2 package Moose::Meta::Attribute;
7 use Scalar::Util 'blessed', 'weaken';
8 use List::MoreUtils 'any';
12 our $VERSION = '0.96';
13 our $AUTHORITY = 'cpan:STEVAN';
15 use Moose::Meta::Method::Accessor;
16 use Moose::Meta::Method::Delegation;
18 use Moose::Util::TypeConstraints ();
20 use base 'Class::MOP::Attribute', 'Moose::Meta::Mixin::AttributeCore';
22 __PACKAGE__->meta->add_attribute('traits' => (
23 reader => 'applied_traits',
24 predicate => 'has_applied_traits',
27 # we need to have a ->does method in here to
28 # more easily support traits, and the introspection
29 # of those traits. We extend the does check to look
30 # for metatrait aliases.
32 my ($self, $role_name) = @_;
34 Moose::Util::resolve_metatrait_alias(Attribute => $role_name)
36 return 0 if !defined($name); # failed to load class
37 return $self->Moose::Object::does($name);
42 my $class = ( ref $self && $self->associated_class ) || "Moose::Meta::Class";
43 unshift @_, "message" if @_ % 2 == 1;
44 unshift @_, attr => $self if ref $self;
46 my $handler = $class->can("throw_error"); # to avoid incrementing depth by 1
51 my ($class, $name, %options) = @_;
52 $class->_process_options($name, \%options) unless $options{__hack_no_process_options}; # used from clone()... YECHKKK FIXME ICKY YUCK GROSS
54 delete $options{__hack_no_process_options};
59 map { $_->init_arg() }
60 $class->meta()->get_all_attributes()
63 my @bad = sort grep { ! $attrs{$_} } keys %options;
67 Carp::cluck "Found unknown argument(s) passed to '$name' attribute constructor in '$class': @bad";
70 return $class->SUPER::new($name, %options);
73 sub interpolate_class_and_new {
74 my ($class, $name, %args) = @_;
76 my ( $new_class, @traits ) = $class->interpolate_class(\%args);
78 $new_class->new($name, %args, ( scalar(@traits) ? ( traits => \@traits ) : () ) );
81 sub interpolate_class {
82 my ($class, $options) = @_;
84 $class = ref($class) || $class;
86 if ( my $metaclass_name = delete $options->{metaclass} ) {
87 my $new_class = Moose::Util::resolve_metaclass_alias( Attribute => $metaclass_name );
89 if ( $class ne $new_class ) {
90 if ( $new_class->can("interpolate_class") ) {
91 return $new_class->interpolate_class($options);
100 if (my $traits = $options->{traits}) {
102 while ($i < @$traits) {
103 my $trait = $traits->[$i++];
104 next if ref($trait); # options to a trait we discarded
106 $trait = Moose::Util::resolve_metatrait_alias(Attribute => $trait)
109 next if $class->does($trait);
111 push @traits, $trait;
114 push @traits, $traits->[$i++]
115 if $traits->[$i] && ref($traits->[$i]);
119 my $anon_class = Moose::Meta::Class->create_anon_class(
120 superclasses => [ $class ],
121 roles => [ @traits ],
125 $class = $anon_class->name;
129 return ( wantarray ? ( $class, @traits ) : $class );
134 my @legal_options_for_inheritance = qw(
135 default coerce required
136 documentation lazy handles
137 builder type_constraint
142 sub legal_options_for_inheritance { @legal_options_for_inheritance }
145 # This method *must* be able to handle
146 # Class::MOP::Attribute instances as
147 # well. Yes, I know that is wrong, but
148 # apparently we didn't realize it was
149 # doing that and now we have some code
150 # which is dependent on it. The real
151 # solution of course is to push this
152 # feature back up into Class::MOP::Attribute
153 # but I not right now, I am too lazy.
154 # However if you are reading this and
155 # looking for something to do,.. please
158 sub clone_and_inherit_options {
159 my ($self, %options) = @_;
166 # we may want to extends a Class::MOP::Attribute
167 # in which case we need to be able to use the
168 # core set of legal options that have always
169 # been here. But we allows Moose::Meta::Attribute
170 # instances to changes them.
