2 package Class::MOP::Class;
8 use Scalar::Util 'blessed', 'reftype', 'weaken';
9 use Sub::Name 'subname';
10 use B 'svref_2object';
12 our $VERSION = '0.17';
14 use base 'Class::MOP::Module';
16 use Class::MOP::Instance;
20 sub meta { Class::MOP::Class->initialize(blessed($_[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::Class$/) {
98 '$: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});
304 @{$self->get_package_symbol('@ISA')} = @supers;
306 # we need to check the metaclass
307 # compatability here so that we can
308 # be sure that the superclass is
309 # not potentially creating an issues
310 # we don't know about
311 $self->check_metaclass_compatability();
313 @{$self->get_package_symbol('@ISA')};
316 sub class_precedence_list {
319 # We need to check for ciruclar inheirtance here.
320 # This will do nothing if all is well, and blow
321 # up otherwise. Yes, it's an ugly hack, better
322 # suggestions are welcome.
323 { ($self->name || return)->isa('This is a test for circular inheritance') }
324 # ... and now back to our regularly scheduled program
328 $self->initialize($_)->class_precedence_list()
329 } $self->superclasses()
336 my ($self, $method_name, $method) = @_;
337 (defined $method_name && $method_name)
338 || confess "You must define a method name";
339 # use reftype here to allow for blessed subs ...
340 ('CODE' eq (reftype($method) || ''))
341 || confess "Your code block must be a CODE reference";
342 my $full_method_name = ($self->name . '::' . $method_name);
345 # dont bless subs, its bad mkay
346 $method = $self->method_metaclass->wrap($method) unless blessed($method);
348 $self->add_package_symbol("&${method_name}" => subname $full_method_name => $method);
352 my $fetch_and_prepare_method = sub {
353 my ($self, $method_name) = @_;
355 my $method = $self->get_method($method_name);
356 # if we dont have local ...
358 # try to find the next method
359 $method = $self->find_next_method_by_name($method_name);
360 # die if it does not exist
362 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
363 # and now make sure to wrap it
364 # even if it is already wrapped
365 # because we need a new sub ref
366 $method = Class::MOP::Method::Wrapped->wrap($method);
369 # now make sure we wrap it properly
370 $method = Class::MOP::Method::Wrapped->wrap($method)
371 unless $method->isa('Class::MOP::Method::Wrapped');
373 $self->add_method($method_name => $method);
377 sub add_before_method_modifier {
378 my ($self, $method_name, $method_modifier) = @_;
379 (defined $method_name && $method_name)
380 || confess "You must pass in a method name";
381 my $method = $fetch_and_prepare_method->($self, $method_name);
382 $method->add_before_modifier(subname ':before' => $method_modifier);
385 sub add_after_method_modifier {
386 my ($self, $method_name, $method_modifier) = @_;
387 (defined $method_name && $method_name)
388 || confess "You must pass in a method name";
389 my $method = $fetch_and_prepare_method->($self, $method_name);
390 $method->add_after_modifier(subname ':after' => $method_modifier);
393 sub add_around_method_modifier {
394 my ($self, $method_name, $method_modifier) = @_;
395 (defined $method_name && $method_name)
396 || confess "You must pass in a method name";
397 my $method = $fetch_and_prepare_method->($self, $method_name);
398 $method->add_around_modifier(subname ':around' => $method_modifier);
402 # the methods above used to be named like this:
403 # ${pkg}::${method}:(before|after|around)
404 # but this proved problematic when using one modifier
405 # to wrap multiple methods (something which is likely
406 # to happen pretty regularly IMO). So instead of naming
407 # it like this, I have chosen to just name them purely
408 # with their modifier names, like so:
409 # :(before|after|around)
410 # The fact is that in a stack trace, it will be fairly
411 # evident from the context what method they are attached
412 # to, and so don't need the fully qualified name.
416 my ($self, $method_name, $method) = @_;
417 (defined $method_name && $method_name)
418 || confess "You must define a method name";
419 # use reftype here to allow for blessed subs ...
