2 package Class::MOP::Class;
8 use Scalar::Util 'blessed', 'reftype';
9 use Sub::Name 'subname';
10 use B 'svref_2object';
12 our $VERSION = '0.13';
16 sub meta { Class::MOP::Class->initialize(blessed($_[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 return $class->construct_instance(@_);
176 sub construct_instance {
177 my ($class, %params) = @_;
178 require Class::MOP::Instance;
179 my $meta_instance = Class::MOP::Instance->new($class);
180 foreach my $attr ($class->compute_all_applicable_attributes()) {
181 $attr->initialize_instance_slot($class, $meta_instance, \%params);
183 return $meta_instance->get_instance;
188 my $instance = shift;
189 (blessed($instance) && $instance->isa($class->name))
190 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
192 # we need to protect the integrity of the
193 # Class::MOP::Class singletons here, they
194 # should not be cloned.
195 return $instance if $instance->isa('Class::MOP::Class');
196 bless $class->clone_instance($instance, @_) => blessed($instance);
200 my ($class, $instance, %params) = @_;
202 || confess "You can only clone instances, \$self is not a blessed instance";
203 my $clone = { %$instance, %params };
209 # &name should be here too, but it is above
210 # because it gets bootstrapped away
214 ${$self->get_package_variable('$VERSION')};
224 @{$self->name . '::ISA'} = @supers;
226 @{$self->name . '::ISA'};
229 sub class_precedence_list {
232 # We need to check for ciruclar inheirtance here.
233 # This will do nothing if all is well, and blow
234 # up otherwise. Yes, it's an ugly hack, better
235 # suggestions are welcome.
236 { ($self->name || return)->isa('This is a test for circular inheritance') }
237 # ... and now back to our regularly scheduled program
242 # we grab the metaclass from the %METAS
243 # hash here to save the initialize() call
244 # if we can, but it is not always possible
245 ($METAS{$_} || $self->initialize($_))->class_precedence_list()
246 } $self->superclasses()
253 my ($self, $method_name, $method) = @_;
254 (defined $method_name && $method_name)
255 || confess "You must define a method name";
256 # use reftype here to allow for blessed subs ...
257 ('CODE' eq (reftype($method) || ''))
258 || confess "Your code block must be a CODE reference";
259 my $full_method_name = ($self->name . '::' . $method_name);
261 $method = $self->method_metaclass->wrap($method) unless blessed($method);
264 no warnings 'redefine';
265 *{$full_method_name} = subname $full_method_name => $method;
269 my $fetch_and_prepare_method = sub {
270 my ($self, $method_name) = @_;
272 my $method = $self->get_method($method_name);
273 # if we dont have local ...
275 # make sure this method even exists ...
276 ($self->find_next_method_by_name($method_name))
277 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
278 # if so, then create a local which just
279 # calls the next applicable method ...
280 $self->add_method($method_name => sub {
281 $self->find_next_method_by_name($method_name)->(@_);
283 $method = $self->get_method($method_name);
286 # now make sure we wrap it properly
287 # (if it isnt already)
288 unless ($method->isa('Class::MOP::Method::Wrapped')) {
289 $method = Class::MOP::Method::Wrapped->wrap($method);
290 $self->add_method($method_name => $method);
295 sub add_before_method_modifier {
296 my ($self, $method_name, $method_modifier) = @_;
297 (defined $method_name && $method_name)
298 || confess "You must pass in a method name";
299 my $method = $fetch_and_prepare_method->($self, $method_name);
300 $method->add_before_modifier(subname ':before' => $method_modifier);
303 sub add_after_method_modifier {
304 my ($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_after_modifier(subname ':after' => $method_modifier);
311 sub add_around_method_modifier {
312 my ($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_around_modifier(subname ':around' => $method_modifier);
320 # the methods above used to be named like this:
321 # ${pkg}::${method}:(before|after|around)
322 # but this proved problematic when using one modifier
323 # to wrap multiple methods (something which is likely
324 # to happen pretty regularly IMO). So instead of naming
325 # it like this, I have chosen to just name them purely
326 # with their modifier names, like so:
327 # :(before|after|around)
328 # The fact is that in a stack trace, it will be fairly
329 # evident from the context what method they are attached
330 # to, and so don't need the fully qualified name.
