2 package Moose::Meta::Attribute;
7 use Scalar::Util 'blessed', 'weaken';
8 use List::MoreUtils 'any';
12 our $VERSION = '1.08';
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;
441 my $val = $self->_coerce_and_verify( shift, $instance );;
443 $meta_instance->set_slot_value($instance, $slot_name, $val);
446 my $initializer = $self->initializer;
448 # most things will just want to set a value, so make it first arg
449 $instance->$initializer($value, $callback, $self);
453 my ($self, $instance, @args) = @_;
454 my $value = $args[0];
456 my $attr_name = $self->name;
458 if ($self->is_required and not @args) {
459 $self->throw_error("Attribute ($attr_name) is required", object => $instance);
462 $value = $self->_coerce_and_verify( $value, $instance );
465 if ( $self->has_trigger && $self->has_value($instance) ) {
466 @old = $self->get_value($instance, 'for trigger');
469 $self->SUPER::set_value($instance, $value);
471 if ( ref $value && $self->is_weak_ref ) {
472 $self->_weaken_value($instance);
475 if ($self->has_trigger) {
476 $self->trigger->($instance, $value, @old);
481 my ( $self, $instance ) = @_;
483 my $meta_instance = Class::MOP::Class->initialize( blessed($instance) )
486 $meta_instance->weaken_slot_value( $instance, $self->name );
490 my ($self, $instance, $for_trigger) = @_;
492 if ($self->is_lazy) {
493 unless ($self->has_value($instance)) {
495 if ($self->has_default) {
496 $value = $self->default($instance);
497 } elsif ( $self->has_builder ) {
498 $value = $self->_call_builder($instance);
501 $value = $self->_coerce_and_verify( $value, $instance );
503 $self->set_initial_value($instance, $value);
507 if ( $self->should_auto_deref && ! $for_trigger ) {
509 my $type_constraint = $self->type_constraint;
511 if ($type_constraint->is_a_type_of('ArrayRef')) {
512 my $rv = $self->SUPER::get_value($instance);
513 return unless defined $rv;
514 return wantarray ? @{ $rv } : $rv;
516 elsif ($type_constraint->is_a_type_of('HashRef')) {
517 my $rv = $self->SUPER::get_value($instance);
518 return unless defined $rv;
519 return wantarray ? %{ $rv } : $rv;
522 $self->throw_error("Can not auto de-reference the type constraint '" . $type_constraint->name . "'", object => $instance, type_constraint => $type_constraint);
528 return $self->SUPER::get_value($instance);
532 ## installing accessors
534 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
536 sub install_accessors {
538 $self->SUPER::install_accessors(@_);
539 $self->install_delegation if $self->has_handles;
543 sub _check_associated_methods {
546 @{ $self->associated_methods }
547 || ($self->_is_metadata || '') eq 'bare'
550 'Attribute (' . $self->name . ') of class '
551 . $self->associated_class->name
552 . ' has no associated methods'
553 . ' (did you mean to provide an "is" argument?)'
559 sub _process_accessors {
561 my ($type, $accessor, $generate_as_inline_methods) = @_;
562 $accessor = (keys %$accessor)[0] if (ref($accessor)||'') eq 'HASH';
563 my $method = $self->associated_class->get_method($accessor);
564 if ($method && !$method->isa('Class::MOP::Method::Accessor')
565 && (!$self->definition_context
566 || $method->package_name eq $self->definition_context->{package})) {
568 "You are overwriting a locally defined method ($accessor) with "
572 $self->SUPER::_process_accessors(@_);
575 sub remove_accessors {
577 $self->SUPER::remove_accessors(@_);
578 $self->remove_delegation if $self->has_handles;
582 sub install_delegation {
586 # Here we canonicalize the 'handles' option
587 # this will sort out any details and always
588 # return an hash of methods which we want
589 # to delagate to, see that method for details
590 my %handles = $self->_canonicalize_handles;
593 # install the delegation ...
594 my $associated_class = $self->associated_class;
595 foreach my $handle (keys %handles) {
596 my $method_to_call = $handles{$handle};
597 my $class_name = $associated_class->name;
598 my $name = "${class_name}::${handle}";
600 (!$associated_class->has_method($handle))
601 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
604 # handles is not allowed to delegate
605 # any of these methods, as they will
606 # override the ones in your class, which
607 # is almost certainly not what you want.
