2 package Moose::Meta::Attribute;
7 use Scalar::Util 'blessed', 'weaken';
10 our $VERSION = '0.84';
11 our $AUTHORITY = 'cpan:STEVAN';
13 use Moose::Meta::Method::Accessor;
14 use Moose::Meta::Method::Delegation;
16 use Moose::Util::TypeConstraints ();
18 use base 'Class::MOP::Attribute';
20 # options which are not directly used
21 # but we store them for metadata purposes
22 __PACKAGE__->meta->add_attribute('isa' => (reader => '_isa_metadata'));
23 __PACKAGE__->meta->add_attribute('does' => (reader => '_does_metadata'));
24 __PACKAGE__->meta->add_attribute('is' => (reader => '_is_metadata'));
26 # these are actual options for the attrs
27 __PACKAGE__->meta->add_attribute('required' => (reader => 'is_required' ));
28 __PACKAGE__->meta->add_attribute('lazy' => (reader => 'is_lazy' ));
29 __PACKAGE__->meta->add_attribute('lazy_build' => (reader => 'is_lazy_build' ));
30 __PACKAGE__->meta->add_attribute('coerce' => (reader => 'should_coerce' ));
31 __PACKAGE__->meta->add_attribute('weak_ref' => (reader => 'is_weak_ref' ));
32 __PACKAGE__->meta->add_attribute('auto_deref' => (reader => 'should_auto_deref'));
33 __PACKAGE__->meta->add_attribute('type_constraint' => (
34 reader => 'type_constraint',
35 predicate => 'has_type_constraint',
37 __PACKAGE__->meta->add_attribute('trigger' => (
39 predicate => 'has_trigger',
41 __PACKAGE__->meta->add_attribute('handles' => (
43 predicate => 'has_handles',
45 __PACKAGE__->meta->add_attribute('documentation' => (
46 reader => 'documentation',
47 predicate => 'has_documentation',
49 __PACKAGE__->meta->add_attribute('traits' => (
50 reader => 'applied_traits',
51 predicate => 'has_applied_traits',
54 # we need to have a ->does method in here to
55 # more easily support traits, and the introspection
56 # of those traits. We extend the does check to look
57 # for metatrait aliases.
59 my ($self, $role_name) = @_;
61 Moose::Util::resolve_metatrait_alias(Attribute => $role_name)
63 return 0 if !defined($name); # failed to load class
64 return $self->Moose::Object::does($name);
69 my $class = ( ref $self && $self->associated_class ) || "Moose::Meta::Class";
70 unshift @_, "message" if @_ % 2 == 1;
71 unshift @_, attr => $self if ref $self;
73 my $handler = $class->can("throw_error"); # to avoid incrementing depth by 1
78 my ($class, $name, %options) = @_;
79 $class->_process_options($name, \%options) unless $options{__hack_no_process_options}; # used from clone()... YECHKKK FIXME ICKY YUCK GROSS
81 delete $options{__hack_no_process_options};
86 map { $_->init_arg() }
87 $class->meta()->get_all_attributes()
90 my @bad = sort grep { ! $attrs{$_} } keys %options;
94 Carp::cluck "Found unknown argument(s) passed to '$name' attribute constructor in '$class': @bad";
97 return $class->SUPER::new($name, %options);
100 sub interpolate_class_and_new {
101 my ($class, $name, %args) = @_;
103 my ( $new_class, @traits ) = $class->interpolate_class(\%args);
105 $new_class->new($name, %args, ( scalar(@traits) ? ( traits => \@traits ) : () ) );
108 sub interpolate_class {
109 my ($class, $options) = @_;
111 $class = ref($class) || $class;
113 if ( my $metaclass_name = delete $options->{metaclass} ) {
114 my $new_class = Moose::Util::resolve_metaclass_alias( Attribute => $metaclass_name );
116 if ( $class ne $new_class ) {
117 if ( $new_class->can("interpolate_class") ) {
118 return $new_class->interpolate_class($options);
127 if (my $traits = $options->{traits}) {
129 while ($i < @$traits) {
130 my $trait = $traits->[$i++];
131 next if ref($trait); # options to a trait we discarded
133 $trait = Moose::Util::resolve_metatrait_alias(Attribute => $trait)
136 next if $class->does($trait);
138 push @traits, $trait;
141 push @traits, $traits->[$i++]
142 if $traits->[$i] && ref($traits->[$i]);
146 my $anon_class = Moose::Meta::Class->create_anon_class(
147 superclasses => [ $class ],
148 roles => [ @traits ],
152 $class = $anon_class->name;
156 return ( wantarray ? ( $class, @traits ) : $class );
161 my @legal_options_for_inheritance = qw(
162 default coerce required
163 documentation lazy handles
164 builder type_constraint
169 sub legal_options_for_inheritance { @legal_options_for_inheritance }
172 # This method *must* be able to handle
173 # Class::MOP::Attribute instances as
174 # well. Yes, I know that is wrong, but
175 # apparently we didn't realize it was
176 # doing that and now we have some code
177 # which is dependent on it. The real
178 # solution of course is to push this
179 # feature back up into Class::MOP::Attribute
180 # but I not right now, I am too lazy.
