10 $VERSION = eval $VERSION;
11 our $AUTHORITY = 'cpan:STEVAN';
13 use Scalar::Util 'blessed';
14 use Carp 'confess', 'croak', 'cluck';
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 => $method );
129 cluck "The make_immutable keyword has been deprecated, " .
130 "please go back to __PACKAGE__->meta->make_immutable\n";
131 Class::MOP::Class->initialize($class)->make_immutable(@_);
134 Moose::Exporter->setup_import_methods(
136 qw( extends with has before after around override augment make_immutable )
141 \&Scalar::Util::blessed,
146 # This used to be called as a function. This hack preserves
147 # backwards compatibility.
148 if ( $_[0] ne __PACKAGE__ ) {
149 return __PACKAGE__->init_meta(
159 my $class = $args{for_class}
160 or Moose->throw_error("Cannot call init_meta without specifying a for_class");
161 my $base_class = $args{base_class} || 'Moose::Object';
162 my $metaclass = $args{metaclass} || 'Moose::Meta::Class';
164 Moose->throw_error("The Metaclass $metaclass must be a subclass of Moose::Meta::Class.")
165 unless $metaclass->isa('Moose::Meta::Class');
167 # make a subtype for each Moose class
169 unless find_type_constraint($class);
173 if ( $meta = Class::MOP::get_metaclass_by_name($class) ) {
174 unless ( $meta->isa("Moose::Meta::Class") ) {
175 Moose->throw_error("$class already has a metaclass, but it does not inherit $metaclass ($meta)");
178 # no metaclass, no 'meta' method
180 # now we check whether our ancestors have metaclass, and if so borrow that
181 my ( undef, @isa ) = @{ $class->mro::get_linear_isa };
183 foreach my $ancestor ( @isa ) {
184 my $ancestor_meta = Class::MOP::get_metaclass_by_name($ancestor) || next;
186 my $ancestor_meta_class = ($ancestor_meta->is_immutable
187 ? $ancestor_meta->get_mutable_metaclass_name
188 : ref($ancestor_meta));
190 # if we have an ancestor metaclass that inherits $metaclass, we use
191 # that. This is like _fix_metaclass_incompatibility, but we can do it now.
193 # the case of having an ancestry is not very common, but arises in
195 unless ( $metaclass->isa( $ancestor_meta_class ) ) {
196 if ( $ancestor_meta_class->isa($metaclass) ) {
197 $metaclass = $ancestor_meta_class;
202 $meta = $metaclass->initialize($class);
205 if ( $class->can('meta') ) {
206 # check 'meta' method
208 # it may be inherited
211 # this is the case where the metaclass pragma
212 # was used before the 'use Moose' statement to
213 # override a specific class
214 my $method_meta = $class->meta;
216 ( blessed($method_meta) && $method_meta->isa('Moose::Meta::Class') )
217 || Moose->throw_error("$class already has a &meta function, but it does not return a Moose::Meta::Class ($meta)");
219 $meta = $method_meta;
222 unless ( $meta->has_method("meta") ) { # don't overwrite
223 # also check for inherited non moose 'meta' method?
224 # FIXME also skip this if the user requested by passing an option
227 # re-initialize so it inherits properly
228 $metaclass->initialize( ref($_[0]) || $_[0] );
233 # make sure they inherit from Moose::Object
234 $meta->superclasses($base_class)
235 unless $meta->superclasses();
240 # This may be used in some older MooseX extensions.
