2 package Moose::Meta::Attribute;
7 use Scalar::Util 'blessed', 'weaken';
10 our $VERSION = '0.89_01';
11 our $AUTHORITY = 'cpan:STEVAN';
13 use Moose::Meta::Method::Accessor;
14 use Moose::Meta::Method::Delegation;
16 use Moose::Util::TypeConstraints ();
18 use base 'Class::MOP::Attribute';
20 # options which are not directly used
21 # but we store them for metadata purposes
22 __PACKAGE__->meta->add_attribute('isa' => (reader => '_isa_metadata'));
23 __PACKAGE__->meta->add_attribute('does' => (reader => '_does_metadata'));
24 __PACKAGE__->meta->add_attribute('is' => (reader => '_is_metadata'));
26 # these are actual options for the attrs
27 __PACKAGE__->meta->add_attribute('required' => (reader => 'is_required' ));
28 __PACKAGE__->meta->add_attribute('lazy' => (reader => 'is_lazy' ));
29 __PACKAGE__->meta->add_attribute('lazy_build' => (reader => 'is_lazy_build' ));
30 __PACKAGE__->meta->add_attribute('coerce' => (reader => 'should_coerce' ));
31 __PACKAGE__->meta->add_attribute('weak_ref' => (reader => 'is_weak_ref' ));
32 __PACKAGE__->meta->add_attribute('auto_deref' => (reader => 'should_auto_deref'));
33 __PACKAGE__->meta->add_attribute('type_constraint' => (
34 reader => 'type_constraint',
35 predicate => 'has_type_constraint',
37 __PACKAGE__->meta->add_attribute('trigger' => (
39 predicate => 'has_trigger',
41 __PACKAGE__->meta->add_attribute('handles' => (
43 writer => '_set_handles',
44 predicate => 'has_handles',
46 __PACKAGE__->meta->add_attribute('documentation' => (
47 reader => 'documentation',
48 predicate => 'has_documentation',
50 __PACKAGE__->meta->add_attribute('traits' => (
51 reader => 'applied_traits',
52 predicate => 'has_applied_traits',
55 # we need to have a ->does method in here to
56 # more easily support traits, and the introspection
57 # of those traits. We extend the does check to look
58 # for metatrait aliases.
60 my ($self, $role_name) = @_;
62 Moose::Util::resolve_metatrait_alias(Attribute => $role_name)
64 return 0 if !defined($name); # failed to load class
65 return $self->Moose::Object::does($name);
70 my $class = ( ref $self && $self->associated_class ) || "Moose::Meta::Class";
71 unshift @_, "message" if @_ % 2 == 1;
72 unshift @_, attr => $self if ref $self;
74 my $handler = $class->can("throw_error"); # to avoid incrementing depth by 1
79 my ($class, $name, %options) = @_;
80 $class->_process_options($name, \%options) unless $options{__hack_no_process_options}; # used from clone()... YECHKKK FIXME ICKY YUCK GROSS
82 delete $options{__hack_no_process_options};
87 map { $_->init_arg() }
88 $class->meta()->get_all_attributes()
91 my @bad = sort grep { ! $attrs{$_} } keys %options;
95 Carp::cluck "Found unknown argument(s) passed to '$name' attribute constructor in '$class': @bad";
98 return $class->SUPER::new($name, %options);
101 sub interpolate_class_and_new {
102 my ($class, $name, %args) = @_;
104 my ( $new_class, @traits ) = $class->interpolate_class(\%args);
106 $new_class->new($name, %args, ( scalar(@traits) ? ( traits => \@traits ) : () ) );
109 sub interpolate_class {
110 my ($class, $options) = @_;
112 $class = ref($class) || $class;
