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 = '0.19';
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]) }
27 my $package_name = shift;
28 (defined $package_name && $package_name && !blessed($package_name))
29 || confess "You must pass a package name and it cannot be blessed";
30 $class->construct_class_instance(':package' => $package_name, @_);
35 my $package_name = shift;
36 (defined $package_name && $package_name && !blessed($package_name))
37 || confess "You must pass a package name and it cannot be blessed";
38 Class::MOP::remove_metaclass_by_name($package_name);
39 $class->construct_class_instance(':package' => $package_name, @_);
42 # NOTE: (meta-circularity)
43 # this is a special form of &construct_instance
44 # (see below), which is used to construct class
45 # meta-object instances for any Class::MOP::*
46 # class. All other classes will use the more
47 # normal &construct_instance.
48 sub construct_class_instance {
51 my $package_name = $options{':package'};
52 (defined $package_name && $package_name)
53 || confess "You must pass a package name";
55 # return the metaclass if we have it cached,
56 # and it is still defined (it has not been
57 # reaped by DESTROY yet, which can happen
58 # annoyingly enough during global destruction)
59 return Class::MOP::get_metaclass_by_name($package_name)
60 if Class::MOP::does_metaclass_exist($package_name);
63 # we need to deal with the possibility
64 # of class immutability here, and then
65 # get the name of the class appropriately
66 $class = (blessed($class)
67 ? ($class->is_immutable
68 ? $class->get_mutable_metaclass_name()
72 $class = blessed($class) || $class;
73 # now create the metaclass
75 if ($class =~ /^Class::MOP::Class$/) {
78 # inherited from Class::MOP::Package
79 '$:package' => $package_name,
82 # since the following attributes will
83 # actually be loaded from the symbol
84 # table, and actually bypass the instance
85 # entirely, we can just leave these things
86 # listed here for reference, because they
87 # should not actually have a value associated
89 '%:namespace' => \undef,
90 # inherited from Class::MOP::Module
91 '$:version' => \undef,
92 '$:authority' => \undef,
93 # defined in Class::MOP::Class
97 '$:attribute_metaclass' => $options{':attribute_metaclass'} || 'Class::MOP::Attribute',
98 '$:method_metaclass' => $options{':method_metaclass'} || 'Class::MOP::Method',
99 '$:instance_metaclass' => $options{':instance_metaclass'} || 'Class::MOP::Instance',
104 # it is safe to use meta here because
105 # class will always be a subclass of
106 # Class::MOP::Class, which defines meta
107 $meta = $class->meta->construct_instance(%options)
110 # and check the metaclass compatibility
111 $meta->check_metaclass_compatability();
113 Class::MOP::store_metaclass_by_name($package_name, $meta);
116 # we need to weaken any anon classes
117 # so that they can call DESTROY properly
118 Class::MOP::weaken_metaclass($package_name) if $meta->is_anon_class;
123 sub check_metaclass_compatability {
126 # this is always okay ...
127 return if blessed($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 $meta = Class::MOP::get_metaclass_by_name($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) . ")";
162 # this should be sufficient, if you have a
163 # use case where it is not, write a test and
165 my $ANON_CLASS_SERIAL = 0;
168 # we need a sufficiently annoying prefix
169 # this should suffice for now, this is
170 # used in a couple of places below, so
171 # need to put it up here for now.
172 my $ANON_CLASS_PREFIX = 'Class::MOP::Class::__ANON__::SERIAL::';
176 $self->name =~ /^$ANON_CLASS_PREFIX/ ? 1 : 0;
179 sub create_anon_class {
180 my ($class, %options) = @_;
181 my $package_name = $ANON_CLASS_PREFIX . ++$ANON_CLASS_SERIAL;
182 return $class->create($package_name, %options);
186 # this will only get called for
187 # anon-classes, all other calls
188 # are assumed to occur during
189 # global destruction and so don't
190 # really need to be handled explicitly
193 return unless $self->name =~ /^$ANON_CLASS_PREFIX/;
194 my ($serial_id) = ($self->name =~ /^$ANON_CLASS_PREFIX(\d+)/);
196 foreach my $key (keys %{$ANON_CLASS_PREFIX . $serial_id}) {
197 delete ${$ANON_CLASS_PREFIX . $serial_id}{$key};
199 delete ${'main::' . $ANON_CLASS_PREFIX}{$serial_id . '::'};
204 # creating classes with MOP ...
