2 package Class::MOP::Class;
8 use Scalar::Util 'blessed', 'reftype', 'weaken';
9 use Sub::Name 'subname';
10 use B 'svref_2object';
12 our $VERSION = '0.14';
14 use Class::MOP::Instance;
18 sub meta { Class::MOP::Class->initialize(blessed($_[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, @_);
53 # we need a sufficiently annoying prefix
54 # this should suffice for now
55 my $ANON_CLASS_PREFIX = 'Class::MOP::Class::__ANON__::SERIAL::';
59 # this should be sufficient, if you have a
60 # use case where it is not, write a test and
62 my $ANON_CLASS_SERIAL = 0;
64 sub create_anon_class {
65 my ($class, %options) = @_;
66 my $package_name = $ANON_CLASS_PREFIX . ++$ANON_CLASS_SERIAL;
67 return $class->create($package_name, '0.00', %options);
71 # NOTE: (meta-circularity)
72 # this is a special form of &construct_instance
73 # (see below), which is used to construct class
74 # meta-object instances for any Class::MOP::*
75 # class. All other classes will use the more
76 # normal &construct_instance.
77 sub construct_class_instance {
80 my $package_name = $options{':package'};
81 (defined $package_name && $package_name)
82 || confess "You must pass a package name";
84 # return the metaclass if we have it cached,
85 # and it is still defined (it has not been
86 # reaped by DESTROY yet, which can happen
87 # annoyingly enough during global destruction)
88 return $METAS{$package_name}
89 if exists $METAS{$package_name} && defined $METAS{$package_name};
90 $class = blessed($class) || $class;
91 # now create the metaclass
93 if ($class =~ /^Class::MOP::/) {
95 '$:package' => $package_name,
97 '$: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)
109 # and check the metaclass compatibility
110 $meta->check_metaclass_compatability();
111 $METAS{$package_name} = $meta;
113 # we need to weaken any anon classes
114 # so that they can call DESTROY properly
115 weaken($METAS{$package_name})
116 if $package_name =~ /^$ANON_CLASS_PREFIX/;
121 # this will only get called for
122 # anon-classes, all other calls
123 # are assumed to occur during
124 # global destruction and so don't
125 # really need to be handled explicitly
128 return unless $self->name =~ /^$ANON_CLASS_PREFIX/;
129 my ($serial_id) = ($self->name =~ /^$ANON_CLASS_PREFIX(\d+)/);
131 foreach my $key (keys %{$ANON_CLASS_PREFIX . $serial_id}) {
132 delete ${$ANON_CLASS_PREFIX . $serial_id}{$key};
134 delete ${'main::' . $ANON_CLASS_PREFIX}{$serial_id . '::'};
137 sub check_metaclass_compatability {
140 # this is always okay ...
141 return if blessed($self) eq 'Class::MOP::Class' &&
142 $self->instance_metaclass eq 'Class::MOP::Instance';
144 my @class_list = $self->class_precedence_list;
145 shift @class_list; # shift off $self->name
147 foreach my $class_name (@class_list) {
148 my $meta = $METAS{$class_name} || next;
149 ($self->isa(blessed($meta)))
150 || confess $self->name . "->meta => (" . (blessed($self)) . ")" .
151 " is not compatible with the " .
152 $class_name . "->meta => (" . (blessed($meta)) . ")";
154 # we also need to check that instance metaclasses
155 # are compatabile in the same the class.
156 ($self->instance_metaclass->isa($meta->instance_metaclass))
157 || confess $self->name . "->meta => (" . ($self->instance_metaclass) . ")" .
158 " is not compatible with the " .
159 $class_name . "->meta => (" . ($meta->instance_metaclass) . ")";
165 my ($class, $package_name, $package_version, %options) = @_;
166 (defined $package_name && $package_name)
167 || confess "You must pass a package name";
168 my $code = "package $package_name;";
169 $code .= "\$$package_name\:\:VERSION = '$package_version';"
170 if defined $package_version;
172 confess "creation of $package_name failed : $@" if $@;
173 my $meta = $class->initialize($package_name);
175 $meta->add_method('meta' => sub {
176 Class::MOP::Class->initialize(blessed($_[0]) || $_[0]);
179 $meta->superclasses(@{$options{superclasses}})
180 if exists $options{superclasses};
182 # process attributes first, so that they can
183 # install accessors, but locally defined methods
184 # can then overwrite them. It is maybe a little odd, but
185 # I think this should be the order of things.
