2 package Class::MOP::Class;
8 use Scalar::Util 'blessed', 'reftype', 'weaken';
9 use Sub::Name 'subname';
10 use B 'svref_2object';
12 our $VERSION = '0.17';
14 use base 'Class::MOP::Module';
16 use Class::MOP::Instance;
20 sub meta { Class::MOP::Class->initialize(blessed($_[0]) || $_[0]) }
25 # we need a sufficiently annoying prefix
26 # this should suffice for now, this is
27 # used in a couple of places below, so
28 # need to put it up here for now.
29 my $ANON_CLASS_PREFIX = 'Class::MOP::Class::__ANON__::SERIAL::';
34 # Metaclasses are singletons, so we cache them here.
35 # there is no need to worry about destruction though
36 # because they should die only when the program dies.
37 # After all, do package definitions even get reaped?
40 # means of accessing all the metaclasses that have
41 # been initialized thus far (for mugwumps obj browser)
42 sub get_all_metaclasses { %METAS }
43 sub get_all_metaclass_instances { values %METAS }
44 sub get_all_metaclass_names { keys %METAS }
48 my $package_name = shift;
49 (defined $package_name && $package_name && !blessed($package_name))
50 || confess "You must pass a package name and it cannot be blessed";
51 $class->construct_class_instance(':package' => $package_name, @_);
56 my $package_name = shift;
57 (defined $package_name && $package_name && !blessed($package_name))
58 || confess "You must pass a package name and it cannot be blessed";
59 $METAS{$package_name} = undef;
60 $class->construct_class_instance(':package' => $package_name, @_);
63 # NOTE: (meta-circularity)
64 # this is a special form of &construct_instance
65 # (see below), which is used to construct class
66 # meta-object instances for any Class::MOP::*
67 # class. All other classes will use the more
68 # normal &construct_instance.
69 sub construct_class_instance {
72 my $package_name = $options{':package'};
73 (defined $package_name && $package_name)
74 || confess "You must pass a package name";
76 # return the metaclass if we have it cached,
77 # and it is still defined (it has not been
78 # reaped by DESTROY yet, which can happen
79 # annoyingly enough during global destruction)
80 return $METAS{$package_name}
81 if exists $METAS{$package_name} && defined $METAS{$package_name};
84 # we need to deal with the possibility
85 # of class immutability here, and then
86 # get the name of the class appropriately
87 $class = (blessed($class)
88 ? ($class->is_immutable
89 ? $class->get_mutable_metaclass_name()
93 $class = blessed($class) || $class;
94 # now create the metaclass
96 if ($class =~ /^Class::MOP::Class$/) {
99 '$:package' => $package_name,
100 '%:namespace' => \%{$package_name . '::'},
101 '%:attributes' => {},
102 '$:attribute_metaclass' => $options{':attribute_metaclass'} || 'Class::MOP::Attribute',
103 '$:method_metaclass' => $options{':method_metaclass'} || 'Class::MOP::Method',
104 '$:instance_metaclass' => $options{':instance_metaclass'} || 'Class::MOP::Instance',
109 # it is safe to use meta here because
110 # class will always be a subclass of
111 # Class::MOP::Class, which defines meta
112 $meta = $class->meta->construct_instance(%options)
115 # and check the metaclass compatibility
116 $meta->check_metaclass_compatability();
117 $METAS{$package_name} = $meta;
119 # we need to weaken any anon classes
120 # so that they can call DESTROY properly
121 weaken($METAS{$package_name})
122 if $package_name =~ /^$ANON_CLASS_PREFIX/;
126 sub check_metaclass_compatability {
129 # this is always okay ...
130 return if blessed($self) eq 'Class::MOP::Class' &&
131 $self->instance_metaclass eq 'Class::MOP::Instance';
133 my @class_list = $self->class_precedence_list;
134 shift @class_list; # shift off $self->name
136 foreach my $class_name (@class_list) {
137 my $meta = $METAS{$class_name} || next;
140 # we need to deal with the possibility
141 # of class immutability here, and then
142 # get the name of the class appropriately
143 my $meta_type = ($meta->is_immutable
144 ? $meta->get_mutable_metaclass_name()
147 ($self->isa($meta_type))
148 || confess $self->name . "->meta => (" . (blessed($self)) . ")" .
149 " is not compatible with the " .
150 $class_name . "->meta => (" . ($meta_type) . ")";
152 # we also need to check that instance metaclasses
153 # are compatabile in the same the class.
