2 package Class::MOP::Class;
8 use Scalar::Util 'blessed', 'reftype';
9 use Sub::Name 'subname';
10 use B 'svref_2object';
12 our $VERSION = '0.12';
16 sub meta { Class::MOP::Class->initialize(blessed($_[0]) || $_[0]) }
21 # Metaclasses are singletons, so we cache them here.
22 # there is no need to worry about destruction though
23 # because they should die only when the program dies.
24 # After all, do package definitions even get reaped?
27 # means of accessing all the metaclasses that have
28 # been initialized thus far (for mugwumps obj browser)
29 sub get_all_metaclasses { %METAS }
30 sub get_all_metaclass_instances { values %METAS }
31 sub get_all_metaclass_names { keys %METAS }
35 my $package_name = shift;
36 (defined $package_name && $package_name && !blessed($package_name))
37 || confess "You must pass a package name and it cannot be blessed";
38 $class->construct_class_instance(':package' => $package_name, @_);
41 # NOTE: (meta-circularity)
42 # this is a special form of &construct_instance
43 # (see below), which is used to construct class
44 # meta-object instances for any Class::MOP::*
45 # class. All other classes will use the more
46 # normal &construct_instance.
47 sub construct_class_instance {
50 my $package_name = $options{':package'};
51 (defined $package_name && $package_name)
52 || confess "You must pass a package name";
54 # return the metaclass if we have it cached,
55 # and it is still defined (it has not been
56 # reaped by DESTROY yet, which can happen
57 # annoyingly enough during global destruction)
58 return $METAS{$package_name}
59 if exists $METAS{$package_name} && defined $METAS{$package_name};
60 $class = blessed($class) || $class;
61 # now create the metaclass
63 if ($class =~ /^Class::MOP::/) {
65 '$:package' => $package_name,
67 '$:attribute_metaclass' => $options{':attribute_metaclass'} || 'Class::MOP::Attribute',
68 '$:method_metaclass' => $options{':method_metaclass'} || 'Class::MOP::Method',
73 # it is safe to use meta here because
74 # class will always be a subclass of
75 # Class::MOP::Class, which defines meta
76 $meta = bless $class->meta->construct_instance(%options) => $class
78 # and check the metaclass compatibility
79 $meta->check_metaclass_compatability();
80 $METAS{$package_name} = $meta;
83 sub check_metaclass_compatability {
86 # this is always okay ...
87 return if blessed($self) eq 'Class::MOP::Class';
89 my @class_list = $self->class_precedence_list;
90 shift @class_list; # shift off $self->name
92 foreach my $class_name (@class_list) {
93 my $meta = $METAS{$class_name} || next;
94 ($self->isa(blessed($meta)))
95 || confess $self->name . "->meta => (" . (blessed($self)) . ")" .
96 " is not compatible with the " .
97 $class_name . "->meta => (" . (blessed($meta)) . ")";
103 my ($class, $package_name, $package_version, %options) = @_;
104 (defined $package_name && $package_name)
105 || confess "You must pass a package name";
106 my $code = "package $package_name;";
107 $code .= "\$$package_name\:\:VERSION = '$package_version';"
108 if defined $package_version;
110 confess "creation of $package_name failed : $@" if $@;
111 my $meta = $class->initialize($package_name);
113 $meta->add_method('meta' => sub {
114 Class::MOP::Class->initialize(blessed($_[0]) || $_[0]);
117 $meta->superclasses(@{$options{superclasses}})
118 if exists $options{superclasses};
120 # process attributes first, so that they can
121 # install accessors, but locally defined methods
122 # can then overwrite them. It is maybe a little odd, but
123 # I think this should be the order of things.
