2 package Class::MOP::Class;
8 use Scalar::Util 'blessed', 'reftype';
9 use Sub::Name 'subname';
10 use B 'svref_2object';
12 our $VERSION = '0.14';
14 use Class::MOP::Instance;
18 sub meta { Class::MOP::Class->initialize(blessed($_[0]) || $_[0]) }
23 # Metaclasses are singletons, so we cache them here.
24 # there is no need to worry about destruction though
25 # because they should die only when the program dies.
26 # After all, do package definitions even get reaped?
29 # means of accessing all the metaclasses that have
30 # been initialized thus far (for mugwumps obj browser)
31 sub get_all_metaclasses { %METAS }
32 sub get_all_metaclass_instances { values %METAS }
33 sub get_all_metaclass_names { keys %METAS }
37 my $package_name = shift;
38 (defined $package_name && $package_name && !blessed($package_name))
39 || confess "You must pass a package name and it cannot be blessed";
40 $class->construct_class_instance(':package' => $package_name, @_);
45 my $package_name = shift;
46 (defined $package_name && $package_name && !blessed($package_name))
47 || confess "You must pass a package name and it cannot be blessed";
48 $METAS{$package_name} = undef;
49 $class->construct_class_instance(':package' => $package_name, @_);
52 # NOTE: (meta-circularity)
53 # this is a special form of &construct_instance
54 # (see below), which is used to construct class
55 # meta-object instances for any Class::MOP::*
56 # class. All other classes will use the more
57 # normal &construct_instance.
58 sub construct_class_instance {
61 my $package_name = $options{':package'};
62 (defined $package_name && $package_name)
63 || confess "You must pass a package name";
65 # return the metaclass if we have it cached,
66 # and it is still defined (it has not been
67 # reaped by DESTROY yet, which can happen
68 # annoyingly enough during global destruction)
69 return $METAS{$package_name}
70 if exists $METAS{$package_name} && defined $METAS{$package_name};
71 $class = blessed($class) || $class;
72 # now create the metaclass
74 if ($class =~ /^Class::MOP::/) {
76 '$:package' => $package_name,
78 '$:attribute_metaclass' => $options{':attribute_metaclass'} || 'Class::MOP::Attribute',
79 '$:method_metaclass' => $options{':method_metaclass'} || 'Class::MOP::Method',
80 '$:instance_metaclass' => $options{':instance_metaclass'} || 'Class::MOP::Instance',
85 # it is safe to use meta here because
86 # class will always be a subclass of
87 # Class::MOP::Class, which defines meta
88 $meta = bless $class->meta->construct_instance(%options) => $class
90 # and check the metaclass compatibility
91 $meta->check_metaclass_compatability();
92 $METAS{$package_name} = $meta;
95 sub check_metaclass_compatability {
98 # this is always okay ...
99 return if blessed($self) eq 'Class::MOP::Class' &&
100 $self->instance_metaclass eq 'Class::MOP::Instance';
102 my @class_list = $self->class_precedence_list;
103 shift @class_list; # shift off $self->name
105 foreach my $class_name (@class_list) {
106 my $meta = $METAS{$class_name} || next;
107 ($self->isa(blessed($meta)))
108 || confess $self->name . "->meta => (" . (blessed($self)) . ")" .
109 " is not compatible with the " .
110 $class_name . "->meta => (" . (blessed($meta)) . ")";
112 # we also need to check that instance metaclasses
113 # are compatabile in the same the class.
114 ($self->instance_metaclass->isa($meta->instance_metaclass))
115 || confess $self->name . "->meta => (" . ($self->instance_metaclass) . ")" .
116 " is not compatible with the " .
117 $class_name . "->meta => (" . ($meta->instance_metaclass) . ")";
123 my ($class, $package_name, $package_version, %options) = @_;
124 (defined $package_name && $package_name)
125 || confess "You must pass a package name";
126 my $code = "package $package_name;";
127 $code .= "\$$package_name\:\:VERSION = '$package_version';"
128 if defined $package_version;
130 confess "creation of $package_name failed : $@" if $@;
131 my $meta = $class->initialize($package_name);
133 $meta->add_method('meta' => sub {
134 Class::MOP::Class->initialize(blessed($_[0]) || $_[0]);
137 $meta->superclasses(@{$options{superclasses}})
138 if exists $options{superclasses};
140 # process attributes first, so that they can
141 # install accessors, but locally defined methods
142 # can then overwrite them. It is maybe a little odd, but
143 # I think this should be the order of things.
