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, @_);
45 my $package_name = shift;
46 (defined $package_name && $package_name && !blessed($package_name))
47 || confess "You must pass a package name and it cannot be blessed";
48 $METAS{$package_name} = undef;
49 $class->construct_class_instance(':package' => $package_name, @_);
52 # NOTE: (meta-circularity)
53 # this is a special form of &construct_instance
54 # (see below), which is used to construct class
55 # meta-object instances for any Class::MOP::*
56 # class. All other classes will use the more
57 # normal &construct_instance.
58 sub construct_class_instance {
61 my $package_name = $options{':package'};
62 (defined $package_name && $package_name)
63 || confess "You must pass a package name";
65 # return the metaclass if we have it cached,
66 # and it is still defined (it has not been
67 # reaped by DESTROY yet, which can happen
68 # annoyingly enough during global destruction)
69 return $METAS{$package_name}
70 if exists $METAS{$package_name} && defined $METAS{$package_name};
71 $class = blessed($class) || $class;
72 # now create the metaclass
74 if ($class =~ /^Class::MOP::/) {
76 '$:package' => $package_name,
78 '$:attribute_metaclass' => $options{':attribute_metaclass'} || 'Class::MOP::Attribute',
79 '$:method_metaclass' => $options{':method_metaclass'} || 'Class::MOP::Method',
80 '$:instance_metaclass' => $options{':instance_metaclass'} || 'Class::MOP::Instance',
85 # it is safe to use meta here because
86 # class will always be a subclass of
87 # Class::MOP::Class, which defines meta
88 $meta = $class->meta->construct_instance(%options)
90 # and check the metaclass compatibility
91 $meta->check_metaclass_compatability();
92 $METAS{$package_name} = $meta;
95 sub check_metaclass_compatability {
98 # this is always okay ...
99 return if blessed($self) eq 'Class::MOP::Class' &&
100 $self->instance_metaclass eq 'Class::MOP::Instance';
102 my @class_list = $self->class_precedence_list;
103 shift @class_list; # shift off $self->name
105 foreach my $class_name (@class_list) {
106 my $meta = $METAS{$class_name} || next;
107 ($self->isa(blessed($meta)))
108 || confess $self->name . "->meta => (" . (blessed($self)) . ")" .
109 " is not compatible with the " .
110 $class_name . "->meta => (" . (blessed($meta)) . ")";
112 # we also need to check that instance metaclasses
113 # are compatabile in the same the class.
114 ($self->instance_metaclass->isa($meta->instance_metaclass))
115 || confess $self->name . "->meta => (" . ($self->instance_metaclass) . ")" .
116 " is not compatible with the " .
117 $class_name . "->meta => (" . ($meta->instance_metaclass) . ")";
123 my ($class, $package_name, $package_version, %options) = @_;
124 (defined $package_name && $package_name)
125 || confess "You must pass a package name";
126 my $code = "package $package_name;";
127 $code .= "\$$package_name\:\:VERSION = '$package_version';"
128 if defined $package_version;
130 confess "creation of $package_name failed : $@" if $@;
131 my $meta = $class->initialize($package_name);
133 $meta->add_method('meta' => sub {
134 Class::MOP::Class->initialize(blessed($_[0]) || $_[0]);
137 $meta->superclasses(@{$options{superclasses}})
138 if exists $options{superclasses};
140 # process attributes first, so that they can
141 # install accessors, but locally defined methods
142 # can then overwrite them. It is maybe a little odd, but
143 # I think this should be the order of things.
144 if (exists $options{attributes}) {
145 foreach my $attr (@{$options{attributes}}) {
146 $meta->add_attribute($attr);
149 if (exists $options{methods}) {
150 foreach my $method_name (keys %{$options{methods}}) {
151 $meta->add_method($method_name, $options{methods}->{$method_name});
158 sub create_anon_class {
159 my ($class, %options) = @_;
160 return Class::MOP::Class::__ANON__->create(%options);
166 # all these attribute readers will be bootstrapped
167 # away in the Class::MOP bootstrap section
169 sub name { $_[0]->{'$:package'} }
170 sub get_attribute_map { $_[0]->{'%:attributes'} }
171 sub attribute_metaclass { $_[0]->{'$:attribute_metaclass'} }
172 sub method_metaclass { $_[0]->{'$:method_metaclass'} }
173 sub instance_metaclass { $_[0]->{'$:instance_metaclass'} }
175 # Instance Construction & Cloning
180 # we need to protect the integrity of the
181 # Class::MOP::Class singletons here, so we
182 # delegate this to &construct_class_instance
183 # which will deal with the singletons
184 return $class->construct_class_instance(@_)
185 if $class->name->isa('Class::MOP::Class');
186 return $class->construct_instance(@_);
189 sub construct_instance {
190 my ($class, %params) = @_;
191 my $meta_instance = $class->get_meta_instance();
192 my $instance = $meta_instance->create_instance();
193 foreach my $attr ($class->compute_all_applicable_attributes()) {
194 $attr->initialize_instance_slot($meta_instance, $instance, \%params);
199 sub get_meta_instance {
201 return $class->instance_metaclass->new(
203 $class->compute_all_applicable_attributes()
209 my $instance = shift;
210 (blessed($instance) && $instance->isa($class->name))
211 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
213 # we need to protect the integrity of the
214 # Class::MOP::Class singletons here, they
215 # should not be cloned.