124 if (exists $options{attributes}) {
125 foreach my $attr (@{$options{attributes}}) {
126 $meta->add_attribute($attr);
129 if (exists $options{methods}) {
130 foreach my $method_name (keys %{$options{methods}}) {
131 $meta->add_method($method_name, $options{methods}->{$method_name});
139 # this should be sufficient, if you have a
140 # use case where it is not, write a test and
142 my $ANON_CLASS_SERIAL = 0;
144 sub create_anon_class {
145 my ($class, %options) = @_;
146 my $package_name = 'Class::MOP::Class::__ANON__::SERIAL::' . ++$ANON_CLASS_SERIAL;
147 return $class->create($package_name, '0.00', %options);
154 # all these attribute readers will be bootstrapped
155 # away in the Class::MOP bootstrap section
157 sub name { $_[0]->{'$:package'} }
158 sub get_attribute_map { $_[0]->{'%:attributes'} }
159 sub attribute_metaclass { $_[0]->{'$:attribute_metaclass'} }
160 sub method_metaclass { $_[0]->{'$:method_metaclass'} }
162 # Instance Construction & Cloning
167 # we need to protect the integrity of the
168 # Class::MOP::Class singletons here, so we
169 # delegate this to &construct_class_instance
170 # which will deal with the singletons
171 return $class->construct_class_instance(@_)
172 if $class->name->isa('Class::MOP::Class');
173 bless $class->construct_instance(@_) => $class->name;
176 sub construct_instance {
177 my ($class, %params) = @_;
179 foreach my $attr ($class->compute_all_applicable_attributes()) {
180 $attr->initialize_instance_slot($class, $instance, \%params);
187 my $instance = shift;
188 (blessed($instance) && $instance->isa($class->name))
189 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
191 # we need to protect the integrity of the
192 # Class::MOP::Class singletons here, they
193 # should not be cloned.
194 return $instance if $instance->isa('Class::MOP::Class');
195 bless $class->clone_instance($instance, @_) => blessed($instance);
199 my ($class, $instance, %params) = @_;
201 || confess "You can only clone instances, \$self is not a blessed instance";
202 my $clone = { %$instance, %params };
208 # &name should be here too, but it is above
209 # because it gets bootstrapped away
213 ${$self->get_package_variable('$VERSION')};
223 @{$self->name . '::ISA'} = @supers;
225 @{$self->name . '::ISA'};
228 sub class_precedence_list {
231 # We need to check for ciruclar inheirtance here.
232 # This will do nothing if all is well, and blow
233 # up otherwise. Yes, it's an ugly hack, better
234 # suggestions are welcome.
235 { $self->name->isa('This is a test for circular inheritance') }
236 # ... and now back to our regularly scheduled program
240 ($METAS{$_} || $self->initialize($_))->class_precedence_list()
241 } $self->superclasses()
248 my ($self, $method_name, $method) = @_;
249 (defined $method_name && $method_name)
250 || confess "You must define a method name";
251 # use reftype here to allow for blessed subs ...
252 ('CODE' eq (reftype($method) || ''))
253 || confess "Your code block must be a CODE reference";
254 my $full_method_name = ($self->name . '::' . $method_name);
256 $method = $self->method_metaclass->wrap($method) unless blessed($method);
259 no warnings 'redefine';
260 *{$full_method_name} = subname $full_method_name => $method;
264 my $fetch_and_prepare_method = sub {
265 my ($self, $method_name) = @_;
267 my $method = $self->get_method($method_name);
268 # if we dont have local ...
270 # make sure this method even exists ...
271 ($self->find_next_method_by_name($method_name))
272 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
273 # if so, then create a local which just
274 # calls the next applicable method ...
275 $self->add_method($method_name => sub {
276 $self->find_next_method_by_name($method_name)->(@_);
278 $method = $self->get_method($method_name);
281 # now make sure we wrap it properly
282 # (if it isnt already)
283 unless ($method->isa('Class::MOP::Method::Wrapped')) {
284 $method = Class::MOP::Method::Wrapped->wrap($method);
285 $self->add_method($method_name => $method);
290 sub add_before_method_modifier {
291 my ($self, $method_name, $method_modifier) = @_;
292 (defined $method_name && $method_name)
293 || confess "You must pass in a method name";
294 my $method = $fetch_and_prepare_method->($self, $method_name);
295 $method->add_before_modifier(subname ':before' => $method_modifier);
298 sub add_after_method_modifier {
299 my ($self, $method_name, $method_modifier) = @_;
300 (defined $method_name && $method_name)
301 || confess "You must pass in a method name";
302 my $method = $fetch_and_prepare_method->($self, $method_name);
303 $method->add_after_modifier(subname ':after' => $method_modifier);
306 sub add_around_method_modifier {
307 my ($self, $method_name, $method_modifier) = @_;
308 (defined $method_name && $method_name)
309 || confess "You must pass in a method name";
310 my $method = $fetch_and_prepare_method->($self, $method_name);
311 $method->add_around_modifier(subname ':around' => $method_modifier);
315 # the methods above used to be named like this:
316 # ${pkg}::${method}:(before|after|around)
317 # but this proved problematic when using one modifier
318 # to wrap multiple methods (something which is likely
319 # to happen pretty regularly IMO). So instead of naming
320 # it like this, I have chosen to just name them purely
321 # with their modifier names, like so:
322 # :(before|after|around)
323 # The fact is that in a stack trace, it will be fairly
324 # evident from the context what method they are attached
325 # to, and so don't need the fully qualified name.