609 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
610 #cluck("Not delegating method '$handle' because it is a core method") and
611 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
613 my $method = $self->_make_delegation_method($handle, $method_to_call);
615 $self->associated_class->add_method($method->name, $method);
616 $self->associate_method($method);
620 sub remove_delegation {
622 my %handles = $self->_canonicalize_handles;
623 my $associated_class = $self->associated_class;
624 foreach my $handle (keys %handles) {
625 next unless any { $handle eq $_ }
627 @{ $self->associated_methods };
628 $self->associated_class->remove_method($handle);
632 # private methods to help delegation ...
634 sub _canonicalize_handles {
636 my $handles = $self->handles;
637 if (my $handle_type = ref($handles)) {
638 if ($handle_type eq 'HASH') {
641 elsif ($handle_type eq 'ARRAY') {
642 return map { $_ => $_ } @{$handles};
644 elsif ($handle_type eq 'Regexp') {
645 ($self->has_type_constraint)
646 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
647 return map { ($_ => $_) }
648 grep { /$handles/ } $self->_get_delegate_method_list;
650 elsif ($handle_type eq 'CODE') {
651 return $handles->($self, $self->_find_delegate_metaclass);
653 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::DuckType')) {
654 return map { $_ => $_ } @{ $handles->methods };
656 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::Role')) {
657 $handles = $handles->role;
660 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
664 Class::MOP::load_class($handles);
665 my $role_meta = Class::MOP::class_of($handles);
667 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
668 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because its metaclass is not a Moose::Meta::Role", data => $handles);
670 return map { $_ => $_ }
671 grep { $_ ne 'meta' } (
672 $role_meta->get_method_list,
673 map { $_->name } $role_meta->get_required_method_list,
677 sub _find_delegate_metaclass {
679 if (my $class = $self->_isa_metadata) {
680 # we might be dealing with a non-Moose class,
681 # and need to make our own metaclass. if there's
682 # already a metaclass, it will be returned
683 return Class::MOP::Class->initialize($class);
685 elsif (my $role = $self->_does_metadata) {
686 return Class::MOP::class_of($role);
689 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
693 sub _get_delegate_method_list {
695 my $meta = $self->_find_delegate_metaclass;
696 if ($meta->isa('Class::MOP::Class')) {
697 return map { $_->name } # NOTE: !never! delegate &meta
698 grep { $_->package_name ne 'Moose::Object' && $_->name ne 'meta' }
699 $meta->get_all_methods;
701 elsif ($meta->isa('Moose::Meta::Role')) {
702 return $meta->get_method_list;
705 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
709 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
711 sub _make_delegation_method {
712 my ( $self, $handle_name, $method_to_call ) = @_;
714 my @curried_arguments;
716 ($method_to_call, @curried_arguments) = @$method_to_call
717 if 'ARRAY' eq ref($method_to_call);
719 return $self->delegation_metaclass->new(
720 name => $handle_name,
721 package_name => $self->associated_class->name,
723 delegate_to_method => $method_to_call,
724 curried_arguments => \@curried_arguments,
728 sub _coerce_and_verify {
731 my $instance = shift;
733 return $val unless $self->has_type_constraint;
735 my $type_constraint = $self->type_constraint;
736 if ($self->should_coerce && $type_constraint->has_coercion) {
737 $val = $type_constraint->coerce($val);
740 $self->verify_against_type_constraint($val, instance => $instance);
745 sub verify_against_type_constraint {
749 return 1 if !$self->has_type_constraint;
751 my $type_constraint = $self->type_constraint;
753 $type_constraint->check($val)
754 || $self->throw_error("Attribute ("
756 . ") does not pass the type constraint because: "
757 . $type_constraint->get_message($val), data => $val, @_);
760 package Moose::Meta::Attribute::Custom::Moose;
761 sub register_implementation { 'Moose::Meta::Attribute' }
771 Moose::Meta::Attribute - The Moose attribute metaclass
775 This class is a subclass of L<Class::MOP::Attribute> that provides
776 additional Moose-specific functionality.
