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, @_);
43 # NOTE: (meta-circularity)
44 # this is a special form of &construct_instance
45 # (see below), which is used to construct class
46 # meta-object instances for any Class::MOP::*
47 # class. All other classes will use the more
48 # normal &construct_instance.
49 sub construct_class_instance {
52 my $package_name = $options{':package'};
53 (defined $package_name && $package_name)
54 || confess "You must pass a package name";
56 # return the metaclass if we have it cached,
57 # and it is still defined (it has not been
58 # reaped by DESTROY yet, which can happen
59 # annoyingly enough during global destruction)
60 return $METAS{$package_name}
61 if exists $METAS{$package_name} && defined $METAS{$package_name};
62 $class = blessed($class) || $class;
63 # now create the metaclass
65 if ($class =~ /^Class::MOP::/) {
67 '$:package' => $package_name,
69 '$:attribute_metaclass' => $options{':attribute_metaclass'} || 'Class::MOP::Attribute',
70 '$:method_metaclass' => $options{':method_metaclass'} || 'Class::MOP::Method',
71 '$:instance_metaclass' => $options{':instance_metaclass'} || 'Class::MOP::Instance',
76 # it is safe to use meta here because
77 # class will always be a subclass of
78 # Class::MOP::Class, which defines meta
79 $meta = bless $class->meta->construct_instance(%options) => $class
81 # and check the metaclass compatibility
82 $meta->check_metaclass_compatability();
83 $METAS{$package_name} = $meta;
86 sub check_metaclass_compatability {
89 # this is always okay ...
90 return if blessed($self) eq 'Class::MOP::Class' &&
91 $self->instance_metaclass eq 'Class::MOP::Instance';
93 my @class_list = $self->class_precedence_list;
94 shift @class_list; # shift off $self->name
96 foreach my $class_name (@class_list) {
97 my $meta = $METAS{$class_name} || next;
98 ($self->isa(blessed($meta)))
99 || confess $self->name . "->meta => (" . (blessed($self)) . ")" .
100 " is not compatible with the " .
101 $class_name . "->meta => (" . (blessed($meta)) . ")";
103 # we also need to check that instance metaclasses
104 # are compatabile in the same the class.
105 ($self->instance_metaclass->isa($meta->instance_metaclass))
106 || confess $self->name . "->meta => (" . ($self->instance_metaclass) . ")" .
107 " is not compatible with the " .
108 $class_name . "->meta => (" . ($meta->instance_metaclass) . ")";
114 my ($class, $package_name, $package_version, %options) = @_;
115 (defined $package_name && $package_name)
116 || confess "You must pass a package name";
117 my $code = "package $package_name;";
118 $code .= "\$$package_name\:\:VERSION = '$package_version';"
119 if defined $package_version;
121 confess "creation of $package_name failed : $@" if $@;
122 my $meta = $class->initialize($package_name);
124 $meta->add_method('meta' => sub {
125 Class::MOP::Class->initialize(blessed($_[0]) || $_[0]);
128 $meta->superclasses(@{$options{superclasses}})
129 if exists $options{superclasses};
131 # process attributes first, so that they can
132 # install accessors, but locally defined methods
133 # can then overwrite them. It is maybe a little odd, but
134 # I think this should be the order of things.
