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))
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;
563 sub _check_associated_methods {
566 @{ $self->associated_methods }
567 || ($self->_is_metadata || '') eq 'bare'
570 'Attribute (' . $self->name . ') of class '
571 . $self->associated_class->name
572 . ' has no associated methods'
573 . ' (did you mean to provide an "is" argument?)'
579 sub _process_accessors {
581 my ($type, $accessor, $generate_as_inline_methods) = @_;
582 $accessor = (keys %$accessor)[0] if (ref($accessor)||'') eq 'HASH';
583 my $method = $self->associated_class->get_method($accessor);
584 if ($method && !$method->isa('Class::MOP::Method::Accessor')
585 && (!$self->definition_context
586 || $method->package_name eq $self->definition_context->{package})) {
588 "You are overwriting a locally defined method ($accessor) with "
592 $self->SUPER::_process_accessors(@_);
595 sub remove_accessors {
597 $self->SUPER::remove_accessors(@_);
598 $self->remove_delegation if $self->has_handles;
602 sub install_delegation {
606 # Here we canonicalize the 'handles' option
607 # this will sort out any details and always
608 # return an hash of methods which we want
609 # to delagate to, see that method for details
610 my %handles = $self->_canonicalize_handles;
613 # install the delegation ...
614 my $associated_class = $self->associated_class;
615 foreach my $handle (keys %handles) {
616 my $method_to_call = $handles{$handle};
617 my $class_name = $associated_class->name;
618 my $name = "${class_name}::${handle}";
620 (!$associated_class->has_method($handle))
621 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
624 # handles is not allowed to delegate
625 # any of these methods, as they will
626 # override the ones in your class, which
627 # is almost certainly not what you want.
629 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
630 #cluck("Not delegating method '$handle' because it is a core method") and
631 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
633 my $method = $self->_make_delegation_method($handle, $method_to_call);
635 $self->associated_class->add_method($method->name, $method);
636 $self->associate_method($method);
640 sub remove_delegation {
642 my %handles = $self->_canonicalize_handles;
643 my $associated_class = $self->associated_class;
644 foreach my $handle (keys %handles) {
645 $self->associated_class->remove_method($handle);
649 # private methods to help delegation ...
651 sub _canonicalize_handles {
653 my $handles = $self->handles;
654 if (my $handle_type = ref($handles)) {
655 if ($handle_type eq 'HASH') {
658 elsif ($handle_type eq 'ARRAY') {
659 return map { $_ => $_ } @{$handles};
661 elsif ($handle_type eq 'Regexp') {
662 ($self->has_type_constraint)
663 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
664 return map { ($_ => $_) }
665 grep { /$handles/ } $self->_get_delegate_method_list;
667 elsif ($handle_type eq 'CODE') {
668 return $handles->($self, $self->_find_delegate_metaclass);
670 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::DuckType')) {
671 return map { $_ => $_ } @{ $handles->methods };
674 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
678 Class::MOP::load_class($handles);
679 my $role_meta = Class::MOP::class_of($handles);
681 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
682 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because its metaclass is not a Moose::Meta::Role", data => $handles);
684 return map { $_ => $_ } (
685 $role_meta->get_method_list,
686 map { $_->name } $role_meta->get_required_method_list,
691 sub _find_delegate_metaclass {
693 if (my $class = $self->_isa_metadata) {
694 # we might be dealing with a non-Moose class,
695 # and need to make our own metaclass. if there's
696 # already a metaclass, it will be returned
697 return Moose::Meta::Class->initialize($class);
699 elsif (my $role = $self->_does_metadata) {
700 return Class::MOP::class_of($role);
703 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
707 sub _get_delegate_method_list {
709 my $meta = $self->_find_delegate_metaclass;
710 if ($meta->isa('Class::MOP::Class')) {
711 return map { $_->name } # NOTE: !never! delegate &meta
712 grep { $_->package_name ne 'Moose::Object' && $_->name ne 'meta' }
713 $meta->get_all_methods;
715 elsif ($meta->isa('Moose::Meta::Role')) {
716 return $meta->get_method_list;
719 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
723 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
725 sub _make_delegation_method {
726 my ( $self, $handle_name, $method_to_call ) = @_;
730 $method_body = $method_to_call
731 if 'CODE' eq ref($method_to_call);
733 return $self->delegation_metaclass->new(
734 name => $handle_name,
735 package_name => $self->associated_class->name,
737 delegate_to_method => $method_to_call,
741 sub _coerce_and_verify {
744 my $instance = shift;
746 return $val unless $self->has_type_constraint;
748 my $type_constraint = $self->type_constraint;
749 if ($self->should_coerce && $type_constraint->has_coercion) {
750 $val = $type_constraint->coerce($val);
753 $self->verify_against_type_constraint($val, instance => $instance);
758 sub verify_against_type_constraint {
762 return 1 if !$self->has_type_constraint;
764 my $type_constraint = $self->type_constraint;
766 $type_constraint->check($val)
767 || $self->throw_error("Attribute ("
769 . ") does not pass the type constraint because: "
770 . $type_constraint->get_message($val), data => $val, @_);
773 package Moose::Meta::Attribute::Custom::Moose;
774 sub register_implementation { 'Moose::Meta::Attribute' }
784 Moose::Meta::Attribute - The Moose attribute metaclass
788 This class is a subclass of L<Class::MOP::Attribute> that provides
789 additional Moose-specific functionality.
