6 $VERSION = eval $VERSION;
7 our $AUTHORITY = 'cpan:STEVAN';
9 use Scalar::Util 'blessed';
16 use Moose::Meta::Class;
17 use Moose::Meta::TypeConstraint;
18 use Moose::Meta::TypeCoercion;
19 use Moose::Meta::Attribute;
20 use Moose::Meta::Instance;
24 use Moose::Meta::Role;
25 use Moose::Meta::Role::Composite;
26 use Moose::Meta::Role::Application;
27 use Moose::Meta::Role::Application::RoleSummation;
28 use Moose::Meta::Role::Application::ToClass;
29 use Moose::Meta::Role::Application::ToRole;
30 use Moose::Meta::Role::Application::ToInstance;
32 use Moose::Util::TypeConstraints;
44 Moose->throw_error("Must derive at least one class") unless @_;
46 # this checks the metaclass to make sure
47 # it is correct, sometimes it can get out
48 # of sync when the classes are being built
49 Moose::Meta::Class->initialize($class)->superclasses(@_);
54 Moose::Util::apply_all_roles(Class::MOP::Class->initialize($class), @_);
61 Moose->throw_error('Usage: has \'name\' => ( key => value, ... )')
64 my %options = ( definition_context => Moose::Util::_caller_info(), @_ );
65 my $attrs = ( ref($name) eq 'ARRAY' ) ? $name : [ ($name) ];
66 Class::MOP::Class->initialize($class)->add_attribute( $_, %options ) for @$attrs;
71 Moose::Util::add_method_modifier($class, 'before', \@_);
76 Moose::Util::add_method_modifier($class, 'after', \@_);
81 Moose::Util::add_method_modifier($class, 'around', \@_);
89 # This check avoids a recursion loop - see
90 # t/100_bugs/020_super_recursion.t
91 return if defined $SUPER_PACKAGE && $SUPER_PACKAGE ne caller();
92 return unless $SUPER_BODY; $SUPER_BODY->(@SUPER_ARGS);
97 my ( $name, $method ) = @_;
98 Class::MOP::Class->initialize($class)->add_override_method_modifier( $name => $method );
103 our ( %INNER_BODY, %INNER_ARGS );
105 if ( my $body = $INNER_BODY{$pkg} ) {
106 my @args = @{ $INNER_ARGS{$pkg} };
107 local $INNER_ARGS{$pkg};
108 local $INNER_BODY{$pkg};
109 return $body->(@args);
117 my ( $name, $method ) = @_;
118 Class::MOP::Class->initialize($class)->add_augment_method_modifier( $name => $method );
121 Moose::Exporter->setup_import_methods(
123 qw( extends with has before after around override augment)
128 \&Scalar::Util::blessed,
133 # This used to be called as a function. This hack preserves
134 # backwards compatibility.
135 if ( $_[0] ne __PACKAGE__ ) {
136 return __PACKAGE__->init_meta(
146 my $class = $args{for_class}
147 or Moose->throw_error("Cannot call init_meta without specifying a for_class");
148 my $base_class = $args{base_class} || 'Moose::Object';
149 my $metaclass = $args{metaclass} || 'Moose::Meta::Class';
151 Moose->throw_error("The Metaclass $metaclass must be a subclass of Moose::Meta::Class.")
152 unless $metaclass->isa('Moose::Meta::Class');
154 # make a subtype for each Moose class
156 unless find_type_constraint($class);
160 if ( $meta = Class::MOP::get_metaclass_by_name($class) ) {
161 unless ( $meta->isa("Moose::Meta::Class") ) {
162 Moose->throw_error("$class already has a metaclass, but it does not inherit $metaclass ($meta)");
165 # no metaclass, no 'meta' method
167 # now we check whether our ancestors have metaclass, and if so borrow that
168 my ( undef, @isa ) = @{ $class->mro::get_linear_isa };
170 foreach my $ancestor ( @isa ) {
171 my $ancestor_meta = Class::MOP::get_metaclass_by_name($ancestor) || next;
173 my $ancestor_meta_class = ($ancestor_meta->is_immutable
174 ? $ancestor_meta->get_mutable_metaclass_name
175 : ref($ancestor_meta));
177 # if we have an ancestor metaclass that inherits $metaclass, we use
178 # that. This is like _fix_metaclass_incompatibility, but we can do it now.
