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} &&
278 defined $map->{$symbol} &&
279 $map->{$symbol}->body == $code;
281 my $gv = svref_2object($code)->GV;
282 next if ($gv->STASH->NAME || '') ne $class_name &&
283 ($gv->NAME || '') ne '__ANON__';
285 $map->{$symbol} = $method_metaclass->wrap($code);
291 # Instance Construction & Cloning
296 # we need to protect the integrity of the
297 # Class::MOP::Class singletons here, so we
298 # delegate this to &construct_class_instance
299 # which will deal with the singletons
300 return $class->construct_class_instance(@_)
301 if $class->name->isa('Class::MOP::Class');
302 return $class->construct_instance(@_);
305 sub construct_instance {
306 my ($class, %params) = @_;
307 my $meta_instance = $class->get_meta_instance();
308 my $instance = $meta_instance->create_instance();
309 foreach my $attr ($class->compute_all_applicable_attributes()) {
310 $attr->initialize_instance_slot($meta_instance, $instance, \%params);
315 sub get_meta_instance {
317 return $class->instance_metaclass->new(
319 $class->compute_all_applicable_attributes()
325 my $instance = shift;
326 (blessed($instance) && $instance->isa($class->name))
327 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
329 # we need to protect the integrity of the
330 # Class::MOP::Class singletons here, they
331 # should not be cloned.
332 return $instance if $instance->isa('Class::MOP::Class');
333 $class->clone_instance($instance, @_);
337 my ($class, $instance, %params) = @_;
339 || confess "You can only clone instances, \$self is not a blessed instance";
340 my $meta_instance = $class->get_meta_instance();
341 my $clone = $meta_instance->clone_instance($instance);
342 foreach my $key (keys %params) {
343 next unless $meta_instance->is_valid_slot($key);
344 $meta_instance->set_slot_value($clone, $key, $params{$key});
355 @{$self->get_package_symbol('@ISA')} = @supers;
357 # we need to check the metaclass
358 # compatability here so that we can
359 # be sure that the superclass is
360 # not potentially creating an issues
361 # we don't know about
362 $self->check_metaclass_compatability();
364 @{$self->get_package_symbol('@ISA')};
367 sub class_precedence_list {
370 # We need to check for ciruclar inheirtance here.
371 # This will do nothing if all is well, and blow
372 # up otherwise. Yes, it's an ugly hack, better
373 # suggestions are welcome.
374 { ($self->name || return)->isa('This is a test for circular inheritance') }
375 # ... and now back to our regularly scheduled program
379 $self->initialize($_)->class_precedence_list()
380 } $self->superclasses()
387 my ($self, $method_name, $method) = @_;
388 (defined $method_name && $method_name)
389 || confess "You must define a method name";
392 if (blessed($method)) {
393 $body = $method->body;
397 ('CODE' eq (reftype($body) || ''))
398 || confess "Your code block must be a CODE reference";
399 $method = $self->method_metaclass->wrap($body);
401 $self->get_method_map->{$method_name} = $method;
403 my $full_method_name = ($self->name . '::' . $method_name);
404 $self->add_package_symbol("&${method_name}" => subname $full_method_name => $body);
408 my $fetch_and_prepare_method = sub {
409 my ($self, $method_name) = @_;
411 my $method = $self->get_method($method_name);
412 # if we dont have local ...
