2 package Class::MOP::Class;
8 use Scalar::Util 'blessed', 'reftype';
9 use Sub::Name 'subname';
10 use B 'svref_2object';
12 our $VERSION = '0.11';
16 sub meta { Class::MOP::Class->initialize(blessed($_[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 my $init_arg = $attr->init_arg();
181 # try to fetch the init arg from the %params ...
183 $val = $params{$init_arg} if exists $params{$init_arg};
184 # if nothing was in the %params, we can use the
185 # attribute's default value (if it has one)
186 if (!defined $val && $attr->has_default) {
187 $val = $attr->default($instance);
189 $instance->{$attr->name} = $val;
196 my $instance = shift;
197 (blessed($instance) && $instance->isa($class->name))
198 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
200 # we need to protect the integrity of the
201 # Class::MOP::Class singletons here, they
202 # should not be cloned.
203 return $instance if $instance->isa('Class::MOP::Class');
204 bless $class->clone_instance($instance, @_) => blessed($instance);
208 my ($class, $instance, %params) = @_;
210 || confess "You can only clone instances, \$self is not a blessed instance";
211 my $clone = { %$instance, %params };
217 # &name should be here too, but it is above
218 # because it gets bootstrapped away
222 ${$self->get_package_variable('$VERSION')};
231 @{$self->get_package_variable('@ISA')} = @supers;
233 @{$self->get_package_variable('@ISA')};
236 sub class_precedence_list {
239 # We need to check for ciruclar inheirtance here.
240 # This will do nothing if all is well, and blow
241 # up otherwise. Yes, it's an ugly hack, better
242 # suggestions are welcome.
243 { $self->name->isa('This is a test for circular inheritance') }
244 # ... and now back to our regularly scheduled program
248 $self->initialize($_)->class_precedence_list()
249 } $self->superclasses()
256 my ($self, $method_name, $method) = @_;
257 (defined $method_name && $method_name)
258 || confess "You must define a method name";
259 # use reftype here to allow for blessed subs ...
260 ('CODE' eq (reftype($method) || ''))
261 || confess "Your code block must be a CODE reference";
262 my $full_method_name = ($self->name . '::' . $method_name);
264 $method = $self->method_metaclass->wrap($method) unless blessed($method);
267 no warnings 'redefine';
268 *{$full_method_name} = subname $full_method_name => $method;
272 my $fetch_and_prepare_method = sub {
273 my ($self, $method_name) = @_;
275 my $method = $self->get_method($method_name);
276 # if we dont have local ...
278 # make sure this method even exists ...
279 ($self->find_next_method_by_name($method_name))
280 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
281 # if so, then create a local which just
282 # calls the next applicable method ...
283 $self->add_method($method_name => sub {
284 $self->find_next_method_by_name($method_name)->(@_);
286 $method = $self->get_method($method_name);
289 # now make sure we wrap it properly
290 # (if it isnt already)
291 unless ($method->isa('Class::MOP::Method::Wrapped')) {
292 $method = Class::MOP::Method::Wrapped->wrap($method);
293 $self->add_method($method_name => $method);
298 sub add_before_method_modifier {
299 my ($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_before_modifier(subname ':before' => $method_modifier);
306 sub add_after_method_modifier {
307 my ($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_after_modifier(subname ':after' => $method_modifier);
314 sub add_around_method_modifier {
315 my ($self, $method_name, $method_modifier) = @_;
316 (defined $method_name && $method_name)
317 || confess "You must pass in a method name";
318 my $method = $fetch_and_prepare_method->($self, $method_name);
319 $method->add_around_modifier(subname ':around' => $method_modifier);
323 # the methods above used to be named like this:
324 # ${pkg}::${method}:(before|after|around)
325 # but this proved problematic when using one modifier
326 # to wrap multiple methods (something which is likely
327 # to happen pretty regularly IMO). So instead of naming
328 # it like this, I have chosen to just name them purely
329 # with their modifier names, like so:
330 # :(before|after|around)
331 # The fact is that in a stack trace, it will be fairly
332 # evident from the context what method they are attached
333 # to, and so don't need the fully qualified name.
