10 $VERSION = eval $VERSION;
11 our $AUTHORITY = 'cpan:STEVAN';
13 use Scalar::Util 'blessed';
14 use Carp 'confess', 'croak', 'cluck';
18 use Class::MOP 0.71_02;
20 use Moose::Meta::Class;
21 use Moose::Meta::TypeConstraint;
22 use Moose::Meta::TypeCoercion;
23 use Moose::Meta::Attribute;
24 use Moose::Meta::Instance;
28 use Moose::Meta::Role;
29 use Moose::Meta::Role::Composite;
30 use Moose::Meta::Role::Application;
31 use Moose::Meta::Role::Application::RoleSummation;
32 use Moose::Meta::Role::Application::ToClass;
33 use Moose::Meta::Role::Application::ToRole;
34 use Moose::Meta::Role::Application::ToInstance;
36 use Moose::Util::TypeConstraints;
48 croak "Must derive at least one class" unless @_;
51 foreach my $super (@supers) {
52 Class::MOP::load_class($super);
53 croak "You cannot inherit from a Moose Role ($super)"
54 if $super->can('meta') &&
55 blessed $super->meta &&
56 $super->meta->isa('Moose::Meta::Role')
61 # this checks the metaclass to make sure
62 # it is correct, sometimes it can get out
63 # of sync when the classes are being built
64 my $meta = Moose::Meta::Class->initialize($class);
65 $meta->superclasses(@supers);
70 Moose::Util::apply_all_roles(Class::MOP::Class->initialize($class), @_);
76 croak 'Usage: has \'name\' => ( key => value, ... )' if @_ == 1;
78 my $attrs = ( ref($name) eq 'ARRAY' ) ? $name : [ ($name) ];
79 Class::MOP::Class->initialize($class)->add_attribute( $_, %options ) for @$attrs;
84 Moose::Util::add_method_modifier($class, 'before', \@_);
89 Moose::Util::add_method_modifier($class, 'after', \@_);
94 Moose::Util::add_method_modifier($class, 'around', \@_);
98 return unless our $SUPER_BODY; $SUPER_BODY->(our @SUPER_ARGS);
103 my ( $name, $method ) = @_;
104 Class::MOP::Class->initialize($class)->add_override_method_modifier( $name => $method );
109 our ( %INNER_BODY, %INNER_ARGS );
111 if ( my $body = $INNER_BODY{$pkg} ) {
112 my @args = @{ $INNER_ARGS{$pkg} };
113 local $INNER_ARGS{$pkg};
114 local $INNER_BODY{$pkg};
115 return $body->(@args);
123 my ( $name, $method ) = @_;
124 Class::MOP::Class->initialize($class)->add_augment_method_modifier( $name => $method );
127 Moose::Exporter->setup_import_methods(
129 qw( extends with has before after around override augment)
134 \&Scalar::Util::blessed,
139 # This used to be called as a function. This hack preserves
140 # backwards compatibility.
141 if ( $_[0] ne __PACKAGE__ ) {
142 return __PACKAGE__->init_meta(
152 my $class = $args{for_class}
153 or Moose->throw_error("Cannot call init_meta without specifying a for_class");
154 my $base_class = $args{base_class} || 'Moose::Object';
155 my $metaclass = $args{metaclass} || 'Moose::Meta::Class';
157 Moose->throw_error("The Metaclass $metaclass must be a subclass of Moose::Meta::Class.")
158 unless $metaclass->isa('Moose::Meta::Class');
160 # make a subtype for each Moose class
162 unless find_type_constraint($class);
166 if ( $meta = Class::MOP::get_metaclass_by_name($class) ) {
167 unless ( $meta->isa("Moose::Meta::Class") ) {
168 Moose->throw_error("$class already has a metaclass, but it does not inherit $metaclass ($meta)");
171 # no metaclass, no 'meta' method
173 # now we check whether our ancestors have metaclass, and if so borrow that
174 my ( undef, @isa ) = @{ $class->mro::get_linear_isa };
176 foreach my $ancestor ( @isa ) {
177 my $ancestor_meta = Class::MOP::get_metaclass_by_name($ancestor) || next;
179 my $ancestor_meta_class = ($ancestor_meta->is_immutable
180 ? $ancestor_meta->get_mutable_metaclass_name
181 : ref($ancestor_meta));
183 # if we have an ancestor metaclass that inherits $metaclass, we use
184 # that. This is like _fix_metaclass_incompatibility, but we can do it now.