216 return $instance if $instance->isa('Class::MOP::Class');
217 $class->clone_instance($instance, @_);
221 my ($class, $instance, %params) = @_;
223 || confess "You can only clone instances, \$self is not a blessed instance";
224 my $meta_instance = $class->get_meta_instance();
225 my $clone = $meta_instance->clone_instance($instance);
226 foreach my $key (%params) {
227 next unless $meta_instance->is_valid_slot($key);
228 $meta_instance->set_slot_value($clone, $key, $params{$key});
235 # &name should be here too, but it is above
236 # because it gets bootstrapped away
240 ${$self->get_package_variable('$VERSION')};
250 @{$self->name . '::ISA'} = @supers;
252 # we need to check the metaclass
253 # compatability here so that we can
254 # be sure that the superclass is
255 # not potentially creating an issues
256 # we don't know about
257 $self->check_metaclass_compatability();
259 @{$self->name . '::ISA'};
262 sub class_precedence_list {
265 # We need to check for ciruclar inheirtance here.
266 # This will do nothing if all is well, and blow
267 # up otherwise. Yes, it's an ugly hack, better
268 # suggestions are welcome.
269 { ($self->name || return)->isa('This is a test for circular inheritance') }
270 # ... and now back to our regularly scheduled program
274 $self->initialize($_)->class_precedence_list()
275 } $self->superclasses()
282 my ($self, $method_name, $method) = @_;
283 (defined $method_name && $method_name)
284 || confess "You must define a method name";
285 # use reftype here to allow for blessed subs ...
286 ('CODE' eq (reftype($method) || ''))
287 || confess "Your code block must be a CODE reference";
288 my $full_method_name = ($self->name . '::' . $method_name);
290 $method = $self->method_metaclass->wrap($method) unless blessed($method);
293 no warnings 'redefine';
294 *{$full_method_name} = subname $full_method_name => $method;
298 my $fetch_and_prepare_method = sub {
299 my ($self, $method_name) = @_;
301 my $method = $self->get_method($method_name);
302 # if we dont have local ...
304 # make sure this method even exists ...
305 ($self->find_next_method_by_name($method_name))
306 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
307 # if so, then create a local which just
308 # calls the next applicable method ...
309 $self->add_method($method_name => sub {
310 $self->find_next_method_by_name($method_name)->(@_);
312 $method = $self->get_method($method_name);
315 # now make sure we wrap it properly
316 # (if it isnt already)
317 unless ($method->isa('Class::MOP::Method::Wrapped')) {
318 $method = Class::MOP::Method::Wrapped->wrap($method);
319 $self->add_method($method_name => $method);
324 sub add_before_method_modifier {
325 my ($self, $method_name, $method_modifier) = @_;
326 (defined $method_name && $method_name)
327 || confess "You must pass in a method name";
328 my $method = $fetch_and_prepare_method->($self, $method_name);
329 $method->add_before_modifier(subname ':before' => $method_modifier);
332 sub add_after_method_modifier {
333 my ($self, $method_name, $method_modifier) = @_;
334 (defined $method_name && $method_name)
335 || confess "You must pass in a method name";
336 my $method = $fetch_and_prepare_method->($self, $method_name);
337 $method->add_after_modifier(subname ':after' => $method_modifier);
340 sub add_around_method_modifier {
341 my ($self, $method_name, $method_modifier) = @_;
342 (defined $method_name && $method_name)
343 || confess "You must pass in a method name";
344 my $method = $fetch_and_prepare_method->($self, $method_name);
345 $method->add_around_modifier(subname ':around' => $method_modifier);
349 # the methods above used to be named like this:
350 # ${pkg}::${method}:(before|after|around)
351 # but this proved problematic when using one modifier
352 # to wrap multiple methods (something which is likely
353 # to happen pretty regularly IMO). So instead of naming
354 # it like this, I have chosen to just name them purely
355 # with their modifier names, like so:
356 # :(before|after|around)
357 # The fact is that in a stack trace, it will be fairly
358 # evident from the context what method they are attached
359 # to, and so don't need the fully qualified name.
