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 }
211 ## --------------------------------------------------------
212 ## Class::MOP::Module
215 # yeah this is kind of stretching things a bit,
216 # but truthfully the version should be an attribute
217 # of the Module, the weirdness comes from having to
218 # stick to Perl 5 convention and store it in the
219 # $VERSION package variable. Basically if you just
220 # squint at it, it will look how you want it to look.
221 # Either as a package variable, or as a attribute of
222 # the metaclass, isn't abstraction great :)
224 Class::MOP::Module->meta->add_attribute(
225 Class::MOP::Attribute->new('version' => (
228 # we just alias the original method
229 # rather than re-produce it here
230 'version' => \&Class::MOP::Module::version
233 default => sub { \undef }
238 # By following the same conventions as version here,
239 # we are opening up the possibility that people can
240 # use the $AUTHORITY in non-Class::MOP modules as
243 Class::MOP::Module->meta->add_attribute(
244 Class::MOP::Attribute->new('authority' => (
247 # we just alias the original method
248 # rather than re-produce it here
249 'authority' => \&Class::MOP::Module::authority
252 default => sub { \undef }
256 ## --------------------------------------------------------
259 Class::MOP::Class->meta->add_attribute(
260 Class::MOP::Attribute->new('attributes' => (
262 # NOTE: we need to do this in order
263 # for the instance meta-object to
264 # not fall into meta-circular death
266 # we just alias the original method
267 # rather than re-produce it here
268 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
270 default => sub { {} }
274 Class::MOP::Class->meta->add_attribute(
275 Class::MOP::Attribute->new('methods' => (
278 # we just alias the original method
279 # rather than re-produce it here
280 'get_method_map' => \&Class::MOP::Class::get_method_map
282 default => sub { {} }
286 Class::MOP::Class->meta->add_attribute(
287 Class::MOP::Attribute->new('superclasses' => (
290 # we just alias the original method
291 # rather than re-produce it here
292 'superclasses' => \&Class::MOP::Class::superclasses
295 default => sub { \undef }
299 Class::MOP::Class->meta->add_attribute(
300 Class::MOP::Attribute->new('attribute_metaclass' => (
303 # we just alias the original method
304 # rather than re-produce it here
305 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
307 default => 'Class::MOP::Attribute',
311 Class::MOP::Class->meta->add_attribute(
312 Class::MOP::Attribute->new('method_metaclass' => (
315 # we just alias the original method
316 # rather than re-produce it here
317 'method_metaclass' => \&Class::MOP::Class::method_metaclass
319 default => 'Class::MOP::Method',
323 Class::MOP::Class->meta->add_attribute(
324 Class::MOP::Attribute->new('instance_metaclass' => (
326 # NOTE: we need to do this in order
327 # for the instance meta-object to
328 # not fall into meta-circular death
330 # we just alias the original method
331 # rather than re-produce it here
332 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
334 default => 'Class::MOP::Instance',
339 # we don't actually need to tie the knot with
340 # Class::MOP::Class here, it is actually handled
341 # within Class::MOP::Class itself in the
342 # construct_class_instance method.
344 ## --------------------------------------------------------
345 ## Class::MOP::Attribute
347 Class::MOP::Attribute->meta->add_attribute(
348 Class::MOP::Attribute->new('name' => (
350 # NOTE: we need to do this in order
351 # for the instance meta-object to
352 # not fall into meta-circular death
354 # we just alias the original method
355 # rather than re-produce it here
356 'name' => \&Class::MOP::Attribute::name
361 Class::MOP::Attribute->meta->add_attribute(
362 Class::MOP::Attribute->new('associated_class' => (
364 # NOTE: we need to do this in order
365 # for the instance meta-object to
366 # not fall into meta-circular death
368 # we just alias the original method
369 # rather than re-produce it here
370 'associated_class' => \&Class::MOP::Attribute::associated_class
375 Class::MOP::Attribute->meta->add_attribute(
376 Class::MOP::Attribute->new('accessor' => (
377 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
378 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
382 Class::MOP::Attribute->meta->add_attribute(
383 Class::MOP::Attribute->new('reader' => (
384 reader => { 'reader' => \&Class::MOP::Attribute::reader },
385 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
389 Class::MOP::Attribute->meta->add_attribute(
390 Class::MOP::Attribute->new('initializer' => (
391 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
392 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
396 Class::MOP::Attribute->meta->add_attribute(
397 Class::MOP::Attribute->new('writer' => (
398 reader => { 'writer' => \&Class::MOP::Attribute::writer },
399 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
403 Class::MOP::Attribute->meta->add_attribute(
404 Class::MOP::Attribute->new('predicate' => (
405 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
406 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
410 Class::MOP::Attribute->meta->add_attribute(
411 Class::MOP::Attribute->new('clearer' => (
412 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
413 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
417 Class::MOP::Attribute->meta->add_attribute(
418 Class::MOP::Attribute->new('builder' => (
419 reader => { 'builder' => \&Class::MOP::Attribute::builder },
420 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
424 Class::MOP::Attribute->meta->add_attribute(
425 Class::MOP::Attribute->new('init_arg' => (
426 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
427 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
431 Class::MOP::Attribute->meta->add_attribute(
432 Class::MOP::Attribute->new('default' => (
433 # default has a custom 'reader' method ...