135 if (exists $options{attributes}) {
136 foreach my $attr (@{$options{attributes}}) {
137 $meta->add_attribute($attr);
140 if (exists $options{methods}) {
141 foreach my $method_name (keys %{$options{methods}}) {
142 $meta->add_method($method_name, $options{methods}->{$method_name});
150 # this should be sufficient, if you have a
151 # use case where it is not, write a test and
153 my $ANON_CLASS_SERIAL = 0;
155 sub create_anon_class {
156 my ($class, %options) = @_;
157 my $package_name = 'Class::MOP::Class::__ANON__::SERIAL::' . ++$ANON_CLASS_SERIAL;
158 return $class->create($package_name, '0.00', %options);
165 # all these attribute readers will be bootstrapped
166 # away in the Class::MOP bootstrap section
168 sub name { $_[0]->{'$:package'} }
169 sub get_attribute_map { $_[0]->{'%:attributes'} }
170 sub attribute_metaclass { $_[0]->{'$:attribute_metaclass'} }
171 sub method_metaclass { $_[0]->{'$:method_metaclass'} }
172 sub instance_metaclass { $_[0]->{'$:instance_metaclass'} }
174 # Instance Construction & Cloning
179 # we need to protect the integrity of the
180 # Class::MOP::Class singletons here, so we
181 # delegate this to &construct_class_instance
182 # which will deal with the singletons
183 return $class->construct_class_instance(@_)
184 if $class->name->isa('Class::MOP::Class');
185 return $class->construct_instance(@_);
188 sub construct_instance {
189 my ($class, %params) = @_;
190 my $meta_instance = $class->get_meta_instance();
191 my $instance = $meta_instance->create_instance();
192 foreach my $attr ($class->compute_all_applicable_attributes()) {
193 $attr->initialize_instance_slot($meta_instance, $instance, \%params);
198 sub get_meta_instance {
200 return $class->instance_metaclass->new(
202 $class->compute_all_applicable_attributes()
208 my $instance = shift;
209 (blessed($instance) && $instance->isa($class->name))
210 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
212 # we need to protect the integrity of the
213 # Class::MOP::Class singletons here, they
214 # should not be cloned.
215 return $instance if $instance->isa('Class::MOP::Class');
216 $class->clone_instance($instance, @_);
220 my ($class, $instance, %params) = @_;
222 || confess "You can only clone instances, \$self is not a blessed instance";
223 my $meta_instance = $class->get_meta_instance();
224 my $clone = $meta_instance->clone_instance($instance);
225 foreach my $key (%params) {
226 next unless $meta_instance->is_valid_slot($key);
227 $meta_instance->set_slot_value($clone, $key, $params{$key});
234 # &name should be here too, but it is above
235 # because it gets bootstrapped away
239 ${$self->get_package_variable('$VERSION')};
249 @{$self->name . '::ISA'} = @supers;
251 # we need to check the metaclass
252 # compatability here so that we can
253 # be sure that the superclass is
254 # not potentially creating an issues
255 # we don't know about
256 $self->check_metaclass_compatability();
258 @{$self->name . '::ISA'};
261 sub class_precedence_list {
264 # We need to check for ciruclar inheirtance here.
265 # This will do nothing if all is well, and blow
266 # up otherwise. Yes, it's an ugly hack, better
267 # suggestions are welcome.
268 { ($self->name || return)->isa('This is a test for circular inheritance') }
269 # ... and now back to our regularly scheduled program
273 $self->initialize($_)->class_precedence_list()
274 } $self->superclasses()
281 my ($self, $method_name, $method) = @_;
282 (defined $method_name && $method_name)
283 || confess "You must define a method name";
284 # use reftype here to allow for blessed subs ...
285 ('CODE' eq (reftype($method) || ''))
286 || confess "Your code block must be a CODE reference";
287 my $full_method_name = ($self->name . '::' . $method_name);
289 $method = $self->method_metaclass->wrap($method) unless blessed($method);
292 no warnings 'redefine';
293 *{$full_method_name} = subname $full_method_name => $method;
297 my $fetch_and_prepare_method = sub {
298 my ($self, $method_name) = @_;
300 my $method = $self->get_method($method_name);
301 # if we dont have local ...
303 # make sure this method even exists ...
304 ($self->find_next_method_by_name($method_name))
305 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
306 # if so, then create a local which just
307 # calls the next applicable method ...
308 $self->add_method($method_name => sub {
309 $self->find_next_method_by_name($method_name)->(@_);
311 $method = $self->get_method($method_name);
314 # now make sure we wrap it properly
315 # (if it isnt already)
316 unless ($method->isa('Class::MOP::Method::Wrapped')) {
317 $method = Class::MOP::Method::Wrapped->wrap($method);
318 $self->add_method($method_name => $method);
323 sub add_before_method_modifier {
324 my ($self, $method_name, $method_modifier) = @_;
325 (defined $method_name && $method_name)
326 || confess "You must pass in a method name";
327 my $method = $fetch_and_prepare_method->($self, $method_name);
328 $method->add_before_modifier(subname ':before' => $method_modifier);
331 sub add_after_method_modifier {
332 my ($self, $method_name, $method_modifier) = @_;
333 (defined $method_name && $method_name)
334 || confess "You must pass in a method name";
335 my $method = $fetch_and_prepare_method->($self, $method_name);
336 $method->add_after_modifier(subname ':after' => $method_modifier);
339 sub add_around_method_modifier {
340 my ($self, $method_name, $method_modifier) = @_;
341 (defined $method_name && $method_name)
342 || confess "You must pass in a method name";
343 my $method = $fetch_and_prepare_method->($self, $method_name);
344 $method->add_around_modifier(subname ':around' => $method_modifier);
348 # the methods above used to be named like this:
349 # ${pkg}::${method}:(before|after|around)
350 # but this proved problematic when using one modifier
351 # to wrap multiple methods (something which is likely
352 # to happen pretty regularly IMO). So instead of naming
353 # it like this, I have chosen to just name them purely
354 # with their modifier names, like so:
355 # :(before|after|around)
356 # The fact is that in a stack trace, it will be fairly
357 # evident from the context what method they are attached
358 # to, and so don't need the fully qualified name.
