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 = '0.18';
13 our $AUTHORITY = 'cpan:STEVAN';
15 use base 'Class::MOP::Module';
17 use Class::MOP::Instance;
21 sub meta { Class::MOP::Class->initialize(blessed($_[0]) || $_[0]) }
26 # we need a sufficiently annoying prefix
27 # this should suffice for now, this is
28 # used in a couple of places below, so
29 # need to put it up here for now.
30 my $ANON_CLASS_PREFIX = 'Class::MOP::Class::__ANON__::SERIAL::';
36 my $package_name = shift;
37 (defined $package_name && $package_name && !blessed($package_name))
38 || confess "You must pass a package name and it cannot be blessed";
39 $class->construct_class_instance(':package' => $package_name, @_);
44 my $package_name = shift;
45 (defined $package_name && $package_name && !blessed($package_name))
46 || confess "You must pass a package name and it cannot be blessed";
47 Class::MOP::remove_metaclass_by_name($package_name);
48 $class->construct_class_instance(':package' => $package_name, @_);
51 # NOTE: (meta-circularity)
52 # this is a special form of &construct_instance
53 # (see below), which is used to construct class
54 # meta-object instances for any Class::MOP::*
55 # class. All other classes will use the more
56 # normal &construct_instance.
57 sub construct_class_instance {
60 my $package_name = $options{':package'};
61 (defined $package_name && $package_name)
62 || confess "You must pass a package name";
64 # return the metaclass if we have it cached,
65 # and it is still defined (it has not been
66 # reaped by DESTROY yet, which can happen
67 # annoyingly enough during global destruction)
68 return Class::MOP::get_metaclass_by_name($package_name)
69 if Class::MOP::does_metaclass_exist($package_name);
72 # we need to deal with the possibility
73 # of class immutability here, and then
74 # get the name of the class appropriately
75 $class = (blessed($class)
76 ? ($class->is_immutable
77 ? $class->get_mutable_metaclass_name()
81 $class = blessed($class) || $class;
82 # now create the metaclass
84 if ($class =~ /^Class::MOP::Class$/) {
87 # inherited from Class::MOP::Package
88 '$:package' => $package_name,
89 '%:namespace' => \%{$package_name . '::'},
90 # inherited from Class::MOP::Module
91 '$:version' => (exists ${$package_name . '::'}{'VERSION'} ? ${$package_name . '::VERSION'} : undef),
92 '$:authority' => (exists ${$package_name . '::'}{'AUTHORITY'} ? ${$package_name . '::AUTHORITY'} : undef),
95 '$:attribute_metaclass' => $options{':attribute_metaclass'} || 'Class::MOP::Attribute',
96 '$:method_metaclass' => $options{':method_metaclass'} || 'Class::MOP::Method',
97 '$:instance_metaclass' => $options{':instance_metaclass'} || 'Class::MOP::Instance',
102 # it is safe to use meta here because
103 # class will always be a subclass of
104 # Class::MOP::Class, which defines meta
105 $meta = $class->meta->construct_instance(%options)
108 # and check the metaclass compatibility
109 $meta->check_metaclass_compatability();
111 Class::MOP::store_metaclass_by_name($package_name, $meta);
113 # we need to weaken any anon classes
114 # so that they can call DESTROY properly
115 Class::MOP::weaken_metaclass($package_name)
116 if $package_name =~ /^$ANON_CLASS_PREFIX/;
120 sub check_metaclass_compatability {
123 # this is always okay ...
124 return if blessed($self) eq 'Class::MOP::Class' &&
125 $self->instance_metaclass eq 'Class::MOP::Instance';
127 my @class_list = $self->class_precedence_list;
128 shift @class_list; # shift off $self->name
130 foreach my $class_name (@class_list) {
131 my $meta = Class::MOP::get_metaclass_by_name($class_name) || next;
134 # we need to deal with the possibility
135 # of class immutability here, and then
136 # get the name of the class appropriately
137 my $meta_type = ($meta->is_immutable
138 ? $meta->get_mutable_metaclass_name()
141 ($self->isa($meta_type))
142 || confess $self->name . "->meta => (" . (blessed($self)) . ")" .
143 " is not compatible with the " .
144 $class_name . "->meta => (" . ($meta_type) . ")";
146 # we also need to check that instance metaclasses
147 # are compatabile in the same the class.
148 ($self->instance_metaclass->isa($meta->instance_metaclass))
149 || confess $self->name . "->meta => (" . ($self->instance_metaclass) . ")" .
