8 $VERSION = eval $VERSION;
9 our $AUTHORITY = 'cpan:STEVAN';
11 use Scalar::Util 'blessed';
18 use Moose::Meta::Class;
19 use Moose::Meta::TypeConstraint;
20 use Moose::Meta::TypeCoercion;
21 use Moose::Meta::Attribute;
22 use Moose::Meta::Instance;
26 use Moose::Meta::Role;
27 use Moose::Meta::Role::Composite;
28 use Moose::Meta::Role::Application;
29 use Moose::Meta::Role::Application::RoleSummation;
30 use Moose::Meta::Role::Application::ToClass;
31 use Moose::Meta::Role::Application::ToRole;
32 use Moose::Meta::Role::Application::ToInstance;
34 use Moose::Util::TypeConstraints;
37 use Moose::Attribute::Native;
48 Moose->throw_error("Must derive at least one class") unless @_;
50 # this checks the metaclass to make sure
51 # it is correct, sometimes it can get out
52 # of sync when the classes are being built
53 Moose::Meta::Class->initialize($class)->superclasses(@_);
58 Moose::Util::apply_all_roles(Class::MOP::Class->initialize($class), @_);
65 Moose->throw_error('Usage: has \'name\' => ( key => value, ... )')
68 my %options = ( definition_context => Moose::Util::_caller_info(), @_ );
69 my $attrs = ( ref($name) eq 'ARRAY' ) ? $name : [ ($name) ];
70 Class::MOP::Class->initialize($class)->add_attribute( $_, %options ) for @$attrs;
75 Moose::Util::add_method_modifier($class, 'before', \@_);
80 Moose::Util::add_method_modifier($class, 'after', \@_);
85 Moose::Util::add_method_modifier($class, 'around', \@_);
93 # This check avoids a recursion loop - see
94 # t/100_bugs/020_super_recursion.t
95 return if defined $SUPER_PACKAGE && $SUPER_PACKAGE ne caller();
96 return unless $SUPER_BODY; $SUPER_BODY->(@SUPER_ARGS);
101 my ( $name, $method ) = @_;
102 Class::MOP::Class->initialize($class)->add_override_method_modifier( $name => $method );
107 our ( %INNER_BODY, %INNER_ARGS );
109 if ( my $body = $INNER_BODY{$pkg} ) {
110 my @args = @{ $INNER_ARGS{$pkg} };
111 local $INNER_ARGS{$pkg};
112 local $INNER_BODY{$pkg};
113 return $body->(@args);
121 my ( $name, $method ) = @_;
122 Class::MOP::Class->initialize($class)->add_augment_method_modifier( $name => $method );
125 Moose::Exporter->setup_import_methods(
127 qw( extends with has before after around override augment)
132 \&Scalar::Util::blessed,
137 # This used to be called as a function. This hack preserves
138 # backwards compatibility.
139 if ( $_[0] ne __PACKAGE__ ) {
140 return __PACKAGE__->init_meta(
150 my $class = $args{for_class}
151 or Moose->throw_error("Cannot call init_meta without specifying a for_class");
152 my $base_class = $args{base_class} || 'Moose::Object';
153 my $metaclass = $args{metaclass} || 'Moose::Meta::Class';
155 Moose->throw_error("The Metaclass $metaclass must be a subclass of Moose::Meta::Class.")
156 unless $metaclass->isa('Moose::Meta::Class');
158 # make a subtype for each Moose class
160 unless find_type_constraint($class);
164 if ( $meta = Class::MOP::get_metaclass_by_name($class) ) {
165 unless ( $meta->isa("Moose::Meta::Class") ) {
166 Moose->throw_error("$class already has a metaclass, but it does not inherit $metaclass ($meta)");
169 # no metaclass, no 'meta' method
171 # now we check whether our ancestors have metaclass, and if so borrow that
172 my ( undef, @isa ) = @{ $class->mro::get_linear_isa };
174 foreach my $ancestor ( @isa ) {
175 my $ancestor_meta = Class::MOP::get_metaclass_by_name($ancestor) || next;
177 my $ancestor_meta_class = ($ancestor_meta->is_immutable
178 ? $ancestor_meta->get_mutable_metaclass_name
179 : ref($ancestor_meta));
181 # if we have an ancestor metaclass that inherits $metaclass, we use
182 # that. This is like _fix_metaclass_incompatibility, but we can do it now.
