2 package Moose::Meta::Attribute;
7 use Scalar::Util 'blessed', 'weaken';
8 use List::MoreUtils 'any';
12 our $VERSION = '1.14';
13 our $AUTHORITY = 'cpan:STEVAN';
15 use Moose::Deprecated;
16 use Moose::Meta::Method::Accessor;
17 use Moose::Meta::Method::Delegation;
19 use Moose::Util::TypeConstraints ();
21 use base 'Class::MOP::Attribute', 'Moose::Meta::Mixin::AttributeCore';
23 __PACKAGE__->meta->add_attribute('traits' => (
24 reader => 'applied_traits',
25 predicate => 'has_applied_traits',
28 # we need to have a ->does method in here to
29 # more easily support traits, and the introspection
30 # of those traits. We extend the does check to look
31 # for metatrait aliases.
33 my ($self, $role_name) = @_;
35 Moose::Util::resolve_metatrait_alias(Attribute => $role_name)
37 return 0 if !defined($name); # failed to load class
38 return $self->Moose::Object::does($name);
43 my $class = ( ref $self && $self->associated_class ) || "Moose::Meta::Class";
44 unshift @_, "message" if @_ % 2 == 1;
45 unshift @_, attr => $self if ref $self;
47 my $handler = $class->can("throw_error"); # to avoid incrementing depth by 1
52 my ($class, $name, %options) = @_;
53 $class->_process_options($name, \%options) unless $options{__hack_no_process_options}; # used from clone()... YECHKKK FIXME ICKY YUCK GROSS
55 delete $options{__hack_no_process_options};
60 map { $_->init_arg() }
61 $class->meta()->get_all_attributes()
64 my @bad = sort grep { ! $attrs{$_} } keys %options;
68 Carp::cluck "Found unknown argument(s) passed to '$name' attribute constructor in '$class': @bad";
71 return $class->SUPER::new($name, %options);
74 sub interpolate_class_and_new {
75 my ($class, $name, %args) = @_;
77 my ( $new_class, @traits ) = $class->interpolate_class(\%args);
79 $new_class->new($name, %args, ( scalar(@traits) ? ( traits => \@traits ) : () ) );
82 sub interpolate_class {
83 my ($class, $options) = @_;
85 $class = ref($class) || $class;
87 if ( my $metaclass_name = delete $options->{metaclass} ) {
88 my $new_class = Moose::Util::resolve_metaclass_alias( Attribute => $metaclass_name );
90 if ( $class ne $new_class ) {
91 if ( $new_class->can("interpolate_class") ) {
92 return $new_class->interpolate_class($options);
101 if (my $traits = $options->{traits}) {
103 while ($i < @$traits) {
104 my $trait = $traits->[$i++];
105 next if ref($trait); # options to a trait we discarded
107 $trait = Moose::Util::resolve_metatrait_alias(Attribute => $trait)
110 next if $class->does($trait);
112 push @traits, $trait;
115 push @traits, $traits->[$i++]
116 if $traits->[$i] && ref($traits->[$i]);
120 my $anon_class = Moose::Meta::Class->create_anon_class(
121 superclasses => [ $class ],
122 roles => [ @traits ],
126 $class = $anon_class->name;
130 return ( wantarray ? ( $class, @traits ) : $class );
135 # method-generating options shouldn't be overridden
136 sub illegal_options_for_inheritance {
137 qw(reader writer accessor clearer predicate)
141 # This method *must* be able to handle
142 # Class::MOP::Attribute instances as
143 # well. Yes, I know that is wrong, but
144 # apparently we didn't realize it was
145 # doing that and now we have some code
146 # which is dependent on it. The real
147 # solution of course is to push this
148 # feature back up into Class::MOP::Attribute
149 # but I not right now, I am too lazy.
150 # However if you are reading this and
151 # looking for something to do,.. please
154 sub clone_and_inherit_options {
155 my ($self, %options) = @_;
158 # we may want to extends a Class::MOP::Attribute
159 # in which case we need to be able to use the
160 # core set of legal options that have always
161 # been here. But we allows Moose::Meta::Attribute
162 # instances to changes them.
