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 = '0.21';
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 ? $class->get_mutable_metaclass_name()
73 # now create the metaclass
75 if ($class =~ /^Class::MOP::Class$/) {
78 # inherited from Class::MOP::Package
79 '$!package' => $package_name,
82 # since the following attributes will
83 # actually be loaded from the symbol
84 # table, and actually bypass the instance
85 # entirely, we can just leave these things
86 # listed here for reference, because they
87 # should not actually have a value associated
89 '%!namespace' => \undef,
90 # inherited from Class::MOP::Module
91 '$!version' => \undef,
92 '$!authority' => \undef,
93 # defined in Class::MOP::Class
94 '@!superclasses' => \undef,
98 '$!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 no warnings 'uninitialized';
178 $self->name =~ /^$ANON_CLASS_PREFIX/ ? 1 : 0;
181 sub create_anon_class {
182 my ($class, %options) = @_;
183 my $package_name = $ANON_CLASS_PREFIX . ++$ANON_CLASS_SERIAL;
184 return $class->create($package_name, %options);
188 # this will only get called for
189 # anon-classes, all other calls
190 # are assumed to occur during
191 # global destruction and so don't
192 # really need to be handled explicitly
195 no warnings 'uninitialized';
196 return unless $self->name =~ /^$ANON_CLASS_PREFIX/;
197 my ($serial_id) = ($self->name =~ /^$ANON_CLASS_PREFIX(\d+)/);
199 foreach my $key (keys %{$ANON_CLASS_PREFIX . $serial_id}) {
200 delete ${$ANON_CLASS_PREFIX . $serial_id}{$key};
202 delete ${'main::' . $ANON_CLASS_PREFIX}{$serial_id . '::'};
207 # creating classes with MOP ...
211 my $package_name = shift;
213 (defined $package_name && $package_name)
214 || confess "You must pass a package name";
217 || confess "You much pass all parameters as name => value pairs " .
218 "(I found an uneven number of params in \@_)";
222 my $code = "package $package_name;";
223 $code .= "\$$package_name\:\:VERSION = '" . $options{version} . "';"
224 if exists $options{version};
225 $code .= "\$$package_name\:\:AUTHORITY = '" . $options{authority} . "';"
226 if exists $options{authority};
229 confess "creation of $package_name failed : $@" if $@;
231 my $meta = $class->initialize($package_name);
233 $meta->add_method('meta' => sub {
234 $class->initialize(blessed($_[0]) || $_[0]);
237 $meta->superclasses(@{$options{superclasses}})
238 if exists $options{superclasses};
240 # process attributes first, so that they can
241 # install accessors, but locally defined methods
242 # can then overwrite them. It is maybe a little odd, but
243 # I think this should be the order of things.
244 if (exists $options{attributes}) {
245 foreach my $attr (@{$options{attributes}}) {
246 $meta->add_attribute($attr);
249 if (exists $options{methods}) {
250 foreach my $method_name (keys %{$options{methods}}) {
251 $meta->add_method($method_name, $options{methods}->{$method_name});
260 # all these attribute readers will be bootstrapped
261 # away in the Class::MOP bootstrap section
263 sub get_attribute_map { $_[0]->{'%!attributes'} }
264 sub attribute_metaclass { $_[0]->{'$!attribute_metaclass'} }
265 sub method_metaclass { $_[0]->{'$!method_metaclass'} }
266 sub instance_metaclass { $_[0]->{'$!instance_metaclass'} }
269 # this is a prime canidate for conversion to XS
272 my $map = $self->{'%!methods'};
274 my $class_name = $self->name;
275 my $method_metaclass = $self->method_metaclass;
277 foreach my $symbol ($self->list_all_package_symbols('CODE')) {
278 my $code = $self->get_package_symbol('&' . $symbol);
280 next if exists $map->{$symbol} &&
281 defined $map->{$symbol} &&
282 $map->{$symbol}->body == $code;
284 my $gv = svref_2object($code)->GV;
285 next if ($gv->STASH->NAME || '') ne $class_name &&
286 ($gv->NAME || '') ne '__ANON__';
288 $map->{$symbol} = $method_metaclass->wrap($code);
294 # Instance Construction & Cloning
299 # we need to protect the integrity of the
300 # Class::MOP::Class singletons here, so we
301 # delegate this to &construct_class_instance
302 # which will deal with the singletons
303 return $class->construct_class_instance(@_)
304 if $class->name->isa('Class::MOP::Class');
305 return $class->construct_instance(@_);
308 sub construct_instance {
309 my ($class, %params) = @_;
310 my $meta_instance = $class->get_meta_instance();
311 my $instance = $meta_instance->create_instance();
312 foreach my $attr ($class->compute_all_applicable_attributes()) {
313 $attr->initialize_instance_slot($meta_instance, $instance, \%params);
318 sub get_meta_instance {
320 return $class->instance_metaclass->new(
322 $class->compute_all_applicable_attributes()
328 my $instance = shift;
329 (blessed($instance) && $instance->isa($class->name))
330 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
332 # we need to protect the integrity of the
333 # Class::MOP::Class singletons here, they
334 # should not be cloned.
