2 package Class::MOP::Class;
7 use Class::MOP::Immutable;
8 use Class::MOP::Instance;
9 use Class::MOP::Method::Wrapped;
12 use Scalar::Util 'blessed', 'reftype', 'weaken';
13 use Sub::Name 'subname';
14 use B 'svref_2object';
16 our $VERSION = '0.21';
17 our $AUTHORITY = 'cpan:STEVAN';
19 use base 'Class::MOP::Module';
23 sub meta { Class::MOP::Class->initialize(blessed($_[0]) || $_[0]) }
29 my $package_name = shift;
30 (defined $package_name && $package_name && !blessed($package_name))
31 || confess "You must pass a package name and it cannot be blessed";
32 $class->construct_class_instance('package' => $package_name, @_);
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::MOP::remove_metaclass_by_name($package_name);
41 $class->construct_class_instance('package' => $package_name, @_);
44 # NOTE: (meta-circularity)
45 # this is a special form of &construct_instance
46 # (see below), which is used to construct class
47 # meta-object instances for any Class::MOP::*
48 # class. All other classes will use the more
49 # normal &construct_instance.
50 sub construct_class_instance {
53 my $package_name = $options{'package'};
54 (defined $package_name && $package_name)
55 || confess "You must pass a package name";
57 # return the metaclass if we have it cached,
58 # and it is still defined (it has not been
59 # reaped by DESTROY yet, which can happen
60 # annoyingly enough during global destruction)
61 return Class::MOP::get_metaclass_by_name($package_name)
62 if Class::MOP::does_metaclass_exist($package_name);
65 # we need to deal with the possibility
66 # of class immutability here, and then
67 # get the name of the class appropriately
68 $class = (blessed($class)
69 ? ($class->is_immutable
70 ? $class->get_mutable_metaclass_name()
74 # now create the metaclass
76 if ($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 '$!authority' => \undef,
94 # defined in Class::MOP::Class
95 '@!superclasses' => \undef,
99 '$!attribute_metaclass' => $options{'attribute_metaclass'} || 'Class::MOP::Attribute',
100 '$!method_metaclass' => $options{'method_metaclass'} || 'Class::MOP::Method',
101 '$!instance_metaclass' => $options{'instance_metaclass'} || 'Class::MOP::Instance',
106 # it is safe to use meta here because
107 # class will always be a subclass of
108 # Class::MOP::Class, which defines meta
109 $meta = $class->meta->construct_instance(%options)
112 # and check the metaclass compatibility
113 $meta->check_metaclass_compatability();
115 Class::MOP::store_metaclass_by_name($package_name, $meta);
118 # we need to weaken any anon classes
119 # so that they can call DESTROY properly
120 Class::MOP::weaken_metaclass($package_name) if $meta->is_anon_class;
125 sub check_metaclass_compatability {
128 # this is always okay ...
129 return if blessed($self) eq 'Class::MOP::Class' &&
130 $self->instance_metaclass eq 'Class::MOP::Instance';
132 my @class_list = $self->class_precedence_list;
133 shift @class_list; # shift off $self->name
135 foreach my $class_name (@class_list) {
136 my $meta = Class::MOP::get_metaclass_by_name($class_name) || next;
139 # we need to deal with the possibility
140 # of class immutability here, and then
141 # get the name of the class appropriately
142 my $meta_type = ($meta->is_immutable
143 ? $meta->get_mutable_metaclass_name()
146 ($self->isa($meta_type))
147 || confess $self->name . "->meta => (" . (blessed($self)) . ")" .
148 " is not compatible with the " .
149 $class_name . "->meta => (" . ($meta_type) . ")";
151 # we also need to check that instance metaclasses
152 # are compatabile in the same the class.
153 ($self->instance_metaclass->isa($meta->instance_metaclass))
154 || confess $self->name . "->meta => (" . ($self->instance_metaclass) . ")" .
155 " is not compatible with the " .
156 $class_name . "->meta => (" . ($meta->instance_metaclass) . ")";
164 # this should be sufficient, if you have a
165 # use case where it is not, write a test and
167 my $ANON_CLASS_SERIAL = 0;
170 # we need a sufficiently annoying prefix
171 # this should suffice for now, this is
172 # used in a couple of places below, so
173 # need to put it up here for now.