154 ($self->instance_metaclass->isa($meta->instance_metaclass))
155 || confess $self->name . "->meta => (" . ($self->instance_metaclass) . ")" .
156 " is not compatible with the " .
157 $class_name . "->meta => (" . ($meta->instance_metaclass) . ")";
166 # this should be sufficient, if you have a
167 # use case where it is not, write a test and
169 my $ANON_CLASS_SERIAL = 0;
171 sub create_anon_class {
172 my ($class, %options) = @_;
173 my $package_name = $ANON_CLASS_PREFIX . ++$ANON_CLASS_SERIAL;
174 return $class->create($package_name, '0.00', %options);
179 # this will only get called for
180 # anon-classes, all other calls
181 # are assumed to occur during
182 # global destruction and so don't
183 # really need to be handled explicitly
186 return unless $self->name =~ /^$ANON_CLASS_PREFIX/;
187 my ($serial_id) = ($self->name =~ /^$ANON_CLASS_PREFIX(\d+)/);
189 foreach my $key (keys %{$ANON_CLASS_PREFIX . $serial_id}) {
190 delete ${$ANON_CLASS_PREFIX . $serial_id}{$key};
192 delete ${'main::' . $ANON_CLASS_PREFIX}{$serial_id . '::'};
195 # creating classes with MOP ...
198 my ($class, $package_name, $package_version, %options) = @_;
199 (defined $package_name && $package_name)
200 || confess "You must pass a package name";
201 my $code = "package $package_name;";
202 $code .= "\$$package_name\:\:VERSION = '$package_version';"
203 if defined $package_version;
205 confess "creation of $package_name failed : $@" if $@;
206 my $meta = $class->initialize($package_name);
208 $meta->add_method('meta' => sub {
209 $class->initialize(blessed($_[0]) || $_[0]);
212 $meta->superclasses(@{$options{superclasses}})
213 if exists $options{superclasses};
215 # process attributes first, so that they can
216 # install accessors, but locally defined methods
217 # can then overwrite them. It is maybe a little odd, but
218 # I think this should be the order of things.
219 if (exists $options{attributes}) {
220 foreach my $attr (@{$options{attributes}}) {
221 $meta->add_attribute($attr);
224 if (exists $options{methods}) {
225 foreach my $method_name (keys %{$options{methods}}) {
226 $meta->add_method($method_name, $options{methods}->{$method_name});
235 # all these attribute readers will be bootstrapped
236 # away in the Class::MOP bootstrap section
238 sub get_attribute_map { $_[0]->{'%:attributes'} }
239 sub attribute_metaclass { $_[0]->{'$:attribute_metaclass'} }
240 sub method_metaclass { $_[0]->{'$:method_metaclass'} }
241 sub instance_metaclass { $_[0]->{'$:instance_metaclass'} }
243 # Instance Construction & Cloning
248 # we need to protect the integrity of the
249 # Class::MOP::Class singletons here, so we
250 # delegate this to &construct_class_instance
251 # which will deal with the singletons
252 return $class->construct_class_instance(@_)
253 if $class->name->isa('Class::MOP::Class');
254 return $class->construct_instance(@_);
257 sub construct_instance {
258 my ($class, %params) = @_;
259 my $meta_instance = $class->get_meta_instance();
260 my $instance = $meta_instance->create_instance();
261 foreach my $attr ($class->compute_all_applicable_attributes()) {
262 $attr->initialize_instance_slot($meta_instance, $instance, \%params);
267 sub get_meta_instance {
269 return $class->instance_metaclass->new(
271 $class->compute_all_applicable_attributes()
277 my $instance = shift;
278 (blessed($instance) && $instance->isa($class->name))
279 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
281 # we need to protect the integrity of the
282 # Class::MOP::Class singletons here, they
283 # should not be cloned.
284 return $instance if $instance->isa('Class::MOP::Class');
285 $class->clone_instance($instance, @_);
289 my ($class, $instance, %params) = @_;
291 || confess "You can only clone instances, \$self is not a blessed instance";
292 my $meta_instance = $class->get_meta_instance();
293 my $clone = $meta_instance->clone_instance($instance);
294 foreach my $key (keys %params) {
295 next unless $meta_instance->is_valid_slot($key);
296 $meta_instance->set_slot_value($clone, $key, $params{$key});
307 @{$self->get_package_symbol('@ISA')} = @supers;
309 # we need to check the metaclass
310 # compatability here so that we can
311 # be sure that the superclass is
312 # not potentially creating an issues
313 # we don't know about
314 $self->check_metaclass_compatability();
316 @{$self->get_package_symbol('@ISA')};
319 sub class_precedence_list {
322 # We need to check for ciruclar inheirtance here.
