2 package Class::MOP::Class;
8 use Scalar::Util 'blessed', 'reftype', 'weaken';
9 use Sub::Name 'subname';
10 use B 'svref_2object';
12 our $VERSION = '0.15';
14 use base 'Class::MOP::Module';
16 use Class::MOP::Instance;
20 sub meta { Class::MOP::Class->initialize(blessed($_[0]) || $_[0]) }
25 # we need a sufficiently annoying prefix
26 # this should suffice for now, this is
27 # used in a couple of places below, so
28 # need to put it up here for now.
29 my $ANON_CLASS_PREFIX = 'Class::MOP::Class::__ANON__::SERIAL::';
34 # Metaclasses are singletons, so we cache them here.
35 # there is no need to worry about destruction though
36 # because they should die only when the program dies.
37 # After all, do package definitions even get reaped?
40 # means of accessing all the metaclasses that have
41 # been initialized thus far (for mugwumps obj browser)
42 sub get_all_metaclasses { %METAS }
43 sub get_all_metaclass_instances { values %METAS }
44 sub get_all_metaclass_names { keys %METAS }
48 my $package_name = shift;
49 (defined $package_name && $package_name && !blessed($package_name))
50 || confess "You must pass a package name and it cannot be blessed";
51 $class->construct_class_instance(':package' => $package_name, @_);
56 my $package_name = shift;
57 (defined $package_name && $package_name && !blessed($package_name))
58 || confess "You must pass a package name and it cannot be blessed";
59 $METAS{$package_name} = undef;
60 $class->construct_class_instance(':package' => $package_name, @_);
63 # NOTE: (meta-circularity)
64 # this is a special form of &construct_instance
65 # (see below), which is used to construct class
66 # meta-object instances for any Class::MOP::*
67 # class. All other classes will use the more
68 # normal &construct_instance.
69 sub construct_class_instance {
72 my $package_name = $options{':package'};
73 (defined $package_name && $package_name)
74 || confess "You must pass a package name";
76 # return the metaclass if we have it cached,
77 # and it is still defined (it has not been
78 # reaped by DESTROY yet, which can happen
79 # annoyingly enough during global destruction)
80 return $METAS{$package_name}
81 if exists $METAS{$package_name} && defined $METAS{$package_name};
84 # we need to deal with the possibility
85 # of class immutability here, and then
86 # get the name of the class appropriately
87 $class = (blessed($class)
88 ? ($class->is_immutable
89 ? $class->get_mutable_metaclass_name()
93 $class = blessed($class) || $class;
94 # now create the metaclass
96 if ($class =~ /^Class::MOP::/) {
98 '$:package' => $package_name,
100 '$:attribute_metaclass' => $options{':attribute_metaclass'} || 'Class::MOP::Attribute',
101 '$:method_metaclass' => $options{':method_metaclass'} || 'Class::MOP::Method',
102 '$:instance_metaclass' => $options{':instance_metaclass'} || 'Class::MOP::Instance',
107 # it is safe to use meta here because
108 # class will always be a subclass of
109 # Class::MOP::Class, which defines meta
110 $meta = $class->meta->construct_instance(%options)
112 # and check the metaclass compatibility
113 $meta->check_metaclass_compatability();
114 $METAS{$package_name} = $meta;
116 # we need to weaken any anon classes
117 # so that they can call DESTROY properly
118 weaken($METAS{$package_name})
119 if $package_name =~ /^$ANON_CLASS_PREFIX/;
123 sub check_metaclass_compatability {
126 # this is always okay ...
127 return if blessed($self) eq 'Class::MOP::Class' &&
128 $self->instance_metaclass eq 'Class::MOP::Instance';
130 my @class_list = $self->class_precedence_list;
131 shift @class_list; # shift off $self->name
133 foreach my $class_name (@class_list) {
134 my $meta = $METAS{$class_name} || next;
137 # we need to deal with the possibility
138 # of class immutability here, and then
139 # get the name of the class appropriately
140 my $meta_type = ($meta->is_immutable
141 ? $meta->get_mutable_metaclass_name()
144 ($self->isa($meta_type))
145 || confess $self->name . "->meta => (" . (blessed($self)) . ")" .
146 " is not compatible with the " .
147 $class_name . "->meta => (" . ($meta_type) . ")";
149 # we also need to check that instance metaclasses
150 # are compatabile in the same the class.
151 ($self->instance_metaclass->isa($meta->instance_metaclass))
152 || confess $self->name . "->meta => (" . ($self->instance_metaclass) . ")" .
