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 $instance = $class->get_meta_instance->create_instance();
183 foreach my $attr ($class->compute_all_applicable_attributes()) {
184 $attr->initialize_instance_slot($instance, \%params);
189 sub get_meta_instance {
191 return $class->instance_metaclass->new(
193 $class->compute_all_applicable_attributes()
199 my $instance = shift;
200 (blessed($instance) && $instance->isa($class->name))
201 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
203 # we need to protect the integrity of the
204 # Class::MOP::Class singletons here, they
205 # should not be cloned.
206 return $instance if $instance->isa('Class::MOP::Class');
207 bless $class->clone_instance($instance, @_) => blessed($instance);
211 my ($class, $instance, %params) = @_;
213 || confess "You can only clone instances, \$self is not a blessed instance";
214 my $clone = { %$instance, %params };
220 # &name should be here too, but it is above
221 # because it gets bootstrapped away
225 ${$self->get_package_variable('$VERSION')};
235 @{$self->name . '::ISA'} = @supers;
237 @{$self->name . '::ISA'};
240 sub class_precedence_list {
243 # We need to check for ciruclar inheirtance here.
244 # This will do nothing if all is well, and blow
245 # up otherwise. Yes, it's an ugly hack, better
246 # suggestions are welcome.
247 { ($self->name || return)->isa('This is a test for circular inheritance') }
248 # ... and now back to our regularly scheduled program
253 # we grab the metaclass from the %METAS
254 # hash here to save the initialize() call
255 # if we can, but it is not always possible
256 ($METAS{$_} || $self->initialize($_))->class_precedence_list()
257 } $self->superclasses()
264 my ($self, $method_name, $method) = @_;
265 (defined $method_name && $method_name)
266 || confess "You must define a method name";
267 # use reftype here to allow for blessed subs ...
268 ('CODE' eq (reftype($method) || ''))
269 || confess "Your code block must be a CODE reference";
270 my $full_method_name = ($self->name . '::' . $method_name);
272 $method = $self->method_metaclass->wrap($method) unless blessed($method);
275 no warnings 'redefine';
276 *{$full_method_name} = subname $full_method_name => $method;
280 my $fetch_and_prepare_method = sub {
281 my ($self, $method_name) = @_;
283 my $method = $self->get_method($method_name);
284 # if we dont have local ...
286 # make sure this method even exists ...
287 ($self->find_next_method_by_name($method_name))
288 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
289 # if so, then create a local which just
290 # calls the next applicable method ...
291 $self->add_method($method_name => sub {
292 $self->find_next_method_by_name($method_name)->(@_);
294 $method = $self->get_method($method_name);
297 # now make sure we wrap it properly
298 # (if it isnt already)
299 unless ($method->isa('Class::MOP::Method::Wrapped')) {
300 $method = Class::MOP::Method::Wrapped->wrap($method);
301 $self->add_method($method_name => $method);
306 sub add_before_method_modifier {
307 my ($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_before_modifier(subname ':before' => $method_modifier);
314 sub add_after_method_modifier {
315 my ($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_after_modifier(subname ':after' => $method_modifier);
322 sub add_around_method_modifier {
323 my ($self, $method_name, $method_modifier) = @_;
324 (defined $method_name && $method_name)
325 || confess "You must pass in a method name";
326 my $method = $fetch_and_prepare_method->($self, $method_name);
327 $method->add_around_modifier(subname ':around' => $method_modifier);
331 # the methods above used to be named like this:
332 # ${pkg}::${method}:(before|after|around)
333 # but this proved problematic when using one modifier
334 # to wrap multiple methods (something which is likely
335 # to happen pretty regularly IMO). So instead of naming
336 # it like this, I have chosen to just name them purely
337 # with their modifier names, like so:
338 # :(before|after|around)
339 # The fact is that in a stack trace, it will be fairly
340 # evident from the context what method they are attached
341 # to, and so don't need the fully qualified name.
345 my ($self, $method_name, $method) = @_;
346 (defined $method_name && $method_name)
347 || confess "You must define a method name";
348 # use reftype here to allow for blessed subs ...
