2 package Moose::Meta::Attribute;
8 use Scalar::Util 'blessed', 'weaken';
9 use List::MoreUtils 'any';
13 our $VERSION = '1.17';
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);
653 && !$method->isa('Class::MOP::Method::Accessor')
654 && ( !$self->definition_context
655 || $method->package_name eq $self->definition_context->{package} )
659 "You are overwriting a locally defined method ($accessor) with "
662 if ( !$self->associated_class->has_method($accessor)
663 && $self->associated_class->has_package_symbol( '&' . $accessor ) ) {
666 "You are overwriting a locally defined function ($accessor) with "
670 $self->SUPER::_process_accessors(@_);
673 sub remove_accessors {
675 $self->SUPER::remove_accessors(@_);
676 $self->remove_delegation if $self->has_handles;
682 my ( $instance, $value ) = @_;
684 my $mi = $self->associated_class->get_meta_instance;
687 = $mi->inline_set_slot_value( $instance, $self->slots, $value ) . ";";
689 .= $mi->inline_weaken_slot_value( $instance, $self->slots, $value )
691 if $self->is_weak_ref;
696 sub install_delegation {
700 # Here we canonicalize the 'handles' option
701 # this will sort out any details and always
702 # return an hash of methods which we want
703 # to delagate to, see that method for details
704 my %handles = $self->_canonicalize_handles;
707 # install the delegation ...
708 my $associated_class = $self->associated_class;
709 foreach my $handle (keys %handles) {
710 my $method_to_call = $handles{$handle};
711 my $class_name = $associated_class->name;
712 my $name = "${class_name}::${handle}";
714 (!$associated_class->has_method($handle))
715 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
718 # handles is not allowed to delegate
719 # any of these methods, as they will
720 # override the ones in your class, which
721 # is almost certainly not what you want.
723 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
724 #cluck("Not delegating method '$handle' because it is a core method") and
725 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
727 my $method = $self->_make_delegation_method($handle, $method_to_call);
729 $self->associated_class->add_method($method->name, $method);
730 $self->associate_method($method);
734 sub remove_delegation {
736 my %handles = $self->_canonicalize_handles;
737 my $associated_class = $self->associated_class;
738 foreach my $handle (keys %handles) {
739 next unless any { $handle eq $_ }
741 @{ $self->associated_methods };
742 $self->associated_class->remove_method($handle);
746 # private methods to help delegation ...
748 sub _canonicalize_handles {
750 my $handles = $self->handles;
751 if (my $handle_type = ref($handles)) {
752 if ($handle_type eq 'HASH') {
755 elsif ($handle_type eq 'ARRAY') {
756 return map { $_ => $_ } @{$handles};
758 elsif ($handle_type eq 'Regexp') {
759 ($self->has_type_constraint)
760 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
761 return map { ($_ => $_) }
762 grep { /$handles/ } $self->_get_delegate_method_list;
764 elsif ($handle_type eq 'CODE') {
765 return $handles->($self, $self->_find_delegate_metaclass);
767 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::DuckType')) {
768 return map { $_ => $_ } @{ $handles->methods };
770 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::Role')) {
771 $handles = $handles->role;
774 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
778 Class::MOP::load_class($handles);
779 my $role_meta = Class::MOP::class_of($handles);
781 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
782 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because its metaclass is not a Moose::Meta::Role", data => $handles);
784 return map { $_ => $_ }
786 grep { !$_->isa('Class::MOP::Method::Meta') } (
787 $role_meta->_get_local_methods,
788 $role_meta->get_required_method_list,
792 sub _get_delegate_method_list {
794 my $meta = $self->_find_delegate_metaclass;
795 if ($meta->isa('Class::MOP::Class')) {
796 return map { $_->name } # NOTE: !never! delegate &meta
797 grep { $_->package_name ne 'Moose::Object' && !$_->isa('Class::MOP::Method::Meta') }
798 $meta->get_all_methods;
800 elsif ($meta->isa('Moose::Meta::Role')) {
801 return $meta->get_method_list;
804 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
808 sub _find_delegate_metaclass {
810 if (my $class = $self->_isa_metadata) {
811 unless ( Class::MOP::is_class_loaded($class) ) {
814 'The %s attribute is trying to delegate to a class which has not been loaded - %s',
819 # we might be dealing with a non-Moose class,
820 # and need to make our own metaclass. if there's
821 # already a metaclass, it will be returned
822 return Class::MOP::Class->initialize($class);
824 elsif (my $role = $self->_does_metadata) {
825 unless ( Class::MOP::is_class_loaded($class) ) {
828 'The %s attribute is trying to delegate to a role which has not been loaded - %s',
834 return Class::MOP::class_of($role);
837 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
841 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
843 sub _make_delegation_method {
844 my ( $self, $handle_name, $method_to_call ) = @_;
846 my @curried_arguments;
848 ($method_to_call, @curried_arguments) = @$method_to_call
849 if 'ARRAY' eq ref($method_to_call);
851 return $self->delegation_metaclass->new(
852 name => $handle_name,
853 package_name => $self->associated_class->name,
855 delegate_to_method => $method_to_call,
856 curried_arguments => \@curried_arguments,
860 sub _coerce_and_verify {
863 my $instance = shift;
865 return $val unless $self->has_type_constraint;
867 $val = $self->type_constraint->coerce($val)
868 if $self->should_coerce && $self->type_constraint->has_coercion;
870 $self->verify_against_type_constraint($val, instance => $instance);
875 sub verify_against_type_constraint {
879 return 1 if !$self->has_type_constraint;
881 my $type_constraint = $self->type_constraint;
883 $type_constraint->check($val)
884 || $self->throw_error("Attribute ("
886 . ") does not pass the type constraint because: "
887 . $type_constraint->get_message($val), data => $val, @_);
890 package Moose::Meta::Attribute::Custom::Moose;
891 sub register_implementation { 'Moose::Meta::Attribute' }
901 Moose::Meta::Attribute - The Moose attribute metaclass
905 This class is a subclass of L<Class::MOP::Attribute> that provides
906 additional Moose-specific functionality.