420 ('CODE' eq (reftype($method) || ''))
421 || confess "Your code block must be a CODE reference";
424 # dont bless subs, its bad mkay
425 $method = $self->method_metaclass->wrap($method) unless blessed($method);
427 $self->add_package_symbol("&${method_name}" => $method);
430 sub find_method_by_name {
431 my ($self, $method_name) = @_;
432 return $self->name->can($method_name);
436 my ($self, $method_name) = @_;
437 (defined $method_name && $method_name)
438 || confess "You must define a method name";
440 return 0 if !$self->has_package_symbol("&${method_name}");
441 my $method = $self->get_package_symbol("&${method_name}");
442 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
443 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
446 # dont bless subs, its bad mkay
447 $self->method_metaclass->wrap($method) unless blessed($method);
453 my ($self, $method_name) = @_;
454 (defined $method_name && $method_name)
455 || confess "You must define a method name";
457 return unless $self->has_method($method_name);
459 return $self->get_package_symbol("&${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);
469 $self->remove_package_symbol("&${method_name}")
470 if defined $removed_method;
472 return $removed_method;
475 sub get_method_list {
477 grep { $self->has_method($_) } $self->list_all_package_symbols;
480 sub compute_all_applicable_methods {
483 # keep a record of what we have seen
484 # here, this will handle all the
485 # inheritence issues because we are
486 # using the &class_precedence_list
487 my (%seen_class, %seen_method);
488 foreach my $class ($self->class_precedence_list()) {
489 next if $seen_class{$class};
490 $seen_class{$class}++;
491 # fetch the meta-class ...
492 my $meta = $self->initialize($class);
493 foreach my $method_name ($meta->get_method_list()) {
494 next if exists $seen_method{$method_name};
495 $seen_method{$method_name}++;
497 name => $method_name,
499 code => $meta->get_method($method_name)
506 sub find_all_methods_by_name {
507 my ($self, $method_name) = @_;
508 (defined $method_name && $method_name)
509 || confess "You must define a method name to find";
511 # keep a record of what we have seen
512 # here, this will handle all the
513 # inheritence issues because we are
514 # using the &class_precedence_list
516 foreach my $class ($self->class_precedence_list()) {
517 next if $seen_class{$class};
518 $seen_class{$class}++;
519 # fetch the meta-class ...
520 my $meta = $self->initialize($class);
522 name => $method_name,
524 code => $meta->get_method($method_name)
525 } if $meta->has_method($method_name);
530 sub find_next_method_by_name {
531 my ($self, $method_name) = @_;
532 (defined $method_name && $method_name)
533 || confess "You must define a method name to find";
534 # keep a record of what we have seen
535 # here, this will handle all the
536 # inheritence issues because we are
537 # using the &class_precedence_list
539 my @cpl = $self->class_precedence_list();
540 shift @cpl; # discard ourselves
541 foreach my $class (@cpl) {
542 next if $seen_class{$class};
543 $seen_class{$class}++;
544 # fetch the meta-class ...
545 my $meta = $self->initialize($class);
546 return $meta->get_method($method_name)
547 if $meta->has_method($method_name);
556 # either we have an attribute object already
557 # or we need to create one from the args provided
558 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
559 # make sure it is derived from the correct type though
560 ($attribute->isa('Class::MOP::Attribute'))
561 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
562 $attribute->attach_to_class($self);
563 $attribute->install_accessors();
564 $self->get_attribute_map->{$attribute->name} = $attribute;
568 my ($self, $attribute_name) = @_;
569 (defined $attribute_name && $attribute_name)
570 || confess "You must define an attribute name";
571 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
575 my ($self, $attribute_name) = @_;
576 (defined $attribute_name && $attribute_name)
577 || confess "You must define an attribute name";
578 return $self->get_attribute_map->{$attribute_name}
579 if $self->has_attribute($attribute_name);
583 sub remove_attribute {
584 my ($self, $attribute_name) = @_;
585 (defined $attribute_name && $attribute_name)
586 || confess "You must define an attribute name";
587 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
588 return unless defined $removed_attribute;
589 delete $self->get_attribute_map->{$attribute_name};
590 $removed_attribute->remove_accessors();
591 $removed_attribute->detach_from_class();
592 return $removed_attribute;
595 sub get_attribute_list {
597 keys %{$self->get_attribute_map};
600 sub compute_all_applicable_attributes {
603 # keep a record of what we have seen
604 # here, this will handle all the
605 # inheritence issues because we are
606 # using the &class_precedence_list
607 my (%seen_class, %seen_attr);
608 foreach my $class ($self->class_precedence_list()) {
609 next if $seen_class{$class};
610 $seen_class{$class}++;
611 # fetch the meta-class ...
