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 '$:authority' => \undef,
93 # defined in Class::MOP::Class
94 '%:methods' => \undef,
97 '$: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'} }
268 # there is a faster/better way
269 # to do this, I am sure :)
272 $_ => $self->get_method($_)
274 $self->has_method($_)
275 } $self->list_all_package_symbols
279 # Instance Construction & Cloning
284 # we need to protect the integrity of the
285 # Class::MOP::Class singletons here, so we
286 # delegate this to &construct_class_instance
287 # which will deal with the singletons
288 return $class->construct_class_instance(@_)
289 if $class->name->isa('Class::MOP::Class');
290 return $class->construct_instance(@_);
293 sub construct_instance {
294 my ($class, %params) = @_;
295 my $meta_instance = $class->get_meta_instance();
296 my $instance = $meta_instance->create_instance();
297 foreach my $attr ($class->compute_all_applicable_attributes()) {
298 $attr->initialize_instance_slot($meta_instance, $instance, \%params);
303 sub get_meta_instance {
305 return $class->instance_metaclass->new(
307 $class->compute_all_applicable_attributes()
313 my $instance = shift;
314 (blessed($instance) && $instance->isa($class->name))
315 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
317 # we need to protect the integrity of the
318 # Class::MOP::Class singletons here, they
319 # should not be cloned.
320 return $instance if $instance->isa('Class::MOP::Class');
321 $class->clone_instance($instance, @_);
325 my ($class, $instance, %params) = @_;
327 || confess "You can only clone instances, \$self is not a blessed instance";
328 my $meta_instance = $class->get_meta_instance();
329 my $clone = $meta_instance->clone_instance($instance);
330 foreach my $key (keys %params) {
331 next unless $meta_instance->is_valid_slot($key);
332 $meta_instance->set_slot_value($clone, $key, $params{$key});
343 @{$self->get_package_symbol('@ISA')} = @supers;
345 # we need to check the metaclass
346 # compatability here so that we can
347 # be sure that the superclass is
348 # not potentially creating an issues
349 # we don't know about
350 $self->check_metaclass_compatability();
352 @{$self->get_package_symbol('@ISA')};
355 sub class_precedence_list {
358 # We need to check for ciruclar inheirtance here.
359 # This will do nothing if all is well, and blow
360 # up otherwise. Yes, it's an ugly hack, better
361 # suggestions are welcome.
362 { ($self->name || return)->isa('This is a test for circular inheritance') }
363 # ... and now back to our regularly scheduled program
367 $self->initialize($_)->class_precedence_list()
368 } $self->superclasses()
375 my ($self, $method_name, $method) = @_;
376 (defined $method_name && $method_name)
377 || confess "You must define a method name";
378 # use reftype here to allow for blessed subs ...
379 ('CODE' eq (reftype($method) || ''))
380 || confess "Your code block must be a CODE reference";
381 my $full_method_name = ($self->name . '::' . $method_name);
384 # dont bless subs, its bad mkay
385 $method = $self->method_metaclass->wrap($method) unless blessed($method);
387 $self->add_package_symbol("&${method_name}" => subname $full_method_name => $method);
391 my $fetch_and_prepare_method = sub {
392 my ($self, $method_name) = @_;
394 my $method = $self->get_method($method_name);
395 # if we dont have local ...
