2 package Class::MOP::Class;
8 use Scalar::Util 'blessed', 'reftype';
9 use Sub::Name 'subname';
10 use B 'svref_2object';
12 our $VERSION = '0.10';
16 sub meta { Class::MOP::Class->initialize(blessed($_[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?
29 my $package_name = shift;
30 (defined $package_name && $package_name && !blessed($package_name))
31 || confess "You must pass a package name and it cannot be blessed";
32 $class->construct_class_instance(':package' => $package_name, @_);
35 # NOTE: (meta-circularity)
36 # this is a special form of &construct_instance
37 # (see below), which is used to construct class
38 # meta-object instances for any Class::MOP::*
39 # class. All other classes will use the more
40 # normal &construct_instance.
41 sub construct_class_instance {
44 my $package_name = $options{':package'};
45 (defined $package_name && $package_name)
46 || confess "You must pass a package name";
48 # return the metaclass if we have it cached,
49 # and it is still defined (it has not been
50 # reaped by DESTROY yet, which can happen
51 # annoyingly enough during global destruction)
52 return $METAS{$package_name}
53 if exists $METAS{$package_name} && defined $METAS{$package_name};
54 $class = blessed($class) || $class;
55 # now create the metaclass
57 if ($class =~ /^Class::MOP::/) {
59 '$:package' => $package_name,
61 '$:attribute_metaclass' => $options{':attribute_metaclass'} || 'Class::MOP::Attribute',
62 '$:method_metaclass' => $options{':method_metaclass'} || 'Class::MOP::Method',
67 # it is safe to use meta here because
68 # class will always be a subclass of
69 # Class::MOP::Class, which defines meta
70 $meta = bless $class->meta->construct_instance(%options) => $class
72 # and check the metaclass compatibility
73 $meta->check_metaclass_compatability();
74 $METAS{$package_name} = $meta;
77 sub check_metaclass_compatability {
80 # this is always okay ...
81 return if blessed($self) eq 'Class::MOP::Class';
83 my @class_list = $self->class_precedence_list;
84 shift @class_list; # shift off $self->name
86 foreach my $class_name (@class_list) {
87 my $meta = $METAS{$class_name} || next;
88 ($self->isa(blessed($meta)))
89 || confess $self->name . "->meta => (" . (blessed($self)) . ")" .
90 " is not compatible with the " .
91 $class_name . "->meta => (" . (blessed($meta)) . ")";
97 my ($class, $package_name, $package_version, %options) = @_;
98 (defined $package_name && $package_name)
99 || confess "You must pass a package name";
100 my $code = "package $package_name;";
101 $code .= "\$$package_name\:\:VERSION = '$package_version';"
102 if defined $package_version;
104 confess "creation of $package_name failed : $@" if $@;
105 my $meta = $class->initialize($package_name);
107 $meta->add_method('meta' => sub {
108 Class::MOP::Class->initialize(blessed($_[0]) || $_[0]);
111 $meta->superclasses(@{$options{superclasses}})
112 if exists $options{superclasses};
114 # process attributes first, so that they can
115 # install accessors, but locally defined methods
116 # can then overwrite them. It is maybe a little odd, but
117 # I think this should be the order of things.
118 if (exists $options{attributes}) {
119 foreach my $attr (@{$options{attributes}}) {
120 $meta->add_attribute($attr);
123 if (exists $options{methods}) {
124 foreach my $method_name (keys %{$options{methods}}) {
125 $meta->add_method($method_name, $options{methods}->{$method_name});
134 # all these attribute readers will be bootstrapped
135 # away in the Class::MOP bootstrap section
137 sub name { $_[0]->{'$:package'} }
138 sub get_attribute_map { $_[0]->{'%:attributes'} }
139 sub attribute_metaclass { $_[0]->{'$:attribute_metaclass'} }
140 sub method_metaclass { $_[0]->{'$:method_metaclass'} }
142 # Instance Construction & Cloning
147 # we need to protect the integrity of the
148 # Class::MOP::Class singletons here, so we
149 # delegate this to &construct_class_instance
150 # which will deal with the singletons
151 return $class->construct_class_instance(@_)
152 if $class->name->isa('Class::MOP::Class');
153 bless $class->construct_instance(@_) => $class->name;
156 sub construct_instance {
157 my ($class, %params) = @_;
159 foreach my $attr ($class->compute_all_applicable_attributes()) {
160 my $init_arg = $attr->init_arg();
161 # try to fetch the init arg from the %params ...