186 if (exists $options{attributes}) {
187 foreach my $attr (@{$options{attributes}}) {
188 $meta->add_attribute($attr);
191 if (exists $options{methods}) {
192 foreach my $method_name (keys %{$options{methods}}) {
193 $meta->add_method($method_name, $options{methods}->{$method_name});
202 # all these attribute readers will be bootstrapped
203 # away in the Class::MOP bootstrap section
205 sub name { $_[0]->{'$:package'} }
206 sub get_attribute_map { $_[0]->{'%:attributes'} }
207 sub attribute_metaclass { $_[0]->{'$:attribute_metaclass'} }
208 sub method_metaclass { $_[0]->{'$:method_metaclass'} }
209 sub instance_metaclass { $_[0]->{'$:instance_metaclass'} }
211 # Instance Construction & Cloning
216 # we need to protect the integrity of the
217 # Class::MOP::Class singletons here, so we
218 # delegate this to &construct_class_instance
219 # which will deal with the singletons
220 return $class->construct_class_instance(@_)
221 if $class->name->isa('Class::MOP::Class');
222 return $class->construct_instance(@_);
225 sub construct_instance {
226 my ($class, %params) = @_;
227 my $meta_instance = $class->get_meta_instance();
228 my $instance = $meta_instance->create_instance();
229 foreach my $attr ($class->compute_all_applicable_attributes()) {
230 $attr->initialize_instance_slot($meta_instance, $instance, \%params);
235 sub get_meta_instance {
237 return $class->instance_metaclass->new(
239 $class->compute_all_applicable_attributes()
245 my $instance = shift;
246 (blessed($instance) && $instance->isa($class->name))
247 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
249 # we need to protect the integrity of the
250 # Class::MOP::Class singletons here, they
251 # should not be cloned.
252 return $instance if $instance->isa('Class::MOP::Class');
253 $class->clone_instance($instance, @_);
257 my ($class, $instance, %params) = @_;
259 || confess "You can only clone instances, \$self is not a blessed instance";
260 my $meta_instance = $class->get_meta_instance();
261 my $clone = $meta_instance->clone_instance($instance);
262 foreach my $key (%params) {
263 next unless $meta_instance->is_valid_slot($key);
264 $meta_instance->set_slot_value($clone, $key, $params{$key});
271 # &name should be here too, but it is above
272 # because it gets bootstrapped away
276 ${$self->get_package_variable('$VERSION')};
286 @{$self->name . '::ISA'} = @supers;
288 # we need to check the metaclass
289 # compatability here so that we can
290 # be sure that the superclass is
291 # not potentially creating an issues
292 # we don't know about
293 $self->check_metaclass_compatability();
295 @{$self->name . '::ISA'};
298 sub class_precedence_list {
301 # We need to check for ciruclar inheirtance here.
302 # This will do nothing if all is well, and blow
303 # up otherwise. Yes, it's an ugly hack, better
304 # suggestions are welcome.
305 { ($self->name || return)->isa('This is a test for circular inheritance') }
306 # ... and now back to our regularly scheduled program
310 $self->initialize($_)->class_precedence_list()
311 } $self->superclasses()
318 my ($self, $method_name, $method) = @_;
319 (defined $method_name && $method_name)
320 || confess "You must define a method name";
321 # use reftype here to allow for blessed subs ...
322 ('CODE' eq (reftype($method) || ''))
323 || confess "Your code block must be a CODE reference";
324 my $full_method_name = ($self->name . '::' . $method_name);
326 $method = $self->method_metaclass->wrap($method) unless blessed($method);
329 no warnings 'redefine';
330 *{$full_method_name} = subname $full_method_name => $method;
334 my $fetch_and_prepare_method = sub {
335 my ($self, $method_name) = @_;
337 my $method = $self->get_method($method_name);
338 # if we dont have local ...
340 # make sure this method even exists ...
341 ($self->find_next_method_by_name($method_name))
342 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
343 # if so, then create a local which just
344 # calls the next applicable method ...
