2 package Class::MOP::Class;
8 use Scalar::Util 'blessed', 'reftype', 'weaken';
9 use Sub::Name 'subname';
10 use B 'svref_2object';
12 our $VERSION = '0.20';
13 our $AUTHORITY = 'cpan:STEVAN';
15 use base 'Class::MOP::Module';
17 use Class::MOP::Instance;
21 sub meta { Class::MOP::Class->initialize(blessed($_[0]) || $_[0]) }
27 my $package_name = shift;
28 (defined $package_name && $package_name && !blessed($package_name))
29 || confess "You must pass a package name and it cannot be blessed";
30 $class->construct_class_instance(':package' => $package_name, @_);
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::MOP::remove_metaclass_by_name($package_name);
39 $class->construct_class_instance(':package' => $package_name, @_);
42 # NOTE: (meta-circularity)
43 # this is a special form of &construct_instance
44 # (see below), which is used to construct class
45 # meta-object instances for any Class::MOP::*
46 # class. All other classes will use the more
47 # normal &construct_instance.
48 sub construct_class_instance {
51 my $package_name = $options{':package'};
52 (defined $package_name && $package_name)
53 || confess "You must pass a package name";
55 # return the metaclass if we have it cached,
56 # and it is still defined (it has not been
57 # reaped by DESTROY yet, which can happen
58 # annoyingly enough during global destruction)
59 return Class::MOP::get_metaclass_by_name($package_name)
60 if Class::MOP::does_metaclass_exist($package_name);
63 # we need to deal with the possibility
64 # of class immutability here, and then
65 # get the name of the class appropriately
66 $class = (blessed($class)
67 ? ($class->is_immutable
68 ? $class->get_mutable_metaclass_name()
72 $class = blessed($class) || $class;
73 # now create the metaclass
75 if ($class =~ /^Class::MOP::Class$/) {
78 # inherited from Class::MOP::Package
79 '$:package' => $package_name,
82 # since the following attributes will
83 # actually be loaded from the symbol
84 # table, and actually bypass the instance
85 # entirely, we can just leave these things
86 # listed here for reference, because they
87 # should not actually have a value associated
89 '%:namespace' => \undef,
90 # inherited from Class::MOP::Module
91 '$:version' => \undef,
92 '$:authority' => \undef,
93 # defined in Class::MOP::Class
97 '$:attribute_metaclass' => $options{':attribute_metaclass'} || 'Class::MOP::Attribute',
98 '$:method_metaclass' => $options{':method_metaclass'} || 'Class::MOP::Method',
99 '$:instance_metaclass' => $options{':instance_metaclass'} || 'Class::MOP::Instance',
104 # it is safe to use meta here because
105 # class will always be a subclass of
106 # Class::MOP::Class, which defines meta
107 $meta = $class->meta->construct_instance(%options)
110 # and check the metaclass compatibility
111 $meta->check_metaclass_compatability();
113 Class::MOP::store_metaclass_by_name($package_name, $meta);
116 # we need to weaken any anon classes
117 # so that they can call DESTROY properly
118 Class::MOP::weaken_metaclass($package_name) if $meta->is_anon_class;
123 sub check_metaclass_compatability {
126 # this is always okay ...
127 return if blessed($self) eq 'Class::MOP::Class' &&
128 $self->instance_metaclass eq 'Class::MOP::Instance';
130 my @class_list = $self->class_precedence_list;
131 shift @class_list; # shift off $self->name
133 foreach my $class_name (@class_list) {
134 my $meta = Class::MOP::get_metaclass_by_name($class_name) || next;
137 # we need to deal with the possibility
138 # of class immutability here, and then
139 # get the name of the class appropriately
140 my $meta_type = ($meta->is_immutable
141 ? $meta->get_mutable_metaclass_name()
144 ($self->isa($meta_type))
145 || confess $self->name . "->meta => (" . (blessed($self)) . ")" .
146 " is not compatible with the " .
147 $class_name . "->meta => (" . ($meta_type) . ")";
149 # we also need to check that instance metaclasses
150 # are compatabile in the same the class.
151 ($self->instance_metaclass->isa($meta->instance_metaclass))
152 || confess $self->name . "->meta => (" . ($self->instance_metaclass) . ")" .
153 " is not compatible with the " .
154 $class_name . "->meta => (" . ($meta->instance_metaclass) . ")";
162 # this should be sufficient, if you have a
163 # use case where it is not, write a test and
165 my $ANON_CLASS_SERIAL = 0;
168 # we need a sufficiently annoying prefix
169 # this should suffice for now, this is
170 # used in a couple of places below, so
171 # need to put it up here for now.
