2 package Class::MOP::Class;
7 use Class::MOP::Immutable;
8 use Class::MOP::Instance;
9 use Class::MOP::Method::Wrapped;
12 use Scalar::Util 'blessed', 'reftype', 'weaken';
13 use Sub::Name 'subname';
14 use B 'svref_2object';
16 our $VERSION = '0.22';
17 our $AUTHORITY = 'cpan:STEVAN';
19 use base 'Class::MOP::Module';
23 sub meta { Class::MOP::Class->initialize(blessed($_[0]) || $_[0]) }
29 my $package_name = shift;
30 (defined $package_name && $package_name && !blessed($package_name))
31 || confess "You must pass a package name and it cannot be blessed";
32 $class->construct_class_instance('package' => $package_name, @_);
37 my $package_name = shift;
38 (defined $package_name && $package_name && !blessed($package_name))
39 || confess "You must pass a package name and it cannot be blessed";
40 Class::MOP::remove_metaclass_by_name($package_name);
41 $class->construct_class_instance('package' => $package_name, @_);
44 # NOTE: (meta-circularity)
45 # this is a special form of &construct_instance
46 # (see below), which is used to construct class
47 # meta-object instances for any Class::MOP::*
48 # class. All other classes will use the more
49 # normal &construct_instance.
50 sub construct_class_instance {
53 my $package_name = $options{'package'};
54 (defined $package_name && $package_name)
55 || confess "You must pass a package name";
57 # return the metaclass if we have it cached,
58 # and it is still defined (it has not been
59 # reaped by DESTROY yet, which can happen
60 # annoyingly enough during global destruction)
61 return Class::MOP::get_metaclass_by_name($package_name)
62 if Class::MOP::does_metaclass_exist($package_name);
65 # we need to deal with the possibility
66 # of class immutability here, and then
67 # get the name of the class appropriately
68 $class = (blessed($class)
69 ? ($class->is_immutable
70 ? $class->get_mutable_metaclass_name()
74 # now create the metaclass
76 if ($class =~ /^Class::MOP::Class$/) {
79 # inherited from Class::MOP::Package
80 '$!package' => $package_name,
83 # since the following attributes will
84 # actually be loaded from the symbol
85 # table, and actually bypass the instance
86 # entirely, we can just leave these things
87 # listed here for reference, because they
88 # should not actually have a value associated
90 '%!namespace' => \undef,
91 # inherited from Class::MOP::Module
92 '$!version' => \undef,
93 '$!authority' => \undef,
94 # defined in Class::MOP::Class
95 '@!superclasses' => \undef,
99 '$!attribute_metaclass' => $options{'attribute_metaclass'} || 'Class::MOP::Attribute',
100 '$!method_metaclass' => $options{'method_metaclass'} || 'Class::MOP::Method',
101 '$!instance_metaclass' => $options{'instance_metaclass'} || 'Class::MOP::Instance',
106 # it is safe to use meta here because
107 # class will always be a subclass of
108 # Class::MOP::Class, which defines meta
109 $meta = $class->meta->construct_instance(%options)
112 # and check the metaclass compatibility
113 $meta->check_metaclass_compatability();
115 Class::MOP::store_metaclass_by_name($package_name, $meta);
118 # we need to weaken any anon classes
119 # so that they can call DESTROY properly
120 Class::MOP::weaken_metaclass($package_name) if $meta->is_anon_class;
125 sub check_metaclass_compatability {
128 # this is always okay ...
129 return if blessed($self) eq 'Class::MOP::Class' &&
130 $self->instance_metaclass eq 'Class::MOP::Instance';
132 my @class_list = $self->class_precedence_list;
133 shift @class_list; # shift off $self->name
135 foreach my $class_name (@class_list) {
136 my $meta = Class::MOP::get_metaclass_by_name($class_name) || next;
139 # we need to deal with the possibility
140 # of class immutability here, and then
141 # get the name of the class appropriately
142 my $meta_type = ($meta->is_immutable
143 ? $meta->get_mutable_metaclass_name()
146 ($self->isa($meta_type))
147 || confess $self->name . "->meta => (" . (blessed($self)) . ")" .
148 " is not compatible with the " .
149 $class_name . "->meta => (" . ($meta_type) . ")";
151 # we also need to check that instance metaclasses
152 # are compatabile in the same the class.
153 ($self->instance_metaclass->isa($meta->instance_metaclass))
154 || confess $self->name . "->meta => (" . ($self->instance_metaclass) . ")" .
155 " is not compatible with the " .
156 $class_name . "->meta => (" . ($meta->instance_metaclass) . ")";
164 # this should be sufficient, if you have a
165 # use case where it is not, write a test and
167 my $ANON_CLASS_SERIAL = 0;
170 # we need a sufficiently annoying prefix
171 # this should suffice for now, this is
172 # used in a couple of places below, so
173 # need to put it up here for now.