208 my $package_name = shift;
210 (defined $package_name && $package_name)
211 || confess "You must pass a package name";
214 || confess "You much pass all parameters as name => value pairs " .
215 "(I found an uneven number of params in \@_)";
219 my $code = "package $package_name;";
220 $code .= "\$$package_name\:\:VERSION = '" . $options{version} . "';"
221 if exists $options{version};
222 $code .= "\$$package_name\:\:AUTHORITY = '" . $options{authority} . "';"
223 if exists $options{authority};
226 confess "creation of $package_name failed : $@" if $@;
228 my $meta = $class->initialize($package_name);
230 $meta->add_method('meta' => sub {
231 $class->initialize(blessed($_[0]) || $_[0]);
234 $meta->superclasses(@{$options{superclasses}})
235 if exists $options{superclasses};
237 # process attributes first, so that they can
238 # install accessors, but locally defined methods
239 # can then overwrite them. It is maybe a little odd, but
240 # I think this should be the order of things.
241 if (exists $options{attributes}) {
242 foreach my $attr (@{$options{attributes}}) {
243 $meta->add_attribute($attr);
246 if (exists $options{methods}) {
247 foreach my $method_name (keys %{$options{methods}}) {
248 $meta->add_method($method_name, $options{methods}->{$method_name});
257 # all these attribute readers will be bootstrapped
258 # away in the Class::MOP bootstrap section
260 sub get_attribute_map { $_[0]->{'%:attributes'} }
261 sub attribute_metaclass { $_[0]->{'$:attribute_metaclass'} }
262 sub method_metaclass { $_[0]->{'$:method_metaclass'} }
263 sub instance_metaclass { $_[0]->{'$:instance_metaclass'} }
267 my $map = $self->{'%:methods'};
269 foreach my $symbol ($self->list_all_package_symbols('CODE')) {
270 next if exists $map->{$symbol} &&
271 $map->{$symbol}->body == $self->get_package_symbol('&' . $symbol);
273 $map->{$symbol} = $self->method_metaclass->wrap(
274 $self->get_package_symbol('&' . $symbol)
281 # Instance Construction & Cloning
286 # we need to protect the integrity of the
287 # Class::MOP::Class singletons here, so we
288 # delegate this to &construct_class_instance
289 # which will deal with the singletons
290 return $class->construct_class_instance(@_)
291 if $class->name->isa('Class::MOP::Class');
292 return $class->construct_instance(@_);
295 sub construct_instance {
296 my ($class, %params) = @_;
297 my $meta_instance = $class->get_meta_instance();
298 my $instance = $meta_instance->create_instance();
299 foreach my $attr ($class->compute_all_applicable_attributes()) {
300 $attr->initialize_instance_slot($meta_instance, $instance, \%params);
305 sub get_meta_instance {
307 return $class->instance_metaclass->new(
309 $class->compute_all_applicable_attributes()
315 my $instance = shift;
316 (blessed($instance) && $instance->isa($class->name))
317 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
319 # we need to protect the integrity of the
320 # Class::MOP::Class singletons here, they
321 # should not be cloned.
322 return $instance if $instance->isa('Class::MOP::Class');
323 $class->clone_instance($instance, @_);
327 my ($class, $instance, %params) = @_;
329 || confess "You can only clone instances, \$self is not a blessed instance";
330 my $meta_instance = $class->get_meta_instance();
331 my $clone = $meta_instance->clone_instance($instance);
332 foreach my $key (keys %params) {
333 next unless $meta_instance->is_valid_slot($key);
334 $meta_instance->set_slot_value($clone, $key, $params{$key});
345 @{$self->get_package_symbol('@ISA')} = @supers;
347 # we need to check the metaclass
348 # compatability here so that we can
349 # be sure that the superclass is
350 # not potentially creating an issues
351 # we don't know about
352 $self->check_metaclass_compatability();
354 @{$self->get_package_symbol('@ISA')};
357 sub class_precedence_list {
360 # We need to check for ciruclar inheirtance here.
361 # This will do nothing if all is well, and blow
362 # up otherwise. Yes, it's an ugly hack, better
363 # suggestions are welcome.