397 # try to find the next method
398 $method = $self->find_next_method_by_name($method_name);
399 # die if it does not exist
401 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
402 # and now make sure to wrap it
403 # even if it is already wrapped
404 # because we need a new sub ref
405 $method = Class::MOP::Method::Wrapped->wrap($method);
408 # now make sure we wrap it properly
409 $method = Class::MOP::Method::Wrapped->wrap($method)
410 unless $method->isa('Class::MOP::Method::Wrapped');
412 $self->add_method($method_name => $method);
416 sub add_before_method_modifier {
417 my ($self, $method_name, $method_modifier) = @_;
418 (defined $method_name && $method_name)
419 || confess "You must pass in a method name";
420 my $method = $fetch_and_prepare_method->($self, $method_name);
421 $method->add_before_modifier(subname ':before' => $method_modifier);
424 sub add_after_method_modifier {
425 my ($self, $method_name, $method_modifier) = @_;
426 (defined $method_name && $method_name)
427 || confess "You must pass in a method name";
428 my $method = $fetch_and_prepare_method->($self, $method_name);
429 $method->add_after_modifier(subname ':after' => $method_modifier);
432 sub add_around_method_modifier {
433 my ($self, $method_name, $method_modifier) = @_;
434 (defined $method_name && $method_name)
435 || confess "You must pass in a method name";
436 my $method = $fetch_and_prepare_method->($self, $method_name);
437 $method->add_around_modifier(subname ':around' => $method_modifier);
441 # the methods above used to be named like this:
442 # ${pkg}::${method}:(before|after|around)
443 # but this proved problematic when using one modifier
444 # to wrap multiple methods (something which is likely
445 # to happen pretty regularly IMO). So instead of naming
446 # it like this, I have chosen to just name them purely
447 # with their modifier names, like so:
448 # :(before|after|around)
449 # The fact is that in a stack trace, it will be fairly
450 # evident from the context what method they are attached
451 # to, and so don't need the fully qualified name.
455 my ($self, $method_name, $method) = @_;
456 (defined $method_name && $method_name)
457 || confess "You must define a method name";
458 # use reftype here to allow for blessed subs ...
459 ('CODE' eq (reftype($method) || ''))
460 || confess "Your code block must be a CODE reference";
463 # dont bless subs, its bad mkay
464 $method = $self->method_metaclass->wrap($method) unless blessed($method);
466 $self->add_package_symbol("&${method_name}" => $method);
469 sub find_method_by_name {
470 my ($self, $method_name) = @_;
471 return $self->name->can($method_name);
475 my ($self, $method_name) = @_;
476 (defined $method_name && $method_name)
477 || confess "You must define a method name";
479 return 0 if !$self->has_package_symbol("&${method_name}");
480 my $method = $self->get_package_symbol("&${method_name}");
481 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
482 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
485 # dont bless subs, its bad mkay
486 $self->method_metaclass->wrap($method) unless blessed($method);
492 my ($self, $method_name) = @_;
493 (defined $method_name && $method_name)
494 || confess "You must define a method name";
496 return unless $self->has_method($method_name);
498 return $self->get_package_symbol("&${method_name}");
502 my ($self, $method_name) = @_;
503 (defined $method_name && $method_name)
504 || confess "You must define a method name";
506 my $removed_method = $self->get_method($method_name);
508 $self->remove_package_symbol("&${method_name}")
509 if defined $removed_method;
511 return $removed_method;
514 sub get_method_list {
516 grep { $self->has_method($_) } $self->list_all_package_symbols;
519 sub compute_all_applicable_methods {
522 # keep a record of what we have seen
523 # here, this will handle all the
524 # inheritence issues because we are
525 # using the &class_precedence_list
526 my (%seen_class, %seen_method);
527 foreach my $class ($self->class_precedence_list()) {
528 next if $seen_class{$class};
529 $seen_class{$class}++;
530 # fetch the meta-class ...
531 my $meta = $self->initialize($class);
532 foreach my $method_name ($meta->get_method_list()) {
533 next if exists $seen_method{$method_name};
534 $seen_method{$method_name}++;
536 name => $method_name,
538 code => $meta->get_method($method_name)
545 sub find_all_methods_by_name {
546 my ($self, $method_name) = @_;
547 (defined $method_name && $method_name)
548 || confess "You must define a method name to find";
550 # keep a record of what we have seen
551 # here, this will handle all the
552 # inheritence issues because we are
553 # using the &class_precedence_list
555 foreach my $class ($self->class_precedence_list()) {
556 next if $seen_class{$class};
557 $seen_class{$class}++;
558 # fetch the meta-class ...