150 " is not compatible with the " .
151 $class_name . "->meta => (" . ($meta->instance_metaclass) . ")";
159 # this should be sufficient, if you have a
160 # use case where it is not, write a test and
162 my $ANON_CLASS_SERIAL = 0;
164 sub create_anon_class {
165 my ($class, %options) = @_;
166 my $package_name = $ANON_CLASS_PREFIX . ++$ANON_CLASS_SERIAL;
167 return $class->create($package_name, '0.00', %options);
172 # this will only get called for
173 # anon-classes, all other calls
174 # are assumed to occur during
175 # global destruction and so don't
176 # really need to be handled explicitly
179 return unless $self->name =~ /^$ANON_CLASS_PREFIX/;
180 my ($serial_id) = ($self->name =~ /^$ANON_CLASS_PREFIX(\d+)/);
182 foreach my $key (keys %{$ANON_CLASS_PREFIX . $serial_id}) {
183 delete ${$ANON_CLASS_PREFIX . $serial_id}{$key};
185 delete ${'main::' . $ANON_CLASS_PREFIX}{$serial_id . '::'};
188 # creating classes with MOP ...
191 my ($class, $package_name, $package_version, %options) = @_;
192 (defined $package_name && $package_name)
193 || confess "You must pass a package name";
194 my $code = "package $package_name;";
195 $code .= "\$$package_name\:\:VERSION = '$package_version';"
196 if defined $package_version;
198 confess "creation of $package_name failed : $@" if $@;
199 my $meta = $class->initialize($package_name);
201 $meta->add_method('meta' => sub {
202 $class->initialize(blessed($_[0]) || $_[0]);
205 $meta->superclasses(@{$options{superclasses}})
206 if exists $options{superclasses};
208 # process attributes first, so that they can
209 # install accessors, but locally defined methods
210 # can then overwrite them. It is maybe a little odd, but
211 # I think this should be the order of things.
212 if (exists $options{attributes}) {
213 foreach my $attr (@{$options{attributes}}) {
214 $meta->add_attribute($attr);
217 if (exists $options{methods}) {
218 foreach my $method_name (keys %{$options{methods}}) {
219 $meta->add_method($method_name, $options{methods}->{$method_name});
228 # all these attribute readers will be bootstrapped
229 # away in the Class::MOP bootstrap section
231 sub get_attribute_map { $_[0]->{'%:attributes'} }
232 sub attribute_metaclass { $_[0]->{'$:attribute_metaclass'} }
233 sub method_metaclass { $_[0]->{'$:method_metaclass'} }
234 sub instance_metaclass { $_[0]->{'$:instance_metaclass'} }
236 # Instance Construction & Cloning
241 # we need to protect the integrity of the
242 # Class::MOP::Class singletons here, so we
243 # delegate this to &construct_class_instance
244 # which will deal with the singletons
245 return $class->construct_class_instance(@_)
246 if $class->name->isa('Class::MOP::Class');
247 return $class->construct_instance(@_);
250 sub construct_instance {
251 my ($class, %params) = @_;
252 my $meta_instance = $class->get_meta_instance();
253 my $instance = $meta_instance->create_instance();
254 foreach my $attr ($class->compute_all_applicable_attributes()) {
255 $attr->initialize_instance_slot($meta_instance, $instance, \%params);
260 sub get_meta_instance {
262 return $class->instance_metaclass->new(
264 $class->compute_all_applicable_attributes()
270 my $instance = shift;
271 (blessed($instance) && $instance->isa($class->name))
272 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
274 # we need to protect the integrity of the
275 # Class::MOP::Class singletons here, they
276 # should not be cloned.
277 return $instance if $instance->isa('Class::MOP::Class');
278 $class->clone_instance($instance, @_);
282 my ($class, $instance, %params) = @_;
284 || confess "You can only clone instances, \$self is not a blessed instance";
285 my $meta_instance = $class->get_meta_instance();
286 my $clone = $meta_instance->clone_instance($instance);
287 foreach my $key (keys %params) {
288 next unless $meta_instance->is_valid_slot($key);
289 $meta_instance->set_slot_value($clone, $key, $params{$key});
300 @{$self->get_package_symbol('@ISA')} = @supers;
302 # we need to check the metaclass
303 # compatability here so that we can
304 # be sure that the superclass is
305 # not potentially creating an issues
306 # we don't know about
307 $self->check_metaclass_compatability();
309 @{$self->get_package_symbol('@ISA')};
312 sub class_precedence_list {
315 # We need to check for ciruclar inheirtance here.