172 my @legal_options = $self->can('legal_options_for_inheritance')
173 ? $self->legal_options_for_inheritance
174 : @legal_options_for_inheritance;
176 foreach my $legal_option (@legal_options) {
177 if (exists $options{$legal_option}) {
178 $actual_options{$legal_option} = $options{$legal_option};
179 delete $options{$legal_option};
185 if (blessed($options{isa}) && $options{isa}->isa('Moose::Meta::TypeConstraint')) {
186 $type_constraint = $options{isa};
189 $type_constraint = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options{isa});
190 (defined $type_constraint)
191 || $self->throw_error("Could not find the type constraint '" . $options{isa} . "'", data => $options{isa});
194 $actual_options{type_constraint} = $type_constraint;
195 delete $options{isa};
198 if ($options{does}) {
200 if (blessed($options{does}) && $options{does}->isa('Moose::Meta::TypeConstraint')) {
201 $type_constraint = $options{does};
204 $type_constraint = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options{does});
205 (defined $type_constraint)
206 || $self->throw_error("Could not find the type constraint '" . $options{does} . "'", data => $options{does});
209 $actual_options{type_constraint} = $type_constraint;
210 delete $options{does};
214 # this doesn't apply to Class::MOP::Attributes,
215 # so we can ignore it for them.
217 if ($self->can('interpolate_class')) {
218 ( $actual_options{metaclass}, my @traits ) = $self->interpolate_class(\%options);
221 my @all_traits = grep { $seen{$_}++ } @{ $self->applied_traits || [] }, @traits;
222 $actual_options{traits} = \@all_traits if @all_traits;
224 delete @options{qw(metaclass traits)};
227 (scalar keys %options == 0)
228 || $self->throw_error("Illegal inherited options => (" . (join ', ' => keys %options) . ")", data => \%options);
231 $self->clone(%actual_options);
235 my ( $self, %params ) = @_;
237 my $class = delete $params{metaclass} || ref $self;
239 my ( @init, @non_init );
241 foreach my $attr ( grep { $_->has_value($self) } Class::MOP::class_of($self)->get_all_attributes ) {
242 push @{ $attr->has_init_arg ? \@init : \@non_init }, $attr;
245 my %new_params = ( ( map { $_->init_arg => $_->get_value($self) } @init ), %params );
247 my $name = delete $new_params{name};
249 my $clone = $class->new($name, %new_params, __hack_no_process_options => 1 );
251 foreach my $attr ( @non_init ) {
252 $attr->set_value($clone, $attr->get_value($self));
258 sub _process_options {
259 my ($class, $name, $options) = @_;
261 if (exists $options->{is}) {
263 ### -------------------------
264 ## is => ro, writer => _foo # turns into (reader => foo, writer => _foo) as before
265 ## is => rw, writer => _foo # turns into (reader => foo, writer => _foo)
266 ## is => rw, accessor => _foo # turns into (accessor => _foo)
267 ## is => ro, accessor => _foo # error, accesor is rw
268 ### -------------------------
270 if ($options->{is} eq 'ro') {
271 $class->throw_error("Cannot define an accessor name on a read-only attribute, accessors are read/write", data => $options)
272 if exists $options->{accessor};
273 $options->{reader} ||= $name;
275 elsif ($options->{is} eq 'rw') {
276 if ($options->{writer}) {
277 $options->{reader} ||= $name;
280 $options->{accessor} ||= $name;
283 elsif ($options->{is} eq 'bare') {
284 # do nothing, but don't complain (later) about missing methods
287 $class->throw_error("I do not understand this option (is => " . $options->{is} . ") on attribute ($name)", data => $options->{is});
291 if (exists $options->{isa}) {
292 if (exists $options->{does}) {
293 if (try { $options->{isa}->can('does') }) {
294 ($options->{isa}->does($options->{does}))
295 || $class->throw_error("Cannot have an isa option and a does option if the isa does not do the does on attribute ($name)", data => $options);
298 $class->throw_error("Cannot have an isa option which cannot ->does() on attribute ($name)", data => $options);
302 # allow for anon-subtypes here ...
303 if (blessed($options->{isa}) && $options->{isa}->isa('Moose::Meta::TypeConstraint')) {
304 $options->{type_constraint} = $options->{isa};
307 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options->{isa});
310 elsif (exists $options->{does}) {
311 # allow for anon-subtypes here ...