144 if (exists $options{attributes}) {
145 foreach my $attr (@{$options{attributes}}) {
146 $meta->add_attribute($attr);
149 if (exists $options{methods}) {
150 foreach my $method_name (keys %{$options{methods}}) {
151 $meta->add_method($method_name, $options{methods}->{$method_name});
159 # this should be sufficient, if you have a
160 # use case where it is not, write a test and
162 my $ANON_CLASS_SERIAL = 0;
164 sub create_anon_class {
165 my ($class, %options) = @_;
166 my $package_name = 'Class::MOP::Class::__ANON__::SERIAL::' . ++$ANON_CLASS_SERIAL;
167 return $class->create($package_name, '0.00', %options);
174 # all these attribute readers will be bootstrapped
175 # away in the Class::MOP bootstrap section
177 sub name { $_[0]->{'$:package'} }
178 sub get_attribute_map { $_[0]->{'%:attributes'} }
179 sub attribute_metaclass { $_[0]->{'$:attribute_metaclass'} }
180 sub method_metaclass { $_[0]->{'$:method_metaclass'} }
181 sub instance_metaclass { $_[0]->{'$:instance_metaclass'} }
183 # Instance Construction & Cloning
188 # we need to protect the integrity of the
189 # Class::MOP::Class singletons here, so we
190 # delegate this to &construct_class_instance
191 # which will deal with the singletons
192 return $class->construct_class_instance(@_)
193 if $class->name->isa('Class::MOP::Class');
194 return $class->construct_instance(@_);
197 sub construct_instance {
198 my ($class, %params) = @_;
199 my $meta_instance = $class->get_meta_instance();
200 my $instance = $meta_instance->create_instance();
201 foreach my $attr ($class->compute_all_applicable_attributes()) {
202 $attr->initialize_instance_slot($meta_instance, $instance, \%params);
207 sub get_meta_instance {
209 return $class->instance_metaclass->new(
211 $class->compute_all_applicable_attributes()
217 my $instance = shift;
218 (blessed($instance) && $instance->isa($class->name))
219 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
221 # we need to protect the integrity of the
222 # Class::MOP::Class singletons here, they
223 # should not be cloned.
224 return $instance if $instance->isa('Class::MOP::Class');
225 $class->clone_instance($instance, @_);
229 my ($class, $instance, %params) = @_;
231 || confess "You can only clone instances, \$self is not a blessed instance";
232 my $meta_instance = $class->get_meta_instance();
233 my $clone = $meta_instance->clone_instance($instance);
234 foreach my $key (%params) {
235 next unless $meta_instance->is_valid_slot($key);
236 $meta_instance->set_slot_value($clone, $key, $params{$key});
243 # &name should be here too, but it is above
244 # because it gets bootstrapped away
248 ${$self->get_package_variable('$VERSION')};
258 @{$self->name . '::ISA'} = @supers;
260 # we need to check the metaclass
261 # compatability here so that we can
262 # be sure that the superclass is
263 # not potentially creating an issues
264 # we don't know about
265 $self->check_metaclass_compatability();
267 @{$self->name . '::ISA'};
270 sub class_precedence_list {
273 # We need to check for ciruclar inheirtance here.
274 # This will do nothing if all is well, and blow
275 # up otherwise. Yes, it's an ugly hack, better
276 # suggestions are welcome.
277 { ($self->name || return)->isa('This is a test for circular inheritance') }
278 # ... and now back to our regularly scheduled program
282 $self->initialize($_)->class_precedence_list()
283 } $self->superclasses()
290 my ($self, $method_name, $method) = @_;
291 (defined $method_name && $method_name)
292 || confess "You must define a method name";
293 # use reftype here to allow for blessed subs ...
294 ('CODE' eq (reftype($method) || ''))
295 || confess "Your code block must be a CODE reference";
296 my $full_method_name = ($self->name . '::' . $method_name);
298 $method = $self->method_metaclass->wrap($method) unless blessed($method);
301 no warnings 'redefine';
302 *{$full_method_name} = subname $full_method_name => $method;
306 my $fetch_and_prepare_method = sub {
307 my ($self, $method_name) = @_;
309 my $method = $self->get_method($method_name);
310 # if we dont have local ...
312 # make sure this method even exists ...
313 ($self->find_next_method_by_name($method_name))
314 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
315 # if so, then create a local which just
316 # calls the next applicable method ...