180 # the case of having an ancestry is not very common, but arises in
182 unless ( $metaclass->isa( $ancestor_meta_class ) ) {
183 if ( $ancestor_meta_class->isa($metaclass) ) {
184 $metaclass = $ancestor_meta_class;
189 $meta = $metaclass->initialize($class);
192 if ( $class->can('meta') ) {
193 # check 'meta' method
195 # it may be inherited
198 # this is the case where the metaclass pragma
199 # was used before the 'use Moose' statement to
200 # override a specific class
201 my $method_meta = $class->meta;
203 ( blessed($method_meta) && $method_meta->isa('Moose::Meta::Class') )
204 || Moose->throw_error("$class already has a &meta function, but it does not return a Moose::Meta::Class ($method_meta)");
206 $meta = $method_meta;
209 unless ( $meta->has_method("meta") ) { # don't overwrite
210 # also check for inherited non moose 'meta' method?
211 # FIXME also skip this if the user requested by passing an option
214 # re-initialize so it inherits properly
215 $metaclass->initialize( ref($_[0]) || $_[0] );
220 # make sure they inherit from Moose::Object
221 $meta->superclasses($base_class)
222 unless $meta->superclasses();
227 # This may be used in some older MooseX extensions.
229 goto &Moose::Exporter::_get_caller;
232 ## make 'em all immutable
235 inline_constructor => 1,
236 constructor_name => "_new",
237 # these are Class::MOP accessors, so they need inlining
238 inline_accessors => 1
239 ) for grep { $_->is_mutable }
242 Moose::Meta::Attribute
244 Moose::Meta::Instance
246 Moose::Meta::TypeCoercion
247 Moose::Meta::TypeCoercion::Union
250 Moose::Meta::Method::Accessor
251 Moose::Meta::Method::Constructor
252 Moose::Meta::Method::Destructor
253 Moose::Meta::Method::Overridden
254 Moose::Meta::Method::Augmented
257 Moose::Meta::Role::Method
258 Moose::Meta::Role::Method::Required
259 Moose::Meta::Role::Method::Conflicting
261 Moose::Meta::Role::Composite
263 Moose::Meta::Role::Application
264 Moose::Meta::Role::Application::RoleSummation
265 Moose::Meta::Role::Application::ToClass
266 Moose::Meta::Role::Application::ToRole
267 Moose::Meta::Role::Application::ToInstance
278 Moose - A postmodern object system for Perl 5
283 use Moose; # automatically turns on strict and warnings
285 has 'x' => (is => 'rw', isa => 'Int');
286 has 'y' => (is => 'rw', isa => 'Int');
299 has 'z' => (is => 'rw', isa => 'Int');
301 after 'clear' => sub {
308 Moose is an extension of the Perl 5 object system.
310 The main goal of Moose is to make Perl 5 Object Oriented programming
311 easier, more consistent and less tedious. With Moose you can to think
312 more about what you want to do and less about the mechanics of OOP.
314 Additionally, Moose is built on top of L<Class::MOP>, which is a
315 metaclass system for Perl 5. This means that Moose not only makes
316 building normal Perl 5 objects better, but it provides the power of
317 metaclass programming as well.
321 If you're new to Moose, the best place to start is the
322 L<Moose::Manual> docs, followed by the L<Moose::Cookbook>. The intro
323 will show you what Moose is, and how it makes Perl 5 OO better.
325 The cookbook recipes on Moose basics will get you up to speed with
326 many of Moose's features quickly. Once you have an idea of what Moose
327 can do, you can use the API documentation to get more detail on
328 features which interest you.
330 =head2 Moose Extensions
332 The C<MooseX::> namespace is the official place to find Moose extensions.
333 These extensions can be found on the CPAN. The easiest way to find them
334 is to search for them (L<http://search.cpan.org/search?query=MooseX::>),
335 or to examine L<Task::Moose> which aims to keep an up-to-date, easily
336 installable list of Moose extensions.
338 =head1 BUILDING CLASSES WITH MOOSE
340 Moose makes every attempt to provide as much convenience as possible during
341 class construction/definition, but still stay out of your way if you want it
342 to. Here are a few items to note when building classes with Moose.
344 Unless specified with C<extends>, any class which uses Moose will
345 inherit from L<Moose::Object>.