414 # try to find the next method
415 $method = $self->find_next_method_by_name($method_name);
416 # die if it does not exist
418 || confess "The method '$method_name' is not found in the inherience hierarchy for class " . $self->name;
419 # and now make sure to wrap it
420 # even if it is already wrapped
421 # because we need a new sub ref
422 $method = Class::MOP::Method::Wrapped->wrap($method);
425 # now make sure we wrap it properly
426 $method = Class::MOP::Method::Wrapped->wrap($method)
427 unless $method->isa('Class::MOP::Method::Wrapped');
429 $self->add_method($method_name => $method);
433 sub add_before_method_modifier {
434 my ($self, $method_name, $method_modifier) = @_;
435 (defined $method_name && $method_name)
436 || confess "You must pass in a method name";
437 my $method = $fetch_and_prepare_method->($self, $method_name);
438 $method->add_before_modifier(subname ':before' => $method_modifier);
441 sub add_after_method_modifier {
442 my ($self, $method_name, $method_modifier) = @_;
443 (defined $method_name && $method_name)
444 || confess "You must pass in a method name";
445 my $method = $fetch_and_prepare_method->($self, $method_name);
446 $method->add_after_modifier(subname ':after' => $method_modifier);
449 sub add_around_method_modifier {
450 my ($self, $method_name, $method_modifier) = @_;
451 (defined $method_name && $method_name)
452 || confess "You must pass in a method name";
453 my $method = $fetch_and_prepare_method->($self, $method_name);
454 $method->add_around_modifier(subname ':around' => $method_modifier);
458 # the methods above used to be named like this:
459 # ${pkg}::${method}:(before|after|around)
460 # but this proved problematic when using one modifier
461 # to wrap multiple methods (something which is likely
462 # to happen pretty regularly IMO). So instead of naming
463 # it like this, I have chosen to just name them purely
464 # with their modifier names, like so:
465 # :(before|after|around)
466 # The fact is that in a stack trace, it will be fairly
467 # evident from the context what method they are attached
468 # to, and so don't need the fully qualified name.
472 my ($self, $method_name, $method) = @_;
473 (defined $method_name && $method_name)
474 || confess "You must define a method name";
476 my $body = (blessed($method) ? $method->body : $method);
477 ('CODE' eq (reftype($body) || ''))
478 || confess "Your code block must be a CODE reference";
480 $self->add_package_symbol("&${method_name}" => $body);
484 my ($self, $method_name) = @_;
485 (defined $method_name && $method_name)
486 || confess "You must define a method name";
488 return 0 unless exists $self->get_method_map->{$method_name};
493 my ($self, $method_name) = @_;
494 (defined $method_name && $method_name)
495 || confess "You must define a method name";
498 # I don't really need this here, because
499 # if the method_map is missing a key it
500 # will just return undef for me now
501 # return unless $self->has_method($method_name);
503 return $self->get_method_map->{$method_name};
507 my ($self, $method_name) = @_;
508 (defined $method_name && $method_name)
509 || confess "You must define a method name";
511 my $removed_method = $self->get_method($method_name);
514 $self->remove_package_symbol("&${method_name}");
515 delete $self->get_method_map->{$method_name};
516 } if defined $removed_method;
518 return $removed_method;
521 sub get_method_list {
523 keys %{$self->get_method_map};
526 sub find_method_by_name {
527 my ($self, $method_name) = @_;
528 (defined $method_name && $method_name)
529 || confess "You must define a method name to find";
530 # keep a record of what we have seen
531 # here, this will handle all the
532 # inheritence issues because we are
533 # using the &class_precedence_list
535 my @cpl = $self->class_precedence_list();
536 foreach my $class (@cpl) {
537 next if $seen_class{$class};
538 $seen_class{$class}++;
539 # fetch the meta-class ...
540 my $meta = $self->initialize($class);
541 return $meta->get_method($method_name)
542 if $meta->has_method($method_name);
547 sub compute_all_applicable_methods {
550 # keep a record of what we have seen
551 # here, this will handle all the
552 # inheritence issues because we are
553 # using the &class_precedence_list
554 my (%seen_class, %seen_method);
555 foreach my $class ($self->class_precedence_list()) {
556 next if $seen_class{$class};
557 $seen_class{$class}++;
558 # fetch the meta-class ...
559 my $meta = $self->initialize($class);
560 foreach my $method_name ($meta->get_method_list()) {
561 next if exists $seen_method{$method_name};
562 $seen_method{$method_name}++;
564 name => $method_name,
566 code => $meta->get_method($method_name)
573 sub find_all_methods_by_name {
574 my ($self, $method_name) = @_;
575 (defined $method_name && $method_name)
576 || confess "You must define a method name to find";
578 # keep a record of what we have seen
579 # here, this will handle all the
580 # inheritence issues because we are
581 # using the &class_precedence_list
583 foreach my $class ($self->class_precedence_list()) {
584 next if $seen_class{$class};
585 $seen_class{$class}++;
586 # fetch the meta-class ...
