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('$VERSION')};
222 @{$self->get_package_variable('@ISA')} = @supers;
224 @{$self->get_package_variable('@ISA')};
227 sub class_precedence_list {
230 # We need to check for ciruclar inheirtance here.
231 # This will do nothing if all is well, and blow
232 # up otherwise. Yes, it's an ugly hack, better
233 # suggestions are welcome.
234 { $self->name->isa('This is a test for circular inheritance') }
235 # ... and now back to our regularly scheduled program
239 $self->initialize($_)->class_precedence_list()
240 } $self->superclasses()
247 my ($self, $method_name, $method) = @_;
248 (defined $method_name && $method_name)
249 || confess "You must define a method name";
250 # use reftype here to allow for blessed subs ...
251 ('CODE' eq (reftype($method) || ''))
252 || confess "Your code block must be a CODE reference";
253 my $full_method_name = ($self->name . '::' . $method_name);
255 $method = $self->method_metaclass->wrap($method) unless blessed($method);
258 no warnings 'redefine';
259 *{$full_method_name} = subname $full_method_name => $method;
263 my $fetch_and_prepare_method = sub {
264 my ($self, $method_name) = @_;
266 my $method = $self->get_method($method_name);
267 # if we dont have local ...
269 # make sure this method even exists ...
270 ($self->find_next_method_by_name($method_name))
271 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
272 # if so, then create a local which just
273 # calls the next applicable method ...
274 $self->add_method($method_name => sub {
275 $self->find_next_method_by_name($method_name)->(@_);
277 $method = $self->get_method($method_name);
280 # now make sure we wrap it properly
281 # (if it isnt already)
282 unless ($method->isa('Class::MOP::Method::Wrapped')) {
283 $method = Class::MOP::Method::Wrapped->wrap($method);
284 $self->add_method($method_name => $method);
289 sub add_before_method_modifier {
290 my ($self, $method_name, $method_modifier) = @_;
291 (defined $method_name && $method_name)
292 || confess "You must pass in a method name";
293 my $method = $fetch_and_prepare_method->($self, $method_name);
294 $method->add_before_modifier(subname ':before' => $method_modifier);
297 sub add_after_method_modifier {
298 my ($self, $method_name, $method_modifier) = @_;
299 (defined $method_name && $method_name)
300 || confess "You must pass in a method name";
301 my $method = $fetch_and_prepare_method->($self, $method_name);
302 $method->add_after_modifier(subname ':after' => $method_modifier);
305 sub add_around_method_modifier {
306 my ($self, $method_name, $method_modifier) = @_;
307 (defined $method_name && $method_name)
308 || confess "You must pass in a method name";
309 my $method = $fetch_and_prepare_method->($self, $method_name);
310 $method->add_around_modifier(subname ':around' => $method_modifier);
314 # the methods above used to be named like this:
315 # ${pkg}::${method}:(before|after|around)
316 # but this proved problematic when using one modifier
317 # to wrap multiple methods (something which is likely
318 # to happen pretty regularly IMO). So instead of naming
319 # it like this, I have chosen to just name them purely
320 # with their modifier names, like so:
321 # :(before|after|around)
322 # The fact is that in a stack trace, it will be fairly
323 # evident from the context what method they are attached
324 # to, and so don't need the fully qualified name.
328 my ($self, $method_name, $method) = @_;
329 (defined $method_name && $method_name)
330 || confess "You must define a method name";
331 # use reftype here to allow for blessed subs ...
