2 package Class::MOP::Class;
7 use Class::MOP::Instance;
8 use Class::MOP::Method::Wrapped;
11 use Scalar::Util 'blessed', 'reftype', 'weaken';
12 use Sub::Name 'subname';
13 use B 'svref_2object';
15 our $VERSION = '0.20';
16 our $AUTHORITY = 'cpan:STEVAN';
18 use base 'Class::MOP::Module';
22 sub meta { Class::MOP::Class->initialize(blessed($_[0]) || $_[0]) }
28 my $package_name = shift;
29 (defined $package_name && $package_name && !blessed($package_name))
30 || confess "You must pass a package name and it cannot be blessed";
31 $class->construct_class_instance(':package' => $package_name, @_);
36 my $package_name = shift;
37 (defined $package_name && $package_name && !blessed($package_name))
38 || confess "You must pass a package name and it cannot be blessed";
39 Class::MOP::remove_metaclass_by_name($package_name);
40 $class->construct_class_instance(':package' => $package_name, @_);
43 # NOTE: (meta-circularity)
44 # this is a special form of &construct_instance
45 # (see below), which is used to construct class
46 # meta-object instances for any Class::MOP::*
47 # class. All other classes will use the more
48 # normal &construct_instance.
49 sub construct_class_instance {
52 my $package_name = $options{':package'};
53 (defined $package_name && $package_name)
54 || confess "You must pass a package name";
56 # return the metaclass if we have it cached,
57 # and it is still defined (it has not been
58 # reaped by DESTROY yet, which can happen
59 # annoyingly enough during global destruction)
60 return Class::MOP::get_metaclass_by_name($package_name)
61 if Class::MOP::does_metaclass_exist($package_name);
64 # we need to deal with the possibility
65 # of class immutability here, and then
66 # get the name of the class appropriately
67 $class = (blessed($class)
68 ? ($class->is_immutable
69 ? $class->get_mutable_metaclass_name()
73 $class = blessed($class) || $class;
74 # now create the metaclass
76 if ($class =~ /^Class::MOP::Class$/) {
79 # inherited from Class::MOP::Package
80 '$:package' => $package_name,
83 # since the following attributes will
84 # actually be loaded from the symbol
85 # table, and actually bypass the instance
86 # entirely, we can just leave these things
87 # listed here for reference, because they
88 # should not actually have a value associated
90 '%:namespace' => \undef,
91 # inherited from Class::MOP::Module
92 '$:version' => \undef,
93 '$:authority' => \undef,
94 # defined in Class::MOP::Class
98 '$:attribute_metaclass' => $options{':attribute_metaclass'} || 'Class::MOP::Attribute',
99 '$:method_metaclass' => $options{':method_metaclass'} || 'Class::MOP::Method',
100 '$:instance_metaclass' => $options{':instance_metaclass'} || 'Class::MOP::Instance',
105 # it is safe to use meta here because
106 # class will always be a subclass of
107 # Class::MOP::Class, which defines meta
108 $meta = $class->meta->construct_instance(%options)
111 # and check the metaclass compatibility
112 $meta->check_metaclass_compatability();
114 Class::MOP::store_metaclass_by_name($package_name, $meta);
117 # we need to weaken any anon classes
118 # so that they can call DESTROY properly
119 Class::MOP::weaken_metaclass($package_name) if $meta->is_anon_class;
124 sub check_metaclass_compatability {
127 # this is always okay ...
128 return if blessed($self) eq 'Class::MOP::Class' &&
129 $self->instance_metaclass eq 'Class::MOP::Instance';
131 my @class_list = $self->class_precedence_list;
132 shift @class_list; # shift off $self->name
134 foreach my $class_name (@class_list) {
135 my $meta = Class::MOP::get_metaclass_by_name($class_name) || next;
138 # we need to deal with the possibility
139 # of class immutability here, and then
140 # get the name of the class appropriately
141 my $meta_type = ($meta->is_immutable
142 ? $meta->get_mutable_metaclass_name()
145 ($self->isa($meta_type))
146 || confess $self->name . "->meta => (" . (blessed($self)) . ")" .
147 " is not compatible with the " .
148 $class_name . "->meta => (" . ($meta_type) . ")";
150 # we also need to check that instance metaclasses
151 # are compatabile in the same the class.
152 ($self->instance_metaclass->isa($meta->instance_metaclass))
153 || confess $self->name . "->meta => (" . ($self->instance_metaclass) . ")" .
154 " is not compatible with the " .