612 my $meta = $self->initialize($class);
613 foreach my $attr_name ($meta->get_attribute_list()) {
614 next if exists $seen_attr{$attr_name};
615 $seen_attr{$attr_name}++;
616 push @attrs => $meta->get_attribute($attr_name);
622 sub find_attribute_by_name {
623 my ($self, $attr_name) = @_;
624 # keep a record of what we have seen
625 # here, this will handle all the
626 # inheritence issues because we are
627 # using the &class_precedence_list
629 foreach my $class ($self->class_precedence_list()) {
630 next if $seen_class{$class};
631 $seen_class{$class}++;
632 # fetch the meta-class ...
633 my $meta = $self->initialize($class);
634 return $meta->get_attribute($attr_name)
635 if $meta->has_attribute($attr_name);
643 sub is_immutable { 0 }
646 return Class::MOP::Class::Immutable->make_metaclass_immutable(@_);
657 Class::MOP::Class - Class Meta Object
661 # assuming that class Foo
662 # has been defined, you can
664 # use this for introspection ...
666 # add a method to Foo ...
667 Foo->meta->add_method('bar' => sub { ... })
669 # get a list of all the classes searched
670 # the method dispatcher in the correct order
671 Foo->meta->class_precedence_list()
673 # remove a method from Foo
674 Foo->meta->remove_method('bar');
676 # or use this to actually create classes ...
678 Class::MOP::Class->create('Bar' => '0.01' => (
679 superclasses => [ 'Foo' ],
681 Class::MOP:::Attribute->new('$bar'),
682 Class::MOP:::Attribute->new('$baz'),
685 calculate_bar => sub { ... },
686 construct_baz => sub { ... }
692 This is the largest and currently most complex part of the Perl 5
693 meta-object protocol. It controls the introspection and
694 manipulation of Perl 5 classes (and it can create them too). The
695 best way to understand what this module can do, is to read the
696 documentation for each of it's methods.
700 =head2 Self Introspection
706 This will return a B<Class::MOP::Class> instance which is related
707 to this class. Thereby allowing B<Class::MOP::Class> to actually
710 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
711 bootstrap this module by installing a number of attribute meta-objects
712 into it's metaclass. This will allow this class to reap all the benifits
713 of the MOP when subclassing it.
715 =item B<get_all_metaclasses>
717 This will return an hash of all the metaclass instances that have
718 been cached by B<Class::MOP::Class> keyed by the package name.
720 =item B<get_all_metaclass_instances>
722 This will return an array of all the metaclass instances that have
723 been cached by B<Class::MOP::Class>.
725 =item B<get_all_metaclass_names>
727 This will return an array of all the metaclass names that have
728 been cached by B<Class::MOP::Class>.
732 =head2 Class construction
734 These methods will handle creating B<Class::MOP::Class> objects,
735 which can be used to both create new classes, and analyze
736 pre-existing classes.
738 This module will internally store references to all the instances
739 you create with these methods, so that they do not need to be
740 created any more than nessecary. Basically, they are singletons.