186 # the case of having an ancestry is not very common, but arises in
188 unless ( $metaclass->isa( $ancestor_meta_class ) ) {
189 if ( $ancestor_meta_class->isa($metaclass) ) {
190 $metaclass = $ancestor_meta_class;
195 $meta = $metaclass->initialize($class);
198 if ( $class->can('meta') ) {
199 # check 'meta' method
201 # it may be inherited
204 # this is the case where the metaclass pragma
205 # was used before the 'use Moose' statement to
206 # override a specific class
207 my $method_meta = $class->meta;
209 ( blessed($method_meta) && $method_meta->isa('Moose::Meta::Class') )
210 || Moose->throw_error("$class already has a &meta function, but it does not return a Moose::Meta::Class ($meta)");
212 $meta = $method_meta;
215 unless ( $meta->has_method("meta") ) { # don't overwrite
216 # also check for inherited non moose 'meta' method?
217 # FIXME also skip this if the user requested by passing an option
220 # re-initialize so it inherits properly
221 $metaclass->initialize( ref($_[0]) || $_[0] );
226 # make sure they inherit from Moose::Object
227 $meta->superclasses($base_class)
228 unless $meta->superclasses();
233 # This may be used in some older MooseX extensions.
235 goto &Moose::Exporter::_get_caller;
238 ## make 'em all immutable
241 inline_constructor => 1,
242 constructor_name => "_new",
243 # these are Class::MOP accessors, so they need inlining
244 inline_accessors => 1
245 ) for grep { $_->is_mutable }
248 Moose::Meta::Attribute
250 Moose::Meta::Instance
252 Moose::Meta::TypeCoercion
253 Moose::Meta::TypeCoercion::Union
256 Moose::Meta::Method::Accessor
257 Moose::Meta::Method::Constructor
258 Moose::Meta::Method::Destructor
259 Moose::Meta::Method::Overriden
260 Moose::Meta::Method::Augmented
263 Moose::Meta::Role::Method
264 Moose::Meta::Role::Method::Required
266 Moose::Meta::Role::Composite
268 Moose::Meta::Role::Application
269 Moose::Meta::Role::Application::RoleSummation
270 Moose::Meta::Role::Application::ToClass
271 Moose::Meta::Role::Application::ToRole
272 Moose::Meta::Role::Application::ToInstance
283 Moose - A postmodern object system for Perl 5
288 use Moose; # automatically turns on strict and warnings
290 has 'x' => (is => 'rw', isa => 'Int');
291 has 'y' => (is => 'rw', isa => 'Int');
304 has 'z' => (is => 'rw', isa => 'Int');
306 after 'clear' => sub {
313 Moose is an extension of the Perl 5 object system.
315 The main goal of Moose is to make Perl 5 Object Oriented programming
316 easier, more consistent and less tedious. With Moose you can to think
317 more about what you want to do and less about the mechanics of OOP.
319 Additionally, Moose is built on top of L<Class::MOP>, which is a
320 metaclass system for Perl 5. This means that Moose not only makes
321 building normal Perl 5 objects better, but it provides the power of
322 metaclass programming as well.
326 If you're new to Moose, the best place to start is the L<Moose::Intro>
327 docs, followed by the L<Moose::Cookbook>. The intro will show you what
328 Moose is, and how it makes Perl 5 OO better.
330 The cookbook recipes on Moose basics will get you up to speed with
331 many of Moose's features quickly. Once you have an idea of what Moose
332 can do, you can use the API documentation to get more detail on
333 features which interest you.
335 =head2 Moose Extensions
337 The C<MooseX::> namespace is the official place to find Moose extensions.
338 These extensions can be found on the CPAN. The easiest way to find them
339 is to search for them (L<http://search.cpan.org/search?query=MooseX::>),
340 or to examine L<Task::Moose> which aims to keep an up-to-date, easily
341 installable list of Moose extensions.
