2 package Class::MOP::Class;
8 use Scalar::Util 'blessed', 'reftype', 'weaken';
9 use Sub::Name 'subname';
10 use B 'svref_2object';
12 our $VERSION = '0.15';
14 use base 'Class::MOP::Module';
16 use Class::MOP::Instance;
20 sub meta { Class::MOP::Class->initialize(blessed($_[0]) || $_[0]) }
25 # we need a sufficiently annoying prefix
26 # this should suffice for now, this is
27 # used in a couple of places below, so
28 # need to put it up here for now.
29 my $ANON_CLASS_PREFIX = 'Class::MOP::Class::__ANON__::SERIAL::';
34 # Metaclasses are singletons, so we cache them here.
35 # there is no need to worry about destruction though
36 # because they should die only when the program dies.
37 # After all, do package definitions even get reaped?
40 # means of accessing all the metaclasses that have
41 # been initialized thus far (for mugwumps obj browser)
42 sub get_all_metaclasses { %METAS }
43 sub get_all_metaclass_instances { values %METAS }
44 sub get_all_metaclass_names { keys %METAS }
48 my $package_name = shift;
49 (defined $package_name && $package_name && !blessed($package_name))
50 || confess "You must pass a package name and it cannot be blessed";
51 $class->construct_class_instance(':package' => $package_name, @_);
56 my $package_name = shift;
57 (defined $package_name && $package_name && !blessed($package_name))
58 || confess "You must pass a package name and it cannot be blessed";
59 $METAS{$package_name} = undef;
60 $class->construct_class_instance(':package' => $package_name, @_);
63 # NOTE: (meta-circularity)
64 # this is a special form of &construct_instance
65 # (see below), which is used to construct class
66 # meta-object instances for any Class::MOP::*
67 # class. All other classes will use the more
68 # normal &construct_instance.
69 sub construct_class_instance {
72 my $package_name = $options{':package'};
73 (defined $package_name && $package_name)
74 || confess "You must pass a package name";
76 # return the metaclass if we have it cached,
77 # and it is still defined (it has not been
78 # reaped by DESTROY yet, which can happen
79 # annoyingly enough during global destruction)
80 return $METAS{$package_name}
81 if exists $METAS{$package_name} && defined $METAS{$package_name};
82 $class = blessed($class) || $class;
83 # now create the metaclass
85 if ($class =~ /^Class::MOP::/) {
87 '$:package' => $package_name,
89 '$:attribute_metaclass' => $options{':attribute_metaclass'} || 'Class::MOP::Attribute',
90 '$:method_metaclass' => $options{':method_metaclass'} || 'Class::MOP::Method',
91 '$:instance_metaclass' => $options{':instance_metaclass'} || 'Class::MOP::Instance',
96 # it is safe to use meta here because
97 # class will always be a subclass of
98 # Class::MOP::Class, which defines meta
99 $meta = $class->meta->construct_instance(%options)
101 # and check the metaclass compatibility
102 $meta->check_metaclass_compatability();
103 $METAS{$package_name} = $meta;
105 # we need to weaken any anon classes
106 # so that they can call DESTROY properly
107 weaken($METAS{$package_name})
108 if $package_name =~ /^$ANON_CLASS_PREFIX/;
112 sub check_metaclass_compatability {
115 # this is always okay ...
116 return if blessed($self) eq 'Class::MOP::Class' &&
117 $self->instance_metaclass eq 'Class::MOP::Instance';
119 my @class_list = $self->class_precedence_list;
120 shift @class_list; # shift off $self->name
122 foreach my $class_name (@class_list) {
123 my $meta = $METAS{$class_name} || next;
124 ($self->isa(blessed($meta)))
125 || confess $self->name . "->meta => (" . (blessed($self)) . ")" .
126 " is not compatible with the " .
127 $class_name . "->meta => (" . (blessed($meta)) . ")";
129 # we also need to check that instance metaclasses
130 # are compatabile in the same the class.
131 ($self->instance_metaclass->isa($meta->instance_metaclass))
132 || confess $self->name . "->meta => (" . ($self->instance_metaclass) . ")" .
133 " is not compatible with the " .