335 return $instance if $instance->isa('Class::MOP::Class');
336 $class->clone_instance($instance, @_);
340 my ($class, $instance, %params) = @_;
342 || confess "You can only clone instances, \$self is not a blessed instance";
343 my $meta_instance = $class->get_meta_instance();
344 my $clone = $meta_instance->clone_instance($instance);
345 foreach my $attr ($class->compute_all_applicable_attributes()) {
346 if ($params{$attr->init_arg}) {
347 $meta_instance->set_slot_value($clone, $attr->name, $params{$attr->init_arg});
359 @{$self->get_package_symbol('@ISA')} = @supers;
361 # we need to check the metaclass
362 # compatability here so that we can
363 # be sure that the superclass is
364 # not potentially creating an issues
365 # we don't know about
366 $self->check_metaclass_compatability();
368 @{$self->get_package_symbol('@ISA')};
371 sub class_precedence_list {
374 # We need to check for ciruclar inheirtance here.
375 # This will do nothing if all is well, and blow
376 # up otherwise. Yes, it's an ugly hack, better
377 # suggestions are welcome.
378 { ($self->name || return)->isa('This is a test for circular inheritance') }
379 # ... and now back to our regularly scheduled program
383 $self->initialize($_)->class_precedence_list()
384 } $self->superclasses()
391 my ($self, $method_name, $method) = @_;
392 (defined $method_name && $method_name)
393 || confess "You must define a method name";
396 if (blessed($method)) {
397 $body = $method->body;
401 ('CODE' eq (reftype($body) || ''))
402 || confess "Your code block must be a CODE reference";
403 $method = $self->method_metaclass->wrap($body);
405 $self->get_method_map->{$method_name} = $method;
407 my $full_method_name = ($self->name . '::' . $method_name);
408 $self->add_package_symbol("&${method_name}" => subname $full_method_name => $body);
412 my $fetch_and_prepare_method = sub {
413 my ($self, $method_name) = @_;
415 my $method = $self->get_method($method_name);
416 # if we dont have local ...
418 # try to find the next method
419 $method = $self->find_next_method_by_name($method_name);
420 # die if it does not exist
422 || confess "The method '$method_name' is not found in the inherience hierarchy for class " . $self->name;
423 # and now make sure to wrap it
424 # even if it is already wrapped
425 # because we need a new sub ref
426 $method = Class::MOP::Method::Wrapped->wrap($method);
429 # now make sure we wrap it properly
430 $method = Class::MOP::Method::Wrapped->wrap($method)
431 unless $method->isa('Class::MOP::Method::Wrapped');
433 $self->add_method($method_name => $method);
437 sub add_before_method_modifier {
438 my ($self, $method_name, $method_modifier) = @_;
439 (defined $method_name && $method_name)
440 || confess "You must pass in a method name";
441 my $method = $fetch_and_prepare_method->($self, $method_name);
442 $method->add_before_modifier(subname ':before' => $method_modifier);
445 sub add_after_method_modifier {
446 my ($self, $method_name, $method_modifier) = @_;
447 (defined $method_name && $method_name)
448 || confess "You must pass in a method name";
449 my $method = $fetch_and_prepare_method->($self, $method_name);
450 $method->add_after_modifier(subname ':after' => $method_modifier);
453 sub add_around_method_modifier {
454 my ($self, $method_name, $method_modifier) = @_;
455 (defined $method_name && $method_name)
456 || confess "You must pass in a method name";
457 my $method = $fetch_and_prepare_method->($self, $method_name);
458 $method->add_around_modifier(subname ':around' => $method_modifier);
462 # the methods above used to be named like this:
463 # ${pkg}::${method}:(before|after|around)
464 # but this proved problematic when using one modifier
465 # to wrap multiple methods (something which is likely
466 # to happen pretty regularly IMO). So instead of naming
467 # it like this, I have chosen to just name them purely
468 # with their modifier names, like so:
469 # :(before|after|around)
470 # The fact is that in a stack trace, it will be fairly
471 # evident from the context what method they are attached
472 # to, and so don't need the fully qualified name.