174 my $ANON_CLASS_PREFIX = 'Class::MOP::Class::__ANON__::SERIAL::';
178 no warnings 'uninitialized';
179 $self->name =~ /^$ANON_CLASS_PREFIX/ ? 1 : 0;
182 sub create_anon_class {
183 my ($class, %options) = @_;
184 my $package_name = $ANON_CLASS_PREFIX . ++$ANON_CLASS_SERIAL;
185 return $class->create($package_name, %options);
189 # this will only get called for
190 # anon-classes, all other calls
191 # are assumed to occur during
192 # global destruction and so don't
193 # really need to be handled explicitly
196 no warnings 'uninitialized';
197 return unless $self->name =~ /^$ANON_CLASS_PREFIX/;
198 my ($serial_id) = ($self->name =~ /^$ANON_CLASS_PREFIX(\d+)/);
200 foreach my $key (keys %{$ANON_CLASS_PREFIX . $serial_id}) {
201 delete ${$ANON_CLASS_PREFIX . $serial_id}{$key};
203 delete ${'main::' . $ANON_CLASS_PREFIX}{$serial_id . '::'};
208 # creating classes with MOP ...
212 my $package_name = shift;
214 (defined $package_name && $package_name)
215 || confess "You must pass a package name";
218 || confess "You much pass all parameters as name => value pairs " .
219 "(I found an uneven number of params in \@_)";
223 my $code = "package $package_name;";
224 $code .= "\$$package_name\:\:VERSION = '" . $options{version} . "';"
225 if exists $options{version};
226 $code .= "\$$package_name\:\:AUTHORITY = '" . $options{authority} . "';"
227 if exists $options{authority};
230 confess "creation of $package_name failed : $@" if $@;
232 my $meta = $class->initialize($package_name);
234 $meta->add_method('meta' => sub {
235 $class->initialize(blessed($_[0]) || $_[0]);
238 $meta->superclasses(@{$options{superclasses}})
239 if exists $options{superclasses};
241 # process attributes first, so that they can
242 # install accessors, but locally defined methods
243 # can then overwrite them. It is maybe a little odd, but
244 # I think this should be the order of things.
245 if (exists $options{attributes}) {
246 foreach my $attr (@{$options{attributes}}) {
247 $meta->add_attribute($attr);
250 if (exists $options{methods}) {
251 foreach my $method_name (keys %{$options{methods}}) {
252 $meta->add_method($method_name, $options{methods}->{$method_name});
261 # all these attribute readers will be bootstrapped
262 # away in the Class::MOP bootstrap section
264 sub get_attribute_map { $_[0]->{'%!attributes'} }
265 sub attribute_metaclass { $_[0]->{'$!attribute_metaclass'} }
266 sub method_metaclass { $_[0]->{'$!method_metaclass'} }
267 sub instance_metaclass { $_[0]->{'$!instance_metaclass'} }
270 # this is a prime canidate for conversion to XS
273 my $map = $self->{'%!methods'};
275 my $class_name = $self->name;
276 my $method_metaclass = $self->method_metaclass;
278 foreach my $symbol ($self->list_all_package_symbols('CODE')) {
279 my $code = $self->get_package_symbol('&' . $symbol);
281 next if exists $map->{$symbol} &&
282 defined $map->{$symbol} &&
283 $map->{$symbol}->body == $code;
285 my $gv = svref_2object($code)->GV;
286 next if ($gv->STASH->NAME || '') ne $class_name &&
287 ($gv->NAME || '') ne '__ANON__';
289 $map->{$symbol} = $method_metaclass->wrap($code);
295 # Instance Construction & Cloning
300 # we need to protect the integrity of the
301 # Class::MOP::Class singletons here, so we
302 # delegate this to &construct_class_instance
303 # which will deal with the singletons
304 return $class->construct_class_instance(@_)
305 if $class->name->isa('Class::MOP::Class');
306 return $class->construct_instance(@_);
309 sub construct_instance {
310 my ($class, %params) = @_;
311 my $meta_instance = $class->get_meta_instance();
312 my $instance = $meta_instance->create_instance();
313 foreach my $attr ($class->compute_all_applicable_attributes()) {
314 $attr->initialize_instance_slot($meta_instance, $instance, \%params);
317 # this will only work for a HASH instance type
318 if ($class->is_anon_class) {
319 (reftype($instance) eq 'HASH')
320 || confess "Currently only HASH based instances are supported with instance of anon-classes";
322 # At some point we should make this official
323 # as a reserved slot name, but right now I am
324 # going to keep it here.
325 # my $RESERVED_MOP_SLOT = '__MOP__';
326 $instance->{'__MOP__'} = $class;
331 sub get_meta_instance {
333 return $class->instance_metaclass->new(
335 $class->compute_all_applicable_attributes()
341 my $instance = shift;
342 (blessed($instance) && $instance->isa($class->name))
343 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
345 # we need to protect the integrity of the
346 # Class::MOP::Class singletons here, they
347 # should not be cloned.
