2 package Moose::Meta::Attribute;
7 use Scalar::Util 'blessed', 'weaken';
10 our $VERSION = '0.88';
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))
499 if ( $self->has_trigger && $self->has_value($instance) ) {
500 @old = $self->get_value($instance, 'for trigger');
503 $meta_instance->set_slot_value($instance, $attr_name, $value);
505 if (ref $value && $self->is_weak_ref) {
506 $meta_instance->weaken_slot_value($instance, $attr_name);
509 if ($self->has_trigger) {
510 $self->trigger->($instance, $value, @old);
515 my ($self, $instance, $for_trigger) = @_;
517 if ($self->is_lazy) {
518 unless ($self->has_value($instance)) {
520 if ($self->has_default) {
521 $value = $self->default($instance);
522 } elsif ( $self->has_builder ) {
523 $value = $self->_call_builder($instance);
526 $value = $self->_coerce_and_verify( $value, $instance );
528 $self->set_initial_value($instance, $value);
532 if ( $self->should_auto_deref && ! $for_trigger ) {
534 my $type_constraint = $self->type_constraint;
536 if ($type_constraint->is_a_type_of('ArrayRef')) {
537 my $rv = $self->SUPER::get_value($instance);
538 return unless defined $rv;
539 return wantarray ? @{ $rv } : $rv;
541 elsif ($type_constraint->is_a_type_of('HashRef')) {
542 my $rv = $self->SUPER::get_value($instance);
543 return unless defined $rv;
544 return wantarray ? %{ $rv } : $rv;
547 $self->throw_error("Can not auto de-reference the type constraint '" . $type_constraint->name . "'", object => $instance, type_constraint => $type_constraint);
553 return $self->SUPER::get_value($instance);
557 ## installing accessors
559 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
561 sub install_accessors {
563 $self->SUPER::install_accessors(@_);
564 $self->install_delegation if $self->has_handles;
568 sub _check_associated_methods {
571 @{ $self->associated_methods }
572 || ($self->_is_metadata || '') eq 'bare'
575 'Attribute (' . $self->name . ') of class '
576 . $self->associated_class->name
577 . ' has no associated methods'
578 . ' (did you mean to provide an "is" argument?)'
584 sub _process_accessors {
586 my ($type, $accessor, $generate_as_inline_methods) = @_;
587 $accessor = (keys %$accessor)[0] if (ref($accessor)||'') eq 'HASH';
588 my $method = $self->associated_class->get_method($accessor);
589 if ($method && !$method->isa('Class::MOP::Method::Accessor')
590 && (!$self->definition_context
591 || $method->package_name eq $self->definition_context->{package})) {
593 "You are overwriting a locally defined method ($accessor) with "
597 $self->SUPER::_process_accessors(@_);
600 sub remove_accessors {
602 $self->SUPER::remove_accessors(@_);
603 $self->remove_delegation if $self->has_handles;
607 sub install_delegation {
611 # Here we canonicalize the 'handles' option
612 # this will sort out any details and always
613 # return an hash of methods which we want
614 # to delagate to, see that method for details
615 my %handles = $self->_canonicalize_handles;
618 # install the delegation ...
619 my $associated_class = $self->associated_class;
620 foreach my $handle (keys %handles) {
621 my $method_to_call = $handles{$handle};
622 my $class_name = $associated_class->name;
623 my $name = "${class_name}::${handle}";
625 (!$associated_class->has_method($handle))
626 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
629 # handles is not allowed to delegate
630 # any of these methods, as they will
631 # override the ones in your class, which
632 # is almost certainly not what you want.
634 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
635 #cluck("Not delegating method '$handle' because it is a core method") and
636 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
638 my $method = $self->_make_delegation_method($handle, $method_to_call);
640 $self->associated_class->add_method($method->name, $method);
641 $self->associate_method($method);
645 sub remove_delegation {
647 my %handles = $self->_canonicalize_handles;
648 my $associated_class = $self->associated_class;
649 foreach my $handle (keys %handles) {
650 $self->associated_class->remove_method($handle);
654 # private methods to help delegation ...
