2 package Moose::Meta::Attribute;
8 use Scalar::Util 'blessed', 'weaken';
9 use List::MoreUtils 'any';
13 our $VERSION = '1.17';
14 our $AUTHORITY = 'cpan:STEVAN';
16 use Moose::Deprecated;
17 use Moose::Meta::Method::Accessor;
18 use Moose::Meta::Method::Delegation;
20 use Moose::Util::TypeConstraints ();
21 use Class::MOP::MiniTrait;
23 use base 'Class::MOP::Attribute', 'Moose::Meta::Mixin::AttributeCore';
25 Class::MOP::MiniTrait::apply(__PACKAGE__, 'Moose::Meta::Object::Trait');
27 __PACKAGE__->meta->add_attribute('traits' => (
28 reader => 'applied_traits',
29 predicate => 'has_applied_traits',
32 # we need to have a ->does method in here to
33 # more easily support traits, and the introspection
34 # of those traits. We extend the does check to look
35 # for metatrait aliases.
37 my ($self, $role_name) = @_;
39 Moose::Util::resolve_metatrait_alias(Attribute => $role_name)
41 return 0 if !defined($name); # failed to load class
42 return $self->Moose::Object::does($name);
47 my $class = ( ref $self && $self->associated_class ) || "Moose::Meta::Class";
48 unshift @_, "message" if @_ % 2 == 1;
49 unshift @_, attr => $self if ref $self;
51 my $handler = $class->can("throw_error"); # to avoid incrementing depth by 1
56 my ($class, $name, %options) = @_;
57 $class->_process_options($name, \%options) unless $options{__hack_no_process_options}; # used from clone()... YECHKKK FIXME ICKY YUCK GROSS
59 delete $options{__hack_no_process_options};
64 map { $_->init_arg() }
65 $class->meta()->get_all_attributes()
68 my @bad = sort grep { ! $attrs{$_} } keys %options;
72 Carp::cluck "Found unknown argument(s) passed to '$name' attribute constructor in '$class': @bad";
75 return $class->SUPER::new($name, %options);
78 sub interpolate_class_and_new {
79 my ($class, $name, %args) = @_;
81 my ( $new_class, @traits ) = $class->interpolate_class(\%args);
83 $new_class->new($name, %args, ( scalar(@traits) ? ( traits => \@traits ) : () ) );
86 sub interpolate_class {
87 my ($class, $options) = @_;
89 $class = ref($class) || $class;
91 if ( my $metaclass_name = delete $options->{metaclass} ) {
92 my $new_class = Moose::Util::resolve_metaclass_alias( Attribute => $metaclass_name );
94 if ( $class ne $new_class ) {
95 if ( $new_class->can("interpolate_class") ) {
96 return $new_class->interpolate_class($options);
105 if (my $traits = $options->{traits}) {
107 while ($i < @$traits) {
108 my $trait = $traits->[$i++];
109 next if ref($trait); # options to a trait we discarded
111 $trait = Moose::Util::resolve_metatrait_alias(Attribute => $trait)
114 next if $class->does($trait);
116 push @traits, $trait;
119 push @traits, $traits->[$i++]
120 if $traits->[$i] && ref($traits->[$i]);
124 my $anon_class = Moose::Meta::Class->create_anon_class(
125 superclasses => [ $class ],
126 roles => [ @traits ],
130 $class = $anon_class->name;
134 return ( wantarray ? ( $class, @traits ) : $class );
139 # method-generating options shouldn't be overridden
140 sub illegal_options_for_inheritance {
141 qw(reader writer accessor clearer predicate)
145 # This method *must* be able to handle
146 # Class::MOP::Attribute instances as
147 # well. Yes, I know that is wrong, but
148 # apparently we didn't realize it was
149 # doing that and now we have some code
150 # which is dependent on it. The real
151 # solution of course is to push this
152 # feature back up into Class::MOP::Attribute
153 # but I not right now, I am too lazy.