334 my ($self, $method_name, $method) = @_;
335 (defined $method_name && $method_name)
336 || confess "You must define a method name";
337 # use reftype here to allow for blessed subs ...
338 ('CODE' eq (reftype($method) || ''))
339 || confess "Your code block must be a CODE reference";
340 my $full_method_name = ($self->name . '::' . $method_name);
342 $method = $self->method_metaclass->wrap($method) unless blessed($method);
345 no warnings 'redefine';
346 *{$full_method_name} = $method;
350 my ($self, $method_name) = @_;
351 (defined $method_name && $method_name)
352 || confess "You must define a method name";
354 my $sub_name = ($self->name . '::' . $method_name);
357 return 0 if !defined(&{$sub_name});
358 my $method = \&{$sub_name};
359 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
360 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
362 # at this point we are relatively sure
363 # it is our method, so we bless/wrap it
364 $self->method_metaclass->wrap($method) unless blessed($method);
369 my ($self, $method_name) = @_;
370 (defined $method_name && $method_name)
371 || confess "You must define a method name";
373 return unless $self->has_method($method_name);
376 return \&{$self->name . '::' . $method_name};
380 my ($self, $method_name) = @_;
381 (defined $method_name && $method_name)
382 || confess "You must define a method name";
384 my $removed_method = $self->get_method($method_name);
387 delete ${$self->name . '::'}{$method_name}
388 if defined $removed_method;
390 return $removed_method;
393 sub get_method_list {
396 grep { $self->has_method($_) } %{$self->name . '::'};
399 sub compute_all_applicable_methods {
402 # keep a record of what we have seen
403 # here, this will handle all the
404 # inheritence issues because we are
405 # using the &class_precedence_list
406 my (%seen_class, %seen_method);
407 foreach my $class ($self->class_precedence_list()) {
408 next if $seen_class{$class};
409 $seen_class{$class}++;
410 # fetch the meta-class ...
411 my $meta = $self->initialize($class);
412 foreach my $method_name ($meta->get_method_list()) {
413 next if exists $seen_method{$method_name};
414 $seen_method{$method_name}++;
416 name => $method_name,
418 code => $meta->get_method($method_name)
425 sub find_all_methods_by_name {
426 my ($self, $method_name) = @_;
427 (defined $method_name && $method_name)
428 || confess "You must define a method name to find";
430 # keep a record of what we have seen
431 # here, this will handle all the
432 # inheritence issues because we are
433 # using the &class_precedence_list
435 foreach my $class ($self->class_precedence_list()) {
436 next if $seen_class{$class};
437 $seen_class{$class}++;
438 # fetch the meta-class ...
439 my $meta = $self->initialize($class);
441 name => $method_name,
443 code => $meta->get_method($method_name)
444 } if $meta->has_method($method_name);
449 sub find_next_method_by_name {
450 my ($self, $method_name) = @_;
451 (defined $method_name && $method_name)
452 || confess "You must define a method name to find";
453 # keep a record of what we have seen
454 # here, this will handle all the
455 # inheritence issues because we are
456 # using the &class_precedence_list
458 my @cpl = $self->class_precedence_list();
459 shift @cpl; # discard ourselves
460 foreach my $class (@cpl) {
461 next if $seen_class{$class};
462 $seen_class{$class}++;
463 # fetch the meta-class ...