134 $class_name . "->meta => (" . ($meta->instance_metaclass) . ")";
143 # this should be sufficient, if you have a
144 # use case where it is not, write a test and
146 my $ANON_CLASS_SERIAL = 0;
148 sub create_anon_class {
149 my ($class, %options) = @_;
150 my $package_name = $ANON_CLASS_PREFIX . ++$ANON_CLASS_SERIAL;
151 return $class->create($package_name, '0.00', %options);
156 # this will only get called for
157 # anon-classes, all other calls
158 # are assumed to occur during
159 # global destruction and so don't
160 # really need to be handled explicitly
163 return unless $self->name =~ /^$ANON_CLASS_PREFIX/;
164 my ($serial_id) = ($self->name =~ /^$ANON_CLASS_PREFIX(\d+)/);
166 foreach my $key (keys %{$ANON_CLASS_PREFIX . $serial_id}) {
167 delete ${$ANON_CLASS_PREFIX . $serial_id}{$key};
169 delete ${'main::' . $ANON_CLASS_PREFIX}{$serial_id . '::'};
172 # creating classes with MOP ...
175 my ($class, $package_name, $package_version, %options) = @_;
176 (defined $package_name && $package_name)
177 || confess "You must pass a package name";
178 my $code = "package $package_name;";
179 $code .= "\$$package_name\:\:VERSION = '$package_version';"
180 if defined $package_version;
182 confess "creation of $package_name failed : $@" if $@;
183 my $meta = $class->initialize($package_name);
185 $meta->add_method('meta' => sub {
186 $class->initialize(blessed($_[0]) || $_[0]);
189 $meta->superclasses(@{$options{superclasses}})
190 if exists $options{superclasses};
192 # process attributes first, so that they can
193 # install accessors, but locally defined methods
194 # can then overwrite them. It is maybe a little odd, but
195 # I think this should be the order of things.
196 if (exists $options{attributes}) {
197 foreach my $attr (@{$options{attributes}}) {
198 $meta->add_attribute($attr);
201 if (exists $options{methods}) {
202 foreach my $method_name (keys %{$options{methods}}) {
203 $meta->add_method($method_name, $options{methods}->{$method_name});
212 # all these attribute readers will be bootstrapped
213 # away in the Class::MOP bootstrap section
215 sub get_attribute_map { $_[0]->{'%:attributes'} }
216 sub attribute_metaclass { $_[0]->{'$:attribute_metaclass'} }
217 sub method_metaclass { $_[0]->{'$:method_metaclass'} }
218 sub instance_metaclass { $_[0]->{'$:instance_metaclass'} }
220 # Instance Construction & Cloning
225 # we need to protect the integrity of the
226 # Class::MOP::Class singletons here, so we
227 # delegate this to &construct_class_instance
228 # which will deal with the singletons
229 return $class->construct_class_instance(@_)
230 if $class->name->isa('Class::MOP::Class');
231 return $class->construct_instance(@_);
234 sub construct_instance {
235 my ($class, %params) = @_;
236 my $meta_instance = $class->get_meta_instance();
237 my $instance = $meta_instance->create_instance();
238 foreach my $attr ($class->compute_all_applicable_attributes()) {
239 $attr->initialize_instance_slot($meta_instance, $instance, \%params);
244 sub get_meta_instance {
246 return $class->instance_metaclass->new(
248 $class->compute_all_applicable_attributes()
254 my $instance = shift;
255 (blessed($instance) && $instance->isa($class->name))
256 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
258 # we need to protect the integrity of the
259 # Class::MOP::Class singletons here, they
260 # should not be cloned.
261 return $instance if $instance->isa('Class::MOP::Class');
262 $class->clone_instance($instance, @_);
266 my ($class, $instance, %params) = @_;
268 || confess "You can only clone instances, \$self is not a blessed instance";
269 my $meta_instance = $class->get_meta_instance();
270 my $clone = $meta_instance->clone_instance($instance);
271 foreach my $key (keys %params) {
272 next unless $meta_instance->is_valid_slot($key);
273 $meta_instance->set_slot_value($clone, $key, $params{$key});
285 @{$self->name . '::ISA'} = @supers;
287 # we need to check the metaclass
288 # compatability here so that we can
289 # be sure that the superclass is
290 # not potentially creating an issues
291 # we don't know about
292 $self->check_metaclass_compatability();
294 @{$self->name . '::ISA'};
297 sub class_precedence_list {
300 # We need to check for ciruclar inheirtance here.
301 # This will do nothing if all is well, and blow
302 # up otherwise. Yes, it's an ugly hack, better
303 # suggestions are welcome.