184 # the case of having an ancestry is not very common, but arises in
186 unless ( $metaclass->isa( $ancestor_meta_class ) ) {
187 if ( $ancestor_meta_class->isa($metaclass) ) {
188 $metaclass = $ancestor_meta_class;
193 $meta = $metaclass->initialize($class);
196 if ( $class->can('meta') ) {
197 # check 'meta' method
199 # it may be inherited
202 # this is the case where the metaclass pragma
203 # was used before the 'use Moose' statement to
204 # override a specific class
205 my $method_meta = $class->meta;
207 ( blessed($method_meta) && $method_meta->isa('Moose::Meta::Class') )
208 || Moose->throw_error("$class already has a &meta function, but it does not return a Moose::Meta::Class ($method_meta)");
210 $meta = $method_meta;
213 unless ( $meta->has_method("meta") ) { # don't overwrite
214 # also check for inherited non moose 'meta' method?
215 # FIXME also skip this if the user requested by passing an option
218 # re-initialize so it inherits properly
219 $metaclass->initialize( ref($_[0]) || $_[0] );
224 # make sure they inherit from Moose::Object
225 $meta->superclasses($base_class)
226 unless $meta->superclasses();
231 # This may be used in some older MooseX extensions.
233 goto &Moose::Exporter::_get_caller;
236 ## make 'em all immutable
239 inline_constructor => 1,
240 constructor_name => "_new",
241 # these are Class::MOP accessors, so they need inlining
242 inline_accessors => 1
243 ) for grep { $_->is_mutable }
246 Moose::Meta::Attribute
248 Moose::Meta::Instance
250 Moose::Meta::TypeCoercion
251 Moose::Meta::TypeCoercion::Union
254 Moose::Meta::Method::Accessor
255 Moose::Meta::Method::Constructor
256 Moose::Meta::Method::Destructor
257 Moose::Meta::Method::Overridden
258 Moose::Meta::Method::Augmented
261 Moose::Meta::Role::Method
262 Moose::Meta::Role::Method::Required
263 Moose::Meta::Role::Method::Conflicting
265 Moose::Meta::Role::Composite
267 Moose::Meta::Role::Application
268 Moose::Meta::Role::Application::RoleSummation
269 Moose::Meta::Role::Application::ToClass
270 Moose::Meta::Role::Application::ToRole
271 Moose::Meta::Role::Application::ToInstance
282 Moose - A postmodern object system for Perl 5
287 use Moose; # automatically turns on strict and warnings
289 has 'x' => (is => 'rw', isa => 'Int');
290 has 'y' => (is => 'rw', isa => 'Int');
303 has 'z' => (is => 'rw', isa => 'Int');
305 after 'clear' => sub {
312 Moose is an extension of the Perl 5 object system.
314 The main goal of Moose is to make Perl 5 Object Oriented programming
315 easier, more consistent and less tedious. With Moose you can to think
316 more about what you want to do and less about the mechanics of OOP.
318 Additionally, Moose is built on top of L<Class::MOP>, which is a
319 metaclass system for Perl 5. This means that Moose not only makes
320 building normal Perl 5 objects better, but it provides the power of
321 metaclass programming as well.
325 If you're new to Moose, the best place to start is the
326 L<Moose::Manual> docs, followed by the L<Moose::Cookbook>. The intro
327 will show you what Moose is, and how it makes Perl 5 OO better.
329 The cookbook recipes on Moose basics will get you up to speed with
330 many of Moose's features quickly. Once you have an idea of what Moose
331 can do, you can use the API documentation to get more detail on
332 features which interest you.
334 =head2 Moose Extensions
336 The C<MooseX::> namespace is the official place to find Moose extensions.
337 These extensions can be found on the CPAN. The easiest way to find them
338 is to search for them (L<http://search.cpan.org/search?query=MooseX::>),
339 or to examine L<Task::Moose> which aims to keep an up-to-date, easily
340 installable list of Moose extensions.
342 =head1 BUILDING CLASSES WITH MOOSE
344 Moose makes every attempt to provide as much convenience as possible during
345 class construction/definition, but still stay out of your way if you want it
346 to. Here are a few items to note when building classes with Moose.
