2 package Class::MOP::Class;
8 use Scalar::Util 'blessed', 'reftype';
9 use Sub::Name 'subname';
10 use B 'svref_2object';
12 our $VERSION = '0.14';
14 use Class::MOP::Instance;
18 sub meta { Class::MOP::Class->initialize(blessed($_[0]) || $_[0]) }
23 # Metaclasses are singletons, so we cache them here.
24 # there is no need to worry about destruction though
25 # because they should die only when the program dies.
26 # After all, do package definitions even get reaped?
29 # means of accessing all the metaclasses that have
30 # been initialized thus far (for mugwumps obj browser)
31 sub get_all_metaclasses { %METAS }
32 sub get_all_metaclass_instances { values %METAS }
33 sub get_all_metaclass_names { keys %METAS }
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->construct_class_instance(':package' => $package_name, @_);
43 # NOTE: (meta-circularity)
44 # this is a special form of &construct_instance
45 # (see below), which is used to construct class
46 # meta-object instances for any Class::MOP::*
47 # class. All other classes will use the more
48 # normal &construct_instance.
49 sub construct_class_instance {
52 my $package_name = $options{':package'};
53 (defined $package_name && $package_name)
54 || confess "You must pass a package name";
56 # return the metaclass if we have it cached,
57 # and it is still defined (it has not been
58 # reaped by DESTROY yet, which can happen
59 # annoyingly enough during global destruction)
60 return $METAS{$package_name}
61 if exists $METAS{$package_name} && defined $METAS{$package_name};
62 $class = blessed($class) || $class;
63 # now create the metaclass
65 if ($class =~ /^Class::MOP::/) {
67 '$:package' => $package_name,
69 '$:attribute_metaclass' => $options{':attribute_metaclass'} || 'Class::MOP::Attribute',
70 '$:method_metaclass' => $options{':method_metaclass'} || 'Class::MOP::Method',
71 '$:instance_metaclass' => $options{':instance_metaclass'} || 'Class::MOP::Instance',
76 # it is safe to use meta here because
77 # class will always be a subclass of
78 # Class::MOP::Class, which defines meta
79 $meta = bless $class->meta->construct_instance(%options) => $class
81 # and check the metaclass compatibility
82 $meta->check_metaclass_compatability();
83 $METAS{$package_name} = $meta;
86 sub check_metaclass_compatability {
89 # this is always okay ...
90 return if blessed($self) eq 'Class::MOP::Class';
92 my @class_list = $self->class_precedence_list;
93 shift @class_list; # shift off $self->name
95 foreach my $class_name (@class_list) {
96 my $meta = $METAS{$class_name} || next;
97 ($self->isa(blessed($meta)))
98 || confess $self->name . "->meta => (" . (blessed($self)) . ")" .
99 " is not compatible with the " .
100 $class_name . "->meta => (" . (blessed($meta)) . ")";
106 my ($class, $package_name, $package_version, %options) = @_;
107 (defined $package_name && $package_name)
108 || confess "You must pass a package name";
109 my $code = "package $package_name;";
110 $code .= "\$$package_name\:\:VERSION = '$package_version';"
111 if defined $package_version;
113 confess "creation of $package_name failed : $@" if $@;
114 my $meta = $class->initialize($package_name);
116 $meta->add_method('meta' => sub {
117 Class::MOP::Class->initialize(blessed($_[0]) || $_[0]);
120 $meta->superclasses(@{$options{superclasses}})
121 if exists $options{superclasses};
123 # process attributes first, so that they can
124 # install accessors, but locally defined methods
125 # can then overwrite them. It is maybe a little odd, but
126 # I think this should be the order of things.