154 # However if you are reading this and
155 # looking for something to do,.. please
158 sub clone_and_inherit_options {
159 my ($self, %options) = @_;
162 # we may want to extends a Class::MOP::Attribute
163 # in which case we need to be able to use the
164 # core set of legal options that have always
165 # been here. But we allows Moose::Meta::Attribute
166 # instances to changes them.
168 my @illegal_options = $self->can('illegal_options_for_inheritance')
169 ? $self->illegal_options_for_inheritance
172 my @found_illegal_options = grep { exists $options{$_} && exists $self->{$_} ? $_ : undef } @illegal_options;
173 (scalar @found_illegal_options == 0)
174 || $self->throw_error("Illegal inherited options => (" . (join ', ' => @found_illegal_options) . ")", data => \%options);
178 if (blessed($options{isa}) && $options{isa}->isa('Moose::Meta::TypeConstraint')) {
179 $type_constraint = $options{isa};
182 $type_constraint = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options{isa});
183 (defined $type_constraint)
184 || $self->throw_error("Could not find the type constraint '" . $options{isa} . "'", data => $options{isa});
187 $options{type_constraint} = $type_constraint;
190 if ($options{does}) {
192 if (blessed($options{does}) && $options{does}->isa('Moose::Meta::TypeConstraint')) {
193 $type_constraint = $options{does};
196 $type_constraint = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options{does});
197 (defined $type_constraint)
198 || $self->throw_error("Could not find the type constraint '" . $options{does} . "'", data => $options{does});
201 $options{type_constraint} = $type_constraint;
205 # this doesn't apply to Class::MOP::Attributes,
206 # so we can ignore it for them.
208 if ($self->can('interpolate_class')) {
209 ( $options{metaclass}, my @traits ) = $self->interpolate_class(\%options);
212 my @all_traits = grep { $seen{$_}++ } @{ $self->applied_traits || [] }, @traits;
213 $options{traits} = \@all_traits if @all_traits;
216 $self->_modify_attr_options_for_lazy_build( $self->name, \%options );
218 $self->clone(%options);
222 my ( $self, %params ) = @_;
224 my $class = delete $params{metaclass} || ref $self;
226 my ( @init, @non_init );
228 foreach my $attr ( grep { $_->has_value($self) } Class::MOP::class_of($self)->get_all_attributes ) {
229 push @{ $attr->has_init_arg ? \@init : \@non_init }, $attr;
232 my %new_params = ( ( map { $_->init_arg => $_->get_value($self) } @init ), %params );
234 my $name = delete $new_params{name};
236 my $clone = $class->new($name, %new_params, __hack_no_process_options => 1 );
238 foreach my $attr ( @non_init ) {
239 $attr->set_value($clone, $attr->get_value($self));
245 sub _process_options {
246 my ($class, $name, $options) = @_;
248 if (exists $options->{is}) {
250 ### -------------------------
251 ## is => ro, writer => _foo # turns into (reader => foo, writer => _foo) as before
252 ## is => rw, writer => _foo # turns into (reader => foo, writer => _foo)
253 ## is => rw, accessor => _foo # turns into (accessor => _foo)
254 ## is => ro, accessor => _foo # error, accesor is rw
255 ### -------------------------
257 if ($options->{is} eq 'ro') {
258 $class->throw_error("Cannot define an accessor name on a read-only attribute, accessors are read/write", data => $options)
259 if exists $options->{accessor};
260 $options->{reader} ||= $name;
262 elsif ($options->{is} eq 'rw') {
263 if ($options->{writer}) {
264 $options->{reader} ||= $name;
267 $options->{accessor} ||= $name;
270 elsif ($options->{is} eq 'bare') {
271 # do nothing, but don't complain (later) about missing methods
274 $class->throw_error("I do not understand this option (is => " . $options->{is} . ") on attribute ($name)", data => $options->{is});
278 if (exists $options->{isa}) {
279 if (exists $options->{does}) {
280 if (try { $options->{isa}->can('does') }) {
281 ($options->{isa}->does($options->{does}))
282 || $class->throw_error("Cannot have an isa option and a does option if the isa does not do the does on attribute ($name)", data => $options);
285 $class->throw_error("Cannot have an isa option which cannot ->does() on attribute ($name)", data => $options);
289 # allow for anon-subtypes here ...