181 # However if you are reading this and
182 # looking for something to do,.. please
185 sub clone_and_inherit_options {
186 my ($self, %options) = @_;
193 # we may want to extends a Class::MOP::Attribute
194 # in which case we need to be able to use the
195 # core set of legal options that have always
196 # been here. But we allows Moose::Meta::Attribute
197 # instances to changes them.
199 my @legal_options = $self->can('legal_options_for_inheritance')
200 ? $self->legal_options_for_inheritance
201 : @legal_options_for_inheritance;
203 foreach my $legal_option (@legal_options) {
204 if (exists $options{$legal_option}) {
205 $actual_options{$legal_option} = $options{$legal_option};
206 delete $options{$legal_option};
212 if (blessed($options{isa}) && $options{isa}->isa('Moose::Meta::TypeConstraint')) {
213 $type_constraint = $options{isa};
216 $type_constraint = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options{isa});
217 (defined $type_constraint)
218 || $self->throw_error("Could not find the type constraint '" . $options{isa} . "'", data => $options{isa});
221 $actual_options{type_constraint} = $type_constraint;
222 delete $options{isa};
225 if ($options{does}) {
227 if (blessed($options{does}) && $options{does}->isa('Moose::Meta::TypeConstraint')) {
228 $type_constraint = $options{does};
231 $type_constraint = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options{does});
232 (defined $type_constraint)
233 || $self->throw_error("Could not find the type constraint '" . $options{does} . "'", data => $options{does});
236 $actual_options{type_constraint} = $type_constraint;
237 delete $options{does};
241 # this doesn't apply to Class::MOP::Attributes,
242 # so we can ignore it for them.
244 if ($self->can('interpolate_class')) {
245 ( $actual_options{metaclass}, my @traits ) = $self->interpolate_class(\%options);
248 my @all_traits = grep { $seen{$_}++ } @{ $self->applied_traits || [] }, @traits;
249 $actual_options{traits} = \@all_traits if @all_traits;
251 delete @options{qw(metaclass traits)};
254 (scalar keys %options == 0)
255 || $self->throw_error("Illegal inherited options => (" . (join ', ' => keys %options) . ")", data => \%options);
258 $self->clone(%actual_options);
262 my ( $self, %params ) = @_;
264 my $class = delete $params{metaclass} || ref $self;
266 my ( @init, @non_init );
268 foreach my $attr ( grep { $_->has_value($self) } Class::MOP::class_of($self)->get_all_attributes ) {
269 push @{ $attr->has_init_arg ? \@init : \@non_init }, $attr;
272 my %new_params = ( ( map { $_->init_arg => $_->get_value($self) } @init ), %params );
274 my $name = delete $new_params{name};
276 my $clone = $class->new($name, %new_params, __hack_no_process_options => 1 );
278 foreach my $attr ( @non_init ) {
279 $attr->set_value($clone, $attr->get_value($self));
285 sub _process_options {
286 my ($class, $name, $options) = @_;
288 if (exists $options->{is}) {
290 ### -------------------------
291 ## is => ro, writer => _foo # turns into (reader => foo, writer => _foo) as before
292 ## is => rw, writer => _foo # turns into (reader => foo, writer => _foo)
293 ## is => rw, accessor => _foo # turns into (accessor => _foo)
294 ## is => ro, accessor => _foo # error, accesor is rw
295 ### -------------------------
297 if ($options->{is} eq 'ro') {
298 $class->throw_error("Cannot define an accessor name on a read-only attribute, accessors are read/write", data => $options)
299 if exists $options->{accessor};
300 $options->{reader} ||= $name;
302 elsif ($options->{is} eq 'rw') {
303 if ($options->{writer}) {
304 $options->{reader} ||= $name;
307 $options->{accessor} ||= $name;
310 elsif ($options->{is} eq 'bare') {
311 # do nothing, but don't complain (later) about missing methods
314 $class->throw_error("I do not understand this option (is => " . $options->{is} . ") on attribute ($name)", data => $options->{is});
318 if (exists $options->{isa}) {
319 if (exists $options->{does}) {
320 if (eval { $options->{isa}->can('does') }) {
321 ($options->{isa}->does($options->{does}))
322 || $class->throw_error("Cannot have an isa option and a does option if the isa does not do the does on attribute ($name)", data => $options);
325 $class->throw_error("Cannot have an isa option which cannot ->does() on attribute ($name)", data => $options);
329 # allow for anon-subtypes here ...
