2 package Class::MOP::Class;
8 use Scalar::Util 'blessed', 'reftype';
9 use Sub::Name 'subname';
10 use B 'svref_2object';
12 our $VERSION = '0.14';
14 use Class::MOP::Instance;
18 sub meta { Class::MOP::Class->initialize(blessed($_[0]) || $_[0]) }
23 # Metaclasses are singletons, so we cache them here.
24 # there is no need to worry about destruction though
25 # because they should die only when the program dies.
26 # After all, do package definitions even get reaped?
29 # means of accessing all the metaclasses that have
30 # been initialized thus far (for mugwumps obj browser)
31 sub get_all_metaclasses { %METAS }
32 sub get_all_metaclass_instances { values %METAS }
33 sub get_all_metaclass_names { keys %METAS }
37 my $package_name = shift;
38 (defined $package_name && $package_name && !blessed($package_name))
39 || confess "You must pass a package name and it cannot be blessed";
40 $class->construct_class_instance(':package' => $package_name, @_);
43 # NOTE: (meta-circularity)
44 # this is a special form of &construct_instance
45 # (see below), which is used to construct class
46 # meta-object instances for any Class::MOP::*
47 # class. All other classes will use the more
48 # normal &construct_instance.
49 sub construct_class_instance {
52 my $package_name = $options{':package'};
53 (defined $package_name && $package_name)
54 || confess "You must pass a package name";
56 # return the metaclass if we have it cached,
57 # and it is still defined (it has not been
58 # reaped by DESTROY yet, which can happen
59 # annoyingly enough during global destruction)
60 return $METAS{$package_name}
61 if exists $METAS{$package_name} && defined $METAS{$package_name};
62 $class = blessed($class) || $class;
63 # now create the metaclass
65 if ($class =~ /^Class::MOP::/) {
67 '$:package' => $package_name,
69 '$:attribute_metaclass' => $options{':attribute_metaclass'} || 'Class::MOP::Attribute',
70 '$:method_metaclass' => $options{':method_metaclass'} || 'Class::MOP::Method',
71 '$:instance_metaclass' => $options{':instance_metaclass'} || 'Class::MOP::Instance',
76 # it is safe to use meta here because
77 # class will always be a subclass of
78 # Class::MOP::Class, which defines meta
79 $meta = bless $class->meta->construct_instance(%options) => $class
81 # and check the metaclass compatibility
82 $meta->check_metaclass_compatability();
83 $METAS{$package_name} = $meta;
86 sub check_metaclass_compatability {
89 # this is always okay ...
90 return if blessed($self) eq 'Class::MOP::Class';
92 my @class_list = $self->class_precedence_list;
93 shift @class_list; # shift off $self->name
95 foreach my $class_name (@class_list) {
96 my $meta = $METAS{$class_name} || next;
97 ($self->isa(blessed($meta)))
98 || confess $self->name . "->meta => (" . (blessed($self)) . ")" .
99 " is not compatible with the " .
100 $class_name . "->meta => (" . (blessed($meta)) . ")";
106 my ($class, $package_name, $package_version, %options) = @_;
107 (defined $package_name && $package_name)
108 || confess "You must pass a package name";
109 my $code = "package $package_name;";
110 $code .= "\$$package_name\:\:VERSION = '$package_version';"
111 if defined $package_version;
113 confess "creation of $package_name failed : $@" if $@;
114 my $meta = $class->initialize($package_name);
116 $meta->add_method('meta' => sub {
117 Class::MOP::Class->initialize(blessed($_[0]) || $_[0]);
120 $meta->superclasses(@{$options{superclasses}})
121 if exists $options{superclasses};
123 # process attributes first, so that they can
124 # install accessors, but locally defined methods
125 # can then overwrite them. It is maybe a little odd, but
126 # I think this should be the order of things.