347 Moose will also manage all attributes (including inherited ones) that are
348 defined with C<has>. And (assuming you call C<new>, which is inherited from
349 L<Moose::Object>) this includes properly initializing all instance slots,
350 setting defaults where appropriate, and performing any type constraint checking
353 =head1 PROVIDED METHODS
355 Moose provides a number of methods to all your classes, mostly through the
356 inheritance of L<Moose::Object>. There is however, one exception.
362 This is a method which provides access to the current class's metaclass.
366 =head1 EXPORTED FUNCTIONS
368 Moose will export a number of functions into the class's namespace which
369 may then be used to set up the class. These functions all work directly
370 on the current class.
374 =item B<extends (@superclasses)>
376 This function will set the superclass(es) for the current class.
378 This approach is recommended instead of C<use base>, because C<use base>
379 actually C<push>es onto the class's C<@ISA>, whereas C<extends> will
380 replace it. This is important to ensure that classes which do not have
381 superclasses still properly inherit from L<Moose::Object>.
383 =item B<with (@roles)>
385 This will apply a given set of C<@roles> to the local class.
387 =item B<has $name|@$names =E<gt> %options>
389 This will install an attribute of a given C<$name> into the current class. If
390 the first parameter is an array reference, it will create an attribute for
391 every C<$name> in the list. The C<%options> are the same as those provided by
392 L<Class::MOP::Attribute>, in addition to the list below which are provided by
393 Moose (L<Moose::Meta::Attribute> to be more specific):
397 =item I<is =E<gt> 'rw'|'ro'>
399 The I<is> option accepts either I<rw> (for read/write) or I<ro> (for read
400 only). These will create either a read/write accessor or a read-only
401 accessor respectively, using the same name as the C<$name> of the attribute.
403 If you need more control over how your accessors are named, you can
404 use the L<reader|Class::MOP::Attribute/reader>,
405 L<writer|Class::MOP::Attribute/writer> and
406 L<accessor|Class::MOP::Attribute/accessor> options inherited from
407 L<Class::MOP::Attribute>, however if you use those, you won't need the
410 =item I<isa =E<gt> $type_name>
412 The I<isa> option uses Moose's type constraint facilities to set up runtime
413 type checking for this attribute. Moose will perform the checks during class
414 construction, and within any accessors. The C<$type_name> argument must be a
415 string. The string may be either a class name or a type defined using
416 Moose's type definition features. (Refer to L<Moose::Util::TypeConstraints>
417 for information on how to define a new type, and how to retrieve type meta-data).
419 =item I<coerce =E<gt> (1|0)>
421 This will attempt to use coercion with the supplied type constraint to change
422 the value passed into any accessors or constructors. You B<must> have supplied
423 a type constraint in order for this to work. See L<Moose::Cookbook::Basics::Recipe5>
426 =item I<does =E<gt> $role_name>
428 This will accept the name of a role which the value stored in this attribute
429 is expected to have consumed.
431 =item I<required =E<gt> (1|0)>
433 This marks the attribute as being required. This means a value must be
434 supplied during class construction, I<or> the attribute must be lazy
435 and have either a default or a builder. Note that c<required> does not
436 say anything about the attribute's value, which can be C<undef>.
438 =item I<weak_ref =E<gt> (1|0)>
440 This will tell the class to store the value of this attribute as a weakened
441 reference. If an attribute is a weakened reference, it B<cannot> also be
444 =item I<lazy =E<gt> (1|0)>
446 This will tell the class to not create this slot until absolutely necessary.
447 If an attribute is marked as lazy it B<must> have a default supplied.
449 =item I<auto_deref =E<gt> (1|0)>
451 This tells the accessor whether to automatically dereference the value returned.
452 This is only legal if your C<isa> option is either C<ArrayRef> or C<HashRef>.
454 =item I<trigger =E<gt> $code>
456 The I<trigger> option is a CODE reference which will be called after
457 the value of the attribute is set. The CODE ref will be passed the
458 instance itself and the updated value. You B<can> have a trigger on
459 a read-only attribute.
461 B<NOTE:> Triggers will only fire when you B<assign> to the attribute,
462 either in the constructor, or using the writer. Default and built values will
463 B<not> cause the trigger to be fired.
465 =item I<handles =E<gt> ARRAY | HASH | REGEXP | ROLE | DUCKTYPE | CODE>
467 The I<handles> option provides Moose classes with automated delegation features.
468 This is a pretty complex and powerful option. It accepts many different option
469 formats, each with its own benefits and drawbacks.
