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});
138 my $ANON_CLASS_SERIAL = 0;
139 sub create_anon_class {
140 my ($class, %options) = @_;
141 my $package_name = 'Class::MOP::Class::__ANON__::SERIAL::' . ++$ANON_CLASS_SERIAL;
142 return $class->create($package_name, '0.00', %options);
149 # all these attribute readers will be bootstrapped
150 # away in the Class::MOP bootstrap section
152 sub name { $_[0]->{'$:package'} }
153 sub get_attribute_map { $_[0]->{'%:attributes'} }
154 sub attribute_metaclass { $_[0]->{'$:attribute_metaclass'} }
155 sub method_metaclass { $_[0]->{'$:method_metaclass'} }
157 # Instance Construction & Cloning
162 # we need to protect the integrity of the
163 # Class::MOP::Class singletons here, so we
164 # delegate this to &construct_class_instance
165 # which will deal with the singletons
166 return $class->construct_class_instance(@_)
167 if $class->name->isa('Class::MOP::Class');
168 bless $class->construct_instance(@_) => $class->name;
171 sub construct_instance {
172 my ($class, %params) = @_;
174 foreach my $attr ($class->compute_all_applicable_attributes()) {
175 my $init_arg = $attr->init_arg();
176 # try to fetch the init arg from the %params ...
178 $val = $params{$init_arg} if exists $params{$init_arg};
179 # if nothing was in the %params, we can use the
180 # attribute's default value (if it has one)
181 if (!defined $val && $attr->has_default) {
182 $val = $attr->default($instance);
184 $instance->{$attr->name} = $val;
191 my $instance = shift;
192 (blessed($instance) && $instance->isa($class->name))
193 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
195 # we need to protect the integrity of the
196 # Class::MOP::Class singletons here, they
197 # should not be cloned.
198 return $instance if $instance->isa('Class::MOP::Class');
199 bless $class->clone_instance($instance, @_) => blessed($instance);
203 my ($class, $instance, %params) = @_;
205 || confess "You can only clone instances, \$self is not a blessed instance";
206 my $clone = { %$instance, %params };
212 # &name should be here too, but it is above
213 # because it gets bootstrapped away
217 ${$self->get_package_variable('$VERSION')};
226 @{$self->get_package_variable('@ISA')} = @supers;
228 @{$self->get_package_variable('@ISA')};
231 sub class_precedence_list {
234 # We need to check for ciruclar inheirtance here.
235 # This will do nothing if all is well, and blow
236 # up otherwise. Yes, it's an ugly hack, better
237 # suggestions are welcome.
238 { $self->name->isa('This is a test for circular inheritance') }
239 # ... and now back to our regularly scheduled program
243 $self->initialize($_)->class_precedence_list()
244 } $self->superclasses()
251 my ($self, $method_name, $method) = @_;
252 (defined $method_name && $method_name)
253 || confess "You must define a method name";
254 # use reftype here to allow for blessed subs ...
255 ('CODE' eq (reftype($method) || ''))
256 || confess "Your code block must be a CODE reference";
257 my $full_method_name = ($self->name . '::' . $method_name);
259 $method = $self->method_metaclass->wrap($method) unless blessed($method);
262 no warnings 'redefine';
263 *{$full_method_name} = subname $full_method_name => $method;
267 my $fetch_and_prepare_method = sub {
268 my ($self, $method_name) = @_;
270 my $method = $self->get_method($method_name);
271 # if we dont have local ...
273 # make sure this method even exists ...
274 ($self->find_next_method_by_name($method_name))
275 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
276 # if so, then create a local which just
277 # calls the next applicable method ...