330 if (blessed($options->{isa}) && $options->{isa}->isa('Moose::Meta::TypeConstraint')) {
331 $options->{type_constraint} = $options->{isa};
334 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options->{isa});
337 elsif (exists $options->{does}) {
338 # allow for anon-subtypes here ...
339 if (blessed($options->{does}) && $options->{does}->isa('Moose::Meta::TypeConstraint')) {
340 $options->{type_constraint} = $options->{does};
343 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options->{does});
347 if (exists $options->{coerce} && $options->{coerce}) {
348 (exists $options->{type_constraint})
349 || $class->throw_error("You cannot have coercion without specifying a type constraint on attribute ($name)", data => $options);
350 $class->throw_error("You cannot have a weak reference to a coerced value on attribute ($name)", data => $options)
351 if $options->{weak_ref};
354 if (exists $options->{trigger}) {
355 ('CODE' eq ref $options->{trigger})
356 || $class->throw_error("Trigger must be a CODE ref on attribute ($name)", data => $options->{trigger});
359 if (exists $options->{auto_deref} && $options->{auto_deref}) {
360 (exists $options->{type_constraint})
361 || $class->throw_error("You cannot auto-dereference without specifying a type constraint on attribute ($name)", data => $options);
362 ($options->{type_constraint}->is_a_type_of('ArrayRef') ||
363 $options->{type_constraint}->is_a_type_of('HashRef'))
364 || $class->throw_error("You cannot auto-dereference anything other than a ArrayRef or HashRef on attribute ($name)", data => $options);
367 if (exists $options->{lazy_build} && $options->{lazy_build} == 1) {
368 $class->throw_error("You can not use lazy_build and default for the same attribute ($name)", data => $options)
369 if exists $options->{default};
370 $options->{lazy} = 1;
371 $options->{builder} ||= "_build_${name}";
373 $options->{clearer} ||= "_clear${name}";
374 $options->{predicate} ||= "_has${name}";
377 $options->{clearer} ||= "clear_${name}";
378 $options->{predicate} ||= "has_${name}";
382 if (exists $options->{lazy} && $options->{lazy}) {
383 (exists $options->{default} || defined $options->{builder} )
384 || $class->throw_error("You cannot have lazy attribute ($name) without specifying a default value for it", data => $options);
387 if ( $options->{required} && !( ( !exists $options->{init_arg} || defined $options->{init_arg} ) || exists $options->{default} || defined $options->{builder} ) ) {
388 $class->throw_error("You cannot have a required attribute ($name) without a default, builder, or an init_arg", data => $options);
393 sub initialize_instance_slot {
394 my ($self, $meta_instance, $instance, $params) = @_;
395 my $init_arg = $self->init_arg();
396 # try to fetch the init arg from the %params ...