304 { ($self->name || return)->isa('This is a test for circular inheritance') }
305 # ... and now back to our regularly scheduled program
309 $self->initialize($_)->class_precedence_list()
310 } $self->superclasses()
317 my ($self, $method_name, $method) = @_;
318 (defined $method_name && $method_name)
319 || confess "You must define a method name";
320 # use reftype here to allow for blessed subs ...
321 ('CODE' eq (reftype($method) || ''))
322 || confess "Your code block must be a CODE reference";
323 my $full_method_name = ($self->name . '::' . $method_name);
325 $method = $self->method_metaclass->wrap($method) unless blessed($method);
328 no warnings 'redefine';
329 *{$full_method_name} = subname $full_method_name => $method;
333 my $fetch_and_prepare_method = sub {
334 my ($self, $method_name) = @_;
336 my $method = $self->get_method($method_name);
337 # if we dont have local ...
339 # try to find the next method
340 $method = $self->find_next_method_by_name($method_name);
341 # die if it does not exist
343 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
344 # and now make sure to wrap it
345 # even if it is already wrapped
346 # because we need a new sub ref
347 $method = Class::MOP::Method::Wrapped->wrap($method);
350 # now make sure we wrap it properly
351 $method = Class::MOP::Method::Wrapped->wrap($method)
352 unless $method->isa('Class::MOP::Method::Wrapped');
354 $self->add_method($method_name => $method);
358 sub add_before_method_modifier {
359 my ($self, $method_name, $method_modifier) = @_;
360 (defined $method_name && $method_name)
361 || confess "You must pass in a method name";
362 my $method = $fetch_and_prepare_method->($self, $method_name);
363 $method->add_before_modifier(subname ':before' => $method_modifier);
366 sub add_after_method_modifier {
367 my ($self, $method_name, $method_modifier) = @_;
368 (defined $method_name && $method_name)
369 || confess "You must pass in a method name";
370 my $method = $fetch_and_prepare_method->($self, $method_name);
371 $method->add_after_modifier(subname ':after' => $method_modifier);
374 sub add_around_method_modifier {
375 my ($self, $method_name, $method_modifier) = @_;
376 (defined $method_name && $method_name)
377 || confess "You must pass in a method name";
378 my $method = $fetch_and_prepare_method->($self, $method_name);
379 $method->add_around_modifier(subname ':around' => $method_modifier);
383 # the methods above used to be named like this:
384 # ${pkg}::${method}:(before|after|around)
385 # but this proved problematic when using one modifier
386 # to wrap multiple methods (something which is likely
387 # to happen pretty regularly IMO). So instead of naming
388 # it like this, I have chosen to just name them purely
389 # with their modifier names, like so:
390 # :(before|after|around)
391 # The fact is that in a stack trace, it will be fairly
392 # evident from the context what method they are attached
393 # to, and so don't need the fully qualified name.
397 my ($self, $method_name, $method) = @_;
398 (defined $method_name && $method_name)
399 || confess "You must define a method name";
400 # use reftype here to allow for blessed subs ...
401 ('CODE' eq (reftype($method) || ''))
402 || confess "Your code block must be a CODE reference";
403 my $full_method_name = ($self->name . '::' . $method_name);
405 $method = $self->method_metaclass->wrap($method) unless blessed($method);
408 no warnings 'redefine';
409 *{$full_method_name} = $method;
413 my ($self, $method_name) = @_;
414 (defined $method_name && $method_name)
415 || confess "You must define a method name";
417 my $sub_name = ($self->name . '::' . $method_name);
420 return 0 if !defined(&{$sub_name});
421 my $method = \&{$sub_name};
422 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
423 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
425 # at this point we are relatively sure
426 # it is our method, so we bless/wrap it
427 $self->method_metaclass->wrap($method) unless blessed($method);
432 my ($self, $method_name) = @_;
433 (defined $method_name && $method_name)
434 || confess "You must define a method name";
436 return unless $self->has_method($method_name);
439 return \&{$self->name . '::' . $method_name};
443 my ($self, $method_name) = @_;
444 (defined $method_name && $method_name)
445 || confess "You must define a method name";
447 my $removed_method = $self->get_method($method_name);
450 delete ${$self->name . '::'}{$method_name}
451 if defined $removed_method;
453 return $removed_method;
456 sub get_method_list {
459 grep { $self->has_method($_) } keys %{$self->name . '::'};
462 sub compute_all_applicable_methods {
465 # keep a record of what we have seen
466 # here, this will handle all the
467 # inheritence issues because we are
468 # using the &class_precedence_list
469 my (%seen_class, %seen_method);
470 foreach my $class ($self->class_precedence_list()) {
471 next if $seen_class{$class};
472 $seen_class{$class}++;
473 # fetch the meta-class ...