290 if (blessed($options->{isa}) && $options->{isa}->isa('Moose::Meta::TypeConstraint')) {
291 $options->{type_constraint} = $options->{isa};
294 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options->{isa});
297 elsif (exists $options->{does}) {
298 # allow for anon-subtypes here ...
299 if (blessed($options->{does}) && $options->{does}->isa('Moose::Meta::TypeConstraint')) {
300 $options->{type_constraint} = $options->{does};
303 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options->{does});
307 if (exists $options->{coerce} && $options->{coerce}) {
308 (exists $options->{type_constraint})
309 || $class->throw_error("You cannot have coercion without specifying a type constraint on attribute ($name)", data => $options);
310 $class->throw_error("You cannot have a weak reference to a coerced value on attribute ($name)", data => $options)
311 if $options->{weak_ref};
313 unless ( $options->{type_constraint}->has_coercion ) {
314 my $type = $options->{type_constraint}->name;
316 Moose::Deprecated::deprecated(
317 feature => 'coerce without coercion',
319 "You cannot coerce an attribute ($name) unless its type ($type) has a coercion"
324 if (exists $options->{trigger}) {
325 ('CODE' eq ref $options->{trigger})
326 || $class->throw_error("Trigger must be a CODE ref on attribute ($name)", data => $options->{trigger});
329 if (exists $options->{auto_deref} && $options->{auto_deref}) {
330 (exists $options->{type_constraint})
331 || $class->throw_error("You cannot auto-dereference without specifying a type constraint on attribute ($name)", data => $options);
332 ($options->{type_constraint}->is_a_type_of('ArrayRef') ||
333 $options->{type_constraint}->is_a_type_of('HashRef'))
334 || $class->throw_error("You cannot auto-dereference anything other than a ArrayRef or HashRef on attribute ($name)", data => $options);
337 $class->_modify_attr_options_for_lazy_build( $name, $options );
339 if (exists $options->{lazy} && $options->{lazy}) {
340 (exists $options->{default} || defined $options->{builder} )
341 || $class->throw_error("You cannot have lazy attribute ($name) without specifying a default value for it", data => $options);
344 if ( $options->{required} && !( ( !exists $options->{init_arg} || defined $options->{init_arg} ) || exists $options->{default} || defined $options->{builder} ) ) {
345 $class->throw_error("You cannot have a required attribute ($name) without a default, builder, or an init_arg", data => $options);
350 sub _modify_attr_options_for_lazy_build {
351 my ( $class, $name, $options ) = @_;
353 return unless $options->{lazy_build};
356 "You can not use lazy_build and default for the same attribute ($name)",
358 if exists $options->{default};
360 $options->{lazy} = 1;
361 $options->{builder} ||= "_build_${name}";
362 if ( $name =~ /^_/ ) {
363 $options->{clearer} ||= "_clear${name}";
364 $options->{predicate} ||= "_has${name}";
367 $options->{clearer} ||= "clear_${name}";
368 $options->{predicate} ||= "has_${name}";
372 sub initialize_instance_slot {
373 my ($self, $meta_instance, $instance, $params) = @_;
374 my $init_arg = $self->init_arg();
375 # try to fetch the init arg from the %params ...