278 $self->add_method($method_name => sub {
279 $self->find_next_method_by_name($method_name)->(@_);
281 $method = $self->get_method($method_name);
284 # now make sure we wrap it properly
285 # (if it isnt already)
286 unless ($method->isa('Class::MOP::Method::Wrapped')) {
287 $method = Class::MOP::Method::Wrapped->wrap($method);
288 $self->add_method($method_name => $method);
293 sub add_before_method_modifier {
294 my ($self, $method_name, $method_modifier) = @_;
295 (defined $method_name && $method_name)
296 || confess "You must pass in a method name";
297 my $method = $fetch_and_prepare_method->($self, $method_name);
298 $method->add_before_modifier(subname ':before' => $method_modifier);
301 sub add_after_method_modifier {
302 my ($self, $method_name, $method_modifier) = @_;
303 (defined $method_name && $method_name)
304 || confess "You must pass in a method name";
305 my $method = $fetch_and_prepare_method->($self, $method_name);
306 $method->add_after_modifier(subname ':after' => $method_modifier);
309 sub add_around_method_modifier {
310 my ($self, $method_name, $method_modifier) = @_;
311 (defined $method_name && $method_name)
312 || confess "You must pass in a method name";
313 my $method = $fetch_and_prepare_method->($self, $method_name);
314 $method->add_around_modifier(subname ':around' => $method_modifier);
318 # the methods above used to be named like this:
319 # ${pkg}::${method}:(before|after|around)
320 # but this proved problematic when using one modifier
321 # to wrap multiple methods (something which is likely
322 # to happen pretty regularly IMO). So instead of naming
323 # it like this, I have chosen to just name them purely
324 # with their modifier names, like so:
325 # :(before|after|around)
326 # The fact is that in a stack trace, it will be fairly
327 # evident from the context what method they are attached
328 # to, and so don't need the fully qualified name.
332 my ($self, $method_name, $method) = @_;
333 (defined $method_name && $method_name)
334 || confess "You must define a method name";
335 # use reftype here to allow for blessed subs ...
336 ('CODE' eq (reftype($method) || ''))
337 || confess "Your code block must be a CODE reference";
338 my $full_method_name = ($self->name . '::' . $method_name);
340 $method = $self->method_metaclass->wrap($method) unless blessed($method);
343 no warnings 'redefine';
344 *{$full_method_name} = $method;
348 my ($self, $method_name) = @_;
349 (defined $method_name && $method_name)
350 || confess "You must define a method name";
352 my $sub_name = ($self->name . '::' . $method_name);
355 return 0 if !defined(&{$sub_name});
356 my $method = \&{$sub_name};
357 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
358 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
360 # at this point we are relatively sure
361 # it is our method, so we bless/wrap it
362 $self->method_metaclass->wrap($method) unless blessed($method);
367 my ($self, $method_name) = @_;
368 (defined $method_name && $method_name)
369 || confess "You must define a method name";
371 return unless $self->has_method($method_name);
374 return \&{$self->name . '::' . $method_name};
378 my ($self, $method_name) = @_;
379 (defined $method_name && $method_name)
380 || confess "You must define a method name";
382 my $removed_method = $self->get_method($method_name);
385 delete ${$self->name . '::'}{$method_name}
386 if defined $removed_method;
388 return $removed_method;
391 sub get_method_list {
394 grep { $self->has_method($_) } %{$self->name . '::'};
397 sub compute_all_applicable_methods {
400 # keep a record of what we have seen
401 # here, this will handle all the
402 # inheritence issues because we are
403 # using the &class_precedence_list
404 my (%seen_class, %seen_method);
405 foreach my $class ($self->class_precedence_list()) {
406 next if $seen_class{$class};
407 $seen_class{$class}++;
408 # fetch the meta-class ...
409 my $meta = $self->initialize($class);
410 foreach my $method_name ($meta->get_method_list()) {
411 next if exists $seen_method{$method_name};
412 $seen_method{$method_name}++;
414 name => $method_name,
416 code => $meta->get_method($method_name)
423 sub find_all_methods_by_name {
424 my ($self, $method_name) = @_;
425 (defined $method_name && $method_name)
426 || confess "You must define a method name to find";
428 # keep a record of what we have seen
429 # here, this will handle all the
430 # inheritence issues because we are
431 # using the &class_precedence_list
433 foreach my $class ($self->class_precedence_list()) {
434 next if $seen_class{$class};
435 $seen_class{$class}++;
436 # fetch the meta-class ...