323 # This will do nothing if all is well, and blow
324 # up otherwise. Yes, it's an ugly hack, better
325 # suggestions are welcome.
326 { ($self->name || return)->isa('This is a test for circular inheritance') }
327 # ... and now back to our regularly scheduled program
331 $self->initialize($_)->class_precedence_list()
332 } $self->superclasses()
339 my ($self, $method_name, $method) = @_;
340 (defined $method_name && $method_name)
341 || confess "You must define a method name";
342 # use reftype here to allow for blessed subs ...
343 ('CODE' eq (reftype($method) || ''))
344 || confess "Your code block must be a CODE reference";
345 my $full_method_name = ($self->name . '::' . $method_name);
348 # dont bless subs, its bad mkay
349 $method = $self->method_metaclass->wrap($method) unless blessed($method);
351 $self->add_package_symbol("&${method_name}" => subname $full_method_name => $method);
355 my $fetch_and_prepare_method = sub {
356 my ($self, $method_name) = @_;
358 my $method = $self->get_method($method_name);
359 # if we dont have local ...
361 # try to find the next method
362 $method = $self->find_next_method_by_name($method_name);
363 # die if it does not exist
365 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
366 # and now make sure to wrap it
367 # even if it is already wrapped
368 # because we need a new sub ref
369 $method = Class::MOP::Method::Wrapped->wrap($method);
372 # now make sure we wrap it properly
373 $method = Class::MOP::Method::Wrapped->wrap($method)
374 unless $method->isa('Class::MOP::Method::Wrapped');
376 $self->add_method($method_name => $method);
380 sub add_before_method_modifier {
381 my ($self, $method_name, $method_modifier) = @_;
382 (defined $method_name && $method_name)
383 || confess "You must pass in a method name";
384 my $method = $fetch_and_prepare_method->($self, $method_name);
385 $method->add_before_modifier(subname ':before' => $method_modifier);
388 sub add_after_method_modifier {
389 my ($self, $method_name, $method_modifier) = @_;
390 (defined $method_name && $method_name)
391 || confess "You must pass in a method name";
392 my $method = $fetch_and_prepare_method->($self, $method_name);
393 $method->add_after_modifier(subname ':after' => $method_modifier);
396 sub add_around_method_modifier {
397 my ($self, $method_name, $method_modifier) = @_;
398 (defined $method_name && $method_name)
399 || confess "You must pass in a method name";
400 my $method = $fetch_and_prepare_method->($self, $method_name);
401 $method->add_around_modifier(subname ':around' => $method_modifier);
405 # the methods above used to be named like this:
406 # ${pkg}::${method}:(before|after|around)
407 # but this proved problematic when using one modifier
408 # to wrap multiple methods (something which is likely
409 # to happen pretty regularly IMO). So instead of naming
410 # it like this, I have chosen to just name them purely
411 # with their modifier names, like so:
412 # :(before|after|around)
413 # The fact is that in a stack trace, it will be fairly
414 # evident from the context what method they are attached
415 # to, and so don't need the fully qualified name.
419 my ($self, $method_name, $method) = @_;
420 (defined $method_name && $method_name)
421 || confess "You must define a method name";
422 # use reftype here to allow for blessed subs ...
423 ('CODE' eq (reftype($method) || ''))
424 || confess "Your code block must be a CODE reference";
427 # dont bless subs, its bad mkay
428 $method = $self->method_metaclass->wrap($method) unless blessed($method);
430 $self->add_package_symbol("&${method_name}" => $method);
433 sub find_method_by_name {
434 my ($self, $method_name) = @_;
435 return $self->name->can($method_name);
439 my ($self, $method_name) = @_;
440 (defined $method_name && $method_name)
441 || confess "You must define a method name";
443 return 0 if !$self->has_package_symbol("&${method_name}");
444 my $method = $self->get_package_symbol("&${method_name}");
445 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
446 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
449 # dont bless subs, its bad mkay
450 $self->method_metaclass->wrap($method) unless blessed($method);
456 my ($self, $method_name) = @_;
457 (defined $method_name && $method_name)
458 || confess "You must define a method name";
460 return unless $self->has_method($method_name);
462 return $self->get_package_symbol("&${method_name}");
466 my ($self, $method_name) = @_;
467 (defined $method_name && $method_name)
468 || confess "You must define a method name";
470 my $removed_method = $self->get_method($method_name);
472 $self->remove_package_symbol("&${method_name}")
473 if defined $removed_method;
475 return $removed_method;
478 sub get_method_list {
480 grep { $self->has_method($_) } $self->list_all_package_symbols;
483 sub compute_all_applicable_methods {
486 # keep a record of what we have seen
487 # here, this will handle all the
488 # inheritence issues because we are
489 # using the &class_precedence_list
490 my (%seen_class, %seen_method);
491 foreach my $class ($self->class_precedence_list()) {
492 next if $seen_class{$class};
493 $seen_class{$class}++;
494 # fetch the meta-class ...
