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'};
268 foreach my $symbol ($self->list_all_package_symbols('CODE')) {
269 my $code = $self->get_package_symbol('&' . $symbol);
270 next if exists $map->{$symbol} && $map->{$symbol}->body == $code;
271 $map->{$symbol} = $self->method_metaclass->wrap($code);
276 # Instance Construction & Cloning
281 # we need to protect the integrity of the
282 # Class::MOP::Class singletons here, so we
283 # delegate this to &construct_class_instance
284 # which will deal with the singletons
285 return $class->construct_class_instance(@_)
286 if $class->name->isa('Class::MOP::Class');
287 return $class->construct_instance(@_);
290 sub construct_instance {
291 my ($class, %params) = @_;
292 my $meta_instance = $class->get_meta_instance();
293 my $instance = $meta_instance->create_instance();
294 foreach my $attr ($class->compute_all_applicable_attributes()) {
295 $attr->initialize_instance_slot($meta_instance, $instance, \%params);
300 sub get_meta_instance {
302 return $class->instance_metaclass->new(
304 $class->compute_all_applicable_attributes()
310 my $instance = shift;
311 (blessed($instance) && $instance->isa($class->name))
312 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
314 # we need to protect the integrity of the
315 # Class::MOP::Class singletons here, they
316 # should not be cloned.
317 return $instance if $instance->isa('Class::MOP::Class');
318 $class->clone_instance($instance, @_);
322 my ($class, $instance, %params) = @_;
324 || confess "You can only clone instances, \$self is not a blessed instance";
325 my $meta_instance = $class->get_meta_instance();
326 my $clone = $meta_instance->clone_instance($instance);
327 foreach my $key (keys %params) {
328 next unless $meta_instance->is_valid_slot($key);
329 $meta_instance->set_slot_value($clone, $key, $params{$key});
340 @{$self->get_package_symbol('@ISA')} = @supers;
342 # we need to check the metaclass
343 # compatability here so that we can
344 # be sure that the superclass is
345 # not potentially creating an issues
346 # we don't know about
347 $self->check_metaclass_compatability();
349 @{$self->get_package_symbol('@ISA')};
352 sub class_precedence_list {
355 # We need to check for ciruclar inheirtance here.
356 # This will do nothing if all is well, and blow
357 # up otherwise. Yes, it's an ugly hack, better
358 # suggestions are welcome.
359 { ($self->name || return)->isa('This is a test for circular inheritance') }
360 # ... and now back to our regularly scheduled program
364 $self->initialize($_)->class_precedence_list()
365 } $self->superclasses()
372 my ($self, $method_name, $method) = @_;
373 (defined $method_name && $method_name)
374 || confess "You must define a method name";
377 if (blessed($method)) {
378 $body = $method->body;
379 $self->get_method_map->{$method_name} = $method;
383 ('CODE' eq (reftype($body) || ''))
384 || confess "Your code block must be a CODE reference";
385 $self->get_method_map->{$method_name} = $self->method_metaclass->wrap($body);
388 my $full_method_name = ($self->name . '::' . $method_name);
389 $self->add_package_symbol("&${method_name}" => subname $full_method_name => $body);
393 my $fetch_and_prepare_method = sub {
394 my ($self, $method_name) = @_;
396 my $method = $self->get_method($method_name);
397 # if we dont have local ...