362 my ($self, $method_name, $method) = @_;
363 (defined $method_name && $method_name)
364 || confess "You must define a method name";
365 # use reftype here to allow for blessed subs ...
366 ('CODE' eq (reftype($method) || ''))
367 || confess "Your code block must be a CODE reference";
368 my $full_method_name = ($self->name . '::' . $method_name);
370 $method = $self->method_metaclass->wrap($method) unless blessed($method);
373 no warnings 'redefine';
374 *{$full_method_name} = $method;
378 my ($self, $method_name) = @_;
379 (defined $method_name && $method_name)
380 || confess "You must define a method name";
382 my $sub_name = ($self->name . '::' . $method_name);
385 return 0 if !defined(&{$sub_name});
386 my $method = \&{$sub_name};
387 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
388 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
390 # at this point we are relatively sure
391 # it is our method, so we bless/wrap it
392 $self->method_metaclass->wrap($method) unless blessed($method);
397 my ($self, $method_name) = @_;
398 (defined $method_name && $method_name)
399 || confess "You must define a method name";
401 return unless $self->has_method($method_name);
404 return \&{$self->name . '::' . $method_name};
408 my ($self, $method_name) = @_;
409 (defined $method_name && $method_name)
410 || confess "You must define a method name";
412 my $removed_method = $self->get_method($method_name);
415 delete ${$self->name . '::'}{$method_name}
416 if defined $removed_method;
418 return $removed_method;
421 sub get_method_list {
424 grep { $self->has_method($_) } keys %{$self->name . '::'};
427 sub compute_all_applicable_methods {
430 # keep a record of what we have seen
431 # here, this will handle all the
432 # inheritence issues because we are
433 # using the &class_precedence_list
434 my (%seen_class, %seen_method);
435 foreach my $class ($self->class_precedence_list()) {
436 next if $seen_class{$class};
437 $seen_class{$class}++;
438 # fetch the meta-class ...
439 my $meta = $self->initialize($class);
440 foreach my $method_name ($meta->get_method_list()) {
441 next if exists $seen_method{$method_name};
442 $seen_method{$method_name}++;
444 name => $method_name,
446 code => $meta->get_method($method_name)
453 sub find_all_methods_by_name {
454 my ($self, $method_name) = @_;
455 (defined $method_name && $method_name)
456 || confess "You must define a method name to find";
458 # keep a record of what we have seen
459 # here, this will handle all the
460 # inheritence issues because we are
461 # using the &class_precedence_list
463 foreach my $class ($self->class_precedence_list()) {
464 next if $seen_class{$class};
465 $seen_class{$class}++;
466 # fetch the meta-class ...
467 my $meta = $self->initialize($class);
469 name => $method_name,
471 code => $meta->get_method($method_name)
472 } if $meta->has_method($method_name);
477 sub find_next_method_by_name {
478 my ($self, $method_name) = @_;
479 (defined $method_name && $method_name)
480 || confess "You must define a method name to find";
481 # keep a record of what we have seen
482 # here, this will handle all the
483 # inheritence issues because we are
484 # using the &class_precedence_list
486 my @cpl = $self->class_precedence_list();
487 shift @cpl; # discard ourselves
488 foreach my $class (@cpl) {
489 next if $seen_class{$class};
490 $seen_class{$class}++;
491 # fetch the meta-class ...