345 $self->add_method($method_name => sub {
346 $self->find_next_method_by_name($method_name)->(@_);
348 $method = $self->get_method($method_name);
351 # now make sure we wrap it properly
352 # (if it isnt already)
353 unless ($method->isa('Class::MOP::Method::Wrapped')) {
354 $method = Class::MOP::Method::Wrapped->wrap($method);
355 $self->add_method($method_name => $method);
360 sub add_before_method_modifier {
361 my ($self, $method_name, $method_modifier) = @_;
362 (defined $method_name && $method_name)
363 || confess "You must pass in a method name";
364 my $method = $fetch_and_prepare_method->($self, $method_name);
365 $method->add_before_modifier(subname ':before' => $method_modifier);
368 sub add_after_method_modifier {
369 my ($self, $method_name, $method_modifier) = @_;
370 (defined $method_name && $method_name)
371 || confess "You must pass in a method name";
372 my $method = $fetch_and_prepare_method->($self, $method_name);
373 $method->add_after_modifier(subname ':after' => $method_modifier);
376 sub add_around_method_modifier {
377 my ($self, $method_name, $method_modifier) = @_;
378 (defined $method_name && $method_name)
379 || confess "You must pass in a method name";
380 my $method = $fetch_and_prepare_method->($self, $method_name);
381 $method->add_around_modifier(subname ':around' => $method_modifier);
385 # the methods above used to be named like this:
386 # ${pkg}::${method}:(before|after|around)
387 # but this proved problematic when using one modifier
388 # to wrap multiple methods (something which is likely
389 # to happen pretty regularly IMO). So instead of naming
390 # it like this, I have chosen to just name them purely
391 # with their modifier names, like so:
392 # :(before|after|around)
393 # The fact is that in a stack trace, it will be fairly
394 # evident from the context what method they are attached
395 # to, and so don't need the fully qualified name.
399 my ($self, $method_name, $method) = @_;
400 (defined $method_name && $method_name)
401 || confess "You must define a method name";
402 # use reftype here to allow for blessed subs ...
403 ('CODE' eq (reftype($method) || ''))
404 || confess "Your code block must be a CODE reference";
405 my $full_method_name = ($self->name . '::' . $method_name);
407 $method = $self->method_metaclass->wrap($method) unless blessed($method);
410 no warnings 'redefine';
411 *{$full_method_name} = $method;
415 my ($self, $method_name) = @_;
416 (defined $method_name && $method_name)
417 || confess "You must define a method name";
419 my $sub_name = ($self->name . '::' . $method_name);
422 return 0 if !defined(&{$sub_name});
423 my $method = \&{$sub_name};
424 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
425 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
427 # at this point we are relatively sure
428 # it is our method, so we bless/wrap it
429 $self->method_metaclass->wrap($method) unless blessed($method);
434 my ($self, $method_name) = @_;
435 (defined $method_name && $method_name)
436 || confess "You must define a method name";
438 return unless $self->has_method($method_name);
441 return \&{$self->name . '::' . $method_name};
445 my ($self, $method_name) = @_;
446 (defined $method_name && $method_name)
447 || confess "You must define a method name";
449 my $removed_method = $self->get_method($method_name);
452 delete ${$self->name . '::'}{$method_name}
453 if defined $removed_method;
455 return $removed_method;
458 sub get_method_list {
461 grep { $self->has_method($_) } keys %{$self->name . '::'};
464 sub compute_all_applicable_methods {
467 # keep a record of what we have seen
468 # here, this will handle all the
469 # inheritence issues because we are
470 # using the &class_precedence_list
471 my (%seen_class, %seen_method);
472 foreach my $class ($self->class_precedence_list()) {
473 next if $seen_class{$class};
474 $seen_class{$class}++;
475 # fetch the meta-class ...
476 my $meta = $self->initialize($class);
477 foreach my $method_name ($meta->get_method_list()) {
478 next if exists $seen_method{$method_name};
479 $seen_method{$method_name}++;
481 name => $method_name,
483 code => $meta->get_method($method_name)
490 sub find_all_methods_by_name {
491 my ($self, $method_name) = @_;
492 (defined $method_name && $method_name)
493 || confess "You must define a method name to find";
495 # keep a record of what we have seen
496 # here, this will handle all the
497 # inheritence issues because we are
498 # using the &class_precedence_list
500 foreach my $class ($self->class_precedence_list()) {
501 next if $seen_class{$class};
502 $seen_class{$class}++;
503 # fetch the meta-class ...
504 my $meta = $self->initialize($class);
506 name => $method_name,
508 code => $meta->get_method($method_name)
509 } if $meta->has_method($method_name);
514 sub find_next_method_by_name {
515 my ($self, $method_name) = @_;
516 (defined $method_name && $method_name)
517 || confess "You must define a method name to find";
518 # keep a record of what we have seen
519 # here, this will handle all the
520 # inheritence issues because we are
521 # using the &class_precedence_list
523 my @cpl = $self->class_precedence_list();
524 shift @cpl; # discard ourselves
525 foreach my $class (@cpl) {
526 next if $seen_class{$class};
527 $seen_class{$class}++;
528 # fetch the meta-class ...