337 my ($self, $method_name, $method) = @_;
338 (defined $method_name && $method_name)
339 || confess "You must define a method name";
340 # use reftype here to allow for blessed subs ...
341 ('CODE' eq (reftype($method) || ''))
342 || confess "Your code block must be a CODE reference";
343 my $full_method_name = ($self->name . '::' . $method_name);
345 $method = $self->method_metaclass->wrap($method) unless blessed($method);
348 no warnings 'redefine';
349 *{$full_method_name} = $method;
353 my ($self, $method_name) = @_;
354 (defined $method_name && $method_name)
355 || confess "You must define a method name";
357 my $sub_name = ($self->name . '::' . $method_name);
360 return 0 if !defined(&{$sub_name});
361 my $method = \&{$sub_name};
362 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
363 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
365 # at this point we are relatively sure
366 # it is our method, so we bless/wrap it
367 $self->method_metaclass->wrap($method) unless blessed($method);
372 my ($self, $method_name) = @_;
373 (defined $method_name && $method_name)
374 || confess "You must define a method name";
376 return unless $self->has_method($method_name);
379 return \&{$self->name . '::' . $method_name};
383 my ($self, $method_name) = @_;
384 (defined $method_name && $method_name)
385 || confess "You must define a method name";
387 my $removed_method = $self->get_method($method_name);
390 delete ${$self->name . '::'}{$method_name}
391 if defined $removed_method;
393 return $removed_method;
396 sub get_method_list {
399 grep { $self->has_method($_) } %{$self->name . '::'};
402 sub compute_all_applicable_methods {
405 # keep a record of what we have seen
406 # here, this will handle all the
407 # inheritence issues because we are
408 # using the &class_precedence_list
409 my (%seen_class, %seen_method);
410 foreach my $class ($self->class_precedence_list()) {
411 next if $seen_class{$class};
412 $seen_class{$class}++;
413 # fetch the meta-class ...
414 my $meta = $self->initialize($class);
415 foreach my $method_name ($meta->get_method_list()) {
416 next if exists $seen_method{$method_name};
417 $seen_method{$method_name}++;
419 name => $method_name,
421 code => $meta->get_method($method_name)
428 sub find_all_methods_by_name {
429 my ($self, $method_name) = @_;
430 (defined $method_name && $method_name)
431 || confess "You must define a method name to find";
433 # keep a record of what we have seen
434 # here, this will handle all the
435 # inheritence issues because we are
436 # using the &class_precedence_list
438 foreach my $class ($self->class_precedence_list()) {
439 next if $seen_class{$class};
440 $seen_class{$class}++;
441 # fetch the meta-class ...
442 my $meta = $self->initialize($class);
444 name => $method_name,
446 code => $meta->get_method($method_name)
447 } if $meta->has_method($method_name);
452 sub find_next_method_by_name {
453 my ($self, $method_name) = @_;
454 (defined $method_name && $method_name)
455 || confess "You must define a method name to find";
456 # keep a record of what we have seen
457 # here, this will handle all the
458 # inheritence issues because we are
459 # using the &class_precedence_list
461 my @cpl = $self->class_precedence_list();
462 shift @cpl; # discard ourselves
463 foreach my $class (@cpl) {
464 next if $seen_class{$class};
465 $seen_class{$class}++;
466 # fetch the meta-class ...