316 # This will do nothing if all is well, and blow
317 # up otherwise. Yes, it's an ugly hack, better
318 # suggestions are welcome.
319 { ($self->name || return)->isa('This is a test for circular inheritance') }
320 # ... and now back to our regularly scheduled program
324 $self->initialize($_)->class_precedence_list()
325 } $self->superclasses()
332 my ($self, $method_name, $method) = @_;
333 (defined $method_name && $method_name)
334 || confess "You must define a method name";
335 # use reftype here to allow for blessed subs ...
336 ('CODE' eq (reftype($method) || ''))
337 || confess "Your code block must be a CODE reference";
338 my $full_method_name = ($self->name . '::' . $method_name);
341 # dont bless subs, its bad mkay
342 $method = $self->method_metaclass->wrap($method) unless blessed($method);
344 $self->add_package_symbol("&${method_name}" => subname $full_method_name => $method);
348 my $fetch_and_prepare_method = sub {
349 my ($self, $method_name) = @_;
351 my $method = $self->get_method($method_name);
352 # if we dont have local ...
354 # try to find the next method
355 $method = $self->find_next_method_by_name($method_name);
356 # die if it does not exist
358 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
359 # and now make sure to wrap it
360 # even if it is already wrapped
361 # because we need a new sub ref
362 $method = Class::MOP::Method::Wrapped->wrap($method);
365 # now make sure we wrap it properly
366 $method = Class::MOP::Method::Wrapped->wrap($method)
367 unless $method->isa('Class::MOP::Method::Wrapped');
369 $self->add_method($method_name => $method);
373 sub add_before_method_modifier {
374 my ($self, $method_name, $method_modifier) = @_;
375 (defined $method_name && $method_name)
376 || confess "You must pass in a method name";
377 my $method = $fetch_and_prepare_method->($self, $method_name);
378 $method->add_before_modifier(subname ':before' => $method_modifier);
381 sub add_after_method_modifier {
382 my ($self, $method_name, $method_modifier) = @_;
383 (defined $method_name && $method_name)
384 || confess "You must pass in a method name";
385 my $method = $fetch_and_prepare_method->($self, $method_name);
386 $method->add_after_modifier(subname ':after' => $method_modifier);
389 sub add_around_method_modifier {
390 my ($self, $method_name, $method_modifier) = @_;
391 (defined $method_name && $method_name)
392 || confess "You must pass in a method name";
393 my $method = $fetch_and_prepare_method->($self, $method_name);
394 $method->add_around_modifier(subname ':around' => $method_modifier);
398 # the methods above used to be named like this:
399 # ${pkg}::${method}:(before|after|around)
400 # but this proved problematic when using one modifier
401 # to wrap multiple methods (something which is likely
402 # to happen pretty regularly IMO). So instead of naming
403 # it like this, I have chosen to just name them purely
404 # with their modifier names, like so:
405 # :(before|after|around)
406 # The fact is that in a stack trace, it will be fairly
407 # evident from the context what method they are attached
408 # to, and so don't need the fully qualified name.
412 my ($self, $method_name, $method) = @_;
413 (defined $method_name && $method_name)
414 || confess "You must define a method name";
415 # use reftype here to allow for blessed subs ...
416 ('CODE' eq (reftype($method) || ''))
417 || confess "Your code block must be a CODE reference";
420 # dont bless subs, its bad mkay
421 $method = $self->method_metaclass->wrap($method) unless blessed($method);
423 $self->add_package_symbol("&${method_name}" => $method);
426 sub find_method_by_name {
427 my ($self, $method_name) = @_;
428 return $self->name->can($method_name);
432 my ($self, $method_name) = @_;
433 (defined $method_name && $method_name)
434 || confess "You must define a method name";
436 return 0 if !$self->has_package_symbol("&${method_name}");
437 my $method = $self->get_package_symbol("&${method_name}");
438 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
439 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
442 # dont bless subs, its bad mkay
443 $self->method_metaclass->wrap($method) unless blessed($method);
449 my ($self, $method_name) = @_;
450 (defined $method_name && $method_name)
451 || confess "You must define a method name";
453 return unless $self->has_method($method_name);
455 return $self->get_package_symbol("&${method_name}");
459 my ($self, $method_name) = @_;
460 (defined $method_name && $method_name)
461 || confess "You must define a method name";
463 my $removed_method = $self->get_method($method_name);
465 $self->remove_package_symbol("&${method_name}")
466 if defined $removed_method;
468 return $removed_method;
471 sub get_method_list {
473 grep { $self->has_method($_) } $self->list_all_package_symbols;
476 sub compute_all_applicable_methods {
479 # keep a record of what we have seen
480 # here, this will handle all the
481 # inheritence issues because we are
482 # using the &class_precedence_list
483 my (%seen_class, %seen_method);
484 foreach my $class ($self->class_precedence_list()) {
485 next if $seen_class{$class};
486 $seen_class{$class}++;
487 # fetch the meta-class ...