474 my $meta = $self->initialize($class);
475 foreach my $method_name ($meta->get_method_list()) {
476 next if exists $seen_method{$method_name};
477 $seen_method{$method_name}++;
479 name => $method_name,
481 code => $meta->get_method($method_name)
488 sub find_all_methods_by_name {
489 my ($self, $method_name) = @_;
490 (defined $method_name && $method_name)
491 || confess "You must define a method name to find";
493 # keep a record of what we have seen
494 # here, this will handle all the
495 # inheritence issues because we are
496 # using the &class_precedence_list
498 foreach my $class ($self->class_precedence_list()) {
499 next if $seen_class{$class};
500 $seen_class{$class}++;
501 # fetch the meta-class ...
502 my $meta = $self->initialize($class);
504 name => $method_name,
506 code => $meta->get_method($method_name)
507 } if $meta->has_method($method_name);
512 sub find_next_method_by_name {
513 my ($self, $method_name) = @_;
514 (defined $method_name && $method_name)
515 || confess "You must define a method name to find";
516 # keep a record of what we have seen
517 # here, this will handle all the
518 # inheritence issues because we are
519 # using the &class_precedence_list
521 my @cpl = $self->class_precedence_list();
522 shift @cpl; # discard ourselves
523 foreach my $class (@cpl) {
524 next if $seen_class{$class};
525 $seen_class{$class}++;
526 # fetch the meta-class ...
527 my $meta = $self->initialize($class);
528 return $meta->get_method($method_name)
529 if $meta->has_method($method_name);
538 # either we have an attribute object already
539 # or we need to create one from the args provided
540 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
541 # make sure it is derived from the correct type though
542 ($attribute->isa('Class::MOP::Attribute'))
543 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
544 $attribute->attach_to_class($self);
545 $attribute->install_accessors();
546 $self->get_attribute_map->{$attribute->name} = $attribute;
549 # in theory we have to tell everyone the slot structure may have changed
553 my ($self, $attribute_name) = @_;
554 (defined $attribute_name && $attribute_name)
555 || confess "You must define an attribute name";
556 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
560 my ($self, $attribute_name) = @_;
561 (defined $attribute_name && $attribute_name)
562 || confess "You must define an attribute name";
563 return $self->get_attribute_map->{$attribute_name}
564 if $self->has_attribute($attribute_name);
568 sub remove_attribute {
569 my ($self, $attribute_name) = @_;
570 (defined $attribute_name && $attribute_name)
571 || confess "You must define an attribute name";
572 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
573 return unless defined $removed_attribute;
574 delete $self->get_attribute_map->{$attribute_name};
575 $removed_attribute->remove_accessors();
576 $removed_attribute->detach_from_class();
577 return $removed_attribute;
580 sub get_attribute_list {
582 keys %{$self->get_attribute_map};
585 sub compute_all_applicable_attributes {
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
592 my (%seen_class, %seen_attr);
593 foreach my $class ($self->class_precedence_list()) {
594 next if $seen_class{$class};
595 $seen_class{$class}++;
596 # fetch the meta-class ...
597 my $meta = $self->initialize($class);
598 foreach my $attr_name ($meta->get_attribute_list()) {
599 next if exists $seen_attr{$attr_name};
600 $seen_attr{$attr_name}++;
601 push @attrs => $meta->get_attribute($attr_name);
607 sub find_attribute_by_name {
608 my ($self, $attr_name) = @_;
609 # keep a record of what we have seen
610 # here, this will handle all the
611 # inheritence issues because we are
612 # using the &class_precedence_list
614 foreach my $class ($self->class_precedence_list()) {
615 next if $seen_class{$class};
616 $seen_class{$class}++;
617 # fetch the meta-class ...
618 my $meta = $self->initialize($class);
619 return $meta->get_attribute($attr_name)
620 if $meta->has_attribute($attr_name);
628 sub is_immutable { 0 }
632 return Class::MOP::Class::Immutable->make_metaclass_immutable($class);
643 Class::MOP::Class - Class Meta Object
647 # assuming that class Foo
648 # has been defined, you can
650 # use this for introspection ...