127 if (exists $options{attributes}) {
128 foreach my $attr (@{$options{attributes}}) {
129 $meta->add_attribute($attr);
132 if (exists $options{methods}) {
133 foreach my $method_name (keys %{$options{methods}}) {
134 $meta->add_method($method_name, $options{methods}->{$method_name});
142 # this should be sufficient, if you have a
143 # use case where it is not, write a test and
145 my $ANON_CLASS_SERIAL = 0;
147 sub create_anon_class {
148 my ($class, %options) = @_;
149 my $package_name = 'Class::MOP::Class::__ANON__::SERIAL::' . ++$ANON_CLASS_SERIAL;
150 return $class->create($package_name, '0.00', %options);
157 # all these attribute readers will be bootstrapped
158 # away in the Class::MOP bootstrap section
160 sub name { $_[0]->{'$:package'} }
161 sub get_attribute_map { $_[0]->{'%:attributes'} }
162 sub attribute_metaclass { $_[0]->{'$:attribute_metaclass'} }
163 sub method_metaclass { $_[0]->{'$:method_metaclass'} }
164 sub instance_metaclass { $_[0]->{'$:instance_metaclass'} }
166 # Instance Construction & Cloning
171 # we need to protect the integrity of the
172 # Class::MOP::Class singletons here, so we
173 # delegate this to &construct_class_instance
174 # which will deal with the singletons
175 return $class->construct_class_instance(@_)
176 if $class->name->isa('Class::MOP::Class');
177 return $class->construct_instance(@_);
180 sub construct_instance {
181 my ($class, %params) = @_;
182 my $instance = $class->get_meta_instance->create_instance();
183 foreach my $attr ($class->compute_all_applicable_attributes()) {
184 $attr->initialize_instance_slot($instance, \%params);
189 sub get_meta_instance {
191 $class->{':instance_meta_object_cache'} ||= $class->instance_metaclass->new($class);
196 my $instance = shift;
197 (blessed($instance) && $instance->isa($class->name))
198 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
200 # we need to protect the integrity of the
201 # Class::MOP::Class singletons here, they
202 # should not be cloned.
203 return $instance if $instance->isa('Class::MOP::Class');
204 bless $class->clone_instance($instance, @_) => blessed($instance);
208 my ($class, $instance, %params) = @_;
210 || confess "You can only clone instances, \$self is not a blessed instance";
211 my $clone = { %$instance, %params };
217 # &name should be here too, but it is above
218 # because it gets bootstrapped away
222 ${$self->get_package_variable('$VERSION')};
232 @{$self->name . '::ISA'} = @supers;
234 @{$self->name . '::ISA'};
237 sub class_precedence_list {
240 # We need to check for ciruclar inheirtance here.
241 # This will do nothing if all is well, and blow
242 # up otherwise. Yes, it's an ugly hack, better
243 # suggestions are welcome.
244 { ($self->name || return)->isa('This is a test for circular inheritance') }
245 # ... and now back to our regularly scheduled program
250 # we grab the metaclass from the %METAS
251 # hash here to save the initialize() call
252 # if we can, but it is not always possible
253 ($METAS{$_} || $self->initialize($_))->class_precedence_list()
254 } $self->superclasses()
261 my ($self, $method_name, $method) = @_;
262 (defined $method_name && $method_name)
263 || confess "You must define a method name";
264 # use reftype here to allow for blessed subs ...
265 ('CODE' eq (reftype($method) || ''))
266 || confess "Your code block must be a CODE reference";
267 my $full_method_name = ($self->name . '::' . $method_name);
269 $method = $self->method_metaclass->wrap($method) unless blessed($method);
272 no warnings 'redefine';
273 *{$full_method_name} = subname $full_method_name => $method;
277 my $fetch_and_prepare_method = sub {
278 my ($self, $method_name) = @_;
280 my $method = $self->get_method($method_name);
281 # if we dont have local ...
283 # make sure this method even exists ...
284 ($self->find_next_method_by_name($method_name))
285 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
286 # if so, then create a local which just
287 # calls the next applicable method ...
288 $self->add_method($method_name => sub {
289 $self->find_next_method_by_name($method_name)->(@_);
291 $method = $self->get_method($method_name);
294 # now make sure we wrap it properly
295 # (if it isnt already)
296 unless ($method->isa('Class::MOP::Method::Wrapped')) {
297 $method = Class::MOP::Method::Wrapped->wrap($method);
298 $self->add_method($method_name => $method);
303 sub add_before_method_modifier {
304 my ($self, $method_name, $method_modifier) = @_;
305 (defined $method_name && $method_name)
306 || confess "You must pass in a method name";
307 my $method = $fetch_and_prepare_method->($self, $method_name);
308 $method->add_before_modifier(subname ':before' => $method_modifier);
311 sub add_after_method_modifier {
312 my ($self, $method_name, $method_modifier) = @_;
313 (defined $method_name && $method_name)
314 || confess "You must pass in a method name";
315 my $method = $fetch_and_prepare_method->($self, $method_name);
316 $method->add_after_modifier(subname ':after' => $method_modifier);
319 sub add_around_method_modifier {
320 my ($self, $method_name, $method_modifier) = @_;
321 (defined $method_name && $method_name)
322 || confess "You must pass in a method name";
323 my $method = $fetch_and_prepare_method->($self, $method_name);
324 $method->add_around_modifier(subname ':around' => $method_modifier);
328 # the methods above used to be named like this:
329 # ${pkg}::${method}:(before|after|around)
330 # but this proved problematic when using one modifier
331 # to wrap multiple methods (something which is likely
332 # to happen pretty regularly IMO). So instead of naming
333 # it like this, I have chosen to just name them purely
334 # with their modifier names, like so:
335 # :(before|after|around)
336 # The fact is that in a stack trace, it will be fairly
337 # evident from the context what method they are attached
338 # to, and so don't need the fully qualified name.