399 # try to find the next method
400 $method = $self->find_next_method_by_name($method_name);
401 # die if it does not exist
403 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
404 # and now make sure to wrap it
405 # even if it is already wrapped
406 # because we need a new sub ref
407 $method = Class::MOP::Method::Wrapped->wrap($method);
410 # now make sure we wrap it properly
411 $method = Class::MOP::Method::Wrapped->wrap($method)
412 unless $method->isa('Class::MOP::Method::Wrapped');
414 $self->add_method($method_name => $method);
418 sub add_before_method_modifier {
419 my ($self, $method_name, $method_modifier) = @_;
420 (defined $method_name && $method_name)
421 || confess "You must pass in a method name";
422 my $method = $fetch_and_prepare_method->($self, $method_name);
423 $method->add_before_modifier(subname ':before' => $method_modifier);
426 sub add_after_method_modifier {
427 my ($self, $method_name, $method_modifier) = @_;
428 (defined $method_name && $method_name)
429 || confess "You must pass in a method name";
430 my $method = $fetch_and_prepare_method->($self, $method_name);
431 $method->add_after_modifier(subname ':after' => $method_modifier);
434 sub add_around_method_modifier {
435 my ($self, $method_name, $method_modifier) = @_;
436 (defined $method_name && $method_name)
437 || confess "You must pass in a method name";
438 my $method = $fetch_and_prepare_method->($self, $method_name);
439 $method->add_around_modifier(subname ':around' => $method_modifier);
443 # the methods above used to be named like this:
444 # ${pkg}::${method}:(before|after|around)
445 # but this proved problematic when using one modifier
446 # to wrap multiple methods (something which is likely
447 # to happen pretty regularly IMO). So instead of naming
448 # it like this, I have chosen to just name them purely
449 # with their modifier names, like so:
450 # :(before|after|around)
451 # The fact is that in a stack trace, it will be fairly
452 # evident from the context what method they are attached
453 # to, and so don't need the fully qualified name.
457 my ($self, $method_name, $method) = @_;
458 (defined $method_name && $method_name)
459 || confess "You must define a method name";
462 if (blessed($method)) {
463 $body = $method->body;
464 $self->get_method_map->{$method_name} = $method;
468 ('CODE' eq (reftype($body) || ''))
469 || confess "Your code block must be a CODE reference";
470 $self->get_method_map->{$method_name} = $self->method_metaclass->wrap($body);
473 $self->add_package_symbol("&${method_name}" => $body);
477 my ($self, $method_name) = @_;
478 (defined $method_name && $method_name)
479 || confess "You must define a method name";
481 my $method_map = $self->get_method_map;
483 return 0 unless exists $self->get_method_map->{$method_name};
485 my $method = $method_map->{$method_name};
486 return 0 if ($method->package_name || '') ne $self->name &&
487 ($method->name || '') ne '__ANON__';
493 my ($self, $method_name) = @_;
494 (defined $method_name && $method_name)
495 || confess "You must define a method name";
497 return unless $self->has_method($method_name);
499 return $self->get_method_map->{$method_name};
503 my ($self, $method_name) = @_;
504 (defined $method_name && $method_name)
505 || confess "You must define a method name";
507 my $removed_method = $self->get_method($method_name);
509 $self->remove_package_symbol("&${method_name}")
510 if defined $removed_method;
512 delete $self->get_method_map->{$method_name}
513 if exists $self->get_method_map->{$method_name};
515 return $removed_method;
518 sub get_method_list {
520 return grep { $self->has_method($_) } keys %{$self->get_method_map};
523 sub find_method_by_name {
524 my ($self, $method_name) = @_;
526 return $self->name->can($method_name);
529 sub compute_all_applicable_methods {
532 # keep a record of what we have seen
533 # here, this will handle all the
534 # inheritence issues because we are
535 # using the &class_precedence_list
536 my (%seen_class, %seen_method);
537 foreach my $class ($self->class_precedence_list()) {
538 next if $seen_class{$class};
539 $seen_class{$class}++;
540 # fetch the meta-class ...
541 my $meta = $self->initialize($class);
542 foreach my $method_name ($meta->get_method_list()) {
543 next if exists $seen_method{$method_name};
544 $seen_method{$method_name}++;
546 name => $method_name,
548 code => $meta->get_method($method_name)
555 sub find_all_methods_by_name {
556 my ($self, $method_name) = @_;
557 (defined $method_name && $method_name)
558 || confess "You must define a method name to find";
560 # keep a record of what we have seen
561 # here, this will handle all the
562 # inheritence issues because we are
563 # using the &class_precedence_list
565 foreach my $class ($self->class_precedence_list()) {
566 next if $seen_class{$class};
567 $seen_class{$class}++;
568 # fetch the meta-class ...
