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 # This method can be called on a CMOP::Attribute object, so we need to
217 # make sure that $self actually has this method.
218 $self->_modify_attr_options_for_lazy_build( $self->name, \%options )
219 if $self->can('_modify_attr_options_for_lazy_build');
221 $self->clone(%options);
225 my ( $self, %params ) = @_;
227 my $class = delete $params{metaclass} || ref $self;
229 my ( @init, @non_init );
231 foreach my $attr ( grep { $_->has_value($self) } Class::MOP::class_of($self)->get_all_attributes ) {
232 push @{ $attr->has_init_arg ? \@init : \@non_init }, $attr;
235 my %new_params = ( ( map { $_->init_arg => $_->get_value($self) } @init ), %params );
237 my $name = delete $new_params{name};
239 my $clone = $class->new($name, %new_params, __hack_no_process_options => 1 );
241 foreach my $attr ( @non_init ) {
242 $attr->set_value($clone, $attr->get_value($self));
248 sub _process_options {
249 my ($class, $name, $options) = @_;
251 if (exists $options->{is}) {
253 ### -------------------------
254 ## is => ro, writer => _foo # turns into (reader => foo, writer => _foo) as before
255 ## is => rw, writer => _foo # turns into (reader => foo, writer => _foo)
256 ## is => rw, accessor => _foo # turns into (accessor => _foo)
257 ## is => ro, accessor => _foo # error, accesor is rw
258 ### -------------------------
260 if ($options->{is} eq 'ro') {
261 $class->throw_error("Cannot define an accessor name on a read-only attribute, accessors are read/write", data => $options)
262 if exists $options->{accessor};
263 $options->{reader} ||= $name;
265 elsif ($options->{is} eq 'rw') {
266 if ($options->{writer}) {
267 $options->{reader} ||= $name;
270 $options->{accessor} ||= $name;
273 elsif ($options->{is} eq 'bare') {
274 # do nothing, but don't complain (later) about missing methods
277 $class->throw_error("I do not understand this option (is => " . $options->{is} . ") on attribute ($name)", data => $options->{is});
281 if (exists $options->{isa}) {
282 if (exists $options->{does}) {
283 if (try { $options->{isa}->can('does') }) {
284 ($options->{isa}->does($options->{does}))
285 || $class->throw_error("Cannot have an isa option and a does option if the isa does not do the does on attribute ($name)", data => $options);
288 $class->throw_error("Cannot have an isa option which cannot ->does() on attribute ($name)", data => $options);
292 # allow for anon-subtypes here ...
293 if (blessed($options->{isa}) && $options->{isa}->isa('Moose::Meta::TypeConstraint')) {
294 $options->{type_constraint} = $options->{isa};
297 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options->{isa});
300 elsif (exists $options->{does}) {
301 # allow for anon-subtypes here ...
302 if (blessed($options->{does}) && $options->{does}->isa('Moose::Meta::TypeConstraint')) {
303 $options->{type_constraint} = $options->{does};
306 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options->{does});
310 if (exists $options->{coerce} && $options->{coerce}) {
311 (exists $options->{type_constraint})
312 || $class->throw_error("You cannot have coercion without specifying a type constraint on attribute ($name)", data => $options);
313 $class->throw_error("You cannot have a weak reference to a coerced value on attribute ($name)", data => $options)
314 if $options->{weak_ref};
316 unless ( $options->{type_constraint}->has_coercion ) {
317 my $type = $options->{type_constraint}->name;
319 Moose::Deprecated::deprecated(
320 feature => 'coerce without coercion',
322 "You cannot coerce an attribute ($name) unless its type ($type) has a coercion"
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 $class->_modify_attr_options_for_lazy_build( $name, $options );
342 if (exists $options->{lazy} && $options->{lazy}) {
343 (exists $options->{default} || defined $options->{builder} )
344 || $class->throw_error("You cannot have lazy attribute ($name) without specifying a default value for it", data => $options);
347 if ( $options->{required} && !( ( !exists $options->{init_arg} || defined $options->{init_arg} ) || exists $options->{default} || defined $options->{builder} ) ) {
348 $class->throw_error("You cannot have a required attribute ($name) without a default, builder, or an init_arg", data => $options);
353 sub _modify_attr_options_for_lazy_build {
354 my ( $class, $name, $options ) = @_;
356 return unless $options->{lazy_build};
359 "You can not use lazy_build and default for the same attribute ($name)",
361 if exists $options->{default};
363 $options->{lazy} = 1;
364 $options->{builder} ||= "_build_${name}";
365 if ( $name =~ /^_/ ) {
366 $options->{clearer} ||= "_clear${name}";
367 $options->{predicate} ||= "_has${name}";
370 $options->{clearer} ||= "clear_${name}";
371 $options->{predicate} ||= "has_${name}";
375 sub initialize_instance_slot {
376 my ($self, $meta_instance, $instance, $params) = @_;
377 my $init_arg = $self->init_arg();
378 # try to fetch the init arg from the %params ...
