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 { $self->name->isa('This is a test for circular inheritance') }
236 # ... and now back to our regularly scheduled program
241 # we grab the metaclass from the %METAS
242 # hash here to save the initialize() call
243 # if we can, but it is not always possible
244 ($METAS{$_} || $self->initialize($_))->class_precedence_list()
245 } $self->superclasses()
252 my ($self, $method_name, $method) = @_;
253 (defined $method_name && $method_name)
254 || confess "You must define a method name";
255 # use reftype here to allow for blessed subs ...
256 ('CODE' eq (reftype($method) || ''))
257 || confess "Your code block must be a CODE reference";
258 my $full_method_name = ($self->name . '::' . $method_name);
260 $method = $self->method_metaclass->wrap($method) unless blessed($method);
263 no warnings 'redefine';
264 *{$full_method_name} = subname $full_method_name => $method;
268 my $fetch_and_prepare_method = sub {
269 my ($self, $method_name) = @_;
271 my $method = $self->get_method($method_name);
272 # if we dont have local ...
274 # make sure this method even exists ...
275 ($self->find_next_method_by_name($method_name))
276 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
277 # if so, then create a local which just
278 # calls the next applicable method ...
279 $self->add_method($method_name => sub {
280 $self->find_next_method_by_name($method_name)->(@_);
282 $method = $self->get_method($method_name);
285 # now make sure we wrap it properly
286 # (if it isnt already)
287 unless ($method->isa('Class::MOP::Method::Wrapped')) {
288 $method = Class::MOP::Method::Wrapped->wrap($method);
289 $self->add_method($method_name => $method);
294 sub add_before_method_modifier {
295 my ($self, $method_name, $method_modifier) = @_;
296 (defined $method_name && $method_name)
297 || confess "You must pass in a method name";
298 my $method = $fetch_and_prepare_method->($self, $method_name);
299 $method->add_before_modifier(subname ':before' => $method_modifier);
302 sub add_after_method_modifier {
303 my ($self, $method_name, $method_modifier) = @_;
304 (defined $method_name && $method_name)
305 || confess "You must pass in a method name";
306 my $method = $fetch_and_prepare_method->($self, $method_name);
307 $method->add_after_modifier(subname ':after' => $method_modifier);
310 sub add_around_method_modifier {
311 my ($self, $method_name, $method_modifier) = @_;
312 (defined $method_name && $method_name)
313 || confess "You must pass in a method name";
314 my $method = $fetch_and_prepare_method->($self, $method_name);
315 $method->add_around_modifier(subname ':around' => $method_modifier);
319 # the methods above used to be named like this:
320 # ${pkg}::${method}:(before|after|around)
321 # but this proved problematic when using one modifier
322 # to wrap multiple methods (something which is likely
323 # to happen pretty regularly IMO). So instead of naming
324 # it like this, I have chosen to just name them purely
325 # with their modifier names, like so:
326 # :(before|after|around)
327 # The fact is that in a stack trace, it will be fairly
328 # evident from the context what method they are attached
329 # to, and so don't need the fully qualified name.
333 my ($self, $method_name, $method) = @_;
334 (defined $method_name && $method_name)
335 || confess "You must define a method name";
336 # use reftype here to allow for blessed subs ...