569 my $meta = $self->initialize($class);
571 name => $method_name,
573 code => $meta->get_method($method_name)
574 } if $meta->has_method($method_name);
579 sub find_next_method_by_name {
580 my ($self, $method_name) = @_;
581 (defined $method_name && $method_name)
582 || confess "You must define a method name to find";
583 # keep a record of what we have seen
584 # here, this will handle all the
585 # inheritence issues because we are
586 # using the &class_precedence_list
588 my @cpl = $self->class_precedence_list();
589 shift @cpl; # discard ourselves
590 foreach my $class (@cpl) {
591 next if $seen_class{$class};
592 $seen_class{$class}++;
593 # fetch the meta-class ...
594 my $meta = $self->initialize($class);
595 return $meta->get_method($method_name)
596 if $meta->has_method($method_name);
605 # either we have an attribute object already
606 # or we need to create one from the args provided
607 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
608 # make sure it is derived from the correct type though
609 ($attribute->isa('Class::MOP::Attribute'))
610 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
611 $attribute->attach_to_class($self);
612 $attribute->install_accessors();
613 $self->get_attribute_map->{$attribute->name} = $attribute;
617 my ($self, $attribute_name) = @_;
618 (defined $attribute_name && $attribute_name)
619 || confess "You must define an attribute name";
620 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
624 my ($self, $attribute_name) = @_;
625 (defined $attribute_name && $attribute_name)
626 || confess "You must define an attribute name";
627 return $self->get_attribute_map->{$attribute_name}
628 if $self->has_attribute($attribute_name);
632 sub remove_attribute {
633 my ($self, $attribute_name) = @_;
634 (defined $attribute_name && $attribute_name)
635 || confess "You must define an attribute name";
636 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
637 return unless defined $removed_attribute;
638 delete $self->get_attribute_map->{$attribute_name};
639 $removed_attribute->remove_accessors();
640 $removed_attribute->detach_from_class();
641 return $removed_attribute;
644 sub get_attribute_list {
646 keys %{$self->get_attribute_map};
649 sub compute_all_applicable_attributes {
652 # keep a record of what we have seen
653 # here, this will handle all the
654 # inheritence issues because we are
655 # using the &class_precedence_list
656 my (%seen_class, %seen_attr);
657 foreach my $class ($self->class_precedence_list()) {
658 next if $seen_class{$class};
659 $seen_class{$class}++;
660 # fetch the meta-class ...
661 my $meta = $self->initialize($class);
662 foreach my $attr_name ($meta->get_attribute_list()) {
663 next if exists $seen_attr{$attr_name};
664 $seen_attr{$attr_name}++;
665 push @attrs => $meta->get_attribute($attr_name);
671 sub find_attribute_by_name {
672 my ($self, $attr_name) = @_;
673 # keep a record of what we have seen
674 # here, this will handle all the
675 # inheritence issues because we are
676 # using the &class_precedence_list
678 foreach my $class ($self->class_precedence_list()) {
679 next if $seen_class{$class};
680 $seen_class{$class}++;
681 # fetch the meta-class ...
682 my $meta = $self->initialize($class);
683 return $meta->get_attribute($attr_name)
684 if $meta->has_attribute($attr_name);
692 sub is_immutable { 0 }
695 return Class::MOP::Class::Immutable->make_metaclass_immutable(@_);
706 Class::MOP::Class - Class Meta Object
710 # assuming that class Foo
711 # has been defined, you can
713 # use this for introspection ...
715 # add a method to Foo ...
716 Foo->meta->add_method('bar' => sub { ... })
718 # get a list of all the classes searched
719 # the method dispatcher in the correct order
720 Foo->meta->class_precedence_list()
722 # remove a method from Foo
723 Foo->meta->remove_method('bar');
725 # or use this to actually create classes ...