163 $val = $params{$init_arg} if exists $params{$init_arg};
164 # if nothing was in the %params, we can use the
165 # attribute's default value (if it has one)
166 if (!defined $val && $attr->has_default) {
167 $val = $attr->default($instance);
169 $instance->{$attr->name} = $val;
176 my $instance = shift;
177 (blessed($instance) && $instance->isa($class->name))
178 || confess "You must pass an instance ($instance) of the metaclass (" . $class->name . ")";
180 # we need to protect the integrity of the
181 # Class::MOP::Class singletons here, they
182 # should not be cloned.
183 return $instance if $instance->isa('Class::MOP::Class');
184 bless $class->clone_instance($instance, @_) => blessed($instance);
188 my ($class, $instance, %params) = @_;
190 || confess "You can only clone instances, \$self is not a blessed instance";
191 my $clone = { %$instance, %params };
197 # &name should be here too, but it is above
198 # because it gets bootstrapped away
202 ${$self->get_package_variable('$VERSION')};
211 @{$self->get_package_variable('@ISA')} = @supers;
213 @{$self->get_package_variable('@ISA')};
216 sub class_precedence_list {
219 # We need to check for ciruclar inheirtance here.
220 # This will do nothing if all is well, and blow
221 # up otherwise. Yes, it's an ugly hack, better
222 # suggestions are welcome.
223 { $self->name->isa('This is a test for circular inheritance') }
224 # ... and now back to our regularly scheduled program
228 $self->initialize($_)->class_precedence_list()
229 } $self->superclasses()
236 my ($self, $method_name, $method) = @_;
237 (defined $method_name && $method_name)
238 || confess "You must define a method name";
239 # use reftype here to allow for blessed subs ...
240 ('CODE' eq (reftype($method) || ''))
241 || confess "Your code block must be a CODE reference";
242 my $full_method_name = ($self->name . '::' . $method_name);
244 $method = $self->method_metaclass->wrap($method) unless blessed($method);
247 no warnings 'redefine';
248 *{$full_method_name} = subname $full_method_name => $method;
252 my $fetch_and_prepare_method = sub {
253 my ($self, $method_name) = @_;
255 my $method = $self->get_method($method_name);
256 # if we dont have local ...
258 # make sure this method even exists ...
259 ($self->find_next_method_by_name($method_name))
260 || confess "The method '$method_name' is not found in the inherience hierarchy for this class";
261 # if so, then create a local which just
262 # calls the next applicable method ...
263 $self->add_method($method_name => sub {
264 $self->find_next_method_by_name($method_name)->(@_);
266 $method = $self->get_method($method_name);
269 # now make sure we wrap it properly
270 # (if it isnt already)
271 unless ($method->isa('Class::MOP::Method::Wrapped')) {
272 $method = Class::MOP::Method::Wrapped->wrap($method);
273 $self->add_method($method_name => $method);
278 sub add_before_method_modifier {
279 my ($self, $method_name, $method_modifier) = @_;
280 (defined $method_name && $method_name)
281 || confess "You must pass in a method name";
282 my $method = $fetch_and_prepare_method->($self, $method_name);
283 $method->add_before_modifier(subname ':before' => $method_modifier);
286 sub add_after_method_modifier {
287 my ($self, $method_name, $method_modifier) = @_;
288 (defined $method_name && $method_name)
289 || confess "You must pass in a method name";
290 my $method = $fetch_and_prepare_method->($self, $method_name);
291 $method->add_after_modifier(subname ':after' => $method_modifier);
294 sub add_around_method_modifier {
295 my ($self, $method_name, $method_modifier) = @_;
296 (defined $method_name && $method_name)
297 || confess "You must pass in a method name";
298 my $method = $fetch_and_prepare_method->($self, $method_name);
299 $method->add_around_modifier(subname ':around' => $method_modifier);
303 # the methods above used to be named like this:
304 # ${pkg}::${method}:(before|after|around)
305 # but this proved problematic when using one modifier
306 # to wrap multiple methods (something which is likely
307 # to happen pretty regularly IMO). So instead of naming
308 # it like this, I have chosen to just name them purely
309 # with their modifier names, like so:
310 # :(before|after|around)
311 # The fact is that in a stack trace, it will be fairly
312 # evident from the context what method they are attached
313 # to, and so don't need the fully qualified name.
