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', 'weaken';
14 our $VERSION = '0.65';
15 our $AUTHORITY = 'cpan:STEVAN';
17 use base 'Class::MOP::Module';
27 $package_name = shift;
30 $package_name = $options{package};
33 (defined $package_name && $package_name && !ref($package_name))
34 || confess "You must pass a package name and it cannot be blessed";
36 return Class::MOP::get_metaclass_by_name($package_name)
37 || $class->construct_class_instance(package => $package_name, @_);
42 my $package_name = shift;
43 (defined $package_name && $package_name && !blessed($package_name))
44 || confess "You must pass a package name and it cannot be blessed";
45 Class::MOP::remove_metaclass_by_name($package_name);
46 $class->construct_class_instance('package' => $package_name, @_);
49 # NOTE: (meta-circularity)
50 # this is a special form of &construct_instance
51 # (see below), which is used to construct class
52 # meta-object instances for any Class::MOP::*
53 # class. All other classes will use the more
54 # normal &construct_instance.
55 sub construct_class_instance {
58 my $package_name = $options{'package'};
59 (defined $package_name && $package_name)
60 || confess "You must pass a package name";
62 # return the metaclass if we have it cached,
63 # and it is still defined (it has not been
64 # reaped by DESTROY yet, which can happen
65 # annoyingly enough during global destruction)
67 if (defined(my $meta = Class::MOP::get_metaclass_by_name($package_name))) {
72 # we need to deal with the possibility
73 # of class immutability here, and then
74 # get the name of the class appropriately
75 $class = (blessed($class)
76 ? ($class->is_immutable
77 ? $class->get_mutable_metaclass_name()
81 # now create the metaclass
83 if ($class eq 'Class::MOP::Class') {
86 # inherited from Class::MOP::Package
87 'package' => $package_name,
90 # since the following attributes will
91 # actually be loaded from the symbol
92 # table, and actually bypass the instance
93 # entirely, we can just leave these things
94 # listed here for reference, because they
95 # should not actually have a value associated
97 'namespace' => \undef,
98 # inherited from Class::MOP::Module
100 'authority' => \undef,
101 # defined in Class::MOP::Class
102 'superclasses' => \undef,
106 'attribute_metaclass' => $options{'attribute_metaclass'} || 'Class::MOP::Attribute',
107 'method_metaclass' => $options{'method_metaclass'} || 'Class::MOP::Method',
108 'instance_metaclass' => $options{'instance_metaclass'} || 'Class::MOP::Instance',
110 ## uber-private variables
112 # this starts out as undef so that
113 # we can tell the first time the
114 # methods are fetched
116 '_package_cache_flag' => undef,
117 '_meta_instance' => undef,
122 # it is safe to use meta here because
123 # class will always be a subclass of
124 # Class::MOP::Class, which defines meta
125 $meta = $class->meta->construct_instance(%options)
128 # and check the metaclass compatibility
129 $meta->check_metaclass_compatability();
131 Class::MOP::store_metaclass_by_name($package_name, $meta);
134 # we need to weaken any anon classes
135 # so that they can call DESTROY properly
136 Class::MOP::weaken_metaclass($package_name) if $meta->is_anon_class;
141 sub reset_package_cache_flag { (shift)->{'_package_cache_flag'} = undef }
142 sub update_package_cache_flag {
145 # we can manually update the cache number
146 # since we are actually adding the method
147 # to our cache as well. This avoids us
148 # having to regenerate the method_map.
150 $self->{'_package_cache_flag'} = Class::MOP::check_package_cache_flag($self->name);
153 sub check_metaclass_compatability {
156 # this is always okay ...
157 return if blessed($self) eq 'Class::MOP::Class' &&
158 $self->instance_metaclass eq 'Class::MOP::Instance';
160 my @class_list = $self->linearized_isa;
161 shift @class_list; # shift off $self->name
163 foreach my $class_name (@class_list) {
164 my $meta = Class::MOP::get_metaclass_by_name($class_name) || next;
167 # we need to deal with the possibility
168 # of class immutability here, and then
169 # get the name of the class appropriately
170 my $meta_type = ($meta->is_immutable
171 ? $meta->get_mutable_metaclass_name()
174 ($self->isa($meta_type))
175 || confess $self->name . "->meta => (" . (blessed($self)) . ")" .
176 " is not compatible with the " .
177 $class_name . "->meta => (" . ($meta_type) . ")";
179 # we also need to check that instance metaclasses
180 # are compatabile in the same the class.
181 ($self->instance_metaclass->isa($meta->instance_metaclass))
182 || confess $self->name . "->meta => (" . ($self->instance_metaclass) . ")" .
183 " is not compatible with the " .
184 $class_name . "->meta => (" . ($meta->instance_metaclass) . ")";
192 # this should be sufficient, if you have a
193 # use case where it is not, write a test and
195 my $ANON_CLASS_SERIAL = 0;
198 # we need a sufficiently annoying prefix
199 # this should suffice for now, this is
200 # used in a couple of places below, so
201 # need to put it up here for now.
202 my $ANON_CLASS_PREFIX = 'Class::MOP::Class::__ANON__::SERIAL::';
206 no warnings 'uninitialized';
207 $self->name =~ /^$ANON_CLASS_PREFIX/ ? 1 : 0;
210 sub create_anon_class {
211 my ($class, %options) = @_;
212 my $package_name = $ANON_CLASS_PREFIX . ++$ANON_CLASS_SERIAL;
213 return $class->create($package_name, %options);
219 require Devel::GlobalDestruction;
220 Devel::GlobalDestruction->import("in_global_destruction");
222 } or *in_global_destruction = sub () { '' };
226 # this will only get called for
227 # anon-classes, all other calls
228 # are assumed to occur during
229 # global destruction and so don't
230 # really need to be handled explicitly
234 return if in_global_destruction; # it'll happen soon anyway and this just makes things more complicated
236 no warnings 'uninitialized';
237 return unless $self->name =~ /^$ANON_CLASS_PREFIX/;
238 my ($serial_id) = ($self->name =~ /^$ANON_CLASS_PREFIX(\d+)/);
240 foreach my $key (keys %{$ANON_CLASS_PREFIX . $serial_id}) {
241 delete ${$ANON_CLASS_PREFIX . $serial_id}{$key};
243 delete ${'main::' . $ANON_CLASS_PREFIX}{$serial_id . '::'};
248 # creating classes with MOP ...