464 my $meta = $self->initialize($class);
465 return $meta->get_method($method_name)
466 if $meta->has_method($method_name);
475 # either we have an attribute object already
476 # or we need to create one from the args provided
477 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
478 # make sure it is derived from the correct type though
479 ($attribute->isa('Class::MOP::Attribute'))
480 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
481 $attribute->attach_to_class($self);
482 $attribute->install_accessors();
483 $self->get_attribute_map->{$attribute->name} = $attribute;
487 my ($self, $attribute_name) = @_;
488 (defined $attribute_name && $attribute_name)
489 || confess "You must define an attribute name";
490 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
494 my ($self, $attribute_name) = @_;
495 (defined $attribute_name && $attribute_name)
496 || confess "You must define an attribute name";
498 # we used to say `if $self->has_attribute($attribute_name)`
499 # here, but since get_attribute is called so often, we
500 # eliminate the function call here
501 return $self->{'%:attributes'}->{$attribute_name}
502 if exists $self->{'%:attributes'}->{$attribute_name};
506 sub remove_attribute {
507 my ($self, $attribute_name) = @_;
508 (defined $attribute_name && $attribute_name)
509 || confess "You must define an attribute name";
510 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
511 return unless defined $removed_attribute;
512 delete $self->get_attribute_map->{$attribute_name};
513 $removed_attribute->remove_accessors();
514 $removed_attribute->detach_from_class();
515 return $removed_attribute;
518 sub get_attribute_list {
521 # We don't use get_attribute_map here because
522 # we ask for the attribute list quite often
523 # in compute_all_applicable_attributes, so
524 # eliminating the function call helps
525 keys %{$self->{'%:attributes'}};
528 sub compute_all_applicable_attributes {
531 # keep a record of what we have seen
532 # here, this will handle all the
533 # inheritence issues because we are
534 # using the &class_precedence_list
535 my (%seen_class, %seen_attr);
536 foreach my $class ($self->class_precedence_list()) {
537 next if $seen_class{$class};
538 $seen_class{$class}++;
539 # fetch the meta-class ...
541 # we grab the metaclass from the %METAS
542 # hash here to save the initialize() call
543 my $meta = $METAS{$class};
544 foreach my $attr_name ($meta->get_attribute_list()) {
545 next if exists $seen_attr{$attr_name};
546 $seen_attr{$attr_name}++;
547 push @attrs => $meta->get_attribute($attr_name);
553 sub find_attribute_by_name {
554 my ($self, $attr_name) = @_;
555 # keep a record of what we have seen
556 # here, this will handle all the
557 # inheritence issues because we are
558 # using the &class_precedence_list
560 foreach my $class ($self->class_precedence_list()) {
561 next if $seen_class{$class};
562 $seen_class{$class}++;
563 # fetch the meta-class ...
564 my $meta = $self->initialize($class);
565 return $meta->get_attribute($attr_name)
566 if $meta->has_attribute($attr_name);
573 sub add_package_variable {
574 my ($self, $variable, $initial_value) = @_;
575 (defined $variable && $variable =~ /^[\$\@\%]/)
576 || confess "variable name does not have a sigil";
578 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
579 if (defined $initial_value) {
581 *{$self->name . '::' . $name} = $initial_value;
587 # We HAVE to localize $@ or all
588 # hell breaks loose. It is not
589 # good, believe me, not good.
591 eval $sigil . $self->name . '::' . $name;
594 confess "Could not create package variable ($variable) because : $e" if $e;
598 sub has_package_variable {
599 my ($self, $variable) = @_;
600 (defined $variable && $variable =~ /^[\$\@\%]/)
601 || confess "variable name does not have a sigil";
602 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
604 defined ${$self->name . '::'}{$name} ? 1 : 0;
607 sub get_package_variable {
608 my ($self, $variable) = @_;
609 (defined $variable && $variable =~ /^[\$\@\%]/)
610 || confess "variable name does not have a sigil";
611 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
615 # We HAVE to localize $@ or all
616 # hell breaks loose. It is not
617 # good, believe me, not good.
619 $ref = eval '\\' . $sigil . $self->name . '::' . $name;
622 confess "Could not get the package variable ($variable) because : $e" if $e;
623 # if we didn't die, then we can return it
627 sub remove_package_variable {
628 my ($self, $variable) = @_;
629 (defined $variable && $variable =~ /^[\$\@\%]/)
630 || confess "variable name does not have a sigil";
631 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
633 delete ${$self->name . '::'}{$name};
644 Class::MOP::Class - Class Meta Object
648 # assuming that class Foo
649 # has been defined, you can
651 # use this for introspection ...
653 # add a method to Foo ...
654 Foo->meta->add_method('bar' => sub { ... })
656 # get a list of all the classes searched
657 # the method dispatcher in the correct order
658 Foo->meta->class_precedence_list()
660 # remove a method from Foo
661 Foo->meta->remove_method('bar');
663 # or use this to actually create classes ...