164 my @illegal_options = $self->can('illegal_options_for_inheritance')
165 ? $self->illegal_options_for_inheritance
168 my @found_illegal_options = grep { exists $options{$_} && exists $self->{$_} ? $_ : undef } @illegal_options;
169 (scalar @found_illegal_options == 0)
170 || $self->throw_error("Illegal inherited options => (" . (join ', ' => @found_illegal_options) . ")", data => \%options);
174 if (blessed($options{isa}) && $options{isa}->isa('Moose::Meta::TypeConstraint')) {
175 $type_constraint = $options{isa};
178 $type_constraint = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options{isa});
179 (defined $type_constraint)
180 || $self->throw_error("Could not find the type constraint '" . $options{isa} . "'", data => $options{isa});
183 $options{type_constraint} = $type_constraint;
186 if ($options{does}) {
188 if (blessed($options{does}) && $options{does}->isa('Moose::Meta::TypeConstraint')) {
189 $type_constraint = $options{does};
192 $type_constraint = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options{does});
193 (defined $type_constraint)
194 || $self->throw_error("Could not find the type constraint '" . $options{does} . "'", data => $options{does});
197 $options{type_constraint} = $type_constraint;
201 # this doesn't apply to Class::MOP::Attributes,
202 # so we can ignore it for them.
204 if ($self->can('interpolate_class')) {
205 ( $options{metaclass}, my @traits ) = $self->interpolate_class(\%options);
208 my @all_traits = grep { $seen{$_}++ } @{ $self->applied_traits || [] }, @traits;
209 $options{traits} = \@all_traits if @all_traits;
212 $self->clone(%options);
216 my ( $self, %params ) = @_;
218 my $class = delete $params{metaclass} || ref $self;
220 my ( @init, @non_init );
222 foreach my $attr ( grep { $_->has_value($self) } Class::MOP::class_of($self)->get_all_attributes ) {
223 push @{ $attr->has_init_arg ? \@init : \@non_init }, $attr;
226 my %new_params = ( ( map { $_->init_arg => $_->get_value($self) } @init ), %params );
228 my $name = delete $new_params{name};
230 my $clone = $class->new($name, %new_params, __hack_no_process_options => 1 );
232 foreach my $attr ( @non_init ) {
233 $attr->set_value($clone, $attr->get_value($self));
239 sub _process_options {
240 my ($class, $name, $options) = @_;
242 if (exists $options->{is}) {
244 ### -------------------------
245 ## is => ro, writer => _foo # turns into (reader => foo, writer => _foo) as before
246 ## is => rw, writer => _foo # turns into (reader => foo, writer => _foo)
247 ## is => rw, accessor => _foo # turns into (accessor => _foo)
248 ## is => ro, accessor => _foo # error, accesor is rw
249 ### -------------------------
251 if ($options->{is} eq 'ro') {
252 $class->throw_error("Cannot define an accessor name on a read-only attribute, accessors are read/write", data => $options)
253 if exists $options->{accessor};
254 $options->{reader} ||= $name;
256 elsif ($options->{is} eq 'rw') {
257 if ($options->{writer}) {
258 $options->{reader} ||= $name;
261 $options->{accessor} ||= $name;
264 elsif ($options->{is} eq 'bare') {
265 # do nothing, but don't complain (later) about missing methods
268 $class->throw_error("I do not understand this option (is => " . $options->{is} . ") on attribute ($name)", data => $options->{is});
272 if (exists $options->{isa}) {
273 if (exists $options->{does}) {
274 if (try { $options->{isa}->can('does') }) {
275 ($options->{isa}->does($options->{does}))
276 || $class->throw_error("Cannot have an isa option and a does option if the isa does not do the does on attribute ($name)", data => $options);
279 $class->throw_error("Cannot have an isa option which cannot ->does() on attribute ($name)", data => $options);
283 # allow for anon-subtypes here ...