492 my $meta = $self->initialize($class);
493 return $meta->get_method($method_name)
494 if $meta->has_method($method_name);
503 # either we have an attribute object already
504 # or we need to create one from the args provided
505 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
506 # make sure it is derived from the correct type though
507 ($attribute->isa('Class::MOP::Attribute'))
508 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
509 $attribute->attach_to_class($self);
510 $attribute->install_accessors();
511 $self->get_attribute_map->{$attribute->name} = $attribute;
514 # in theory we have to tell everyone the slot structure may have changed
518 my ($self, $attribute_name) = @_;
519 (defined $attribute_name && $attribute_name)
520 || confess "You must define an attribute name";
521 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
525 my ($self, $attribute_name) = @_;
526 (defined $attribute_name && $attribute_name)
527 || confess "You must define an attribute name";
528 return $self->get_attribute_map->{$attribute_name}
529 if $self->has_attribute($attribute_name);
533 sub remove_attribute {
534 my ($self, $attribute_name) = @_;
535 (defined $attribute_name && $attribute_name)
536 || confess "You must define an attribute name";
537 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
538 return unless defined $removed_attribute;
539 delete $self->get_attribute_map->{$attribute_name};
540 $removed_attribute->remove_accessors();
541 $removed_attribute->detach_from_class();
542 return $removed_attribute;
545 sub get_attribute_list {
547 keys %{$self->get_attribute_map};
550 sub compute_all_applicable_attributes {
553 # keep a record of what we have seen
554 # here, this will handle all the
555 # inheritence issues because we are
556 # using the &class_precedence_list
557 my (%seen_class, %seen_attr);
558 foreach my $class ($self->class_precedence_list()) {
559 next if $seen_class{$class};
560 $seen_class{$class}++;
561 # fetch the meta-class ...
562 my $meta = $self->initialize($class);
563 foreach my $attr_name ($meta->get_attribute_list()) {
564 next if exists $seen_attr{$attr_name};
565 $seen_attr{$attr_name}++;
566 push @attrs => $meta->get_attribute($attr_name);
572 sub find_attribute_by_name {
573 my ($self, $attr_name) = @_;
574 # keep a record of what we have seen
575 # here, this will handle all the
576 # inheritence issues because we are
577 # using the &class_precedence_list
579 foreach my $class ($self->class_precedence_list()) {
580 next if $seen_class{$class};
581 $seen_class{$class}++;
582 # fetch the meta-class ...
583 my $meta = $self->initialize($class);
584 return $meta->get_attribute($attr_name)
585 if $meta->has_attribute($attr_name);
592 sub add_package_variable {
593 my ($self, $variable, $initial_value) = @_;
594 (defined $variable && $variable =~ /^[\$\@\%]/)
595 || confess "variable name does not have a sigil";
597 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
598 if (defined $initial_value) {
600 *{$self->name . '::' . $name} = $initial_value;
606 # We HAVE to localize $@ or all
607 # hell breaks loose. It is not
608 # good, believe me, not good.
610 eval $sigil . $self->name . '::' . $name;
613 confess "Could not create package variable ($variable) because : $e" if $e;
617 sub has_package_variable {
618 my ($self, $variable) = @_;
619 (defined $variable && $variable =~ /^[\$\@\%]/)
620 || confess "variable name does not have a sigil";
621 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
623 defined ${$self->name . '::'}{$name} ? 1 : 0;
626 sub get_package_variable {
627 my ($self, $variable) = @_;
628 (defined $variable && $variable =~ /^[\$\@\%]/)
629 || confess "variable name does not have a sigil";
630 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
634 # We HAVE to localize $@ or all
635 # hell breaks loose. It is not
636 # good, believe me, not good.
638 $ref = eval '\\' . $sigil . $self->name . '::' . $name;
641 confess "Could not get the package variable ($variable) because : $e" if $e;
642 # if we didn't die, then we can return it
646 sub remove_package_variable {
647 my ($self, $variable) = @_;
648 (defined $variable && $variable =~ /^[\$\@\%]/)
649 || confess "variable name does not have a sigil";
650 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
652 delete ${$self->name . '::'}{$name};
663 Class::MOP::Class - Class Meta Object
667 # assuming that class Foo
668 # has been defined, you can
670 # use this for introspection ...
672 # add a method to Foo ...