251 my ( $class, @args ) = @_;
253 unshift @args, 'package' if @args % 2 == 1;
255 my (%options) = @args;
256 my $package_name = $options{package};
258 (defined $package_name && $package_name)
259 || confess "You must pass a package name";
261 (ref $options{superclasses} eq 'ARRAY')
262 || confess "You must pass an ARRAY ref of superclasses"
263 if exists $options{superclasses};
265 (ref $options{attributes} eq 'ARRAY')
266 || confess "You must pass an ARRAY ref of attributes"
267 if exists $options{attributes};
269 (ref $options{methods} eq 'HASH')
270 || confess "You must pass an HASH ref of methods"
271 if exists $options{methods};
273 my $code = "package $package_name;";
274 $code .= "\$$package_name\:\:VERSION = '" . $options{version} . "';"
275 if exists $options{version};
276 $code .= "\$$package_name\:\:AUTHORITY = '" . $options{authority} . "';"
277 if exists $options{authority};
280 confess "creation of $package_name failed : $@" if $@;
282 my $meta = $class->initialize($package_name);
285 $meta->add_method('meta' => sub {
286 $class->initialize(blessed($_[0]) || $_[0]);
289 $meta->superclasses(@{$options{superclasses}})
290 if exists $options{superclasses};
292 # process attributes first, so that they can
293 # install accessors, but locally defined methods
294 # can then overwrite them. It is maybe a little odd, but
295 # I think this should be the order of things.
296 if (exists $options{attributes}) {
297 foreach my $attr (@{$options{attributes}}) {
298 $meta->add_attribute($attr);
301 if (exists $options{methods}) {
302 foreach my $method_name (keys %{$options{methods}}) {
303 $meta->add_method($method_name, $options{methods}->{$method_name});
312 # all these attribute readers will be bootstrapped
313 # away in the Class::MOP bootstrap section
315 sub get_attribute_map { $_[0]->{'attributes'} }
316 sub attribute_metaclass { $_[0]->{'attribute_metaclass'} }
317 sub method_metaclass { $_[0]->{'method_metaclass'} }
318 sub instance_metaclass { $_[0]->{'instance_metaclass'} }
321 # this is a prime canidate for conversion to XS
325 my $current = Class::MOP::check_package_cache_flag($self->name);
327 if (defined $self->{'_package_cache_flag'} && $self->{'_package_cache_flag'} == $current) {
328 return $self->{'methods'};
331 $self->{_package_cache_flag} = $current;
333 my $map = $self->{'methods'};
335 my $class_name = $self->name;
336 my $method_metaclass = $self->method_metaclass;
338 my %all_code = $self->get_all_package_symbols('CODE');
340 foreach my $symbol (keys %all_code) {
341 my $code = $all_code{$symbol};
343 next if exists $map->{$symbol} &&
344 defined $map->{$symbol} &&
345 $map->{$symbol}->body == $code;
347 my ($pkg, $name) = Class::MOP::get_code_info($code);
350 # in 5.10 constant.pm the constants show up
351 # as being in the right package, but in pre-5.10
352 # they show up as constant::__ANON__ so we
353 # make an exception here to be sure that things
354 # work as expected in both.
356 unless ($pkg eq 'constant' && $name eq '__ANON__') {
357 next if ($pkg || '') ne $class_name ||
358 (($name || '') ne '__ANON__' && ($pkg || '') ne $class_name);
361 $map->{$symbol} = $method_metaclass->wrap(
363 associated_metaclass => $self,
364 package_name => $class_name,
372 # Instance Construction & Cloning
378 # we need to protect the integrity of the
379 # Class::MOP::Class singletons here, so we
380 # delegate this to &construct_class_instance
381 # which will deal with the singletons
382 return $class->construct_class_instance(@_)
383 if $class->name->isa('Class::MOP::Class');
384 return $class->construct_instance(@_);
387 sub construct_instance {
388 my ($class, %params) = @_;
389 my $meta_instance = $class->get_meta_instance();
390 my $instance = $meta_instance->create_instance();
391 foreach my $attr ($class->compute_all_applicable_attributes()) {
392 $attr->initialize_instance_slot($meta_instance, $instance, \%params);
395 # this will only work for a HASH instance type
396 if ($class->is_anon_class) {
397 (Scalar::Util::reftype($instance) eq 'HASH')
398 || confess "Currently only HASH based instances are supported with instance of anon-classes";
400 # At some point we should make this official
401 # as a reserved slot name, but right now I am
402 # going to keep it here.
403 # my $RESERVED_MOP_SLOT = '__MOP__';
404 $instance->{'__MOP__'} = $class;
410 sub get_meta_instance {
412 $self->{'_meta_instance'} ||= $self->create_meta_instance();
415 sub create_meta_instance {
418 my $instance = $self->instance_metaclass->new(
419 associated_metaclass => $self,
420 attributes => [ $self->compute_all_applicable_attributes() ],
423 $self->add_meta_instance_dependencies()
424 if $instance->is_dependent_on_superclasses();
431 my $instance = shift;
432 (blessed($instance) && $instance->isa($class->name))
433 || confess "You must pass an instance of the metaclass (" . $class->name . "), not ($instance)";
436 # we need to protect the integrity of the
437 # Class::MOP::Class singletons here, they
438 # should not be cloned.