172 my $ANON_CLASS_PREFIX = 'Class::MOP::Class::__ANON__::SERIAL::';
176 $self->name =~ /^$ANON_CLASS_PREFIX/ ? 1 : 0;
179 sub create_anon_class {
180 my ($class, %options) = @_;
181 my $package_name = $ANON_CLASS_PREFIX . ++$ANON_CLASS_SERIAL;
182 return $class->create($package_name, %options);
186 # this will only get called for
187 # anon-classes, all other calls
188 # are assumed to occur during
189 # global destruction and so don't
190 # really need to be handled explicitly
193 return unless $self->name =~ /^$ANON_CLASS_PREFIX/;
194 my ($serial_id) = ($self->name =~ /^$ANON_CLASS_PREFIX(\d+)/);
196 foreach my $key (keys %{$ANON_CLASS_PREFIX . $serial_id}) {
197 delete ${$ANON_CLASS_PREFIX . $serial_id}{$key};
199 delete ${'main::' . $ANON_CLASS_PREFIX}{$serial_id . '::'};
204 # creating classes with MOP ...
208 my $package_name = shift;
210 (defined $package_name && $package_name)
211 || confess "You must pass a package name";
214 || confess "You much pass all parameters as name => value pairs " .
215 "(I found an uneven number of params in \@_)";
219 my $code = "package $package_name;";
220 $code .= "\$$package_name\:\:VERSION = '" . $options{version} . "';"
221 if exists $options{version};
222 $code .= "\$$package_name\:\:AUTHORITY = '" . $options{authority} . "';"
223 if exists $options{authority};
226 confess "creation of $package_name failed : $@" if $@;
228 my $meta = $class->initialize($package_name);
230 $meta->add_method('meta' => sub {
231 $class->initialize(blessed($_[0]) || $_[0]);
234 $meta->superclasses(@{$options{superclasses}})
235 if exists $options{superclasses};
237 # process attributes first, so that they can
238 # install accessors, but locally defined methods
239 # can then overwrite them. It is maybe a little odd, but
240 # I think this should be the order of things.
241 if (exists $options{attributes}) {
242 foreach my $attr (@{$options{attributes}}) {
243 $meta->add_attribute($attr);
246 if (exists $options{methods}) {
247 foreach my $method_name (keys %{$options{methods}}) {
248 $meta->add_method($method_name, $options{methods}->{$method_name});
257 # all these attribute readers will be bootstrapped
258 # away in the Class::MOP bootstrap section
260 sub get_attribute_map { $_[0]->{'%:attributes'} }
261 sub attribute_metaclass { $_[0]->{'$:attribute_metaclass'} }
262 sub method_metaclass { $_[0]->{'$:method_metaclass'} }
263 sub instance_metaclass { $_[0]->{'$:instance_metaclass'} }
266 # this is a prime canidate for conversion to XS
269 my $map = $self->{'%:methods'};
271 my $class_name = $self->name;
272 my $method_metaclass = $self->method_metaclass;
274 foreach my $symbol ($self->list_all_package_symbols('CODE')) {
275 my $code = $self->get_package_symbol('&' . $symbol);
277 next if exists $map->{$symbol} && $map->{$symbol}->body == $code;
279 my $gv = svref_2object($code)->GV;
280 next if ($gv->STASH->NAME || '') ne $class_name &&
281 ($gv->NAME || '') ne '__ANON__';
283 $map->{$symbol} = $method_metaclass->wrap($code);
289 # Instance Construction & Cloning
294 # we need to protect the integrity of the
295 # Class::MOP::Class singletons here, so we
296 # delegate this to &construct_class_instance
297 # which will deal with the singletons
298 return $class->construct_class_instance(@_)
299 if $class->name->isa('Class::MOP::Class');
300 return $class->construct_instance(@_);
303 sub construct_instance {
304 my ($class, %params) = @_;
305 my $meta_instance = $class->get_meta_instance();
306 my $instance = $meta_instance->create_instance();
307 foreach my $attr ($class->compute_all_applicable_attributes()) {
308 $attr->initialize_instance_slot($meta_instance, $instance, \%params);
313 sub get_meta_instance {
315 return $class->instance_metaclass->new(
317 $class->compute_all_applicable_attributes()
323 my $instance = shift;
324 (blessed($instance) && $instance->isa($class->name))
325 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
327 # we need to protect the integrity of the
328 # Class::MOP::Class singletons here, they
329 # should not be cloned.
