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 '"
512 sub _make_initializer_writer_callback {
514 my ($meta_instance, $instance, $slot_name) = @_;
515 my $old_callback = $self->SUPER::_make_initializer_writer_callback(@_);
517 $old_callback->($self->_coerce_and_verify($_[0], $instance));
522 my ($self, $instance, @args) = @_;
523 my $value = $args[0];
525 my $attr_name = $self->name;
527 if ($self->is_required and not @args) {
528 $self->throw_error("Attribute ($attr_name) is required", object => $instance);
531 $value = $self->_coerce_and_verify( $value, $instance );
534 if ( $self->has_trigger && $self->has_value($instance) ) {
535 @old = $self->get_value($instance, 'for trigger');
538 $self->SUPER::set_value($instance, $value);
540 if ( ref $value && $self->is_weak_ref ) {
541 $self->_weaken_value($instance);
544 if ($self->has_trigger) {
545 $self->trigger->($instance, $value, @old);
550 my ( $self, $instance ) = @_;
552 my $meta_instance = Class::MOP::Class->initialize( blessed($instance) )
555 $meta_instance->weaken_slot_value( $instance, $self->name );
559 my ($self, $instance, $for_trigger) = @_;
561 if ($self->is_lazy) {
562 unless ($self->has_value($instance)) {
564 if ($self->has_default) {
565 $value = $self->default($instance);
566 } elsif ( $self->has_builder ) {
567 $value = $self->_call_builder($instance);
570 $value = $self->_coerce_and_verify( $value, $instance );
572 $self->set_initial_value($instance, $value);
576 if ( $self->should_auto_deref && ! $for_trigger ) {
578 my $type_constraint = $self->type_constraint;
580 if ($type_constraint->is_a_type_of('ArrayRef')) {
581 my $rv = $self->SUPER::get_value($instance);
582 return unless defined $rv;
583 return wantarray ? @{ $rv } : $rv;
585 elsif ($type_constraint->is_a_type_of('HashRef')) {
586 my $rv = $self->SUPER::get_value($instance);
587 return unless defined $rv;
588 return wantarray ? %{ $rv } : $rv;
591 $self->throw_error("Can not auto de-reference the type constraint '" . $type_constraint->name . "'", object => $instance, type_constraint => $type_constraint);
597 return $self->SUPER::get_value($instance);
601 ## installing accessors
603 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
605 sub install_accessors {
607 $self->SUPER::install_accessors(@_);
608 $self->install_delegation if $self->has_handles;
612 sub _check_associated_methods {
615 @{ $self->associated_methods }
616 || ($self->_is_metadata || '') eq 'bare'
619 'Attribute (' . $self->name . ') of class '
620 . $self->associated_class->name
621 . ' has no associated methods'
622 . ' (did you mean to provide an "is" argument?)'
628 sub _process_accessors {
630 my ($type, $accessor, $generate_as_inline_methods) = @_;
632 $accessor = ( keys %$accessor )[0] if ( ref($accessor) || '' ) eq 'HASH';
633 my $method = $self->associated_class->get_method($accessor);
636 && $method->isa('Class::MOP::Method::Accessor')
637 && $method->associated_attribute->name ne $self->name ) {
639 my $other_attr_name = $method->associated_attribute->name;
640 my $name = $self->name;
643 "You are overwriting an accessor ($accessor) for the $other_attr_name attribute"
644 . " with a new accessor method for the $name attribute" );
649 && !$method->isa('Class::MOP::Method::Accessor')
650 && ( !$self->definition_context
651 || $method->package_name eq $self->definition_context->{package} )
655 "You are overwriting a locally defined method ($accessor) with "
659 if ( !$self->associated_class->has_method($accessor)
660 && $self->associated_class->has_package_symbol( '&' . $accessor ) ) {
663 "You are overwriting a locally defined function ($accessor) with "
667 $self->SUPER::_process_accessors(@_);
670 sub remove_accessors {
672 $self->SUPER::remove_accessors(@_);
673 $self->remove_delegation if $self->has_handles;
677 sub _inline_set_value {
679 my ($instance, $value) = @_;
681 my $mi = $self->associated_class->get_meta_instance;
683 my @code = ($self->SUPER::_inline_set_value(@_));
686 $mi->inline_weaken_slot_value($instance, $self->name, $value),
687 'if ref ' . $value . ';',
688 ) if $self->is_weak_ref;
693 sub install_delegation {
697 # Here we canonicalize the 'handles' option
698 # this will sort out any details and always
699 # return an hash of methods which we want
700 # to delagate to, see that method for details
701 my %handles = $self->_canonicalize_handles;
704 # install the delegation ...