155 $class_name . "->meta => (" . ($meta->instance_metaclass) . ")";
163 # this should be sufficient, if you have a
164 # use case where it is not, write a test and
166 my $ANON_CLASS_SERIAL = 0;
169 # we need a sufficiently annoying prefix
170 # this should suffice for now, this is
171 # used in a couple of places below, so
172 # need to put it up here for now.
173 my $ANON_CLASS_PREFIX = 'Class::MOP::Class::__ANON__::SERIAL::';
177 $self->name =~ /^$ANON_CLASS_PREFIX/ ? 1 : 0;
180 sub create_anon_class {
181 my ($class, %options) = @_;
182 my $package_name = $ANON_CLASS_PREFIX . ++$ANON_CLASS_SERIAL;
183 return $class->create($package_name, %options);
187 # this will only get called for
188 # anon-classes, all other calls
189 # are assumed to occur during
190 # global destruction and so don't
191 # really need to be handled explicitly
194 return unless $self->name =~ /^$ANON_CLASS_PREFIX/;
195 my ($serial_id) = ($self->name =~ /^$ANON_CLASS_PREFIX(\d+)/);
197 foreach my $key (keys %{$ANON_CLASS_PREFIX . $serial_id}) {
198 delete ${$ANON_CLASS_PREFIX . $serial_id}{$key};
200 delete ${'main::' . $ANON_CLASS_PREFIX}{$serial_id . '::'};
205 # creating classes with MOP ...
209 my $package_name = shift;
211 (defined $package_name && $package_name)
212 || confess "You must pass a package name";
215 || confess "You much pass all parameters as name => value pairs " .
216 "(I found an uneven number of params in \@_)";
220 my $code = "package $package_name;";
221 $code .= "\$$package_name\:\:VERSION = '" . $options{version} . "';"
222 if exists $options{version};
223 $code .= "\$$package_name\:\:AUTHORITY = '" . $options{authority} . "';"
224 if exists $options{authority};
227 confess "creation of $package_name failed : $@" if $@;
229 my $meta = $class->initialize($package_name);
231 $meta->add_method('meta' => sub {
232 $class->initialize(blessed($_[0]) || $_[0]);
235 $meta->superclasses(@{$options{superclasses}})
236 if exists $options{superclasses};
238 # process attributes first, so that they can
239 # install accessors, but locally defined methods
240 # can then overwrite them. It is maybe a little odd, but
241 # I think this should be the order of things.
242 if (exists $options{attributes}) {
243 foreach my $attr (@{$options{attributes}}) {
244 $meta->add_attribute($attr);
247 if (exists $options{methods}) {
248 foreach my $method_name (keys %{$options{methods}}) {
249 $meta->add_method($method_name, $options{methods}->{$method_name});
258 # all these attribute readers will be bootstrapped
259 # away in the Class::MOP bootstrap section
261 sub get_attribute_map { $_[0]->{'%:attributes'} }
262 sub attribute_metaclass { $_[0]->{'$:attribute_metaclass'} }
263 sub method_metaclass { $_[0]->{'$:method_metaclass'} }
264 sub instance_metaclass { $_[0]->{'$:instance_metaclass'} }
267 # this is a prime canidate for conversion to XS
270 my $map = $self->{'%:methods'};
272 my $class_name = $self->name;
273 my $method_metaclass = $self->method_metaclass;
275 foreach my $symbol ($self->list_all_package_symbols('CODE')) {
276 my $code = $self->get_package_symbol('&' . $symbol);
278 next if exists $map->{$symbol} &&
279 defined $map->{$symbol} &&
280 $map->{$symbol}->body == $code;
282 my $gv = svref_2object($code)->GV;
283 next if ($gv->STASH->NAME || '') ne $class_name &&
284 ($gv->NAME || '') ne '__ANON__';
286 $map->{$symbol} = $method_metaclass->wrap($code);
292 # Instance Construction & Cloning
297 # we need to protect the integrity of the
298 # Class::MOP::Class singletons here, so we
299 # delegate this to &construct_class_instance
300 # which will deal with the singletons
301 return $class->construct_class_instance(@_)
302 if $class->name->isa('Class::MOP::Class');
303 return $class->construct_instance(@_);
306 sub construct_instance {
307 my ($class, %params) = @_;
308 my $meta_instance = $class->get_meta_instance();
309 my $instance = $meta_instance->create_instance();
310 foreach my $attr ($class->compute_all_applicable_attributes()) {
311 $attr->initialize_instance_slot($meta_instance, $instance, \%params);
316 sub get_meta_instance {
318 return $class->instance_metaclass->new(
320 $class->compute_all_applicable_attributes()
326 my $instance = shift;
327 (blessed($instance) && $instance->isa($class->name))
328 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
330 # we need to protect the integrity of the
331 # Class::MOP::Class singletons here, they
332 # should not be cloned.