656 sub _canonicalize_handles {
658 my $handles = $self->handles;
659 if (my $handle_type = ref($handles)) {
660 if ($handle_type eq 'HASH') {
663 elsif ($handle_type eq 'ARRAY') {
664 return map { $_ => $_ } @{$handles};
666 elsif ($handle_type eq 'Regexp') {
667 ($self->has_type_constraint)
668 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
669 return map { ($_ => $_) }
670 grep { /$handles/ } $self->_get_delegate_method_list;
672 elsif ($handle_type eq 'CODE') {
673 return $handles->($self, $self->_find_delegate_metaclass);
675 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::DuckType')) {
676 return map { $_ => $_ } @{ $handles->methods };
679 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
683 Class::MOP::load_class($handles);
684 my $role_meta = Class::MOP::class_of($handles);
686 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
687 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because its metaclass is not a Moose::Meta::Role", data => $handles);
689 return map { $_ => $_ } (
690 $role_meta->get_method_list,
691 map { $_->name } $role_meta->get_required_method_list,
696 sub _find_delegate_metaclass {
698 if (my $class = $self->_isa_metadata) {
699 # we might be dealing with a non-Moose class,
700 # and need to make our own metaclass. if there's
701 # already a metaclass, it will be returned
702 return Moose::Meta::Class->initialize($class);
704 elsif (my $role = $self->_does_metadata) {
705 return Class::MOP::class_of($role);
708 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
712 sub _get_delegate_method_list {
714 my $meta = $self->_find_delegate_metaclass;
715 if ($meta->isa('Class::MOP::Class')) {
716 return map { $_->name } # NOTE: !never! delegate &meta
717 grep { $_->package_name ne 'Moose::Object' && $_->name ne 'meta' }
718 $meta->get_all_methods;
720 elsif ($meta->isa('Moose::Meta::Role')) {
721 return $meta->get_method_list;
724 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
728 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
730 sub _make_delegation_method {
731 my ( $self, $handle_name, $method_to_call ) = @_;
735 $method_body = $method_to_call
736 if 'CODE' eq ref($method_to_call);
738 return $self->delegation_metaclass->new(
739 name => $handle_name,
740 package_name => $self->associated_class->name,
742 delegate_to_method => $method_to_call,
746 sub _coerce_and_verify {
749 my $instance = shift;
751 return $val unless $self->has_type_constraint;
753 my $type_constraint = $self->type_constraint;
754 if ($self->should_coerce && $type_constraint->has_coercion) {
755 $val = $type_constraint->coerce($val);
758 $self->verify_against_type_constraint($val, instance => $instance);
763 sub verify_against_type_constraint {
767 return 1 if !$self->has_type_constraint;
769 my $type_constraint = $self->type_constraint;
771 $type_constraint->check($val)
772 || $self->throw_error("Attribute ("
774 . ") does not pass the type constraint because: "
775 . $type_constraint->get_message($val), data => $val, @_);
778 package Moose::Meta::Attribute::Custom::Moose;
779 sub register_implementation { 'Moose::Meta::Attribute' }
789 Moose::Meta::Attribute - The Moose attribute metaclass
793 This class is a subclass of L<Class::MOP::Attribute> that provides
794 additional Moose-specific functionality.
796 To really understand this class, you will need to start with the
797 L<Class::MOP::Attribute> documentation. This class can be understood
798 as a set of additional features on top of the basic feature provided
799 by that parent class.
803 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
807 Many of the documented below override methods in
808 L<Class::MOP::Attribute> and add Moose specific features.
814 =item B<< Moose::Meta::Attribute->new(%options) >>
816 This method overrides the L<Class::MOP::Attribute> constructor.
818 Many of the options below are described in more detail in the
819 L<Moose::Manual::Attributes> document.
821 It adds the following options to the constructor:
825 =item * is => 'ro', 'rw', 'bare'
827 This provides a shorthand for specifying the C<reader>, C<writer>, or
828 C<accessor> names. If the attribute is read-only ('ro') then it will
829 have a C<reader> method with the same attribute as the name.
