2 package Class::MOP::Class;
8 use Scalar::Util 'blessed', 'reftype';
9 use Sub::Name 'subname';
10 use B 'svref_2object';
12 our $VERSION = '0.12';
16 sub meta { Class::MOP::Class->initialize(blessed($_[0]) || $_[0]) }
21 # Metaclasses are singletons, so we cache them here.
22 # there is no need to worry about destruction though
23 # because they should die only when the program dies.
24 # After all, do package definitions even get reaped?
27 # means of accessing all the metaclasses that have
28 # been initialized thus far (for mugwumps obj browser)
29 sub get_all_metaclasses { %METAS }
30 sub get_all_metaclass_instances { values %METAS }
31 sub get_all_metaclass_names { keys %METAS }
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->construct_class_instance(':package' => $package_name, @_);
41 # NOTE: (meta-circularity)
42 # this is a special form of &construct_instance
43 # (see below), which is used to construct class
44 # meta-object instances for any Class::MOP::*
45 # class. All other classes will use the more
46 # normal &construct_instance.
47 sub construct_class_instance {
50 my $package_name = $options{':package'};
51 (defined $package_name && $package_name)
52 || confess "You must pass a package name";
54 # return the metaclass if we have it cached,
55 # and it is still defined (it has not been
56 # reaped by DESTROY yet, which can happen
57 # annoyingly enough during global destruction)
58 return $METAS{$package_name}
59 if exists $METAS{$package_name} && defined $METAS{$package_name};
60 $class = blessed($class) || $class;
61 # now create the metaclass
63 if ($class =~ /^Class::MOP::/) {
65 '$:package' => $package_name,
67 '$:attribute_metaclass' => $options{':attribute_metaclass'} || 'Class::MOP::Attribute',
68 '$:method_metaclass' => $options{':method_metaclass'} || 'Class::MOP::Method',
73 # it is safe to use meta here because
74 # class will always be a subclass of
75 # Class::MOP::Class, which defines meta
76 $meta = bless $class->meta->construct_instance(%options) => $class
78 # and check the metaclass compatibility
79 $meta->check_metaclass_compatability();
80 $METAS{$package_name} = $meta;
83 sub check_metaclass_compatability {
86 # this is always okay ...
87 return if blessed($self) eq 'Class::MOP::Class';
89 my @class_list = $self->class_precedence_list;
90 shift @class_list; # shift off $self->name
92 foreach my $class_name (@class_list) {
93 my $meta = $METAS{$class_name} || next;
94 ($self->isa(blessed($meta)))
95 || confess $self->name . "->meta => (" . (blessed($self)) . ")" .
96 " is not compatible with the " .
97 $class_name . "->meta => (" . (blessed($meta)) . ")";
103 my ($class, $package_name, $package_version, %options) = @_;
104 (defined $package_name && $package_name)
105 || confess "You must pass a package name";
106 my $code = "package $package_name;";
107 $code .= "\$$package_name\:\:VERSION = '$package_version';"
108 if defined $package_version;
110 confess "creation of $package_name failed : $@" if $@;
111 my $meta = $class->initialize($package_name);
113 $meta->add_method('meta' => sub {
114 Class::MOP::Class->initialize(blessed($_[0]) || $_[0]);
117 $meta->superclasses(@{$options{superclasses}})
118 if exists $options{superclasses};
120 # process attributes first, so that they can
121 # install accessors, but locally defined methods
122 # can then overwrite them. It is maybe a little odd, but
123 # I think this should be the order of things.