127 if (exists $options{attributes}) {
128 foreach my $attr (@{$options{attributes}}) {
129 $meta->add_attribute($attr);
132 if (exists $options{methods}) {
133 foreach my $method_name (keys %{$options{methods}}) {
134 $meta->add_method($method_name, $options{methods}->{$method_name});
142 # this should be sufficient, if you have a
143 # use case where it is not, write a test and
145 my $ANON_CLASS_SERIAL = 0;
147 sub create_anon_class {
148 my ($class, %options) = @_;
149 my $package_name = 'Class::MOP::Class::__ANON__::SERIAL::' . ++$ANON_CLASS_SERIAL;
150 return $class->create($package_name, '0.00', %options);
157 # all these attribute readers will be bootstrapped
158 # away in the Class::MOP bootstrap section
160 sub name { $_[0]->{'$:package'} }
161 sub get_attribute_map { $_[0]->{'%:attributes'} }
162 sub attribute_metaclass { $_[0]->{'$:attribute_metaclass'} }
163 sub method_metaclass { $_[0]->{'$:method_metaclass'} }
164 sub instance_metaclass { $_[0]->{'$:instance_metaclass'} }
166 # Instance Construction & Cloning
171 # we need to protect the integrity of the
172 # Class::MOP::Class singletons here, so we
173 # delegate this to &construct_class_instance
174 # which will deal with the singletons
175 return $class->construct_class_instance(@_)
176 if $class->name->isa('Class::MOP::Class');
177 return $class->construct_instance(@_);
180 sub construct_instance {
181 my ($class, %params) = @_;
182 my $meta_instance = $class->get_meta_instance();
183 my $instance = $meta_instance->create_instance();
184 $meta_instance->initialize_all_slots($instance);
185 foreach my $attr ($class->compute_all_applicable_attributes()) {
186 $attr->initialize_instance_slot($meta_instance, $instance, \%params);
191 sub get_meta_instance {
193 return $class->instance_metaclass->new(
195 $class->compute_all_applicable_attributes()
201 my $instance = shift;
202 (blessed($instance) && $instance->isa($class->name))
203 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
205 # we need to protect the integrity of the
206 # Class::MOP::Class singletons here, they
207 # should not be cloned.
208 return $instance if $instance->isa('Class::MOP::Class');
209 bless $class->clone_instance($instance, @_) => blessed($instance);
213 my ($class, $instance, %params) = @_;
215 || confess "You can only clone instances, \$self is not a blessed instance";
216 my $clone = { %$instance, %params };
222 # &name should be here too, but it is above
223 # because it gets bootstrapped away
227 ${$self->get_package_variable('$VERSION')};
237 @{$self->name . '::ISA'} = @supers;
239 @{$self->name . '::ISA'};
242 sub class_precedence_list {
245 # We need to check for ciruclar inheirtance here.
246 # This will do nothing if all is well, and blow
247 # up otherwise. Yes, it's an ugly hack, better
248 # suggestions are welcome.
249 { ($self->name || return)->isa('This is a test for circular inheritance') }
250 # ... and now back to our regularly scheduled program
255 # we grab the metaclass from the %METAS
256 # hash here to save the initialize() call
257 # if we can, but it is not always possible
258 ($METAS{$_} || $self->initialize($_))->class_precedence_list()
259 } $self->superclasses()
266 my ($self, $method_name, $method) = @_;
267 (defined $method_name && $method_name)
268 || confess "You must define a method name";
269 # use reftype here to allow for blessed subs ...
270 ('CODE' eq (reftype($method) || ''))
271 || confess "Your code block must be a CODE reference";
272 my $full_method_name = ($self->name . '::' . $method_name);
274 $method = $self->method_metaclass->wrap($method) unless blessed($method);
277 no warnings 'redefine';
278 *{$full_method_name} = subname $full_method_name => $method;
282 my $fetch_and_prepare_method = sub {
283 my ($self, $method_name) = @_;
285 my $method = $self->get_method($method_name);
286 # if we dont have local ...
288 # make sure this method even exists ...
289 ($self->find_next_method_by_name($method_name))
290 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
291 # if so, then create a local which just
292 # calls the next applicable method ...