665 Class::MOP::Class->create('Bar' => '0.01' => (
666 superclasses => [ 'Foo' ],
668 Class::MOP:::Attribute->new('$bar'),
669 Class::MOP:::Attribute->new('$baz'),
672 calculate_bar => sub { ... },
673 construct_baz => sub { ... }
679 This is the largest and currently most complex part of the Perl 5
680 meta-object protocol. It controls the introspection and
681 manipulation of Perl 5 classes (and it can create them too). The
682 best way to understand what this module can do, is to read the
683 documentation for each of it's methods.
687 =head2 Self Introspection
693 This will return a B<Class::MOP::Class> instance which is related
694 to this class. Thereby allowing B<Class::MOP::Class> to actually
697 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
698 bootstrap this module by installing a number of attribute meta-objects
699 into it's metaclass. This will allow this class to reap all the benifits
700 of the MOP when subclassing it.
702 =item B<get_all_metaclasses>
704 This will return an hash of all the metaclass instances that have
705 been cached by B<Class::MOP::Class> keyed by the package name.
707 =item B<get_all_metaclass_instances>
709 This will return an array of all the metaclass instances that have
710 been cached by B<Class::MOP::Class>.
712 =item B<get_all_metaclass_names>
714 This will return an array of all the metaclass names that have
715 been cached by B<Class::MOP::Class>.
719 =head2 Class construction
721 These methods will handle creating B<Class::MOP::Class> objects,
722 which can be used to both create new classes, and analyze
723 pre-existing classes.
725 This module will internally store references to all the instances
726 you create with these methods, so that they do not need to be
727 created any more than nessecary. Basically, they are singletons.
731 =item B<create ($package_name, ?$package_version,
732 superclasses =E<gt> ?@superclasses,
733 methods =E<gt> ?%methods,
734 attributes =E<gt> ?%attributes)>
736 This returns a B<Class::MOP::Class> object, bringing the specified
737 C<$package_name> into existence and adding any of the
738 C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
741 =item B<create_anon_class (superclasses =E<gt> ?@superclasses,
742 methods =E<gt> ?%methods,
743 attributes =E<gt> ?%attributes)>
745 This will create an anonymous class, it works much like C<create> but
746 it does not need a C<$package_name>. Instead it will create a suitably
747 unique package name for you to stash things into.
749 =item B<initialize ($package_name)>
751 This initializes and returns returns a B<Class::MOP::Class> object
752 for a given a C<$package_name>.
754 =item B<construct_class_instance (%options)>
756 This will construct an instance of B<Class::MOP::Class>, it is
757 here so that we can actually "tie the knot" for B<Class::MOP::Class>
758 to use C<construct_instance> once all the bootstrapping is done. This
759 method is used internally by C<initialize> and should never be called
760 from outside of that method really.
762 =item B<check_metaclass_compatability>
764 This method is called as the very last thing in the
765 C<construct_class_instance> method. This will check that the
766 metaclass you are creating is compatible with the metaclasses of all
767 your ancestors. For more inforamtion about metaclass compatibility
768 see the C<About Metaclass compatibility> section in L<Class::MOP>.
772 =head2 Object instance construction and cloning
774 These methods are B<entirely optional>, it is up to you whether you want
779 =item B<new_object (%params)>
781 This is a convience method for creating a new object of the class, and
782 blessing it into the appropriate package as well. Ideally your class
783 would call a C<new> this method like so:
786 my ($class, %param) = @_;
787 $class->meta->new_object(%params);
790 Of course the ideal place for this would actually be in C<UNIVERSAL::>
791 but that is considered bad style, so we do not do that.
793 =item B<construct_instance (%params)>
795 This method is used to construct an instace structure suitable for
796 C<bless>-ing into your package of choice. It works in conjunction
797 with the Attribute protocol to collect all applicable attributes.
799 This will construct and instance using a HASH ref as storage
800 (currently only HASH references are supported). This will collect all
801 the applicable attributes and layout out the fields in the HASH ref,
802 it will then initialize them using either use the corresponding key
803 in C<%params> or any default value or initializer found in the
804 attribute meta-object.