349 ('CODE' eq (reftype($method) || ''))
350 || confess "Your code block must be a CODE reference";
351 my $full_method_name = ($self->name . '::' . $method_name);
353 $method = $self->method_metaclass->wrap($method) unless blessed($method);
356 no warnings 'redefine';
357 *{$full_method_name} = $method;
361 my ($self, $method_name) = @_;
362 (defined $method_name && $method_name)
363 || confess "You must define a method name";
365 my $sub_name = ($self->name . '::' . $method_name);
368 return 0 if !defined(&{$sub_name});
369 my $method = \&{$sub_name};
370 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
371 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
373 # at this point we are relatively sure
374 # it is our method, so we bless/wrap it
375 $self->method_metaclass->wrap($method) unless blessed($method);
380 my ($self, $method_name) = @_;
381 (defined $method_name && $method_name)
382 || confess "You must define a method name";
384 return unless $self->has_method($method_name);
387 return \&{$self->name . '::' . $method_name};
391 my ($self, $method_name) = @_;
392 (defined $method_name && $method_name)
393 || confess "You must define a method name";
395 my $removed_method = $self->get_method($method_name);
398 delete ${$self->name . '::'}{$method_name}
399 if defined $removed_method;
401 return $removed_method;
404 sub get_method_list {
407 grep { $self->has_method($_) } %{$self->name . '::'};
410 sub compute_all_applicable_methods {
413 # keep a record of what we have seen
414 # here, this will handle all the
415 # inheritence issues because we are
416 # using the &class_precedence_list
417 my (%seen_class, %seen_method);
418 foreach my $class ($self->class_precedence_list()) {
419 next if $seen_class{$class};
420 $seen_class{$class}++;
421 # fetch the meta-class ...
422 my $meta = $self->initialize($class);
423 foreach my $method_name ($meta->get_method_list()) {
424 next if exists $seen_method{$method_name};
425 $seen_method{$method_name}++;
427 name => $method_name,
429 code => $meta->get_method($method_name)
436 sub find_all_methods_by_name {
437 my ($self, $method_name) = @_;
438 (defined $method_name && $method_name)
439 || confess "You must define a method name to find";
441 # keep a record of what we have seen
442 # here, this will handle all the
443 # inheritence issues because we are
444 # using the &class_precedence_list
446 foreach my $class ($self->class_precedence_list()) {
447 next if $seen_class{$class};
448 $seen_class{$class}++;
449 # fetch the meta-class ...
450 my $meta = $self->initialize($class);
452 name => $method_name,
454 code => $meta->get_method($method_name)
455 } if $meta->has_method($method_name);
460 sub find_next_method_by_name {
461 my ($self, $method_name) = @_;
462 (defined $method_name && $method_name)
463 || confess "You must define a method name to find";
464 # keep a record of what we have seen
465 # here, this will handle all the
466 # inheritence issues because we are
467 # using the &class_precedence_list
469 my @cpl = $self->class_precedence_list();
470 shift @cpl; # discard ourselves
471 foreach my $class (@cpl) {
472 next if $seen_class{$class};
473 $seen_class{$class}++;
474 # fetch the meta-class ...
475 my $meta = $self->initialize($class);
476 return $meta->get_method($method_name)
477 if $meta->has_method($method_name);
486 # either we have an attribute object already
487 # or we need to create one from the args provided
488 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
489 # make sure it is derived from the correct type though
490 ($attribute->isa('Class::MOP::Attribute'))
491 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
492 $attribute->attach_to_class($self);
493 $attribute->install_accessors();
494 $self->get_attribute_map->{$attribute->name} = $attribute;
498 my ($self, $attribute_name) = @_;
499 (defined $attribute_name && $attribute_name)
500 || confess "You must define an attribute name";
501 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
505 my ($self, $attribute_name) = @_;
506 (defined $attribute_name && $attribute_name)
507 || confess "You must define an attribute name";
509 # we used to say `if $self->has_attribute($attribute_name)`
510 # here, but since get_attribute is called so often, we
511 # eliminate the function call here
512 return $self->{'%:attributes'}->{$attribute_name}
513 if exists $self->{'%:attributes'}->{$attribute_name};
517 sub remove_attribute {
518 my ($self, $attribute_name) = @_;
519 (defined $attribute_name && $attribute_name)
520 || confess "You must define an attribute name";
521 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
522 return unless defined $removed_attribute;
523 delete $self->get_attribute_map->{$attribute_name};
524 $removed_attribute->remove_accessors();
525 $removed_attribute->detach_from_class();
526 return $removed_attribute;
529 sub get_attribute_list {
532 # We don't use get_attribute_map here because
533 # we ask for the attribute list quite often
534 # in compute_all_applicable_attributes, so
535 # eliminating the function call helps
536 keys %{$self->{'%:attributes'}};
539 sub compute_all_applicable_attributes {
542 # keep a record of what we have seen
543 # here, this will handle all the
544 # inheritence issues because we are
545 # using the &class_precedence_list
546 my (%seen_class, %seen_attr);
547 foreach my $class ($self->class_precedence_list()) {
548 next if $seen_class{$class};
549 $seen_class{$class}++;
550 # fetch the meta-class ...