382 if ( defined($init_arg) and exists $params->{$init_arg}) {
383 $val = $params->{$init_arg};
387 # skip it if it's lazy
388 return if $self->is_lazy;
389 # and die if it's required and doesn't have a default value
390 $self->throw_error("Attribute (" . $self->name . ") is required", object => $instance, data => $params)
391 if $self->is_required && !$self->has_default && !$self->has_builder;
393 # if nothing was in the %params, we can use the
394 # attribute's default value (if it has one)
395 if ($self->has_default) {
396 $val = $self->default($instance);
399 elsif ($self->has_builder) {
400 $val = $self->_call_builder($instance);
405 return unless $value_is_set;
407 $val = $self->_coerce_and_verify( $val, $instance );
409 $self->set_initial_value($instance, $val);
411 if ( ref $val && $self->is_weak_ref ) {
412 $self->_weaken_value($instance);
417 my ( $self, $instance ) = @_;
419 my $builder = $self->builder();
421 return $instance->$builder()
422 if $instance->can( $self->builder );
424 $self->throw_error( blessed($instance)
425 . " does not support builder method '"
427 . "' for attribute '"
437 # this duplicates too much code from
438 # Class::MOP::Attribute, we need to
439 # refactor these bits eventually.
441 sub _set_initial_slot_value {
442 my ($self, $meta_instance, $instance, $value) = @_;
444 my $slot_name = $self->name;
446 return $meta_instance->set_slot_value($instance, $slot_name, $value)
447 unless $self->has_initializer;
450 my $val = $self->_coerce_and_verify( shift, $instance );;
452 $meta_instance->set_slot_value($instance, $slot_name, $val);
455 my $initializer = $self->initializer;
457 # most things will just want to set a value, so make it first arg
458 $instance->$initializer($value, $callback, $self);
462 my ($self, $instance, @args) = @_;
463 my $value = $args[0];
465 my $attr_name = $self->name;
467 if ($self->is_required and not @args) {
468 $self->throw_error("Attribute ($attr_name) is required", object => $instance);
471 $value = $self->_coerce_and_verify( $value, $instance );
474 if ( $self->has_trigger && $self->has_value($instance) ) {
475 @old = $self->get_value($instance, 'for trigger');
478 $self->SUPER::set_value($instance, $value);
480 if ( ref $value && $self->is_weak_ref ) {
481 $self->_weaken_value($instance);
484 if ($self->has_trigger) {
485 $self->trigger->($instance, $value, @old);
490 my ( $self, $instance ) = @_;
492 my $meta_instance = Class::MOP::Class->initialize( blessed($instance) )
495 $meta_instance->weaken_slot_value( $instance, $self->name );
499 my ($self, $instance, $for_trigger) = @_;
501 if ($self->is_lazy) {
502 unless ($self->has_value($instance)) {
504 if ($self->has_default) {
505 $value = $self->default($instance);
506 } elsif ( $self->has_builder ) {
507 $value = $self->_call_builder($instance);
510 $value = $self->_coerce_and_verify( $value, $instance );
512 $self->set_initial_value($instance, $value);
516 if ( $self->should_auto_deref && ! $for_trigger ) {
518 my $type_constraint = $self->type_constraint;
520 if ($type_constraint->is_a_type_of('ArrayRef')) {
521 my $rv = $self->SUPER::get_value($instance);
522 return unless defined $rv;
523 return wantarray ? @{ $rv } : $rv;
525 elsif ($type_constraint->is_a_type_of('HashRef')) {
526 my $rv = $self->SUPER::get_value($instance);
527 return unless defined $rv;
528 return wantarray ? %{ $rv } : $rv;
531 $self->throw_error("Can not auto de-reference the type constraint '" . $type_constraint->name . "'", object => $instance, type_constraint => $type_constraint);
537 return $self->SUPER::get_value($instance);
541 ## installing accessors
543 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
545 sub install_accessors {
547 $self->SUPER::install_accessors(@_);
548 $self->install_delegation if $self->has_handles;
552 sub _check_associated_methods {
555 @{ $self->associated_methods }
556 || ($self->_is_metadata || '') eq 'bare'
559 'Attribute (' . $self->name . ') of class '
560 . $self->associated_class->name
561 . ' has no associated methods'
562 . ' (did you mean to provide an "is" argument?)'