348 Unless specified with C<extends>, any class which uses Moose will
349 inherit from L<Moose::Object>.
351 Moose will also manage all attributes (including inherited ones) that are
352 defined with C<has>. And (assuming you call C<new>, which is inherited from
353 L<Moose::Object>) this includes properly initializing all instance slots,
354 setting defaults where appropriate, and performing any type constraint checking
357 =head1 PROVIDED METHODS
359 Moose provides a number of methods to all your classes, mostly through the
360 inheritance of L<Moose::Object>. There is however, one exception.
366 This is a method which provides access to the current class's metaclass.
370 =head1 EXPORTED FUNCTIONS
372 Moose will export a number of functions into the class's namespace which
373 may then be used to set up the class. These functions all work directly
374 on the current class.
378 =item B<extends (@superclasses)>
380 This function will set the superclass(es) for the current class.
382 This approach is recommended instead of C<use base>, because C<use base>
383 actually C<push>es onto the class's C<@ISA>, whereas C<extends> will
384 replace it. This is important to ensure that classes which do not have
385 superclasses still properly inherit from L<Moose::Object>.
387 =item B<with (@roles)>
389 This will apply a given set of C<@roles> to the local class.
391 =item B<has $name|@$names =E<gt> %options>
393 This will install an attribute of a given C<$name> into the current class. If
394 the first parameter is an array reference, it will create an attribute for
395 every C<$name> in the list. The C<%options> are the same as those provided by
396 L<Class::MOP::Attribute>, in addition to the list below which are provided by
397 Moose (L<Moose::Meta::Attribute> to be more specific):
401 =item I<is =E<gt> 'rw'|'ro'>
403 The I<is> option accepts either I<rw> (for read/write) or I<ro> (for read
404 only). These will create either a read/write accessor or a read-only
405 accessor respectively, using the same name as the C<$name> of the attribute.
407 If you need more control over how your accessors are named, you can
408 use the L<reader|Class::MOP::Attribute/reader>,
409 L<writer|Class::MOP::Attribute/writer> and
410 L<accessor|Class::MOP::Attribute/accessor> options inherited from
411 L<Class::MOP::Attribute>, however if you use those, you won't need the
414 =item I<isa =E<gt> $type_name>
416 The I<isa> option uses Moose's type constraint facilities to set up runtime
417 type checking for this attribute. Moose will perform the checks during class
418 construction, and within any accessors. The C<$type_name> argument must be a
419 string. The string may be either a class name or a type defined using
420 Moose's type definition features. (Refer to L<Moose::Util::TypeConstraints>
421 for information on how to define a new type, and how to retrieve type meta-data).
423 =item I<coerce =E<gt> (1|0)>
425 This will attempt to use coercion with the supplied type constraint to change
426 the value passed into any accessors or constructors. You B<must> have supplied
427 a type constraint in order for this to work. See L<Moose::Cookbook::Basics::Recipe5>
430 =item I<does =E<gt> $role_name>
432 This will accept the name of a role which the value stored in this attribute
433 is expected to have consumed.
435 =item I<required =E<gt> (1|0)>
437 This marks the attribute as being required. This means a value must be
438 supplied during class construction, I<or> the attribute must be lazy
439 and have either a default or a builder. Note that c<required> does not
440 say anything about the attribute's value, which can be C<undef>.
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
461 the value of the attribute is set. The CODE ref will be passed the
462 instance itself and the updated value. You B<can> have a trigger on
463 a read-only attribute.
465 B<NOTE:> Triggers will only fire when you B<assign> to the attribute,
466 either in the constructor, or using the writer. Default and built values will
467 B<not> cause the trigger to be fired.
469 =item I<handles =E<gt> ARRAY | HASH | REGEXP | ROLE | DUCKTYPE | CODE>
471 The I<handles> option provides Moose classes with automated delegation features.
472 This is a pretty complex and powerful option. It accepts many different option
473 formats, each with its own benefits and drawbacks.
475 B<NOTE:> The class being delegated to does not need to be a Moose based class,
476 which is why this feature is especially useful when wrapping non-Moose classes.