342 my ($self, $method_name, $method) = @_;
343 (defined $method_name && $method_name)
344 || confess "You must define a method name";
345 # use reftype here to allow for blessed subs ...
346 ('CODE' eq (reftype($method) || ''))
347 || confess "Your code block must be a CODE reference";
348 my $full_method_name = ($self->name . '::' . $method_name);
350 $method = $self->method_metaclass->wrap($method) unless blessed($method);
353 no warnings 'redefine';
354 *{$full_method_name} = $method;
358 my ($self, $method_name) = @_;
359 (defined $method_name && $method_name)
360 || confess "You must define a method name";
362 my $sub_name = ($self->name . '::' . $method_name);
365 return 0 if !defined(&{$sub_name});
366 my $method = \&{$sub_name};
367 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
368 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
370 # at this point we are relatively sure
371 # it is our method, so we bless/wrap it
372 $self->method_metaclass->wrap($method) unless blessed($method);
377 my ($self, $method_name) = @_;
378 (defined $method_name && $method_name)
379 || confess "You must define a method name";
381 return unless $self->has_method($method_name);
384 return \&{$self->name . '::' . $method_name};
388 my ($self, $method_name) = @_;
389 (defined $method_name && $method_name)
390 || confess "You must define a method name";
392 my $removed_method = $self->get_method($method_name);
395 delete ${$self->name . '::'}{$method_name}
396 if defined $removed_method;
398 return $removed_method;
401 sub get_method_list {
404 grep { $self->has_method($_) } %{$self->name . '::'};
407 sub compute_all_applicable_methods {
410 # keep a record of what we have seen
411 # here, this will handle all the
412 # inheritence issues because we are
413 # using the &class_precedence_list
414 my (%seen_class, %seen_method);
415 foreach my $class ($self->class_precedence_list()) {
416 next if $seen_class{$class};
417 $seen_class{$class}++;
418 # fetch the meta-class ...
419 my $meta = $self->initialize($class);
420 foreach my $method_name ($meta->get_method_list()) {
421 next if exists $seen_method{$method_name};
422 $seen_method{$method_name}++;
424 name => $method_name,
426 code => $meta->get_method($method_name)
433 sub find_all_methods_by_name {
434 my ($self, $method_name) = @_;
435 (defined $method_name && $method_name)
436 || confess "You must define a method name to find";
438 # keep a record of what we have seen
439 # here, this will handle all the
440 # inheritence issues because we are
441 # using the &class_precedence_list
443 foreach my $class ($self->class_precedence_list()) {
444 next if $seen_class{$class};
445 $seen_class{$class}++;
446 # fetch the meta-class ...
447 my $meta = $self->initialize($class);
449 name => $method_name,
451 code => $meta->get_method($method_name)
452 } if $meta->has_method($method_name);
457 sub find_next_method_by_name {
458 my ($self, $method_name) = @_;
459 (defined $method_name && $method_name)
460 || confess "You must define a method name to find";
461 # keep a record of what we have seen
462 # here, this will handle all the
463 # inheritence issues because we are
464 # using the &class_precedence_list
466 my @cpl = $self->class_precedence_list();
467 shift @cpl; # discard ourselves
468 foreach my $class (@cpl) {
469 next if $seen_class{$class};
470 $seen_class{$class}++;
471 # fetch the meta-class ...