348 return $instance if $instance->isa('Class::MOP::Class');
349 $class->clone_instance($instance, @_);
353 my ($class, $instance, %params) = @_;
355 || confess "You can only clone instances, \$self is not a blessed instance";
356 my $meta_instance = $class->get_meta_instance();
357 my $clone = $meta_instance->clone_instance($instance);
358 foreach my $attr ($class->compute_all_applicable_attributes()) {
359 if (exists $params{$attr->init_arg}) {
360 $meta_instance->set_slot_value($clone, $attr->name, $params{$attr->init_arg});
372 @{$self->get_package_symbol('@ISA')} = @supers;
374 # we need to check the metaclass
375 # compatability here so that we can
376 # be sure that the superclass is
377 # not potentially creating an issues
378 # we don't know about
379 $self->check_metaclass_compatability();
381 @{$self->get_package_symbol('@ISA')};
384 sub class_precedence_list {
387 # We need to check for ciruclar inheirtance here.
388 # This will do nothing if all is well, and blow
389 # up otherwise. Yes, it's an ugly hack, better
390 # suggestions are welcome.
391 { ($self->name || return)->isa('This is a test for circular inheritance') }
396 $self->initialize($_)->class_precedence_list()
397 } $self->superclasses()
404 my ($self, $method_name, $method) = @_;
405 (defined $method_name && $method_name)
406 || confess "You must define a method name";
409 if (blessed($method)) {
410 $body = $method->body;
414 ('CODE' eq (reftype($body) || ''))
415 || confess "Your code block must be a CODE reference";
416 $method = $self->method_metaclass->wrap($body);
418 $self->get_method_map->{$method_name} = $method;
420 my $full_method_name = ($self->name . '::' . $method_name);
421 $self->add_package_symbol("&${method_name}" => subname $full_method_name => $body);
425 my $fetch_and_prepare_method = sub {
426 my ($self, $method_name) = @_;
428 my $method = $self->get_method($method_name);
429 # if we dont have local ...
431 # try to find the next method
432 $method = $self->find_next_method_by_name($method_name);
433 # die if it does not exist
435 || confess "The method '$method_name' is not found in the inheritance hierarchy for class " . $self->name;
436 # and now make sure to wrap it
437 # even if it is already wrapped
438 # because we need a new sub ref
439 $method = Class::MOP::Method::Wrapped->wrap($method);
442 # now make sure we wrap it properly
443 $method = Class::MOP::Method::Wrapped->wrap($method)
444 unless $method->isa('Class::MOP::Method::Wrapped');
446 $self->add_method($method_name => $method);
450 sub add_before_method_modifier {
451 my ($self, $method_name, $method_modifier) = @_;
452 (defined $method_name && $method_name)
453 || confess "You must pass in a method name";
454 my $method = $fetch_and_prepare_method->($self, $method_name);
455 $method->add_before_modifier(subname ':before' => $method_modifier);
458 sub add_after_method_modifier {
459 my ($self, $method_name, $method_modifier) = @_;
460 (defined $method_name && $method_name)
461 || confess "You must pass in a method name";
462 my $method = $fetch_and_prepare_method->($self, $method_name);
463 $method->add_after_modifier(subname ':after' => $method_modifier);
466 sub add_around_method_modifier {
467 my ($self, $method_name, $method_modifier) = @_;
468 (defined $method_name && $method_name)
469 || confess "You must pass in a method name";
470 my $method = $fetch_and_prepare_method->($self, $method_name);
471 $method->add_around_modifier(subname ':around' => $method_modifier);
475 # the methods above used to be named like this:
476 # ${pkg}::${method}:(before|after|around)
477 # but this proved problematic when using one modifier
478 # to wrap multiple methods (something which is likely
479 # to happen pretty regularly IMO). So instead of naming
480 # it like this, I have chosen to just name them purely
481 # with their modifier names, like so:
482 # :(before|after|around)
483 # The fact is that in a stack trace, it will be fairly
484 # evident from the context what method they are attached
485 # to, and so don't need the fully qualified name.
489 my ($self, $method_name, $method) = @_;
490 (defined $method_name && $method_name)
491 || confess "You must define a method name";
493 my $body = (blessed($method) ? $method->body : $method);
494 ('CODE' eq (reftype($body) || ''))
495 || confess "Your code block must be a CODE reference";
497 $self->add_package_symbol("&${method_name}" => $body);
501 my ($self, $method_name) = @_;
502 (defined $method_name && $method_name)
503 || confess "You must define a method name";
505 return 0 unless exists $self->get_method_map->{$method_name};
510 my ($self, $method_name) = @_;
511 (defined $method_name && $method_name)
512 || confess "You must define a method name";
515 # I don't really need this here, because
516 # if the method_map is missing a key it
517 # will just return undef for me now
518 # return unless $self->has_method($method_name);
520 return $self->get_method_map->{$method_name};
524 my ($self, $method_name) = @_;
525 (defined $method_name && $method_name)
526 || confess "You must define a method name";
528 my $removed_method = $self->get_method($method_name);
531 $self->remove_package_symbol("&${method_name}");
532 delete $self->get_method_map->{$method_name};
533 } if defined $removed_method;
535 return $removed_method;
538 sub get_method_list {
540 keys %{$self->get_method_map};
543 sub find_method_by_name {
544 my ($self, $method_name) = @_;
545 (defined $method_name && $method_name)
546 || confess "You must define a method name to find";
547 # keep a record of what we have seen
548 # here, this will handle all the
549 # inheritence issues because we are
550 # using the &class_precedence_list
552 my @cpl = $self->class_precedence_list();
553 foreach my $class (@cpl) {
554 next if $seen_class{$class};
555 $seen_class{$class}++;
556 # fetch the meta-class ...