478 All I<handles> option formats share the following traits:
480 You cannot override a locally defined method with a delegated method; an
481 exception will be thrown if you try. That is to say, if you define C<foo> in
482 your class, you cannot override it with a delegated C<foo>. This is almost never
483 something you would want to do, and if it is, you should do it by hand and not
486 You cannot override any of the methods found in Moose::Object, or the C<BUILD>
487 and C<DEMOLISH> methods. These will not throw an exception, but will silently
488 move on to the next method in the list. My reasoning for this is that you would
489 almost never want to do this, since it usually breaks your class. As with
490 overriding locally defined methods, if you do want to do this, you should do it
491 manually, not with Moose.
493 You do not I<need> to have a reader (or accessor) for the attribute in order
494 to delegate to it. Moose will create a means of accessing the value for you,
495 however this will be several times B<less> efficient then if you had given
496 the attribute a reader (or accessor) to use.
498 Below is the documentation for each option format:
504 This is the most common usage for I<handles>. You basically pass a list of
505 method names to be delegated, and Moose will install a delegation method
510 This is the second most common usage for I<handles>. Instead of a list of
511 method names, you pass a HASH ref where each key is the method name you
512 want installed locally, and its value is the name of the original method
513 in the class being delegated to.
515 This can be very useful for recursive classes like trees. Here is a
516 quick example (soon to be expanded into a Moose::Cookbook recipe):
521 has 'node' => (is => 'rw', isa => 'Any');
526 default => sub { [] }
534 parent_node => 'node',
535 siblings => 'children',
539 In this example, the Tree package gets C<parent_node> and C<siblings> methods,
540 which delegate to the C<node> and C<children> methods (respectively) of the Tree
541 instance stored in the C<parent> slot.
543 You may also use an array reference to curry arguments to the original method.
547 handles => { set_foo => [ set => [ 'foo' ] ] },
550 # $self->set_foo(...) calls $self->thing->set('foo', ...)
552 The first element of the array reference is the original method name, and the
553 second is an array reference of curried arguments.
557 The regexp option works very similar to the ARRAY option, except that it builds
558 the list of methods for you. It starts by collecting all possible methods of the
559 class being delegated to, then filters that list using the regexp supplied here.
561 B<NOTE:> An I<isa> option is required when using the regexp option format. This
562 is so that we can determine (at compile time) the method list from the class.
563 Without an I<isa> this is just not possible.
567 With the role option, you specify the name of a role whose "interface" then
568 becomes the list of methods to handle. The "interface" can be defined as; the
569 methods of the role and any required methods of the role. It should be noted
570 that this does B<not> include any method modifiers or generated attribute
571 methods (which is consistent with role composition).
575 With the duck type option, you pass a duck type object whose "interface" then
576 becomes the list of methods to handle. The "interface" can be defined as; the
577 list of methods passed to C<duck_type> to create a duck type object. For more
578 information on C<duck_type> please check
579 L<Moose::Util::TypeConstraints>.
583 This is the option to use when you really want to do something funky. You should
584 only use it if you really know what you are doing, as it involves manual
587 This takes a code reference, which should expect two arguments. The first is the
588 attribute meta-object this I<handles> is attached to. The second is the
589 metaclass of the class being delegated to. It expects you to return a hash (not
590 a HASH ref) of the methods you want mapped.
594 =item I<metaclass =E<gt> $metaclass_name>
596 This tells the class to use a custom attribute metaclass for this particular
597 attribute. Custom attribute metaclasses are useful for extending the
598 capabilities of the I<has> keyword: they are the simplest way to extend the MOP,
599 but they are still a fairly advanced topic and too much to cover here, see
600 L<Moose::Cookbook::Meta::Recipe1> for more information.
602 The default behavior here is to just load C<$metaclass_name>; however, we also
603 have a way to alias to a shorter name. This will first look to see if
604 B<Moose::Meta::Attribute::Custom::$metaclass_name> exists. If it does, Moose
605 will then check to see if that has the method C<register_implementation>, which
606 should return the actual name of the custom attribute metaclass. If there is no
607 C<register_implementation> method, it will fall back to using
608 B<Moose::Meta::Attribute::Custom::$metaclass_name> as the metaclass name.
610 =item I<traits =E<gt> [ @role_names ]>
612 This tells Moose to take the list of C<@role_names> and apply them to the
613 attribute meta-object. This is very similar to the I<metaclass> option, but
614 allows you to use more than one extension at a time.