330 return $instance if $instance->isa('Class::MOP::Class');
331 $class->clone_instance($instance, @_);
335 my ($class, $instance, %params) = @_;
337 || confess "You can only clone instances, \$self is not a blessed instance";
338 my $meta_instance = $class->get_meta_instance();
339 my $clone = $meta_instance->clone_instance($instance);
340 foreach my $key (keys %params) {
341 next unless $meta_instance->is_valid_slot($key);
342 $meta_instance->set_slot_value($clone, $key, $params{$key});
353 @{$self->get_package_symbol('@ISA')} = @supers;
355 # we need to check the metaclass
356 # compatability here so that we can
357 # be sure that the superclass is
358 # not potentially creating an issues
359 # we don't know about
360 $self->check_metaclass_compatability();
362 @{$self->get_package_symbol('@ISA')};
365 sub class_precedence_list {
368 # We need to check for ciruclar inheirtance here.
369 # This will do nothing if all is well, and blow
370 # up otherwise. Yes, it's an ugly hack, better
371 # suggestions are welcome.
372 { ($self->name || return)->isa('This is a test for circular inheritance') }
373 # ... and now back to our regularly scheduled program
377 $self->initialize($_)->class_precedence_list()
378 } $self->superclasses()
385 my ($self, $method_name, $method) = @_;
386 (defined $method_name && $method_name)
387 || confess "You must define a method name";
390 if (blessed($method)) {
391 $body = $method->body;
395 ('CODE' eq (reftype($body) || ''))
396 || confess "Your code block must be a CODE reference";
397 $method = $self->method_metaclass->wrap($body);
399 $self->get_method_map->{$method_name} = $method;
401 my $full_method_name = ($self->name . '::' . $method_name);
402 $self->add_package_symbol("&${method_name}" => subname $full_method_name => $body);
406 my $fetch_and_prepare_method = sub {
407 my ($self, $method_name) = @_;
409 my $method = $self->get_method($method_name);
410 # if we dont have local ...
412 # try to find the next method
413 $method = $self->find_next_method_by_name($method_name);
414 # die if it does not exist
416 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
417 # and now make sure to wrap it
418 # even if it is already wrapped
419 # because we need a new sub ref
420 $method = Class::MOP::Method::Wrapped->wrap($method);
423 # now make sure we wrap it properly
424 $method = Class::MOP::Method::Wrapped->wrap($method)
425 unless $method->isa('Class::MOP::Method::Wrapped');
427 $self->add_method($method_name => $method);
431 sub add_before_method_modifier {
432 my ($self, $method_name, $method_modifier) = @_;
433 (defined $method_name && $method_name)
434 || confess "You must pass in a method name";
435 my $method = $fetch_and_prepare_method->($self, $method_name);
436 $method->add_before_modifier(subname ':before' => $method_modifier);
439 sub add_after_method_modifier {
440 my ($self, $method_name, $method_modifier) = @_;
441 (defined $method_name && $method_name)
442 || confess "You must pass in a method name";
443 my $method = $fetch_and_prepare_method->($self, $method_name);
444 $method->add_after_modifier(subname ':after' => $method_modifier);
447 sub add_around_method_modifier {
448 my ($self, $method_name, $method_modifier) = @_;
449 (defined $method_name && $method_name)
450 || confess "You must pass in a method name";
451 my $method = $fetch_and_prepare_method->($self, $method_name);
452 $method->add_around_modifier(subname ':around' => $method_modifier);
456 # the methods above used to be named like this:
457 # ${pkg}::${method}:(before|after|around)
458 # but this proved problematic when using one modifier
459 # to wrap multiple methods (something which is likely
460 # to happen pretty regularly IMO). So instead of naming
461 # it like this, I have chosen to just name them purely
462 # with their modifier names, like so:
463 # :(before|after|around)
464 # The fact is that in a stack trace, it will be fairly
465 # evident from the context what method they are attached
466 # to, and so don't need the fully qualified name.