153 " is not compatible with the " .
154 $class_name . "->meta => (" . ($meta->instance_metaclass) . ")";
163 # this should be sufficient, if you have a
164 # use case where it is not, write a test and
166 my $ANON_CLASS_SERIAL = 0;
168 sub create_anon_class {
169 my ($class, %options) = @_;
170 my $package_name = $ANON_CLASS_PREFIX . ++$ANON_CLASS_SERIAL;
171 return $class->create($package_name, '0.00', %options);
176 # this will only get called for
177 # anon-classes, all other calls
178 # are assumed to occur during
179 # global destruction and so don't
180 # really need to be handled explicitly
183 return unless $self->name =~ /^$ANON_CLASS_PREFIX/;
184 my ($serial_id) = ($self->name =~ /^$ANON_CLASS_PREFIX(\d+)/);
186 foreach my $key (keys %{$ANON_CLASS_PREFIX . $serial_id}) {
187 delete ${$ANON_CLASS_PREFIX . $serial_id}{$key};
189 delete ${'main::' . $ANON_CLASS_PREFIX}{$serial_id . '::'};
192 # creating classes with MOP ...
195 my ($class, $package_name, $package_version, %options) = @_;
196 (defined $package_name && $package_name)
197 || confess "You must pass a package name";
198 my $code = "package $package_name;";
199 $code .= "\$$package_name\:\:VERSION = '$package_version';"
200 if defined $package_version;
202 confess "creation of $package_name failed : $@" if $@;
203 my $meta = $class->initialize($package_name);
205 $meta->add_method('meta' => sub {
206 $class->initialize(blessed($_[0]) || $_[0]);
209 $meta->superclasses(@{$options{superclasses}})
210 if exists $options{superclasses};
212 # process attributes first, so that they can
213 # install accessors, but locally defined methods
214 # can then overwrite them. It is maybe a little odd, but
215 # I think this should be the order of things.
216 if (exists $options{attributes}) {
217 foreach my $attr (@{$options{attributes}}) {
218 $meta->add_attribute($attr);
221 if (exists $options{methods}) {
222 foreach my $method_name (keys %{$options{methods}}) {
223 $meta->add_method($method_name, $options{methods}->{$method_name});
232 # all these attribute readers will be bootstrapped
233 # away in the Class::MOP bootstrap section
235 sub get_attribute_map { $_[0]->{'%:attributes'} }
236 sub attribute_metaclass { $_[0]->{'$:attribute_metaclass'} }
237 sub method_metaclass { $_[0]->{'$:method_metaclass'} }
238 sub instance_metaclass { $_[0]->{'$:instance_metaclass'} }
240 # Instance Construction & Cloning
245 # we need to protect the integrity of the
246 # Class::MOP::Class singletons here, so we
247 # delegate this to &construct_class_instance
248 # which will deal with the singletons
249 return $class->construct_class_instance(@_)
250 if $class->name->isa('Class::MOP::Class');
251 return $class->construct_instance(@_);
254 sub construct_instance {
255 my ($class, %params) = @_;
256 my $meta_instance = $class->get_meta_instance();
257 my $instance = $meta_instance->create_instance();
258 foreach my $attr ($class->compute_all_applicable_attributes()) {
259 $attr->initialize_instance_slot($meta_instance, $instance, \%params);
264 sub get_meta_instance {
266 return $class->instance_metaclass->new(
268 $class->compute_all_applicable_attributes()
274 my $instance = shift;
275 (blessed($instance) && $instance->isa($class->name))
276 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
278 # we need to protect the integrity of the
279 # Class::MOP::Class singletons here, they
280 # should not be cloned.
281 return $instance if $instance->isa('Class::MOP::Class');
282 $class->clone_instance($instance, @_);
286 my ($class, $instance, %params) = @_;
288 || confess "You can only clone instances, \$self is not a blessed instance";
289 my $meta_instance = $class->get_meta_instance();
290 my $clone = $meta_instance->clone_instance($instance);
291 foreach my $key (keys %params) {
292 next unless $meta_instance->is_valid_slot($key);
293 $meta_instance->set_slot_value($clone, $key, $params{$key});
305 @{$self->name . '::ISA'} = @supers;
307 # we need to check the metaclass
308 # compatability here so that we can
309 # be sure that the superclass is
310 # not potentially creating an issues
311 # we don't know about
312 $self->check_metaclass_compatability();
314 @{$self->name . '::ISA'};
317 sub class_precedence_list {
320 # We need to check for ciruclar inheirtance here.