312 if (blessed($options->{does}) && $options->{does}->isa('Moose::Meta::TypeConstraint')) {
313 $options->{type_constraint} = $options->{does};
316 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options->{does});
320 if (exists $options->{coerce} && $options->{coerce}) {
321 (exists $options->{type_constraint})
322 || $class->throw_error("You cannot have coercion without specifying a type constraint on attribute ($name)", data => $options);
323 $class->throw_error("You cannot have a weak reference to a coerced value on attribute ($name)", data => $options)
324 if $options->{weak_ref};
327 if (exists $options->{trigger}) {
328 ('CODE' eq ref $options->{trigger})
329 || $class->throw_error("Trigger must be a CODE ref on attribute ($name)", data => $options->{trigger});
332 if (exists $options->{auto_deref} && $options->{auto_deref}) {
333 (exists $options->{type_constraint})
334 || $class->throw_error("You cannot auto-dereference without specifying a type constraint on attribute ($name)", data => $options);
335 ($options->{type_constraint}->is_a_type_of('ArrayRef') ||
336 $options->{type_constraint}->is_a_type_of('HashRef'))
337 || $class->throw_error("You cannot auto-dereference anything other than a ArrayRef or HashRef on attribute ($name)", data => $options);
340 if (exists $options->{lazy_build} && $options->{lazy_build} == 1) {
341 $class->throw_error("You can not use lazy_build and default for the same attribute ($name)", data => $options)
342 if exists $options->{default};
343 $options->{lazy} = 1;
344 $options->{builder} ||= "_build_${name}";
346 $options->{clearer} ||= "_clear${name}";
347 $options->{predicate} ||= "_has${name}";
350 $options->{clearer} ||= "clear_${name}";
351 $options->{predicate} ||= "has_${name}";
355 if (exists $options->{lazy} && $options->{lazy}) {
356 (exists $options->{default} || defined $options->{builder} )
357 || $class->throw_error("You cannot have lazy attribute ($name) without specifying a default value for it", data => $options);
360 if ( $options->{required} && !( ( !exists $options->{init_arg} || defined $options->{init_arg} ) || exists $options->{default} || defined $options->{builder} ) ) {
361 $class->throw_error("You cannot have a required attribute ($name) without a default, builder, or an init_arg", data => $options);
366 sub initialize_instance_slot {
367 my ($self, $meta_instance, $instance, $params) = @_;
368 my $init_arg = $self->init_arg();
369 # try to fetch the init arg from the %params ...
373 if ( defined($init_arg) and exists $params->{$init_arg}) {
374 $val = $params->{$init_arg};
378 # skip it if it's lazy
379 return if $self->is_lazy;
380 # and die if it's required and doesn't have a default value
381 $self->throw_error("Attribute (" . $self->name . ") is required", object => $instance, data => $params)
382 if $self->is_required && !$self->has_default && !$self->has_builder;
384 # if nothing was in the %params, we can use the
385 # attribute's default value (if it has one)
386 if ($self->has_default) {
387 $val = $self->default($instance);
390 elsif ($self->has_builder) {
391 $val = $self->_call_builder($instance);
396 return unless $value_is_set;
398 $val = $self->_coerce_and_verify( $val, $instance );
400 $self->set_initial_value($instance, $val);
402 if ( ref $val && $self->is_weak_ref ) {
403 $self->_weaken_value($instance);
408 my ( $self, $instance ) = @_;
410 my $builder = $self->builder();
412 return $instance->$builder()
413 if $instance->can( $self->builder );
415 $self->throw_error( blessed($instance)
416 . " does not support builder method '"
418 . "' for attribute '"
428 # this duplicates too much code from
429 # Class::MOP::Attribute, we need to
430 # refactor these bits eventually.