174 my $ANON_CLASS_PREFIX = 'Class::MOP::Class::__ANON__::SERIAL::';
178 no warnings 'uninitialized';
179 $self->name =~ /^$ANON_CLASS_PREFIX/ ? 1 : 0;
182 sub create_anon_class {
183 my ($class, %options) = @_;
184 my $package_name = $ANON_CLASS_PREFIX . ++$ANON_CLASS_SERIAL;
185 return $class->create($package_name, %options);
189 # this will only get called for
190 # anon-classes, all other calls
191 # are assumed to occur during
192 # global destruction and so don't
193 # really need to be handled explicitly
196 no warnings 'uninitialized';
197 return unless $self->name =~ /^$ANON_CLASS_PREFIX/;
198 my ($serial_id) = ($self->name =~ /^$ANON_CLASS_PREFIX(\d+)/);
200 foreach my $key (keys %{$ANON_CLASS_PREFIX . $serial_id}) {
201 delete ${$ANON_CLASS_PREFIX . $serial_id}{$key};
203 delete ${'main::' . $ANON_CLASS_PREFIX}{$serial_id . '::'};
208 # creating classes with MOP ...
212 my $package_name = shift;
214 (defined $package_name && $package_name)
215 || confess "You must pass a package name";
218 || confess "You much pass all parameters as name => value pairs " .
219 "(I found an uneven number of params in \@_)";
223 my $code = "package $package_name;";
224 $code .= "\$$package_name\:\:VERSION = '" . $options{version} . "';"
225 if exists $options{version};
226 $code .= "\$$package_name\:\:AUTHORITY = '" . $options{authority} . "';"
227 if exists $options{authority};
230 confess "creation of $package_name failed : $@" if $@;
232 my $meta = $class->initialize($package_name);
234 $meta->add_method('meta' => sub {
235 $class->initialize(blessed($_[0]) || $_[0]);
238 $meta->superclasses(@{$options{superclasses}})
239 if exists $options{superclasses};
241 # process attributes first, so that they can
242 # install accessors, but locally defined methods
243 # can then overwrite them. It is maybe a little odd, but
244 # I think this should be the order of things.
245 if (exists $options{attributes}) {
246 foreach my $attr (@{$options{attributes}}) {
247 $meta->add_attribute($attr);
250 if (exists $options{methods}) {
251 foreach my $method_name (keys %{$options{methods}}) {
252 $meta->add_method($method_name, $options{methods}->{$method_name});
261 # all these attribute readers will be bootstrapped
262 # away in the Class::MOP bootstrap section
264 sub get_attribute_map { $_[0]->{'%!attributes'} }
265 sub attribute_metaclass { $_[0]->{'$!attribute_metaclass'} }
266 sub method_metaclass { $_[0]->{'$!method_metaclass'} }
267 sub instance_metaclass { $_[0]->{'$!instance_metaclass'} }
270 # this is a prime canidate for conversion to XS
273 my $map = $self->{'%!methods'};
275 my $class_name = $self->name;
276 my $method_metaclass = $self->method_metaclass;
278 foreach my $symbol ($self->list_all_package_symbols('CODE')) {
279 my $code = $self->get_package_symbol('&' . $symbol);
281 next if exists $map->{$symbol} &&
282 defined $map->{$symbol} &&
283 $map->{$symbol}->body == $code;
285 my $gv = svref_2object($code)->GV;
286 next if ($gv->STASH->NAME || '') ne $class_name &&
287 ($gv->NAME || '') ne '__ANON__';
289 $map->{$symbol} = $method_metaclass->wrap($code);
295 # Instance Construction & Cloning
300 # we need to protect the integrity of the
301 # Class::MOP::Class singletons here, so we
302 # delegate this to &construct_class_instance
303 # which will deal with the singletons
304 return $class->construct_class_instance(@_)
305 if $class->name->isa('Class::MOP::Class');
306 return $class->construct_instance(@_);
309 sub construct_instance {
310 my ($class, %params) = @_;
311 my $meta_instance = $class->get_meta_instance();
312 my $instance = $meta_instance->create_instance();
313 foreach my $attr ($class->compute_all_applicable_attributes()) {
314 $attr->initialize_instance_slot($meta_instance, $instance, \%params);
319 sub get_meta_instance {
321 return $class->instance_metaclass->new(
323 $class->compute_all_applicable_attributes()
329 my $instance = shift;
330 (blessed($instance) && $instance->isa($class->name))
331 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
333 # we need to protect the integrity of the
334 # Class::MOP::Class singletons here, they
335 # should not be cloned.
336 return $instance if $instance->isa('Class::MOP::Class');
337 $class->clone_instance($instance, @_);
341 my ($class, $instance, %params) = @_;
343 || confess "You can only clone instances, \$self is not a blessed instance";
344 my $meta_instance = $class->get_meta_instance();
345 my $clone = $meta_instance->clone_instance($instance);
346 foreach my $attr ($class->compute_all_applicable_attributes()) {
347 if ($params{$attr->init_arg}) {
348 $meta_instance->set_slot_value($clone, $attr->name, $params{$attr->init_arg});
360 @{$self->get_package_symbol('@ISA')} = @supers;
362 # we need to check the metaclass
363 # compatability here so that we can
364 # be sure that the superclass is
365 # not potentially creating an issues
366 # we don't know about
367 $self->check_metaclass_compatability();
369 @{$self->get_package_symbol('@ISA')};
372 sub class_precedence_list {
375 # We need to check for ciruclar inheirtance here.