476 my ($self, $method_name, $method) = @_;
477 (defined $method_name && $method_name)
478 || confess "You must define a method name";
480 my $body = (blessed($method) ? $method->body : $method);
481 ('CODE' eq (reftype($body) || ''))
482 || confess "Your code block must be a CODE reference";
484 $self->add_package_symbol("&${method_name}" => $body);
488 my ($self, $method_name) = @_;
489 (defined $method_name && $method_name)
490 || confess "You must define a method name";
492 return 0 unless exists $self->get_method_map->{$method_name};
497 my ($self, $method_name) = @_;
498 (defined $method_name && $method_name)
499 || confess "You must define a method name";
502 # I don't really need this here, because
503 # if the method_map is missing a key it
504 # will just return undef for me now
505 # return unless $self->has_method($method_name);
507 return $self->get_method_map->{$method_name};
511 my ($self, $method_name) = @_;
512 (defined $method_name && $method_name)
513 || confess "You must define a method name";
515 my $removed_method = $self->get_method($method_name);
518 $self->remove_package_symbol("&${method_name}");
519 delete $self->get_method_map->{$method_name};
520 } if defined $removed_method;
522 return $removed_method;
525 sub get_method_list {
527 keys %{$self->get_method_map};
530 sub find_method_by_name {
531 my ($self, $method_name) = @_;
532 (defined $method_name && $method_name)
533 || confess "You must define a method name to find";
534 # keep a record of what we have seen
535 # here, this will handle all the
536 # inheritence issues because we are
537 # using the &class_precedence_list
539 my @cpl = $self->class_precedence_list();
540 foreach my $class (@cpl) {
541 next if $seen_class{$class};
542 $seen_class{$class}++;
543 # fetch the meta-class ...
544 my $meta = $self->initialize($class);
545 return $meta->get_method($method_name)
546 if $meta->has_method($method_name);
551 sub compute_all_applicable_methods {
554 # keep a record of what we have seen
555 # here, this will handle all the
556 # inheritence issues because we are
557 # using the &class_precedence_list
558 my (%seen_class, %seen_method);
559 foreach my $class ($self->class_precedence_list()) {
560 next if $seen_class{$class};
561 $seen_class{$class}++;
562 # fetch the meta-class ...
563 my $meta = $self->initialize($class);
564 foreach my $method_name ($meta->get_method_list()) {
565 next if exists $seen_method{$method_name};
566 $seen_method{$method_name}++;
568 name => $method_name,
570 code => $meta->get_method($method_name)
577 sub find_all_methods_by_name {
578 my ($self, $method_name) = @_;
579 (defined $method_name && $method_name)
580 || confess "You must define a method name to find";
582 # keep a record of what we have seen
583 # here, this will handle all the
584 # inheritence issues because we are
585 # using the &class_precedence_list
587 foreach my $class ($self->class_precedence_list()) {
588 next if $seen_class{$class};
589 $seen_class{$class}++;
590 # fetch the meta-class ...
591 my $meta = $self->initialize($class);
593 name => $method_name,
595 code => $meta->get_method($method_name)
596 } if $meta->has_method($method_name);
601 sub find_next_method_by_name {
602 my ($self, $method_name) = @_;
603 (defined $method_name && $method_name)
604 || confess "You must define a method name to find";
605 # keep a record of what we have seen
606 # here, this will handle all the
607 # inheritence issues because we are
608 # using the &class_precedence_list
610 my @cpl = $self->class_precedence_list();
611 shift @cpl; # discard ourselves
612 foreach my $class (@cpl) {
613 next if $seen_class{$class};
614 $seen_class{$class}++;
615 # fetch the meta-class ...