495 my $meta = $self->initialize($class);
496 foreach my $method_name ($meta->get_method_list()) {
497 next if exists $seen_method{$method_name};
498 $seen_method{$method_name}++;
500 name => $method_name,
502 code => $meta->get_method($method_name)
509 sub find_all_methods_by_name {
510 my ($self, $method_name) = @_;
511 (defined $method_name && $method_name)
512 || confess "You must define a method name to find";
514 # keep a record of what we have seen
515 # here, this will handle all the
516 # inheritence issues because we are
517 # using the &class_precedence_list
519 foreach my $class ($self->class_precedence_list()) {
520 next if $seen_class{$class};
521 $seen_class{$class}++;
522 # fetch the meta-class ...
523 my $meta = $self->initialize($class);
525 name => $method_name,
527 code => $meta->get_method($method_name)
528 } if $meta->has_method($method_name);
533 sub find_next_method_by_name {
534 my ($self, $method_name) = @_;
535 (defined $method_name && $method_name)
536 || confess "You must define a method name to find";
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
542 my @cpl = $self->class_precedence_list();
543 shift @cpl; # discard ourselves
544 foreach my $class (@cpl) {
545 next if $seen_class{$class};
546 $seen_class{$class}++;
547 # fetch the meta-class ...
548 my $meta = $self->initialize($class);
549 return $meta->get_method($method_name)
550 if $meta->has_method($method_name);
559 # either we have an attribute object already
560 # or we need to create one from the args provided
561 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
562 # make sure it is derived from the correct type though
563 ($attribute->isa('Class::MOP::Attribute'))
564 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
565 $attribute->attach_to_class($self);
566 $attribute->install_accessors();
567 $self->get_attribute_map->{$attribute->name} = $attribute;
571 my ($self, $attribute_name) = @_;
572 (defined $attribute_name && $attribute_name)
573 || confess "You must define an attribute name";
574 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
578 my ($self, $attribute_name) = @_;
579 (defined $attribute_name && $attribute_name)
580 || confess "You must define an attribute name";
581 return $self->get_attribute_map->{$attribute_name}
582 if $self->has_attribute($attribute_name);
586 sub remove_attribute {
587 my ($self, $attribute_name) = @_;
588 (defined $attribute_name && $attribute_name)
589 || confess "You must define an attribute name";
590 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
591 return unless defined $removed_attribute;
592 delete $self->get_attribute_map->{$attribute_name};
593 $removed_attribute->remove_accessors();
594 $removed_attribute->detach_from_class();
595 return $removed_attribute;
598 sub get_attribute_list {
600 keys %{$self->get_attribute_map};
603 sub compute_all_applicable_attributes {
606 # keep a record of what we have seen
607 # here, this will handle all the
608 # inheritence issues because we are
609 # using the &class_precedence_list
610 my (%seen_class, %seen_attr);
611 foreach my $class ($self->class_precedence_list()) {
612 next if $seen_class{$class};
613 $seen_class{$class}++;
614 # fetch the meta-class ...
615 my $meta = $self->initialize($class);
616 foreach my $attr_name ($meta->get_attribute_list()) {
617 next if exists $seen_attr{$attr_name};
618 $seen_attr{$attr_name}++;
619 push @attrs => $meta->get_attribute($attr_name);
625 sub find_attribute_by_name {
626 my ($self, $attr_name) = @_;
627 # keep a record of what we have seen
628 # here, this will handle all the
629 # inheritence issues because we are
630 # using the &class_precedence_list
632 foreach my $class ($self->class_precedence_list()) {
633 next if $seen_class{$class};
634 $seen_class{$class}++;
635 # fetch the meta-class ...
636 my $meta = $self->initialize($class);
637 return $meta->get_attribute($attr_name)
638 if $meta->has_attribute($attr_name);
646 sub is_immutable { 0 }
649 return Class::MOP::Class::Immutable->make_metaclass_immutable(@_);
660 Class::MOP::Class - Class Meta Object
664 # assuming that class Foo
665 # has been defined, you can
667 # use this for introspection ...