376 # This will do nothing if all is well, and blow
377 # up otherwise. Yes, it's an ugly hack, better
378 # suggestions are welcome.
379 { ($self->name || return)->isa('This is a test for circular inheritance') }
380 # ... and now back to our regularly scheduled program
384 $self->initialize($_)->class_precedence_list()
385 } $self->superclasses()
392 my ($self, $method_name, $method) = @_;
393 (defined $method_name && $method_name)
394 || confess "You must define a method name";
397 if (blessed($method)) {
398 $body = $method->body;
402 ('CODE' eq (reftype($body) || ''))
403 || confess "Your code block must be a CODE reference";
404 $method = $self->method_metaclass->wrap($body);
406 $self->get_method_map->{$method_name} = $method;
408 my $full_method_name = ($self->name . '::' . $method_name);
409 $self->add_package_symbol("&${method_name}" => subname $full_method_name => $body);
413 my $fetch_and_prepare_method = sub {
414 my ($self, $method_name) = @_;
416 my $method = $self->get_method($method_name);
417 # if we dont have local ...
419 # try to find the next method
420 $method = $self->find_next_method_by_name($method_name);
421 # die if it does not exist
423 || confess "The method '$method_name' is not found in the inherience hierarchy for class " . $self->name;
424 # and now make sure to wrap it
425 # even if it is already wrapped
426 # because we need a new sub ref
427 $method = Class::MOP::Method::Wrapped->wrap($method);
430 # now make sure we wrap it properly
431 $method = Class::MOP::Method::Wrapped->wrap($method)
432 unless $method->isa('Class::MOP::Method::Wrapped');
434 $self->add_method($method_name => $method);
438 sub add_before_method_modifier {
439 my ($self, $method_name, $method_modifier) = @_;
440 (defined $method_name && $method_name)
441 || confess "You must pass in a method name";
442 my $method = $fetch_and_prepare_method->($self, $method_name);
443 $method->add_before_modifier(subname ':before' => $method_modifier);
446 sub add_after_method_modifier {
447 my ($self, $method_name, $method_modifier) = @_;
448 (defined $method_name && $method_name)
449 || confess "You must pass in a method name";
450 my $method = $fetch_and_prepare_method->($self, $method_name);
451 $method->add_after_modifier(subname ':after' => $method_modifier);
454 sub add_around_method_modifier {
455 my ($self, $method_name, $method_modifier) = @_;
456 (defined $method_name && $method_name)
457 || confess "You must pass in a method name";
458 my $method = $fetch_and_prepare_method->($self, $method_name);
459 $method->add_around_modifier(subname ':around' => $method_modifier);
463 # the methods above used to be named like this:
464 # ${pkg}::${method}:(before|after|around)
465 # but this proved problematic when using one modifier
466 # to wrap multiple methods (something which is likely
467 # to happen pretty regularly IMO). So instead of naming
468 # it like this, I have chosen to just name them purely
469 # with their modifier names, like so:
470 # :(before|after|around)
471 # The fact is that in a stack trace, it will be fairly
472 # evident from the context what method they are attached
473 # to, and so don't need the fully qualified name.
477 my ($self, $method_name, $method) = @_;
478 (defined $method_name && $method_name)
479 || confess "You must define a method name";
481 my $body = (blessed($method) ? $method->body : $method);
482 ('CODE' eq (reftype($body) || ''))
483 || confess "Your code block must be a CODE reference";
485 $self->add_package_symbol("&${method_name}" => $body);
489 my ($self, $method_name) = @_;
490 (defined $method_name && $method_name)
491 || confess "You must define a method name";
493 return 0 unless exists $self->get_method_map->{$method_name};
498 my ($self, $method_name) = @_;
499 (defined $method_name && $method_name)
500 || confess "You must define a method name";
503 # I don't really need this here, because
504 # if the method_map is missing a key it
505 # will just return undef for me now
506 # return unless $self->has_method($method_name);
508 return $self->get_method_map->{$method_name};
512 my ($self, $method_name) = @_;
513 (defined $method_name && $method_name)
514 || confess "You must define a method name";
516 my $removed_method = $self->get_method($method_name);
519 $self->remove_package_symbol("&${method_name}");
520 delete $self->get_method_map->{$method_name};
521 } if defined $removed_method;
523 return $removed_method;
526 sub get_method_list {
528 keys %{$self->get_method_map};
531 sub find_method_by_name {
532 my ($self, $method_name) = @_;
533 (defined $method_name && $method_name)
534 || confess "You must define a method name to find";
535 # keep a record of what we have seen
536 # here, this will handle all the
537 # inheritence issues because we are
538 # using the &class_precedence_list
540 my @cpl = $self->class_precedence_list();
541 foreach my $class (@cpl) {
542 next if $seen_class{$class};
543 $seen_class{$class}++;
544 # fetch the meta-class ...
