2 package Moose::Meta::Attribute;
7 use Scalar::Util 'blessed', 'weaken';
10 our $VERSION = '0.88';
11 our $AUTHORITY = 'cpan:STEVAN';
13 use Moose::Meta::Method::Accessor;
14 use Moose::Meta::Method::Delegation;
16 use Moose::Util::TypeConstraints ();
18 use base 'Class::MOP::Attribute';
20 # options which are not directly used
21 # but we store them for metadata purposes
22 __PACKAGE__->meta->add_attribute('isa' => (reader => '_isa_metadata'));
23 __PACKAGE__->meta->add_attribute('does' => (reader => '_does_metadata'));
24 __PACKAGE__->meta->add_attribute('is' => (reader => '_is_metadata'));
26 # these are actual options for the attrs
27 __PACKAGE__->meta->add_attribute('required' => (reader => 'is_required' ));
28 __PACKAGE__->meta->add_attribute('lazy' => (reader => 'is_lazy' ));
29 __PACKAGE__->meta->add_attribute('lazy_build' => (reader => 'is_lazy_build' ));
30 __PACKAGE__->meta->add_attribute('coerce' => (reader => 'should_coerce' ));
31 __PACKAGE__->meta->add_attribute('weak_ref' => (reader => 'is_weak_ref' ));
32 __PACKAGE__->meta->add_attribute('auto_deref' => (reader => 'should_auto_deref'));
33 __PACKAGE__->meta->add_attribute('type_constraint' => (
34 reader => 'type_constraint',
35 predicate => 'has_type_constraint',
37 __PACKAGE__->meta->add_attribute('trigger' => (
39 predicate => 'has_trigger',
41 __PACKAGE__->meta->add_attribute('handles' => (
43 writer => '_set_handles',
44 predicate => 'has_handles',
46 __PACKAGE__->meta->add_attribute('documentation' => (
47 reader => 'documentation',
48 predicate => 'has_documentation',
50 __PACKAGE__->meta->add_attribute('traits' => (
51 reader => 'applied_traits',
52 predicate => 'has_applied_traits',
55 # we need to have a ->does method in here to
56 # more easily support traits, and the introspection
57 # of those traits. We extend the does check to look
58 # for metatrait aliases.
60 my ($self, $role_name) = @_;
62 Moose::Util::resolve_metatrait_alias(Attribute => $role_name)
64 return 0 if !defined($name); # failed to load class
65 return $self->Moose::Object::does($name);
70 my $class = ( ref $self && $self->associated_class ) || "Moose::Meta::Class";
71 unshift @_, "message" if @_ % 2 == 1;
72 unshift @_, attr => $self if ref $self;
74 my $handler = $class->can("throw_error"); # to avoid incrementing depth by 1
79 my ($class, $name, %options) = @_;
80 $class->_process_options($name, \%options) unless $options{__hack_no_process_options}; # used from clone()... YECHKKK FIXME ICKY YUCK GROSS
82 delete $options{__hack_no_process_options};
87 map { $_->init_arg() }
88 $class->meta()->get_all_attributes()
91 my @bad = sort grep { ! $attrs{$_} } keys %options;
95 Carp::cluck "Found unknown argument(s) passed to '$name' attribute constructor in '$class': @bad";
98 return $class->SUPER::new($name, %options);
101 sub interpolate_class_and_new {
102 my ($class, $name, %args) = @_;
104 my ( $new_class, @traits ) = $class->interpolate_class(\%args);
106 $new_class->new($name, %args, ( scalar(@traits) ? ( traits => \@traits ) : () ) );
109 sub interpolate_class {
110 my ($class, $options) = @_;
112 $class = ref($class) || $class;
114 if ( my $metaclass_name = delete $options->{metaclass} ) {
115 my $new_class = Moose::Util::resolve_metaclass_alias( Attribute => $metaclass_name );
117 if ( $class ne $new_class ) {
118 if ( $new_class->can("interpolate_class") ) {
119 return $new_class->interpolate_class($options);
128 if (my $traits = $options->{traits}) {
130 while ($i < @$traits) {
131 my $trait = $traits->[$i++];
132 next if ref($trait); # options to a trait we discarded
134 $trait = Moose::Util::resolve_metatrait_alias(Attribute => $trait)
137 next if $class->does($trait);
139 push @traits, $trait;
142 push @traits, $traits->[$i++]
143 if $traits->[$i] && ref($traits->[$i]);
147 my $anon_class = Moose::Meta::Class->create_anon_class(
148 superclasses => [ $class ],
149 roles => [ @traits ],
153 $class = $anon_class->name;
157 return ( wantarray ? ( $class, @traits ) : $class );
162 my @legal_options_for_inheritance = qw(
163 default coerce required
164 documentation lazy handles
165 builder type_constraint
170 sub legal_options_for_inheritance { @legal_options_for_inheritance }
173 # This method *must* be able to handle
174 # Class::MOP::Attribute instances as
175 # well. Yes, I know that is wrong, but
176 # apparently we didn't realize it was
177 # doing that and now we have some code
178 # which is dependent on it. The real
179 # solution of course is to push this
180 # feature back up into Class::MOP::Attribute
181 # but I not right now, I am too lazy.