332 ('CODE' eq (reftype($method) || ''))
333 || confess "Your code block must be a CODE reference";
334 my $full_method_name = ($self->name . '::' . $method_name);
336 $method = $self->method_metaclass->wrap($method) unless blessed($method);
339 no warnings 'redefine';
340 *{$full_method_name} = $method;
344 my ($self, $method_name) = @_;
345 (defined $method_name && $method_name)
346 || confess "You must define a method name";
348 my $sub_name = ($self->name . '::' . $method_name);
351 return 0 if !defined(&{$sub_name});
352 my $method = \&{$sub_name};
353 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
354 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
356 # at this point we are relatively sure
357 # it is our method, so we bless/wrap it
358 $self->method_metaclass->wrap($method) unless blessed($method);
363 my ($self, $method_name) = @_;
364 (defined $method_name && $method_name)
365 || confess "You must define a method name";
367 return unless $self->has_method($method_name);
370 return \&{$self->name . '::' . $method_name};
374 my ($self, $method_name) = @_;
375 (defined $method_name && $method_name)
376 || confess "You must define a method name";
378 my $removed_method = $self->get_method($method_name);
381 delete ${$self->name . '::'}{$method_name}
382 if defined $removed_method;
384 return $removed_method;
387 sub get_method_list {
390 grep { $self->has_method($_) } %{$self->name . '::'};
393 sub compute_all_applicable_methods {
396 # keep a record of what we have seen
397 # here, this will handle all the
398 # inheritence issues because we are
399 # using the &class_precedence_list
400 my (%seen_class, %seen_method);
401 foreach my $class ($self->class_precedence_list()) {
402 next if $seen_class{$class};
403 $seen_class{$class}++;
404 # fetch the meta-class ...
405 my $meta = $self->initialize($class);
406 foreach my $method_name ($meta->get_method_list()) {
407 next if exists $seen_method{$method_name};
408 $seen_method{$method_name}++;
410 name => $method_name,
412 code => $meta->get_method($method_name)
419 sub find_all_methods_by_name {
420 my ($self, $method_name) = @_;
421 (defined $method_name && $method_name)
422 || confess "You must define a method name to find";
424 # keep a record of what we have seen
425 # here, this will handle all the
426 # inheritence issues because we are
427 # using the &class_precedence_list
429 foreach my $class ($self->class_precedence_list()) {
430 next if $seen_class{$class};
431 $seen_class{$class}++;
432 # fetch the meta-class ...
433 my $meta = $self->initialize($class);
435 name => $method_name,
437 code => $meta->get_method($method_name)
438 } if $meta->has_method($method_name);
443 sub find_next_method_by_name {
444 my ($self, $method_name) = @_;
445 (defined $method_name && $method_name)
446 || confess "You must define a method name to find";
447 # keep a record of what we have seen
448 # here, this will handle all the
449 # inheritence issues because we are
450 # using the &class_precedence_list
452 my @cpl = $self->class_precedence_list();
453 shift @cpl; # discard ourselves
454 foreach my $class (@cpl) {
455 next if $seen_class{$class};
456 $seen_class{$class}++;
457 # fetch the meta-class ...
458 my $meta = $self->initialize($class);
459 return $meta->get_method($method_name)
460 if $meta->has_method($method_name);
469 # either we have an attribute object already
470 # or we need to create one from the args provided
471 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
472 # make sure it is derived from the correct type though
473 ($attribute->isa('Class::MOP::Attribute'))
474 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
475 $attribute->attach_to_class($self);
476 $attribute->install_accessors();
477 $self->get_attribute_map->{$attribute->name} = $attribute;
481 my ($self, $attribute_name) = @_;
482 (defined $attribute_name && $attribute_name)
483 || confess "You must define an attribute name";
484 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
488 my ($self, $attribute_name) = @_;
489 (defined $attribute_name && $attribute_name)
490 || confess "You must define an attribute name";
491 return $self->get_attribute_map->{$attribute_name}
492 if $self->has_attribute($attribute_name);
496 sub remove_attribute {
497 my ($self, $attribute_name) = @_;
498 (defined $attribute_name && $attribute_name)
499 || confess "You must define an attribute name";
500 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
501 return unless defined $removed_attribute;
502 delete $self->get_attribute_map->{$attribute_name};
503 $removed_attribute->remove_accessors();
504 $removed_attribute->detach_from_class();
505 return $removed_attribute;
508 sub get_attribute_list {
510 keys %{$self->get_attribute_map};
513 sub compute_all_applicable_attributes {
516 # keep a record of what we have seen
517 # here, this will handle all the
518 # inheritence issues because we are
519 # using the &class_precedence_list
520 my (%seen_class, %seen_attr);
521 foreach my $class ($self->class_precedence_list()) {
522 next if $seen_class{$class};
523 $seen_class{$class}++;
524 # fetch the meta-class ...