337 ('CODE' eq (reftype($method) || ''))
338 || confess "Your code block must be a CODE reference";
339 my $full_method_name = ($self->name . '::' . $method_name);
341 $method = $self->method_metaclass->wrap($method) unless blessed($method);
344 no warnings 'redefine';
345 *{$full_method_name} = $method;
349 my ($self, $method_name) = @_;
350 (defined $method_name && $method_name)
351 || confess "You must define a method name";
353 my $sub_name = ($self->name . '::' . $method_name);
356 return 0 if !defined(&{$sub_name});
357 my $method = \&{$sub_name};
358 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
359 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
361 # at this point we are relatively sure
362 # it is our method, so we bless/wrap it
363 $self->method_metaclass->wrap($method) unless blessed($method);
368 my ($self, $method_name) = @_;
369 (defined $method_name && $method_name)
370 || confess "You must define a method name";
372 return unless $self->has_method($method_name);
375 return \&{$self->name . '::' . $method_name};
379 my ($self, $method_name) = @_;
380 (defined $method_name && $method_name)
381 || confess "You must define a method name";
383 my $removed_method = $self->get_method($method_name);
386 delete ${$self->name . '::'}{$method_name}
387 if defined $removed_method;
389 return $removed_method;
392 sub get_method_list {
395 grep { $self->has_method($_) } %{$self->name . '::'};
398 sub compute_all_applicable_methods {
401 # keep a record of what we have seen
402 # here, this will handle all the
403 # inheritence issues because we are
404 # using the &class_precedence_list
405 my (%seen_class, %seen_method);
406 foreach my $class ($self->class_precedence_list()) {
407 next if $seen_class{$class};
408 $seen_class{$class}++;
409 # fetch the meta-class ...
410 my $meta = $self->initialize($class);
411 foreach my $method_name ($meta->get_method_list()) {
412 next if exists $seen_method{$method_name};
413 $seen_method{$method_name}++;
415 name => $method_name,
417 code => $meta->get_method($method_name)
424 sub find_all_methods_by_name {
425 my ($self, $method_name) = @_;
426 (defined $method_name && $method_name)
427 || confess "You must define a method name to find";
429 # keep a record of what we have seen
430 # here, this will handle all the
431 # inheritence issues because we are
432 # using the &class_precedence_list
434 foreach my $class ($self->class_precedence_list()) {
435 next if $seen_class{$class};
436 $seen_class{$class}++;
437 # fetch the meta-class ...
438 my $meta = $self->initialize($class);
440 name => $method_name,
442 code => $meta->get_method($method_name)
443 } if $meta->has_method($method_name);
448 sub find_next_method_by_name {
449 my ($self, $method_name) = @_;
450 (defined $method_name && $method_name)
451 || confess "You must define a method name to find";
452 # keep a record of what we have seen
453 # here, this will handle all the
454 # inheritence issues because we are
455 # using the &class_precedence_list
457 my @cpl = $self->class_precedence_list();
458 shift @cpl; # discard ourselves
459 foreach my $class (@cpl) {
460 next if $seen_class{$class};
461 $seen_class{$class}++;
462 # fetch the meta-class ...
463 my $meta = $self->initialize($class);
464 return $meta->get_method($method_name)
465 if $meta->has_method($method_name);
474 # either we have an attribute object already
475 # or we need to create one from the args provided
476 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
477 # make sure it is derived from the correct type though
478 ($attribute->isa('Class::MOP::Attribute'))
479 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
480 $attribute->attach_to_class($self);
481 $attribute->install_accessors();
482 $self->get_attribute_map->{$attribute->name} = $attribute;
486 my ($self, $attribute_name) = @_;
487 (defined $attribute_name && $attribute_name)
488 || confess "You must define an attribute name";
489 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
493 my ($self, $attribute_name) = @_;
494 (defined $attribute_name && $attribute_name)
495 || confess "You must define an attribute name";
497 # we used to say `if $self->has_attribute($attribute_name)`
498 # here, but since get_attribute is called so often, we
499 # eliminate the function call here
500 return $self->{'%:attributes'}->{$attribute_name}
501 if exists $self->{'%:attributes'}->{$attribute_name};
505 sub remove_attribute {
506 my ($self, $attribute_name) = @_;
507 (defined $attribute_name && $attribute_name)
508 || confess "You must define an attribute name";
509 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
510 return unless defined $removed_attribute;
511 delete $self->get_attribute_map->{$attribute_name};
512 $removed_attribute->remove_accessors();
513 $removed_attribute->detach_from_class();
514 return $removed_attribute;
517 sub get_attribute_list {
520 # We don't use get_attribute_map here because
521 # we ask for the attribute list quite often
522 # in compute_all_applicable_attributes, so
523 # eliminating the function call helps
524 keys %{$self->{'%:attributes'}};
527 sub compute_all_applicable_attributes {
530 # keep a record of what we have seen
531 # here, this will handle all the
532 # inheritence issues because we are
533 # using the &class_precedence_list
534 my (%seen_class, %seen_attr);
535 foreach my $class ($self->class_precedence_list()) {
536 next if $seen_class{$class};
537 $seen_class{$class}++;
538 # fetch the meta-class ...