669 # add a method to Foo ...
670 Foo->meta->add_method('bar' => sub { ... })
672 # get a list of all the classes searched
673 # the method dispatcher in the correct order
674 Foo->meta->class_precedence_list()
676 # remove a method from Foo
677 Foo->meta->remove_method('bar');
679 # or use this to actually create classes ...
681 Class::MOP::Class->create('Bar' => '0.01' => (
682 superclasses => [ 'Foo' ],
684 Class::MOP:::Attribute->new('$bar'),
685 Class::MOP:::Attribute->new('$baz'),
688 calculate_bar => sub { ... },
689 construct_baz => sub { ... }
695 This is the largest and currently most complex part of the Perl 5
696 meta-object protocol. It controls the introspection and
697 manipulation of Perl 5 classes (and it can create them too). The
698 best way to understand what this module can do, is to read the
699 documentation for each of it's methods.
703 =head2 Self Introspection
709 This will return a B<Class::MOP::Class> instance which is related
710 to this class. Thereby allowing B<Class::MOP::Class> to actually
713 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
714 bootstrap this module by installing a number of attribute meta-objects
715 into it's metaclass. This will allow this class to reap all the benifits
716 of the MOP when subclassing it.
718 =item B<get_all_metaclasses>
720 This will return an hash of all the metaclass instances that have
721 been cached by B<Class::MOP::Class> keyed by the package name.
723 =item B<get_all_metaclass_instances>
725 This will return an array of all the metaclass instances that have
726 been cached by B<Class::MOP::Class>.
728 =item B<get_all_metaclass_names>
730 This will return an array of all the metaclass names that have
731 been cached by B<Class::MOP::Class>.
735 =head2 Class construction
737 These methods will handle creating B<Class::MOP::Class> objects,
738 which can be used to both create new classes, and analyze
739 pre-existing classes.
741 This module will internally store references to all the instances
742 you create with these methods, so that they do not need to be
743 created any more than nessecary. Basically, they are singletons.
747 =item B<create ($package_name, ?$package_version,
748 superclasses =E<gt> ?@superclasses,
749 methods =E<gt> ?%methods,
750 attributes =E<gt> ?%attributes)>
752 This returns a B<Class::MOP::Class> object, bringing the specified
753 C<$package_name> into existence and adding any of the
754 C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
757 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
758 methods =E<gt> ?%methods,
759 attributes =E<gt> ?%attributes)>
761 This will create an anonymous class, it works much like C<create> but
762 it does not need a C<$package_name>. Instead it will create a suitably
763 unique package name for you to stash things into.
765 =item B<initialize ($package_name, %options)>
767 This initializes and returns returns a B<Class::MOP::Class> object
768 for a given a C<$package_name>.
770 =item B<reinitialize ($package_name, %options)>
772 This removes the old metaclass, and creates a new one in it's place.
773 Do B<not> use this unless you really know what you are doing, it could
774 very easily make a very large mess of your program.
776 =item B<construct_class_instance (%options)>
778 This will construct an instance of B<Class::MOP::Class>, it is
779 here so that we can actually "tie the knot" for B<Class::MOP::Class>
780 to use C<construct_instance> once all the bootstrapping is done. This
781 method is used internally by C<initialize> and should never be called
782 from outside of that method really.
784 =item B<check_metaclass_compatability>
786 This method is called as the very last thing in the
787 C<construct_class_instance> method. This will check that the
788 metaclass you are creating is compatible with the metaclasses of all
789 your ancestors. For more inforamtion about metaclass compatibility
790 see the C<About Metaclass compatibility> section in L<Class::MOP>.
794 =head2 Object instance construction and cloning
796 These methods are B<entirely optional>, it is up to you whether you want
801 =item B<instance_metaclass>
803 =item B<get_meta_instance>
805 =item B<new_object (%params)>
807 This is a convience method for creating a new object of the class, and
808 blessing it into the appropriate package as well. Ideally your class
809 would call a C<new> this method like so:
812 my ($class, %param) = @_;
813 $class->meta->new_object(%params);
816 Of course the ideal place for this would actually be in C<UNIVERSAL::>
817 but that is considered bad style, so we do not do that.
819 =item B<construct_instance (%params)>
821 This method is used to construct an instace structure suitable for
822 C<bless>-ing into your package of choice. It works in conjunction
823 with the Attribute protocol to collect all applicable attributes.