529 my $meta = $self->initialize($class);
530 return $meta->get_method($method_name)
531 if $meta->has_method($method_name);
540 # either we have an attribute object already
541 # or we need to create one from the args provided
542 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
543 # make sure it is derived from the correct type though
544 ($attribute->isa('Class::MOP::Attribute'))
545 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
546 $attribute->attach_to_class($self);
547 $attribute->install_accessors();
548 $self->get_attribute_map->{$attribute->name} = $attribute;
551 # in theory we have to tell everyone the slot structure may have changed
555 my ($self, $attribute_name) = @_;
556 (defined $attribute_name && $attribute_name)
557 || confess "You must define an attribute name";
558 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
562 my ($self, $attribute_name) = @_;
563 (defined $attribute_name && $attribute_name)
564 || confess "You must define an attribute name";
565 return $self->get_attribute_map->{$attribute_name}
566 if $self->has_attribute($attribute_name);
570 sub remove_attribute {
571 my ($self, $attribute_name) = @_;
572 (defined $attribute_name && $attribute_name)
573 || confess "You must define an attribute name";
574 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
575 return unless defined $removed_attribute;
576 delete $self->get_attribute_map->{$attribute_name};
577 $removed_attribute->remove_accessors();
578 $removed_attribute->detach_from_class();
579 return $removed_attribute;
582 sub get_attribute_list {
584 keys %{$self->get_attribute_map};
587 sub compute_all_applicable_attributes {
590 # keep a record of what we have seen
591 # here, this will handle all the
592 # inheritence issues because we are
593 # using the &class_precedence_list
594 my (%seen_class, %seen_attr);
595 foreach my $class ($self->class_precedence_list()) {
596 next if $seen_class{$class};
597 $seen_class{$class}++;
598 # fetch the meta-class ...
599 my $meta = $self->initialize($class);
600 foreach my $attr_name ($meta->get_attribute_list()) {
601 next if exists $seen_attr{$attr_name};
602 $seen_attr{$attr_name}++;
603 push @attrs => $meta->get_attribute($attr_name);
609 sub find_attribute_by_name {
610 my ($self, $attr_name) = @_;
611 # keep a record of what we have seen
612 # here, this will handle all the
613 # inheritence issues because we are
614 # using the &class_precedence_list
616 foreach my $class ($self->class_precedence_list()) {
617 next if $seen_class{$class};
618 $seen_class{$class}++;
619 # fetch the meta-class ...
620 my $meta = $self->initialize($class);
621 return $meta->get_attribute($attr_name)
622 if $meta->has_attribute($attr_name);
629 sub add_package_variable {
630 my ($self, $variable, $initial_value) = @_;
631 (defined $variable && $variable =~ /^[\$\@\%]/)
632 || confess "variable name does not have a sigil";
634 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
635 if (defined $initial_value) {
637 *{$self->name . '::' . $name} = $initial_value;
643 # We HAVE to localize $@ or all
644 # hell breaks loose. It is not
645 # good, believe me, not good.
647 eval $sigil . $self->name . '::' . $name;
650 confess "Could not create package variable ($variable) because : $e" if $e;
654 sub has_package_variable {
655 my ($self, $variable) = @_;
656 (defined $variable && $variable =~ /^[\$\@\%]/)
657 || confess "variable name does not have a sigil";
658 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
660 defined ${$self->name . '::'}{$name} ? 1 : 0;
663 sub get_package_variable {
664 my ($self, $variable) = @_;
665 (defined $variable && $variable =~ /^[\$\@\%]/)
666 || confess "variable name does not have a sigil";
667 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
671 # We HAVE to localize $@ or all
672 # hell breaks loose. It is not
673 # good, believe me, not good.
675 $ref = eval '\\' . $sigil . $self->name . '::' . $name;
678 confess "Could not get the package variable ($variable) because : $e" if $e;
679 # if we didn't die, then we can return it
683 sub remove_package_variable {
684 my ($self, $variable) = @_;
685 (defined $variable && $variable =~ /^[\$\@\%]/)
686 || confess "variable name does not have a sigil";
687 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
689 delete ${$self->name . '::'}{$name};
700 Class::MOP::Class - Class Meta Object
704 # assuming that class Foo
705 # has been defined, you can
707 # use this for introspection ...