439 return $instance if $instance->isa('Class::MOP::Class');
440 $class->clone_instance($instance, @_);
444 my ($class, $instance, %params) = @_;
446 || confess "You can only clone instances, ($instance) is not a blessed instance";
447 my $meta_instance = $class->get_meta_instance();
448 my $clone = $meta_instance->clone_instance($instance);
449 foreach my $attr ($class->compute_all_applicable_attributes()) {
450 if ( defined( my $init_arg = $attr->init_arg ) ) {
451 if (exists $params{$init_arg}) {
452 $attr->set_value($clone, $params{$init_arg});
459 sub rebless_instance {
460 my ($self, $instance, %params) = @_;
463 if ($instance->can('meta')) {
464 ($instance->meta->isa('Class::MOP::Class'))
465 || confess 'Cannot rebless instance if ->meta is not an instance of Class::MOP::Class';
466 $old_metaclass = $instance->meta;
469 $old_metaclass = $self->initialize(blessed($instance));
472 my $meta_instance = $self->get_meta_instance();
474 $self->name->isa($old_metaclass->name)
475 || confess "You may rebless only into a subclass of (". $old_metaclass->name ."), of which (". $self->name .") isn't.";
478 $meta_instance->rebless_instance_structure($instance, $self);
480 foreach my $attr ( $self->compute_all_applicable_attributes ) {
481 if ( $attr->has_value($instance) ) {
482 if ( defined( my $init_arg = $attr->init_arg ) ) {
483 $params{$init_arg} = $attr->get_value($instance)
484 unless exists $params{$init_arg};
487 $attr->set_value($instance, $attr->get_value($instance));
492 foreach my $attr ($self->compute_all_applicable_attributes) {
493 $attr->initialize_instance_slot($meta_instance, $instance, \%params);
503 my $var_spec = { sigil => '@', type => 'ARRAY', name => 'ISA' };
506 @{$self->get_package_symbol($var_spec)} = @supers;
508 # we need to check the metaclass
509 # compatibility here so that we can
510 # be sure that the superclass is
511 # not potentially creating an issues
512 # we don't know about
513 $self->check_metaclass_compatability();
514 $self->update_meta_instance_dependencies();
516 @{$self->get_package_symbol($var_spec)};
522 my $super_class = $self->name;
524 if ( Class::MOP::HAVE_ISAREV() ) {
525 return @{ $super_class->mro::get_isarev() };
529 my $find_derived_classes;
530 $find_derived_classes = sub {
531 my ($outer_class) = @_;
533 my $symbol_table_hashref = do { no strict 'refs'; \%{"${outer_class}::"} };
536 for my $symbol ( keys %$symbol_table_hashref ) {
537 next SYMBOL if $symbol !~ /\A (\w+):: \z/x;
538 my $inner_class = $1;
540 next SYMBOL if $inner_class eq 'SUPER'; # skip '*::SUPER'
544 ? "${outer_class}::$inner_class"
547 if ( $class->isa($super_class) and $class ne $super_class ) {
548 push @derived_classes, $class;
551 next SYMBOL if $class eq 'main'; # skip 'main::*'
553 $find_derived_classes->($class);
557 my $root_class = q{};
558 $find_derived_classes->($root_class);
560 undef $find_derived_classes;
562 @derived_classes = sort { $a->isa($b) ? 1 : $b->isa($a) ? -1 : 0 } @derived_classes;
564 return @derived_classes;
570 return @{ mro::get_linear_isa( (shift)->name ) };
573 sub class_precedence_list {
575 my $name = $self->name;
577 unless (Class::MOP::IS_RUNNING_ON_5_10()) {
579 # We need to check for circular inheritance here
580 # if we are are not on 5.10, cause 5.8 detects it
581 # late. This will do nothing if all is well, and
582 # blow up otherwise. Yes, it's an ugly hack, better
583 # suggestions are welcome.
585 ($name || return)->isa('This is a test for circular inheritance')
588 # if our mro is c3, we can
589 # just grab the linear_isa
590 if (mro::get_mro($name) eq 'c3') {
591 return @{ mro::get_linear_isa($name) }
595 # we can't grab the linear_isa for dfs
596 # since it has all the duplicates
601 $self->initialize($_)->class_precedence_list()
602 } $self->superclasses()
610 my ($self, $method_name, $method) = @_;
611 (defined $method_name && $method_name)
612 || confess "You must define a method name";
615 if (blessed($method)) {
616 $body = $method->body;
617 if ($method->package_name ne $self->name &&
618 $method->name ne $method_name) {
619 warn "Hello there, got something for you."
620 . " Method says " . $method->package_name . " " . $method->name
621 . " Class says " . $self->name . " " . $method_name;
622 $method = $method->clone(
623 package_name => $self->name,
625 ) if $method->can('clone');
630 ('CODE' eq ref($body))
631 || confess "Your code block must be a CODE reference";
632 $method = $self->method_metaclass->wrap(
634 package_name => $self->name,
640 $method->attach_to_class($self);
642 $self->get_method_map->{$method_name} = $method;
644 my $full_method_name = ($self->name . '::' . $method_name);
645 $self->add_package_symbol(
646 { sigil => '&', type => 'CODE', name => $method_name },
647 Class::MOP::subname($full_method_name => $body)
650 $self->update_package_cache_flag; # still valid, since we just added the method to the map, and if it was invalid before that then get_method_map updated it
654 my $fetch_and_prepare_method = sub {
655 my ($self, $method_name) = @_;
657 my $method = $self->get_method($method_name);
658 # if we dont have local ...
660 # try to find the next method
661 $method = $self->find_next_method_by_name($method_name);
662 # die if it does not exist
664 || confess "The method '$method_name' is not found in the inheritance hierarchy for class " . $self->name;
665 # and now make sure to wrap it
666 # even if it is already wrapped
667 # because we need a new sub ref
668 $method = Class::MOP::Method::Wrapped->wrap($method);
671 # now make sure we wrap it properly
672 $method = Class::MOP::Method::Wrapped->wrap($method)
673 unless $method->isa('Class::MOP::Method::Wrapped');
675 $self->add_method($method_name => $method);
679 sub add_before_method_modifier {
680 my ($self, $method_name, $method_modifier) = @_;
681 (defined $method_name && $method_name)
682 || confess "You must pass in a method name";
683 my $method = $fetch_and_prepare_method->($self, $method_name);
684 $method->add_before_modifier(
685 Class::MOP::subname(':before' => $method_modifier)
689 sub add_after_method_modifier {
690 my ($self, $method_name, $method_modifier) = @_;
691 (defined $method_name && $method_name)
692 || confess "You must pass in a method name";
693 my $method = $fetch_and_prepare_method->($self, $method_name);
694 $method->add_after_modifier(
695 Class::MOP::subname(':after' => $method_modifier)
699 sub add_around_method_modifier {
700 my ($self, $method_name, $method_modifier) = @_;
701 (defined $method_name && $method_name)
702 || confess "You must pass in a method name";
703 my $method = $fetch_and_prepare_method->($self, $method_name);
704 $method->add_around_modifier(
705 Class::MOP::subname(':around' => $method_modifier)
710 # the methods above used to be named like this:
711 # ${pkg}::${method}:(before|after|around)
712 # but this proved problematic when using one modifier
713 # to wrap multiple methods (something which is likely
714 # to happen pretty regularly IMO). So instead of naming
715 # it like this, I have chosen to just name them purely
716 # with their modifier names, like so:
717 # :(before|after|around)
718 # The fact is that in a stack trace, it will be fairly
719 # evident from the context what method they are attached
720 # to, and so don't need the fully qualified name.