568 sub _process_accessors {
570 my ($type, $accessor, $generate_as_inline_methods) = @_;
572 $accessor = ( keys %$accessor )[0] if ( ref($accessor) || '' ) eq 'HASH';
573 my $method = $self->associated_class->get_method($accessor);
577 && !$method->isa('Class::MOP::Method::Accessor')
578 && ( !$self->definition_context
579 || $method->package_name eq $self->definition_context->{package} )
583 "You are overwriting a locally defined method ($accessor) with "
586 if ( !$self->associated_class->has_method($accessor)
587 && $self->associated_class->has_package_symbol( '&' . $accessor ) ) {
590 "You are overwriting a locally defined function ($accessor) with "
594 $self->SUPER::_process_accessors(@_);
597 sub remove_accessors {
599 $self->SUPER::remove_accessors(@_);
600 $self->remove_delegation if $self->has_handles;
606 my ( $instance, $value ) = @_;
608 my $mi = $self->associated_class->get_meta_instance;
611 = $mi->inline_set_slot_value( $instance, $self->slots, $value ) . ";";
613 .= $mi->inline_weaken_slot_value( $instance, $self->slots, $value )
615 if $self->is_weak_ref;
620 sub install_delegation {
624 # Here we canonicalize the 'handles' option
625 # this will sort out any details and always
626 # return an hash of methods which we want
627 # to delagate to, see that method for details
628 my %handles = $self->_canonicalize_handles;
631 # install the delegation ...
632 my $associated_class = $self->associated_class;
633 foreach my $handle (keys %handles) {
634 my $method_to_call = $handles{$handle};
635 my $class_name = $associated_class->name;
636 my $name = "${class_name}::${handle}";
638 (!$associated_class->has_method($handle))
639 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
642 # handles is not allowed to delegate
643 # any of these methods, as they will
644 # override the ones in your class, which
645 # is almost certainly not what you want.
647 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
648 #cluck("Not delegating method '$handle' because it is a core method") and
649 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
651 my $method = $self->_make_delegation_method($handle, $method_to_call);
653 $self->associated_class->add_method($method->name, $method);
654 $self->associate_method($method);
658 sub remove_delegation {
660 my %handles = $self->_canonicalize_handles;
661 my $associated_class = $self->associated_class;
662 foreach my $handle (keys %handles) {
663 next unless any { $handle eq $_ }
665 @{ $self->associated_methods };
666 $self->associated_class->remove_method($handle);
670 # private methods to help delegation ...
