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) = @_;
183 my $instance = $class->get_meta_instance->create_instance();
185 foreach my $attr ($class->compute_all_applicable_attributes()) {
186 $attr->initialize_instance_slot($instance, \%params);
191 sub get_meta_instance {
193 # make it work,.. *then* make it right ... # yeah that was my plan, i just thought we'll make it async
194 $class->{meta_instance} ||= $class->instance_metaclass->new( $class );
199 my $instance = shift;
200 (blessed($instance) && $instance->isa($class->name))
201 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
203 # we need to protect the integrity of the
204 # Class::MOP::Class singletons here, they
205 # should not be cloned.
206 return $instance if $instance->isa('Class::MOP::Class');
207 bless $class->clone_instance($instance, @_) => blessed($instance);
211 my ($class, $instance, %params) = @_;
213 || confess "You can only clone instances, \$self is not a blessed instance";
214 my $clone = { %$instance, %params };
220 # &name should be here too, but it is above
221 # because it gets bootstrapped away
225 ${$self->get_package_variable('$VERSION')};
235 @{$self->name . '::ISA'} = @supers;
237 @{$self->name . '::ISA'};
240 sub class_precedence_list {
243 # We need to check for ciruclar inheirtance here.
244 # This will do nothing if all is well, and blow
245 # up otherwise. Yes, it's an ugly hack, better
246 # suggestions are welcome.
247 { ($self->name || return)->isa('This is a test for circular inheritance') }
248 # ... and now back to our regularly scheduled program
253 # we grab the metaclass from the %METAS
254 # hash here to save the initialize() call
255 # if we can, but it is not always possible
256 ($METAS{$_} || $self->initialize($_))->class_precedence_list()
257 } $self->superclasses()
264 my ($self, $method_name, $method) = @_;
265 (defined $method_name && $method_name)
266 || confess "You must define a method name";
267 # use reftype here to allow for blessed subs ...
268 ('CODE' eq (reftype($method) || ''))
269 || confess "Your code block must be a CODE reference";
270 my $full_method_name = ($self->name . '::' . $method_name);
272 $method = $self->method_metaclass->wrap($method) unless blessed($method);
275 no warnings 'redefine';
276 *{$full_method_name} = subname $full_method_name => $method;
280 my $fetch_and_prepare_method = sub {
281 my ($self, $method_name) = @_;
283 my $method = $self->get_method($method_name);
284 # if we dont have local ...
286 # make sure this method even exists ...
287 ($self->find_next_method_by_name($method_name))
288 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
289 # if so, then create a local which just
290 # calls the next applicable method ...
291 $self->add_method($method_name => sub {
292 $self->find_next_method_by_name($method_name)->(@_);
294 $method = $self->get_method($method_name);
297 # now make sure we wrap it properly
298 # (if it isnt already)
299 unless ($method->isa('Class::MOP::Method::Wrapped')) {
300 $method = Class::MOP::Method::Wrapped->wrap($method);
301 $self->add_method($method_name => $method);
306 sub add_before_method_modifier {
307 my ($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_before_modifier(subname ':before' => $method_modifier);
314 sub add_after_method_modifier {
315 my ($self, $method_name, $method_modifier) = @_;
316 (defined $method_name && $method_name)
317 || confess "You must pass in a method name";
318 my $method = $fetch_and_prepare_method->($self, $method_name);
319 $method->add_after_modifier(subname ':after' => $method_modifier);
322 sub add_around_method_modifier {
323 my ($self, $method_name, $method_modifier) = @_;
324 (defined $method_name && $method_name)
325 || confess "You must pass in a method name";
326 my $method = $fetch_and_prepare_method->($self, $method_name);
327 $method->add_around_modifier(subname ':around' => $method_modifier);
331 # the methods above used to be named like this:
332 # ${pkg}::${method}:(before|after|around)
333 # but this proved problematic when using one modifier
334 # to wrap multiple methods (something which is likely
335 # to happen pretty regularly IMO). So instead of naming
336 # it like this, I have chosen to just name them purely
337 # with their modifier names, like so:
338 # :(before|after|around)
339 # The fact is that in a stack trace, it will be fairly
340 # evident from the context what method they are attached
341 # to, and so don't need the fully qualified name.