616 my $meta = $self->initialize($class);
617 return $meta->get_method($method_name)
618 if $meta->has_method($method_name);
627 # either we have an attribute object already
628 # or we need to create one from the args provided
629 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
630 # make sure it is derived from the correct type though
631 ($attribute->isa('Class::MOP::Attribute'))
632 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
634 # first we attach our new attribute
635 # because it might need certain information
636 # about the class which it is attached to
637 $attribute->attach_to_class($self);
639 # then we remove attributes of a conflicting
640 # name here so that we can properly detach
641 # the old attr object, and remove any
642 # accessors it would have generated
643 $self->remove_attribute($attribute->name)
644 if $self->has_attribute($attribute->name);
646 # then onto installing the new accessors
647 $attribute->install_accessors();
648 $self->get_attribute_map->{$attribute->name} = $attribute;
652 my ($self, $attribute_name) = @_;
653 (defined $attribute_name && $attribute_name)
654 || confess "You must define an attribute name";
655 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
659 my ($self, $attribute_name) = @_;
660 (defined $attribute_name && $attribute_name)
661 || confess "You must define an attribute name";
662 return $self->get_attribute_map->{$attribute_name}
664 # this will return undef anyway, so no need ...
665 # if $self->has_attribute($attribute_name);
669 sub remove_attribute {
670 my ($self, $attribute_name) = @_;
671 (defined $attribute_name && $attribute_name)
672 || confess "You must define an attribute name";
673 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
674 return unless defined $removed_attribute;
675 delete $self->get_attribute_map->{$attribute_name};
676 $removed_attribute->remove_accessors();
677 $removed_attribute->detach_from_class();
678 return $removed_attribute;
681 sub get_attribute_list {
683 keys %{$self->get_attribute_map};
686 sub compute_all_applicable_attributes {
689 # keep a record of what we have seen
690 # here, this will handle all the
691 # inheritence issues because we are
692 # using the &class_precedence_list
693 my (%seen_class, %seen_attr);
694 foreach my $class ($self->class_precedence_list()) {
695 next if $seen_class{$class};
696 $seen_class{$class}++;
697 # fetch the meta-class ...
698 my $meta = $self->initialize($class);
699 foreach my $attr_name ($meta->get_attribute_list()) {
700 next if exists $seen_attr{$attr_name};
701 $seen_attr{$attr_name}++;
702 push @attrs => $meta->get_attribute($attr_name);
708 sub find_attribute_by_name {
709 my ($self, $attr_name) = @_;
710 # keep a record of what we have seen
711 # here, this will handle all the
712 # inheritence issues because we are
713 # using the &class_precedence_list
715 foreach my $class ($self->class_precedence_list()) {
716 next if $seen_class{$class};
717 $seen_class{$class}++;
718 # fetch the meta-class ...
719 my $meta = $self->initialize($class);
720 return $meta->get_attribute($attr_name)
721 if $meta->has_attribute($attr_name);
729 sub is_immutable { 0 }
732 use Class::MOP::Immutable;
739 $IMMUTABLE_META ||= Class::MOP::Immutable->new($self->meta, {
740 read_only => [qw/superclasses/],
748 remove_package_symbol
751 class_precedence_list => 'ARRAY',
752 compute_all_applicable_attributes => 'ARRAY',
753 get_meta_instance => 'SCALAR',
754 get_method_map => 'SCALAR',
756 })->create_immutable_metaclass;
758 $IMMUTABLE_META->make_metaclass_immutable(@_);
770 Class::MOP::Class - Class Meta Object
774 # assuming that class Foo
775 # has been defined, you can
777 # use this for introspection ...
779 # add a method to Foo ...
780 Foo->meta->add_method('bar' => sub { ... })
782 # get a list of all the classes searched
783 # the method dispatcher in the correct order
784 Foo->meta->class_precedence_list()
786 # remove a method from Foo
787 Foo->meta->remove_method('bar');
789 # or use this to actually create classes ...