705 my $associated_class = $self->associated_class;
706 foreach my $handle (keys %handles) {
707 my $method_to_call = $handles{$handle};
708 my $class_name = $associated_class->name;
709 my $name = "${class_name}::${handle}";
711 (!$associated_class->has_method($handle))
712 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
715 # handles is not allowed to delegate
716 # any of these methods, as they will
717 # override the ones in your class, which
718 # is almost certainly not what you want.
720 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
721 #cluck("Not delegating method '$handle' because it is a core method") and
722 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
724 my $method = $self->_make_delegation_method($handle, $method_to_call);
726 $self->associated_class->add_method($method->name, $method);
727 $self->associate_method($method);
731 sub remove_delegation {
733 my %handles = $self->_canonicalize_handles;
734 my $associated_class = $self->associated_class;
735 foreach my $handle (keys %handles) {
736 next unless any { $handle eq $_ }
738 @{ $self->associated_methods };
739 $self->associated_class->remove_method($handle);
743 # private methods to help delegation ...
745 sub _canonicalize_handles {
747 my $handles = $self->handles;
748 if (my $handle_type = ref($handles)) {
749 if ($handle_type eq 'HASH') {
752 elsif ($handle_type eq 'ARRAY') {
753 return map { $_ => $_ } @{$handles};
755 elsif ($handle_type eq 'Regexp') {
756 ($self->has_type_constraint)
757 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
758 return map { ($_ => $_) }
759 grep { /$handles/ } $self->_get_delegate_method_list;
761 elsif ($handle_type eq 'CODE') {
762 return $handles->($self, $self->_find_delegate_metaclass);
764 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::DuckType')) {
765 return map { $_ => $_ } @{ $handles->methods };
767 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::Role')) {
768 $handles = $handles->role;
771 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
775 Class::MOP::load_class($handles);
776 my $role_meta = Class::MOP::class_of($handles);
778 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
779 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because its metaclass is not a Moose::Meta::Role", data => $handles);
781 return map { $_ => $_ }
783 grep { !$_->isa('Class::MOP::Method::Meta') } (
784 $role_meta->_get_local_methods,
785 $role_meta->get_required_method_list,
789 sub _get_delegate_method_list {
791 my $meta = $self->_find_delegate_metaclass;
792 if ($meta->isa('Class::MOP::Class')) {
793 return map { $_->name } # NOTE: !never! delegate &meta
794 grep { $_->package_name ne 'Moose::Object' && !$_->isa('Class::MOP::Method::Meta') }
795 $meta->get_all_methods;
797 elsif ($meta->isa('Moose::Meta::Role')) {
798 return $meta->get_method_list;
801 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
805 sub _find_delegate_metaclass {
807 if (my $class = $self->_isa_metadata) {
808 unless ( Class::MOP::is_class_loaded($class) ) {
811 'The %s attribute is trying to delegate to a class which has not been loaded - %s',
816 # we might be dealing with a non-Moose class,
817 # and need to make our own metaclass. if there's
818 # already a metaclass, it will be returned
819 return Class::MOP::Class->initialize($class);
821 elsif (my $role = $self->_does_metadata) {
822 unless ( Class::MOP::is_class_loaded($class) ) {
825 'The %s attribute is trying to delegate to a role which has not been loaded - %s',
831 return Class::MOP::class_of($role);
834 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
838 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
840 sub _make_delegation_method {
841 my ( $self, $handle_name, $method_to_call ) = @_;
843 my @curried_arguments;
845 ($method_to_call, @curried_arguments) = @$method_to_call
846 if 'ARRAY' eq ref($method_to_call);
848 return $self->delegation_metaclass->new(
849 name => $handle_name,
850 package_name => $self->associated_class->name,
852 delegate_to_method => $method_to_call,
853 curried_arguments => \@curried_arguments,
857 sub _coerce_and_verify {
860 my $instance = shift;
862 return $val unless $self->has_type_constraint;
864 $val = $self->type_constraint->coerce($val)
865 if $self->should_coerce && $self->type_constraint->has_coercion;
867 $self->verify_against_type_constraint($val, instance => $instance);
872 sub verify_against_type_constraint {
876 return 1 if !$self->has_type_constraint;
878 my $type_constraint = $self->type_constraint;
880 $type_constraint->check($val)
881 || $self->throw_error("Attribute ("
883 . ") does not pass the type constraint because: "
884 . $type_constraint->get_message($val), data => $val, @_);
887 package Moose::Meta::Attribute::Custom::Moose;
888 sub register_implementation { 'Moose::Meta::Attribute' }
898 Moose::Meta::Attribute - The Moose attribute metaclass
902 This class is a subclass of L<Class::MOP::Attribute> that provides
903 additional Moose-specific functionality.