345 my ($self, $method_name, $method) = @_;
346 (defined $method_name && $method_name)
347 || confess "You must define a method name";
348 # use reftype here to allow for blessed subs ...
349 ('CODE' eq (reftype($method) || ''))
350 || confess "Your code block must be a CODE reference";
351 my $full_method_name = ($self->name . '::' . $method_name);
353 $method = $self->method_metaclass->wrap($method) unless blessed($method);
356 no warnings 'redefine';
357 *{$full_method_name} = $method;
361 my ($self, $method_name) = @_;
362 (defined $method_name && $method_name)
363 || confess "You must define a method name";
365 my $sub_name = ($self->name . '::' . $method_name);
368 return 0 if !defined(&{$sub_name});
369 my $method = \&{$sub_name};
370 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
371 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
373 # at this point we are relatively sure
374 # it is our method, so we bless/wrap it
375 $self->method_metaclass->wrap($method) unless blessed($method);
380 my ($self, $method_name) = @_;
381 (defined $method_name && $method_name)
382 || confess "You must define a method name";
384 return unless $self->has_method($method_name);
387 return \&{$self->name . '::' . $method_name};
391 my ($self, $method_name) = @_;
392 (defined $method_name && $method_name)
393 || confess "You must define a method name";
395 my $removed_method = $self->get_method($method_name);
398 delete ${$self->name . '::'}{$method_name}
399 if defined $removed_method;
401 return $removed_method;
404 sub get_method_list {
407 grep { $self->has_method($_) } %{$self->name . '::'};
410 sub compute_all_applicable_methods {
413 # keep a record of what we have seen
414 # here, this will handle all the
415 # inheritence issues because we are
416 # using the &class_precedence_list
417 my (%seen_class, %seen_method);
418 foreach my $class ($self->class_precedence_list()) {
419 next if $seen_class{$class};
420 $seen_class{$class}++;
421 # fetch the meta-class ...
422 my $meta = $self->initialize($class);
423 foreach my $method_name ($meta->get_method_list()) {
424 next if exists $seen_method{$method_name};
425 $seen_method{$method_name}++;
427 name => $method_name,
429 code => $meta->get_method($method_name)
436 sub find_all_methods_by_name {
437 my ($self, $method_name) = @_;
438 (defined $method_name && $method_name)
439 || confess "You must define a method name to find";
441 # keep a record of what we have seen
442 # here, this will handle all the
443 # inheritence issues because we are
444 # using the &class_precedence_list
446 foreach my $class ($self->class_precedence_list()) {
447 next if $seen_class{$class};
448 $seen_class{$class}++;
449 # fetch the meta-class ...
450 my $meta = $self->initialize($class);
452 name => $method_name,
454 code => $meta->get_method($method_name)
455 } if $meta->has_method($method_name);
460 sub find_next_method_by_name {
461 my ($self, $method_name) = @_;
462 (defined $method_name && $method_name)
463 || confess "You must define a method name to find";
464 # keep a record of what we have seen
465 # here, this will handle all the
466 # inheritence issues because we are
467 # using the &class_precedence_list
469 my @cpl = $self->class_precedence_list();
470 shift @cpl; # discard ourselves
471 foreach my $class (@cpl) {
472 next if $seen_class{$class};
473 $seen_class{$class}++;
474 # fetch the meta-class ...