831 If it is read-write ('rw') then it will have an C<accessor> method
832 with the same name. If you provide an explicit C<writer> for a
833 read-write attribute, then you will have a C<reader> with the same
834 name as the attribute, and a C<writer> with the name you provided.
836 Use 'bare' when you are deliberately not installing any methods
837 (accessor, reader, etc.) associated with this attribute; otherwise,
838 Moose will issue a deprecation warning when this attribute is added to a
843 This option accepts a type. The type can be a string, which should be
844 a type name. If the type name is unknown, it is assumed to be a class
847 This option can also accept a L<Moose::Meta::TypeConstraint> object.
849 If you I<also> provide a C<does> option, then your C<isa> option must
850 be a class name, and that class must do the role specified with
853 =item * does => $role
855 This is short-hand for saying that the attribute's type must be an
856 object which does the named role.
858 =item * coerce => $bool
860 This option is only valid for objects with a type constraint
861 (C<isa>). If this is true, then coercions will be applied whenever
862 this attribute is set.
864 You can make both this and the C<weak_ref> option true.
866 =item * trigger => $sub
868 This option accepts a subroutine reference, which will be called after
869 the attribute is set.
871 =item * required => $bool
873 An attribute which is required must be provided to the constructor. An
874 attribute which is required can also have a C<default> or C<builder>,
875 which will satisfy its required-ness.
877 A required attribute must have a C<default>, C<builder> or a
878 non-C<undef> C<init_arg>
880 =item * lazy => $bool
882 A lazy attribute must have a C<default> or C<builder>. When an
883 attribute is lazy, the default value will not be calculated until the
886 =item * weak_ref => $bool
888 If this is true, the attribute's value will be stored as a weak
891 =item * auto_deref => $bool
893 If this is true, then the reader will dereference the value when it is
894 called. The attribute must have a type constraint which defines the
895 attribute as an array or hash reference.
897 =item * lazy_build => $bool
899 Setting this to true makes the attribute lazy and provides a number of
907 is equivalent to this:
912 builder => '_build_size',
913 clearer => 'clear_size',
914 predicate => 'has_size',
917 =item * documentation
919 An arbitrary string that can be retrieved later by calling C<<
920 $attr->documentation >>.
924 =item B<< $attr->clone(%options) >>
926 This creates a new attribute based on attribute being cloned. You must
927 supply a C<name> option to provide a new name for the attribute.
929 The C<%options> can only specify options handled by
930 L<Class::MOP::Attribute>.
934 =head2 Value management
938 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
940 This method is used internally to initialize the attribute's slot in
941 the object C<$instance>.
943 This overrides the L<Class::MOP::Attribute> method to handle lazy
944 attributes, weak references, and type constraints.
950 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
955 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
957 Before setting the value, a check is made on the type constraint of
958 the attribute, if it has one, to see if the value passes it. If the
959 value fails to pass, the set operation dies with a L<throw_error>.
961 Any coercion to convert values is done before checking the type constraint.
963 To check a value against a type constraint before setting it, fetch the
964 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
965 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
966 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
971 =head2 Attribute Accessor generation
975 =item B<< $attr->install_accessors >>
977 This method overrides the parent to also install delegation methods.
979 If, after installing all methods, the attribute object has no associated
980 methods, it throws an error unless C<< is => 'bare' >> was passed to the
981 attribute constructor. (Trying to add an attribute that has no associated
982 methods is almost always an error.)
984 =item B<< $attr->remove_accessors >>
986 This method overrides the parent to also remove delegation methods.
988 =item B<< $attr->install_delegation >>
990 This method adds its delegation methods to the attribute's associated
991 class, if it has any to add.