321 # This will do nothing if all is well, and blow
322 # up otherwise. Yes, it's an ugly hack, better
323 # suggestions are welcome.
324 { ($self->name || return)->isa('This is a test for circular inheritance') }
325 # ... and now back to our regularly scheduled program
329 $self->initialize($_)->class_precedence_list()
330 } $self->superclasses()
337 my ($self, $method_name, $method) = @_;
338 (defined $method_name && $method_name)
339 || confess "You must define a method name";
340 # use reftype here to allow for blessed subs ...
341 ('CODE' eq (reftype($method) || ''))
342 || confess "Your code block must be a CODE reference";
343 my $full_method_name = ($self->name . '::' . $method_name);
345 $method = $self->method_metaclass->wrap($method) unless blessed($method);
348 no warnings 'redefine';
349 *{$full_method_name} = subname $full_method_name => $method;
353 my $fetch_and_prepare_method = sub {
354 my ($self, $method_name) = @_;
356 my $method = $self->get_method($method_name);
357 # if we dont have local ...
359 # try to find the next method
360 $method = $self->find_next_method_by_name($method_name);
361 # die if it does not exist
363 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
364 # and now make sure to wrap it
365 # even if it is already wrapped
366 # because we need a new sub ref
367 $method = Class::MOP::Method::Wrapped->wrap($method);
370 # now make sure we wrap it properly
371 $method = Class::MOP::Method::Wrapped->wrap($method)
372 unless $method->isa('Class::MOP::Method::Wrapped');
374 $self->add_method($method_name => $method);
378 sub add_before_method_modifier {
379 my ($self, $method_name, $method_modifier) = @_;
380 (defined $method_name && $method_name)
381 || confess "You must pass in a method name";
382 my $method = $fetch_and_prepare_method->($self, $method_name);
383 $method->add_before_modifier(subname ':before' => $method_modifier);
386 sub add_after_method_modifier {
387 my ($self, $method_name, $method_modifier) = @_;
388 (defined $method_name && $method_name)
389 || confess "You must pass in a method name";
390 my $method = $fetch_and_prepare_method->($self, $method_name);
391 $method->add_after_modifier(subname ':after' => $method_modifier);
394 sub add_around_method_modifier {
395 my ($self, $method_name, $method_modifier) = @_;
396 (defined $method_name && $method_name)
397 || confess "You must pass in a method name";
398 my $method = $fetch_and_prepare_method->($self, $method_name);
399 $method->add_around_modifier(subname ':around' => $method_modifier);
403 # the methods above used to be named like this:
404 # ${pkg}::${method}:(before|after|around)
405 # but this proved problematic when using one modifier
406 # to wrap multiple methods (something which is likely
407 # to happen pretty regularly IMO). So instead of naming
408 # it like this, I have chosen to just name them purely
409 # with their modifier names, like so:
410 # :(before|after|around)
411 # The fact is that in a stack trace, it will be fairly
412 # evident from the context what method they are attached
413 # to, and so don't need the fully qualified name.
417 my ($self, $method_name, $method) = @_;
418 (defined $method_name && $method_name)
419 || confess "You must define a method name";
420 # use reftype here to allow for blessed subs ...
421 ('CODE' eq (reftype($method) || ''))
422 || confess "Your code block must be a CODE reference";
423 my $full_method_name = ($self->name . '::' . $method_name);
425 $method = $self->method_metaclass->wrap($method) unless blessed($method);
428 no warnings 'redefine';
429 *{$full_method_name} = $method;
433 my ($self, $method_name) = @_;
434 (defined $method_name && $method_name)
435 || confess "You must define a method name";
437 my $sub_name = ($self->name . '::' . $method_name);
440 return 0 if !defined(&{$sub_name});
441 my $method = \&{$sub_name};
442 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
443 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
445 # at this point we are relatively sure
446 # it is our method, so we bless/wrap it
447 $self->method_metaclass->wrap($method) unless blessed($method);
452 my ($self, $method_name) = @_;
453 (defined $method_name && $method_name)
454 || confess "You must define a method name";
456 return unless $self->has_method($method_name);
459 return \&{$self->name . '::' . $method_name};
463 my ($self, $method_name) = @_;
464 (defined $method_name && $method_name)
465 || confess "You must define a method name";
467 my $removed_method = $self->get_method($method_name);
470 delete ${$self->name . '::'}{$method_name}
471 if defined $removed_method;
473 return $removed_method;
476 sub get_method_list {
479 grep { $self->has_method($_) } keys %{$self->name . '::'};
482 sub compute_all_applicable_methods {
485 # keep a record of what we have seen
486 # here, this will handle all the
487 # inheritence issues because we are
488 # using the &class_precedence_list
489 my (%seen_class, %seen_method);
490 foreach my $class ($self->class_precedence_list()) {
491 next if $seen_class{$class};
492 $seen_class{$class}++;
493 # fetch the meta-class ...