333 return $instance if $instance->isa('Class::MOP::Class');
334 $class->clone_instance($instance, @_);
338 my ($class, $instance, %params) = @_;
340 || confess "You can only clone instances, \$self is not a blessed instance";
341 my $meta_instance = $class->get_meta_instance();
342 my $clone = $meta_instance->clone_instance($instance);
343 foreach my $key (keys %params) {
344 next unless $meta_instance->is_valid_slot($key);
345 $meta_instance->set_slot_value($clone, $key, $params{$key});
356 @{$self->get_package_symbol('@ISA')} = @supers;
358 # we need to check the metaclass
359 # compatability here so that we can
360 # be sure that the superclass is
361 # not potentially creating an issues
362 # we don't know about
363 $self->check_metaclass_compatability();
365 @{$self->get_package_symbol('@ISA')};
368 sub class_precedence_list {
371 # We need to check for ciruclar inheirtance here.
372 # This will do nothing if all is well, and blow
373 # up otherwise. Yes, it's an ugly hack, better
374 # suggestions are welcome.
375 { ($self->name || return)->isa('This is a test for circular inheritance') }
376 # ... and now back to our regularly scheduled program
380 $self->initialize($_)->class_precedence_list()
381 } $self->superclasses()
388 my ($self, $method_name, $method) = @_;
389 (defined $method_name && $method_name)
390 || confess "You must define a method name";
393 if (blessed($method)) {
394 $body = $method->body;
398 ('CODE' eq (reftype($body) || ''))
399 || confess "Your code block must be a CODE reference";
400 $method = $self->method_metaclass->wrap($body);
402 $self->get_method_map->{$method_name} = $method;
404 my $full_method_name = ($self->name . '::' . $method_name);
405 $self->add_package_symbol("&${method_name}" => subname $full_method_name => $body);
409 my $fetch_and_prepare_method = sub {
410 my ($self, $method_name) = @_;
412 my $method = $self->get_method($method_name);
413 # if we dont have local ...
415 # try to find the next method
416 $method = $self->find_next_method_by_name($method_name);
417 # die if it does not exist
419 || confess "The method '$method_name' is not found in the inherience hierarchy for class " . $self->name;
420 # and now make sure to wrap it
421 # even if it is already wrapped
422 # because we need a new sub ref
423 $method = Class::MOP::Method::Wrapped->wrap($method);
426 # now make sure we wrap it properly
427 $method = Class::MOP::Method::Wrapped->wrap($method)
428 unless $method->isa('Class::MOP::Method::Wrapped');
430 $self->add_method($method_name => $method);
434 sub add_before_method_modifier {
435 my ($self, $method_name, $method_modifier) = @_;
436 (defined $method_name && $method_name)
437 || confess "You must pass in a method name";
438 my $method = $fetch_and_prepare_method->($self, $method_name);
439 $method->add_before_modifier(subname ':before' => $method_modifier);
442 sub add_after_method_modifier {
443 my ($self, $method_name, $method_modifier) = @_;
444 (defined $method_name && $method_name)
445 || confess "You must pass in a method name";
446 my $method = $fetch_and_prepare_method->($self, $method_name);
447 $method->add_after_modifier(subname ':after' => $method_modifier);
450 sub add_around_method_modifier {
451 my ($self, $method_name, $method_modifier) = @_;
452 (defined $method_name && $method_name)
453 || confess "You must pass in a method name";
454 my $method = $fetch_and_prepare_method->($self, $method_name);
455 $method->add_around_modifier(subname ':around' => $method_modifier);
459 # the methods above used to be named like this:
460 # ${pkg}::${method}:(before|after|around)
461 # but this proved problematic when using one modifier
462 # to wrap multiple methods (something which is likely
463 # to happen pretty regularly IMO). So instead of naming
464 # it like this, I have chosen to just name them purely
465 # with their modifier names, like so:
466 # :(before|after|around)
467 # The fact is that in a stack trace, it will be fairly
468 # evident from the context what method they are attached
469 # to, and so don't need the fully qualified name.