363 my ($self, $method_name, $method) = @_;
364 (defined $method_name && $method_name)
365 || confess "You must define a method name";
366 # use reftype here to allow for blessed subs ...
367 ('CODE' eq (reftype($method) || ''))
368 || confess "Your code block must be a CODE reference";
369 my $full_method_name = ($self->name . '::' . $method_name);
371 $method = $self->method_metaclass->wrap($method) unless blessed($method);
374 no warnings 'redefine';
375 *{$full_method_name} = $method;
379 my ($self, $method_name) = @_;
380 (defined $method_name && $method_name)
381 || confess "You must define a method name";
383 my $sub_name = ($self->name . '::' . $method_name);
386 return 0 if !defined(&{$sub_name});
387 my $method = \&{$sub_name};
388 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
389 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
391 # at this point we are relatively sure
392 # it is our method, so we bless/wrap it
393 $self->method_metaclass->wrap($method) unless blessed($method);
398 my ($self, $method_name) = @_;
399 (defined $method_name && $method_name)
400 || confess "You must define a method name";
402 return unless $self->has_method($method_name);
405 return \&{$self->name . '::' . $method_name};
409 my ($self, $method_name) = @_;
410 (defined $method_name && $method_name)
411 || confess "You must define a method name";
413 my $removed_method = $self->get_method($method_name);
416 delete ${$self->name . '::'}{$method_name}
417 if defined $removed_method;
419 return $removed_method;
422 sub get_method_list {
425 grep { $self->has_method($_) } keys %{$self->name . '::'};
428 sub compute_all_applicable_methods {
431 # keep a record of what we have seen
432 # here, this will handle all the
433 # inheritence issues because we are
434 # using the &class_precedence_list
435 my (%seen_class, %seen_method);
436 foreach my $class ($self->class_precedence_list()) {
437 next if $seen_class{$class};
438 $seen_class{$class}++;
439 # fetch the meta-class ...
440 my $meta = $self->initialize($class);
441 foreach my $method_name ($meta->get_method_list()) {
442 next if exists $seen_method{$method_name};
443 $seen_method{$method_name}++;
445 name => $method_name,
447 code => $meta->get_method($method_name)
454 sub find_all_methods_by_name {
455 my ($self, $method_name) = @_;
456 (defined $method_name && $method_name)
457 || confess "You must define a method name to find";
459 # keep a record of what we have seen
460 # here, this will handle all the
461 # inheritence issues because we are
462 # using the &class_precedence_list
464 foreach my $class ($self->class_precedence_list()) {
465 next if $seen_class{$class};
466 $seen_class{$class}++;
467 # fetch the meta-class ...
468 my $meta = $self->initialize($class);
470 name => $method_name,
472 code => $meta->get_method($method_name)
473 } if $meta->has_method($method_name);
478 sub find_next_method_by_name {
479 my ($self, $method_name) = @_;
480 (defined $method_name && $method_name)
481 || confess "You must define a method name to find";
482 # keep a record of what we have seen
483 # here, this will handle all the
484 # inheritence issues because we are
485 # using the &class_precedence_list
487 my @cpl = $self->class_precedence_list();
488 shift @cpl; # discard ourselves
489 foreach my $class (@cpl) {
490 next if $seen_class{$class};
491 $seen_class{$class}++;
492 # fetch the meta-class ...