545 my $meta = $self->initialize($class);
546 return $meta->get_method($method_name)
547 if $meta->has_method($method_name);
552 sub compute_all_applicable_methods {
555 # keep a record of what we have seen
556 # here, this will handle all the
557 # inheritence issues because we are
558 # using the &class_precedence_list
559 my (%seen_class, %seen_method);
560 foreach my $class ($self->class_precedence_list()) {
561 next if $seen_class{$class};
562 $seen_class{$class}++;
563 # fetch the meta-class ...
564 my $meta = $self->initialize($class);
565 foreach my $method_name ($meta->get_method_list()) {
566 next if exists $seen_method{$method_name};
567 $seen_method{$method_name}++;
569 name => $method_name,
571 code => $meta->get_method($method_name)
578 sub find_all_methods_by_name {
579 my ($self, $method_name) = @_;
580 (defined $method_name && $method_name)
581 || confess "You must define a method name to find";
583 # keep a record of what we have seen
584 # here, this will handle all the
585 # inheritence issues because we are
586 # using the &class_precedence_list
588 foreach my $class ($self->class_precedence_list()) {
589 next if $seen_class{$class};
590 $seen_class{$class}++;
591 # fetch the meta-class ...
592 my $meta = $self->initialize($class);
594 name => $method_name,
596 code => $meta->get_method($method_name)
597 } if $meta->has_method($method_name);
602 sub find_next_method_by_name {
603 my ($self, $method_name) = @_;
604 (defined $method_name && $method_name)
605 || confess "You must define a method name to find";
606 # keep a record of what we have seen
607 # here, this will handle all the
608 # inheritence issues because we are
609 # using the &class_precedence_list
611 my @cpl = $self->class_precedence_list();
612 shift @cpl; # discard ourselves
613 foreach my $class (@cpl) {
614 next if $seen_class{$class};
615 $seen_class{$class}++;
616 # fetch the meta-class ...
617 my $meta = $self->initialize($class);
618 return $meta->get_method($method_name)
619 if $meta->has_method($method_name);
628 # either we have an attribute object already
629 # or we need to create one from the args provided
630 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
631 # make sure it is derived from the correct type though
632 ($attribute->isa('Class::MOP::Attribute'))
633 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
635 # first we attach our new attribute
636 # because it might need certain information
637 # about the class which it is attached to
638 $attribute->attach_to_class($self);
640 # then we remove attributes of a conflicting
641 # name here so that we can properly detach
642 # the old attr object, and remove any
643 # accessors it would have generated
644 $self->remove_attribute($attribute->name)
645 if $self->has_attribute($attribute->name);
647 # then onto installing the new accessors
648 $attribute->install_accessors();
649 $self->get_attribute_map->{$attribute->name} = $attribute;
653 my ($self, $attribute_name) = @_;
654 (defined $attribute_name && $attribute_name)
655 || confess "You must define an attribute name";
656 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
660 my ($self, $attribute_name) = @_;
661 (defined $attribute_name && $attribute_name)
662 || confess "You must define an attribute name";
663 return $self->get_attribute_map->{$attribute_name}
665 # this will return undef anyway, so no need ...
666 # if $self->has_attribute($attribute_name);
670 sub remove_attribute {
671 my ($self, $attribute_name) = @_;
672 (defined $attribute_name && $attribute_name)
673 || confess "You must define an attribute name";
674 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
675 return unless defined $removed_attribute;
676 delete $self->get_attribute_map->{$attribute_name};
677 $removed_attribute->remove_accessors();
678 $removed_attribute->detach_from_class();
679 return $removed_attribute;
682 sub get_attribute_list {
684 keys %{$self->get_attribute_map};
687 sub compute_all_applicable_attributes {
690 # keep a record of what we have seen
691 # here, this will handle all the
692 # inheritence issues because we are
693 # using the &class_precedence_list
694 my (%seen_class, %seen_attr);
695 foreach my $class ($self->class_precedence_list()) {
696 next if $seen_class{$class};
697 $seen_class{$class}++;
698 # fetch the meta-class ...