317 $self->add_method($method_name => sub {
318 $self->find_next_method_by_name($method_name)->(@_);
320 $method = $self->get_method($method_name);
323 # now make sure we wrap it properly
324 # (if it isnt already)
325 unless ($method->isa('Class::MOP::Method::Wrapped')) {
326 $method = Class::MOP::Method::Wrapped->wrap($method);
327 $self->add_method($method_name => $method);
332 sub add_before_method_modifier {
333 my ($self, $method_name, $method_modifier) = @_;
334 (defined $method_name && $method_name)
335 || confess "You must pass in a method name";
336 my $method = $fetch_and_prepare_method->($self, $method_name);
337 $method->add_before_modifier(subname ':before' => $method_modifier);
340 sub add_after_method_modifier {
341 my ($self, $method_name, $method_modifier) = @_;
342 (defined $method_name && $method_name)
343 || confess "You must pass in a method name";
344 my $method = $fetch_and_prepare_method->($self, $method_name);
345 $method->add_after_modifier(subname ':after' => $method_modifier);
348 sub add_around_method_modifier {
349 my ($self, $method_name, $method_modifier) = @_;
350 (defined $method_name && $method_name)
351 || confess "You must pass in a method name";
352 my $method = $fetch_and_prepare_method->($self, $method_name);
353 $method->add_around_modifier(subname ':around' => $method_modifier);
357 # the methods above used to be named like this:
358 # ${pkg}::${method}:(before|after|around)
359 # but this proved problematic when using one modifier
360 # to wrap multiple methods (something which is likely
361 # to happen pretty regularly IMO). So instead of naming
362 # it like this, I have chosen to just name them purely
363 # with their modifier names, like so:
364 # :(before|after|around)
365 # The fact is that in a stack trace, it will be fairly
366 # evident from the context what method they are attached
367 # to, and so don't need the fully qualified name.
371 my ($self, $method_name, $method) = @_;
372 (defined $method_name && $method_name)
373 || confess "You must define a method name";
374 # use reftype here to allow for blessed subs ...
375 ('CODE' eq (reftype($method) || ''))
376 || confess "Your code block must be a CODE reference";
377 my $full_method_name = ($self->name . '::' . $method_name);
379 $method = $self->method_metaclass->wrap($method) unless blessed($method);
382 no warnings 'redefine';
383 *{$full_method_name} = $method;
387 my ($self, $method_name) = @_;
388 (defined $method_name && $method_name)
389 || confess "You must define a method name";
391 my $sub_name = ($self->name . '::' . $method_name);
394 return 0 if !defined(&{$sub_name});
395 my $method = \&{$sub_name};
396 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
397 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
399 # at this point we are relatively sure
400 # it is our method, so we bless/wrap it
401 $self->method_metaclass->wrap($method) unless blessed($method);
406 my ($self, $method_name) = @_;
407 (defined $method_name && $method_name)
408 || confess "You must define a method name";
410 return unless $self->has_method($method_name);
413 return \&{$self->name . '::' . $method_name};
417 my ($self, $method_name) = @_;
418 (defined $method_name && $method_name)
419 || confess "You must define a method name";
421 my $removed_method = $self->get_method($method_name);
424 delete ${$self->name . '::'}{$method_name}
425 if defined $removed_method;
427 return $removed_method;
430 sub get_method_list {
433 grep { $self->has_method($_) } keys %{$self->name . '::'};
436 sub compute_all_applicable_methods {
439 # keep a record of what we have seen
440 # here, this will handle all the
441 # inheritence issues because we are
442 # using the &class_precedence_list
443 my (%seen_class, %seen_method);
444 foreach my $class ($self->class_precedence_list()) {
445 next if $seen_class{$class};
446 $seen_class{$class}++;
447 # fetch the meta-class ...
448 my $meta = $self->initialize($class);
449 foreach my $method_name ($meta->get_method_list()) {
450 next if exists $seen_method{$method_name};
451 $seen_method{$method_name}++;
453 name => $method_name,
455 code => $meta->get_method($method_name)
462 sub find_all_methods_by_name {
463 my ($self, $method_name) = @_;
464 (defined $method_name && $method_name)
465 || confess "You must define a method name to find";
467 # keep a record of what we have seen
468 # here, this will handle all the
469 # inheritence issues because we are
470 # using the &class_precedence_list
472 foreach my $class ($self->class_precedence_list()) {
473 next if $seen_class{$class};
474 $seen_class{$class}++;
475 # fetch the meta-class ...