724 my ($self, $method_name, $method) = @_;
725 (defined $method_name && $method_name)
726 || confess "You must define a method name";
728 my $body = (blessed($method) ? $method->body : $method);
729 ('CODE' eq ref($body))
730 || confess "Your code block must be a CODE reference";
732 $self->add_package_symbol(
733 { sigil => '&', type => 'CODE', name => $method_name } => $body
738 my ($self, $method_name) = @_;
739 (defined $method_name && $method_name)
740 || confess "You must define a method name";
742 return 0 unless exists $self->get_method_map->{$method_name};
747 my ($self, $method_name) = @_;
748 (defined $method_name && $method_name)
749 || confess "You must define a method name";
752 # I don't really need this here, because
753 # if the method_map is missing a key it
754 # will just return undef for me now
755 # return unless $self->has_method($method_name);
757 return $self->get_method_map->{$method_name};
761 my ($self, $method_name) = @_;
762 (defined $method_name && $method_name)
763 || confess "You must define a method name";
765 my $removed_method = delete $self->get_method_map->{$method_name};
767 $self->remove_package_symbol(
768 { sigil => '&', type => 'CODE', name => $method_name }
771 $removed_method->detach_from_class if $removed_method;
773 $self->update_package_cache_flag; # still valid, since we just removed the method from the map
775 return $removed_method;
778 sub get_method_list {
780 keys %{$self->get_method_map};
783 sub find_method_by_name {
784 my ($self, $method_name) = @_;
785 (defined $method_name && $method_name)
786 || confess "You must define a method name to find";
787 foreach my $class ($self->linearized_isa) {
788 # fetch the meta-class ...
789 my $meta = $self->initialize($class);
790 return $meta->get_method($method_name)
791 if $meta->has_method($method_name);
796 sub compute_all_applicable_methods {
798 my %methods = map { %{ $self->initialize($_)->get_method_map } } reverse $self->linearized_isa;
799 # return values %methods # TODO make some new API that does this
803 class => $_->package_name,
804 code => $_, # sigh, overloading
809 sub find_all_methods_by_name {
810 my ($self, $method_name) = @_;
811 (defined $method_name && $method_name)
812 || confess "You must define a method name to find";
814 foreach my $class ($self->linearized_isa) {
815 # fetch the meta-class ...
816 my $meta = $self->initialize($class);
818 name => $method_name,
820 code => $meta->get_method($method_name)
821 } if $meta->has_method($method_name);
826 sub find_next_method_by_name {
827 my ($self, $method_name) = @_;
828 (defined $method_name && $method_name)
829 || confess "You must define a method name to find";
830 my @cpl = $self->linearized_isa;
831 shift @cpl; # discard ourselves
832 foreach my $class (@cpl) {
833 # fetch the meta-class ...
834 my $meta = $self->initialize($class);
835 return $meta->get_method($method_name)
836 if $meta->has_method($method_name);
845 # either we have an attribute object already
846 # or we need to create one from the args provided
847 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
848 # make sure it is derived from the correct type though
849 ($attribute->isa('Class::MOP::Attribute'))
850 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
852 # first we attach our new attribute
853 # because it might need certain information
854 # about the class which it is attached to
855 $attribute->attach_to_class($self);
857 # then we remove attributes of a conflicting
858 # name here so that we can properly detach
859 # the old attr object, and remove any
860 # accessors it would have generated
861 if ( $self->has_attribute($attribute->name) ) {
862 $self->remove_attribute($attribute->name);
864 $self->invalidate_meta_instances();
867 # then onto installing the new accessors
868 $self->get_attribute_map->{$attribute->name} = $attribute;
870 # invalidate package flag here
871 my $e = do { local $@; eval { $attribute->install_accessors() }; $@ };
873 $self->remove_attribute($attribute->name);
880 sub update_meta_instance_dependencies {
883 if ( $self->{meta_instance_dependencies} ) {
884 return $self->add_meta_instance_dependencies;
888 sub add_meta_instance_dependencies {
891 $self->remove_meta_instance_depdendencies;
893 my @attrs = $self->compute_all_applicable_attributes();
896 my @classes = grep { not $seen{$_->name}++ } map { $_->associated_class } @attrs;
898 foreach my $class ( @classes ) {
899 $class->add_dependent_meta_instance($self);
902 $self->{meta_instance_dependencies} = \@classes;
905 sub remove_meta_instance_depdendencies {
908 if ( my $classes = delete $self->{meta_instance_dependencies} ) {
909 foreach my $class ( @$classes ) {
910 $class->remove_dependent_meta_instance($self);
920 sub add_dependent_meta_instance {
921 my ( $self, $metaclass ) = @_;
922 push @{ $self->{dependent_meta_instances} }, $metaclass;
925 sub remove_dependent_meta_instance {
926 my ( $self, $metaclass ) = @_;
927 my $name = $metaclass->name;
928 @$_ = grep { $_->name ne $name } @$_ for $self->{dependent_meta_instances};
931 sub invalidate_meta_instances {
933 $_->invalidate_meta_instance() for $self, @{ $self->{dependent_meta_instances} };
936 sub invalidate_meta_instance {
938 undef $self->{_meta_instance};
942 my ($self, $attribute_name) = @_;
943 (defined $attribute_name && $attribute_name)
944 || confess "You must define an attribute name";
945 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
949 my ($self, $attribute_name) = @_;
950 (defined $attribute_name && $attribute_name)
951 || confess "You must define an attribute name";
952 return $self->get_attribute_map->{$attribute_name}
954 # this will return undef anyway, so no need ...