284 if (blessed($options->{isa}) && $options->{isa}->isa('Moose::Meta::TypeConstraint')) {
285 $options->{type_constraint} = $options->{isa};
288 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options->{isa});
291 elsif (exists $options->{does}) {
292 # allow for anon-subtypes here ...
293 if (blessed($options->{does}) && $options->{does}->isa('Moose::Meta::TypeConstraint')) {
294 $options->{type_constraint} = $options->{does};
297 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options->{does});
301 if (exists $options->{coerce} && $options->{coerce}) {
302 (exists $options->{type_constraint})
303 || $class->throw_error("You cannot have coercion without specifying a type constraint on attribute ($name)", data => $options);
304 $class->throw_error("You cannot have a weak reference to a coerced value on attribute ($name)", data => $options)
305 if $options->{weak_ref};
307 unless ( $options->{type_constraint}->has_coercion ) {
308 my $type = $options->{type_constraint}->name;
310 Moose::Deprecated::deprecated(
311 feature => 'coerce without coercion',
313 "You cannot coerce an attribute ($name) unless its type ($type) has a coercion"
318 if (exists $options->{trigger}) {
319 ('CODE' eq ref $options->{trigger})
320 || $class->throw_error("Trigger must be a CODE ref on attribute ($name)", data => $options->{trigger});
323 if (exists $options->{auto_deref} && $options->{auto_deref}) {
324 (exists $options->{type_constraint})
325 || $class->throw_error("You cannot auto-dereference without specifying a type constraint on attribute ($name)", data => $options);
326 ($options->{type_constraint}->is_a_type_of('ArrayRef') ||
327 $options->{type_constraint}->is_a_type_of('HashRef'))
328 || $class->throw_error("You cannot auto-dereference anything other than a ArrayRef or HashRef on attribute ($name)", data => $options);
331 if (exists $options->{lazy_build} && $options->{lazy_build} == 1) {
332 $class->throw_error("You can not use lazy_build and default for the same attribute ($name)", data => $options)
333 if exists $options->{default};
334 $options->{lazy} = 1;
335 $options->{builder} ||= "_build_${name}";
337 $options->{clearer} ||= "_clear${name}";
338 $options->{predicate} ||= "_has${name}";
341 $options->{clearer} ||= "clear_${name}";
342 $options->{predicate} ||= "has_${name}";
346 if (exists $options->{lazy} && $options->{lazy}) {
347 (exists $options->{default} || defined $options->{builder} )
348 || $class->throw_error("You cannot have lazy attribute ($name) without specifying a default value for it", data => $options);
351 if ( $options->{required} && !( ( !exists $options->{init_arg} || defined $options->{init_arg} ) || exists $options->{default} || defined $options->{builder} ) ) {
352 $class->throw_error("You cannot have a required attribute ($name) without a default, builder, or an init_arg", data => $options);
357 sub initialize_instance_slot {
358 my ($self, $meta_instance, $instance, $params) = @_;
359 my $init_arg = $self->init_arg();
360 # try to fetch the init arg from the %params ...
364 if ( defined($init_arg) and exists $params->{$init_arg}) {
365 $val = $params->{$init_arg};
369 # skip it if it's lazy
370 return if $self->is_lazy;
371 # and die if it's required and doesn't have a default value
372 $self->throw_error("Attribute (" . $self->name . ") is required", object => $instance, data => $params)
373 if $self->is_required && !$self->has_default && !$self->has_builder;
375 # if nothing was in the %params, we can use the
376 # attribute's default value (if it has one)
377 if ($self->has_default) {
378 $val = $self->default($instance);
381 elsif ($self->has_builder) {
382 $val = $self->_call_builder($instance);
387 return unless $value_is_set;
389 $val = $self->_coerce_and_verify( $val, $instance );
391 $self->set_initial_value($instance, $val);
393 if ( ref $val && $self->is_weak_ref ) {
394 $self->_weaken_value($instance);
399 my ( $self, $instance ) = @_;
401 my $builder = $self->builder();
403 return $instance->$builder()
404 if $instance->can( $self->builder );
406 $self->throw_error( blessed($instance)
407 . " does not support builder method '"
409 . "' for attribute '"
419 # this duplicates too much code from
420 # Class::MOP::Attribute, we need to
421 # refactor these bits eventually.