557 my $meta = $self->initialize($class);
558 return $meta->get_method($method_name)
559 if $meta->has_method($method_name);
564 sub compute_all_applicable_methods {
567 # keep a record of what we have seen
568 # here, this will handle all the
569 # inheritence issues because we are
570 # using the &class_precedence_list
571 my (%seen_class, %seen_method);
572 foreach my $class ($self->class_precedence_list()) {
573 next if $seen_class{$class};
574 $seen_class{$class}++;
575 # fetch the meta-class ...
576 my $meta = $self->initialize($class);
577 foreach my $method_name ($meta->get_method_list()) {
578 next if exists $seen_method{$method_name};
579 $seen_method{$method_name}++;
581 name => $method_name,
583 code => $meta->get_method($method_name)
590 sub find_all_methods_by_name {
591 my ($self, $method_name) = @_;
592 (defined $method_name && $method_name)
593 || confess "You must define a method name to find";
595 # keep a record of what we have seen
596 # here, this will handle all the
597 # inheritence issues because we are
598 # using the &class_precedence_list
600 foreach my $class ($self->class_precedence_list()) {
601 next if $seen_class{$class};
602 $seen_class{$class}++;
603 # fetch the meta-class ...
604 my $meta = $self->initialize($class);
606 name => $method_name,
608 code => $meta->get_method($method_name)
609 } if $meta->has_method($method_name);
614 sub find_next_method_by_name {
615 my ($self, $method_name) = @_;
616 (defined $method_name && $method_name)
617 || confess "You must define a method name to find";
618 # keep a record of what we have seen
619 # here, this will handle all the
620 # inheritence issues because we are
621 # using the &class_precedence_list
623 my @cpl = $self->class_precedence_list();
624 shift @cpl; # discard ourselves
625 foreach my $class (@cpl) {
626 next if $seen_class{$class};
627 $seen_class{$class}++;
628 # fetch the meta-class ...
629 my $meta = $self->initialize($class);
630 return $meta->get_method($method_name)
631 if $meta->has_method($method_name);
640 # either we have an attribute object already
641 # or we need to create one from the args provided
642 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
643 # make sure it is derived from the correct type though
644 ($attribute->isa('Class::MOP::Attribute'))
645 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
647 # first we attach our new attribute
648 # because it might need certain information
649 # about the class which it is attached to
650 $attribute->attach_to_class($self);
652 # then we remove attributes of a conflicting
653 # name here so that we can properly detach
654 # the old attr object, and remove any
655 # accessors it would have generated
656 $self->remove_attribute($attribute->name)
657 if $self->has_attribute($attribute->name);
659 # then onto installing the new accessors
660 $attribute->install_accessors();
661 $self->get_attribute_map->{$attribute->name} = $attribute;
665 my ($self, $attribute_name) = @_;
666 (defined $attribute_name && $attribute_name)
667 || confess "You must define an attribute name";
668 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
672 my ($self, $attribute_name) = @_;
673 (defined $attribute_name && $attribute_name)
674 || confess "You must define an attribute name";
675 return $self->get_attribute_map->{$attribute_name}
677 # this will return undef anyway, so no need ...
678 # if $self->has_attribute($attribute_name);
682 sub remove_attribute {
683 my ($self, $attribute_name) = @_;
684 (defined $attribute_name && $attribute_name)
685 || confess "You must define an attribute name";
686 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
687 return unless defined $removed_attribute;
688 delete $self->get_attribute_map->{$attribute_name};
689 $removed_attribute->remove_accessors();
690 $removed_attribute->detach_from_class();
691 return $removed_attribute;
694 sub get_attribute_list {
696 keys %{$self->get_attribute_map};
699 sub compute_all_applicable_attributes {
702 # keep a record of what we have seen
703 # here, this will handle all the
704 # inheritence issues because we are
705 # using the &class_precedence_list
706 my (%seen_class, %seen_attr);
707 foreach my $class ($self->class_precedence_list()) {
708 next if $seen_class{$class};
709 $seen_class{$class}++;
710 # fetch the meta-class ...
