2 package Moose::Meta::Attribute;
7 use Scalar::Util 'blessed', 'weaken';
8 use List::MoreUtils 'any';
12 our $VERSION = '1.04';
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 if $self->has_handles;
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 # Here we canonicalize the 'handles' option
593 # this will sort out any details and always
594 # return an hash of methods which we want
595 # to delagate to, see that method for details
596 my %handles = $self->_canonicalize_handles;
599 # install the delegation ...
600 my $associated_class = $self->associated_class;
601 foreach my $handle (keys %handles) {
602 my $method_to_call = $handles{$handle};
603 my $class_name = $associated_class->name;
604 my $name = "${class_name}::${handle}";
606 (!$associated_class->has_method($handle))
607 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
610 # handles is not allowed to delegate
611 # any of these methods, as they will
612 # override the ones in your class, which
613 # is almost certainly not what you want.
615 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
616 #cluck("Not delegating method '$handle' because it is a core method") and
617 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
619 my $method = $self->_make_delegation_method($handle, $method_to_call);
621 $self->associated_class->add_method($method->name, $method);
622 $self->associate_method($method);
626 sub remove_delegation {
628 my %handles = $self->_canonicalize_handles;
629 my $associated_class = $self->associated_class;
630 foreach my $handle (keys %handles) {
631 next unless any { $handle eq $_ }
633 @{ $self->associated_methods };
634 $self->associated_class->remove_method($handle);
638 # private methods to help delegation ...
640 sub _canonicalize_handles {
642 my $handles = $self->handles;
643 if (my $handle_type = ref($handles)) {
644 if ($handle_type eq 'HASH') {
647 elsif ($handle_type eq 'ARRAY') {
648 return map { $_ => $_ } @{$handles};
650 elsif ($handle_type eq 'Regexp') {
651 ($self->has_type_constraint)
652 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
653 return map { ($_ => $_) }
654 grep { /$handles/ } $self->_get_delegate_method_list;
656 elsif ($handle_type eq 'CODE') {
657 return $handles->($self, $self->_find_delegate_metaclass);
659 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::DuckType')) {
660 return map { $_ => $_ } @{ $handles->methods };
662 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::Role')) {
663 $handles = $handles->role;
666 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
670 Class::MOP::load_class($handles);
671 my $role_meta = Class::MOP::class_of($handles);
673 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
674 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because its metaclass is not a Moose::Meta::Role", data => $handles);
676 return map { $_ => $_ }
677 grep { $_ ne 'meta' } (
678 $role_meta->get_method_list,
679 map { $_->name } $role_meta->get_required_method_list,
683 sub _find_delegate_metaclass {
685 if (my $class = $self->_isa_metadata) {
686 # we might be dealing with a non-Moose class,
687 # and need to make our own metaclass. if there's
688 # already a metaclass, it will be returned
689 return Class::MOP::Class->initialize($class);
691 elsif (my $role = $self->_does_metadata) {
692 return Class::MOP::class_of($role);
695 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
699 sub _get_delegate_method_list {
701 my $meta = $self->_find_delegate_metaclass;
702 if ($meta->isa('Class::MOP::Class')) {
703 return map { $_->name } # NOTE: !never! delegate &meta
704 grep { $_->package_name ne 'Moose::Object' && $_->name ne 'meta' }
705 $meta->get_all_methods;
707 elsif ($meta->isa('Moose::Meta::Role')) {
708 return $meta->get_method_list;
711 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
715 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
717 sub _make_delegation_method {
718 my ( $self, $handle_name, $method_to_call ) = @_;
720 my @curried_arguments;
722 ($method_to_call, @curried_arguments) = @$method_to_call
723 if 'ARRAY' eq ref($method_to_call);
725 return $self->delegation_metaclass->new(
726 name => $handle_name,
727 package_name => $self->associated_class->name,
729 delegate_to_method => $method_to_call,
730 curried_arguments => \@curried_arguments,
734 sub _coerce_and_verify {
737 my $instance = shift;
739 return $val unless $self->has_type_constraint;
741 my $type_constraint = $self->type_constraint;
742 if ($self->should_coerce && $type_constraint->has_coercion) {
743 $val = $type_constraint->coerce($val);
746 $self->verify_against_type_constraint($val, instance => $instance);
751 sub verify_against_type_constraint {
755 return 1 if !$self->has_type_constraint;
757 my $type_constraint = $self->type_constraint;
759 $type_constraint->check($val)
760 || $self->throw_error("Attribute ("
762 . ") does not pass the type constraint because: "
763 . $type_constraint->get_message($val), data => $val, @_);
766 package Moose::Meta::Attribute::Custom::Moose;
767 sub register_implementation { 'Moose::Meta::Attribute' }
777 Moose::Meta::Attribute - The Moose attribute metaclass
781 This class is a subclass of L<Class::MOP::Attribute> that provides
782 additional Moose-specific functionality.