182 # However if you are reading this and
183 # looking for something to do,.. please
186 sub clone_and_inherit_options {
187 my ($self, %options) = @_;
194 # we may want to extends a Class::MOP::Attribute
195 # in which case we need to be able to use the
196 # core set of legal options that have always
197 # been here. But we allows Moose::Meta::Attribute
198 # instances to changes them.
200 my @legal_options = $self->can('legal_options_for_inheritance')
201 ? $self->legal_options_for_inheritance
202 : @legal_options_for_inheritance;
204 foreach my $legal_option (@legal_options) {
205 if (exists $options{$legal_option}) {
206 $actual_options{$legal_option} = $options{$legal_option};
207 delete $options{$legal_option};
213 if (blessed($options{isa}) && $options{isa}->isa('Moose::Meta::TypeConstraint')) {
214 $type_constraint = $options{isa};
217 $type_constraint = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options{isa});
218 (defined $type_constraint)
219 || $self->throw_error("Could not find the type constraint '" . $options{isa} . "'", data => $options{isa});
222 $actual_options{type_constraint} = $type_constraint;
223 delete $options{isa};
226 if ($options{does}) {
228 if (blessed($options{does}) && $options{does}->isa('Moose::Meta::TypeConstraint')) {
229 $type_constraint = $options{does};
232 $type_constraint = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options{does});
233 (defined $type_constraint)
234 || $self->throw_error("Could not find the type constraint '" . $options{does} . "'", data => $options{does});
237 $actual_options{type_constraint} = $type_constraint;
238 delete $options{does};
242 # this doesn't apply to Class::MOP::Attributes,
243 # so we can ignore it for them.
245 if ($self->can('interpolate_class')) {
246 ( $actual_options{metaclass}, my @traits ) = $self->interpolate_class(\%options);
249 my @all_traits = grep { $seen{$_}++ } @{ $self->applied_traits || [] }, @traits;
250 $actual_options{traits} = \@all_traits if @all_traits;
252 delete @options{qw(metaclass traits)};
255 (scalar keys %options == 0)
256 || $self->throw_error("Illegal inherited options => (" . (join ', ' => keys %options) . ")", data => \%options);
259 $self->clone(%actual_options);
263 my ( $self, %params ) = @_;
265 my $class = delete $params{metaclass} || ref $self;
267 my ( @init, @non_init );
269 foreach my $attr ( grep { $_->has_value($self) } Class::MOP::class_of($self)->get_all_attributes ) {
270 push @{ $attr->has_init_arg ? \@init : \@non_init }, $attr;
273 my %new_params = ( ( map { $_->init_arg => $_->get_value($self) } @init ), %params );
275 my $name = delete $new_params{name};
277 my $clone = $class->new($name, %new_params, __hack_no_process_options => 1 );
279 foreach my $attr ( @non_init ) {
280 $attr->set_value($clone, $attr->get_value($self));
286 sub _process_options {
287 my ($class, $name, $options) = @_;
289 if (exists $options->{is}) {
291 ### -------------------------
292 ## is => ro, writer => _foo # turns into (reader => foo, writer => _foo) as before
293 ## is => rw, writer => _foo # turns into (reader => foo, writer => _foo)
294 ## is => rw, accessor => _foo # turns into (accessor => _foo)
295 ## is => ro, accessor => _foo # error, accesor is rw
296 ### -------------------------
298 if ($options->{is} eq 'ro') {
299 $class->throw_error("Cannot define an accessor name on a read-only attribute, accessors are read/write", data => $options)
300 if exists $options->{accessor};
301 $options->{reader} ||= $name;
303 elsif ($options->{is} eq 'rw') {
304 if ($options->{writer}) {
305 $options->{reader} ||= $name;
308 $options->{accessor} ||= $name;
311 elsif ($options->{is} eq 'bare') {
312 # do nothing, but don't complain (later) about missing methods
315 $class->throw_error("I do not understand this option (is => " . $options->{is} . ") on attribute ($name)", data => $options->{is});
319 if (exists $options->{isa}) {
320 if (exists $options->{does}) {
321 if (eval { $options->{isa}->can('does') }) {
322 ($options->{isa}->does($options->{does}))
323 || $class->throw_error("Cannot have an isa option and a does option if the isa does not do the does on attribute ($name)", data => $options);
326 $class->throw_error("Cannot have an isa option which cannot ->does() on attribute ($name)", data => $options);
330 # allow for anon-subtypes here ...