488 my $meta = $self->initialize($class);
489 foreach my $method_name ($meta->get_method_list()) {
490 next if exists $seen_method{$method_name};
491 $seen_method{$method_name}++;
493 name => $method_name,
495 code => $meta->get_method($method_name)
502 sub find_all_methods_by_name {
503 my ($self, $method_name) = @_;
504 (defined $method_name && $method_name)
505 || confess "You must define a method name to find";
507 # keep a record of what we have seen
508 # here, this will handle all the
509 # inheritence issues because we are
510 # using the &class_precedence_list
512 foreach my $class ($self->class_precedence_list()) {
513 next if $seen_class{$class};
514 $seen_class{$class}++;
515 # fetch the meta-class ...
516 my $meta = $self->initialize($class);
518 name => $method_name,
520 code => $meta->get_method($method_name)
521 } if $meta->has_method($method_name);
526 sub find_next_method_by_name {
527 my ($self, $method_name) = @_;
528 (defined $method_name && $method_name)
529 || confess "You must define a method name to find";
530 # keep a record of what we have seen
531 # here, this will handle all the
532 # inheritence issues because we are
533 # using the &class_precedence_list
535 my @cpl = $self->class_precedence_list();
536 shift @cpl; # discard ourselves
537 foreach my $class (@cpl) {
538 next if $seen_class{$class};
539 $seen_class{$class}++;
540 # fetch the meta-class ...
541 my $meta = $self->initialize($class);
542 return $meta->get_method($method_name)
543 if $meta->has_method($method_name);
552 # either we have an attribute object already
553 # or we need to create one from the args provided
554 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
555 # make sure it is derived from the correct type though
556 ($attribute->isa('Class::MOP::Attribute'))
557 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
558 $attribute->attach_to_class($self);
559 $attribute->install_accessors();
560 $self->get_attribute_map->{$attribute->name} = $attribute;
564 my ($self, $attribute_name) = @_;
565 (defined $attribute_name && $attribute_name)
566 || confess "You must define an attribute name";
567 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
571 my ($self, $attribute_name) = @_;
572 (defined $attribute_name && $attribute_name)
573 || confess "You must define an attribute name";
574 return $self->get_attribute_map->{$attribute_name}
575 if $self->has_attribute($attribute_name);
579 sub remove_attribute {
580 my ($self, $attribute_name) = @_;
581 (defined $attribute_name && $attribute_name)
582 || confess "You must define an attribute name";
583 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
584 return unless defined $removed_attribute;
585 delete $self->get_attribute_map->{$attribute_name};
586 $removed_attribute->remove_accessors();
587 $removed_attribute->detach_from_class();
588 return $removed_attribute;
591 sub get_attribute_list {
593 keys %{$self->get_attribute_map};
596 sub compute_all_applicable_attributes {
599 # keep a record of what we have seen
600 # here, this will handle all the
601 # inheritence issues because we are
602 # using the &class_precedence_list
603 my (%seen_class, %seen_attr);
604 foreach my $class ($self->class_precedence_list()) {
605 next if $seen_class{$class};
606 $seen_class{$class}++;
607 # fetch the meta-class ...
608 my $meta = $self->initialize($class);
609 foreach my $attr_name ($meta->get_attribute_list()) {
610 next if exists $seen_attr{$attr_name};
611 $seen_attr{$attr_name}++;
612 push @attrs => $meta->get_attribute($attr_name);
618 sub find_attribute_by_name {
619 my ($self, $attr_name) = @_;
620 # keep a record of what we have seen
621 # here, this will handle all the
622 # inheritence issues because we are
623 # using the &class_precedence_list
625 foreach my $class ($self->class_precedence_list()) {
626 next if $seen_class{$class};
627 $seen_class{$class}++;
628 # fetch the meta-class ...