470 my ($self, $method_name, $method) = @_;
471 (defined $method_name && $method_name)
472 || confess "You must define a method name";
474 my $body = (blessed($method) ? $method->body : $method);
475 ('CODE' eq (reftype($body) || ''))
476 || confess "Your code block must be a CODE reference";
478 $self->add_package_symbol("&${method_name}" => $body);
482 my ($self, $method_name) = @_;
483 (defined $method_name && $method_name)
484 || confess "You must define a method name";
486 return 0 unless exists $self->get_method_map->{$method_name};
491 my ($self, $method_name) = @_;
492 (defined $method_name && $method_name)
493 || confess "You must define a method name";
496 # I don't really need this here, because
497 # if the method_map is missing a key it
498 # will just return undef for me now
499 # return unless $self->has_method($method_name);
501 return $self->get_method_map->{$method_name};
505 my ($self, $method_name) = @_;
506 (defined $method_name && $method_name)
507 || confess "You must define a method name";
509 my $removed_method = $self->get_method($method_name);
512 $self->remove_package_symbol("&${method_name}");
513 delete $self->get_method_map->{$method_name};
514 } if defined $removed_method;
516 return $removed_method;
519 sub get_method_list {
521 keys %{$self->get_method_map};
524 sub find_method_by_name {
525 my ($self, $method_name) = @_;
527 return $self->name->can($method_name);
530 sub compute_all_applicable_methods {
533 # keep a record of what we have seen
534 # here, this will handle all the
535 # inheritence issues because we are
536 # using the &class_precedence_list
537 my (%seen_class, %seen_method);
538 foreach my $class ($self->class_precedence_list()) {
539 next if $seen_class{$class};
540 $seen_class{$class}++;
541 # fetch the meta-class ...
542 my $meta = $self->initialize($class);
543 foreach my $method_name ($meta->get_method_list()) {
544 next if exists $seen_method{$method_name};
545 $seen_method{$method_name}++;
547 name => $method_name,
549 code => $meta->get_method($method_name)
556 sub find_all_methods_by_name {
557 my ($self, $method_name) = @_;
558 (defined $method_name && $method_name)
559 || confess "You must define a method name to find";
561 # keep a record of what we have seen
562 # here, this will handle all the
563 # inheritence issues because we are
564 # using the &class_precedence_list
566 foreach my $class ($self->class_precedence_list()) {
567 next if $seen_class{$class};
568 $seen_class{$class}++;
569 # fetch the meta-class ...
570 my $meta = $self->initialize($class);
572 name => $method_name,
574 code => $meta->get_method($method_name)
575 } if $meta->has_method($method_name);
580 sub find_next_method_by_name {
581 my ($self, $method_name) = @_;
582 (defined $method_name && $method_name)
583 || confess "You must define a method name to find";
584 # keep a record of what we have seen
585 # here, this will handle all the
586 # inheritence issues because we are
587 # using the &class_precedence_list
589 my @cpl = $self->class_precedence_list();
590 shift @cpl; # discard ourselves
591 foreach my $class (@cpl) {
592 next if $seen_class{$class};
593 $seen_class{$class}++;
594 # fetch the meta-class ...
595 my $meta = $self->initialize($class);
596 return $meta->get_method($method_name)
597 if $meta->has_method($method_name);
606 # either we have an attribute object already
607 # or we need to create one from the args provided
608 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
609 # make sure it is derived from the correct type though
610 ($attribute->isa('Class::MOP::Attribute'))
611 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
613 # first we attach our new attribute
614 # because it might need certain information
615 # about the class which it is attached to
616 $attribute->attach_to_class($self);
618 # then we remove attributes of a conflicting
619 # name here so that we can properly detach
620 # the old attr object, and remove any
621 # accessors it would have generated
622 $self->remove_attribute($attribute->name)
623 if $self->has_attribute($attribute->name);
625 # then onto installing the new accessors
626 $attribute->install_accessors();
627 $self->get_attribute_map->{$attribute->name} = $attribute;
631 my ($self, $attribute_name) = @_;
632 (defined $attribute_name && $attribute_name)
633 || confess "You must define an attribute name";
634 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
638 my ($self, $attribute_name) = @_;
639 (defined $attribute_name && $attribute_name)
640 || confess "You must define an attribute name";
641 return $self->get_attribute_map->{$attribute_name}
643 # this will return undef anyway, so no need ...
644 # if $self->has_attribute($attribute_name);
648 sub remove_attribute {
649 my ($self, $attribute_name) = @_;
650 (defined $attribute_name && $attribute_name)
651 || confess "You must define an attribute name";
652 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
653 return unless defined $removed_attribute;
654 delete $self->get_attribute_map->{$attribute_name};
655 $removed_attribute->remove_accessors();
656 $removed_attribute->detach_from_class();
657 return $removed_attribute;
660 sub get_attribute_list {
662 keys %{$self->get_attribute_map};
665 sub compute_all_applicable_attributes {
668 # keep a record of what we have seen
669 # here, this will handle all the
670 # inheritence issues because we are
671 # using the &class_precedence_list
672 my (%seen_class, %seen_attr);
673 foreach my $class ($self->class_precedence_list()) {
674 next if $seen_class{$class};
675 $seen_class{$class}++;
676 # fetch the meta-class ...
