2 package Moose::Meta::Attribute;
7 use Scalar::Util 'blessed', 'weaken';
8 use List::MoreUtils 'any';
12 our $VERSION = '0.94';
13 our $AUTHORITY = 'cpan:STEVAN';
15 use Moose::Meta::Method::Accessor;
16 use Moose::Meta::Method::Delegation;
18 use Moose::Util::TypeConstraints ();
20 use base 'Class::MOP::Attribute', 'Moose::Meta::Mixin::AttributeCore';
22 __PACKAGE__->meta->add_attribute('traits' => (
23 reader => 'applied_traits',
24 predicate => 'has_applied_traits',
27 # we need to have a ->does method in here to
28 # more easily support traits, and the introspection
29 # of those traits. We extend the does check to look
30 # for metatrait aliases.
32 my ($self, $role_name) = @_;
34 Moose::Util::resolve_metatrait_alias(Attribute => $role_name)
36 return 0 if !defined($name); # failed to load class
37 return $self->Moose::Object::does($name);
42 my $class = ( ref $self && $self->associated_class ) || "Moose::Meta::Class";
43 unshift @_, "message" if @_ % 2 == 1;
44 unshift @_, attr => $self if ref $self;
46 my $handler = $class->can("throw_error"); # to avoid incrementing depth by 1
51 my ($class, $name, %options) = @_;
52 $class->_process_options($name, \%options) unless $options{__hack_no_process_options}; # used from clone()... YECHKKK FIXME ICKY YUCK GROSS
54 delete $options{__hack_no_process_options};
59 map { $_->init_arg() }
60 $class->meta()->get_all_attributes()
63 my @bad = sort grep { ! $attrs{$_} } keys %options;
67 Carp::cluck "Found unknown argument(s) passed to '$name' attribute constructor in '$class': @bad";
70 return $class->SUPER::new($name, %options);
73 sub interpolate_class_and_new {
74 my ($class, $name, %args) = @_;
76 my ( $new_class, @traits ) = $class->interpolate_class(\%args);
78 $new_class->new($name, %args, ( scalar(@traits) ? ( traits => \@traits ) : () ) );
81 sub interpolate_class {
82 my ($class, $options) = @_;
84 $class = ref($class) || $class;
86 if ( my $metaclass_name = delete $options->{metaclass} ) {
87 my $new_class = Moose::Util::resolve_metaclass_alias( Attribute => $metaclass_name );
89 if ( $class ne $new_class ) {
90 if ( $new_class->can("interpolate_class") ) {
91 return $new_class->interpolate_class($options);
100 if (my $traits = $options->{traits}) {
102 while ($i < @$traits) {
103 my $trait = $traits->[$i++];
104 next if ref($trait); # options to a trait we discarded
106 $trait = Moose::Util::resolve_metatrait_alias(Attribute => $trait)
109 next if $class->does($trait);
111 push @traits, $trait;
114 push @traits, $traits->[$i++]
115 if $traits->[$i] && ref($traits->[$i]);
119 my $anon_class = Moose::Meta::Class->create_anon_class(
120 superclasses => [ $class ],
121 roles => [ @traits ],
125 $class = $anon_class->name;
129 return ( wantarray ? ( $class, @traits ) : $class );
134 my @legal_options_for_inheritance = qw(
135 default coerce required
136 documentation lazy handles
137 builder type_constraint
142 sub legal_options_for_inheritance { @legal_options_for_inheritance }
145 # This method *must* be able to handle
146 # Class::MOP::Attribute instances as
147 # well. Yes, I know that is wrong, but
148 # apparently we didn't realize it was
149 # doing that and now we have some code
150 # which is dependent on it. The real
151 # solution of course is to push this
152 # feature back up into Class::MOP::Attribute
153 # but I not right now, I am too lazy.
154 # However if you are reading this and
155 # looking for something to do,.. please
158 sub clone_and_inherit_options {
159 my ($self, %options) = @_;
166 # we may want to extends a Class::MOP::Attribute
167 # in which case we need to be able to use the
168 # core set of legal options that have always
169 # been here. But we allows Moose::Meta::Attribute
170 # instances to changes them.