329 my ($self, $method_name, $method) = @_;
330 (defined $method_name && $method_name)
331 || confess "You must define a method name";
332 # use reftype here to allow for blessed subs ...
333 ('CODE' eq (reftype($method) || ''))
334 || confess "Your code block must be a CODE reference";
335 my $full_method_name = ($self->name . '::' . $method_name);
337 $method = $self->method_metaclass->wrap($method) unless blessed($method);
340 no warnings 'redefine';
341 *{$full_method_name} = $method;
345 my ($self, $method_name) = @_;
346 (defined $method_name && $method_name)
347 || confess "You must define a method name";
349 my $sub_name = ($self->name . '::' . $method_name);
352 return 0 if !defined(&{$sub_name});
353 my $method = \&{$sub_name};
354 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
355 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
357 # at this point we are relatively sure
358 # it is our method, so we bless/wrap it
359 $self->method_metaclass->wrap($method) unless blessed($method);
364 my ($self, $method_name) = @_;
365 (defined $method_name && $method_name)
366 || confess "You must define a method name";
368 return unless $self->has_method($method_name);
371 return \&{$self->name . '::' . $method_name};
375 my ($self, $method_name) = @_;
376 (defined $method_name && $method_name)
377 || confess "You must define a method name";
379 my $removed_method = $self->get_method($method_name);
382 delete ${$self->name . '::'}{$method_name}
383 if defined $removed_method;
385 return $removed_method;
388 sub get_method_list {
391 grep { $self->has_method($_) } %{$self->name . '::'};
394 sub compute_all_applicable_methods {
397 # keep a record of what we have seen
398 # here, this will handle all the
399 # inheritence issues because we are
400 # using the &class_precedence_list
401 my (%seen_class, %seen_method);
402 foreach my $class ($self->class_precedence_list()) {
403 next if $seen_class{$class};
404 $seen_class{$class}++;
405 # fetch the meta-class ...
406 my $meta = $self->initialize($class);
407 foreach my $method_name ($meta->get_method_list()) {
408 next if exists $seen_method{$method_name};
409 $seen_method{$method_name}++;
411 name => $method_name,
413 code => $meta->get_method($method_name)
420 sub find_all_methods_by_name {
421 my ($self, $method_name) = @_;
422 (defined $method_name && $method_name)
423 || confess "You must define a method name to find";
425 # keep a record of what we have seen
426 # here, this will handle all the
427 # inheritence issues because we are
428 # using the &class_precedence_list
430 foreach my $class ($self->class_precedence_list()) {
431 next if $seen_class{$class};
432 $seen_class{$class}++;
433 # fetch the meta-class ...
434 my $meta = $self->initialize($class);
436 name => $method_name,
438 code => $meta->get_method($method_name)
439 } if $meta->has_method($method_name);
444 sub find_next_method_by_name {
445 my ($self, $method_name) = @_;
446 (defined $method_name && $method_name)
447 || confess "You must define a method name to find";
448 # keep a record of what we have seen
449 # here, this will handle all the
450 # inheritence issues because we are
451 # using the &class_precedence_list
453 my @cpl = $self->class_precedence_list();
454 shift @cpl; # discard ourselves
455 foreach my $class (@cpl) {
456 next if $seen_class{$class};
457 $seen_class{$class}++;
458 # fetch the meta-class ...
