10 use Scalar::Util 'weaken';
12 use Class::MOP::Class;
13 use Class::MOP::Attribute;
14 use Class::MOP::Method;
16 use Class::MOP::Immutable;
19 our $VERSION = '0.56';
20 our $AUTHORITY = 'cpan:STEVAN';
22 *IS_RUNNING_ON_5_10 = ($] < 5.009_005)
27 # we may not use this yet, but once
28 # the get_code_info XS gets merged
29 # upstream to it, we will always use
30 # it. But for now it is just kinda
33 require Sub::Identify;
35 # stash these for a sec, and see how things go
36 my $_PP_subname = sub { $_[1] };
37 my $_PP_get_code_info = sub ($) {
39 Sub::Identify::stash_name($_[0]),
40 Sub::Identify::sub_name($_[0])
44 if ($ENV{CLASS_MOP_NO_XS} == 1) {
46 # this is if you really want things
47 # to be slow, then you can force the
48 # no-XS rule this way, otherwise we
49 # make an effort to load as much of
52 no warnings 'prototype', 'redefine';
53 # get this from MRO::Compat ...
54 *check_package_cache_flag = \&MRO::Compat::__get_pkg_gen_pp;
55 # our own version of Sub::Name
56 *subname = $_PP_subname;
57 # and the Sub::Identify version of the get_code_info
58 *get_code_info = $_PP_get_code_info;
61 # now try our best to get as much
62 # of the XS loaded as possible
67 XSLoader::load( 'Class::MOP', $VERSION );
69 die $@ if $@ && $@ !~ /object version|loadable object/;
71 # okay, so the XS failed to load, so
72 # use the pure perl one instead.
73 *get_code_info = $_PP_get_code_info if $@;
76 # get it from MRO::Compat
77 *check_package_cache_flag = \&mro::get_pkg_gen;
79 # now try and load the Sub::Name
80 # module and use that as a means
81 # for naming our CVs, if not, we
82 # use the workaround instead.
83 if ( eval { require Sub::Name } ) {
85 #warn "Class::MOP::subname called with @_";
86 Sub::Name::subname(@_);
90 *subname = $_PP_subname;
96 # Metaclasses are singletons, so we cache them here.
97 # there is no need to worry about destruction though
98 # because they should die only when the program dies.
99 # After all, do package definitions even get reaped?
102 # means of accessing all the metaclasses that have
103 # been initialized thus far (for mugwumps obj browser)
104 sub get_all_metaclasses { %METAS }
105 sub get_all_metaclass_instances { values %METAS }
106 sub get_all_metaclass_names { keys %METAS }
107 sub get_metaclass_by_name { $METAS{$_[0]} }
108 sub store_metaclass_by_name { $METAS{$_[0]} = $_[1] }
109 sub weaken_metaclass { weaken($METAS{$_[0]}) }
110 sub does_metaclass_exist { exists $METAS{$_[0]} && defined $METAS{$_[0]} }
111 sub remove_metaclass_by_name { $METAS{$_[0]} = undef }
114 # We only cache metaclasses, meaning instances of
115 # Class::MOP::Class. We do not cache instance of
116 # Class::MOP::Package or Class::MOP::Module. Mostly
117 # because I don't yet see a good reason to do so.
122 # see if this is already
123 # loaded in the symbol table
124 return 1 if is_class_loaded($class);
125 # otherwise require it ...
126 my $file = $class . '.pm';
128 eval { CORE::require($file) };
129 confess "Could not load class ($class) because : $@" if $@;
130 unless (does_metaclass_exist($class)) {
131 eval { Class::MOP::Class->initialize($class) };
132 confess "Could not initialize class ($class) because : $@" if $@;
134 1; # return true if it worked
137 sub is_class_loaded {
140 return 1 if defined ${"${class}::VERSION"} || defined @{"${class}::ISA"};
141 foreach my $symbol (keys %{"${class}::"}) {
142 next if substr($symbol, -2, 2) eq '::';
143 return 1 if defined &{"${class}::${symbol}"};
149 ## ----------------------------------------------------------------------------
150 ## Setting up our environment ...
151 ## ----------------------------------------------------------------------------
152 ## Class::MOP needs to have a few things in the global perl environment so
153 ## that it can operate effectively. Those things are done here.