114 if ( my $metaclass_name = delete $options->{metaclass} ) {
115 my $new_class = Moose::Util::resolve_metaclass_alias( Attribute => $metaclass_name );
117 if ( $class ne $new_class ) {
118 if ( $new_class->can("interpolate_class") ) {
119 return $new_class->interpolate_class($options);
128 if (my $traits = $options->{traits}) {
130 while ($i < @$traits) {
131 my $trait = $traits->[$i++];
132 next if ref($trait); # options to a trait we discarded
134 $trait = Moose::Util::resolve_metatrait_alias(Attribute => $trait)
137 next if $class->does($trait);
139 push @traits, $trait;
142 push @traits, $traits->[$i++]
143 if $traits->[$i] && ref($traits->[$i]);
147 my $anon_class = Moose::Meta::Class->create_anon_class(
148 superclasses => [ $class ],
149 roles => [ @traits ],
153 $class = $anon_class->name;
157 return ( wantarray ? ( $class, @traits ) : $class );
162 my @legal_options_for_inheritance = qw(
163 default coerce required
164 documentation lazy handles
165 builder type_constraint
170 sub legal_options_for_inheritance { @legal_options_for_inheritance }
173 # This method *must* be able to handle
174 # Class::MOP::Attribute instances as
175 # well. Yes, I know that is wrong, but
176 # apparently we didn't realize it was
177 # doing that and now we have some code
178 # which is dependent on it. The real
179 # solution of course is to push this
180 # feature back up into Class::MOP::Attribute
181 # but I not right now, I am too lazy.
182 # However if you are reading this and
183 # looking for something to do,.. please
186 sub clone_and_inherit_options {
187 my ($self, %options) = @_;
194 # we may want to extends a Class::MOP::Attribute
195 # in which case we need to be able to use the
196 # core set of legal options that have always
197 # been here. But we allows Moose::Meta::Attribute
198 # instances to changes them.
200 my @legal_options = $self->can('legal_options_for_inheritance')
201 ? $self->legal_options_for_inheritance
202 : @legal_options_for_inheritance;
204 foreach my $legal_option (@legal_options) {
205 if (exists $options{$legal_option}) {
206 $actual_options{$legal_option} = $options{$legal_option};
207 delete $options{$legal_option};
213 if (blessed($options{isa}) && $options{isa}->isa('Moose::Meta::TypeConstraint')) {
214 $type_constraint = $options{isa};
217 $type_constraint = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options{isa});
218 (defined $type_constraint)
219 || $self->throw_error("Could not find the type constraint '" . $options{isa} . "'", data => $options{isa});
222 $actual_options{type_constraint} = $type_constraint;
223 delete $options{isa};
226 if ($options{does}) {
228 if (blessed($options{does}) && $options{does}->isa('Moose::Meta::TypeConstraint')) {
229 $type_constraint = $options{does};
232 $type_constraint = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options{does});
233 (defined $type_constraint)
234 || $self->throw_error("Could not find the type constraint '" . $options{does} . "'", data => $options{does});
237 $actual_options{type_constraint} = $type_constraint;
238 delete $options{does};
242 # this doesn't apply to Class::MOP::Attributes,
243 # so we can ignore it for them.