806 =item B<clone_object ($instance, %params)>
808 This is a convience method for cloning an object instance, then
809 blessing it into the appropriate package. This method will call
810 C<clone_instance>, which performs a shallow copy of the object,
811 see that methods documentation for more details. Ideally your
812 class would call a C<clone> this method like so:
815 my ($self, %param) = @_;
816 $self->meta->clone_object($self, %params);
819 Of course the ideal place for this would actually be in C<UNIVERSAL::>
820 but that is considered bad style, so we do not do that.
822 =item B<clone_instance($instance, %params)>
824 This method is a compliment of C<construct_instance> (which means if
825 you override C<construct_instance>, you need to override this one too),
826 and clones the instance shallowly.
828 The cloned structure returned is (like with C<construct_instance>) an
829 unC<bless>ed HASH reference, it is your responsibility to then bless
830 this cloned structure into the right class (which C<clone_object> will
833 As of 0.11, this method will clone the C<$instance> structure shallowly,
834 as opposed to the deep cloning implemented in prior versions. After much
835 thought, research and discussion, I have decided that anything but basic
836 shallow cloning is outside the scope of the meta-object protocol. I
837 think Yuval "nothingmuch" Kogman put it best when he said that cloning
838 is too I<context-specific> to be part of the MOP.
848 This is a read-only attribute which returns the package name for the
849 given B<Class::MOP::Class> instance.
853 This is a read-only attribute which returns the C<$VERSION> of the
854 package for the given B<Class::MOP::Class> instance.
858 =head2 Inheritance Relationships
862 =item B<superclasses (?@superclasses)>
864 This is a read-write attribute which represents the superclass
865 relationships of the class the B<Class::MOP::Class> instance is
866 associated with. Basically, it can get and set the C<@ISA> for you.
869 Perl will occasionally perform some C<@ISA> and method caching, if
870 you decide to change your superclass relationship at runtime (which
871 is quite insane and very much not recommened), then you should be
872 aware of this and the fact that this module does not make any
873 attempt to address this issue.
875 =item B<class_precedence_list>
877 This computes the a list of all the class's ancestors in the same order
878 in which method dispatch will be done. This is similair to
879 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
887 =item B<method_metaclass>
889 =item B<add_method ($method_name, $method)>
891 This will take a C<$method_name> and CODE reference to that
892 C<$method> and install it into the class's package.
895 This does absolutely nothing special to C<$method>
896 other than use B<Sub::Name> to make sure it is tagged with the
897 correct name, and therefore show up correctly in stack traces and
900 =item B<alias_method ($method_name, $method)>
902 This will take a C<$method_name> and CODE reference to that
903 C<$method> and alias the method into the class's package.
906 Unlike C<add_method>, this will B<not> try to name the
907 C<$method> using B<Sub::Name>, it only aliases the method in
910 =item B<has_method ($method_name)>
912 This just provides a simple way to check if the class implements
913 a specific C<$method_name>. It will I<not> however, attempt to check
914 if the class inherits the method (use C<UNIVERSAL::can> for that).
916 This will correctly handle functions defined outside of the package
917 that use a fully qualified name (C<sub Package::name { ... }>).
919 This will correctly handle functions renamed with B<Sub::Name> and
920 installed using the symbol tables. However, if you are naming the
921 subroutine outside of the package scope, you must use the fully
922 qualified name, including the package name, for C<has_method> to
923 correctly identify it.
925 This will attempt to correctly ignore functions imported from other
926 packages using B<Exporter>. It breaks down if the function imported
927 is an C<__ANON__> sub (such as with C<use constant>), which very well
928 may be a valid method being applied to the class.
930 In short, this method cannot always be trusted to determine if the
931 C<$method_name> is actually a method. However, it will DWIM about
932 90% of the time, so it's a small trade off I think.
934 =item B<get_method ($method_name)>
936 This will return a CODE reference of the specified C<$method_name>,
937 or return undef if that method does not exist.
939 =item B<remove_method ($method_name)>
941 This will attempt to remove a given C<$method_name> from the class.
942 It will return the CODE reference that it has removed, and will
943 attempt to use B<Sub::Name> to clear the methods associated name.
945 =item B<get_method_list>
947 This will return a list of method names for all I<locally> defined
948 methods. It does B<not> provide a list of all applicable methods,
949 including any inherited ones. If you want a list of all applicable
950 methods, use the C<compute_all_applicable_methods> method.