587 my $meta = $self->initialize($class);
589 name => $method_name,
591 code => $meta->get_method($method_name)
592 } if $meta->has_method($method_name);
597 sub find_next_method_by_name {
598 my ($self, $method_name) = @_;
599 (defined $method_name && $method_name)
600 || confess "You must define a method name to find";
601 # keep a record of what we have seen
602 # here, this will handle all the
603 # inheritence issues because we are
604 # using the &class_precedence_list
606 my @cpl = $self->class_precedence_list();
607 shift @cpl; # discard ourselves
608 foreach my $class (@cpl) {
609 next if $seen_class{$class};
610 $seen_class{$class}++;
611 # fetch the meta-class ...
612 my $meta = $self->initialize($class);
613 return $meta->get_method($method_name)
614 if $meta->has_method($method_name);
623 # either we have an attribute object already
624 # or we need to create one from the args provided
625 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
626 # make sure it is derived from the correct type though
627 ($attribute->isa('Class::MOP::Attribute'))
628 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
630 # first we attach our new attribute
631 # because it might need certain information
632 # about the class which it is attached to
633 $attribute->attach_to_class($self);
635 # then we remove attributes of a conflicting
636 # name here so that we can properly detach
637 # the old attr object, and remove any
638 # accessors it would have generated
639 $self->remove_attribute($attribute->name)
640 if $self->has_attribute($attribute->name);
642 # then onto installing the new accessors
643 $attribute->install_accessors();
644 $self->get_attribute_map->{$attribute->name} = $attribute;
648 my ($self, $attribute_name) = @_;
649 (defined $attribute_name && $attribute_name)
650 || confess "You must define an attribute name";
651 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
655 my ($self, $attribute_name) = @_;
656 (defined $attribute_name && $attribute_name)
657 || confess "You must define an attribute name";
658 return $self->get_attribute_map->{$attribute_name}
660 # this will return undef anyway, so no need ...
661 # if $self->has_attribute($attribute_name);
665 sub remove_attribute {
666 my ($self, $attribute_name) = @_;
667 (defined $attribute_name && $attribute_name)
668 || confess "You must define an attribute name";
669 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
670 return unless defined $removed_attribute;
671 delete $self->get_attribute_map->{$attribute_name};
672 $removed_attribute->remove_accessors();
673 $removed_attribute->detach_from_class();
674 return $removed_attribute;
677 sub get_attribute_list {
679 keys %{$self->get_attribute_map};
682 sub compute_all_applicable_attributes {
685 # keep a record of what we have seen
686 # here, this will handle all the
687 # inheritence issues because we are
688 # using the &class_precedence_list
689 my (%seen_class, %seen_attr);
690 foreach my $class ($self->class_precedence_list()) {
691 next if $seen_class{$class};
692 $seen_class{$class}++;
693 # fetch the meta-class ...
694 my $meta = $self->initialize($class);
695 foreach my $attr_name ($meta->get_attribute_list()) {
696 next if exists $seen_attr{$attr_name};
697 $seen_attr{$attr_name}++;
698 push @attrs => $meta->get_attribute($attr_name);
704 sub find_attribute_by_name {
705 my ($self, $attr_name) = @_;
706 # keep a record of what we have seen
707 # here, this will handle all the
708 # inheritence issues because we are
709 # using the &class_precedence_list
711 foreach my $class ($self->class_precedence_list()) {
712 next if $seen_class{$class};
713 $seen_class{$class}++;
714 # fetch the meta-class ...
715 my $meta = $self->initialize($class);
716 return $meta->get_attribute($attr_name)
717 if $meta->has_attribute($attr_name);
725 sub is_immutable { 0 }
728 return Class::MOP::Class::Immutable->make_metaclass_immutable(@_);
739 Class::MOP::Class - Class Meta Object
743 # assuming that class Foo
744 # has been defined, you can
746 # use this for introspection ...
748 # add a method to Foo ...
749 Foo->meta->add_method('bar' => sub { ... })
751 # get a list of all the classes searched
752 # the method dispatcher in the correct order
753 Foo->meta->class_precedence_list()
755 # remove a method from Foo
756 Foo->meta->remove_method('bar');
758 # or use this to actually create classes ...