540 # we grab the metaclass from the %METAS
541 # hash here to save the initialize() call
542 my $meta = $METAS{$class};
543 foreach my $attr_name ($meta->get_attribute_list()) {
544 next if exists $seen_attr{$attr_name};
545 $seen_attr{$attr_name}++;
546 push @attrs => $meta->get_attribute($attr_name);
552 sub find_attribute_by_name {
553 my ($self, $attr_name) = @_;
554 # keep a record of what we have seen
555 # here, this will handle all the
556 # inheritence issues because we are
557 # using the &class_precedence_list
559 foreach my $class ($self->class_precedence_list()) {
560 next if $seen_class{$class};
561 $seen_class{$class}++;
562 # fetch the meta-class ...
563 my $meta = $self->initialize($class);
564 return $meta->get_attribute($attr_name)
565 if $meta->has_attribute($attr_name);
572 sub add_package_variable {
573 my ($self, $variable, $initial_value) = @_;
574 (defined $variable && $variable =~ /^[\$\@\%]/)
575 || confess "variable name does not have a sigil";
577 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
578 if (defined $initial_value) {
580 *{$self->name . '::' . $name} = $initial_value;
586 # We HAVE to localize $@ or all
587 # hell breaks loose. It is not
588 # good, believe me, not good.
590 eval $sigil . $self->name . '::' . $name;
593 confess "Could not create package variable ($variable) because : $e" if $e;
597 sub has_package_variable {
598 my ($self, $variable) = @_;
599 (defined $variable && $variable =~ /^[\$\@\%]/)
600 || confess "variable name does not have a sigil";
601 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
603 defined ${$self->name . '::'}{$name} ? 1 : 0;
606 sub get_package_variable {
607 my ($self, $variable) = @_;
608 (defined $variable && $variable =~ /^[\$\@\%]/)
609 || confess "variable name does not have a sigil";
610 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
614 # We HAVE to localize $@ or all
615 # hell breaks loose. It is not
616 # good, believe me, not good.
618 $ref = eval '\\' . $sigil . $self->name . '::' . $name;
621 confess "Could not get the package variable ($variable) because : $e" if $e;
622 # if we didn't die, then we can return it
626 sub remove_package_variable {
627 my ($self, $variable) = @_;
628 (defined $variable && $variable =~ /^[\$\@\%]/)
629 || confess "variable name does not have a sigil";
630 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
632 delete ${$self->name . '::'}{$name};
643 Class::MOP::Class - Class Meta Object
647 # assuming that class Foo
648 # has been defined, you can
650 # use this for introspection ...
652 # add a method to Foo ...
653 Foo->meta->add_method('bar' => sub { ... })
655 # get a list of all the classes searched
656 # the method dispatcher in the correct order
657 Foo->meta->class_precedence_list()
659 # remove a method from Foo
660 Foo->meta->remove_method('bar');
662 # or use this to actually create classes ...
664 Class::MOP::Class->create('Bar' => '0.01' => (
665 superclasses => [ 'Foo' ],
667 Class::MOP:::Attribute->new('$bar'),
668 Class::MOP:::Attribute->new('$baz'),
671 calculate_bar => sub { ... },
672 construct_baz => sub { ... }
678 This is the largest and currently most complex part of the Perl 5
679 meta-object protocol. It controls the introspection and
680 manipulation of Perl 5 classes (and it can create them too). The
681 best way to understand what this module can do, is to read the
682 documentation for each of it's methods.
686 =head2 Self Introspection
692 This will return a B<Class::MOP::Class> instance which is related
693 to this class. Thereby allowing B<Class::MOP::Class> to actually
696 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
697 bootstrap this module by installing a number of attribute meta-objects
698 into it's metaclass. This will allow this class to reap all the benifits
699 of the MOP when subclassing it.