154 ## ----------------------------------------------------------------------------
156 # ... nothing yet actually ;)
158 ## ----------------------------------------------------------------------------
160 ## ----------------------------------------------------------------------------
161 ## The code below here is to bootstrap our MOP with itself. This is also
162 ## sometimes called "tying the knot". By doing this, we make it much easier
163 ## to extend the MOP through subclassing and such since now you can use the
164 ## MOP itself to extend itself.
166 ## Yes, I know, thats weird and insane, but it's a good thing, trust me :)
167 ## ----------------------------------------------------------------------------
169 # We need to add in the meta-attributes here so that
170 # any subclass of Class::MOP::* will be able to
171 # inherit them using &construct_instance
173 ## --------------------------------------------------------
174 ## Class::MOP::Package
176 Class::MOP::Package->meta->add_attribute(
177 Class::MOP::Attribute->new('$!package' => (
179 # NOTE: we need to do this in order
180 # for the instance meta-object to
181 # not fall into meta-circular death
183 # we just alias the original method
184 # rather than re-produce it here
185 'name' => \&Class::MOP::Package::name
187 init_arg => 'package',
191 Class::MOP::Package->meta->add_attribute(
192 Class::MOP::Attribute->new('%!namespace' => (
195 # we just alias the original method
196 # rather than re-produce it here
197 'namespace' => \&Class::MOP::Package::namespace
200 default => sub { \undef }
205 # use the metaclass to construct the meta-package
206 # which is a superclass of the metaclass itself :P
207 Class::MOP::Package->meta->add_method('initialize' => sub {
209 my $package_name = shift;
210 $class->meta->new_object('package' => $package_name, @_);
213 ## --------------------------------------------------------
214 ## Class::MOP::Module
217 # yeah this is kind of stretching things a bit,
218 # but truthfully the version should be an attribute
219 # of the Module, the weirdness comes from having to
220 # stick to Perl 5 convention and store it in the
221 # $VERSION package variable. Basically if you just
222 # squint at it, it will look how you want it to look.
223 # Either as a package variable, or as a attribute of
224 # the metaclass, isn't abstraction great :)
226 Class::MOP::Module->meta->add_attribute(
227 Class::MOP::Attribute->new('$!version' => (
230 # we just alias the original method
231 # rather than re-produce it here
232 'version' => \&Class::MOP::Module::version
235 default => sub { \undef }
240 # By following the same conventions as version here,
241 # we are opening up the possibility that people can
242 # use the $AUTHORITY in non-Class::MOP modules as
245 Class::MOP::Module->meta->add_attribute(
246 Class::MOP::Attribute->new('$!authority' => (
249 # we just alias the original method
250 # rather than re-produce it here
251 'authority' => \&Class::MOP::Module::authority
254 default => sub { \undef }
258 ## --------------------------------------------------------
261 Class::MOP::Class->meta->add_attribute(
262 Class::MOP::Attribute->new('%!attributes' => (
264 # NOTE: we need to do this in order
265 # for the instance meta-object to
266 # not fall into meta-circular death
268 # we just alias the original method
269 # rather than re-produce it here
270 'get_attribute_map' => \&Class::MOP::Class::get_attribute_map
272 init_arg => 'attributes',
273 default => sub { {} }
277 Class::MOP::Class->meta->add_attribute(
278 Class::MOP::Attribute->new('%!methods' => (
279 init_arg => 'methods',
282 # we just alias the original method
283 # rather than re-produce it here
284 'get_method_map' => \&Class::MOP::Class::get_method_map
286 default => sub { {} }
290 Class::MOP::Class->meta->add_attribute(
291 Class::MOP::Attribute->new('@!superclasses' => (
294 # we just alias the original method
295 # rather than re-produce it here
296 'superclasses' => \&Class::MOP::Class::superclasses
299 default => sub { \undef }
303 Class::MOP::Class->meta->add_attribute(
304 Class::MOP::Attribute->new('$!attribute_metaclass' => (
307 # we just alias the original method
308 # rather than re-produce it here
309 'attribute_metaclass' => \&Class::MOP::Class::attribute_metaclass
311 init_arg => 'attribute_metaclass',
312 default => 'Class::MOP::Attribute',
316 Class::MOP::Class->meta->add_attribute(
317 Class::MOP::Attribute->new('$!method_metaclass' => (
320 # we just alias the original method
321 # rather than re-produce it here
322 'method_metaclass' => \&Class::MOP::Class::method_metaclass
324 init_arg => 'method_metaclass',
325 default => 'Class::MOP::Method',
329 Class::MOP::Class->meta->add_attribute(
330 Class::MOP::Attribute->new('$!instance_metaclass' => (
332 # NOTE: we need to do this in order
333 # for the instance meta-object to
334 # not fall into meta-circular death
336 # we just alias the original method
337 # rather than re-produce it here
338 'instance_metaclass' => \&Class::MOP::Class::instance_metaclass
340 init_arg => 'instance_metaclass',
341 default => 'Class::MOP::Instance',
346 # we don't actually need to tie the knot with
347 # Class::MOP::Class here, it is actually handled
348 # within Class::MOP::Class itself in the
349 # construct_class_instance method.