475 my $meta = $self->initialize($class);
476 return $meta->get_method($method_name)
477 if $meta->has_method($method_name);
486 # either we have an attribute object already
487 # or we need to create one from the args provided
488 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
489 # make sure it is derived from the correct type though
490 ($attribute->isa('Class::MOP::Attribute'))
491 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
492 $attribute->attach_to_class($self);
493 $attribute->install_accessors();
494 $attribute->allocate_slots;
496 $self->get_attribute_map->{$attribute->name} = $attribute;
500 my ($self, $attribute_name) = @_;
501 (defined $attribute_name && $attribute_name)
502 || confess "You must define an attribute name";
503 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
507 my ($self, $attribute_name) = @_;
508 (defined $attribute_name && $attribute_name)
509 || confess "You must define an attribute name";
511 # we used to say `if $self->has_attribute($attribute_name)`
512 # here, but since get_attribute is called so often, we
513 # eliminate the function call here
514 return $self->{'%:attributes'}->{$attribute_name}
515 if exists $self->{'%:attributes'}->{$attribute_name};
519 sub remove_attribute {
520 my ($self, $attribute_name) = @_;
521 (defined $attribute_name && $attribute_name)
522 || confess "You must define an attribute name";
523 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
524 return unless defined $removed_attribute;
525 delete $self->get_attribute_map->{$attribute_name};
526 $removed_attribute->remove_accessors();
527 $removed_attribute->deallocate_slots();
528 $removed_attribute->detach_from_class();
529 return $removed_attribute;
532 sub get_attribute_list {
535 # We don't use get_attribute_map here because
536 # we ask for the attribute list quite often
537 # in compute_all_applicable_attributes, so
538 # eliminating the function call helps
539 keys %{$self->{'%:attributes'}};
542 sub compute_all_applicable_attributes {
545 # keep a record of what we have seen
546 # here, this will handle all the
547 # inheritence issues because we are
548 # using the &class_precedence_list
549 my (%seen_class, %seen_attr);
550 foreach my $class ($self->class_precedence_list()) {
551 next if $seen_class{$class};
552 $seen_class{$class}++;
553 # fetch the meta-class ...
555 # we grab the metaclass from the %METAS
556 # hash here to save the initialize() call
557 my $meta = $METAS{$class};
558 foreach my $attr_name ($meta->get_attribute_list()) {
559 next if exists $seen_attr{$attr_name};
560 $seen_attr{$attr_name}++;
561 push @attrs => $meta->get_attribute($attr_name);
567 sub find_attribute_by_name {
568 my ($self, $attr_name) = @_;
569 # keep a record of what we have seen
570 # here, this will handle all the
571 # inheritence issues because we are
572 # using the &class_precedence_list
574 foreach my $class ($self->class_precedence_list()) {
575 next if $seen_class{$class};
576 $seen_class{$class}++;
577 # fetch the meta-class ...
578 my $meta = $self->initialize($class);
579 return $meta->get_attribute($attr_name)
580 if $meta->has_attribute($attr_name);
587 sub add_package_variable {
588 my ($self, $variable, $initial_value) = @_;
589 (defined $variable && $variable =~ /^[\$\@\%]/)
590 || confess "variable name does not have a sigil";
592 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
593 if (defined $initial_value) {
595 *{$self->name . '::' . $name} = $initial_value;
601 # We HAVE to localize $@ or all
602 # hell breaks loose. It is not
603 # good, believe me, not good.
605 eval $sigil . $self->name . '::' . $name;
608 confess "Could not create package variable ($variable) because : $e" if $e;
612 sub has_package_variable {
613 my ($self, $variable) = @_;
614 (defined $variable && $variable =~ /^[\$\@\%]/)
615 || confess "variable name does not have a sigil";
616 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
618 defined ${$self->name . '::'}{$name} ? 1 : 0;
621 sub get_package_variable {
622 my ($self, $variable) = @_;
623 (defined $variable && $variable =~ /^[\$\@\%]/)
624 || confess "variable name does not have a sigil";
625 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
629 # We HAVE to localize $@ or all
630 # hell breaks loose. It is not
631 # good, believe me, not good.
633 $ref = eval '\\' . $sigil . $self->name . '::' . $name;
636 confess "Could not get the package variable ($variable) because : $e" if $e;
637 # if we didn't die, then we can return it
641 sub remove_package_variable {
642 my ($self, $variable) = @_;
643 (defined $variable && $variable =~ /^[\$\@\%]/)
644 || confess "variable name does not have a sigil";
645 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
647 delete ${$self->name . '::'}{$name};
658 Class::MOP::Class - Class Meta Object
662 # assuming that class Foo
663 # has been defined, you can
665 # use this for introspection ...
667 # add a method to Foo ...
668 Foo->meta->add_method('bar' => sub { ... })
670 # get a list of all the classes searched
671 # the method dispatcher in the correct order
672 Foo->meta->class_precedence_list()
674 # remove a method from Foo
675 Foo->meta->remove_method('bar');
677 # or use this to actually create classes ...