493 my $meta = $self->initialize($class);
494 return $meta->get_method($method_name)
495 if $meta->has_method($method_name);
504 # either we have an attribute object already
505 # or we need to create one from the args provided
506 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
507 # make sure it is derived from the correct type though
508 ($attribute->isa('Class::MOP::Attribute'))
509 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
510 $attribute->attach_to_class($self);
511 $attribute->install_accessors();
512 $self->get_attribute_map->{$attribute->name} = $attribute;
515 # in theory we have to tell everyone the slot structure may have changed
519 my ($self, $attribute_name) = @_;
520 (defined $attribute_name && $attribute_name)
521 || confess "You must define an attribute name";
522 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
526 my ($self, $attribute_name) = @_;
527 (defined $attribute_name && $attribute_name)
528 || confess "You must define an attribute name";
529 return $self->get_attribute_map->{$attribute_name}
530 if $self->has_attribute($attribute_name);
534 sub remove_attribute {
535 my ($self, $attribute_name) = @_;
536 (defined $attribute_name && $attribute_name)
537 || confess "You must define an attribute name";
538 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
539 return unless defined $removed_attribute;
540 delete $self->get_attribute_map->{$attribute_name};
541 $removed_attribute->remove_accessors();
542 $removed_attribute->detach_from_class();
543 return $removed_attribute;
546 sub get_attribute_list {
548 keys %{$self->get_attribute_map};
551 sub compute_all_applicable_attributes {
554 # keep a record of what we have seen
555 # here, this will handle all the
556 # inheritence issues because we are
557 # using the &class_precedence_list
558 my (%seen_class, %seen_attr);
559 foreach my $class ($self->class_precedence_list()) {
560 next if $seen_class{$class};
561 $seen_class{$class}++;
562 # fetch the meta-class ...
563 my $meta = $self->initialize($class);
564 foreach my $attr_name ($meta->get_attribute_list()) {
565 next if exists $seen_attr{$attr_name};
566 $seen_attr{$attr_name}++;
567 push @attrs => $meta->get_attribute($attr_name);
573 sub find_attribute_by_name {
574 my ($self, $attr_name) = @_;
575 # keep a record of what we have seen
576 # here, this will handle all the
577 # inheritence issues because we are
578 # using the &class_precedence_list
580 foreach my $class ($self->class_precedence_list()) {
581 next if $seen_class{$class};
582 $seen_class{$class}++;
583 # fetch the meta-class ...
584 my $meta = $self->initialize($class);
585 return $meta->get_attribute($attr_name)
586 if $meta->has_attribute($attr_name);
593 sub add_package_variable {
594 my ($self, $variable, $initial_value) = @_;
595 (defined $variable && $variable =~ /^[\$\@\%]/)
596 || confess "variable name does not have a sigil";
598 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
599 if (defined $initial_value) {
601 *{$self->name . '::' . $name} = $initial_value;
607 # We HAVE to localize $@ or all
608 # hell breaks loose. It is not
609 # good, believe me, not good.
611 eval $sigil . $self->name . '::' . $name;
614 confess "Could not create package variable ($variable) because : $e" if $e;
618 sub has_package_variable {
619 my ($self, $variable) = @_;
620 (defined $variable && $variable =~ /^[\$\@\%]/)
621 || confess "variable name does not have a sigil";
622 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
624 defined ${$self->name . '::'}{$name} ? 1 : 0;
627 sub get_package_variable {
628 my ($self, $variable) = @_;
629 (defined $variable && $variable =~ /^[\$\@\%]/)
630 || confess "variable name does not have a sigil";
631 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
635 # We HAVE to localize $@ or all
636 # hell breaks loose. It is not
637 # good, believe me, not good.
639 $ref = eval '\\' . $sigil . $self->name . '::' . $name;
642 confess "Could not get the package variable ($variable) because : $e" if $e;
643 # if we didn't die, then we can return it
647 sub remove_package_variable {
648 my ($self, $variable) = @_;
649 (defined $variable && $variable =~ /^[\$\@\%]/)
650 || confess "variable name does not have a sigil";
651 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
653 delete ${$self->name . '::'}{$name};
656 package Class::MOP::Class::__ANON__;
661 use Scalar::Util 'weaken';
663 our $VERSION = '0.01';
665 use base 'Class::MOP::Class';
669 # we hold a weakened cache here
673 # this should be sufficient, if you have a
674 # use case where it is not, write a test and
676 my $ANON_CLASS_SERIAL = 0;
679 my ($class, %options) = @_;
680 my $package_name = __PACKAGE__ . '::SERIAL::' . ++$ANON_CLASS_SERIAL;
681 return $class->SUPER::create($package_name, '0.00', %options);
684 sub construct_class_instance {
685 my ($class, %options) = @_;
686 my $package_name = $options{':package'};
688 # we cache the anon metaclasses as well
689 # but we weaken them (see below)
690 return $ANON_METAS{$package_name}
691 if exists $ANON_METAS{$package_name} &&
692 defined $ANON_METAS{$package_name};
693 my $meta = $class->meta->construct_instance(%options);
694 $meta->check_metaclass_compatability();
695 # weaken the metaclass cache so that
696 # DESTROY gets called as expected
697 weaken($ANON_METAS{$package_name} = $meta);
704 my $prefix = __PACKAGE__ . '::SERIAL::';
705 my ($serial_id) = ($self->name =~ /$prefix(\d+)/);
707 foreach my $key (keys %{$prefix . $serial_id}) {
708 delete ${$prefix . $serial_id}{$key};
710 delete ${'main::' . $prefix}{$serial_id . '::'};
721 Class::MOP::Class - Class Meta Object
725 # assuming that class Foo
726 # has been defined, you can
728 # use this for introspection ...