952 =item B<compute_all_applicable_methods>
954 This will return a list of all the methods names this class will
955 respond to, taking into account inheritance. The list will be a list of
956 HASH references, each one containing the following information; method
957 name, the name of the class in which the method lives and a CODE
958 reference for the actual method.
960 =item B<find_all_methods_by_name ($method_name)>
962 This will traverse the inheritence hierarchy and locate all methods
963 with a given C<$method_name>. Similar to
964 C<compute_all_applicable_methods> it returns a list of HASH references
965 with the following information; method name (which will always be the
966 same as C<$method_name>), the name of the class in which the method
967 lives and a CODE reference for the actual method.
969 The list of methods produced is a distinct list, meaning there are no
970 duplicates in it. This is especially useful for things like object
971 initialization and destruction where you only want the method called
972 once, and in the correct order.
974 =item B<find_next_method_by_name ($method_name)>
976 This will return the first method to match a given C<$method_name> in
977 the superclasses, this is basically equivalent to calling
978 C<SUPER::$method_name>, but it can be dispatched at runtime.
982 =head2 Method Modifiers
984 Method modifiers are a concept borrowed from CLOS, in which a method
985 can be wrapped with I<before>, I<after> and I<around> method modifiers
986 that will be called everytime the method is called.
988 =head3 How method modifiers work?
990 Method modifiers work by wrapping the original method and then replacing
991 it in the classes symbol table. The wrappers will handle calling all the
992 modifiers in the appropariate orders and preserving the calling context
993 for the original method.
995 Each method modifier serves a particular purpose, which may not be
996 obvious to users of other method wrapping modules. To start with, the
997 return values of I<before> and I<after> modifiers are ignored. This is
998 because thier purpose is B<not> to filter the input and output of the
999 primary method (this is done with an I<around> modifier). This may seem
1000 like an odd restriction to some, but doing this allows for simple code
1001 to be added at the begining or end of a method call without jeapordizing
1002 the normal functioning of the primary method or placing any extra
1003 responsibility on the code of the modifier. Of course if you have more
1004 complex needs, then use the I<around> modifier, which uses a variation
1005 of continutation passing style to allow for a high degree of flexibility.
1007 Before and around modifiers are called in last-defined-first-called order,
1008 while after modifiers are called in first-defined-first-called order. So
1009 the call tree might looks something like this:
1019 To see examples of using method modifiers, see the following examples
1020 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
1021 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
1022 classic CLOS usage example in the test F<017_add_method_modifier.t>.
1024 =head3 What is the performance impact?
1026 Of course there is a performance cost associated with method modifiers,
1027 but we have made every effort to make that cost be directly proportional
1028 to the amount of modifier features you utilize.
1030 The wrapping method does it's best to B<only> do as much work as it
1031 absolutely needs to. In order to do this we have moved some of the
1032 performance costs to set-up time, where they are easier to amortize.
1034 All this said, my benchmarks have indicated the following:
1036 simple wrapper with no modifiers 100% slower
1037 simple wrapper with simple before modifier 400% slower
1038 simple wrapper with simple after modifier 450% slower
1039 simple wrapper with simple around modifier 500-550% slower
1040 simple wrapper with all 3 modifiers 1100% slower
1042 These numbers may seem daunting, but you must remember, every feature
1043 comes with some cost. To put things in perspective, just doing a simple
1044 C<AUTOLOAD> which does nothing but extract the name of the method called
1045 and return it costs about 400% over a normal method call.
1049 =item B<add_before_method_modifier ($method_name, $code)>
1051 This will wrap the method at C<$method_name> and the supplied C<$code>
1052 will be passed the C<@_> arguments, and called before the original
1053 method is called. As specified above, the return value of the I<before>
1054 method modifiers is ignored, and it's ability to modify C<@_> is
1055 fairly limited. If you need to do either of these things, use an
1056 C<around> method modifier.
1058 =item B<add_after_method_modifier ($method_name, $code)>
1060 This will wrap the method at C<$method_name> so that the original
1061 method will be called, it's return values stashed, and then the
1062 supplied C<$code> will be passed the C<@_> arguments, and called.