744 =item B<create ($package_name, ?$package_version,
745 superclasses =E<gt> ?@superclasses,
746 methods =E<gt> ?%methods,
747 attributes =E<gt> ?%attributes)>
749 This returns a B<Class::MOP::Class> object, bringing the specified
750 C<$package_name> into existence and adding any of the
751 C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
754 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
755 methods =E<gt> ?%methods,
756 attributes =E<gt> ?%attributes)>
758 This will create an anonymous class, it works much like C<create> but
759 it does not need a C<$package_name>. Instead it will create a suitably
760 unique package name for you to stash things into.
762 =item B<initialize ($package_name, %options)>
764 This initializes and returns returns a B<Class::MOP::Class> object
765 for a given a C<$package_name>.
767 =item B<reinitialize ($package_name, %options)>
769 This removes the old metaclass, and creates a new one in it's place.
770 Do B<not> use this unless you really know what you are doing, it could
771 very easily make a very large mess of your program.
773 =item B<construct_class_instance (%options)>
775 This will construct an instance of B<Class::MOP::Class>, it is
776 here so that we can actually "tie the knot" for B<Class::MOP::Class>
777 to use C<construct_instance> once all the bootstrapping is done. This
778 method is used internally by C<initialize> and should never be called
779 from outside of that method really.
781 =item B<check_metaclass_compatability>
783 This method is called as the very last thing in the
784 C<construct_class_instance> method. This will check that the
785 metaclass you are creating is compatible with the metaclasses of all
786 your ancestors. For more inforamtion about metaclass compatibility
787 see the C<About Metaclass compatibility> section in L<Class::MOP>.
791 =head2 Object instance construction and cloning
793 These methods are B<entirely optional>, it is up to you whether you want
798 =item B<instance_metaclass>
800 =item B<get_meta_instance>
802 =item B<new_object (%params)>
804 This is a convience method for creating a new object of the class, and
805 blessing it into the appropriate package as well. Ideally your class
806 would call a C<new> this method like so:
809 my ($class, %param) = @_;
810 $class->meta->new_object(%params);
813 Of course the ideal place for this would actually be in C<UNIVERSAL::>
814 but that is considered bad style, so we do not do that.
816 =item B<construct_instance (%params)>
818 This method is used to construct an instace structure suitable for
819 C<bless>-ing into your package of choice. It works in conjunction
820 with the Attribute protocol to collect all applicable attributes.
822 This will construct and instance using a HASH ref as storage
823 (currently only HASH references are supported). This will collect all
824 the applicable attributes and layout out the fields in the HASH ref,
825 it will then initialize them using either use the corresponding key
826 in C<%params> or any default value or initializer found in the
827 attribute meta-object.
829 =item B<clone_object ($instance, %params)>
831 This is a convience method for cloning an object instance, then
832 blessing it into the appropriate package. This method will call
833 C<clone_instance>, which performs a shallow copy of the object,
834 see that methods documentation for more details. Ideally your
835 class would call a C<clone> this method like so:
838 my ($self, %param) = @_;
839 $self->meta->clone_object($self, %params);
842 Of course the ideal place for this would actually be in C<UNIVERSAL::>
843 but that is considered bad style, so we do not do that.
845 =item B<clone_instance($instance, %params)>
847 This method is a compliment of C<construct_instance> (which means if
848 you override C<construct_instance>, you need to override this one too),
849 and clones the instance shallowly.
851 The cloned structure returned is (like with C<construct_instance>) an
852 unC<bless>ed HASH reference, it is your responsibility to then bless
853 this cloned structure into the right class (which C<clone_object> will
856 As of 0.11, this method will clone the C<$instance> structure shallowly,
857 as opposed to the deep cloning implemented in prior versions. After much
858 thought, research and discussion, I have decided that anything but basic
859 shallow cloning is outside the scope of the meta-object protocol. I
860 think Yuval "nothingmuch" Kogman put it best when he said that cloning
861 is too I<context-specific> to be part of the MOP.
871 This is a read-only attribute which returns the package name for the
872 given B<Class::MOP::Class> instance.