242 goto &Moose::Exporter::_get_caller;
245 ## make 'em all immutable
247 $_->meta->make_immutable(
248 inline_constructor => 1,
249 constructor_name => "_new",
250 inline_accessors => 1, # these are Class::MOP accessors, so they need inlining
253 Moose::Meta::Attribute
255 Moose::Meta::Instance
257 Moose::Meta::TypeConstraint
258 Moose::Meta::TypeConstraint::Union
259 Moose::Meta::TypeConstraint::Parameterized
260 Moose::Meta::TypeConstraint::Parameterizable
261 Moose::Meta::TypeConstraint::Enum
262 Moose::Meta::TypeConstraint::Class
263 Moose::Meta::TypeConstraint::Role
264 Moose::Meta::TypeConstraint::Registry
265 Moose::Meta::TypeCoercion
266 Moose::Meta::TypeCoercion::Union
269 Moose::Meta::Method::Accessor
270 Moose::Meta::Method::Constructor
271 Moose::Meta::Method::Destructor
272 Moose::Meta::Method::Overriden
273 Moose::Meta::Method::Augmented
276 Moose::Meta::Role::Method
277 Moose::Meta::Role::Method::Required
279 Moose::Meta::Role::Composite
281 Moose::Meta::Role::Application
282 Moose::Meta::Role::Application::RoleSummation
283 Moose::Meta::Role::Application::ToClass
284 Moose::Meta::Role::Application::ToRole
285 Moose::Meta::Role::Application::ToInstance
296 Moose - A postmodern object system for Perl 5
301 use Moose; # automatically turns on strict and warnings
303 has 'x' => (is => 'rw', isa => 'Int');
304 has 'y' => (is => 'rw', isa => 'Int');
317 has 'z' => (is => 'rw', isa => 'Int');
319 after 'clear' => sub {
326 Moose is an extension of the Perl 5 object system.
328 The main goal of Moose is to make Perl 5 Object Oriented programming
329 easier, more consistent and less tedious. With Moose you can to think
330 more about what you want to do and less about the mechanics of OOP.
332 Additionally, Moose is built on top of L<Class::MOP>, which is a
333 metaclass system for Perl 5. This means that Moose not only makes
334 building normal Perl 5 objects better, but it provides the power of
335 metaclass programming as well.
339 If you're new to Moose, the best place to start is the L<Moose::Intro>
340 docs, followed by the L<Moose::Cookbook>. The intro will show you what
341 Moose is, and how it makes Perl 5 OO better.
343 The cookbook recipes on Moose basics will get you up to speed with
344 many of Moose's features quickly. Once you have an idea of what Moose
345 can do, you can use the API documentation to get more detail on
346 features which interest you.
348 =head2 Moose Extensions
350 The C<MooseX::> namespace is the official place to find Moose extensions.
351 These extensions can be found on the CPAN. The easiest way to find them
352 is to search for them (L<http://search.cpan.org/search?query=MooseX::>),
353 or to examine L<Task::Moose> which aims to keep an up-to-date, easily
354 installable list of Moose extensions.
356 =head1 BUILDING CLASSES WITH MOOSE
358 Moose makes every attempt to provide as much convenience as possible during
359 class construction/definition, but still stay out of your way if you want it
360 to. Here are a few items to note when building classes with Moose.
362 Unless specified with C<extends>, any class which uses Moose will
363 inherit from L<Moose::Object>.
365 Moose will also manage all attributes (including inherited ones) that are
366 defined with C<has>. And (assuming you call C<new>, which is inherited from
367 L<Moose::Object>) this includes properly initializing all instance slots,
368 setting defaults where appropriate, and performing any type constraint checking
371 =head1 PROVIDED METHODS
373 Moose provides a number of methods to all your classes, mostly through the
374 inheritance of L<Moose::Object>. There is however, one exception.
380 This is a method which provides access to the current class's metaclass.
384 =head1 EXPORTED FUNCTIONS
386 Moose will export a number of functions into the class's namespace which
387 may then be used to set up the class. These functions all work directly
388 on the current class.
392 =item B<extends (@superclasses)>
394 This function will set the superclass(es) for the current class.
396 This approach is recommended instead of C<use base>, because C<use base>
397 actually C<push>es onto the class's C<@ISA>, whereas C<extends> will
398 replace it. This is important to ensure that classes which do not have
399 superclasses still properly inherit from L<Moose::Object>.
401 =item B<with (@roles)>
403 This will apply a given set of C<@roles> to the local class.
405 =item B<has $name =E<gt> %options>
407 This will install an attribute of a given C<$name> into the current class.
408 The C<%options> are the same as those provided by
409 L<Class::MOP::Attribute>, in addition to the list below which are provided
410 by Moose (L<Moose::Meta::Attribute> to be more specific):
414 =item I<is =E<gt> 'rw'|'ro'>
416 The I<is> option accepts either I<rw> (for read/write) or I<ro> (for read
417 only). These will create either a read/write accessor or a read-only
418 accessor respectively, using the same name as the C<$name> of the attribute.