343 =head1 BUILDING CLASSES WITH MOOSE
345 Moose makes every attempt to provide as much convenience as possible during
346 class construction/definition, but still stay out of your way if you want it
347 to. Here are a few items to note when building classes with Moose.
349 Unless specified with C<extends>, any class which uses Moose will
350 inherit from L<Moose::Object>.
352 Moose will also manage all attributes (including inherited ones) that are
353 defined with C<has>. And (assuming you call C<new>, which is inherited from
354 L<Moose::Object>) this includes properly initializing all instance slots,
355 setting defaults where appropriate, and performing any type constraint checking
358 =head1 PROVIDED METHODS
360 Moose provides a number of methods to all your classes, mostly through the
361 inheritance of L<Moose::Object>. There is however, one exception.
367 This is a method which provides access to the current class's metaclass.
371 =head1 EXPORTED FUNCTIONS
373 Moose will export a number of functions into the class's namespace which
374 may then be used to set up the class. These functions all work directly
375 on the current class.
379 =item B<extends (@superclasses)>
381 This function will set the superclass(es) for the current class.
383 This approach is recommended instead of C<use base>, because C<use base>
384 actually C<push>es onto the class's C<@ISA>, whereas C<extends> will
385 replace it. This is important to ensure that classes which do not have
386 superclasses still properly inherit from L<Moose::Object>.
388 =item B<with (@roles)>
390 This will apply a given set of C<@roles> to the local class.
392 =item B<has $name|@$names =E<gt> %options>
394 This will install an attribute of a given C<$name> into the current class. If
395 the first parameter is an array reference, it will create an attribute for
396 every C<$name> in the list. The C<%options> are the same as those provided by
397 L<Class::MOP::Attribute>, in addition to the list below which are provided by
398 Moose (L<Moose::Meta::Attribute> to be more specific):
402 =item I<is =E<gt> 'rw'|'ro'>
404 The I<is> option accepts either I<rw> (for read/write) or I<ro> (for read
405 only). These will create either a read/write accessor or a read-only
406 accessor respectively, using the same name as the C<$name> of the attribute.
408 If you need more control over how your accessors are named, you can
409 use the L<reader|Class::MOP::Attribute/reader>,
410 L<writer|Class::MOP::Attribute/writer> and
411 L<accessor|Class::MOP::Attribute/accessor> options inherited from
412 L<Class::MOP::Attribute>, however if you use those, you won't need the
415 =item I<isa =E<gt> $type_name>
417 The I<isa> option uses Moose's type constraint facilities to set up runtime
418 type checking for this attribute. Moose will perform the checks during class
419 construction, and within any accessors. The C<$type_name> argument must be a
420 string. The string may be either a class name or a type defined using
421 Moose's type definition features. (Refer to L<Moose::Util::TypeConstraints>
422 for information on how to define a new type, and how to retrieve type meta-data).
424 =item I<coerce =E<gt> (1|0)>
426 This will attempt to use coercion with the supplied type constraint to change
427 the value passed into any accessors or constructors. You B<must> have supplied
428 a type constraint in order for this to work. See L<Moose::Cookbook::Basics::Recipe5>
431 =item I<does =E<gt> $role_name>
433 This will accept the name of a role which the value stored in this attribute
434 is expected to have consumed.