437 my $meta = $self->initialize($class);
439 name => $method_name,
441 code => $meta->get_method($method_name)
442 } if $meta->has_method($method_name);
447 sub find_next_method_by_name {
448 my ($self, $method_name) = @_;
449 (defined $method_name && $method_name)
450 || confess "You must define a method name to find";
451 # keep a record of what we have seen
452 # here, this will handle all the
453 # inheritence issues because we are
454 # using the &class_precedence_list
456 my @cpl = $self->class_precedence_list();
457 shift @cpl; # discard ourselves
458 foreach my $class (@cpl) {
459 next if $seen_class{$class};
460 $seen_class{$class}++;
461 # fetch the meta-class ...
462 my $meta = $self->initialize($class);
463 return $meta->get_method($method_name)
464 if $meta->has_method($method_name);
473 # either we have an attribute object already
474 # or we need to create one from the args provided
475 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
476 # make sure it is derived from the correct type though
477 ($attribute->isa('Class::MOP::Attribute'))
478 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
479 $attribute->attach_to_class($self);
480 $attribute->install_accessors();
481 $self->get_attribute_map->{$attribute->name} = $attribute;
485 my ($self, $attribute_name) = @_;
486 (defined $attribute_name && $attribute_name)
487 || confess "You must define an attribute name";
488 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
492 my ($self, $attribute_name) = @_;
493 (defined $attribute_name && $attribute_name)
494 || confess "You must define an attribute name";
495 return $self->get_attribute_map->{$attribute_name}
496 if $self->has_attribute($attribute_name);
500 sub remove_attribute {
501 my ($self, $attribute_name) = @_;
502 (defined $attribute_name && $attribute_name)
503 || confess "You must define an attribute name";
504 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
505 return unless defined $removed_attribute;
506 delete $self->get_attribute_map->{$attribute_name};
507 $removed_attribute->remove_accessors();
508 $removed_attribute->detach_from_class();
509 return $removed_attribute;
512 sub get_attribute_list {
514 keys %{$self->get_attribute_map};
517 sub compute_all_applicable_attributes {
520 # keep a record of what we have seen
521 # here, this will handle all the
522 # inheritence issues because we are
523 # using the &class_precedence_list
524 my (%seen_class, %seen_attr);
525 foreach my $class ($self->class_precedence_list()) {
526 next if $seen_class{$class};
527 $seen_class{$class}++;
528 # fetch the meta-class ...
529 my $meta = $self->initialize($class);
530 foreach my $attr_name ($meta->get_attribute_list()) {
531 next if exists $seen_attr{$attr_name};
532 $seen_attr{$attr_name}++;
533 push @attrs => $meta->get_attribute($attr_name);
541 sub add_package_variable {
542 my ($self, $variable, $initial_value) = @_;
543 (defined $variable && $variable =~ /^[\$\@\%]/)
544 || confess "variable name does not have a sigil";
546 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
547 if (defined $initial_value) {
549 *{$self->name . '::' . $name} = $initial_value;
555 # We HAVE to localize $@ or all
556 # hell breaks loose. It is not
557 # good, believe me, not good.
559 eval $sigil . $self->name . '::' . $name;
562 confess "Could not create package variable ($variable) because : $e" if $e;
566 sub has_package_variable {
567 my ($self, $variable) = @_;
568 (defined $variable && $variable =~ /^[\$\@\%]/)
569 || confess "variable name does not have a sigil";
570 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
572 defined ${$self->name . '::'}{$name} ? 1 : 0;
575 sub get_package_variable {
576 my ($self, $variable) = @_;
577 (defined $variable && $variable =~ /^[\$\@\%]/)
578 || confess "variable name does not have a sigil";
579 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
583 # We HAVE to localize $@ or all
584 # hell breaks loose. It is not
585 # good, believe me, not good.
587 $ref = eval '\\' . $sigil . $self->name . '::' . $name;
590 confess "Could not get the package variable ($variable) because : $e" if $e;
591 # if we didn't die, then we can return it
595 sub remove_package_variable {
596 my ($self, $variable) = @_;
597 (defined $variable && $variable =~ /^[\$\@\%]/)
598 || confess "variable name does not have a sigil";
599 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
601 delete ${$self->name . '::'}{$name};
612 Class::MOP::Class - Class Meta Object
616 # assuming that class Foo
617 # has been defined, you can
619 # use this for introspection ...
621 # add a method to Foo ...