364 { ($self->name || return)->isa('This is a test for circular inheritance') }
365 # ... and now back to our regularly scheduled program
369 $self->initialize($_)->class_precedence_list()
370 } $self->superclasses()
377 my ($self, $method_name, $method) = @_;
378 (defined $method_name && $method_name)
379 || confess "You must define a method name";
382 if (blessed($method)) {
383 $body = $method->body;
384 $self->get_method_map->{$method_name} = $method;
388 ('CODE' eq (reftype($body) || ''))
389 || confess "Your code block must be a CODE reference";
390 $self->get_method_map->{$method_name} = $self->method_metaclass->wrap($body);
393 my $full_method_name = ($self->name . '::' . $method_name);
394 $self->add_package_symbol("&${method_name}" => subname $full_method_name => $body);
398 my $fetch_and_prepare_method = sub {
399 my ($self, $method_name) = @_;
401 my $method = $self->get_method($method_name);
402 # if we dont have local ...
404 # try to find the next method
405 $method = $self->find_next_method_by_name($method_name);
406 # die if it does not exist
408 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
409 # and now make sure to wrap it
410 # even if it is already wrapped
411 # because we need a new sub ref
412 $method = Class::MOP::Method::Wrapped->wrap($method);
415 # now make sure we wrap it properly
416 $method = Class::MOP::Method::Wrapped->wrap($method)
417 unless $method->isa('Class::MOP::Method::Wrapped');
419 $self->add_method($method_name => $method);
423 sub add_before_method_modifier {
424 my ($self, $method_name, $method_modifier) = @_;
425 (defined $method_name && $method_name)
426 || confess "You must pass in a method name";
427 my $method = $fetch_and_prepare_method->($self, $method_name);
428 $method->add_before_modifier(subname ':before' => $method_modifier);
431 sub add_after_method_modifier {
432 my ($self, $method_name, $method_modifier) = @_;
433 (defined $method_name && $method_name)
434 || confess "You must pass in a method name";
435 my $method = $fetch_and_prepare_method->($self, $method_name);
436 $method->add_after_modifier(subname ':after' => $method_modifier);
439 sub add_around_method_modifier {
440 my ($self, $method_name, $method_modifier) = @_;
441 (defined $method_name && $method_name)
442 || confess "You must pass in a method name";
443 my $method = $fetch_and_prepare_method->($self, $method_name);
444 $method->add_around_modifier(subname ':around' => $method_modifier);
448 # the methods above used to be named like this:
449 # ${pkg}::${method}:(before|after|around)
450 # but this proved problematic when using one modifier
451 # to wrap multiple methods (something which is likely
452 # to happen pretty regularly IMO). So instead of naming
453 # it like this, I have chosen to just name them purely
454 # with their modifier names, like so:
455 # :(before|after|around)
456 # The fact is that in a stack trace, it will be fairly
457 # evident from the context what method they are attached
458 # to, and so don't need the fully qualified name.
462 my ($self, $method_name, $method) = @_;
463 (defined $method_name && $method_name)
464 || confess "You must define a method name";
467 if (blessed($method)) {
468 $body = $method->body;
469 $self->get_method_map->{$method_name} = $method;
473 ('CODE' eq (reftype($body) || ''))
474 || confess "Your code block must be a CODE reference";
475 $self->get_method_map->{$method_name} = $self->method_metaclass->wrap($body);
478 $self->add_package_symbol("&${method_name}" => $body);
482 my ($self, $method_name) = @_;
483 (defined $method_name && $method_name)
484 || confess "You must define a method name";
486 my $method_map = $self->get_method_map;
488 return 0 unless exists $self->get_method_map->{$method_name};
490 my $method = $method_map->{$method_name};
491 return 0 if ($method->package_name || '') ne $self->name &&
492 ($method->name || '') ne '__ANON__';
498 my ($self, $method_name) = @_;
499 (defined $method_name && $method_name)
500 || confess "You must define a method name";
502 return unless $self->has_method($method_name);
504 return $self->get_method_map->{$method_name};
508 my ($self, $method_name) = @_;
509 (defined $method_name && $method_name)
510 || confess "You must define a method name";
512 my $removed_method = $self->get_method($method_name);
514 $self->remove_package_symbol("&${method_name}")
515 if defined $removed_method;
517 delete $self->get_method_map->{$method_name}
518 if exists $self->get_method_map->{$method_name};
520 return $removed_method;
523 sub get_method_list {
525 return grep { $self->has_method($_) } keys %{$self->get_method_map};
528 sub find_method_by_name {
529 my ($self, $method_name) = @_;
531 return $self->name->can($method_name);
534 sub compute_all_applicable_methods {
537 # keep a record of what we have seen
538 # here, this will handle all the
539 # inheritence issues because we are
540 # using the &class_precedence_list
541 my (%seen_class, %seen_method);
542 foreach my $class ($self->class_precedence_list()) {
543 next if $seen_class{$class};
544 $seen_class{$class}++;
545 # fetch the meta-class ...
