2 package Moose::Meta::Attribute;
8 use Scalar::Util 'blessed', 'weaken';
9 use List::MoreUtils 'any';
13 our $VERSION = '1.19';
14 our $AUTHORITY = 'cpan:STEVAN';
16 use Moose::Deprecated;
17 use Moose::Meta::Method::Accessor;
18 use Moose::Meta::Method::Delegation;
20 use Moose::Util::TypeConstraints ();
21 use Class::MOP::MiniTrait;
23 use base 'Class::MOP::Attribute', 'Moose::Meta::Mixin::AttributeCore';
25 Class::MOP::MiniTrait::apply(__PACKAGE__, 'Moose::Meta::Object::Trait');
27 __PACKAGE__->meta->add_attribute('traits' => (
28 reader => 'applied_traits',
29 predicate => 'has_applied_traits',
32 # we need to have a ->does method in here to
33 # more easily support traits, and the introspection
34 # of those traits. We extend the does check to look
35 # for metatrait aliases.
37 my ($self, $role_name) = @_;
39 Moose::Util::resolve_metatrait_alias(Attribute => $role_name)
41 return 0 if !defined($name); # failed to load class
42 return $self->Moose::Object::does($name);
47 my $class = ( ref $self && $self->associated_class ) || "Moose::Meta::Class";
48 unshift @_, "message" if @_ % 2 == 1;
49 unshift @_, attr => $self if ref $self;
51 my $handler = $class->can("throw_error"); # to avoid incrementing depth by 1
56 my ($class, $name, %options) = @_;
57 $class->_process_options($name, \%options) unless $options{__hack_no_process_options}; # used from clone()... YECHKKK FIXME ICKY YUCK GROSS
59 delete $options{__hack_no_process_options};
64 map { $_->init_arg() }
65 $class->meta()->get_all_attributes()
68 my @bad = sort grep { ! $attrs{$_} } keys %options;
72 Carp::cluck "Found unknown argument(s) passed to '$name' attribute constructor in '$class': @bad";
75 return $class->SUPER::new($name, %options);
78 sub interpolate_class_and_new {
79 my ($class, $name, %args) = @_;
81 my ( $new_class, @traits ) = $class->interpolate_class(\%args);
83 $new_class->new($name, %args, ( scalar(@traits) ? ( traits => \@traits ) : () ) );
86 sub interpolate_class {
87 my ($class, $options) = @_;
89 $class = ref($class) || $class;
91 if ( my $metaclass_name = delete $options->{metaclass} ) {
92 my $new_class = Moose::Util::resolve_metaclass_alias( Attribute => $metaclass_name );
94 if ( $class ne $new_class ) {
95 if ( $new_class->can("interpolate_class") ) {
96 return $new_class->interpolate_class($options);
105 if (my $traits = $options->{traits}) {
107 while ($i < @$traits) {
108 my $trait = $traits->[$i++];
109 next if ref($trait); # options to a trait we discarded
111 $trait = Moose::Util::resolve_metatrait_alias(Attribute => $trait)
114 next if $class->does($trait);
116 push @traits, $trait;
119 push @traits, $traits->[$i++]
120 if $traits->[$i] && ref($traits->[$i]);
124 my $anon_class = Moose::Meta::Class->create_anon_class(
125 superclasses => [ $class ],
126 roles => [ @traits ],
130 $class = $anon_class->name;
134 return ( wantarray ? ( $class, @traits ) : $class );
139 # method-generating options shouldn't be overridden
140 sub illegal_options_for_inheritance {
141 qw(reader writer accessor clearer predicate)
145 # This method *must* be able to handle
146 # Class::MOP::Attribute instances as
147 # well. Yes, I know that is wrong, but
148 # apparently we didn't realize it was
149 # doing that and now we have some code
150 # which is dependent on it. The real
151 # solution of course is to push this
152 # feature back up into Class::MOP::Attribute
153 # but I not right now, I am too lazy.