905 To really understand this class, you will need to start with the
906 L<Class::MOP::Attribute> documentation. This class can be understood
907 as a set of additional features on top of the basic feature provided
908 by that parent class.
912 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
916 Many of the documented below override methods in
917 L<Class::MOP::Attribute> and add Moose specific features.
923 =item B<< Moose::Meta::Attribute->new(%options) >>
925 This method overrides the L<Class::MOP::Attribute> constructor.
927 Many of the options below are described in more detail in the
928 L<Moose::Manual::Attributes> document.
930 It adds the following options to the constructor:
934 =item * is => 'ro', 'rw', 'bare'
936 This provides a shorthand for specifying the C<reader>, C<writer>, or
937 C<accessor> names. If the attribute is read-only ('ro') then it will
938 have a C<reader> method with the same attribute as the name.
940 If it is read-write ('rw') then it will have an C<accessor> method
941 with the same name. If you provide an explicit C<writer> for a
942 read-write attribute, then you will have a C<reader> with the same
943 name as the attribute, and a C<writer> with the name you provided.
945 Use 'bare' when you are deliberately not installing any methods
946 (accessor, reader, etc.) associated with this attribute; otherwise,
947 Moose will issue a deprecation warning when this attribute is added to a
952 This option accepts a type. The type can be a string, which should be
953 a type name. If the type name is unknown, it is assumed to be a class
956 This option can also accept a L<Moose::Meta::TypeConstraint> object.
958 If you I<also> provide a C<does> option, then your C<isa> option must
959 be a class name, and that class must do the role specified with
962 =item * does => $role
964 This is short-hand for saying that the attribute's type must be an
965 object which does the named role.
967 =item * coerce => $bool
969 This option is only valid for objects with a type constraint
970 (C<isa>) that defined a coercion. If this is true, then coercions will be applied whenever
971 this attribute is set.
973 You can make both this and the C<weak_ref> option true.
975 =item * trigger => $sub
977 This option accepts a subroutine reference, which will be called after
978 the attribute is set.
980 =item * required => $bool
982 An attribute which is required must be provided to the constructor. An
983 attribute which is required can also have a C<default> or C<builder>,
984 which will satisfy its required-ness.
986 A required attribute must have a C<default>, C<builder> or a
987 non-C<undef> C<init_arg>
989 =item * lazy => $bool
991 A lazy attribute must have a C<default> or C<builder>. When an
992 attribute is lazy, the default value will not be calculated until the
995 =item * weak_ref => $bool
997 If this is true, the attribute's value will be stored as a weak
1000 =item * auto_deref => $bool
1002 If this is true, then the reader will dereference the value when it is
1003 called. The attribute must have a type constraint which defines the
1004 attribute as an array or hash reference.
1006 =item * lazy_build => $bool
1008 Setting this to true makes the attribute lazy and provides a number of
1016 is equivalent to this:
1021 builder => '_build_size',
1022 clearer => 'clear_size',
1023 predicate => 'has_size',
1027 If your attribute name starts with an underscore (C<_>), then the clearer
1028 and predicate will as well:
1040 builder => '_build__size',
1041 clearer => '_clear_size',
1042 predicate => '_has_size',
1045 Note the doubled underscore in the builder name. Internally, Moose
1046 simply prepends the attribute name with "_build_" to come up with the
1049 =item * documentation
1051 An arbitrary string that can be retrieved later by calling C<<
1052 $attr->documentation >>.
1056 =item B<< $attr->clone(%options) >>
1058 This creates a new attribute based on attribute being cloned. You must
1059 supply a C<name> option to provide a new name for the attribute.
1061 The C<%options> can only specify options handled by
1062 L<Class::MOP::Attribute>.
1066 =head2 Value management
1070 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
1072 This method is used internally to initialize the attribute's slot in
1073 the object C<$instance>.
1075 This overrides the L<Class::MOP::Attribute> method to handle lazy
1076 attributes, weak references, and type constraints.
1082 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
1087 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
1089 Before setting the value, a check is made on the type constraint of
1090 the attribute, if it has one, to see if the value passes it. If the
1091 value fails to pass, the set operation dies with a L</throw_error>.
1093 Any coercion to convert values is done before checking the type constraint.
1095 To check a value against a type constraint before setting it, fetch the
1096 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
1097 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
1098 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
1103 =head2 Attribute Accessor generation
1107 =item B<< $attr->install_accessors >>
1109 This method overrides the parent to also install delegation methods.
1111 If, after installing all methods, the attribute object has no associated
1112 methods, it throws an error unless C<< is => 'bare' >> was passed to the
1113 attribute constructor. (Trying to add an attribute that has no associated
1114 methods is almost always an error.)