494 my $meta = $self->initialize($class);
495 foreach my $method_name ($meta->get_method_list()) {
496 next if exists $seen_method{$method_name};
497 $seen_method{$method_name}++;
499 name => $method_name,
501 code => $meta->get_method($method_name)
508 sub find_all_methods_by_name {
509 my ($self, $method_name) = @_;
510 (defined $method_name && $method_name)
511 || confess "You must define a method name to find";
513 # keep a record of what we have seen
514 # here, this will handle all the
515 # inheritence issues because we are
516 # using the &class_precedence_list
518 foreach my $class ($self->class_precedence_list()) {
519 next if $seen_class{$class};
520 $seen_class{$class}++;
521 # fetch the meta-class ...
522 my $meta = $self->initialize($class);
524 name => $method_name,
526 code => $meta->get_method($method_name)
527 } if $meta->has_method($method_name);
532 sub find_next_method_by_name {
533 my ($self, $method_name) = @_;
534 (defined $method_name && $method_name)
535 || confess "You must define a method name to find";
536 # keep a record of what we have seen
537 # here, this will handle all the
538 # inheritence issues because we are
539 # using the &class_precedence_list
541 my @cpl = $self->class_precedence_list();
542 shift @cpl; # discard ourselves
543 foreach my $class (@cpl) {
544 next if $seen_class{$class};
545 $seen_class{$class}++;
546 # fetch the meta-class ...
547 my $meta = $self->initialize($class);
548 return $meta->get_method($method_name)
549 if $meta->has_method($method_name);
558 # either we have an attribute object already
559 # or we need to create one from the args provided
560 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
561 # make sure it is derived from the correct type though
562 ($attribute->isa('Class::MOP::Attribute'))
563 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
564 $attribute->attach_to_class($self);
565 $attribute->install_accessors();
566 $self->get_attribute_map->{$attribute->name} = $attribute;
569 # in theory we have to tell everyone the slot structure may have changed
573 my ($self, $attribute_name) = @_;
574 (defined $attribute_name && $attribute_name)
575 || confess "You must define an attribute name";
576 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
580 my ($self, $attribute_name) = @_;
581 (defined $attribute_name && $attribute_name)
582 || confess "You must define an attribute name";
583 return $self->get_attribute_map->{$attribute_name}
584 if $self->has_attribute($attribute_name);
588 sub remove_attribute {
589 my ($self, $attribute_name) = @_;
590 (defined $attribute_name && $attribute_name)
591 || confess "You must define an attribute name";
592 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
593 return unless defined $removed_attribute;
594 delete $self->get_attribute_map->{$attribute_name};
595 $removed_attribute->remove_accessors();
596 $removed_attribute->detach_from_class();
597 return $removed_attribute;
600 sub get_attribute_list {
602 keys %{$self->get_attribute_map};
605 sub compute_all_applicable_attributes {
608 # keep a record of what we have seen
609 # here, this will handle all the
610 # inheritence issues because we are
611 # using the &class_precedence_list
612 my (%seen_class, %seen_attr);
613 foreach my $class ($self->class_precedence_list()) {
614 next if $seen_class{$class};
615 $seen_class{$class}++;
616 # fetch the meta-class ...
617 my $meta = $self->initialize($class);
618 foreach my $attr_name ($meta->get_attribute_list()) {
619 next if exists $seen_attr{$attr_name};
620 $seen_attr{$attr_name}++;
621 push @attrs => $meta->get_attribute($attr_name);
627 sub find_attribute_by_name {
628 my ($self, $attr_name) = @_;
629 # keep a record of what we have seen
630 # here, this will handle all the
631 # inheritence issues because we are
632 # using the &class_precedence_list
634 foreach my $class ($self->class_precedence_list()) {
635 next if $seen_class{$class};
636 $seen_class{$class}++;
637 # fetch the meta-class ...