711 my $meta = $self->initialize($class);
712 foreach my $attr_name ($meta->get_attribute_list()) {
713 next if exists $seen_attr{$attr_name};
714 $seen_attr{$attr_name}++;
715 push @attrs => $meta->get_attribute($attr_name);
721 sub find_attribute_by_name {
722 my ($self, $attr_name) = @_;
723 # keep a record of what we have seen
724 # here, this will handle all the
725 # inheritence issues because we are
726 # using the &class_precedence_list
728 foreach my $class ($self->class_precedence_list()) {
729 next if $seen_class{$class};
730 $seen_class{$class}++;
731 # fetch the meta-class ...
732 my $meta = $self->initialize($class);
733 return $meta->get_attribute($attr_name)
734 if $meta->has_attribute($attr_name);
742 sub is_immutable { 0 }
746 # the immutable version of a
747 # particular metaclass is
748 # really class-level data so
749 # we don't want to regenerate
750 # it any more than we need to
751 my $IMMUTABLE_METACLASS;
752 my %IMMUTABLE_OPTIONS;
755 %IMMUTABLE_OPTIONS = @_;
757 $IMMUTABLE_METACLASS ||= Class::MOP::Immutable->new($self, {
758 read_only => [qw/superclasses/],
766 remove_package_symbol
769 class_precedence_list => 'ARRAY',
770 compute_all_applicable_attributes => 'ARRAY',
771 get_meta_instance => 'SCALAR',
772 get_method_map => 'SCALAR',
776 $IMMUTABLE_METACLASS->make_metaclass_immutable($self, %IMMUTABLE_OPTIONS);
781 return if $self->is_mutable;
782 $IMMUTABLE_METACLASS->make_metaclass_mutable($self, %IMMUTABLE_OPTIONS);
795 Class::MOP::Class - Class Meta Object
799 # assuming that class Foo
800 # has been defined, you can
802 # use this for introspection ...
804 # add a method to Foo ...
805 Foo->meta->add_method('bar' => sub { ... })
807 # get a list of all the classes searched
808 # the method dispatcher in the correct order
809 Foo->meta->class_precedence_list()
811 # remove a method from Foo
812 Foo->meta->remove_method('bar');
814 # or use this to actually create classes ...
816 Class::MOP::Class->create('Bar' => (
818 superclasses => [ 'Foo' ],
820 Class::MOP:::Attribute->new('$bar'),
821 Class::MOP:::Attribute->new('$baz'),
824 calculate_bar => sub { ... },
825 construct_baz => sub { ... }
831 This is the largest and currently most complex part of the Perl 5
832 meta-object protocol. It controls the introspection and
833 manipulation of Perl 5 classes (and it can create them too). The
834 best way to understand what this module can do, is to read the
835 documentation for each of it's methods.
839 =head2 Self Introspection
845 This will return a B<Class::MOP::Class> instance which is related
846 to this class. Thereby allowing B<Class::MOP::Class> to actually
849 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
850 bootstrap this module by installing a number of attribute meta-objects
851 into it's metaclass. This will allow this class to reap all the benifits
852 of the MOP when subclassing it.
856 =head2 Class construction
858 These methods will handle creating B<Class::MOP::Class> objects,
859 which can be used to both create new classes, and analyze
860 pre-existing classes.
862 This module will internally store references to all the instances
863 you create with these methods, so that they do not need to be
864 created any more than nessecary. Basically, they are singletons.
868 =item B<create ($package_name,
869 version =E<gt> ?$version,
870 authority =E<gt> ?$authority,
871 superclasses =E<gt> ?@superclasses,
872 methods =E<gt> ?%methods,
873 attributes =E<gt> ?%attributes)>
875 This returns a B<Class::MOP::Class> object, bringing the specified
876 C<$package_name> into existence and adding any of the C<$version>,
877 C<$authority>, C<@superclasses>, C<%methods> and C<%attributes> to
880 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
881 methods =E<gt> ?%methods,
882 attributes =E<gt> ?%attributes)>
884 This will create an anonymous class, it works much like C<create> but
885 it does not need a C<$package_name>. Instead it will create a suitably
886 unique package name for you to stash things into.
888 On very important distinction is that anon classes are destroyed once
889 the metaclass they are attached to goes out of scope. In the DESTROY
890 method, the created package will be removed from the symbol table.
892 It is also worth noting that any instances created with an anon-class
893 will keep a special reference to the anon-meta which will prevent the
894 anon-class from going out of scope until all instances of it have also
895 been destroyed. This however only works for HASH based instance types,
896 as we use a special reserved slot (C<__MOP__>) to store this.
898 =item B<initialize ($package_name, %options)>
900 This initializes and returns returns a B<Class::MOP::Class> object
901 for a given a C<$package_name>.
903 =item B<reinitialize ($package_name, %options)>
905 This removes the old metaclass, and creates a new one in it's place.
906 Do B<not> use this unless you really know what you are doing, it could
907 very easily make a very large mess of your program.