471 B<NOTE:> The class being delegated to does not need to be a Moose based class,
472 which is why this feature is especially useful when wrapping non-Moose classes.
474 All I<handles> option formats share the following traits:
476 You cannot override a locally defined method with a delegated method; an
477 exception will be thrown if you try. That is to say, if you define C<foo> in
478 your class, you cannot override it with a delegated C<foo>. This is almost never
479 something you would want to do, and if it is, you should do it by hand and not
482 You cannot override any of the methods found in Moose::Object, or the C<BUILD>
483 and C<DEMOLISH> methods. These will not throw an exception, but will silently
484 move on to the next method in the list. My reasoning for this is that you would
485 almost never want to do this, since it usually breaks your class. As with
486 overriding locally defined methods, if you do want to do this, you should do it
487 manually, not with Moose.
489 You do not I<need> to have a reader (or accessor) for the attribute in order
490 to delegate to it. Moose will create a means of accessing the value for you,
491 however this will be several times B<less> efficient then if you had given
492 the attribute a reader (or accessor) to use.
494 Below is the documentation for each option format:
500 This is the most common usage for I<handles>. You basically pass a list of
501 method names to be delegated, and Moose will install a delegation method
506 This is the second most common usage for I<handles>. Instead of a list of
507 method names, you pass a HASH ref where each key is the method name you
508 want installed locally, and its value is the name of the original method
509 in the class being delegated to.
511 This can be very useful for recursive classes like trees. Here is a
512 quick example (soon to be expanded into a Moose::Cookbook recipe):
517 has 'node' => (is => 'rw', isa => 'Any');
522 default => sub { [] }
530 parent_node => 'node',
531 siblings => 'children',
535 In this example, the Tree package gets C<parent_node> and C<siblings> methods,
536 which delegate to the C<node> and C<children> methods (respectively) of the Tree
537 instance stored in the C<parent> slot.
539 You may also use an array reference to curry arguments to the original method.
543 handles => { set_foo => [ set => [ 'foo' ] ] },
546 # $self->set_foo(...) calls $self->thing->set('foo', ...)
548 The first element of the array reference is the original method name, and the
549 second is an array reference of curried arguments.
553 The regexp option works very similar to the ARRAY option, except that it builds
554 the list of methods for you. It starts by collecting all possible methods of the
555 class being delegated to, then filters that list using the regexp supplied here.
557 B<NOTE:> An I<isa> option is required when using the regexp option format. This
558 is so that we can determine (at compile time) the method list from the class.
559 Without an I<isa> this is just not possible.
563 With the role option, you specify the name of a role whose "interface" then
564 becomes the list of methods to handle. The "interface" can be defined as; the
565 methods of the role and any required methods of the role. It should be noted
566 that this does B<not> include any method modifiers or generated attribute
567 methods (which is consistent with role composition).
571 With the duck type option, you pass a duck type object whose "interface" then
572 becomes the list of methods to handle. The "interface" can be defined as; the
573 list of methods passed to C<duck_type> to create a duck type object. For more
574 information on C<duck_type> please check
575 L<Moose::Util::TypeConstraint|Moose::Util::TypeConstraint>.
579 This is the option to use when you really want to do something funky. You should
580 only use it if you really know what you are doing, as it involves manual
583 This takes a code reference, which should expect two arguments. The first is the
584 attribute meta-object this I<handles> is attached to. The second is the
585 metaclass of the class being delegated to. It expects you to return a hash (not
586 a HASH ref) of the methods you want mapped.
590 =item I<metaclass =E<gt> $metaclass_name>
592 This tells the class to use a custom attribute metaclass for this particular
593 attribute. Custom attribute metaclasses are useful for extending the
594 capabilities of the I<has> keyword: they are the simplest way to extend the MOP,
595 but they are still a fairly advanced topic and too much to cover here, see
596 L<Moose::Cookbook::Meta::Recipe1> for more information.
598 The default behavior here is to just load C<$metaclass_name>; however, we also
599 have a way to alias to a shorter name. This will first look to see if
600 B<Moose::Meta::Attribute::Custom::$metaclass_name> exists. If it does, Moose
601 will then check to see if that has the method C<register_implementation>, which
602 should return the actual name of the custom attribute metaclass. If there is no
603 C<register_implementation> method, it will fall back to using
604 B<Moose::Meta::Attribute::Custom::$metaclass_name> as the metaclass name.
606 =item I<traits =E<gt> [ @role_names ]>
608 This tells Moose to take the list of C<@role_names> and apply them to the
609 attribute meta-object. This is very similar to the I<metaclass> option, but
610 allows you to use more than one extension at a time.