473 my ($self, $method_name, $method) = @_;
474 (defined $method_name && $method_name)
475 || confess "You must define a method name";
477 my $body = (blessed($method) ? $method->body : $method);
478 ('CODE' eq (reftype($body) || ''))
479 || confess "Your code block must be a CODE reference";
481 $self->add_package_symbol("&${method_name}" => $body);
485 my ($self, $method_name) = @_;
486 (defined $method_name && $method_name)
487 || confess "You must define a method name";
489 return 0 unless exists $self->get_method_map->{$method_name};
494 my ($self, $method_name) = @_;
495 (defined $method_name && $method_name)
496 || confess "You must define a method name";
499 # I don't really need this here, because
500 # if the method_map is missing a key it
501 # will just return undef for me now
502 # return unless $self->has_method($method_name);
504 return $self->get_method_map->{$method_name};
508 my ($self, $method_name) = @_;
509 (defined $method_name && $method_name)
510 || confess "You must define a method name";
512 my $removed_method = $self->get_method($method_name);
515 $self->remove_package_symbol("&${method_name}");
516 delete $self->get_method_map->{$method_name};
517 } if defined $removed_method;
519 return $removed_method;
522 sub get_method_list {
524 keys %{$self->get_method_map};
527 sub find_method_by_name {
528 my ($self, $method_name) = @_;
529 (defined $method_name && $method_name)
530 || confess "You must define a method name to find";
531 # keep a record of what we have seen
532 # here, this will handle all the
533 # inheritence issues because we are
534 # using the &class_precedence_list
536 my @cpl = $self->class_precedence_list();
537 foreach my $class (@cpl) {
538 next if $seen_class{$class};
539 $seen_class{$class}++;
540 # fetch the meta-class ...
541 my $meta = $self->initialize($class);
542 return $meta->get_method($method_name)
543 if $meta->has_method($method_name);
548 sub compute_all_applicable_methods {
551 # keep a record of what we have seen
552 # here, this will handle all the
553 # inheritence issues because we are
554 # using the &class_precedence_list
555 my (%seen_class, %seen_method);
556 foreach my $class ($self->class_precedence_list()) {
557 next if $seen_class{$class};
558 $seen_class{$class}++;
559 # fetch the meta-class ...
560 my $meta = $self->initialize($class);
561 foreach my $method_name ($meta->get_method_list()) {
562 next if exists $seen_method{$method_name};
563 $seen_method{$method_name}++;
565 name => $method_name,
567 code => $meta->get_method($method_name)
574 sub find_all_methods_by_name {
575 my ($self, $method_name) = @_;
576 (defined $method_name && $method_name)
577 || confess "You must define a method name to find";
579 # keep a record of what we have seen
580 # here, this will handle all the
581 # inheritence issues because we are
582 # using the &class_precedence_list
584 foreach my $class ($self->class_precedence_list()) {
585 next if $seen_class{$class};
586 $seen_class{$class}++;
587 # fetch the meta-class ...
588 my $meta = $self->initialize($class);
590 name => $method_name,
592 code => $meta->get_method($method_name)
593 } if $meta->has_method($method_name);
598 sub find_next_method_by_name {
599 my ($self, $method_name) = @_;
600 (defined $method_name && $method_name)
601 || confess "You must define a method name to find";
602 # keep a record of what we have seen
603 # here, this will handle all the
604 # inheritence issues because we are
605 # using the &class_precedence_list
607 my @cpl = $self->class_precedence_list();
608 shift @cpl; # discard ourselves
609 foreach my $class (@cpl) {
610 next if $seen_class{$class};
611 $seen_class{$class}++;
612 # fetch the meta-class ...
613 my $meta = $self->initialize($class);
614 return $meta->get_method($method_name)
615 if $meta->has_method($method_name);
624 # either we have an attribute object already
625 # or we need to create one from the args provided
626 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
627 # make sure it is derived from the correct type though
628 ($attribute->isa('Class::MOP::Attribute'))
629 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
631 # first we attach our new attribute
632 # because it might need certain information
633 # about the class which it is attached to
634 $attribute->attach_to_class($self);
636 # then we remove attributes of a conflicting
637 # name here so that we can properly detach
638 # the old attr object, and remove any
639 # accessors it would have generated
640 $self->remove_attribute($attribute->name)
641 if $self->has_attribute($attribute->name);
643 # then onto installing the new accessors
644 $attribute->install_accessors();
645 $self->get_attribute_map->{$attribute->name} = $attribute;
649 my ($self, $attribute_name) = @_;
650 (defined $attribute_name && $attribute_name)
651 || confess "You must define an attribute name";
652 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
656 my ($self, $attribute_name) = @_;
657 (defined $attribute_name && $attribute_name)
658 || confess "You must define an attribute name";
659 return $self->get_attribute_map->{$attribute_name}
661 # this will return undef anyway, so no need ...