331 if (blessed($options->{isa}) && $options->{isa}->isa('Moose::Meta::TypeConstraint')) {
332 $options->{type_constraint} = $options->{isa};
335 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options->{isa});
338 elsif (exists $options->{does}) {
339 # allow for anon-subtypes here ...
340 if (blessed($options->{does}) && $options->{does}->isa('Moose::Meta::TypeConstraint')) {
341 $options->{type_constraint} = $options->{does};
344 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options->{does});
348 if (exists $options->{coerce} && $options->{coerce}) {
349 (exists $options->{type_constraint})
350 || $class->throw_error("You cannot have coercion without specifying a type constraint on attribute ($name)", data => $options);
351 $class->throw_error("You cannot have a weak reference to a coerced value on attribute ($name)", data => $options)
352 if $options->{weak_ref};
355 if (exists $options->{trigger}) {
356 ('CODE' eq ref $options->{trigger})
357 || $class->throw_error("Trigger must be a CODE ref on attribute ($name)", data => $options->{trigger});
360 if (exists $options->{auto_deref} && $options->{auto_deref}) {
361 (exists $options->{type_constraint})
362 || $class->throw_error("You cannot auto-dereference without specifying a type constraint on attribute ($name)", data => $options);
363 ($options->{type_constraint}->is_a_type_of('ArrayRef') ||
364 $options->{type_constraint}->is_a_type_of('HashRef'))
365 || $class->throw_error("You cannot auto-dereference anything other than a ArrayRef or HashRef on attribute ($name)", data => $options);
368 if (exists $options->{lazy_build} && $options->{lazy_build} == 1) {
369 $class->throw_error("You can not use lazy_build and default for the same attribute ($name)", data => $options)
370 if exists $options->{default};
371 $options->{lazy} = 1;
372 $options->{builder} ||= "_build_${name}";
374 $options->{clearer} ||= "_clear${name}";
375 $options->{predicate} ||= "_has${name}";
378 $options->{clearer} ||= "clear_${name}";
379 $options->{predicate} ||= "has_${name}";
383 if (exists $options->{lazy} && $options->{lazy}) {
384 (exists $options->{default} || defined $options->{builder} )
385 || $class->throw_error("You cannot have lazy attribute ($name) without specifying a default value for it", data => $options);
388 if ( $options->{required} && !( ( !exists $options->{init_arg} || defined $options->{init_arg} ) || exists $options->{default} || defined $options->{builder} ) ) {
389 $class->throw_error("You cannot have a required attribute ($name) without a default, builder, or an init_arg", data => $options);
394 sub initialize_instance_slot {
395 my ($self, $meta_instance, $instance, $params) = @_;
396 my $init_arg = $self->init_arg();
397 # try to fetch the init arg from the %params ...