616 See L<TRAIT NAME RESOLUTION> for details on how a trait name is
617 resolved to a class name.
619 Also see L<Moose::Cookbook::Meta::Recipe3> for a metaclass trait
622 =item I<builder> => Str
624 The value of this key is the name of the method that will be called to
625 obtain the value used to initialize the attribute. See the L<builder
626 option docs in Class::MOP::Attribute|Class::MOP::Attribute/builder>
627 and/or L<Moose::Cookbook::Basics::Recipe9> for more information.
629 =item I<default> => SCALAR | CODE
631 The value of this key is the default value which will initialize the attribute.
633 NOTE: If the value is a simple scalar (string or number), then it can
634 be just passed as is. However, if you wish to initialize it with a
635 HASH or ARRAY ref, then you need to wrap that inside a CODE reference.
636 See the L<default option docs in
637 Class::MOP::Attribute|Class::MOP::Attribute/default> for more
640 =item I<clearer> => Str
642 Creates a method allowing you to clear the value, see the L<clearer option
643 docs in Class::MOP::Attribute|Class::MOP::Attribute/clearer> for more
646 =item I<predicate> => Str
648 Creates a method to perform a basic test to see if a value has been set in the
649 attribute, see the L<predicate option docs in
650 Class::MOP::Attribute|Class::MOP::Attribute/predicate> for more information.
652 =item I<lazy_build> => (0|1)
654 Automatically define lazy => 1 as well as builder => "_build_$attr", clearer =>
655 "clear_$attr', predicate => 'has_$attr' unless they are already defined.
657 =item I<initializer> => Str
659 This may be a method name (referring to a method on the class with
660 this attribute) or a CODE ref. The initializer is used to set the
661 attribute value on an instance when the attribute is set during
662 instance initialization (but not when the value is being assigned
663 to). See the L<initializer option docs in
664 Class::MOP::Attribute|Class::MOP::Attribute/initializer> for more
667 =item I<documentation> => $string
669 An arbitrary string that can be retrieved later by calling C<<
670 $attr->documentation >>.
676 =item B<has +$name =E<gt> %options>
678 This is variation on the normal attribute creator C<has> which allows you to
679 clone and extend an attribute from a superclass or from a role. Here is an
680 example of the superclass usage:
688 default => 'Hello, I am a Foo'
696 has '+message' => (default => 'Hello I am My::Foo');
698 What is happening here is that B<My::Foo> is cloning the C<message> attribute
699 from its parent class B<Foo>, retaining the C<is =E<gt> 'rw'> and C<isa =E<gt>
700 'Str'> characteristics, but changing the value in C<default>.
702 Here is another example, but within the context of a role:
710 default => 'Hello, I am a Foo'
718 has '+message' => (default => 'Hello I am My::Foo');
720 In this case, we are basically taking the attribute which the role supplied
721 and altering it within the bounds of this feature.
723 Note that you can only extend an attribute from either a superclass or a role,
724 you cannot extend an attribute in a role that composes over an attribute from
727 Aside from where the attributes come from (one from superclass, the other
728 from a role), this feature works exactly the same. This feature is restricted
729 somewhat, so as to try and force at least I<some> sanity into it. You are only
730 allowed to change the following attributes:
736 Change the default value of an attribute.
740 Change whether the attribute attempts to coerce a value passed to it.
744 Change if the attribute is required to have a value.
746 =item I<documentation>
748 Change the documentation string associated with the attribute.
752 Change if the attribute lazily initializes the slot.
756 You I<are> allowed to change the type without restriction.
758 It is recommended that you use this freedom with caution. We used to
759 only allow for extension only if the type was a subtype of the parent's
760 type, but we felt that was too restrictive and is better left as a
765 You are allowed to B<add> a new C<handles> definition, but you are B<not>
766 allowed to I<change> one.
770 You are allowed to B<add> a new C<builder> definition, but you are B<not>
771 allowed to I<change> one.