459 my $meta = $self->initialize($class);
460 return $meta->get_method($method_name)
461 if $meta->has_method($method_name);
470 # either we have an attribute object already
471 # or we need to create one from the args provided
472 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
473 # make sure it is derived from the correct type though
474 ($attribute->isa('Class::MOP::Attribute'))
475 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
476 $attribute->attach_to_class($self);
477 $attribute->install_accessors();
478 $self->get_attribute_map->{$attribute->name} = $attribute;
482 my ($self, $attribute_name) = @_;
483 (defined $attribute_name && $attribute_name)
484 || confess "You must define an attribute name";
485 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
489 my ($self, $attribute_name) = @_;
490 (defined $attribute_name && $attribute_name)
491 || confess "You must define an attribute name";
493 # we used to say `if $self->has_attribute($attribute_name)`
494 # here, but since get_attribute is called so often, we
495 # eliminate the function call here
496 return $self->{'%:attributes'}->{$attribute_name}
497 if exists $self->{'%:attributes'}->{$attribute_name};
501 sub remove_attribute {
502 my ($self, $attribute_name) = @_;
503 (defined $attribute_name && $attribute_name)
504 || confess "You must define an attribute name";
505 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
506 return unless defined $removed_attribute;
507 delete $self->get_attribute_map->{$attribute_name};
508 $removed_attribute->remove_accessors();
509 $removed_attribute->detach_from_class();
510 return $removed_attribute;
513 sub get_attribute_list {
516 # We don't use get_attribute_map here because
517 # we ask for the attribute list quite often
518 # in compute_all_applicable_attributes, so
519 # eliminating the function call helps
520 keys %{$self->{'%:attributes'}};
523 sub compute_all_applicable_attributes {
526 # keep a record of what we have seen
527 # here, this will handle all the
528 # inheritence issues because we are
529 # using the &class_precedence_list
530 my (%seen_class, %seen_attr);
531 foreach my $class ($self->class_precedence_list()) {
532 next if $seen_class{$class};
533 $seen_class{$class}++;
534 # fetch the meta-class ...
535 my $meta = ($METAS{$class} || $self->initialize($class));
536 foreach my $attr_name ($meta->get_attribute_list()) {
537 next if exists $seen_attr{$attr_name};
538 $seen_attr{$attr_name}++;
539 push @attrs => $meta->get_attribute($attr_name);
545 sub find_attribute_by_name {
546 my ($self, $attr_name) = @_;
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 foreach my $class ($self->class_precedence_list()) {
553 next if $seen_class{$class};
554 $seen_class{$class}++;
555 # fetch the meta-class ...
556 my $meta = $self->initialize($class);
557 return $meta->get_attribute($attr_name)
558 if $meta->has_attribute($attr_name);
565 sub add_package_variable {
566 my ($self, $variable, $initial_value) = @_;
567 (defined $variable && $variable =~ /^[\$\@\%]/)
568 || confess "variable name does not have a sigil";
570 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
571 if (defined $initial_value) {
573 *{$self->name . '::' . $name} = $initial_value;
579 # We HAVE to localize $@ or all
580 # hell breaks loose. It is not
581 # good, believe me, not good.
583 eval $sigil . $self->name . '::' . $name;
586 confess "Could not create package variable ($variable) because : $e" if $e;
590 sub has_package_variable {
591 my ($self, $variable) = @_;
592 (defined $variable && $variable =~ /^[\$\@\%]/)
593 || confess "variable name does not have a sigil";
594 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
596 defined ${$self->name . '::'}{$name} ? 1 : 0;
599 sub get_package_variable {
600 my ($self, $variable) = @_;
601 (defined $variable && $variable =~ /^[\$\@\%]/)
602 || confess "variable name does not have a sigil";
603 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
607 # We HAVE to localize $@ or all
608 # hell breaks loose. It is not
609 # good, believe me, not good.
611 $ref = eval '\\' . $sigil . $self->name . '::' . $name;
614 confess "Could not get the package variable ($variable) because : $e" if $e;
615 # if we didn't die, then we can return it
619 sub remove_package_variable {
620 my ($self, $variable) = @_;
621 (defined $variable && $variable =~ /^[\$\@\%]/)
622 || confess "variable name does not have a sigil";
623 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
625 delete ${$self->name . '::'}{$name};
636 Class::MOP::Class - Class Meta Object
640 # assuming that class Foo
641 # has been defined, you can
643 # use this for introspection ...
645 # add a method to Foo ...