245 if ($self->can('interpolate_class')) {
246 ( $actual_options{metaclass}, my @traits ) = $self->interpolate_class(\%options);
249 my @all_traits = grep { $seen{$_}++ } @{ $self->applied_traits || [] }, @traits;
250 $actual_options{traits} = \@all_traits if @all_traits;
252 delete @options{qw(metaclass traits)};
255 (scalar keys %options == 0)
256 || $self->throw_error("Illegal inherited options => (" . (join ', ' => keys %options) . ")", data => \%options);
259 $self->clone(%actual_options);
263 my ( $self, %params ) = @_;
265 my $class = delete $params{metaclass} || ref $self;
267 my ( @init, @non_init );
269 foreach my $attr ( grep { $_->has_value($self) } Class::MOP::class_of($self)->get_all_attributes ) {
270 push @{ $attr->has_init_arg ? \@init : \@non_init }, $attr;
273 my %new_params = ( ( map { $_->init_arg => $_->get_value($self) } @init ), %params );
275 my $name = delete $new_params{name};
277 my $clone = $class->new($name, %new_params, __hack_no_process_options => 1 );
279 foreach my $attr ( @non_init ) {
280 $attr->set_value($clone, $attr->get_value($self));
286 sub _process_options {
287 my ($class, $name, $options) = @_;
289 if (exists $options->{is}) {
291 ### -------------------------
292 ## is => ro, writer => _foo # turns into (reader => foo, writer => _foo) as before
293 ## is => rw, writer => _foo # turns into (reader => foo, writer => _foo)
294 ## is => rw, accessor => _foo # turns into (accessor => _foo)
295 ## is => ro, accessor => _foo # error, accesor is rw
296 ### -------------------------
298 if ($options->{is} eq 'ro') {
299 $class->throw_error("Cannot define an accessor name on a read-only attribute, accessors are read/write", data => $options)
300 if exists $options->{accessor};
301 $options->{reader} ||= $name;
303 elsif ($options->{is} eq 'rw') {
304 if ($options->{writer}) {
305 $options->{reader} ||= $name;
308 $options->{accessor} ||= $name;
311 elsif ($options->{is} eq 'bare') {
312 # do nothing, but don't complain (later) about missing methods
315 $class->throw_error("I do not understand this option (is => " . $options->{is} . ") on attribute ($name)", data => $options->{is});
319 if (exists $options->{isa}) {
320 if (exists $options->{does}) {
321 if (eval { $options->{isa}->can('does') }) {
322 ($options->{isa}->does($options->{does}))
323 || $class->throw_error("Cannot have an isa option and a does option if the isa does not do the does on attribute ($name)", data => $options);
326 $class->throw_error("Cannot have an isa option which cannot ->does() on attribute ($name)", data => $options);
330 # allow for anon-subtypes here ...
331 if (blessed($options->{isa}) && $options->{isa}->isa('Moose::Meta::TypeConstraint')) {
332 $options->{type_constraint} = $options->{isa};
335 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options->{isa});
338 elsif (exists $options->{does}) {
339 # allow for anon-subtypes here ...
340 if (blessed($options->{does}) && $options->{does}->isa('Moose::Meta::TypeConstraint')) {
341 $options->{type_constraint} = $options->{does};
344 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options->{does});
348 if (exists $options->{coerce} && $options->{coerce}) {
349 (exists $options->{type_constraint})
350 || $class->throw_error("You cannot have coercion without specifying a type constraint on attribute ($name)", data => $options);
351 $class->throw_error("You cannot have a weak reference to a coerced value on attribute ($name)", data => $options)
352 if $options->{weak_ref};
355 if (exists $options->{trigger}) {
356 ('CODE' eq ref $options->{trigger})
357 || $class->throw_error("Trigger must be a CODE ref on attribute ($name)", data => $options->{trigger});
360 if (exists $options->{auto_deref} && $options->{auto_deref}) {
361 (exists $options->{type_constraint})
362 || $class->throw_error("You cannot auto-dereference without specifying a type constraint on attribute ($name)", data => $options);
363 ($options->{type_constraint}->is_a_type_of('ArrayRef') ||
364 $options->{type_constraint}->is_a_type_of('HashRef'))
365 || $class->throw_error("You cannot auto-dereference anything other than a ArrayRef or HashRef on attribute ($name)", data => $options);
368 if (exists $options->{lazy_build} && $options->{lazy_build} == 1) {
369 $class->throw_error("You can not use lazy_build and default for the same attribute ($name)", data => $options)
370 if exists $options->{default};
371 $options->{lazy} = 1;
372 $options->{builder} ||= "_build_${name}";
374 $options->{clearer} ||= "_clear${name}";
375 $options->{predicate} ||= "_has${name}";
378 $options->{clearer} ||= "clear_${name}";
379 $options->{predicate} ||= "has_${name}";
383 if (exists $options->{lazy} && $options->{lazy}) {
384 (exists $options->{default} || defined $options->{builder} )
385 || $class->throw_error("You cannot have lazy attribute ($name) without specifying a default value for it", data => $options);
388 if ( $options->{required} && !( ( !exists $options->{init_arg} || defined $options->{init_arg} ) || exists $options->{default} || defined $options->{builder} ) ) {
389 $class->throw_error("You cannot have a required attribute ($name) without a default, builder, or an init_arg", data => $options);
394 sub initialize_instance_slot {
395 my ($self, $meta_instance, $instance, $params) = @_;
396 my $init_arg = $self->init_arg();
397 # try to fetch the init arg from the %params ...