701 =item B<get_all_metaclasses>
703 This will return an hash of all the metaclass instances that have
704 been cached by B<Class::MOP::Class> keyed by the package name.
706 =item B<get_all_metaclass_instances>
708 This will return an array of all the metaclass instances that have
709 been cached by B<Class::MOP::Class>.
711 =item B<get_all_metaclass_names>
713 This will return an array of all the metaclass names that have
714 been cached by B<Class::MOP::Class>.
718 =head2 Class construction
720 These methods will handle creating B<Class::MOP::Class> objects,
721 which can be used to both create new classes, and analyze
722 pre-existing classes.
724 This module will internally store references to all the instances
725 you create with these methods, so that they do not need to be
726 created any more than nessecary. Basically, they are singletons.
730 =item B<create ($package_name, ?$package_version,
731 superclasses =E<gt> ?@superclasses,
732 methods =E<gt> ?%methods,
733 attributes =E<gt> ?%attributes)>
735 This returns a B<Class::MOP::Class> object, bringing the specified
736 C<$package_name> into existence and adding any of the
737 C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
740 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
741 methods =E<gt> ?%methods,
742 attributes =E<gt> ?%attributes)>
744 This will create an anonymous class, it works much like C<create> but
745 it does not need a C<$package_name>. Instead it will create a suitably
746 unique package name for you to stash things into.
748 =item B<initialize ($package_name)>
750 This initializes and returns returns a B<Class::MOP::Class> object
751 for a given a C<$package_name>.
753 =item B<construct_class_instance (%options)>
755 This will construct an instance of B<Class::MOP::Class>, it is
756 here so that we can actually "tie the knot" for B<Class::MOP::Class>
757 to use C<construct_instance> once all the bootstrapping is done. This
758 method is used internally by C<initialize> and should never be called
759 from outside of that method really.
761 =item B<check_metaclass_compatability>
763 This method is called as the very last thing in the
764 C<construct_class_instance> method. This will check that the
765 metaclass you are creating is compatible with the metaclasses of all
766 your ancestors. For more inforamtion about metaclass compatibility
767 see the C<About Metaclass compatibility> section in L<Class::MOP>.
771 =head2 Object instance construction and cloning
773 These methods are B<entirely optional>, it is up to you whether you want
778 =item B<new_object (%params)>
780 This is a convience method for creating a new object of the class, and
781 blessing it into the appropriate package as well. Ideally your class
782 would call a C<new> this method like so:
785 my ($class, %param) = @_;
786 $class->meta->new_object(%params);
789 Of course the ideal place for this would actually be in C<UNIVERSAL::>
790 but that is considered bad style, so we do not do that.
792 =item B<construct_instance (%params)>
794 This method is used to construct an instace structure suitable for
795 C<bless>-ing into your package of choice. It works in conjunction
796 with the Attribute protocol to collect all applicable attributes.
798 This will construct and instance using a HASH ref as storage
799 (currently only HASH references are supported). This will collect all
800 the applicable attributes and layout out the fields in the HASH ref,
801 it will then initialize them using either use the corresponding key
802 in C<%params> or any default value or initializer found in the
803 attribute meta-object.
805 =item B<clone_object ($instance, %params)>
807 This is a convience method for cloning an object instance, then
808 blessing it into the appropriate package. This method will call
809 C<clone_instance>, which performs a shallow copy of the object,
810 see that methods documentation for more details. Ideally your
811 class would call a C<clone> this method like so:
814 my ($self, %param) = @_;
815 $self->meta->clone_object($self, %params);
818 Of course the ideal place for this would actually be in C<UNIVERSAL::>
819 but that is considered bad style, so we do not do that.
821 =item B<clone_instance($instance, %params)>
823 This method is a compliment of C<construct_instance> (which means if
824 you override C<construct_instance>, you need to override this one too),
825 and clones the instance shallowly.