638 my $meta = $self->initialize($class);
639 return $meta->get_attribute($attr_name)
640 if $meta->has_attribute($attr_name);
648 sub is_immutable { 0 }
651 return Class::MOP::Class::Immutable->make_metaclass_immutable(@_);
662 Class::MOP::Class - Class Meta Object
666 # assuming that class Foo
667 # has been defined, you can
669 # use this for introspection ...
671 # add a method to Foo ...
672 Foo->meta->add_method('bar' => sub { ... })
674 # get a list of all the classes searched
675 # the method dispatcher in the correct order
676 Foo->meta->class_precedence_list()
678 # remove a method from Foo
679 Foo->meta->remove_method('bar');
681 # or use this to actually create classes ...
683 Class::MOP::Class->create('Bar' => '0.01' => (
684 superclasses => [ 'Foo' ],
686 Class::MOP:::Attribute->new('$bar'),
687 Class::MOP:::Attribute->new('$baz'),
690 calculate_bar => sub { ... },
691 construct_baz => sub { ... }
697 This is the largest and currently most complex part of the Perl 5
698 meta-object protocol. It controls the introspection and
699 manipulation of Perl 5 classes (and it can create them too). The
700 best way to understand what this module can do, is to read the
701 documentation for each of it's methods.
705 =head2 Self Introspection
711 This will return a B<Class::MOP::Class> instance which is related
712 to this class. Thereby allowing B<Class::MOP::Class> to actually
715 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
716 bootstrap this module by installing a number of attribute meta-objects
717 into it's metaclass. This will allow this class to reap all the benifits
718 of the MOP when subclassing it.
720 =item B<get_all_metaclasses>
722 This will return an hash of all the metaclass instances that have
723 been cached by B<Class::MOP::Class> keyed by the package name.
725 =item B<get_all_metaclass_instances>
727 This will return an array of all the metaclass instances that have
728 been cached by B<Class::MOP::Class>.
730 =item B<get_all_metaclass_names>
732 This will return an array of all the metaclass names that have
733 been cached by B<Class::MOP::Class>.
737 =head2 Class construction
739 These methods will handle creating B<Class::MOP::Class> objects,
740 which can be used to both create new classes, and analyze
741 pre-existing classes.
743 This module will internally store references to all the instances
744 you create with these methods, so that they do not need to be
745 created any more than nessecary. Basically, they are singletons.
749 =item B<create ($package_name, ?$package_version,
750 superclasses =E<gt> ?@superclasses,
751 methods =E<gt> ?%methods,
752 attributes =E<gt> ?%attributes)>
754 This returns a B<Class::MOP::Class> object, bringing the specified
755 C<$package_name> into existence and adding any of the
756 C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
759 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
760 methods =E<gt> ?%methods,
761 attributes =E<gt> ?%attributes)>
763 This will create an anonymous class, it works much like C<create> but
764 it does not need a C<$package_name>. Instead it will create a suitably
765 unique package name for you to stash things into.
767 =item B<initialize ($package_name, %options)>
769 This initializes and returns returns a B<Class::MOP::Class> object
770 for a given a C<$package_name>.
772 =item B<reinitialize ($package_name, %options)>
774 This removes the old metaclass, and creates a new one in it's place.
775 Do B<not> use this unless you really know what you are doing, it could
776 very easily make a very large mess of your program.
778 =item B<construct_class_instance (%options)>
780 This will construct an instance of B<Class::MOP::Class>, it is
781 here so that we can actually "tie the knot" for B<Class::MOP::Class>
782 to use C<construct_instance> once all the bootstrapping is done. This
783 method is used internally by C<initialize> and should never be called
784 from outside of that method really.
786 =item B<check_metaclass_compatability>
788 This method is called as the very last thing in the
789 C<construct_class_instance> method. This will check that the
790 metaclass you are creating is compatible with the metaclasses of all
791 your ancestors. For more inforamtion about metaclass compatibility
792 see the C<About Metaclass compatibility> section in L<Class::MOP>.
796 =head2 Object instance construction and cloning
798 These methods are B<entirely optional>, it is up to you whether you want
803 =item B<instance_metaclass>
805 =item B<get_meta_instance>
807 =item B<new_object (%params)>
809 This is a convience method for creating a new object of the class, and
810 blessing it into the appropriate package as well. Ideally your class
811 would call a C<new> this method like so:
814 my ($class, %param) = @_;
815 $class->meta->new_object(%params);
818 Of course the ideal place for this would actually be in C<UNIVERSAL::>
819 but that is considered bad style, so we do not do that.