401 if ( defined($init_arg) and exists $params->{$init_arg}) {
402 $val = $params->{$init_arg};
406 # skip it if it's lazy
407 return if $self->is_lazy;
408 # and die if it's required and doesn't have a default value
409 $self->throw_error("Attribute (" . $self->name . ") is required", object => $instance, data => $params)
410 if $self->is_required && !$self->has_default && !$self->has_builder;
412 # if nothing was in the %params, we can use the
413 # attribute's default value (if it has one)
414 if ($self->has_default) {
415 $val = $self->default($instance);
418 elsif ($self->has_builder) {
419 $val = $self->_call_builder($instance);
424 return unless $value_is_set;
426 $val = $self->_coerce_and_verify( $val, $instance );
428 $self->set_initial_value($instance, $val);
429 $meta_instance->weaken_slot_value($instance, $self->name)
430 if ref $val && $self->is_weak_ref;
434 my ( $self, $instance ) = @_;
436 my $builder = $self->builder();
438 return $instance->$builder()
439 if $instance->can( $self->builder );
441 $self->throw_error( blessed($instance)
442 . " does not support builder method '"
444 . "' for attribute '"
454 # this duplicates too much code from
455 # Class::MOP::Attribute, we need to
456 # refactor these bits eventually.
458 sub _set_initial_slot_value {
459 my ($self, $meta_instance, $instance, $value) = @_;
461 my $slot_name = $self->name;
463 return $meta_instance->set_slot_value($instance, $slot_name, $value)
464 unless $self->has_initializer;
466 my ($type_constraint, $can_coerce);
467 if ($self->has_type_constraint) {
468 $type_constraint = $self->type_constraint;
469 $can_coerce = ($self->should_coerce && $type_constraint->has_coercion);
473 my $val = $self->_coerce_and_verify( shift, $instance );;
475 $meta_instance->set_slot_value($instance, $slot_name, $val);
478 my $initializer = $self->initializer;
480 # most things will just want to set a value, so make it first arg
481 $instance->$initializer($value, $callback, $self);
485 my ($self, $instance, @args) = @_;
486 my $value = $args[0];
488 my $attr_name = $self->name;
490 if ($self->is_required and not @args) {
491 $self->throw_error("Attribute ($attr_name) is required", object => $instance);
494 $value = $self->_coerce_and_verify( $value, $instance );
496 my $meta_instance = Class::MOP::Class->initialize(blessed($instance))
500 if ( $self->has_trigger && $self->has_value($instance) ) {
501 @old = $self->get_value($instance, 'for trigger');
504 $meta_instance->set_slot_value($instance, $attr_name, $value);
506 if (ref $value && $self->is_weak_ref) {
507 $meta_instance->weaken_slot_value($instance, $attr_name);
510 if ($self->has_trigger) {
511 $self->trigger->($instance, $value, @old);
516 my ($self, $instance, $for_trigger) = @_;
518 if ($self->is_lazy) {
519 unless ($self->has_value($instance)) {
521 if ($self->has_default) {
522 $value = $self->default($instance);
523 } elsif ( $self->has_builder ) {
524 $value = $self->_call_builder($instance);
527 $value = $self->_coerce_and_verify( $value, $instance );
529 $self->set_initial_value($instance, $value);
533 if ( $self->should_auto_deref && ! $for_trigger ) {
535 my $type_constraint = $self->type_constraint;
537 if ($type_constraint->is_a_type_of('ArrayRef')) {
538 my $rv = $self->SUPER::get_value($instance);
539 return unless defined $rv;