525 my $meta = $self->initialize($class);
526 foreach my $attr_name ($meta->get_attribute_list()) {
527 next if exists $seen_attr{$attr_name};
528 $seen_attr{$attr_name}++;
529 push @attrs => $meta->get_attribute($attr_name);
535 sub find_attribute_by_name {
536 my ($self, $attr_name) = @_;
537 # keep a record of what we have seen
538 # here, this will handle all the
539 # inheritence issues because we are
540 # using the &class_precedence_list
542 foreach my $class ($self->class_precedence_list()) {
543 next if $seen_class{$class};
544 $seen_class{$class}++;
545 # fetch the meta-class ...
546 my $meta = $self->initialize($class);
547 return $meta->get_attribute($attr_name)
548 if $meta->has_attribute($attr_name);
555 sub add_package_variable {
556 my ($self, $variable, $initial_value) = @_;
557 (defined $variable && $variable =~ /^[\$\@\%]/)
558 || confess "variable name does not have a sigil";
560 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
561 if (defined $initial_value) {
563 *{$self->name . '::' . $name} = $initial_value;
569 # We HAVE to localize $@ or all
570 # hell breaks loose. It is not
571 # good, believe me, not good.
573 eval $sigil . $self->name . '::' . $name;
576 confess "Could not create package variable ($variable) because : $e" if $e;
580 sub has_package_variable {
581 my ($self, $variable) = @_;
582 (defined $variable && $variable =~ /^[\$\@\%]/)
583 || confess "variable name does not have a sigil";
584 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
586 defined ${$self->name . '::'}{$name} ? 1 : 0;
589 sub get_package_variable {
590 my ($self, $variable) = @_;
591 (defined $variable && $variable =~ /^[\$\@\%]/)
592 || confess "variable name does not have a sigil";
593 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
597 # We HAVE to localize $@ or all
598 # hell breaks loose. It is not
599 # good, believe me, not good.
601 $ref = eval '\\' . $sigil . $self->name . '::' . $name;
604 confess "Could not get the package variable ($variable) because : $e" if $e;
605 # if we didn't die, then we can return it
609 sub remove_package_variable {
610 my ($self, $variable) = @_;
611 (defined $variable && $variable =~ /^[\$\@\%]/)
612 || confess "variable name does not have a sigil";
613 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
615 delete ${$self->name . '::'}{$name};
626 Class::MOP::Class - Class Meta Object
630 # assuming that class Foo
631 # has been defined, you can
633 # use this for introspection ...
635 # add a method to Foo ...
636 Foo->meta->add_method('bar' => sub { ... })
638 # get a list of all the classes searched
639 # the method dispatcher in the correct order
640 Foo->meta->class_precedence_list()
642 # remove a method from Foo
643 Foo->meta->remove_method('bar');
645 # or use this to actually create classes ...
647 Class::MOP::Class->create('Bar' => '0.01' => (
648 superclasses => [ 'Foo' ],
650 Class::MOP:::Attribute->new('$bar'),
651 Class::MOP:::Attribute->new('$baz'),
654 calculate_bar => sub { ... },
655 construct_baz => sub { ... }
661 This is the largest and currently most complex part of the Perl 5
662 meta-object protocol. It controls the introspection and
663 manipulation of Perl 5 classes (and it can create them too). The
664 best way to understand what this module can do, is to read the
665 documentation for each of it's methods.
669 =head2 Self Introspection
675 This will return a B<Class::MOP::Class> instance which is related
676 to this class. Thereby allowing B<Class::MOP::Class> to actually
679 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
680 bootstrap this module by installing a number of attribute meta-objects
681 into it's metaclass. This will allow this class to reap all the benifits
682 of the MOP when subclassing it.