432 sub _set_initial_slot_value {
433 my ($self, $meta_instance, $instance, $value) = @_;
435 my $slot_name = $self->name;
437 return $meta_instance->set_slot_value($instance, $slot_name, $value)
438 unless $self->has_initializer;
440 my ($type_constraint, $can_coerce);
441 if ($self->has_type_constraint) {
442 $type_constraint = $self->type_constraint;
443 $can_coerce = ($self->should_coerce && $type_constraint->has_coercion);
447 my $val = $self->_coerce_and_verify( shift, $instance );;
449 $meta_instance->set_slot_value($instance, $slot_name, $val);
452 my $initializer = $self->initializer;
454 # most things will just want to set a value, so make it first arg
455 $instance->$initializer($value, $callback, $self);
459 my ($self, $instance, @args) = @_;
460 my $value = $args[0];
462 my $attr_name = $self->name;
464 if ($self->is_required and not @args) {
465 $self->throw_error("Attribute ($attr_name) is required", object => $instance);
468 $value = $self->_coerce_and_verify( $value, $instance );
471 if ( $self->has_trigger && $self->has_value($instance) ) {
472 @old = $self->get_value($instance, 'for trigger');
475 $self->SUPER::set_value($instance, $value);
477 if ( ref $value && $self->is_weak_ref ) {
478 $self->_weaken_value($instance);
481 if ($self->has_trigger) {
482 $self->trigger->($instance, $value, @old);
487 my ( $self, $instance ) = @_;
489 my $meta_instance = Class::MOP::Class->initialize( blessed($instance) )
492 $meta_instance->weaken_slot_value( $instance, $self->name );
496 my ($self, $instance, $for_trigger) = @_;
498 if ($self->is_lazy) {
499 unless ($self->has_value($instance)) {
501 if ($self->has_default) {
502 $value = $self->default($instance);
503 } elsif ( $self->has_builder ) {
504 $value = $self->_call_builder($instance);
507 $value = $self->_coerce_and_verify( $value, $instance );
509 $self->set_initial_value($instance, $value);
513 if ( $self->should_auto_deref && ! $for_trigger ) {
515 my $type_constraint = $self->type_constraint;
517 if ($type_constraint->is_a_type_of('ArrayRef')) {
518 my $rv = $self->SUPER::get_value($instance);
519 return unless defined $rv;
520 return wantarray ? @{ $rv } : $rv;
522 elsif ($type_constraint->is_a_type_of('HashRef')) {
523 my $rv = $self->SUPER::get_value($instance);
524 return unless defined $rv;
525 return wantarray ? %{ $rv } : $rv;
528 $self->throw_error("Can not auto de-reference the type constraint '" . $type_constraint->name . "'", object => $instance, type_constraint => $type_constraint);
534 return $self->SUPER::get_value($instance);
538 ## installing accessors
540 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
542 sub install_accessors {
544 $self->SUPER::install_accessors(@_);
545 $self->install_delegation if $self->has_handles;
549 sub _check_associated_methods {
552 @{ $self->associated_methods }
553 || ($self->_is_metadata || '') eq 'bare'
556 'Attribute (' . $self->name . ') of class '
557 . $self->associated_class->name
558 . ' has no associated methods'
559 . ' (did you mean to provide an "is" argument?)'
565 sub _process_accessors {
567 my ($type, $accessor, $generate_as_inline_methods) = @_;
568 $accessor = (keys %$accessor)[0] if (ref($accessor)||'') eq 'HASH';
569 my $method = $self->associated_class->get_method($accessor);
570 if ($method && !$method->isa('Class::MOP::Method::Accessor')
571 && (!$self->definition_context
572 || $method->package_name eq $self->definition_context->{package})) {
574 "You are overwriting a locally defined method ($accessor) with "
578 $self->SUPER::_process_accessors(@_);
581 sub remove_accessors {
583 $self->SUPER::remove_accessors(@_);
584 $self->remove_delegation if $self->has_handles;
588 sub install_delegation {
592 # Here we canonicalize the 'handles' option
593 # this will sort out any details and always
594 # return an hash of methods which we want
595 # to delagate to, see that method for details
596 my %handles = $self->_canonicalize_handles;
599 # install the delegation ...
600 my $associated_class = $self->associated_class;
601 foreach my $handle (keys %handles) {
602 my $method_to_call = $handles{$handle};
603 my $class_name = $associated_class->name;
604 my $name = "${class_name}::${handle}";
606 (!$associated_class->has_method($handle))
607 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
610 # handles is not allowed to delegate
611 # any of these methods, as they will
612 # override the ones in your class, which
613 # is almost certainly not what you want.