612 See L<TRAIT NAME RESOLUTION> for details on how a trait name is
613 resolved to a class name.
615 Also see L<Moose::Cookbook::Meta::Recipe3> for a metaclass trait
618 =item I<builder> => Str
620 The value of this key is the name of the method that will be called to
621 obtain the value used to initialize the attribute. See the L<builder
622 option docs in Class::MOP::Attribute|Class::MOP::Attribute/builder>
623 and/or L<Moose::Cookbook::Basics::Recipe9> for more information.
625 =item I<default> => SCALAR | CODE
627 The value of this key is the default value which will initialize the attribute.
629 NOTE: If the value is a simple scalar (string or number), then it can
630 be just passed as is. However, if you wish to initialize it with a
631 HASH or ARRAY ref, then you need to wrap that inside a CODE reference.
632 See the L<default option docs in
633 Class::MOP::Attribute|Class::MOP::Attribute/default> for more
636 =item I<clearer> => Str
638 Creates a method allowing you to clear the value, see the L<clearer option
639 docs in Class::MOP::Attribute|Class::MOP::Attribute/clearer> for more
642 =item I<predicate> => Str
644 Creates a method to perform a basic test to see if a value has been set in the
645 attribute, see the L<predicate option docs in
646 Class::MOP::Attribute|Class::MOP::Attribute/predicate> for more information.
648 =item I<lazy_build> => (0|1)
650 Automatically define lazy => 1 as well as builder => "_build_$attr", clearer =>
651 "clear_$attr', predicate => 'has_$attr' unless they are already defined.
653 =item I<initializer> => Str
655 This may be a method name (referring to a method on the class with
656 this attribute) or a CODE ref. The initializer is used to set the
657 attribute value on an instance when the attribute is set during
658 instance initialization (but not when the value is being assigned
659 to). See the L<initializer option docs in
660 Class::MOP::Attribute|Class::MOP::Attribute/initializer> for more
663 =item I<documentation> => $string
665 An arbitrary string that can be retrieved later by calling C<<
666 $attr->documentation >>.
672 =item B<has +$name =E<gt> %options>
674 This is variation on the normal attribute creator C<has> which allows you to
675 clone and extend an attribute from a superclass or from a role. Here is an
676 example of the superclass usage:
684 default => 'Hello, I am a Foo'
692 has '+message' => (default => 'Hello I am My::Foo');
694 What is happening here is that B<My::Foo> is cloning the C<message> attribute
695 from its parent class B<Foo>, retaining the C<is =E<gt> 'rw'> and C<isa =E<gt>
696 'Str'> characteristics, but changing the value in C<default>.
698 Here is another example, but within the context of a role:
706 default => 'Hello, I am a Foo'
714 has '+message' => (default => 'Hello I am My::Foo');
716 In this case, we are basically taking the attribute which the role supplied
717 and altering it within the bounds of this feature.
719 Note that you can only extend an attribute from either a superclass or a role,
720 you cannot extend an attribute in a role that composes over an attribute from
723 Aside from where the attributes come from (one from superclass, the other
724 from a role), this feature works exactly the same. This feature is restricted
725 somewhat, so as to try and force at least I<some> sanity into it. You are only
726 allowed to change the following attributes:
732 Change the default value of an attribute.
736 Change whether the attribute attempts to coerce a value passed to it.
740 Change if the attribute is required to have a value.
742 =item I<documentation>
744 Change the documentation string associated with the attribute.
748 Change if the attribute lazily initializes the slot.
752 You I<are> allowed to change the type without restriction.
754 It is recommended that you use this freedom with caution. We used to
755 only allow for extension only if the type was a subtype of the parent's
756 type, but we felt that was too restrictive and is better left as a
761 You are allowed to B<add> a new C<handles> definition, but you are B<not>
762 allowed to I<change> one.