172 my @legal_options = $self->can('legal_options_for_inheritance')
173 ? $self->legal_options_for_inheritance
174 : @legal_options_for_inheritance;
176 foreach my $legal_option (@legal_options) {
177 if (exists $options{$legal_option}) {
178 $actual_options{$legal_option} = $options{$legal_option};
179 delete $options{$legal_option};
185 if (blessed($options{isa}) && $options{isa}->isa('Moose::Meta::TypeConstraint')) {
186 $type_constraint = $options{isa};
189 $type_constraint = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options{isa});
190 (defined $type_constraint)
191 || $self->throw_error("Could not find the type constraint '" . $options{isa} . "'", data => $options{isa});
194 $actual_options{type_constraint} = $type_constraint;
195 delete $options{isa};
198 if ($options{does}) {
200 if (blessed($options{does}) && $options{does}->isa('Moose::Meta::TypeConstraint')) {
201 $type_constraint = $options{does};
204 $type_constraint = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options{does});
205 (defined $type_constraint)
206 || $self->throw_error("Could not find the type constraint '" . $options{does} . "'", data => $options{does});
209 $actual_options{type_constraint} = $type_constraint;
210 delete $options{does};
214 # this doesn't apply to Class::MOP::Attributes,
215 # so we can ignore it for them.
217 if ($self->can('interpolate_class')) {
218 ( $actual_options{metaclass}, my @traits ) = $self->interpolate_class(\%options);
221 my @all_traits = grep { $seen{$_}++ } @{ $self->applied_traits || [] }, @traits;
222 $actual_options{traits} = \@all_traits if @all_traits;
224 delete @options{qw(metaclass traits)};
227 (scalar keys %options == 0)
228 || $self->throw_error("Illegal inherited options => (" . (join ', ' => keys %options) . ")", data => \%options);
231 $self->clone(%actual_options);
235 my ( $self, %params ) = @_;
237 my $class = delete $params{metaclass} || ref $self;
239 my ( @init, @non_init );
241 foreach my $attr ( grep { $_->has_value($self) } Class::MOP::class_of($self)->get_all_attributes ) {
242 push @{ $attr->has_init_arg ? \@init : \@non_init }, $attr;
245 my %new_params = ( ( map { $_->init_arg => $_->get_value($self) } @init ), %params );
247 my $name = delete $new_params{name};
249 my $clone = $class->new($name, %new_params, __hack_no_process_options => 1 );
251 foreach my $attr ( @non_init ) {
252 $attr->set_value($clone, $attr->get_value($self));
258 sub _process_options {
259 my ($class, $name, $options) = @_;
261 if (exists $options->{is}) {
263 ### -------------------------
264 ## is => ro, writer => _foo # turns into (reader => foo, writer => _foo) as before
265 ## is => rw, writer => _foo # turns into (reader => foo, writer => _foo)
266 ## is => rw, accessor => _foo # turns into (accessor => _foo)
267 ## is => ro, accessor => _foo # error, accesor is rw
268 ### -------------------------
270 if ($options->{is} eq 'ro') {
271 $class->throw_error("Cannot define an accessor name on a read-only attribute, accessors are read/write", data => $options)
272 if exists $options->{accessor};
273 $options->{reader} ||= $name;
275 elsif ($options->{is} eq 'rw') {
276 if ($options->{writer}) {
277 $options->{reader} ||= $name;
280 $options->{accessor} ||= $name;
283 elsif ($options->{is} eq 'bare') {
284 # do nothing, but don't complain (later) about missing methods
287 $class->throw_error("I do not understand this option (is => " . $options->{is} . ") on attribute ($name)", data => $options->{is});
291 if (exists $options->{isa}) {
292 if (exists $options->{does}) {
293 if (try { $options->{isa}->can('does') }) {
294 ($options->{isa}->does($options->{does}))
295 || $class->throw_error("Cannot have an isa option and a does option if the isa does not do the does on attribute ($name)", data => $options);
298 $class->throw_error("Cannot have an isa option which cannot ->does() on attribute ($name)", data => $options);
302 # allow for anon-subtypes here ...