791 To really understand this class, you will need to start with the
792 L<Class::MOP::Attribute> documentation. This class can be understood
793 as a set of additional features on top of the basic feature provided
794 by that parent class.
798 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
802 Many of the documented below override methods in
803 L<Class::MOP::Attribute> and add Moose specific features.
809 =item B<< Moose::Meta::Attribute->new(%options) >>
811 This method overrides the L<Class::MOP::Attribute> constructor.
813 Many of the options below are described in more detail in the
814 L<Moose::Manual::Attributes> document.
816 It adds the following options to the constructor:
820 =item * is => 'ro', 'rw', 'bare'
822 This provides a shorthand for specifying the C<reader>, C<writer>, or
823 C<accessor> names. If the attribute is read-only ('ro') then it will
824 have a C<reader> method with the same attribute as the name.
826 If it is read-write ('rw') then it will have an C<accessor> method
827 with the same name. If you provide an explicit C<writer> for a
828 read-write attribute, then you will have a C<reader> with the same
829 name as the attribute, and a C<writer> with the name you provided.
831 Use 'bare' when you are deliberately not installing any methods
832 (accessor, reader, etc.) associated with this attribute; otherwise,
833 Moose will issue a deprecation warning when this attribute is added to a
838 This option accepts a type. The type can be a string, which should be
839 a type name. If the type name is unknown, it is assumed to be a class
842 This option can also accept a L<Moose::Meta::TypeConstraint> object.
844 If you I<also> provide a C<does> option, then your C<isa> option must
845 be a class name, and that class must do the role specified with
848 =item * does => $role
850 This is short-hand for saying that the attribute's type must be an
851 object which does the named role.
853 =item * coerce => $bool
855 This option is only valid for objects with a type constraint
856 (C<isa>). If this is true, then coercions will be applied whenever
857 this attribute is set.
859 You can make both this and the C<weak_ref> option true.
861 =item * trigger => $sub
863 This option accepts a subroutine reference, which will be called after
864 the attribute is set.
866 =item * required => $bool
868 An attribute which is required must be provided to the constructor. An
869 attribute which is required can also have a C<default> or C<builder>,
870 which will satisfy its required-ness.
872 A required attribute must have a C<default>, C<builder> or a
873 non-C<undef> C<init_arg>
875 =item * lazy => $bool
877 A lazy attribute must have a C<default> or C<builder>. When an
878 attribute is lazy, the default value will not be calculated until the
881 =item * weak_ref => $bool
883 If this is true, the attribute's value will be stored as a weak
886 =item * auto_deref => $bool
888 If this is true, then the reader will dereference the value when it is
889 called. The attribute must have a type constraint which defines the
890 attribute as an array or hash reference.
892 =item * lazy_build => $bool
894 Setting this to true makes the attribute lazy and provides a number of
902 is equivalent to this:
907 builder => '_build_size',
908 clearer => 'clear_size',
909 predicate => 'has_size',
912 =item * documentation
914 An arbitrary string that can be retrieved later by calling C<<
915 $attr->documentation >>.
919 =item B<< $attr->clone(%options) >>
921 This creates a new attribute based on attribute being cloned. You must
922 supply a C<name> option to provide a new name for the attribute.
924 The C<%options> can only specify options handled by
925 L<Class::MOP::Attribute>.
929 =head2 Value management
933 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
935 This method is used internally to initialize the attribute's slot in
936 the object C<$instance>.
938 This overrides the L<Class::MOP::Attribute> method to handle lazy
939 attributes, weak references, and type constraints.
945 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
950 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
952 Before setting the value, a check is made on the type constraint of
953 the attribute, if it has one, to see if the value passes it. If the
954 value fails to pass, the set operation dies with a L<throw_error>.