652 # add a method to Foo ...
653 Foo->meta->add_method('bar' => sub { ... })
655 # get a list of all the classes searched
656 # the method dispatcher in the correct order
657 Foo->meta->class_precedence_list()
659 # remove a method from Foo
660 Foo->meta->remove_method('bar');
662 # or use this to actually create classes ...
664 Class::MOP::Class->create('Bar' => '0.01' => (
665 superclasses => [ 'Foo' ],
667 Class::MOP:::Attribute->new('$bar'),
668 Class::MOP:::Attribute->new('$baz'),
671 calculate_bar => sub { ... },
672 construct_baz => sub { ... }
678 This is the largest and currently most complex part of the Perl 5
679 meta-object protocol. It controls the introspection and
680 manipulation of Perl 5 classes (and it can create them too). The
681 best way to understand what this module can do, is to read the
682 documentation for each of it's methods.
686 =head2 Self Introspection
692 This will return a B<Class::MOP::Class> instance which is related
693 to this class. Thereby allowing B<Class::MOP::Class> to actually
696 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
697 bootstrap this module by installing a number of attribute meta-objects
698 into it's metaclass. This will allow this class to reap all the benifits
699 of the MOP when subclassing it.
701 =item B<get_all_metaclasses>
703 This will return an hash of all the metaclass instances that have
704 been cached by B<Class::MOP::Class> keyed by the package name.
706 =item B<get_all_metaclass_instances>
708 This will return an array of all the metaclass instances that have
709 been cached by B<Class::MOP::Class>.
711 =item B<get_all_metaclass_names>
713 This will return an array of all the metaclass names that have
714 been cached by B<Class::MOP::Class>.
718 =head2 Class construction
720 These methods will handle creating B<Class::MOP::Class> objects,
721 which can be used to both create new classes, and analyze
722 pre-existing classes.
724 This module will internally store references to all the instances
725 you create with these methods, so that they do not need to be
726 created any more than nessecary. Basically, they are singletons.
730 =item B<create ($package_name, ?$package_version,
731 superclasses =E<gt> ?@superclasses,
732 methods =E<gt> ?%methods,
733 attributes =E<gt> ?%attributes)>
735 This returns a B<Class::MOP::Class> object, bringing the specified
736 C<$package_name> into existence and adding any of the
737 C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
740 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
741 methods =E<gt> ?%methods,
742 attributes =E<gt> ?%attributes)>
744 This will create an anonymous class, it works much like C<create> but
745 it does not need a C<$package_name>. Instead it will create a suitably
746 unique package name for you to stash things into.
748 =item B<initialize ($package_name, %options)>
750 This initializes and returns returns a B<Class::MOP::Class> object
751 for a given a C<$package_name>.
753 =item B<reinitialize ($package_name, %options)>
755 This removes the old metaclass, and creates a new one in it's place.
756 Do B<not> use this unless you really know what you are doing, it could
757 very easily make a very large mess of your program.
759 =item B<construct_class_instance (%options)>
761 This will construct an instance of B<Class::MOP::Class>, it is
762 here so that we can actually "tie the knot" for B<Class::MOP::Class>
763 to use C<construct_instance> once all the bootstrapping is done. This
764 method is used internally by C<initialize> and should never be called
765 from outside of that method really.
767 =item B<check_metaclass_compatability>
769 This method is called as the very last thing in the
770 C<construct_class_instance> method. This will check that the
771 metaclass you are creating is compatible with the metaclasses of all
772 your ancestors. For more inforamtion about metaclass compatibility
773 see the C<About Metaclass compatibility> section in L<Class::MOP>.
777 =head2 Object instance construction and cloning
779 These methods are B<entirely optional>, it is up to you whether you want
784 =item B<instance_metaclass>
786 =item B<get_meta_instance>
788 =item B<new_object (%params)>
790 This is a convience method for creating a new object of the class, and
791 blessing it into the appropriate package as well. Ideally your class
792 would call a C<new> this method like so:
795 my ($class, %param) = @_;
796 $class->meta->new_object(%params);
799 Of course the ideal place for this would actually be in C<UNIVERSAL::>
800 but that is considered bad style, so we do not do that.
802 =item B<construct_instance (%params)>
804 This method is used to construct an instace structure suitable for
805 C<bless>-ing into your package of choice. It works in conjunction
806 with the Attribute protocol to collect all applicable attributes.