760 Class::MOP::Class->create('Bar' => (
762 superclasses => [ 'Foo' ],
764 Class::MOP:::Attribute->new('$bar'),
765 Class::MOP:::Attribute->new('$baz'),
768 calculate_bar => sub { ... },
769 construct_baz => sub { ... }
775 This is the largest and currently most complex part of the Perl 5
776 meta-object protocol. It controls the introspection and
777 manipulation of Perl 5 classes (and it can create them too). The
778 best way to understand what this module can do, is to read the
779 documentation for each of it's methods.
783 =head2 Self Introspection
789 This will return a B<Class::MOP::Class> instance which is related
790 to this class. Thereby allowing B<Class::MOP::Class> to actually
793 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
794 bootstrap this module by installing a number of attribute meta-objects
795 into it's metaclass. This will allow this class to reap all the benifits
796 of the MOP when subclassing it.
800 =head2 Class construction
802 These methods will handle creating B<Class::MOP::Class> objects,
803 which can be used to both create new classes, and analyze
804 pre-existing classes.
806 This module will internally store references to all the instances
807 you create with these methods, so that they do not need to be
808 created any more than nessecary. Basically, they are singletons.
812 =item B<create ($package_name,
813 version =E<gt> ?$version,
814 authority =E<gt> ?$authority,
815 superclasses =E<gt> ?@superclasses,
816 methods =E<gt> ?%methods,
817 attributes =E<gt> ?%attributes)>
819 This returns a B<Class::MOP::Class> object, bringing the specified
820 C<$package_name> into existence and adding any of the C<$version>,
821 C<$authority>, C<@superclasses>, C<%methods> and C<%attributes> to
824 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
825 methods =E<gt> ?%methods,
826 attributes =E<gt> ?%attributes)>
828 This will create an anonymous class, it works much like C<create> but
829 it does not need a C<$package_name>. Instead it will create a suitably
830 unique package name for you to stash things into.
832 =item B<initialize ($package_name, %options)>
834 This initializes and returns returns a B<Class::MOP::Class> object
835 for a given a C<$package_name>.
837 =item B<reinitialize ($package_name, %options)>
839 This removes the old metaclass, and creates a new one in it's place.
840 Do B<not> use this unless you really know what you are doing, it could
841 very easily make a very large mess of your program.
843 =item B<construct_class_instance (%options)>
845 This will construct an instance of B<Class::MOP::Class>, it is
846 here so that we can actually "tie the knot" for B<Class::MOP::Class>
847 to use C<construct_instance> once all the bootstrapping is done. This
848 method is used internally by C<initialize> and should never be called
849 from outside of that method really.
851 =item B<check_metaclass_compatability>
853 This method is called as the very last thing in the
854 C<construct_class_instance> method. This will check that the
855 metaclass you are creating is compatible with the metaclasses of all
856 your ancestors. For more inforamtion about metaclass compatibility
857 see the C<About Metaclass compatibility> section in L<Class::MOP>.
861 =head2 Object instance construction and cloning
863 These methods are B<entirely optional>, it is up to you whether you want
868 =item B<instance_metaclass>
870 =item B<get_meta_instance>
872 =item B<new_object (%params)>
874 This is a convience method for creating a new object of the class, and
875 blessing it into the appropriate package as well. Ideally your class
876 would call a C<new> this method like so:
879 my ($class, %param) = @_;
880 $class->meta->new_object(%params);
883 Of course the ideal place for this would actually be in C<UNIVERSAL::>
884 but that is considered bad style, so we do not do that.
886 =item B<construct_instance (%params)>
888 This method is used to construct an instace structure suitable for
889 C<bless>-ing into your package of choice. It works in conjunction
890 with the Attribute protocol to collect all applicable attributes.
892 This will construct and instance using a HASH ref as storage
893 (currently only HASH references are supported). This will collect all
894 the applicable attributes and layout out the fields in the HASH ref,
895 it will then initialize them using either use the corresponding key
896 in C<%params> or any default value or initializer found in the
897 attribute meta-object.