679 Class::MOP::Class->create('Bar' => '0.01' => (
680 superclasses => [ 'Foo' ],
682 Class::MOP:::Attribute->new('$bar'),
683 Class::MOP:::Attribute->new('$baz'),
686 calculate_bar => sub { ... },
687 construct_baz => sub { ... }
693 This is the largest and currently most complex part of the Perl 5
694 meta-object protocol. It controls the introspection and
695 manipulation of Perl 5 classes (and it can create them too). The
696 best way to understand what this module can do, is to read the
697 documentation for each of it's methods.
701 =head2 Self Introspection
707 This will return a B<Class::MOP::Class> instance which is related
708 to this class. Thereby allowing B<Class::MOP::Class> to actually
711 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
712 bootstrap this module by installing a number of attribute meta-objects
713 into it's metaclass. This will allow this class to reap all the benifits
714 of the MOP when subclassing it.
716 =item B<get_all_metaclasses>
718 This will return an hash of all the metaclass instances that have
719 been cached by B<Class::MOP::Class> keyed by the package name.
721 =item B<get_all_metaclass_instances>
723 This will return an array of all the metaclass instances that have
724 been cached by B<Class::MOP::Class>.
726 =item B<get_all_metaclass_names>
728 This will return an array of all the metaclass names that have
729 been cached by B<Class::MOP::Class>.
733 =head2 Class construction
735 These methods will handle creating B<Class::MOP::Class> objects,
736 which can be used to both create new classes, and analyze
737 pre-existing classes.
739 This module will internally store references to all the instances
740 you create with these methods, so that they do not need to be
741 created any more than nessecary. Basically, they are singletons.
745 =item B<create ($package_name, ?$package_version,
746 superclasses =E<gt> ?@superclasses,
747 methods =E<gt> ?%methods,
748 attributes =E<gt> ?%attributes)>
750 This returns a B<Class::MOP::Class> object, bringing the specified
751 C<$package_name> into existence and adding any of the
752 C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
755 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
756 methods =E<gt> ?%methods,
757 attributes =E<gt> ?%attributes)>
759 This will create an anonymous class, it works much like C<create> but
760 it does not need a C<$package_name>. Instead it will create a suitably
761 unique package name for you to stash things into.
763 =item B<initialize ($package_name)>
765 This initializes and returns returns a B<Class::MOP::Class> object
766 for a given a C<$package_name>.
768 =item B<construct_class_instance (%options)>
770 This will construct an instance of B<Class::MOP::Class>, it is
771 here so that we can actually "tie the knot" for B<Class::MOP::Class>
772 to use C<construct_instance> once all the bootstrapping is done. This
773 method is used internally by C<initialize> and should never be called
774 from outside of that method really.
776 =item B<check_metaclass_compatability>
778 This method is called as the very last thing in the
779 C<construct_class_instance> method. This will check that the
780 metaclass you are creating is compatible with the metaclasses of all
781 your ancestors. For more inforamtion about metaclass compatibility
782 see the C<About Metaclass compatibility> section in L<Class::MOP>.
786 =head2 Object instance construction and cloning
788 These methods are B<entirely optional>, it is up to you whether you want
793 =item B<instance_metaclass>
795 =item B<get_meta_instance>
797 =item B<new_object (%params)>
799 This is a convience method for creating a new object of the class, and
800 blessing it into the appropriate package as well. Ideally your class
801 would call a C<new> this method like so:
804 my ($class, %param) = @_;
805 $class->meta->new_object(%params);
808 Of course the ideal place for this would actually be in C<UNIVERSAL::>
809 but that is considered bad style, so we do not do that.
811 =item B<construct_instance (%params)>
813 This method is used to construct an instace structure suitable for
814 C<bless>-ing into your package of choice. It works in conjunction
815 with the Attribute protocol to collect all applicable attributes.
817 This will construct and instance using a HASH ref as storage
818 (currently only HASH references are supported). This will collect all
819 the applicable attributes and layout out the fields in the HASH ref,
820 it will then initialize them using either use the corresponding key
821 in C<%params> or any default value or initializer found in the
822 attribute meta-object.