673 Foo->meta->add_method('bar' => sub { ... })
675 # get a list of all the classes searched
676 # the method dispatcher in the correct order
677 Foo->meta->class_precedence_list()
679 # remove a method from Foo
680 Foo->meta->remove_method('bar');
682 # or use this to actually create classes ...
684 Class::MOP::Class->create('Bar' => '0.01' => (
685 superclasses => [ 'Foo' ],
687 Class::MOP:::Attribute->new('$bar'),
688 Class::MOP:::Attribute->new('$baz'),
691 calculate_bar => sub { ... },
692 construct_baz => sub { ... }
698 This is the largest and currently most complex part of the Perl 5
699 meta-object protocol. It controls the introspection and
700 manipulation of Perl 5 classes (and it can create them too). The
701 best way to understand what this module can do, is to read the
702 documentation for each of it's methods.
706 =head2 Self Introspection
712 This will return a B<Class::MOP::Class> instance which is related
713 to this class. Thereby allowing B<Class::MOP::Class> to actually
716 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
717 bootstrap this module by installing a number of attribute meta-objects
718 into it's metaclass. This will allow this class to reap all the benifits
719 of the MOP when subclassing it.
721 =item B<get_all_metaclasses>
723 This will return an hash of all the metaclass instances that have
724 been cached by B<Class::MOP::Class> keyed by the package name.
726 =item B<get_all_metaclass_instances>
728 This will return an array of all the metaclass instances that have
729 been cached by B<Class::MOP::Class>.
731 =item B<get_all_metaclass_names>
733 This will return an array of all the metaclass names that have
734 been cached by B<Class::MOP::Class>.
738 =head2 Class construction
740 These methods will handle creating B<Class::MOP::Class> objects,
741 which can be used to both create new classes, and analyze
742 pre-existing classes.
744 This module will internally store references to all the instances
745 you create with these methods, so that they do not need to be
746 created any more than nessecary. Basically, they are singletons.
750 =item B<create ($package_name, ?$package_version,
751 superclasses =E<gt> ?@superclasses,
752 methods =E<gt> ?%methods,
753 attributes =E<gt> ?%attributes)>
755 This returns a B<Class::MOP::Class> object, bringing the specified
756 C<$package_name> into existence and adding any of the
757 C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
760 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
761 methods =E<gt> ?%methods,
762 attributes =E<gt> ?%attributes)>
764 This will create an anonymous class, it works much like C<create> but
765 it does not need a C<$package_name>. Instead it will create a suitably
766 unique package name for you to stash things into.
768 =item B<initialize ($package_name)>
770 This initializes and returns returns a B<Class::MOP::Class> object
771 for a given a C<$package_name>.
773 =item B<construct_class_instance (%options)>
775 This will construct an instance of B<Class::MOP::Class>, it is
776 here so that we can actually "tie the knot" for B<Class::MOP::Class>
777 to use C<construct_instance> once all the bootstrapping is done. This
778 method is used internally by C<initialize> and should never be called
779 from outside of that method really.
781 =item B<check_metaclass_compatability>
783 This method is called as the very last thing in the
784 C<construct_class_instance> method. This will check that the
785 metaclass you are creating is compatible with the metaclasses of all
786 your ancestors. For more inforamtion about metaclass compatibility
787 see the C<About Metaclass compatibility> section in L<Class::MOP>.
791 =head2 Object instance construction and cloning
793 These methods are B<entirely optional>, it is up to you whether you want
798 =item B<instance_metaclass>
800 =item B<get_meta_instance>
802 =item B<new_object (%params)>
804 This is a convience method for creating a new object of the class, and
805 blessing it into the appropriate package as well. Ideally your class
806 would call a C<new> this method like so:
809 my ($class, %param) = @_;
810 $class->meta->new_object(%params);
813 Of course the ideal place for this would actually be in C<UNIVERSAL::>
814 but that is considered bad style, so we do not do that.
816 =item B<construct_instance (%params)>
818 This method is used to construct an instace structure suitable for
819 C<bless>-ing into your package of choice. It works in conjunction
820 with the Attribute protocol to collect all applicable attributes.
822 This will construct and instance using a HASH ref as storage
823 (currently only HASH references are supported). This will collect all
824 the applicable attributes and layout out the fields in the HASH ref,
825 it will then initialize them using either use the corresponding key
826 in C<%params> or any default value or initializer found in the
827 attribute meta-object.