559 my $meta = $self->initialize($class);
561 name => $method_name,
563 code => $meta->get_method($method_name)
564 } if $meta->has_method($method_name);
569 sub find_next_method_by_name {
570 my ($self, $method_name) = @_;
571 (defined $method_name && $method_name)
572 || confess "You must define a method name to find";
573 # keep a record of what we have seen
574 # here, this will handle all the
575 # inheritence issues because we are
576 # using the &class_precedence_list
578 my @cpl = $self->class_precedence_list();
579 shift @cpl; # discard ourselves
580 foreach my $class (@cpl) {
581 next if $seen_class{$class};
582 $seen_class{$class}++;
583 # fetch the meta-class ...
584 my $meta = $self->initialize($class);
585 return $meta->get_method($method_name)
586 if $meta->has_method($method_name);
595 # either we have an attribute object already
596 # or we need to create one from the args provided
597 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
598 # make sure it is derived from the correct type though
599 ($attribute->isa('Class::MOP::Attribute'))
600 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
601 $attribute->attach_to_class($self);
602 $attribute->install_accessors();
603 $self->get_attribute_map->{$attribute->name} = $attribute;
607 my ($self, $attribute_name) = @_;
608 (defined $attribute_name && $attribute_name)
609 || confess "You must define an attribute name";
610 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
614 my ($self, $attribute_name) = @_;
615 (defined $attribute_name && $attribute_name)
616 || confess "You must define an attribute name";
617 return $self->get_attribute_map->{$attribute_name}
618 if $self->has_attribute($attribute_name);
622 sub remove_attribute {
623 my ($self, $attribute_name) = @_;
624 (defined $attribute_name && $attribute_name)
625 || confess "You must define an attribute name";
626 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
627 return unless defined $removed_attribute;
628 delete $self->get_attribute_map->{$attribute_name};
629 $removed_attribute->remove_accessors();
630 $removed_attribute->detach_from_class();
631 return $removed_attribute;
634 sub get_attribute_list {
636 keys %{$self->get_attribute_map};
639 sub compute_all_applicable_attributes {
642 # keep a record of what we have seen
643 # here, this will handle all the
644 # inheritence issues because we are
645 # using the &class_precedence_list
646 my (%seen_class, %seen_attr);
647 foreach my $class ($self->class_precedence_list()) {
648 next if $seen_class{$class};
649 $seen_class{$class}++;
650 # fetch the meta-class ...
651 my $meta = $self->initialize($class);
652 foreach my $attr_name ($meta->get_attribute_list()) {
653 next if exists $seen_attr{$attr_name};
654 $seen_attr{$attr_name}++;
655 push @attrs => $meta->get_attribute($attr_name);
661 sub find_attribute_by_name {
662 my ($self, $attr_name) = @_;
663 # keep a record of what we have seen
664 # here, this will handle all the
665 # inheritence issues because we are
666 # using the &class_precedence_list
668 foreach my $class ($self->class_precedence_list()) {
669 next if $seen_class{$class};
670 $seen_class{$class}++;
671 # fetch the meta-class ...
672 my $meta = $self->initialize($class);
673 return $meta->get_attribute($attr_name)
674 if $meta->has_attribute($attr_name);
682 sub is_immutable { 0 }
685 return Class::MOP::Class::Immutable->make_metaclass_immutable(@_);
696 Class::MOP::Class - Class Meta Object
700 # assuming that class Foo
701 # has been defined, you can
703 # use this for introspection ...
705 # add a method to Foo ...
706 Foo->meta->add_method('bar' => sub { ... })
708 # get a list of all the classes searched
709 # the method dispatcher in the correct order
710 Foo->meta->class_precedence_list()
712 # remove a method from Foo
713 Foo->meta->remove_method('bar');
715 # or use this to actually create classes ...