622 Foo->meta->add_method('bar' => sub { ... })
624 # get a list of all the classes searched
625 # the method dispatcher in the correct order
626 Foo->meta->class_precedence_list()
628 # remove a method from Foo
629 Foo->meta->remove_method('bar');
631 # or use this to actually create classes ...
633 Class::MOP::Class->create('Bar' => '0.01' => (
634 superclasses => [ 'Foo' ],
636 Class::MOP:::Attribute->new('$bar'),
637 Class::MOP:::Attribute->new('$baz'),
640 calculate_bar => sub { ... },
641 construct_baz => sub { ... }
647 This is the largest and currently most complex part of the Perl 5
648 meta-object protocol. It controls the introspection and
649 manipulation of Perl 5 classes (and it can create them too). The
650 best way to understand what this module can do, is to read the
651 documentation for each of it's methods.
655 =head2 Self Introspection
661 This will return a B<Class::MOP::Class> instance which is related
662 to this class. Thereby allowing B<Class::MOP::Class> to actually
665 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
666 bootstrap this module by installing a number of attribute meta-objects
667 into it's metaclass. This will allow this class to reap all the benifits
668 of the MOP when subclassing it.
670 =item B<get_all_metaclasses>
672 This will return an hash of all the metaclass instances that have
673 been cached by B<Class::MOP::Class> keyed by the package name.
675 =item B<get_all_metaclass_instances>
677 This will return an array of all the metaclass instances that have
678 been cached by B<Class::MOP::Class>.
680 =item B<get_all_metaclass_names>
682 This will return an array of all the metaclass names that have
683 been cached by B<Class::MOP::Class>.
687 =head2 Class construction
689 These methods will handle creating B<Class::MOP::Class> objects,
690 which can be used to both create new classes, and analyze
691 pre-existing classes.
693 This module will internally store references to all the instances
694 you create with these methods, so that they do not need to be
695 created any more than nessecary. Basically, they are singletons.
699 =item B<create ($package_name, ?$package_version,
700 superclasses =E<gt> ?@superclasses,
701 methods =E<gt> ?%methods,
702 attributes =E<gt> ?%attributes)>
704 This returns a B<Class::MOP::Class> object, bringing the specified
705 C<$package_name> into existence and adding any of the
706 C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
709 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
710 methods =E<gt> ?%methods,
711 attributes =E<gt> ?%attributes)>
713 This will create an anonymous class, it works much like C<create> but
714 it does not need a C<$package_name>. Instead it will create a suitably
715 unique package name for you to stash things into.
717 =item B<initialize ($package_name)>
719 This initializes and returns returns a B<Class::MOP::Class> object
720 for a given a C<$package_name>.
722 =item B<construct_class_instance (%options)>
724 This will construct an instance of B<Class::MOP::Class>, it is
725 here so that we can actually "tie the knot" for B<Class::MOP::Class>
726 to use C<construct_instance> once all the bootstrapping is done. This
727 method is used internally by C<initialize> and should never be called
728 from outside of that method really.
730 =item B<check_metaclass_compatability>
732 This method is called as the very last thing in the
733 C<construct_class_instance> method. This will check that the
734 metaclass you are creating is compatible with the metaclasses of all
735 your ancestors. For more inforamtion about metaclass compatibility
736 see the C<About Metaclass compatibility> section in L<Class::MOP>.
740 =head2 Object instance construction and cloning
742 These methods are B<entirely optional>, it is up to you whether you want
747 =item B<new_object (%params)>
749 This is a convience method for creating a new object of the class, and
750 blessing it into the appropriate package as well. Ideally your class
751 would call a C<new> this method like so:
754 my ($class, %param) = @_;
755 $class->meta->new_object(%params);
758 Of course the ideal place for this would actually be in C<UNIVERSAL::>
759 but that is considered bad style, so we do not do that.
761 =item B<construct_instance (%params)>
763 This method is used to construct an instace structure suitable for
764 C<bless>-ing into your package of choice. It works in conjunction
765 with the Attribute protocol to collect all applicable attributes.
767 This will construct and instance using a HASH ref as storage
768 (currently only HASH references are supported). This will collect all
769 the applicable attributes and layout out the fields in the HASH ref,
770 it will then initialize them using either use the corresponding key
771 in C<%params> or any default value or initializer found in the
772 attribute meta-object.