317 my ($self, $method_name, $method) = @_;
318 (defined $method_name && $method_name)
319 || confess "You must define a method name";
320 # use reftype here to allow for blessed subs ...
321 ('CODE' eq (reftype($method) || ''))
322 || confess "Your code block must be a CODE reference";
323 my $full_method_name = ($self->name . '::' . $method_name);
325 $method = $self->method_metaclass->wrap($method) unless blessed($method);
328 no warnings 'redefine';
329 *{$full_method_name} = $method;
333 my ($self, $method_name) = @_;
334 (defined $method_name && $method_name)
335 || confess "You must define a method name";
337 my $sub_name = ($self->name . '::' . $method_name);
340 return 0 if !defined(&{$sub_name});
341 my $method = \&{$sub_name};
342 return 0 if (svref_2object($method)->GV->STASH->NAME || '') ne $self->name &&
343 (svref_2object($method)->GV->NAME || '') ne '__ANON__';
345 # at this point we are relatively sure
346 # it is our method, so we bless/wrap it
347 $self->method_metaclass->wrap($method) unless blessed($method);
352 my ($self, $method_name) = @_;
353 (defined $method_name && $method_name)
354 || confess "You must define a method name";
356 return unless $self->has_method($method_name);
359 return \&{$self->name . '::' . $method_name};
363 my ($self, $method_name) = @_;
364 (defined $method_name && $method_name)
365 || confess "You must define a method name";
367 my $removed_method = $self->get_method($method_name);
370 delete ${$self->name . '::'}{$method_name}
371 if defined $removed_method;
373 return $removed_method;
376 sub get_method_list {
379 grep { $self->has_method($_) } %{$self->name . '::'};
382 sub compute_all_applicable_methods {
385 # keep a record of what we have seen
386 # here, this will handle all the
387 # inheritence issues because we are
388 # using the &class_precedence_list
389 my (%seen_class, %seen_method);
390 foreach my $class ($self->class_precedence_list()) {
391 next if $seen_class{$class};
392 $seen_class{$class}++;
393 # fetch the meta-class ...
394 my $meta = $self->initialize($class);
395 foreach my $method_name ($meta->get_method_list()) {
396 next if exists $seen_method{$method_name};
397 $seen_method{$method_name}++;
399 name => $method_name,
401 code => $meta->get_method($method_name)
408 sub find_all_methods_by_name {
409 my ($self, $method_name) = @_;
410 (defined $method_name && $method_name)
411 || confess "You must define a method name to find";
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
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);
424 name => $method_name,
426 code => $meta->get_method($method_name)
427 } if $meta->has_method($method_name);
432 sub find_next_method_by_name {
433 my ($self, $method_name) = @_;
434 (defined $method_name && $method_name)
435 || confess "You must define a method name to find";
436 # keep a record of what we have seen
437 # here, this will handle all the
438 # inheritence issues because we are
439 # using the &class_precedence_list
441 my @cpl = $self->class_precedence_list();
442 shift @cpl; # discard ourselves
443 foreach my $class (@cpl) {
444 next if $seen_class{$class};
445 $seen_class{$class}++;
446 # fetch the meta-class ...