824 =item B<clone_object ($instance, %params)>
826 This is a convience method for cloning an object instance, then
827 blessing it into the appropriate package. This method will call
828 C<clone_instance>, which performs a shallow copy of the object,
829 see that methods documentation for more details. Ideally your
830 class would call a C<clone> this method like so:
833 my ($self, %param) = @_;
834 $self->meta->clone_object($self, %params);
837 Of course the ideal place for this would actually be in C<UNIVERSAL::>
838 but that is considered bad style, so we do not do that.
840 =item B<clone_instance($instance, %params)>
842 This method is a compliment of C<construct_instance> (which means if
843 you override C<construct_instance>, you need to override this one too),
844 and clones the instance shallowly.
846 The cloned structure returned is (like with C<construct_instance>) an
847 unC<bless>ed HASH reference, it is your responsibility to then bless
848 this cloned structure into the right class (which C<clone_object> will
851 As of 0.11, this method will clone the C<$instance> structure shallowly,
852 as opposed to the deep cloning implemented in prior versions. After much
853 thought, research and discussion, I have decided that anything but basic
854 shallow cloning is outside the scope of the meta-object protocol. I
855 think Yuval "nothingmuch" Kogman put it best when he said that cloning
856 is too I<context-specific> to be part of the MOP.
866 This is a read-only attribute which returns the package name for the
867 given B<Class::MOP::Class> instance.
871 This is a read-only attribute which returns the C<$VERSION> of the
872 package for the given B<Class::MOP::Class> instance.
876 =head2 Inheritance Relationships
880 =item B<superclasses (?@superclasses)>
882 This is a read-write attribute which represents the superclass
883 relationships of the class the B<Class::MOP::Class> instance is
884 associated with. Basically, it can get and set the C<@ISA> for you.
887 Perl will occasionally perform some C<@ISA> and method caching, if
888 you decide to change your superclass relationship at runtime (which
889 is quite insane and very much not recommened), then you should be
890 aware of this and the fact that this module does not make any
891 attempt to address this issue.
893 =item B<class_precedence_list>
895 This computes the a list of all the class's ancestors in the same order
896 in which method dispatch will be done. This is similair to
897 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
905 =item B<method_metaclass>
907 =item B<add_method ($method_name, $method)>
909 This will take a C<$method_name> and CODE reference to that
910 C<$method> and install it into the class's package.
913 This does absolutely nothing special to C<$method>
914 other than use B<Sub::Name> to make sure it is tagged with the
915 correct name, and therefore show up correctly in stack traces and
918 =item B<alias_method ($method_name, $method)>
920 This will take a C<$method_name> and CODE reference to that
921 C<$method> and alias the method into the class's package.
924 Unlike C<add_method>, this will B<not> try to name the
925 C<$method> using B<Sub::Name>, it only aliases the method in
928 =item B<has_method ($method_name)>
930 This just provides a simple way to check if the class implements
931 a specific C<$method_name>. It will I<not> however, attempt to check
932 if the class inherits the method (use C<UNIVERSAL::can> for that).
934 This will correctly handle functions defined outside of the package
935 that use a fully qualified name (C<sub Package::name { ... }>).
937 This will correctly handle functions renamed with B<Sub::Name> and
938 installed using the symbol tables. However, if you are naming the
939 subroutine outside of the package scope, you must use the fully
940 qualified name, including the package name, for C<has_method> to
941 correctly identify it.
943 This will attempt to correctly ignore functions imported from other
944 packages using B<Exporter>. It breaks down if the function imported
945 is an C<__ANON__> sub (such as with C<use constant>), which very well
946 may be a valid method being applied to the class.
948 In short, this method cannot always be trusted to determine if the
949 C<$method_name> is actually a method. However, it will DWIM about
950 90% of the time, so it's a small trade off I think.
952 =item B<get_method ($method_name)>
954 This will return a CODE reference of the specified C<$method_name>,
955 or return undef if that method does not exist.
957 =item B<remove_method ($method_name)>
959 This will attempt to remove a given C<$method_name> from the class.
960 It will return the CODE reference that it has removed, and will
961 attempt to use B<Sub::Name> to clear the methods associated name.
963 =item B<get_method_list>
965 This will return a list of method names for all I<locally> defined
966 methods. It does B<not> provide a list of all applicable methods,
967 including any inherited ones. If you want a list of all applicable
968 methods, use the C<compute_all_applicable_methods> method.