808 This will construct and instance using a HASH ref as storage
809 (currently only HASH references are supported). This will collect all
810 the applicable attributes and layout out the fields in the HASH ref,
811 it will then initialize them using either use the corresponding key
812 in C<%params> or any default value or initializer found in the
813 attribute meta-object.
815 =item B<clone_object ($instance, %params)>
817 This is a convience method for cloning an object instance, then
818 blessing it into the appropriate package. This method will call
819 C<clone_instance>, which performs a shallow copy of the object,
820 see that methods documentation for more details. Ideally your
821 class would call a C<clone> this method like so:
824 my ($self, %param) = @_;
825 $self->meta->clone_object($self, %params);
828 Of course the ideal place for this would actually be in C<UNIVERSAL::>
829 but that is considered bad style, so we do not do that.
831 =item B<clone_instance($instance, %params)>
833 This method is a compliment of C<construct_instance> (which means if
834 you override C<construct_instance>, you need to override this one too),
835 and clones the instance shallowly.
837 The cloned structure returned is (like with C<construct_instance>) an
838 unC<bless>ed HASH reference, it is your responsibility to then bless
839 this cloned structure into the right class (which C<clone_object> will
842 As of 0.11, this method will clone the C<$instance> structure shallowly,
843 as opposed to the deep cloning implemented in prior versions. After much
844 thought, research and discussion, I have decided that anything but basic
845 shallow cloning is outside the scope of the meta-object protocol. I
846 think Yuval "nothingmuch" Kogman put it best when he said that cloning
847 is too I<context-specific> to be part of the MOP.
857 This is a read-only attribute which returns the package name for the
858 given B<Class::MOP::Class> instance.
862 This is a read-only attribute which returns the C<$VERSION> of the
863 package for the given B<Class::MOP::Class> instance.
867 =head2 Inheritance Relationships
871 =item B<superclasses (?@superclasses)>
873 This is a read-write attribute which represents the superclass
874 relationships of the class the B<Class::MOP::Class> instance is
875 associated with. Basically, it can get and set the C<@ISA> for you.
878 Perl will occasionally perform some C<@ISA> and method caching, if
879 you decide to change your superclass relationship at runtime (which
880 is quite insane and very much not recommened), then you should be
881 aware of this and the fact that this module does not make any
882 attempt to address this issue.
884 =item B<class_precedence_list>
886 This computes the a list of all the class's ancestors in the same order
887 in which method dispatch will be done. This is similair to
888 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
896 =item B<method_metaclass>
898 =item B<add_method ($method_name, $method)>
900 This will take a C<$method_name> and CODE reference to that
901 C<$method> and install it into the class's package.
904 This does absolutely nothing special to C<$method>
905 other than use B<Sub::Name> to make sure it is tagged with the
906 correct name, and therefore show up correctly in stack traces and
909 =item B<alias_method ($method_name, $method)>
911 This will take a C<$method_name> and CODE reference to that
912 C<$method> and alias the method into the class's package.
915 Unlike C<add_method>, this will B<not> try to name the
916 C<$method> using B<Sub::Name>, it only aliases the method in
919 =item B<has_method ($method_name)>
921 This just provides a simple way to check if the class implements
922 a specific C<$method_name>. It will I<not> however, attempt to check
923 if the class inherits the method (use C<UNIVERSAL::can> for that).
925 This will correctly handle functions defined outside of the package
926 that use a fully qualified name (C<sub Package::name { ... }>).
928 This will correctly handle functions renamed with B<Sub::Name> and
929 installed using the symbol tables. However, if you are naming the
930 subroutine outside of the package scope, you must use the fully
931 qualified name, including the package name, for C<has_method> to
932 correctly identify it.
934 This will attempt to correctly ignore functions imported from other
935 packages using B<Exporter>. It breaks down if the function imported
936 is an C<__ANON__> sub (such as with C<use constant>), which very well
937 may be a valid method being applied to the class.
939 In short, this method cannot always be trusted to determine if the
940 C<$method_name> is actually a method. However, it will DWIM about
941 90% of the time, so it's a small trade off I think.
943 =item B<get_method ($method_name)>
945 This will return a CODE reference of the specified C<$method_name>,
946 or return undef if that method does not exist.
948 =item B<remove_method ($method_name)>
950 This will attempt to remove a given C<$method_name> from the class.
951 It will return the CODE reference that it has removed, and will
952 attempt to use B<Sub::Name> to clear the methods associated name.