672 sub _canonicalize_handles {
674 my $handles = $self->handles;
675 if (my $handle_type = ref($handles)) {
676 if ($handle_type eq 'HASH') {
679 elsif ($handle_type eq 'ARRAY') {
680 return map { $_ => $_ } @{$handles};
682 elsif ($handle_type eq 'Regexp') {
683 ($self->has_type_constraint)
684 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
685 return map { ($_ => $_) }
686 grep { /$handles/ } $self->_get_delegate_method_list;
688 elsif ($handle_type eq 'CODE') {
689 return $handles->($self, $self->_find_delegate_metaclass);
691 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::DuckType')) {
692 return map { $_ => $_ } @{ $handles->methods };
694 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::Role')) {
695 $handles = $handles->role;
698 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
702 Class::MOP::load_class($handles);
703 my $role_meta = Class::MOP::class_of($handles);
705 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
706 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because its metaclass is not a Moose::Meta::Role", data => $handles);
708 return map { $_ => $_ }
710 grep { !$_->isa('Class::MOP::Method::Meta') } (
711 $role_meta->_get_local_methods,
712 $role_meta->get_required_method_list,
716 sub _get_delegate_method_list {
718 my $meta = $self->_find_delegate_metaclass;
719 if ($meta->isa('Class::MOP::Class')) {
720 return map { $_->name } # NOTE: !never! delegate &meta
721 grep { $_->package_name ne 'Moose::Object' && !$_->isa('Class::MOP::Method::Meta') }
722 $meta->get_all_methods;
724 elsif ($meta->isa('Moose::Meta::Role')) {
725 return $meta->get_method_list;
728 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
732 sub _find_delegate_metaclass {
734 if (my $class = $self->_isa_metadata) {
735 unless ( Class::MOP::is_class_loaded($class) ) {
738 'The %s attribute is trying to delegate to a class which has not been loaded - %s',
743 # we might be dealing with a non-Moose class,
744 # and need to make our own metaclass. if there's
745 # already a metaclass, it will be returned
746 return Class::MOP::Class->initialize($class);
748 elsif (my $role = $self->_does_metadata) {
749 unless ( Class::MOP::is_class_loaded($class) ) {
752 'The %s attribute is trying to delegate to a role which has not been loaded - %s',
758 return Class::MOP::class_of($role);
761 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
765 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
767 sub _make_delegation_method {
768 my ( $self, $handle_name, $method_to_call ) = @_;
770 my @curried_arguments;
772 ($method_to_call, @curried_arguments) = @$method_to_call
773 if 'ARRAY' eq ref($method_to_call);
775 return $self->delegation_metaclass->new(
776 name => $handle_name,
777 package_name => $self->associated_class->name,
779 delegate_to_method => $method_to_call,
780 curried_arguments => \@curried_arguments,
784 sub _coerce_and_verify {
787 my $instance = shift;
789 return $val unless $self->has_type_constraint;
791 $val = $self->type_constraint->coerce($val)
792 if $self->should_coerce && $self->type_constraint->has_coercion;
794 $self->verify_against_type_constraint($val, instance => $instance);
799 sub verify_against_type_constraint {
803 return 1 if !$self->has_type_constraint;
805 my $type_constraint = $self->type_constraint;
807 $type_constraint->check($val)
808 || $self->throw_error("Attribute ("
810 . ") does not pass the type constraint because: "
811 . $type_constraint->get_message($val), data => $val, @_);
814 package Moose::Meta::Attribute::Custom::Moose;
815 sub register_implementation { 'Moose::Meta::Attribute' }
825 Moose::Meta::Attribute - The Moose attribute metaclass
829 This class is a subclass of L<Class::MOP::Attribute> that provides
830 additional Moose-specific functionality.
832 To really understand this class, you will need to start with the
833 L<Class::MOP::Attribute> documentation. This class can be understood
834 as a set of additional features on top of the basic feature provided
835 by that parent class.
839 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
843 Many of the documented below override methods in
844 L<Class::MOP::Attribute> and add Moose specific features.
850 =item B<< Moose::Meta::Attribute->new(%options) >>
852 This method overrides the L<Class::MOP::Attribute> constructor.
854 Many of the options below are described in more detail in the
855 L<Moose::Manual::Attributes> document.
857 It adds the following options to the constructor:
861 =item * is => 'ro', 'rw', 'bare'
863 This provides a shorthand for specifying the C<reader>, C<writer>, or
864 C<accessor> names. If the attribute is read-only ('ro') then it will
865 have a C<reader> method with the same attribute as the name.