774 =item B<clone_object ($instance, %params)>
776 This is a convience method for cloning an object instance, then
777 blessing it into the appropriate package. This method will call
778 C<clone_instance>, which performs a shallow copy of the object,
779 see that methods documentation for more details. Ideally your
780 class would call a C<clone> this method like so:
783 my ($self, %param) = @_;
784 $self->meta->clone_object($self, %params);
787 Of course the ideal place for this would actually be in C<UNIVERSAL::>
788 but that is considered bad style, so we do not do that.
790 =item B<clone_instance($instance, %params)>
792 This method is a compliment of C<construct_instance> (which means if
793 you override C<construct_instance>, you need to override this one too),
794 and clones the instance shallowly.
796 The cloned structure returned is (like with C<construct_instance>) an
797 unC<bless>ed HASH reference, it is your responsibility to then bless
798 this cloned structure into the right class (which C<clone_object> will
801 As of 0.11, this method will clone the C<$instance> structure shallowly,
802 as opposed to the deep cloning implemented in prior versions. After much
803 thought, research and discussion, I have decided that anything but basic
804 shallow cloning is outside the scope of the meta-object protocol. I
805 think Yuval "nothingmuch" Kogman put it best when he said that cloning
806 is too I<context-specific> to be part of the MOP.
816 This is a read-only attribute which returns the package name for the
817 given B<Class::MOP::Class> instance.
821 This is a read-only attribute which returns the C<$VERSION> of the
822 package for the given B<Class::MOP::Class> instance.
826 =head2 Inheritance Relationships
830 =item B<superclasses (?@superclasses)>
832 This is a read-write attribute which represents the superclass
833 relationships of the class the B<Class::MOP::Class> instance is
834 associated with. Basically, it can get and set the C<@ISA> for you.
837 Perl will occasionally perform some C<@ISA> and method caching, if
838 you decide to change your superclass relationship at runtime (which
839 is quite insane and very much not recommened), then you should be
840 aware of this and the fact that this module does not make any
841 attempt to address this issue.
843 =item B<class_precedence_list>
845 This computes the a list of all the class's ancestors in the same order
846 in which method dispatch will be done. This is similair to
847 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
855 =item B<method_metaclass>
857 =item B<add_method ($method_name, $method)>
859 This will take a C<$method_name> and CODE reference to that
860 C<$method> and install it into the class's package.
863 This does absolutely nothing special to C<$method>
864 other than use B<Sub::Name> to make sure it is tagged with the
865 correct name, and therefore show up correctly in stack traces and
868 =item B<alias_method ($method_name, $method)>
870 This will take a C<$method_name> and CODE reference to that
871 C<$method> and alias the method into the class's package.
874 Unlike C<add_method>, this will B<not> try to name the
875 C<$method> using B<Sub::Name>, it only aliases the method in
878 =item B<has_method ($method_name)>
880 This just provides a simple way to check if the class implements
881 a specific C<$method_name>. It will I<not> however, attempt to check
882 if the class inherits the method (use C<UNIVERSAL::can> for that).
884 This will correctly handle functions defined outside of the package
885 that use a fully qualified name (C<sub Package::name { ... }>).
887 This will correctly handle functions renamed with B<Sub::Name> and
888 installed using the symbol tables. However, if you are naming the
889 subroutine outside of the package scope, you must use the fully
890 qualified name, including the package name, for C<has_method> to
891 correctly identify it.
893 This will attempt to correctly ignore functions imported from other
894 packages using B<Exporter>. It breaks down if the function imported
895 is an C<__ANON__> sub (such as with C<use constant>), which very well
896 may be a valid method being applied to the class.
898 In short, this method cannot always be trusted to determine if the
899 C<$method_name> is actually a method. However, it will DWIM about
900 90% of the time, so it's a small trade off I think.
902 =item B<get_method ($method_name)>
904 This will return a CODE reference of the specified C<$method_name>,
905 or return undef if that method does not exist.
907 =item B<remove_method ($method_name)>
909 This will attempt to remove a given C<$method_name> from the class.
910 It will return the CODE reference that it has removed, and will
911 attempt to use B<Sub::Name> to clear the methods associated name.