1063 As specified above, the return value of the I<after> method
1064 modifiers is ignored, and it cannot modify the return values of
1065 the original method. If you need to do either of these things, use an
1066 C<around> method modifier.
1068 =item B<add_around_method_modifier ($method_name, $code)>
1070 This will wrap the method at C<$method_name> so that C<$code>
1071 will be called and passed the original method as an extra argument
1072 at the begining of the C<@_> argument list. This is a variation of
1073 continuation passing style, where the function prepended to C<@_>
1074 can be considered a continuation. It is up to C<$code> if it calls
1075 the original method or not, there is no restriction on what the
1076 C<$code> can or cannot do.
1082 It should be noted that since there is no one consistent way to define
1083 the attributes of a class in Perl 5. These methods can only work with
1084 the information given, and can not easily discover information on
1085 their own. See L<Class::MOP::Attribute> for more details.
1089 =item B<attribute_metaclass>
1091 =item B<get_attribute_map>
1093 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1095 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1096 instance associated with the given class, and associates it with
1097 the C<$attribute_name>. Unlike methods, attributes within the MOP
1098 are stored as meta-information only. They will be used later to
1099 construct instances from (see C<construct_instance> above).
1100 More details about the attribute meta-objects can be found in the
1101 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1104 It should be noted that any accessor, reader/writer or predicate
1105 methods which the C<$attribute_meta_object> has will be installed
1106 into the class at this time.
1108 =item B<has_attribute ($attribute_name)>
1110 Checks to see if this class has an attribute by the name of
1111 C<$attribute_name> and returns a boolean.
1113 =item B<get_attribute ($attribute_name)>
1115 Returns the attribute meta-object associated with C<$attribute_name>,
1116 if none is found, it will return undef.
1118 =item B<remove_attribute ($attribute_name)>
1120 This will remove the attribute meta-object stored at
1121 C<$attribute_name>, then return the removed attribute meta-object.
1124 Removing an attribute will only affect future instances of
1125 the class, it will not make any attempt to remove the attribute from
1126 any existing instances of the class.
1128 It should be noted that any accessor, reader/writer or predicate
1129 methods which the attribute meta-object stored at C<$attribute_name>
1130 has will be removed from the class at this time. This B<will> make
1131 these attributes somewhat inaccessable in previously created
1132 instances. But if you are crazy enough to do this at runtime, then
1133 you are crazy enough to deal with something like this :).
1135 =item B<get_attribute_list>
1137 This returns a list of attribute names which are defined in the local
1138 class. If you want a list of all applicable attributes for a class,
1139 use the C<compute_all_applicable_attributes> method.
1141 =item B<compute_all_applicable_attributes>
1143 This will traverse the inheritance heirachy and return a list of all
1144 the applicable attributes for this class. It does not construct a
1145 HASH reference like C<compute_all_applicable_methods> because all
1146 that same information is discoverable through the attribute
1149 =item B<find_attribute_by_name ($attr_name)>
1151 This method will traverse the inheritance heirachy and find the
1152 first attribute whose name matches C<$attr_name>, then return it.
1153 It will return undef if nothing is found.
1157 =head2 Package Variables
1159 Since Perl's classes are built atop the Perl package system, it is
1160 fairly common to use package scoped variables for things like static
1161 class variables. The following methods are convience methods for
1162 the creation and inspection of package scoped variables.
1166 =item B<add_package_variable ($variable_name, ?$initial_value)>
1168 Given a C<$variable_name>, which must contain a leading sigil, this
1169 method will create that variable within the package which houses the
1170 class. It also takes an optional C<$initial_value>, which must be a
1171 reference of the same type as the sigil of the C<$variable_name>
1174 =item B<get_package_variable ($variable_name)>
1176 This will return a reference to the package variable in
1179 =item B<has_package_variable ($variable_name)>
1181 Returns true (C<1>) if there is a package variable defined for
1182 C<$variable_name>, and false (C<0>) otherwise.
1184 =item B<remove_package_variable ($variable_name)>
1186 This will attempt to remove the package variable at C<$variable_name>.
1192 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1194 =head1 COPYRIGHT AND LICENSE
1196 Copyright 2006 by Infinity Interactive, Inc.
1198 L<http://www.iinteractive.com>
1200 This library is free software; you can redistribute it and/or modify
1201 it under the same terms as Perl itself.