124 if (exists $options{attributes}) {
125 foreach my $attr (@{$options{attributes}}) {
126 $meta->add_attribute($attr);
129 if (exists $options{methods}) {
130 foreach my $method_name (keys %{$options{methods}}) {
131 $meta->add_method($method_name, $options{methods}->{$method_name});
139 # this should be sufficient, if you have a
140 # use case where it is not, write a test and
142 my $ANON_CLASS_SERIAL = 0;
144 sub create_anon_class {
145 my ($class, %options) = @_;
146 my $package_name = 'Class::MOP::Class::__ANON__::SERIAL::' . ++$ANON_CLASS_SERIAL;
147 return $class->create($package_name, '0.00', %options);
154 # all these attribute readers will be bootstrapped
155 # away in the Class::MOP bootstrap section
157 sub name { $_[0]->{'$:package'} }
158 sub get_attribute_map { $_[0]->{'%:attributes'} }
159 sub attribute_metaclass { $_[0]->{'$:attribute_metaclass'} }
160 sub method_metaclass { $_[0]->{'$:method_metaclass'} }
162 # Instance Construction & Cloning
167 # we need to protect the integrity of the
168 # Class::MOP::Class singletons here, so we
169 # delegate this to &construct_class_instance
170 # which will deal with the singletons
171 return $class->construct_class_instance(@_)
172 if $class->name->isa('Class::MOP::Class');
173 bless $class->construct_instance(@_) => $class->name;
176 sub construct_instance {
177 my ($class, %params) = @_;
179 foreach my $attr ($class->compute_all_applicable_attributes()) {
180 $attr->initialize_instance_slot($class, $instance, \%params);
187 my $instance = shift;
188 (blessed($instance) && $instance->isa($class->name))
189 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
191 # we need to protect the integrity of the
192 # Class::MOP::Class singletons here, they
193 # should not be cloned.
194 return $instance if $instance->isa('Class::MOP::Class');
195 bless $class->clone_instance($instance, @_) => blessed($instance);
199 my ($class, $instance, %params) = @_;
201 || confess "You can only clone instances, \$self is not a blessed instance";
202 my $clone = { %$instance, %params };
208 # &name should be here too, but it is above
209 # because it gets bootstrapped away
213 ${$self->get_package_variable('$VERSION')};
223 @{$self->name . '::ISA'} = @supers;
225 @{$self->name . '::ISA'};
228 sub class_precedence_list {
231 # We need to check for ciruclar inheirtance here.
232 # This will do nothing if all is well, and blow
233 # up otherwise. Yes, it's an ugly hack, better
234 # suggestions are welcome.
235 { $self->name->isa('This is a test for circular inheritance') }
236 # ... and now back to our regularly scheduled program
240 $self->initialize($_)->class_precedence_list()
241 } $self->superclasses()
248 my ($self, $method_name, $method) = @_;
249 (defined $method_name && $method_name)
250 || confess "You must define a method name";
251 # use reftype here to allow for blessed subs ...
252 ('CODE' eq (reftype($method) || ''))
253 || confess "Your code block must be a CODE reference";
254 my $full_method_name = ($self->name . '::' . $method_name);
256 $method = $self->method_metaclass->wrap($method) unless blessed($method);
259 no warnings 'redefine';
260 *{$full_method_name} = subname $full_method_name => $method;
264 my $fetch_and_prepare_method = sub {
265 my ($self, $method_name) = @_;
267 my $method = $self->get_method($method_name);
268 # if we dont have local ...
270 # make sure this method even exists ...
271 ($self->find_next_method_by_name($method_name))
272 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
273 # if so, then create a local which just
274 # calls the next applicable method ...
275 $self->add_method($method_name => sub {
276 $self->find_next_method_by_name($method_name)->(@_);
278 $method = $self->get_method($method_name);
281 # now make sure we wrap it properly
282 # (if it isnt already)
283 unless ($method->isa('Class::MOP::Method::Wrapped')) {
284 $method = Class::MOP::Method::Wrapped->wrap($method);
285 $self->add_method($method_name => $method);
290 sub add_before_method_modifier {
291 my ($self, $method_name, $method_modifier) = @_;
292 (defined $method_name && $method_name)
293 || confess "You must pass in a method name";
294 my $method = $fetch_and_prepare_method->($self, $method_name);
295 $method->add_before_modifier(subname ':before' => $method_modifier);
298 sub add_after_method_modifier {
299 my ($self, $method_name, $method_modifier) = @_;
300 (defined $method_name && $method_name)
301 || confess "You must pass in a method name";
302 my $method = $fetch_and_prepare_method->($self, $method_name);
303 $method->add_after_modifier(subname ':after' => $method_modifier);
306 sub add_around_method_modifier {
307 my ($self, $method_name, $method_modifier) = @_;
308 (defined $method_name && $method_name)
309 || confess "You must pass in a method name";
310 my $method = $fetch_and_prepare_method->($self, $method_name);
311 $method->add_around_modifier(subname ':around' => $method_modifier);
315 # the methods above used to be named like this:
316 # ${pkg}::${method}:(before|after|around)
317 # but this proved problematic when using one modifier
318 # to wrap multiple methods (something which is likely
319 # to happen pretty regularly IMO). So instead of naming
320 # it like this, I have chosen to just name them purely
321 # with their modifier names, like so:
322 # :(before|after|around)
323 # The fact is that in a stack trace, it will be fairly
324 # evident from the context what method they are attached
325 # to, and so don't need the fully qualified name.