825 This will construct and instance using a HASH ref as storage
826 (currently only HASH references are supported). This will collect all
827 the applicable attributes and layout out the fields in the HASH ref,
828 it will then initialize them using either use the corresponding key
829 in C<%params> or any default value or initializer found in the
830 attribute meta-object.
832 =item B<clone_object ($instance, %params)>
834 This is a convience method for cloning an object instance, then
835 blessing it into the appropriate package. This method will call
836 C<clone_instance>, which performs a shallow copy of the object,
837 see that methods documentation for more details. Ideally your
838 class would call a C<clone> this method like so:
841 my ($self, %param) = @_;
842 $self->meta->clone_object($self, %params);
845 Of course the ideal place for this would actually be in C<UNIVERSAL::>
846 but that is considered bad style, so we do not do that.
848 =item B<clone_instance($instance, %params)>
850 This method is a compliment of C<construct_instance> (which means if
851 you override C<construct_instance>, you need to override this one too),
852 and clones the instance shallowly.
854 The cloned structure returned is (like with C<construct_instance>) an
855 unC<bless>ed HASH reference, it is your responsibility to then bless
856 this cloned structure into the right class (which C<clone_object> will
859 As of 0.11, this method will clone the C<$instance> structure shallowly,
860 as opposed to the deep cloning implemented in prior versions. After much
861 thought, research and discussion, I have decided that anything but basic
862 shallow cloning is outside the scope of the meta-object protocol. I
863 think Yuval "nothingmuch" Kogman put it best when he said that cloning
864 is too I<context-specific> to be part of the MOP.
874 This is a read-only attribute which returns the package name for the
875 given B<Class::MOP::Class> instance.
879 This is a read-only attribute which returns the C<$VERSION> of the
880 package for the given B<Class::MOP::Class> instance.
884 =head2 Inheritance Relationships
888 =item B<superclasses (?@superclasses)>
890 This is a read-write attribute which represents the superclass
891 relationships of the class the B<Class::MOP::Class> instance is
892 associated with. Basically, it can get and set the C<@ISA> for you.
895 Perl will occasionally perform some C<@ISA> and method caching, if
896 you decide to change your superclass relationship at runtime (which
897 is quite insane and very much not recommened), then you should be
898 aware of this and the fact that this module does not make any
899 attempt to address this issue.
901 =item B<class_precedence_list>
903 This computes the a list of all the class's ancestors in the same order
904 in which method dispatch will be done. This is similair to
905 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
913 =item B<method_metaclass>
915 =item B<add_method ($method_name, $method)>
917 This will take a C<$method_name> and CODE reference to that
918 C<$method> and install it into the class's package.
921 This does absolutely nothing special to C<$method>
922 other than use B<Sub::Name> to make sure it is tagged with the
923 correct name, and therefore show up correctly in stack traces and
926 =item B<alias_method ($method_name, $method)>
928 This will take a C<$method_name> and CODE reference to that
929 C<$method> and alias the method into the class's package.
932 Unlike C<add_method>, this will B<not> try to name the
933 C<$method> using B<Sub::Name>, it only aliases the method in
936 =item B<has_method ($method_name)>
938 This just provides a simple way to check if the class implements
939 a specific C<$method_name>. It will I<not> however, attempt to check
940 if the class inherits the method (use C<UNIVERSAL::can> for that).
942 This will correctly handle functions defined outside of the package
943 that use a fully qualified name (C<sub Package::name { ... }>).
945 This will correctly handle functions renamed with B<Sub::Name> and
946 installed using the symbol tables. However, if you are naming the
947 subroutine outside of the package scope, you must use the fully
948 qualified name, including the package name, for C<has_method> to
949 correctly identify it.
951 This will attempt to correctly ignore functions imported from other
952 packages using B<Exporter>. It breaks down if the function imported
953 is an C<__ANON__> sub (such as with C<use constant>), which very well
954 may be a valid method being applied to the class.
956 In short, this method cannot always be trusted to determine if the
957 C<$method_name> is actually a method. However, it will DWIM about
958 90% of the time, so it's a small trade off I think.
960 =item B<get_method ($method_name)>
962 This will return a CODE reference of the specified C<$method_name>,
963 or return undef if that method does not exist.
965 =item B<find_method_by_name ($method_name>
967 This will return a CODE reference of the specified C<$method_name>,
968 or return undef if that method does not exist.