791 Class::MOP::Class->create('Bar' => (
793 superclasses => [ 'Foo' ],
795 Class::MOP:::Attribute->new('$bar'),
796 Class::MOP:::Attribute->new('$baz'),
799 calculate_bar => sub { ... },
800 construct_baz => sub { ... }
806 This is the largest and currently most complex part of the Perl 5
807 meta-object protocol. It controls the introspection and
808 manipulation of Perl 5 classes (and it can create them too). The
809 best way to understand what this module can do, is to read the
810 documentation for each of it's methods.
814 =head2 Self Introspection
820 This will return a B<Class::MOP::Class> instance which is related
821 to this class. Thereby allowing B<Class::MOP::Class> to actually
824 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
825 bootstrap this module by installing a number of attribute meta-objects
826 into it's metaclass. This will allow this class to reap all the benifits
827 of the MOP when subclassing it.
831 =head2 Class construction
833 These methods will handle creating B<Class::MOP::Class> objects,
834 which can be used to both create new classes, and analyze
835 pre-existing classes.
837 This module will internally store references to all the instances
838 you create with these methods, so that they do not need to be
839 created any more than nessecary. Basically, they are singletons.
843 =item B<create ($package_name,
844 version =E<gt> ?$version,
845 authority =E<gt> ?$authority,
846 superclasses =E<gt> ?@superclasses,
847 methods =E<gt> ?%methods,
848 attributes =E<gt> ?%attributes)>
850 This returns a B<Class::MOP::Class> object, bringing the specified
851 C<$package_name> into existence and adding any of the C<$version>,
852 C<$authority>, C<@superclasses>, C<%methods> and C<%attributes> to
855 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
856 methods =E<gt> ?%methods,
857 attributes =E<gt> ?%attributes)>
859 This will create an anonymous class, it works much like C<create> but
860 it does not need a C<$package_name>. Instead it will create a suitably
861 unique package name for you to stash things into.
863 =item B<initialize ($package_name, %options)>
865 This initializes and returns returns a B<Class::MOP::Class> object
866 for a given a C<$package_name>.
868 =item B<reinitialize ($package_name, %options)>
870 This removes the old metaclass, and creates a new one in it's place.
871 Do B<not> use this unless you really know what you are doing, it could
872 very easily make a very large mess of your program.
874 =item B<construct_class_instance (%options)>
876 This will construct an instance of B<Class::MOP::Class>, it is
877 here so that we can actually "tie the knot" for B<Class::MOP::Class>
878 to use C<construct_instance> once all the bootstrapping is done. This
879 method is used internally by C<initialize> and should never be called
880 from outside of that method really.
882 =item B<check_metaclass_compatability>
884 This method is called as the very last thing in the
885 C<construct_class_instance> method. This will check that the
886 metaclass you are creating is compatible with the metaclasses of all
887 your ancestors. For more inforamtion about metaclass compatibility
888 see the C<About Metaclass compatibility> section in L<Class::MOP>.
892 =head2 Object instance construction and cloning
894 These methods are B<entirely optional>, it is up to you whether you want
899 =item B<instance_metaclass>
901 =item B<get_meta_instance>
903 =item B<new_object (%params)>
905 This is a convience method for creating a new object of the class, and
906 blessing it into the appropriate package as well. Ideally your class
907 would call a C<new> this method like so:
910 my ($class, %param) = @_;
911 $class->meta->new_object(%params);
914 Of course the ideal place for this would actually be in C<UNIVERSAL::>
915 but that is considered bad style, so we do not do that.
917 =item B<construct_instance (%params)>
919 This method is used to construct an instace structure suitable for
920 C<bless>-ing into your package of choice. It works in conjunction
921 with the Attribute protocol to collect all applicable attributes.
923 This will construct and instance using a HASH ref as storage
924 (currently only HASH references are supported). This will collect all
925 the applicable attributes and layout out the fields in the HASH ref,
926 it will then initialize them using either use the corresponding key
927 in C<%params> or any default value or initializer found in the
928 attribute meta-object.