423 sub _set_initial_slot_value {
424 my ($self, $meta_instance, $instance, $value) = @_;
426 my $slot_name = $self->name;
428 return $meta_instance->set_slot_value($instance, $slot_name, $value)
429 unless $self->has_initializer;
432 my $val = $self->_coerce_and_verify( shift, $instance );;
434 $meta_instance->set_slot_value($instance, $slot_name, $val);
437 my $initializer = $self->initializer;
439 # most things will just want to set a value, so make it first arg
440 $instance->$initializer($value, $callback, $self);
444 my ($self, $instance, @args) = @_;
445 my $value = $args[0];
447 my $attr_name = $self->name;
449 if ($self->is_required and not @args) {
450 $self->throw_error("Attribute ($attr_name) is required", object => $instance);
453 $value = $self->_coerce_and_verify( $value, $instance );
456 if ( $self->has_trigger && $self->has_value($instance) ) {
457 @old = $self->get_value($instance, 'for trigger');
460 $self->SUPER::set_value($instance, $value);
462 if ( ref $value && $self->is_weak_ref ) {
463 $self->_weaken_value($instance);
466 if ($self->has_trigger) {
467 $self->trigger->($instance, $value, @old);
472 my ( $self, $instance ) = @_;
474 my $meta_instance = Class::MOP::Class->initialize( blessed($instance) )
477 $meta_instance->weaken_slot_value( $instance, $self->name );
481 my ($self, $instance, $for_trigger) = @_;
483 if ($self->is_lazy) {
484 unless ($self->has_value($instance)) {
486 if ($self->has_default) {
487 $value = $self->default($instance);
488 } elsif ( $self->has_builder ) {
489 $value = $self->_call_builder($instance);
492 $value = $self->_coerce_and_verify( $value, $instance );
494 $self->set_initial_value($instance, $value);
498 if ( $self->should_auto_deref && ! $for_trigger ) {
500 my $type_constraint = $self->type_constraint;
502 if ($type_constraint->is_a_type_of('ArrayRef')) {
503 my $rv = $self->SUPER::get_value($instance);
504 return unless defined $rv;
505 return wantarray ? @{ $rv } : $rv;
507 elsif ($type_constraint->is_a_type_of('HashRef')) {
508 my $rv = $self->SUPER::get_value($instance);
509 return unless defined $rv;
510 return wantarray ? %{ $rv } : $rv;
513 $self->throw_error("Can not auto de-reference the type constraint '" . $type_constraint->name . "'", object => $instance, type_constraint => $type_constraint);
519 return $self->SUPER::get_value($instance);
523 ## installing accessors
525 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
527 sub install_accessors {
529 $self->SUPER::install_accessors(@_);
530 $self->install_delegation if $self->has_handles;
534 sub _check_associated_methods {
537 @{ $self->associated_methods }
538 || ($self->_is_metadata || '') eq 'bare'
541 'Attribute (' . $self->name . ') of class '
542 . $self->associated_class->name
543 . ' has no associated methods'
544 . ' (did you mean to provide an "is" argument?)'