909 =item B<construct_class_instance (%options)>
911 This will construct an instance of B<Class::MOP::Class>, it is
912 here so that we can actually "tie the knot" for B<Class::MOP::Class>
913 to use C<construct_instance> once all the bootstrapping is done. This
914 method is used internally by C<initialize> and should never be called
915 from outside of that method really.
917 =item B<check_metaclass_compatability>
919 This method is called as the very last thing in the
920 C<construct_class_instance> method. This will check that the
921 metaclass you are creating is compatible with the metaclasses of all
922 your ancestors. For more inforamtion about metaclass compatibility
923 see the C<About Metaclass compatibility> section in L<Class::MOP>.
927 =head2 Object instance construction and cloning
929 These methods are B<entirely optional>, it is up to you whether you want
934 =item B<instance_metaclass>
936 =item B<get_meta_instance>
938 =item B<new_object (%params)>
940 This is a convience method for creating a new object of the class, and
941 blessing it into the appropriate package as well. Ideally your class
942 would call a C<new> this method like so:
945 my ($class, %param) = @_;
946 $class->meta->new_object(%params);
949 Of course the ideal place for this would actually be in C<UNIVERSAL::>
950 but that is considered bad style, so we do not do that.
952 =item B<construct_instance (%params)>
954 This method is used to construct an instace structure suitable for
955 C<bless>-ing into your package of choice. It works in conjunction
956 with the Attribute protocol to collect all applicable attributes.
958 This will construct and instance using a HASH ref as storage
959 (currently only HASH references are supported). This will collect all
960 the applicable attributes and layout out the fields in the HASH ref,
961 it will then initialize them using either use the corresponding key
962 in C<%params> or any default value or initializer found in the
963 attribute meta-object.
965 =item B<clone_object ($instance, %params)>
967 This is a convience method for cloning an object instance, then
968 blessing it into the appropriate package. This method will call
969 C<clone_instance>, which performs a shallow copy of the object,
970 see that methods documentation for more details. Ideally your
971 class would call a C<clone> this method like so:
974 my ($self, %param) = @_;
975 $self->meta->clone_object($self, %params);
978 Of course the ideal place for this would actually be in C<UNIVERSAL::>
979 but that is considered bad style, so we do not do that.
981 =item B<clone_instance($instance, %params)>
983 This method is a compliment of C<construct_instance> (which means if
984 you override C<construct_instance>, you need to override this one too),
985 and clones the instance shallowly.
987 The cloned structure returned is (like with C<construct_instance>) an
988 unC<bless>ed HASH reference, it is your responsibility to then bless
989 this cloned structure into the right class (which C<clone_object> will
992 As of 0.11, this method will clone the C<$instance> structure shallowly,
993 as opposed to the deep cloning implemented in prior versions. After much
994 thought, research and discussion, I have decided that anything but basic
995 shallow cloning is outside the scope of the meta-object protocol. I
996 think Yuval "nothingmuch" Kogman put it best when he said that cloning
997 is too I<context-specific> to be part of the MOP.
1001 =head2 Informational
1003 These are a few predicate methods for asking information about the class.
1007 =item B<is_anon_class>
1009 This returns true if the class is a C<Class::MOP::Class> created anon class.
1013 This returns true if the class is still mutable.
1015 =item B<is_immutable>
1017 This returns true if the class has been made immutable.
1021 =head2 Inheritance Relationships
1025 =item B<superclasses (?@superclasses)>
1027 This is a read-write attribute which represents the superclass
1028 relationships of the class the B<Class::MOP::Class> instance is
1029 associated with. Basically, it can get and set the C<@ISA> for you.
1032 Perl will occasionally perform some C<@ISA> and method caching, if
1033 you decide to change your superclass relationship at runtime (which
1034 is quite insane and very much not recommened), then you should be
1035 aware of this and the fact that this module does not make any
1036 attempt to address this issue.
1038 =item B<class_precedence_list>
1040 This computes the a list of all the class's ancestors in the same order
1041 in which method dispatch will be done. This is similair to
1042 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
1050 =item B<get_method_map>
1052 =item B<method_metaclass>
1054 =item B<add_method ($method_name, $method)>
1056 This will take a C<$method_name> and CODE reference to that
1057 C<$method> and install it into the class's package.
1060 This does absolutely nothing special to C<$method>
1061 other than use B<Sub::Name> to make sure it is tagged with the
1062 correct name, and therefore show up correctly in stack traces and
1065 =item B<alias_method ($method_name, $method)>
1067 This will take a C<$method_name> and CODE reference to that
1068 C<$method> and alias the method into the class's package.
1071 Unlike C<add_method>, this will B<not> try to name the
1072 C<$method> using B<Sub::Name>, it only aliases the method in
1073 the class's package.
1075 =item B<has_method ($method_name)>
1077 This just provides a simple way to check if the class implements
1078 a specific C<$method_name>. It will I<not> however, attempt to check
1079 if the class inherits the method (use C<UNIVERSAL::can> for that).
1081 This will correctly handle functions defined outside of the package
1082 that use a fully qualified name (C<sub Package::name { ... }>).