778 To really understand this class, you will need to start with the
779 L<Class::MOP::Attribute> documentation. This class can be understood
780 as a set of additional features on top of the basic feature provided
781 by that parent class.
785 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
789 Many of the documented below override methods in
790 L<Class::MOP::Attribute> and add Moose specific features.
796 =item B<< Moose::Meta::Attribute->new(%options) >>
798 This method overrides the L<Class::MOP::Attribute> constructor.
800 Many of the options below are described in more detail in the
801 L<Moose::Manual::Attributes> document.
803 It adds the following options to the constructor:
807 =item * is => 'ro', 'rw', 'bare'
809 This provides a shorthand for specifying the C<reader>, C<writer>, or
810 C<accessor> names. If the attribute is read-only ('ro') then it will
811 have a C<reader> method with the same attribute as the name.
813 If it is read-write ('rw') then it will have an C<accessor> method
814 with the same name. If you provide an explicit C<writer> for a
815 read-write attribute, then you will have a C<reader> with the same
816 name as the attribute, and a C<writer> with the name you provided.
818 Use 'bare' when you are deliberately not installing any methods
819 (accessor, reader, etc.) associated with this attribute; otherwise,
820 Moose will issue a deprecation warning when this attribute is added to a
825 This option accepts a type. The type can be a string, which should be
826 a type name. If the type name is unknown, it is assumed to be a class
829 This option can also accept a L<Moose::Meta::TypeConstraint> object.
831 If you I<also> provide a C<does> option, then your C<isa> option must
832 be a class name, and that class must do the role specified with
835 =item * does => $role
837 This is short-hand for saying that the attribute's type must be an
838 object which does the named role.
840 =item * coerce => $bool
842 This option is only valid for objects with a type constraint
843 (C<isa>). If this is true, then coercions will be applied whenever
844 this attribute is set.
846 You can make both this and the C<weak_ref> option true.
848 =item * trigger => $sub
850 This option accepts a subroutine reference, which will be called after
851 the attribute is set.
853 =item * required => $bool
855 An attribute which is required must be provided to the constructor. An
856 attribute which is required can also have a C<default> or C<builder>,
857 which will satisfy its required-ness.
859 A required attribute must have a C<default>, C<builder> or a
860 non-C<undef> C<init_arg>
862 =item * lazy => $bool
864 A lazy attribute must have a C<default> or C<builder>. When an
865 attribute is lazy, the default value will not be calculated until the
868 =item * weak_ref => $bool
870 If this is true, the attribute's value will be stored as a weak
873 =item * auto_deref => $bool
875 If this is true, then the reader will dereference the value when it is
876 called. The attribute must have a type constraint which defines the
877 attribute as an array or hash reference.
879 =item * lazy_build => $bool
881 Setting this to true makes the attribute lazy and provides a number of
889 is equivalent to this:
894 builder => '_build_size',
895 clearer => 'clear_size',
896 predicate => 'has_size',
899 =item * documentation
901 An arbitrary string that can be retrieved later by calling C<<
902 $attr->documentation >>.
906 =item B<< $attr->clone(%options) >>
908 This creates a new attribute based on attribute being cloned. You must
909 supply a C<name> option to provide a new name for the attribute.
911 The C<%options> can only specify options handled by
912 L<Class::MOP::Attribute>.
916 =head2 Value management
920 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
922 This method is used internally to initialize the attribute's slot in
923 the object C<$instance>.
925 This overrides the L<Class::MOP::Attribute> method to handle lazy
926 attributes, weak references, and type constraints.
932 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
937 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
939 Before setting the value, a check is made on the type constraint of
940 the attribute, if it has one, to see if the value passes it. If the
941 value fails to pass, the set operation dies with a L</throw_error>.
943 Any coercion to convert values is done before checking the type constraint.
945 To check a value against a type constraint before setting it, fetch the
946 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
947 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
948 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
953 =head2 Attribute Accessor generation
957 =item B<< $attr->install_accessors >>
959 This method overrides the parent to also install delegation methods.
961 If, after installing all methods, the attribute object has no associated
962 methods, it throws an error unless C<< is => 'bare' >> was passed to the
963 attribute constructor. (Trying to add an attribute that has no associated
964 methods is almost always an error.)