546 my $meta = $self->initialize($class);
547 foreach my $method_name ($meta->get_method_list()) {
548 next if exists $seen_method{$method_name};
549 $seen_method{$method_name}++;
551 name => $method_name,
553 code => $meta->get_method($method_name)
560 sub find_all_methods_by_name {
561 my ($self, $method_name) = @_;
562 (defined $method_name && $method_name)
563 || confess "You must define a method name to find";
565 # keep a record of what we have seen
566 # here, this will handle all the
567 # inheritence issues because we are
568 # using the &class_precedence_list
570 foreach my $class ($self->class_precedence_list()) {
571 next if $seen_class{$class};
572 $seen_class{$class}++;
573 # fetch the meta-class ...
574 my $meta = $self->initialize($class);
576 name => $method_name,
578 code => $meta->get_method($method_name)
579 } if $meta->has_method($method_name);
584 sub find_next_method_by_name {
585 my ($self, $method_name) = @_;
586 (defined $method_name && $method_name)
587 || confess "You must define a method name to find";
588 # keep a record of what we have seen
589 # here, this will handle all the
590 # inheritence issues because we are
591 # using the &class_precedence_list
593 my @cpl = $self->class_precedence_list();
594 shift @cpl; # discard ourselves
595 foreach my $class (@cpl) {
596 next if $seen_class{$class};
597 $seen_class{$class}++;
598 # fetch the meta-class ...
599 my $meta = $self->initialize($class);
600 return $meta->get_method($method_name)
601 if $meta->has_method($method_name);
610 # either we have an attribute object already
611 # or we need to create one from the args provided
612 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
613 # make sure it is derived from the correct type though
614 ($attribute->isa('Class::MOP::Attribute'))
615 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
616 $attribute->attach_to_class($self);
617 $attribute->install_accessors();
618 $self->get_attribute_map->{$attribute->name} = $attribute;
622 my ($self, $attribute_name) = @_;
623 (defined $attribute_name && $attribute_name)
624 || confess "You must define an attribute name";
625 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
629 my ($self, $attribute_name) = @_;
630 (defined $attribute_name && $attribute_name)
631 || confess "You must define an attribute name";
632 return $self->get_attribute_map->{$attribute_name}
633 if $self->has_attribute($attribute_name);
637 sub remove_attribute {
638 my ($self, $attribute_name) = @_;
639 (defined $attribute_name && $attribute_name)
640 || confess "You must define an attribute name";
641 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
642 return unless defined $removed_attribute;
643 delete $self->get_attribute_map->{$attribute_name};
644 $removed_attribute->remove_accessors();
645 $removed_attribute->detach_from_class();
646 return $removed_attribute;
649 sub get_attribute_list {
651 keys %{$self->get_attribute_map};
654 sub compute_all_applicable_attributes {
657 # keep a record of what we have seen
658 # here, this will handle all the
659 # inheritence issues because we are
660 # using the &class_precedence_list
661 my (%seen_class, %seen_attr);
662 foreach my $class ($self->class_precedence_list()) {
663 next if $seen_class{$class};
664 $seen_class{$class}++;
665 # fetch the meta-class ...
666 my $meta = $self->initialize($class);
667 foreach my $attr_name ($meta->get_attribute_list()) {
668 next if exists $seen_attr{$attr_name};
669 $seen_attr{$attr_name}++;
670 push @attrs => $meta->get_attribute($attr_name);
676 sub find_attribute_by_name {
677 my ($self, $attr_name) = @_;
678 # keep a record of what we have seen
679 # here, this will handle all the
680 # inheritence issues because we are
681 # using the &class_precedence_list
683 foreach my $class ($self->class_precedence_list()) {
684 next if $seen_class{$class};
685 $seen_class{$class}++;
686 # fetch the meta-class ...