827 The cloned structure returned is (like with C<construct_instance>) an
828 unC<bless>ed HASH reference, it is your responsibility to then bless
829 this cloned structure into the right class (which C<clone_object> will
832 As of 0.11, this method will clone the C<$instance> structure shallowly,
833 as opposed to the deep cloning implemented in prior versions. After much
834 thought, research and discussion, I have decided that anything but basic
835 shallow cloning is outside the scope of the meta-object protocol. I
836 think Yuval "nothingmuch" Kogman put it best when he said that cloning
837 is too I<context-specific> to be part of the MOP.
847 This is a read-only attribute which returns the package name for the
848 given B<Class::MOP::Class> instance.
852 This is a read-only attribute which returns the C<$VERSION> of the
853 package for the given B<Class::MOP::Class> instance.
857 =head2 Inheritance Relationships
861 =item B<superclasses (?@superclasses)>
863 This is a read-write attribute which represents the superclass
864 relationships of the class the B<Class::MOP::Class> instance is
865 associated with. Basically, it can get and set the C<@ISA> for you.
868 Perl will occasionally perform some C<@ISA> and method caching, if
869 you decide to change your superclass relationship at runtime (which
870 is quite insane and very much not recommened), then you should be
871 aware of this and the fact that this module does not make any
872 attempt to address this issue.
874 =item B<class_precedence_list>
876 This computes the a list of all the class's ancestors in the same order
877 in which method dispatch will be done. This is similair to
878 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
886 =item B<method_metaclass>
888 =item B<add_method ($method_name, $method)>
890 This will take a C<$method_name> and CODE reference to that
891 C<$method> and install it into the class's package.
894 This does absolutely nothing special to C<$method>
895 other than use B<Sub::Name> to make sure it is tagged with the
896 correct name, and therefore show up correctly in stack traces and
899 =item B<alias_method ($method_name, $method)>
901 This will take a C<$method_name> and CODE reference to that
902 C<$method> and alias the method into the class's package.
905 Unlike C<add_method>, this will B<not> try to name the
906 C<$method> using B<Sub::Name>, it only aliases the method in
909 =item B<has_method ($method_name)>
911 This just provides a simple way to check if the class implements
912 a specific C<$method_name>. It will I<not> however, attempt to check
913 if the class inherits the method (use C<UNIVERSAL::can> for that).
915 This will correctly handle functions defined outside of the package
916 that use a fully qualified name (C<sub Package::name { ... }>).
918 This will correctly handle functions renamed with B<Sub::Name> and
919 installed using the symbol tables. However, if you are naming the
920 subroutine outside of the package scope, you must use the fully
921 qualified name, including the package name, for C<has_method> to
922 correctly identify it.
924 This will attempt to correctly ignore functions imported from other
925 packages using B<Exporter>. It breaks down if the function imported
926 is an C<__ANON__> sub (such as with C<use constant>), which very well
927 may be a valid method being applied to the class.
929 In short, this method cannot always be trusted to determine if the
930 C<$method_name> is actually a method. However, it will DWIM about
931 90% of the time, so it's a small trade off I think.
933 =item B<get_method ($method_name)>
935 This will return a CODE reference of the specified C<$method_name>,
936 or return undef if that method does not exist.
938 =item B<remove_method ($method_name)>
940 This will attempt to remove a given C<$method_name> from the class.
941 It will return the CODE reference that it has removed, and will
942 attempt to use B<Sub::Name> to clear the methods associated name.
944 =item B<get_method_list>
946 This will return a list of method names for all I<locally> defined
947 methods. It does B<not> provide a list of all applicable methods,
948 including any inherited ones. If you want a list of all applicable
949 methods, use the C<compute_all_applicable_methods> method.
951 =item B<compute_all_applicable_methods>
953 This will return a list of all the methods names this class will
954 respond to, taking into account inheritance. The list will be a list of
955 HASH references, each one containing the following information; method
956 name, the name of the class in which the method lives and a CODE
957 reference for the actual method.