329 my ($self, $method_name, $method) = @_;
330 (defined $method_name && $method_name)
331 || confess "You must define a method name";
332 # use reftype here to allow for blessed subs ...
333 ('CODE' eq (reftype($method) || ''))
334 || confess "Your code block must be a CODE reference";
335 my $full_method_name = ($self->name . '::' . $method_name);
337 $method = $self->method_metaclass->wrap($method) unless blessed($method);
340 no warnings 'redefine';
341 *{$full_method_name} = $method;
345 my ($self, $method_name) = @_;
346 (defined $method_name && $method_name)
347 || confess "You must define a method name";
349 my $sub_name = ($self->name . '::' . $method_name);
352 return 0 if !defined(&{$sub_name});
353 my $method = \&{$sub_name};
354 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
355 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
357 # at this point we are relatively sure
358 # it is our method, so we bless/wrap it
359 $self->method_metaclass->wrap($method) unless blessed($method);
364 my ($self, $method_name) = @_;
365 (defined $method_name && $method_name)
366 || confess "You must define a method name";
368 return unless $self->has_method($method_name);
371 return \&{$self->name . '::' . $method_name};
375 my ($self, $method_name) = @_;
376 (defined $method_name && $method_name)
377 || confess "You must define a method name";
379 my $removed_method = $self->get_method($method_name);
382 delete ${$self->name . '::'}{$method_name}
383 if defined $removed_method;
385 return $removed_method;
388 sub get_method_list {
391 grep { $self->has_method($_) } %{$self->name . '::'};
394 sub compute_all_applicable_methods {
397 # keep a record of what we have seen
398 # here, this will handle all the
399 # inheritence issues because we are
400 # using the &class_precedence_list
401 my (%seen_class, %seen_method);
402 foreach my $class ($self->class_precedence_list()) {
403 next if $seen_class{$class};
404 $seen_class{$class}++;
405 # fetch the meta-class ...
406 my $meta = $self->initialize($class);
407 foreach my $method_name ($meta->get_method_list()) {
408 next if exists $seen_method{$method_name};
409 $seen_method{$method_name}++;
411 name => $method_name,
413 code => $meta->get_method($method_name)
420 sub find_all_methods_by_name {
421 my ($self, $method_name) = @_;
422 (defined $method_name && $method_name)
423 || confess "You must define a method name to find";
425 # keep a record of what we have seen
426 # here, this will handle all the
427 # inheritence issues because we are
428 # using the &class_precedence_list
430 foreach my $class ($self->class_precedence_list()) {
431 next if $seen_class{$class};
432 $seen_class{$class}++;
433 # fetch the meta-class ...
434 my $meta = $self->initialize($class);
436 name => $method_name,
438 code => $meta->get_method($method_name)
439 } if $meta->has_method($method_name);
444 sub find_next_method_by_name {
445 my ($self, $method_name) = @_;
446 (defined $method_name && $method_name)
447 || confess "You must define a method name to find";
448 # keep a record of what we have seen
449 # here, this will handle all the
450 # inheritence issues because we are
451 # using the &class_precedence_list
453 my @cpl = $self->class_precedence_list();
454 shift @cpl; # discard ourselves
455 foreach my $class (@cpl) {
456 next if $seen_class{$class};
457 $seen_class{$class}++;
458 # fetch the meta-class ...