467 my $meta = $self->initialize($class);
468 return $meta->get_method($method_name)
469 if $meta->has_method($method_name);
478 # either we have an attribute object already
479 # or we need to create one from the args provided
480 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
481 # make sure it is derived from the correct type though
482 ($attribute->isa('Class::MOP::Attribute'))
483 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
484 $attribute->attach_to_class($self);
485 $attribute->install_accessors();
486 $self->get_attribute_map->{$attribute->name} = $attribute;
490 my ($self, $attribute_name) = @_;
491 (defined $attribute_name && $attribute_name)
492 || confess "You must define an attribute name";
493 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
497 my ($self, $attribute_name) = @_;
498 (defined $attribute_name && $attribute_name)
499 || confess "You must define an attribute name";
500 return $self->get_attribute_map->{$attribute_name}
501 if $self->has_attribute($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 $removed_attribute;
517 sub get_attribute_list {
519 keys %{$self->get_attribute_map};
522 sub compute_all_applicable_attributes {
525 # keep a record of what we have seen
526 # here, this will handle all the
527 # inheritence issues because we are
528 # using the &class_precedence_list
529 my (%seen_class, %seen_attr);
530 foreach my $class ($self->class_precedence_list()) {
531 next if $seen_class{$class};
532 $seen_class{$class}++;
533 # fetch the meta-class ...
534 my $meta = $self->initialize($class);
535 foreach my $attr_name ($meta->get_attribute_list()) {
536 next if exists $seen_attr{$attr_name};
537 $seen_attr{$attr_name}++;
538 push @attrs => $meta->get_attribute($attr_name);
546 sub add_package_variable {
547 my ($self, $variable, $initial_value) = @_;
548 (defined $variable && $variable =~ /^[\$\@\%]/)
549 || confess "variable name does not have a sigil";
551 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
552 if (defined $initial_value) {
554 *{$self->name . '::' . $name} = $initial_value;
560 # We HAVE to localize $@ or all
561 # hell breaks loose. It is not
562 # good, believe me, not good.
564 eval $sigil . $self->name . '::' . $name;
567 confess "Could not create package variable ($variable) because : $e" if $e;
571 sub has_package_variable {
572 my ($self, $variable) = @_;
573 (defined $variable && $variable =~ /^[\$\@\%]/)
574 || confess "variable name does not have a sigil";
575 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
577 defined ${$self->name . '::'}{$name} ? 1 : 0;
580 sub get_package_variable {
581 my ($self, $variable) = @_;
582 (defined $variable && $variable =~ /^[\$\@\%]/)
583 || confess "variable name does not have a sigil";
584 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
588 # We HAVE to localize $@ or all
589 # hell breaks loose. It is not
590 # good, believe me, not good.
592 $ref = eval '\\' . $sigil . $self->name . '::' . $name;
595 confess "Could not get the package variable ($variable) because : $e" if $e;
596 # if we didn't die, then we can return it
600 sub remove_package_variable {
601 my ($self, $variable) = @_;
602 (defined $variable && $variable =~ /^[\$\@\%]/)
603 || confess "variable name does not have a sigil";
604 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
606 delete ${$self->name . '::'}{$name};
617 Class::MOP::Class - Class Meta Object
621 # assuming that class Foo
622 # has been defined, you can
624 # use this for introspection ...
626 # add a method to Foo ...
627 Foo->meta->add_method('bar' => sub { ... })
629 # get a list of all the classes searched
630 # the method dispatcher in the correct order
631 Foo->meta->class_precedence_list()
633 # remove a method from Foo
634 Foo->meta->remove_method('bar');
636 # or use this to actually create classes ...
638 Class::MOP::Class->create('Bar' => '0.01' => (
639 superclasses => [ 'Foo' ],
641 Class::MOP:::Attribute->new('$bar'),
642 Class::MOP:::Attribute->new('$baz'),
645 calculate_bar => sub { ... },
646 construct_baz => sub { ... }
652 This is the largest and currently most complex part of the Perl 5
653 meta-object protocol. It controls the introspection and
654 manipulation of Perl 5 classes (and it can create them too). The
655 best way to understand what this module can do, is to read the
656 documentation for each of it's methods.
660 =head2 Self Introspection
666 This will return a B<Class::MOP::Class> instance which is related
667 to this class. Thereby allowing B<Class::MOP::Class> to actually
670 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
671 bootstrap this module by installing a number of attribute meta-objects
672 into it's metaclass. This will allow this class to reap all the benifits
673 of the MOP when subclassing it.