646 Foo->meta->add_method('bar' => sub { ... })
648 # get a list of all the classes searched
649 # the method dispatcher in the correct order
650 Foo->meta->class_precedence_list()
652 # remove a method from Foo
653 Foo->meta->remove_method('bar');
655 # or use this to actually create classes ...
657 Class::MOP::Class->create('Bar' => '0.01' => (
658 superclasses => [ 'Foo' ],
660 Class::MOP:::Attribute->new('$bar'),
661 Class::MOP:::Attribute->new('$baz'),
664 calculate_bar => sub { ... },
665 construct_baz => sub { ... }
671 This is the largest and currently most complex part of the Perl 5
672 meta-object protocol. It controls the introspection and
673 manipulation of Perl 5 classes (and it can create them too). The
674 best way to understand what this module can do, is to read the
675 documentation for each of it's methods.
679 =head2 Self Introspection
685 This will return a B<Class::MOP::Class> instance which is related
686 to this class. Thereby allowing B<Class::MOP::Class> to actually
689 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
690 bootstrap this module by installing a number of attribute meta-objects
691 into it's metaclass. This will allow this class to reap all the benifits
692 of the MOP when subclassing it.
694 =item B<get_all_metaclasses>
696 This will return an hash of all the metaclass instances that have
697 been cached by B<Class::MOP::Class> keyed by the package name.
699 =item B<get_all_metaclass_instances>
701 This will return an array of all the metaclass instances that have
702 been cached by B<Class::MOP::Class>.
704 =item B<get_all_metaclass_names>
706 This will return an array of all the metaclass names that have
707 been cached by B<Class::MOP::Class>.
711 =head2 Class construction
713 These methods will handle creating B<Class::MOP::Class> objects,
714 which can be used to both create new classes, and analyze
715 pre-existing classes.
717 This module will internally store references to all the instances
718 you create with these methods, so that they do not need to be
719 created any more than nessecary. Basically, they are singletons.
723 =item B<create ($package_name, ?$package_version,
724 superclasses =E<gt> ?@superclasses,
725 methods =E<gt> ?%methods,
726 attributes =E<gt> ?%attributes)>
728 This returns a B<Class::MOP::Class> object, bringing the specified
729 C<$package_name> into existence and adding any of the
730 C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
733 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
734 methods =E<gt> ?%methods,
735 attributes =E<gt> ?%attributes)>
737 This will create an anonymous class, it works much like C<create> but
738 it does not need a C<$package_name>. Instead it will create a suitably
739 unique package name for you to stash things into.
741 =item B<initialize ($package_name)>
743 This initializes and returns returns a B<Class::MOP::Class> object
744 for a given a C<$package_name>.
746 =item B<construct_class_instance (%options)>
748 This will construct an instance of B<Class::MOP::Class>, it is
749 here so that we can actually "tie the knot" for B<Class::MOP::Class>
750 to use C<construct_instance> once all the bootstrapping is done. This
751 method is used internally by C<initialize> and should never be called
752 from outside of that method really.
754 =item B<check_metaclass_compatability>
756 This method is called as the very last thing in the
757 C<construct_class_instance> method. This will check that the
758 metaclass you are creating is compatible with the metaclasses of all
759 your ancestors. For more inforamtion about metaclass compatibility
760 see the C<About Metaclass compatibility> section in L<Class::MOP>.
764 =head2 Object instance construction and cloning
766 These methods are B<entirely optional>, it is up to you whether you want
771 =item B<new_object (%params)>
773 This is a convience method for creating a new object of the class, and
774 blessing it into the appropriate package as well. Ideally your class
775 would call a C<new> this method like so:
778 my ($class, %param) = @_;
779 $class->meta->new_object(%params);
782 Of course the ideal place for this would actually be in C<UNIVERSAL::>
783 but that is considered bad style, so we do not do that.
785 =item B<construct_instance (%params)>
787 This method is used to construct an instace structure suitable for
788 C<bless>-ing into your package of choice. It works in conjunction
789 with the Attribute protocol to collect all applicable attributes.
791 This will construct and instance using a HASH ref as storage
792 (currently only HASH references are supported). This will collect all
793 the applicable attributes and layout out the fields in the HASH ref,
794 it will then initialize them using either use the corresponding key
795 in C<%params> or any default value or initializer found in the
796 attribute meta-object.