687 my $meta = $self->initialize($class);
688 return $meta->get_attribute($attr_name)
689 if $meta->has_attribute($attr_name);
697 sub is_immutable { 0 }
700 return Class::MOP::Class::Immutable->make_metaclass_immutable(@_);
711 Class::MOP::Class - Class Meta Object
715 # assuming that class Foo
716 # has been defined, you can
718 # use this for introspection ...
720 # add a method to Foo ...
721 Foo->meta->add_method('bar' => sub { ... })
723 # get a list of all the classes searched
724 # the method dispatcher in the correct order
725 Foo->meta->class_precedence_list()
727 # remove a method from Foo
728 Foo->meta->remove_method('bar');
730 # or use this to actually create classes ...
732 Class::MOP::Class->create('Bar' => (
734 superclasses => [ 'Foo' ],
736 Class::MOP:::Attribute->new('$bar'),
737 Class::MOP:::Attribute->new('$baz'),
740 calculate_bar => sub { ... },
741 construct_baz => sub { ... }
747 This is the largest and currently most complex part of the Perl 5
748 meta-object protocol. It controls the introspection and
749 manipulation of Perl 5 classes (and it can create them too). The
750 best way to understand what this module can do, is to read the
751 documentation for each of it's methods.
755 =head2 Self Introspection
761 This will return a B<Class::MOP::Class> instance which is related
762 to this class. Thereby allowing B<Class::MOP::Class> to actually
765 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
766 bootstrap this module by installing a number of attribute meta-objects
767 into it's metaclass. This will allow this class to reap all the benifits
768 of the MOP when subclassing it.
772 =head2 Class construction
774 These methods will handle creating B<Class::MOP::Class> objects,
775 which can be used to both create new classes, and analyze
776 pre-existing classes.
778 This module will internally store references to all the instances
779 you create with these methods, so that they do not need to be
780 created any more than nessecary. Basically, they are singletons.
784 =item B<create ($package_name,
785 version =E<gt> ?$version,
786 authority =E<gt> ?$authority,
787 superclasses =E<gt> ?@superclasses,
788 methods =E<gt> ?%methods,
789 attributes =E<gt> ?%attributes)>
791 This returns a B<Class::MOP::Class> object, bringing the specified
792 C<$package_name> into existence and adding any of the C<$version>,
793 C<$authority>, C<@superclasses>, C<%methods> and C<%attributes> to
796 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
797 methods =E<gt> ?%methods,
798 attributes =E<gt> ?%attributes)>
800 This will create an anonymous class, it works much like C<create> but
801 it does not need a C<$package_name>. Instead it will create a suitably
802 unique package name for you to stash things into.
804 =item B<initialize ($package_name, %options)>
806 This initializes and returns returns a B<Class::MOP::Class> object
807 for a given a C<$package_name>.
809 =item B<reinitialize ($package_name, %options)>
811 This removes the old metaclass, and creates a new one in it's place.
812 Do B<not> use this unless you really know what you are doing, it could
813 very easily make a very large mess of your program.
815 =item B<construct_class_instance (%options)>
817 This will construct an instance of B<Class::MOP::Class>, it is
818 here so that we can actually "tie the knot" for B<Class::MOP::Class>
819 to use C<construct_instance> once all the bootstrapping is done. This
820 method is used internally by C<initialize> and should never be called
821 from outside of that method really.
823 =item B<check_metaclass_compatability>
825 This method is called as the very last thing in the
826 C<construct_class_instance> method. This will check that the
827 metaclass you are creating is compatible with the metaclasses of all
828 your ancestors. For more inforamtion about metaclass compatibility
829 see the C<About Metaclass compatibility> section in L<Class::MOP>.
833 =head2 Object instance construction and cloning
835 These methods are B<entirely optional>, it is up to you whether you want
840 =item B<instance_metaclass>
842 =item B<get_meta_instance>
844 =item B<new_object (%params)>
846 This is a convience method for creating a new object of the class, and
847 blessing it into the appropriate package as well. Ideally your class
848 would call a C<new> this method like so:
851 my ($class, %param) = @_;
852 $class->meta->new_object(%params);
855 Of course the ideal place for this would actually be in C<UNIVERSAL::>
856 but that is considered bad style, so we do not do that.