930 =item B<clone_object ($instance, %params)>
932 This is a convience method for cloning an object instance, then
933 blessing it into the appropriate package. This method will call
934 C<clone_instance>, which performs a shallow copy of the object,
935 see that methods documentation for more details. Ideally your
936 class would call a C<clone> this method like so:
939 my ($self, %param) = @_;
940 $self->meta->clone_object($self, %params);
943 Of course the ideal place for this would actually be in C<UNIVERSAL::>
944 but that is considered bad style, so we do not do that.
946 =item B<clone_instance($instance, %params)>
948 This method is a compliment of C<construct_instance> (which means if
949 you override C<construct_instance>, you need to override this one too),
950 and clones the instance shallowly.
952 The cloned structure returned is (like with C<construct_instance>) an
953 unC<bless>ed HASH reference, it is your responsibility to then bless
954 this cloned structure into the right class (which C<clone_object> will
957 As of 0.11, this method will clone the C<$instance> structure shallowly,
958 as opposed to the deep cloning implemented in prior versions. After much
959 thought, research and discussion, I have decided that anything but basic
960 shallow cloning is outside the scope of the meta-object protocol. I
961 think Yuval "nothingmuch" Kogman put it best when he said that cloning
962 is too I<context-specific> to be part of the MOP.
968 These are a few predicate methods for asking information about the class.
972 =item B<is_anon_class>
976 =item B<is_immutable>
980 =head2 Inheritance Relationships
984 =item B<superclasses (?@superclasses)>
986 This is a read-write attribute which represents the superclass
987 relationships of the class the B<Class::MOP::Class> instance is
988 associated with. Basically, it can get and set the C<@ISA> for you.
991 Perl will occasionally perform some C<@ISA> and method caching, if
992 you decide to change your superclass relationship at runtime (which
993 is quite insane and very much not recommened), then you should be
994 aware of this and the fact that this module does not make any
995 attempt to address this issue.
997 =item B<class_precedence_list>
999 This computes the a list of all the class's ancestors in the same order
1000 in which method dispatch will be done. This is similair to
1001 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
1009 =item B<get_method_map>
1011 =item B<method_metaclass>
1013 =item B<add_method ($method_name, $method)>
1015 This will take a C<$method_name> and CODE reference to that
1016 C<$method> and install it into the class's package.
1019 This does absolutely nothing special to C<$method>
1020 other than use B<Sub::Name> to make sure it is tagged with the
1021 correct name, and therefore show up correctly in stack traces and
1024 =item B<alias_method ($method_name, $method)>
1026 This will take a C<$method_name> and CODE reference to that
1027 C<$method> and alias the method into the class's package.
1030 Unlike C<add_method>, this will B<not> try to name the
1031 C<$method> using B<Sub::Name>, it only aliases the method in
1032 the class's package.
1034 =item B<has_method ($method_name)>
1036 This just provides a simple way to check if the class implements
1037 a specific C<$method_name>. It will I<not> however, attempt to check
1038 if the class inherits the method (use C<UNIVERSAL::can> for that).
1040 This will correctly handle functions defined outside of the package
1041 that use a fully qualified name (C<sub Package::name { ... }>).
1043 This will correctly handle functions renamed with B<Sub::Name> and
1044 installed using the symbol tables. However, if you are naming the
1045 subroutine outside of the package scope, you must use the fully
1046 qualified name, including the package name, for C<has_method> to
1047 correctly identify it.
1049 This will attempt to correctly ignore functions imported from other
1050 packages using B<Exporter>. It breaks down if the function imported
1051 is an C<__ANON__> sub (such as with C<use constant>), which very well
1052 may be a valid method being applied to the class.
1054 In short, this method cannot always be trusted to determine if the
1055 C<$method_name> is actually a method. However, it will DWIM about
1056 90% of the time, so it's a small trade off I think.
1058 =item B<get_method ($method_name)>
1060 This will return a Class::MOP::Method instance related to the specified
1061 C<$method_name>, or return undef if that method does not exist.
1063 The Class::MOP::Method is codifiable, so you can use it like a normal
1064 CODE reference, see L<Class::MOP::Method> for more information.
1066 =item B<find_method_by_name ($method_name>
1068 This will return a CODE reference of the specified C<$method_name>,
1069 or return undef if that method does not exist.