775 You are allowed to B<add> a new C<metaclass> definition, but you are
776 B<not> allowed to I<change> one.
780 You are allowed to B<add> additional traits to the C<traits> definition.
781 These traits will be composed into the attribute, but preexisting traits
782 B<are not> overridden, or removed.
786 =item B<before $name|@names =E<gt> sub { ... }>
788 =item B<after $name|@names =E<gt> sub { ... }>
790 =item B<around $name|@names =E<gt> sub { ... }>
792 These three items are syntactic sugar for the before, after, and around method
793 modifier features that L<Class::MOP> provides. More information on these may be
794 found in the L<Class::MOP::Class documentation|Class::MOP::Class/"Method
799 The keyword C<super> is a no-op when called outside of an C<override> method. In
800 the context of an C<override> method, it will call the next most appropriate
801 superclass method with the same arguments as the original method.
803 =item B<override ($name, &sub)>
805 An C<override> method is a way of explicitly saying "I am overriding this
806 method from my superclass". You can call C<super> within this method, and
807 it will work as expected. The same thing I<can> be accomplished with a normal
808 method call and the C<SUPER::> pseudo-package; it is really your choice.
812 The keyword C<inner>, much like C<super>, is a no-op outside of the context of
813 an C<augment> method. You can think of C<inner> as being the inverse of
814 C<super>; the details of how C<inner> and C<augment> work is best described in
815 the L<Moose::Cookbook::Basics::Recipe6>.
817 =item B<augment ($name, &sub)>
819 An C<augment> method, is a way of explicitly saying "I am augmenting this
820 method from my superclass". Once again, the details of how C<inner> and
821 C<augment> work is best described in the L<Moose::Cookbook::Basics::Recipe6>.
825 This is the C<Carp::confess> function, and exported here because I use it
830 This is the C<Scalar::Util::blessed> function, it is exported here because I
831 use it all the time. It is highly recommended that this is used instead of
832 C<ref> anywhere you need to test for an object's class name.
838 When you use Moose, you can specify which metaclass to use:
840 use Moose -metaclass => 'My::Meta::Class';
842 You can also specify traits which will be applied to your metaclass:
844 use Moose -traits => 'My::Trait';
846 This is very similar to the attribute traits feature. When you do
847 this, your class's C<meta> object will have the specified traits
848 applied to it. See L<TRAIT NAME RESOLUTION> for more details.
850 =head2 Trait Name Resolution
852 By default, when given a trait name, Moose simply tries to load a
853 class of the same name. If such a class does not exist, it then looks
854 for for a class matching
855 B<Moose::Meta::$type::Custom::Trait::$trait_name>. The C<$type>
856 variable here will be one of B<Attribute> or B<Class>, depending on
857 what the trait is being applied to.
859 If a class with this long name exists, Moose checks to see if it has
860 the method C<register_implementation>. This method is expected to
861 return the I<real> class name of the trait. If there is no
862 C<register_implementation> method, it will fall back to using
863 B<Moose::Meta::$type::Custom::Trait::$trait> as the trait name.
865 If all this is confusing, take a look at
866 L<Moose::Cookbook::Meta::Recipe3>, which demonstrates how to create an
869 =head1 UNIMPORTING FUNCTIONS
873 Moose offers a way to remove the keywords it exports, through the C<unimport>
874 method. You simply have to say C<no Moose> at the bottom of your code for this
875 to work. Here is an example:
880 has 'first_name' => (is => 'rw', isa => 'Str');
881 has 'last_name' => (is => 'rw', isa => 'Str');
885 $self->first_name . ' ' . $self->last_name
888 no Moose; # keywords are removed from the Person package
890 =head1 EXTENDING AND EMBEDDING MOOSE
892 To learn more about extending Moose, we recommend checking out the
893 "Extending" recipes in the L<Moose::Cookbook>, starting with
894 L<Moose::Cookbook::Extending::Recipe1>, which provides an overview of
895 all the different ways you might extend Moose.
897 =head2 B<< Moose->init_meta(for_class => $class, base_class => $baseclass, metaclass => $metaclass) >>
899 The C<init_meta> method sets up the metaclass object for the class
900 specified by C<for_class>. This method injects a a C<meta> accessor
901 into the class so you can get at this object. It also sets the class's
902 superclass to C<base_class>, with L<Moose::Object> as the default.