472 my $meta = $self->initialize($class);
473 return $meta->get_method($method_name)
474 if $meta->has_method($method_name);
483 # either we have an attribute object already
484 # or we need to create one from the args provided
485 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
486 # make sure it is derived from the correct type though
487 ($attribute->isa('Class::MOP::Attribute'))
488 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
489 $attribute->attach_to_class($self);
490 $attribute->install_accessors();
491 $self->get_attribute_map->{$attribute->name} = $attribute;
495 my ($self, $attribute_name) = @_;
496 (defined $attribute_name && $attribute_name)
497 || confess "You must define an attribute name";
498 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
502 my ($self, $attribute_name) = @_;
503 (defined $attribute_name && $attribute_name)
504 || confess "You must define an attribute name";
506 # we used to say `if $self->has_attribute($attribute_name)`
507 # here, but since get_attribute is called so often, we
508 # eliminate the function call here
509 return $self->{'%:attributes'}->{$attribute_name}
510 if exists $self->{'%:attributes'}->{$attribute_name};
514 sub remove_attribute {
515 my ($self, $attribute_name) = @_;
516 (defined $attribute_name && $attribute_name)
517 || confess "You must define an attribute name";
518 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
519 return unless defined $removed_attribute;
520 delete $self->get_attribute_map->{$attribute_name};
521 $removed_attribute->remove_accessors();
522 $removed_attribute->detach_from_class();
523 return $removed_attribute;
526 sub get_attribute_list {
529 # We don't use get_attribute_map here because
530 # we ask for the attribute list quite often
531 # in compute_all_applicable_attributes, so
532 # eliminating the function call helps
533 keys %{$self->{'%:attributes'}};
536 sub compute_all_applicable_attributes {
539 # keep a record of what we have seen
540 # here, this will handle all the
541 # inheritence issues because we are
542 # using the &class_precedence_list
543 my (%seen_class, %seen_attr);
544 foreach my $class ($self->class_precedence_list()) {
545 next if $seen_class{$class};
546 $seen_class{$class}++;
547 # fetch the meta-class ...
549 # we grab the metaclass from the %METAS
550 # hash here to save the initialize() call
551 my $meta = $METAS{$class};
552 foreach my $attr_name ($meta->get_attribute_list()) {
553 next if exists $seen_attr{$attr_name};
554 $seen_attr{$attr_name}++;
555 push @attrs => $meta->get_attribute($attr_name);
561 sub find_attribute_by_name {
562 my ($self, $attr_name) = @_;
563 # keep a record of what we have seen
564 # here, this will handle all the
565 # inheritence issues because we are
566 # using the &class_precedence_list
568 foreach my $class ($self->class_precedence_list()) {
569 next if $seen_class{$class};
570 $seen_class{$class}++;
571 # fetch the meta-class ...
572 my $meta = $self->initialize($class);
573 return $meta->get_attribute($attr_name)
574 if $meta->has_attribute($attr_name);
581 sub add_package_variable {
582 my ($self, $variable, $initial_value) = @_;
583 (defined $variable && $variable =~ /^[\$\@\%]/)
584 || confess "variable name does not have a sigil";
586 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
587 if (defined $initial_value) {
589 *{$self->name . '::' . $name} = $initial_value;
595 # We HAVE to localize $@ or all
596 # hell breaks loose. It is not
597 # good, believe me, not good.
599 eval $sigil . $self->name . '::' . $name;
602 confess "Could not create package variable ($variable) because : $e" if $e;
606 sub has_package_variable {
607 my ($self, $variable) = @_;
608 (defined $variable && $variable =~ /^[\$\@\%]/)
609 || confess "variable name does not have a sigil";
610 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
612 defined ${$self->name . '::'}{$name} ? 1 : 0;
615 sub get_package_variable {
616 my ($self, $variable) = @_;
617 (defined $variable && $variable =~ /^[\$\@\%]/)
618 || confess "variable name does not have a sigil";
619 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
623 # We HAVE to localize $@ or all
624 # hell breaks loose. It is not
625 # good, believe me, not good.
627 $ref = eval '\\' . $sigil . $self->name . '::' . $name;
630 confess "Could not get the package variable ($variable) because : $e" if $e;
631 # if we didn't die, then we can return it
635 sub remove_package_variable {
636 my ($self, $variable) = @_;
637 (defined $variable && $variable =~ /^[\$\@\%]/)
638 || confess "variable name does not have a sigil";
639 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
641 delete ${$self->name . '::'}{$name};
652 Class::MOP::Class - Class Meta Object
656 # assuming that class Foo
657 # has been defined, you can
659 # use this for introspection ...