154 # However if you are reading this and
155 # looking for something to do,.. please
158 sub clone_and_inherit_options {
159 my ($self, %options) = @_;
162 # we may want to extends a Class::MOP::Attribute
163 # in which case we need to be able to use the
164 # core set of legal options that have always
165 # been here. But we allows Moose::Meta::Attribute
166 # instances to changes them.
168 my @illegal_options = $self->can('illegal_options_for_inheritance')
169 ? $self->illegal_options_for_inheritance
172 my @found_illegal_options = grep { exists $options{$_} && exists $self->{$_} ? $_ : undef } @illegal_options;
173 (scalar @found_illegal_options == 0)
174 || $self->throw_error("Illegal inherited options => (" . (join ', ' => @found_illegal_options) . ")", data => \%options);
178 if (blessed($options{isa}) && $options{isa}->isa('Moose::Meta::TypeConstraint')) {
179 $type_constraint = $options{isa};
182 $type_constraint = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options{isa});
183 (defined $type_constraint)
184 || $self->throw_error("Could not find the type constraint '" . $options{isa} . "'", data => $options{isa});
187 $options{type_constraint} = $type_constraint;
190 if ($options{does}) {
192 if (blessed($options{does}) && $options{does}->isa('Moose::Meta::TypeConstraint')) {
193 $type_constraint = $options{does};
196 $type_constraint = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options{does});
197 (defined $type_constraint)
198 || $self->throw_error("Could not find the type constraint '" . $options{does} . "'", data => $options{does});
201 $options{type_constraint} = $type_constraint;
205 # this doesn't apply to Class::MOP::Attributes,
206 # so we can ignore it for them.
208 if ($self->can('interpolate_class')) {
209 ( $options{metaclass}, my @traits ) = $self->interpolate_class(\%options);
212 my @all_traits = grep { $seen{$_}++ } @{ $self->applied_traits || [] }, @traits;
213 $options{traits} = \@all_traits if @all_traits;
216 # This method can be called on a CMOP::Attribute object, so we need to
217 # make sure we can call this method.
218 $self->_process_lazy_build_option( $self->name, \%options )
219 if $self->can('_process_lazy_build_option');
221 $self->clone(%options);
225 my ( $self, %params ) = @_;
227 my $class = delete $params{metaclass} || ref $self;
229 my ( @init, @non_init );
231 foreach my $attr ( grep { $_->has_value($self) } Class::MOP::class_of($self)->get_all_attributes ) {
232 push @{ $attr->has_init_arg ? \@init : \@non_init }, $attr;
235 my %new_params = ( ( map { $_->init_arg => $_->get_value($self) } @init ), %params );
237 my $name = delete $new_params{name};
239 my $clone = $class->new($name, %new_params, __hack_no_process_options => 1 );
241 foreach my $attr ( @non_init ) {
242 $attr->set_value($clone, $attr->get_value($self));
248 sub _process_options {
249 my ( $class, $name, $options ) = @_;
251 $class->_process_is_option( $name, $options );
252 $class->_process_isa_option( $name, $options );
253 $class->_process_does_option( $name, $options );
254 $class->_process_coerce_option( $name, $options );
255 $class->_process_trigger_option( $name, $options );
256 $class->_process_auto_deref_option( $name, $options );
257 $class->_process_lazy_build_option( $name, $options );
258 $class->_process_lazy_option( $name, $options );
259 $class->_process_required_option( $name, $options );
262 sub _process_is_option {
263 my ( $class, $name, $options ) = @_;
265 return unless $options->{is};
267 ### -------------------------
268 ## is => ro, writer => _foo # turns into (reader => foo, writer => _foo) as before
269 ## is => rw, writer => _foo # turns into (reader => foo, writer => _foo)
270 ## is => rw, accessor => _foo # turns into (accessor => _foo)
271 ## is => ro, accessor => _foo # error, accesor is rw
272 ### -------------------------
274 if ( $options->{is} eq 'ro' ) {
276 "Cannot define an accessor name on a read-only attribute, accessors are read/write",
278 if exists $options->{accessor};
279 $options->{reader} ||= $name;
281 elsif ( $options->{is} eq 'rw' ) {
282 if ( $options->{writer} ) {
283 $options->{reader} ||= $name;
286 $options->{accessor} ||= $name;
289 elsif ( $options->{is} eq 'bare' ) {
291 # do nothing, but don't complain (later) about missing methods
294 $class->throw_error( "I do not understand this option (is => "
296 . ") on attribute ($name)", data => $options->{is} );
300 sub _process_isa_option {
301 my ( $class, $name, $options ) = @_;
303 return unless exists $options->{isa};
305 if ( exists $options->{does} ) {
306 if ( try { $options->{isa}->can('does') } ) {
307 ( $options->{isa}->does( $options->{does} ) )
308 || $class->throw_error(
309 "Cannot have an isa option and a does option if the isa does not do the does on attribute ($name)",
314 "Cannot have an isa option which cannot ->does() on attribute ($name)",
319 # allow for anon-subtypes here ...