293 $self->add_method($method_name => sub {
294 $self->find_next_method_by_name($method_name)->(@_);
296 $method = $self->get_method($method_name);
299 # now make sure we wrap it properly
300 # (if it isnt already)
301 unless ($method->isa('Class::MOP::Method::Wrapped')) {
302 $method = Class::MOP::Method::Wrapped->wrap($method);
303 $self->add_method($method_name => $method);
308 sub add_before_method_modifier {
309 my ($self, $method_name, $method_modifier) = @_;
310 (defined $method_name && $method_name)
311 || confess "You must pass in a method name";
312 my $method = $fetch_and_prepare_method->($self, $method_name);
313 $method->add_before_modifier(subname ':before' => $method_modifier);
316 sub add_after_method_modifier {
317 my ($self, $method_name, $method_modifier) = @_;
318 (defined $method_name && $method_name)
319 || confess "You must pass in a method name";
320 my $method = $fetch_and_prepare_method->($self, $method_name);
321 $method->add_after_modifier(subname ':after' => $method_modifier);
324 sub add_around_method_modifier {
325 my ($self, $method_name, $method_modifier) = @_;
326 (defined $method_name && $method_name)
327 || confess "You must pass in a method name";
328 my $method = $fetch_and_prepare_method->($self, $method_name);
329 $method->add_around_modifier(subname ':around' => $method_modifier);
333 # the methods above used to be named like this:
334 # ${pkg}::${method}:(before|after|around)
335 # but this proved problematic when using one modifier
336 # to wrap multiple methods (something which is likely
337 # to happen pretty regularly IMO). So instead of naming
338 # it like this, I have chosen to just name them purely
339 # with their modifier names, like so:
340 # :(before|after|around)
341 # The fact is that in a stack trace, it will be fairly
342 # evident from the context what method they are attached
343 # to, and so don't need the fully qualified name.
347 my ($self, $method_name, $method) = @_;
348 (defined $method_name && $method_name)
349 || confess "You must define a method name";
350 # use reftype here to allow for blessed subs ...
351 ('CODE' eq (reftype($method) || ''))
352 || confess "Your code block must be a CODE reference";
353 my $full_method_name = ($self->name . '::' . $method_name);
355 $method = $self->method_metaclass->wrap($method) unless blessed($method);
358 no warnings 'redefine';
359 *{$full_method_name} = $method;
363 my ($self, $method_name) = @_;
364 (defined $method_name && $method_name)
365 || confess "You must define a method name";
367 my $sub_name = ($self->name . '::' . $method_name);
370 return 0 if !defined(&{$sub_name});
371 my $method = \&{$sub_name};
372 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
373 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
375 # at this point we are relatively sure
376 # it is our method, so we bless/wrap it
377 $self->method_metaclass->wrap($method) unless blessed($method);
382 my ($self, $method_name) = @_;
383 (defined $method_name && $method_name)
384 || confess "You must define a method name";
386 return unless $self->has_method($method_name);
389 return \&{$self->name . '::' . $method_name};
393 my ($self, $method_name) = @_;
394 (defined $method_name && $method_name)
395 || confess "You must define a method name";
397 my $removed_method = $self->get_method($method_name);
400 delete ${$self->name . '::'}{$method_name}
401 if defined $removed_method;
403 return $removed_method;
406 sub get_method_list {
409 grep { $self->has_method($_) } %{$self->name . '::'};
412 sub compute_all_applicable_methods {
415 # keep a record of what we have seen
416 # here, this will handle all the
417 # inheritence issues because we are
418 # using the &class_precedence_list
419 my (%seen_class, %seen_method);
420 foreach my $class ($self->class_precedence_list()) {
421 next if $seen_class{$class};
422 $seen_class{$class}++;
423 # fetch the meta-class ...
424 my $meta = $self->initialize($class);
425 foreach my $method_name ($meta->get_method_list()) {
426 next if exists $seen_method{$method_name};
427 $seen_method{$method_name}++;
429 name => $method_name,
431 code => $meta->get_method($method_name)
438 sub find_all_methods_by_name {
439 my ($self, $method_name) = @_;
440 (defined $method_name && $method_name)
441 || confess "You must define a method name to find";
443 # keep a record of what we have seen
444 # here, this will handle all the
445 # inheritence issues because we are
446 # using the &class_precedence_list
448 foreach my $class ($self->class_precedence_list()) {
449 next if $seen_class{$class};
450 $seen_class{$class}++;
451 # fetch the meta-class ...
452 my $meta = $self->initialize($class);
454 name => $method_name,
456 code => $meta->get_method($method_name)
457 } if $meta->has_method($method_name);
462 sub find_next_method_by_name {
463 my ($self, $method_name) = @_;
464 (defined $method_name && $method_name)
465 || confess "You must define a method name to find";
466 # keep a record of what we have seen
467 # here, this will handle all the
468 # inheritence issues because we are
469 # using the &class_precedence_list
471 my @cpl = $self->class_precedence_list();
472 shift @cpl; # discard ourselves
473 foreach my $class (@cpl) {
474 next if $seen_class{$class};
475 $seen_class{$class}++;
476 # fetch the meta-class ...