1116 =item B<< $attr->remove_accessors >>
1118 This method overrides the parent to also remove delegation methods.
1120 =item B<< $attr->inline_set($instance_var, $value_var) >>
1122 This method return a code snippet suitable for inlining the relevant
1123 operation. It expect strings containing variable names to be used in the
1124 inlining, like C<'$self'> or C<'$_[1]'>.
1126 =item B<< $attr->install_delegation >>
1128 This method adds its delegation methods to the attribute's associated
1129 class, if it has any to add.
1131 =item B<< $attr->remove_delegation >>
1133 This method remove its delegation methods from the attribute's
1136 =item B<< $attr->accessor_metaclass >>
1138 Returns the accessor metaclass name, which defaults to
1139 L<Moose::Meta::Method::Accessor>.
1141 =item B<< $attr->delegation_metaclass >>
1143 Returns the delegation metaclass name, which defaults to
1144 L<Moose::Meta::Method::Delegation>.
1148 =head2 Additional Moose features
1150 These methods are not found in the superclass. They support features
1155 =item B<< $attr->does($role) >>
1157 This indicates whether the I<attribute itself> does the given
1158 role. The role can be given as a full class name, or as a resolvable
1161 Note that this checks the attribute itself, not its type constraint,
1162 so it is checking the attribute's metaclass and any traits applied to
1165 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
1167 This is an alternate constructor that handles the C<metaclass> and
1170 Effectively, this method is a factory that finds or creates the
1171 appropriate class for the given C<metaclass> and/or C<traits>.
1173 Once it has the appropriate class, it will call C<< $class->new($name,
1174 %options) >> on that class.
1176 =item B<< $attr->clone_and_inherit_options(%options) >>
1178 This method supports the C<has '+foo'> feature. It does various bits
1179 of processing on the supplied C<%options> before ultimately calling
1180 the C<clone> method.
1182 One of its main tasks is to make sure that the C<%options> provided
1183 does not include the options returned by the
1184 C<illegal_options_for_inheritance> method.
1186 =item B<< $attr->illegal_options_for_inheritance >>
1188 This returns a blacklist of options that can not be overridden in a
1189 subclass's attribute definition.
1191 This exists to allow a custom metaclass to change or add to the list
1192 of options which can not be changed.
1194 =item B<< $attr->type_constraint >>
1196 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1199 =item B<< $attr->has_type_constraint >>
1201 Returns true if this attribute has a type constraint.
1203 =item B<< $attr->verify_against_type_constraint($value) >>
1205 Given a value, this method returns true if the value is valid for the
1206 attribute's type constraint. If the value is not valid, it throws an
1209 =item B<< $attr->handles >>
1211 This returns the value of the C<handles> option passed to the
1214 =item B<< $attr->has_handles >>
1216 Returns true if this attribute performs delegation.
1218 =item B<< $attr->is_weak_ref >>
1220 Returns true if this attribute stores its value as a weak reference.
1222 =item B<< $attr->is_required >>
1224 Returns true if this attribute is required to have a value.
1226 =item B<< $attr->is_lazy >>
1228 Returns true if this attribute is lazy.
1230 =item B<< $attr->is_lazy_build >>
1232 Returns true if the C<lazy_build> option was true when passed to the
1235 =item B<< $attr->should_coerce >>
1237 Returns true if the C<coerce> option passed to the constructor was
1240 =item B<< $attr->should_auto_deref >>
1242 Returns true if the C<auto_deref> option passed to the constructor was
1245 =item B<< $attr->trigger >>
1247 This is the subroutine reference that was in the C<trigger> option
1248 passed to the constructor, if any.
1250 =item B<< $attr->has_trigger >>
1252 Returns true if this attribute has a trigger set.
1254 =item B<< $attr->documentation >>
1256 Returns the value that was in the C<documentation> option passed to
1257 the constructor, if any.
1259 =item B<< $attr->has_documentation >>
1261 Returns true if this attribute has any documentation.
1263 =item B<< $attr->applied_traits >>
1265 This returns an array reference of all the traits which were applied
1266 to this attribute. If none were applied, this returns C<undef>.
1268 =item B<< $attr->has_applied_traits >>
1270 Returns true if this attribute has any traits applied.
1276 See L<Moose/BUGS> for details on reporting bugs.
1280 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1282 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1284 =head1 COPYRIGHT AND LICENSE
1286 Copyright 2006-2010 by Infinity Interactive, Inc.
1288 L<http://www.iinteractive.com>
1290 This library is free software; you can redistribute it and/or modify
1291 it under the same terms as Perl itself.