320 if ( blessed( $options->{isa} )
321 && $options->{isa}->isa('Moose::Meta::TypeConstraint') ) {
322 $options->{type_constraint} = $options->{isa};
325 $options->{type_constraint}
326 = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint(
331 sub _process_does_option {
332 my ( $class, $name, $options ) = @_;
334 return unless exists $options->{does} && ! exists $options->{isa};
336 # allow for anon-subtypes here ...
337 if ( blessed( $options->{does} )
338 && $options->{does}->isa('Moose::Meta::TypeConstraint') ) {
339 $options->{type_constraint} = $options->{does};
342 $options->{type_constraint}
343 = Moose::Util::TypeConstraints::find_or_create_does_type_constraint(
348 sub _process_coerce_option {
349 my ( $class, $name, $options ) = @_;
351 return unless $options->{coerce};
353 ( exists $options->{type_constraint} )
354 || $class->throw_error(
355 "You cannot have coercion without specifying a type constraint on attribute ($name)",
359 "You cannot have a weak reference to a coerced value on attribute ($name)",
361 if $options->{weak_ref};
363 unless ( $options->{type_constraint}->has_coercion ) {
364 my $type = $options->{type_constraint}->name;
366 Moose::Deprecated::deprecated(
367 feature => 'coerce without coercion',
369 "You cannot coerce an attribute ($name) unless its type ($type) has a coercion"
374 sub _process_trigger_option {
375 my ( $class, $name, $options ) = @_;
377 return unless exists $options->{trigger};
379 ( 'CODE' eq ref $options->{trigger} )
380 || $class->throw_error("Trigger must be a CODE ref on attribute ($name)", data => $options->{trigger});
383 sub _process_auto_deref_option {
384 my ( $class, $name, $options ) = @_;
386 return unless $options->{auto_deref};
388 ( exists $options->{type_constraint} )
389 || $class->throw_error(
390 "You cannot auto-dereference without specifying a type constraint on attribute ($name)",
393 ( $options->{type_constraint}->is_a_type_of('ArrayRef')
394 || $options->{type_constraint}->is_a_type_of('HashRef') )
395 || $class->throw_error(
396 "You cannot auto-dereference anything other than a ArrayRef or HashRef on attribute ($name)",
400 sub _process_lazy_build_option {
401 my ( $class, $name, $options ) = @_;
403 return unless $options->{lazy_build};
406 "You can not use lazy_build and default for the same attribute ($name)",
408 if exists $options->{default};
410 $options->{lazy} = 1;
411 $options->{builder} ||= "_build_${name}";
413 if ( $name =~ /^_/ ) {
414 $options->{clearer} ||= "_clear${name}";
415 $options->{predicate} ||= "_has${name}";
418 $options->{clearer} ||= "clear_${name}";
419 $options->{predicate} ||= "has_${name}";
423 sub _process_lazy_option {
424 my ( $class, $name, $options ) = @_;
426 return unless $options->{lazy};
428 ( exists $options->{default} || defined $options->{builder} )
429 || $class->throw_error(
430 "You cannot have a lazy attribute ($name) without specifying a default value for it",
434 sub _process_required_option {
435 my ( $class, $name, $options ) = @_;
440 ( !exists $options->{init_arg} || defined $options->{init_arg} )
441 || exists $options->{default}
442 || defined $options->{builder}
446 "You cannot have a required attribute ($name) without a default, builder, or an init_arg",
451 sub initialize_instance_slot {
452 my ($self, $meta_instance, $instance, $params) = @_;
453 my $init_arg = $self->init_arg();
454 # try to fetch the init arg from the %params ...