477 my $meta = $self->initialize($class);
478 return $meta->get_method($method_name)
479 if $meta->has_method($method_name);
488 # either we have an attribute object already
489 # or we need to create one from the args provided
490 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
491 # make sure it is derived from the correct type though
492 ($attribute->isa('Class::MOP::Attribute'))
493 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
494 $attribute->attach_to_class($self);
495 $attribute->install_accessors();
496 $self->get_attribute_map->{$attribute->name} = $attribute;
499 # in theory we have to tell everyone the slot structure may have changed
503 my ($self, $attribute_name) = @_;
504 (defined $attribute_name && $attribute_name)
505 || confess "You must define an attribute name";
506 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
510 my ($self, $attribute_name) = @_;
511 (defined $attribute_name && $attribute_name)
512 || confess "You must define an attribute name";
514 # we used to say `if $self->has_attribute($attribute_name)`
515 # here, but since get_attribute is called so often, we
516 # eliminate the function call here
517 return $self->{'%:attributes'}->{$attribute_name}
518 if exists $self->{'%:attributes'}->{$attribute_name};
522 sub remove_attribute {
523 my ($self, $attribute_name) = @_;
524 (defined $attribute_name && $attribute_name)
525 || confess "You must define an attribute name";
526 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
527 return unless defined $removed_attribute;
528 delete $self->get_attribute_map->{$attribute_name};
529 $removed_attribute->remove_accessors();
530 $removed_attribute->detach_from_class();
531 return $removed_attribute;
534 sub get_attribute_list {
537 # We don't use get_attribute_map here because
538 # we ask for the attribute list quite often
539 # in compute_all_applicable_attributes, so
540 # eliminating the function call helps
541 keys %{$self->{'%:attributes'}};
544 sub compute_all_applicable_attributes {
547 # keep a record of what we have seen
548 # here, this will handle all the
549 # inheritence issues because we are
550 # using the &class_precedence_list
551 my (%seen_class, %seen_attr);
552 foreach my $class ($self->class_precedence_list()) {
553 next if $seen_class{$class};
554 $seen_class{$class}++;
555 # fetch the meta-class ...
557 # we grab the metaclass from the %METAS
558 # hash here to save the initialize() call
559 my $meta = $METAS{$class};
560 foreach my $attr_name ($meta->get_attribute_list()) {
561 next if exists $seen_attr{$attr_name};
562 $seen_attr{$attr_name}++;
563 push @attrs => $meta->get_attribute($attr_name);
569 sub find_attribute_by_name {
570 my ($self, $attr_name) = @_;
571 # keep a record of what we have seen
572 # here, this will handle all the
573 # inheritence issues because we are
574 # using the &class_precedence_list
576 foreach my $class ($self->class_precedence_list()) {
577 next if $seen_class{$class};
578 $seen_class{$class}++;
579 # fetch the meta-class ...
580 my $meta = $self->initialize($class);
581 return $meta->get_attribute($attr_name)
582 if $meta->has_attribute($attr_name);
589 sub add_package_variable {
590 my ($self, $variable, $initial_value) = @_;
591 (defined $variable && $variable =~ /^[\$\@\%]/)
592 || confess "variable name does not have a sigil";
594 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
595 if (defined $initial_value) {
597 *{$self->name . '::' . $name} = $initial_value;
603 # We HAVE to localize $@ or all
604 # hell breaks loose. It is not
605 # good, believe me, not good.
607 eval $sigil . $self->name . '::' . $name;
610 confess "Could not create package variable ($variable) because : $e" if $e;
614 sub has_package_variable {
615 my ($self, $variable) = @_;
616 (defined $variable && $variable =~ /^[\$\@\%]/)
617 || confess "variable name does not have a sigil";
618 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
620 defined ${$self->name . '::'}{$name} ? 1 : 0;
623 sub get_package_variable {
624 my ($self, $variable) = @_;
625 (defined $variable && $variable =~ /^[\$\@\%]/)
626 || confess "variable name does not have a sigil";
627 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
631 # We HAVE to localize $@ or all
632 # hell breaks loose. It is not
633 # good, believe me, not good.
635 $ref = eval '\\' . $sigil . $self->name . '::' . $name;
638 confess "Could not get the package variable ($variable) because : $e" if $e;
639 # if we didn't die, then we can return it
643 sub remove_package_variable {
644 my ($self, $variable) = @_;
645 (defined $variable && $variable =~ /^[\$\@\%]/)
646 || confess "variable name does not have a sigil";
647 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
649 delete ${$self->name . '::'}{$name};
660 Class::MOP::Class - Class Meta Object
664 # assuming that class Foo
665 # has been defined, you can
667 # use this for introspection ...