684 =item B<get_all_metaclasses>
686 This will return an hash of all the metaclass instances that have
687 been cached by B<Class::MOP::Class> keyed by the package name.
689 =item B<get_all_metaclass_instances>
691 This will return an array of all the metaclass instances that have
692 been cached by B<Class::MOP::Class>.
694 =item B<get_all_metaclass_names>
696 This will return an array of all the metaclass names that have
697 been cached by B<Class::MOP::Class>.
701 =head2 Class construction
703 These methods will handle creating B<Class::MOP::Class> objects,
704 which can be used to both create new classes, and analyze
705 pre-existing classes.
707 This module will internally store references to all the instances
708 you create with these methods, so that they do not need to be
709 created any more than nessecary. Basically, they are singletons.
713 =item B<create ($package_name, ?$package_version,
714 superclasses =E<gt> ?@superclasses,
715 methods =E<gt> ?%methods,
716 attributes =E<gt> ?%attributes)>
718 This returns a B<Class::MOP::Class> object, bringing the specified
719 C<$package_name> into existence and adding any of the
720 C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
723 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
724 methods =E<gt> ?%methods,
725 attributes =E<gt> ?%attributes)>
727 This will create an anonymous class, it works much like C<create> but
728 it does not need a C<$package_name>. Instead it will create a suitably
729 unique package name for you to stash things into.
731 =item B<initialize ($package_name)>
733 This initializes and returns returns a B<Class::MOP::Class> object
734 for a given a C<$package_name>.
736 =item B<construct_class_instance (%options)>
738 This will construct an instance of B<Class::MOP::Class>, it is
739 here so that we can actually "tie the knot" for B<Class::MOP::Class>
740 to use C<construct_instance> once all the bootstrapping is done. This
741 method is used internally by C<initialize> and should never be called
742 from outside of that method really.
744 =item B<check_metaclass_compatability>
746 This method is called as the very last thing in the
747 C<construct_class_instance> method. This will check that the
748 metaclass you are creating is compatible with the metaclasses of all
749 your ancestors. For more inforamtion about metaclass compatibility
750 see the C<About Metaclass compatibility> section in L<Class::MOP>.
754 =head2 Object instance construction and cloning
756 These methods are B<entirely optional>, it is up to you whether you want
761 =item B<new_object (%params)>
763 This is a convience method for creating a new object of the class, and
764 blessing it into the appropriate package as well. Ideally your class
765 would call a C<new> this method like so:
768 my ($class, %param) = @_;
769 $class->meta->new_object(%params);
772 Of course the ideal place for this would actually be in C<UNIVERSAL::>
773 but that is considered bad style, so we do not do that.
775 =item B<construct_instance (%params)>
777 This method is used to construct an instace structure suitable for
778 C<bless>-ing into your package of choice. It works in conjunction
779 with the Attribute protocol to collect all applicable attributes.
781 This will construct and instance using a HASH ref as storage
782 (currently only HASH references are supported). This will collect all
783 the applicable attributes and layout out the fields in the HASH ref,
784 it will then initialize them using either use the corresponding key
785 in C<%params> or any default value or initializer found in the
786 attribute meta-object.
788 =item B<clone_object ($instance, %params)>
790 This is a convience method for cloning an object instance, then
791 blessing it into the appropriate package. This method will call
792 C<clone_instance>, which performs a shallow copy of the object,
793 see that methods documentation for more details. Ideally your
794 class would call a C<clone> this method like so:
797 my ($self, %param) = @_;
798 $self->meta->clone_object($self, %params);
801 Of course the ideal place for this would actually be in C<UNIVERSAL::>
802 but that is considered bad style, so we do not do that.
804 =item B<clone_instance($instance, %params)>
806 This method is a compliment of C<construct_instance> (which means if
807 you override C<construct_instance>, you need to override this one too),
808 and clones the instance shallowly.