458 if ( defined($init_arg) and exists $params->{$init_arg}) {
459 $val = $params->{$init_arg};
463 # skip it if it's lazy
464 return if $self->is_lazy;
465 # and die if it's required and doesn't have a default value
466 $self->throw_error("Attribute (" . $self->name . ") is required", object => $instance, data => $params)
467 if $self->is_required && !$self->has_default && !$self->has_builder;
469 # if nothing was in the %params, we can use the
470 # attribute's default value (if it has one)
471 if ($self->has_default) {
472 $val = $self->default($instance);
475 elsif ($self->has_builder) {
476 $val = $self->_call_builder($instance);
481 return unless $value_is_set;
483 $val = $self->_coerce_and_verify( $val, $instance );
485 $self->set_initial_value($instance, $val);
487 if ( ref $val && $self->is_weak_ref ) {
488 $self->_weaken_value($instance);
493 my ( $self, $instance ) = @_;
495 my $builder = $self->builder();
497 return $instance->$builder()
498 if $instance->can( $self->builder );
500 $self->throw_error( blessed($instance)
501 . " does not support builder method '"
503 . "' for attribute '"
513 # this duplicates too much code from
514 # Class::MOP::Attribute, we need to
515 # refactor these bits eventually.
517 sub _set_initial_slot_value {
518 my ($self, $meta_instance, $instance, $value) = @_;
520 my $slot_name = $self->name;
522 return $meta_instance->set_slot_value($instance, $slot_name, $value)
523 unless $self->has_initializer;
526 my $val = $self->_coerce_and_verify( shift, $instance );;
528 $meta_instance->set_slot_value($instance, $slot_name, $val);
531 my $initializer = $self->initializer;
533 # most things will just want to set a value, so make it first arg
534 $instance->$initializer($value, $callback, $self);
538 my ($self, $instance, @args) = @_;
539 my $value = $args[0];
541 my $attr_name = $self->name;
543 if ($self->is_required and not @args) {
544 $self->throw_error("Attribute ($attr_name) is required", object => $instance);
547 $value = $self->_coerce_and_verify( $value, $instance );
550 if ( $self->has_trigger && $self->has_value($instance) ) {
551 @old = $self->get_value($instance, 'for trigger');
554 $self->SUPER::set_value($instance, $value);
556 if ( ref $value && $self->is_weak_ref ) {
557 $self->_weaken_value($instance);
560 if ($self->has_trigger) {
561 $self->trigger->($instance, $value, @old);
566 my ( $self, $instance ) = @_;
568 my $meta_instance = Class::MOP::Class->initialize( blessed($instance) )
571 $meta_instance->weaken_slot_value( $instance, $self->name );
575 my ($self, $instance, $for_trigger) = @_;
577 if ($self->is_lazy) {
578 unless ($self->has_value($instance)) {
580 if ($self->has_default) {
581 $value = $self->default($instance);
582 } elsif ( $self->has_builder ) {
583 $value = $self->_call_builder($instance);
586 $value = $self->_coerce_and_verify( $value, $instance );
588 $self->set_initial_value($instance, $value);
592 if ( $self->should_auto_deref && ! $for_trigger ) {
594 my $type_constraint = $self->type_constraint;
596 if ($type_constraint->is_a_type_of('ArrayRef')) {
597 my $rv = $self->SUPER::get_value($instance);
598 return unless defined $rv;
599 return wantarray ? @{ $rv } : $rv;
601 elsif ($type_constraint->is_a_type_of('HashRef')) {
602 my $rv = $self->SUPER::get_value($instance);
603 return unless defined $rv;
604 return wantarray ? %{ $rv } : $rv;
607 $self->throw_error("Can not auto de-reference the type constraint '" . $type_constraint->name . "'", object => $instance, type_constraint => $type_constraint);
613 return $self->SUPER::get_value($instance);
617 ## installing accessors
619 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
621 sub install_accessors {
623 $self->SUPER::install_accessors(@_);
624 $self->install_delegation if $self->has_handles;
628 sub _check_associated_methods {
631 @{ $self->associated_methods }
632 || ($self->_is_metadata || '') eq 'bare'
635 'Attribute (' . $self->name . ') of class '
636 . $self->associated_class->name
637 . ' has no associated methods'
638 . ' (did you mean to provide an "is" argument?)'