476 my $meta = $self->initialize($class);
478 name => $method_name,
480 code => $meta->get_method($method_name)
481 } if $meta->has_method($method_name);
486 sub find_next_method_by_name {
487 my ($self, $method_name) = @_;
488 (defined $method_name && $method_name)
489 || confess "You must define a method name to find";
490 # keep a record of what we have seen
491 # here, this will handle all the
492 # inheritence issues because we are
493 # using the &class_precedence_list
495 my @cpl = $self->class_precedence_list();
496 shift @cpl; # discard ourselves
497 foreach my $class (@cpl) {
498 next if $seen_class{$class};
499 $seen_class{$class}++;
500 # fetch the meta-class ...
501 my $meta = $self->initialize($class);
502 return $meta->get_method($method_name)
503 if $meta->has_method($method_name);
512 # either we have an attribute object already
513 # or we need to create one from the args provided
514 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
515 # make sure it is derived from the correct type though
516 ($attribute->isa('Class::MOP::Attribute'))
517 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
518 $attribute->attach_to_class($self);
519 $attribute->install_accessors();
520 $self->get_attribute_map->{$attribute->name} = $attribute;
523 # in theory we have to tell everyone the slot structure may have changed
527 my ($self, $attribute_name) = @_;
528 (defined $attribute_name && $attribute_name)
529 || confess "You must define an attribute name";
530 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
534 my ($self, $attribute_name) = @_;
535 (defined $attribute_name && $attribute_name)
536 || confess "You must define an attribute name";
537 return $self->get_attribute_map->{$attribute_name}
538 if $self->has_attribute($attribute_name);
542 sub remove_attribute {
543 my ($self, $attribute_name) = @_;
544 (defined $attribute_name && $attribute_name)
545 || confess "You must define an attribute name";
546 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
547 return unless defined $removed_attribute;
548 delete $self->get_attribute_map->{$attribute_name};
549 $removed_attribute->remove_accessors();
550 $removed_attribute->detach_from_class();
551 return $removed_attribute;
554 sub get_attribute_list {
556 keys %{$self->get_attribute_map};
559 sub compute_all_applicable_attributes {
562 # keep a record of what we have seen
563 # here, this will handle all the
564 # inheritence issues because we are
565 # using the &class_precedence_list
566 my (%seen_class, %seen_attr);
567 foreach my $class ($self->class_precedence_list()) {
568 next if $seen_class{$class};
569 $seen_class{$class}++;
570 # fetch the meta-class ...
571 my $meta = $self->initialize($class);
572 foreach my $attr_name ($meta->get_attribute_list()) {
573 next if exists $seen_attr{$attr_name};
574 $seen_attr{$attr_name}++;
575 push @attrs => $meta->get_attribute($attr_name);
581 sub find_attribute_by_name {
582 my ($self, $attr_name) = @_;
583 # keep a record of what we have seen
584 # here, this will handle all the
585 # inheritence issues because we are
586 # using the &class_precedence_list
588 foreach my $class ($self->class_precedence_list()) {
589 next if $seen_class{$class};
590 $seen_class{$class}++;
591 # fetch the meta-class ...
592 my $meta = $self->initialize($class);
593 return $meta->get_attribute($attr_name)
594 if $meta->has_attribute($attr_name);
601 sub add_package_variable {
602 my ($self, $variable, $initial_value) = @_;
603 (defined $variable && $variable =~ /^[\$\@\%]/)
604 || confess "variable name does not have a sigil";
606 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
607 if (defined $initial_value) {
609 *{$self->name . '::' . $name} = $initial_value;
615 # We HAVE to localize $@ or all
616 # hell breaks loose. It is not
617 # good, believe me, not good.
619 eval $sigil . $self->name . '::' . $name;
622 confess "Could not create package variable ($variable) because : $e" if $e;
626 sub has_package_variable {
627 my ($self, $variable) = @_;
628 (defined $variable && $variable =~ /^[\$\@\%]/)
629 || confess "variable name does not have a sigil";
630 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
632 defined ${$self->name . '::'}{$name} ? 1 : 0;
635 sub get_package_variable {
636 my ($self, $variable) = @_;
637 (defined $variable && $variable =~ /^[\$\@\%]/)
638 || confess "variable name does not have a sigil";
639 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
643 # We HAVE to localize $@ or all
644 # hell breaks loose. It is not
645 # good, believe me, not good.