730 # add a method to Foo ...
731 Foo->meta->add_method('bar' => sub { ... })
733 # get a list of all the classes searched
734 # the method dispatcher in the correct order
735 Foo->meta->class_precedence_list()
737 # remove a method from Foo
738 Foo->meta->remove_method('bar');
740 # or use this to actually create classes ...
742 Class::MOP::Class->create('Bar' => '0.01' => (
743 superclasses => [ 'Foo' ],
745 Class::MOP:::Attribute->new('$bar'),
746 Class::MOP:::Attribute->new('$baz'),
749 calculate_bar => sub { ... },
750 construct_baz => sub { ... }
756 This is the largest and currently most complex part of the Perl 5
757 meta-object protocol. It controls the introspection and
758 manipulation of Perl 5 classes (and it can create them too). The
759 best way to understand what this module can do, is to read the
760 documentation for each of it's methods.
764 =head2 Self Introspection
770 This will return a B<Class::MOP::Class> instance which is related
771 to this class. Thereby allowing B<Class::MOP::Class> to actually
774 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
775 bootstrap this module by installing a number of attribute meta-objects
776 into it's metaclass. This will allow this class to reap all the benifits
777 of the MOP when subclassing it.
779 =item B<get_all_metaclasses>
781 This will return an hash of all the metaclass instances that have
782 been cached by B<Class::MOP::Class> keyed by the package name.
784 =item B<get_all_metaclass_instances>
786 This will return an array of all the metaclass instances that have
787 been cached by B<Class::MOP::Class>.
789 =item B<get_all_metaclass_names>
791 This will return an array of all the metaclass names that have
792 been cached by B<Class::MOP::Class>.
796 =head2 Class construction
798 These methods will handle creating B<Class::MOP::Class> objects,
799 which can be used to both create new classes, and analyze
800 pre-existing classes.
802 This module will internally store references to all the instances
803 you create with these methods, so that they do not need to be
804 created any more than nessecary. Basically, they are singletons.
808 =item B<create ($package_name, ?$package_version,
809 superclasses =E<gt> ?@superclasses,
810 methods =E<gt> ?%methods,
811 attributes =E<gt> ?%attributes)>
813 This returns a B<Class::MOP::Class> object, bringing the specified
814 C<$package_name> into existence and adding any of the
815 C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
818 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
819 methods =E<gt> ?%methods,
820 attributes =E<gt> ?%attributes)>
822 This will create an anonymous class, it works much like C<create> but
823 it does not need a C<$package_name>. Instead it will create a suitably
824 unique package name for you to stash things into.
826 =item B<initialize ($package_name, %options)>
828 This initializes and returns returns a B<Class::MOP::Class> object
829 for a given a C<$package_name>.
831 =item B<reinitialize ($package_name, %options)>
833 This removes the old metaclass, and creates a new one in it's place.
834 Do B<not> use this unless you really know what you are doing, it could
835 very easily make a very large mess of your program.
837 =item B<construct_class_instance (%options)>
839 This will construct an instance of B<Class::MOP::Class>, it is
840 here so that we can actually "tie the knot" for B<Class::MOP::Class>
841 to use C<construct_instance> once all the bootstrapping is done. This
842 method is used internally by C<initialize> and should never be called
843 from outside of that method really.
845 =item B<check_metaclass_compatability>
847 This method is called as the very last thing in the
848 C<construct_class_instance> method. This will check that the
849 metaclass you are creating is compatible with the metaclasses of all
850 your ancestors. For more inforamtion about metaclass compatibility
851 see the C<About Metaclass compatibility> section in L<Class::MOP>.
855 =head2 Object instance construction and cloning
857 These methods are B<entirely optional>, it is up to you whether you want
862 =item B<instance_metaclass>
864 =item B<get_meta_instance>
866 =item B<new_object (%params)>
868 This is a convience method for creating a new object of the class, and
869 blessing it into the appropriate package as well. Ideally your class
870 would call a C<new> this method like so:
873 my ($class, %param) = @_;
874 $class->meta->new_object(%params);
877 Of course the ideal place for this would actually be in C<UNIVERSAL::>
878 but that is considered bad style, so we do not do that.