644 sub _process_accessors {
646 my ($type, $accessor, $generate_as_inline_methods) = @_;
648 $accessor = ( keys %$accessor )[0] if ( ref($accessor) || '' ) eq 'HASH';
649 my $method = $self->associated_class->get_method($accessor);
652 && $method->isa('Class::MOP::Method::Accessor')
653 && $method->associated_attribute->name ne $self->name ) {
655 my $other_attr_name = $method->associated_attribute->name;
656 my $name = $self->name;
659 "You are overwriting an accessor ($accessor) for the $other_attr_name attribute"
660 . " with a new accessor method for the $name attribute" );
665 && !$method->isa('Class::MOP::Method::Accessor')
666 && ( !$self->definition_context
667 || $method->package_name eq $self->definition_context->{package} )
671 "You are overwriting a locally defined method ($accessor) with "
675 if ( !$self->associated_class->has_method($accessor)
676 && $self->associated_class->has_package_symbol( '&' . $accessor ) ) {
679 "You are overwriting a locally defined function ($accessor) with "
683 $self->SUPER::_process_accessors(@_);
686 sub remove_accessors {
688 $self->SUPER::remove_accessors(@_);
689 $self->remove_delegation if $self->has_handles;
693 sub _inline_set_value {
695 my ($instance, $value) = @_;
697 my $mi = $self->associated_class->get_meta_instance;
699 my @code = ($self->SUPER::_inline_set_value(@_));
702 $mi->inline_weaken_slot_value($instance, $self->name, $value),
703 'if ref ' . $value . ';',
704 ) if $self->is_weak_ref;
709 sub install_delegation {
713 # Here we canonicalize the 'handles' option
714 # this will sort out any details and always
715 # return an hash of methods which we want
716 # to delagate to, see that method for details
717 my %handles = $self->_canonicalize_handles;
720 # install the delegation ...
721 my $associated_class = $self->associated_class;
722 foreach my $handle (keys %handles) {
723 my $method_to_call = $handles{$handle};
724 my $class_name = $associated_class->name;
725 my $name = "${class_name}::${handle}";
727 (!$associated_class->has_method($handle))
728 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
731 # handles is not allowed to delegate
732 # any of these methods, as they will
733 # override the ones in your class, which
734 # is almost certainly not what you want.
736 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
737 #cluck("Not delegating method '$handle' because it is a core method") and
738 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
740 my $method = $self->_make_delegation_method($handle, $method_to_call);
742 $self->associated_class->add_method($method->name, $method);
743 $self->associate_method($method);
747 sub remove_delegation {
749 my %handles = $self->_canonicalize_handles;
750 my $associated_class = $self->associated_class;
751 foreach my $handle (keys %handles) {
752 next unless any { $handle eq $_ }
754 @{ $self->associated_methods };
755 $self->associated_class->remove_method($handle);
759 # private methods to help delegation ...