858 =item B<construct_instance (%params)>
860 This method is used to construct an instace structure suitable for
861 C<bless>-ing into your package of choice. It works in conjunction
862 with the Attribute protocol to collect all applicable attributes.
864 This will construct and instance using a HASH ref as storage
865 (currently only HASH references are supported). This will collect all
866 the applicable attributes and layout out the fields in the HASH ref,
867 it will then initialize them using either use the corresponding key
868 in C<%params> or any default value or initializer found in the
869 attribute meta-object.
871 =item B<clone_object ($instance, %params)>
873 This is a convience method for cloning an object instance, then
874 blessing it into the appropriate package. This method will call
875 C<clone_instance>, which performs a shallow copy of the object,
876 see that methods documentation for more details. Ideally your
877 class would call a C<clone> this method like so:
880 my ($self, %param) = @_;
881 $self->meta->clone_object($self, %params);
884 Of course the ideal place for this would actually be in C<UNIVERSAL::>
885 but that is considered bad style, so we do not do that.
887 =item B<clone_instance($instance, %params)>
889 This method is a compliment of C<construct_instance> (which means if
890 you override C<construct_instance>, you need to override this one too),
891 and clones the instance shallowly.
893 The cloned structure returned is (like with C<construct_instance>) an
894 unC<bless>ed HASH reference, it is your responsibility to then bless
895 this cloned structure into the right class (which C<clone_object> will
898 As of 0.11, this method will clone the C<$instance> structure shallowly,
899 as opposed to the deep cloning implemented in prior versions. After much
900 thought, research and discussion, I have decided that anything but basic
901 shallow cloning is outside the scope of the meta-object protocol. I
902 think Yuval "nothingmuch" Kogman put it best when he said that cloning
903 is too I<context-specific> to be part of the MOP.
909 These are a few predicate methods for asking information about the class.
913 =item B<is_anon_class>
917 =item B<is_immutable>
921 =head2 Inheritance Relationships
925 =item B<superclasses (?@superclasses)>
927 This is a read-write attribute which represents the superclass
928 relationships of the class the B<Class::MOP::Class> instance is
929 associated with. Basically, it can get and set the C<@ISA> for you.
932 Perl will occasionally perform some C<@ISA> and method caching, if
933 you decide to change your superclass relationship at runtime (which
934 is quite insane and very much not recommened), then you should be
935 aware of this and the fact that this module does not make any
936 attempt to address this issue.
938 =item B<class_precedence_list>
940 This computes the a list of all the class's ancestors in the same order
941 in which method dispatch will be done. This is similair to
942 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
950 =item B<get_method_map>
952 =item B<method_metaclass>
954 =item B<add_method ($method_name, $method)>
956 This will take a C<$method_name> and CODE reference to that
957 C<$method> and install it into the class's package.
960 This does absolutely nothing special to C<$method>
961 other than use B<Sub::Name> to make sure it is tagged with the
962 correct name, and therefore show up correctly in stack traces and
965 =item B<alias_method ($method_name, $method)>
967 This will take a C<$method_name> and CODE reference to that
968 C<$method> and alias the method into the class's package.
971 Unlike C<add_method>, this will B<not> try to name the
972 C<$method> using B<Sub::Name>, it only aliases the method in
975 =item B<has_method ($method_name)>
977 This just provides a simple way to check if the class implements
978 a specific C<$method_name>. It will I<not> however, attempt to check
979 if the class inherits the method (use C<UNIVERSAL::can> for that).
981 This will correctly handle functions defined outside of the package
982 that use a fully qualified name (C<sub Package::name { ... }>).
984 This will correctly handle functions renamed with B<Sub::Name> and
985 installed using the symbol tables. However, if you are naming the
986 subroutine outside of the package scope, you must use the fully
987 qualified name, including the package name, for C<has_method> to
988 correctly identify it.
990 This will attempt to correctly ignore functions imported from other
991 packages using B<Exporter>. It breaks down if the function imported
992 is an C<__ANON__> sub (such as with C<use constant>), which very well
993 may be a valid method being applied to the class.