1084 This will correctly handle functions renamed with B<Sub::Name> and
1085 installed using the symbol tables. However, if you are naming the
1086 subroutine outside of the package scope, you must use the fully
1087 qualified name, including the package name, for C<has_method> to
1088 correctly identify it.
1090 This will attempt to correctly ignore functions imported from other
1091 packages using B<Exporter>. It breaks down if the function imported
1092 is an C<__ANON__> sub (such as with C<use constant>), which very well
1093 may be a valid method being applied to the class.
1095 In short, this method cannot always be trusted to determine if the
1096 C<$method_name> is actually a method. However, it will DWIM about
1097 90% of the time, so it's a small trade off I think.
1099 =item B<get_method ($method_name)>
1101 This will return a Class::MOP::Method instance related to the specified
1102 C<$method_name>, or return undef if that method does not exist.
1104 The Class::MOP::Method is codifiable, so you can use it like a normal
1105 CODE reference, see L<Class::MOP::Method> for more information.
1107 =item B<find_method_by_name ($method_name>
1109 This will return a CODE reference of the specified C<$method_name>,
1110 or return undef if that method does not exist.
1112 Unlike C<get_method> this will also look in the superclasses.
1114 =item B<remove_method ($method_name)>
1116 This will attempt to remove a given C<$method_name> from the class.
1117 It will return the CODE reference that it has removed, and will
1118 attempt to use B<Sub::Name> to clear the methods associated name.
1120 =item B<get_method_list>
1122 This will return a list of method names for all I<locally> defined
1123 methods. It does B<not> provide a list of all applicable methods,
1124 including any inherited ones. If you want a list of all applicable
1125 methods, use the C<compute_all_applicable_methods> method.
1127 =item B<compute_all_applicable_methods>
1129 This will return a list of all the methods names this class will
1130 respond to, taking into account inheritance. The list will be a list of
1131 HASH references, each one containing the following information; method
1132 name, the name of the class in which the method lives and a CODE
1133 reference for the actual method.
1135 =item B<find_all_methods_by_name ($method_name)>
1137 This will traverse the inheritence hierarchy and locate all methods
1138 with a given C<$method_name>. Similar to
1139 C<compute_all_applicable_methods> it returns a list of HASH references
1140 with the following information; method name (which will always be the
1141 same as C<$method_name>), the name of the class in which the method
1142 lives and a CODE reference for the actual method.
1144 The list of methods produced is a distinct list, meaning there are no
1145 duplicates in it. This is especially useful for things like object
1146 initialization and destruction where you only want the method called
1147 once, and in the correct order.
1149 =item B<find_next_method_by_name ($method_name)>
1151 This will return the first method to match a given C<$method_name> in
1152 the superclasses, this is basically equivalent to calling
1153 C<SUPER::$method_name>, but it can be dispatched at runtime.
1157 =head2 Method Modifiers
1159 Method modifiers are a concept borrowed from CLOS, in which a method
1160 can be wrapped with I<before>, I<after> and I<around> method modifiers
1161 that will be called everytime the method is called.
1163 =head3 How method modifiers work?
1165 Method modifiers work by wrapping the original method and then replacing
1166 it in the classes symbol table. The wrappers will handle calling all the
1167 modifiers in the appropariate orders and preserving the calling context
1168 for the original method.
1170 Each method modifier serves a particular purpose, which may not be
1171 obvious to users of other method wrapping modules. To start with, the
1172 return values of I<before> and I<after> modifiers are ignored. This is
1173 because thier purpose is B<not> to filter the input and output of the
1174 primary method (this is done with an I<around> modifier). This may seem
1175 like an odd restriction to some, but doing this allows for simple code
1176 to be added at the begining or end of a method call without jeapordizing
1177 the normal functioning of the primary method or placing any extra
1178 responsibility on the code of the modifier. Of course if you have more
1179 complex needs, then use the I<around> modifier, which uses a variation
1180 of continutation passing style to allow for a high degree of flexibility.
1182 Before and around modifiers are called in last-defined-first-called order,
1183 while after modifiers are called in first-defined-first-called order. So
1184 the call tree might looks something like this:
1194 To see examples of using method modifiers, see the following examples
1195 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1196 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1197 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1199 =head3 What is the performance impact?
1201 Of course there is a performance cost associated with method modifiers,
1202 but we have made every effort to make that cost be directly proportional
1203 to the amount of modifier features you utilize.
1205 The wrapping method does it's best to B<only> do as much work as it
1206 absolutely needs to. In order to do this we have moved some of the
1207 performance costs to set-up time, where they are easier to amortize.
1209 All this said, my benchmarks have indicated the following:
1211 simple wrapper with no modifiers 100% slower
1212 simple wrapper with simple before modifier 400% slower
1213 simple wrapper with simple after modifier 450% slower
1214 simple wrapper with simple around modifier 500-550% slower
1215 simple wrapper with all 3 modifiers 1100% slower
1217 These numbers may seem daunting, but you must remember, every feature
1218 comes with some cost. To put things in perspective, just doing a simple
1219 C<AUTOLOAD> which does nothing but extract the name of the method called
1220 and return it costs about 400% over a normal method call.