436 =item I<required =E<gt> (1|0)>
438 This marks the attribute as being required. This means a I<defined> value must be
439 supplied during class construction, and the attribute may never be set to
440 C<undef> with an accessor.
442 =item I<weak_ref =E<gt> (1|0)>
444 This will tell the class to store the value of this attribute as a weakened
445 reference. If an attribute is a weakened reference, it B<cannot> also be
448 =item I<lazy =E<gt> (1|0)>
450 This will tell the class to not create this slot until absolutely necessary.
451 If an attribute is marked as lazy it B<must> have a default supplied.
453 =item I<auto_deref =E<gt> (1|0)>
455 This tells the accessor whether to automatically dereference the value returned.
456 This is only legal if your C<isa> option is either C<ArrayRef> or C<HashRef>.
458 =item I<trigger =E<gt> $code>
460 The I<trigger> option is a CODE reference which will be called after the value of
461 the attribute is set. The CODE ref will be passed the instance itself, the
462 updated value and the attribute meta-object (this is for more advanced fiddling
463 and can typically be ignored). You B<cannot> have a trigger on a read-only
466 B<NOTE:> Triggers will only fire when you B<assign> to the attribute,
467 either in the constructor, or using the writer. Default and built values will
468 B<not> cause the trigger to be fired.
470 =item I<handles =E<gt> ARRAY | HASH | REGEXP | ROLE | CODE>
472 The I<handles> option provides Moose classes with automated delegation features.
473 This is a pretty complex and powerful option. It accepts many different option
474 formats, each with its own benefits and drawbacks.
476 B<NOTE:> The class being delegated to does not need to be a Moose based class,
477 which is why this feature is especially useful when wrapping non-Moose classes.
479 All I<handles> option formats share the following traits:
481 You cannot override a locally defined method with a delegated method; an
482 exception will be thrown if you try. That is to say, if you define C<foo> in
483 your class, you cannot override it with a delegated C<foo>. This is almost never
484 something you would want to do, and if it is, you should do it by hand and not
487 You cannot override any of the methods found in Moose::Object, or the C<BUILD>
488 and C<DEMOLISH> methods. These will not throw an exception, but will silently
489 move on to the next method in the list. My reasoning for this is that you would
490 almost never want to do this, since it usually breaks your class. As with
491 overriding locally defined methods, if you do want to do this, you should do it
492 manually, not with Moose.
494 You do not I<need> to have a reader (or accessor) for the attribute in order
495 to delegate to it. Moose will create a means of accessing the value for you,
496 however this will be several times B<less> efficient then if you had given
497 the attribute a reader (or accessor) to use.
499 Below is the documentation for each option format:
505 This is the most common usage for I<handles>. You basically pass a list of
506 method names to be delegated, and Moose will install a delegation method
511 This is the second most common usage for I<handles>. Instead of a list of
512 method names, you pass a HASH ref where each key is the method name you
513 want installed locally, and its value is the name of the original method
514 in the class being delegated to.
516 This can be very useful for recursive classes like trees. Here is a
517 quick example (soon to be expanded into a Moose::Cookbook recipe):
522 has 'node' => (is => 'rw', isa => 'Any');
527 default => sub { [] }
535 parent_node => 'node',
536 siblings => 'children',
540 In this example, the Tree package gets C<parent_node> and C<siblings> methods,
541 which delegate to the C<node> and C<children> methods (respectively) of the Tree
542 instance stored in the C<parent> slot.
546 The regexp option works very similar to the ARRAY option, except that it builds
547 the list of methods for you. It starts by collecting all possible methods of the
548 class being delegated to, then filters that list using the regexp supplied here.
550 B<NOTE:> An I<isa> option is required when using the regexp option format. This
551 is so that we can determine (at compile time) the method list from the class.
552 Without an I<isa> this is just not possible.
556 With the role option, you specify the name of a role whose "interface" then
557 becomes the list of methods to handle. The "interface" can be defined as; the
558 methods of the role and any required methods of the role. It should be noted
559 that this does B<not> include any method modifiers or generated attribute
560 methods (which is consistent with role composition).
564 This is the option to use when you really want to do something funky. You should
565 only use it if you really know what you are doing, as it involves manual
568 This takes a code reference, which should expect two arguments. The first is the
569 attribute meta-object this I<handles> is attached to. The second is the
570 metaclass of the class being delegated to. It expects you to return a hash (not
571 a HASH ref) of the methods you want mapped.