954 =item B<get_method_list>
956 This will return a list of method names for all I<locally> defined
957 methods. It does B<not> provide a list of all applicable methods,
958 including any inherited ones. If you want a list of all applicable
959 methods, use the C<compute_all_applicable_methods> method.
961 =item B<compute_all_applicable_methods>
963 This will return a list of all the methods names this class will
964 respond to, taking into account inheritance. The list will be a list of
965 HASH references, each one containing the following information; method
966 name, the name of the class in which the method lives and a CODE
967 reference for the actual method.
969 =item B<find_all_methods_by_name ($method_name)>
971 This will traverse the inheritence hierarchy and locate all methods
972 with a given C<$method_name>. Similar to
973 C<compute_all_applicable_methods> it returns a list of HASH references
974 with the following information; method name (which will always be the
975 same as C<$method_name>), the name of the class in which the method
976 lives and a CODE reference for the actual method.
978 The list of methods produced is a distinct list, meaning there are no
979 duplicates in it. This is especially useful for things like object
980 initialization and destruction where you only want the method called
981 once, and in the correct order.
983 =item B<find_next_method_by_name ($method_name)>
985 This will return the first method to match a given C<$method_name> in
986 the superclasses, this is basically equivalent to calling
987 C<SUPER::$method_name>, but it can be dispatched at runtime.
991 =head2 Method Modifiers
993 Method modifiers are a concept borrowed from CLOS, in which a method
994 can be wrapped with I<before>, I<after> and I<around> method modifiers
995 that will be called everytime the method is called.
997 =head3 How method modifiers work?
999 Method modifiers work by wrapping the original method and then replacing
1000 it in the classes symbol table. The wrappers will handle calling all the
1001 modifiers in the appropariate orders and preserving the calling context
1002 for the original method.
1004 Each method modifier serves a particular purpose, which may not be
1005 obvious to users of other method wrapping modules. To start with, the
1006 return values of I<before> and I<after> modifiers are ignored. This is
1007 because thier purpose is B<not> to filter the input and output of the
1008 primary method (this is done with an I<around> modifier). This may seem
1009 like an odd restriction to some, but doing this allows for simple code
1010 to be added at the begining or end of a method call without jeapordizing
1011 the normal functioning of the primary method or placing any extra
1012 responsibility on the code of the modifier. Of course if you have more
1013 complex needs, then use the I<around> modifier, which uses a variation
1014 of continutation passing style to allow for a high degree of flexibility.
1016 Before and around modifiers are called in last-defined-first-called order,
1017 while after modifiers are called in first-defined-first-called order. So
1018 the call tree might looks something like this:
1028 To see examples of using method modifiers, see the following examples
1029 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1030 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1031 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1033 =head3 What is the performance impact?
1035 Of course there is a performance cost associated with method modifiers,
1036 but we have made every effort to make that cost be directly proportional
1037 to the amount of modifier features you utilize.
1039 The wrapping method does it's best to B<only> do as much work as it
1040 absolutely needs to. In order to do this we have moved some of the
1041 performance costs to set-up time, where they are easier to amortize.
1043 All this said, my benchmarks have indicated the following:
1045 simple wrapper with no modifiers 100% slower
1046 simple wrapper with simple before modifier 400% slower
1047 simple wrapper with simple after modifier 450% slower
1048 simple wrapper with simple around modifier 500-550% slower
1049 simple wrapper with all 3 modifiers 1100% slower
1051 These numbers may seem daunting, but you must remember, every feature
1052 comes with some cost. To put things in perspective, just doing a simple
1053 C<AUTOLOAD> which does nothing but extract the name of the method called
1054 and return it costs about 400% over a normal method call.
1058 =item B<add_before_method_modifier ($method_name, $code)>
1060 This will wrap the method at C<$method_name> and the supplied C<$code>
1061 will be passed the C<@_> arguments, and called before the original
1062 method is called. As specified above, the return value of the I<before>
1063 method modifiers is ignored, and it's ability to modify C<@_> is
1064 fairly limited. If you need to do either of these things, use an
1065 C<around> method modifier.
1067 =item B<add_after_method_modifier ($method_name, $code)>
1069 This will wrap the method at C<$method_name> so that the original
1070 method will be called, it's return values stashed, and then the
1071 supplied C<$code> will be passed the C<@_> arguments, and called.