829 =item B<clone_object ($instance, %params)>
831 This is a convience method for cloning an object instance, then
832 blessing it into the appropriate package. This method will call
833 C<clone_instance>, which performs a shallow copy of the object,
834 see that methods documentation for more details. Ideally your
835 class would call a C<clone> this method like so:
838 my ($self, %param) = @_;
839 $self->meta->clone_object($self, %params);
842 Of course the ideal place for this would actually be in C<UNIVERSAL::>
843 but that is considered bad style, so we do not do that.
845 =item B<clone_instance($instance, %params)>
847 This method is a compliment of C<construct_instance> (which means if
848 you override C<construct_instance>, you need to override this one too),
849 and clones the instance shallowly.
851 The cloned structure returned is (like with C<construct_instance>) an
852 unC<bless>ed HASH reference, it is your responsibility to then bless
853 this cloned structure into the right class (which C<clone_object> will
856 As of 0.11, this method will clone the C<$instance> structure shallowly,
857 as opposed to the deep cloning implemented in prior versions. After much
858 thought, research and discussion, I have decided that anything but basic
859 shallow cloning is outside the scope of the meta-object protocol. I
860 think Yuval "nothingmuch" Kogman put it best when he said that cloning
861 is too I<context-specific> to be part of the MOP.
871 This is a read-only attribute which returns the package name for the
872 given B<Class::MOP::Class> instance.
876 This is a read-only attribute which returns the C<$VERSION> of the
877 package for the given B<Class::MOP::Class> instance.
881 =head2 Inheritance Relationships
885 =item B<superclasses (?@superclasses)>
887 This is a read-write attribute which represents the superclass
888 relationships of the class the B<Class::MOP::Class> instance is
889 associated with. Basically, it can get and set the C<@ISA> for you.
892 Perl will occasionally perform some C<@ISA> and method caching, if
893 you decide to change your superclass relationship at runtime (which
894 is quite insane and very much not recommened), then you should be
895 aware of this and the fact that this module does not make any
896 attempt to address this issue.
898 =item B<class_precedence_list>
900 This computes the a list of all the class's ancestors in the same order
901 in which method dispatch will be done. This is similair to
902 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
910 =item B<method_metaclass>
912 =item B<add_method ($method_name, $method)>
914 This will take a C<$method_name> and CODE reference to that
915 C<$method> and install it into the class's package.
918 This does absolutely nothing special to C<$method>
919 other than use B<Sub::Name> to make sure it is tagged with the
920 correct name, and therefore show up correctly in stack traces and
923 =item B<alias_method ($method_name, $method)>
925 This will take a C<$method_name> and CODE reference to that
926 C<$method> and alias the method into the class's package.
929 Unlike C<add_method>, this will B<not> try to name the
930 C<$method> using B<Sub::Name>, it only aliases the method in
933 =item B<has_method ($method_name)>
935 This just provides a simple way to check if the class implements
936 a specific C<$method_name>. It will I<not> however, attempt to check
937 if the class inherits the method (use C<UNIVERSAL::can> for that).
939 This will correctly handle functions defined outside of the package
940 that use a fully qualified name (C<sub Package::name { ... }>).
942 This will correctly handle functions renamed with B<Sub::Name> and
943 installed using the symbol tables. However, if you are naming the
944 subroutine outside of the package scope, you must use the fully
945 qualified name, including the package name, for C<has_method> to
946 correctly identify it.
948 This will attempt to correctly ignore functions imported from other
949 packages using B<Exporter>. It breaks down if the function imported
950 is an C<__ANON__> sub (such as with C<use constant>), which very well
951 may be a valid method being applied to the class.
953 In short, this method cannot always be trusted to determine if the
954 C<$method_name> is actually a method. However, it will DWIM about
955 90% of the time, so it's a small trade off I think.
957 =item B<get_method ($method_name)>
959 This will return a CODE reference of the specified C<$method_name>,
960 or return undef if that method does not exist.
962 =item B<remove_method ($method_name)>
964 This will attempt to remove a given C<$method_name> from the class.
965 It will return the CODE reference that it has removed, and will
966 attempt to use B<Sub::Name> to clear the methods associated name.