717 Class::MOP::Class->create('Bar' => (
719 superclasses => [ 'Foo' ],
721 Class::MOP:::Attribute->new('$bar'),
722 Class::MOP:::Attribute->new('$baz'),
725 calculate_bar => sub { ... },
726 construct_baz => sub { ... }
732 This is the largest and currently most complex part of the Perl 5
733 meta-object protocol. It controls the introspection and
734 manipulation of Perl 5 classes (and it can create them too). The
735 best way to understand what this module can do, is to read the
736 documentation for each of it's methods.
740 =head2 Self Introspection
746 This will return a B<Class::MOP::Class> instance which is related
747 to this class. Thereby allowing B<Class::MOP::Class> to actually
750 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
751 bootstrap this module by installing a number of attribute meta-objects
752 into it's metaclass. This will allow this class to reap all the benifits
753 of the MOP when subclassing it.
757 =head2 Class construction
759 These methods will handle creating B<Class::MOP::Class> objects,
760 which can be used to both create new classes, and analyze
761 pre-existing classes.
763 This module will internally store references to all the instances
764 you create with these methods, so that they do not need to be
765 created any more than nessecary. Basically, they are singletons.
769 =item B<create ($package_name,
770 version =E<gt> ?$version,
771 authority =E<gt> ?$authority,
772 superclasses =E<gt> ?@superclasses,
773 methods =E<gt> ?%methods,
774 attributes =E<gt> ?%attributes)>
776 This returns a B<Class::MOP::Class> object, bringing the specified
777 C<$package_name> into existence and adding any of the C<$version>,
778 C<$authority>, C<@superclasses>, C<%methods> and C<%attributes> to
781 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
782 methods =E<gt> ?%methods,
783 attributes =E<gt> ?%attributes)>
785 This will create an anonymous class, it works much like C<create> but
786 it does not need a C<$package_name>. Instead it will create a suitably
787 unique package name for you to stash things into.
789 =item B<initialize ($package_name, %options)>
791 This initializes and returns returns a B<Class::MOP::Class> object
792 for a given a C<$package_name>.
794 =item B<reinitialize ($package_name, %options)>
796 This removes the old metaclass, and creates a new one in it's place.
797 Do B<not> use this unless you really know what you are doing, it could
798 very easily make a very large mess of your program.
800 =item B<construct_class_instance (%options)>
802 This will construct an instance of B<Class::MOP::Class>, it is
803 here so that we can actually "tie the knot" for B<Class::MOP::Class>
804 to use C<construct_instance> once all the bootstrapping is done. This
805 method is used internally by C<initialize> and should never be called
806 from outside of that method really.
808 =item B<check_metaclass_compatability>
810 This method is called as the very last thing in the
811 C<construct_class_instance> method. This will check that the
812 metaclass you are creating is compatible with the metaclasses of all
813 your ancestors. For more inforamtion about metaclass compatibility
814 see the C<About Metaclass compatibility> section in L<Class::MOP>.
818 =head2 Object instance construction and cloning
820 These methods are B<entirely optional>, it is up to you whether you want
825 =item B<instance_metaclass>
827 =item B<get_meta_instance>
829 =item B<new_object (%params)>
831 This is a convience method for creating a new object of the class, and
832 blessing it into the appropriate package as well. Ideally your class
833 would call a C<new> this method like so:
836 my ($class, %param) = @_;
837 $class->meta->new_object(%params);
840 Of course the ideal place for this would actually be in C<UNIVERSAL::>
841 but that is considered bad style, so we do not do that.
843 =item B<construct_instance (%params)>
845 This method is used to construct an instace structure suitable for
846 C<bless>-ing into your package of choice. It works in conjunction
847 with the Attribute protocol to collect all applicable attributes.
849 This will construct and instance using a HASH ref as storage
850 (currently only HASH references are supported). This will collect all
851 the applicable attributes and layout out the fields in the HASH ref,
852 it will then initialize them using either use the corresponding key
853 in C<%params> or any default value or initializer found in the
854 attribute meta-object.