867 If it is read-write ('rw') then it will have an C<accessor> method
868 with the same name. If you provide an explicit C<writer> for a
869 read-write attribute, then you will have a C<reader> with the same
870 name as the attribute, and a C<writer> with the name you provided.
872 Use 'bare' when you are deliberately not installing any methods
873 (accessor, reader, etc.) associated with this attribute; otherwise,
874 Moose will issue a deprecation warning when this attribute is added to a
879 This option accepts a type. The type can be a string, which should be
880 a type name. If the type name is unknown, it is assumed to be a class
883 This option can also accept a L<Moose::Meta::TypeConstraint> object.
885 If you I<also> provide a C<does> option, then your C<isa> option must
886 be a class name, and that class must do the role specified with
889 =item * does => $role
891 This is short-hand for saying that the attribute's type must be an
892 object which does the named role.
894 =item * coerce => $bool
896 This option is only valid for objects with a type constraint
897 (C<isa>) that defined a coercion. If this is true, then coercions will be applied whenever
898 this attribute is set.
900 You can make both this and the C<weak_ref> option true.
902 =item * trigger => $sub
904 This option accepts a subroutine reference, which will be called after
905 the attribute is set.
907 =item * required => $bool
909 An attribute which is required must be provided to the constructor. An
910 attribute which is required can also have a C<default> or C<builder>,
911 which will satisfy its required-ness.
913 A required attribute must have a C<default>, C<builder> or a
914 non-C<undef> C<init_arg>
916 =item * lazy => $bool
918 A lazy attribute must have a C<default> or C<builder>. When an
919 attribute is lazy, the default value will not be calculated until the
922 =item * weak_ref => $bool
924 If this is true, the attribute's value will be stored as a weak
927 =item * auto_deref => $bool
929 If this is true, then the reader will dereference the value when it is
930 called. The attribute must have a type constraint which defines the
931 attribute as an array or hash reference.
933 =item * lazy_build => $bool
935 Setting this to true makes the attribute lazy and provides a number of
943 is equivalent to this:
948 builder => '_build_size',
949 clearer => 'clear_size',
950 predicate => 'has_size',
953 =item * documentation
955 An arbitrary string that can be retrieved later by calling C<<
956 $attr->documentation >>.
960 =item B<< $attr->clone(%options) >>
962 This creates a new attribute based on attribute being cloned. You must
963 supply a C<name> option to provide a new name for the attribute.
965 The C<%options> can only specify options handled by
966 L<Class::MOP::Attribute>.
970 =head2 Value management
974 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
976 This method is used internally to initialize the attribute's slot in
977 the object C<$instance>.
979 This overrides the L<Class::MOP::Attribute> method to handle lazy
980 attributes, weak references, and type constraints.
986 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
991 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
993 Before setting the value, a check is made on the type constraint of
994 the attribute, if it has one, to see if the value passes it. If the
995 value fails to pass, the set operation dies with a L</throw_error>.
997 Any coercion to convert values is done before checking the type constraint.
999 To check a value against a type constraint before setting it, fetch the
1000 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
1001 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
1002 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
1007 =head2 Attribute Accessor generation
1011 =item B<< $attr->install_accessors >>
1013 This method overrides the parent to also install delegation methods.
1015 If, after installing all methods, the attribute object has no associated
1016 methods, it throws an error unless C<< is => 'bare' >> was passed to the
1017 attribute constructor. (Trying to add an attribute that has no associated
1018 methods is almost always an error.)
1020 =item B<< $attr->remove_accessors >>
1022 This method overrides the parent to also remove delegation methods.
1024 =item B<< $attr->inline_set($instance_var, $value_var) >>
1026 This method return a code snippet suitable for inlining the relevant
1027 operation. It expect strings containing variable names to be used in the
1028 inlining, like C<'$self'> or C<'$_[1]'>.
1030 =item B<< $attr->install_delegation >>
1032 This method adds its delegation methods to the attribute's associated
1033 class, if it has any to add.