447 my $meta = $self->initialize($class);
448 return $meta->get_method($method_name)
449 if $meta->has_method($method_name);
458 # either we have an attribute object already
459 # or we need to create one from the args provided
460 my $attribute = blessed($_[0]) ? $_[0] : $self->attribute_metaclass->new(@_);
461 # make sure it is derived from the correct type though
462 ($attribute->isa('Class::MOP::Attribute'))
463 || confess "Your attribute must be an instance of Class::MOP::Attribute (or a subclass)";
464 $attribute->attach_to_class($self);
465 $attribute->install_accessors();
466 $self->get_attribute_map->{$attribute->name} = $attribute;
470 my ($self, $attribute_name) = @_;
471 (defined $attribute_name && $attribute_name)
472 || confess "You must define an attribute name";
473 exists $self->get_attribute_map->{$attribute_name} ? 1 : 0;
477 my ($self, $attribute_name) = @_;
478 (defined $attribute_name && $attribute_name)
479 || confess "You must define an attribute name";
480 return $self->get_attribute_map->{$attribute_name}
481 if $self->has_attribute($attribute_name);
485 sub remove_attribute {
486 my ($self, $attribute_name) = @_;
487 (defined $attribute_name && $attribute_name)
488 || confess "You must define an attribute name";
489 my $removed_attribute = $self->get_attribute_map->{$attribute_name};
490 return unless defined $removed_attribute;
491 delete $self->get_attribute_map->{$attribute_name};
492 $removed_attribute->remove_accessors();
493 $removed_attribute->detach_from_class();
494 return $removed_attribute;
497 sub get_attribute_list {
499 keys %{$self->get_attribute_map};
502 sub compute_all_applicable_attributes {
505 # keep a record of what we have seen
506 # here, this will handle all the
507 # inheritence issues because we are
508 # using the &class_precedence_list
509 my (%seen_class, %seen_attr);
510 foreach my $class ($self->class_precedence_list()) {
511 next if $seen_class{$class};
512 $seen_class{$class}++;
513 # fetch the meta-class ...
514 my $meta = $self->initialize($class);
515 foreach my $attr_name ($meta->get_attribute_list()) {
516 next if exists $seen_attr{$attr_name};
517 $seen_attr{$attr_name}++;
518 push @attrs => $meta->get_attribute($attr_name);
526 sub add_package_variable {
527 my ($self, $variable, $initial_value) = @_;
528 (defined $variable && $variable =~ /^[\$\@\%]/)
529 || confess "variable name does not have a sigil";
531 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
532 if (defined $initial_value) {
534 *{$self->name . '::' . $name} = $initial_value;
540 # We HAVE to localize $@ or all
541 # hell breaks loose. It is not
542 # good, believe me, not good.
544 eval $sigil . $self->name . '::' . $name;
547 confess "Could not create package variable ($variable) because : $e" if $e;
551 sub has_package_variable {
552 my ($self, $variable) = @_;
553 (defined $variable && $variable =~ /^[\$\@\%]/)
554 || confess "variable name does not have a sigil";
555 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
557 defined ${$self->name . '::'}{$name} ? 1 : 0;
560 sub get_package_variable {
561 my ($self, $variable) = @_;
562 (defined $variable && $variable =~ /^[\$\@\%]/)
563 || confess "variable name does not have a sigil";
564 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
568 # We HAVE to localize $@ or all
569 # hell breaks loose. It is not
570 # good, believe me, not good.
572 $ref = eval '\\' . $sigil . $self->name . '::' . $name;
575 confess "Could not get the package variable ($variable) because : $e" if $e;
576 # if we didn't die, then we can return it
580 sub remove_package_variable {
581 my ($self, $variable) = @_;
582 (defined $variable && $variable =~ /^[\$\@\%]/)
583 || confess "variable name does not have a sigil";
584 my ($sigil, $name) = ($variable =~ /^(.)(.*)$/);
586 delete ${$self->name . '::'}{$name};
597 Class::MOP::Class - Class Meta Object
601 # assuming that class Foo
602 # has been defined, you can
604 # use this for introspection ...
606 # add a method to Foo ...
607 Foo->meta->add_method('bar' => sub { ... })
609 # get a list of all the classes searched
610 # the method dispatcher in the correct order
611 Foo->meta->class_precedence_list()
613 # remove a method from Foo
614 Foo->meta->remove_method('bar');
616 # or use this to actually create classes ...