575 =item I<metaclass =E<gt> $metaclass_name>
577 This tells the class to use a custom attribute metaclass for this particular
578 attribute. Custom attribute metaclasses are useful for extending the
579 capabilities of the I<has> keyword: they are the simplest way to extend the MOP,
580 but they are still a fairly advanced topic and too much to cover here, see
581 L<Moose::Cookbook::Meta::Recipe1> for more information.
583 The default behavior here is to just load C<$metaclass_name>; however, we also
584 have a way to alias to a shorter name. This will first look to see if
585 B<Moose::Meta::Attribute::Custom::$metaclass_name> exists. If it does, Moose
586 will then check to see if that has the method C<register_implementation>, which
587 should return the actual name of the custom attribute metaclass. If there is no
588 C<register_implementation> method, it will fall back to using
589 B<Moose::Meta::Attribute::Custom::$metaclass_name> as the metaclass name.
591 =item I<traits =E<gt> [ @role_names ]>
593 This tells Moose to take the list of C<@role_names> and apply them to the
594 attribute meta-object. This is very similar to the I<metaclass> option, but
595 allows you to use more than one extension at a time.
597 See L<TRAIT NAME RESOLUTION> for details on how a trait name is
598 resolved to a class name.
600 Also see L<Moose::Cookbook::Meta::Recipe3> for a metaclass trait
603 =item I<builder> => Str
605 The value of this key is the name of the method that will be called to
606 obtain the value used to initialize the attribute. See the L<builder
607 option docs in Class::MOP::Attribute|Class::MOP::Attribute/builder>
608 for more information.
610 =item I<default> => SCALAR | CODE
612 The value of this key is the default value which will initialize the attribute.
614 NOTE: If the value is a simple scalar (string or number), then it can
615 be just passed as is. However, if you wish to initialize it with a
616 HASH or ARRAY ref, then you need to wrap that inside a CODE reference.
617 See the L<default option docs in
618 Class::MOP::Attribute|Class::MOP::Attribute/default> for more
621 =item I<clearer> => Str
623 Allows you to clear the value, see the L<clearer option docs in
624 Class::MOP::Attribute|Class::MOP::Attribute/clearer> for more
627 =item I<predicate> => Str
629 Basic test to see if a value has been set in the attribute, see the
630 L<predicate option docs in
631 Class::MOP::Attribute|Class::MOP::Attribute/predicate> for more
634 =item I<lazy_build> => (0|1)
636 Automatically define lazy => 1 as well as builder => "_build_$attr", clearer =>
637 "clear_$attr', predicate => 'has_$attr' unless they are already defined.
639 =item I<initializer> => Str
641 This may be a method name (referring to a method on the class with
642 this attribute) or a CODE ref. The initializer is used to set the
643 attribute value on an instance when the attribute is set during
644 instance initialization (but not when the value is being assigned
645 to). See the L<initializer option docs in
646 Class::MOP::Attribute|Class::MOP::Attribute/initializer> for more
651 =item B<has +$name =E<gt> %options>
653 This is variation on the normal attribute creator C<has> which allows you to
654 clone and extend an attribute from a superclass or from a role. Here is an
655 example of the superclass usage:
663 default => 'Hello, I am a Foo'
671 has '+message' => (default => 'Hello I am My::Foo');
673 What is happening here is that B<My::Foo> is cloning the C<message> attribute
674 from its parent class B<Foo>, retaining the C<is =E<gt> 'rw'> and C<isa =E<gt>
675 'Str'> characteristics, but changing the value in C<default>.
677 Here is another example, but within the context of a role:
685 default => 'Hello, I am a Foo'
693 has '+message' => (default => 'Hello I am My::Foo');
695 In this case, we are basically taking the attribute which the role supplied
696 and altering it within the bounds of this feature.
698 Aside from where the attributes come from (one from superclass, the other
699 from a role), this feature works exactly the same. This feature is restricted
700 somewhat, so as to try and force at least I<some> sanity into it. You are only
701 allowed to change the following attributes:
707 Change the default value of an attribute.
711 Change whether the attribute attempts to coerce a value passed to it.
715 Change if the attribute is required to have a value.
717 =item I<documentation>
719 Change the documentation string associated with the attribute.
723 Change if the attribute lazily initializes the slot.
727 You I<are> allowed to change the type without restriction.
729 It is recommended that you use this freedom with caution. We used to
730 only allow for extension only if the type was a subtype of the parent's
731 type, but we felt that was too restrictive and is better left as a
736 You are allowed to B<add> a new C<handles> definition, but you are B<not>
737 allowed to I<change> one.