662 # if $self->has_attribute($attribute_name);
666 sub remove_attribute {
667 my ($self, $attribute_name) = @_;
668 (defined $attribute_name && $attribute_name)
669 || confess "You must define an attribute name";
670 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
671 return unless defined $removed_attribute;
672 delete $self->get_attribute_map->{$attribute_name};
673 $removed_attribute->remove_accessors();
674 $removed_attribute->detach_from_class();
675 return $removed_attribute;
678 sub get_attribute_list {
680 keys %{$self->get_attribute_map};
683 sub compute_all_applicable_attributes {
686 # keep a record of what we have seen
687 # here, this will handle all the
688 # inheritence issues because we are
689 # using the &class_precedence_list
690 my (%seen_class, %seen_attr);
691 foreach my $class ($self->class_precedence_list()) {
692 next if $seen_class{$class};
693 $seen_class{$class}++;
694 # fetch the meta-class ...
695 my $meta = $self->initialize($class);
696 foreach my $attr_name ($meta->get_attribute_list()) {
697 next if exists $seen_attr{$attr_name};
698 $seen_attr{$attr_name}++;
699 push @attrs => $meta->get_attribute($attr_name);
705 sub find_attribute_by_name {
706 my ($self, $attr_name) = @_;
707 # keep a record of what we have seen
708 # here, this will handle all the
709 # inheritence issues because we are
710 # using the &class_precedence_list
712 foreach my $class ($self->class_precedence_list()) {
713 next if $seen_class{$class};
714 $seen_class{$class}++;
715 # fetch the meta-class ...
716 my $meta = $self->initialize($class);
717 return $meta->get_attribute($attr_name)
718 if $meta->has_attribute($attr_name);
726 sub is_immutable { 0 }
729 return Class::MOP::Class::Immutable->make_metaclass_immutable(@_);
740 Class::MOP::Class - Class Meta Object
744 # assuming that class Foo
745 # has been defined, you can
747 # use this for introspection ...
749 # add a method to Foo ...
750 Foo->meta->add_method('bar' => sub { ... })
752 # get a list of all the classes searched
753 # the method dispatcher in the correct order
754 Foo->meta->class_precedence_list()
756 # remove a method from Foo
757 Foo->meta->remove_method('bar');
759 # or use this to actually create classes ...
761 Class::MOP::Class->create('Bar' => (
763 superclasses => [ 'Foo' ],
765 Class::MOP:::Attribute->new('$bar'),
766 Class::MOP:::Attribute->new('$baz'),
769 calculate_bar => sub { ... },
770 construct_baz => sub { ... }
776 This is the largest and currently most complex part of the Perl 5
777 meta-object protocol. It controls the introspection and
778 manipulation of Perl 5 classes (and it can create them too). The
779 best way to understand what this module can do, is to read the
780 documentation for each of it's methods.
784 =head2 Self Introspection
790 This will return a B<Class::MOP::Class> instance which is related
791 to this class. Thereby allowing B<Class::MOP::Class> to actually
794 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
795 bootstrap this module by installing a number of attribute meta-objects
796 into it's metaclass. This will allow this class to reap all the benifits
797 of the MOP when subclassing it.
801 =head2 Class construction
803 These methods will handle creating B<Class::MOP::Class> objects,
804 which can be used to both create new classes, and analyze
805 pre-existing classes.
807 This module will internally store references to all the instances
808 you create with these methods, so that they do not need to be
809 created any more than nessecary. Basically, they are singletons.
813 =item B<create ($package_name,
814 version =E<gt> ?$version,
815 authority =E<gt> ?$authority,
816 superclasses =E<gt> ?@superclasses,
817 methods =E<gt> ?%methods,
818 attributes =E<gt> ?%attributes)>
820 This returns a B<Class::MOP::Class> object, bringing the specified
821 C<$package_name> into existence and adding any of the C<$version>,
822 C<$authority>, C<@superclasses>, C<%methods> and C<%attributes> to
825 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
826 methods =E<gt> ?%methods,
827 attributes =E<gt> ?%attributes)>
829 This will create an anonymous class, it works much like C<create> but
830 it does not need a C<$package_name>. Instead it will create a suitably
831 unique package name for you to stash things into.
833 =item B<initialize ($package_name, %options)>
835 This initializes and returns returns a B<Class::MOP::Class> object
836 for a given a C<$package_name>.
838 =item B<reinitialize ($package_name, %options)>
840 This removes the old metaclass, and creates a new one in it's place.
841 Do B<not> use this unless you really know what you are doing, it could
842 very easily make a very large mess of your program.
844 =item B<construct_class_instance (%options)>
846 This will construct an instance of B<Class::MOP::Class>, it is
847 here so that we can actually "tie the knot" for B<Class::MOP::Class>
848 to use C<construct_instance> once all the bootstrapping is done. This
849 method is used internally by C<initialize> and should never be called
850 from outside of that method really.