459 my $meta = $self->initialize($class);
460 return $meta->get_method($method_name)
461 if $meta->has_method($method_name);
470 # either we have an attribute object already
471 # or we need to create one from the args provided
472 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
473 # make sure it is derived from the correct type though
474 ($attribute->isa('Class::MOP::Attribute'))
475 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
476 $attribute->attach_to_class($self);
477 $attribute->install_accessors();
478 $self->get_attribute_map->{$attribute->name} = $attribute;
482 my ($self, $attribute_name) = @_;
483 (defined $attribute_name && $attribute_name)
484 || confess "You must define an attribute name";
485 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
489 my ($self, $attribute_name) = @_;
490 (defined $attribute_name && $attribute_name)
491 || confess "You must define an attribute name";
492 return $self->get_attribute_map->{$attribute_name}
493 if $self->has_attribute($attribute_name);
497 sub remove_attribute {
498 my ($self, $attribute_name) = @_;
499 (defined $attribute_name && $attribute_name)
500 || confess "You must define an attribute name";
501 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
502 return unless defined $removed_attribute;
503 delete $self->get_attribute_map->{$attribute_name};
504 $removed_attribute->remove_accessors();
505 $removed_attribute->detach_from_class();
506 return $removed_attribute;
509 sub get_attribute_list {
511 keys %{$self->get_attribute_map};
514 sub compute_all_applicable_attributes {
517 # keep a record of what we have seen
518 # here, this will handle all the
519 # inheritence issues because we are
520 # using the &class_precedence_list
521 my (%seen_class, %seen_attr);
522 foreach my $class ($self->class_precedence_list()) {
523 next if $seen_class{$class};
524 $seen_class{$class}++;
525 # fetch the meta-class ...
526 my $meta = $self->initialize($class);
527 foreach my $attr_name ($meta->get_attribute_list()) {
528 next if exists $seen_attr{$attr_name};
529 $seen_attr{$attr_name}++;
530 push @attrs => $meta->get_attribute($attr_name);
536 sub find_attribute_by_name {
537 my ($self, $attr_name) = @_;
538 # keep a record of what we have seen
539 # here, this will handle all the
540 # inheritence issues because we are
541 # using the &class_precedence_list
543 foreach my $class ($self->class_precedence_list()) {
544 next if $seen_class{$class};
545 $seen_class{$class}++;
546 # fetch the meta-class ...
547 my $meta = $self->initialize($class);
548 return $meta->get_attribute($attr_name)
549 if $meta->has_attribute($attr_name);
556 sub add_package_variable {
557 my ($self, $variable, $initial_value) = @_;
558 (defined $variable && $variable =~ /^[\$\@\%]/)
559 || confess "variable name does not have a sigil";
561 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
562 if (defined $initial_value) {
564 *{$self->name . '::' . $name} = $initial_value;
570 # We HAVE to localize $@ or all
571 # hell breaks loose. It is not
572 # good, believe me, not good.
574 eval $sigil . $self->name . '::' . $name;
577 confess "Could not create package variable ($variable) because : $e" if $e;
581 sub has_package_variable {
582 my ($self, $variable) = @_;
583 (defined $variable && $variable =~ /^[\$\@\%]/)
584 || confess "variable name does not have a sigil";
585 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
587 defined ${$self->name . '::'}{$name} ? 1 : 0;
590 sub get_package_variable {
591 my ($self, $variable) = @_;
592 (defined $variable && $variable =~ /^[\$\@\%]/)
593 || confess "variable name does not have a sigil";
594 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
598 # We HAVE to localize $@ or all
599 # hell breaks loose. It is not
600 # good, believe me, not good.
602 $ref = eval '\\' . $sigil . $self->name . '::' . $name;
605 confess "Could not get the package variable ($variable) because : $e" if $e;
606 # if we didn't die, then we can return it
610 sub remove_package_variable {
611 my ($self, $variable) = @_;
612 (defined $variable && $variable =~ /^[\$\@\%]/)
613 || confess "variable name does not have a sigil";
614 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
616 delete ${$self->name . '::'}{$name};
627 Class::MOP::Class - Class Meta Object
631 # assuming that class Foo
632 # has been defined, you can
634 # use this for introspection ...
636 # add a method to Foo ...
637 Foo->meta->add_method('bar' => sub { ... })
639 # get a list of all the classes searched
640 # the method dispatcher in the correct order
641 Foo->meta->class_precedence_list()
643 # remove a method from Foo
644 Foo->meta->remove_method('bar');
646 # or use this to actually create classes ...