420 If you need more control over how your accessors are named, you can use the
421 L<reader|Class::MOP::Attribute#reader>, I<|Class::MOP::Attribute#writer> and
422 I<|Class::MOP::Attribute#accessor> options inherited from
423 L<Class::MOP::Attribute>, however if you use those, you won't need the I<is>
426 =item I<isa =E<gt> $type_name>
428 The I<isa> option uses Moose's type constraint facilities to set up runtime
429 type checking for this attribute. Moose will perform the checks during class
430 construction, and within any accessors. The C<$type_name> argument must be a
431 string. The string may be either a class name or a type defined using
432 Moose's type definition features. (Refer to L<Moose::Util::TypeConstraints>
433 for information on how to define a new type, and how to retrieve type meta-data).
435 =item I<coerce =E<gt> (1|0)>
437 This will attempt to use coercion with the supplied type constraint to change
438 the value passed into any accessors or constructors. You B<must> have supplied
439 a type constraint in order for this to work. See L<Moose::Cookbook::Basics::Recipe5>
442 =item I<does =E<gt> $role_name>
444 This will accept the name of a role which the value stored in this attribute
445 is expected to have consumed.
447 =item I<required =E<gt> (1|0)>
449 This marks the attribute as being required. This means a I<defined> value must be
450 supplied during class construction, and the attribute may never be set to
451 C<undef> with an accessor.
453 =item I<weak_ref =E<gt> (1|0)>
455 This will tell the class to store the value of this attribute as a weakened
456 reference. If an attribute is a weakened reference, it B<cannot> also be
459 =item I<lazy =E<gt> (1|0)>
461 This will tell the class to not create this slot until absolutely necessary.
462 If an attribute is marked as lazy it B<must> have a default supplied.
464 =item I<auto_deref =E<gt> (1|0)>
466 This tells the accessor whether to automatically dereference the value returned.
467 This is only legal if your C<isa> option is either C<ArrayRef> or C<HashRef>.
469 =item I<trigger =E<gt> $code>
471 The I<trigger> option is a CODE reference which will be called after the value of
472 the attribute is set. The CODE ref will be passed the instance itself, the
473 updated value and the attribute meta-object (this is for more advanced fiddling
474 and can typically be ignored). You B<cannot> have a trigger on a read-only
477 B<NOTE:> Triggers will only fire when you B<assign> to the attribute,
478 either in the constructor, or using the writer. Default and built values will
479 B<not> cause the trigger to be fired.
481 =item I<handles =E<gt> ARRAY | HASH | REGEXP | ROLE | CODE>
483 The I<handles> option provides Moose classes with automated delegation features.
484 This is a pretty complex and powerful option. It accepts many different option
485 formats, each with its own benefits and drawbacks.
487 B<NOTE:> The class being delegated to does not need to be a Moose based class,
488 which is why this feature is especially useful when wrapping non-Moose classes.
490 All I<handles> option formats share the following traits:
492 You cannot override a locally defined method with a delegated method; an
493 exception will be thrown if you try. That is to say, if you define C<foo> in
494 your class, you cannot override it with a delegated C<foo>. This is almost never
495 something you would want to do, and if it is, you should do it by hand and not
498 You cannot override any of the methods found in Moose::Object, or the C<BUILD>
499 and C<DEMOLISH> methods. These will not throw an exception, but will silently
500 move on to the next method in the list. My reasoning for this is that you would
501 almost never want to do this, since it usually breaks your class. As with
502 overriding locally defined methods, if you do want to do this, you should do it
503 manually, not with Moose.
505 You do not I<need> to have a reader (or accessor) for the attribute in order
506 to delegate to it. Moose will create a means of accessing the value for you,
507 however this will be several times B<less> efficient then if you had given
508 the attribute a reader (or accessor) to use.