852 =item B<check_metaclass_compatability>
854 This method is called as the very last thing in the
855 C<construct_class_instance> method. This will check that the
856 metaclass you are creating is compatible with the metaclasses of all
857 your ancestors. For more inforamtion about metaclass compatibility
858 see the C<About Metaclass compatibility> section in L<Class::MOP>.
862 =head2 Object instance construction and cloning
864 These methods are B<entirely optional>, it is up to you whether you want
869 =item B<instance_metaclass>
871 =item B<get_meta_instance>
873 =item B<new_object (%params)>
875 This is a convience method for creating a new object of the class, and
876 blessing it into the appropriate package as well. Ideally your class
877 would call a C<new> this method like so:
880 my ($class, %param) = @_;
881 $class->meta->new_object(%params);
884 Of course the ideal place for this would actually be in C<UNIVERSAL::>
885 but that is considered bad style, so we do not do that.
887 =item B<construct_instance (%params)>
889 This method is used to construct an instace structure suitable for
890 C<bless>-ing into your package of choice. It works in conjunction
891 with the Attribute protocol to collect all applicable attributes.
893 This will construct and instance using a HASH ref as storage
894 (currently only HASH references are supported). This will collect all
895 the applicable attributes and layout out the fields in the HASH ref,
896 it will then initialize them using either use the corresponding key
897 in C<%params> or any default value or initializer found in the
898 attribute meta-object.
900 =item B<clone_object ($instance, %params)>
902 This is a convience method for cloning an object instance, then
903 blessing it into the appropriate package. This method will call
904 C<clone_instance>, which performs a shallow copy of the object,
905 see that methods documentation for more details. Ideally your
906 class would call a C<clone> this method like so:
909 my ($self, %param) = @_;
910 $self->meta->clone_object($self, %params);
913 Of course the ideal place for this would actually be in C<UNIVERSAL::>
914 but that is considered bad style, so we do not do that.
916 =item B<clone_instance($instance, %params)>
918 This method is a compliment of C<construct_instance> (which means if
919 you override C<construct_instance>, you need to override this one too),
920 and clones the instance shallowly.
922 The cloned structure returned is (like with C<construct_instance>) an
923 unC<bless>ed HASH reference, it is your responsibility to then bless
924 this cloned structure into the right class (which C<clone_object> will
927 As of 0.11, this method will clone the C<$instance> structure shallowly,
928 as opposed to the deep cloning implemented in prior versions. After much
929 thought, research and discussion, I have decided that anything but basic
930 shallow cloning is outside the scope of the meta-object protocol. I
931 think Yuval "nothingmuch" Kogman put it best when he said that cloning
932 is too I<context-specific> to be part of the MOP.
938 These are a few predicate methods for asking information about the class.
942 =item B<is_anon_class>
946 =item B<is_immutable>
950 =head2 Inheritance Relationships
954 =item B<superclasses (?@superclasses)>
956 This is a read-write attribute which represents the superclass
957 relationships of the class the B<Class::MOP::Class> instance is
958 associated with. Basically, it can get and set the C<@ISA> for you.
961 Perl will occasionally perform some C<@ISA> and method caching, if
962 you decide to change your superclass relationship at runtime (which
963 is quite insane and very much not recommened), then you should be
964 aware of this and the fact that this module does not make any
965 attempt to address this issue.
967 =item B<class_precedence_list>
969 This computes the a list of all the class's ancestors in the same order
970 in which method dispatch will be done. This is similair to
971 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
979 =item B<get_method_map>
981 =item B<method_metaclass>
983 =item B<add_method ($method_name, $method)>
985 This will take a C<$method_name> and CODE reference to that
986 C<$method> and install it into the class's package.
989 This does absolutely nothing special to C<$method>
990 other than use B<Sub::Name> to make sure it is tagged with the
991 correct name, and therefore show up correctly in stack traces and
994 =item B<alias_method ($method_name, $method)>
996 This will take a C<$method_name> and CODE reference to that
997 C<$method> and alias the method into the class's package.
1000 Unlike C<add_method>, this will B<not> try to name the
1001 C<$method> using B<Sub::Name>, it only aliases the method in
1002 the class's package.
1004 =item B<has_method ($method_name)>
1006 This just provides a simple way to check if the class implements
1007 a specific C<$method_name>. It will I<not> however, attempt to check
1008 if the class inherits the method (use C<UNIVERSAL::can> for that).
1010 This will correctly handle functions defined outside of the package
1011 that use a fully qualified name (C<sub Package::name { ... }>).
1013 This will correctly handle functions renamed with B<Sub::Name> and
1014 installed using the symbol tables. However, if you are naming the
1015 subroutine outside of the package scope, you must use the fully
1016 qualified name, including the package name, for C<has_method> to
1017 correctly identify it.