899 =item B<clone_object ($instance, %params)>
901 This is a convience method for cloning an object instance, then
902 blessing it into the appropriate package. This method will call
903 C<clone_instance>, which performs a shallow copy of the object,
904 see that methods documentation for more details. Ideally your
905 class would call a C<clone> this method like so:
908 my ($self, %param) = @_;
909 $self->meta->clone_object($self, %params);
912 Of course the ideal place for this would actually be in C<UNIVERSAL::>
913 but that is considered bad style, so we do not do that.
915 =item B<clone_instance($instance, %params)>
917 This method is a compliment of C<construct_instance> (which means if
918 you override C<construct_instance>, you need to override this one too),
919 and clones the instance shallowly.
921 The cloned structure returned is (like with C<construct_instance>) an
922 unC<bless>ed HASH reference, it is your responsibility to then bless
923 this cloned structure into the right class (which C<clone_object> will
926 As of 0.11, this method will clone the C<$instance> structure shallowly,
927 as opposed to the deep cloning implemented in prior versions. After much
928 thought, research and discussion, I have decided that anything but basic
929 shallow cloning is outside the scope of the meta-object protocol. I
930 think Yuval "nothingmuch" Kogman put it best when he said that cloning
931 is too I<context-specific> to be part of the MOP.
937 These are a few predicate methods for asking information about the class.
941 =item B<is_anon_class>
945 =item B<is_immutable>
949 =head2 Inheritance Relationships
953 =item B<superclasses (?@superclasses)>
955 This is a read-write attribute which represents the superclass
956 relationships of the class the B<Class::MOP::Class> instance is
957 associated with. Basically, it can get and set the C<@ISA> for you.
960 Perl will occasionally perform some C<@ISA> and method caching, if
961 you decide to change your superclass relationship at runtime (which
962 is quite insane and very much not recommened), then you should be
963 aware of this and the fact that this module does not make any
964 attempt to address this issue.
966 =item B<class_precedence_list>
968 This computes the a list of all the class's ancestors in the same order
969 in which method dispatch will be done. This is similair to
970 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
978 =item B<get_method_map>
980 =item B<method_metaclass>
982 =item B<add_method ($method_name, $method)>
984 This will take a C<$method_name> and CODE reference to that
985 C<$method> and install it into the class's package.
988 This does absolutely nothing special to C<$method>
989 other than use B<Sub::Name> to make sure it is tagged with the
990 correct name, and therefore show up correctly in stack traces and
993 =item B<alias_method ($method_name, $method)>
995 This will take a C<$method_name> and CODE reference to that
996 C<$method> and alias the method into the class's package.
999 Unlike C<add_method>, this will B<not> try to name the
1000 C<$method> using B<Sub::Name>, it only aliases the method in
1001 the class's package.
1003 =item B<has_method ($method_name)>
1005 This just provides a simple way to check if the class implements
1006 a specific C<$method_name>. It will I<not> however, attempt to check
1007 if the class inherits the method (use C<UNIVERSAL::can> for that).
1009 This will correctly handle functions defined outside of the package
1010 that use a fully qualified name (C<sub Package::name { ... }>).
1012 This will correctly handle functions renamed with B<Sub::Name> and
1013 installed using the symbol tables. However, if you are naming the
1014 subroutine outside of the package scope, you must use the fully
1015 qualified name, including the package name, for C<has_method> to
1016 correctly identify it.
1018 This will attempt to correctly ignore functions imported from other
1019 packages using B<Exporter>. It breaks down if the function imported
1020 is an C<__ANON__> sub (such as with C<use constant>), which very well
1021 may be a valid method being applied to the class.
1023 In short, this method cannot always be trusted to determine if the
1024 C<$method_name> is actually a method. However, it will DWIM about
1025 90% of the time, so it's a small trade off I think.
1027 =item B<get_method ($method_name)>
1029 This will return a Class::MOP::Method instance related to the specified
1030 C<$method_name>, or return undef if that method does not exist.
1032 The Class::MOP::Method is codifiable, so you can use it like a normal
1033 CODE reference, see L<Class::MOP::Method> for more information.
1035 =item B<find_method_by_name ($method_name>
1037 This will return a CODE reference of the specified C<$method_name>,
1038 or return undef if that method does not exist.