401 if ( defined($init_arg) and exists $params->{$init_arg}) {
402 $val = $params->{$init_arg};
406 # skip it if it's lazy
407 return if $self->is_lazy;
408 # and die if it's required and doesn't have a default value
409 $self->throw_error("Attribute (" . $self->name . ") is required", object => $instance, data => $params)
410 if $self->is_required && !$self->has_default && !$self->has_builder;
412 # if nothing was in the %params, we can use the
413 # attribute's default value (if it has one)
414 if ($self->has_default) {
415 $val = $self->default($instance);
418 elsif ($self->has_builder) {
419 $val = $self->_call_builder($instance);
424 return unless $value_is_set;
426 $val = $self->_coerce_and_verify( $val, $instance );
428 $self->set_initial_value($instance, $val);
429 $meta_instance->weaken_slot_value($instance, $self->name)
430 if ref $val && $self->is_weak_ref;
434 my ( $self, $instance ) = @_;
436 my $builder = $self->builder();
438 return $instance->$builder()
439 if $instance->can( $self->builder );
441 $self->throw_error( blessed($instance)
442 . " does not support builder method '"
444 . "' for attribute '"
454 # this duplicates too much code from
455 # Class::MOP::Attribute, we need to
456 # refactor these bits eventually.
458 sub _set_initial_slot_value {
459 my ($self, $meta_instance, $instance, $value) = @_;
461 my $slot_name = $self->name;
463 return $meta_instance->set_slot_value($instance, $slot_name, $value)
464 unless $self->has_initializer;
466 my ($type_constraint, $can_coerce);
467 if ($self->has_type_constraint) {
468 $type_constraint = $self->type_constraint;
469 $can_coerce = ($self->should_coerce && $type_constraint->has_coercion);
473 my $val = $self->_coerce_and_verify( shift, $instance );;
475 $meta_instance->set_slot_value($instance, $slot_name, $val);
478 my $initializer = $self->initializer;
480 # most things will just want to set a value, so make it first arg
481 $instance->$initializer($value, $callback, $self);
485 my ($self, $instance, @args) = @_;
486 my $value = $args[0];
488 my $attr_name = $self->name;
490 if ($self->is_required and not @args) {
491 $self->throw_error("Attribute ($attr_name) is required", object => $instance);
494 $value = $self->_coerce_and_verify( $value, $instance );
496 my $meta_instance = Class::MOP::Class->initialize(blessed($instance))
499 $meta_instance->set_slot_value($instance, $attr_name, $value);
501 if (ref $value && $self->is_weak_ref) {
502 $meta_instance->weaken_slot_value($instance, $attr_name);
505 if ($self->has_trigger) {
506 $self->trigger->($instance, $value);
511 my ($self, $instance) = @_;
513 if ($self->is_lazy) {
514 unless ($self->has_value($instance)) {
516 if ($self->has_default) {
517 $value = $self->default($instance);
518 } elsif ( $self->has_builder ) {
519 $value = $self->_call_builder($instance);
522 $value = $self->_coerce_and_verify( $value, $instance );
524 $self->set_initial_value($instance, $value);
528 if ($self->should_auto_deref) {
530 my $type_constraint = $self->type_constraint;
532 if ($type_constraint->is_a_type_of('ArrayRef')) {
533 my $rv = $self->SUPER::get_value($instance);
534 return unless defined $rv;
535 return wantarray ? @{ $rv } : $rv;
537 elsif ($type_constraint->is_a_type_of('HashRef')) {
538 my $rv = $self->SUPER::get_value($instance);
539 return unless defined $rv;
540 return wantarray ? %{ $rv } : $rv;
543 $self->throw_error("Can not auto de-reference the type constraint '" . $type_constraint->name . "'", object => $instance, type_constraint => $type_constraint);
549 return $self->SUPER::get_value($instance);
553 ## installing accessors
555 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
557 sub install_accessors {
559 $self->SUPER::install_accessors(@_);
560 $self->install_delegation if $self->has_handles;
564 sub _check_associated_methods {
567 @{ $self->associated_methods }
568 || ($self->_is_metadata || '') eq 'bare'
571 'Attribute (' . $self->name . ') of class '
572 . $self->associated_class->name
573 . ' has no associated methods'
574 . ' (did you mean to provide an "is" argument?)'
580 sub _process_accessors {
582 my ($type, $accessor, $generate_as_inline_methods) = @_;
583 $accessor = (keys %$accessor)[0] if (ref($accessor)||'') eq 'HASH';
584 my $method = $self->associated_class->get_method($accessor);
585 if ($method && !$method->isa('Class::MOP::Method::Accessor')
586 && (!$self->definition_context
587 || $method->package_name eq $self->definition_context->{package})) {
589 "You are overwriting a locally defined method ($accessor) with "
593 $self->SUPER::_process_accessors(@_);
596 sub remove_accessors {
598 $self->SUPER::remove_accessors(@_);
599 $self->remove_delegation if $self->has_handles;
603 sub install_delegation {
607 # Here we canonicalize the 'handles' option
608 # this will sort out any details and always
609 # return an hash of methods which we want
610 # to delagate to, see that method for details
611 my %handles = $self->_canonicalize_handles;
614 # install the delegation ...
