_name> is loaded, it
925 is probably correct about 99% of the time.
927 =item B<check_package_cache_flag ($pkg)>
929 This will return an integer that is managed by C<Class::MOP::Class>
930 to determine if a module's symbol table has been altered.
932 In Perl 5.10 or greater, this flag is package specific. However in
933 versions prior to 5.10, this will use the C<PL_sub_generation> variable
934 which is not package specific.
936 =item B<get_code_info ($code)>
938 This function returns two values, the name of the package the C<$code>
939 is from and the name of the C<$code> itself. This is used by several
940 elements of the MOP to detemine where a given C<$code> reference is from.
942 =item B<subname ($name, $code)>
944 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
946 If possible, we will load the L<Sub::Name> module and this will function
947 as C<Sub::Name::subname> does, otherwise it will just return the C<$code>
950 =item B<in_global_destruction>
952 If L<Devel::GlobalDestruction> is available, this returns true under global
955 Otherwise it's a constant returning false.
959 =head2 Metaclass cache functions
961 Class::MOP holds a cache of metaclasses, the following are functions
962 (B<not methods>) which can be used to access that cache. It is not
963 recommended that you mess with this, bad things could happen. But if
964 you are brave and willing to risk it, go for it.
968 =item B<get_all_metaclasses>
970 This will return an hash of all the metaclass instances that have
971 been cached by B<Class::MOP::Class> keyed by the package name.
973 =item B<get_all_metaclass_instances>
975 This will return an array of all the metaclass instances that have
976 been cached by B<Class::MOP::Class>.
978 =item B<get_all_metaclass_names>
980 This will return an array of all the metaclass names that have
981 been cached by B<Class::MOP::Class>.
983 =item B<get_metaclass_by_name ($name)>
985 This will return a cached B<Class::MOP::Class> instance of nothing
986 if no metaclass exist by that C<$name>.
988 =item B<store_metaclass_by_name ($name, $meta)>
990 This will store a metaclass in the cache at the supplied C<$key>.
992 =item B<weaken_metaclass ($name)>
994 In rare cases it is desireable to store a weakened reference in
995 the metaclass cache. This function will weaken the reference to
996 the metaclass stored in C<$name>.
998 =item B<does_metaclass_exist ($name)>
1000 This will return true of there exists a metaclass stored in the
1001 C<$name> key and return false otherwise.
1003 =item B<remove_metaclass_by_name ($name)>
1005 This will remove a the metaclass stored in the C<$name> key.
1013 There are very few books out on Meta Object Protocols and Metaclasses
1014 because it is such an esoteric topic. The following books are really
1015 the only ones I have found. If you know of any more, B<I<please>>
1016 email me and let me know, I would love to hear about them.
1020 =item "The Art of the Meta Object Protocol"
1022 =item "Advances in Object-Oriented Metalevel Architecture and Reflection"
1024 =item "Putting MetaClasses to Work"
1026 =item "Smalltalk: The Language"
1034 =item Uniform and safe metaclass composition
1036 An excellent paper by the people who brought us the original Traits paper.
1037 This paper is on how Traits can be used to do safe metaclass composition,
1038 and offers an excellent introduction section which delves into the topic of
1039 metaclass compatibility.
1041 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
1043 =item Safe Metaclass Programming
1045 This paper seems to precede the above paper, and propose a mix-in based
1046 approach as opposed to the Traits based approach. Both papers have similar
1047 information on the metaclass compatibility problem space.
1049 L<http://citeseer.ist.psu.edu/37617.html>
1057 =item The Perl 6 MetaModel work in the Pugs project
1061 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
1063 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1073 =item CPAN Module Review of Class::MOP
1075 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1079 =head1 SIMILAR MODULES
1081 As I have said above, this module is a class-builder-builder, so it is
1082 not the same thing as modules like L<Class::Accessor> and
1083 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1084 with similar goals to this module. The one I have found which is most
1085 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1086 creates are very different from this modules.
1090 All complex software has bugs lurking in it, and this module is no
1091 exception. If you find a bug please either email me, or add the bug
1094 =head1 ACKNOWLEDGEMENTS
1100 Thanks to Rob for actually getting the development of this module kick-started.
1106 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1108 B<with contributions from:>
1110 Brandon (blblack) Black
1112 Guillermo (groditi) Roditi
1116 Rob (robkinyon) Kinyon
1118 Yuval (nothingmuch) Kogman
1120 Scott (konobi) McWhirter
1122 =head1 COPYRIGHT AND LICENSE
1124 Copyright 2006-2008 by Infinity Interactive, Inc.
1126 L<http://www.iinteractive.com>
1128 This library is free software; you can redistribute it and/or modify
1129 it under the same terms as Perl itself.