970 Unlike C<get_method> this will also look in the superclasses.
972 =item B<remove_method ($method_name)>
974 This will attempt to remove a given C<$method_name> from the class.
975 It will return the CODE reference that it has removed, and will
976 attempt to use B<Sub::Name> to clear the methods associated name.
978 =item B<get_method_list>
980 This will return a list of method names for all I<locally> defined
981 methods. It does B<not> provide a list of all applicable methods,
982 including any inherited ones. If you want a list of all applicable
983 methods, use the C<compute_all_applicable_methods> method.
985 =item B<compute_all_applicable_methods>
987 This will return a list of all the methods names this class will
988 respond to, taking into account inheritance. The list will be a list of
989 HASH references, each one containing the following information; method
990 name, the name of the class in which the method lives and a CODE
991 reference for the actual method.
993 =item B<find_all_methods_by_name ($method_name)>
995 This will traverse the inheritence hierarchy and locate all methods
996 with a given C<$method_name>. Similar to
997 C<compute_all_applicable_methods> it returns a list of HASH references
998 with the following information; method name (which will always be the
999 same as C<$method_name>), the name of the class in which the method
1000 lives and a CODE reference for the actual method.
1002 The list of methods produced is a distinct list, meaning there are no
1003 duplicates in it. This is especially useful for things like object
1004 initialization and destruction where you only want the method called
1005 once, and in the correct order.
1007 =item B<find_next_method_by_name ($method_name)>
1009 This will return the first method to match a given C<$method_name> in
1010 the superclasses, this is basically equivalent to calling
1011 C<SUPER::$method_name>, but it can be dispatched at runtime.
1015 =head2 Method Modifiers
1017 Method modifiers are a concept borrowed from CLOS, in which a method
1018 can be wrapped with I<before>, I<after> and I<around> method modifiers
1019 that will be called everytime the method is called.
1021 =head3 How method modifiers work?
1023 Method modifiers work by wrapping the original method and then replacing
1024 it in the classes symbol table. The wrappers will handle calling all the
1025 modifiers in the appropariate orders and preserving the calling context
1026 for the original method.
1028 Each method modifier serves a particular purpose, which may not be
1029 obvious to users of other method wrapping modules. To start with, the
1030 return values of I<before> and I<after> modifiers are ignored. This is
1031 because thier purpose is B<not> to filter the input and output of the
1032 primary method (this is done with an I<around> modifier). This may seem
1033 like an odd restriction to some, but doing this allows for simple code
1034 to be added at the begining or end of a method call without jeapordizing
1035 the normal functioning of the primary method or placing any extra
1036 responsibility on the code of the modifier. Of course if you have more
1037 complex needs, then use the I<around> modifier, which uses a variation
1038 of continutation passing style to allow for a high degree of flexibility.
1040 Before and around modifiers are called in last-defined-first-called order,
1041 while after modifiers are called in first-defined-first-called order. So
1042 the call tree might looks something like this:
1052 To see examples of using method modifiers, see the following examples
1053 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1054 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1055 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1057 =head3 What is the performance impact?
1059 Of course there is a performance cost associated with method modifiers,
1060 but we have made every effort to make that cost be directly proportional
1061 to the amount of modifier features you utilize.
1063 The wrapping method does it's best to B<only> do as much work as it
1064 absolutely needs to. In order to do this we have moved some of the
1065 performance costs to set-up time, where they are easier to amortize.
1067 All this said, my benchmarks have indicated the following:
1069 simple wrapper with no modifiers 100% slower
1070 simple wrapper with simple before modifier 400% slower
1071 simple wrapper with simple after modifier 450% slower
1072 simple wrapper with simple around modifier 500-550% slower
1073 simple wrapper with all 3 modifiers 1100% slower
1075 These numbers may seem daunting, but you must remember, every feature
1076 comes with some cost. To put things in perspective, just doing a simple
1077 C<AUTOLOAD> which does nothing but extract the name of the method called
1078 and return it costs about 400% over a normal method call.
1082 =item B<add_before_method_modifier ($method_name, $code)>
1084 This will wrap the method at C<$method_name> and the supplied C<$code>
1085 will be passed the C<@_> arguments, and called before the original
1086 method is called. As specified above, the return value of the I<before>
1087 method modifiers is ignored, and it's ability to modify C<@_> is
1088 fairly limited. If you need to do either of these things, use an
1089 C<around> method modifier.
1091 =item B<add_after_method_modifier ($method_name, $code)>
1093 This will wrap the method at C<$method_name> so that the original
1094 method will be called, it's return values stashed, and then the
1095 supplied C<$code> will be passed the C<@_> arguments, and called.