379 if ( defined($init_arg) and exists $params->{$init_arg}) {
380 $val = $params->{$init_arg};
384 # skip it if it's lazy
385 return if $self->is_lazy;
386 # and die if it's required and doesn't have a default value
387 $self->throw_error("Attribute (" . $self->name . ") is required", object => $instance, data => $params)
388 if $self->is_required && !$self->has_default && !$self->has_builder;
390 # if nothing was in the %params, we can use the
391 # attribute's default value (if it has one)
392 if ($self->has_default) {
393 $val = $self->default($instance);
396 elsif ($self->has_builder) {
397 $val = $self->_call_builder($instance);
402 return unless $value_is_set;
404 $val = $self->_coerce_and_verify( $val, $instance );
406 $self->set_initial_value($instance, $val);
408 if ( ref $val && $self->is_weak_ref ) {
409 $self->_weaken_value($instance);
414 my ( $self, $instance ) = @_;
416 my $builder = $self->builder();
418 return $instance->$builder()
419 if $instance->can( $self->builder );
421 $self->throw_error( blessed($instance)
422 . " does not support builder method '"
424 . "' for attribute '"
434 # this duplicates too much code from
435 # Class::MOP::Attribute, we need to
436 # refactor these bits eventually.
438 sub _set_initial_slot_value {
439 my ($self, $meta_instance, $instance, $value) = @_;
441 my $slot_name = $self->name;
443 return $meta_instance->set_slot_value($instance, $slot_name, $value)
444 unless $self->has_initializer;
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 if (!$self->associated_class->has_method($accessor)
579 && $self->associated_class->has_package_symbol('&' . $accessor)) {
581 "You are overwriting a locally defined function ($accessor) with "
585 $self->SUPER::_process_accessors(@_);
588 sub remove_accessors {
590 $self->SUPER::remove_accessors(@_);
591 $self->remove_delegation if $self->has_handles;
597 my ( $instance, $value ) = @_;
599 my $mi = $self->associated_class->get_meta_instance;
602 = $mi->inline_set_slot_value( $instance, $self->slots, $value ) . ";";
604 .= $mi->inline_weaken_slot_value( $instance, $self->slots, $value )
606 if $self->is_weak_ref;
611 sub install_delegation {
615 # Here we canonicalize the 'handles' option
616 # this will sort out any details and always
617 # return an hash of methods which we want
618 # to delagate to, see that method for details
619 my %handles = $self->_canonicalize_handles;
622 # install the delegation ...
623 my $associated_class = $self->associated_class;
624 foreach my $handle (keys %handles) {
625 my $method_to_call = $handles{$handle};
626 my $class_name = $associated_class->name;
627 my $name = "${class_name}::${handle}";
629 (!$associated_class->has_method($handle))
630 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
633 # handles is not allowed to delegate
634 # any of these methods, as they will
635 # override the ones in your class, which
636 # is almost certainly not what you want.
638 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
639 #cluck("Not delegating method '$handle' because it is a core method") and
640 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
642 my $method = $self->_make_delegation_method($handle, $method_to_call);
644 $self->associated_class->add_method($method->name, $method);
645 $self->associate_method($method);
649 sub remove_delegation {
651 my %handles = $self->_canonicalize_handles;
652 my $associated_class = $self->associated_class;
653 foreach my $handle (keys %handles) {
654 next unless any { $handle eq $_ }
656 @{ $self->associated_methods };
657 $self->associated_class->remove_method($handle);
661 # private methods to help delegation ...