1071 Unlike C<get_method> this will also look in the superclasses.
1073 =item B<remove_method ($method_name)>
1075 This will attempt to remove a given C<$method_name> from the class.
1076 It will return the CODE reference that it has removed, and will
1077 attempt to use B<Sub::Name> to clear the methods associated name.
1079 =item B<get_method_list>
1081 This will return a list of method names for all I<locally> defined
1082 methods. It does B<not> provide a list of all applicable methods,
1083 including any inherited ones. If you want a list of all applicable
1084 methods, use the C<compute_all_applicable_methods> method.
1086 =item B<compute_all_applicable_methods>
1088 This will return a list of all the methods names this class will
1089 respond to, taking into account inheritance. The list will be a list of
1090 HASH references, each one containing the following information; method
1091 name, the name of the class in which the method lives and a CODE
1092 reference for the actual method.
1094 =item B<find_all_methods_by_name ($method_name)>
1096 This will traverse the inheritence hierarchy and locate all methods
1097 with a given C<$method_name>. Similar to
1098 C<compute_all_applicable_methods> it returns a list of HASH references
1099 with the following information; method name (which will always be the
1100 same as C<$method_name>), the name of the class in which the method
1101 lives and a CODE reference for the actual method.
1103 The list of methods produced is a distinct list, meaning there are no
1104 duplicates in it. This is especially useful for things like object
1105 initialization and destruction where you only want the method called
1106 once, and in the correct order.
1108 =item B<find_next_method_by_name ($method_name)>
1110 This will return the first method to match a given C<$method_name> in
1111 the superclasses, this is basically equivalent to calling
1112 C<SUPER::$method_name>, but it can be dispatched at runtime.
1116 =head2 Method Modifiers
1118 Method modifiers are a concept borrowed from CLOS, in which a method
1119 can be wrapped with I<before>, I<after> and I<around> method modifiers
1120 that will be called everytime the method is called.
1122 =head3 How method modifiers work?
1124 Method modifiers work by wrapping the original method and then replacing
1125 it in the classes symbol table. The wrappers will handle calling all the
1126 modifiers in the appropariate orders and preserving the calling context
1127 for the original method.
1129 Each method modifier serves a particular purpose, which may not be
1130 obvious to users of other method wrapping modules. To start with, the
1131 return values of I<before> and I<after> modifiers are ignored. This is
1132 because thier purpose is B<not> to filter the input and output of the
1133 primary method (this is done with an I<around> modifier). This may seem
1134 like an odd restriction to some, but doing this allows for simple code
1135 to be added at the begining or end of a method call without jeapordizing
1136 the normal functioning of the primary method or placing any extra
1137 responsibility on the code of the modifier. Of course if you have more
1138 complex needs, then use the I<around> modifier, which uses a variation
1139 of continutation passing style to allow for a high degree of flexibility.
1141 Before and around modifiers are called in last-defined-first-called order,
1142 while after modifiers are called in first-defined-first-called order. So
1143 the call tree might looks something like this:
1153 To see examples of using method modifiers, see the following examples
1154 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1155 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1156 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1158 =head3 What is the performance impact?
1160 Of course there is a performance cost associated with method modifiers,
1161 but we have made every effort to make that cost be directly proportional
1162 to the amount of modifier features you utilize.
1164 The wrapping method does it's best to B<only> do as much work as it
1165 absolutely needs to. In order to do this we have moved some of the
1166 performance costs to set-up time, where they are easier to amortize.
1168 All this said, my benchmarks have indicated the following:
1170 simple wrapper with no modifiers 100% slower
1171 simple wrapper with simple before modifier 400% slower
1172 simple wrapper with simple after modifier 450% slower
1173 simple wrapper with simple around modifier 500-550% slower
1174 simple wrapper with all 3 modifiers 1100% slower
1176 These numbers may seem daunting, but you must remember, every feature
1177 comes with some cost. To put things in perspective, just doing a simple
1178 C<AUTOLOAD> which does nothing but extract the name of the method called
1179 and return it costs about 400% over a normal method call.