880 =item B<construct_instance (%params)>
882 This method is used to construct an instace structure suitable for
883 C<bless>-ing into your package of choice. It works in conjunction
884 with the Attribute protocol to collect all applicable attributes.
886 This will construct and instance using a HASH ref as storage
887 (currently only HASH references are supported). This will collect all
888 the applicable attributes and layout out the fields in the HASH ref,
889 it will then initialize them using either use the corresponding key
890 in C<%params> or any default value or initializer found in the
891 attribute meta-object.
893 =item B<clone_object ($instance, %params)>
895 This is a convience method for cloning an object instance, then
896 blessing it into the appropriate package. This method will call
897 C<clone_instance>, which performs a shallow copy of the object,
898 see that methods documentation for more details. Ideally your
899 class would call a C<clone> this method like so:
902 my ($self, %param) = @_;
903 $self->meta->clone_object($self, %params);
906 Of course the ideal place for this would actually be in C<UNIVERSAL::>
907 but that is considered bad style, so we do not do that.
909 =item B<clone_instance($instance, %params)>
911 This method is a compliment of C<construct_instance> (which means if
912 you override C<construct_instance>, you need to override this one too),
913 and clones the instance shallowly.
915 The cloned structure returned is (like with C<construct_instance>) an
916 unC<bless>ed HASH reference, it is your responsibility to then bless
917 this cloned structure into the right class (which C<clone_object> will
920 As of 0.11, this method will clone the C<$instance> structure shallowly,
921 as opposed to the deep cloning implemented in prior versions. After much
922 thought, research and discussion, I have decided that anything but basic
923 shallow cloning is outside the scope of the meta-object protocol. I
924 think Yuval "nothingmuch" Kogman put it best when he said that cloning
925 is too I<context-specific> to be part of the MOP.
935 This is a read-only attribute which returns the package name for the
936 given B<Class::MOP::Class> instance.
940 This is a read-only attribute which returns the C<$VERSION> of the
941 package for the given B<Class::MOP::Class> instance.
945 =head2 Inheritance Relationships
949 =item B<superclasses (?@superclasses)>
951 This is a read-write attribute which represents the superclass
952 relationships of the class the B<Class::MOP::Class> instance is
953 associated with. Basically, it can get and set the C<@ISA> for you.
956 Perl will occasionally perform some C<@ISA> and method caching, if
957 you decide to change your superclass relationship at runtime (which
958 is quite insane and very much not recommened), then you should be
959 aware of this and the fact that this module does not make any
960 attempt to address this issue.
962 =item B<class_precedence_list>
964 This computes the a list of all the class's ancestors in the same order
965 in which method dispatch will be done. This is similair to
966 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
974 =item B<method_metaclass>
976 =item B<add_method ($method_name, $method)>
978 This will take a C<$method_name> and CODE reference to that
979 C<$method> and install it into the class's package.
982 This does absolutely nothing special to C<$method>
983 other than use B<Sub::Name> to make sure it is tagged with the
984 correct name, and therefore show up correctly in stack traces and
987 =item B<alias_method ($method_name, $method)>
989 This will take a C<$method_name> and CODE reference to that
990 C<$method> and alias the method into the class's package.
993 Unlike C<add_method>, this will B<not> try to name the
994 C<$method> using B<Sub::Name>, it only aliases the method in
997 =item B<has_method ($method_name)>
999 This just provides a simple way to check if the class implements
1000 a specific C<$method_name>. It will I<not> however, attempt to check
1001 if the class inherits the method (use C<UNIVERSAL::can> for that).
1003 This will correctly handle functions defined outside of the package
1004 that use a fully qualified name (C<sub Package::name { ... }>).
1006 This will correctly handle functions renamed with B<Sub::Name> and
1007 installed using the symbol tables. However, if you are naming the
1008 subroutine outside of the package scope, you must use the fully
1009 qualified name, including the package name, for C<has_method> to
1010 correctly identify it.
1012 This will attempt to correctly ignore functions imported from other
1013 packages using B<Exporter>. It breaks down if the function imported
1014 is an C<__ANON__> sub (such as with C<use constant>), which very well
1015 may be a valid method being applied to the class.
1017 In short, this method cannot always be trusted to determine if the
1018 C<$method_name> is actually a method. However, it will DWIM about
1019 90% of the time, so it's a small trade off I think.
1021 =item B<get_method ($method_name)>
1023 This will return a CODE reference of the specified C<$method_name>,
1024 or return undef if that method does not exist.