904 C<init_meta> returns the metaclass object for C<$class>.
906 You can specify an alternate metaclass with the C<metaclass> option.
908 For more detail on this topic, see L<Moose::Cookbook::Extending::Recipe2>.
910 This method used to be documented as a function which accepted
911 positional parameters. This calling style will still work for
912 backwards compatibility, but is deprecated.
916 Moose's C<import> method supports the L<Sub::Exporter> form of C<{into =E<gt> $pkg}>
917 and C<{into_level =E<gt> 1}>.
919 B<NOTE>: Doing this is more or less deprecated. Use L<Moose::Exporter>
920 instead, which lets you stack multiple C<Moose.pm>-alike modules
921 sanely. It handles getting the exported functions into the right place
924 =head2 B<throw_error>
926 An alias for C<confess>, used by internally by Moose.
928 =head1 METACLASS COMPATIBILITY AND MOOSE
930 Metaclass compatibility is a thorny subject. You should start by
931 reading the "About Metaclass compatibility" section in the
934 Moose will attempt to resolve a few cases of metaclass incompatibility
935 when you set the superclasses for a class, unlike C<Class::MOP>, which
936 simply dies if the metaclasses are incompatible.
938 In actuality, Moose fixes incompatibility for I<all> of a class's
939 metaclasses, not just the class metaclass. That includes the instance
940 metaclass, attribute metaclass, as well as its constructor class and
941 destructor class. However, for simplicity this discussion will just
942 refer to "metaclass", meaning the class metaclass, most of the time.
944 Moose has two algorithms for fixing metaclass incompatibility.
946 The first algorithm is very simple. If all the metaclass for the
947 parent is a I<subclass> of the child's metaclass, then we simply
948 replace the child's metaclass with the parent's.
950 The second algorithm is more complicated. It tries to determine if the
951 metaclasses only "differ by roles". This means that the parent and
952 child's metaclass share a common ancestor in their respective
953 hierarchies, and that the subclasses under the common ancestor are
954 only different because of role applications. This case is actually
955 fairly common when you mix and match various C<MooseX::*> modules,
956 many of which apply roles to the metaclass.
958 If the parent and child do differ by roles, Moose replaces the
959 metaclass in the child with a newly created metaclass. This metaclass
960 is a subclass of the parent's metaclass, does all of the roles that
961 the child's metaclass did before being replaced. Effectively, this
962 means the new metaclass does all of the roles done by both the
963 parent's and child's original metaclasses.
965 Ultimately, this is all transparent to you except in the case of an
966 unresolvable conflict.
968 =head2 The MooseX:: namespace
970 Generally if you're writing an extension I<for> Moose itself you'll want
971 to put your extension in the C<MooseX::> namespace. This namespace is
972 specifically for extensions that make Moose better or different in some
973 fundamental way. It is traditionally B<not> for a package that just happens
974 to use Moose. This namespace follows from the examples of the C<LWPx::>
975 and C<DBIx::> namespaces that perform the same function for C<LWP> and C<DBI>
984 It should be noted that C<super> and C<inner> B<cannot> be used in the same
985 method. However, they may be combined within the same class hierarchy; see
986 F<t/014_override_augment_inner_super.t> for an example.
988 The reason for this is that C<super> is only valid within a method
989 with the C<override> modifier, and C<inner> will never be valid within an
990 C<override> method. In fact, C<augment> will skip over any C<override> methods
991 when searching for its appropriate C<inner>.
993 This might seem like a restriction, but I am of the opinion that keeping these
994 two features separate (yet interoperable) actually makes them easy to use, since
995 their behavior is then easier to predict. Time will tell whether I am right or
996 not (UPDATE: so far so good).
1002 We offer both a mailing list and a very active IRC channel.
1004 The mailing list is L<moose@perl.org>. You must be subscribed to send
1005 a message. To subscribe, send an empty message to
1006 L<moose-subscribe@perl.org>
1008 You can also visit us at L<#moose on
1009 irc.perl.org|irc://irc.perl.org/#moose>. This channel is quite active,
1010 and questions at all levels (on Moose-related topics ;) are welcome.
1012 =head1 ACKNOWLEDGEMENTS
1016 =item I blame Sam Vilain for introducing me to the insanity that is meta-models.
1018 =item I blame Audrey Tang for then encouraging my meta-model habit in #perl6.