675 =item B<get_all_metaclasses>
677 This will return an hash of all the metaclass instances that have
678 been cached by B<Class::MOP::Class> keyed by the package name.
680 =item B<get_all_metaclass_instances>
682 This will return an array of all the metaclass instances that have
683 been cached by B<Class::MOP::Class>.
685 =item B<get_all_metaclass_names>
687 This will return an array of all the metaclass names that have
688 been cached by B<Class::MOP::Class>.
692 =head2 Class construction
694 These methods will handle creating B<Class::MOP::Class> objects,
695 which can be used to both create new classes, and analyze
696 pre-existing classes.
698 This module will internally store references to all the instances
699 you create with these methods, so that they do not need to be
700 created any more than nessecary. Basically, they are singletons.
704 =item B<create ($package_name, ?$package_version,
705 superclasses =E<gt> ?@superclasses,
706 methods =E<gt> ?%methods,
707 attributes =E<gt> ?%attributes)>
709 This returns a B<Class::MOP::Class> object, bringing the specified
710 C<$package_name> into existence and adding any of the
711 C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
714 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
715 methods =E<gt> ?%methods,
716 attributes =E<gt> ?%attributes)>
718 This will create an anonymous class, it works much like C<create> but
719 it does not need a C<$package_name>. Instead it will create a suitably
720 unique package name for you to stash things into.
722 =item B<initialize ($package_name)>
724 This initializes and returns returns a B<Class::MOP::Class> object
725 for a given a C<$package_name>.
727 =item B<construct_class_instance (%options)>
729 This will construct an instance of B<Class::MOP::Class>, it is
730 here so that we can actually "tie the knot" for B<Class::MOP::Class>
731 to use C<construct_instance> once all the bootstrapping is done. This
732 method is used internally by C<initialize> and should never be called
733 from outside of that method really.
735 =item B<check_metaclass_compatability>
737 This method is called as the very last thing in the
738 C<construct_class_instance> method. This will check that the
739 metaclass you are creating is compatible with the metaclasses of all
740 your ancestors. For more inforamtion about metaclass compatibility
741 see the C<About Metaclass compatibility> section in L<Class::MOP>.
745 =head2 Object instance construction and cloning
747 These methods are B<entirely optional>, it is up to you whether you want
752 =item B<new_object (%params)>
754 This is a convience method for creating a new object of the class, and
755 blessing it into the appropriate package as well. Ideally your class
756 would call a C<new> this method like so:
759 my ($class, %param) = @_;
760 $class->meta->new_object(%params);
763 Of course the ideal place for this would actually be in C<UNIVERSAL::>
764 but that is considered bad style, so we do not do that.
766 =item B<construct_instance (%params)>
768 This method is used to construct an instace structure suitable for
769 C<bless>-ing into your package of choice. It works in conjunction
770 with the Attribute protocol to collect all applicable attributes.
772 This will construct and instance using a HASH ref as storage
773 (currently only HASH references are supported). This will collect all
774 the applicable attributes and layout out the fields in the HASH ref,
775 it will then initialize them using either use the corresponding key
776 in C<%params> or any default value or initializer found in the
777 attribute meta-object.
779 =item B<clone_object ($instance, %params)>
781 This is a convience method for cloning an object instance, then
782 blessing it into the appropriate package. This method will call
783 C<clone_instance>, which performs a shallow copy of the object,
784 see that methods documentation for more details. Ideally your
785 class would call a C<clone> this method like so:
788 my ($self, %param) = @_;
789 $self->meta->clone_object($self, %params);
792 Of course the ideal place for this would actually be in C<UNIVERSAL::>
793 but that is considered bad style, so we do not do that.
795 =item B<clone_instance($instance, %params)>
797 This method is a compliment of C<construct_instance> (which means if
798 you override C<construct_instance>, you need to override this one too),
799 and clones the instance shallowly.