663 sub _canonicalize_handles {
665 my $handles = $self->handles;
666 if (my $handle_type = ref($handles)) {
667 if ($handle_type eq 'HASH') {
670 elsif ($handle_type eq 'ARRAY') {
671 return map { $_ => $_ } @{$handles};
673 elsif ($handle_type eq 'Regexp') {
674 ($self->has_type_constraint)
675 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
676 return map { ($_ => $_) }
677 grep { /$handles/ } $self->_get_delegate_method_list;
679 elsif ($handle_type eq 'CODE') {
680 return $handles->($self, $self->_find_delegate_metaclass);
682 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::DuckType')) {
683 return map { $_ => $_ } @{ $handles->methods };
685 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::Role')) {
686 $handles = $handles->role;
689 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
693 Class::MOP::load_class($handles);
694 my $role_meta = Class::MOP::class_of($handles);
696 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
697 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because its metaclass is not a Moose::Meta::Role", data => $handles);
699 return map { $_ => $_ }
701 grep { !$_->isa('Class::MOP::Method::Meta') } (
702 $role_meta->_get_local_methods,
703 $role_meta->get_required_method_list,
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 { $_->package_name ne 'Moose::Object' && !$_->isa('Class::MOP::Method::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 _find_delegate_metaclass {
725 if (my $class = $self->_isa_metadata) {
726 unless ( Class::MOP::is_class_loaded($class) ) {
729 'The %s attribute is trying to delegate to a class which has not been loaded - %s',
734 # we might be dealing with a non-Moose class,
735 # and need to make our own metaclass. if there's
736 # already a metaclass, it will be returned
737 return Class::MOP::Class->initialize($class);
739 elsif (my $role = $self->_does_metadata) {
740 unless ( Class::MOP::is_class_loaded($class) ) {
743 'The %s attribute is trying to delegate to a role which has not been loaded - %s',
749 return Class::MOP::class_of($role);
752 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
756 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
758 sub _make_delegation_method {
759 my ( $self, $handle_name, $method_to_call ) = @_;
761 my @curried_arguments;
763 ($method_to_call, @curried_arguments) = @$method_to_call
764 if 'ARRAY' eq ref($method_to_call);
766 return $self->delegation_metaclass->new(
767 name => $handle_name,
768 package_name => $self->associated_class->name,
770 delegate_to_method => $method_to_call,
771 curried_arguments => \@curried_arguments,
775 sub _coerce_and_verify {
778 my $instance = shift;
780 return $val unless $self->has_type_constraint;
782 $val = $self->type_constraint->coerce($val)
783 if $self->should_coerce && $self->type_constraint->has_coercion;
785 $self->verify_against_type_constraint($val, instance => $instance);
790 sub verify_against_type_constraint {
794 return 1 if !$self->has_type_constraint;
796 my $type_constraint = $self->type_constraint;
798 $type_constraint->check($val)
799 || $self->throw_error("Attribute ("
801 . ") does not pass the type constraint because: "
802 . $type_constraint->get_message($val), data => $val, @_);
805 package Moose::Meta::Attribute::Custom::Moose;
806 sub register_implementation { 'Moose::Meta::Attribute' }
816 Moose::Meta::Attribute - The Moose attribute metaclass
820 This class is a subclass of L<Class::MOP::Attribute> that provides
821 additional Moose-specific functionality.
823 To really understand this class, you will need to start with the
824 L<Class::MOP::Attribute> documentation. This class can be understood
825 as a set of additional features on top of the basic feature provided
826 by that parent class.
830 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
834 Many of the documented below override methods in
835 L<Class::MOP::Attribute> and add Moose specific features.
841 =item B<< Moose::Meta::Attribute->new(%options) >>
843 This method overrides the L<Class::MOP::Attribute> constructor.
845 Many of the options below are described in more detail in the
846 L<Moose::Manual::Attributes> document.
848 It adds the following options to the constructor:
852 =item * is => 'ro', 'rw', 'bare'
854 This provides a shorthand for specifying the C<reader>, C<writer>, or
855 C<accessor> names. If the attribute is read-only ('ro') then it will
856 have a C<reader> method with the same attribute as the name.
858 If it is read-write ('rw') then it will have an C<accessor> method
859 with the same name. If you provide an explicit C<writer> for a
860 read-write attribute, then you will have a C<reader> with the same
861 name as the attribute, and a C<writer> with the name you provided.