1019 This will attempt to correctly ignore functions imported from other
1020 packages using B<Exporter>. It breaks down if the function imported
1021 is an C<__ANON__> sub (such as with C<use constant>), which very well
1022 may be a valid method being applied to the class.
1024 In short, this method cannot always be trusted to determine if the
1025 C<$method_name> is actually a method. However, it will DWIM about
1026 90% of the time, so it's a small trade off I think.
1028 =item B<get_method ($method_name)>
1030 This will return a Class::MOP::Method instance related to the specified
1031 C<$method_name>, or return undef if that method does not exist.
1033 The Class::MOP::Method is codifiable, so you can use it like a normal
1034 CODE reference, see L<Class::MOP::Method> for more information.
1036 =item B<find_method_by_name ($method_name>
1038 This will return a CODE reference of the specified C<$method_name>,
1039 or return undef if that method does not exist.
1041 Unlike C<get_method> this will also look in the superclasses.
1043 =item B<remove_method ($method_name)>
1045 This will attempt to remove a given C<$method_name> from the class.
1046 It will return the CODE reference that it has removed, and will
1047 attempt to use B<Sub::Name> to clear the methods associated name.
1049 =item B<get_method_list>
1051 This will return a list of method names for all I<locally> defined
1052 methods. It does B<not> provide a list of all applicable methods,
1053 including any inherited ones. If you want a list of all applicable
1054 methods, use the C<compute_all_applicable_methods> method.
1056 =item B<compute_all_applicable_methods>
1058 This will return a list of all the methods names this class will
1059 respond to, taking into account inheritance. The list will be a list of
1060 HASH references, each one containing the following information; method
1061 name, the name of the class in which the method lives and a CODE
1062 reference for the actual method.
1064 =item B<find_all_methods_by_name ($method_name)>
1066 This will traverse the inheritence hierarchy and locate all methods
1067 with a given C<$method_name>. Similar to
1068 C<compute_all_applicable_methods> it returns a list of HASH references
1069 with the following information; method name (which will always be the
1070 same as C<$method_name>), the name of the class in which the method
1071 lives and a CODE reference for the actual method.
1073 The list of methods produced is a distinct list, meaning there are no
1074 duplicates in it. This is especially useful for things like object
1075 initialization and destruction where you only want the method called
1076 once, and in the correct order.
1078 =item B<find_next_method_by_name ($method_name)>
1080 This will return the first method to match a given C<$method_name> in
1081 the superclasses, this is basically equivalent to calling
1082 C<SUPER::$method_name>, but it can be dispatched at runtime.
1086 =head2 Method Modifiers
1088 Method modifiers are a concept borrowed from CLOS, in which a method
1089 can be wrapped with I<before>, I<after> and I<around> method modifiers
1090 that will be called everytime the method is called.
1092 =head3 How method modifiers work?
1094 Method modifiers work by wrapping the original method and then replacing
1095 it in the classes symbol table. The wrappers will handle calling all the
1096 modifiers in the appropariate orders and preserving the calling context
1097 for the original method.
1099 Each method modifier serves a particular purpose, which may not be
1100 obvious to users of other method wrapping modules. To start with, the
1101 return values of I<before> and I<after> modifiers are ignored. This is
1102 because thier purpose is B<not> to filter the input and output of the
1103 primary method (this is done with an I<around> modifier). This may seem
1104 like an odd restriction to some, but doing this allows for simple code
1105 to be added at the begining or end of a method call without jeapordizing
1106 the normal functioning of the primary method or placing any extra
1107 responsibility on the code of the modifier. Of course if you have more
1108 complex needs, then use the I<around> modifier, which uses a variation
1109 of continutation passing style to allow for a high degree of flexibility.
1111 Before and around modifiers are called in last-defined-first-called order,
1112 while after modifiers are called in first-defined-first-called order. So
1113 the call tree might looks something like this:
1123 To see examples of using method modifiers, see the following examples
1124 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1125 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1126 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1128 =head3 What is the performance impact?
1130 Of course there is a performance cost associated with method modifiers,
1131 but we have made every effort to make that cost be directly proportional
1132 to the amount of modifier features you utilize.
1134 The wrapping method does it's best to B<only> do as much work as it
1135 absolutely needs to. In order to do this we have moved some of the
1136 performance costs to set-up time, where they are easier to amortize.