1040 Unlike C<get_method> this will also look in the superclasses.
1042 =item B<remove_method ($method_name)>
1044 This will attempt to remove a given C<$method_name> from the class.
1045 It will return the CODE reference that it has removed, and will
1046 attempt to use B<Sub::Name> to clear the methods associated name.
1048 =item B<get_method_list>
1050 This will return a list of method names for all I<locally> defined
1051 methods. It does B<not> provide a list of all applicable methods,
1052 including any inherited ones. If you want a list of all applicable
1053 methods, use the C<compute_all_applicable_methods> method.
1055 =item B<compute_all_applicable_methods>
1057 This will return a list of all the methods names this class will
1058 respond to, taking into account inheritance. The list will be a list of
1059 HASH references, each one containing the following information; method
1060 name, the name of the class in which the method lives and a CODE
1061 reference for the actual method.
1063 =item B<find_all_methods_by_name ($method_name)>
1065 This will traverse the inheritence hierarchy and locate all methods
1066 with a given C<$method_name>. Similar to
1067 C<compute_all_applicable_methods> it returns a list of HASH references
1068 with the following information; method name (which will always be the
1069 same as C<$method_name>), the name of the class in which the method
1070 lives and a CODE reference for the actual method.
1072 The list of methods produced is a distinct list, meaning there are no
1073 duplicates in it. This is especially useful for things like object
1074 initialization and destruction where you only want the method called
1075 once, and in the correct order.
1077 =item B<find_next_method_by_name ($method_name)>
1079 This will return the first method to match a given C<$method_name> in
1080 the superclasses, this is basically equivalent to calling
1081 C<SUPER::$method_name>, but it can be dispatched at runtime.
1085 =head2 Method Modifiers
1087 Method modifiers are a concept borrowed from CLOS, in which a method
1088 can be wrapped with I<before>, I<after> and I<around> method modifiers
1089 that will be called everytime the method is called.
1091 =head3 How method modifiers work?
1093 Method modifiers work by wrapping the original method and then replacing
1094 it in the classes symbol table. The wrappers will handle calling all the
1095 modifiers in the appropariate orders and preserving the calling context
1096 for the original method.
1098 Each method modifier serves a particular purpose, which may not be
1099 obvious to users of other method wrapping modules. To start with, the
1100 return values of I<before> and I<after> modifiers are ignored. This is
1101 because thier purpose is B<not> to filter the input and output of the
1102 primary method (this is done with an I<around> modifier). This may seem
1103 like an odd restriction to some, but doing this allows for simple code
1104 to be added at the begining or end of a method call without jeapordizing
1105 the normal functioning of the primary method or placing any extra
1106 responsibility on the code of the modifier. Of course if you have more
1107 complex needs, then use the I<around> modifier, which uses a variation
1108 of continutation passing style to allow for a high degree of flexibility.
1110 Before and around modifiers are called in last-defined-first-called order,
1111 while after modifiers are called in first-defined-first-called order. So
1112 the call tree might looks something like this:
1122 To see examples of using method modifiers, see the following examples
1123 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1124 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1125 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1127 =head3 What is the performance impact?
1129 Of course there is a performance cost associated with method modifiers,
1130 but we have made every effort to make that cost be directly proportional
1131 to the amount of modifier features you utilize.
1133 The wrapping method does it's best to B<only> do as much work as it
1134 absolutely needs to. In order to do this we have moved some of the
1135 performance costs to set-up time, where they are easier to amortize.
1137 All this said, my benchmarks have indicated the following:
1139 simple wrapper with no modifiers 100% slower
1140 simple wrapper with simple before modifier 400% slower
1141 simple wrapper with simple after modifier 450% slower
1142 simple wrapper with simple around modifier 500-550% slower
1143 simple wrapper with all 3 modifiers 1100% slower
1145 These numbers may seem daunting, but you must remember, every feature
1146 comes with some cost. To put things in perspective, just doing a simple
1147 C<AUTOLOAD> which does nothing but extract the name of the method called
1148 and return it costs about 400% over a normal method call.