648 Class::MOP::Class->create('Bar' => '0.01' => (
649 superclasses => [ 'Foo' ],
651 Class::MOP:::Attribute->new('$bar'),
652 Class::MOP:::Attribute->new('$baz'),
655 calculate_bar => sub { ... },
656 construct_baz => sub { ... }
662 This is the largest and currently most complex part of the Perl 5
663 meta-object protocol. It controls the introspection and
664 manipulation of Perl 5 classes (and it can create them too). The
665 best way to understand what this module can do, is to read the
666 documentation for each of it's methods.
670 =head2 Self Introspection
676 This will return a B<Class::MOP::Class> instance which is related
677 to this class. Thereby allowing B<Class::MOP::Class> to actually
680 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
681 bootstrap this module by installing a number of attribute meta-objects
682 into it's metaclass. This will allow this class to reap all the benifits
683 of the MOP when subclassing it.
685 =item B<get_all_metaclasses>
687 This will return an hash of all the metaclass instances that have
688 been cached by B<Class::MOP::Class> keyed by the package name.
690 =item B<get_all_metaclass_instances>
692 This will return an array of all the metaclass instances that have
693 been cached by B<Class::MOP::Class>.
695 =item B<get_all_metaclass_names>
697 This will return an array of all the metaclass names that have
698 been cached by B<Class::MOP::Class>.
702 =head2 Class construction
704 These methods will handle creating B<Class::MOP::Class> objects,
705 which can be used to both create new classes, and analyze
706 pre-existing classes.
708 This module will internally store references to all the instances
709 you create with these methods, so that they do not need to be
710 created any more than nessecary. Basically, they are singletons.
714 =item B<create ($package_name, ?$package_version,
715 superclasses =E<gt> ?@superclasses,
716 methods =E<gt> ?%methods,
717 attributes =E<gt> ?%attributes)>
719 This returns a B<Class::MOP::Class> object, bringing the specified
720 C<$package_name> into existence and adding any of the
721 C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
724 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
725 methods =E<gt> ?%methods,
726 attributes =E<gt> ?%attributes)>
728 This will create an anonymous class, it works much like C<create> but
729 it does not need a C<$package_name>. Instead it will create a suitably
730 unique package name for you to stash things into.
732 =item B<initialize ($package_name)>
734 This initializes and returns returns a B<Class::MOP::Class> object
735 for a given a C<$package_name>.
737 =item B<construct_class_instance (%options)>
739 This will construct an instance of B<Class::MOP::Class>, it is
740 here so that we can actually "tie the knot" for B<Class::MOP::Class>
741 to use C<construct_instance> once all the bootstrapping is done. This
742 method is used internally by C<initialize> and should never be called
743 from outside of that method really.
745 =item B<check_metaclass_compatability>
747 This method is called as the very last thing in the
748 C<construct_class_instance> method. This will check that the
749 metaclass you are creating is compatible with the metaclasses of all
750 your ancestors. For more inforamtion about metaclass compatibility
751 see the C<About Metaclass compatibility> section in L<Class::MOP>.
755 =head2 Object instance construction and cloning
757 These methods are B<entirely optional>, it is up to you whether you want
762 =item B<new_object (%params)>
764 This is a convience method for creating a new object of the class, and
765 blessing it into the appropriate package as well. Ideally your class
766 would call a C<new> this method like so:
769 my ($class, %param) = @_;
770 $class->meta->new_object(%params);
773 Of course the ideal place for this would actually be in C<UNIVERSAL::>
774 but that is considered bad style, so we do not do that.
776 =item B<construct_instance (%params)>
778 This method is used to construct an instace structure suitable for
779 C<bless>-ing into your package of choice. It works in conjunction
780 with the Attribute protocol to collect all applicable attributes.
782 This will construct and instance using a HASH ref as storage
783 (currently only HASH references are supported). This will collect all
784 the applicable attributes and layout out the fields in the HASH ref,
785 it will then initialize them using either use the corresponding key
786 in C<%params> or any default value or initializer found in the
787 attribute meta-object.