434 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
438 Class::MOP::Attribute->meta->add_attribute(
439 Class::MOP::Attribute->new('associated_methods' => (
440 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
441 default => sub { [] }
445 Class::MOP::Attribute->meta->add_method('clone' => sub {
447 $self->meta->clone_object($self, @_);
450 ## --------------------------------------------------------
451 ## Class::MOP::Method
452 Class::MOP::Method->meta->add_attribute(
453 Class::MOP::Attribute->new('body' => (
454 reader => { 'body' => \&Class::MOP::Method::body },
458 Class::MOP::Method->meta->add_attribute(
459 Class::MOP::Attribute->new('associated_metaclass' => (
460 reader => { 'associated_metaclass' => \&Class::MOP::Method::associated_metaclass },
464 Class::MOP::Method->meta->add_attribute(
465 Class::MOP::Attribute->new('package_name' => (
466 reader => { 'package_name' => \&Class::MOP::Method::package_name },
470 Class::MOP::Method->meta->add_attribute(
471 Class::MOP::Attribute->new('name' => (
472 reader => { 'name' => \&Class::MOP::Method::name },
476 Class::MOP::Method->meta->add_method('clone' => sub {
478 $self->meta->clone_object($self, @_);
481 ## --------------------------------------------------------
482 ## Class::MOP::Method::Wrapped
485 # the way this item is initialized, this
486 # really does not follow the standard
487 # practices of attributes, but we put
488 # it here for completeness
489 Class::MOP::Method::Wrapped->meta->add_attribute(
490 Class::MOP::Attribute->new('modifier_table')
493 ## --------------------------------------------------------
494 ## Class::MOP::Method::Generated
496 Class::MOP::Method::Generated->meta->add_attribute(
497 Class::MOP::Attribute->new('is_inline' => (
498 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
503 Class::MOP::Method::Generated->meta->add_method('new' => sub {
504 my ($class, %options) = @_;
505 ($options{package_name} && $options{name})
506 || confess "You must supply the package_name and name parameters";
507 my $self = $class->_new(%options);
508 $self->initialize_body;
512 ## --------------------------------------------------------
513 ## Class::MOP::Method::Accessor
515 Class::MOP::Method::Accessor->meta->add_attribute(
516 Class::MOP::Attribute->new('attribute' => (
518 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
523 Class::MOP::Method::Accessor->meta->add_attribute(
524 Class::MOP::Attribute->new('accessor_type' => (
525 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
529 Class::MOP::Method::Accessor->meta->add_method('new' => sub {
533 (exists $options{attribute})
534 || confess "You must supply an attribute to construct with";
536 (exists $options{accessor_type})
537 || confess "You must supply an accessor_type to construct with";
539 (Scalar::Util::blessed($options{attribute}) && $options{attribute}->isa('Class::MOP::Attribute'))
540 || confess "You must supply an attribute which is a 'Class::MOP::Attribute' instance";
542 ($options{package_name} && $options{name})
543 || confess "You must supply the package_name and name parameters";
545 # return the new object
546 my $self = $class->_new(%options);
548 # we don't want this creating
549 # a cycle in the code, if not
551 Scalar::Util::weaken($self->{'attribute'});
553 $self->initialize_body;
559 ## --------------------------------------------------------
560 ## Class::MOP::Method::Constructor
562 Class::MOP::Method::Constructor->meta->add_attribute(
563 Class::MOP::Attribute->new('options' => (
565 'options' => \&Class::MOP::Method::Constructor::options
567 default => sub { +{} }
571 Class::MOP::Method::Constructor->meta->add_attribute(