351 ## --------------------------------------------------------
352 ## Class::MOP::Attribute
354 Class::MOP::Attribute->meta->add_attribute(
355 Class::MOP::Attribute->new('$!name' => (
358 # NOTE: we need to do this in order
359 # for the instance meta-object to
360 # not fall into meta-circular death
362 # we just alias the original method
363 # rather than re-produce it here
364 'name' => \&Class::MOP::Attribute::name
369 Class::MOP::Attribute->meta->add_attribute(
370 Class::MOP::Attribute->new('$!associated_class' => (
371 init_arg => 'associated_class',
373 # NOTE: we need to do this in order
374 # for the instance meta-object to
375 # not fall into meta-circular death
377 # we just alias the original method
378 # rather than re-produce it here
379 'associated_class' => \&Class::MOP::Attribute::associated_class
384 Class::MOP::Attribute->meta->add_attribute(
385 Class::MOP::Attribute->new('$!accessor' => (
386 init_arg => 'accessor',
387 reader => { 'accessor' => \&Class::MOP::Attribute::accessor },
388 predicate => { 'has_accessor' => \&Class::MOP::Attribute::has_accessor },
392 Class::MOP::Attribute->meta->add_attribute(
393 Class::MOP::Attribute->new('$!reader' => (
394 init_arg => 'reader',
395 reader => { 'reader' => \&Class::MOP::Attribute::reader },
396 predicate => { 'has_reader' => \&Class::MOP::Attribute::has_reader },
400 Class::MOP::Attribute->meta->add_attribute(
401 Class::MOP::Attribute->new('$!initializer' => (
402 init_arg => 'initializer',
403 reader => { 'initializer' => \&Class::MOP::Attribute::initializer },
404 predicate => { 'has_initializer' => \&Class::MOP::Attribute::has_initializer },
408 Class::MOP::Attribute->meta->add_attribute(
409 Class::MOP::Attribute->new('$!writer' => (
410 init_arg => 'writer',
411 reader => { 'writer' => \&Class::MOP::Attribute::writer },
412 predicate => { 'has_writer' => \&Class::MOP::Attribute::has_writer },
416 Class::MOP::Attribute->meta->add_attribute(
417 Class::MOP::Attribute->new('$!predicate' => (
418 init_arg => 'predicate',
419 reader => { 'predicate' => \&Class::MOP::Attribute::predicate },
420 predicate => { 'has_predicate' => \&Class::MOP::Attribute::has_predicate },
424 Class::MOP::Attribute->meta->add_attribute(
425 Class::MOP::Attribute->new('$!clearer' => (
426 init_arg => 'clearer',
427 reader => { 'clearer' => \&Class::MOP::Attribute::clearer },
428 predicate => { 'has_clearer' => \&Class::MOP::Attribute::has_clearer },
432 Class::MOP::Attribute->meta->add_attribute(
433 Class::MOP::Attribute->new('$!builder' => (
434 init_arg => 'builder',
435 reader => { 'builder' => \&Class::MOP::Attribute::builder },
436 predicate => { 'has_builder' => \&Class::MOP::Attribute::has_builder },
440 Class::MOP::Attribute->meta->add_attribute(
441 Class::MOP::Attribute->new('$!init_arg' => (
442 init_arg => 'init_arg',
443 reader => { 'init_arg' => \&Class::MOP::Attribute::init_arg },
444 predicate => { 'has_init_arg' => \&Class::MOP::Attribute::has_init_arg },
448 Class::MOP::Attribute->meta->add_attribute(
449 Class::MOP::Attribute->new('$!default' => (
450 init_arg => 'default',
451 # default has a custom 'reader' method ...