727 Class::MOP::Class->create('Bar' => (
729 superclasses => [ 'Foo' ],
731 Class::MOP:::Attribute->new('$bar'),
732 Class::MOP:::Attribute->new('$baz'),
735 calculate_bar => sub { ... },
736 construct_baz => sub { ... }
742 This is the largest and currently most complex part of the Perl 5
743 meta-object protocol. It controls the introspection and
744 manipulation of Perl 5 classes (and it can create them too). The
745 best way to understand what this module can do, is to read the
746 documentation for each of it's methods.
750 =head2 Self Introspection
756 This will return a B<Class::MOP::Class> instance which is related
757 to this class. Thereby allowing B<Class::MOP::Class> to actually
760 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
761 bootstrap this module by installing a number of attribute meta-objects
762 into it's metaclass. This will allow this class to reap all the benifits
763 of the MOP when subclassing it.
767 =head2 Class construction
769 These methods will handle creating B<Class::MOP::Class> objects,
770 which can be used to both create new classes, and analyze
771 pre-existing classes.
773 This module will internally store references to all the instances
774 you create with these methods, so that they do not need to be
775 created any more than nessecary. Basically, they are singletons.
779 =item B<create ($package_name,
780 version =E<gt> ?$version,
781 authority =E<gt> ?$authority,
782 superclasses =E<gt> ?@superclasses,
783 methods =E<gt> ?%methods,
784 attributes =E<gt> ?%attributes)>
786 This returns a B<Class::MOP::Class> object, bringing the specified
787 C<$package_name> into existence and adding any of the C<$version>,
788 C<$authority>, C<@superclasses>, C<%methods> and C<%attributes> to
791 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
792 methods =E<gt> ?%methods,
793 attributes =E<gt> ?%attributes)>
795 This will create an anonymous class, it works much like C<create> but
796 it does not need a C<$package_name>. Instead it will create a suitably
797 unique package name for you to stash things into.
799 =item B<initialize ($package_name, %options)>
801 This initializes and returns returns a B<Class::MOP::Class> object
802 for a given a C<$package_name>.
804 =item B<reinitialize ($package_name, %options)>
806 This removes the old metaclass, and creates a new one in it's place.
807 Do B<not> use this unless you really know what you are doing, it could
808 very easily make a very large mess of your program.
810 =item B<construct_class_instance (%options)>
812 This will construct an instance of B<Class::MOP::Class>, it is
813 here so that we can actually "tie the knot" for B<Class::MOP::Class>
814 to use C<construct_instance> once all the bootstrapping is done. This
815 method is used internally by C<initialize> and should never be called
816 from outside of that method really.
818 =item B<check_metaclass_compatability>
820 This method is called as the very last thing in the
821 C<construct_class_instance> method. This will check that the
822 metaclass you are creating is compatible with the metaclasses of all
823 your ancestors. For more inforamtion about metaclass compatibility
824 see the C<About Metaclass compatibility> section in L<Class::MOP>.
828 =head2 Object instance construction and cloning
830 These methods are B<entirely optional>, it is up to you whether you want
835 =item B<instance_metaclass>
837 =item B<get_meta_instance>
839 =item B<new_object (%params)>
841 This is a convience method for creating a new object of the class, and
842 blessing it into the appropriate package as well. Ideally your class
843 would call a C<new> this method like so:
846 my ($class, %param) = @_;
847 $class->meta->new_object(%params);
850 Of course the ideal place for this would actually be in C<UNIVERSAL::>
851 but that is considered bad style, so we do not do that.
853 =item B<construct_instance (%params)>
855 This method is used to construct an instace structure suitable for
856 C<bless>-ing into your package of choice. It works in conjunction
857 with the Attribute protocol to collect all applicable attributes.
859 This will construct and instance using a HASH ref as storage
860 (currently only HASH references are supported). This will collect all
861 the applicable attributes and layout out the fields in the HASH ref,
862 it will then initialize them using either use the corresponding key
863 in C<%params> or any default value or initializer found in the
864 attribute meta-object.