968 =item B<get_method_list>
970 This will return a list of method names for all I<locally> defined
971 methods. It does B<not> provide a list of all applicable methods,
972 including any inherited ones. If you want a list of all applicable
973 methods, use the C<compute_all_applicable_methods> method.
975 =item B<compute_all_applicable_methods>
977 This will return a list of all the methods names this class will
978 respond to, taking into account inheritance. The list will be a list of
979 HASH references, each one containing the following information; method
980 name, the name of the class in which the method lives and a CODE
981 reference for the actual method.
983 =item B<find_all_methods_by_name ($method_name)>
985 This will traverse the inheritence hierarchy and locate all methods
986 with a given C<$method_name>. Similar to
987 C<compute_all_applicable_methods> it returns a list of HASH references
988 with the following information; method name (which will always be the
989 same as C<$method_name>), the name of the class in which the method
990 lives and a CODE reference for the actual method.
992 The list of methods produced is a distinct list, meaning there are no
993 duplicates in it. This is especially useful for things like object
994 initialization and destruction where you only want the method called
995 once, and in the correct order.
997 =item B<find_next_method_by_name ($method_name)>
999 This will return the first method to match a given C<$method_name> in
1000 the superclasses, this is basically equivalent to calling
1001 C<SUPER::$method_name>, but it can be dispatched at runtime.
1005 =head2 Method Modifiers
1007 Method modifiers are a concept borrowed from CLOS, in which a method
1008 can be wrapped with I<before>, I<after> and I<around> method modifiers
1009 that will be called everytime the method is called.
1011 =head3 How method modifiers work?
1013 Method modifiers work by wrapping the original method and then replacing
1014 it in the classes symbol table. The wrappers will handle calling all the
1015 modifiers in the appropariate orders and preserving the calling context
1016 for the original method.
1018 Each method modifier serves a particular purpose, which may not be
1019 obvious to users of other method wrapping modules. To start with, the
1020 return values of I<before> and I<after> modifiers are ignored. This is
1021 because thier purpose is B<not> to filter the input and output of the
1022 primary method (this is done with an I<around> modifier). This may seem
1023 like an odd restriction to some, but doing this allows for simple code
1024 to be added at the begining or end of a method call without jeapordizing
1025 the normal functioning of the primary method or placing any extra
1026 responsibility on the code of the modifier. Of course if you have more
1027 complex needs, then use the I<around> modifier, which uses a variation
1028 of continutation passing style to allow for a high degree of flexibility.
1030 Before and around modifiers are called in last-defined-first-called order,
1031 while after modifiers are called in first-defined-first-called order. So
1032 the call tree might looks something like this:
1042 To see examples of using method modifiers, see the following examples
1043 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1044 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1045 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1047 =head3 What is the performance impact?
1049 Of course there is a performance cost associated with method modifiers,
1050 but we have made every effort to make that cost be directly proportional
1051 to the amount of modifier features you utilize.
1053 The wrapping method does it's best to B<only> do as much work as it
1054 absolutely needs to. In order to do this we have moved some of the
1055 performance costs to set-up time, where they are easier to amortize.
1057 All this said, my benchmarks have indicated the following:
1059 simple wrapper with no modifiers 100% slower
1060 simple wrapper with simple before modifier 400% slower
1061 simple wrapper with simple after modifier 450% slower
1062 simple wrapper with simple around modifier 500-550% slower
1063 simple wrapper with all 3 modifiers 1100% slower
1065 These numbers may seem daunting, but you must remember, every feature
1066 comes with some cost. To put things in perspective, just doing a simple
1067 C<AUTOLOAD> which does nothing but extract the name of the method called
1068 and return it costs about 400% over a normal method call.
1072 =item B<add_before_method_modifier ($method_name, $code)>
1074 This will wrap the method at C<$method_name> and the supplied C<$code>
1075 will be passed the C<@_> arguments, and called before the original
1076 method is called. As specified above, the return value of the I<before>
1077 method modifiers is ignored, and it's ability to modify C<@_> is
1078 fairly limited. If you need to do either of these things, use an
1079 C<around> method modifier.
1081 =item B<add_after_method_modifier ($method_name, $code)>
1083 This will wrap the method at C<$method_name> so that the original
1084 method will be called, it's return values stashed, and then the
1085 supplied C<$code> will be passed the C<@_> arguments, and called.