784 To really understand this class, you will need to start with the
785 L<Class::MOP::Attribute> documentation. This class can be understood
786 as a set of additional features on top of the basic feature provided
787 by that parent class.
791 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
795 Many of the documented below override methods in
796 L<Class::MOP::Attribute> and add Moose specific features.
802 =item B<< Moose::Meta::Attribute->new(%options) >>
804 This method overrides the L<Class::MOP::Attribute> constructor.
806 Many of the options below are described in more detail in the
807 L<Moose::Manual::Attributes> document.
809 It adds the following options to the constructor:
813 =item * is => 'ro', 'rw', 'bare'
815 This provides a shorthand for specifying the C<reader>, C<writer>, or
816 C<accessor> names. If the attribute is read-only ('ro') then it will
817 have a C<reader> method with the same attribute as the name.
819 If it is read-write ('rw') then it will have an C<accessor> method
820 with the same name. If you provide an explicit C<writer> for a
821 read-write attribute, then you will have a C<reader> with the same
822 name as the attribute, and a C<writer> with the name you provided.
824 Use 'bare' when you are deliberately not installing any methods
825 (accessor, reader, etc.) associated with this attribute; otherwise,
826 Moose will issue a deprecation warning when this attribute is added to a
831 This option accepts a type. The type can be a string, which should be
832 a type name. If the type name is unknown, it is assumed to be a class
835 This option can also accept a L<Moose::Meta::TypeConstraint> object.
837 If you I<also> provide a C<does> option, then your C<isa> option must
838 be a class name, and that class must do the role specified with
841 =item * does => $role
843 This is short-hand for saying that the attribute's type must be an
844 object which does the named role.
846 =item * coerce => $bool
848 This option is only valid for objects with a type constraint
849 (C<isa>). If this is true, then coercions will be applied whenever
850 this attribute is set.
852 You can make both this and the C<weak_ref> option true.
854 =item * trigger => $sub
856 This option accepts a subroutine reference, which will be called after
857 the attribute is set.
859 =item * required => $bool
861 An attribute which is required must be provided to the constructor. An
862 attribute which is required can also have a C<default> or C<builder>,
863 which will satisfy its required-ness.
865 A required attribute must have a C<default>, C<builder> or a
866 non-C<undef> C<init_arg>
868 =item * lazy => $bool
870 A lazy attribute must have a C<default> or C<builder>. When an
871 attribute is lazy, the default value will not be calculated until the
874 =item * weak_ref => $bool
876 If this is true, the attribute's value will be stored as a weak
879 =item * auto_deref => $bool
881 If this is true, then the reader will dereference the value when it is
882 called. The attribute must have a type constraint which defines the
883 attribute as an array or hash reference.
885 =item * lazy_build => $bool
887 Setting this to true makes the attribute lazy and provides a number of
895 is equivalent to this:
900 builder => '_build_size',
901 clearer => 'clear_size',
902 predicate => 'has_size',
905 =item * documentation
907 An arbitrary string that can be retrieved later by calling C<<
908 $attr->documentation >>.
912 =item B<< $attr->clone(%options) >>
914 This creates a new attribute based on attribute being cloned. You must
915 supply a C<name> option to provide a new name for the attribute.
917 The C<%options> can only specify options handled by
918 L<Class::MOP::Attribute>.
922 =head2 Value management
926 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
928 This method is used internally to initialize the attribute's slot in
929 the object C<$instance>.
931 This overrides the L<Class::MOP::Attribute> method to handle lazy
932 attributes, weak references, and type constraints.
938 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
943 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
945 Before setting the value, a check is made on the type constraint of
946 the attribute, if it has one, to see if the value passes it. If the
947 value fails to pass, the set operation dies with a L</throw_error>.
949 Any coercion to convert values is done before checking the type constraint.
951 To check a value against a type constraint before setting it, fetch the
952 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
953 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
954 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
959 =head2 Attribute Accessor generation
963 =item B<< $attr->install_accessors >>
965 This method overrides the parent to also install delegation methods.
967 If, after installing all methods, the attribute object has no associated
968 methods, it throws an error unless C<< is => 'bare' >> was passed to the
969 attribute constructor. (Trying to add an attribute that has no associated
970 methods is almost always an error.)