709 # add a method to Foo ...
710 Foo->meta->add_method('bar' => sub { ... })
712 # get a list of all the classes searched
713 # the method dispatcher in the correct order
714 Foo->meta->class_precedence_list()
716 # remove a method from Foo
717 Foo->meta->remove_method('bar');
719 # or use this to actually create classes ...
721 Class::MOP::Class->create('Bar' => '0.01' => (
722 superclasses => [ 'Foo' ],
724 Class::MOP:::Attribute->new('$bar'),
725 Class::MOP:::Attribute->new('$baz'),
728 calculate_bar => sub { ... },
729 construct_baz => sub { ... }
735 This is the largest and currently most complex part of the Perl 5
736 meta-object protocol. It controls the introspection and
737 manipulation of Perl 5 classes (and it can create them too). The
738 best way to understand what this module can do, is to read the
739 documentation for each of it's methods.
743 =head2 Self Introspection
749 This will return a B<Class::MOP::Class> instance which is related
750 to this class. Thereby allowing B<Class::MOP::Class> to actually
753 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
754 bootstrap this module by installing a number of attribute meta-objects
755 into it's metaclass. This will allow this class to reap all the benifits
756 of the MOP when subclassing it.
758 =item B<get_all_metaclasses>
760 This will return an hash of all the metaclass instances that have
761 been cached by B<Class::MOP::Class> keyed by the package name.
763 =item B<get_all_metaclass_instances>
765 This will return an array of all the metaclass instances that have
766 been cached by B<Class::MOP::Class>.
768 =item B<get_all_metaclass_names>
770 This will return an array of all the metaclass names that have
771 been cached by B<Class::MOP::Class>.
775 =head2 Class construction
777 These methods will handle creating B<Class::MOP::Class> objects,
778 which can be used to both create new classes, and analyze
779 pre-existing classes.
781 This module will internally store references to all the instances
782 you create with these methods, so that they do not need to be
783 created any more than nessecary. Basically, they are singletons.
787 =item B<create ($package_name, ?$package_version,
788 superclasses =E<gt> ?@superclasses,
789 methods =E<gt> ?%methods,
790 attributes =E<gt> ?%attributes)>
792 This returns a B<Class::MOP::Class> object, bringing the specified
793 C<$package_name> into existence and adding any of the
794 C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
797 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
798 methods =E<gt> ?%methods,
799 attributes =E<gt> ?%attributes)>
801 This will create an anonymous class, it works much like C<create> but
802 it does not need a C<$package_name>. Instead it will create a suitably
803 unique package name for you to stash things into.
805 =item B<initialize ($package_name, %options)>
807 This initializes and returns returns a B<Class::MOP::Class> object
808 for a given a C<$package_name>.
810 =item B<reinitialize ($package_name, %options)>
812 This removes the old metaclass, and creates a new one in it's place.
813 Do B<not> use this unless you really know what you are doing, it could
814 very easily make a very large mess of your program.
816 =item B<construct_class_instance (%options)>
818 This will construct an instance of B<Class::MOP::Class>, it is
819 here so that we can actually "tie the knot" for B<Class::MOP::Class>
820 to use C<construct_instance> once all the bootstrapping is done. This
821 method is used internally by C<initialize> and should never be called
822 from outside of that method really.
824 =item B<check_metaclass_compatability>
826 This method is called as the very last thing in the
827 C<construct_class_instance> method. This will check that the
828 metaclass you are creating is compatible with the metaclasses of all
829 your ancestors. For more inforamtion about metaclass compatibility
830 see the C<About Metaclass compatibility> section in L<Class::MOP>.
834 =head2 Object instance construction and cloning
836 These methods are B<entirely optional>, it is up to you whether you want
841 =item B<instance_metaclass>
843 =item B<get_meta_instance>
845 =item B<new_object (%params)>
847 This is a convience method for creating a new object of the class, and
848 blessing it into the appropriate package as well. Ideally your class
849 would call a C<new> this method like so:
852 my ($class, %param) = @_;
853 $class->meta->new_object(%params);
856 Of course the ideal place for this would actually be in C<UNIVERSAL::>
857 but that is considered bad style, so we do not do that.
859 =item B<construct_instance (%params)>
861 This method is used to construct an instace structure suitable for
862 C<bless>-ing into your package of choice. It works in conjunction
863 with the Attribute protocol to collect all applicable attributes.