618 Class::MOP::Class->create('Bar' => '0.01' => (
619 superclasses => [ 'Foo' ],
621 Class::MOP:::Attribute->new('$bar'),
622 Class::MOP:::Attribute->new('$baz'),
625 calculate_bar => sub { ... },
626 construct_baz => sub { ... }
632 This is the largest and currently most complex part of the Perl 5
633 meta-object protocol. It controls the introspection and
634 manipulation of Perl 5 classes (and it can create them too). The
635 best way to understand what this module can do, is to read the
636 documentation for each of it's methods.
640 =head2 Self Introspection
646 This will return a B<Class::MOP::Class> instance which is related
647 to this class. Thereby allowing B<Class::MOP::Class> to actually
650 As with B<Class::MOP::Attribute>, B<Class::MOP> will actually
651 bootstrap this module by installing a number of attribute meta-objects
652 into it's metaclass. This will allow this class to reap all the benifits
653 of the MOP when subclassing it.
657 =head2 Class construction
659 These methods will handle creating B<Class::MOP::Class> objects,
660 which can be used to both create new classes, and analyze
661 pre-existing classes.
663 This module will internally store references to all the instances
664 you create with these methods, so that they do not need to be
665 created any more than nessecary. Basically, they are singletons.
669 =item B<create ($package_name, ?$package_version,
670 superclasses =E<gt> ?@superclasses,
671 methods =E<gt> ?%methods,
672 attributes =E<gt> ?%attributes)>
674 This returns a B<Class::MOP::Class> object, bringing the specified
675 C<$package_name> into existence and adding any of the
676 C<$package_version>, C<@superclasses>, C<%methods> and C<%attributes>
679 =item B<initialize ($package_name)>
681 This initializes and returns returns a B<Class::MOP::Class> object
682 for a given a C<$package_name>.
684 =item B<construct_class_instance (%options)>
686 This will construct an instance of B<Class::MOP::Class>, it is
687 here so that we can actually "tie the knot" for B<Class::MOP::Class>
688 to use C<construct_instance> once all the bootstrapping is done. This
689 method is used internally by C<initialize> and should never be called
690 from outside of that method really.
692 =item B<check_metaclass_compatability>
694 This method is called as the very last thing in the
695 C<construct_class_instance> method. This will check that the
696 metaclass you are creating is compatible with the metaclasses of all
697 your ancestors. For more inforamtion about metaclass compatibility
698 see the C<About Metaclass compatibility> section in L<Class::MOP>.
702 =head2 Object instance construction and cloning
704 These methods are B<entirely optional>, it is up to you whether you want
709 =item B<new_object (%params)>
711 This is a convience method for creating a new object of the class, and
712 blessing it into the appropriate package as well. Ideally your class
713 would call a C<new> this method like so:
716 my ($class, %param) = @_;
717 $class->meta->new_object(%params);
720 Of course the ideal place for this would actually be in C<UNIVERSAL::>
721 but that is considered bad style, so we do not do that.
723 =item B<construct_instance (%params)>
725 This method is used to construct an instace structure suitable for
726 C<bless>-ing into your package of choice. It works in conjunction
727 with the Attribute protocol to collect all applicable attributes.
729 This will construct and instance using a HASH ref as storage
730 (currently only HASH references are supported). This will collect all
731 the applicable attributes and layout out the fields in the HASH ref,
732 it will then initialize them using either use the corresponding key
733 in C<%params> or any default value or initializer found in the
734 attribute meta-object.
736 =item B<clone_object ($instance, %params)>
738 This is a convience method for cloning an object instance, then
739 blessing it into the appropriate package. This method will call
740 C<clone_instance>, which performs a shallow copy of the object,
741 see that methods documentation for more details. Ideally your
742 class would call a C<clone> this method like so:
745 my ($self, %param) = @_;
746 $self->meta->clone_object($self, %params);
749 Of course the ideal place for this would actually be in C<UNIVERSAL::>
750 but that is considered bad style, so we do not do that.
752 =item B<clone_instance($instance, %params)>
754 This method is a compliment of C<construct_instance> (which means if
755 you override C<construct_instance>, you need to override this one too),
756 and clones the instance shallowly.