908 To really understand this class, you will need to start with the
909 L<Class::MOP::Attribute> documentation. This class can be understood
910 as a set of additional features on top of the basic feature provided
911 by that parent class.
915 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
919 Many of the documented below override methods in
920 L<Class::MOP::Attribute> and add Moose specific features.
926 =item B<< Moose::Meta::Attribute->new(%options) >>
928 This method overrides the L<Class::MOP::Attribute> constructor.
930 Many of the options below are described in more detail in the
931 L<Moose::Manual::Attributes> document.
933 It adds the following options to the constructor:
937 =item * is => 'ro', 'rw', 'bare'
939 This provides a shorthand for specifying the C<reader>, C<writer>, or
940 C<accessor> names. If the attribute is read-only ('ro') then it will
941 have a C<reader> method with the same attribute as the name.
943 If it is read-write ('rw') then it will have an C<accessor> method
944 with the same name. If you provide an explicit C<writer> for a
945 read-write attribute, then you will have a C<reader> with the same
946 name as the attribute, and a C<writer> with the name you provided.
948 Use 'bare' when you are deliberately not installing any methods
949 (accessor, reader, etc.) associated with this attribute; otherwise,
950 Moose will issue a deprecation warning when this attribute is added to a
955 This option accepts a type. The type can be a string, which should be
956 a type name. If the type name is unknown, it is assumed to be a class
959 This option can also accept a L<Moose::Meta::TypeConstraint> object.
961 If you I<also> provide a C<does> option, then your C<isa> option must
962 be a class name, and that class must do the role specified with
965 =item * does => $role
967 This is short-hand for saying that the attribute's type must be an
968 object which does the named role.
970 =item * coerce => $bool
972 This option is only valid for objects with a type constraint
973 (C<isa>) that defined a coercion. If this is true, then coercions will be applied whenever
974 this attribute is set.
976 You can make both this and the C<weak_ref> option true.
978 =item * trigger => $sub
980 This option accepts a subroutine reference, which will be called after
981 the attribute is set.
983 =item * required => $bool
985 An attribute which is required must be provided to the constructor. An
986 attribute which is required can also have a C<default> or C<builder>,
987 which will satisfy its required-ness.
989 A required attribute must have a C<default>, C<builder> or a
990 non-C<undef> C<init_arg>
992 =item * lazy => $bool
994 A lazy attribute must have a C<default> or C<builder>. When an
995 attribute is lazy, the default value will not be calculated until the
998 =item * weak_ref => $bool
1000 If this is true, the attribute's value will be stored as a weak
1003 =item * auto_deref => $bool
1005 If this is true, then the reader will dereference the value when it is
1006 called. The attribute must have a type constraint which defines the
1007 attribute as an array or hash reference.
1009 =item * lazy_build => $bool
1011 Setting this to true makes the attribute lazy and provides a number of
1019 is equivalent to this:
1024 builder => '_build_size',
1025 clearer => 'clear_size',
1026 predicate => 'has_size',
1029 =item * documentation
1031 An arbitrary string that can be retrieved later by calling C<<
1032 $attr->documentation >>.
1036 =item B<< $attr->clone(%options) >>
1038 This creates a new attribute based on attribute being cloned. You must
1039 supply a C<name> option to provide a new name for the attribute.
1041 The C<%options> can only specify options handled by
1042 L<Class::MOP::Attribute>.
1046 =head2 Value management
1050 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
1052 This method is used internally to initialize the attribute's slot in
1053 the object C<$instance>.
1055 This overrides the L<Class::MOP::Attribute> method to handle lazy
1056 attributes, weak references, and type constraints.
1062 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
1067 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
1069 Before setting the value, a check is made on the type constraint of
1070 the attribute, if it has one, to see if the value passes it. If the
1071 value fails to pass, the set operation dies with a L</throw_error>.