1096 As specified above, the return value of the I<after> method
1097 modifiers is ignored, and it cannot modify the return values of
1098 the original method. If you need to do either of these things, use an
1099 C<around> method modifier.
1101 =item B<add_around_method_modifier ($method_name, $code)>
1103 This will wrap the method at C<$method_name> so that C<$code>
1104 will be called and passed the original method as an extra argument
1105 at the begining of the C<@_> argument list. This is a variation of
1106 continuation passing style, where the function prepended to C<@_>
1107 can be considered a continuation. It is up to C<$code> if it calls
1108 the original method or not, there is no restriction on what the
1109 C<$code> can or cannot do.
1115 It should be noted that since there is no one consistent way to define
1116 the attributes of a class in Perl 5. These methods can only work with
1117 the information given, and can not easily discover information on
1118 their own. See L<Class::MOP::Attribute> for more details.
1122 =item B<attribute_metaclass>
1124 =item B<get_attribute_map>
1126 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1128 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1129 instance associated with the given class, and associates it with
1130 the C<$attribute_name>. Unlike methods, attributes within the MOP
1131 are stored as meta-information only. They will be used later to
1132 construct instances from (see C<construct_instance> above).
1133 More details about the attribute meta-objects can be found in the
1134 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1137 It should be noted that any accessor, reader/writer or predicate
1138 methods which the C<$attribute_meta_object> has will be installed
1139 into the class at this time.
1141 =item B<has_attribute ($attribute_name)>
1143 Checks to see if this class has an attribute by the name of
1144 C<$attribute_name> and returns a boolean.
1146 =item B<get_attribute ($attribute_name)>
1148 Returns the attribute meta-object associated with C<$attribute_name>,
1149 if none is found, it will return undef.
1151 =item B<remove_attribute ($attribute_name)>
1153 This will remove the attribute meta-object stored at
1154 C<$attribute_name>, then return the removed attribute meta-object.
1157 Removing an attribute will only affect future instances of
1158 the class, it will not make any attempt to remove the attribute from
1159 any existing instances of the class.
1161 It should be noted that any accessor, reader/writer or predicate
1162 methods which the attribute meta-object stored at C<$attribute_name>
1163 has will be removed from the class at this time. This B<will> make
1164 these attributes somewhat inaccessable in previously created
1165 instances. But if you are crazy enough to do this at runtime, then
1166 you are crazy enough to deal with something like this :).
1168 =item B<get_attribute_list>
1170 This returns a list of attribute names which are defined in the local
1171 class. If you want a list of all applicable attributes for a class,
1172 use the C<compute_all_applicable_attributes> method.
1174 =item B<compute_all_applicable_attributes>
1176 This will traverse the inheritance heirachy and return a list of all
1177 the applicable attributes for this class. It does not construct a
1178 HASH reference like C<compute_all_applicable_methods> because all
1179 that same information is discoverable through the attribute
1182 =item B<find_attribute_by_name ($attr_name)>
1184 This method will traverse the inheritance heirachy and find the
1185 first attribute whose name matches C<$attr_name>, then return it.
1186 It will return undef if nothing is found.
1190 =head2 Package Variables
1192 Since Perl's classes are built atop the Perl package system, it is
1193 fairly common to use package scoped variables for things like static
1194 class variables. The following methods are convience methods for
1195 the creation and inspection of package scoped variables.
1199 =item B<add_package_symbol ($variable_name, ?$initial_value)>
1201 Given a C<$variable_name>, which must contain a leading sigil, this
1202 method will create that variable within the package which houses the
1203 class. It also takes an optional C<$initial_value>, which must be a
1204 reference of the same type as the sigil of the C<$variable_name>
1207 =item B<get_package_symbol ($variable_name)>
1209 This will return a reference to the package variable in
1212 =item B<has_package_symbol ($variable_name)>
1214 Returns true (C<1>) if there is a package variable defined for
1215 C<$variable_name>, and false (C<0>) otherwise.
1217 =item B<remove_package_symbol ($variable_name)>
1219 This will attempt to remove the package variable at C<$variable_name>.
1223 =head2 Class closing
1229 =item B<is_immutable>
1231 =item B<make_immutable>
1237 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1239 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1241 =head1 COPYRIGHT AND LICENSE
1243 Copyright 2006 by Infinity Interactive, Inc.
1245 L<http://www.iinteractive.com>
1247 This library is free software; you can redistribute it and/or modify
1248 it under the same terms as Perl itself.