955 # if $self->has_attribute($attribute_name);
959 sub remove_attribute {
960 my ($self, $attribute_name) = @_;
961 (defined $attribute_name && $attribute_name)
962 || confess "You must define an attribute name";
963 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
964 return unless defined $removed_attribute;
965 delete $self->get_attribute_map->{$attribute_name};
966 $self->invalidate_meta_instances();
967 $removed_attribute->remove_accessors();
968 $removed_attribute->detach_from_class();
969 return $removed_attribute;
972 sub get_attribute_list {
974 keys %{$self->get_attribute_map};
977 sub compute_all_applicable_attributes {
979 my %attrs = map { %{ $self->initialize($_)->get_attribute_map } } reverse $self->linearized_isa;
980 return values %attrs;
983 sub find_attribute_by_name {
984 my ($self, $attr_name) = @_;
985 foreach my $class ($self->linearized_isa) {
986 # fetch the meta-class ...
987 my $meta = $self->initialize($class);
988 return $meta->get_attribute($attr_name)
989 if $meta->has_attribute($attr_name);
997 sub is_immutable { 0 }
1000 # Why I changed this (groditi)
1001 # - One Metaclass may have many Classes through many Metaclass instances
1002 # - One Metaclass should only have one Immutable Transformer instance
1003 # - Each Class may have different Immutabilizing options
1004 # - Therefore each Metaclass instance may have different Immutabilizing options
1005 # - We need to store one Immutable Transformer instance per Metaclass
1006 # - We need to store one set of Immutable Transformer options per Class
1007 # - Upon make_mutable we may delete the Immutabilizing options
1008 # - We could clean the immutable Transformer instance when there is no more
1009 # immutable Classes of that type, but we can also keep it in case
1010 # another class with this same Metaclass becomes immutable. It is a case
1011 # of trading of storing an instance to avoid unnecessary instantiations of
1012 # Immutable Transformers. You may view this as a memory leak, however
1013 # Because we have few Metaclasses, in practice it seems acceptable
1014 # - To allow Immutable Transformers instances to be cleaned up we could weaken
1015 # the reference stored in $IMMUTABLE_TRANSFORMERS{$class} and ||= should DWIM
1019 my %IMMUTABLE_TRANSFORMERS;
1020 my %IMMUTABLE_OPTIONS;
1022 sub get_immutable_options {
1024 return if $self->is_mutable;
1025 confess "unable to find immutabilizing options"
1026 unless exists $IMMUTABLE_OPTIONS{$self->name};
1027 my %options = %{$IMMUTABLE_OPTIONS{$self->name}};
1028 delete $options{IMMUTABLE_TRANSFORMER};
1032 sub get_immutable_transformer {
1034 if( $self->is_mutable ){
1035 my $class = blessed $self || $self;
1036 return $IMMUTABLE_TRANSFORMERS{$class} ||= $self->create_immutable_transformer;
1038 confess "unable to find transformer for immutable class"
1039 unless exists $IMMUTABLE_OPTIONS{$self->name};
1040 return $IMMUTABLE_OPTIONS{$self->name}->{IMMUTABLE_TRANSFORMER};
1043 sub make_immutable {
1047 my $transformer = $self->get_immutable_transformer;
1048 $transformer->make_metaclass_immutable($self, \%options);
1049 $IMMUTABLE_OPTIONS{$self->name} =
1050 { %options, IMMUTABLE_TRANSFORMER => $transformer };
1052 if( exists $options{debug} && $options{debug} ){
1053 print STDERR "# of Metaclass options: ", keys %IMMUTABLE_OPTIONS;
1054 print STDERR "# of Immutable transformers: ", keys %IMMUTABLE_TRANSFORMERS;
1062 return if $self->is_mutable;
1063 my $options = delete $IMMUTABLE_OPTIONS{$self->name};
1064 confess "unable to find immutabilizing options" unless ref $options;
1065 my $transformer = delete $options->{IMMUTABLE_TRANSFORMER};
1066 $transformer->make_metaclass_mutable($self, $options);
1071 sub create_immutable_transformer {
1073 my $class = Class::MOP::Immutable->new($self, {
1074 read_only => [qw/superclasses/],
1081 remove_package_symbol
1084 class_precedence_list => 'ARRAY',
1085 linearized_isa => 'ARRAY',
1086 compute_all_applicable_attributes => 'ARRAY',
1087 get_meta_instance => 'SCALAR',
1088 get_method_map => 'SCALAR',
1091 # this is ugly, but so are typeglobs,
1092 # so whattayahgonnadoboutit
1095 add_package_symbol => sub {
1096 my $original = shift;
1097 confess "Cannot add package symbols to an immutable metaclass"
1098 unless (caller(2))[3] eq 'Class::MOP::Package::get_package_symbol';
1099 goto $original->body;
1114 Class::MOP::Class - Class Meta Object
1118 # assuming that class Foo
1119 # has been defined, you can
1121 # use this for introspection ...
1123 # add a method to Foo ...
1124 Foo->meta->add_method('bar' => sub { ... })
1126 # get a list of all the classes searched
1127 # the method dispatcher in the correct order
1128 Foo->meta->class_precedence_list()
1130 # remove a method from Foo
1131 Foo->meta->remove_method('bar');
1133 # or use this to actually create classes ...
1135 Class::MOP::Class->create('Bar' => (
1137 superclasses => [ 'Foo' ],
1139 Class::MOP:::Attribute->new('$bar'),
1140 Class::MOP:::Attribute->new('$baz'),
1143 calculate_bar => sub { ... },
1144 construct_baz => sub { ... }
1150 This is the largest and currently most complex part of the Perl 5
1151 meta-object protocol. It controls the introspection and
1152 manipulation of Perl 5 classes (and it can create them too). The
1153 best way to understand what this module can do, is to read the
1154 documentation for each of it's methods.
1158 =head2 Self Introspection
1164 This will return a B<Class::MOP::Class> instance which is related
1165 to this class. Thereby allowing B<Class::MOP::Class> to actually
1168 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
1169 bootstrap this module by installing a number of attribute meta-objects
1170 into it's metaclass. This will allow this class to reap all the benifits
1171 of the MOP when subclassing it.
1175 =head2 Class construction
1177 These methods will handle creating B<Class::MOP::Class> objects,
1178 which can be used to both create new classes, and analyze
1179 pre-existing classes.
1181 This module will internally store references to all the instances
1182 you create with these methods, so that they do not need to be
1183 created any more than nessecary. Basically, they are singletons.