699 my $meta = $self->initialize($class);
700 foreach my $attr_name ($meta->get_attribute_list()) {
701 next if exists $seen_attr{$attr_name};
702 $seen_attr{$attr_name}++;
703 push @attrs => $meta->get_attribute($attr_name);
709 sub find_attribute_by_name {
710 my ($self, $attr_name) = @_;
711 # keep a record of what we have seen
712 # here, this will handle all the
713 # inheritence issues because we are
714 # using the &class_precedence_list
716 foreach my $class ($self->class_precedence_list()) {
717 next if $seen_class{$class};
718 $seen_class{$class}++;
719 # fetch the meta-class ...
720 my $meta = $self->initialize($class);
721 return $meta->get_attribute($attr_name)
722 if $meta->has_attribute($attr_name);
730 sub is_immutable { 0 }
734 # the immutable version of a
735 # particular metaclass is
736 # really class-level data so
737 # we don't want to regenerate
738 # it any more than we need to
739 my $IMMUTABLE_METACLASS;
743 $IMMUTABLE_METACLASS ||= Class::MOP::Immutable->new($self, {
744 read_only => [qw/superclasses/],
752 remove_package_symbol
755 class_precedence_list => 'ARRAY',
756 compute_all_applicable_attributes => 'ARRAY',
757 get_meta_instance => 'SCALAR',
758 get_method_map => 'SCALAR',
762 $IMMUTABLE_METACLASS->make_metaclass_immutable(@_)
774 Class::MOP::Class - Class Meta Object
778 # assuming that class Foo
779 # has been defined, you can
781 # use this for introspection ...
783 # add a method to Foo ...
784 Foo->meta->add_method('bar' => sub { ... })
786 # get a list of all the classes searched
787 # the method dispatcher in the correct order
788 Foo->meta->class_precedence_list()
790 # remove a method from Foo
791 Foo->meta->remove_method('bar');
793 # or use this to actually create classes ...
795 Class::MOP::Class->create('Bar' => (
797 superclasses => [ 'Foo' ],
799 Class::MOP:::Attribute->new('$bar'),
800 Class::MOP:::Attribute->new('$baz'),
803 calculate_bar => sub { ... },
804 construct_baz => sub { ... }
810 This is the largest and currently most complex part of the Perl 5
811 meta-object protocol. It controls the introspection and
812 manipulation of Perl 5 classes (and it can create them too). The
813 best way to understand what this module can do, is to read the
814 documentation for each of it's methods.
818 =head2 Self Introspection
824 This will return a B<Class::MOP::Class> instance which is related
825 to this class. Thereby allowing B<Class::MOP::Class> to actually
828 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
829 bootstrap this module by installing a number of attribute meta-objects
830 into it's metaclass. This will allow this class to reap all the benifits
831 of the MOP when subclassing it.
835 =head2 Class construction
837 These methods will handle creating B<Class::MOP::Class> objects,
838 which can be used to both create new classes, and analyze
839 pre-existing classes.
841 This module will internally store references to all the instances
842 you create with these methods, so that they do not need to be
843 created any more than nessecary. Basically, they are singletons.
847 =item B<create ($package_name,
848 version =E<gt> ?$version,
849 authority =E<gt> ?$authority,
850 superclasses =E<gt> ?@superclasses,
851 methods =E<gt> ?%methods,
852 attributes =E<gt> ?%attributes)>
854 This returns a B<Class::MOP::Class> object, bringing the specified
855 C<$package_name> into existence and adding any of the C<$version>,
856 C<$authority>, C<@superclasses>, C<%methods> and C<%attributes> to
859 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
860 methods =E<gt> ?%methods,
861 attributes =E<gt> ?%attributes)>
863 This will create an anonymous class, it works much like C<create> but
864 it does not need a C<$package_name>. Instead it will create a suitably
865 unique package name for you to stash things into.
867 =item B<initialize ($package_name, %options)>
869 This initializes and returns returns a B<Class::MOP::Class> object
870 for a given a C<$package_name>.
872 =item B<reinitialize ($package_name, %options)>
874 This removes the old metaclass, and creates a new one in it's place.
875 Do B<not> use this unless you really know what you are doing, it could
876 very easily make a very large mess of your program.
878 =item B<construct_class_instance (%options)>
880 This will construct an instance of B<Class::MOP::Class>, it is
881 here so that we can actually "tie the knot" for B<Class::MOP::Class>
882 to use C<construct_instance> once all the bootstrapping is done. This
883 method is used internally by C<initialize> and should never be called
884 from outside of that method really.
886 =item B<check_metaclass_compatability>
888 This method is called as the very last thing in the
889 C<construct_class_instance> method. This will check that the
890 metaclass you are creating is compatible with the metaclasses of all
891 your ancestors. For more inforamtion about metaclass compatibility
892 see the C<About Metaclass compatibility> section in L<Class::MOP>.