865 This will construct and instance using a HASH ref as storage
866 (currently only HASH references are supported). This will collect all
867 the applicable attributes and layout out the fields in the HASH ref,
868 it will then initialize them using either use the corresponding key
869 in C<%params> or any default value or initializer found in the
870 attribute meta-object.
872 =item B<clone_object ($instance, %params)>
874 This is a convience method for cloning an object instance, then
875 blessing it into the appropriate package. This method will call
876 C<clone_instance>, which performs a shallow copy of the object,
877 see that methods documentation for more details. Ideally your
878 class would call a C<clone> this method like so:
881 my ($self, %param) = @_;
882 $self->meta->clone_object($self, %params);
885 Of course the ideal place for this would actually be in C<UNIVERSAL::>
886 but that is considered bad style, so we do not do that.
888 =item B<clone_instance($instance, %params)>
890 This method is a compliment of C<construct_instance> (which means if
891 you override C<construct_instance>, you need to override this one too),
892 and clones the instance shallowly.
894 The cloned structure returned is (like with C<construct_instance>) an
895 unC<bless>ed HASH reference, it is your responsibility to then bless
896 this cloned structure into the right class (which C<clone_object> will
899 As of 0.11, this method will clone the C<$instance> structure shallowly,
900 as opposed to the deep cloning implemented in prior versions. After much
901 thought, research and discussion, I have decided that anything but basic
902 shallow cloning is outside the scope of the meta-object protocol. I
903 think Yuval "nothingmuch" Kogman put it best when he said that cloning
904 is too I<context-specific> to be part of the MOP.
914 This is a read-only attribute which returns the package name for the
915 given B<Class::MOP::Class> instance.
919 This is a read-only attribute which returns the C<$VERSION> of the
920 package for the given B<Class::MOP::Class> instance.
924 =head2 Inheritance Relationships
928 =item B<superclasses (?@superclasses)>
930 This is a read-write attribute which represents the superclass
931 relationships of the class the B<Class::MOP::Class> instance is
932 associated with. Basically, it can get and set the C<@ISA> for you.
935 Perl will occasionally perform some C<@ISA> and method caching, if
936 you decide to change your superclass relationship at runtime (which
937 is quite insane and very much not recommened), then you should be
938 aware of this and the fact that this module does not make any
939 attempt to address this issue.
941 =item B<class_precedence_list>
943 This computes the a list of all the class's ancestors in the same order
944 in which method dispatch will be done. This is similair to
945 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
953 =item B<method_metaclass>
955 =item B<add_method ($method_name, $method)>
957 This will take a C<$method_name> and CODE reference to that
958 C<$method> and install it into the class's package.
961 This does absolutely nothing special to C<$method>
962 other than use B<Sub::Name> to make sure it is tagged with the
963 correct name, and therefore show up correctly in stack traces and
966 =item B<alias_method ($method_name, $method)>
968 This will take a C<$method_name> and CODE reference to that
969 C<$method> and alias the method into the class's package.
972 Unlike C<add_method>, this will B<not> try to name the
973 C<$method> using B<Sub::Name>, it only aliases the method in
976 =item B<has_method ($method_name)>
978 This just provides a simple way to check if the class implements
979 a specific C<$method_name>. It will I<not> however, attempt to check
980 if the class inherits the method (use C<UNIVERSAL::can> for that).
982 This will correctly handle functions defined outside of the package
983 that use a fully qualified name (C<sub Package::name { ... }>).
985 This will correctly handle functions renamed with B<Sub::Name> and
986 installed using the symbol tables. However, if you are naming the
987 subroutine outside of the package scope, you must use the fully
988 qualified name, including the package name, for C<has_method> to
989 correctly identify it.
991 This will attempt to correctly ignore functions imported from other
992 packages using B<Exporter>. It breaks down if the function imported
993 is an C<__ANON__> sub (such as with C<use constant>), which very well
994 may be a valid method being applied to the class.
996 In short, this method cannot always be trusted to determine if the
997 C<$method_name> is actually a method. However, it will DWIM about
998 90% of the time, so it's a small trade off I think.
1000 =item B<get_method ($method_name)>
1002 This will return a CODE reference of the specified C<$method_name>,
1003 or return undef if that method does not exist.