550 sub _process_accessors {
552 my ($type, $accessor, $generate_as_inline_methods) = @_;
553 $accessor = (keys %$accessor)[0] if (ref($accessor)||'') eq 'HASH';
554 my $method = $self->associated_class->get_method($accessor);
555 if ($method && !$method->isa('Class::MOP::Method::Accessor')
556 && (!$self->definition_context
557 || $method->package_name eq $self->definition_context->{package})) {
559 "You are overwriting a locally defined method ($accessor) with "
563 if (!$self->associated_class->has_method($accessor)
564 && $self->associated_class->has_package_symbol('&' . $accessor)) {
566 "You are overwriting a locally defined function ($accessor) with "
570 $self->SUPER::_process_accessors(@_);
573 sub remove_accessors {
575 $self->SUPER::remove_accessors(@_);
576 $self->remove_delegation if $self->has_handles;
582 my ( $instance, $value ) = @_;
584 my $mi = $self->associated_class->get_meta_instance;
587 = $mi->inline_set_slot_value( $instance, $self->slots, $value ) . ";";
589 .= $mi->inline_weaken_slot_value( $instance, $self->slots, $value )
591 if $self->is_weak_ref;
596 sub install_delegation {
600 # Here we canonicalize the 'handles' option
601 # this will sort out any details and always
602 # return an hash of methods which we want
603 # to delagate to, see that method for details
604 my %handles = $self->_canonicalize_handles;
607 # install the delegation ...
608 my $associated_class = $self->associated_class;
609 foreach my $handle (keys %handles) {
610 my $method_to_call = $handles{$handle};
611 my $class_name = $associated_class->name;
612 my $name = "${class_name}::${handle}";
614 (!$associated_class->has_method($handle))
615 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
618 # handles is not allowed to delegate
619 # any of these methods, as they will
620 # override the ones in your class, which
621 # is almost certainly not what you want.
623 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
624 #cluck("Not delegating method '$handle' because it is a core method") and
625 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
627 my $method = $self->_make_delegation_method($handle, $method_to_call);
629 $self->associated_class->add_method($method->name, $method);
630 $self->associate_method($method);
634 sub remove_delegation {
636 my %handles = $self->_canonicalize_handles;
637 my $associated_class = $self->associated_class;
638 foreach my $handle (keys %handles) {
639 next unless any { $handle eq $_ }
641 @{ $self->associated_methods };
642 $self->associated_class->remove_method($handle);
646 # private methods to help delegation ...
648 sub _canonicalize_handles {
650 my $handles = $self->handles;
651 if (my $handle_type = ref($handles)) {
652 if ($handle_type eq 'HASH') {
655 elsif ($handle_type eq 'ARRAY') {
656 return map { $_ => $_ } @{$handles};
658 elsif ($handle_type eq 'Regexp') {
659 ($self->has_type_constraint)
660 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
661 return map { ($_ => $_) }
662 grep { /$handles/ } $self->_get_delegate_method_list;
664 elsif ($handle_type eq 'CODE') {
665 return $handles->($self, $self->_find_delegate_metaclass);
667 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::DuckType')) {
668 return map { $_ => $_ } @{ $handles->methods };
670 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::Role')) {
671 $handles = $handles->role;
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 grep { $_ ne 'meta' } (
686 $role_meta->get_method_list,
687 map { $_->name } $role_meta->get_required_method_list,
691 sub _find_delegate_metaclass {
693 if (my $class = $self->_isa_metadata) {
694 # we might be dealing with a non-Moose class,
695 # and need to make our own metaclass. if there's
696 # already a metaclass, it will be returned
697 return Class::MOP::Class->initialize($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, $method_to_call ) = @_;
728 my @curried_arguments;
730 ($method_to_call, @curried_arguments) = @$method_to_call
731 if 'ARRAY' eq ref($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,
738 curried_arguments => \@curried_arguments,
742 sub _coerce_and_verify {
745 my $instance = shift;
747 return $val unless $self->has_type_constraint;
749 $val = $self->type_constraint->coerce($val)
750 if $self->should_coerce && $self->type_constraint->has_coercion;
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>) that defined a coercion. 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<< $attr->inline_set($instance_var, $value_var) >>
984 This method return a code snippet suitable for inlining the relevant
985 operation. It expect strings containing variable names to be used in the
986 inlining, like C<'$self'> or C<'$_[1]'>.
988 =item B<< $attr->install_delegation >>
990 This method adds its delegation methods to the attribute's associated
991 class, if it has any to add.