629 my $meta = $self->initialize($class);
630 return $meta->get_attribute($attr_name)
631 if $meta->has_attribute($attr_name);
639 sub is_immutable { 0 }
642 return Class::MOP::Class::Immutable->make_metaclass_immutable(@_);
653 Class::MOP::Class - Class Meta Object
657 # assuming that class Foo
658 # has been defined, you can
660 # use this for introspection ...
662 # add a method to Foo ...
663 Foo->meta->add_method('bar' => sub { ... })
665 # get a list of all the classes searched
666 # the method dispatcher in the correct order
667 Foo->meta->class_precedence_list()
669 # remove a method from Foo
670 Foo->meta->remove_method('bar');
672 # or use this to actually create classes ...
674 Class::MOP::Class->create('Bar' => '0.01' => (
675 superclasses => [ 'Foo' ],
677 Class::MOP:::Attribute->new('$bar'),
678 Class::MOP:::Attribute->new('$baz'),
681 calculate_bar => sub { ... },
682 construct_baz => sub { ... }
688 This is the largest and currently most complex part of the Perl 5
689 meta-object protocol. It controls the introspection and
690 manipulation of Perl 5 classes (and it can create them too). The
691 best way to understand what this module can do, is to read the
692 documentation for each of it's methods.
696 =head2 Self Introspection
702 This will return a B<Class::MOP::Class> instance which is related
703 to this class. Thereby allowing B<Class::MOP::Class> to actually
706 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
707 bootstrap this module by installing a number of attribute meta-objects
708 into it's metaclass. This will allow this class to reap all the benifits
709 of the MOP when subclassing it.
711 =item B<get_all_metaclasses>
713 This will return an hash of all the metaclass instances that have
714 been cached by B<Class::MOP::Class> keyed by the package name.
716 =item B<get_all_metaclass_instances>
718 This will return an array of all the metaclass instances that have
719 been cached by B<Class::MOP::Class>.
721 =item B<get_all_metaclass_names>
723 This will return an array of all the metaclass names that have
724 been cached by B<Class::MOP::Class>.
728 =head2 Class construction
730 These methods will handle creating B<Class::MOP::Class> objects,
731 which can be used to both create new classes, and analyze
732 pre-existing classes.
734 This module will internally store references to all the instances
735 you create with these methods, so that they do not need to be
736 created any more than nessecary. Basically, they are singletons.
740 =item B<create ($package_name, ?$package_version,
741 superclasses =E<gt> ?@superclasses,
742 methods =E<gt> ?%methods,
743 attributes =E<gt> ?%attributes)>
745 This returns a B<Class::MOP::Class> object, bringing the specified
746 C<$package_name> into existence and adding any of the
747 C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
750 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
751 methods =E<gt> ?%methods,
752 attributes =E<gt> ?%attributes)>
754 This will create an anonymous class, it works much like C<create> but
755 it does not need a C<$package_name>. Instead it will create a suitably
756 unique package name for you to stash things into.
758 =item B<initialize ($package_name, %options)>
760 This initializes and returns returns a B<Class::MOP::Class> object
761 for a given a C<$package_name>.
763 =item B<reinitialize ($package_name, %options)>
765 This removes the old metaclass, and creates a new one in it's place.
766 Do B<not> use this unless you really know what you are doing, it could
767 very easily make a very large mess of your program.
769 =item B<construct_class_instance (%options)>
771 This will construct an instance of B<Class::MOP::Class>, it is
772 here so that we can actually "tie the knot" for B<Class::MOP::Class>
773 to use C<construct_instance> once all the bootstrapping is done. This
774 method is used internally by C<initialize> and should never be called
775 from outside of that method really.
777 =item B<check_metaclass_compatability>
779 This method is called as the very last thing in the
780 C<construct_class_instance> method. This will check that the
781 metaclass you are creating is compatible with the metaclasses of all
782 your ancestors. For more inforamtion about metaclass compatibility
783 see the C<About Metaclass compatibility> section in L<Class::MOP>.
787 =head2 Object instance construction and cloning
789 These methods are B<entirely optional>, it is up to you whether you want
794 =item B<instance_metaclass>
796 =item B<get_meta_instance>
798 =item B<new_object (%params)>
800 This is a convience method for creating a new object of the class, and
801 blessing it into the appropriate package as well. Ideally your class
802 would call a C<new> this method like so:
805 my ($class, %param) = @_;
806 $class->meta->new_object(%params);
809 Of course the ideal place for this would actually be in C<UNIVERSAL::>
810 but that is considered bad style, so we do not do that.