970 =item B<compute_all_applicable_methods>
972 This will return a list of all the methods names this class will
973 respond to, taking into account inheritance. The list will be a list of
974 HASH references, each one containing the following information; method
975 name, the name of the class in which the method lives and a CODE
976 reference for the actual method.
978 =item B<find_all_methods_by_name ($method_name)>
980 This will traverse the inheritence hierarchy and locate all methods
981 with a given C<$method_name>. Similar to
982 C<compute_all_applicable_methods> it returns a list of HASH references
983 with the following information; method name (which will always be the
984 same as C<$method_name>), the name of the class in which the method
985 lives and a CODE reference for the actual method.
987 The list of methods produced is a distinct list, meaning there are no
988 duplicates in it. This is especially useful for things like object
989 initialization and destruction where you only want the method called
990 once, and in the correct order.
992 =item B<find_next_method_by_name ($method_name)>
994 This will return the first method to match a given C<$method_name> in
995 the superclasses, this is basically equivalent to calling
996 C<SUPER::$method_name>, but it can be dispatched at runtime.
1000 =head2 Method Modifiers
1002 Method modifiers are a concept borrowed from CLOS, in which a method
1003 can be wrapped with I<before>, I<after> and I<around> method modifiers
1004 that will be called everytime the method is called.
1006 =head3 How method modifiers work?
1008 Method modifiers work by wrapping the original method and then replacing
1009 it in the classes symbol table. The wrappers will handle calling all the
1010 modifiers in the appropariate orders and preserving the calling context
1011 for the original method.
1013 Each method modifier serves a particular purpose, which may not be
1014 obvious to users of other method wrapping modules. To start with, the
1015 return values of I<before> and I<after> modifiers are ignored. This is
1016 because thier purpose is B<not> to filter the input and output of the
1017 primary method (this is done with an I<around> modifier). This may seem
1018 like an odd restriction to some, but doing this allows for simple code
1019 to be added at the begining or end of a method call without jeapordizing
1020 the normal functioning of the primary method or placing any extra
1021 responsibility on the code of the modifier. Of course if you have more
1022 complex needs, then use the I<around> modifier, which uses a variation
1023 of continutation passing style to allow for a high degree of flexibility.
1025 Before and around modifiers are called in last-defined-first-called order,
1026 while after modifiers are called in first-defined-first-called order. So
1027 the call tree might looks something like this:
1037 To see examples of using method modifiers, see the following examples
1038 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1039 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1040 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1042 =head3 What is the performance impact?
1044 Of course there is a performance cost associated with method modifiers,
1045 but we have made every effort to make that cost be directly proportional
1046 to the amount of modifier features you utilize.
1048 The wrapping method does it's best to B<only> do as much work as it
1049 absolutely needs to. In order to do this we have moved some of the
1050 performance costs to set-up time, where they are easier to amortize.
1052 All this said, my benchmarks have indicated the following:
1054 simple wrapper with no modifiers 100% slower
1055 simple wrapper with simple before modifier 400% slower
1056 simple wrapper with simple after modifier 450% slower
1057 simple wrapper with simple around modifier 500-550% slower
1058 simple wrapper with all 3 modifiers 1100% slower
1060 These numbers may seem daunting, but you must remember, every feature
1061 comes with some cost. To put things in perspective, just doing a simple
1062 C<AUTOLOAD> which does nothing but extract the name of the method called
1063 and return it costs about 400% over a normal method call.
1067 =item B<add_before_method_modifier ($method_name, $code)>
1069 This will wrap the method at C<$method_name> and the supplied C<$code>
1070 will be passed the C<@_> arguments, and called before the original
1071 method is called. As specified above, the return value of the I<before>
1072 method modifiers is ignored, and it's ability to modify C<@_> is
1073 fairly limited. If you need to do either of these things, use an
1074 C<around> method modifier.
1076 =item B<add_after_method_modifier ($method_name, $code)>
1078 This will wrap the method at C<$method_name> so that the original
1079 method will be called, it's return values stashed, and then the
1080 supplied C<$code> will be passed the C<@_> arguments, and called.