896 =head2 Object instance construction and cloning
898 These methods are B<entirely optional>, it is up to you whether you want
903 =item B<instance_metaclass>
905 =item B<get_meta_instance>
907 =item B<new_object (%params)>
909 This is a convience method for creating a new object of the class, and
910 blessing it into the appropriate package as well. Ideally your class
911 would call a C<new> this method like so:
914 my ($class, %param) = @_;
915 $class->meta->new_object(%params);
918 Of course the ideal place for this would actually be in C<UNIVERSAL::>
919 but that is considered bad style, so we do not do that.
921 =item B<construct_instance (%params)>
923 This method is used to construct an instace structure suitable for
924 C<bless>-ing into your package of choice. It works in conjunction
925 with the Attribute protocol to collect all applicable attributes.
927 This will construct and instance using a HASH ref as storage
928 (currently only HASH references are supported). This will collect all
929 the applicable attributes and layout out the fields in the HASH ref,
930 it will then initialize them using either use the corresponding key
931 in C<%params> or any default value or initializer found in the
932 attribute meta-object.
934 =item B<clone_object ($instance, %params)>
936 This is a convience method for cloning an object instance, then
937 blessing it into the appropriate package. This method will call
938 C<clone_instance>, which performs a shallow copy of the object,
939 see that methods documentation for more details. Ideally your
940 class would call a C<clone> this method like so:
943 my ($self, %param) = @_;
944 $self->meta->clone_object($self, %params);
947 Of course the ideal place for this would actually be in C<UNIVERSAL::>
948 but that is considered bad style, so we do not do that.
950 =item B<clone_instance($instance, %params)>
952 This method is a compliment of C<construct_instance> (which means if
953 you override C<construct_instance>, you need to override this one too),
954 and clones the instance shallowly.
956 The cloned structure returned is (like with C<construct_instance>) an
957 unC<bless>ed HASH reference, it is your responsibility to then bless
958 this cloned structure into the right class (which C<clone_object> will
961 As of 0.11, this method will clone the C<$instance> structure shallowly,
962 as opposed to the deep cloning implemented in prior versions. After much
963 thought, research and discussion, I have decided that anything but basic
964 shallow cloning is outside the scope of the meta-object protocol. I
965 think Yuval "nothingmuch" Kogman put it best when he said that cloning
966 is too I<context-specific> to be part of the MOP.
972 These are a few predicate methods for asking information about the class.
976 =item B<is_anon_class>
978 This returns true if the class is a C<Class::MOP::Class> created anon class.
982 This returns true if the class is still mutable.
984 =item B<is_immutable>
986 This returns true if the class has been made immutable.
990 =head2 Inheritance Relationships
994 =item B<superclasses (?@superclasses)>
996 This is a read-write attribute which represents the superclass
997 relationships of the class the B<Class::MOP::Class> instance is
998 associated with. Basically, it can get and set the C<@ISA> for you.
1001 Perl will occasionally perform some C<@ISA> and method caching, if
1002 you decide to change your superclass relationship at runtime (which
1003 is quite insane and very much not recommened), then you should be
1004 aware of this and the fact that this module does not make any
1005 attempt to address this issue.
1007 =item B<class_precedence_list>
1009 This computes the a list of all the class's ancestors in the same order
1010 in which method dispatch will be done. This is similair to
1011 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
1019 =item B<get_method_map>
1021 =item B<method_metaclass>
1023 =item B<add_method ($method_name, $method)>
1025 This will take a C<$method_name> and CODE reference to that
1026 C<$method> and install it into the class's package.
1029 This does absolutely nothing special to C<$method>
1030 other than use B<Sub::Name> to make sure it is tagged with the
1031 correct name, and therefore show up correctly in stack traces and
1034 =item B<alias_method ($method_name, $method)>
1036 This will take a C<$method_name> and CODE reference to that
1037 C<$method> and alias the method into the class's package.
1040 Unlike C<add_method>, this will B<not> try to name the
1041 C<$method> using B<Sub::Name>, it only aliases the method in
1042 the class's package.
1044 =item B<has_method ($method_name)>
1046 This just provides a simple way to check if the class implements
1047 a specific C<$method_name>. It will I<not> however, attempt to check
1048 if the class inherits the method (use C<UNIVERSAL::can> for that).
1050 This will correctly handle functions defined outside of the package
1051 that use a fully qualified name (C<sub Package::name { ... }>).
1053 This will correctly handle functions renamed with B<Sub::Name> and
1054 installed using the symbol tables. However, if you are naming the
1055 subroutine outside of the package scope, you must use the fully
1056 qualified name, including the package name, for C<has_method> to
1057 correctly identify it.