552 # we grab the metaclass from the %METAS
553 # hash here to save the initialize() call
554 my $meta = $METAS{$class};
555 foreach my $attr_name ($meta->get_attribute_list()) {
556 next if exists $seen_attr{$attr_name};
557 $seen_attr{$attr_name}++;
558 push @attrs => $meta->get_attribute($attr_name);
564 sub find_attribute_by_name {
565 my ($self, $attr_name) = @_;
566 # keep a record of what we have seen
567 # here, this will handle all the
568 # inheritence issues because we are
569 # using the &class_precedence_list
571 foreach my $class ($self->class_precedence_list()) {
572 next if $seen_class{$class};
573 $seen_class{$class}++;
574 # fetch the meta-class ...
575 my $meta = $self->initialize($class);
576 return $meta->get_attribute($attr_name)
577 if $meta->has_attribute($attr_name);
584 sub add_package_variable {
585 my ($self, $variable, $initial_value) = @_;
586 (defined $variable && $variable =~ /^[\$\@\%]/)
587 || confess "variable name does not have a sigil";
589 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
590 if (defined $initial_value) {
592 *{$self->name . '::' . $name} = $initial_value;
598 # We HAVE to localize $@ or all
599 # hell breaks loose. It is not
600 # good, believe me, not good.
602 eval $sigil . $self->name . '::' . $name;
605 confess "Could not create package variable ($variable) because : $e" if $e;
609 sub has_package_variable {
610 my ($self, $variable) = @_;
611 (defined $variable && $variable =~ /^[\$\@\%]/)
612 || confess "variable name does not have a sigil";
613 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
615 defined ${$self->name . '::'}{$name} ? 1 : 0;
618 sub get_package_variable {
619 my ($self, $variable) = @_;
620 (defined $variable && $variable =~ /^[\$\@\%]/)
621 || confess "variable name does not have a sigil";
622 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
626 # We HAVE to localize $@ or all
627 # hell breaks loose. It is not
628 # good, believe me, not good.
630 $ref = eval '\\' . $sigil . $self->name . '::' . $name;
633 confess "Could not get the package variable ($variable) because : $e" if $e;
634 # if we didn't die, then we can return it
638 sub remove_package_variable {
639 my ($self, $variable) = @_;
640 (defined $variable && $variable =~ /^[\$\@\%]/)
641 || confess "variable name does not have a sigil";
642 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
644 delete ${$self->name . '::'}{$name};
655 Class::MOP::Class - Class Meta Object
659 # assuming that class Foo
660 # has been defined, you can
662 # use this for introspection ...
664 # add a method to Foo ...
665 Foo->meta->add_method('bar' => sub { ... })
667 # get a list of all the classes searched
668 # the method dispatcher in the correct order
669 Foo->meta->class_precedence_list()
671 # remove a method from Foo
672 Foo->meta->remove_method('bar');
674 # or use this to actually create classes ...
676 Class::MOP::Class->create('Bar' => '0.01' => (
677 superclasses => [ 'Foo' ],
679 Class::MOP:::Attribute->new('$bar'),
680 Class::MOP:::Attribute->new('$baz'),
683 calculate_bar => sub { ... },
684 construct_baz => sub { ... }
690 This is the largest and currently most complex part of the Perl 5
691 meta-object protocol. It controls the introspection and
692 manipulation of Perl 5 classes (and it can create them too). The
693 best way to understand what this module can do, is to read the
694 documentation for each of it's methods.