1026 =item B<remove_method ($method_name)>
1028 This will attempt to remove a given C<$method_name> from the class.
1029 It will return the CODE reference that it has removed, and will
1030 attempt to use B<Sub::Name> to clear the methods associated name.
1032 =item B<get_method_list>
1034 This will return a list of method names for all I<locally> defined
1035 methods. It does B<not> provide a list of all applicable methods,
1036 including any inherited ones. If you want a list of all applicable
1037 methods, use the C<compute_all_applicable_methods> method.
1039 =item B<compute_all_applicable_methods>
1041 This will return a list of all the methods names this class will
1042 respond to, taking into account inheritance. The list will be a list of
1043 HASH references, each one containing the following information; method
1044 name, the name of the class in which the method lives and a CODE
1045 reference for the actual method.
1047 =item B<find_all_methods_by_name ($method_name)>
1049 This will traverse the inheritence hierarchy and locate all methods
1050 with a given C<$method_name>. Similar to
1051 C<compute_all_applicable_methods> it returns a list of HASH references
1052 with the following information; method name (which will always be the
1053 same as C<$method_name>), the name of the class in which the method
1054 lives and a CODE reference for the actual method.
1056 The list of methods produced is a distinct list, meaning there are no
1057 duplicates in it. This is especially useful for things like object
1058 initialization and destruction where you only want the method called
1059 once, and in the correct order.
1061 =item B<find_next_method_by_name ($method_name)>
1063 This will return the first method to match a given C<$method_name> in
1064 the superclasses, this is basically equivalent to calling
1065 C<SUPER::$method_name>, but it can be dispatched at runtime.
1069 =head2 Method Modifiers
1071 Method modifiers are a concept borrowed from CLOS, in which a method
1072 can be wrapped with I<before>, I<after> and I<around> method modifiers
1073 that will be called everytime the method is called.
1075 =head3 How method modifiers work?
1077 Method modifiers work by wrapping the original method and then replacing
1078 it in the classes symbol table. The wrappers will handle calling all the
1079 modifiers in the appropariate orders and preserving the calling context
1080 for the original method.
1082 Each method modifier serves a particular purpose, which may not be
1083 obvious to users of other method wrapping modules. To start with, the
1084 return values of I<before> and I<after> modifiers are ignored. This is
1085 because thier purpose is B<not> to filter the input and output of the
1086 primary method (this is done with an I<around> modifier). This may seem
1087 like an odd restriction to some, but doing this allows for simple code
1088 to be added at the begining or end of a method call without jeapordizing
1089 the normal functioning of the primary method or placing any extra
1090 responsibility on the code of the modifier. Of course if you have more
1091 complex needs, then use the I<around> modifier, which uses a variation
1092 of continutation passing style to allow for a high degree of flexibility.
1094 Before and around modifiers are called in last-defined-first-called order,
1095 while after modifiers are called in first-defined-first-called order. So
1096 the call tree might looks something like this:
1106 To see examples of using method modifiers, see the following examples
1107 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1108 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1109 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1111 =head3 What is the performance impact?
1113 Of course there is a performance cost associated with method modifiers,
1114 but we have made every effort to make that cost be directly proportional
1115 to the amount of modifier features you utilize.
1117 The wrapping method does it's best to B<only> do as much work as it
1118 absolutely needs to. In order to do this we have moved some of the
1119 performance costs to set-up time, where they are easier to amortize.
1121 All this said, my benchmarks have indicated the following:
1123 simple wrapper with no modifiers 100% slower
1124 simple wrapper with simple before modifier 400% slower
1125 simple wrapper with simple after modifier 450% slower
1126 simple wrapper with simple around modifier 500-550% slower
1127 simple wrapper with all 3 modifiers 1100% slower
1129 These numbers may seem daunting, but you must remember, every feature
1130 comes with some cost. To put things in perspective, just doing a simple
1131 C<AUTOLOAD> which does nothing but extract the name of the method called
1132 and return it costs about 400% over a normal method call.
1136 =item B<add_before_method_modifier ($method_name, $code)>
1138 This will wrap the method at C<$method_name> and the supplied C<$code>
1139 will be passed the C<@_> arguments, and called before the original
1140 method is called. As specified above, the return value of the I<before>
1141 method modifiers is ignored, and it's ability to modify C<@_> is
1142 fairly limited. If you need to do either of these things, use an
1143 C<around> method modifier.
1145 =item B<add_after_method_modifier ($method_name, $code)>
1147 This will wrap the method at C<$method_name> so that the original
1148 method will be called, it's return values stashed, and then the
1149 supplied C<$code> will be passed the C<@_> arguments, and called.