510 Below is the documentation for each option format:
516 This is the most common usage for I<handles>. You basically pass a list of
517 method names to be delegated, and Moose will install a delegation method
522 This is the second most common usage for I<handles>. Instead of a list of
523 method names, you pass a HASH ref where each key is the method name you
524 want installed locally, and its value is the name of the original method
525 in the class being delegated to.
527 This can be very useful for recursive classes like trees. Here is a
528 quick example (soon to be expanded into a Moose::Cookbook recipe):
533 has 'node' => (is => 'rw', isa => 'Any');
538 default => sub { [] }
546 parent_node => 'node',
547 siblings => 'children',
551 In this example, the Tree package gets C<parent_node> and C<siblings> methods,
552 which delegate to the C<node> and C<children> methods (respectively) of the Tree
553 instance stored in the C<parent> slot.
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 This is the option to use when you really want to do something funky. You should
576 only use it if you really know what you are doing, as it involves manual
579 This takes a code reference, which should expect two arguments. The first is the
580 attribute meta-object this I<handles> is attached to. The second is the
581 metaclass of the class being delegated to. It expects you to return a hash (not
582 a HASH ref) of the methods you want mapped.
586 =item I<metaclass =E<gt> $metaclass_name>
588 This tells the class to use a custom attribute metaclass for this particular
589 attribute. Custom attribute metaclasses are useful for extending the
590 capabilities of the I<has> keyword: they are the simplest way to extend the MOP,
591 but they are still a fairly advanced topic and too much to cover here, see
592 L<Moose::Cookbook::Meta::Recipe1> for more information.
594 The default behavior here is to just load C<$metaclass_name>; however, we also
595 have a way to alias to a shorter name. This will first look to see if
596 B<Moose::Meta::Attribute::Custom::$metaclass_name> exists. If it does, Moose
597 will then check to see if that has the method C<register_implementation>, which
598 should return the actual name of the custom attribute metaclass. If there is no
599 C<register_implementation> method, it will fall back to using
600 B<Moose::Meta::Attribute::Custom::$metaclass_name> as the metaclass name.
602 =item I<traits =E<gt> [ @role_names ]>
604 This tells Moose to take the list of C<@role_names> and apply them to the
605 attribute meta-object. This is very similar to the I<metaclass> option, but
606 allows you to use more than one extension at a time.
608 See L<TRAIT NAME RESOLUTION> for details on how a trait name is
609 resolved to a class name.
611 Also see L<Moose::Cookbook::Meta::Recipe3> for a metaclass trait
616 The value of this key is the name of the method that will be called to obtain the value used to
617 initialize the attribute. See the documentation in
618 L<Class::MOP::Attribute|Class::MOP::Attribute#builder> for more information.
622 The value of this key is the default value which will initialize the attribute.
624 NOTE: If the value is a simple scalar (string or number), then it can be just passed as is.
625 However, if you wish to initialize it with a HASH or ARRAY ref, then you need to wrap that inside a CODE reference.
626 See the documentation in L<Class::MOP::Attribute|Class::MOP::Attribute#default> for more information.
630 This may be a method name (referring to a method on the class with this attribute) or a CODE ref.
631 The initializer is used to set the attribute value on an instance when the attribute is set during
632 instance initialization (but not when the value is being assigned to). See the documentation in
633 L<Class::MOP::Attribute|Class::MOP::Attribute#initializer> for more information.
637 Allows you to clear the value, see the documentation in
638 L<Class::MOP::Attribute|Class::MOP::Attribute#clearer> for more information.
642 Basic test to see if a value has been set in the attribute, see the documentation in
643 L<Class::MOP::Attribute|Class::MOP::Attribute#predicate> for more information.
647 =item B<has +$name =E<gt> %options>
649 This is variation on the normal attibute creator C<has> which allows you to
650 clone and extend an attribute from a superclass or from a role. Here is an
651 example of the superclass usage:
659 default => 'Hello, I am a Foo'
667 has '+message' => (default => 'Hello I am My::Foo');
669 What is happening here is that B<My::Foo> is cloning the C<message> attribute
670 from its parent class B<Foo>, retaining the C<is =E<gt> 'rw'> and C<isa =E<gt>
671 'Str'> characteristics, but changing the value in C<default>.