1152 =item B<add_before_method_modifier ($method_name, $code)>
1154 This will wrap the method at C<$method_name> and the supplied C<$code>
1155 will be passed the C<@_> arguments, and called before the original
1156 method is called. As specified above, the return value of the I<before>
1157 method modifiers is ignored, and it's ability to modify C<@_> is
1158 fairly limited. If you need to do either of these things, use an
1159 C<around> method modifier.
1161 =item B<add_after_method_modifier ($method_name, $code)>
1163 This will wrap the method at C<$method_name> so that the original
1164 method will be called, it's return values stashed, and then the
1165 supplied C<$code> will be passed the C<@_> arguments, and called.
1166 As specified above, the return value of the I<after> method
1167 modifiers is ignored, and it cannot modify the return values of
1168 the original method. If you need to do either of these things, use an
1169 C<around> method modifier.
1171 =item B<add_around_method_modifier ($method_name, $code)>
1173 This will wrap the method at C<$method_name> so that C<$code>
1174 will be called and passed the original method as an extra argument
1175 at the begining of the C<@_> argument list. This is a variation of
1176 continuation passing style, where the function prepended to C<@_>
1177 can be considered a continuation. It is up to C<$code> if it calls
1178 the original method or not, there is no restriction on what the
1179 C<$code> can or cannot do.
1185 It should be noted that since there is no one consistent way to define
1186 the attributes of a class in Perl 5. These methods can only work with
1187 the information given, and can not easily discover information on
1188 their own. See L<Class::MOP::Attribute> for more details.
1192 =item B<attribute_metaclass>
1194 =item B<get_attribute_map>
1196 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1198 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1199 instance associated with the given class, and associates it with
1200 the C<$attribute_name>. Unlike methods, attributes within the MOP
1201 are stored as meta-information only. They will be used later to
1202 construct instances from (see C<construct_instance> above).
1203 More details about the attribute meta-objects can be found in the
1204 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1207 It should be noted that any accessor, reader/writer or predicate
1208 methods which the C<$attribute_meta_object> has will be installed
1209 into the class at this time.
1212 If an attribute already exists for C<$attribute_name>, the old one
1213 will be removed (as well as removing all it's accessors), and then
1216 =item B<has_attribute ($attribute_name)>
1218 Checks to see if this class has an attribute by the name of
1219 C<$attribute_name> and returns a boolean.
1221 =item B<get_attribute ($attribute_name)>
1223 Returns the attribute meta-object associated with C<$attribute_name>,
1224 if none is found, it will return undef.
1226 =item B<remove_attribute ($attribute_name)>
1228 This will remove the attribute meta-object stored at
1229 C<$attribute_name>, then return the removed attribute meta-object.
1232 Removing an attribute will only affect future instances of
1233 the class, it will not make any attempt to remove the attribute from
1234 any existing instances of the class.
1236 It should be noted that any accessor, reader/writer or predicate
1237 methods which the attribute meta-object stored at C<$attribute_name>
1238 has will be removed from the class at this time. This B<will> make
1239 these attributes somewhat inaccessable in previously created
1240 instances. But if you are crazy enough to do this at runtime, then
1241 you are crazy enough to deal with something like this :).
1243 =item B<get_attribute_list>
1245 This returns a list of attribute names which are defined in the local
1246 class. If you want a list of all applicable attributes for a class,
1247 use the C<compute_all_applicable_attributes> method.
1249 =item B<compute_all_applicable_attributes>
1251 This will traverse the inheritance heirachy and return a list of all
1252 the applicable attributes for this class. It does not construct a
1253 HASH reference like C<compute_all_applicable_methods> because all
1254 that same information is discoverable through the attribute
1257 =item B<find_attribute_by_name ($attr_name)>
1259 This method will traverse the inheritance heirachy and find the
1260 first attribute whose name matches C<$attr_name>, then return it.
1261 It will return undef if nothing is found.
1265 =head2 Class closing
1269 =item B<make_immutable>
1275 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1277 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1279 =head1 COPYRIGHT AND LICENSE
1281 Copyright 2006 by Infinity Interactive, Inc.
1283 L<http://www.iinteractive.com>
1285 This library is free software; you can redistribute it and/or modify
1286 it under the same terms as Perl itself.