1086 As specified above, the return value of the I<after> method
1087 modifiers is ignored, and it cannot modify the return values of
1088 the original method. If you need to do either of these things, use an
1089 C<around> method modifier.
1091 =item B<add_around_method_modifier ($method_name, $code)>
1093 This will wrap the method at C<$method_name> so that C<$code>
1094 will be called and passed the original method as an extra argument
1095 at the begining of the C<@_> argument list. This is a variation of
1096 continuation passing style, where the function prepended to C<@_>
1097 can be considered a continuation. It is up to C<$code> if it calls
1098 the original method or not, there is no restriction on what the
1099 C<$code> can or cannot do.
1105 It should be noted that since there is no one consistent way to define
1106 the attributes of a class in Perl 5. These methods can only work with
1107 the information given, and can not easily discover information on
1108 their own. See L<Class::MOP::Attribute> for more details.
1112 =item B<attribute_metaclass>
1114 =item B<get_attribute_map>
1116 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1118 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1119 instance associated with the given class, and associates it with
1120 the C<$attribute_name>. Unlike methods, attributes within the MOP
1121 are stored as meta-information only. They will be used later to
1122 construct instances from (see C<construct_instance> above).
1123 More details about the attribute meta-objects can be found in the
1124 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1127 It should be noted that any accessor, reader/writer or predicate
1128 methods which the C<$attribute_meta_object> has will be installed
1129 into the class at this time.
1131 =item B<has_attribute ($attribute_name)>
1133 Checks to see if this class has an attribute by the name of
1134 C<$attribute_name> and returns a boolean.
1136 =item B<get_attribute ($attribute_name)>
1138 Returns the attribute meta-object associated with C<$attribute_name>,
1139 if none is found, it will return undef.
1141 =item B<remove_attribute ($attribute_name)>
1143 This will remove the attribute meta-object stored at
1144 C<$attribute_name>, then return the removed attribute meta-object.
1147 Removing an attribute will only affect future instances of
1148 the class, it will not make any attempt to remove the attribute from
1149 any existing instances of the class.
1151 It should be noted that any accessor, reader/writer or predicate
1152 methods which the attribute meta-object stored at C<$attribute_name>
1153 has will be removed from the class at this time. This B<will> make
1154 these attributes somewhat inaccessable in previously created
1155 instances. But if you are crazy enough to do this at runtime, then
1156 you are crazy enough to deal with something like this :).
1158 =item B<get_attribute_list>
1160 This returns a list of attribute names which are defined in the local
1161 class. If you want a list of all applicable attributes for a class,
1162 use the C<compute_all_applicable_attributes> method.
1164 =item B<compute_all_applicable_attributes>
1166 This will traverse the inheritance heirachy and return a list of all
1167 the applicable attributes for this class. It does not construct a
1168 HASH reference like C<compute_all_applicable_methods> because all
1169 that same information is discoverable through the attribute
1172 =item B<find_attribute_by_name ($attr_name)>
1174 This method will traverse the inheritance heirachy and find the
1175 first attribute whose name matches C<$attr_name>, then return it.
1176 It will return undef if nothing is found.
1180 =head2 Package Variables
1182 Since Perl's classes are built atop the Perl package system, it is
1183 fairly common to use package scoped variables for things like static
1184 class variables. The following methods are convience methods for
1185 the creation and inspection of package scoped variables.
1189 =item B<add_package_variable ($variable_name, ?$initial_value)>
1191 Given a C<$variable_name>, which must contain a leading sigil, this
1192 method will create that variable within the package which houses the
1193 class. It also takes an optional C<$initial_value>, which must be a
1194 reference of the same type as the sigil of the C<$variable_name>
1197 =item B<get_package_variable ($variable_name)>
1199 This will return a reference to the package variable in
1202 =item B<has_package_variable ($variable_name)>
1204 Returns true (C<1>) if there is a package variable defined for
1205 C<$variable_name>, and false (C<0>) otherwise.
1207 =item B<remove_package_variable ($variable_name)>
1209 This will attempt to remove the package variable at C<$variable_name>.
1215 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1217 =head1 COPYRIGHT AND LICENSE
1219 Copyright 2006 by Infinity Interactive, Inc.
1221 L<http://www.iinteractive.com>
1223 This library is free software; you can redistribute it and/or modify
1224 it under the same terms as Perl itself.