673 Here is another example, but within the context of a role:
681 default => 'Hello, I am a Foo'
689 has '+message' => (default => 'Hello I am My::Foo');
691 In this case, we are basically taking the attribute which the role supplied
692 and altering it within the bounds of this feature.
694 Aside from where the attributes come from (one from superclass, the other
695 from a role), this feature works exactly the same. This feature is restricted
696 somewhat, so as to try and force at least I<some> sanity into it. You are only
697 allowed to change the following attributes:
703 Change the default value of an attribute.
707 Change whether the attribute attempts to coerce a value passed to it.
711 Change if the attribute is required to have a value.
713 =item I<documentation>
715 Change the documentation string associated with the attribute.
719 Change if the attribute lazily initializes the slot.
723 You I<are> allowed to change the type without restriction.
725 It is recommended that you use this freedom with caution. We used to
726 only allow for extension only if the type was a subtype of the parent's
727 type, but we felt that was too restrictive and is better left as a
732 You are allowed to B<add> a new C<handles> definition, but you are B<not>
733 allowed to I<change> one.
737 You are allowed to B<add> a new C<builder> definition, but you are B<not>
738 allowed to I<change> one.
742 You are allowed to B<add> a new C<metaclass> definition, but you are
743 B<not> allowed to I<change> one.
747 You are allowed to B<add> additional traits to the C<traits> definition.
748 These traits will be composed into the attribute, but pre-existing traits
749 B<are not> overridden, or removed.
753 =item B<before $name|@names =E<gt> sub { ... }>
755 =item B<after $name|@names =E<gt> sub { ... }>
757 =item B<around $name|@names =E<gt> sub { ... }>
759 This three items are syntactic sugar for the before, after, and around method
760 modifier features that L<Class::MOP> provides. More information on these may be
761 found in the L<Class::MOP::Class documentation|Class::MOP::Class/"Method
766 The keyword C<super> is a no-op when called outside of an C<override> method. In
767 the context of an C<override> method, it will call the next most appropriate
768 superclass method with the same arguments as the original method.
770 =item B<override ($name, &sub)>
772 An C<override> method is a way of explicitly saying "I am overriding this
773 method from my superclass". You can call C<super> within this method, and
774 it will work as expected. The same thing I<can> be accomplished with a normal
775 method call and the C<SUPER::> pseudo-package; it is really your choice.
779 The keyword C<inner>, much like C<super>, is a no-op outside of the context of
780 an C<augment> method. You can think of C<inner> as being the inverse of
781 C<super>; the details of how C<inner> and C<augment> work is best described in
782 the L<Moose::Cookbook::Basics::Recipe6>.
784 =item B<augment ($name, &sub)>
786 An C<augment> method, is a way of explicitly saying "I am augmenting this
787 method from my superclass". Once again, the details of how C<inner> and
788 C<augment> work is best described in the L<Moose::Cookbook::Basics::Recipe6>.
792 This is the C<Carp::confess> function, and exported here because I use it
797 This is the C<Scalar::Util::blessed> function, it is exported here because I
798 use it all the time. It is highly recommended that this is used instead of
799 C<ref> anywhere you need to test for an object's class name.
803 =head1 METACLASS TRAITS
805 When you use Moose, you can also specify traits which will be applied
808 use Moose -traits => 'My::Trait';
810 This is very similar to the attribute traits feature. When you do
811 this, your class's C<meta> object will have the specified traits
812 applied to it. See L<TRAIT NAME RESOLUTION> for more details.
814 =head1 TRAIT NAME RESOLUTION
816 By default, when given a trait name, Moose simply tries to load a
817 class of the same name. If such a class does not exist, it then looks
818 for for a class matching
819 B<Moose::Meta::$type::Custom::Trait::$trait_name>. The C<$type>
820 variable here will be one of B<Attribute> or B<Class>, depending on
821 what the trait is being applied to.