995 In short, this method cannot always be trusted to determine if the
996 C<$method_name> is actually a method. However, it will DWIM about
997 90% of the time, so it's a small trade off I think.
999 =item B<get_method ($method_name)>
1001 This will return a CODE reference of the specified C<$method_name>,
1002 or return undef if that method does not exist.
1004 =item B<find_method_by_name ($method_name>
1006 This will return a CODE reference of the specified C<$method_name>,
1007 or return undef if that method does not exist.
1009 Unlike C<get_method> this will also look in the superclasses.
1011 =item B<remove_method ($method_name)>
1013 This will attempt to remove a given C<$method_name> from the class.
1014 It will return the CODE reference that it has removed, and will
1015 attempt to use B<Sub::Name> to clear the methods associated name.
1017 =item B<get_method_list>
1019 This will return a list of method names for all I<locally> defined
1020 methods. It does B<not> provide a list of all applicable methods,
1021 including any inherited ones. If you want a list of all applicable
1022 methods, use the C<compute_all_applicable_methods> method.
1024 =item B<compute_all_applicable_methods>
1026 This will return a list of all the methods names this class will
1027 respond to, taking into account inheritance. The list will be a list of
1028 HASH references, each one containing the following information; method
1029 name, the name of the class in which the method lives and a CODE
1030 reference for the actual method.
1032 =item B<find_all_methods_by_name ($method_name)>
1034 This will traverse the inheritence hierarchy and locate all methods
1035 with a given C<$method_name>. Similar to
1036 C<compute_all_applicable_methods> it returns a list of HASH references
1037 with the following information; method name (which will always be the
1038 same as C<$method_name>), the name of the class in which the method
1039 lives and a CODE reference for the actual method.
1041 The list of methods produced is a distinct list, meaning there are no
1042 duplicates in it. This is especially useful for things like object
1043 initialization and destruction where you only want the method called
1044 once, and in the correct order.
1046 =item B<find_next_method_by_name ($method_name)>
1048 This will return the first method to match a given C<$method_name> in
1049 the superclasses, this is basically equivalent to calling
1050 C<SUPER::$method_name>, but it can be dispatched at runtime.
1054 =head2 Method Modifiers
1056 Method modifiers are a concept borrowed from CLOS, in which a method
1057 can be wrapped with I<before>, I<after> and I<around> method modifiers
1058 that will be called everytime the method is called.
1060 =head3 How method modifiers work?
1062 Method modifiers work by wrapping the original method and then replacing
1063 it in the classes symbol table. The wrappers will handle calling all the
1064 modifiers in the appropariate orders and preserving the calling context
1065 for the original method.
1067 Each method modifier serves a particular purpose, which may not be
1068 obvious to users of other method wrapping modules. To start with, the
1069 return values of I<before> and I<after> modifiers are ignored. This is
1070 because thier purpose is B<not> to filter the input and output of the
1071 primary method (this is done with an I<around> modifier). This may seem
1072 like an odd restriction to some, but doing this allows for simple code
1073 to be added at the begining or end of a method call without jeapordizing
1074 the normal functioning of the primary method or placing any extra
1075 responsibility on the code of the modifier. Of course if you have more
1076 complex needs, then use the I<around> modifier, which uses a variation
1077 of continutation passing style to allow for a high degree of flexibility.
1079 Before and around modifiers are called in last-defined-first-called order,
1080 while after modifiers are called in first-defined-first-called order. So
1081 the call tree might looks something like this:
1091 To see examples of using method modifiers, see the following examples
1092 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1093 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1094 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1096 =head3 What is the performance impact?
1098 Of course there is a performance cost associated with method modifiers,
1099 but we have made every effort to make that cost be directly proportional
1100 to the amount of modifier features you utilize.
1102 The wrapping method does it's best to B<only> do as much work as it
1103 absolutely needs to. In order to do this we have moved some of the
1104 performance costs to set-up time, where they are easier to amortize.
1106 All this said, my benchmarks have indicated the following:
1108 simple wrapper with no modifiers 100% slower
1109 simple wrapper with simple before modifier 400% slower
1110 simple wrapper with simple after modifier 450% slower
1111 simple wrapper with simple around modifier 500-550% slower
1112 simple wrapper with all 3 modifiers 1100% slower
1114 These numbers may seem daunting, but you must remember, every feature
1115 comes with some cost. To put things in perspective, just doing a simple
1116 C<AUTOLOAD> which does nothing but extract the name of the method called
1117 and return it costs about 400% over a normal method call.