647 $ref = eval '\\' . $sigil . $self->name . '::' . $name;
650 confess "Could not get the package variable ($variable) because : $e" if $e;
651 # if we didn't die, then we can return it
655 sub remove_package_variable {
656 my ($self, $variable) = @_;
657 (defined $variable && $variable =~ /^[\$\@\%]/)
658 || confess "variable name does not have a sigil";
659 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
661 delete ${$self->name . '::'}{$name};
672 Class::MOP::Class - Class Meta Object
676 # assuming that class Foo
677 # has been defined, you can
679 # use this for introspection ...
681 # add a method to Foo ...
682 Foo->meta->add_method('bar' => sub { ... })
684 # get a list of all the classes searched
685 # the method dispatcher in the correct order
686 Foo->meta->class_precedence_list()
688 # remove a method from Foo
689 Foo->meta->remove_method('bar');
691 # or use this to actually create classes ...
693 Class::MOP::Class->create('Bar' => '0.01' => (
694 superclasses => [ 'Foo' ],
696 Class::MOP:::Attribute->new('$bar'),
697 Class::MOP:::Attribute->new('$baz'),
700 calculate_bar => sub { ... },
701 construct_baz => sub { ... }
707 This is the largest and currently most complex part of the Perl 5
708 meta-object protocol. It controls the introspection and
709 manipulation of Perl 5 classes (and it can create them too). The
710 best way to understand what this module can do, is to read the
711 documentation for each of it's methods.
715 =head2 Self Introspection
721 This will return a B<Class::MOP::Class> instance which is related
722 to this class. Thereby allowing B<Class::MOP::Class> to actually
725 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
726 bootstrap this module by installing a number of attribute meta-objects
727 into it's metaclass. This will allow this class to reap all the benifits
728 of the MOP when subclassing it.
730 =item B<get_all_metaclasses>
732 This will return an hash of all the metaclass instances that have
733 been cached by B<Class::MOP::Class> keyed by the package name.
735 =item B<get_all_metaclass_instances>
737 This will return an array of all the metaclass instances that have
738 been cached by B<Class::MOP::Class>.
740 =item B<get_all_metaclass_names>
742 This will return an array of all the metaclass names that have
743 been cached by B<Class::MOP::Class>.
747 =head2 Class construction
749 These methods will handle creating B<Class::MOP::Class> objects,
750 which can be used to both create new classes, and analyze
751 pre-existing classes.
753 This module will internally store references to all the instances
754 you create with these methods, so that they do not need to be
755 created any more than nessecary. Basically, they are singletons.
759 =item B<create ($package_name, ?$package_version,
760 superclasses =E<gt> ?@superclasses,
761 methods =E<gt> ?%methods,
762 attributes =E<gt> ?%attributes)>
764 This returns a B<Class::MOP::Class> object, bringing the specified
765 C<$package_name> into existence and adding any of the
766 C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
769 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
770 methods =E<gt> ?%methods,
771 attributes =E<gt> ?%attributes)>
773 This will create an anonymous class, it works much like C<create> but
774 it does not need a C<$package_name>. Instead it will create a suitably
775 unique package name for you to stash things into.
777 =item B<initialize ($package_name, %options)>
779 This initializes and returns returns a B<Class::MOP::Class> object
780 for a given a C<$package_name>.
782 =item B<reinitialize ($package_name, %options)>
784 This removes the old metaclass, and creates a new one in it's place.
785 Do B<not> use this unless you really know what you are doing, it could
786 very easily make a very large mess of your program.
788 =item B<construct_class_instance (%options)>
790 This will construct an instance of B<Class::MOP::Class>, it is
791 here so that we can actually "tie the knot" for B<Class::MOP::Class>
792 to use C<construct_instance> once all the bootstrapping is done. This
793 method is used internally by C<initialize> and should never be called
794 from outside of that method really.
796 =item B<check_metaclass_compatability>
798 This method is called as the very last thing in the
799 C<construct_class_instance> method. This will check that the
800 metaclass you are creating is compatible with the metaclasses of all
801 your ancestors. For more inforamtion about metaclass compatibility
802 see the C<About Metaclass compatibility> section in L<Class::MOP>.
806 =head2 Object instance construction and cloning
808 These methods are B<entirely optional>, it is up to you whether you want
813 =item B<instance_metaclass>
815 =item B<get_meta_instance>
817 =item B<new_object (%params)>
819 This is a convience method for creating a new object of the class, and
820 blessing it into the appropriate package as well. Ideally your class
821 would call a C<new> this method like so:
824 my ($class, %param) = @_;
825 $class->meta->new_object(%params);
828 Of course the ideal place for this would actually be in C<UNIVERSAL::>
829 but that is considered bad style, so we do not do that.