856 =item B<clone_object ($instance, %params)>
858 This is a convience method for cloning an object instance, then
859 blessing it into the appropriate package. This method will call
860 C<clone_instance>, which performs a shallow copy of the object,
861 see that methods documentation for more details. Ideally your
862 class would call a C<clone> this method like so:
865 my ($self, %param) = @_;
866 $self->meta->clone_object($self, %params);
869 Of course the ideal place for this would actually be in C<UNIVERSAL::>
870 but that is considered bad style, so we do not do that.
872 =item B<clone_instance($instance, %params)>
874 This method is a compliment of C<construct_instance> (which means if
875 you override C<construct_instance>, you need to override this one too),
876 and clones the instance shallowly.
878 The cloned structure returned is (like with C<construct_instance>) an
879 unC<bless>ed HASH reference, it is your responsibility to then bless
880 this cloned structure into the right class (which C<clone_object> will
883 As of 0.11, this method will clone the C<$instance> structure shallowly,
884 as opposed to the deep cloning implemented in prior versions. After much
885 thought, research and discussion, I have decided that anything but basic
886 shallow cloning is outside the scope of the meta-object protocol. I
887 think Yuval "nothingmuch" Kogman put it best when he said that cloning
888 is too I<context-specific> to be part of the MOP.
894 These are a few predicate methods for asking information about the class.
898 =item B<is_anon_class>
902 =item B<is_immutable>
906 =head2 Inheritance Relationships
910 =item B<superclasses (?@superclasses)>
912 This is a read-write attribute which represents the superclass
913 relationships of the class the B<Class::MOP::Class> instance is
914 associated with. Basically, it can get and set the C<@ISA> for you.
917 Perl will occasionally perform some C<@ISA> and method caching, if
918 you decide to change your superclass relationship at runtime (which
919 is quite insane and very much not recommened), then you should be
920 aware of this and the fact that this module does not make any
921 attempt to address this issue.
923 =item B<class_precedence_list>
925 This computes the a list of all the class's ancestors in the same order
926 in which method dispatch will be done. This is similair to
927 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
935 =item B<get_method_map>
937 =item B<method_metaclass>
939 =item B<add_method ($method_name, $method)>
941 This will take a C<$method_name> and CODE reference to that
942 C<$method> and install it into the class's package.
945 This does absolutely nothing special to C<$method>
946 other than use B<Sub::Name> to make sure it is tagged with the
947 correct name, and therefore show up correctly in stack traces and
950 =item B<alias_method ($method_name, $method)>
952 This will take a C<$method_name> and CODE reference to that
953 C<$method> and alias the method into the class's package.
956 Unlike C<add_method>, this will B<not> try to name the
957 C<$method> using B<Sub::Name>, it only aliases the method in
960 =item B<has_method ($method_name)>
962 This just provides a simple way to check if the class implements
963 a specific C<$method_name>. It will I<not> however, attempt to check
964 if the class inherits the method (use C<UNIVERSAL::can> for that).
966 This will correctly handle functions defined outside of the package
967 that use a fully qualified name (C<sub Package::name { ... }>).
969 This will correctly handle functions renamed with B<Sub::Name> and
970 installed using the symbol tables. However, if you are naming the
971 subroutine outside of the package scope, you must use the fully
972 qualified name, including the package name, for C<has_method> to
973 correctly identify it.
975 This will attempt to correctly ignore functions imported from other
976 packages using B<Exporter>. It breaks down if the function imported
977 is an C<__ANON__> sub (such as with C<use constant>), which very well
978 may be a valid method being applied to the class.
980 In short, this method cannot always be trusted to determine if the
981 C<$method_name> is actually a method. However, it will DWIM about
982 90% of the time, so it's a small trade off I think.
984 =item B<get_method ($method_name)>
986 This will return a CODE reference of the specified C<$method_name>,
987 or return undef if that method does not exist.
989 =item B<find_method_by_name ($method_name>
991 This will return a CODE reference of the specified C<$method_name>,
992 or return undef if that method does not exist.
994 Unlike C<get_method> this will also look in the superclasses.
996 =item B<remove_method ($method_name)>
998 This will attempt to remove a given C<$method_name> from the class.
999 It will return the CODE reference that it has removed, and will
1000 attempt to use B<Sub::Name> to clear the methods associated name.