400 if ( defined($init_arg) and exists $params->{$init_arg}) {
401 $val = $params->{$init_arg};
405 # skip it if it's lazy
406 return if $self->is_lazy;
407 # and die if it's required and doesn't have a default value
408 $self->throw_error("Attribute (" . $self->name . ") is required", object => $instance, data => $params)
409 if $self->is_required && !$self->has_default && !$self->has_builder;
411 # if nothing was in the %params, we can use the
412 # attribute's default value (if it has one)
413 if ($self->has_default) {
414 $val = $self->default($instance);
417 elsif ($self->has_builder) {
418 $val = $self->_call_builder($instance);
423 return unless $value_is_set;
425 $val = $self->_coerce_and_verify( $val, $instance );
427 $self->set_initial_value($instance, $val);
428 $meta_instance->weaken_slot_value($instance, $self->name)
429 if ref $val && $self->is_weak_ref;
433 my ( $self, $instance ) = @_;
435 my $builder = $self->builder();
437 return $instance->$builder()
438 if $instance->can( $self->builder );
440 $self->throw_error( blessed($instance)
441 . " does not support builder method '"
443 . "' for attribute '"
453 # this duplicates too much code from
454 # Class::MOP::Attribute, we need to
455 # refactor these bits eventually.
457 sub _set_initial_slot_value {
458 my ($self, $meta_instance, $instance, $value) = @_;
460 my $slot_name = $self->name;
462 return $meta_instance->set_slot_value($instance, $slot_name, $value)
463 unless $self->has_initializer;
465 my ($type_constraint, $can_coerce);
466 if ($self->has_type_constraint) {
467 $type_constraint = $self->type_constraint;
468 $can_coerce = ($self->should_coerce && $type_constraint->has_coercion);
472 my $val = $self->_coerce_and_verify( shift, $instance );;
474 $meta_instance->set_slot_value($instance, $slot_name, $val);
477 my $initializer = $self->initializer;
479 # most things will just want to set a value, so make it first arg
480 $instance->$initializer($value, $callback, $self);
484 my ($self, $instance, @args) = @_;
485 my $value = $args[0];
487 my $attr_name = $self->name;
489 if ($self->is_required and not @args) {
490 $self->throw_error("Attribute ($attr_name) is required", object => $instance);
493 $value = $self->_coerce_and_verify( $value, $instance );
495 my $meta_instance = Class::MOP::Class->initialize(blessed($instance))
498 $meta_instance->set_slot_value($instance, $attr_name, $value);
500 if (ref $value && $self->is_weak_ref) {
501 $meta_instance->weaken_slot_value($instance, $attr_name);
504 if ($self->has_trigger) {
505 $self->trigger->($instance, $value);
510 my ($self, $instance) = @_;
512 if ($self->is_lazy) {
513 unless ($self->has_value($instance)) {
515 if ($self->has_default) {
516 $value = $self->default($instance);
517 } elsif ( $self->has_builder ) {
518 $value = $self->_call_builder($instance);
521 $value = $self->_coerce_and_verify( $value, $instance );
523 $self->set_initial_value($instance, $value);
527 if ($self->should_auto_deref) {
529 my $type_constraint = $self->type_constraint;
531 if ($type_constraint->is_a_type_of('ArrayRef')) {
532 my $rv = $self->SUPER::get_value($instance);
533 return unless defined $rv;
534 return wantarray ? @{ $rv } : $rv;
536 elsif ($type_constraint->is_a_type_of('HashRef')) {
537 my $rv = $self->SUPER::get_value($instance);
538 return unless defined $rv;
539 return wantarray ? %{ $rv } : $rv;
542 $self->throw_error("Can not auto de-reference the type constraint '" . $type_constraint->name . "'", object => $instance, type_constraint => $type_constraint);
548 return $self->SUPER::get_value($instance);
552 ## installing accessors
554 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
556 sub install_accessors {
558 $self->SUPER::install_accessors(@_);
559 $self->install_delegation if $self->has_handles;
561 @{ $self->associated_methods }
562 || ($self->_is_metadata || '') eq 'bare'
565 'Attribute (' . $self->name . ') of class '
566 . $self->associated_class->name
567 . ' has no associated methods'
568 . ' (did you mean to provide an "is" argument?)'
575 sub _process_accessors {
577 my ($type, $accessor, $generate_as_inline_methods) = @_;
578 $accessor = (keys %$accessor)[0] if (ref($accessor)||'') eq 'HASH';
579 my $method = $self->associated_class->get_method($accessor);
580 if ($method && !$method->isa('Class::MOP::Method::Accessor')
581 && (!$self->definition_context
582 || $method->package_name eq $self->definition_context->{package})) {
584 "You cannot overwrite a locally defined method ($accessor) with "
588 $self->SUPER::_process_accessors(@_);
591 sub remove_accessors {
593 $self->SUPER::remove_accessors(@_);
594 $self->remove_delegation if $self->has_handles;
598 sub install_delegation {
602 # Here we canonicalize the 'handles' option
603 # this will sort out any details and always
604 # return an hash of methods which we want
605 # to delagate to, see that method for details
606 my %handles = $self->_canonicalize_handles;
609 # install the delegation ...