766 You are allowed to B<add> a new C<builder> definition, but you are B<not>
767 allowed to I<change> one.
771 You are allowed to B<add> a new C<metaclass> definition, but you are
772 B<not> allowed to I<change> one.
776 You are allowed to B<add> additional traits to the C<traits> definition.
777 These traits will be composed into the attribute, but preexisting traits
778 B<are not> overridden, or removed.
782 =item B<before $name|@names =E<gt> sub { ... }>
784 =item B<after $name|@names =E<gt> sub { ... }>
786 =item B<around $name|@names =E<gt> sub { ... }>
788 This three items are syntactic sugar for the before, after, and around method
789 modifier features that L<Class::MOP> provides. More information on these may be
790 found in the L<Class::MOP::Class documentation|Class::MOP::Class/"Method
795 The keyword C<super> is a no-op when called outside of an C<override> method. In
796 the context of an C<override> method, it will call the next most appropriate
797 superclass method with the same arguments as the original method.
799 =item B<override ($name, &sub)>
801 An C<override> method is a way of explicitly saying "I am overriding this
802 method from my superclass". You can call C<super> within this method, and
803 it will work as expected. The same thing I<can> be accomplished with a normal
804 method call and the C<SUPER::> pseudo-package; it is really your choice.
808 The keyword C<inner>, much like C<super>, is a no-op outside of the context of
809 an C<augment> method. You can think of C<inner> as being the inverse of
810 C<super>; the details of how C<inner> and C<augment> work is best described in
811 the L<Moose::Cookbook::Basics::Recipe6>.
813 =item B<augment ($name, &sub)>
815 An C<augment> method, is a way of explicitly saying "I am augmenting this
816 method from my superclass". Once again, the details of how C<inner> and
817 C<augment> work is best described in the L<Moose::Cookbook::Basics::Recipe6>.
821 This is the C<Carp::confess> function, and exported here because I use it
826 This is the C<Scalar::Util::blessed> function, it is exported here because I
827 use it all the time. It is highly recommended that this is used instead of
828 C<ref> anywhere you need to test for an object's class name.
834 When you use Moose, you can specify which metaclass to use:
836 use Moose -metaclass => 'My::Meta::Class';
838 You can also specify traits which will be applied to your metaclass:
840 use Moose -traits => 'My::Trait';
842 This is very similar to the attribute traits feature. When you do
843 this, your class's C<meta> object will have the specified traits
844 applied to it. See L<TRAIT NAME RESOLUTION> for more details.
846 =head2 Trait Name Resolution
848 By default, when given a trait name, Moose simply tries to load a
849 class of the same name. If such a class does not exist, it then looks
850 for for a class matching
851 B<Moose::Meta::$type::Custom::Trait::$trait_name>. The C<$type>
852 variable here will be one of B<Attribute> or B<Class>, depending on
853 what the trait is being applied to.
855 If a class with this long name exists, Moose checks to see if it has
856 the method C<register_implementation>. This method is expected to
857 return the I<real> class name of the trait. If there is no
858 C<register_implementation> method, it will fall back to using
859 B<Moose::Meta::$type::Custom::Trait::$trait> as the trait name.
861 If all this is confusing, take a look at
862 L<Moose::Cookbook::Meta::Recipe3>, which demonstrates how to create an
865 =head1 UNIMPORTING FUNCTIONS
869 Moose offers a way to remove the keywords it exports, through the C<unimport>
870 method. You simply have to say C<no Moose> at the bottom of your code for this
871 to work. Here is an example:
876 has 'first_name' => (is => 'rw', isa => 'Str');
877 has 'last_name' => (is => 'rw', isa => 'Str');
881 $self->first_name . ' ' . $self->last_name
884 no Moose; # keywords are removed from the Person package
886 =head1 EXTENDING AND EMBEDDING MOOSE
888 To learn more about extending Moose, we recommend checking out the
889 "Extending" recipes in the L<Moose::Cookbook>, starting with
890 L<Moose::Cookbook::Extending::Recipe1>, which provides an overview of
891 all the different ways you might extend Moose.
893 =head2 B<< Moose->init_meta(for_class => $class, base_class => $baseclass, metaclass => $metaclass) >>
895 The C<init_meta> method sets up the metaclass object for the class
896 specified by C<for_class>. This method injects a a C<meta> accessor
897 into the class so you can get at this object. It also sets the class's
898 superclass to C<base_class>, with L<Moose::Object> as the default.