540 return wantarray ? @{ $rv } : $rv;
542 elsif ($type_constraint->is_a_type_of('HashRef')) {
543 my $rv = $self->SUPER::get_value($instance);
544 return unless defined $rv;
545 return wantarray ? %{ $rv } : $rv;
548 $self->throw_error("Can not auto de-reference the type constraint '" . $type_constraint->name . "'", object => $instance, type_constraint => $type_constraint);
554 return $self->SUPER::get_value($instance);
558 ## installing accessors
560 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
562 sub install_accessors {
564 $self->SUPER::install_accessors(@_);
565 $self->install_delegation if $self->has_handles;
569 sub _check_associated_methods {
572 @{ $self->associated_methods }
573 || ($self->_is_metadata || '') eq 'bare'
576 'Attribute (' . $self->name . ') of class '
577 . $self->associated_class->name
578 . ' has no associated methods'
579 . ' (did you mean to provide an "is" argument?)'
585 sub _looks_like_overwriting_local_method {
586 my ($self, $accessor) = @_;
587 my $method = $self->associated_class->get_method($accessor);
588 return 0 unless $method;
590 # get ourselves down to the original method
591 while ($method->isa('Class::MOP::Method::Wrapped')) {
592 $method = $method->get_original_method;
594 return 0 if $method->isa('Class::MOP::Method::Accessor');
595 return 1 if !$self->definition_context;
596 return 0 if $method->package_name ne $self->definition_context->{package};
600 sub _process_accessors {
602 my ($type, $accessor, $generate_as_inline_methods) = @_;
603 $accessor = (keys %$accessor)[0] if (ref($accessor)||'') eq 'HASH';
604 if ($self->_looks_like_overwriting_local_method($accessor)) {
606 "You are overwriting a locally defined method ($accessor) with "
610 $self->SUPER::_process_accessors(@_);
613 sub remove_accessors {
615 $self->SUPER::remove_accessors(@_);
616 $self->remove_delegation if $self->has_handles;
620 sub install_delegation {
624 # Here we canonicalize the 'handles' option
625 # this will sort out any details and always
626 # return an hash of methods which we want
627 # to delagate to, see that method for details
628 my %handles = $self->_canonicalize_handles;
631 # install the delegation ...
632 my $associated_class = $self->associated_class;
633 foreach my $handle (keys %handles) {
634 my $method_to_call = $handles{$handle};
635 my $class_name = $associated_class->name;
636 my $name = "${class_name}::${handle}";
638 (!$associated_class->has_method($handle))
639 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
642 # handles is not allowed to delegate
643 # any of these methods, as they will
644 # override the ones in your class, which
645 # is almost certainly not what you want.
647 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
648 #cluck("Not delegating method '$handle' because it is a core method") and
649 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
651 my $method = $self->_make_delegation_method($handle, $method_to_call);
653 $self->associated_class->add_method($method->name, $method);
654 $self->associate_method($method);
658 sub remove_delegation {
660 my %handles = $self->_canonicalize_handles;
661 my $associated_class = $self->associated_class;
662 foreach my $handle (keys %handles) {
663 $self->associated_class->remove_method($handle);
667 # private methods to help delegation ...