1224 =item B<add_before_method_modifier ($method_name, $code)>
1226 This will wrap the method at C<$method_name> and the supplied C<$code>
1227 will be passed the C<@_> arguments, and called before the original
1228 method is called. As specified above, the return value of the I<before>
1229 method modifiers is ignored, and it's ability to modify C<@_> is
1230 fairly limited. If you need to do either of these things, use an
1231 C<around> method modifier.
1233 =item B<add_after_method_modifier ($method_name, $code)>
1235 This will wrap the method at C<$method_name> so that the original
1236 method will be called, it's return values stashed, and then the
1237 supplied C<$code> will be passed the C<@_> arguments, and called.
1238 As specified above, the return value of the I<after> method
1239 modifiers is ignored, and it cannot modify the return values of
1240 the original method. If you need to do either of these things, use an
1241 C<around> method modifier.
1243 =item B<add_around_method_modifier ($method_name, $code)>
1245 This will wrap the method at C<$method_name> so that C<$code>
1246 will be called and passed the original method as an extra argument
1247 at the begining of the C<@_> argument list. This is a variation of
1248 continuation passing style, where the function prepended to C<@_>
1249 can be considered a continuation. It is up to C<$code> if it calls
1250 the original method or not, there is no restriction on what the
1251 C<$code> can or cannot do.
1257 It should be noted that since there is no one consistent way to define
1258 the attributes of a class in Perl 5. These methods can only work with
1259 the information given, and can not easily discover information on
1260 their own. See L<Class::MOP::Attribute> for more details.
1264 =item B<attribute_metaclass>
1266 =item B<get_attribute_map>
1268 =item B<add_attribute ($attribute_meta_object | $attribute_name, %attribute_spec)>
1270 This stores the C<$attribute_meta_object> (or creates one from the
1271 C<$attribute_name> and C<%attribute_spec>) in the B<Class::MOP::Class>
1272 instance associated with the given class. Unlike methods, attributes
1273 within the MOP are stored as meta-information only. They will be used
1274 later to construct instances from (see C<construct_instance> above).
1275 More details about the attribute meta-objects can be found in the
1276 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1279 It should be noted that any accessor, reader/writer or predicate
1280 methods which the C<$attribute_meta_object> has will be installed
1281 into the class at this time.
1284 If an attribute already exists for C<$attribute_name>, the old one
1285 will be removed (as well as removing all it's accessors), and then
1288 =item B<has_attribute ($attribute_name)>
1290 Checks to see if this class has an attribute by the name of
1291 C<$attribute_name> and returns a boolean.
1293 =item B<get_attribute ($attribute_name)>
1295 Returns the attribute meta-object associated with C<$attribute_name>,
1296 if none is found, it will return undef.
1298 =item B<remove_attribute ($attribute_name)>
1300 This will remove the attribute meta-object stored at
1301 C<$attribute_name>, then return the removed attribute meta-object.
1304 Removing an attribute will only affect future instances of
1305 the class, it will not make any attempt to remove the attribute from
1306 any existing instances of the class.
1308 It should be noted that any accessor, reader/writer or predicate
1309 methods which the attribute meta-object stored at C<$attribute_name>
1310 has will be removed from the class at this time. This B<will> make
1311 these attributes somewhat inaccessable in previously created
1312 instances. But if you are crazy enough to do this at runtime, then
1313 you are crazy enough to deal with something like this :).
1315 =item B<get_attribute_list>
1317 This returns a list of attribute names which are defined in the local
1318 class. If you want a list of all applicable attributes for a class,
1319 use the C<compute_all_applicable_attributes> method.
1321 =item B<compute_all_applicable_attributes>
1323 This will traverse the inheritance heirachy and return a list of all
1324 the applicable attributes for this class. It does not construct a
1325 HASH reference like C<compute_all_applicable_methods> because all
1326 that same information is discoverable through the attribute
1329 =item B<find_attribute_by_name ($attr_name)>
1331 This method will traverse the inheritance heirachy and find the
1332 first attribute whose name matches C<$attr_name>, then return it.
1333 It will return undef if nothing is found.
1337 =head2 Class Immutability
1341 =item B<make_immutable (%options)>
1343 This method will invoke a tranforamtion upon the class which will
1344 make it immutable. Details of this transformation can be found in
1345 the L<Class::MOP::Immutable> documentation.
1347 =item B<make_mutable>
1349 This method will reverse tranforamtion upon the class which
1356 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1358 =head1 COPYRIGHT AND LICENSE
1360 Copyright 2006, 2007 by Infinity Interactive, Inc.
1362 L<http://www.iinteractive.com>
1364 This library is free software; you can redistribute it and/or modify
1365 it under the same terms as Perl itself.