452 predicate => { 'has_default' => \&Class::MOP::Attribute::has_default },
456 Class::MOP::Attribute->meta->add_attribute(
457 Class::MOP::Attribute->new('@!associated_methods' => (
458 init_arg => 'associated_methods',
459 reader => { 'associated_methods' => \&Class::MOP::Attribute::associated_methods },
460 default => sub { [] }
464 # NOTE: (meta-circularity)
465 # This should be one of the last things done
466 # it will "tie the knot" with Class::MOP::Attribute
467 # so that it uses the attributes meta-objects
468 # to construct itself.
469 Class::MOP::Attribute->meta->add_method('new' => sub {
474 (defined $name && $name)
475 || confess "You must provide a name for the attribute";
476 $options{init_arg} = $name
477 if not exists $options{init_arg};
479 if(exists $options{builder}){
480 confess("builder must be a defined scalar value which is a method name")
481 if ref $options{builder} || !(defined $options{builder});
482 confess("Setting both default and builder is not allowed.")
483 if exists $options{default};
485 (Class::MOP::Attribute::is_default_a_coderef(\%options))
486 || confess("References are not allowed as default values, you must ".
487 "wrap the default of '$name' in a CODE reference (ex: sub { [] } and not [])")
488 if exists $options{default} && ref $options{default};
490 # return the new object
491 $class->meta->new_object(name => $name, %options);
494 Class::MOP::Attribute->meta->add_method('clone' => sub {
496 $self->meta->clone_object($self, @_);
499 ## --------------------------------------------------------
500 ## Class::MOP::Method
502 Class::MOP::Method->meta->add_attribute(
503 Class::MOP::Attribute->new('&!body' => (
505 reader => { 'body' => \&Class::MOP::Method::body },
509 Class::MOP::Method->meta->add_attribute(
510 Class::MOP::Attribute->new('$!package_name' => (
511 init_arg => 'package_name',
512 reader => { 'package_name' => \&Class::MOP::Method::package_name },
516 Class::MOP::Method->meta->add_attribute(
517 Class::MOP::Attribute->new('$!name' => (
519 reader => { 'name' => \&Class::MOP::Method::name },
523 Class::MOP::Method->meta->add_method('wrap' => sub {
528 ('CODE' eq (Scalar::Util::reftype($code) || ''))
529 || confess "You must supply a CODE reference to bless, not (" . ($code || 'undef') . ")";
531 # return the new object
532 $class->meta->new_object(body => $code, %options);
535 Class::MOP::Method->meta->add_method('clone' => sub {
537 $self->meta->clone_object($self, @_);
540 ## --------------------------------------------------------
541 ## Class::MOP::Method::Wrapped
544 # the way this item is initialized, this
545 # really does not follow the standard
546 # practices of attributes, but we put
547 # it here for completeness
548 Class::MOP::Method::Wrapped->meta->add_attribute(
549 Class::MOP::Attribute->new('%!modifier_table')
552 ## --------------------------------------------------------
553 ## Class::MOP::Method::Generated
555 Class::MOP::Method::Generated->meta->add_attribute(
556 Class::MOP::Attribute->new('$!is_inline' => (
557 init_arg => 'is_inline',
558 reader => { 'is_inline' => \&Class::MOP::Method::Generated::is_inline },
563 Class::MOP::Method::Generated->meta->add_method('new' => sub {
564 my ($class, %options) = @_;
565 my $self = $class->meta->new_object(%options);
566 $self->initialize_body;
570 ## --------------------------------------------------------
571 ## Class::MOP::Method::Accessor
573 Class::MOP::Method::Accessor->meta->add_attribute(
574 Class::MOP::Attribute->new('$!attribute' => (
575 init_arg => 'attribute',
577 'associated_attribute' => \&Class::MOP::Method::Accessor::associated_attribute
582 Class::MOP::Method::Accessor->meta->add_attribute(
583 Class::MOP::Attribute->new('$!accessor_type' => (
584 init_arg => 'accessor_type',
585 reader => { 'accessor_type' => \&Class::MOP::Method::Accessor::accessor_type },
589 Class::MOP::Method::Accessor->meta->add_method('new' => sub {
593 (exists $options{attribute})
594 || confess "You must supply an attribute to construct with";
596 (exists $options{accessor_type})