993 =item B<< $attr->remove_delegation >>
995 This method remove its delegation methods from the attribute's
998 =item B<< $attr->accessor_metaclass >>
1000 Returns the accessor metaclass name, which defaults to
1001 L<Moose::Meta::Method::Accessor>.
1003 =item B<< $attr->delegation_metaclass >>
1005 Returns the delegation metaclass name, which defaults to
1006 L<Moose::Meta::Method::Delegation>.
1010 =head2 Additional Moose features
1012 These methods are not found in the superclass. They support features
1017 =item B<< $attr->does($role) >>
1019 This indicates whether the I<attribute itself> does the given
1020 role. The role can be given as a full class name, or as a resolvable
1023 Note that this checks the attribute itself, not its type constraint,
1024 so it is checking the attribute's metaclass and any traits applied to
1027 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
1029 This is an alternate constructor that handles the C<metaclass> and
1032 Effectively, this method is a factory that finds or creates the
1033 appropriate class for the given C<metaclass> and/or C<traits>.
1035 Once it has the appropriate class, it will call C<< $class->new($name,
1036 %options) >> on that class.
1038 =item B<< $attr->clone_and_inherit_options(%options) >>
1040 This method supports the C<has '+foo'> feature. It does various bits
1041 of processing on the supplied C<%options> before ultimately calling
1042 the C<clone> method.
1044 One of its main tasks is to make sure that the C<%options> provided
1045 does not include the options returned by the
1046 C<illegal_options_for_inheritance> method.
1048 =item B<< $attr->illegal_options_for_inheritance >>
1050 This returns a blacklist of options that can not be overridden in a
1051 subclass's attribute definition.
1053 This exists to allow a custom metaclass to change or add to the list
1054 of options which can not be changed.
1056 =item B<< $attr->type_constraint >>
1058 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1061 =item B<< $attr->has_type_constraint >>
1063 Returns true if this attribute has a type constraint.
1065 =item B<< $attr->verify_against_type_constraint($value) >>
1067 Given a value, this method returns true if the value is valid for the
1068 attribute's type constraint. If the value is not valid, it throws an
1071 =item B<< $attr->handles >>
1073 This returns the value of the C<handles> option passed to the
1076 =item B<< $attr->has_handles >>
1078 Returns true if this attribute performs delegation.
1080 =item B<< $attr->is_weak_ref >>
1082 Returns true if this attribute stores its value as a weak reference.
1084 =item B<< $attr->is_required >>
1086 Returns true if this attribute is required to have a value.
1088 =item B<< $attr->is_lazy >>
1090 Returns true if this attribute is lazy.
1092 =item B<< $attr->is_lazy_build >>
1094 Returns true if the C<lazy_build> option was true when passed to the
1097 =item B<< $attr->should_coerce >>
1099 Returns true if the C<coerce> option passed to the constructor was
1102 =item B<< $attr->should_auto_deref >>
1104 Returns true if the C<auto_deref> option passed to the constructor was
1107 =item B<< $attr->trigger >>
1109 This is the subroutine reference that was in the C<trigger> option
1110 passed to the constructor, if any.
1112 =item B<< $attr->has_trigger >>
1114 Returns true if this attribute has a trigger set.
1116 =item B<< $attr->documentation >>
1118 Returns the value that was in the C<documentation> option passed to
1119 the constructor, if any.
1121 =item B<< $attr->has_documentation >>
1123 Returns true if this attribute has any documentation.
1125 =item B<< $attr->applied_traits >>
1127 This returns an array reference of all the traits which were applied
1128 to this attribute. If none were applied, this returns C<undef>.
1130 =item B<< $attr->has_applied_traits >>
1132 Returns true if this attribute has any traits applied.
1138 See L<Moose/BUGS> for details on reporting bugs.
1142 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1144 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1146 =head1 COPYRIGHT AND LICENSE
1148 Copyright 2006-2010 by Infinity Interactive, Inc.
1150 L<http://www.iinteractive.com>
1152 This library is free software; you can redistribute it and/or modify
1153 it under the same terms as Perl itself.