1121 =item B<add_before_method_modifier ($method_name, $code)>
1123 This will wrap the method at C<$method_name> and the supplied C<$code>
1124 will be passed the C<@_> arguments, and called before the original
1125 method is called. As specified above, the return value of the I<before>
1126 method modifiers is ignored, and it's ability to modify C<@_> is
1127 fairly limited. If you need to do either of these things, use an
1128 C<around> method modifier.
1130 =item B<add_after_method_modifier ($method_name, $code)>
1132 This will wrap the method at C<$method_name> so that the original
1133 method will be called, it's return values stashed, and then the
1134 supplied C<$code> will be passed the C<@_> arguments, and called.
1135 As specified above, the return value of the I<after> method
1136 modifiers is ignored, and it cannot modify the return values of
1137 the original method. If you need to do either of these things, use an
1138 C<around> method modifier.
1140 =item B<add_around_method_modifier ($method_name, $code)>
1142 This will wrap the method at C<$method_name> so that C<$code>
1143 will be called and passed the original method as an extra argument
1144 at the begining of the C<@_> argument list. This is a variation of
1145 continuation passing style, where the function prepended to C<@_>
1146 can be considered a continuation. It is up to C<$code> if it calls
1147 the original method or not, there is no restriction on what the
1148 C<$code> can or cannot do.
1154 It should be noted that since there is no one consistent way to define
1155 the attributes of a class in Perl 5. These methods can only work with
1156 the information given, and can not easily discover information on
1157 their own. See L<Class::MOP::Attribute> for more details.
1161 =item B<attribute_metaclass>
1163 =item B<get_attribute_map>
1165 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1167 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1168 instance associated with the given class, and associates it with
1169 the C<$attribute_name>. Unlike methods, attributes within the MOP
1170 are stored as meta-information only. They will be used later to
1171 construct instances from (see C<construct_instance> above).
1172 More details about the attribute meta-objects can be found in the
1173 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1176 It should be noted that any accessor, reader/writer or predicate
1177 methods which the C<$attribute_meta_object> has will be installed
1178 into the class at this time.
1180 =item B<has_attribute ($attribute_name)>
1182 Checks to see if this class has an attribute by the name of
1183 C<$attribute_name> and returns a boolean.
1185 =item B<get_attribute ($attribute_name)>
1187 Returns the attribute meta-object associated with C<$attribute_name>,
1188 if none is found, it will return undef.
1190 =item B<remove_attribute ($attribute_name)>
1192 This will remove the attribute meta-object stored at
1193 C<$attribute_name>, then return the removed attribute meta-object.
1196 Removing an attribute will only affect future instances of
1197 the class, it will not make any attempt to remove the attribute from
1198 any existing instances of the class.
1200 It should be noted that any accessor, reader/writer or predicate
1201 methods which the attribute meta-object stored at C<$attribute_name>
1202 has will be removed from the class at this time. This B<will> make
1203 these attributes somewhat inaccessable in previously created
1204 instances. But if you are crazy enough to do this at runtime, then
1205 you are crazy enough to deal with something like this :).
1207 =item B<get_attribute_list>
1209 This returns a list of attribute names which are defined in the local
1210 class. If you want a list of all applicable attributes for a class,
1211 use the C<compute_all_applicable_attributes> method.
1213 =item B<compute_all_applicable_attributes>
1215 This will traverse the inheritance heirachy and return a list of all
1216 the applicable attributes for this class. It does not construct a
1217 HASH reference like C<compute_all_applicable_methods> because all
1218 that same information is discoverable through the attribute
1221 =item B<find_attribute_by_name ($attr_name)>
1223 This method will traverse the inheritance heirachy and find the
1224 first attribute whose name matches C<$attr_name>, then return it.
1225 It will return undef if nothing is found.
1229 =head2 Class closing
1233 =item B<make_immutable>
1239 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1241 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1243 =head1 COPYRIGHT AND LICENSE
1245 Copyright 2006 by Infinity Interactive, Inc.
1247 L<http://www.iinteractive.com>
1249 This library is free software; you can redistribute it and/or modify
1250 it under the same terms as Perl itself.