1183 =item B<add_before_method_modifier ($method_name, $code)>
1185 This will wrap the method at C<$method_name> and the supplied C<$code>
1186 will be passed the C<@_> arguments, and called before the original
1187 method is called. As specified above, the return value of the I<before>
1188 method modifiers is ignored, and it's ability to modify C<@_> is
1189 fairly limited. If you need to do either of these things, use an
1190 C<around> method modifier.
1192 =item B<add_after_method_modifier ($method_name, $code)>
1194 This will wrap the method at C<$method_name> so that the original
1195 method will be called, it's return values stashed, and then the
1196 supplied C<$code> will be passed the C<@_> arguments, and called.
1197 As specified above, the return value of the I<after> method
1198 modifiers is ignored, and it cannot modify the return values of
1199 the original method. If you need to do either of these things, use an
1200 C<around> method modifier.
1202 =item B<add_around_method_modifier ($method_name, $code)>
1204 This will wrap the method at C<$method_name> so that C<$code>
1205 will be called and passed the original method as an extra argument
1206 at the begining of the C<@_> argument list. This is a variation of
1207 continuation passing style, where the function prepended to C<@_>
1208 can be considered a continuation. It is up to C<$code> if it calls
1209 the original method or not, there is no restriction on what the
1210 C<$code> can or cannot do.
1216 It should be noted that since there is no one consistent way to define
1217 the attributes of a class in Perl 5. These methods can only work with
1218 the information given, and can not easily discover information on
1219 their own. See L<Class::MOP::Attribute> for more details.
1223 =item B<attribute_metaclass>
1225 =item B<get_attribute_map>
1227 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1229 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1230 instance associated with the given class, and associates it with
1231 the C<$attribute_name>. Unlike methods, attributes within the MOP
1232 are stored as meta-information only. They will be used later to
1233 construct instances from (see C<construct_instance> above).
1234 More details about the attribute meta-objects can be found in the
1235 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1238 It should be noted that any accessor, reader/writer or predicate
1239 methods which the C<$attribute_meta_object> has will be installed
1240 into the class at this time.
1243 If an attribute already exists for C<$attribute_name>, the old one
1244 will be removed (as well as removing all it's accessors), and then
1247 =item B<has_attribute ($attribute_name)>
1249 Checks to see if this class has an attribute by the name of
1250 C<$attribute_name> and returns a boolean.
1252 =item B<get_attribute ($attribute_name)>
1254 Returns the attribute meta-object associated with C<$attribute_name>,
1255 if none is found, it will return undef.
1257 =item B<remove_attribute ($attribute_name)>
1259 This will remove the attribute meta-object stored at
1260 C<$attribute_name>, then return the removed attribute meta-object.
1263 Removing an attribute will only affect future instances of
1264 the class, it will not make any attempt to remove the attribute from
1265 any existing instances of the class.
1267 It should be noted that any accessor, reader/writer or predicate
1268 methods which the attribute meta-object stored at C<$attribute_name>
1269 has will be removed from the class at this time. This B<will> make
1270 these attributes somewhat inaccessable in previously created
1271 instances. But if you are crazy enough to do this at runtime, then
1272 you are crazy enough to deal with something like this :).
1274 =item B<get_attribute_list>
1276 This returns a list of attribute names which are defined in the local
1277 class. If you want a list of all applicable attributes for a class,
1278 use the C<compute_all_applicable_attributes> method.
1280 =item B<compute_all_applicable_attributes>
1282 This will traverse the inheritance heirachy and return a list of all
1283 the applicable attributes for this class. It does not construct a
1284 HASH reference like C<compute_all_applicable_methods> because all
1285 that same information is discoverable through the attribute
1288 =item B<find_attribute_by_name ($attr_name)>
1290 This method will traverse the inheritance heirachy and find the
1291 first attribute whose name matches C<$attr_name>, then return it.
1292 It will return undef if nothing is found.
1296 =head2 Class closing
1300 =item B<make_immutable>
1306 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1308 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1310 =head1 COPYRIGHT AND LICENSE
1312 Copyright 2006 by Infinity Interactive, Inc.
1314 L<http://www.iinteractive.com>
1316 This library is free software; you can redistribute it and/or modify
1317 it under the same terms as Perl itself.