831 =item B<construct_instance (%params)>
833 This method is used to construct an instace structure suitable for
834 C<bless>-ing into your package of choice. It works in conjunction
835 with the Attribute protocol to collect all applicable attributes.
837 This will construct and instance using a HASH ref as storage
838 (currently only HASH references are supported). This will collect all
839 the applicable attributes and layout out the fields in the HASH ref,
840 it will then initialize them using either use the corresponding key
841 in C<%params> or any default value or initializer found in the
842 attribute meta-object.
844 =item B<clone_object ($instance, %params)>
846 This is a convience method for cloning an object instance, then
847 blessing it into the appropriate package. This method will call
848 C<clone_instance>, which performs a shallow copy of the object,
849 see that methods documentation for more details. Ideally your
850 class would call a C<clone> this method like so:
853 my ($self, %param) = @_;
854 $self->meta->clone_object($self, %params);
857 Of course the ideal place for this would actually be in C<UNIVERSAL::>
858 but that is considered bad style, so we do not do that.
860 =item B<clone_instance($instance, %params)>
862 This method is a compliment of C<construct_instance> (which means if
863 you override C<construct_instance>, you need to override this one too),
864 and clones the instance shallowly.
866 The cloned structure returned is (like with C<construct_instance>) an
867 unC<bless>ed HASH reference, it is your responsibility to then bless
868 this cloned structure into the right class (which C<clone_object> will
871 As of 0.11, this method will clone the C<$instance> structure shallowly,
872 as opposed to the deep cloning implemented in prior versions. After much
873 thought, research and discussion, I have decided that anything but basic
874 shallow cloning is outside the scope of the meta-object protocol. I
875 think Yuval "nothingmuch" Kogman put it best when he said that cloning
876 is too I<context-specific> to be part of the MOP.
886 This is a read-only attribute which returns the package name for the
887 given B<Class::MOP::Class> instance.
891 This is a read-only attribute which returns the C<$VERSION> of the
892 package for the given B<Class::MOP::Class> instance.
896 =head2 Inheritance Relationships
900 =item B<superclasses (?@superclasses)>
902 This is a read-write attribute which represents the superclass
903 relationships of the class the B<Class::MOP::Class> instance is
904 associated with. Basically, it can get and set the C<@ISA> for you.
907 Perl will occasionally perform some C<@ISA> and method caching, if
908 you decide to change your superclass relationship at runtime (which
909 is quite insane and very much not recommened), then you should be
910 aware of this and the fact that this module does not make any
911 attempt to address this issue.
913 =item B<class_precedence_list>
915 This computes the a list of all the class's ancestors in the same order
916 in which method dispatch will be done. This is similair to
917 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
925 =item B<method_metaclass>
927 =item B<add_method ($method_name, $method)>
929 This will take a C<$method_name> and CODE reference to that
930 C<$method> and install it into the class's package.
933 This does absolutely nothing special to C<$method>
934 other than use B<Sub::Name> to make sure it is tagged with the
935 correct name, and therefore show up correctly in stack traces and
938 =item B<alias_method ($method_name, $method)>
940 This will take a C<$method_name> and CODE reference to that
941 C<$method> and alias the method into the class's package.
944 Unlike C<add_method>, this will B<not> try to name the
945 C<$method> using B<Sub::Name>, it only aliases the method in
948 =item B<has_method ($method_name)>
950 This just provides a simple way to check if the class implements
951 a specific C<$method_name>. It will I<not> however, attempt to check
952 if the class inherits the method (use C<UNIVERSAL::can> for that).
954 This will correctly handle functions defined outside of the package
955 that use a fully qualified name (C<sub Package::name { ... }>).
957 This will correctly handle functions renamed with B<Sub::Name> and
958 installed using the symbol tables. However, if you are naming the
959 subroutine outside of the package scope, you must use the fully
960 qualified name, including the package name, for C<has_method> to
961 correctly identify it.
963 This will attempt to correctly ignore functions imported from other
964 packages using B<Exporter>. It breaks down if the function imported
965 is an C<__ANON__> sub (such as with C<use constant>), which very well
966 may be a valid method being applied to the class.
968 In short, this method cannot always be trusted to determine if the
969 C<$method_name> is actually a method. However, it will DWIM about
970 90% of the time, so it's a small trade off I think.
972 =item B<get_method ($method_name)>
974 This will return a CODE reference of the specified C<$method_name>,
975 or return undef if that method does not exist.