597 || confess "You must supply an accessor_type to construct with";
599 (Scalar::Util::blessed($options{attribute}) && $options{attribute}->isa('Class::MOP::Attribute'))
600 || confess "You must supply an attribute which is a 'Class::MOP::Attribute' instance";
602 # return the new object
603 my $self = $class->meta->new_object(%options);
605 # we don't want this creating
606 # a cycle in the code, if not
608 Scalar::Util::weaken($self->{'$!attribute'});
610 $self->initialize_body;
616 ## --------------------------------------------------------
617 ## Class::MOP::Method::Constructor
619 Class::MOP::Method::Constructor->meta->add_attribute(
620 Class::MOP::Attribute->new('%!options' => (
621 init_arg => 'options',
623 'options' => \&Class::MOP::Method::Constructor::options
625 default => sub { +{} }
629 Class::MOP::Method::Constructor->meta->add_attribute(
630 Class::MOP::Attribute->new('$!associated_metaclass' => (
631 init_arg => 'metaclass',
633 'associated_metaclass' => \&Class::MOP::Method::Constructor::associated_metaclass
638 Class::MOP::Method::Constructor->meta->add_method('new' => sub {
642 (Scalar::Util::blessed $options{metaclass} && $options{metaclass}->isa('Class::MOP::Class'))
643 || confess "You must pass a metaclass instance if you want to inline"
644 if $options{is_inline};
646 # return the new object
647 my $self = $class->meta->new_object(%options);
649 # we don't want this creating
650 # a cycle in the code, if not
652 Scalar::Util::weaken($self->{'$!associated_metaclass'});
654 $self->initialize_body;
659 ## --------------------------------------------------------
660 ## Class::MOP::Instance
663 # these don't yet do much of anything, but are just
664 # included for completeness
666 Class::MOP::Instance->meta->add_attribute(
667 Class::MOP::Attribute->new('$!meta')
670 Class::MOP::Instance->meta->add_attribute(
671 Class::MOP::Attribute->new('@!slots')
674 ## --------------------------------------------------------
675 ## Now close all the Class::MOP::* classes
678 # we don't need to inline the
679 # constructors or the accessors
680 # this only lengthens the compile
681 # time of the MOP, and gives us
682 # no actual benefits.
684 $_->meta->make_immutable(
685 inline_constructor => 0,
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 =head2 Utility functions
906 =item B<load_class ($class_name)>
908 This will load a given C<$class_name> and if it does not have an
909 already initialized metaclass, then it will intialize one for it.
910 This function can be used in place of tricks like
911 C<eval "use $module"> or using C<require>.
913 =item B<is_class_loaded ($class_name)>
915 This will return a boolean depending on if the C<$class_name> has
918 NOTE: This does a basic check of the symbol table to try and
919 determine as best it can if the C<$class_name> is loaded, it
920 is probably correct about 99% of the time.
922 =item B<check_package_cache_flag ($pkg)>
924 This will return an integer that is managed by C<Class::MOP::Class>
925 to determine if a module's symbol table has been altered.
927 In Perl 5.10 or greater, this flag is package specific. However in
928 versions prior to 5.10, this will use the C<PL_sub_generation> variable
929 which is not package specific.
931 =item B<get_code_info ($code)>
933 This function returns two values, the name of the package the C<$code>
934 is from and the name of the C<$code> itself. This is used by several
935 elements of the MOP to detemine where a given C<$code> reference is from.
937 =item B<subname ($name, $code)>
939 B<NOTE: DO NOT USE THIS FUNCTION, IT IS FOR INTERNAL USE ONLY!>
941 If possible, we will load the L<Sub::Name> module and this will function
942 as C<Sub::Name::subname> does, otherwise it will just return the C<$code>
947 =head2 Metaclass cache functions
949 Class::MOP holds a cache of metaclasses, the following are functions
950 (B<not methods>) which can be used to access that cache. It is not
951 recommended that you mess with this, bad things could happen. But if
952 you are brave and willing to risk it, go for it.