810 The cloned structure returned is (like with C<construct_instance>) an
811 unC<bless>ed HASH reference, it is your responsibility to then bless
812 this cloned structure into the right class (which C<clone_object> will
815 As of 0.11, this method will clone the C<$instance> structure shallowly,
816 as opposed to the deep cloning implemented in prior versions. After much
817 thought, research and discussion, I have decided that anything but basic
818 shallow cloning is outside the scope of the meta-object protocol. I
819 think Yuval "nothingmuch" Kogman put it best when he said that cloning
820 is too I<context-specific> to be part of the MOP.
830 This is a read-only attribute which returns the package name for the
831 given B<Class::MOP::Class> instance.
835 This is a read-only attribute which returns the C<$VERSION> of the
836 package for the given B<Class::MOP::Class> instance.
840 =head2 Inheritance Relationships
844 =item B<superclasses (?@superclasses)>
846 This is a read-write attribute which represents the superclass
847 relationships of the class the B<Class::MOP::Class> instance is
848 associated with. Basically, it can get and set the C<@ISA> for you.
851 Perl will occasionally perform some C<@ISA> and method caching, if
852 you decide to change your superclass relationship at runtime (which
853 is quite insane and very much not recommened), then you should be
854 aware of this and the fact that this module does not make any
855 attempt to address this issue.
857 =item B<class_precedence_list>
859 This computes the a list of all the class's ancestors in the same order
860 in which method dispatch will be done. This is similair to
861 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
869 =item B<method_metaclass>
871 =item B<add_method ($method_name, $method)>
873 This will take a C<$method_name> and CODE reference to that
874 C<$method> and install it into the class's package.
877 This does absolutely nothing special to C<$method>
878 other than use B<Sub::Name> to make sure it is tagged with the
879 correct name, and therefore show up correctly in stack traces and
882 =item B<alias_method ($method_name, $method)>
884 This will take a C<$method_name> and CODE reference to that
885 C<$method> and alias the method into the class's package.
888 Unlike C<add_method>, this will B<not> try to name the
889 C<$method> using B<Sub::Name>, it only aliases the method in
892 =item B<has_method ($method_name)>
894 This just provides a simple way to check if the class implements
895 a specific C<$method_name>. It will I<not> however, attempt to check
896 if the class inherits the method (use C<UNIVERSAL::can> for that).
898 This will correctly handle functions defined outside of the package
899 that use a fully qualified name (C<sub Package::name { ... }>).
901 This will correctly handle functions renamed with B<Sub::Name> and
902 installed using the symbol tables. However, if you are naming the
903 subroutine outside of the package scope, you must use the fully
904 qualified name, including the package name, for C<has_method> to
905 correctly identify it.
907 This will attempt to correctly ignore functions imported from other
908 packages using B<Exporter>. It breaks down if the function imported
909 is an C<__ANON__> sub (such as with C<use constant>), which very well
910 may be a valid method being applied to the class.
912 In short, this method cannot always be trusted to determine if the
913 C<$method_name> is actually a method. However, it will DWIM about
914 90% of the time, so it's a small trade off I think.
916 =item B<get_method ($method_name)>
918 This will return a CODE reference of the specified C<$method_name>,
919 or return undef if that method does not exist.
921 =item B<remove_method ($method_name)>
923 This will attempt to remove a given C<$method_name> from the class.
924 It will return the CODE reference that it has removed, and will
925 attempt to use B<Sub::Name> to clear the methods associated name.
927 =item B<get_method_list>
929 This will return a list of method names for all I<locally> defined
930 methods. It does B<not> provide a list of all applicable methods,
931 including any inherited ones. If you want a list of all applicable
932 methods, use the C<compute_all_applicable_methods> method.
934 =item B<compute_all_applicable_methods>
936 This will return a list of all the methods names this class will
937 respond to, taking into account inheritance. The list will be a list of
938 HASH references, each one containing the following information; method
939 name, the name of the class in which the method lives and a CODE
940 reference for the actual method.