615 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
616 #cluck("Not delegating method '$handle' because it is a core method") and
617 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
619 my $method = $self->_make_delegation_method($handle, $method_to_call);
621 $self->associated_class->add_method($method->name, $method);
622 $self->associate_method($method);
626 sub remove_delegation {
628 my %handles = $self->_canonicalize_handles;
629 my $associated_class = $self->associated_class;
630 foreach my $handle (keys %handles) {
631 next unless any { $handle eq $_ }
633 @{ $self->associated_methods };
634 $self->associated_class->remove_method($handle);
638 # private methods to help delegation ...
640 sub _canonicalize_handles {
642 my $handles = $self->handles;
643 if (my $handle_type = ref($handles)) {
644 if ($handle_type eq 'HASH') {
647 elsif ($handle_type eq 'ARRAY') {
648 return map { $_ => $_ } @{$handles};
650 elsif ($handle_type eq 'Regexp') {
651 ($self->has_type_constraint)
652 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
653 return map { ($_ => $_) }
654 grep { /$handles/ } $self->_get_delegate_method_list;
656 elsif ($handle_type eq 'CODE') {
657 return $handles->($self, $self->_find_delegate_metaclass);
659 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::DuckType')) {
660 return map { $_ => $_ } @{ $handles->methods };
663 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
667 Class::MOP::load_class($handles);
668 my $role_meta = Class::MOP::class_of($handles);
670 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
671 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because its metaclass is not a Moose::Meta::Role", data => $handles);
673 return map { $_ => $_ }
674 grep { $_ ne 'meta' } (
675 $role_meta->get_method_list,
676 map { $_->name } $role_meta->get_required_method_list,
681 sub _find_delegate_metaclass {
683 if (my $class = $self->_isa_metadata) {
684 # we might be dealing with a non-Moose class,
685 # and need to make our own metaclass. if there's
686 # already a metaclass, it will be returned
687 return Moose::Meta::Class->initialize($class);
689 elsif (my $role = $self->_does_metadata) {
690 return Class::MOP::class_of($role);
693 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
697 sub _get_delegate_method_list {
699 my $meta = $self->_find_delegate_metaclass;
700 if ($meta->isa('Class::MOP::Class')) {
701 return map { $_->name } # NOTE: !never! delegate &meta
702 grep { $_->package_name ne 'Moose::Object' && $_->name ne 'meta' }
703 $meta->get_all_methods;
705 elsif ($meta->isa('Moose::Meta::Role')) {
706 return $meta->get_method_list;
709 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
713 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
715 sub _make_delegation_method {
716 my ( $self, $handle_name, $method_to_call ) = @_;
718 my @curried_arguments;
720 ($method_to_call, @curried_arguments) = @$method_to_call
721 if 'ARRAY' eq ref($method_to_call);
723 return $self->delegation_metaclass->new(
724 name => $handle_name,
725 package_name => $self->associated_class->name,
727 delegate_to_method => $method_to_call,
728 curried_arguments => \@curried_arguments,
732 sub _coerce_and_verify {
735 my $instance = shift;
737 return $val unless $self->has_type_constraint;
739 my $type_constraint = $self->type_constraint;
740 if ($self->should_coerce && $type_constraint->has_coercion) {
741 $val = $type_constraint->coerce($val);
744 $self->verify_against_type_constraint($val, instance => $instance);
749 sub verify_against_type_constraint {
753 return 1 if !$self->has_type_constraint;
755 my $type_constraint = $self->type_constraint;
757 $type_constraint->check($val)
758 || $self->throw_error("Attribute ("
760 . ") does not pass the type constraint because: "
761 . $type_constraint->get_message($val), data => $val, @_);
764 package Moose::Meta::Attribute::Custom::Moose;
765 sub register_implementation { 'Moose::Meta::Attribute' }
775 Moose::Meta::Attribute - The Moose attribute metaclass
779 This class is a subclass of L<Class::MOP::Attribute> that provides
780 additional Moose-specific functionality.
782 To really understand this class, you will need to start with the
783 L<Class::MOP::Attribute> documentation. This class can be understood
784 as a set of additional features on top of the basic feature provided
785 by that parent class.