823 If a class with this long name exists, Moose checks to see if it has
824 the method C<register_implementation>. This method is expected to
825 return the I<real> class name of the trait. If there is no
826 C<register_implementation> method, it will fall back to using
827 B<Moose::Meta::$type::Custom::Trait::$trait> as the trait name.
829 If all this is confusing, take a look at
830 L<Moose::Cookbook::Meta::Recipe3>, which demonstrates how to create an
833 =head1 UNIMPORTING FUNCTIONS
837 Moose offers a way to remove the keywords it exports, through the C<unimport>
838 method. You simply have to say C<no Moose> at the bottom of your code for this
839 to work. Here is an example:
844 has 'first_name' => (is => 'rw', isa => 'Str');
845 has 'last_name' => (is => 'rw', isa => 'Str');
849 $self->first_name . ' ' . $self->last_name
852 no Moose; # keywords are removed from the Person package
854 =head1 EXTENDING AND EMBEDDING MOOSE
856 To learn more about extending Moose, we recommend checking out the
857 "Extending" recipes in the L<Moose::Cookbook>, starting with
858 L<Moose::Cookbook::Extending::Recipe1>, which provides an overview of
859 all the different ways you might extend Moose.
861 =head2 B<< Moose->init_meta(for_class => $class, base_class => $baseclass, metaclass => $metaclass) >>
863 The C<init_meta> method sets up the metaclass object for the class
864 specified by C<for_class>. This method injects a a C<meta> accessor
865 into the class so you can get at this object. It also sets the class's
866 superclass to C<base_class>, with L<Moose::Object> as the default.
868 You can specify an alternate metaclass with the C<metaclass> parameter.
870 For more detail on this topic, see L<Moose::Cookbook::Extending::Recipe2>.
872 This method used to be documented as a function which accepted
873 positional parameters. This calling style will still work for
874 backwards compatibility, but is deprecated.
878 Moose's C<import> method supports the L<Sub::Exporter> form of C<{into =E<gt> $pkg}>
879 and C<{into_level =E<gt> 1}>.
881 B<NOTE>: Doing this is more or less deprecated. Use L<Moose::Exporter>
882 instead, which lets you stack multiple C<Moose.pm>-alike modules
883 sanely. It handles getting the exported functions into the right place
886 =head2 B<throw_error>
888 An alias for C<confess>, used by internally by Moose.
890 =head1 METACLASS COMPATIBILITY AND MOOSE
892 Metaclass compatibility is a thorny subject. You should start by
893 reading the "About Metaclass compatibility" section in the
896 Moose will attempt to resolve a few cases of metaclass incompatibility
897 when you set the superclasses for a class, unlike C<Class::MOP>, which
898 simply dies if the metaclasses are incompatible.
900 In actuality, Moose fixes incompatibility for I<all> of a class's
901 metaclasses, not just the class metaclass. That includes the instance
902 metaclass, attribute metaclass, as well as its constructor class and
903 destructor class. However, for simplicity this discussion will just
904 refer to "metaclass", meaning the class metaclass, most of the time.
906 Moose has two algorithms for fixing metaclass incompatibility.
908 The first algorithm is very simple. If all the metaclass for the
909 parent is a I<subclass> of the child's metaclass, then we simply
910 replace the child's metaclass with the parent's.
912 The second algorithm is more complicated. It tries to determine if the
913 metaclasses only "differ by roles". This means that the parent and
914 child's metaclass share a common ancestor in their respective
915 hierarchies, and that the subclasses under the common ancestor are
916 only different because of role applications. This case is actually
917 fairly common when you mix and match various C<MooseX::*> modules,
918 many of which apply roles to the metaclass.
920 If the parent and child do differ by roles, Moose replaces the
921 metaclass in the child with a newly created metaclass. This metaclass
922 is a subclass of the parent's metaclass, does all of the roles that
923 the child's metaclass did before being replaced. Effectively, this
924 means the new metaclass does all of the roles done by both the
925 parent's and child's original metaclasses.
927 Ultimately, this is all transparent to you except in the case of an
928 unresolvable conflict.
936 It should be noted that C<super> and C<inner> B<cannot> be used in the same
937 method. However, they may be combined within the same class hierarchy; see
938 F<t/014_override_augment_inner_super.t> for an example.
940 The reason for this is that C<super> is only valid within a method
941 with the C<override> modifier, and C<inner> will never be valid within an
942 C<override> method. In fact, C<augment> will skip over any C<override> methods
943 when searching for its appropriate C<inner>.