303 if (blessed($options->{isa}) && $options->{isa}->isa('Moose::Meta::TypeConstraint')) {
304 $options->{type_constraint} = $options->{isa};
307 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options->{isa});
310 elsif (exists $options->{does}) {
311 # allow for anon-subtypes here ...
312 if (blessed($options->{does}) && $options->{does}->isa('Moose::Meta::TypeConstraint')) {
313 $options->{type_constraint} = $options->{does};
316 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options->{does});
320 if (exists $options->{coerce} && $options->{coerce}) {
321 (exists $options->{type_constraint})
322 || $class->throw_error("You cannot have coercion without specifying a type constraint on attribute ($name)", data => $options);
323 $class->throw_error("You cannot have a weak reference to a coerced value on attribute ($name)", data => $options)
324 if $options->{weak_ref};
327 if (exists $options->{trigger}) {
328 ('CODE' eq ref $options->{trigger})
329 || $class->throw_error("Trigger must be a CODE ref on attribute ($name)", data => $options->{trigger});
332 if (exists $options->{auto_deref} && $options->{auto_deref}) {
333 (exists $options->{type_constraint})
334 || $class->throw_error("You cannot auto-dereference without specifying a type constraint on attribute ($name)", data => $options);
335 ($options->{type_constraint}->is_a_type_of('ArrayRef') ||
336 $options->{type_constraint}->is_a_type_of('HashRef'))
337 || $class->throw_error("You cannot auto-dereference anything other than a ArrayRef or HashRef on attribute ($name)", data => $options);
340 if (exists $options->{lazy_build} && $options->{lazy_build} == 1) {
341 $class->throw_error("You can not use lazy_build and default for the same attribute ($name)", data => $options)
342 if exists $options->{default};
343 $options->{lazy} = 1;
344 $options->{builder} ||= "_build_${name}";
346 $options->{clearer} ||= "_clear${name}";
347 $options->{predicate} ||= "_has${name}";
350 $options->{clearer} ||= "clear_${name}";
351 $options->{predicate} ||= "has_${name}";
355 if (exists $options->{lazy} && $options->{lazy}) {
356 (exists $options->{default} || defined $options->{builder} )
357 || $class->throw_error("You cannot have lazy attribute ($name) without specifying a default value for it", data => $options);
360 if ( $options->{required} && !( ( !exists $options->{init_arg} || defined $options->{init_arg} ) || exists $options->{default} || defined $options->{builder} ) ) {
361 $class->throw_error("You cannot have a required attribute ($name) without a default, builder, or an init_arg", data => $options);
366 sub initialize_instance_slot {
367 my ($self, $meta_instance, $instance, $params) = @_;
368 my $init_arg = $self->init_arg();
369 # try to fetch the init arg from the %params ...
373 if ( defined($init_arg) and exists $params->{$init_arg}) {
374 $val = $params->{$init_arg};
378 # skip it if it's lazy
379 return if $self->is_lazy;
380 # and die if it's required and doesn't have a default value
381 $self->throw_error("Attribute (" . $self->name . ") is required", object => $instance, data => $params)
382 if $self->is_required && !$self->has_default && !$self->has_builder;
384 # if nothing was in the %params, we can use the
385 # attribute's default value (if it has one)
386 if ($self->has_default) {
387 $val = $self->default($instance);
390 elsif ($self->has_builder) {
391 $val = $self->_call_builder($instance);
396 return unless $value_is_set;
398 $val = $self->_coerce_and_verify( $val, $instance );
400 $self->set_initial_value($instance, $val);
402 if ( ref $val && $self->is_weak_ref ) {
403 $self->_weaken_value($instance);
408 my ( $self, $instance ) = @_;
410 my $builder = $self->builder();
412 return $instance->$builder()
413 if $instance->can( $self->builder );
415 $self->throw_error( blessed($instance)
416 . " does not support builder method '"
418 . "' for attribute '"
428 # this duplicates too much code from
429 # Class::MOP::Attribute, we need to
430 # refactor these bits eventually.