812 =item B<construct_instance (%params)>
814 This method is used to construct an instace structure suitable for
815 C<bless>-ing into your package of choice. It works in conjunction
816 with the Attribute protocol to collect all applicable attributes.
818 This will construct and instance using a HASH ref as storage
819 (currently only HASH references are supported). This will collect all
820 the applicable attributes and layout out the fields in the HASH ref,
821 it will then initialize them using either use the corresponding key
822 in C<%params> or any default value or initializer found in the
823 attribute meta-object.
825 =item B<clone_object ($instance, %params)>
827 This is a convience method for cloning an object instance, then
828 blessing it into the appropriate package. This method will call
829 C<clone_instance>, which performs a shallow copy of the object,
830 see that methods documentation for more details. Ideally your
831 class would call a C<clone> this method like so:
834 my ($self, %param) = @_;
835 $self->meta->clone_object($self, %params);
838 Of course the ideal place for this would actually be in C<UNIVERSAL::>
839 but that is considered bad style, so we do not do that.
841 =item B<clone_instance($instance, %params)>
843 This method is a compliment of C<construct_instance> (which means if
844 you override C<construct_instance>, you need to override this one too),
845 and clones the instance shallowly.
847 The cloned structure returned is (like with C<construct_instance>) an
848 unC<bless>ed HASH reference, it is your responsibility to then bless
849 this cloned structure into the right class (which C<clone_object> will
852 As of 0.11, this method will clone the C<$instance> structure shallowly,
853 as opposed to the deep cloning implemented in prior versions. After much
854 thought, research and discussion, I have decided that anything but basic
855 shallow cloning is outside the scope of the meta-object protocol. I
856 think Yuval "nothingmuch" Kogman put it best when he said that cloning
857 is too I<context-specific> to be part of the MOP.
867 This is a read-only attribute which returns the package name for the
868 given B<Class::MOP::Class> instance.
872 This is a read-only attribute which returns the C<$VERSION> of the
873 package for the given B<Class::MOP::Class> instance.
877 =head2 Inheritance Relationships
881 =item B<superclasses (?@superclasses)>
883 This is a read-write attribute which represents the superclass
884 relationships of the class the B<Class::MOP::Class> instance is
885 associated with. Basically, it can get and set the C<@ISA> for you.
888 Perl will occasionally perform some C<@ISA> and method caching, if
889 you decide to change your superclass relationship at runtime (which
890 is quite insane and very much not recommened), then you should be
891 aware of this and the fact that this module does not make any
892 attempt to address this issue.
894 =item B<class_precedence_list>
896 This computes the a list of all the class's ancestors in the same order
897 in which method dispatch will be done. This is similair to
898 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
906 =item B<method_metaclass>
908 =item B<add_method ($method_name, $method)>
910 This will take a C<$method_name> and CODE reference to that
911 C<$method> and install it into the class's package.
914 This does absolutely nothing special to C<$method>
915 other than use B<Sub::Name> to make sure it is tagged with the
916 correct name, and therefore show up correctly in stack traces and
919 =item B<alias_method ($method_name, $method)>
921 This will take a C<$method_name> and CODE reference to that
922 C<$method> and alias the method into the class's package.
925 Unlike C<add_method>, this will B<not> try to name the
926 C<$method> using B<Sub::Name>, it only aliases the method in
929 =item B<has_method ($method_name)>
931 This just provides a simple way to check if the class implements
932 a specific C<$method_name>. It will I<not> however, attempt to check
933 if the class inherits the method (use C<UNIVERSAL::can> for that).
935 This will correctly handle functions defined outside of the package
936 that use a fully qualified name (C<sub Package::name { ... }>).
938 This will correctly handle functions renamed with B<Sub::Name> and
939 installed using the symbol tables. However, if you are naming the
940 subroutine outside of the package scope, you must use the fully
941 qualified name, including the package name, for C<has_method> to
942 correctly identify it.
944 This will attempt to correctly ignore functions imported from other
945 packages using B<Exporter>. It breaks down if the function imported
946 is an C<__ANON__> sub (such as with C<use constant>), which very well
947 may be a valid method being applied to the class.
949 In short, this method cannot always be trusted to determine if the
950 C<$method_name> is actually a method. However, it will DWIM about
951 90% of the time, so it's a small trade off I think.
953 =item B<get_method ($method_name)>
955 This will return a CODE reference of the specified C<$method_name>,
956 or return undef if that method does not exist.
958 =item B<find_method_by_name ($method_name>
960 This will return a CODE reference of the specified C<$method_name>,
961 or return undef if that method does not exist.