789 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
793 Many of the documented below override methods in
794 L<Class::MOP::Attribute> and add Moose specific features.
800 =item B<< Moose::Meta::Attribute->new(%options) >>
802 This method overrides the L<Class::MOP::Attribute> constructor.
804 Many of the options below are described in more detail in the
805 L<Moose::Manual::Attributes> document.
807 It adds the following options to the constructor:
811 =item * is => 'ro', 'rw', 'bare'
813 This provides a shorthand for specifying the C<reader>, C<writer>, or
814 C<accessor> names. If the attribute is read-only ('ro') then it will
815 have a C<reader> method with the same attribute as the name.
817 If it is read-write ('rw') then it will have an C<accessor> method
818 with the same name. If you provide an explicit C<writer> for a
819 read-write attribute, then you will have a C<reader> with the same
820 name as the attribute, and a C<writer> with the name you provided.
822 Use 'bare' when you are deliberately not installing any methods
823 (accessor, reader, etc.) associated with this attribute; otherwise,
824 Moose will issue a deprecation warning when this attribute is added to a
829 This option accepts a type. The type can be a string, which should be
830 a type name. If the type name is unknown, it is assumed to be a class
833 This option can also accept a L<Moose::Meta::TypeConstraint> object.
835 If you I<also> provide a C<does> option, then your C<isa> option must
836 be a class name, and that class must do the role specified with
839 =item * does => $role
841 This is short-hand for saying that the attribute's type must be an
842 object which does the named role.
844 =item * coerce => $bool
846 This option is only valid for objects with a type constraint
847 (C<isa>). If this is true, then coercions will be applied whenever
848 this attribute is set.
850 You can make both this and the C<weak_ref> option true.
852 =item * trigger => $sub
854 This option accepts a subroutine reference, which will be called after
855 the attribute is set.
857 =item * required => $bool
859 An attribute which is required must be provided to the constructor. An
860 attribute which is required can also have a C<default> or C<builder>,
861 which will satisfy its required-ness.
863 A required attribute must have a C<default>, C<builder> or a
864 non-C<undef> C<init_arg>
866 =item * lazy => $bool
868 A lazy attribute must have a C<default> or C<builder>. When an
869 attribute is lazy, the default value will not be calculated until the
872 =item * weak_ref => $bool
874 If this is true, the attribute's value will be stored as a weak
877 =item * auto_deref => $bool
879 If this is true, then the reader will dereference the value when it is
880 called. The attribute must have a type constraint which defines the
881 attribute as an array or hash reference.
883 =item * lazy_build => $bool
885 Setting this to true makes the attribute lazy and provides a number of
893 is equivalent to this:
898 builder => '_build_size',
899 clearer => 'clear_size',
900 predicate => 'has_size',
903 =item * documentation
905 An arbitrary string that can be retrieved later by calling C<<
906 $attr->documentation >>.
910 =item B<< $attr->clone(%options) >>
912 This creates a new attribute based on attribute being cloned. You must
913 supply a C<name> option to provide a new name for the attribute.
915 The C<%options> can only specify options handled by
916 L<Class::MOP::Attribute>.
920 =head2 Value management
924 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
926 This method is used internally to initialize the attribute's slot in
927 the object C<$instance>.
929 This overrides the L<Class::MOP::Attribute> method to handle lazy
930 attributes, weak references, and type constraints.
936 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
941 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
943 Before setting the value, a check is made on the type constraint of
944 the attribute, if it has one, to see if the value passes it. If the
945 value fails to pass, the set operation dies with a L<throw_error>.
947 Any coercion to convert values is done before checking the type constraint.
949 To check a value against a type constraint before setting it, fetch the
950 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
951 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
952 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
957 =head2 Attribute Accessor generation
961 =item B<< $attr->install_accessors >>
963 This method overrides the parent to also install delegation methods.
965 If, after installing all methods, the attribute object has no associated
966 methods, it throws an error unless C<< is => 'bare' >> was passed to the
967 attribute constructor. (Trying to add an attribute that has no associated
968 methods is almost always an error.)