677 my $meta = $self->initialize($class);
678 foreach my $attr_name ($meta->get_attribute_list()) {
679 next if exists $seen_attr{$attr_name};
680 $seen_attr{$attr_name}++;
681 push @attrs => $meta->get_attribute($attr_name);
687 sub find_attribute_by_name {
688 my ($self, $attr_name) = @_;
689 # keep a record of what we have seen
690 # here, this will handle all the
691 # inheritence issues because we are
692 # using the &class_precedence_list
694 foreach my $class ($self->class_precedence_list()) {
695 next if $seen_class{$class};
696 $seen_class{$class}++;
697 # fetch the meta-class ...
698 my $meta = $self->initialize($class);
699 return $meta->get_attribute($attr_name)
700 if $meta->has_attribute($attr_name);
708 sub is_immutable { 0 }
711 return Class::MOP::Class::Immutable->make_metaclass_immutable(@_);
722 Class::MOP::Class - Class Meta Object
726 # assuming that class Foo
727 # has been defined, you can
729 # use this for introspection ...
731 # add a method to Foo ...
732 Foo->meta->add_method('bar' => sub { ... })
734 # get a list of all the classes searched
735 # the method dispatcher in the correct order
736 Foo->meta->class_precedence_list()
738 # remove a method from Foo
739 Foo->meta->remove_method('bar');
741 # or use this to actually create classes ...
743 Class::MOP::Class->create('Bar' => (
745 superclasses => [ 'Foo' ],
747 Class::MOP:::Attribute->new('$bar'),
748 Class::MOP:::Attribute->new('$baz'),
751 calculate_bar => sub { ... },
752 construct_baz => sub { ... }
758 This is the largest and currently most complex part of the Perl 5
759 meta-object protocol. It controls the introspection and
760 manipulation of Perl 5 classes (and it can create them too). The
761 best way to understand what this module can do, is to read the
762 documentation for each of it's methods.
766 =head2 Self Introspection
772 This will return a B<Class::MOP::Class> instance which is related
773 to this class. Thereby allowing B<Class::MOP::Class> to actually
776 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
777 bootstrap this module by installing a number of attribute meta-objects
778 into it's metaclass. This will allow this class to reap all the benifits
779 of the MOP when subclassing it.
783 =head2 Class construction
785 These methods will handle creating B<Class::MOP::Class> objects,
786 which can be used to both create new classes, and analyze
787 pre-existing classes.
789 This module will internally store references to all the instances
790 you create with these methods, so that they do not need to be
791 created any more than nessecary. Basically, they are singletons.
795 =item B<create ($package_name,
796 version =E<gt> ?$version,
797 authority =E<gt> ?$authority,
798 superclasses =E<gt> ?@superclasses,
799 methods =E<gt> ?%methods,
800 attributes =E<gt> ?%attributes)>
802 This returns a B<Class::MOP::Class> object, bringing the specified
803 C<$package_name> into existence and adding any of the C<$version>,
804 C<$authority>, C<@superclasses>, C<%methods> and C<%attributes> to
807 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
808 methods =E<gt> ?%methods,
809 attributes =E<gt> ?%attributes)>
811 This will create an anonymous class, it works much like C<create> but
812 it does not need a C<$package_name>. Instead it will create a suitably
813 unique package name for you to stash things into.
815 =item B<initialize ($package_name, %options)>
817 This initializes and returns returns a B<Class::MOP::Class> object
818 for a given a C<$package_name>.
820 =item B<reinitialize ($package_name, %options)>
822 This removes the old metaclass, and creates a new one in it's place.
823 Do B<not> use this unless you really know what you are doing, it could
824 very easily make a very large mess of your program.
826 =item B<construct_class_instance (%options)>
828 This will construct an instance of B<Class::MOP::Class>, it is
829 here so that we can actually "tie the knot" for B<Class::MOP::Class>
830 to use C<construct_instance> once all the bootstrapping is done. This
831 method is used internally by C<initialize> and should never be called
832 from outside of that method really.
834 =item B<check_metaclass_compatability>
836 This method is called as the very last thing in the
837 C<construct_class_instance> method. This will check that the
838 metaclass you are creating is compatible with the metaclasses of all
839 your ancestors. For more inforamtion about metaclass compatibility
840 see the C<About Metaclass compatibility> section in L<Class::MOP>.