698 =head2 Self Introspection
704 This will return a B<Class::MOP::Class> instance which is related
705 to this class. Thereby allowing B<Class::MOP::Class> to actually
708 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
709 bootstrap this module by installing a number of attribute meta-objects
710 into it's metaclass. This will allow this class to reap all the benifits
711 of the MOP when subclassing it.
713 =item B<get_all_metaclasses>
715 This will return an hash of all the metaclass instances that have
716 been cached by B<Class::MOP::Class> keyed by the package name.
718 =item B<get_all_metaclass_instances>
720 This will return an array of all the metaclass instances that have
721 been cached by B<Class::MOP::Class>.
723 =item B<get_all_metaclass_names>
725 This will return an array of all the metaclass names that have
726 been cached by B<Class::MOP::Class>.
730 =head2 Class construction
732 These methods will handle creating B<Class::MOP::Class> objects,
733 which can be used to both create new classes, and analyze
734 pre-existing classes.
736 This module will internally store references to all the instances
737 you create with these methods, so that they do not need to be
738 created any more than nessecary. Basically, they are singletons.
742 =item B<create ($package_name, ?$package_version,
743 superclasses =E<gt> ?@superclasses,
744 methods =E<gt> ?%methods,
745 attributes =E<gt> ?%attributes)>
747 This returns a B<Class::MOP::Class> object, bringing the specified
748 C<$package_name> into existence and adding any of the
749 C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
752 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
753 methods =E<gt> ?%methods,
754 attributes =E<gt> ?%attributes)>
756 This will create an anonymous class, it works much like C<create> but
757 it does not need a C<$package_name>. Instead it will create a suitably
758 unique package name for you to stash things into.
760 =item B<initialize ($package_name)>
762 This initializes and returns returns a B<Class::MOP::Class> object
763 for a given a C<$package_name>.
765 =item B<construct_class_instance (%options)>
767 This will construct an instance of B<Class::MOP::Class>, it is
768 here so that we can actually "tie the knot" for B<Class::MOP::Class>
769 to use C<construct_instance> once all the bootstrapping is done. This
770 method is used internally by C<initialize> and should never be called
771 from outside of that method really.
773 =item B<check_metaclass_compatability>
775 This method is called as the very last thing in the
776 C<construct_class_instance> method. This will check that the
777 metaclass you are creating is compatible with the metaclasses of all
778 your ancestors. For more inforamtion about metaclass compatibility
779 see the C<About Metaclass compatibility> section in L<Class::MOP>.
783 =head2 Object instance construction and cloning
785 These methods are B<entirely optional>, it is up to you whether you want
790 =item B<instance_metaclass>
792 =item B<get_meta_instance>
794 =item B<new_object (%params)>
796 This is a convience method for creating a new object of the class, and
797 blessing it into the appropriate package as well. Ideally your class
798 would call a C<new> this method like so:
801 my ($class, %param) = @_;
802 $class->meta->new_object(%params);
805 Of course the ideal place for this would actually be in C<UNIVERSAL::>
806 but that is considered bad style, so we do not do that.
808 =item B<construct_instance (%params)>
810 This method is used to construct an instace structure suitable for
811 C<bless>-ing into your package of choice. It works in conjunction
812 with the Attribute protocol to collect all applicable attributes.
814 This will construct and instance using a HASH ref as storage
815 (currently only HASH references are supported). This will collect all
816 the applicable attributes and layout out the fields in the HASH ref,
817 it will then initialize them using either use the corresponding key
818 in C<%params> or any default value or initializer found in the
819 attribute meta-object.
821 =item B<clone_object ($instance, %params)>
823 This is a convience method for cloning an object instance, then
824 blessing it into the appropriate package. This method will call
825 C<clone_instance>, which performs a shallow copy of the object,
826 see that methods documentation for more details. Ideally your
827 class would call a C<clone> this method like so:
830 my ($self, %param) = @_;
831 $self->meta->clone_object($self, %params);
834 Of course the ideal place for this would actually be in C<UNIVERSAL::>
835 but that is considered bad style, so we do not do that.