970 =item B<< $attr->remove_accessors >>
972 This method overrides the parent to also remove delegation methods.
974 =item B<< $attr->install_delegation >>
976 This method adds its delegation methods to the attribute's associated
977 class, if it has any to add.
979 =item B<< $attr->remove_delegation >>
981 This method remove its delegation methods from the attribute's
984 =item B<< $attr->accessor_metaclass >>
986 Returns the accessor metaclass name, which defaults to
987 L<Moose::Meta::Method::Accessor>.
989 =item B<< $attr->delegation_metaclass >>
991 Returns the delegation metaclass name, which defaults to
992 L<Moose::Meta::Method::Delegation>.
996 =head2 Additional Moose features
998 These methods are not found in the superclass. They support features
1003 =item B<< $attr->does($role) >>
1005 This indicates whether the I<attribute itself> does the given
1006 role. The role can be given as a full class name, or as a resolvable
1009 Note that this checks the attribute itself, not its type constraint,
1010 so it is checking the attribute's metaclass and any traits applied to
1013 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
1015 This is an alternate constructor that handles the C<metaclass> and
1018 Effectively, this method is a factory that finds or creates the
1019 appropriate class for the given C<metaclass> and/or C<traits>.
1021 Once it has the appropriate class, it will call C<< $class->new($name,
1022 %options) >> on that class.
1024 =item B<< $attr->clone_and_inherit_options(%options) >>
1026 This method supports the C<has '+foo'> feature. It does various bits
1027 of processing on the supplied C<%options> before ultimately calling
1028 the C<clone> method.
1030 One of its main tasks is to make sure that the C<%options> provided
1031 only includes the options returned by the
1032 C<legal_options_for_inheritance> method.
1034 =item B<< $attr->legal_options_for_inheritance >>
1036 This returns a whitelist of options that can be overridden in a
1037 subclass's attribute definition.
1039 This exists to allow a custom metaclass to change or add to the list
1040 of options which can be changed.
1042 =item B<< $attr->type_constraint >>
1044 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1047 =item B<< $attr->has_type_constraint >>
1049 Returns true if this attribute has a type constraint.
1051 =item B<< $attr->verify_against_type_constraint($value) >>
1053 Given a value, this method returns true if the value is valid for the
1054 attribute's type constraint. If the value is not valid, it throws an
1057 =item B<< $attr->handles >>
1059 This returns the value of the C<handles> option passed to the
1062 =item B<< $attr->has_handles >>
1064 Returns true if this attribute performs delegation.
1066 =item B<< $attr->is_weak_ref >>
1068 Returns true if this attribute stores its value as a weak reference.
1070 =item B<< $attr->is_required >>
1072 Returns true if this attribute is required to have a value.
1074 =item B<< $attr->is_lazy >>
1076 Returns true if this attribute is lazy.
1078 =item B<< $attr->is_lazy_build >>
1080 Returns true if the C<lazy_build> option was true when passed to the
1083 =item B<< $attr->should_coerce >>
1085 Returns true if the C<coerce> option passed to the constructor was
1088 =item B<< $attr->should_auto_deref >>
1090 Returns true if the C<auto_deref> option passed to the constructor was
1093 =item B<< $attr->trigger >>
1095 This is the subroutine reference that was in the C<trigger> option
1096 passed to the constructor, if any.
1098 =item B<< $attr->has_trigger >>
1100 Returns true if this attribute has a trigger set.
1102 =item B<< $attr->documentation >>
1104 Returns the value that was in the C<documentation> option passed to
1105 the constructor, if any.
1107 =item B<< $attr->has_documentation >>
1109 Returns true if this attribute has any documentation.
1111 =item B<< $attr->applied_traits >>
1113 This returns an array reference of all the traits which were applied
1114 to this attribute. If none were applied, this returns C<undef>.
1116 =item B<< $attr->has_applied_traits >>
1118 Returns true if this attribute has any traits applied.
1124 See L<Moose/BUGS> for details on reporting bugs.
1128 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1130 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1132 =head1 COPYRIGHT AND LICENSE
1134 Copyright 2006-2010 by Infinity Interactive, Inc.
1136 L<http://www.iinteractive.com>
1138 This library is free software; you can redistribute it and/or modify
1139 it under the same terms as Perl itself.