669 sub _canonicalize_handles {
671 my $handles = $self->handles;
672 if (my $handle_type = ref($handles)) {
673 if ($handle_type eq 'HASH') {
676 elsif ($handle_type eq 'ARRAY') {
677 return map { $_ => $_ } @{$handles};
679 elsif ($handle_type eq 'Regexp') {
680 ($self->has_type_constraint)
681 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
682 return map { ($_ => $_) }
683 grep { /$handles/ } $self->_get_delegate_method_list;
685 elsif ($handle_type eq 'CODE') {
686 return $handles->($self, $self->_find_delegate_metaclass);
688 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::DuckType')) {
689 return map { $_ => $_ } @{ $handles->methods };
692 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
696 Class::MOP::load_class($handles);
697 my $role_meta = Class::MOP::class_of($handles);
699 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
700 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because its metaclass is not a Moose::Meta::Role", data => $handles);
702 return map { $_ => $_ } (
703 $role_meta->get_method_list,
704 map { $_->name } $role_meta->get_required_method_list,
709 sub _find_delegate_metaclass {
711 if (my $class = $self->_isa_metadata) {
712 # we might be dealing with a non-Moose class,
713 # and need to make our own metaclass. if there's
714 # already a metaclass, it will be returned
715 return Moose::Meta::Class->initialize($class);
717 elsif (my $role = $self->_does_metadata) {
718 return Class::MOP::class_of($role);
721 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
725 sub _get_delegate_method_list {
727 my $meta = $self->_find_delegate_metaclass;
728 if ($meta->isa('Class::MOP::Class')) {
729 return map { $_->name } # NOTE: !never! delegate &meta
730 grep { $_->package_name ne 'Moose::Object' && $_->name ne 'meta' }
731 $meta->get_all_methods;
733 elsif ($meta->isa('Moose::Meta::Role')) {
734 return $meta->get_method_list;
737 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
741 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
743 sub _make_delegation_method {
744 my ( $self, $handle_name, $method_to_call ) = @_;
748 $method_body = $method_to_call
749 if 'CODE' eq ref($method_to_call);
751 my @curried_arguments;
753 ($method_to_call, @curried_arguments) = @$method_to_call
754 if 'ARRAY' eq ref($method_to_call);
756 return $self->delegation_metaclass->new(
757 name => $handle_name,
758 package_name => $self->associated_class->name,
760 delegate_to_method => $method_to_call,
761 curried_arguments => \@curried_arguments,
765 sub _coerce_and_verify {
768 my $instance = shift;
770 return $val unless $self->has_type_constraint;
772 my $type_constraint = $self->type_constraint;
773 if ($self->should_coerce && $type_constraint->has_coercion) {
774 $val = $type_constraint->coerce($val);
777 $self->verify_against_type_constraint($val, instance => $instance);
782 sub verify_against_type_constraint {
786 return 1 if !$self->has_type_constraint;
788 my $type_constraint = $self->type_constraint;
790 $type_constraint->check($val)
791 || $self->throw_error("Attribute ("
793 . ") does not pass the type constraint because: "
794 . $type_constraint->get_message($val), data => $val, @_);
797 package Moose::Meta::Attribute::Custom::Moose;
798 sub register_implementation { 'Moose::Meta::Attribute' }
808 Moose::Meta::Attribute - The Moose attribute metaclass
812 This class is a subclass of L<Class::MOP::Attribute> that provides
813 additional Moose-specific functionality.
815 To really understand this class, you will need to start with the
816 L<Class::MOP::Attribute> documentation. This class can be understood
817 as a set of additional features on top of the basic feature provided
818 by that parent class.
822 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
826 Many of the documented below override methods in
827 L<Class::MOP::Attribute> and add Moose specific features.
833 =item B<< Moose::Meta::Attribute->new(%options) >>
835 This method overrides the L<Class::MOP::Attribute> constructor.
837 Many of the options below are described in more detail in the
838 L<Moose::Manual::Attributes> document.
840 It adds the following options to the constructor:
844 =item * is => 'ro', 'rw', 'bare'
846 This provides a shorthand for specifying the C<reader>, C<writer>, or
847 C<accessor> names. If the attribute is read-only ('ro') then it will
848 have a C<reader> method with the same attribute as the name.