669 # add a method to Foo ...
670 Foo->meta->add_method('bar' => sub { ... })
672 # get a list of all the classes searched
673 # the method dispatcher in the correct order
674 Foo->meta->class_precedence_list()
676 # remove a method from Foo
677 Foo->meta->remove_method('bar');
679 # or use this to actually create classes ...
681 Class::MOP::Class->create('Bar' => '0.01' => (
682 superclasses => [ 'Foo' ],
684 Class::MOP:::Attribute->new('$bar'),
685 Class::MOP:::Attribute->new('$baz'),
688 calculate_bar => sub { ... },
689 construct_baz => sub { ... }
695 This is the largest and currently most complex part of the Perl 5
696 meta-object protocol. It controls the introspection and
697 manipulation of Perl 5 classes (and it can create them too). The
698 best way to understand what this module can do, is to read the
699 documentation for each of it's methods.
703 =head2 Self Introspection
709 This will return a B<Class::MOP::Class> instance which is related
710 to this class. Thereby allowing B<Class::MOP::Class> to actually
713 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
714 bootstrap this module by installing a number of attribute meta-objects
715 into it's metaclass. This will allow this class to reap all the benifits
716 of the MOP when subclassing it.
718 =item B<get_all_metaclasses>
720 This will return an hash of all the metaclass instances that have
721 been cached by B<Class::MOP::Class> keyed by the package name.
723 =item B<get_all_metaclass_instances>
725 This will return an array of all the metaclass instances that have
726 been cached by B<Class::MOP::Class>.
728 =item B<get_all_metaclass_names>
730 This will return an array of all the metaclass names that have
731 been cached by B<Class::MOP::Class>.
735 =head2 Class construction
737 These methods will handle creating B<Class::MOP::Class> objects,
738 which can be used to both create new classes, and analyze
739 pre-existing classes.
741 This module will internally store references to all the instances
742 you create with these methods, so that they do not need to be
743 created any more than nessecary. Basically, they are singletons.
747 =item B<create ($package_name, ?$package_version,
748 superclasses =E<gt> ?@superclasses,
749 methods =E<gt> ?%methods,
750 attributes =E<gt> ?%attributes)>
752 This returns a B<Class::MOP::Class> object, bringing the specified
753 C<$package_name> into existence and adding any of the
754 C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
757 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
758 methods =E<gt> ?%methods,
759 attributes =E<gt> ?%attributes)>
761 This will create an anonymous class, it works much like C<create> but
762 it does not need a C<$package_name>. Instead it will create a suitably
763 unique package name for you to stash things into.
765 =item B<initialize ($package_name)>
767 This initializes and returns returns a B<Class::MOP::Class> object
768 for a given a C<$package_name>.
770 =item B<construct_class_instance (%options)>
772 This will construct an instance of B<Class::MOP::Class>, it is
773 here so that we can actually "tie the knot" for B<Class::MOP::Class>
774 to use C<construct_instance> once all the bootstrapping is done. This
775 method is used internally by C<initialize> and should never be called
776 from outside of that method really.
778 =item B<check_metaclass_compatability>
780 This method is called as the very last thing in the
781 C<construct_class_instance> method. This will check that the
782 metaclass you are creating is compatible with the metaclasses of all
783 your ancestors. For more inforamtion about metaclass compatibility
784 see the C<About Metaclass compatibility> section in L<Class::MOP>.
788 =head2 Object instance construction and cloning
790 These methods are B<entirely optional>, it is up to you whether you want
795 =item B<instance_metaclass>
797 =item B<get_meta_instance>
799 =item B<new_object (%params)>
801 This is a convience method for creating a new object of the class, and
802 blessing it into the appropriate package as well. Ideally your class
803 would call a C<new> this method like so:
806 my ($class, %param) = @_;
807 $class->meta->new_object(%params);
810 Of course the ideal place for this would actually be in C<UNIVERSAL::>
811 but that is considered bad style, so we do not do that.
813 =item B<construct_instance (%params)>
815 This method is used to construct an instace structure suitable for
816 C<bless>-ing into your package of choice. It works in conjunction
817 with the Attribute protocol to collect all applicable attributes.