758 The cloned structure returned is (like with C<construct_instance>) an
759 unC<bless>ed HASH reference, it is your responsibility to then bless
760 this cloned structure into the right class (which C<clone_object> will
763 As of 0.11, this method will clone the C<$instance> structure shallowly,
764 as opposed to the deep cloning implemented in prior versions. After much
765 thought, research and discussion, I have decided that anything but basic
766 shallow cloning is outside the scope of the meta-object protocol. I
767 think Yuval "nothingmuch" Kogman put it best when he said that cloning
768 is too I<context-specific> to be part of the MOP.
778 This is a read-only attribute which returns the package name for the
779 given B<Class::MOP::Class> instance.
783 This is a read-only attribute which returns the C<$VERSION> of the
784 package for the given B<Class::MOP::Class> instance.
788 =head2 Inheritance Relationships
792 =item B<superclasses (?@superclasses)>
794 This is a read-write attribute which represents the superclass
795 relationships of the class the B<Class::MOP::Class> instance is
796 associated with. Basically, it can get and set the C<@ISA> for you.
799 Perl will occasionally perform some C<@ISA> and method caching, if
800 you decide to change your superclass relationship at runtime (which
801 is quite insane and very much not recommened), then you should be
802 aware of this and the fact that this module does not make any
803 attempt to address this issue.
805 =item B<class_precedence_list>
807 This computes the a list of all the class's ancestors in the same order
808 in which method dispatch will be done. This is similair to
809 what B<Class::ISA::super_path> does, but we don't remove duplicate names.
817 =item B<method_metaclass>
819 =item B<add_method ($method_name, $method)>
821 This will take a C<$method_name> and CODE reference to that
822 C<$method> and install it into the class's package.
825 This does absolutely nothing special to C<$method>
826 other than use B<Sub::Name> to make sure it is tagged with the
827 correct name, and therefore show up correctly in stack traces and
830 =item B<alias_method ($method_name, $method)>
832 This will take a C<$method_name> and CODE reference to that
833 C<$method> and alias the method into the class's package.
836 Unlike C<add_method>, this will B<not> try to name the
837 C<$method> using B<Sub::Name>, it only aliases the method in
840 =item B<has_method ($method_name)>
842 This just provides a simple way to check if the class implements
843 a specific C<$method_name>. It will I<not> however, attempt to check
844 if the class inherits the method (use C<UNIVERSAL::can> for that).
846 This will correctly handle functions defined outside of the package
847 that use a fully qualified name (C<sub Package::name { ... }>).
849 This will correctly handle functions renamed with B<Sub::Name> and
850 installed using the symbol tables. However, if you are naming the
851 subroutine outside of the package scope, you must use the fully
852 qualified name, including the package name, for C<has_method> to
853 correctly identify it.
855 This will attempt to correctly ignore functions imported from other
856 packages using B<Exporter>. It breaks down if the function imported
857 is an C<__ANON__> sub (such as with C<use constant>), which very well
858 may be a valid method being applied to the class.
860 In short, this method cannot always be trusted to determine if the
861 C<$method_name> is actually a method. However, it will DWIM about
862 90% of the time, so it's a small trade off I think.
864 =item B<get_method ($method_name)>
866 This will return a CODE reference of the specified C<$method_name>,
867 or return undef if that method does not exist.
869 =item B<remove_method ($method_name)>
871 This will attempt to remove a given C<$method_name> from the class.
872 It will return the CODE reference that it has removed, and will
873 attempt to use B<Sub::Name> to clear the methods associated name.
875 =item B<get_method_list>
877 This will return a list of method names for all I<locally> defined
878 methods. It does B<not> provide a list of all applicable methods,
879 including any inherited ones. If you want a list of all applicable
880 methods, use the C<compute_all_applicable_methods> method.
882 =item B<compute_all_applicable_methods>
884 This will return a list of all the methods names this class will
885 respond to, taking into account inheritance. The list will be a list of
886 HASH references, each one containing the following information; method
887 name, the name of the class in which the method lives and a CODE
888 reference for the actual method.