866 =item B<clone_object ($instance, %params)>
868 This is a convience method for cloning an object instance, then
869 blessing it into the appropriate package. This method will call
870 C<clone_instance>, which performs a shallow copy of the object,
871 see that methods documentation for more details. Ideally your
872 class would call a C<clone> this method like so:
875 my ($self, %param) = @_;
876 $self->meta->clone_object($self, %params);
879 Of course the ideal place for this would actually be in C<UNIVERSAL::>
880 but that is considered bad style, so we do not do that.
882 =item B<clone_instance($instance, %params)>
884 This method is a compliment of C<construct_instance> (which means if
885 you override C<construct_instance>, you need to override this one too),
886 and clones the instance shallowly.
888 The cloned structure returned is (like with C<construct_instance>) an
889 unC<bless>ed HASH reference, it is your responsibility to then bless
890 this cloned structure into the right class (which C<clone_object> will
893 As of 0.11, this method will clone the C<$instance> structure shallowly,
894 as opposed to the deep cloning implemented in prior versions. After much
895 thought, research and discussion, I have decided that anything but basic
896 shallow cloning is outside the scope of the meta-object protocol. I
897 think Yuval "nothingmuch" Kogman put it best when he said that cloning
898 is too I<context-specific> to be part of the MOP.
904 These are a few predicate methods for asking information about the class.
908 =item B<is_anon_class>
912 =item B<is_immutable>
916 =head2 Inheritance Relationships
920 =item B<superclasses (?@superclasses)>
922 This is a read-write attribute which represents the superclass
923 relationships of the class the B<Class::MOP::Class> instance is
924 associated with. Basically, it can get and set the C<@ISA> for you.
927 Perl will occasionally perform some C<@ISA> and method caching, if
928 you decide to change your superclass relationship at runtime (which
929 is quite insane and very much not recommened), then you should be
930 aware of this and the fact that this module does not make any
931 attempt to address this issue.
933 =item B<class_precedence_list>
935 This computes the a list of all the class's ancestors in the same order
936 in which method dispatch will be done. This is similair to
937 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
945 =item B<get_method_map>
947 =item B<method_metaclass>
949 =item B<add_method ($method_name, $method)>
951 This will take a C<$method_name> and CODE reference to that
952 C<$method> and install it into the class's package.
955 This does absolutely nothing special to C<$method>
956 other than use B<Sub::Name> to make sure it is tagged with the
957 correct name, and therefore show up correctly in stack traces and
960 =item B<alias_method ($method_name, $method)>
962 This will take a C<$method_name> and CODE reference to that
963 C<$method> and alias the method into the class's package.
966 Unlike C<add_method>, this will B<not> try to name the
967 C<$method> using B<Sub::Name>, it only aliases the method in
970 =item B<has_method ($method_name)>
972 This just provides a simple way to check if the class implements
973 a specific C<$method_name>. It will I<not> however, attempt to check
974 if the class inherits the method (use C<UNIVERSAL::can> for that).
976 This will correctly handle functions defined outside of the package
977 that use a fully qualified name (C<sub Package::name { ... }>).
979 This will correctly handle functions renamed with B<Sub::Name> and
980 installed using the symbol tables. However, if you are naming the
981 subroutine outside of the package scope, you must use the fully
982 qualified name, including the package name, for C<has_method> to
983 correctly identify it.
985 This will attempt to correctly ignore functions imported from other
986 packages using B<Exporter>. It breaks down if the function imported
987 is an C<__ANON__> sub (such as with C<use constant>), which very well
988 may be a valid method being applied to the class.
990 In short, this method cannot always be trusted to determine if the
991 C<$method_name> is actually a method. However, it will DWIM about
992 90% of the time, so it's a small trade off I think.
994 =item B<get_method ($method_name)>
996 This will return a CODE reference of the specified C<$method_name>,
997 or return undef if that method does not exist.