798 =item B<clone_object ($instance, %params)>
800 This is a convience method for cloning an object instance, then
801 blessing it into the appropriate package. This method will call
802 C<clone_instance>, which performs a shallow copy of the object,
803 see that methods documentation for more details. Ideally your
804 class would call a C<clone> this method like so:
807 my ($self, %param) = @_;
808 $self->meta->clone_object($self, %params);
811 Of course the ideal place for this would actually be in C<UNIVERSAL::>
812 but that is considered bad style, so we do not do that.
814 =item B<clone_instance($instance, %params)>
816 This method is a compliment of C<construct_instance> (which means if
817 you override C<construct_instance>, you need to override this one too),
818 and clones the instance shallowly.
820 The cloned structure returned is (like with C<construct_instance>) an
821 unC<bless>ed HASH reference, it is your responsibility to then bless
822 this cloned structure into the right class (which C<clone_object> will
825 As of 0.11, this method will clone the C<$instance> structure shallowly,
826 as opposed to the deep cloning implemented in prior versions. After much
827 thought, research and discussion, I have decided that anything but basic
828 shallow cloning is outside the scope of the meta-object protocol. I
829 think Yuval "nothingmuch" Kogman put it best when he said that cloning
830 is too I<context-specific> to be part of the MOP.
840 This is a read-only attribute which returns the package name for the
841 given B<Class::MOP::Class> instance.
845 This is a read-only attribute which returns the C<$VERSION> of the
846 package for the given B<Class::MOP::Class> instance.
850 =head2 Inheritance Relationships
854 =item B<superclasses (?@superclasses)>
856 This is a read-write attribute which represents the superclass
857 relationships of the class the B<Class::MOP::Class> instance is
858 associated with. Basically, it can get and set the C<@ISA> for you.
861 Perl will occasionally perform some C<@ISA> and method caching, if
862 you decide to change your superclass relationship at runtime (which
863 is quite insane and very much not recommened), then you should be
864 aware of this and the fact that this module does not make any
865 attempt to address this issue.
867 =item B<class_precedence_list>
869 This computes the a list of all the class's ancestors in the same order
870 in which method dispatch will be done. This is similair to
871 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
879 =item B<method_metaclass>
881 =item B<add_method ($method_name, $method)>
883 This will take a C<$method_name> and CODE reference to that
884 C<$method> and install it into the class's package.
887 This does absolutely nothing special to C<$method>
888 other than use B<Sub::Name> to make sure it is tagged with the
889 correct name, and therefore show up correctly in stack traces and
892 =item B<alias_method ($method_name, $method)>
894 This will take a C<$method_name> and CODE reference to that
895 C<$method> and alias the method into the class's package.
898 Unlike C<add_method>, this will B<not> try to name the
899 C<$method> using B<Sub::Name>, it only aliases the method in
902 =item B<has_method ($method_name)>
904 This just provides a simple way to check if the class implements
905 a specific C<$method_name>. It will I<not> however, attempt to check
906 if the class inherits the method (use C<UNIVERSAL::can> for that).
908 This will correctly handle functions defined outside of the package
909 that use a fully qualified name (C<sub Package::name { ... }>).
911 This will correctly handle functions renamed with B<Sub::Name> and
912 installed using the symbol tables. However, if you are naming the
913 subroutine outside of the package scope, you must use the fully
914 qualified name, including the package name, for C<has_method> to
915 correctly identify it.
917 This will attempt to correctly ignore functions imported from other
918 packages using B<Exporter>. It breaks down if the function imported
919 is an C<__ANON__> sub (such as with C<use constant>), which very well
920 may be a valid method being applied to the class.
922 In short, this method cannot always be trusted to determine if the
923 C<$method_name> is actually a method. However, it will DWIM about
924 90% of the time, so it's a small trade off I think.
926 =item B<get_method ($method_name)>
928 This will return a CODE reference of the specified C<$method_name>,
929 or return undef if that method does not exist.
931 =item B<remove_method ($method_name)>
933 This will attempt to remove a given C<$method_name> from the class.
934 It will return the CODE reference that it has removed, and will
935 attempt to use B<Sub::Name> to clear the methods associated name.