610 my $associated_class = $self->associated_class;
611 foreach my $handle (keys %handles) {
612 my $method_to_call = $handles{$handle};
613 my $class_name = $associated_class->name;
614 my $name = "${class_name}::${handle}";
616 (!$associated_class->has_method($handle))
617 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
620 # handles is not allowed to delegate
621 # any of these methods, as they will
622 # override the ones in your class, which
623 # is almost certainly not what you want.
625 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
626 #cluck("Not delegating method '$handle' because it is a core method") and
627 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
629 my $method = $self->_make_delegation_method($handle, $method_to_call);
631 $self->associated_class->add_method($method->name, $method);
632 $self->associate_method($method);
636 sub remove_delegation {
638 my %handles = $self->_canonicalize_handles;
639 my $associated_class = $self->associated_class;
640 foreach my $handle (keys %handles) {
641 $self->associated_class->remove_method($handle);
645 # private methods to help delegation ...
647 sub _canonicalize_handles {
649 my $handles = $self->handles;
650 if (my $handle_type = ref($handles)) {
651 if ($handle_type eq 'HASH') {
654 elsif ($handle_type eq 'ARRAY') {
655 return map { $_ => $_ } @{$handles};
657 elsif ($handle_type eq 'Regexp') {
658 ($self->has_type_constraint)
659 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
660 return map { ($_ => $_) }
661 grep { /$handles/ } $self->_get_delegate_method_list;
663 elsif ($handle_type eq 'CODE') {
664 return $handles->($self, $self->_find_delegate_metaclass);
666 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::DuckType')) {
667 return map { $_ => $_ } @{ $handles->methods };
670 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
674 Class::MOP::load_class($handles);
675 my $role_meta = Class::MOP::class_of($handles);
677 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
678 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because its metaclass is not a Moose::Meta::Role", data => $handles);
680 return map { $_ => $_ } (
681 $role_meta->get_method_list,
682 map { $_->name } $role_meta->get_required_method_list,
687 sub _find_delegate_metaclass {
689 if (my $class = $self->_isa_metadata) {
690 # we might be dealing with a non-Moose class,
691 # and need to make our own metaclass. if there's
692 # already a metaclass, it will be returned
693 return Moose::Meta::Class->initialize($class);
695 elsif (my $role = $self->_does_metadata) {
696 return Class::MOP::class_of($role);
699 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
703 sub _get_delegate_method_list {
705 my $meta = $self->_find_delegate_metaclass;
706 if ($meta->isa('Class::MOP::Class')) {
707 return map { $_->name } # NOTE: !never! delegate &meta
708 grep { $_->package_name ne 'Moose::Object' && $_->name ne 'meta' }
709 $meta->get_all_methods;
711 elsif ($meta->isa('Moose::Meta::Role')) {
712 return $meta->get_method_list;
715 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
719 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
721 sub _make_delegation_method {
722 my ( $self, $handle_name, $method_to_call ) = @_;
726 $method_body = $method_to_call
727 if 'CODE' eq ref($method_to_call);
729 return $self->delegation_metaclass->new(
730 name => $handle_name,
731 package_name => $self->associated_class->name,
733 delegate_to_method => $method_to_call,
737 sub _coerce_and_verify {
740 my $instance = shift;
742 return $val unless $self->has_type_constraint;
744 my $type_constraint = $self->type_constraint;
745 if ($self->should_coerce && $type_constraint->has_coercion) {
746 $val = $type_constraint->coerce($val);
749 $self->verify_against_type_constraint($val, instance => $instance);
754 sub verify_against_type_constraint {
758 return 1 if !$self->has_type_constraint;
760 my $type_constraint = $self->type_constraint;
762 $type_constraint->check($val)
763 || $self->throw_error("Attribute ("
765 . ") does not pass the type constraint because: "
766 . $type_constraint->get_message($val), data => $val, @_);
769 package Moose::Meta::Attribute::Custom::Moose;
770 sub register_implementation { 'Moose::Meta::Attribute' }
780 Moose::Meta::Attribute - The Moose attribute metaclass
784 This class is a subclass of L<Class::MOP::Attribute> that provides
785 additional Moose-specific functionality.