863 Use 'bare' when you are deliberately not installing any methods
864 (accessor, reader, etc.) associated with this attribute; otherwise,
865 Moose will issue a deprecation warning when this attribute is added to a
870 This option accepts a type. The type can be a string, which should be
871 a type name. If the type name is unknown, it is assumed to be a class
874 This option can also accept a L<Moose::Meta::TypeConstraint> object.
876 If you I<also> provide a C<does> option, then your C<isa> option must
877 be a class name, and that class must do the role specified with
880 =item * does => $role
882 This is short-hand for saying that the attribute's type must be an
883 object which does the named role.
885 =item * coerce => $bool
887 This option is only valid for objects with a type constraint
888 (C<isa>) that defined a coercion. If this is true, then coercions will be applied whenever
889 this attribute is set.
891 You can make both this and the C<weak_ref> option true.
893 =item * trigger => $sub
895 This option accepts a subroutine reference, which will be called after
896 the attribute is set.
898 =item * required => $bool
900 An attribute which is required must be provided to the constructor. An
901 attribute which is required can also have a C<default> or C<builder>,
902 which will satisfy its required-ness.
904 A required attribute must have a C<default>, C<builder> or a
905 non-C<undef> C<init_arg>
907 =item * lazy => $bool
909 A lazy attribute must have a C<default> or C<builder>. When an
910 attribute is lazy, the default value will not be calculated until the
913 =item * weak_ref => $bool
915 If this is true, the attribute's value will be stored as a weak
918 =item * auto_deref => $bool
920 If this is true, then the reader will dereference the value when it is
921 called. The attribute must have a type constraint which defines the
922 attribute as an array or hash reference.
924 =item * lazy_build => $bool
926 Setting this to true makes the attribute lazy and provides a number of
934 is equivalent to this:
939 builder => '_build_size',
940 clearer => 'clear_size',
941 predicate => 'has_size',
944 =item * documentation
946 An arbitrary string that can be retrieved later by calling C<<
947 $attr->documentation >>.
951 =item B<< $attr->clone(%options) >>
953 This creates a new attribute based on attribute being cloned. You must
954 supply a C<name> option to provide a new name for the attribute.
956 The C<%options> can only specify options handled by
957 L<Class::MOP::Attribute>.
961 =head2 Value management
965 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
967 This method is used internally to initialize the attribute's slot in
968 the object C<$instance>.
970 This overrides the L<Class::MOP::Attribute> method to handle lazy
971 attributes, weak references, and type constraints.
977 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
982 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
984 Before setting the value, a check is made on the type constraint of
985 the attribute, if it has one, to see if the value passes it. If the
986 value fails to pass, the set operation dies with a L</throw_error>.
988 Any coercion to convert values is done before checking the type constraint.
990 To check a value against a type constraint before setting it, fetch the
991 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
992 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
993 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
998 =head2 Attribute Accessor generation
1002 =item B<< $attr->install_accessors >>
1004 This method overrides the parent to also install delegation methods.
1006 If, after installing all methods, the attribute object has no associated
1007 methods, it throws an error unless C<< is => 'bare' >> was passed to the
1008 attribute constructor. (Trying to add an attribute that has no associated
1009 methods is almost always an error.)
1011 =item B<< $attr->remove_accessors >>
1013 This method overrides the parent to also remove delegation methods.
1015 =item B<< $attr->inline_set($instance_var, $value_var) >>
1017 This method return a code snippet suitable for inlining the relevant
1018 operation. It expect strings containing variable names to be used in the
1019 inlining, like C<'$self'> or C<'$_[1]'>.
1021 =item B<< $attr->install_delegation >>
1023 This method adds its delegation methods to the attribute's associated
1024 class, if it has any to add.