789 =item B<clone_object ($instance, %params)>
791 This is a convience method for cloning an object instance, then
792 blessing it into the appropriate package. This method will call
793 C<clone_instance>, which performs a shallow copy of the object,
794 see that methods documentation for more details. Ideally your
795 class would call a C<clone> this method like so:
798 my ($self, %param) = @_;
799 $self->meta->clone_object($self, %params);
802 Of course the ideal place for this would actually be in C<UNIVERSAL::>
803 but that is considered bad style, so we do not do that.
805 =item B<clone_instance($instance, %params)>
807 This method is a compliment of C<construct_instance> (which means if
808 you override C<construct_instance>, you need to override this one too),
809 and clones the instance shallowly.
811 The cloned structure returned is (like with C<construct_instance>) an
812 unC<bless>ed HASH reference, it is your responsibility to then bless
813 this cloned structure into the right class (which C<clone_object> will
816 As of 0.11, this method will clone the C<$instance> structure shallowly,
817 as opposed to the deep cloning implemented in prior versions. After much
818 thought, research and discussion, I have decided that anything but basic
819 shallow cloning is outside the scope of the meta-object protocol. I
820 think Yuval "nothingmuch" Kogman put it best when he said that cloning
821 is too I<context-specific> to be part of the MOP.
831 This is a read-only attribute which returns the package name for the
832 given B<Class::MOP::Class> instance.
836 This is a read-only attribute which returns the C<$VERSION> of the
837 package for the given B<Class::MOP::Class> instance.
841 =head2 Inheritance Relationships
845 =item B<superclasses (?@superclasses)>
847 This is a read-write attribute which represents the superclass
848 relationships of the class the B<Class::MOP::Class> instance is
849 associated with. Basically, it can get and set the C<@ISA> for you.
852 Perl will occasionally perform some C<@ISA> and method caching, if
853 you decide to change your superclass relationship at runtime (which
854 is quite insane and very much not recommened), then you should be
855 aware of this and the fact that this module does not make any
856 attempt to address this issue.
858 =item B<class_precedence_list>
860 This computes the a list of all the class's ancestors in the same order
861 in which method dispatch will be done. This is similair to
862 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
870 =item B<method_metaclass>
872 =item B<add_method ($method_name, $method)>
874 This will take a C<$method_name> and CODE reference to that
875 C<$method> and install it into the class's package.
878 This does absolutely nothing special to C<$method>
879 other than use B<Sub::Name> to make sure it is tagged with the
880 correct name, and therefore show up correctly in stack traces and
883 =item B<alias_method ($method_name, $method)>
885 This will take a C<$method_name> and CODE reference to that
886 C<$method> and alias the method into the class's package.
889 Unlike C<add_method>, this will B<not> try to name the
890 C<$method> using B<Sub::Name>, it only aliases the method in
893 =item B<has_method ($method_name)>
895 This just provides a simple way to check if the class implements
896 a specific C<$method_name>. It will I<not> however, attempt to check
897 if the class inherits the method (use C<UNIVERSAL::can> for that).
899 This will correctly handle functions defined outside of the package
900 that use a fully qualified name (C<sub Package::name { ... }>).
902 This will correctly handle functions renamed with B<Sub::Name> and
903 installed using the symbol tables. However, if you are naming the
904 subroutine outside of the package scope, you must use the fully
905 qualified name, including the package name, for C<has_method> to
906 correctly identify it.
908 This will attempt to correctly ignore functions imported from other
909 packages using B<Exporter>. It breaks down if the function imported
910 is an C<__ANON__> sub (such as with C<use constant>), which very well
911 may be a valid method being applied to the class.
913 In short, this method cannot always be trusted to determine if the
914 C<$method_name> is actually a method. However, it will DWIM about
915 90% of the time, so it's a small trade off I think.
917 =item B<get_method ($method_name)>
919 This will return a CODE reference of the specified C<$method_name>,
920 or return undef if that method does not exist.
922 =item B<remove_method ($method_name)>
924 This will attempt to remove a given C<$method_name> from the class.
925 It will return the CODE reference that it has removed, and will
926 attempt to use B<Sub::Name> to clear the methods associated name.
928 =item B<get_method_list>
930 This will return a list of method names for all I<locally> defined
931 methods. It does B<not> provide a list of all applicable methods,
932 including any inherited ones. If you want a list of all applicable
933 methods, use the C<compute_all_applicable_methods> method.