1020 =item Without Yuval "nothingmuch" Kogman this module would not be possible,
1021 and it certainly wouldn't have this name ;P
1023 =item The basis of the TypeContraints module was Rob Kinyon's idea
1024 originally, I just ran with it.
1026 =item Thanks to mst & chansen and the whole #moose posse for all the
1027 early ideas/feature-requests/encouragement/bug-finding.
1029 =item Thanks to David "Theory" Wheeler for meta-discussions and spelling fixes.
1037 =item L<http://www.iinteractive.com/moose>
1039 This is the official web home of Moose, it contains links to our public SVN repository
1040 as well as links to a number of talks and articles on Moose and Moose related
1043 =item The Moose is flying, a tutorial by Randal Schwartz
1045 Part 1 - L<http://www.stonehenge.com/merlyn/LinuxMag/col94.html>
1047 Part 2 - L<http://www.stonehenge.com/merlyn/LinuxMag/col95.html>
1049 =item Several Moose extension modules in the C<MooseX::> namespace.
1051 See L<http://search.cpan.org/search?query=MooseX::> for extensions.
1053 =item Moose stats on ohloh.net - L<http://www.ohloh.net/projects/moose>
1061 =item The Art of the MetaObject Protocol
1063 I mention this in the L<Class::MOP> docs too, this book was critical in
1064 the development of both modules and is highly recommended.
1072 =item L<http://www.cs.utah.edu/plt/publications/oopsla04-gff.pdf>
1074 This paper (suggested by lbr on #moose) was what lead to the implementation
1075 of the C<super>/C<override> and C<inner>/C<augment> features. If you really
1076 want to understand them, I suggest you read this.
1082 All complex software has bugs lurking in it, and this module is no
1085 Please report any bugs to C<bug-moose@rt.cpan.org>, or through the web
1086 interface at L<http://rt.cpan.org>.
1088 =head1 FEATURE REQUESTS
1090 We are very strict about what features we add to the Moose core, especially
1091 the user-visible features. Instead we have made sure that the underlying
1092 meta-system of Moose is as extensible as possible so that you can add your
1093 own features easily.
1095 That said, occasionally there is a feature needed in the meta-system
1096 to support your planned extension, in which case you should either
1097 email the mailing list (moose@perl.org) or join us on IRC at
1098 L<irc://irc.perl.org/#moose> to discuss. The
1099 L<Moose::Manual::Contributing> has more detail about how and when you
1104 Moose is an open project, there are at this point dozens of people who have
1105 contributed, and can contribute. If you have added anything to the Moose
1106 project you have a commit bit on this file and can add your name to the list.
1110 However there are only a few people with the rights to release a new version
1111 of Moose. The Moose Cabal are the people to go to with questions regarding
1112 the wider purview of Moose, and help out maintaining not just the code
1113 but the community as well.
1115 Stevan (stevan) Little E<lt>stevan@iinteractive.comE<gt>
1117 Yuval (nothingmuch) Kogman
1119 Shawn (sartak) Moore E<lt>sartak@bestpractical.comE<gt>
1121 Dave (autarch) Rolsky E<lt>autarch@urth.orgE<gt>
1123 =head2 OTHER CONTRIBUTORS
1127 Adam (Alias) Kennedy
1129 Anders (Debolaz) Nor Berle
1131 Nathan (kolibrie) Gray
1133 Christian (chansen) Hansen
1135 Hans Dieter (confound) Pearcey
1137 Eric (ewilhelm) Wilhelm
1139 Guillermo (groditi) Roditi
1141 Jess (castaway) Robinson
1145 Robert (phaylon) Sedlacek
1149 Scott (konobi) McWhirter
1151 Shlomi (rindolf) Fish
1153 Chris (perigrin) Prather
1155 Wallace (wreis) Reis
1157 Jonathan (jrockway) Rockway
1159 Piotr (dexter) Roszatycki
1161 Sam (mugwump) Vilain
1165 Dylan Hardison (doc fixes)
1167 ... and many other #moose folks
1169 =head1 COPYRIGHT AND LICENSE
1171 Copyright 2006-2009 by Infinity Interactive, Inc.
1173 L<http://www.iinteractive.com>
1175 This library is free software; you can redistribute it and/or modify
1176 it under the same terms as Perl itself.