761 sub _canonicalize_handles {
763 my $handles = $self->handles;
764 if (my $handle_type = ref($handles)) {
765 if ($handle_type eq 'HASH') {
768 elsif ($handle_type eq 'ARRAY') {
769 return map { $_ => $_ } @{$handles};
771 elsif ($handle_type eq 'Regexp') {
772 ($self->has_type_constraint)
773 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
774 return map { ($_ => $_) }
775 grep { /$handles/ } $self->_get_delegate_method_list;
777 elsif ($handle_type eq 'CODE') {
778 return $handles->($self, $self->_find_delegate_metaclass);
780 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::DuckType')) {
781 return map { $_ => $_ } @{ $handles->methods };
783 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::Role')) {
784 $handles = $handles->role;
787 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
791 Class::MOP::load_class($handles);
792 my $role_meta = Class::MOP::class_of($handles);
794 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
795 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because its metaclass is not a Moose::Meta::Role", data => $handles);
797 return map { $_ => $_ }
799 grep { !$_->isa('Class::MOP::Method::Meta') } (
800 $role_meta->_get_local_methods,
801 $role_meta->get_required_method_list,
805 sub _get_delegate_method_list {
807 my $meta = $self->_find_delegate_metaclass;
808 if ($meta->isa('Class::MOP::Class')) {
809 return map { $_->name } # NOTE: !never! delegate &meta
810 grep { $_->package_name ne 'Moose::Object' && !$_->isa('Class::MOP::Method::Meta') }
811 $meta->get_all_methods;
813 elsif ($meta->isa('Moose::Meta::Role')) {
814 return $meta->get_method_list;
817 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
821 sub _find_delegate_metaclass {
823 if (my $class = $self->_isa_metadata) {
824 unless ( Class::MOP::is_class_loaded($class) ) {
827 'The %s attribute is trying to delegate to a class which has not been loaded - %s',
832 # we might be dealing with a non-Moose class,
833 # and need to make our own metaclass. if there's
834 # already a metaclass, it will be returned
835 return Class::MOP::Class->initialize($class);
837 elsif (my $role = $self->_does_metadata) {
838 unless ( Class::MOP::is_class_loaded($class) ) {
841 'The %s attribute is trying to delegate to a role which has not been loaded - %s',
847 return Class::MOP::class_of($role);
850 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
854 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
856 sub _make_delegation_method {
857 my ( $self, $handle_name, $method_to_call ) = @_;
859 my @curried_arguments;
861 ($method_to_call, @curried_arguments) = @$method_to_call
862 if 'ARRAY' eq ref($method_to_call);
864 return $self->delegation_metaclass->new(
865 name => $handle_name,
866 package_name => $self->associated_class->name,
868 delegate_to_method => $method_to_call,
869 curried_arguments => \@curried_arguments,
873 sub _coerce_and_verify {
876 my $instance = shift;
878 return $val unless $self->has_type_constraint;
880 $val = $self->type_constraint->coerce($val)
881 if $self->should_coerce && $self->type_constraint->has_coercion;
883 $self->verify_against_type_constraint($val, instance => $instance);
888 sub verify_against_type_constraint {
892 return 1 if !$self->has_type_constraint;
894 my $type_constraint = $self->type_constraint;
896 $type_constraint->check($val)
897 || $self->throw_error("Attribute ("
899 . ") does not pass the type constraint because: "
900 . $type_constraint->get_message($val), data => $val, @_);
903 package Moose::Meta::Attribute::Custom::Moose;
904 sub register_implementation { 'Moose::Meta::Attribute' }
914 Moose::Meta::Attribute - The Moose attribute metaclass
918 This class is a subclass of L<Class::MOP::Attribute> that provides
919 additional Moose-specific functionality.
921 To really understand this class, you will need to start with the
922 L<Class::MOP::Attribute> documentation. This class can be understood
923 as a set of additional features on top of the basic feature provided
924 by that parent class.
928 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
932 Many of the documented below override methods in
933 L<Class::MOP::Attribute> and add Moose specific features.
939 =item B<< Moose::Meta::Attribute->new(%options) >>
941 This method overrides the L<Class::MOP::Attribute> constructor.
943 Many of the options below are described in more detail in the
944 L<Moose::Manual::Attributes> document.
946 It adds the following options to the constructor:
950 =item * is => 'ro', 'rw', 'bare'
952 This provides a shorthand for specifying the C<reader>, C<writer>, or
953 C<accessor> names. If the attribute is read-only ('ro') then it will
954 have a C<reader> method with the same attribute as the name.
956 If it is read-write ('rw') then it will have an C<accessor> method
957 with the same name. If you provide an explicit C<writer> for a
958 read-write attribute, then you will have a C<reader> with the same
959 name as the attribute, and a C<writer> with the name you provided.