850 If it is read-write ('rw') then it will have an C<accessor> method
851 with the same name. If you provide an explicit C<writer> for a
852 read-write attribute, then you will have a C<reader> with the same
853 name as the attribute, and a C<writer> with the name you provided.
855 Use 'bare' when you are deliberately not installing any methods
856 (accessor, reader, etc.) associated with this attribute; otherwise,
857 Moose will issue a deprecation warning when this attribute is added to a
862 This option accepts a type. The type can be a string, which should be
863 a type name. If the type name is unknown, it is assumed to be a class
866 This option can also accept a L<Moose::Meta::TypeConstraint> object.
868 If you I<also> provide a C<does> option, then your C<isa> option must
869 be a class name, and that class must do the role specified with
872 =item * does => $role
874 This is short-hand for saying that the attribute's type must be an
875 object which does the named role.
877 =item * coerce => $bool
879 This option is only valid for objects with a type constraint
880 (C<isa>). If this is true, then coercions will be applied whenever
881 this attribute is set.
883 You can make both this and the C<weak_ref> option true.
885 =item * trigger => $sub
887 This option accepts a subroutine reference, which will be called after
888 the attribute is set.
890 =item * required => $bool
892 An attribute which is required must be provided to the constructor. An
893 attribute which is required can also have a C<default> or C<builder>,
894 which will satisfy its required-ness.
896 A required attribute must have a C<default>, C<builder> or a
897 non-C<undef> C<init_arg>
899 =item * lazy => $bool
901 A lazy attribute must have a C<default> or C<builder>. When an
902 attribute is lazy, the default value will not be calculated until the
905 =item * weak_ref => $bool
907 If this is true, the attribute's value will be stored as a weak
910 =item * auto_deref => $bool
912 If this is true, then the reader will dereference the value when it is
913 called. The attribute must have a type constraint which defines the
914 attribute as an array or hash reference.
916 =item * lazy_build => $bool
918 Setting this to true makes the attribute lazy and provides a number of
926 is equivalent to this:
931 builder => '_build_size',
932 clearer => 'clear_size',
933 predicate => 'has_size',
936 =item * documentation
938 An arbitrary string that can be retrieved later by calling C<<
939 $attr->documentation >>.
943 =item B<< $attr->clone(%options) >>
945 This creates a new attribute based on attribute being cloned. You must
946 supply a C<name> option to provide a new name for the attribute.
948 The C<%options> can only specify options handled by
949 L<Class::MOP::Attribute>.
953 =head2 Value management
957 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
959 This method is used internally to initialize the attribute's slot in
960 the object C<$instance>.
962 This overrides the L<Class::MOP::Attribute> method to handle lazy
963 attributes, weak references, and type constraints.
969 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
974 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
976 Before setting the value, a check is made on the type constraint of
977 the attribute, if it has one, to see if the value passes it. If the
978 value fails to pass, the set operation dies with a L<throw_error>.
980 Any coercion to convert values is done before checking the type constraint.
982 To check a value against a type constraint before setting it, fetch the
983 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
984 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
985 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
990 =head2 Attribute Accessor generation
994 =item B<< $attr->install_accessors >>
996 This method overrides the parent to also install delegation methods.
998 If, after installing all methods, the attribute object has no associated
999 methods, it throws an error unless C<< is => 'bare' >> was passed to the
1000 attribute constructor. (Trying to add an attribute that has no associated
1001 methods is almost always an error.)
1003 =item B<< $attr->remove_accessors >>
1005 This method overrides the parent to also remove delegation methods.
1007 =item B<< $attr->install_delegation >>
1009 This method adds its delegation methods to the attribute's associated
1010 class, if it has any to add.