1187 =item B<create ($package_name,
1188 version =E<gt> ?$version,
1189 authority =E<gt> ?$authority,
1190 superclasses =E<gt> ?@superclasses,
1191 methods =E<gt> ?%methods,
1192 attributes =E<gt> ?%attributes)>
1194 This returns a B<Class::MOP::Class> object, bringing the specified
1195 C<$package_name> into existence and adding any of the C<$version>,
1196 C<$authority>, C<@superclasses>, C<%methods> and C<%attributes> to
1199 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
1200 methods =E<gt> ?%methods,
1201 attributes =E<gt> ?%attributes)>
1203 This will create an anonymous class, it works much like C<create> but
1204 it does not need a C<$package_name>. Instead it will create a suitably
1205 unique package name for you to stash things into.
1207 On very important distinction is that anon classes are destroyed once
1208 the metaclass they are attached to goes out of scope. In the DESTROY
1209 method, the created package will be removed from the symbol table.
1211 It is also worth noting that any instances created with an anon-class
1212 will keep a special reference to the anon-meta which will prevent the
1213 anon-class from going out of scope until all instances of it have also
1214 been destroyed. This however only works for HASH based instance types,
1215 as we use a special reserved slot (C<__MOP__>) to store this.
1217 =item B<initialize ($package_name, %options)>
1219 This initializes and returns returns a B<Class::MOP::Class> object
1220 for a given a C<$package_name>.
1222 =item B<reinitialize ($package_name, %options)>
1224 This removes the old metaclass, and creates a new one in it's place.
1225 Do B<not> use this unless you really know what you are doing, it could
1226 very easily make a very large mess of your program.
1228 =item B<construct_class_instance (%options)>
1230 This will construct an instance of B<Class::MOP::Class>, it is
1231 here so that we can actually "tie the knot" for B<Class::MOP::Class>
1232 to use C<construct_instance> once all the bootstrapping is done. This
1233 method is used internally by C<initialize> and should never be called
1234 from outside of that method really.
1236 =item B<check_metaclass_compatability>
1238 This method is called as the very last thing in the
1239 C<construct_class_instance> method. This will check that the
1240 metaclass you are creating is compatible with the metaclasses of all
1241 your ancestors. For more inforamtion about metaclass compatibility
1242 see the C<About Metaclass compatibility> section in L<Class::MOP>.
1244 =item B<update_package_cache_flag>
1246 This will reset the package cache flag for this particular metaclass
1247 it is basically the value of the C<Class::MOP::get_package_cache_flag>
1248 function. This is very rarely needed from outside of C<Class::MOP::Class>
1249 but in some cases you might want to use it, so it is here.
1251 =item B<reset_package_cache_flag>
1253 Clears the package cache flag to announce to the internals that we need
1254 to rebuild the method map.
1256 =item B<add_meta_instance_dependencies>
1258 Registers this class as dependent on its superclasses.
1260 Only superclasses from which this class inherits attributes will be added.
1262 =item B<remove_meta_instance_depdendencies>
1264 Unregisters this class from its superclasses.
1266 =item B<update_meta_instance_dependencies>
1268 Reregisters if necessary.
1270 =item B<add_dependent_meta_instance> $metaclass
1272 Registers the class as having a meta instance dependent on this class.
1274 =item B<remove_dependent_meta_instance> $metaclass
1276 Remove the class from the list of dependent classes.
1278 =item B<invalidate_meta_instances>
1280 Clears the cached meta instance for this metaclass and all of the registered
1281 classes with dependent meta instances.
1283 Called by C<add_attribute> and C<remove_attribute> to recalculate the attribute
1286 =item B<invalidate_meta_instance>
1288 Used by C<invalidate_meta_instances>.
1292 =head2 Object instance construction and cloning
1294 These methods are B<entirely optional>, it is up to you whether you want
1299 =item B<instance_metaclass>
1301 Returns the class name of the instance metaclass, see L<Class::MOP::Instance>
1302 for more information on the instance metaclasses.
1304 =item B<get_meta_instance>
1306 Returns an instance of L<Class::MOP::Instance> to be used in the construction
1307 of a new instance of the class.
1309 =item B<create_meta_instance>
1311 Called by C<get_meta_instance> if necessary.
1313 =item B<new_object (%params)>
1315 This is a convience method for creating a new object of the class, and
1316 blessing it into the appropriate package as well. Ideally your class
1317 would call a C<new> this method like so:
1320 my ($class, %param) = @_;
1321 $class->meta->new_object(%params);
1324 =item B<construct_instance (%params)>
1326 This method is used to construct an instance structure suitable for
1327 C<bless>-ing into your package of choice. It works in conjunction
1328 with the Attribute protocol to collect all applicable attributes.
1330 This will construct and instance using a HASH ref as storage
1331 (currently only HASH references are supported). This will collect all
1332 the applicable attributes and layout out the fields in the HASH ref,
1333 it will then initialize them using either use the corresponding key
1334 in C<%params> or any default value or initializer found in the
1335 attribute meta-object.
1337 =item B<clone_object ($instance, %params)>
1339 This is a convience method for cloning an object instance, then
1340 blessing it into the appropriate package. This method will call
1341 C<clone_instance>, which performs a shallow copy of the object,
1342 see that methods documentation for more details. Ideally your
1343 class would call a C<clone> this method like so:
1345 sub MyClass::clone {
1346 my ($self, %param) = @_;
1347 $self->meta->clone_object($self, %params);
1350 =item B<clone_instance($instance, %params)>
1352 This method is a compliment of C<construct_instance> (which means if
1353 you override C<construct_instance>, you need to override this one too),
1354 and clones the instance shallowly.
1356 The cloned structure returned is (like with C<construct_instance>) an
1357 unC<bless>ed HASH reference, it is your responsibility to then bless
1358 this cloned structure into the right class (which C<clone_object> will
1361 As of 0.11, this method will clone the C<$instance> structure shallowly,
1362 as opposed to the deep cloning implemented in prior versions. After much
1363 thought, research and discussion, I have decided that anything but basic
1364 shallow cloning is outside the scope of the meta-object protocol. I
1365 think Yuval "nothingmuch" Kogman put it best when he said that cloning
1366 is too I<context-specific> to be part of the MOP.
1368 =item B<rebless_instance($instance, ?%params)>
1370 This will change the class of C<$instance> to the class of the invoking
1371 C<Class::MOP::Class>. You may only rebless the instance to a subclass of
1372 itself. You may pass in optional C<%params> which are like constructor
1373 params and will override anything already defined in the instance.