961 Use 'bare' when you are deliberately not installing any methods
962 (accessor, reader, etc.) associated with this attribute; otherwise,
963 Moose will issue a deprecation warning when this attribute is added to a
968 This option accepts a type. The type can be a string, which should be
969 a type name. If the type name is unknown, it is assumed to be a class
972 This option can also accept a L<Moose::Meta::TypeConstraint> object.
974 If you I<also> provide a C<does> option, then your C<isa> option must
975 be a class name, and that class must do the role specified with
978 =item * does => $role
980 This is short-hand for saying that the attribute's type must be an
981 object which does the named role.
983 =item * coerce => $bool
985 This option is only valid for objects with a type constraint
986 (C<isa>) that defined a coercion. If this is true, then coercions will be applied whenever
987 this attribute is set.
989 You can make both this and the C<weak_ref> option true.
991 =item * trigger => $sub
993 This option accepts a subroutine reference, which will be called after
994 the attribute is set.
996 =item * required => $bool
998 An attribute which is required must be provided to the constructor. An
999 attribute which is required can also have a C<default> or C<builder>,
1000 which will satisfy its required-ness.
1002 A required attribute must have a C<default>, C<builder> or a
1003 non-C<undef> C<init_arg>
1005 =item * lazy => $bool
1007 A lazy attribute must have a C<default> or C<builder>. When an
1008 attribute is lazy, the default value will not be calculated until the
1011 =item * weak_ref => $bool
1013 If this is true, the attribute's value will be stored as a weak
1016 =item * auto_deref => $bool
1018 If this is true, then the reader will dereference the value when it is
1019 called. The attribute must have a type constraint which defines the
1020 attribute as an array or hash reference.
1022 =item * lazy_build => $bool
1024 Setting this to true makes the attribute lazy and provides a number of
1032 is equivalent to this:
1037 builder => '_build_size',
1038 clearer => 'clear_size',
1039 predicate => 'has_size',
1043 If your attribute name starts with an underscore (C<_>), then the clearer
1044 and predicate will as well:
1056 builder => '_build__size',
1057 clearer => '_clear_size',
1058 predicate => '_has_size',
1061 Note the doubled underscore in the builder name. Internally, Moose
1062 simply prepends the attribute name with "_build_" to come up with the
1065 =item * documentation
1067 An arbitrary string that can be retrieved later by calling C<<
1068 $attr->documentation >>.
1072 =item B<< $attr->clone(%options) >>
1074 This creates a new attribute based on attribute being cloned. You must
1075 supply a C<name> option to provide a new name for the attribute.
1077 The C<%options> can only specify options handled by
1078 L<Class::MOP::Attribute>.
1082 =head2 Value management
1086 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
1088 This method is used internally to initialize the attribute's slot in
1089 the object C<$instance>.
1091 This overrides the L<Class::MOP::Attribute> method to handle lazy
1092 attributes, weak references, and type constraints.
1098 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
1103 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
1105 Before setting the value, a check is made on the type constraint of
1106 the attribute, if it has one, to see if the value passes it. If the
1107 value fails to pass, the set operation dies with a L</throw_error>.
1109 Any coercion to convert values is done before checking the type constraint.
1111 To check a value against a type constraint before setting it, fetch the
1112 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
1113 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
1114 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
1119 =head2 Attribute Accessor generation
1123 =item B<< $attr->install_accessors >>
1125 This method overrides the parent to also install delegation methods.
1127 If, after installing all methods, the attribute object has no associated
1128 methods, it throws an error unless C<< is => 'bare' >> was passed to the
1129 attribute constructor. (Trying to add an attribute that has no associated
1130 methods is almost always an error.)
1132 =item B<< $attr->remove_accessors >>
1134 This method overrides the parent to also remove delegation methods.
1136 =item B<< $attr->inline_set($instance_var, $value_var) >>
1138 This method return a code snippet suitable for inlining the relevant
1139 operation. It expect strings containing variable names to be used in the
1140 inlining, like C<'$self'> or C<'$_[1]'>.
1142 =item B<< $attr->install_delegation >>
1144 This method adds its delegation methods to the attribute's associated
1145 class, if it has any to add.