999 =item B<find_method_by_name ($method_name>
1001 This will return a CODE reference of the specified C<$method_name>,
1002 or return undef if that method does not exist.
1004 Unlike C<get_method> this will also look in the superclasses.
1006 =item B<remove_method ($method_name)>
1008 This will attempt to remove a given C<$method_name> from the class.
1009 It will return the CODE reference that it has removed, and will
1010 attempt to use B<Sub::Name> to clear the methods associated name.
1012 =item B<get_method_list>
1014 This will return a list of method names for all I<locally> defined
1015 methods. It does B<not> provide a list of all applicable methods,
1016 including any inherited ones. If you want a list of all applicable
1017 methods, use the C<compute_all_applicable_methods> method.
1019 =item B<compute_all_applicable_methods>
1021 This will return a list of all the methods names this class will
1022 respond to, taking into account inheritance. The list will be a list of
1023 HASH references, each one containing the following information; method
1024 name, the name of the class in which the method lives and a CODE
1025 reference for the actual method.
1027 =item B<find_all_methods_by_name ($method_name)>
1029 This will traverse the inheritence hierarchy and locate all methods
1030 with a given C<$method_name>. Similar to
1031 C<compute_all_applicable_methods> it returns a list of HASH references
1032 with the following information; method name (which will always be the
1033 same as C<$method_name>), the name of the class in which the method
1034 lives and a CODE reference for the actual method.
1036 The list of methods produced is a distinct list, meaning there are no
1037 duplicates in it. This is especially useful for things like object
1038 initialization and destruction where you only want the method called
1039 once, and in the correct order.
1041 =item B<find_next_method_by_name ($method_name)>
1043 This will return the first method to match a given C<$method_name> in
1044 the superclasses, this is basically equivalent to calling
1045 C<SUPER::$method_name>, but it can be dispatched at runtime.
1049 =head2 Method Modifiers
1051 Method modifiers are a concept borrowed from CLOS, in which a method
1052 can be wrapped with I<before>, I<after> and I<around> method modifiers
1053 that will be called everytime the method is called.
1055 =head3 How method modifiers work?
1057 Method modifiers work by wrapping the original method and then replacing
1058 it in the classes symbol table. The wrappers will handle calling all the
1059 modifiers in the appropariate orders and preserving the calling context
1060 for the original method.
1062 Each method modifier serves a particular purpose, which may not be
1063 obvious to users of other method wrapping modules. To start with, the
1064 return values of I<before> and I<after> modifiers are ignored. This is
1065 because thier purpose is B<not> to filter the input and output of the
1066 primary method (this is done with an I<around> modifier). This may seem
1067 like an odd restriction to some, but doing this allows for simple code
1068 to be added at the begining or end of a method call without jeapordizing
1069 the normal functioning of the primary method or placing any extra
1070 responsibility on the code of the modifier. Of course if you have more
1071 complex needs, then use the I<around> modifier, which uses a variation
1072 of continutation passing style to allow for a high degree of flexibility.
1074 Before and around modifiers are called in last-defined-first-called order,
1075 while after modifiers are called in first-defined-first-called order. So
1076 the call tree might looks something like this:
1086 To see examples of using method modifiers, see the following examples
1087 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1088 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1089 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1091 =head3 What is the performance impact?
1093 Of course there is a performance cost associated with method modifiers,
1094 but we have made every effort to make that cost be directly proportional
1095 to the amount of modifier features you utilize.
1097 The wrapping method does it's best to B<only> do as much work as it
1098 absolutely needs to. In order to do this we have moved some of the
1099 performance costs to set-up time, where they are easier to amortize.
1101 All this said, my benchmarks have indicated the following:
1103 simple wrapper with no modifiers 100% slower
1104 simple wrapper with simple before modifier 400% slower
1105 simple wrapper with simple after modifier 450% slower
1106 simple wrapper with simple around modifier 500-550% slower
1107 simple wrapper with all 3 modifiers 1100% slower
1109 These numbers may seem daunting, but you must remember, every feature
1110 comes with some cost. To put things in perspective, just doing a simple
1111 C<AUTOLOAD> which does nothing but extract the name of the method called
1112 and return it costs about 400% over a normal method call.