1002 =item B<get_method_list>
1004 This will return a list of method names for all I<locally> defined
1005 methods. It does B<not> provide a list of all applicable methods,
1006 including any inherited ones. If you want a list of all applicable
1007 methods, use the C<compute_all_applicable_methods> method.
1009 =item B<compute_all_applicable_methods>
1011 This will return a list of all the methods names this class will
1012 respond to, taking into account inheritance. The list will be a list of
1013 HASH references, each one containing the following information; method
1014 name, the name of the class in which the method lives and a CODE
1015 reference for the actual method.
1017 =item B<find_all_methods_by_name ($method_name)>
1019 This will traverse the inheritence hierarchy and locate all methods
1020 with a given C<$method_name>. Similar to
1021 C<compute_all_applicable_methods> it returns a list of HASH references
1022 with the following information; method name (which will always be the
1023 same as C<$method_name>), the name of the class in which the method
1024 lives and a CODE reference for the actual method.
1026 The list of methods produced is a distinct list, meaning there are no
1027 duplicates in it. This is especially useful for things like object
1028 initialization and destruction where you only want the method called
1029 once, and in the correct order.
1031 =item B<find_next_method_by_name ($method_name)>
1033 This will return the first method to match a given C<$method_name> in
1034 the superclasses, this is basically equivalent to calling
1035 C<SUPER::$method_name>, but it can be dispatched at runtime.
1039 =head2 Method Modifiers
1041 Method modifiers are a concept borrowed from CLOS, in which a method
1042 can be wrapped with I<before>, I<after> and I<around> method modifiers
1043 that will be called everytime the method is called.
1045 =head3 How method modifiers work?
1047 Method modifiers work by wrapping the original method and then replacing
1048 it in the classes symbol table. The wrappers will handle calling all the
1049 modifiers in the appropariate orders and preserving the calling context
1050 for the original method.
1052 Each method modifier serves a particular purpose, which may not be
1053 obvious to users of other method wrapping modules. To start with, the
1054 return values of I<before> and I<after> modifiers are ignored. This is
1055 because thier purpose is B<not> to filter the input and output of the
1056 primary method (this is done with an I<around> modifier). This may seem
1057 like an odd restriction to some, but doing this allows for simple code
1058 to be added at the begining or end of a method call without jeapordizing
1059 the normal functioning of the primary method or placing any extra
1060 responsibility on the code of the modifier. Of course if you have more
1061 complex needs, then use the I<around> modifier, which uses a variation
1062 of continutation passing style to allow for a high degree of flexibility.
1064 Before and around modifiers are called in last-defined-first-called order,
1065 while after modifiers are called in first-defined-first-called order. So
1066 the call tree might looks something like this:
1076 To see examples of using method modifiers, see the following examples
1077 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1078 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1079 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1081 =head3 What is the performance impact?
1083 Of course there is a performance cost associated with method modifiers,
1084 but we have made every effort to make that cost be directly proportional
1085 to the amount of modifier features you utilize.
1087 The wrapping method does it's best to B<only> do as much work as it
1088 absolutely needs to. In order to do this we have moved some of the
1089 performance costs to set-up time, where they are easier to amortize.
1091 All this said, my benchmarks have indicated the following:
1093 simple wrapper with no modifiers 100% slower
1094 simple wrapper with simple before modifier 400% slower
1095 simple wrapper with simple after modifier 450% slower
1096 simple wrapper with simple around modifier 500-550% slower
1097 simple wrapper with all 3 modifiers 1100% slower
1099 These numbers may seem daunting, but you must remember, every feature
1100 comes with some cost. To put things in perspective, just doing a simple
1101 C<AUTOLOAD> which does nothing but extract the name of the method called
1102 and return it costs about 400% over a normal method call.