1147 =item B<< $attr->remove_delegation >>
1149 This method remove its delegation methods from the attribute's
1152 =item B<< $attr->accessor_metaclass >>
1154 Returns the accessor metaclass name, which defaults to
1155 L<Moose::Meta::Method::Accessor>.
1157 =item B<< $attr->delegation_metaclass >>
1159 Returns the delegation metaclass name, which defaults to
1160 L<Moose::Meta::Method::Delegation>.
1164 =head2 Additional Moose features
1166 These methods are not found in the superclass. They support features
1171 =item B<< $attr->does($role) >>
1173 This indicates whether the I<attribute itself> does the given
1174 role. The role can be given as a full class name, or as a resolvable
1177 Note that this checks the attribute itself, not its type constraint,
1178 so it is checking the attribute's metaclass and any traits applied to
1181 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
1183 This is an alternate constructor that handles the C<metaclass> and
1186 Effectively, this method is a factory that finds or creates the
1187 appropriate class for the given C<metaclass> and/or C<traits>.
1189 Once it has the appropriate class, it will call C<< $class->new($name,
1190 %options) >> on that class.
1192 =item B<< $attr->clone_and_inherit_options(%options) >>
1194 This method supports the C<has '+foo'> feature. It does various bits
1195 of processing on the supplied C<%options> before ultimately calling
1196 the C<clone> method.
1198 One of its main tasks is to make sure that the C<%options> provided
1199 does not include the options returned by the
1200 C<illegal_options_for_inheritance> method.
1202 =item B<< $attr->illegal_options_for_inheritance >>
1204 This returns a blacklist of options that can not be overridden in a
1205 subclass's attribute definition.
1207 This exists to allow a custom metaclass to change or add to the list
1208 of options which can not be changed.
1210 =item B<< $attr->type_constraint >>
1212 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1215 =item B<< $attr->has_type_constraint >>
1217 Returns true if this attribute has a type constraint.
1219 =item B<< $attr->verify_against_type_constraint($value) >>
1221 Given a value, this method returns true if the value is valid for the
1222 attribute's type constraint. If the value is not valid, it throws an
1225 =item B<< $attr->handles >>
1227 This returns the value of the C<handles> option passed to the
1230 =item B<< $attr->has_handles >>
1232 Returns true if this attribute performs delegation.
1234 =item B<< $attr->is_weak_ref >>
1236 Returns true if this attribute stores its value as a weak reference.
1238 =item B<< $attr->is_required >>
1240 Returns true if this attribute is required to have a value.
1242 =item B<< $attr->is_lazy >>
1244 Returns true if this attribute is lazy.
1246 =item B<< $attr->is_lazy_build >>
1248 Returns true if the C<lazy_build> option was true when passed to the
1251 =item B<< $attr->should_coerce >>
1253 Returns true if the C<coerce> option passed to the constructor was
1256 =item B<< $attr->should_auto_deref >>
1258 Returns true if the C<auto_deref> option passed to the constructor was
1261 =item B<< $attr->trigger >>
1263 This is the subroutine reference that was in the C<trigger> option
1264 passed to the constructor, if any.
1266 =item B<< $attr->has_trigger >>
1268 Returns true if this attribute has a trigger set.
1270 =item B<< $attr->documentation >>
1272 Returns the value that was in the C<documentation> option passed to
1273 the constructor, if any.
1275 =item B<< $attr->has_documentation >>
1277 Returns true if this attribute has any documentation.
1279 =item B<< $attr->applied_traits >>
1281 This returns an array reference of all the traits which were applied
1282 to this attribute. If none were applied, this returns C<undef>.
1284 =item B<< $attr->has_applied_traits >>
1286 Returns true if this attribute has any traits applied.
1292 See L<Moose/BUGS> for details on reporting bugs.
1296 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1298 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1300 =head1 COPYRIGHT AND LICENSE
1302 Copyright 2006-2010 by Infinity Interactive, Inc.
1304 L<http://www.iinteractive.com>
1306 This library is free software; you can redistribute it and/or modify
1307 it under the same terms as Perl itself.