876 This is a read-only attribute which returns the C<$VERSION> of the
877 package for the given B<Class::MOP::Class> instance.
881 =head2 Inheritance Relationships
885 =item B<superclasses (?@superclasses)>
887 This is a read-write attribute which represents the superclass
888 relationships of the class the B<Class::MOP::Class> instance is
889 associated with. Basically, it can get and set the C<@ISA> for you.
892 Perl will occasionally perform some C<@ISA> and method caching, if
893 you decide to change your superclass relationship at runtime (which
894 is quite insane and very much not recommened), then you should be
895 aware of this and the fact that this module does not make any
896 attempt to address this issue.
898 =item B<class_precedence_list>
900 This computes the a list of all the class's ancestors in the same order
901 in which method dispatch will be done. This is similair to
902 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
910 =item B<method_metaclass>
912 =item B<add_method ($method_name, $method)>
914 This will take a C<$method_name> and CODE reference to that
915 C<$method> and install it into the class's package.
918 This does absolutely nothing special to C<$method>
919 other than use B<Sub::Name> to make sure it is tagged with the
920 correct name, and therefore show up correctly in stack traces and
923 =item B<alias_method ($method_name, $method)>
925 This will take a C<$method_name> and CODE reference to that
926 C<$method> and alias the method into the class's package.
929 Unlike C<add_method>, this will B<not> try to name the
930 C<$method> using B<Sub::Name>, it only aliases the method in
933 =item B<has_method ($method_name)>
935 This just provides a simple way to check if the class implements
936 a specific C<$method_name>. It will I<not> however, attempt to check
937 if the class inherits the method (use C<UNIVERSAL::can> for that).
939 This will correctly handle functions defined outside of the package
940 that use a fully qualified name (C<sub Package::name { ... }>).
942 This will correctly handle functions renamed with B<Sub::Name> and
943 installed using the symbol tables. However, if you are naming the
944 subroutine outside of the package scope, you must use the fully
945 qualified name, including the package name, for C<has_method> to
946 correctly identify it.
948 This will attempt to correctly ignore functions imported from other
949 packages using B<Exporter>. It breaks down if the function imported
950 is an C<__ANON__> sub (such as with C<use constant>), which very well
951 may be a valid method being applied to the class.
953 In short, this method cannot always be trusted to determine if the
954 C<$method_name> is actually a method. However, it will DWIM about
955 90% of the time, so it's a small trade off I think.
957 =item B<get_method ($method_name)>
959 This will return a CODE reference of the specified C<$method_name>,
960 or return undef if that method does not exist.
962 =item B<find_method_by_name ($method_name>
964 This will return a CODE reference of the specified C<$method_name>,
965 or return undef if that method does not exist.
967 Unlike C<get_method> this will also look in the superclasses.
969 =item B<remove_method ($method_name)>
971 This will attempt to remove a given C<$method_name> from the class.
972 It will return the CODE reference that it has removed, and will
973 attempt to use B<Sub::Name> to clear the methods associated name.
975 =item B<get_method_list>
977 This will return a list of method names for all I<locally> defined
978 methods. It does B<not> provide a list of all applicable methods,
979 including any inherited ones. If you want a list of all applicable
980 methods, use the C<compute_all_applicable_methods> method.
982 =item B<compute_all_applicable_methods>
984 This will return a list of all the methods names this class will
985 respond to, taking into account inheritance. The list will be a list of
986 HASH references, each one containing the following information; method
987 name, the name of the class in which the method lives and a CODE
988 reference for the actual method.
990 =item B<find_all_methods_by_name ($method_name)>
992 This will traverse the inheritence hierarchy and locate all methods
993 with a given C<$method_name>. Similar to
994 C<compute_all_applicable_methods> it returns a list of HASH references
995 with the following information; method name (which will always be the
996 same as C<$method_name>), the name of the class in which the method
997 lives and a CODE reference for the actual method.