900 C<init_meta> returns the metaclass object for C<$class>.
902 You can specify an alternate metaclass with the C<metaclass> option.
904 For more detail on this topic, see L<Moose::Cookbook::Extending::Recipe2>.
906 This method used to be documented as a function which accepted
907 positional parameters. This calling style will still work for
908 backwards compatibility, but is deprecated.
912 Moose's C<import> method supports the L<Sub::Exporter> form of C<{into =E<gt> $pkg}>
913 and C<{into_level =E<gt> 1}>.
915 B<NOTE>: Doing this is more or less deprecated. Use L<Moose::Exporter>
916 instead, which lets you stack multiple C<Moose.pm>-alike modules
917 sanely. It handles getting the exported functions into the right place
920 =head2 B<throw_error>
922 An alias for C<confess>, used by internally by Moose.
924 =head1 METACLASS COMPATIBILITY AND MOOSE
926 Metaclass compatibility is a thorny subject. You should start by
927 reading the "About Metaclass compatibility" section in the
930 Moose will attempt to resolve a few cases of metaclass incompatibility
931 when you set the superclasses for a class, unlike C<Class::MOP>, which
932 simply dies if the metaclasses are incompatible.
934 In actuality, Moose fixes incompatibility for I<all> of a class's
935 metaclasses, not just the class metaclass. That includes the instance
936 metaclass, attribute metaclass, as well as its constructor class and
937 destructor class. However, for simplicity this discussion will just
938 refer to "metaclass", meaning the class metaclass, most of the time.
940 Moose has two algorithms for fixing metaclass incompatibility.
942 The first algorithm is very simple. If all the metaclass for the
943 parent is a I<subclass> of the child's metaclass, then we simply
944 replace the child's metaclass with the parent's.
946 The second algorithm is more complicated. It tries to determine if the
947 metaclasses only "differ by roles". This means that the parent and
948 child's metaclass share a common ancestor in their respective
949 hierarchies, and that the subclasses under the common ancestor are
950 only different because of role applications. This case is actually
951 fairly common when you mix and match various C<MooseX::*> modules,
952 many of which apply roles to the metaclass.
954 If the parent and child do differ by roles, Moose replaces the
955 metaclass in the child with a newly created metaclass. This metaclass
956 is a subclass of the parent's metaclass, does all of the roles that
957 the child's metaclass did before being replaced. Effectively, this
958 means the new metaclass does all of the roles done by both the
959 parent's and child's original metaclasses.
961 Ultimately, this is all transparent to you except in the case of an
962 unresolvable conflict.
964 =head2 The MooseX:: namespace
966 Generally if you're writing an extension I<for> Moose itself you'll want
967 to put your extension in the C<MooseX::> namespace. This namespace is
968 specifically for extensions that make Moose better or different in some
969 fundamental way. It is traditionally B<not> for a package that just happens
970 to use Moose. This namespace follows from the examples of the C<LWPx::>
971 and C<DBIx::> namespaces that perform the same function for C<LWP> and C<DBI>
980 It should be noted that C<super> and C<inner> B<cannot> be used in the same
981 method. However, they may be combined within the same class hierarchy; see
982 F<t/014_override_augment_inner_super.t> for an example.
984 The reason for this is that C<super> is only valid within a method
985 with the C<override> modifier, and C<inner> will never be valid within an
986 C<override> method. In fact, C<augment> will skip over any C<override> methods
987 when searching for its appropriate C<inner>.
989 This might seem like a restriction, but I am of the opinion that keeping these
990 two features separate (yet interoperable) actually makes them easy to use, since
991 their behavior is then easier to predict. Time will tell whether I am right or
992 not (UPDATE: so far so good).
998 We offer both a mailing list and a very active IRC channel.
1000 The mailing list is L<moose@perl.org>. You must be subscribed to send
1001 a message. To subscribe, send an empty message to
1002 L<moose-subscribe@perl.org>
1004 You can also visit us at L<#moose on
1005 irc.perl.org|irc://irc.perl.org/#moose>. This channel is quite active,
1006 and questions at all levels (on Moose-related topics ;) are welcome.
1008 =head1 ACKNOWLEDGEMENTS
1012 =item I blame Sam Vilain for introducing me to the insanity that is meta-models.