1005 =item B<remove_method ($method_name)>
1007 This will attempt to remove a given C<$method_name> from the class.
1008 It will return the CODE reference that it has removed, and will
1009 attempt to use B<Sub::Name> to clear the methods associated name.
1011 =item B<get_method_list>
1013 This will return a list of method names for all I<locally> defined
1014 methods. It does B<not> provide a list of all applicable methods,
1015 including any inherited ones. If you want a list of all applicable
1016 methods, use the C<compute_all_applicable_methods> method.
1018 =item B<compute_all_applicable_methods>
1020 This will return a list of all the methods names this class will
1021 respond to, taking into account inheritance. The list will be a list of
1022 HASH references, each one containing the following information; method
1023 name, the name of the class in which the method lives and a CODE
1024 reference for the actual method.
1026 =item B<find_all_methods_by_name ($method_name)>
1028 This will traverse the inheritence hierarchy and locate all methods
1029 with a given C<$method_name>. Similar to
1030 C<compute_all_applicable_methods> it returns a list of HASH references
1031 with the following information; method name (which will always be the
1032 same as C<$method_name>), the name of the class in which the method
1033 lives and a CODE reference for the actual method.
1035 The list of methods produced is a distinct list, meaning there are no
1036 duplicates in it. This is especially useful for things like object
1037 initialization and destruction where you only want the method called
1038 once, and in the correct order.
1040 =item B<find_next_method_by_name ($method_name)>
1042 This will return the first method to match a given C<$method_name> in
1043 the superclasses, this is basically equivalent to calling
1044 C<SUPER::$method_name>, but it can be dispatched at runtime.
1048 =head2 Method Modifiers
1050 Method modifiers are a concept borrowed from CLOS, in which a method
1051 can be wrapped with I<before>, I<after> and I<around> method modifiers
1052 that will be called everytime the method is called.
1054 =head3 How method modifiers work?
1056 Method modifiers work by wrapping the original method and then replacing
1057 it in the classes symbol table. The wrappers will handle calling all the
1058 modifiers in the appropariate orders and preserving the calling context
1059 for the original method.
1061 Each method modifier serves a particular purpose, which may not be
1062 obvious to users of other method wrapping modules. To start with, the
1063 return values of I<before> and I<after> modifiers are ignored. This is
1064 because thier purpose is B<not> to filter the input and output of the
1065 primary method (this is done with an I<around> modifier). This may seem
1066 like an odd restriction to some, but doing this allows for simple code
1067 to be added at the begining or end of a method call without jeapordizing
1068 the normal functioning of the primary method or placing any extra
1069 responsibility on the code of the modifier. Of course if you have more
1070 complex needs, then use the I<around> modifier, which uses a variation
1071 of continutation passing style to allow for a high degree of flexibility.
1073 Before and around modifiers are called in last-defined-first-called order,
1074 while after modifiers are called in first-defined-first-called order. So
1075 the call tree might looks something like this:
1085 To see examples of using method modifiers, see the following examples
1086 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1087 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1088 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1090 =head3 What is the performance impact?
1092 Of course there is a performance cost associated with method modifiers,
1093 but we have made every effort to make that cost be directly proportional
1094 to the amount of modifier features you utilize.
1096 The wrapping method does it's best to B<only> do as much work as it
1097 absolutely needs to. In order to do this we have moved some of the
1098 performance costs to set-up time, where they are easier to amortize.
1100 All this said, my benchmarks have indicated the following:
1102 simple wrapper with no modifiers 100% slower
1103 simple wrapper with simple before modifier 400% slower
1104 simple wrapper with simple after modifier 450% slower
1105 simple wrapper with simple around modifier 500-550% slower
1106 simple wrapper with all 3 modifiers 1100% slower
1108 These numbers may seem daunting, but you must remember, every feature
1109 comes with some cost. To put things in perspective, just doing a simple
1110 C<AUTOLOAD> which does nothing but extract the name of the method called
1111 and return it costs about 400% over a normal method call.
1115 =item B<add_before_method_modifier ($method_name, $code)>
1117 This will wrap the method at C<$method_name> and the supplied C<$code>
1118 will be passed the C<@_> arguments, and called before the original
1119 method is called. As specified above, the return value of the I<before>
1120 method modifiers is ignored, and it's ability to modify C<@_> is
1121 fairly limited. If you need to do either of these things, use an
1122 C<around> method modifier.
1124 =item B<add_after_method_modifier ($method_name, $code)>
1126 This will wrap the method at C<$method_name> so that the original
1127 method will be called, it's return values stashed, and then the
1128 supplied C<$code> will be passed the C<@_> arguments, and called.