937 =item B<get_method_list>
939 This will return a list of method names for all I<locally> defined
940 methods. It does B<not> provide a list of all applicable methods,
941 including any inherited ones. If you want a list of all applicable
942 methods, use the C<compute_all_applicable_methods> method.
944 =item B<compute_all_applicable_methods>
946 This will return a list of all the methods names this class will
947 respond to, taking into account inheritance. The list will be a list of
948 HASH references, each one containing the following information; method
949 name, the name of the class in which the method lives and a CODE
950 reference for the actual method.
952 =item B<find_all_methods_by_name ($method_name)>
954 This will traverse the inheritence hierarchy and locate all methods
955 with a given C<$method_name>. Similar to
956 C<compute_all_applicable_methods> it returns a list of HASH references
957 with the following information; method name (which will always be the
958 same as C<$method_name>), the name of the class in which the method
959 lives and a CODE reference for the actual method.
961 The list of methods produced is a distinct list, meaning there are no
962 duplicates in it. This is especially useful for things like object
963 initialization and destruction where you only want the method called
964 once, and in the correct order.
966 =item B<find_next_method_by_name ($method_name)>
968 This will return the first method to match a given C<$method_name> in
969 the superclasses, this is basically equivalent to calling
970 C<SUPER::$method_name>, but it can be dispatched at runtime.
974 =head2 Method Modifiers
976 Method modifiers are a concept borrowed from CLOS, in which a method
977 can be wrapped with I<before>, I<after> and I<around> method modifiers
978 that will be called everytime the method is called.
980 =head3 How method modifiers work?
982 Method modifiers work by wrapping the original method and then replacing
983 it in the classes symbol table. The wrappers will handle calling all the
984 modifiers in the appropariate orders and preserving the calling context
985 for the original method.
987 Each method modifier serves a particular purpose, which may not be
988 obvious to users of other method wrapping modules. To start with, the
989 return values of I<before> and I<after> modifiers are ignored. This is
990 because thier purpose is B<not> to filter the input and output of the
991 primary method (this is done with an I<around> modifier). This may seem
992 like an odd restriction to some, but doing this allows for simple code
993 to be added at the begining or end of a method call without jeapordizing
994 the normal functioning of the primary method or placing any extra
995 responsibility on the code of the modifier. Of course if you have more
996 complex needs, then use the I<around> modifier, which uses a variation
997 of continutation passing style to allow for a high degree of flexibility.
999 Before and around modifiers are called in last-defined-first-called order,
1000 while after modifiers are called in first-defined-first-called order. So
1001 the call tree might looks something like this:
1011 To see examples of using method modifiers, see the following examples
1012 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1013 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1014 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1016 =head3 What is the performance impact?
1018 Of course there is a performance cost associated with method modifiers,
1019 but we have made every effort to make that cost be directly proportional
1020 to the amount of modifier features you utilize.
1022 The wrapping method does it's best to B<only> do as much work as it
1023 absolutely needs to. In order to do this we have moved some of the
1024 performance costs to set-up time, where they are easier to amortize.
1026 All this said, my benchmarks have indicated the following:
1028 simple wrapper with no modifiers 100% slower
1029 simple wrapper with simple before modifier 400% slower
1030 simple wrapper with simple after modifier 450% slower
1031 simple wrapper with simple around modifier 500-550% slower
1032 simple wrapper with all 3 modifiers 1100% slower
1034 These numbers may seem daunting, but you must remember, every feature
1035 comes with some cost. To put things in perspective, just doing a simple
1036 C<AUTOLOAD> which does nothing but extract the name of the method called
1037 and return it costs about 400% over a normal method call.
1041 =item B<add_before_method_modifier ($method_name, $code)>
1043 This will wrap the method at C<$method_name> and the supplied C<$code>
1044 will be passed the C<@_> arguments, and called before the original
1045 method is called. As specified above, the return value of the I<before>
1046 method modifiers is ignored, and it's ability to modify C<@_> is
1047 fairly limited. If you need to do either of these things, use an
1048 C<around> method modifier.
1050 =item B<add_after_method_modifier ($method_name, $code)>
1052 This will wrap the method at C<$method_name> so that the original
1053 method will be called, it's return values stashed, and then the
1054 supplied C<$code> will be passed the C<@_> arguments, and called.