890 =item B<find_all_methods_by_name ($method_name)>
892 This will traverse the inheritence hierarchy and locate all methods
893 with a given C<$method_name>. Similar to
894 C<compute_all_applicable_methods> it returns a list of HASH references
895 with the following information; method name (which will always be the
896 same as C<$method_name>), the name of the class in which the method
897 lives and a CODE reference for the actual method.
899 The list of methods produced is a distinct list, meaning there are no
900 duplicates in it. This is especially useful for things like object
901 initialization and destruction where you only want the method called
902 once, and in the correct order.
904 =item B<find_next_method_by_name ($method_name)>
906 This will return the first method to match a given C<$method_name> in
907 the superclasses, this is basically equivalent to calling
908 C<SUPER::$method_name>, but it can be dispatched at runtime.
912 =head2 Method Modifiers
914 Method modifiers are a concept borrowed from CLOS, in which a method
915 can be wrapped with I<before>, I<after> and I<around> method modifiers
916 that will be called everytime the method is called.
918 =head3 How method modifiers work?
920 Method modifiers work by wrapping the original method and then replacing
921 it in the classes symbol table. The wrappers will handle calling all the
922 modifiers in the appropariate orders and preserving the calling context
923 for the original method.
925 Each method modifier serves a particular purpose, which may not be
926 obvious to users of other method wrapping modules. To start with, the
927 return values of I<before> and I<after> modifiers are ignored. This is
928 because thier purpose is B<not> to filter the input and output of the
929 primary method (this is done with an I<around> modifier). This may seem
930 like an odd restriction to some, but doing this allows for simple code
931 to be added at the begining or end of a method call without jeapordizing
932 the normal functioning of the primary method or placing any extra
933 responsibility on the code of the modifier. Of course if you have more
934 complex needs, then use the I<around> modifier, which uses a variation
935 of continutation passing style to allow for a high degree of flexibility.
937 Before and around modifiers are called in last-defined-first-called order,
938 while after modifiers are called in first-defined-first-called order. So
939 the call tree might looks something like this:
949 To see examples of using method modifiers, see the following examples
950 included in the distribution; F<InstanceCountingClass>, F<Perl6Attribute>,
951 F<AttributesWithHistory> and F<C3MethodDispatchOrder>. There is also a
952 classic CLOS usage example in the test F<017_add_method_modifier.t>.
954 =head3 What is the performance impact?
956 Of course there is a performance cost associated with method modifiers,
957 but we have made every effort to make that cost be directly proportional
958 to the amount of modifier features you utilize.
960 The wrapping method does it's best to B<only> do as much work as it
961 absolutely needs to. In order to do this we have moved some of the
962 performance costs to set-up time, where they are easier to amortize.
964 All this said, my benchmarks have indicated the following:
966 simple wrapper with no modifiers 100% slower
967 simple wrapper with simple before modifier 400% slower
968 simple wrapper with simple after modifier 450% slower
969 simple wrapper with simple around modifier 500-550% slower
970 simple wrapper with all 3 modifiers 1100% slower
972 These numbers may seem daunting, but you must remember, every feature
973 comes with some cost. To put things in perspective, just doing a simple
974 C<AUTOLOAD> which does nothing but extract the name of the method called
975 and return it costs about 400% over a normal method call.
979 =item B<add_before_method_modifier ($method_name, $code)>
981 This will wrap the method at C<$method_name> and the supplied C<$code>
982 will be passed the C<@_> arguments, and called before the original
983 method is called. As specified above, the return value of the I<before>
984 method modifiers is ignored, and it's ability to modify C<@_> is
985 fairly limited. If you need to do either of these things, use an
986 C<around> method modifier.
988 =item B<add_after_method_modifier ($method_name, $code)>
990 This will wrap the method at C<$method_name> so that the original
991 method will be called, it's return values stashed, and then the
992 supplied C<$code> will be passed the C<@_> arguments, and called.