837 =item B<clone_instance($instance, %params)>
839 This method is a compliment of C<construct_instance> (which means if
840 you override C<construct_instance>, you need to override this one too),
841 and clones the instance shallowly.
843 The cloned structure returned is (like with C<construct_instance>) an
844 unC<bless>ed HASH reference, it is your responsibility to then bless
845 this cloned structure into the right class (which C<clone_object> will
848 As of 0.11, this method will clone the C<$instance> structure shallowly,
849 as opposed to the deep cloning implemented in prior versions. After much
850 thought, research and discussion, I have decided that anything but basic
851 shallow cloning is outside the scope of the meta-object protocol. I
852 think Yuval "nothingmuch" Kogman put it best when he said that cloning
853 is too I<context-specific> to be part of the MOP.
863 This is a read-only attribute which returns the package name for the
864 given B<Class::MOP::Class> instance.
868 This is a read-only attribute which returns the C<$VERSION> of the
869 package for the given B<Class::MOP::Class> instance.
873 =head2 Inheritance Relationships
877 =item B<superclasses (?@superclasses)>
879 This is a read-write attribute which represents the superclass
880 relationships of the class the B<Class::MOP::Class> instance is
881 associated with. Basically, it can get and set the C<@ISA> for you.
884 Perl will occasionally perform some C<@ISA> and method caching, if
885 you decide to change your superclass relationship at runtime (which
886 is quite insane and very much not recommened), then you should be
887 aware of this and the fact that this module does not make any
888 attempt to address this issue.
890 =item B<class_precedence_list>
892 This computes the a list of all the class's ancestors in the same order
893 in which method dispatch will be done. This is similair to
894 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
902 =item B<method_metaclass>
904 =item B<add_method ($method_name, $method)>
906 This will take a C<$method_name> and CODE reference to that
907 C<$method> and install it into the class's package.
910 This does absolutely nothing special to C<$method>
911 other than use B<Sub::Name> to make sure it is tagged with the
912 correct name, and therefore show up correctly in stack traces and
915 =item B<alias_method ($method_name, $method)>
917 This will take a C<$method_name> and CODE reference to that
918 C<$method> and alias the method into the class's package.
921 Unlike C<add_method>, this will B<not> try to name the
922 C<$method> using B<Sub::Name>, it only aliases the method in
925 =item B<has_method ($method_name)>
927 This just provides a simple way to check if the class implements
928 a specific C<$method_name>. It will I<not> however, attempt to check
929 if the class inherits the method (use C<UNIVERSAL::can> for that).
931 This will correctly handle functions defined outside of the package
932 that use a fully qualified name (C<sub Package::name { ... }>).
934 This will correctly handle functions renamed with B<Sub::Name> and
935 installed using the symbol tables. However, if you are naming the
936 subroutine outside of the package scope, you must use the fully
937 qualified name, including the package name, for C<has_method> to
938 correctly identify it.
940 This will attempt to correctly ignore functions imported from other
941 packages using B<Exporter>. It breaks down if the function imported
942 is an C<__ANON__> sub (such as with C<use constant>), which very well
943 may be a valid method being applied to the class.
945 In short, this method cannot always be trusted to determine if the
946 C<$method_name> is actually a method. However, it will DWIM about
947 90% of the time, so it's a small trade off I think.
949 =item B<get_method ($method_name)>
951 This will return a CODE reference of the specified C<$method_name>,
952 or return undef if that method does not exist.
954 =item B<remove_method ($method_name)>
956 This will attempt to remove a given C<$method_name> from the class.
957 It will return the CODE reference that it has removed, and will
958 attempt to use B<Sub::Name> to clear the methods associated name.
960 =item B<get_method_list>
962 This will return a list of method names for all I<locally> defined
963 methods. It does B<not> provide a list of all applicable methods,
964 including any inherited ones. If you want a list of all applicable
965 methods, use the C<compute_all_applicable_methods> method.