913 =item B<get_method_list>
915 This will return a list of method names for all I<locally> defined
916 methods. It does B<not> provide a list of all applicable methods,
917 including any inherited ones. If you want a list of all applicable
918 methods, use the C<compute_all_applicable_methods> method.
920 =item B<compute_all_applicable_methods>
922 This will return a list of all the methods names this class will
923 respond to, taking into account inheritance. The list will be a list of
924 HASH references, each one containing the following information; method
925 name, the name of the class in which the method lives and a CODE
926 reference for the actual method.
928 =item B<find_all_methods_by_name ($method_name)>
930 This will traverse the inheritence hierarchy and locate all methods
931 with a given C<$method_name>. Similar to
932 C<compute_all_applicable_methods> it returns a list of HASH references
933 with the following information; method name (which will always be the
934 same as C<$method_name>), the name of the class in which the method
935 lives and a CODE reference for the actual method.
937 The list of methods produced is a distinct list, meaning there are no
938 duplicates in it. This is especially useful for things like object
939 initialization and destruction where you only want the method called
940 once, and in the correct order.
942 =item B<find_next_method_by_name ($method_name)>
944 This will return the first method to match a given C<$method_name> in
945 the superclasses, this is basically equivalent to calling
946 C<SUPER::$method_name>, but it can be dispatched at runtime.
950 =head2 Method Modifiers
952 Method modifiers are a concept borrowed from CLOS, in which a method
953 can be wrapped with I<before>, I<after> and I<around> method modifiers
954 that will be called everytime the method is called.
956 =head3 How method modifiers work?
958 Method modifiers work by wrapping the original method and then replacing
959 it in the classes symbol table. The wrappers will handle calling all the
960 modifiers in the appropariate orders and preserving the calling context
961 for the original method.
963 Each method modifier serves a particular purpose, which may not be
964 obvious to users of other method wrapping modules. To start with, the
965 return values of I<before> and I<after> modifiers are ignored. This is
966 because thier purpose is B<not> to filter the input and output of the
967 primary method (this is done with an I<around> modifier). This may seem
968 like an odd restriction to some, but doing this allows for simple code
969 to be added at the begining or end of a method call without jeapordizing
970 the normal functioning of the primary method or placing any extra
971 responsibility on the code of the modifier. Of course if you have more
972 complex needs, then use the I<around> modifier, which uses a variation
973 of continutation passing style to allow for a high degree of flexibility.
975 Before and around modifiers are called in last-defined-first-called order,
976 while after modifiers are called in first-defined-first-called order. So
977 the call tree might looks something like this:
987 To see examples of using method modifiers, see the following examples
988 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
989 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
990 classic CLOS usage example in the test F<017_add_method_modifier.t>.
992 =head3 What is the performance impact?
994 Of course there is a performance cost associated with method modifiers,
995 but we have made every effort to make that cost be directly proportional
996 to the amount of modifier features you utilize.
998 The wrapping method does it's best to B<only> do as much work as it
999 absolutely needs to. In order to do this we have moved some of the
1000 performance costs to set-up time, where they are easier to amortize.
1002 All this said, my benchmarks have indicated the following:
1004 simple wrapper with no modifiers 100% slower
1005 simple wrapper with simple before modifier 400% slower
1006 simple wrapper with simple after modifier 450% slower
1007 simple wrapper with simple around modifier 500-550% slower
1008 simple wrapper with all 3 modifiers 1100% slower
1010 These numbers may seem daunting, but you must remember, every feature
1011 comes with some cost. To put things in perspective, just doing a simple
1012 C<AUTOLOAD> which does nothing but extract the name of the method called
1013 and return it costs about 400% over a normal method call.
1017 =item B<add_before_method_modifier ($method_name, $code)>
1019 This will wrap the method at C<$method_name> and the supplied C<$code>
1020 will be passed the C<@_> arguments, and called before the original
1021 method is called. As specified above, the return value of the I<before>
1022 method modifiers is ignored, and it's ability to modify C<@_> is
1023 fairly limited. If you need to do either of these things, use an
1024 C<around> method modifier.
1026 =item B<add_after_method_modifier ($method_name, $code)>
1028 This will wrap the method at C<$method_name> so that the original
1029 method will be called, it's return values stashed, and then the
1030 supplied C<$code> will be passed the C<@_> arguments, and called.