1014 =item I blame Audrey Tang for then encouraging my meta-model habit in #perl6.
1016 =item Without Yuval "nothingmuch" Kogman this module would not be possible,
1017 and it certainly wouldn't have this name ;P
1019 =item The basis of the TypeContraints module was Rob Kinyon's idea
1020 originally, I just ran with it.
1022 =item Thanks to mst & chansen and the whole #moose posse for all the
1023 early ideas/feature-requests/encouragement/bug-finding.
1025 =item Thanks to David "Theory" Wheeler for meta-discussions and spelling fixes.
1033 =item L<http://www.iinteractive.com/moose>
1035 This is the official web home of Moose, it contains links to our public SVN repository
1036 as well as links to a number of talks and articles on Moose and Moose related
1039 =item The Moose is flying, a tutorial by Randal Schwartz
1041 Part 1 - L<http://www.stonehenge.com/merlyn/LinuxMag/col94.html>
1043 Part 2 - L<http://www.stonehenge.com/merlyn/LinuxMag/col95.html>
1045 =item Several Moose extension modules in the C<MooseX::> namespace.
1047 See L<http://search.cpan.org/search?query=MooseX::> for extensions.
1049 =item Moose stats on ohloh.net - L<http://www.ohloh.net/projects/moose>
1057 =item The Art of the MetaObject Protocol
1059 I mention this in the L<Class::MOP> docs too, this book was critical in
1060 the development of both modules and is highly recommended.
1068 =item L<http://www.cs.utah.edu/plt/publications/oopsla04-gff.pdf>
1070 This paper (suggested by lbr on #moose) was what lead to the implementation
1071 of the C<super>/C<override> and C<inner>/C<augment> features. If you really
1072 want to understand them, I suggest you read this.
1078 All complex software has bugs lurking in it, and this module is no
1081 Please report any bugs to C<bug-moose@rt.cpan.org>, or through the web
1082 interface at L<http://rt.cpan.org>.
1084 =head1 FEATURE REQUESTS
1086 We are very strict about what features we add to the Moose core, especially
1087 the user-visible features. Instead we have made sure that the underlying
1088 meta-system of Moose is as extensible as possible so that you can add your
1089 own features easily.
1091 That said, occasionally there is a feature needed in the meta-system
1092 to support your planned extension, in which case you should either
1093 email the mailing list (moose@perl.org) or join us on IRC at
1094 L<irc://irc.perl.org/#moose> to discuss. The
1095 L<Moose::Manual::Contributing> has more detail about how and when you
1100 Moose is an open project, there are at this point dozens of people who have
1101 contributed, and can contribute. If you have added anything to the Moose
1102 project you have a commit bit on this file and can add your name to the list.
1106 However there are only a few people with the rights to release a new version
1107 of Moose. The Moose Cabal are the people to go to with questions regarding
1108 the wider purview of Moose, and help out maintaining not just the code
1109 but the community as well.
1111 Stevan (stevan) Little E<lt>stevan@iinteractive.comE<gt>
1113 Yuval (nothingmuch) Kogman
1115 Shawn (sartak) Moore
1117 Dave (autarch) Rolsky E<lt>autarch@urth.orgE<gt>
1119 =head2 OTHER CONTRIBUTORS
1123 Adam (Alias) Kennedy
1125 Anders (Debolaz) Nor Berle
1127 Nathan (kolibrie) Gray
1129 Christian (chansen) Hansen
1131 Hans Dieter (confound) Pearcey
1133 Eric (ewilhelm) Wilhelm
1135 Guillermo (groditi) Roditi
1137 Jess (castaway) Robinson
1141 Robert (phaylon) Sedlacek
1145 Scott (konobi) McWhirter
1147 Shlomi (rindolf) Fish
1149 Chris (perigrin) Prather
1151 Wallace (wreis) Reis
1153 Jonathan (jrockway) Rockway
1155 Piotr (dexter) Roszatycki
1157 Sam (mugwump) Vilain
1161 Dylan Hardison (doc fixes)
1163 ... and many other #moose folks
1165 =head1 COPYRIGHT AND LICENSE
1167 Copyright 2006-2009 by Infinity Interactive, Inc.
1169 L<http://www.iinteractive.com>
1171 This library is free software; you can redistribute it and/or modify
1172 it under the same terms as Perl itself.