1059 This will attempt to correctly ignore functions imported from other
1060 packages using B<Exporter>. It breaks down if the function imported
1061 is an C<__ANON__> sub (such as with C<use constant>), which very well
1062 may be a valid method being applied to the class.
1064 In short, this method cannot always be trusted to determine if the
1065 C<$method_name> is actually a method. However, it will DWIM about
1066 90% of the time, so it's a small trade off I think.
1068 =item B<get_method ($method_name)>
1070 This will return a Class::MOP::Method instance related to the specified
1071 C<$method_name>, or return undef if that method does not exist.
1073 The Class::MOP::Method is codifiable, so you can use it like a normal
1074 CODE reference, see L<Class::MOP::Method> for more information.
1076 =item B<find_method_by_name ($method_name>
1078 This will return a CODE reference of the specified C<$method_name>,
1079 or return undef if that method does not exist.
1081 Unlike C<get_method> this will also look in the superclasses.
1083 =item B<remove_method ($method_name)>
1085 This will attempt to remove a given C<$method_name> from the class.
1086 It will return the CODE reference that it has removed, and will
1087 attempt to use B<Sub::Name> to clear the methods associated name.
1089 =item B<get_method_list>
1091 This will return a list of method names for all I<locally> defined
1092 methods. It does B<not> provide a list of all applicable methods,
1093 including any inherited ones. If you want a list of all applicable
1094 methods, use the C<compute_all_applicable_methods> method.
1096 =item B<compute_all_applicable_methods>
1098 This will return a list of all the methods names this class will
1099 respond to, taking into account inheritance. The list will be a list of
1100 HASH references, each one containing the following information; method
1101 name, the name of the class in which the method lives and a CODE
1102 reference for the actual method.
1104 =item B<find_all_methods_by_name ($method_name)>
1106 This will traverse the inheritence hierarchy and locate all methods
1107 with a given C<$method_name>. Similar to
1108 C<compute_all_applicable_methods> it returns a list of HASH references
1109 with the following information; method name (which will always be the
1110 same as C<$method_name>), the name of the class in which the method
1111 lives and a CODE reference for the actual method.
1113 The list of methods produced is a distinct list, meaning there are no
1114 duplicates in it. This is especially useful for things like object
1115 initialization and destruction where you only want the method called
1116 once, and in the correct order.
1118 =item B<find_next_method_by_name ($method_name)>
1120 This will return the first method to match a given C<$method_name> in
1121 the superclasses, this is basically equivalent to calling
1122 C<SUPER::$method_name>, but it can be dispatched at runtime.
1126 =head2 Method Modifiers
1128 Method modifiers are a concept borrowed from CLOS, in which a method
1129 can be wrapped with I<before>, I<after> and I<around> method modifiers
1130 that will be called everytime the method is called.
1132 =head3 How method modifiers work?
1134 Method modifiers work by wrapping the original method and then replacing
1135 it in the classes symbol table. The wrappers will handle calling all the
1136 modifiers in the appropariate orders and preserving the calling context
1137 for the original method.
1139 Each method modifier serves a particular purpose, which may not be
1140 obvious to users of other method wrapping modules. To start with, the
1141 return values of I<before> and I<after> modifiers are ignored. This is
1142 because thier purpose is B<not> to filter the input and output of the
1143 primary method (this is done with an I<around> modifier). This may seem
1144 like an odd restriction to some, but doing this allows for simple code
1145 to be added at the begining or end of a method call without jeapordizing
1146 the normal functioning of the primary method or placing any extra
1147 responsibility on the code of the modifier. Of course if you have more
1148 complex needs, then use the I<around> modifier, which uses a variation
1149 of continutation passing style to allow for a high degree of flexibility.
1151 Before and around modifiers are called in last-defined-first-called order,
1152 while after modifiers are called in first-defined-first-called order. So
1153 the call tree might looks something like this:
1163 To see examples of using method modifiers, see the following examples
1164 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1165 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1166 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1168 =head3 What is the performance impact?
1170 Of course there is a performance cost associated with method modifiers,
1171 but we have made every effort to make that cost be directly proportional
1172 to the amount of modifier features you utilize.
1174 The wrapping method does it's best to B<only> do as much work as it
1175 absolutely needs to. In order to do this we have moved some of the
1176 performance costs to set-up time, where they are easier to amortize.
1178 All this said, my benchmarks have indicated the following:
1180 simple wrapper with no modifiers 100% slower
1181 simple wrapper with simple before modifier 400% slower
1182 simple wrapper with simple after modifier 450% slower
1183 simple wrapper with simple around modifier 500-550% slower
1184 simple wrapper with all 3 modifiers 1100% slower
1186 These numbers may seem daunting, but you must remember, every feature
1187 comes with some cost. To put things in perspective, just doing a simple
1188 C<AUTOLOAD> which does nothing but extract the name of the method called
1189 and return it costs about 400% over a normal method call.