977 =item B<remove_method ($method_name)>
979 This will attempt to remove a given C<$method_name> from the class.
980 It will return the CODE reference that it has removed, and will
981 attempt to use B<Sub::Name> to clear the methods associated name.
983 =item B<get_method_list>
985 This will return a list of method names for all I<locally> defined
986 methods. It does B<not> provide a list of all applicable methods,
987 including any inherited ones. If you want a list of all applicable
988 methods, use the C<compute_all_applicable_methods> method.
990 =item B<compute_all_applicable_methods>
992 This will return a list of all the methods names this class will
993 respond to, taking into account inheritance. The list will be a list of
994 HASH references, each one containing the following information; method
995 name, the name of the class in which the method lives and a CODE
996 reference for the actual method.
998 =item B<find_all_methods_by_name ($method_name)>
1000 This will traverse the inheritence hierarchy and locate all methods
1001 with a given C<$method_name>. Similar to
1002 C<compute_all_applicable_methods> it returns a list of HASH references
1003 with the following information; method name (which will always be the
1004 same as C<$method_name>), the name of the class in which the method
1005 lives and a CODE reference for the actual method.
1007 The list of methods produced is a distinct list, meaning there are no
1008 duplicates in it. This is especially useful for things like object
1009 initialization and destruction where you only want the method called
1010 once, and in the correct order.
1012 =item B<find_next_method_by_name ($method_name)>
1014 This will return the first method to match a given C<$method_name> in
1015 the superclasses, this is basically equivalent to calling
1016 C<SUPER::$method_name>, but it can be dispatched at runtime.
1020 =head2 Method Modifiers
1022 Method modifiers are a concept borrowed from CLOS, in which a method
1023 can be wrapped with I<before>, I<after> and I<around> method modifiers
1024 that will be called everytime the method is called.
1026 =head3 How method modifiers work?
1028 Method modifiers work by wrapping the original method and then replacing
1029 it in the classes symbol table. The wrappers will handle calling all the
1030 modifiers in the appropariate orders and preserving the calling context
1031 for the original method.
1033 Each method modifier serves a particular purpose, which may not be
1034 obvious to users of other method wrapping modules. To start with, the
1035 return values of I<before> and I<after> modifiers are ignored. This is
1036 because thier purpose is B<not> to filter the input and output of the
1037 primary method (this is done with an I<around> modifier). This may seem
1038 like an odd restriction to some, but doing this allows for simple code
1039 to be added at the begining or end of a method call without jeapordizing
1040 the normal functioning of the primary method or placing any extra
1041 responsibility on the code of the modifier. Of course if you have more
1042 complex needs, then use the I<around> modifier, which uses a variation
1043 of continutation passing style to allow for a high degree of flexibility.
1045 Before and around modifiers are called in last-defined-first-called order,
1046 while after modifiers are called in first-defined-first-called order. So
1047 the call tree might looks something like this:
1057 To see examples of using method modifiers, see the following examples
1058 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1059 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1060 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1062 =head3 What is the performance impact?
1064 Of course there is a performance cost associated with method modifiers,
1065 but we have made every effort to make that cost be directly proportional
1066 to the amount of modifier features you utilize.
1068 The wrapping method does it's best to B<only> do as much work as it
1069 absolutely needs to. In order to do this we have moved some of the
1070 performance costs to set-up time, where they are easier to amortize.
1072 All this said, my benchmarks have indicated the following:
1074 simple wrapper with no modifiers 100% slower
1075 simple wrapper with simple before modifier 400% slower
1076 simple wrapper with simple after modifier 450% slower
1077 simple wrapper with simple around modifier 500-550% slower
1078 simple wrapper with all 3 modifiers 1100% slower
1080 These numbers may seem daunting, but you must remember, every feature
1081 comes with some cost. To put things in perspective, just doing a simple
1082 C<AUTOLOAD> which does nothing but extract the name of the method called
1083 and return it costs about 400% over a normal method call.
1087 =item B<add_before_method_modifier ($method_name, $code)>
1089 This will wrap the method at C<$method_name> and the supplied C<$code>
1090 will be passed the C<@_> arguments, and called before the original
1091 method is called. As specified above, the return value of the I<before>
1092 method modifiers is ignored, and it's ability to modify C<@_> is
1093 fairly limited. If you need to do either of these things, use an
1094 C<around> method modifier.
1096 =item B<add_after_method_modifier ($method_name, $code)>
1098 This will wrap the method at C<$method_name> so that the original
1099 method will be called, it's return values stashed, and then the
1100 supplied C<$code> will be passed the C<@_> arguments, and called.