1012 =item B<< $attr->remove_delegation >>
1014 This method remove its delegation methods from the attribute's
1017 =item B<< $attr->accessor_metaclass >>
1019 Returns the accessor metaclass name, which defaults to
1020 L<Moose::Meta::Method::Accessor>.
1022 =item B<< $attr->delegation_metaclass >>
1024 Returns the delegation metaclass name, which defaults to
1025 L<Moose::Meta::Method::Delegation>.
1029 =head2 Additional Moose features
1031 These methods are not found in the superclass. They support features
1036 =item B<< $attr->does($role) >>
1038 This indicates whether the I<attribute itself> does the given
1039 role. The role can be given as a full class name, or as a resolvable
1042 Note that this checks the attribute itself, not its type constraint,
1043 so it is checking the attribute's metaclass and any traits applied to
1046 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
1048 This is an alternate constructor that handles the C<metaclass> and
1051 Effectively, this method is a factory that finds or creates the
1052 appropriate class for the given C<metaclass> and/or C<traits>.
1054 Once it has the appropriate class, it will call C<< $class->new($name,
1055 %options) >> on that class.
1057 =item B<< $attr->clone_and_inherit_options(%options) >>
1059 This method supports the C<has '+foo'> feature. It does various bits
1060 of processing on the supplied C<%options> before ultimately calling
1061 the C<clone> method.
1063 One of its main tasks is to make sure that the C<%options> provided
1064 only includes the options returned by the
1065 C<legal_options_for_inheritance> method.
1067 =item B<< $attr->legal_options_for_inheritance >>
1069 This returns a whitelist of options that can be overridden in a
1070 subclass's attribute definition.
1072 This exists to allow a custom metaclass to change or add to the list
1073 of options which can be changed.
1075 =item B<< $attr->type_constraint >>
1077 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1080 =item B<< $attr->has_type_constraint >>
1082 Returns true if this attribute has a type constraint.
1084 =item B<< $attr->verify_against_type_constraint($value) >>
1086 Given a value, this method returns true if the value is valid for the
1087 attribute's type constraint. If the value is not valid, it throws an
1090 =item B<< $attr->handles >>
1092 This returns the value of the C<handles> option passed to the
1095 =item B<< $attr->has_handles >>
1097 Returns true if this attribute performs delegation.
1099 =item B<< $attr->is_weak_ref >>
1101 Returns true if this attribute stores its value as a weak reference.
1103 =item B<< $attr->is_required >>
1105 Returns true if this attribute is required to have a value.
1107 =item B<< $attr->is_lazy >>
1109 Returns true if this attribute is lazy.
1111 =item B<< $attr->is_lazy_build >>
1113 Returns true if the C<lazy_build> option was true when passed to the
1116 =item B<< $attr->should_coerce >>
1118 Returns true if the C<coerce> option passed to the constructor was
1121 =item B<< $attr->should_auto_deref >>
1123 Returns true if the C<auto_deref> option passed to the constructor was
1126 =item B<< $attr->trigger >>
1128 This is the subroutine reference that was in the C<trigger> option
1129 passed to the constructor, if any.
1131 =item B<< $attr->has_trigger >>
1133 Returns true if this attribute has a trigger set.
1135 =item B<< $attr->documentation >>
1137 Returns the value that was in the C<documentation> option passed to
1138 the constructor, if any.
1140 =item B<< $attr->has_documentation >>
1142 Returns true if this attribute has any documentation.
1144 =item B<< $attr->applied_traits >>
1146 This returns an array reference of all the traits which were applied
1147 to this attribute. If none were applied, this returns C<undef>.
1149 =item B<< $attr->has_applied_traits >>
1151 Returns true if this attribute has any traits applied.
1157 All complex software has bugs lurking in it, and this module is no
1158 exception. If you find a bug please either email me, or add the bug
1163 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1165 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1167 =head1 COPYRIGHT AND LICENSE
1169 Copyright 2006-2009 by Infinity Interactive, Inc.
1171 L<http://www.iinteractive.com>
1173 This library is free software; you can redistribute it and/or modify
1174 it under the same terms as Perl itself.