661 # add a method to Foo ...
662 Foo->meta->add_method('bar' => sub { ... })
664 # get a list of all the classes searched
665 # the method dispatcher in the correct order
666 Foo->meta->class_precedence_list()
668 # remove a method from Foo
669 Foo->meta->remove_method('bar');
671 # or use this to actually create classes ...
673 Class::MOP::Class->create('Bar' => '0.01' => (
674 superclasses => [ 'Foo' ],
676 Class::MOP:::Attribute->new('$bar'),
677 Class::MOP:::Attribute->new('$baz'),
680 calculate_bar => sub { ... },
681 construct_baz => sub { ... }
687 This is the largest and currently most complex part of the Perl 5
688 meta-object protocol. It controls the introspection and
689 manipulation of Perl 5 classes (and it can create them too). The
690 best way to understand what this module can do, is to read the
691 documentation for each of it's methods.
695 =head2 Self Introspection
701 This will return a B<Class::MOP::Class> instance which is related
702 to this class. Thereby allowing B<Class::MOP::Class> to actually
705 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
706 bootstrap this module by installing a number of attribute meta-objects
707 into it's metaclass. This will allow this class to reap all the benifits
708 of the MOP when subclassing it.
710 =item B<get_all_metaclasses>
712 This will return an hash of all the metaclass instances that have
713 been cached by B<Class::MOP::Class> keyed by the package name.
715 =item B<get_all_metaclass_instances>
717 This will return an array of all the metaclass instances that have
718 been cached by B<Class::MOP::Class>.
720 =item B<get_all_metaclass_names>
722 This will return an array of all the metaclass names that have
723 been cached by B<Class::MOP::Class>.
727 =head2 Class construction
729 These methods will handle creating B<Class::MOP::Class> objects,
730 which can be used to both create new classes, and analyze
731 pre-existing classes.
733 This module will internally store references to all the instances
734 you create with these methods, so that they do not need to be
735 created any more than nessecary. Basically, they are singletons.
739 =item B<create ($package_name, ?$package_version,
740 superclasses =E<gt> ?@superclasses,
741 methods =E<gt> ?%methods,
742 attributes =E<gt> ?%attributes)>
744 This returns a B<Class::MOP::Class> object, bringing the specified
745 C<$package_name> into existence and adding any of the
746 C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
749 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
750 methods =E<gt> ?%methods,
751 attributes =E<gt> ?%attributes)>
753 This will create an anonymous class, it works much like C<create> but
754 it does not need a C<$package_name>. Instead it will create a suitably
755 unique package name for you to stash things into.
757 =item B<initialize ($package_name)>
759 This initializes and returns returns a B<Class::MOP::Class> object
760 for a given a C<$package_name>.
762 =item B<construct_class_instance (%options)>
764 This will construct an instance of B<Class::MOP::Class>, it is
765 here so that we can actually "tie the knot" for B<Class::MOP::Class>
766 to use C<construct_instance> once all the bootstrapping is done. This
767 method is used internally by C<initialize> and should never be called
768 from outside of that method really.
770 =item B<check_metaclass_compatability>
772 This method is called as the very last thing in the
773 C<construct_class_instance> method. This will check that the
774 metaclass you are creating is compatible with the metaclasses of all
775 your ancestors. For more inforamtion about metaclass compatibility
776 see the C<About Metaclass compatibility> section in L<Class::MOP>.
780 =head2 Object instance construction and cloning
782 These methods are B<entirely optional>, it is up to you whether you want
787 =item B<instance_metaclass>
789 =item B<get_meta_instance>
791 =item B<new_object (%params)>
793 This is a convience method for creating a new object of the class, and
794 blessing it into the appropriate package as well. Ideally your class
795 would call a C<new> this method like so:
798 my ($class, %param) = @_;
799 $class->meta->new_object(%params);
802 Of course the ideal place for this would actually be in C<UNIVERSAL::>
803 but that is considered bad style, so we do not do that.
805 =item B<construct_instance (%params)>
807 This method is used to construct an instace structure suitable for
808 C<bless>-ing into your package of choice. It works in conjunction
809 with the Attribute protocol to collect all applicable attributes.