993 As specified above, the return value of the I<after> method
994 modifiers is ignored, and it cannot modify the return values of
995 the original method. If you need to do either of these things, use an
996 C<around> method modifier.
998 =item B<add_around_method_modifier ($method_name, $code)>
1000 This will wrap the method at C<$method_name> so that C<$code>
1001 will be called and passed the original method as an extra argument
1002 at the begining of the C<@_> argument list. This is a variation of
1003 continuation passing style, where the function prepended to C<@_>
1004 can be considered a continuation. It is up to C<$code> if it calls
1005 the original method or not, there is no restriction on what the
1006 C<$code> can or cannot do.
1012 It should be noted that since there is no one consistent way to define
1013 the attributes of a class in Perl 5. These methods can only work with
1014 the information given, and can not easily discover information on
1015 their own. See L<Class::MOP::Attribute> for more details.
1019 =item B<attribute_metaclass>
1021 =item B<get_attribute_map>
1023 =item B<add_attribute ($attribute_name, $attribute_meta_object)>
1025 This stores a C<$attribute_meta_object> in the B<Class::MOP::Class>
1026 instance associated with the given class, and associates it with
1027 the C<$attribute_name>. Unlike methods, attributes within the MOP
1028 are stored as meta-information only. They will be used later to
1029 construct instances from (see C<construct_instance> above).
1030 More details about the attribute meta-objects can be found in the
1031 L<Class::MOP::Attribute> or the L<Class::MOP/The Attribute protocol>
1034 It should be noted that any accessor, reader/writer or predicate
1035 methods which the C<$attribute_meta_object> has will be installed
1036 into the class at this time.
1038 =item B<has_attribute ($attribute_name)>
1040 Checks to see if this class has an attribute by the name of
1041 C<$attribute_name> and returns a boolean.
1043 =item B<get_attribute ($attribute_name)>
1045 Returns the attribute meta-object associated with C<$attribute_name>,
1046 if none is found, it will return undef.
1048 =item B<remove_attribute ($attribute_name)>
1050 This will remove the attribute meta-object stored at
1051 C<$attribute_name>, then return the removed attribute meta-object.
1054 Removing an attribute will only affect future instances of
1055 the class, it will not make any attempt to remove the attribute from
1056 any existing instances of the class.
1058 It should be noted that any accessor, reader/writer or predicate
1059 methods which the attribute meta-object stored at C<$attribute_name>
1060 has will be removed from the class at this time. This B<will> make
1061 these attributes somewhat inaccessable in previously created
1062 instances. But if you are crazy enough to do this at runtime, then
1063 you are crazy enough to deal with something like this :).
1065 =item B<get_attribute_list>
1067 This returns a list of attribute names which are defined in the local
1068 class. If you want a list of all applicable attributes for a class,
1069 use the C<compute_all_applicable_attributes> method.
1071 =item B<compute_all_applicable_attributes>
1073 This will traverse the inheritance heirachy and return a list of all
1074 the applicable attributes for this class. It does not construct a
1075 HASH reference like C<compute_all_applicable_methods> because all
1076 that same information is discoverable through the attribute
1081 =head2 Package Variables
1083 Since Perl's classes are built atop the Perl package system, it is
1084 fairly common to use package scoped variables for things like static
1085 class variables. The following methods are convience methods for
1086 the creation and inspection of package scoped variables.
1090 =item B<add_package_variable ($variable_name, ?$initial_value)>
1092 Given a C<$variable_name>, which must contain a leading sigil, this
1093 method will create that variable within the package which houses the
1094 class. It also takes an optional C<$initial_value>, which must be a
1095 reference of the same type as the sigil of the C<$variable_name>
1098 =item B<get_package_variable ($variable_name)>
1100 This will return a reference to the package variable in
1103 =item B<has_package_variable ($variable_name)>
1105 Returns true (C<1>) if there is a package variable defined for
1106 C<$variable_name>, and false (C<0>) otherwise.
1108 =item B<remove_package_variable ($variable_name)>
1110 This will attempt to remove the package variable at C<$variable_name>.
1116 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1118 =head1 COPYRIGHT AND LICENSE
1120 Copyright 2006 by Infinity Interactive, Inc.
1122 L<http://www.iinteractive.com>
1124 This library is free software; you can redistribute it and/or modify
1125 it under the same terms as Perl itself.