741 You are allowed to B<add> a new C<builder> definition, but you are B<not>
742 allowed to I<change> one.
746 You are allowed to B<add> a new C<metaclass> definition, but you are
747 B<not> allowed to I<change> one.
751 You are allowed to B<add> additional traits to the C<traits> definition.
752 These traits will be composed into the attribute, but pre-existing traits
753 B<are not> overridden, or removed.
757 =item B<before $name|@names =E<gt> sub { ... }>
759 =item B<after $name|@names =E<gt> sub { ... }>
761 =item B<around $name|@names =E<gt> sub { ... }>
763 This three items are syntactic sugar for the before, after, and around method
764 modifier features that L<Class::MOP> provides. More information on these may be
765 found in the L<Class::MOP::Class documentation|Class::MOP::Class/"Method
770 The keyword C<super> is a no-op when called outside of an C<override> method. In
771 the context of an C<override> method, it will call the next most appropriate
772 superclass method with the same arguments as the original method.
774 =item B<override ($name, &sub)>
776 An C<override> method is a way of explicitly saying "I am overriding this
777 method from my superclass". You can call C<super> within this method, and
778 it will work as expected. The same thing I<can> be accomplished with a normal
779 method call and the C<SUPER::> pseudo-package; it is really your choice.
783 The keyword C<inner>, much like C<super>, is a no-op outside of the context of
784 an C<augment> method. You can think of C<inner> as being the inverse of
785 C<super>; the details of how C<inner> and C<augment> work is best described in
786 the L<Moose::Cookbook::Basics::Recipe6>.
788 =item B<augment ($name, &sub)>
790 An C<augment> method, is a way of explicitly saying "I am augmenting this
791 method from my superclass". Once again, the details of how C<inner> and
792 C<augment> work is best described in the L<Moose::Cookbook::Basics::Recipe6>.
796 This is the C<Carp::confess> function, and exported here because I use it
801 This is the C<Scalar::Util::blessed> function, it is exported here because I
802 use it all the time. It is highly recommended that this is used instead of
803 C<ref> anywhere you need to test for an object's class name.
807 =head1 METACLASS TRAITS
809 When you use Moose, you can also specify traits which will be applied
812 use Moose -traits => 'My::Trait';
814 This is very similar to the attribute traits feature. When you do
815 this, your class's C<meta> object will have the specified traits
816 applied to it. See L<TRAIT NAME RESOLUTION> for more details.
818 =head1 TRAIT NAME RESOLUTION
820 By default, when given a trait name, Moose simply tries to load a
821 class of the same name. If such a class does not exist, it then looks
822 for for a class matching
823 B<Moose::Meta::$type::Custom::Trait::$trait_name>. The C<$type>
824 variable here will be one of B<Attribute> or B<Class>, depending on
825 what the trait is being applied to.
827 If a class with this long name exists, Moose checks to see if it has
828 the method C<register_implementation>. This method is expected to
829 return the I<real> class name of the trait. If there is no
830 C<register_implementation> method, it will fall back to using
831 B<Moose::Meta::$type::Custom::Trait::$trait> as the trait name.
833 If all this is confusing, take a look at
834 L<Moose::Cookbook::Meta::Recipe3>, which demonstrates how to create an
837 =head1 UNIMPORTING FUNCTIONS
841 Moose offers a way to remove the keywords it exports, through the C<unimport>
842 method. You simply have to say C<no Moose> at the bottom of your code for this
843 to work. Here is an example:
848 has 'first_name' => (is => 'rw', isa => 'Str');
849 has 'last_name' => (is => 'rw', isa => 'Str');
853 $self->first_name . ' ' . $self->last_name
856 no Moose; # keywords are removed from the Person package
858 =head1 EXTENDING AND EMBEDDING MOOSE
860 To learn more about extending Moose, we recommend checking out the
861 "Extending" recipes in the L<Moose::Cookbook>, starting with
862 L<Moose::Cookbook::Extending::Recipe1>, which provides an overview of
863 all the different ways you might extend Moose.