999 The list of methods produced is a distinct list, meaning there are no
1000 duplicates in it. This is especially useful for things like object
1001 initialization and destruction where you only want the method called
1002 once, and in the correct order.
1004 =item B<find_next_method_by_name ($method_name)>
1006 This will return the first method to match a given C<$method_name> in
1007 the superclasses, this is basically equivalent to calling
1008 C<SUPER::$method_name>, but it can be dispatched at runtime.
1012 =head2 Method Modifiers
1014 Method modifiers are a concept borrowed from CLOS, in which a method
1015 can be wrapped with I<before>, I<after> and I<around> method modifiers
1016 that will be called everytime the method is called.
1018 =head3 How method modifiers work?
1020 Method modifiers work by wrapping the original method and then replacing
1021 it in the classes symbol table. The wrappers will handle calling all the
1022 modifiers in the appropariate orders and preserving the calling context
1023 for the original method.
1025 Each method modifier serves a particular purpose, which may not be
1026 obvious to users of other method wrapping modules. To start with, the
1027 return values of I<before> and I<after> modifiers are ignored. This is
1028 because thier purpose is B<not> to filter the input and output of the
1029 primary method (this is done with an I<around> modifier). This may seem
1030 like an odd restriction to some, but doing this allows for simple code
1031 to be added at the begining or end of a method call without jeapordizing
1032 the normal functioning of the primary method or placing any extra
1033 responsibility on the code of the modifier. Of course if you have more
1034 complex needs, then use the I<around> modifier, which uses a variation
1035 of continutation passing style to allow for a high degree of flexibility.
1037 Before and around modifiers are called in last-defined-first-called order,
1038 while after modifiers are called in first-defined-first-called order. So
1039 the call tree might looks something like this:
1049 To see examples of using method modifiers, see the following examples
1050 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1051 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1052 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1054 =head3 What is the performance impact?
1056 Of course there is a performance cost associated with method modifiers,
1057 but we have made every effort to make that cost be directly proportional
1058 to the amount of modifier features you utilize.
1060 The wrapping method does it's best to B<only> do as much work as it
1061 absolutely needs to. In order to do this we have moved some of the
1062 performance costs to set-up time, where they are easier to amortize.
1064 All this said, my benchmarks have indicated the following:
1066 simple wrapper with no modifiers 100% slower
1067 simple wrapper with simple before modifier 400% slower
1068 simple wrapper with simple after modifier 450% slower
1069 simple wrapper with simple around modifier 500-550% slower
1070 simple wrapper with all 3 modifiers 1100% slower
1072 These numbers may seem daunting, but you must remember, every feature
1073 comes with some cost. To put things in perspective, just doing a simple
1074 C<AUTOLOAD> which does nothing but extract the name of the method called
1075 and return it costs about 400% over a normal method call.
1079 =item B<add_before_method_modifier ($method_name, $code)>
1081 This will wrap the method at C<$method_name> and the supplied C<$code>
1082 will be passed the C<@_> arguments, and called before the original
1083 method is called. As specified above, the return value of the I<before>
1084 method modifiers is ignored, and it's ability to modify C<@_> is
1085 fairly limited. If you need to do either of these things, use an
1086 C<around> method modifier.
1088 =item B<add_after_method_modifier ($method_name, $code)>
1090 This will wrap the method at C<$method_name> so that the original
1091 method will be called, it's return values stashed, and then the
1092 supplied C<$code> will be passed the C<@_> arguments, and called.
1093 As specified above, the return value of the I<after> method
1094 modifiers is ignored, and it cannot modify the return values of
1095 the original method. If you need to do either of these things, use an
1096 C<around> method modifier.
1098 =item B<add_around_method_modifier ($method_name, $code)>
1100 This will wrap the method at C<$method_name> so that C<$code>
1101 will be called and passed the original method as an extra argument
1102 at the begining of the C<@_> argument list. This is a variation of
1103 continuation passing style, where the function prepended to C<@_>
1104 can be considered a continuation. It is up to C<$code> if it calls
1105 the original method or not, there is no restriction on what the
1106 C<$code> can or cannot do.
1112 It should be noted that since there is no one consistent way to define
1113 the attributes of a class in Perl 5. These methods can only work with
1114 the information given, and can not easily discover information on
1115 their own. See L<Class::MOP::Attribute> for more details.