432 sub _set_initial_slot_value {
433 my ($self, $meta_instance, $instance, $value) = @_;
435 my $slot_name = $self->name;
437 return $meta_instance->set_slot_value($instance, $slot_name, $value)
438 unless $self->has_initializer;
440 my ($type_constraint, $can_coerce);
441 if ($self->has_type_constraint) {
442 $type_constraint = $self->type_constraint;
443 $can_coerce = ($self->should_coerce && $type_constraint->has_coercion);
447 my $val = $self->_coerce_and_verify( shift, $instance );;
449 $meta_instance->set_slot_value($instance, $slot_name, $val);
452 my $initializer = $self->initializer;
454 # most things will just want to set a value, so make it first arg
455 $instance->$initializer($value, $callback, $self);
459 my ($self, $instance, @args) = @_;
460 my $value = $args[0];
462 my $attr_name = $self->name;
464 if ($self->is_required and not @args) {
465 $self->throw_error("Attribute ($attr_name) is required", object => $instance);
468 $value = $self->_coerce_and_verify( $value, $instance );
471 if ( $self->has_trigger && $self->has_value($instance) ) {
472 @old = $self->get_value($instance, 'for trigger');
475 $self->SUPER::set_value($instance, $value);
477 if ( ref $value && $self->is_weak_ref ) {
478 $self->_weaken_value($instance);
481 if ($self->has_trigger) {
482 $self->trigger->($instance, $value, @old);
487 my ( $self, $instance ) = @_;
489 my $meta_instance = Class::MOP::Class->initialize( blessed($instance) )
492 $meta_instance->weaken_slot_value( $instance, $self->name );
496 my ($self, $instance, $for_trigger) = @_;
498 if ($self->is_lazy) {
499 unless ($self->has_value($instance)) {
501 if ($self->has_default) {
502 $value = $self->default($instance);
503 } elsif ( $self->has_builder ) {
504 $value = $self->_call_builder($instance);
507 $value = $self->_coerce_and_verify( $value, $instance );
509 $self->set_initial_value($instance, $value);
513 if ( $self->should_auto_deref && ! $for_trigger ) {
515 my $type_constraint = $self->type_constraint;
517 if ($type_constraint->is_a_type_of('ArrayRef')) {
518 my $rv = $self->SUPER::get_value($instance);
519 return unless defined $rv;
520 return wantarray ? @{ $rv } : $rv;
522 elsif ($type_constraint->is_a_type_of('HashRef')) {
523 my $rv = $self->SUPER::get_value($instance);
524 return unless defined $rv;
525 return wantarray ? %{ $rv } : $rv;
528 $self->throw_error("Can not auto de-reference the type constraint '" . $type_constraint->name . "'", object => $instance, type_constraint => $type_constraint);
534 return $self->SUPER::get_value($instance);
538 ## installing accessors
540 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
542 sub install_accessors {
544 $self->SUPER::install_accessors(@_);
545 $self->install_delegation(@_);
549 sub _check_associated_methods {
552 @{ $self->associated_methods }
553 || ($self->_is_metadata || '') eq 'bare'
556 'Attribute (' . $self->name . ') of class '
557 . $self->associated_class->name
558 . ' has no associated methods'
559 . ' (did you mean to provide an "is" argument?)'
565 sub _process_accessors {
567 my ($type, $accessor, $generate_as_inline_methods) = @_;
568 $accessor = (keys %$accessor)[0] if (ref($accessor)||'') eq 'HASH';
569 my $method = $self->associated_class->get_method($accessor);
570 if ($method && !$method->isa('Class::MOP::Method::Accessor')
571 && (!$self->definition_context
572 || $method->package_name eq $self->definition_context->{package})) {
574 "You are overwriting a locally defined method ($accessor) with "
578 $self->SUPER::_process_accessors(@_);
581 sub remove_accessors {
583 $self->SUPER::remove_accessors(@_);
584 $self->remove_delegation if $self->has_handles;
588 sub install_delegation {
592 return unless $self->has_handles;
595 # Here we canonicalize the 'handles' option
596 # this will sort out any details and always
597 # return an hash of methods which we want
598 # to delagate to, see that method for details
599 my %handles = $self->_canonicalize_handles;
602 # install the delegation ...