844 =head2 Object instance construction and cloning
846 These methods are B<entirely optional>, it is up to you whether you want
851 =item B<instance_metaclass>
853 =item B<get_meta_instance>
855 =item B<new_object (%params)>
857 This is a convience method for creating a new object of the class, and
858 blessing it into the appropriate package as well. Ideally your class
859 would call a C<new> this method like so:
862 my ($class, %param) = @_;
863 $class->meta->new_object(%params);
866 Of course the ideal place for this would actually be in C<UNIVERSAL::>
867 but that is considered bad style, so we do not do that.
869 =item B<construct_instance (%params)>
871 This method is used to construct an instace structure suitable for
872 C<bless>-ing into your package of choice. It works in conjunction
873 with the Attribute protocol to collect all applicable attributes.
875 This will construct and instance using a HASH ref as storage
876 (currently only HASH references are supported). This will collect all
877 the applicable attributes and layout out the fields in the HASH ref,
878 it will then initialize them using either use the corresponding key
879 in C<%params> or any default value or initializer found in the
880 attribute meta-object.
882 =item B<clone_object ($instance, %params)>
884 This is a convience method for cloning an object instance, then
885 blessing it into the appropriate package. This method will call
886 C<clone_instance>, which performs a shallow copy of the object,
887 see that methods documentation for more details. Ideally your
888 class would call a C<clone> this method like so:
891 my ($self, %param) = @_;
892 $self->meta->clone_object($self, %params);
895 Of course the ideal place for this would actually be in C<UNIVERSAL::>
896 but that is considered bad style, so we do not do that.
898 =item B<clone_instance($instance, %params)>
900 This method is a compliment of C<construct_instance> (which means if
901 you override C<construct_instance>, you need to override this one too),
902 and clones the instance shallowly.
904 The cloned structure returned is (like with C<construct_instance>) an
905 unC<bless>ed HASH reference, it is your responsibility to then bless
906 this cloned structure into the right class (which C<clone_object> will
909 As of 0.11, this method will clone the C<$instance> structure shallowly,
910 as opposed to the deep cloning implemented in prior versions. After much
911 thought, research and discussion, I have decided that anything but basic
912 shallow cloning is outside the scope of the meta-object protocol. I
913 think Yuval "nothingmuch" Kogman put it best when he said that cloning
914 is too I<context-specific> to be part of the MOP.
920 These are a few predicate methods for asking information about the class.
924 =item B<is_anon_class>
928 =item B<is_immutable>
932 =head2 Inheritance Relationships
936 =item B<superclasses (?@superclasses)>
938 This is a read-write attribute which represents the superclass
939 relationships of the class the B<Class::MOP::Class> instance is
940 associated with. Basically, it can get and set the C<@ISA> for you.
943 Perl will occasionally perform some C<@ISA> and method caching, if
944 you decide to change your superclass relationship at runtime (which
945 is quite insane and very much not recommened), then you should be
946 aware of this and the fact that this module does not make any
947 attempt to address this issue.
949 =item B<class_precedence_list>
951 This computes the a list of all the class's ancestors in the same order
952 in which method dispatch will be done. This is similair to
953 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
961 =item B<get_method_map>
963 =item B<method_metaclass>
965 =item B<add_method ($method_name, $method)>
967 This will take a C<$method_name> and CODE reference to that
968 C<$method> and install it into the class's package.
971 This does absolutely nothing special to C<$method>
972 other than use B<Sub::Name> to make sure it is tagged with the
973 correct name, and therefore show up correctly in stack traces and
976 =item B<alias_method ($method_name, $method)>
978 This will take a C<$method_name> and CODE reference to that
979 C<$method> and alias the method into the class's package.
982 Unlike C<add_method>, this will B<not> try to name the
983 C<$method> using B<Sub::Name>, it only aliases the method in
986 =item B<has_method ($method_name)>
988 This just provides a simple way to check if the class implements
989 a specific C<$method_name>. It will I<not> however, attempt to check
990 if the class inherits the method (use C<UNIVERSAL::can> for that).
992 This will correctly handle functions defined outside of the package
993 that use a fully qualified name (C<sub Package::name { ... }>).
995 This will correctly handle functions renamed with B<Sub::Name> and
996 installed using the symbol tables. However, if you are naming the
997 subroutine outside of the package scope, you must use the fully
998 qualified name, including the package name, for C<has_method> to
999 correctly identify it.