1106 =item B<add_before_method_modifier ($method_name, $code)>
1108 This will wrap the method at C<$method_name> and the supplied C<$code>
1109 will be passed the C<@_> arguments, and called before the original
1110 method is called. As specified above, the return value of the I<before>
1111 method modifiers is ignored, and it's ability to modify C<@_> is
1112 fairly limited. If you need to do either of these things, use an
1113 C<around> method modifier.
1115 =item B<add_after_method_modifier ($method_name, $code)>
1117 This will wrap the method at C<$method_name> so that the original
1118 method will be called, it's return values stashed, and then the
1119 supplied C<$code> will be passed the C<@_> arguments, and called.
1120 As specified above, the return value of the I<after> method
1121 modifiers is ignored, and it cannot modify the return values of
1122 the original method. If you need to do either of these things, use an
1123 C<around> method modifier.
1125 =item B<add_around_method_modifier ($method_name, $code)>
1127 This will wrap the method at C<$method_name> so that C<$code>
1128 will be called and passed the original method as an extra argument
1129 at the begining of the C<@_> argument list. This is a variation of
1130 continuation passing style, where the function prepended to C<@_>
1131 can be considered a continuation. It is up to C<$code> if it calls
1132 the original method or not, there is no restriction on what the
1133 C<$code> can or cannot do.
1139 It should be noted that since there is no one consistent way to define
1140 the attributes of a class in Perl 5. These methods can only work with
1141 the information given, and can not easily discover information on
1142 their own. See L<Class::MOP::Attribute> for more details.
1146 =item B<attribute_metaclass>
1148 =item B<get_attribute_map>
1150 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1152 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1153 instance associated with the given class, and associates it with
1154 the C<$attribute_name>. Unlike methods, attributes within the MOP
1155 are stored as meta-information only. They will be used later to
1156 construct instances from (see C<construct_instance> above).
1157 More details about the attribute meta-objects can be found in the
1158 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1161 It should be noted that any accessor, reader/writer or predicate
1162 methods which the C<$attribute_meta_object> has will be installed
1163 into the class at this time.
1165 =item B<has_attribute ($attribute_name)>
1167 Checks to see if this class has an attribute by the name of
1168 C<$attribute_name> and returns a boolean.
1170 =item B<get_attribute ($attribute_name)>
1172 Returns the attribute meta-object associated with C<$attribute_name>,
1173 if none is found, it will return undef.
1175 =item B<remove_attribute ($attribute_name)>
1177 This will remove the attribute meta-object stored at
1178 C<$attribute_name>, then return the removed attribute meta-object.
1181 Removing an attribute will only affect future instances of
1182 the class, it will not make any attempt to remove the attribute from
1183 any existing instances of the class.
1185 It should be noted that any accessor, reader/writer or predicate
1186 methods which the attribute meta-object stored at C<$attribute_name>
1187 has will be removed from the class at this time. This B<will> make
1188 these attributes somewhat inaccessable in previously created
1189 instances. But if you are crazy enough to do this at runtime, then
1190 you are crazy enough to deal with something like this :).
1192 =item B<get_attribute_list>
1194 This returns a list of attribute names which are defined in the local
1195 class. If you want a list of all applicable attributes for a class,
1196 use the C<compute_all_applicable_attributes> method.
1198 =item B<compute_all_applicable_attributes>
1200 This will traverse the inheritance heirachy and return a list of all
1201 the applicable attributes for this class. It does not construct a
1202 HASH reference like C<compute_all_applicable_methods> because all
1203 that same information is discoverable through the attribute
1206 =item B<find_attribute_by_name ($attr_name)>
1208 This method will traverse the inheritance heirachy and find the
1209 first attribute whose name matches C<$attr_name>, then return it.
1210 It will return undef if nothing is found.
1214 =head2 Class closing
1218 =item B<make_immutable>
1224 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1226 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1228 =head1 COPYRIGHT AND LICENSE
1230 Copyright 2006 by Infinity Interactive, Inc.
1232 L<http://www.iinteractive.com>
1234 This library is free software; you can redistribute it and/or modify
1235 it under the same terms as Perl itself.