603 my $associated_class = $self->associated_class;
604 foreach my $handle (keys %handles) {
605 my $method_to_call = $handles{$handle};
606 my $class_name = $associated_class->name;
607 my $name = "${class_name}::${handle}";
609 if ($associated_class->has_method($handle)) {
611 "You cannot overwrite a locally defined method ($handle) with a delegation",
612 method_name => $handle
617 # handles is not allowed to delegate
618 # any of these methods, as they will
619 # override the ones in your class, which
620 # is almost certainly not what you want.
622 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
623 #cluck("Not delegating method '$handle' because it is a core method") and
624 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
626 my $method = $self->_make_delegation_method($handle, $method_to_call, $inline);
628 $self->associated_class->add_method($method->name, $method);
629 $self->associate_method($method);
633 sub remove_delegation {
635 my %handles = $self->_canonicalize_handles;
636 my $associated_class = $self->associated_class;
637 foreach my $handle (keys %handles) {
638 next unless any { $handle eq $_ }
640 @{ $self->associated_methods };
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 grep { $_ ne 'meta' } (
682 $role_meta->get_method_list,
683 map { $_->name } $role_meta->get_required_method_list,
688 sub _find_delegate_metaclass {
690 if (my $class = $self->_isa_metadata) {
691 # we might be dealing with a non-Moose class,
692 # and need to make our own metaclass. if there's
693 # already a metaclass, it will be returned
694 return Moose::Meta::Class->initialize($class);
696 elsif (my $role = $self->_does_metadata) {
697 return Class::MOP::class_of($role);
700 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
704 sub _get_delegate_method_list {
706 my $meta = $self->_find_delegate_metaclass;
707 if ($meta->isa('Class::MOP::Class')) {
708 return map { $_->name } # NOTE: !never! delegate &meta
709 grep { $_->package_name ne 'Moose::Object' && $_->name ne 'meta' }
710 $meta->get_all_methods;
712 elsif ($meta->isa('Moose::Meta::Role')) {
713 return $meta->get_method_list;
716 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
720 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
722 sub _make_delegation_method {
723 my ( $self, $handle_name, $method_to_call, $is_inline ) = @_;
725 my @curried_arguments;
727 ($method_to_call, @curried_arguments) = @$method_to_call
728 if 'ARRAY' eq ref($method_to_call);
730 return $self->delegation_metaclass->new(
731 name => $handle_name,
732 package_name => $self->associated_class->name,
734 delegate_to_method => $method_to_call,
735 curried_arguments => \@curried_arguments,
736 is_inline => $is_inline,
740 sub _coerce_and_verify {
743 my $instance = shift;
745 return $val unless $self->has_type_constraint;
747 my $type_constraint = $self->type_constraint;
748 if ($self->should_coerce && $type_constraint->has_coercion) {
749 $val = $type_constraint->coerce($val);
752 $self->verify_against_type_constraint($val, instance => $instance);
757 sub verify_against_type_constraint {
761 return 1 if !$self->has_type_constraint;
763 my $type_constraint = $self->type_constraint;
765 $type_constraint->check($val)
766 || $self->throw_error("Attribute ("
768 . ") does not pass the type constraint because: "
769 . $type_constraint->get_message($val), data => $val, @_);
772 package Moose::Meta::Attribute::Custom::Moose;
773 sub register_implementation { 'Moose::Meta::Attribute' }
783 Moose::Meta::Attribute - The Moose attribute metaclass
787 This class is a subclass of L<Class::MOP::Attribute> that provides
788 additional Moose-specific functionality.
790 To really understand this class, you will need to start with the
791 L<Class::MOP::Attribute> documentation. This class can be understood
792 as a set of additional features on top of the basic feature provided
793 by that parent class.