615 my $associated_class = $self->associated_class;
616 foreach my $handle (keys %handles) {
617 my $method_to_call = $handles{$handle};
618 my $class_name = $associated_class->name;
619 my $name = "${class_name}::${handle}";
621 (!$associated_class->has_method($handle))
622 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
625 # handles is not allowed to delegate
626 # any of these methods, as they will
627 # override the ones in your class, which
628 # is almost certainly not what you want.
630 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
631 #cluck("Not delegating method '$handle' because it is a core method") and
632 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
634 my $method = $self->_make_delegation_method($handle, $method_to_call);
636 $self->associated_class->add_method($method->name, $method);
637 $self->associate_method($method);
641 sub remove_delegation {
643 my %handles = $self->_canonicalize_handles;
644 my $associated_class = $self->associated_class;
645 foreach my $handle (keys %handles) {
646 $self->associated_class->remove_method($handle);
650 # private methods to help delegation ...
652 sub _canonicalize_handles {
654 my $handles = $self->handles;
655 if (my $handle_type = ref($handles)) {
656 if ($handle_type eq 'HASH') {
659 elsif ($handle_type eq 'ARRAY') {
660 return map { $_ => $_ } @{$handles};
662 elsif ($handle_type eq 'Regexp') {
663 ($self->has_type_constraint)
664 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
665 return map { ($_ => $_) }
666 grep { /$handles/ } $self->_get_delegate_method_list;
668 elsif ($handle_type eq 'CODE') {
669 return $handles->($self, $self->_find_delegate_metaclass);
671 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::DuckType')) {
672 return map { $_ => $_ } @{ $handles->methods };
675 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
679 Class::MOP::load_class($handles);
680 my $role_meta = Class::MOP::class_of($handles);
682 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
683 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because its metaclass is not a Moose::Meta::Role", data => $handles);
685 return map { $_ => $_ } (
686 $role_meta->get_method_list,
687 map { $_->name } $role_meta->get_required_method_list,
692 sub _find_delegate_metaclass {
694 if (my $class = $self->_isa_metadata) {
695 # we might be dealing with a non-Moose class,
696 # and need to make our own metaclass. if there's
697 # already a metaclass, it will be returned
698 return Moose::Meta::Class->initialize($class);
700 elsif (my $role = $self->_does_metadata) {
701 return Class::MOP::class_of($role);
704 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
708 sub _get_delegate_method_list {
710 my $meta = $self->_find_delegate_metaclass;
711 if ($meta->isa('Class::MOP::Class')) {
712 return map { $_->name } # NOTE: !never! delegate &meta
713 grep { $_->package_name ne 'Moose::Object' && $_->name ne 'meta' }
714 $meta->get_all_methods;
716 elsif ($meta->isa('Moose::Meta::Role')) {
717 return $meta->get_method_list;
720 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
724 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
726 sub _make_delegation_method {
727 my ( $self, $handle_name, $method_to_call ) = @_;
731 $method_body = $method_to_call
732 if 'CODE' eq ref($method_to_call);
734 my $curried_arguments = [];
736 ($method_to_call, $curried_arguments) = @$method_to_call
737 if 'ARRAY' eq ref($method_to_call);
739 return $self->delegation_metaclass->new(
740 name => $handle_name,
741 package_name => $self->associated_class->name,
743 delegate_to_method => $method_to_call,
744 curried_arguments => $curried_arguments || [],
748 sub _coerce_and_verify {
751 my $instance = shift;
753 return $val unless $self->has_type_constraint;
755 my $type_constraint = $self->type_constraint;
756 if ($self->should_coerce && $type_constraint->has_coercion) {
757 $val = $type_constraint->coerce($val);
760 $self->verify_against_type_constraint($val, instance => $instance);
765 sub verify_against_type_constraint {
769 return 1 if !$self->has_type_constraint;
771 my $type_constraint = $self->type_constraint;
773 $type_constraint->check($val)
774 || $self->throw_error("Attribute ("
776 . ") does not pass the type constraint because: "
777 . $type_constraint->get_message($val), data => $val, @_);
780 package Moose::Meta::Attribute::Custom::Moose;
781 sub register_implementation { 'Moose::Meta::Attribute' }
791 Moose::Meta::Attribute - The Moose attribute metaclass
795 This class is a subclass of L<Class::MOP::Attribute> that provides
796 additional Moose-specific functionality.