1031 As specified above, the return value of the I<after> method
1032 modifiers is ignored, and it cannot modify the return values of
1033 the original method. If you need to do either of these things, use an
1034 C<around> method modifier.
1036 =item B<add_around_method_modifier ($method_name, $code)>
1038 This will wrap the method at C<$method_name> so that C<$code>
1039 will be called and passed the original method as an extra argument
1040 at the begining of the C<@_> argument list. This is a variation of
1041 continuation passing style, where the function prepended to C<@_>
1042 can be considered a continuation. It is up to C<$code> if it calls
1043 the original method or not, there is no restriction on what the
1044 C<$code> can or cannot do.
1050 It should be noted that since there is no one consistent way to define
1051 the attributes of a class in Perl 5. These methods can only work with
1052 the information given, and can not easily discover information on
1053 their own. See L<Class::MOP::Attribute> for more details.
1057 =item B<attribute_metaclass>
1059 =item B<get_attribute_map>
1061 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1063 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1064 instance associated with the given class, and associates it with
1065 the C<$attribute_name>. Unlike methods, attributes within the MOP
1066 are stored as meta-information only. They will be used later to
1067 construct instances from (see C<construct_instance> above).
1068 More details about the attribute meta-objects can be found in the
1069 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1072 It should be noted that any accessor, reader/writer or predicate
1073 methods which the C<$attribute_meta_object> has will be installed
1074 into the class at this time.
1076 =item B<has_attribute ($attribute_name)>
1078 Checks to see if this class has an attribute by the name of
1079 C<$attribute_name> and returns a boolean.
1081 =item B<get_attribute ($attribute_name)>
1083 Returns the attribute meta-object associated with C<$attribute_name>,
1084 if none is found, it will return undef.
1086 =item B<remove_attribute ($attribute_name)>
1088 This will remove the attribute meta-object stored at
1089 C<$attribute_name>, then return the removed attribute meta-object.
1092 Removing an attribute will only affect future instances of
1093 the class, it will not make any attempt to remove the attribute from
1094 any existing instances of the class.
1096 It should be noted that any accessor, reader/writer or predicate
1097 methods which the attribute meta-object stored at C<$attribute_name>
1098 has will be removed from the class at this time. This B<will> make
1099 these attributes somewhat inaccessable in previously created
1100 instances. But if you are crazy enough to do this at runtime, then
1101 you are crazy enough to deal with something like this :).
1103 =item B<get_attribute_list>
1105 This returns a list of attribute names which are defined in the local
1106 class. If you want a list of all applicable attributes for a class,
1107 use the C<compute_all_applicable_attributes> method.
1109 =item B<compute_all_applicable_attributes>
1111 This will traverse the inheritance heirachy and return a list of all
1112 the applicable attributes for this class. It does not construct a
1113 HASH reference like C<compute_all_applicable_methods> because all
1114 that same information is discoverable through the attribute
1119 =head2 Package Variables
1121 Since Perl's classes are built atop the Perl package system, it is
1122 fairly common to use package scoped variables for things like static
1123 class variables. The following methods are convience methods for
1124 the creation and inspection of package scoped variables.
1128 =item B<add_package_variable ($variable_name, ?$initial_value)>
1130 Given a C<$variable_name>, which must contain a leading sigil, this
1131 method will create that variable within the package which houses the
1132 class. It also takes an optional C<$initial_value>, which must be a
1133 reference of the same type as the sigil of the C<$variable_name>
1136 =item B<get_package_variable ($variable_name)>
1138 This will return a reference to the package variable in
1141 =item B<has_package_variable ($variable_name)>
1143 Returns true (C<1>) if there is a package variable defined for
1144 C<$variable_name>, and false (C<0>) otherwise.
1146 =item B<remove_package_variable ($variable_name)>
1148 This will attempt to remove the package variable at C<$variable_name>.
1154 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1156 =head1 COPYRIGHT AND LICENSE
1158 Copyright 2006 by Infinity Interactive, Inc.
1160 L<http://www.iinteractive.com>
1162 This library is free software; you can redistribute it and/or modify
1163 it under the same terms as Perl itself.