1119 =item B<attribute_metaclass>
1121 =item B<get_attribute_map>
1123 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1125 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1126 instance associated with the given class, and associates it with
1127 the C<$attribute_name>. Unlike methods, attributes within the MOP
1128 are stored as meta-information only. They will be used later to
1129 construct instances from (see C<construct_instance> above).
1130 More details about the attribute meta-objects can be found in the
1131 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1134 It should be noted that any accessor, reader/writer or predicate
1135 methods which the C<$attribute_meta_object> has will be installed
1136 into the class at this time.
1138 =item B<has_attribute ($attribute_name)>
1140 Checks to see if this class has an attribute by the name of
1141 C<$attribute_name> and returns a boolean.
1143 =item B<get_attribute ($attribute_name)>
1145 Returns the attribute meta-object associated with C<$attribute_name>,
1146 if none is found, it will return undef.
1148 =item B<remove_attribute ($attribute_name)>
1150 This will remove the attribute meta-object stored at
1151 C<$attribute_name>, then return the removed attribute meta-object.
1154 Removing an attribute will only affect future instances of
1155 the class, it will not make any attempt to remove the attribute from
1156 any existing instances of the class.
1158 It should be noted that any accessor, reader/writer or predicate
1159 methods which the attribute meta-object stored at C<$attribute_name>
1160 has will be removed from the class at this time. This B<will> make
1161 these attributes somewhat inaccessable in previously created
1162 instances. But if you are crazy enough to do this at runtime, then
1163 you are crazy enough to deal with something like this :).
1165 =item B<get_attribute_list>
1167 This returns a list of attribute names which are defined in the local
1168 class. If you want a list of all applicable attributes for a class,
1169 use the C<compute_all_applicable_attributes> method.
1171 =item B<compute_all_applicable_attributes>
1173 This will traverse the inheritance heirachy and return a list of all
1174 the applicable attributes for this class. It does not construct a
1175 HASH reference like C<compute_all_applicable_methods> because all
1176 that same information is discoverable through the attribute
1179 =item B<find_attribute_by_name ($attr_name)>
1181 This method will traverse the inheritance heirachy and find the
1182 first attribute whose name matches C<$attr_name>, then return it.
1183 It will return undef if nothing is found.
1187 =head2 Package Variables
1189 Since Perl's classes are built atop the Perl package system, it is
1190 fairly common to use package scoped variables for things like static
1191 class variables. The following methods are convience methods for
1192 the creation and inspection of package scoped variables.
1196 =item B<add_package_symbol ($variable_name, ?$initial_value)>
1198 Given a C<$variable_name>, which must contain a leading sigil, this
1199 method will create that variable within the package which houses the
1200 class. It also takes an optional C<$initial_value>, which must be a
1201 reference of the same type as the sigil of the C<$variable_name>
1204 =item B<get_package_symbol ($variable_name)>
1206 This will return a reference to the package variable in
1209 =item B<has_package_symbol ($variable_name)>
1211 Returns true (C<1>) if there is a package variable defined for
1212 C<$variable_name>, and false (C<0>) otherwise.
1214 =item B<remove_package_symbol ($variable_name)>
1216 This will attempt to remove the package variable at C<$variable_name>.
1220 =head2 Class closing
1226 =item B<is_immutable>
1228 =item B<make_immutable>
1234 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1236 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1238 =head1 COPYRIGHT AND LICENSE
1240 Copyright 2006 by Infinity Interactive, Inc.
1242 L<http://www.iinteractive.com>
1244 This library is free software; you can redistribute it and/or modify
1245 it under the same terms as Perl itself.