801 The cloned structure returned is (like with C<construct_instance>) an
802 unC<bless>ed HASH reference, it is your responsibility to then bless
803 this cloned structure into the right class (which C<clone_object> will
806 As of 0.11, this method will clone the C<$instance> structure shallowly,
807 as opposed to the deep cloning implemented in prior versions. After much
808 thought, research and discussion, I have decided that anything but basic
809 shallow cloning is outside the scope of the meta-object protocol. I
810 think Yuval "nothingmuch" Kogman put it best when he said that cloning
811 is too I<context-specific> to be part of the MOP.
821 This is a read-only attribute which returns the package name for the
822 given B<Class::MOP::Class> instance.
826 This is a read-only attribute which returns the C<$VERSION> of the
827 package for the given B<Class::MOP::Class> instance.
831 =head2 Inheritance Relationships
835 =item B<superclasses (?@superclasses)>
837 This is a read-write attribute which represents the superclass
838 relationships of the class the B<Class::MOP::Class> instance is
839 associated with. Basically, it can get and set the C<@ISA> for you.
842 Perl will occasionally perform some C<@ISA> and method caching, if
843 you decide to change your superclass relationship at runtime (which
844 is quite insane and very much not recommened), then you should be
845 aware of this and the fact that this module does not make any
846 attempt to address this issue.
848 =item B<class_precedence_list>
850 This computes the a list of all the class's ancestors in the same order
851 in which method dispatch will be done. This is similair to
852 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
860 =item B<method_metaclass>
862 =item B<add_method ($method_name, $method)>
864 This will take a C<$method_name> and CODE reference to that
865 C<$method> and install it into the class's package.
868 This does absolutely nothing special to C<$method>
869 other than use B<Sub::Name> to make sure it is tagged with the
870 correct name, and therefore show up correctly in stack traces and
873 =item B<alias_method ($method_name, $method)>
875 This will take a C<$method_name> and CODE reference to that
876 C<$method> and alias the method into the class's package.
879 Unlike C<add_method>, this will B<not> try to name the
880 C<$method> using B<Sub::Name>, it only aliases the method in
883 =item B<has_method ($method_name)>
885 This just provides a simple way to check if the class implements
886 a specific C<$method_name>. It will I<not> however, attempt to check
887 if the class inherits the method (use C<UNIVERSAL::can> for that).
889 This will correctly handle functions defined outside of the package
890 that use a fully qualified name (C<sub Package::name { ... }>).
892 This will correctly handle functions renamed with B<Sub::Name> and
893 installed using the symbol tables. However, if you are naming the
894 subroutine outside of the package scope, you must use the fully
895 qualified name, including the package name, for C<has_method> to
896 correctly identify it.
898 This will attempt to correctly ignore functions imported from other
899 packages using B<Exporter>. It breaks down if the function imported
900 is an C<__ANON__> sub (such as with C<use constant>), which very well
901 may be a valid method being applied to the class.
903 In short, this method cannot always be trusted to determine if the
904 C<$method_name> is actually a method. However, it will DWIM about
905 90% of the time, so it's a small trade off I think.
907 =item B<get_method ($method_name)>
909 This will return a CODE reference of the specified C<$method_name>,
910 or return undef if that method does not exist.
912 =item B<remove_method ($method_name)>
914 This will attempt to remove a given C<$method_name> from the class.
915 It will return the CODE reference that it has removed, and will
916 attempt to use B<Sub::Name> to clear the methods associated name.
918 =item B<get_method_list>
920 This will return a list of method names for all I<locally> defined
921 methods. It does B<not> provide a list of all applicable methods,
922 including any inherited ones. If you want a list of all applicable
923 methods, use the C<compute_all_applicable_methods> method.
925 =item B<compute_all_applicable_methods>
927 This will return a list of all the methods names this class will
928 respond to, taking into account inheritance. The list will be a list of
929 HASH references, each one containing the following information; method
930 name, the name of the class in which the method lives and a CODE
931 reference for the actual method.