1081 As specified above, the return value of the I<after> method
1082 modifiers is ignored, and it cannot modify the return values of
1083 the original method. If you need to do either of these things, use an
1084 C<around> method modifier.
1086 =item B<add_around_method_modifier ($method_name, $code)>
1088 This will wrap the method at C<$method_name> so that C<$code>
1089 will be called and passed the original method as an extra argument
1090 at the begining of the C<@_> argument list. This is a variation of
1091 continuation passing style, where the function prepended to C<@_>
1092 can be considered a continuation. It is up to C<$code> if it calls
1093 the original method or not, there is no restriction on what the
1094 C<$code> can or cannot do.
1100 It should be noted that since there is no one consistent way to define
1101 the attributes of a class in Perl 5. These methods can only work with
1102 the information given, and can not easily discover information on
1103 their own. See L<Class::MOP::Attribute> for more details.
1107 =item B<attribute_metaclass>
1109 =item B<get_attribute_map>
1111 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1113 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1114 instance associated with the given class, and associates it with
1115 the C<$attribute_name>. Unlike methods, attributes within the MOP
1116 are stored as meta-information only. They will be used later to
1117 construct instances from (see C<construct_instance> above).
1118 More details about the attribute meta-objects can be found in the
1119 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1122 It should be noted that any accessor, reader/writer or predicate
1123 methods which the C<$attribute_meta_object> has will be installed
1124 into the class at this time.
1126 =item B<has_attribute ($attribute_name)>
1128 Checks to see if this class has an attribute by the name of
1129 C<$attribute_name> and returns a boolean.
1131 =item B<get_attribute ($attribute_name)>
1133 Returns the attribute meta-object associated with C<$attribute_name>,
1134 if none is found, it will return undef.
1136 =item B<remove_attribute ($attribute_name)>
1138 This will remove the attribute meta-object stored at
1139 C<$attribute_name>, then return the removed attribute meta-object.
1142 Removing an attribute will only affect future instances of
1143 the class, it will not make any attempt to remove the attribute from
1144 any existing instances of the class.
1146 It should be noted that any accessor, reader/writer or predicate
1147 methods which the attribute meta-object stored at C<$attribute_name>
1148 has will be removed from the class at this time. This B<will> make
1149 these attributes somewhat inaccessable in previously created
1150 instances. But if you are crazy enough to do this at runtime, then
1151 you are crazy enough to deal with something like this :).
1153 =item B<get_attribute_list>
1155 This returns a list of attribute names which are defined in the local
1156 class. If you want a list of all applicable attributes for a class,
1157 use the C<compute_all_applicable_attributes> method.
1159 =item B<compute_all_applicable_attributes>
1161 This will traverse the inheritance heirachy and return a list of all
1162 the applicable attributes for this class. It does not construct a
1163 HASH reference like C<compute_all_applicable_methods> because all
1164 that same information is discoverable through the attribute
1167 =item B<find_attribute_by_name ($attr_name)>
1169 This method will traverse the inheritance heirachy and find the
1170 first attribute whose name matches C<$attr_name>, then return it.
1171 It will return undef if nothing is found.
1175 =head2 Package Variables
1177 Since Perl's classes are built atop the Perl package system, it is
1178 fairly common to use package scoped variables for things like static
1179 class variables. The following methods are convience methods for
1180 the creation and inspection of package scoped variables.
1184 =item B<add_package_variable ($variable_name, ?$initial_value)>
1186 Given a C<$variable_name>, which must contain a leading sigil, this
1187 method will create that variable within the package which houses the
1188 class. It also takes an optional C<$initial_value>, which must be a
1189 reference of the same type as the sigil of the C<$variable_name>
1192 =item B<get_package_variable ($variable_name)>
1194 This will return a reference to the package variable in
1197 =item B<has_package_variable ($variable_name)>
1199 Returns true (C<1>) if there is a package variable defined for
1200 C<$variable_name>, and false (C<0>) otherwise.
1202 =item B<remove_package_variable ($variable_name)>
1204 This will attempt to remove the package variable at C<$variable_name>.
1210 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1212 =head1 COPYRIGHT AND LICENSE
1214 Copyright 2006 by Infinity Interactive, Inc.
1216 L<http://www.iinteractive.com>
1218 This library is free software; you can redistribute it and/or modify
1219 it under the same terms as Perl itself.