572 Class::MOP::Attribute->new('associated_metaclass' => (
573 init_arg => "metaclass", # FIXME alias and rename
575 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
580 Class::MOP::Method::Constructor->meta->add_method('new' => sub {
584 (Scalar::Util::blessed $options{metaclass} && $options{metaclass}->isa('Class::MOP::Class'))
585 || confess "You must pass a metaclass instance if you want to inline"
586 if $options{is_inline};
588 ($options{package_name} && $options{name})
589 || confess "You must supply the package_name and name parameters";
591 # return the new object
592 my $self = $class->_new(%options);
594 # we don't want this creating
595 # a cycle in the code, if not
597 Scalar::Util::weaken($self->{'associated_metaclass'});
599 $self->initialize_body;
604 ## --------------------------------------------------------
605 ## Class::MOP::Instance
608 # these don't yet do much of anything, but are just
609 # included for completeness
611 Class::MOP::Instance->meta->add_attribute(
612 Class::MOP::Attribute->new('associated_metaclass',
613 reader => { associated_metaclass => \&Class::MOP::Instance::associated_metaclass },
617 Class::MOP::Instance->meta->add_attribute(
618 Class::MOP::Attribute->new('_class_name',
620 reader => { _class_name => \&Class::MOP::Instance::_class_name },
621 #lazy => 1, # not yet supported by Class::MOP but out our version does it anyway
622 #default => sub { $_[0]->associated_metaclass->name },
626 Class::MOP::Instance->meta->add_attribute(
627 Class::MOP::Attribute->new('attributes',
628 reader => { attributes => \&Class::MOP::Instance::attributes },
632 Class::MOP::Instance->meta->add_attribute(
633 Class::MOP::Attribute->new('slots',
634 reader => { slots => \&Class::MOP::Instance::slots },
638 Class::MOP::Instance->meta->add_attribute(
639 Class::MOP::Attribute->new('slot_hash',
640 reader => { slot_hash => \&Class::MOP::Instance::slot_hash },
645 # we need the meta instance of the meta instance to be created now, in order
646 # for the constructor to be able to use it
647 Class::MOP::Instance->meta->get_meta_instance;
649 Class::MOP::Instance->meta->add_method('new' => sub {
651 my $options = $class->BUILDARGS(@_);
653 my $self = $class->_new(%$options);
655 Scalar::Util::weaken($self->{'associated_metaclass'});
660 # pretend the add_method never happenned. it hasn't yet affected anything
661 undef Class::MOP::Instance->meta->{_package_cache_flag};
663 ## --------------------------------------------------------
664 ## Now close all the Class::MOP::* classes
667 # we don't need to inline the
668 # constructors or the accessors
669 # this only lengthens the compile
670 # time of the MOP, and gives us
671 # 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 =head2 Utility functions
902 =item B<load_class ($class_name)>
904 This will load a given C<$class_name> and if it does not have an
905 already initialized metaclass, then it will intialize one for it.
906 This function can be used in place of tricks like
907 C<eval "use $module"> or using C<require>.
909 =item B<is_class_loaded ($class_name)>
911 This will return a boolean depending on if the C<$class_name> has
914 NOTE: This does a basic check of the symbol table to try and
915 determine as best it can if the C<$class_name> is loaded, it
916 is probably correct about 99% of the time.
918 =item B<check_package_cache_flag ($pkg)>
920 This will return an integer that is managed by C<Class::MOP::Class>
921 to determine if a module's symbol table has been altered.
923 In Perl 5.10 or greater, this flag is package specific. However in
924 versions prior to 5.10, this will use the C<PL_sub_generation> variable
925 which is not package specific.