966 =item B<< $attr->remove_accessors >>
968 This method overrides the parent to also remove delegation methods.
970 =item B<< $attr->install_delegation >>
972 This method adds its delegation methods to the attribute's associated
973 class, if it has any to add.
975 =item B<< $attr->remove_delegation >>
977 This method remove its delegation methods from the attribute's
980 =item B<< $attr->accessor_metaclass >>
982 Returns the accessor metaclass name, which defaults to
983 L<Moose::Meta::Method::Accessor>.
985 =item B<< $attr->delegation_metaclass >>
987 Returns the delegation metaclass name, which defaults to
988 L<Moose::Meta::Method::Delegation>.
992 =head2 Additional Moose features
994 These methods are not found in the superclass. They support features
999 =item B<< $attr->does($role) >>
1001 This indicates whether the I<attribute itself> does the given
1002 role. The role can be given as a full class name, or as a resolvable
1005 Note that this checks the attribute itself, not its type constraint,
1006 so it is checking the attribute's metaclass and any traits applied to
1009 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
1011 This is an alternate constructor that handles the C<metaclass> and
1014 Effectively, this method is a factory that finds or creates the
1015 appropriate class for the given C<metaclass> and/or C<traits>.
1017 Once it has the appropriate class, it will call C<< $class->new($name,
1018 %options) >> on that class.
1020 =item B<< $attr->clone_and_inherit_options(%options) >>
1022 This method supports the C<has '+foo'> feature. It does various bits
1023 of processing on the supplied C<%options> before ultimately calling
1024 the C<clone> method.
1026 One of its main tasks is to make sure that the C<%options> provided
1027 only includes the options returned by the
1028 C<legal_options_for_inheritance> method.
1030 =item B<< $attr->legal_options_for_inheritance >>
1032 This returns a whitelist of options that can be overridden in a
1033 subclass's attribute definition.
1035 This exists to allow a custom metaclass to change or add to the list
1036 of options which can be changed.
1038 =item B<< $attr->type_constraint >>
1040 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1043 =item B<< $attr->has_type_constraint >>
1045 Returns true if this attribute has a type constraint.
1047 =item B<< $attr->verify_against_type_constraint($value) >>
1049 Given a value, this method returns true if the value is valid for the
1050 attribute's type constraint. If the value is not valid, it throws an
1053 =item B<< $attr->handles >>
1055 This returns the value of the C<handles> option passed to the
1058 =item B<< $attr->has_handles >>
1060 Returns true if this attribute performs delegation.
1062 =item B<< $attr->is_weak_ref >>
1064 Returns true if this attribute stores its value as a weak reference.
1066 =item B<< $attr->is_required >>
1068 Returns true if this attribute is required to have a value.
1070 =item B<< $attr->is_lazy >>
1072 Returns true if this attribute is lazy.
1074 =item B<< $attr->is_lazy_build >>
1076 Returns true if the C<lazy_build> option was true when passed to the
1079 =item B<< $attr->should_coerce >>
1081 Returns true if the C<coerce> option passed to the constructor was
1084 =item B<< $attr->should_auto_deref >>
1086 Returns true if the C<auto_deref> option passed to the constructor was
1089 =item B<< $attr->trigger >>
1091 This is the subroutine reference that was in the C<trigger> option
1092 passed to the constructor, if any.
1094 =item B<< $attr->has_trigger >>
1096 Returns true if this attribute has a trigger set.
1098 =item B<< $attr->documentation >>
1100 Returns the value that was in the C<documentation> option passed to
1101 the constructor, if any.
1103 =item B<< $attr->has_documentation >>
1105 Returns true if this attribute has any documentation.
1107 =item B<< $attr->applied_traits >>
1109 This returns an array reference of all the traits which were applied
1110 to this attribute. If none were applied, this returns C<undef>.
1112 =item B<< $attr->has_applied_traits >>
1114 Returns true if this attribute has any traits applied.
1120 See L<Moose/BUGS> for details on reporting bugs.
1124 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1126 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1128 =head1 COPYRIGHT AND LICENSE
1130 Copyright 2006-2010 by Infinity Interactive, Inc.
1132 L<http://www.iinteractive.com>
1134 This library is free software; you can redistribute it and/or modify
1135 it under the same terms as Perl itself.