933 =item B<find_all_methods_by_name ($method_name)>
935 This will traverse the inheritence hierarchy and locate all methods
936 with a given C<$method_name>. Similar to
937 C<compute_all_applicable_methods> it returns a list of HASH references
938 with the following information; method name (which will always be the
939 same as C<$method_name>), the name of the class in which the method
940 lives and a CODE reference for the actual method.
942 The list of methods produced is a distinct list, meaning there are no
943 duplicates in it. This is especially useful for things like object
944 initialization and destruction where you only want the method called
945 once, and in the correct order.
947 =item B<find_next_method_by_name ($method_name)>
949 This will return the first method to match a given C<$method_name> in
950 the superclasses, this is basically equivalent to calling
951 C<SUPER::$method_name>, but it can be dispatched at runtime.
955 =head2 Method Modifiers
957 Method modifiers are a concept borrowed from CLOS, in which a method
958 can be wrapped with I<before>, I<after> and I<around> method modifiers
959 that will be called everytime the method is called.
961 =head3 How method modifiers work?
963 Method modifiers work by wrapping the original method and then replacing
964 it in the classes symbol table. The wrappers will handle calling all the
965 modifiers in the appropariate orders and preserving the calling context
966 for the original method.
968 Each method modifier serves a particular purpose, which may not be
969 obvious to users of other method wrapping modules. To start with, the
970 return values of I<before> and I<after> modifiers are ignored. This is
971 because thier purpose is B<not> to filter the input and output of the
972 primary method (this is done with an I<around> modifier). This may seem
973 like an odd restriction to some, but doing this allows for simple code
974 to be added at the begining or end of a method call without jeapordizing
975 the normal functioning of the primary method or placing any extra
976 responsibility on the code of the modifier. Of course if you have more
977 complex needs, then use the I<around> modifier, which uses a variation
978 of continutation passing style to allow for a high degree of flexibility.
980 Before and around modifiers are called in last-defined-first-called order,
981 while after modifiers are called in first-defined-first-called order. So
982 the call tree might looks something like this:
992 To see examples of using method modifiers, see the following examples
993 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
994 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
995 classic CLOS usage example in the test F<017_add_method_modifier.t>.
997 =head3 What is the performance impact?
999 Of course there is a performance cost associated with method modifiers,
1000 but we have made every effort to make that cost be directly proportional
1001 to the amount of modifier features you utilize.
1003 The wrapping method does it's best to B<only> do as much work as it
1004 absolutely needs to. In order to do this we have moved some of the
1005 performance costs to set-up time, where they are easier to amortize.
1007 All this said, my benchmarks have indicated the following:
1009 simple wrapper with no modifiers 100% slower
1010 simple wrapper with simple before modifier 400% slower
1011 simple wrapper with simple after modifier 450% slower
1012 simple wrapper with simple around modifier 500-550% slower
1013 simple wrapper with all 3 modifiers 1100% slower
1015 These numbers may seem daunting, but you must remember, every feature
1016 comes with some cost. To put things in perspective, just doing a simple
1017 C<AUTOLOAD> which does nothing but extract the name of the method called
1018 and return it costs about 400% over a normal method call.
1022 =item B<add_before_method_modifier ($method_name, $code)>
1024 This will wrap the method at C<$method_name> and the supplied C<$code>
1025 will be passed the C<@_> arguments, and called before the original
1026 method is called. As specified above, the return value of the I<before>
1027 method modifiers is ignored, and it's ability to modify C<@_> is
1028 fairly limited. If you need to do either of these things, use an
1029 C<around> method modifier.
1031 =item B<add_after_method_modifier ($method_name, $code)>
1033 This will wrap the method at C<$method_name> so that the original
1034 method will be called, it's return values stashed, and then the
1035 supplied C<$code> will be passed the C<@_> arguments, and called.