959 =item B<find_all_methods_by_name ($method_name)>
961 This will traverse the inheritence hierarchy and locate all methods
962 with a given C<$method_name>. Similar to
963 C<compute_all_applicable_methods> it returns a list of HASH references
964 with the following information; method name (which will always be the
965 same as C<$method_name>), the name of the class in which the method
966 lives and a CODE reference for the actual method.
968 The list of methods produced is a distinct list, meaning there are no
969 duplicates in it. This is especially useful for things like object
970 initialization and destruction where you only want the method called
971 once, and in the correct order.
973 =item B<find_next_method_by_name ($method_name)>
975 This will return the first method to match a given C<$method_name> in
976 the superclasses, this is basically equivalent to calling
977 C<SUPER::$method_name>, but it can be dispatched at runtime.
981 =head2 Method Modifiers
983 Method modifiers are a concept borrowed from CLOS, in which a method
984 can be wrapped with I<before>, I<after> and I<around> method modifiers
985 that will be called everytime the method is called.
987 =head3 How method modifiers work?
989 Method modifiers work by wrapping the original method and then replacing
990 it in the classes symbol table. The wrappers will handle calling all the
991 modifiers in the appropariate orders and preserving the calling context
992 for the original method.
994 Each method modifier serves a particular purpose, which may not be
995 obvious to users of other method wrapping modules. To start with, the
996 return values of I<before> and I<after> modifiers are ignored. This is
997 because thier purpose is B<not> to filter the input and output of the
998 primary method (this is done with an I<around> modifier). This may seem
999 like an odd restriction to some, but doing this allows for simple code
1000 to be added at the begining or end of a method call without jeapordizing
1001 the normal functioning of the primary method or placing any extra
1002 responsibility on the code of the modifier. Of course if you have more
1003 complex needs, then use the I<around> modifier, which uses a variation
1004 of continutation passing style to allow for a high degree of flexibility.
1006 Before and around modifiers are called in last-defined-first-called order,
1007 while after modifiers are called in first-defined-first-called order. So
1008 the call tree might looks something like this:
1018 To see examples of using method modifiers, see the following examples
1019 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1020 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1021 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1023 =head3 What is the performance impact?
1025 Of course there is a performance cost associated with method modifiers,
1026 but we have made every effort to make that cost be directly proportional
1027 to the amount of modifier features you utilize.
1029 The wrapping method does it's best to B<only> do as much work as it
1030 absolutely needs to. In order to do this we have moved some of the
1031 performance costs to set-up time, where they are easier to amortize.
1033 All this said, my benchmarks have indicated the following:
1035 simple wrapper with no modifiers 100% slower
1036 simple wrapper with simple before modifier 400% slower
1037 simple wrapper with simple after modifier 450% slower
1038 simple wrapper with simple around modifier 500-550% slower
1039 simple wrapper with all 3 modifiers 1100% slower
1041 These numbers may seem daunting, but you must remember, every feature
1042 comes with some cost. To put things in perspective, just doing a simple
1043 C<AUTOLOAD> which does nothing but extract the name of the method called
1044 and return it costs about 400% over a normal method call.
1048 =item B<add_before_method_modifier ($method_name, $code)>
1050 This will wrap the method at C<$method_name> and the supplied C<$code>
1051 will be passed the C<@_> arguments, and called before the original
1052 method is called. As specified above, the return value of the I<before>
1053 method modifiers is ignored, and it's ability to modify C<@_> is
1054 fairly limited. If you need to do either of these things, use an
1055 C<around> method modifier.
1057 =item B<add_after_method_modifier ($method_name, $code)>
1059 This will wrap the method at C<$method_name> so that the original
1060 method will be called, it's return values stashed, and then the
1061 supplied C<$code> will be passed the C<@_> arguments, and called.