963 Unlike C<get_method> this will also look in the superclasses.
965 =item B<remove_method ($method_name)>
967 This will attempt to remove a given C<$method_name> from the class.
968 It will return the CODE reference that it has removed, and will
969 attempt to use B<Sub::Name> to clear the methods associated name.
971 =item B<get_method_list>
973 This will return a list of method names for all I<locally> defined
974 methods. It does B<not> provide a list of all applicable methods,
975 including any inherited ones. If you want a list of all applicable
976 methods, use the C<compute_all_applicable_methods> method.
978 =item B<compute_all_applicable_methods>
980 This will return a list of all the methods names this class will
981 respond to, taking into account inheritance. The list will be a list of
982 HASH references, each one containing the following information; method
983 name, the name of the class in which the method lives and a CODE
984 reference for the actual method.
986 =item B<find_all_methods_by_name ($method_name)>
988 This will traverse the inheritence hierarchy and locate all methods
989 with a given C<$method_name>. Similar to
990 C<compute_all_applicable_methods> it returns a list of HASH references
991 with the following information; method name (which will always be the
992 same as C<$method_name>), the name of the class in which the method
993 lives and a CODE reference for the actual method.
995 The list of methods produced is a distinct list, meaning there are no
996 duplicates in it. This is especially useful for things like object
997 initialization and destruction where you only want the method called
998 once, and in the correct order.
1000 =item B<find_next_method_by_name ($method_name)>
1002 This will return the first method to match a given C<$method_name> in
1003 the superclasses, this is basically equivalent to calling
1004 C<SUPER::$method_name>, but it can be dispatched at runtime.
1008 =head2 Method Modifiers
1010 Method modifiers are a concept borrowed from CLOS, in which a method
1011 can be wrapped with I<before>, I<after> and I<around> method modifiers
1012 that will be called everytime the method is called.
1014 =head3 How method modifiers work?
1016 Method modifiers work by wrapping the original method and then replacing
1017 it in the classes symbol table. The wrappers will handle calling all the
1018 modifiers in the appropariate orders and preserving the calling context
1019 for the original method.
1021 Each method modifier serves a particular purpose, which may not be
1022 obvious to users of other method wrapping modules. To start with, the
1023 return values of I<before> and I<after> modifiers are ignored. This is
1024 because thier purpose is B<not> to filter the input and output of the
1025 primary method (this is done with an I<around> modifier). This may seem
1026 like an odd restriction to some, but doing this allows for simple code
1027 to be added at the begining or end of a method call without jeapordizing
1028 the normal functioning of the primary method or placing any extra
1029 responsibility on the code of the modifier. Of course if you have more
1030 complex needs, then use the I<around> modifier, which uses a variation
1031 of continutation passing style to allow for a high degree of flexibility.
1033 Before and around modifiers are called in last-defined-first-called order,
1034 while after modifiers are called in first-defined-first-called order. So
1035 the call tree might looks something like this:
1045 To see examples of using method modifiers, see the following examples
1046 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1047 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1048 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1050 =head3 What is the performance impact?
1052 Of course there is a performance cost associated with method modifiers,
1053 but we have made every effort to make that cost be directly proportional
1054 to the amount of modifier features you utilize.
1056 The wrapping method does it's best to B<only> do as much work as it
1057 absolutely needs to. In order to do this we have moved some of the
1058 performance costs to set-up time, where they are easier to amortize.
1060 All this said, my benchmarks have indicated the following:
1062 simple wrapper with no modifiers 100% slower
1063 simple wrapper with simple before modifier 400% slower
1064 simple wrapper with simple after modifier 450% slower
1065 simple wrapper with simple around modifier 500-550% slower
1066 simple wrapper with all 3 modifiers 1100% slower
1068 These numbers may seem daunting, but you must remember, every feature
1069 comes with some cost. To put things in perspective, just doing a simple
1070 C<AUTOLOAD> which does nothing but extract the name of the method called
1071 and return it costs about 400% over a normal method call.
1075 =item B<add_before_method_modifier ($method_name, $code)>
1077 This will wrap the method at C<$method_name> and the supplied C<$code>
1078 will be passed the C<@_> arguments, and called before the original
1079 method is called. As specified above, the return value of the I<before>
1080 method modifiers is ignored, and it's ability to modify C<@_> is
1081 fairly limited. If you need to do either of these things, use an
1082 C<around> method modifier.
1084 =item B<add_after_method_modifier ($method_name, $code)>
1086 This will wrap the method at C<$method_name> so that the original
1087 method will be called, it's return values stashed, and then the
1088 supplied C<$code> will be passed the C<@_> arguments, and called.