935 =item B<compute_all_applicable_methods>
937 This will return a list of all the methods names this class will
938 respond to, taking into account inheritance. The list will be a list of
939 HASH references, each one containing the following information; method
940 name, the name of the class in which the method lives and a CODE
941 reference for the actual method.
943 =item B<find_all_methods_by_name ($method_name)>
945 This will traverse the inheritence hierarchy and locate all methods
946 with a given C<$method_name>. Similar to
947 C<compute_all_applicable_methods> it returns a list of HASH references
948 with the following information; method name (which will always be the
949 same as C<$method_name>), the name of the class in which the method
950 lives and a CODE reference for the actual method.
952 The list of methods produced is a distinct list, meaning there are no
953 duplicates in it. This is especially useful for things like object
954 initialization and destruction where you only want the method called
955 once, and in the correct order.
957 =item B<find_next_method_by_name ($method_name)>
959 This will return the first method to match a given C<$method_name> in
960 the superclasses, this is basically equivalent to calling
961 C<SUPER::$method_name>, but it can be dispatched at runtime.
965 =head2 Method Modifiers
967 Method modifiers are a concept borrowed from CLOS, in which a method
968 can be wrapped with I<before>, I<after> and I<around> method modifiers
969 that will be called everytime the method is called.
971 =head3 How method modifiers work?
973 Method modifiers work by wrapping the original method and then replacing
974 it in the classes symbol table. The wrappers will handle calling all the
975 modifiers in the appropariate orders and preserving the calling context
976 for the original method.
978 Each method modifier serves a particular purpose, which may not be
979 obvious to users of other method wrapping modules. To start with, the
980 return values of I<before> and I<after> modifiers are ignored. This is
981 because thier purpose is B<not> to filter the input and output of the
982 primary method (this is done with an I<around> modifier). This may seem
983 like an odd restriction to some, but doing this allows for simple code
984 to be added at the begining or end of a method call without jeapordizing
985 the normal functioning of the primary method or placing any extra
986 responsibility on the code of the modifier. Of course if you have more
987 complex needs, then use the I<around> modifier, which uses a variation
988 of continutation passing style to allow for a high degree of flexibility.
990 Before and around modifiers are called in last-defined-first-called order,
991 while after modifiers are called in first-defined-first-called order. So
992 the call tree might looks something like this:
1002 To see examples of using method modifiers, see the following examples
1003 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1004 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1005 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1007 =head3 What is the performance impact?
1009 Of course there is a performance cost associated with method modifiers,
1010 but we have made every effort to make that cost be directly proportional
1011 to the amount of modifier features you utilize.
1013 The wrapping method does it's best to B<only> do as much work as it
1014 absolutely needs to. In order to do this we have moved some of the
1015 performance costs to set-up time, where they are easier to amortize.
1017 All this said, my benchmarks have indicated the following:
1019 simple wrapper with no modifiers 100% slower
1020 simple wrapper with simple before modifier 400% slower
1021 simple wrapper with simple after modifier 450% slower
1022 simple wrapper with simple around modifier 500-550% slower
1023 simple wrapper with all 3 modifiers 1100% slower
1025 These numbers may seem daunting, but you must remember, every feature
1026 comes with some cost. To put things in perspective, just doing a simple
1027 C<AUTOLOAD> which does nothing but extract the name of the method called
1028 and return it costs about 400% over a normal method call.
1032 =item B<add_before_method_modifier ($method_name, $code)>
1034 This will wrap the method at C<$method_name> and the supplied C<$code>
1035 will be passed the C<@_> arguments, and called before the original
1036 method is called. As specified above, the return value of the I<before>
1037 method modifiers is ignored, and it's ability to modify C<@_> is
1038 fairly limited. If you need to do either of these things, use an
1039 C<around> method modifier.
1041 =item B<add_after_method_modifier ($method_name, $code)>
1043 This will wrap the method at C<$method_name> so that the original
1044 method will be called, it's return values stashed, and then the
1045 supplied C<$code> will be passed the C<@_> arguments, and called.