797 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
801 Many of the documented below override methods in
802 L<Class::MOP::Attribute> and add Moose specific features.
808 =item B<< Moose::Meta::Attribute->new(%options) >>
810 This method overrides the L<Class::MOP::Attribute> constructor.
812 Many of the options below are described in more detail in the
813 L<Moose::Manual::Attributes> document.
815 It adds the following options to the constructor:
819 =item * is => 'ro', 'rw', 'bare'
821 This provides a shorthand for specifying the C<reader>, C<writer>, or
822 C<accessor> names. If the attribute is read-only ('ro') then it will
823 have a C<reader> method with the same attribute as the name.
825 If it is read-write ('rw') then it will have an C<accessor> method
826 with the same name. If you provide an explicit C<writer> for a
827 read-write attribute, then you will have a C<reader> with the same
828 name as the attribute, and a C<writer> with the name you provided.
830 Use 'bare' when you are deliberately not installing any methods
831 (accessor, reader, etc.) associated with this attribute; otherwise,
832 Moose will issue a deprecation warning when this attribute is added to a
837 This option accepts a type. The type can be a string, which should be
838 a type name. If the type name is unknown, it is assumed to be a class
841 This option can also accept a L<Moose::Meta::TypeConstraint> object.
843 If you I<also> provide a C<does> option, then your C<isa> option must
844 be a class name, and that class must do the role specified with
847 =item * does => $role
849 This is short-hand for saying that the attribute's type must be an
850 object which does the named role.
852 =item * coerce => $bool
854 This option is only valid for objects with a type constraint
855 (C<isa>). If this is true, then coercions will be applied whenever
856 this attribute is set.
858 You can make both this and the C<weak_ref> option true.
860 =item * trigger => $sub
862 This option accepts a subroutine reference, which will be called after
863 the attribute is set.
865 =item * required => $bool
867 An attribute which is required must be provided to the constructor. An
868 attribute which is required can also have a C<default> or C<builder>,
869 which will satisfy its required-ness.
871 A required attribute must have a C<default>, C<builder> or a
872 non-C<undef> C<init_arg>
874 =item * lazy => $bool
876 A lazy attribute must have a C<default> or C<builder>. When an
877 attribute is lazy, the default value will not be calculated until the
880 =item * weak_ref => $bool
882 If this is true, the attribute's value will be stored as a weak
885 =item * auto_deref => $bool
887 If this is true, then the reader will dereference the value when it is
888 called. The attribute must have a type constraint which defines the
889 attribute as an array or hash reference.
891 =item * lazy_build => $bool
893 Setting this to true makes the attribute lazy and provides a number of
901 is equivalent to this:
906 builder => '_build_size',
907 clearer => 'clear_size',
908 predicate => 'has_size',
911 =item * documentation
913 An arbitrary string that can be retrieved later by calling C<<
914 $attr->documentation >>.
918 =item B<< $attr->clone(%options) >>
920 This creates a new attribute based on attribute being cloned. You must
921 supply a C<name> option to provide a new name for the attribute.
923 The C<%options> can only specify options handled by
924 L<Class::MOP::Attribute>.
928 =head2 Value management
932 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
934 This method is used internally to initialize the attribute's slot in
935 the object C<$instance>.
937 This overrides the L<Class::MOP::Attribute> method to handle lazy
938 attributes, weak references, and type constraints.
944 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
949 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
951 Before setting the value, a check is made on the type constraint of
952 the attribute, if it has one, to see if the value passes it. If the
953 value fails to pass, the set operation dies with a L<throw_error>.
955 Any coercion to convert values is done before checking the type constraint.
957 To check a value against a type constraint before setting it, fetch the
958 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
959 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
960 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
965 =head2 Attribute Accessor generation
969 =item B<< $attr->install_accessors >>
971 This method overrides the parent to also install delegation methods.
973 If, after installing all methods, the attribute object has no associated
974 methods, it throws an error unless C<< is => 'bare' >> was passed to the
975 attribute constructor. (Trying to add an attribute that has no associated
976 methods is almost always an error.)
978 =item B<< $attr->remove_accessors >>
980 This method overrides the parent to also remove delegation methods.
982 =item B<< $attr->install_delegation >>
984 This method adds its delegation methods to the attribute's associated
985 class, if it has any to add.