1377 =head2 Informational
1379 These are a few predicate methods for asking information about the class.
1383 =item B<is_anon_class>
1385 This returns true if the class is a C<Class::MOP::Class> created anon class.
1389 This returns true if the class is still mutable.
1391 =item B<is_immutable>
1393 This returns true if the class has been made immutable.
1397 =head2 Inheritance Relationships
1401 =item B<superclasses (?@superclasses)>
1403 This is a read-write attribute which represents the superclass
1404 relationships of the class the B<Class::MOP::Class> instance is
1405 associated with. Basically, it can get and set the C<@ISA> for you.
1407 =item B<class_precedence_list>
1409 This computes the a list of all the class's ancestors in the same order
1410 in which method dispatch will be done. This is similair to what
1411 B<Class::ISA::super_path> does, but we don't remove duplicate names.
1413 =item B<linearized_isa>
1415 This returns a list based on C<class_precedence_list> but with all
1420 This returns a list of subclasses for this class.
1428 =item B<get_method_map>
1430 Returns a HASH ref of name to CODE reference mapping for this class.
1432 =item B<method_metaclass>
1434 Returns the class name of the method metaclass, see L<Class::MOP::Method>
1435 for more information on the method metaclasses.
1437 =item B<add_method ($method_name, $method)>
1439 This will take a C<$method_name> and CODE reference to that
1440 C<$method> and install it into the class's package.
1443 This does absolutely nothing special to C<$method>
1444 other than use B<Sub::Name> to make sure it is tagged with the
1445 correct name, and therefore show up correctly in stack traces and
1448 =item B<alias_method ($method_name, $method)>
1450 This will take a C<$method_name> and CODE reference to that
1451 C<$method> and alias the method into the class's package.
1454 Unlike C<add_method>, this will B<not> try to name the
1455 C<$method> using B<Sub::Name>, it only aliases the method in
1456 the class's package.
1458 =item B<has_method ($method_name)>
1460 This just provides a simple way to check if the class implements
1461 a specific C<$method_name>. It will I<not> however, attempt to check
1462 if the class inherits the method (use C<UNIVERSAL::can> for that).
1464 This will correctly handle functions defined outside of the package
1465 that use a fully qualified name (C<sub Package::name { ... }>).
1467 This will correctly handle functions renamed with B<Sub::Name> and
1468 installed using the symbol tables. However, if you are naming the
1469 subroutine outside of the package scope, you must use the fully
1470 qualified name, including the package name, for C<has_method> to
1471 correctly identify it.
1473 This will attempt to correctly ignore functions imported from other
1474 packages using B<Exporter>. It breaks down if the function imported
1475 is an C<__ANON__> sub (such as with C<use constant>), which very well
1476 may be a valid method being applied to the class.
1478 In short, this method cannot always be trusted to determine if the
1479 C<$method_name> is actually a method. However, it will DWIM about
1480 90% of the time, so it's a small trade off I think.
1482 =item B<get_method ($method_name)>
1484 This will return a Class::MOP::Method instance related to the specified
1485 C<$method_name>, or return undef if that method does not exist.
1487 The Class::MOP::Method is codifiable, so you can use it like a normal
1488 CODE reference, see L<Class::MOP::Method> for more information.
1490 =item B<find_method_by_name ($method_name)>
1492 This will return a CODE reference of the specified C<$method_name>,
1493 or return undef if that method does not exist.
1495 Unlike C<get_method> this will also look in the superclasses.
1497 =item B<remove_method ($method_name)>
1499 This will attempt to remove a given C<$method_name> from the class.
1500 It will return the CODE reference that it has removed, and will
1501 attempt to use B<Sub::Name> to clear the methods associated name.
1503 =item B<get_method_list>
1505 This will return a list of method names for all I<locally> defined
1506 methods. It does B<not> provide a list of all applicable methods,
1507 including any inherited ones. If you want a list of all applicable
1508 methods, use the C<compute_all_applicable_methods> method.
1510 =item B<compute_all_applicable_methods>
1512 This will return a list of all the methods names this class will
1513 respond to, taking into account inheritance. The list will be a list of
1514 HASH references, each one containing the following information; method
1515 name, the name of the class in which the method lives and a CODE
1516 reference for the actual method.
1518 =item B<find_all_methods_by_name ($method_name)>
1520 This will traverse the inheritence hierarchy and locate all methods
1521 with a given C<$method_name>. Similar to
1522 C<compute_all_applicable_methods> it returns a list of HASH references
1523 with the following information; method name (which will always be the
1524 same as C<$method_name>), the name of the class in which the method
1525 lives and a CODE reference for the actual method.
1527 The list of methods produced is a distinct list, meaning there are no
1528 duplicates in it. This is especially useful for things like object
1529 initialization and destruction where you only want the method called
1530 once, and in the correct order.
1532 =item B<find_next_method_by_name ($method_name)>
1534 This will return the first method to match a given C<$method_name> in
1535 the superclasses, this is basically equivalent to calling
1536 C<SUPER::$method_name>, but it can be dispatched at runtime.
1540 =head2 Method Modifiers
1542 Method modifiers are a concept borrowed from CLOS, in which a method
1543 can be wrapped with I<before>, I<after> and I<around> method modifiers
1544 that will be called everytime the method is called.
1546 =head3 How method modifiers work?
1548 Method modifiers work by wrapping the original method and then replacing
1549 it in the classes symbol table. The wrappers will handle calling all the
1550 modifiers in the appropariate orders and preserving the calling context
1551 for the original method.
1553 Each method modifier serves a particular purpose, which may not be
1554 obvious to users of other method wrapping modules. To start with, the
1555 return values of I<before> and I<after> modifiers are ignored. This is
1556 because thier purpose is B<not> to filter the input and output of the
1557 primary method (this is done with an I<around> modifier). This may seem
1558 like an odd restriction to some, but doing this allows for simple code
1559 to be added at the begining or end of a method call without jeapordizing
1560 the normal functioning of the primary method or placing any extra
1561 responsibility on the code of the modifier. Of course if you have more
1562 complex needs, then use the I<around> modifier, which uses a variation
1563 of continutation passing style to allow for a high degree of flexibility.