927 =item B<get_code_info ($code)>
929 This function returns two values, the name of the package the C<$code>
930 is from and the name of the C<$code> itself. This is used by several
931 elements of the MOP to detemine where a given C<$code> reference is from.
933 =item B<subname ($name, $code)>
935 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
937 If possible, we will load the L<Sub::Name> module and this will function
938 as C<Sub::Name::subname> does, otherwise it will just return the C<$code>
941 =item B<in_global_destruction>
943 If L<Devel::GlobalDestruction> is available, this returns true under global
946 Otherwise it's a constant returning false.
950 =head2 Metaclass cache functions
952 Class::MOP holds a cache of metaclasses, the following are functions
953 (B<not methods>) which can be used to access that cache. It is not
954 recommended that you mess with this, bad things could happen. But if
955 you are brave and willing to risk it, go for it.
959 =item B<get_all_metaclasses>
961 This will return an hash of all the metaclass instances that have
962 been cached by B<Class::MOP::Class> keyed by the package name.
964 =item B<get_all_metaclass_instances>
966 This will return an array of all the metaclass instances that have
967 been cached by B<Class::MOP::Class>.
969 =item B<get_all_metaclass_names>
971 This will return an array of all the metaclass names that have
972 been cached by B<Class::MOP::Class>.
974 =item B<get_metaclass_by_name ($name)>
976 This will return a cached B<Class::MOP::Class> instance of nothing
977 if no metaclass exist by that C<$name>.
979 =item B<store_metaclass_by_name ($name, $meta)>
981 This will store a metaclass in the cache at the supplied C<$key>.
983 =item B<weaken_metaclass ($name)>
985 In rare cases it is desireable to store a weakened reference in
986 the metaclass cache. This function will weaken the reference to
987 the metaclass stored in C<$name>.
989 =item B<does_metaclass_exist ($name)>
991 This will return true of there exists a metaclass stored in the
992 C<$name> key and return false otherwise.
994 =item B<remove_metaclass_by_name ($name)>
996 This will remove a the metaclass stored in the C<$name> key.
1004 There are very few books out on Meta Object Protocols and Metaclasses
1005 because it is such an esoteric topic. The following books are really
1006 the only ones I have found. If you know of any more, B<I<please>>
1007 email me and let me know, I would love to hear about them.
1011 =item "The Art of the Meta Object Protocol"
1013 =item "Advances in Object-Oriented Metalevel Architecture and Reflection"
1015 =item "Putting MetaClasses to Work"
1017 =item "Smalltalk: The Language"
1025 =item Uniform and safe metaclass composition
1027 An excellent paper by the people who brought us the original Traits paper.
1028 This paper is on how Traits can be used to do safe metaclass composition,
1029 and offers an excellent introduction section which delves into the topic of
1030 metaclass compatibility.
1032 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
1034 =item Safe Metaclass Programming
1036 This paper seems to precede the above paper, and propose a mix-in based
1037 approach as opposed to the Traits based approach. Both papers have similar
1038 information on the metaclass compatibility problem space.
1040 L<http://citeseer.ist.psu.edu/37617.html>
1048 =item The Perl 6 MetaModel work in the Pugs project
1052 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
1054 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1064 =item CPAN Module Review of Class::MOP
1066 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1070 =head1 SIMILAR MODULES
1072 As I have said above, this module is a class-builder-builder, so it is
1073 not the same thing as modules like L<Class::Accessor> and
1074 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1075 with similar goals to this module. The one I have found which is most
1076 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1077 creates are very different from this modules.
1081 All complex software has bugs lurking in it, and this module is no
1082 exception. If you find a bug please either email me, or add the bug
1085 =head1 ACKNOWLEDGEMENTS
1091 Thanks to Rob for actually getting the development of this module kick-started.
1097 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1099 B<with contributions from:>
1101 Brandon (blblack) Black
1103 Guillermo (groditi) Roditi
1107 Rob (robkinyon) Kinyon
1109 Yuval (nothingmuch) Kogman
1111 Scott (konobi) McWhirter
1113 =head1 COPYRIGHT AND LICENSE
1115 Copyright 2006-2008 by Infinity Interactive, Inc.
1117 L<http://www.iinteractive.com>
1119 This library is free software; you can redistribute it and/or modify
1120 it under the same terms as Perl itself.