1150 As specified above, the return value of the I<after> method
1151 modifiers is ignored, and it cannot modify the return values of
1152 the original method. If you need to do either of these things, use an
1153 C<around> method modifier.
1155 =item B<add_around_method_modifier ($method_name, $code)>
1157 This will wrap the method at C<$method_name> so that C<$code>
1158 will be called and passed the original method as an extra argument
1159 at the begining of the C<@_> argument list. This is a variation of
1160 continuation passing style, where the function prepended to C<@_>
1161 can be considered a continuation. It is up to C<$code> if it calls
1162 the original method or not, there is no restriction on what the
1163 C<$code> can or cannot do.
1169 It should be noted that since there is no one consistent way to define
1170 the attributes of a class in Perl 5. These methods can only work with
1171 the information given, and can not easily discover information on
1172 their own. See L<Class::MOP::Attribute> for more details.
1176 =item B<attribute_metaclass>
1178 =item B<get_attribute_map>
1180 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1182 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1183 instance associated with the given class, and associates it with
1184 the C<$attribute_name>. Unlike methods, attributes within the MOP
1185 are stored as meta-information only. They will be used later to
1186 construct instances from (see C<construct_instance> above).
1187 More details about the attribute meta-objects can be found in the
1188 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1191 It should be noted that any accessor, reader/writer or predicate
1192 methods which the C<$attribute_meta_object> has will be installed
1193 into the class at this time.
1195 =item B<has_attribute ($attribute_name)>
1197 Checks to see if this class has an attribute by the name of
1198 C<$attribute_name> and returns a boolean.
1200 =item B<get_attribute ($attribute_name)>
1202 Returns the attribute meta-object associated with C<$attribute_name>,
1203 if none is found, it will return undef.
1205 =item B<remove_attribute ($attribute_name)>
1207 This will remove the attribute meta-object stored at
1208 C<$attribute_name>, then return the removed attribute meta-object.
1211 Removing an attribute will only affect future instances of
1212 the class, it will not make any attempt to remove the attribute from
1213 any existing instances of the class.
1215 It should be noted that any accessor, reader/writer or predicate
1216 methods which the attribute meta-object stored at C<$attribute_name>
1217 has will be removed from the class at this time. This B<will> make
1218 these attributes somewhat inaccessable in previously created
1219 instances. But if you are crazy enough to do this at runtime, then
1220 you are crazy enough to deal with something like this :).
1222 =item B<get_attribute_list>
1224 This returns a list of attribute names which are defined in the local
1225 class. If you want a list of all applicable attributes for a class,
1226 use the C<compute_all_applicable_attributes> method.
1228 =item B<compute_all_applicable_attributes>
1230 This will traverse the inheritance heirachy and return a list of all
1231 the applicable attributes for this class. It does not construct a
1232 HASH reference like C<compute_all_applicable_methods> because all
1233 that same information is discoverable through the attribute
1236 =item B<find_attribute_by_name ($attr_name)>
1238 This method will traverse the inheritance heirachy and find the
1239 first attribute whose name matches C<$attr_name>, then return it.
1240 It will return undef if nothing is found.
1244 =head2 Package Variables
1246 Since Perl's classes are built atop the Perl package system, it is
1247 fairly common to use package scoped variables for things like static
1248 class variables. The following methods are convience methods for
1249 the creation and inspection of package scoped variables.
1253 =item B<add_package_variable ($variable_name, ?$initial_value)>
1255 Given a C<$variable_name>, which must contain a leading sigil, this
1256 method will create that variable within the package which houses the
1257 class. It also takes an optional C<$initial_value>, which must be a
1258 reference of the same type as the sigil of the C<$variable_name>
1261 =item B<get_package_variable ($variable_name)>
1263 This will return a reference to the package variable in
1266 =item B<has_package_variable ($variable_name)>
1268 Returns true (C<1>) if there is a package variable defined for
1269 C<$variable_name>, and false (C<0>) otherwise.
1271 =item B<remove_package_variable ($variable_name)>
1273 This will attempt to remove the package variable at C<$variable_name>.
1279 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1281 =head1 COPYRIGHT AND LICENSE
1283 Copyright 2006 by Infinity Interactive, Inc.
1285 L<http://www.iinteractive.com>
1287 This library is free software; you can redistribute it and/or modify
1288 it under the same terms as Perl itself.