1565 Before and around modifiers are called in last-defined-first-called order,
1566 while after modifiers are called in first-defined-first-called order. So
1567 the call tree might looks something like this:
1577 To see examples of using method modifiers, see the following examples
1578 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1579 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1580 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1582 =head3 What is the performance impact?
1584 Of course there is a performance cost associated with method modifiers,
1585 but we have made every effort to make that cost be directly proportional
1586 to the amount of modifier features you utilize.
1588 The wrapping method does it's best to B<only> do as much work as it
1589 absolutely needs to. In order to do this we have moved some of the
1590 performance costs to set-up time, where they are easier to amortize.
1592 All this said, my benchmarks have indicated the following:
1594 simple wrapper with no modifiers 100% slower
1595 simple wrapper with simple before modifier 400% slower
1596 simple wrapper with simple after modifier 450% slower
1597 simple wrapper with simple around modifier 500-550% slower
1598 simple wrapper with all 3 modifiers 1100% slower
1600 These numbers may seem daunting, but you must remember, every feature
1601 comes with some cost. To put things in perspective, just doing a simple
1602 C<AUTOLOAD> which does nothing but extract the name of the method called
1603 and return it costs about 400% over a normal method call.
1607 =item B<add_before_method_modifier ($method_name, $code)>
1609 This will wrap the method at C<$method_name> and the supplied C<$code>
1610 will be passed the C<@_> arguments, and called before the original
1611 method is called. As specified above, the return value of the I<before>
1612 method modifiers is ignored, and it's ability to modify C<@_> is
1613 fairly limited. If you need to do either of these things, use an
1614 C<around> method modifier.
1616 =item B<add_after_method_modifier ($method_name, $code)>
1618 This will wrap the method at C<$method_name> so that the original
1619 method will be called, it's return values stashed, and then the
1620 supplied C<$code> will be passed the C<@_> arguments, and called.
1621 As specified above, the return value of the I<after> method
1622 modifiers is ignored, and it cannot modify the return values of
1623 the original method. If you need to do either of these things, use an
1624 C<around> method modifier.
1626 =item B<add_around_method_modifier ($method_name, $code)>
1628 This will wrap the method at C<$method_name> so that C<$code>
1629 will be called and passed the original method as an extra argument
1630 at the begining of the C<@_> argument list. This is a variation of
1631 continuation passing style, where the function prepended to C<@_>
1632 can be considered a continuation. It is up to C<$code> if it calls
1633 the original method or not, there is no restriction on what the
1634 C<$code> can or cannot do.
1640 It should be noted that since there is no one consistent way to define
1641 the attributes of a class in Perl 5. These methods can only work with
1642 the information given, and can not easily discover information on
1643 their own. See L<Class::MOP::Attribute> for more details.
1647 =item B<attribute_metaclass>
1649 Returns the class name of the attribute metaclass, see L<Class::MOP::Attribute>
1650 for more information on the attribute metaclasses.
1652 =item B<get_attribute_map>
1654 This returns a HASH ref of name to attribute meta-object mapping.
1656 =item B<add_attribute ($attribute_meta_object | ($attribute_name, %attribute_spec))>
1658 This stores the C<$attribute_meta_object> (or creates one from the
1659 C<$attribute_name> and C<%attribute_spec>) in the B<Class::MOP::Class>
1660 instance associated with the given class. Unlike methods, attributes
1661 within the MOP are stored as meta-information only. They will be used
1662 later to construct instances from (see C<construct_instance> above).
1663 More details about the attribute meta-objects can be found in the
1664 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1667 It should be noted that any accessor, reader/writer or predicate
1668 methods which the C<$attribute_meta_object> has will be installed
1669 into the class at this time.
1672 If an attribute already exists for C<$attribute_name>, the old one
1673 will be removed (as well as removing all it's accessors), and then
1676 =item B<has_attribute ($attribute_name)>
1678 Checks to see if this class has an attribute by the name of
1679 C<$attribute_name> and returns a boolean.
1681 =item B<get_attribute ($attribute_name)>
1683 Returns the attribute meta-object associated with C<$attribute_name>,
1684 if none is found, it will return undef.
1686 =item B<remove_attribute ($attribute_name)>
1688 This will remove the attribute meta-object stored at
1689 C<$attribute_name>, then return the removed attribute meta-object.
1692 Removing an attribute will only affect future instances of
1693 the class, it will not make any attempt to remove the attribute from
1694 any existing instances of the class.
1696 It should be noted that any accessor, reader/writer or predicate
1697 methods which the attribute meta-object stored at C<$attribute_name>
1698 has will be removed from the class at this time. This B<will> make
1699 these attributes somewhat inaccessable in previously created
1700 instances. But if you are crazy enough to do this at runtime, then
1701 you are crazy enough to deal with something like this :).
1703 =item B<get_attribute_list>
1705 This returns a list of attribute names which are defined in the local
1706 class. If you want a list of all applicable attributes for a class,
1707 use the C<compute_all_applicable_attributes> method.
1709 =item B<compute_all_applicable_attributes>
1711 This will traverse the inheritance heirachy and return a list of all
1712 the applicable attributes for this class. It does not construct a
1713 HASH reference like C<compute_all_applicable_methods> because all
1714 that same information is discoverable through the attribute
1717 =item B<find_attribute_by_name ($attr_name)>
1719 This method will traverse the inheritance heirachy and find the
1720 first attribute whose name matches C<$attr_name>, then return it.
1721 It will return undef if nothing is found.
1725 =head2 Class Immutability
1729 =item B<make_immutable (%options)>
1731 This method will invoke a tranforamtion upon the class which will
1732 make it immutable. Details of this transformation can be found in
1733 the L<Class::MOP::Immutable> documentation.
1735 =item B<make_mutable>
1737 This method will reverse tranforamtion upon the class which
1740 =item B<get_immutable_transformer>
1742 Return a transformer suitable for making this class immutable or, if this
1743 class is immutable, the transformer used to make it immutable.
1745 =item B<get_immutable_options>
1747 If the class is immutable, return the options used to make it immutable.
1749 =item B<create_immutable_transformer>
1751 Create a transformer suitable for making this class immutable
1757 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1759 =head1 COPYRIGHT AND LICENSE
1761 Copyright 2006-2008 by Infinity Interactive, Inc.
1763 L<http://www.iinteractive.com>
1765 This library is free software; you can redistribute it and/or modify
1766 it under the same terms as Perl itself.