942 =item B<find_all_methods_by_name ($method_name)>
944 This will traverse the inheritence hierarchy and locate all methods
945 with a given C<$method_name>. Similar to
946 C<compute_all_applicable_methods> it returns a list of HASH references
947 with the following information; method name (which will always be the
948 same as C<$method_name>), the name of the class in which the method
949 lives and a CODE reference for the actual method.
951 The list of methods produced is a distinct list, meaning there are no
952 duplicates in it. This is especially useful for things like object
953 initialization and destruction where you only want the method called
954 once, and in the correct order.
956 =item B<find_next_method_by_name ($method_name)>
958 This will return the first method to match a given C<$method_name> in
959 the superclasses, this is basically equivalent to calling
960 C<SUPER::$method_name>, but it can be dispatched at runtime.
964 =head2 Method Modifiers
966 Method modifiers are a concept borrowed from CLOS, in which a method
967 can be wrapped with I<before>, I<after> and I<around> method modifiers
968 that will be called everytime the method is called.
970 =head3 How method modifiers work?
972 Method modifiers work by wrapping the original method and then replacing
973 it in the classes symbol table. The wrappers will handle calling all the
974 modifiers in the appropariate orders and preserving the calling context
975 for the original method.
977 Each method modifier serves a particular purpose, which may not be
978 obvious to users of other method wrapping modules. To start with, the
979 return values of I<before> and I<after> modifiers are ignored. This is
980 because thier purpose is B<not> to filter the input and output of the
981 primary method (this is done with an I<around> modifier). This may seem
982 like an odd restriction to some, but doing this allows for simple code
983 to be added at the begining or end of a method call without jeapordizing
984 the normal functioning of the primary method or placing any extra
985 responsibility on the code of the modifier. Of course if you have more
986 complex needs, then use the I<around> modifier, which uses a variation
987 of continutation passing style to allow for a high degree of flexibility.
989 Before and around modifiers are called in last-defined-first-called order,
990 while after modifiers are called in first-defined-first-called order. So
991 the call tree might looks something like this:
1001 To see examples of using method modifiers, see the following examples
1002 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1003 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1004 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1006 =head3 What is the performance impact?
1008 Of course there is a performance cost associated with method modifiers,
1009 but we have made every effort to make that cost be directly proportional
1010 to the amount of modifier features you utilize.
1012 The wrapping method does it's best to B<only> do as much work as it
1013 absolutely needs to. In order to do this we have moved some of the
1014 performance costs to set-up time, where they are easier to amortize.
1016 All this said, my benchmarks have indicated the following:
1018 simple wrapper with no modifiers 100% slower
1019 simple wrapper with simple before modifier 400% slower
1020 simple wrapper with simple after modifier 450% slower
1021 simple wrapper with simple around modifier 500-550% slower
1022 simple wrapper with all 3 modifiers 1100% slower
1024 These numbers may seem daunting, but you must remember, every feature
1025 comes with some cost. To put things in perspective, just doing a simple
1026 C<AUTOLOAD> which does nothing but extract the name of the method called
1027 and return it costs about 400% over a normal method call.
1031 =item B<add_before_method_modifier ($method_name, $code)>
1033 This will wrap the method at C<$method_name> and the supplied C<$code>
1034 will be passed the C<@_> arguments, and called before the original
1035 method is called. As specified above, the return value of the I<before>
1036 method modifiers is ignored, and it's ability to modify C<@_> is
1037 fairly limited. If you need to do either of these things, use an
1038 C<around> method modifier.
1040 =item B<add_after_method_modifier ($method_name, $code)>
1042 This will wrap the method at C<$method_name> so that the original
1043 method will be called, it's return values stashed, and then the
1044 supplied C<$code> will be passed the C<@_> arguments, and called.