865 =head2 B<< Moose->init_meta(for_class => $class, base_class => $baseclass, metaclass => $metaclass) >>
867 The C<init_meta> method sets up the metaclass object for the class
868 specified by C<for_class>. This method injects a a C<meta> accessor
869 into the class so you can get at this object. It also sets the class's
870 superclass to C<base_class>, with L<Moose::Object> as the default.
872 You can specify an alternate metaclass with the C<metaclass> parameter.
874 For more detail on this topic, see L<Moose::Cookbook::Extending::Recipe2>.
876 This method used to be documented as a function which accepted
877 positional parameters. This calling style will still work for
878 backwards compatibility, but is deprecated.
882 Moose's C<import> method supports the L<Sub::Exporter> form of C<{into =E<gt> $pkg}>
883 and C<{into_level =E<gt> 1}>.
885 B<NOTE>: Doing this is more or less deprecated. Use L<Moose::Exporter>
886 instead, which lets you stack multiple C<Moose.pm>-alike modules
887 sanely. It handles getting the exported functions into the right place
890 =head2 B<throw_error>
892 An alias for C<confess>, used by internally by Moose.
894 =head1 METACLASS COMPATIBILITY AND MOOSE
896 Metaclass compatibility is a thorny subject. You should start by
897 reading the "About Metaclass compatibility" section in the
900 Moose will attempt to resolve a few cases of metaclass incompatibility
901 when you set the superclasses for a class, unlike C<Class::MOP>, which
902 simply dies if the metaclasses are incompatible.
904 In actuality, Moose fixes incompatibility for I<all> of a class's
905 metaclasses, not just the class metaclass. That includes the instance
906 metaclass, attribute metaclass, as well as its constructor class and
907 destructor class. However, for simplicity this discussion will just
908 refer to "metaclass", meaning the class metaclass, most of the time.
910 Moose has two algorithms for fixing metaclass incompatibility.
912 The first algorithm is very simple. If all the metaclass for the
913 parent is a I<subclass> of the child's metaclass, then we simply
914 replace the child's metaclass with the parent's.
916 The second algorithm is more complicated. It tries to determine if the
917 metaclasses only "differ by roles". This means that the parent and
918 child's metaclass share a common ancestor in their respective
919 hierarchies, and that the subclasses under the common ancestor are
920 only different because of role applications. This case is actually
921 fairly common when you mix and match various C<MooseX::*> modules,
922 many of which apply roles to the metaclass.
924 If the parent and child do differ by roles, Moose replaces the
925 metaclass in the child with a newly created metaclass. This metaclass
926 is a subclass of the parent's metaclass, does all of the roles that
927 the child's metaclass did before being replaced. Effectively, this
928 means the new metaclass does all of the roles done by both the
929 parent's and child's original metaclasses.
931 Ultimately, this is all transparent to you except in the case of an
932 unresolvable conflict.
934 =head2 The MooseX:: namespace
936 Generally if you're writing an extension I<for> Moose itself you'll want
937 to put your extension in the C<MooseX::> namespace. This namespace is
938 specifically for extensions that make Moose better or different in some
939 fundamental way. It is traditionally B<not> for a package that just happens
940 to use Moose. This namespace follows from the examples of the C<LWPx::>
941 and C<DBIx::> namespaces that perform the same function for C<LWP> and C<DBI>
950 It should be noted that C<super> and C<inner> B<cannot> be used in the same
951 method. However, they may be combined within the same class hierarchy; see
952 F<t/014_override_augment_inner_super.t> for an example.
954 The reason for this is that C<super> is only valid within a method
955 with the C<override> modifier, and C<inner> will never be valid within an
956 C<override> method. In fact, C<augment> will skip over any C<override> methods
957 when searching for its appropriate C<inner>.
959 This might seem like a restriction, but I am of the opinion that keeping these
960 two features separate (yet interoperable) actually makes them easy to use, since
961 their behavior is then easier to predict. Time will tell whether I am right or
962 not (UPDATE: so far so good).
966 =head1 ACKNOWLEDGEMENTS
970 =item I blame Sam Vilain for introducing me to the insanity that is meta-models.
972 =item I blame Audrey Tang for then encouraging my meta-model habit in #perl6.