1116 =item B<add_before_method_modifier ($method_name, $code)>
1118 This will wrap the method at C<$method_name> and the supplied C<$code>
1119 will be passed the C<@_> arguments, and called before the original
1120 method is called. As specified above, the return value of the I<before>
1121 method modifiers is ignored, and it's ability to modify C<@_> is
1122 fairly limited. If you need to do either of these things, use an
1123 C<around> method modifier.
1125 =item B<add_after_method_modifier ($method_name, $code)>
1127 This will wrap the method at C<$method_name> so that the original
1128 method will be called, it's return values stashed, and then the
1129 supplied C<$code> will be passed the C<@_> arguments, and called.
1130 As specified above, the return value of the I<after> method
1131 modifiers is ignored, and it cannot modify the return values of
1132 the original method. If you need to do either of these things, use an
1133 C<around> method modifier.
1135 =item B<add_around_method_modifier ($method_name, $code)>
1137 This will wrap the method at C<$method_name> so that C<$code>
1138 will be called and passed the original method as an extra argument
1139 at the begining of the C<@_> argument list. This is a variation of
1140 continuation passing style, where the function prepended to C<@_>
1141 can be considered a continuation. It is up to C<$code> if it calls
1142 the original method or not, there is no restriction on what the
1143 C<$code> can or cannot do.
1149 It should be noted that since there is no one consistent way to define
1150 the attributes of a class in Perl 5. These methods can only work with
1151 the information given, and can not easily discover information on
1152 their own. See L<Class::MOP::Attribute> for more details.
1156 =item B<attribute_metaclass>
1158 =item B<get_attribute_map>
1160 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1162 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1163 instance associated with the given class, and associates it with
1164 the C<$attribute_name>. Unlike methods, attributes within the MOP
1165 are stored as meta-information only. They will be used later to
1166 construct instances from (see C<construct_instance> above).
1167 More details about the attribute meta-objects can be found in the
1168 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1171 It should be noted that any accessor, reader/writer or predicate
1172 methods which the C<$attribute_meta_object> has will be installed
1173 into the class at this time.
1175 =item B<has_attribute ($attribute_name)>
1177 Checks to see if this class has an attribute by the name of
1178 C<$attribute_name> and returns a boolean.
1180 =item B<get_attribute ($attribute_name)>
1182 Returns the attribute meta-object associated with C<$attribute_name>,
1183 if none is found, it will return undef.
1185 =item B<remove_attribute ($attribute_name)>
1187 This will remove the attribute meta-object stored at
1188 C<$attribute_name>, then return the removed attribute meta-object.
1191 Removing an attribute will only affect future instances of
1192 the class, it will not make any attempt to remove the attribute from
1193 any existing instances of the class.
1195 It should be noted that any accessor, reader/writer or predicate
1196 methods which the attribute meta-object stored at C<$attribute_name>
1197 has will be removed from the class at this time. This B<will> make
1198 these attributes somewhat inaccessable in previously created
1199 instances. But if you are crazy enough to do this at runtime, then
1200 you are crazy enough to deal with something like this :).
1202 =item B<get_attribute_list>
1204 This returns a list of attribute names which are defined in the local
1205 class. If you want a list of all applicable attributes for a class,
1206 use the C<compute_all_applicable_attributes> method.
1208 =item B<compute_all_applicable_attributes>
1210 This will traverse the inheritance heirachy and return a list of all
1211 the applicable attributes for this class. It does not construct a
1212 HASH reference like C<compute_all_applicable_methods> because all
1213 that same information is discoverable through the attribute
1216 =item B<find_attribute_by_name ($attr_name)>
1218 This method will traverse the inheritance heirachy and find the
1219 first attribute whose name matches C<$attr_name>, then return it.
1220 It will return undef if nothing is found.
1224 =head2 Class closing
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.