987 =item B<< $attr->remove_delegation >>
989 This method remove its delegation methods from the attribute's
992 =item B<< $attr->accessor_metaclass >>
994 Returns the accessor metaclass name, which defaults to
995 L<Moose::Meta::Method::Accessor>.
997 =item B<< $attr->delegation_metaclass >>
999 Returns the delegation metaclass name, which defaults to
1000 L<Moose::Meta::Method::Delegation>.
1004 =head2 Additional Moose features
1006 These methods are not found in the superclass. They support features
1011 =item B<< $attr->does($role) >>
1013 This indicates whether the I<attribute itself> does the given
1014 role. The role can be given as a full class name, or as a resolvable
1017 Note that this checks the attribute itself, not its type constraint,
1018 so it is checking the attribute's metaclass and any traits applied to
1021 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
1023 This is an alternate constructor that handles the C<metaclass> and
1026 Effectively, this method is a factory that finds or creates the
1027 appropriate class for the given C<metaclass> and/or C<traits>.
1029 Once it has the appropriate class, it will call C<< $class->new($name,
1030 %options) >> on that class.
1032 =item B<< $attr->clone_and_inherit_options(%options) >>
1034 This method supports the C<has '+foo'> feature. It does various bits
1035 of processing on the supplied C<%options> before ultimately calling
1036 the C<clone> method.
1038 One of its main tasks is to make sure that the C<%options> provided
1039 only includes the options returned by the
1040 C<legal_options_for_inheritance> method.
1042 =item B<< $attr->legal_options_for_inheritance >>
1044 This returns a whitelist of options that can be overridden in a
1045 subclass's attribute definition.
1047 This exists to allow a custom metaclass to change or add to the list
1048 of options which can be changed.
1050 =item B<< $attr->type_constraint >>
1052 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1055 =item B<< $attr->has_type_constraint >>
1057 Returns true if this attribute has a type constraint.
1059 =item B<< $attr->verify_against_type_constraint($value) >>
1061 Given a value, this method returns true if the value is valid for the
1062 attribute's type constraint. If the value is not valid, it throws an
1065 =item B<< $attr->handles >>
1067 This returns the value of the C<handles> option passed to the
1070 =item B<< $attr->has_handles >>
1072 Returns true if this attribute performs delegation.
1074 =item B<< $attr->is_weak_ref >>
1076 Returns true if this attribute stores its value as a weak reference.
1078 =item B<< $attr->is_required >>
1080 Returns true if this attribute is required to have a value.
1082 =item B<< $attr->is_lazy >>
1084 Returns true if this attribute is lazy.
1086 =item B<< $attr->is_lazy_build >>
1088 Returns true if the C<lazy_build> option was true when passed to the
1091 =item B<< $attr->should_coerce >>
1093 Returns true if the C<coerce> option passed to the constructor was
1096 =item B<< $attr->should_auto_deref >>
1098 Returns true if the C<auto_deref> option passed to the constructor was
1101 =item B<< $attr->trigger >>
1103 This is the subroutine reference that was in the C<trigger> option
1104 passed to the constructor, if any.
1106 =item B<< $attr->has_trigger >>
1108 Returns true if this attribute has a trigger set.
1110 =item B<< $attr->documentation >>
1112 Returns the value that was in the C<documentation> option passed to
1113 the constructor, if any.
1115 =item B<< $attr->has_documentation >>
1117 Returns true if this attribute has any documentation.
1119 =item B<< $attr->applied_traits >>
1121 This returns an array reference of all the traits which were applied
1122 to this attribute. If none were applied, this returns C<undef>.
1124 =item B<< $attr->has_applied_traits >>
1126 Returns true if this attribute has any traits applied.
1132 See L<Moose/BUGS> for details on reporting bugs.
1136 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1138 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1140 =head1 COPYRIGHT AND LICENSE
1142 Copyright 2006-2010 by Infinity Interactive, Inc.
1144 L<http://www.iinteractive.com>
1146 This library is free software; you can redistribute it and/or modify
1147 it under the same terms as Perl itself.