811 This will construct and instance using a HASH ref as storage
812 (currently only HASH references are supported). This will collect all
813 the applicable attributes and layout out the fields in the HASH ref,
814 it will then initialize them using either use the corresponding key
815 in C<%params> or any default value or initializer found in the
816 attribute meta-object.
818 =item B<clone_object ($instance, %params)>
820 This is a convience method for cloning an object instance, then
821 blessing it into the appropriate package. This method will call
822 C<clone_instance>, which performs a shallow copy of the object,
823 see that methods documentation for more details. Ideally your
824 class would call a C<clone> this method like so:
827 my ($self, %param) = @_;
828 $self->meta->clone_object($self, %params);
831 Of course the ideal place for this would actually be in C<UNIVERSAL::>
832 but that is considered bad style, so we do not do that.
834 =item B<clone_instance($instance, %params)>
836 This method is a compliment of C<construct_instance> (which means if
837 you override C<construct_instance>, you need to override this one too),
838 and clones the instance shallowly.
840 The cloned structure returned is (like with C<construct_instance>) an
841 unC<bless>ed HASH reference, it is your responsibility to then bless
842 this cloned structure into the right class (which C<clone_object> will
845 As of 0.11, this method will clone the C<$instance> structure shallowly,
846 as opposed to the deep cloning implemented in prior versions. After much
847 thought, research and discussion, I have decided that anything but basic
848 shallow cloning is outside the scope of the meta-object protocol. I
849 think Yuval "nothingmuch" Kogman put it best when he said that cloning
850 is too I<context-specific> to be part of the MOP.
860 This is a read-only attribute which returns the package name for the
861 given B<Class::MOP::Class> instance.
865 This is a read-only attribute which returns the C<$VERSION> of the
866 package for the given B<Class::MOP::Class> instance.
870 =head2 Inheritance Relationships
874 =item B<superclasses (?@superclasses)>
876 This is a read-write attribute which represents the superclass
877 relationships of the class the B<Class::MOP::Class> instance is
878 associated with. Basically, it can get and set the C<@ISA> for you.
881 Perl will occasionally perform some C<@ISA> and method caching, if
882 you decide to change your superclass relationship at runtime (which
883 is quite insane and very much not recommened), then you should be
884 aware of this and the fact that this module does not make any
885 attempt to address this issue.
887 =item B<class_precedence_list>
889 This computes the a list of all the class's ancestors in the same order
890 in which method dispatch will be done. This is similair to
891 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
899 =item B<method_metaclass>
901 =item B<add_method ($method_name, $method)>
903 This will take a C<$method_name> and CODE reference to that
904 C<$method> and install it into the class's package.
907 This does absolutely nothing special to C<$method>
908 other than use B<Sub::Name> to make sure it is tagged with the
909 correct name, and therefore show up correctly in stack traces and
912 =item B<alias_method ($method_name, $method)>
914 This will take a C<$method_name> and CODE reference to that
915 C<$method> and alias the method into the class's package.
918 Unlike C<add_method>, this will B<not> try to name the
919 C<$method> using B<Sub::Name>, it only aliases the method in
922 =item B<has_method ($method_name)>
924 This just provides a simple way to check if the class implements
925 a specific C<$method_name>. It will I<not> however, attempt to check
926 if the class inherits the method (use C<UNIVERSAL::can> for that).
928 This will correctly handle functions defined outside of the package
929 that use a fully qualified name (C<sub Package::name { ... }>).
931 This will correctly handle functions renamed with B<Sub::Name> and
932 installed using the symbol tables. However, if you are naming the
933 subroutine outside of the package scope, you must use the fully
934 qualified name, including the package name, for C<has_method> to
935 correctly identify it.
937 This will attempt to correctly ignore functions imported from other
938 packages using B<Exporter>. It breaks down if the function imported
939 is an C<__ANON__> sub (such as with C<use constant>), which very well
940 may be a valid method being applied to the class.
942 In short, this method cannot always be trusted to determine if the
943 C<$method_name> is actually a method. However, it will DWIM about
944 90% of the time, so it's a small trade off I think.
946 =item B<get_method ($method_name)>
948 This will return a CODE reference of the specified C<$method_name>,
949 or return undef if that method does not exist.
951 =item B<remove_method ($method_name)>
953 This will attempt to remove a given C<$method_name> from the class.
954 It will return the CODE reference that it has removed, and will
955 attempt to use B<Sub::Name> to clear the methods associated name.