956 Any coercion to convert values is done before checking the type constraint.
958 To check a value against a type constraint before setting it, fetch the
959 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
960 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
961 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
966 =head2 Attribute Accessor generation
970 =item B<< $attr->install_accessors >>
972 This method overrides the parent to also install delegation methods.
974 If, after installing all methods, the attribute object has no associated
975 methods, it throws an error unless C<< is => 'bare' >> was passed to the
976 attribute constructor. (Trying to add an attribute that has no associated
977 methods is almost always an error.)
979 =item B<< $attr->remove_accessors >>
981 This method overrides the parent to also remove delegation methods.
983 =item B<< $attr->install_delegation >>
985 This method adds its delegation methods to the attribute's associated
986 class, if it has any to add.
988 =item B<< $attr->remove_delegation >>
990 This method remove its delegation methods from the attribute's
993 =item B<< $attr->accessor_metaclass >>
995 Returns the accessor metaclass name, which defaults to
996 L<Moose::Meta::Method::Accessor>.
998 =item B<< $attr->delegation_metaclass >>
1000 Returns the delegation metaclass name, which defaults to
1001 L<Moose::Meta::Method::Delegation>.
1005 =head2 Additional Moose features
1007 These methods are not found in the superclass. They support features
1012 =item B<< $attr->does($role) >>
1014 This indicates whether the I<attribute itself> does the given
1015 role. The role can be given as a full class name, or as a resolvable
1018 Note that this checks the attribute itself, not its type constraint,
1019 so it is checking the attribute's metaclass and any traits applied to
1022 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
1024 This is an alternate constructor that handles the C<metaclass> and
1027 Effectively, this method is a factory that finds or creates the
1028 appropriate class for the given C<metaclass> and/or C<traits>.
1030 Once it has the appropriate class, it will call C<< $class->new($name,
1031 %options) >> on that class.
1033 =item B<< $attr->clone_and_inherit_options(%options) >>
1035 This method supports the C<has '+foo'> feature. It does various bits
1036 of processing on the supplied C<%options> before ultimately calling
1037 the C<clone> method.
1039 One of its main tasks is to make sure that the C<%options> provided
1040 only includes the options returned by the
1041 C<legal_options_for_inheritance> method.
1043 =item B<< $attr->legal_options_for_inheritance >>
1045 This returns a whitelist of options that can be overridden in a
1046 subclass's attribute definition.
1048 This exists to allow a custom metaclass to change or add to the list
1049 of options which can be changed.
1051 =item B<< $attr->type_constraint >>
1053 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1056 =item B<< $attr->has_type_constraint >>
1058 Returns true if this attribute has a type constraint.
1060 =item B<< $attr->verify_against_type_constraint($value) >>
1062 Given a value, this method returns true if the value is valid for the
1063 attribute's type constraint. If the value is not valid, it throws an
1066 =item B<< $attr->handles >>
1068 This returns the value of the C<handles> option passed to the
1071 =item B<< $attr->has_handles >>
1073 Returns true if this attribute performs delegation.
1075 =item B<< $attr->is_weak_ref >>
1077 Returns true if this attribute stores its value as a weak reference.
1079 =item B<< $attr->is_required >>
1081 Returns true if this attribute is required to have a value.
1083 =item B<< $attr->is_lazy >>
1085 Returns true if this attribute is lazy.
1087 =item B<< $attr->is_lazy_build >>
1089 Returns true if the C<lazy_build> option was true when passed to the
1092 =item B<< $attr->should_coerce >>
1094 Returns true if the C<coerce> option passed to the constructor was
1097 =item B<< $attr->should_auto_deref >>
1099 Returns true if the C<auto_deref> option passed to the constructor was
1102 =item B<< $attr->trigger >>
1104 This is the subroutine reference that was in the C<trigger> option
1105 passed to the constructor, if any.
1107 =item B<< $attr->has_trigger >>
1109 Returns true if this attribute has a trigger set.
1111 =item B<< $attr->documentation >>
1113 Returns the value that was in the C<documentation> option passed to
1114 the constructor, if any.
1116 =item B<< $attr->has_documentation >>
1118 Returns true if this attribute has any documentation.
1120 =item B<< $attr->applied_traits >>
1122 This returns an array reference of all the traits which were applied
1123 to this attribute. If none were applied, this returns C<undef>.
1125 =item B<< $attr->has_applied_traits >>
1127 Returns true if this attribute has any traits applied.
1133 All complex software has bugs lurking in it, and this module is no
1134 exception. If you find a bug please either email me, or add the bug
1139 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1141 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1143 =head1 COPYRIGHT AND LICENSE
1145 Copyright 2006-2009 by Infinity Interactive, Inc.
1147 L<http://www.iinteractive.com>
1149 This library is free software; you can redistribute it and/or modify
1150 it under the same terms as Perl itself.