1035 =item B<< $attr->remove_delegation >>
1037 This method remove its delegation methods from the attribute's
1040 =item B<< $attr->accessor_metaclass >>
1042 Returns the accessor metaclass name, which defaults to
1043 L<Moose::Meta::Method::Accessor>.
1045 =item B<< $attr->delegation_metaclass >>
1047 Returns the delegation metaclass name, which defaults to
1048 L<Moose::Meta::Method::Delegation>.
1052 =head2 Additional Moose features
1054 These methods are not found in the superclass. They support features
1059 =item B<< $attr->does($role) >>
1061 This indicates whether the I<attribute itself> does the given
1062 role. The role can be given as a full class name, or as a resolvable
1065 Note that this checks the attribute itself, not its type constraint,
1066 so it is checking the attribute's metaclass and any traits applied to
1069 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
1071 This is an alternate constructor that handles the C<metaclass> and
1074 Effectively, this method is a factory that finds or creates the
1075 appropriate class for the given C<metaclass> and/or C<traits>.
1077 Once it has the appropriate class, it will call C<< $class->new($name,
1078 %options) >> on that class.
1080 =item B<< $attr->clone_and_inherit_options(%options) >>
1082 This method supports the C<has '+foo'> feature. It does various bits
1083 of processing on the supplied C<%options> before ultimately calling
1084 the C<clone> method.
1086 One of its main tasks is to make sure that the C<%options> provided
1087 does not include the options returned by the
1088 C<illegal_options_for_inheritance> method.
1090 =item B<< $attr->illegal_options_for_inheritance >>
1092 This returns a blacklist of options that can not be overridden in a
1093 subclass's attribute definition.
1095 This exists to allow a custom metaclass to change or add to the list
1096 of options which can not be changed.
1098 =item B<< $attr->type_constraint >>
1100 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1103 =item B<< $attr->has_type_constraint >>
1105 Returns true if this attribute has a type constraint.
1107 =item B<< $attr->verify_against_type_constraint($value) >>
1109 Given a value, this method returns true if the value is valid for the
1110 attribute's type constraint. If the value is not valid, it throws an
1113 =item B<< $attr->handles >>
1115 This returns the value of the C<handles> option passed to the
1118 =item B<< $attr->has_handles >>
1120 Returns true if this attribute performs delegation.
1122 =item B<< $attr->is_weak_ref >>
1124 Returns true if this attribute stores its value as a weak reference.
1126 =item B<< $attr->is_required >>
1128 Returns true if this attribute is required to have a value.
1130 =item B<< $attr->is_lazy >>
1132 Returns true if this attribute is lazy.
1134 =item B<< $attr->is_lazy_build >>
1136 Returns true if the C<lazy_build> option was true when passed to the
1139 =item B<< $attr->should_coerce >>
1141 Returns true if the C<coerce> option passed to the constructor was
1144 =item B<< $attr->should_auto_deref >>
1146 Returns true if the C<auto_deref> option passed to the constructor was
1149 =item B<< $attr->trigger >>
1151 This is the subroutine reference that was in the C<trigger> option
1152 passed to the constructor, if any.
1154 =item B<< $attr->has_trigger >>
1156 Returns true if this attribute has a trigger set.
1158 =item B<< $attr->documentation >>
1160 Returns the value that was in the C<documentation> option passed to
1161 the constructor, if any.
1163 =item B<< $attr->has_documentation >>
1165 Returns true if this attribute has any documentation.
1167 =item B<< $attr->applied_traits >>
1169 This returns an array reference of all the traits which were applied
1170 to this attribute. If none were applied, this returns C<undef>.
1172 =item B<< $attr->has_applied_traits >>
1174 Returns true if this attribute has any traits applied.
1180 See L<Moose/BUGS> for details on reporting bugs.
1184 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1186 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1188 =head1 COPYRIGHT AND LICENSE
1190 Copyright 2006-2010 by Infinity Interactive, Inc.
1192 L<http://www.iinteractive.com>
1194 This library is free software; you can redistribute it and/or modify
1195 it under the same terms as Perl itself.