972 =item B<< $attr->remove_accessors >>
974 This method overrides the parent to also remove delegation methods.
976 =item B<< $attr->install_delegation >>
978 This method adds its delegation methods to the attribute's associated
979 class, if it has any to add.
981 =item B<< $attr->remove_delegation >>
983 This method remove its delegation methods from the attribute's
986 =item B<< $attr->accessor_metaclass >>
988 Returns the accessor metaclass name, which defaults to
989 L<Moose::Meta::Method::Accessor>.
991 =item B<< $attr->delegation_metaclass >>
993 Returns the delegation metaclass name, which defaults to
994 L<Moose::Meta::Method::Delegation>.
998 =head2 Additional Moose features
1000 These methods are not found in the superclass. They support features
1005 =item B<< $attr->does($role) >>
1007 This indicates whether the I<attribute itself> does the given
1008 role. The role can be given as a full class name, or as a resolvable
1011 Note that this checks the attribute itself, not its type constraint,
1012 so it is checking the attribute's metaclass and any traits applied to
1015 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
1017 This is an alternate constructor that handles the C<metaclass> and
1020 Effectively, this method is a factory that finds or creates the
1021 appropriate class for the given C<metaclass> and/or C<traits>.
1023 Once it has the appropriate class, it will call C<< $class->new($name,
1024 %options) >> on that class.
1026 =item B<< $attr->clone_and_inherit_options(%options) >>
1028 This method supports the C<has '+foo'> feature. It does various bits
1029 of processing on the supplied C<%options> before ultimately calling
1030 the C<clone> method.
1032 One of its main tasks is to make sure that the C<%options> provided
1033 only includes the options returned by the
1034 C<legal_options_for_inheritance> method.
1036 =item B<< $attr->legal_options_for_inheritance >>
1038 This returns a whitelist of options that can be overridden in a
1039 subclass's attribute definition.
1041 This exists to allow a custom metaclass to change or add to the list
1042 of options which can be changed.
1044 =item B<< $attr->type_constraint >>
1046 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1049 =item B<< $attr->has_type_constraint >>
1051 Returns true if this attribute has a type constraint.
1053 =item B<< $attr->verify_against_type_constraint($value) >>
1055 Given a value, this method returns true if the value is valid for the
1056 attribute's type constraint. If the value is not valid, it throws an
1059 =item B<< $attr->handles >>
1061 This returns the value of the C<handles> option passed to the
1064 =item B<< $attr->has_handles >>
1066 Returns true if this attribute performs delegation.
1068 =item B<< $attr->is_weak_ref >>
1070 Returns true if this attribute stores its value as a weak reference.
1072 =item B<< $attr->is_required >>
1074 Returns true if this attribute is required to have a value.
1076 =item B<< $attr->is_lazy >>
1078 Returns true if this attribute is lazy.
1080 =item B<< $attr->is_lazy_build >>
1082 Returns true if the C<lazy_build> option was true when passed to the
1085 =item B<< $attr->should_coerce >>
1087 Returns true if the C<coerce> option passed to the constructor was
1090 =item B<< $attr->should_auto_deref >>
1092 Returns true if the C<auto_deref> option passed to the constructor was
1095 =item B<< $attr->trigger >>
1097 This is the subroutine reference that was in the C<trigger> option
1098 passed to the constructor, if any.
1100 =item B<< $attr->has_trigger >>
1102 Returns true if this attribute has a trigger set.
1104 =item B<< $attr->documentation >>
1106 Returns the value that was in the C<documentation> option passed to
1107 the constructor, if any.
1109 =item B<< $attr->has_documentation >>
1111 Returns true if this attribute has any documentation.
1113 =item B<< $attr->applied_traits >>
1115 This returns an array reference of all the traits which were applied
1116 to this attribute. If none were applied, this returns C<undef>.
1118 =item B<< $attr->has_applied_traits >>
1120 Returns true if this attribute has any traits applied.
1126 See L<Moose/BUGS> for details on reporting bugs.
1130 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1132 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1134 =head1 COPYRIGHT AND LICENSE
1136 Copyright 2006-2010 by Infinity Interactive, Inc.
1138 L<http://www.iinteractive.com>
1140 This library is free software; you can redistribute it and/or modify
1141 it under the same terms as Perl itself.