956 =item B<get_all_metaclasses>
958 This will return an hash of all the metaclass instances that have
959 been cached by B<Class::MOP::Class> keyed by the package name.
961 =item B<get_all_metaclass_instances>
963 This will return an array of all the metaclass instances that have
964 been cached by B<Class::MOP::Class>.
966 =item B<get_all_metaclass_names>
968 This will return an array of all the metaclass names that have
969 been cached by B<Class::MOP::Class>.
971 =item B<get_metaclass_by_name ($name)>
973 This will return a cached B<Class::MOP::Class> instance of nothing
974 if no metaclass exist by that C<$name>.
976 =item B<store_metaclass_by_name ($name, $meta)>
978 This will store a metaclass in the cache at the supplied C<$key>.
980 =item B<weaken_metaclass ($name)>
982 In rare cases it is desireable to store a weakened reference in
983 the metaclass cache. This function will weaken the reference to
984 the metaclass stored in C<$name>.
986 =item B<does_metaclass_exist ($name)>
988 This will return true of there exists a metaclass stored in the
989 C<$name> key and return false otherwise.
991 =item B<remove_metaclass_by_name ($name)>
993 This will remove a the metaclass stored in the C<$name> key.
1001 There are very few books out on Meta Object Protocols and Metaclasses
1002 because it is such an esoteric topic. The following books are really
1003 the only ones I have found. If you know of any more, B<I<please>>
1004 email me and let me know, I would love to hear about them.
1008 =item "The Art of the Meta Object Protocol"
1010 =item "Advances in Object-Oriented Metalevel Architecture and Reflection"
1012 =item "Putting MetaClasses to Work"
1014 =item "Smalltalk: The Language"
1022 =item Uniform and safe metaclass composition
1024 An excellent paper by the people who brought us the original Traits paper.
1025 This paper is on how Traits can be used to do safe metaclass composition,
1026 and offers an excellent introduction section which delves into the topic of
1027 metaclass compatibility.
1029 L<http://www.iam.unibe.ch/~scg/Archive/Papers/Duca05ySafeMetaclassTrait.pdf>
1031 =item Safe Metaclass Programming
1033 This paper seems to precede the above paper, and propose a mix-in based
1034 approach as opposed to the Traits based approach. Both papers have similar
1035 information on the metaclass compatibility problem space.
1037 L<http://citeseer.ist.psu.edu/37617.html>
1045 =item The Perl 6 MetaModel work in the Pugs project
1049 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-MetaModel>
1051 =item L<http://svn.openfoundry.org/pugs/perl5/Perl6-ObjectSpace>
1061 =item CPAN Module Review of Class::MOP
1063 L<http://www.oreillynet.com/onlamp/blog/2006/06/cpan_module_review_classmop.html>
1067 =head1 SIMILAR MODULES
1069 As I have said above, this module is a class-builder-builder, so it is
1070 not the same thing as modules like L<Class::Accessor> and
1071 L<Class::MethodMaker>. That being said there are very few modules on CPAN
1072 with similar goals to this module. The one I have found which is most
1073 like this module is L<Class::Meta>, although it's philosophy and the MOP it
1074 creates are very different from this modules.
1078 All complex software has bugs lurking in it, and this module is no
1079 exception. If you find a bug please either email me, or add the bug
1082 =head1 ACKNOWLEDGEMENTS
1088 Thanks to Rob for actually getting the development of this module kick-started.
1094 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1096 B<with contributions from:>
1098 Brandon (blblack) Black
1100 Guillermo (groditi) Roditi
1104 Rob (robkinyon) Kinyon
1106 Yuval (nothingmuch) Kogman
1108 Scott (konobi) McWhirter
1110 =head1 COPYRIGHT AND LICENSE
1112 Copyright 2006-2008 by Infinity Interactive, Inc.
1114 L<http://www.iinteractive.com>
1116 This library is free software; you can redistribute it and/or modify
1117 it under the same terms as Perl itself.