1036 As specified above, the return value of the I<after> method
1037 modifiers is ignored, and it cannot modify the return values of
1038 the original method. If you need to do either of these things, use an
1039 C<around> method modifier.
1041 =item B<add_around_method_modifier ($method_name, $code)>
1043 This will wrap the method at C<$method_name> so that C<$code>
1044 will be called and passed the original method as an extra argument
1045 at the begining of the C<@_> argument list. This is a variation of
1046 continuation passing style, where the function prepended to C<@_>
1047 can be considered a continuation. It is up to C<$code> if it calls
1048 the original method or not, there is no restriction on what the
1049 C<$code> can or cannot do.
1055 It should be noted that since there is no one consistent way to define
1056 the attributes of a class in Perl 5. These methods can only work with
1057 the information given, and can not easily discover information on
1058 their own. See L<Class::MOP::Attribute> for more details.
1062 =item B<attribute_metaclass>
1064 =item B<get_attribute_map>
1066 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1068 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1069 instance associated with the given class, and associates it with
1070 the C<$attribute_name>. Unlike methods, attributes within the MOP
1071 are stored as meta-information only. They will be used later to
1072 construct instances from (see C<construct_instance> above).
1073 More details about the attribute meta-objects can be found in the
1074 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1077 It should be noted that any accessor, reader/writer or predicate
1078 methods which the C<$attribute_meta_object> has will be installed
1079 into the class at this time.
1081 =item B<has_attribute ($attribute_name)>
1083 Checks to see if this class has an attribute by the name of
1084 C<$attribute_name> and returns a boolean.
1086 =item B<get_attribute ($attribute_name)>
1088 Returns the attribute meta-object associated with C<$attribute_name>,
1089 if none is found, it will return undef.
1091 =item B<remove_attribute ($attribute_name)>
1093 This will remove the attribute meta-object stored at
1094 C<$attribute_name>, then return the removed attribute meta-object.
1097 Removing an attribute will only affect future instances of
1098 the class, it will not make any attempt to remove the attribute from
1099 any existing instances of the class.
1101 It should be noted that any accessor, reader/writer or predicate
1102 methods which the attribute meta-object stored at C<$attribute_name>
1103 has will be removed from the class at this time. This B<will> make
1104 these attributes somewhat inaccessable in previously created
1105 instances. But if you are crazy enough to do this at runtime, then
1106 you are crazy enough to deal with something like this :).
1108 =item B<get_attribute_list>
1110 This returns a list of attribute names which are defined in the local
1111 class. If you want a list of all applicable attributes for a class,
1112 use the C<compute_all_applicable_attributes> method.
1114 =item B<compute_all_applicable_attributes>
1116 This will traverse the inheritance heirachy and return a list of all
1117 the applicable attributes for this class. It does not construct a
1118 HASH reference like C<compute_all_applicable_methods> because all
1119 that same information is discoverable through the attribute
1124 =head2 Package Variables
1126 Since Perl's classes are built atop the Perl package system, it is
1127 fairly common to use package scoped variables for things like static
1128 class variables. The following methods are convience methods for
1129 the creation and inspection of package scoped variables.
1133 =item B<add_package_variable ($variable_name, ?$initial_value)>
1135 Given a C<$variable_name>, which must contain a leading sigil, this
1136 method will create that variable within the package which houses the
1137 class. It also takes an optional C<$initial_value>, which must be a
1138 reference of the same type as the sigil of the C<$variable_name>
1141 =item B<get_package_variable ($variable_name)>
1143 This will return a reference to the package variable in
1146 =item B<has_package_variable ($variable_name)>
1148 Returns true (C<1>) if there is a package variable defined for
1149 C<$variable_name>, and false (C<0>) otherwise.
1151 =item B<remove_package_variable ($variable_name)>
1153 This will attempt to remove the package variable at C<$variable_name>.
1159 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1161 =head1 COPYRIGHT AND LICENSE
1163 Copyright 2006 by Infinity Interactive, Inc.
1165 L<http://www.iinteractive.com>
1167 This library is free software; you can redistribute it and/or modify
1168 it under the same terms as Perl itself.