1129 As specified above, the return value of the I<after> method
1130 modifiers is ignored, and it cannot modify the return values of
1131 the original method. If you need to do either of these things, use an
1132 C<around> method modifier.
1134 =item B<add_around_method_modifier ($method_name, $code)>
1136 This will wrap the method at C<$method_name> so that C<$code>
1137 will be called and passed the original method as an extra argument
1138 at the begining of the C<@_> argument list. This is a variation of
1139 continuation passing style, where the function prepended to C<@_>
1140 can be considered a continuation. It is up to C<$code> if it calls
1141 the original method or not, there is no restriction on what the
1142 C<$code> can or cannot do.
1148 It should be noted that since there is no one consistent way to define
1149 the attributes of a class in Perl 5. These methods can only work with
1150 the information given, and can not easily discover information on
1151 their own. See L<Class::MOP::Attribute> for more details.
1155 =item B<attribute_metaclass>
1157 =item B<get_attribute_map>
1159 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1161 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1162 instance associated with the given class, and associates it with
1163 the C<$attribute_name>. Unlike methods, attributes within the MOP
1164 are stored as meta-information only. They will be used later to
1165 construct instances from (see C<construct_instance> above).
1166 More details about the attribute meta-objects can be found in the
1167 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1170 It should be noted that any accessor, reader/writer or predicate
1171 methods which the C<$attribute_meta_object> has will be installed
1172 into the class at this time.
1174 =item B<has_attribute ($attribute_name)>
1176 Checks to see if this class has an attribute by the name of
1177 C<$attribute_name> and returns a boolean.
1179 =item B<get_attribute ($attribute_name)>
1181 Returns the attribute meta-object associated with C<$attribute_name>,
1182 if none is found, it will return undef.
1184 =item B<remove_attribute ($attribute_name)>
1186 This will remove the attribute meta-object stored at
1187 C<$attribute_name>, then return the removed attribute meta-object.
1190 Removing an attribute will only affect future instances of
1191 the class, it will not make any attempt to remove the attribute from
1192 any existing instances of the class.
1194 It should be noted that any accessor, reader/writer or predicate
1195 methods which the attribute meta-object stored at C<$attribute_name>
1196 has will be removed from the class at this time. This B<will> make
1197 these attributes somewhat inaccessable in previously created
1198 instances. But if you are crazy enough to do this at runtime, then
1199 you are crazy enough to deal with something like this :).
1201 =item B<get_attribute_list>
1203 This returns a list of attribute names which are defined in the local
1204 class. If you want a list of all applicable attributes for a class,
1205 use the C<compute_all_applicable_attributes> method.
1207 =item B<compute_all_applicable_attributes>
1209 This will traverse the inheritance heirachy and return a list of all
1210 the applicable attributes for this class. It does not construct a
1211 HASH reference like C<compute_all_applicable_methods> because all
1212 that same information is discoverable through the attribute
1215 =item B<find_attribute_by_name ($attr_name)>
1217 This method will traverse the inheritance heirachy and find the
1218 first attribute whose name matches C<$attr_name>, then return it.
1219 It will return undef if nothing is found.
1223 =head2 Package Variables
1225 Since Perl's classes are built atop the Perl package system, it is
1226 fairly common to use package scoped variables for things like static
1227 class variables. The following methods are convience methods for
1228 the creation and inspection of package scoped variables.
1232 =item B<add_package_variable ($variable_name, ?$initial_value)>
1234 Given a C<$variable_name>, which must contain a leading sigil, this
1235 method will create that variable within the package which houses the
1236 class. It also takes an optional C<$initial_value>, which must be a
1237 reference of the same type as the sigil of the C<$variable_name>
1240 =item B<get_package_variable ($variable_name)>
1242 This will return a reference to the package variable in
1245 =item B<has_package_variable ($variable_name)>
1247 Returns true (C<1>) if there is a package variable defined for
1248 C<$variable_name>, and false (C<0>) otherwise.
1250 =item B<remove_package_variable ($variable_name)>
1252 This will attempt to remove the package variable at C<$variable_name>.
1258 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1260 =head1 COPYRIGHT AND LICENSE
1262 Copyright 2006 by Infinity Interactive, Inc.
1264 L<http://www.iinteractive.com>
1266 This library is free software; you can redistribute it and/or modify
1267 it under the same terms as Perl itself.