1073 Any coercion to convert values is done before checking the type constraint.
1075 To check a value against a type constraint before setting it, fetch the
1076 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
1077 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
1078 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
1083 =head2 Attribute Accessor generation
1087 =item B<< $attr->install_accessors >>
1089 This method overrides the parent to also install delegation methods.
1091 If, after installing all methods, the attribute object has no associated
1092 methods, it throws an error unless C<< is => 'bare' >> was passed to the
1093 attribute constructor. (Trying to add an attribute that has no associated
1094 methods is almost always an error.)
1096 =item B<< $attr->remove_accessors >>
1098 This method overrides the parent to also remove delegation methods.
1100 =item B<< $attr->inline_set($instance_var, $value_var) >>
1102 This method return a code snippet suitable for inlining the relevant
1103 operation. It expect strings containing variable names to be used in the
1104 inlining, like C<'$self'> or C<'$_[1]'>.
1106 =item B<< $attr->install_delegation >>
1108 This method adds its delegation methods to the attribute's associated
1109 class, if it has any to add.
1111 =item B<< $attr->remove_delegation >>
1113 This method remove its delegation methods from the attribute's
1116 =item B<< $attr->accessor_metaclass >>
1118 Returns the accessor metaclass name, which defaults to
1119 L<Moose::Meta::Method::Accessor>.
1121 =item B<< $attr->delegation_metaclass >>
1123 Returns the delegation metaclass name, which defaults to
1124 L<Moose::Meta::Method::Delegation>.
1128 =head2 Additional Moose features
1130 These methods are not found in the superclass. They support features
1135 =item B<< $attr->does($role) >>
1137 This indicates whether the I<attribute itself> does the given
1138 role. The role can be given as a full class name, or as a resolvable
1141 Note that this checks the attribute itself, not its type constraint,
1142 so it is checking the attribute's metaclass and any traits applied to
1145 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
1147 This is an alternate constructor that handles the C<metaclass> and
1150 Effectively, this method is a factory that finds or creates the
1151 appropriate class for the given C<metaclass> and/or C<traits>.
1153 Once it has the appropriate class, it will call C<< $class->new($name,
1154 %options) >> on that class.
1156 =item B<< $attr->clone_and_inherit_options(%options) >>
1158 This method supports the C<has '+foo'> feature. It does various bits
1159 of processing on the supplied C<%options> before ultimately calling
1160 the C<clone> method.
1162 One of its main tasks is to make sure that the C<%options> provided
1163 does not include the options returned by the
1164 C<illegal_options_for_inheritance> method.
1166 =item B<< $attr->illegal_options_for_inheritance >>
1168 This returns a blacklist of options that can not be overridden in a
1169 subclass's attribute definition.
1171 This exists to allow a custom metaclass to change or add to the list
1172 of options which can not be changed.
1174 =item B<< $attr->type_constraint >>
1176 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1179 =item B<< $attr->has_type_constraint >>
1181 Returns true if this attribute has a type constraint.
1183 =item B<< $attr->verify_against_type_constraint($value) >>
1185 Given a value, this method returns true if the value is valid for the
1186 attribute's type constraint. If the value is not valid, it throws an
1189 =item B<< $attr->handles >>
1191 This returns the value of the C<handles> option passed to the
1194 =item B<< $attr->has_handles >>
1196 Returns true if this attribute performs delegation.
1198 =item B<< $attr->is_weak_ref >>
1200 Returns true if this attribute stores its value as a weak reference.
1202 =item B<< $attr->is_required >>
1204 Returns true if this attribute is required to have a value.
1206 =item B<< $attr->is_lazy >>
1208 Returns true if this attribute is lazy.
1210 =item B<< $attr->is_lazy_build >>
1212 Returns true if the C<lazy_build> option was true when passed to the
1215 =item B<< $attr->should_coerce >>
1217 Returns true if the C<coerce> option passed to the constructor was
1220 =item B<< $attr->should_auto_deref >>
1222 Returns true if the C<auto_deref> option passed to the constructor was
1225 =item B<< $attr->trigger >>
1227 This is the subroutine reference that was in the C<trigger> option
1228 passed to the constructor, if any.
1230 =item B<< $attr->has_trigger >>
1232 Returns true if this attribute has a trigger set.
1234 =item B<< $attr->documentation >>
1236 Returns the value that was in the C<documentation> option passed to
1237 the constructor, if any.
1239 =item B<< $attr->has_documentation >>
1241 Returns true if this attribute has any documentation.
1243 =item B<< $attr->applied_traits >>
1245 This returns an array reference of all the traits which were applied
1246 to this attribute. If none were applied, this returns C<undef>.
1248 =item B<< $attr->has_applied_traits >>
1250 Returns true if this attribute has any traits applied.
1256 See L<Moose/BUGS> for details on reporting bugs.
1260 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1262 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1264 =head1 COPYRIGHT AND LICENSE
1266 Copyright 2006-2010 by Infinity Interactive, Inc.
1268 L<http://www.iinteractive.com>
1270 This library is free software; you can redistribute it and/or modify
1271 it under the same terms as Perl itself.