1045 As specified above, the return value of the I<after> method
1046 modifiers is ignored, and it cannot modify the return values of
1047 the original method. If you need to do either of these things, use an
1048 C<around> method modifier.
1050 =item B<add_around_method_modifier ($method_name, $code)>
1052 This will wrap the method at C<$method_name> so that C<$code>
1053 will be called and passed the original method as an extra argument
1054 at the begining of the C<@_> argument list. This is a variation of
1055 continuation passing style, where the function prepended to C<@_>
1056 can be considered a continuation. It is up to C<$code> if it calls
1057 the original method or not, there is no restriction on what the
1058 C<$code> can or cannot do.
1064 It should be noted that since there is no one consistent way to define
1065 the attributes of a class in Perl 5. These methods can only work with
1066 the information given, and can not easily discover information on
1067 their own. See L<Class::MOP::Attribute> for more details.
1071 =item B<attribute_metaclass>
1073 =item B<get_attribute_map>
1075 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1077 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1078 instance associated with the given class, and associates it with
1079 the C<$attribute_name>. Unlike methods, attributes within the MOP
1080 are stored as meta-information only. They will be used later to
1081 construct instances from (see C<construct_instance> above).
1082 More details about the attribute meta-objects can be found in the
1083 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1086 It should be noted that any accessor, reader/writer or predicate
1087 methods which the C<$attribute_meta_object> has will be installed
1088 into the class at this time.
1090 =item B<has_attribute ($attribute_name)>
1092 Checks to see if this class has an attribute by the name of
1093 C<$attribute_name> and returns a boolean.
1095 =item B<get_attribute ($attribute_name)>
1097 Returns the attribute meta-object associated with C<$attribute_name>,
1098 if none is found, it will return undef.
1100 =item B<remove_attribute ($attribute_name)>
1102 This will remove the attribute meta-object stored at
1103 C<$attribute_name>, then return the removed attribute meta-object.
1106 Removing an attribute will only affect future instances of
1107 the class, it will not make any attempt to remove the attribute from
1108 any existing instances of the class.
1110 It should be noted that any accessor, reader/writer or predicate
1111 methods which the attribute meta-object stored at C<$attribute_name>
1112 has will be removed from the class at this time. This B<will> make
1113 these attributes somewhat inaccessable in previously created
1114 instances. But if you are crazy enough to do this at runtime, then
1115 you are crazy enough to deal with something like this :).
1117 =item B<get_attribute_list>
1119 This returns a list of attribute names which are defined in the local
1120 class. If you want a list of all applicable attributes for a class,
1121 use the C<compute_all_applicable_attributes> method.
1123 =item B<compute_all_applicable_attributes>
1125 This will traverse the inheritance heirachy and return a list of all
1126 the applicable attributes for this class. It does not construct a
1127 HASH reference like C<compute_all_applicable_methods> because all
1128 that same information is discoverable through the attribute
1131 =item B<find_attribute_by_name ($attr_name)>
1133 This method will traverse the inheritance heirachy and find the
1134 first attribute whose name matches C<$attr_name>, then return it.
1135 It will return undef if nothing is found.
1139 =head2 Package Variables
1141 Since Perl's classes are built atop the Perl package system, it is
1142 fairly common to use package scoped variables for things like static
1143 class variables. The following methods are convience methods for
1144 the creation and inspection of package scoped variables.
1148 =item B<add_package_variable ($variable_name, ?$initial_value)>
1150 Given a C<$variable_name>, which must contain a leading sigil, this
1151 method will create that variable within the package which houses the
1152 class. It also takes an optional C<$initial_value>, which must be a
1153 reference of the same type as the sigil of the C<$variable_name>
1156 =item B<get_package_variable ($variable_name)>
1158 This will return a reference to the package variable in
1161 =item B<has_package_variable ($variable_name)>
1163 Returns true (C<1>) if there is a package variable defined for
1164 C<$variable_name>, and false (C<0>) otherwise.
1166 =item B<remove_package_variable ($variable_name)>
1168 This will attempt to remove the package variable at C<$variable_name>.
1174 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1176 =head1 COPYRIGHT AND LICENSE
1178 Copyright 2006 by Infinity Interactive, Inc.
1180 L<http://www.iinteractive.com>
1182 This library is free software; you can redistribute it and/or modify
1183 it under the same terms as Perl itself.