821 =item B<construct_instance (%params)>
823 This method is used to construct an instace structure suitable for
824 C<bless>-ing into your package of choice. It works in conjunction
825 with the Attribute protocol to collect all applicable attributes.
827 This will construct and instance using a HASH ref as storage
828 (currently only HASH references are supported). This will collect all
829 the applicable attributes and layout out the fields in the HASH ref,
830 it will then initialize them using either use the corresponding key
831 in C<%params> or any default value or initializer found in the
832 attribute meta-object.
834 =item B<clone_object ($instance, %params)>
836 This is a convience method for cloning an object instance, then
837 blessing it into the appropriate package. This method will call
838 C<clone_instance>, which performs a shallow copy of the object,
839 see that methods documentation for more details. Ideally your
840 class would call a C<clone> this method like so:
843 my ($self, %param) = @_;
844 $self->meta->clone_object($self, %params);
847 Of course the ideal place for this would actually be in C<UNIVERSAL::>
848 but that is considered bad style, so we do not do that.
850 =item B<clone_instance($instance, %params)>
852 This method is a compliment of C<construct_instance> (which means if
853 you override C<construct_instance>, you need to override this one too),
854 and clones the instance shallowly.
856 The cloned structure returned is (like with C<construct_instance>) an
857 unC<bless>ed HASH reference, it is your responsibility to then bless
858 this cloned structure into the right class (which C<clone_object> will
861 As of 0.11, this method will clone the C<$instance> structure shallowly,
862 as opposed to the deep cloning implemented in prior versions. After much
863 thought, research and discussion, I have decided that anything but basic
864 shallow cloning is outside the scope of the meta-object protocol. I
865 think Yuval "nothingmuch" Kogman put it best when he said that cloning
866 is too I<context-specific> to be part of the MOP.
876 This is a read-only attribute which returns the package name for the
877 given B<Class::MOP::Class> instance.
881 This is a read-only attribute which returns the C<$VERSION> of the
882 package for the given B<Class::MOP::Class> instance.
886 =head2 Inheritance Relationships
890 =item B<superclasses (?@superclasses)>
892 This is a read-write attribute which represents the superclass
893 relationships of the class the B<Class::MOP::Class> instance is
894 associated with. Basically, it can get and set the C<@ISA> for you.
897 Perl will occasionally perform some C<@ISA> and method caching, if
898 you decide to change your superclass relationship at runtime (which
899 is quite insane and very much not recommened), then you should be
900 aware of this and the fact that this module does not make any
901 attempt to address this issue.
903 =item B<class_precedence_list>
905 This computes the a list of all the class's ancestors in the same order
906 in which method dispatch will be done. This is similair to
907 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
915 =item B<method_metaclass>
917 =item B<add_method ($method_name, $method)>
919 This will take a C<$method_name> and CODE reference to that
920 C<$method> and install it into the class's package.
923 This does absolutely nothing special to C<$method>
924 other than use B<Sub::Name> to make sure it is tagged with the
925 correct name, and therefore show up correctly in stack traces and
928 =item B<alias_method ($method_name, $method)>
930 This will take a C<$method_name> and CODE reference to that
931 C<$method> and alias the method into the class's package.
934 Unlike C<add_method>, this will B<not> try to name the
935 C<$method> using B<Sub::Name>, it only aliases the method in
938 =item B<has_method ($method_name)>
940 This just provides a simple way to check if the class implements
941 a specific C<$method_name>. It will I<not> however, attempt to check
942 if the class inherits the method (use C<UNIVERSAL::can> for that).
944 This will correctly handle functions defined outside of the package
945 that use a fully qualified name (C<sub Package::name { ... }>).
947 This will correctly handle functions renamed with B<Sub::Name> and
948 installed using the symbol tables. However, if you are naming the
949 subroutine outside of the package scope, you must use the fully
950 qualified name, including the package name, for C<has_method> to
951 correctly identify it.
953 This will attempt to correctly ignore functions imported from other
954 packages using B<Exporter>. It breaks down if the function imported
955 is an C<__ANON__> sub (such as with C<use constant>), which very well
956 may be a valid method being applied to the class.
958 In short, this method cannot always be trusted to determine if the
959 C<$method_name> is actually a method. However, it will DWIM about
960 90% of the time, so it's a small trade off I think.
962 =item B<get_method ($method_name)>
964 This will return a CODE reference of the specified C<$method_name>,
965 or return undef if that method does not exist.