957 =item B<get_method_list>
959 This will return a list of method names for all I<locally> defined
960 methods. It does B<not> provide a list of all applicable methods,
961 including any inherited ones. If you want a list of all applicable
962 methods, use the C<compute_all_applicable_methods> method.
964 =item B<compute_all_applicable_methods>
966 This will return a list of all the methods names this class will
967 respond to, taking into account inheritance. The list will be a list of
968 HASH references, each one containing the following information; method
969 name, the name of the class in which the method lives and a CODE
970 reference for the actual method.
972 =item B<find_all_methods_by_name ($method_name)>
974 This will traverse the inheritence hierarchy and locate all methods
975 with a given C<$method_name>. Similar to
976 C<compute_all_applicable_methods> it returns a list of HASH references
977 with the following information; method name (which will always be the
978 same as C<$method_name>), the name of the class in which the method
979 lives and a CODE reference for the actual method.
981 The list of methods produced is a distinct list, meaning there are no
982 duplicates in it. This is especially useful for things like object
983 initialization and destruction where you only want the method called
984 once, and in the correct order.
986 =item B<find_next_method_by_name ($method_name)>
988 This will return the first method to match a given C<$method_name> in
989 the superclasses, this is basically equivalent to calling
990 C<SUPER::$method_name>, but it can be dispatched at runtime.
994 =head2 Method Modifiers
996 Method modifiers are a concept borrowed from CLOS, in which a method
997 can be wrapped with I<before>, I<after> and I<around> method modifiers
998 that will be called everytime the method is called.
1000 =head3 How method modifiers work?
1002 Method modifiers work by wrapping the original method and then replacing
1003 it in the classes symbol table. The wrappers will handle calling all the
1004 modifiers in the appropariate orders and preserving the calling context
1005 for the original method.
1007 Each method modifier serves a particular purpose, which may not be
1008 obvious to users of other method wrapping modules. To start with, the
1009 return values of I<before> and I<after> modifiers are ignored. This is
1010 because thier purpose is B<not> to filter the input and output of the
1011 primary method (this is done with an I<around> modifier). This may seem
1012 like an odd restriction to some, but doing this allows for simple code
1013 to be added at the begining or end of a method call without jeapordizing
1014 the normal functioning of the primary method or placing any extra
1015 responsibility on the code of the modifier. Of course if you have more
1016 complex needs, then use the I<around> modifier, which uses a variation
1017 of continutation passing style to allow for a high degree of flexibility.
1019 Before and around modifiers are called in last-defined-first-called order,
1020 while after modifiers are called in first-defined-first-called order. So
1021 the call tree might looks something like this:
1031 To see examples of using method modifiers, see the following examples
1032 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1033 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1034 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1036 =head3 What is the performance impact?
1038 Of course there is a performance cost associated with method modifiers,
1039 but we have made every effort to make that cost be directly proportional
1040 to the amount of modifier features you utilize.
1042 The wrapping method does it's best to B<only> do as much work as it
1043 absolutely needs to. In order to do this we have moved some of the
1044 performance costs to set-up time, where they are easier to amortize.
1046 All this said, my benchmarks have indicated the following:
1048 simple wrapper with no modifiers 100% slower
1049 simple wrapper with simple before modifier 400% slower
1050 simple wrapper with simple after modifier 450% slower
1051 simple wrapper with simple around modifier 500-550% slower
1052 simple wrapper with all 3 modifiers 1100% slower
1054 These numbers may seem daunting, but you must remember, every feature
1055 comes with some cost. To put things in perspective, just doing a simple
1056 C<AUTOLOAD> which does nothing but extract the name of the method called
1057 and return it costs about 400% over a normal method call.
1061 =item B<add_before_method_modifier ($method_name, $code)>
1063 This will wrap the method at C<$method_name> and the supplied C<$code>
1064 will be passed the C<@_> arguments, and called before the original
1065 method is called. As specified above, the return value of the I<before>
1066 method modifiers is ignored, and it's ability to modify C<@_> is
1067 fairly limited. If you need to do either of these things, use an
1068 C<around> method modifier.
1070 =item B<add_after_method_modifier ($method_name, $code)>
1072 This will wrap the method at C<$method_name> so that the original
1073 method will be called, it's return values stashed, and then the
1074 supplied C<$code> will be passed the C<@_> arguments, and called.