1072 As specified above, the return value of the I<after> method
1073 modifiers is ignored, and it cannot modify the return values of
1074 the original method. If you need to do either of these things, use an
1075 C<around> method modifier.
1077 =item B<add_around_method_modifier ($method_name, $code)>
1079 This will wrap the method at C<$method_name> so that C<$code>
1080 will be called and passed the original method as an extra argument
1081 at the begining of the C<@_> argument list. This is a variation of
1082 continuation passing style, where the function prepended to C<@_>
1083 can be considered a continuation. It is up to C<$code> if it calls
1084 the original method or not, there is no restriction on what the
1085 C<$code> can or cannot do.
1091 It should be noted that since there is no one consistent way to define
1092 the attributes of a class in Perl 5. These methods can only work with
1093 the information given, and can not easily discover information on
1094 their own. See L<Class::MOP::Attribute> for more details.
1098 =item B<attribute_metaclass>
1100 =item B<get_attribute_map>
1102 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1104 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1105 instance associated with the given class, and associates it with
1106 the C<$attribute_name>. Unlike methods, attributes within the MOP
1107 are stored as meta-information only. They will be used later to
1108 construct instances from (see C<construct_instance> above).
1109 More details about the attribute meta-objects can be found in the
1110 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1113 It should be noted that any accessor, reader/writer or predicate
1114 methods which the C<$attribute_meta_object> has will be installed
1115 into the class at this time.
1117 =item B<has_attribute ($attribute_name)>
1119 Checks to see if this class has an attribute by the name of
1120 C<$attribute_name> and returns a boolean.
1122 =item B<get_attribute ($attribute_name)>
1124 Returns the attribute meta-object associated with C<$attribute_name>,
1125 if none is found, it will return undef.
1127 =item B<remove_attribute ($attribute_name)>
1129 This will remove the attribute meta-object stored at
1130 C<$attribute_name>, then return the removed attribute meta-object.
1133 Removing an attribute will only affect future instances of
1134 the class, it will not make any attempt to remove the attribute from
1135 any existing instances of the class.
1137 It should be noted that any accessor, reader/writer or predicate
1138 methods which the attribute meta-object stored at C<$attribute_name>
1139 has will be removed from the class at this time. This B<will> make
1140 these attributes somewhat inaccessable in previously created
1141 instances. But if you are crazy enough to do this at runtime, then
1142 you are crazy enough to deal with something like this :).
1144 =item B<get_attribute_list>
1146 This returns a list of attribute names which are defined in the local
1147 class. If you want a list of all applicable attributes for a class,
1148 use the C<compute_all_applicable_attributes> method.
1150 =item B<compute_all_applicable_attributes>
1152 This will traverse the inheritance heirachy and return a list of all
1153 the applicable attributes for this class. It does not construct a
1154 HASH reference like C<compute_all_applicable_methods> because all
1155 that same information is discoverable through the attribute
1158 =item B<find_attribute_by_name ($attr_name)>
1160 This method will traverse the inheritance heirachy and find the
1161 first attribute whose name matches C<$attr_name>, then return it.
1162 It will return undef if nothing is found.
1166 =head2 Package Variables
1168 Since Perl's classes are built atop the Perl package system, it is
1169 fairly common to use package scoped variables for things like static
1170 class variables. The following methods are convience methods for
1171 the creation and inspection of package scoped variables.
1175 =item B<add_package_variable ($variable_name, ?$initial_value)>
1177 Given a C<$variable_name>, which must contain a leading sigil, this
1178 method will create that variable within the package which houses the
1179 class. It also takes an optional C<$initial_value>, which must be a
1180 reference of the same type as the sigil of the C<$variable_name>
1183 =item B<get_package_variable ($variable_name)>
1185 This will return a reference to the package variable in
1188 =item B<has_package_variable ($variable_name)>
1190 Returns true (C<1>) if there is a package variable defined for
1191 C<$variable_name>, and false (C<0>) otherwise.
1193 =item B<remove_package_variable ($variable_name)>
1195 This will attempt to remove the package variable at C<$variable_name>.
1199 =head2 Class closing
1205 =item B<is_immutable>
1207 =item B<make_immutable>
1213 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1215 =head1 COPYRIGHT AND LICENSE
1217 Copyright 2006 by Infinity Interactive, Inc.
1219 L<http://www.iinteractive.com>
1221 This library is free software; you can redistribute it and/or modify
1222 it under the same terms as Perl itself.