967 =item B<remove_method ($method_name)>
969 This will attempt to remove a given C<$method_name> from the class.
970 It will return the CODE reference that it has removed, and will
971 attempt to use B<Sub::Name> to clear the methods associated name.
973 =item B<get_method_list>
975 This will return a list of method names for all I<locally> defined
976 methods. It does B<not> provide a list of all applicable methods,
977 including any inherited ones. If you want a list of all applicable
978 methods, use the C<compute_all_applicable_methods> method.
980 =item B<compute_all_applicable_methods>
982 This will return a list of all the methods names this class will
983 respond to, taking into account inheritance. The list will be a list of
984 HASH references, each one containing the following information; method
985 name, the name of the class in which the method lives and a CODE
986 reference for the actual method.
988 =item B<find_all_methods_by_name ($method_name)>
990 This will traverse the inheritence hierarchy and locate all methods
991 with a given C<$method_name>. Similar to
992 C<compute_all_applicable_methods> it returns a list of HASH references
993 with the following information; method name (which will always be the
994 same as C<$method_name>), the name of the class in which the method
995 lives and a CODE reference for the actual method.
997 The list of methods produced is a distinct list, meaning there are no
998 duplicates in it. This is especially useful for things like object
999 initialization and destruction where you only want the method called
1000 once, and in the correct order.
1002 =item B<find_next_method_by_name ($method_name)>
1004 This will return the first method to match a given C<$method_name> in
1005 the superclasses, this is basically equivalent to calling
1006 C<SUPER::$method_name>, but it can be dispatched at runtime.
1010 =head2 Method Modifiers
1012 Method modifiers are a concept borrowed from CLOS, in which a method
1013 can be wrapped with I<before>, I<after> and I<around> method modifiers
1014 that will be called everytime the method is called.
1016 =head3 How method modifiers work?
1018 Method modifiers work by wrapping the original method and then replacing
1019 it in the classes symbol table. The wrappers will handle calling all the
1020 modifiers in the appropariate orders and preserving the calling context
1021 for the original method.
1023 Each method modifier serves a particular purpose, which may not be
1024 obvious to users of other method wrapping modules. To start with, the
1025 return values of I<before> and I<after> modifiers are ignored. This is
1026 because thier purpose is B<not> to filter the input and output of the
1027 primary method (this is done with an I<around> modifier). This may seem
1028 like an odd restriction to some, but doing this allows for simple code
1029 to be added at the begining or end of a method call without jeapordizing
1030 the normal functioning of the primary method or placing any extra
1031 responsibility on the code of the modifier. Of course if you have more
1032 complex needs, then use the I<around> modifier, which uses a variation
1033 of continutation passing style to allow for a high degree of flexibility.
1035 Before and around modifiers are called in last-defined-first-called order,
1036 while after modifiers are called in first-defined-first-called order. So
1037 the call tree might looks something like this:
1047 To see examples of using method modifiers, see the following examples
1048 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1049 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1050 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1052 =head3 What is the performance impact?
1054 Of course there is a performance cost associated with method modifiers,
1055 but we have made every effort to make that cost be directly proportional
1056 to the amount of modifier features you utilize.
1058 The wrapping method does it's best to B<only> do as much work as it
1059 absolutely needs to. In order to do this we have moved some of the
1060 performance costs to set-up time, where they are easier to amortize.
1062 All this said, my benchmarks have indicated the following:
1064 simple wrapper with no modifiers 100% slower
1065 simple wrapper with simple before modifier 400% slower
1066 simple wrapper with simple after modifier 450% slower
1067 simple wrapper with simple around modifier 500-550% slower
1068 simple wrapper with all 3 modifiers 1100% slower
1070 These numbers may seem daunting, but you must remember, every feature
1071 comes with some cost. To put things in perspective, just doing a simple
1072 C<AUTOLOAD> which does nothing but extract the name of the method called
1073 and return it costs about 400% over a normal method call.
1077 =item B<add_before_method_modifier ($method_name, $code)>
1079 This will wrap the method at C<$method_name> and the supplied C<$code>
1080 will be passed the C<@_> arguments, and called before the original
1081 method is called. As specified above, the return value of the I<before>
1082 method modifiers is ignored, and it's ability to modify C<@_> is
1083 fairly limited. If you need to do either of these things, use an
1084 C<around> method modifier.
1086 =item B<add_after_method_modifier ($method_name, $code)>
1088 This will wrap the method at C<$method_name> so that the original
1089 method will be called, it's return values stashed, and then the
1090 supplied C<$code> will be passed the C<@_> arguments, and called.