787 To really understand this class, you will need to start with the
788 L<Class::MOP::Attribute> documentation. This class can be understood
789 as a set of additional features on top of the basic feature provided
790 by that parent class.
794 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
798 Many of the documented below override methods in
799 L<Class::MOP::Attribute> and add Moose specific features.
805 =item B<< Moose::Meta::Attribute->new(%options) >>
807 This method overrides the L<Class::MOP::Attribute> constructor.
809 Many of the options below are described in more detail in the
810 L<Moose::Manual::Attributes> document.
812 It adds the following options to the constructor:
816 =item * is => 'ro', 'rw', 'bare'
818 This provides a shorthand for specifying the C<reader>, C<writer>, or
819 C<accessor> names. If the attribute is read-only ('ro') then it will
820 have a C<reader> method with the same attribute as the name.
822 If it is read-write ('rw') then it will have an C<accessor> method
823 with the same name. If you provide an explicit C<writer> for a
824 read-write attribute, then you will have a C<reader> with the same
825 name as the attribute, and a C<writer> with the name you provided.
827 Use 'bare' when you are deliberately not installing any methods
828 (accessor, reader, etc.) associated with this attribute; otherwise,
829 Moose will issue a deprecation warning when this attribute is added to a
834 This option accepts a type. The type can be a string, which should be
835 a type name. If the type name is unknown, it is assumed to be a class
838 This option can also accept a L<Moose::Meta::TypeConstraint> object.
840 If you I<also> provide a C<does> option, then your C<isa> option must
841 be a class name, and that class must do the role specified with
844 =item * does => $role
846 This is short-hand for saying that the attribute's type must be an
847 object which does the named role.
849 =item * coerce => $bool
851 This option is only valid for objects with a type constraint
852 (C<isa>). If this is true, then coercions will be applied whenever
853 this attribute is set.
855 You can make both this and the C<weak_ref> option true.
857 =item * trigger => $sub
859 This option accepts a subroutine reference, which will be called after
860 the attribute is set.
862 =item * required => $bool
864 An attribute which is required must be provided to the constructor. An
865 attribute which is required can also have a C<default> or C<builder>,
866 which will satisfy its required-ness.
868 A required attribute must have a C<default>, C<builder> or a
869 non-C<undef> C<init_arg>
871 =item * lazy => $bool
873 A lazy attribute must have a C<default> or C<builder>. When an
874 attribute is lazy, the default value will not be calculated until the
877 =item * weak_ref => $bool
879 If this is true, the attribute's value will be stored as a weak
882 =item * auto_deref => $bool
884 If this is true, then the reader will dereference the value when it is
885 called. The attribute must have a type constraint which defines the
886 attribute as an array or hash reference.
888 =item * lazy_build => $bool
890 Setting this to true makes the attribute lazy and provides a number of
898 is equivalent to this:
903 builder => '_build_size',
904 clearer => 'clear_size',
905 predicate => 'has_size',
908 =item * documentation
910 An arbitrary string that can be retrieved later by calling C<<
911 $attr->documentation >>.
915 =item B<< $attr->clone(%options) >>
917 This creates a new attribute based on attribute being cloned. You must
918 supply a C<name> option to provide a new name for the attribute.
920 The C<%options> can only specify options handled by
921 L<Class::MOP::Attribute>.
925 =head2 Value management
929 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
931 This method is used internally to initialize the attribute's slot in
932 the object C<$instance>.
934 This overrides the L<Class::MOP::Attribute> method to handle lazy
935 attributes, weak references, and type constraints.
941 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
946 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
948 Before setting the value, a check is made on the type constraint of
949 the attribute, if it has one, to see if the value passes it. If the
950 value fails to pass, the set operation dies with a L<throw_error>.
952 Any coercion to convert values is done before checking the type constraint.
954 To check a value against a type constraint before setting it, fetch the
955 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
956 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
957 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
962 =head2 Attribute Accessor generation
966 =item B<< $attr->install_accessors >>
968 This method overrides the parent to also install delegation methods.
970 If, after installing all methods, the attribute object has no associated
971 methods, it throws an error unless C<< is => 'bare' >> was passed to the
972 attribute constructor. (Trying to add an attribute that has no associated
973 methods is almost always an error.)