945 This might seem like a restriction, but I am of the opinion that keeping these
946 two features separate (yet interoperable) actually makes them easy to use, since
947 their behavior is then easier to predict. Time will tell whether I am right or
948 not (UPDATE: so far so good).
952 =head1 ACKNOWLEDGEMENTS
956 =item I blame Sam Vilain for introducing me to the insanity that is meta-models.
958 =item I blame Audrey Tang for then encouraging my meta-model habit in #perl6.
960 =item Without Yuval "nothingmuch" Kogman this module would not be possible,
961 and it certainly wouldn't have this name ;P
963 =item The basis of the TypeContraints module was Rob Kinyon's idea
964 originally, I just ran with it.
966 =item Thanks to mst & chansen and the whole #moose posse for all the
967 early ideas/feature-requests/encouragement/bug-finding.
969 =item Thanks to David "Theory" Wheeler for meta-discussions and spelling fixes.
977 =item L<http://www.iinteractive.com/moose>
979 This is the official web home of Moose, it contains links to our public SVN repo
980 as well as links to a number of talks and articles on Moose and Moose related
983 =item L<Moose::Cookbook> - How to cook a Moose
985 =item The Moose is flying, a tutorial by Randal Schwartz
987 Part 1 - L<http://www.stonehenge.com/merlyn/LinuxMag/col94.html>
989 Part 2 - L<http://www.stonehenge.com/merlyn/LinuxMag/col95.html>
991 =item L<Class::MOP> documentation
993 =item The #moose channel on irc.perl.org
995 =item The Moose mailing list - moose@perl.org
997 =item Moose stats on ohloh.net - L<http://www.ohloh.net/projects/moose>
999 =item Several Moose extension modules in the C<MooseX::> namespace.
1001 See L<http://search.cpan.org/search?query=MooseX::> for extensions.
1009 =item The Art of the MetaObject Protocol
1011 I mention this in the L<Class::MOP> docs too, this book was critical in
1012 the development of both modules and is highly recommended.
1020 =item L<http://www.cs.utah.edu/plt/publications/oopsla04-gff.pdf>
1022 This paper (suggested by lbr on #moose) was what lead to the implementation
1023 of the C<super>/C<override> and C<inner>/C<augment> features. If you really
1024 want to understand them, I suggest you read this.
1030 All complex software has bugs lurking in it, and this module is no
1031 exception. If you find a bug please either email me, or add the bug
1034 =head1 FEATURE REQUESTS
1036 We are very strict about what features we add to the Moose core, especially
1037 the user-visible features. Instead we have made sure that the underlying
1038 meta-system of Moose is as extensible as possible so that you can add your
1039 own features easily. That said, occasionally there is a feature needed in the
1040 meta-system to support your planned extension, in which case you should
1041 either email the mailing list or join us on irc at #moose to discuss.
1045 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1047 B<with contributions from:>
1051 Adam (Alias) Kennedy
1053 Anders (Debolaz) Nor Berle
1055 Nathan (kolibre) Gray
1057 Christian (chansen) Hansen
1059 Hans Dieter (confound) Pearcey
1061 Eric (ewilhelm) Wilhelm
1063 Guillermo (groditi) Roditi
1065 Jess (castaway) Robinson
1069 Robert (phaylon) Sedlacek
1073 Scott (konobi) McWhirter
1075 Shlomi (rindolf) Fish
1077 Yuval (nothingmuch) Kogman
1079 Chris (perigrin) Prather
1081 Wallace (wreis) Reis
1083 Jonathan (jrockway) Rockway
1085 Dave (autarch) Rolsky
1087 Piotr (dexter) Roszatycki
1089 Sam (mugwump) Vilain
1091 Shawn (sartak) Moore
1093 ... and many other #moose folks
1095 =head1 COPYRIGHT AND LICENSE
1097 Copyright 2006-2008 by Infinity Interactive, Inc.
1099 L<http://www.iinteractive.com>
1101 This library is free software; you can redistribute it and/or modify
1102 it under the same terms as Perl itself.