1089 As specified above, the return value of the I<after> method
1090 modifiers is ignored, and it cannot modify the return values of
1091 the original method. If you need to do either of these things, use an
1092 C<around> method modifier.
1094 =item B<add_around_method_modifier ($method_name, $code)>
1096 This will wrap the method at C<$method_name> so that C<$code>
1097 will be called and passed the original method as an extra argument
1098 at the begining of the C<@_> argument list. This is a variation of
1099 continuation passing style, where the function prepended to C<@_>
1100 can be considered a continuation. It is up to C<$code> if it calls
1101 the original method or not, there is no restriction on what the
1102 C<$code> can or cannot do.
1108 It should be noted that since there is no one consistent way to define
1109 the attributes of a class in Perl 5. These methods can only work with
1110 the information given, and can not easily discover information on
1111 their own. See L<Class::MOP::Attribute> for more details.
1115 =item B<attribute_metaclass>
1117 =item B<get_attribute_map>
1119 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1121 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1122 instance associated with the given class, and associates it with
1123 the C<$attribute_name>. Unlike methods, attributes within the MOP
1124 are stored as meta-information only. They will be used later to
1125 construct instances from (see C<construct_instance> above).
1126 More details about the attribute meta-objects can be found in the
1127 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1130 It should be noted that any accessor, reader/writer or predicate
1131 methods which the C<$attribute_meta_object> has will be installed
1132 into the class at this time.
1134 =item B<has_attribute ($attribute_name)>
1136 Checks to see if this class has an attribute by the name of
1137 C<$attribute_name> and returns a boolean.
1139 =item B<get_attribute ($attribute_name)>
1141 Returns the attribute meta-object associated with C<$attribute_name>,
1142 if none is found, it will return undef.
1144 =item B<remove_attribute ($attribute_name)>
1146 This will remove the attribute meta-object stored at
1147 C<$attribute_name>, then return the removed attribute meta-object.
1150 Removing an attribute will only affect future instances of
1151 the class, it will not make any attempt to remove the attribute from
1152 any existing instances of the class.
1154 It should be noted that any accessor, reader/writer or predicate
1155 methods which the attribute meta-object stored at C<$attribute_name>
1156 has will be removed from the class at this time. This B<will> make
1157 these attributes somewhat inaccessable in previously created
1158 instances. But if you are crazy enough to do this at runtime, then
1159 you are crazy enough to deal with something like this :).
1161 =item B<get_attribute_list>
1163 This returns a list of attribute names which are defined in the local
1164 class. If you want a list of all applicable attributes for a class,
1165 use the C<compute_all_applicable_attributes> method.
1167 =item B<compute_all_applicable_attributes>
1169 This will traverse the inheritance heirachy and return a list of all
1170 the applicable attributes for this class. It does not construct a
1171 HASH reference like C<compute_all_applicable_methods> because all
1172 that same information is discoverable through the attribute
1175 =item B<find_attribute_by_name ($attr_name)>
1177 This method will traverse the inheritance heirachy and find the
1178 first attribute whose name matches C<$attr_name>, then return it.
1179 It will return undef if nothing is found.
1183 =head2 Package Variables
1185 Since Perl's classes are built atop the Perl package system, it is
1186 fairly common to use package scoped variables for things like static
1187 class variables. The following methods are convience methods for
1188 the creation and inspection of package scoped variables.
1192 =item B<add_package_symbol ($variable_name, ?$initial_value)>
1194 Given a C<$variable_name>, which must contain a leading sigil, this
1195 method will create that variable within the package which houses the
1196 class. It also takes an optional C<$initial_value>, which must be a
1197 reference of the same type as the sigil of the C<$variable_name>
1200 =item B<get_package_symbol ($variable_name)>
1202 This will return a reference to the package variable in
1205 =item B<has_package_symbol ($variable_name)>
1207 Returns true (C<1>) if there is a package variable defined for
1208 C<$variable_name>, and false (C<0>) otherwise.
1210 =item B<remove_package_symbol ($variable_name)>
1212 This will attempt to remove the package variable at C<$variable_name>.
1216 =head2 Class closing
1222 =item B<is_immutable>
1224 =item B<make_immutable>
1230 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1232 Yuval Kogman E<lt>nothingmuch@woobling.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.