1193 =item B<add_before_method_modifier ($method_name, $code)>
1195 This will wrap the method at C<$method_name> and the supplied C<$code>
1196 will be passed the C<@_> arguments, and called before the original
1197 method is called. As specified above, the return value of the I<before>
1198 method modifiers is ignored, and it's ability to modify C<@_> is
1199 fairly limited. If you need to do either of these things, use an
1200 C<around> method modifier.
1202 =item B<add_after_method_modifier ($method_name, $code)>
1204 This will wrap the method at C<$method_name> so that the original
1205 method will be called, it's return values stashed, and then the
1206 supplied C<$code> will be passed the C<@_> arguments, and called.
1207 As specified above, the return value of the I<after> method
1208 modifiers is ignored, and it cannot modify the return values of
1209 the original method. If you need to do either of these things, use an
1210 C<around> method modifier.
1212 =item B<add_around_method_modifier ($method_name, $code)>
1214 This will wrap the method at C<$method_name> so that C<$code>
1215 will be called and passed the original method as an extra argument
1216 at the begining of the C<@_> argument list. This is a variation of
1217 continuation passing style, where the function prepended to C<@_>
1218 can be considered a continuation. It is up to C<$code> if it calls
1219 the original method or not, there is no restriction on what the
1220 C<$code> can or cannot do.
1226 It should be noted that since there is no one consistent way to define
1227 the attributes of a class in Perl 5. These methods can only work with
1228 the information given, and can not easily discover information on
1229 their own. See L<Class::MOP::Attribute> for more details.
1233 =item B<attribute_metaclass>
1235 =item B<get_attribute_map>
1237 =item B<add_attribute ($attribute_meta_object | $attribute_name, %attribute_spec)>
1239 This stores the C<$attribute_meta_object> (or creates one from the
1240 C<$attribute_name> and C<%attribute_spec>) in the B<Class::MOP::Class>
1241 instance associated with the given class. Unlike methods, attributes
1242 within the MOP are stored as meta-information only. They will be used
1243 later to construct instances from (see C<construct_instance> above).
1244 More details about the attribute meta-objects can be found in the
1245 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1248 It should be noted that any accessor, reader/writer or predicate
1249 methods which the C<$attribute_meta_object> has will be installed
1250 into the class at this time.
1253 If an attribute already exists for C<$attribute_name>, the old one
1254 will be removed (as well as removing all it's accessors), and then
1257 =item B<has_attribute ($attribute_name)>
1259 Checks to see if this class has an attribute by the name of
1260 C<$attribute_name> and returns a boolean.
1262 =item B<get_attribute ($attribute_name)>
1264 Returns the attribute meta-object associated with C<$attribute_name>,
1265 if none is found, it will return undef.
1267 =item B<remove_attribute ($attribute_name)>
1269 This will remove the attribute meta-object stored at
1270 C<$attribute_name>, then return the removed attribute meta-object.
1273 Removing an attribute will only affect future instances of
1274 the class, it will not make any attempt to remove the attribute from
1275 any existing instances of the class.
1277 It should be noted that any accessor, reader/writer or predicate
1278 methods which the attribute meta-object stored at C<$attribute_name>
1279 has will be removed from the class at this time. This B<will> make
1280 these attributes somewhat inaccessable in previously created
1281 instances. But if you are crazy enough to do this at runtime, then
1282 you are crazy enough to deal with something like this :).
1284 =item B<get_attribute_list>
1286 This returns a list of attribute names which are defined in the local
1287 class. If you want a list of all applicable attributes for a class,
1288 use the C<compute_all_applicable_attributes> method.
1290 =item B<compute_all_applicable_attributes>
1292 This will traverse the inheritance heirachy and return a list of all
1293 the applicable attributes for this class. It does not construct a
1294 HASH reference like C<compute_all_applicable_methods> because all
1295 that same information is discoverable through the attribute
1298 =item B<find_attribute_by_name ($attr_name)>
1300 This method will traverse the inheritance heirachy and find the
1301 first attribute whose name matches C<$attr_name>, then return it.
1302 It will return undef if nothing is found.
1306 =head2 Class Immutability
1310 =item B<make_immutable (%options)>
1312 This method will invoke a tranforamtion upon the class which will
1313 make it immutable. Details of this transformation can be found in
1314 the L<Class::MOP::Immutable> documentation.
1320 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1322 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1324 =head1 COPYRIGHT AND LICENSE
1326 Copyright 2006, 2007 by Infinity Interactive, Inc.
1328 L<http://www.iinteractive.com>
1330 This library is free software; you can redistribute it and/or modify
1331 it under the same terms as Perl itself.