1001 This will attempt to correctly ignore functions imported from other
1002 packages using B<Exporter>. It breaks down if the function imported
1003 is an C<__ANON__> sub (such as with C<use constant>), which very well
1004 may be a valid method being applied to the class.
1006 In short, this method cannot always be trusted to determine if the
1007 C<$method_name> is actually a method. However, it will DWIM about
1008 90% of the time, so it's a small trade off I think.
1010 =item B<get_method ($method_name)>
1012 This will return a Class::MOP::Method instance related to the specified
1013 C<$method_name>, or return undef if that method does not exist.
1015 The Class::MOP::Method is codifiable, so you can use it like a normal
1016 CODE reference, see L<Class::MOP::Method> for more information.
1018 =item B<find_method_by_name ($method_name>
1020 This will return a CODE reference of the specified C<$method_name>,
1021 or return undef if that method does not exist.
1023 Unlike C<get_method> this will also look in the superclasses.
1025 =item B<remove_method ($method_name)>
1027 This will attempt to remove a given C<$method_name> from the class.
1028 It will return the CODE reference that it has removed, and will
1029 attempt to use B<Sub::Name> to clear the methods associated name.
1031 =item B<get_method_list>
1033 This will return a list of method names for all I<locally> defined
1034 methods. It does B<not> provide a list of all applicable methods,
1035 including any inherited ones. If you want a list of all applicable
1036 methods, use the C<compute_all_applicable_methods> method.
1038 =item B<compute_all_applicable_methods>
1040 This will return a list of all the methods names this class will
1041 respond to, taking into account inheritance. The list will be a list of
1042 HASH references, each one containing the following information; method
1043 name, the name of the class in which the method lives and a CODE
1044 reference for the actual method.
1046 =item B<find_all_methods_by_name ($method_name)>
1048 This will traverse the inheritence hierarchy and locate all methods
1049 with a given C<$method_name>. Similar to
1050 C<compute_all_applicable_methods> it returns a list of HASH references
1051 with the following information; method name (which will always be the
1052 same as C<$method_name>), the name of the class in which the method
1053 lives and a CODE reference for the actual method.
1055 The list of methods produced is a distinct list, meaning there are no
1056 duplicates in it. This is especially useful for things like object
1057 initialization and destruction where you only want the method called
1058 once, and in the correct order.
1060 =item B<find_next_method_by_name ($method_name)>
1062 This will return the first method to match a given C<$method_name> in
1063 the superclasses, this is basically equivalent to calling
1064 C<SUPER::$method_name>, but it can be dispatched at runtime.
1068 =head2 Method Modifiers
1070 Method modifiers are a concept borrowed from CLOS, in which a method
1071 can be wrapped with I<before>, I<after> and I<around> method modifiers
1072 that will be called everytime the method is called.
1074 =head3 How method modifiers work?
1076 Method modifiers work by wrapping the original method and then replacing
1077 it in the classes symbol table. The wrappers will handle calling all the
1078 modifiers in the appropariate orders and preserving the calling context
1079 for the original method.
1081 Each method modifier serves a particular purpose, which may not be
1082 obvious to users of other method wrapping modules. To start with, the
1083 return values of I<before> and I<after> modifiers are ignored. This is
1084 because thier purpose is B<not> to filter the input and output of the
1085 primary method (this is done with an I<around> modifier). This may seem
1086 like an odd restriction to some, but doing this allows for simple code
1087 to be added at the begining or end of a method call without jeapordizing
1088 the normal functioning of the primary method or placing any extra
1089 responsibility on the code of the modifier. Of course if you have more
1090 complex needs, then use the I<around> modifier, which uses a variation
1091 of continutation passing style to allow for a high degree of flexibility.
1093 Before and around modifiers are called in last-defined-first-called order,
1094 while after modifiers are called in first-defined-first-called order. So
1095 the call tree might looks something like this:
1105 To see examples of using method modifiers, see the following examples
1106 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1107 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1108 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1110 =head3 What is the performance impact?
1112 Of course there is a performance cost associated with method modifiers,
1113 but we have made every effort to make that cost be directly proportional
1114 to the amount of modifier features you utilize.
1116 The wrapping method does it's best to B<only> do as much work as it
1117 absolutely needs to. In order to do this we have moved some of the
1118 performance costs to set-up time, where they are easier to amortize.
1120 All this said, my benchmarks have indicated the following:
1122 simple wrapper with no modifiers 100% slower
1123 simple wrapper with simple before modifier 400% slower
1124 simple wrapper with simple after modifier 450% slower
1125 simple wrapper with simple around modifier 500-550% slower
1126 simple wrapper with all 3 modifiers 1100% slower
1128 These numbers may seem daunting, but you must remember, every feature
1129 comes with some cost. To put things in perspective, just doing a simple
1130 C<AUTOLOAD> which does nothing but extract the name of the method called
1131 and return it costs about 400% over a normal method call.