993 =item B<< $attr->remove_delegation >>
995 This method remove its delegation methods from the attribute's
998 =item B<< $attr->accessor_metaclass >>
1000 Returns the accessor metaclass name, which defaults to
1001 L<Moose::Meta::Method::Accessor>.
1003 =item B<< $attr->delegation_metaclass >>
1005 Returns the delegation metaclass name, which defaults to
1006 L<Moose::Meta::Method::Delegation>.
1010 =head2 Additional Moose features
1012 These methods are not found in the superclass. They support features
1017 =item B<< $attr->does($role) >>
1019 This indicates whether the I<attribute itself> does the given
1020 role. The role can be given as a full class name, or as a resolvable
1023 Note that this checks the attribute itself, not its type constraint,
1024 so it is checking the attribute's metaclass and any traits applied to
1027 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
1029 This is an alternate constructor that handles the C<metaclass> and
1032 Effectively, this method is a factory that finds or creates the
1033 appropriate class for the given C<metaclass> and/or C<traits>.
1035 Once it has the appropriate class, it will call C<< $class->new($name,
1036 %options) >> on that class.
1038 =item B<< $attr->clone_and_inherit_options(%options) >>
1040 This method supports the C<has '+foo'> feature. It does various bits
1041 of processing on the supplied C<%options> before ultimately calling
1042 the C<clone> method.
1044 One of its main tasks is to make sure that the C<%options> provided
1045 only includes the options returned by the
1046 C<legal_options_for_inheritance> method.
1048 =item B<< $attr->legal_options_for_inheritance >>
1050 This returns a whitelist of options that can be overridden in a
1051 subclass's attribute definition.
1053 This exists to allow a custom metaclass to change or add to the list
1054 of options which can be changed.
1056 =item B<< $attr->type_constraint >>
1058 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1061 =item B<< $attr->has_type_constraint >>
1063 Returns true if this attribute has a type constraint.
1065 =item B<< $attr->verify_against_type_constraint($value) >>
1067 Given a value, this method returns true if the value is valid for the
1068 attribute's type constraint. If the value is not valid, it throws an
1071 =item B<< $attr->handles >>
1073 This returns the value of the C<handles> option passed to the
1076 =item B<< $attr->has_handles >>
1078 Returns true if this attribute performs delegation.
1080 =item B<< $attr->is_weak_ref >>
1082 Returns true if this attribute stores its value as a weak reference.
1084 =item B<< $attr->is_required >>
1086 Returns true if this attribute is required to have a value.
1088 =item B<< $attr->is_lazy >>
1090 Returns true if this attribute is lazy.
1092 =item B<< $attr->is_lazy_build >>
1094 Returns true if the C<lazy_build> option was true when passed to the
1097 =item B<< $attr->should_coerce >>
1099 Returns true if the C<coerce> option passed to the constructor was
1102 =item B<< $attr->should_auto_deref >>
1104 Returns true if the C<auto_deref> option passed to the constructor was
1107 =item B<< $attr->trigger >>
1109 This is the subroutine reference that was in the C<trigger> option
1110 passed to the constructor, if any.
1112 =item B<< $attr->has_trigger >>
1114 Returns true if this attribute has a trigger set.
1116 =item B<< $attr->documentation >>
1118 Returns the value that was in the C<documentation> option passed to
1119 the constructor, if any.
1121 =item B<< $attr->has_documentation >>
1123 Returns true if this attribute has any documentation.
1125 =item B<< $attr->applied_traits >>
1127 This returns an array reference of all the traits which were applied
1128 to this attribute. If none were applied, this returns C<undef>.
1130 =item B<< $attr->has_applied_traits >>
1132 Returns true if this attribute has any traits applied.
1138 All complex software has bugs lurking in it, and this module is no
1139 exception. If you find a bug please either email me, or add the bug
1144 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1146 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1148 =head1 COPYRIGHT AND LICENSE
1150 Copyright 2006-2009 by Infinity Interactive, Inc.
1152 L<http://www.iinteractive.com>
1154 This library is free software; you can redistribute it and/or modify
1155 it under the same terms as Perl itself.