819 This will construct and instance using a HASH ref as storage
820 (currently only HASH references are supported). This will collect all
821 the applicable attributes and layout out the fields in the HASH ref,
822 it will then initialize them using either use the corresponding key
823 in C<%params> or any default value or initializer found in the
824 attribute meta-object.
826 =item B<clone_object ($instance, %params)>
828 This is a convience method for cloning an object instance, then
829 blessing it into the appropriate package. This method will call
830 C<clone_instance>, which performs a shallow copy of the object,
831 see that methods documentation for more details. Ideally your
832 class would call a C<clone> this method like so:
835 my ($self, %param) = @_;
836 $self->meta->clone_object($self, %params);
839 Of course the ideal place for this would actually be in C<UNIVERSAL::>
840 but that is considered bad style, so we do not do that.
842 =item B<clone_instance($instance, %params)>
844 This method is a compliment of C<construct_instance> (which means if
845 you override C<construct_instance>, you need to override this one too),
846 and clones the instance shallowly.
848 The cloned structure returned is (like with C<construct_instance>) an
849 unC<bless>ed HASH reference, it is your responsibility to then bless
850 this cloned structure into the right class (which C<clone_object> will
853 As of 0.11, this method will clone the C<$instance> structure shallowly,
854 as opposed to the deep cloning implemented in prior versions. After much
855 thought, research and discussion, I have decided that anything but basic
856 shallow cloning is outside the scope of the meta-object protocol. I
857 think Yuval "nothingmuch" Kogman put it best when he said that cloning
858 is too I<context-specific> to be part of the MOP.
868 This is a read-only attribute which returns the package name for the
869 given B<Class::MOP::Class> instance.
873 This is a read-only attribute which returns the C<$VERSION> of the
874 package for the given B<Class::MOP::Class> instance.
878 =head2 Inheritance Relationships
882 =item B<superclasses (?@superclasses)>
884 This is a read-write attribute which represents the superclass
885 relationships of the class the B<Class::MOP::Class> instance is
886 associated with. Basically, it can get and set the C<@ISA> for you.
889 Perl will occasionally perform some C<@ISA> and method caching, if
890 you decide to change your superclass relationship at runtime (which
891 is quite insane and very much not recommened), then you should be
892 aware of this and the fact that this module does not make any
893 attempt to address this issue.
895 =item B<class_precedence_list>
897 This computes the a list of all the class's ancestors in the same order
898 in which method dispatch will be done. This is similair to
899 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
907 =item B<method_metaclass>
909 =item B<add_method ($method_name, $method)>
911 This will take a C<$method_name> and CODE reference to that
912 C<$method> and install it into the class's package.
915 This does absolutely nothing special to C<$method>
916 other than use B<Sub::Name> to make sure it is tagged with the
917 correct name, and therefore show up correctly in stack traces and
920 =item B<alias_method ($method_name, $method)>
922 This will take a C<$method_name> and CODE reference to that
923 C<$method> and alias the method into the class's package.
926 Unlike C<add_method>, this will B<not> try to name the
927 C<$method> using B<Sub::Name>, it only aliases the method in
930 =item B<has_method ($method_name)>
932 This just provides a simple way to check if the class implements
933 a specific C<$method_name>. It will I<not> however, attempt to check
934 if the class inherits the method (use C<UNIVERSAL::can> for that).
936 This will correctly handle functions defined outside of the package
937 that use a fully qualified name (C<sub Package::name { ... }>).
939 This will correctly handle functions renamed with B<Sub::Name> and
940 installed using the symbol tables. However, if you are naming the
941 subroutine outside of the package scope, you must use the fully
942 qualified name, including the package name, for C<has_method> to
943 correctly identify it.
945 This will attempt to correctly ignore functions imported from other
946 packages using B<Exporter>. It breaks down if the function imported
947 is an C<__ANON__> sub (such as with C<use constant>), which very well
948 may be a valid method being applied to the class.
950 In short, this method cannot always be trusted to determine if the
951 C<$method_name> is actually a method. However, it will DWIM about
952 90% of the time, so it's a small trade off I think.
954 =item B<get_method ($method_name)>
956 This will return a CODE reference of the specified C<$method_name>,
957 or return undef if that method does not exist.
959 =item B<remove_method ($method_name)>
961 This will attempt to remove a given C<$method_name> from the class.
962 It will return the CODE reference that it has removed, and will
963 attempt to use B<Sub::Name> to clear the methods associated name.