1075 As specified above, the return value of the I<after> method
1076 modifiers is ignored, and it cannot modify the return values of
1077 the original method. If you need to do either of these things, use an
1078 C<around> method modifier.
1080 =item B<add_around_method_modifier ($method_name, $code)>
1082 This will wrap the method at C<$method_name> so that C<$code>
1083 will be called and passed the original method as an extra argument
1084 at the begining of the C<@_> argument list. This is a variation of
1085 continuation passing style, where the function prepended to C<@_>
1086 can be considered a continuation. It is up to C<$code> if it calls
1087 the original method or not, there is no restriction on what the
1088 C<$code> can or cannot do.
1094 It should be noted that since there is no one consistent way to define
1095 the attributes of a class in Perl 5. These methods can only work with
1096 the information given, and can not easily discover information on
1097 their own. See L<Class::MOP::Attribute> for more details.
1101 =item B<attribute_metaclass>
1103 =item B<get_attribute_map>
1105 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1107 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1108 instance associated with the given class, and associates it with
1109 the C<$attribute_name>. Unlike methods, attributes within the MOP
1110 are stored as meta-information only. They will be used later to
1111 construct instances from (see C<construct_instance> above).
1112 More details about the attribute meta-objects can be found in the
1113 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1116 It should be noted that any accessor, reader/writer or predicate
1117 methods which the C<$attribute_meta_object> has will be installed
1118 into the class at this time.
1120 =item B<has_attribute ($attribute_name)>
1122 Checks to see if this class has an attribute by the name of
1123 C<$attribute_name> and returns a boolean.
1125 =item B<get_attribute ($attribute_name)>
1127 Returns the attribute meta-object associated with C<$attribute_name>,
1128 if none is found, it will return undef.
1130 =item B<remove_attribute ($attribute_name)>
1132 This will remove the attribute meta-object stored at
1133 C<$attribute_name>, then return the removed attribute meta-object.
1136 Removing an attribute will only affect future instances of
1137 the class, it will not make any attempt to remove the attribute from
1138 any existing instances of the class.
1140 It should be noted that any accessor, reader/writer or predicate
1141 methods which the attribute meta-object stored at C<$attribute_name>
1142 has will be removed from the class at this time. This B<will> make
1143 these attributes somewhat inaccessable in previously created
1144 instances. But if you are crazy enough to do this at runtime, then
1145 you are crazy enough to deal with something like this :).
1147 =item B<get_attribute_list>
1149 This returns a list of attribute names which are defined in the local
1150 class. If you want a list of all applicable attributes for a class,
1151 use the C<compute_all_applicable_attributes> method.
1153 =item B<compute_all_applicable_attributes>
1155 This will traverse the inheritance heirachy and return a list of all
1156 the applicable attributes for this class. It does not construct a
1157 HASH reference like C<compute_all_applicable_methods> because all
1158 that same information is discoverable through the attribute
1161 =item B<find_attribute_by_name ($attr_name)>
1163 This method will traverse the inheritance heirachy and find the
1164 first attribute whose name matches C<$attr_name>, then return it.
1165 It will return undef if nothing is found.
1169 =head2 Package Variables
1171 Since Perl's classes are built atop the Perl package system, it is
1172 fairly common to use package scoped variables for things like static
1173 class variables. The following methods are convience methods for
1174 the creation and inspection of package scoped variables.
1178 =item B<add_package_variable ($variable_name, ?$initial_value)>
1180 Given a C<$variable_name>, which must contain a leading sigil, this
1181 method will create that variable within the package which houses the
1182 class. It also takes an optional C<$initial_value>, which must be a
1183 reference of the same type as the sigil of the C<$variable_name>
1186 =item B<get_package_variable ($variable_name)>
1188 This will return a reference to the package variable in
1191 =item B<has_package_variable ($variable_name)>
1193 Returns true (C<1>) if there is a package variable defined for
1194 C<$variable_name>, and false (C<0>) otherwise.
1196 =item B<remove_package_variable ($variable_name)>
1198 This will attempt to remove the package variable at C<$variable_name>.
1204 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1206 =head1 COPYRIGHT AND LICENSE
1208 Copyright 2006 by Infinity Interactive, Inc.
1210 L<http://www.iinteractive.com>
1212 This library is free software; you can redistribute it and/or modify
1213 it under the same terms as Perl itself.