967 =item B<compute_all_applicable_methods>
969 This will return a list of all the methods names this class will
970 respond to, taking into account inheritance. The list will be a list of
971 HASH references, each one containing the following information; method
972 name, the name of the class in which the method lives and a CODE
973 reference for the actual method.
975 =item B<find_all_methods_by_name ($method_name)>
977 This will traverse the inheritence hierarchy and locate all methods
978 with a given C<$method_name>. Similar to
979 C<compute_all_applicable_methods> it returns a list of HASH references
980 with the following information; method name (which will always be the
981 same as C<$method_name>), the name of the class in which the method
982 lives and a CODE reference for the actual method.
984 The list of methods produced is a distinct list, meaning there are no
985 duplicates in it. This is especially useful for things like object
986 initialization and destruction where you only want the method called
987 once, and in the correct order.
989 =item B<find_next_method_by_name ($method_name)>
991 This will return the first method to match a given C<$method_name> in
992 the superclasses, this is basically equivalent to calling
993 C<SUPER::$method_name>, but it can be dispatched at runtime.
997 =head2 Method Modifiers
999 Method modifiers are a concept borrowed from CLOS, in which a method
1000 can be wrapped with I<before>, I<after> and I<around> method modifiers
1001 that will be called everytime the method is called.
1003 =head3 How method modifiers work?
1005 Method modifiers work by wrapping the original method and then replacing
1006 it in the classes symbol table. The wrappers will handle calling all the
1007 modifiers in the appropariate orders and preserving the calling context
1008 for the original method.
1010 Each method modifier serves a particular purpose, which may not be
1011 obvious to users of other method wrapping modules. To start with, the
1012 return values of I<before> and I<after> modifiers are ignored. This is
1013 because thier purpose is B<not> to filter the input and output of the
1014 primary method (this is done with an I<around> modifier). This may seem
1015 like an odd restriction to some, but doing this allows for simple code
1016 to be added at the begining or end of a method call without jeapordizing
1017 the normal functioning of the primary method or placing any extra
1018 responsibility on the code of the modifier. Of course if you have more
1019 complex needs, then use the I<around> modifier, which uses a variation
1020 of continutation passing style to allow for a high degree of flexibility.
1022 Before and around modifiers are called in last-defined-first-called order,
1023 while after modifiers are called in first-defined-first-called order. So
1024 the call tree might looks something like this:
1034 To see examples of using method modifiers, see the following examples
1035 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1036 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1037 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1039 =head3 What is the performance impact?
1041 Of course there is a performance cost associated with method modifiers,
1042 but we have made every effort to make that cost be directly proportional
1043 to the amount of modifier features you utilize.
1045 The wrapping method does it's best to B<only> do as much work as it
1046 absolutely needs to. In order to do this we have moved some of the
1047 performance costs to set-up time, where they are easier to amortize.
1049 All this said, my benchmarks have indicated the following:
1051 simple wrapper with no modifiers 100% slower
1052 simple wrapper with simple before modifier 400% slower
1053 simple wrapper with simple after modifier 450% slower
1054 simple wrapper with simple around modifier 500-550% slower
1055 simple wrapper with all 3 modifiers 1100% slower
1057 These numbers may seem daunting, but you must remember, every feature
1058 comes with some cost. To put things in perspective, just doing a simple
1059 C<AUTOLOAD> which does nothing but extract the name of the method called
1060 and return it costs about 400% over a normal method call.
1064 =item B<add_before_method_modifier ($method_name, $code)>
1066 This will wrap the method at C<$method_name> and the supplied C<$code>
1067 will be passed the C<@_> arguments, and called before the original
1068 method is called. As specified above, the return value of the I<before>
1069 method modifiers is ignored, and it's ability to modify C<@_> is
1070 fairly limited. If you need to do either of these things, use an
1071 C<around> method modifier.
1073 =item B<add_after_method_modifier ($method_name, $code)>
1075 This will wrap the method at C<$method_name> so that the original
1076 method will be called, it's return values stashed, and then the
1077 supplied C<$code> will be passed the C<@_> arguments, and called.