1062 As specified above, the return value of the I<after> method
1063 modifiers is ignored, and it cannot modify the return values of
1064 the original method. If you need to do either of these things, use an
1065 C<around> method modifier.
1067 =item B<add_around_method_modifier ($method_name, $code)>
1069 This will wrap the method at C<$method_name> so that C<$code>
1070 will be called and passed the original method as an extra argument
1071 at the begining of the C<@_> argument list. This is a variation of
1072 continuation passing style, where the function prepended to C<@_>
1073 can be considered a continuation. It is up to C<$code> if it calls
1074 the original method or not, there is no restriction on what the
1075 C<$code> can or cannot do.
1081 It should be noted that since there is no one consistent way to define
1082 the attributes of a class in Perl 5. These methods can only work with
1083 the information given, and can not easily discover information on
1084 their own. See L<Class::MOP::Attribute> for more details.
1088 =item B<attribute_metaclass>
1090 =item B<get_attribute_map>
1092 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1094 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1095 instance associated with the given class, and associates it with
1096 the C<$attribute_name>. Unlike methods, attributes within the MOP
1097 are stored as meta-information only. They will be used later to
1098 construct instances from (see C<construct_instance> above).
1099 More details about the attribute meta-objects can be found in the
1100 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1103 It should be noted that any accessor, reader/writer or predicate
1104 methods which the C<$attribute_meta_object> has will be installed
1105 into the class at this time.
1107 =item B<has_attribute ($attribute_name)>
1109 Checks to see if this class has an attribute by the name of
1110 C<$attribute_name> and returns a boolean.
1112 =item B<get_attribute ($attribute_name)>
1114 Returns the attribute meta-object associated with C<$attribute_name>,
1115 if none is found, it will return undef.
1117 =item B<remove_attribute ($attribute_name)>
1119 This will remove the attribute meta-object stored at
1120 C<$attribute_name>, then return the removed attribute meta-object.
1123 Removing an attribute will only affect future instances of
1124 the class, it will not make any attempt to remove the attribute from
1125 any existing instances of the class.
1127 It should be noted that any accessor, reader/writer or predicate
1128 methods which the attribute meta-object stored at C<$attribute_name>
1129 has will be removed from the class at this time. This B<will> make
1130 these attributes somewhat inaccessable in previously created
1131 instances. But if you are crazy enough to do this at runtime, then
1132 you are crazy enough to deal with something like this :).
1134 =item B<get_attribute_list>
1136 This returns a list of attribute names which are defined in the local
1137 class. If you want a list of all applicable attributes for a class,
1138 use the C<compute_all_applicable_attributes> method.
1140 =item B<compute_all_applicable_attributes>
1142 This will traverse the inheritance heirachy and return a list of all
1143 the applicable attributes for this class. It does not construct a
1144 HASH reference like C<compute_all_applicable_methods> because all
1145 that same information is discoverable through the attribute
1148 =item B<find_attribute_by_name ($attr_name)>
1150 This method will traverse the inheritance heirachy and find the
1151 first attribute whose name matches C<$attr_name>, then return it.
1152 It will return undef if nothing is found.
1156 =head2 Package Variables
1158 Since Perl's classes are built atop the Perl package system, it is
1159 fairly common to use package scoped variables for things like static
1160 class variables. The following methods are convience methods for
1161 the creation and inspection of package scoped variables.
1165 =item B<add_package_variable ($variable_name, ?$initial_value)>
1167 Given a C<$variable_name>, which must contain a leading sigil, this
1168 method will create that variable within the package which houses the
1169 class. It also takes an optional C<$initial_value>, which must be a
1170 reference of the same type as the sigil of the C<$variable_name>
1173 =item B<get_package_variable ($variable_name)>
1175 This will return a reference to the package variable in
1178 =item B<has_package_variable ($variable_name)>
1180 Returns true (C<1>) if there is a package variable defined for
1181 C<$variable_name>, and false (C<0>) otherwise.
1183 =item B<remove_package_variable ($variable_name)>
1185 This will attempt to remove the package variable at C<$variable_name>.
1191 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1193 =head1 COPYRIGHT AND LICENSE
1195 Copyright 2006 by Infinity Interactive, Inc.
1197 L<http://www.iinteractive.com>
1199 This library is free software; you can redistribute it and/or modify
1200 it under the same terms as Perl itself.