1135 =item B<add_before_method_modifier ($method_name, $code)>
1137 This will wrap the method at C<$method_name> and the supplied C<$code>
1138 will be passed the C<@_> arguments, and called before the original
1139 method is called. As specified above, the return value of the I<before>
1140 method modifiers is ignored, and it's ability to modify C<@_> is
1141 fairly limited. If you need to do either of these things, use an
1142 C<around> method modifier.
1144 =item B<add_after_method_modifier ($method_name, $code)>
1146 This will wrap the method at C<$method_name> so that the original
1147 method will be called, it's return values stashed, and then the
1148 supplied C<$code> will be passed the C<@_> arguments, and called.
1149 As specified above, the return value of the I<after> method
1150 modifiers is ignored, and it cannot modify the return values of
1151 the original method. If you need to do either of these things, use an
1152 C<around> method modifier.
1154 =item B<add_around_method_modifier ($method_name, $code)>
1156 This will wrap the method at C<$method_name> so that C<$code>
1157 will be called and passed the original method as an extra argument
1158 at the begining of the C<@_> argument list. This is a variation of
1159 continuation passing style, where the function prepended to C<@_>
1160 can be considered a continuation. It is up to C<$code> if it calls
1161 the original method or not, there is no restriction on what the
1162 C<$code> can or cannot do.
1168 It should be noted that since there is no one consistent way to define
1169 the attributes of a class in Perl 5. These methods can only work with
1170 the information given, and can not easily discover information on
1171 their own. See L<Class::MOP::Attribute> for more details.
1175 =item B<attribute_metaclass>
1177 =item B<get_attribute_map>
1179 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1181 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1182 instance associated with the given class, and associates it with
1183 the C<$attribute_name>. Unlike methods, attributes within the MOP
1184 are stored as meta-information only. They will be used later to
1185 construct instances from (see C<construct_instance> above).
1186 More details about the attribute meta-objects can be found in the
1187 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1190 It should be noted that any accessor, reader/writer or predicate
1191 methods which the C<$attribute_meta_object> has will be installed
1192 into the class at this time.
1195 If an attribute already exists for C<$attribute_name>, the old one
1196 will be removed (as well as removing all it's accessors), and then
1199 =item B<has_attribute ($attribute_name)>
1201 Checks to see if this class has an attribute by the name of
1202 C<$attribute_name> and returns a boolean.
1204 =item B<get_attribute ($attribute_name)>
1206 Returns the attribute meta-object associated with C<$attribute_name>,
1207 if none is found, it will return undef.
1209 =item B<remove_attribute ($attribute_name)>
1211 This will remove the attribute meta-object stored at
1212 C<$attribute_name>, then return the removed attribute meta-object.
1215 Removing an attribute will only affect future instances of
1216 the class, it will not make any attempt to remove the attribute from
1217 any existing instances of the class.
1219 It should be noted that any accessor, reader/writer or predicate
1220 methods which the attribute meta-object stored at C<$attribute_name>
1221 has will be removed from the class at this time. This B<will> make
1222 these attributes somewhat inaccessable in previously created
1223 instances. But if you are crazy enough to do this at runtime, then
1224 you are crazy enough to deal with something like this :).
1226 =item B<get_attribute_list>
1228 This returns a list of attribute names which are defined in the local
1229 class. If you want a list of all applicable attributes for a class,
1230 use the C<compute_all_applicable_attributes> method.
1232 =item B<compute_all_applicable_attributes>
1234 This will traverse the inheritance heirachy and return a list of all
1235 the applicable attributes for this class. It does not construct a
1236 HASH reference like C<compute_all_applicable_methods> because all
1237 that same information is discoverable through the attribute
1240 =item B<find_attribute_by_name ($attr_name)>
1242 This method will traverse the inheritance heirachy and find the
1243 first attribute whose name matches C<$attr_name>, then return it.
1244 It will return undef if nothing is found.
1248 =head2 Class closing
1252 =item B<make_immutable>
1258 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1260 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1262 =head1 COPYRIGHT AND LICENSE
1264 Copyright 2006 by Infinity Interactive, Inc.
1266 L<http://www.iinteractive.com>
1268 This library is free software; you can redistribute it and/or modify
1269 it under the same terms as Perl itself.