975 =item B<< $attr->remove_accessors >>
977 This method overrides the parent to also remove delegation methods.
979 =item B<< $attr->install_delegation >>
981 This method adds its delegation methods to the attribute's associated
982 class, if it has any to add.
984 =item B<< $attr->remove_delegation >>
986 This method remove its delegation methods from the attribute's
989 =item B<< $attr->accessor_metaclass >>
991 Returns the accessor metaclass name, which defaults to
992 L<Moose::Meta::Method::Accessor>.
994 =item B<< $attr->delegation_metaclass >>
996 Returns the delegation metaclass name, which defaults to
997 L<Moose::Meta::Method::Delegation>.
1001 =head2 Additional Moose features
1003 These methods are not found in the superclass. They support features
1008 =item B<< $attr->does($role) >>
1010 This indicates whether the I<attribute itself> does the given
1011 role. The role can be given as a full class name, or as a resolvable
1014 Note that this checks the attribute itself, not its type constraint,
1015 so it is checking the attribute's metaclass and any traits applied to
1018 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
1020 This is an alternate constructor that handles the C<metaclass> and
1023 Effectively, this method is a factory that finds or creates the
1024 appropriate class for the given C<metaclass> and/or C<traits>.
1026 Once it has the appropriate class, it will call C<< $class->new($name,
1027 %options) >> on that class.
1029 =item B<< $attr->clone_and_inherit_options(%options) >>
1031 This method supports the C<has '+foo'> feature. It does various bits
1032 of processing on the supplied C<%options> before ultimately calling
1033 the C<clone> method.
1035 One of its main tasks is to make sure that the C<%options> provided
1036 only includes the options returned by the
1037 C<legal_options_for_inheritance> method.
1039 =item B<< $attr->legal_options_for_inheritance >>
1041 This returns a whitelist of options that can be overridden in a
1042 subclass's attribute definition.
1044 This exists to allow a custom metaclass to change or add to the list
1045 of options which can be changed.
1047 =item B<< $attr->type_constraint >>
1049 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1052 =item B<< $attr->has_type_constraint >>
1054 Returns true if this attribute has a type constraint.
1056 =item B<< $attr->verify_against_type_constraint($value) >>
1058 Given a value, this method returns true if the value is valid for the
1059 attribute's type constraint. If the value is not valid, it throws an
1062 =item B<< $attr->handles >>
1064 This returns the value of the C<handles> option passed to the
1067 =item B<< $attr->has_handles >>
1069 Returns true if this attribute performs delegation.
1071 =item B<< $attr->is_weak_ref >>
1073 Returns true if this attribute stores its value as a weak reference.
1075 =item B<< $attr->is_required >>
1077 Returns true if this attribute is required to have a value.
1079 =item B<< $attr->is_lazy >>
1081 Returns true if this attribute is lazy.
1083 =item B<< $attr->is_lazy_build >>
1085 Returns true if the C<lazy_build> option was true when passed to the
1088 =item B<< $attr->should_coerce >>
1090 Returns true if the C<coerce> option passed to the constructor was
1093 =item B<< $attr->should_auto_deref >>
1095 Returns true if the C<auto_deref> option passed to the constructor was
1098 =item B<< $attr->trigger >>
1100 This is the subroutine reference that was in the C<trigger> option
1101 passed to the constructor, if any.
1103 =item B<< $attr->has_trigger >>
1105 Returns true if this attribute has a trigger set.
1107 =item B<< $attr->documentation >>
1109 Returns the value that was in the C<documentation> option passed to
1110 the constructor, if any.
1112 =item B<< $attr->has_documentation >>
1114 Returns true if this attribute has any documentation.
1116 =item B<< $attr->applied_traits >>
1118 This returns an array reference of all the traits which were applied
1119 to this attribute. If none were applied, this returns C<undef>.
1121 =item B<< $attr->has_applied_traits >>
1123 Returns true if this attribute has any traits applied.
1129 All complex software has bugs lurking in it, and this module is no
1130 exception. If you find a bug please either email me, or add the bug
1135 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1137 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1139 =head1 COPYRIGHT AND LICENSE
1141 Copyright 2006-2009 by Infinity Interactive, Inc.
1143 L<http://www.iinteractive.com>
1145 This library is free software; you can redistribute it and/or modify
1146 it under the same terms as Perl itself.