1078 As specified above, the return value of the I<after> method
1079 modifiers is ignored, and it cannot modify the return values of
1080 the original method. If you need to do either of these things, use an
1081 C<around> method modifier.
1083 =item B<add_around_method_modifier ($method_name, $code)>
1085 This will wrap the method at C<$method_name> so that C<$code>
1086 will be called and passed the original method as an extra argument
1087 at the begining of the C<@_> argument list. This is a variation of
1088 continuation passing style, where the function prepended to C<@_>
1089 can be considered a continuation. It is up to C<$code> if it calls
1090 the original method or not, there is no restriction on what the
1091 C<$code> can or cannot do.
1097 It should be noted that since there is no one consistent way to define
1098 the attributes of a class in Perl 5. These methods can only work with
1099 the information given, and can not easily discover information on
1100 their own. See L<Class::MOP::Attribute> for more details.
1104 =item B<attribute_metaclass>
1106 =item B<get_attribute_map>
1108 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1110 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1111 instance associated with the given class, and associates it with
1112 the C<$attribute_name>. Unlike methods, attributes within the MOP
1113 are stored as meta-information only. They will be used later to
1114 construct instances from (see C<construct_instance> above).
1115 More details about the attribute meta-objects can be found in the
1116 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1119 It should be noted that any accessor, reader/writer or predicate
1120 methods which the C<$attribute_meta_object> has will be installed
1121 into the class at this time.
1123 =item B<has_attribute ($attribute_name)>
1125 Checks to see if this class has an attribute by the name of
1126 C<$attribute_name> and returns a boolean.
1128 =item B<get_attribute ($attribute_name)>
1130 Returns the attribute meta-object associated with C<$attribute_name>,
1131 if none is found, it will return undef.
1133 =item B<remove_attribute ($attribute_name)>
1135 This will remove the attribute meta-object stored at
1136 C<$attribute_name>, then return the removed attribute meta-object.
1139 Removing an attribute will only affect future instances of
1140 the class, it will not make any attempt to remove the attribute from
1141 any existing instances of the class.
1143 It should be noted that any accessor, reader/writer or predicate
1144 methods which the attribute meta-object stored at C<$attribute_name>
1145 has will be removed from the class at this time. This B<will> make
1146 these attributes somewhat inaccessable in previously created
1147 instances. But if you are crazy enough to do this at runtime, then
1148 you are crazy enough to deal with something like this :).
1150 =item B<get_attribute_list>
1152 This returns a list of attribute names which are defined in the local
1153 class. If you want a list of all applicable attributes for a class,
1154 use the C<compute_all_applicable_attributes> method.
1156 =item B<compute_all_applicable_attributes>
1158 This will traverse the inheritance heirachy and return a list of all
1159 the applicable attributes for this class. It does not construct a
1160 HASH reference like C<compute_all_applicable_methods> because all
1161 that same information is discoverable through the attribute
1164 =item B<find_attribute_by_name ($attr_name)>
1166 This method will traverse the inheritance heirachy and find the
1167 first attribute whose name matches C<$attr_name>, then return it.
1168 It will return undef if nothing is found.
1172 =head2 Package Variables
1174 Since Perl's classes are built atop the Perl package system, it is
1175 fairly common to use package scoped variables for things like static
1176 class variables. The following methods are convience methods for
1177 the creation and inspection of package scoped variables.
1181 =item B<add_package_variable ($variable_name, ?$initial_value)>
1183 Given a C<$variable_name>, which must contain a leading sigil, this
1184 method will create that variable within the package which houses the
1185 class. It also takes an optional C<$initial_value>, which must be a
1186 reference of the same type as the sigil of the C<$variable_name>
1189 =item B<get_package_variable ($variable_name)>
1191 This will return a reference to the package variable in
1194 =item B<has_package_variable ($variable_name)>
1196 Returns true (C<1>) if there is a package variable defined for
1197 C<$variable_name>, and false (C<0>) otherwise.
1199 =item B<remove_package_variable ($variable_name)>
1201 This will attempt to remove the package variable at C<$variable_name>.
1207 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1209 =head1 COPYRIGHT AND LICENSE
1211 Copyright 2006 by Infinity Interactive, Inc.
1213 L<http://www.iinteractive.com>
1215 This library is free software; you can redistribute it and/or modify
1216 it under the same terms as Perl itself.