1091 As specified above, the return value of the I<after> method
1092 modifiers is ignored, and it cannot modify the return values of
1093 the original method. If you need to do either of these things, use an
1094 C<around> method modifier.
1096 =item B<add_around_method_modifier ($method_name, $code)>
1098 This will wrap the method at C<$method_name> so that C<$code>
1099 will be called and passed the original method as an extra argument
1100 at the begining of the C<@_> argument list. This is a variation of
1101 continuation passing style, where the function prepended to C<@_>
1102 can be considered a continuation. It is up to C<$code> if it calls
1103 the original method or not, there is no restriction on what the
1104 C<$code> can or cannot do.
1110 It should be noted that since there is no one consistent way to define
1111 the attributes of a class in Perl 5. These methods can only work with
1112 the information given, and can not easily discover information on
1113 their own. See L<Class::MOP::Attribute> for more details.
1117 =item B<attribute_metaclass>
1119 =item B<get_attribute_map>
1121 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1123 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1124 instance associated with the given class, and associates it with
1125 the C<$attribute_name>. Unlike methods, attributes within the MOP
1126 are stored as meta-information only. They will be used later to
1127 construct instances from (see C<construct_instance> above).
1128 More details about the attribute meta-objects can be found in the
1129 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1132 It should be noted that any accessor, reader/writer or predicate
1133 methods which the C<$attribute_meta_object> has will be installed
1134 into the class at this time.
1136 =item B<has_attribute ($attribute_name)>
1138 Checks to see if this class has an attribute by the name of
1139 C<$attribute_name> and returns a boolean.
1141 =item B<get_attribute ($attribute_name)>
1143 Returns the attribute meta-object associated with C<$attribute_name>,
1144 if none is found, it will return undef.
1146 =item B<remove_attribute ($attribute_name)>
1148 This will remove the attribute meta-object stored at
1149 C<$attribute_name>, then return the removed attribute meta-object.
1152 Removing an attribute will only affect future instances of
1153 the class, it will not make any attempt to remove the attribute from
1154 any existing instances of the class.
1156 It should be noted that any accessor, reader/writer or predicate
1157 methods which the attribute meta-object stored at C<$attribute_name>
1158 has will be removed from the class at this time. This B<will> make
1159 these attributes somewhat inaccessable in previously created
1160 instances. But if you are crazy enough to do this at runtime, then
1161 you are crazy enough to deal with something like this :).
1163 =item B<get_attribute_list>
1165 This returns a list of attribute names which are defined in the local
1166 class. If you want a list of all applicable attributes for a class,
1167 use the C<compute_all_applicable_attributes> method.
1169 =item B<compute_all_applicable_attributes>
1171 This will traverse the inheritance heirachy and return a list of all
1172 the applicable attributes for this class. It does not construct a
1173 HASH reference like C<compute_all_applicable_methods> because all
1174 that same information is discoverable through the attribute
1177 =item B<find_attribute_by_name ($attr_name)>
1179 This method will traverse the inheritance heirachy and find the
1180 first attribute whose name matches C<$attr_name>, then return it.
1181 It will return undef if nothing is found.
1185 =head2 Package Variables
1187 Since Perl's classes are built atop the Perl package system, it is
1188 fairly common to use package scoped variables for things like static
1189 class variables. The following methods are convience methods for
1190 the creation and inspection of package scoped variables.
1194 =item B<add_package_symbol ($variable_name, ?$initial_value)>
1196 Given a C<$variable_name>, which must contain a leading sigil, this
1197 method will create that variable within the package which houses the
1198 class. It also takes an optional C<$initial_value>, which must be a
1199 reference of the same type as the sigil of the C<$variable_name>
1202 =item B<get_package_symbol ($variable_name)>
1204 This will return a reference to the package variable in
1207 =item B<has_package_symbol ($variable_name)>
1209 Returns true (C<1>) if there is a package variable defined for
1210 C<$variable_name>, and false (C<0>) otherwise.
1212 =item B<remove_package_symbol ($variable_name)>
1214 This will attempt to remove the package variable at C<$variable_name>.
1218 =head2 Class closing
1224 =item B<is_immutable>
1226 =item B<make_immutable>
1232 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1234 =head1 COPYRIGHT AND LICENSE
1236 Copyright 2006 by Infinity Interactive, Inc.
1238 L<http://www.iinteractive.com>
1240 This library is free software; you can redistribute it and/or modify
1241 it under the same terms as Perl itself.