1026 =item B<< $attr->remove_delegation >>
1028 This method remove its delegation methods from the attribute's
1031 =item B<< $attr->accessor_metaclass >>
1033 Returns the accessor metaclass name, which defaults to
1034 L<Moose::Meta::Method::Accessor>.
1036 =item B<< $attr->delegation_metaclass >>
1038 Returns the delegation metaclass name, which defaults to
1039 L<Moose::Meta::Method::Delegation>.
1043 =head2 Additional Moose features
1045 These methods are not found in the superclass. They support features
1050 =item B<< $attr->does($role) >>
1052 This indicates whether the I<attribute itself> does the given
1053 role. The role can be given as a full class name, or as a resolvable
1056 Note that this checks the attribute itself, not its type constraint,
1057 so it is checking the attribute's metaclass and any traits applied to
1060 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
1062 This is an alternate constructor that handles the C<metaclass> and
1065 Effectively, this method is a factory that finds or creates the
1066 appropriate class for the given C<metaclass> and/or C<traits>.
1068 Once it has the appropriate class, it will call C<< $class->new($name,
1069 %options) >> on that class.
1071 =item B<< $attr->clone_and_inherit_options(%options) >>
1073 This method supports the C<has '+foo'> feature. It does various bits
1074 of processing on the supplied C<%options> before ultimately calling
1075 the C<clone> method.
1077 One of its main tasks is to make sure that the C<%options> provided
1078 does not include the options returned by the
1079 C<illegal_options_for_inheritance> method.
1081 =item B<< $attr->illegal_options_for_inheritance >>
1083 This returns a blacklist of options that can not be overridden in a
1084 subclass's attribute definition.
1086 This exists to allow a custom metaclass to change or add to the list
1087 of options which can not be changed.
1089 =item B<< $attr->type_constraint >>
1091 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1094 =item B<< $attr->has_type_constraint >>
1096 Returns true if this attribute has a type constraint.
1098 =item B<< $attr->verify_against_type_constraint($value) >>
1100 Given a value, this method returns true if the value is valid for the
1101 attribute's type constraint. If the value is not valid, it throws an
1104 =item B<< $attr->handles >>
1106 This returns the value of the C<handles> option passed to the
1109 =item B<< $attr->has_handles >>
1111 Returns true if this attribute performs delegation.
1113 =item B<< $attr->is_weak_ref >>
1115 Returns true if this attribute stores its value as a weak reference.
1117 =item B<< $attr->is_required >>
1119 Returns true if this attribute is required to have a value.
1121 =item B<< $attr->is_lazy >>
1123 Returns true if this attribute is lazy.
1125 =item B<< $attr->is_lazy_build >>
1127 Returns true if the C<lazy_build> option was true when passed to the
1130 =item B<< $attr->should_coerce >>
1132 Returns true if the C<coerce> option passed to the constructor was
1135 =item B<< $attr->should_auto_deref >>
1137 Returns true if the C<auto_deref> option passed to the constructor was
1140 =item B<< $attr->trigger >>
1142 This is the subroutine reference that was in the C<trigger> option
1143 passed to the constructor, if any.
1145 =item B<< $attr->has_trigger >>
1147 Returns true if this attribute has a trigger set.
1149 =item B<< $attr->documentation >>
1151 Returns the value that was in the C<documentation> option passed to
1152 the constructor, if any.
1154 =item B<< $attr->has_documentation >>
1156 Returns true if this attribute has any documentation.
1158 =item B<< $attr->applied_traits >>
1160 This returns an array reference of all the traits which were applied
1161 to this attribute. If none were applied, this returns C<undef>.
1163 =item B<< $attr->has_applied_traits >>
1165 Returns true if this attribute has any traits applied.
1171 See L<Moose/BUGS> for details on reporting bugs.
1175 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1177 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1179 =head1 COPYRIGHT AND LICENSE
1181 Copyright 2006-2010 by Infinity Interactive, Inc.
1183 L<http://www.iinteractive.com>
1185 This library is free software; you can redistribute it and/or modify
1186 it under the same terms as Perl itself.