965 =item B<get_method_list>
967 This will return a list of method names for all I<locally> defined
968 methods. It does B<not> provide a list of all applicable methods,
969 including any inherited ones. If you want a list of all applicable
970 methods, use the C<compute_all_applicable_methods> method.
972 =item B<compute_all_applicable_methods>
974 This will return a list of all the methods names this class will
975 respond to, taking into account inheritance. The list will be a list of
976 HASH references, each one containing the following information; method
977 name, the name of the class in which the method lives and a CODE
978 reference for the actual method.
980 =item B<find_all_methods_by_name ($method_name)>
982 This will traverse the inheritence hierarchy and locate all methods
983 with a given C<$method_name>. Similar to
984 C<compute_all_applicable_methods> it returns a list of HASH references
985 with the following information; method name (which will always be the
986 same as C<$method_name>), the name of the class in which the method
987 lives and a CODE reference for the actual method.
989 The list of methods produced is a distinct list, meaning there are no
990 duplicates in it. This is especially useful for things like object
991 initialization and destruction where you only want the method called
992 once, and in the correct order.
994 =item B<find_next_method_by_name ($method_name)>
996 This will return the first method to match a given C<$method_name> in
997 the superclasses, this is basically equivalent to calling
998 C<SUPER::$method_name>, but it can be dispatched at runtime.
1002 =head2 Method Modifiers
1004 Method modifiers are a concept borrowed from CLOS, in which a method
1005 can be wrapped with I<before>, I<after> and I<around> method modifiers
1006 that will be called everytime the method is called.
1008 =head3 How method modifiers work?
1010 Method modifiers work by wrapping the original method and then replacing
1011 it in the classes symbol table. The wrappers will handle calling all the
1012 modifiers in the appropariate orders and preserving the calling context
1013 for the original method.
1015 Each method modifier serves a particular purpose, which may not be
1016 obvious to users of other method wrapping modules. To start with, the
1017 return values of I<before> and I<after> modifiers are ignored. This is
1018 because thier purpose is B<not> to filter the input and output of the
1019 primary method (this is done with an I<around> modifier). This may seem
1020 like an odd restriction to some, but doing this allows for simple code
1021 to be added at the begining or end of a method call without jeapordizing
1022 the normal functioning of the primary method or placing any extra
1023 responsibility on the code of the modifier. Of course if you have more
1024 complex needs, then use the I<around> modifier, which uses a variation
1025 of continutation passing style to allow for a high degree of flexibility.
1027 Before and around modifiers are called in last-defined-first-called order,
1028 while after modifiers are called in first-defined-first-called order. So
1029 the call tree might looks something like this:
1039 To see examples of using method modifiers, see the following examples
1040 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1041 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1042 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1044 =head3 What is the performance impact?
1046 Of course there is a performance cost associated with method modifiers,
1047 but we have made every effort to make that cost be directly proportional
1048 to the amount of modifier features you utilize.
1050 The wrapping method does it's best to B<only> do as much work as it
1051 absolutely needs to. In order to do this we have moved some of the
1052 performance costs to set-up time, where they are easier to amortize.
1054 All this said, my benchmarks have indicated the following:
1056 simple wrapper with no modifiers 100% slower
1057 simple wrapper with simple before modifier 400% slower
1058 simple wrapper with simple after modifier 450% slower
1059 simple wrapper with simple around modifier 500-550% slower
1060 simple wrapper with all 3 modifiers 1100% slower
1062 These numbers may seem daunting, but you must remember, every feature
1063 comes with some cost. To put things in perspective, just doing a simple
1064 C<AUTOLOAD> which does nothing but extract the name of the method called
1065 and return it costs about 400% over a normal method call.
1069 =item B<add_before_method_modifier ($method_name, $code)>
1071 This will wrap the method at C<$method_name> and the supplied C<$code>
1072 will be passed the C<@_> arguments, and called before the original
1073 method is called. As specified above, the return value of the I<before>
1074 method modifiers is ignored, and it's ability to modify C<@_> is
1075 fairly limited. If you need to do either of these things, use an
1076 C<around> method modifier.
1078 =item B<add_after_method_modifier ($method_name, $code)>
1080 This will wrap the method at C<$method_name> so that the original
1081 method will be called, it's return values stashed, and then the
1082 supplied C<$code> will be passed the C<@_> arguments, and called.