974 =item Without Yuval "nothingmuch" Kogman this module would not be possible,
975 and it certainly wouldn't have this name ;P
977 =item The basis of the TypeContraints module was Rob Kinyon's idea
978 originally, I just ran with it.
980 =item Thanks to mst & chansen and the whole #moose posse for all the
981 early ideas/feature-requests/encouragement/bug-finding.
983 =item Thanks to David "Theory" Wheeler for meta-discussions and spelling fixes.
991 =item L<http://www.iinteractive.com/moose>
993 This is the official web home of Moose, it contains links to our public SVN repo
994 as well as links to a number of talks and articles on Moose and Moose related
997 =item L<Moose::Cookbook> - How to cook a Moose
999 =item The Moose is flying, a tutorial by Randal Schwartz
1001 Part 1 - L<http://www.stonehenge.com/merlyn/LinuxMag/col94.html>
1003 Part 2 - L<http://www.stonehenge.com/merlyn/LinuxMag/col95.html>
1005 =item L<Class::MOP> documentation
1007 =item The #moose channel on irc.perl.org
1009 =item The Moose mailing list - moose@perl.org
1011 =item Moose stats on ohloh.net - L<http://www.ohloh.net/projects/moose>
1013 =item Several Moose extension modules in the C<MooseX::> namespace.
1015 See L<http://search.cpan.org/search?query=MooseX::> for extensions.
1023 =item The Art of the MetaObject Protocol
1025 I mention this in the L<Class::MOP> docs too, this book was critical in
1026 the development of both modules and is highly recommended.
1034 =item L<http://www.cs.utah.edu/plt/publications/oopsla04-gff.pdf>
1036 This paper (suggested by lbr on #moose) was what lead to the implementation
1037 of the C<super>/C<override> and C<inner>/C<augment> features. If you really
1038 want to understand them, I suggest you read this.
1044 All complex software has bugs lurking in it, and this module is no
1045 exception. If you find a bug please either email me, or add the bug
1048 =head1 FEATURE REQUESTS
1050 We are very strict about what features we add to the Moose core, especially
1051 the user-visible features. Instead we have made sure that the underlying
1052 meta-system of Moose is as extensible as possible so that you can add your
1053 own features easily. That said, occasionally there is a feature needed in the
1054 meta-system to support your planned extension, in which case you should
1055 either email the mailing list or join us on irc at #moose to discuss.
1059 Moose is an open project, there are at this point dozens of people who have
1060 contributed, and can contribute. If you have added anything to the Moose
1061 project you have a commit bit on this file and can add your name to the list.
1065 However there are only a few people with the rights to release a new version
1066 of Moose. The Moose Cabal are the people to go to with questions regarding
1067 the wider purview of Moose, and help out maintaining not just the code
1068 but the community as well.
1070 Stevan (stevan) Little E<lt>stevan@iinteractive.comE<gt>
1072 Yuval (nothingmuch) Kogman
1074 Shawn (sartak) Moore
1076 Dave (autarch) Rolsky E<lt>autarch@urth.orgE<gt>
1078 =head2 OTHER CONTRIBUTORS
1082 Adam (Alias) Kennedy
1084 Anders (Debolaz) Nor Berle
1086 Nathan (kolibre) Gray
1088 Christian (chansen) Hansen
1090 Hans Dieter (confound) Pearcey
1092 Eric (ewilhelm) Wilhelm
1094 Guillermo (groditi) Roditi
1096 Jess (castaway) Robinson
1100 Robert (phaylon) Sedlacek
1104 Scott (konobi) McWhirter
1106 Shlomi (rindolf) Fish
1108 Chris (perigrin) Prather
1110 Wallace (wreis) Reis
1112 Jonathan (jrockway) Rockway
1114 Piotr (dexter) Roszatycki
1116 Sam (mugwump) Vilain
1118 ... and many other #moose folks
1120 =head1 COPYRIGHT AND LICENSE
1122 Copyright 2006-2008 by Infinity Interactive, Inc.
1124 L<http://www.iinteractive.com>
1126 This library is free software; you can redistribute it and/or modify
1127 it under the same terms as Perl itself.