1138 All this said, my benchmarks have indicated the following:
1140 simple wrapper with no modifiers 100% slower
1141 simple wrapper with simple before modifier 400% slower
1142 simple wrapper with simple after modifier 450% slower
1143 simple wrapper with simple around modifier 500-550% slower
1144 simple wrapper with all 3 modifiers 1100% slower
1146 These numbers may seem daunting, but you must remember, every feature
1147 comes with some cost. To put things in perspective, just doing a simple
1148 C<AUTOLOAD> which does nothing but extract the name of the method called
1149 and return it costs about 400% over a normal method call.
1153 =item B<add_before_method_modifier ($method_name, $code)>
1155 This will wrap the method at C<$method_name> and the supplied C<$code>
1156 will be passed the C<@_> arguments, and called before the original
1157 method is called. As specified above, the return value of the I<before>
1158 method modifiers is ignored, and it's ability to modify C<@_> is
1159 fairly limited. If you need to do either of these things, use an
1160 C<around> method modifier.
1162 =item B<add_after_method_modifier ($method_name, $code)>
1164 This will wrap the method at C<$method_name> so that the original
1165 method will be called, it's return values stashed, and then the
1166 supplied C<$code> will be passed the C<@_> arguments, and called.
1167 As specified above, the return value of the I<after> method
1168 modifiers is ignored, and it cannot modify the return values of
1169 the original method. If you need to do either of these things, use an
1170 C<around> method modifier.
1172 =item B<add_around_method_modifier ($method_name, $code)>
1174 This will wrap the method at C<$method_name> so that C<$code>
1175 will be called and passed the original method as an extra argument
1176 at the begining of the C<@_> argument list. This is a variation of
1177 continuation passing style, where the function prepended to C<@_>
1178 can be considered a continuation. It is up to C<$code> if it calls
1179 the original method or not, there is no restriction on what the
1180 C<$code> can or cannot do.
1186 It should be noted that since there is no one consistent way to define
1187 the attributes of a class in Perl 5. These methods can only work with
1188 the information given, and can not easily discover information on
1189 their own. See L<Class::MOP::Attribute> for more details.
1193 =item B<attribute_metaclass>
1195 =item B<get_attribute_map>
1197 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1199 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1200 instance associated with the given class, and associates it with
1201 the C<$attribute_name>. Unlike methods, attributes within the MOP
1202 are stored as meta-information only. They will be used later to
1203 construct instances from (see C<construct_instance> above).
1204 More details about the attribute meta-objects can be found in the
1205 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1208 It should be noted that any accessor, reader/writer or predicate
1209 methods which the C<$attribute_meta_object> has will be installed
1210 into the class at this time.
1213 If an attribute already exists for C<$attribute_name>, the old one
1214 will be removed (as well as removing all it's accessors), and then
1217 =item B<has_attribute ($attribute_name)>
1219 Checks to see if this class has an attribute by the name of
1220 C<$attribute_name> and returns a boolean.
1222 =item B<get_attribute ($attribute_name)>
1224 Returns the attribute meta-object associated with C<$attribute_name>,
1225 if none is found, it will return undef.
1227 =item B<remove_attribute ($attribute_name)>
1229 This will remove the attribute meta-object stored at
1230 C<$attribute_name>, then return the removed attribute meta-object.
1233 Removing an attribute will only affect future instances of
1234 the class, it will not make any attempt to remove the attribute from
1235 any existing instances of the class.
1237 It should be noted that any accessor, reader/writer or predicate
1238 methods which the attribute meta-object stored at C<$attribute_name>
1239 has will be removed from the class at this time. This B<will> make
1240 these attributes somewhat inaccessable in previously created
1241 instances. But if you are crazy enough to do this at runtime, then
1242 you are crazy enough to deal with something like this :).
1244 =item B<get_attribute_list>
1246 This returns a list of attribute names which are defined in the local
1247 class. If you want a list of all applicable attributes for a class,
1248 use the C<compute_all_applicable_attributes> method.
1250 =item B<compute_all_applicable_attributes>
1252 This will traverse the inheritance heirachy and return a list of all
1253 the applicable attributes for this class. It does not construct a
1254 HASH reference like C<compute_all_applicable_methods> because all
1255 that same information is discoverable through the attribute
1258 =item B<find_attribute_by_name ($attr_name)>
1260 This method will traverse the inheritance heirachy and find the
1261 first attribute whose name matches C<$attr_name>, then return it.
1262 It will return undef if nothing is found.
1266 =head2 Class closing
1270 =item B<make_immutable>
1276 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1278 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1280 =head1 COPYRIGHT AND LICENSE
1282 Copyright 2006 by Infinity Interactive, Inc.
1284 L<http://www.iinteractive.com>
1286 This library is free software; you can redistribute it and/or modify
1287 it under the same terms as Perl itself.