1083 As specified above, the return value of the I<after> method
1084 modifiers is ignored, and it cannot modify the return values of
1085 the original method. If you need to do either of these things, use an
1086 C<around> method modifier.
1088 =item B<add_around_method_modifier ($method_name, $code)>
1090 This will wrap the method at C<$method_name> so that C<$code>
1091 will be called and passed the original method as an extra argument
1092 at the begining of the C<@_> argument list. This is a variation of
1093 continuation passing style, where the function prepended to C<@_>
1094 can be considered a continuation. It is up to C<$code> if it calls
1095 the original method or not, there is no restriction on what the
1096 C<$code> can or cannot do.
1102 It should be noted that since there is no one consistent way to define
1103 the attributes of a class in Perl 5. These methods can only work with
1104 the information given, and can not easily discover information on
1105 their own. See L<Class::MOP::Attribute> for more details.
1109 =item B<attribute_metaclass>
1111 =item B<get_attribute_map>
1113 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1115 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1116 instance associated with the given class, and associates it with
1117 the C<$attribute_name>. Unlike methods, attributes within the MOP
1118 are stored as meta-information only. They will be used later to
1119 construct instances from (see C<construct_instance> above).
1120 More details about the attribute meta-objects can be found in the
1121 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1124 It should be noted that any accessor, reader/writer or predicate
1125 methods which the C<$attribute_meta_object> has will be installed
1126 into the class at this time.
1128 =item B<has_attribute ($attribute_name)>
1130 Checks to see if this class has an attribute by the name of
1131 C<$attribute_name> and returns a boolean.
1133 =item B<get_attribute ($attribute_name)>
1135 Returns the attribute meta-object associated with C<$attribute_name>,
1136 if none is found, it will return undef.
1138 =item B<remove_attribute ($attribute_name)>
1140 This will remove the attribute meta-object stored at
1141 C<$attribute_name>, then return the removed attribute meta-object.
1144 Removing an attribute will only affect future instances of
1145 the class, it will not make any attempt to remove the attribute from
1146 any existing instances of the class.
1148 It should be noted that any accessor, reader/writer or predicate
1149 methods which the attribute meta-object stored at C<$attribute_name>
1150 has will be removed from the class at this time. This B<will> make
1151 these attributes somewhat inaccessable in previously created
1152 instances. But if you are crazy enough to do this at runtime, then
1153 you are crazy enough to deal with something like this :).
1155 =item B<get_attribute_list>
1157 This returns a list of attribute names which are defined in the local
1158 class. If you want a list of all applicable attributes for a class,
1159 use the C<compute_all_applicable_attributes> method.
1161 =item B<compute_all_applicable_attributes>
1163 This will traverse the inheritance heirachy and return a list of all
1164 the applicable attributes for this class. It does not construct a
1165 HASH reference like C<compute_all_applicable_methods> because all
1166 that same information is discoverable through the attribute
1169 =item B<find_attribute_by_name ($attr_name)>
1171 This method will traverse the inheritance heirachy and find the
1172 first attribute whose name matches C<$attr_name>, then return it.
1173 It will return undef if nothing is found.
1177 =head2 Package Variables
1179 Since Perl's classes are built atop the Perl package system, it is
1180 fairly common to use package scoped variables for things like static
1181 class variables. The following methods are convience methods for
1182 the creation and inspection of package scoped variables.
1186 =item B<add_package_variable ($variable_name, ?$initial_value)>
1188 Given a C<$variable_name>, which must contain a leading sigil, this
1189 method will create that variable within the package which houses the
1190 class. It also takes an optional C<$initial_value>, which must be a
1191 reference of the same type as the sigil of the C<$variable_name>
1194 =item B<get_package_variable ($variable_name)>
1196 This will return a reference to the package variable in
1199 =item B<has_package_variable ($variable_name)>
1201 Returns true (C<1>) if there is a package variable defined for
1202 C<$variable_name>, and false (C<0>) otherwise.
1204 =item B<remove_package_variable ($variable_name)>
1206 This will attempt to remove the package variable at C<$variable_name>.
1212 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1214 =head1 COPYRIGHT AND LICENSE
1216 Copyright 2006 by Infinity Interactive, Inc.
1218 L<http://www.iinteractive.com>
1220 This library is free software; you can redistribute it and/or modify
1221 it under the same terms as Perl itself.