1055 As specified above, the return value of the I<after> method
1056 modifiers is ignored, and it cannot modify the return values of
1057 the original method. If you need to do either of these things, use an
1058 C<around> method modifier.
1060 =item B<add_around_method_modifier ($method_name, $code)>
1062 This will wrap the method at C<$method_name> so that C<$code>
1063 will be called and passed the original method as an extra argument
1064 at the begining of the C<@_> argument list. This is a variation of
1065 continuation passing style, where the function prepended to C<@_>
1066 can be considered a continuation. It is up to C<$code> if it calls
1067 the original method or not, there is no restriction on what the
1068 C<$code> can or cannot do.
1074 It should be noted that since there is no one consistent way to define
1075 the attributes of a class in Perl 5. These methods can only work with
1076 the information given, and can not easily discover information on
1077 their own. See L<Class::MOP::Attribute> for more details.
1081 =item B<attribute_metaclass>
1083 =item B<get_attribute_map>
1085 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1087 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1088 instance associated with the given class, and associates it with
1089 the C<$attribute_name>. Unlike methods, attributes within the MOP
1090 are stored as meta-information only. They will be used later to
1091 construct instances from (see C<construct_instance> above).
1092 More details about the attribute meta-objects can be found in the
1093 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1096 It should be noted that any accessor, reader/writer or predicate
1097 methods which the C<$attribute_meta_object> has will be installed
1098 into the class at this time.
1100 =item B<has_attribute ($attribute_name)>
1102 Checks to see if this class has an attribute by the name of
1103 C<$attribute_name> and returns a boolean.
1105 =item B<get_attribute ($attribute_name)>
1107 Returns the attribute meta-object associated with C<$attribute_name>,
1108 if none is found, it will return undef.
1110 =item B<remove_attribute ($attribute_name)>
1112 This will remove the attribute meta-object stored at
1113 C<$attribute_name>, then return the removed attribute meta-object.
1116 Removing an attribute will only affect future instances of
1117 the class, it will not make any attempt to remove the attribute from
1118 any existing instances of the class.
1120 It should be noted that any accessor, reader/writer or predicate
1121 methods which the attribute meta-object stored at C<$attribute_name>
1122 has will be removed from the class at this time. This B<will> make
1123 these attributes somewhat inaccessable in previously created
1124 instances. But if you are crazy enough to do this at runtime, then
1125 you are crazy enough to deal with something like this :).
1127 =item B<get_attribute_list>
1129 This returns a list of attribute names which are defined in the local
1130 class. If you want a list of all applicable attributes for a class,
1131 use the C<compute_all_applicable_attributes> method.
1133 =item B<compute_all_applicable_attributes>
1135 This will traverse the inheritance heirachy and return a list of all
1136 the applicable attributes for this class. It does not construct a
1137 HASH reference like C<compute_all_applicable_methods> because all
1138 that same information is discoverable through the attribute
1141 =item B<find_attribute_by_name ($attr_name)>
1143 This method will traverse the inheritance heirachy and find the
1144 first attribute whose name matches C<$attr_name>, then return it.
1145 It will return undef if nothing is found.
1149 =head2 Package Variables
1151 Since Perl's classes are built atop the Perl package system, it is
1152 fairly common to use package scoped variables for things like static
1153 class variables. The following methods are convience methods for
1154 the creation and inspection of package scoped variables.
1158 =item B<add_package_variable ($variable_name, ?$initial_value)>
1160 Given a C<$variable_name>, which must contain a leading sigil, this
1161 method will create that variable within the package which houses the
1162 class. It also takes an optional C<$initial_value>, which must be a
1163 reference of the same type as the sigil of the C<$variable_name>
1166 =item B<get_package_variable ($variable_name)>
1168 This will return a reference to the package variable in
1171 =item B<has_package_variable ($variable_name)>
1173 Returns true (C<1>) if there is a package variable defined for
1174 C<$variable_name>, and false (C<0>) otherwise.
1176 =item B<remove_package_variable ($variable_name)>
1178 This will attempt to remove the package variable at C<$variable_name>.
1184 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1186 =head1 COPYRIGHT AND LICENSE
1188 Copyright 2006 by Infinity Interactive, Inc.
1190 L<http://www.iinteractive.com>
1192 This library is free software; you can redistribute it and/or modify
1193 it under the same terms as Perl itself.