1046 As specified above, the return value of the I<after> method
1047 modifiers is ignored, and it cannot modify the return values of
1048 the original method. If you need to do either of these things, use an
1049 C<around> method modifier.
1051 =item B<add_around_method_modifier ($method_name, $code)>
1053 This will wrap the method at C<$method_name> so that C<$code>
1054 will be called and passed the original method as an extra argument
1055 at the begining of the C<@_> argument list. This is a variation of
1056 continuation passing style, where the function prepended to C<@_>
1057 can be considered a continuation. It is up to C<$code> if it calls
1058 the original method or not, there is no restriction on what the
1059 C<$code> can or cannot do.
1065 It should be noted that since there is no one consistent way to define
1066 the attributes of a class in Perl 5. These methods can only work with
1067 the information given, and can not easily discover information on
1068 their own. See L<Class::MOP::Attribute> for more details.
1072 =item B<attribute_metaclass>
1074 =item B<get_attribute_map>
1076 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1078 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1079 instance associated with the given class, and associates it with
1080 the C<$attribute_name>. Unlike methods, attributes within the MOP
1081 are stored as meta-information only. They will be used later to
1082 construct instances from (see C<construct_instance> above).
1083 More details about the attribute meta-objects can be found in the
1084 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1087 It should be noted that any accessor, reader/writer or predicate
1088 methods which the C<$attribute_meta_object> has will be installed
1089 into the class at this time.
1091 =item B<has_attribute ($attribute_name)>
1093 Checks to see if this class has an attribute by the name of
1094 C<$attribute_name> and returns a boolean.
1096 =item B<get_attribute ($attribute_name)>
1098 Returns the attribute meta-object associated with C<$attribute_name>,
1099 if none is found, it will return undef.
1101 =item B<remove_attribute ($attribute_name)>
1103 This will remove the attribute meta-object stored at
1104 C<$attribute_name>, then return the removed attribute meta-object.
1107 Removing an attribute will only affect future instances of
1108 the class, it will not make any attempt to remove the attribute from
1109 any existing instances of the class.
1111 It should be noted that any accessor, reader/writer or predicate
1112 methods which the attribute meta-object stored at C<$attribute_name>
1113 has will be removed from the class at this time. This B<will> make
1114 these attributes somewhat inaccessable in previously created
1115 instances. But if you are crazy enough to do this at runtime, then
1116 you are crazy enough to deal with something like this :).
1118 =item B<get_attribute_list>
1120 This returns a list of attribute names which are defined in the local
1121 class. If you want a list of all applicable attributes for a class,
1122 use the C<compute_all_applicable_attributes> method.
1124 =item B<compute_all_applicable_attributes>
1126 This will traverse the inheritance heirachy and return a list of all
1127 the applicable attributes for this class. It does not construct a
1128 HASH reference like C<compute_all_applicable_methods> because all
1129 that same information is discoverable through the attribute
1132 =item B<find_attribute_by_name ($attr_name)>
1134 This method will traverse the inheritance heirachy and find the
1135 first attribute whose name matches C<$attr_name>, then return it.
1136 It will return undef if nothing is found.
1140 =head2 Package Variables
1142 Since Perl's classes are built atop the Perl package system, it is
1143 fairly common to use package scoped variables for things like static
1144 class variables. The following methods are convience methods for
1145 the creation and inspection of package scoped variables.
1149 =item B<add_package_variable ($variable_name, ?$initial_value)>
1151 Given a C<$variable_name>, which must contain a leading sigil, this
1152 method will create that variable within the package which houses the
1153 class. It also takes an optional C<$initial_value>, which must be a
1154 reference of the same type as the sigil of the C<$variable_name>
1157 =item B<get_package_variable ($variable_name)>
1159 This will return a reference to the package variable in
1162 =item B<has_package_variable ($variable_name)>
1164 Returns true (C<1>) if there is a package variable defined for
1165 C<$variable_name>, and false (C<0>) otherwise.
1167 =item B<remove_package_variable ($variable_name)>
1169 This will attempt to remove the package variable at C<$variable_name>.
1175 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1177 =head1 COPYRIGHT AND LICENSE
1179 Copyright 2006 by Infinity Interactive, Inc.
1181 L<http://www.iinteractive.com>
1183 This library is free software; you can redistribute it and/or modify
1184 it under the same terms as Perl itself.