1101 As specified above, the return value of the I<after> method
1102 modifiers is ignored, and it cannot modify the return values of
1103 the original method. If you need to do either of these things, use an
1104 C<around> method modifier.
1106 =item B<add_around_method_modifier ($method_name, $code)>
1108 This will wrap the method at C<$method_name> so that C<$code>
1109 will be called and passed the original method as an extra argument
1110 at the begining of the C<@_> argument list. This is a variation of
1111 continuation passing style, where the function prepended to C<@_>
1112 can be considered a continuation. It is up to C<$code> if it calls
1113 the original method or not, there is no restriction on what the
1114 C<$code> can or cannot do.
1120 It should be noted that since there is no one consistent way to define
1121 the attributes of a class in Perl 5. These methods can only work with
1122 the information given, and can not easily discover information on
1123 their own. See L<Class::MOP::Attribute> for more details.
1127 =item B<attribute_metaclass>
1129 =item B<get_attribute_map>
1131 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1133 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1134 instance associated with the given class, and associates it with
1135 the C<$attribute_name>. Unlike methods, attributes within the MOP
1136 are stored as meta-information only. They will be used later to
1137 construct instances from (see C<construct_instance> above).
1138 More details about the attribute meta-objects can be found in the
1139 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1142 It should be noted that any accessor, reader/writer or predicate
1143 methods which the C<$attribute_meta_object> has will be installed
1144 into the class at this time.
1146 =item B<has_attribute ($attribute_name)>
1148 Checks to see if this class has an attribute by the name of
1149 C<$attribute_name> and returns a boolean.
1151 =item B<get_attribute ($attribute_name)>
1153 Returns the attribute meta-object associated with C<$attribute_name>,
1154 if none is found, it will return undef.
1156 =item B<remove_attribute ($attribute_name)>
1158 This will remove the attribute meta-object stored at
1159 C<$attribute_name>, then return the removed attribute meta-object.
1162 Removing an attribute will only affect future instances of
1163 the class, it will not make any attempt to remove the attribute from
1164 any existing instances of the class.
1166 It should be noted that any accessor, reader/writer or predicate
1167 methods which the attribute meta-object stored at C<$attribute_name>
1168 has will be removed from the class at this time. This B<will> make
1169 these attributes somewhat inaccessable in previously created
1170 instances. But if you are crazy enough to do this at runtime, then
1171 you are crazy enough to deal with something like this :).
1173 =item B<get_attribute_list>
1175 This returns a list of attribute names which are defined in the local
1176 class. If you want a list of all applicable attributes for a class,
1177 use the C<compute_all_applicable_attributes> method.
1179 =item B<compute_all_applicable_attributes>
1181 This will traverse the inheritance heirachy and return a list of all
1182 the applicable attributes for this class. It does not construct a
1183 HASH reference like C<compute_all_applicable_methods> because all
1184 that same information is discoverable through the attribute
1187 =item B<find_attribute_by_name ($attr_name)>
1189 This method will traverse the inheritance heirachy and find the
1190 first attribute whose name matches C<$attr_name>, then return it.
1191 It will return undef if nothing is found.
1195 =head2 Package Variables
1197 Since Perl's classes are built atop the Perl package system, it is
1198 fairly common to use package scoped variables for things like static
1199 class variables. The following methods are convience methods for
1200 the creation and inspection of package scoped variables.
1204 =item B<add_package_variable ($variable_name, ?$initial_value)>
1206 Given a C<$variable_name>, which must contain a leading sigil, this
1207 method will create that variable within the package which houses the
1208 class. It also takes an optional C<$initial_value>, which must be a
1209 reference of the same type as the sigil of the C<$variable_name>
1212 =item B<get_package_variable ($variable_name)>
1214 This will return a reference to the package variable in
1217 =item B<has_package_variable ($variable_name)>
1219 Returns true (C<1>) if there is a package variable defined for
1220 C<$variable_name>, and false (C<0>) otherwise.
1222 =item B<remove_package_variable ($variable_name)>
1224 This will attempt to remove the package variable at C<$variable_name>.
1230 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1232 =head1 COPYRIGHT AND LICENSE
1234 Copyright 2006 by Infinity Interactive, Inc.
1236 L<http://www.iinteractive.com>
1238 This library is free software; you can redistribute it and/or modify
1239 it under the same terms as Perl itself.