798 To really understand this class, you will need to start with the
799 L<Class::MOP::Attribute> documentation. This class can be understood
800 as a set of additional features on top of the basic feature provided
801 by that parent class.
805 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
809 Many of the documented below override methods in
810 L<Class::MOP::Attribute> and add Moose specific features.
816 =item B<< Moose::Meta::Attribute->new(%options) >>
818 This method overrides the L<Class::MOP::Attribute> constructor.
820 Many of the options below are described in more detail in the
821 L<Moose::Manual::Attributes> document.
823 It adds the following options to the constructor:
827 =item * is => 'ro', 'rw', 'bare'
829 This provides a shorthand for specifying the C<reader>, C<writer>, or
830 C<accessor> names. If the attribute is read-only ('ro') then it will
831 have a C<reader> method with the same attribute as the name.
833 If it is read-write ('rw') then it will have an C<accessor> method
834 with the same name. If you provide an explicit C<writer> for a
835 read-write attribute, then you will have a C<reader> with the same
836 name as the attribute, and a C<writer> with the name you provided.
838 Use 'bare' when you are deliberately not installing any methods
839 (accessor, reader, etc.) associated with this attribute; otherwise,
840 Moose will issue a deprecation warning when this attribute is added to a
845 This option accepts a type. The type can be a string, which should be
846 a type name. If the type name is unknown, it is assumed to be a class
849 This option can also accept a L<Moose::Meta::TypeConstraint> object.
851 If you I<also> provide a C<does> option, then your C<isa> option must
852 be a class name, and that class must do the role specified with
855 =item * does => $role
857 This is short-hand for saying that the attribute's type must be an
858 object which does the named role.
860 =item * coerce => $bool
862 This option is only valid for objects with a type constraint
863 (C<isa>). If this is true, then coercions will be applied whenever
864 this attribute is set.
866 You can make both this and the C<weak_ref> option true.
868 =item * trigger => $sub
870 This option accepts a subroutine reference, which will be called after
871 the attribute is set.
873 =item * required => $bool
875 An attribute which is required must be provided to the constructor. An
876 attribute which is required can also have a C<default> or C<builder>,
877 which will satisfy its required-ness.
879 A required attribute must have a C<default>, C<builder> or a
880 non-C<undef> C<init_arg>
882 =item * lazy => $bool
884 A lazy attribute must have a C<default> or C<builder>. When an
885 attribute is lazy, the default value will not be calculated until the
888 =item * weak_ref => $bool
890 If this is true, the attribute's value will be stored as a weak
893 =item * auto_deref => $bool
895 If this is true, then the reader will dereference the value when it is
896 called. The attribute must have a type constraint which defines the
897 attribute as an array or hash reference.
899 =item * lazy_build => $bool
901 Setting this to true makes the attribute lazy and provides a number of
909 is equivalent to this:
914 builder => '_build_size',
915 clearer => 'clear_size',
916 predicate => 'has_size',
919 =item * documentation
921 An arbitrary string that can be retrieved later by calling C<<
922 $attr->documentation >>.
926 =item B<< $attr->clone(%options) >>
928 This creates a new attribute based on attribute being cloned. You must
929 supply a C<name> option to provide a new name for the attribute.
931 The C<%options> can only specify options handled by
932 L<Class::MOP::Attribute>.
936 =head2 Value management
940 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
942 This method is used internally to initialize the attribute's slot in
943 the object C<$instance>.
945 This overrides the L<Class::MOP::Attribute> method to handle lazy
946 attributes, weak references, and type constraints.
952 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
957 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
959 Before setting the value, a check is made on the type constraint of
960 the attribute, if it has one, to see if the value passes it. If the
961 value fails to pass, the set operation dies with a L<throw_error>.
963 Any coercion to convert values is done before checking the type constraint.
965 To check a value against a type constraint before setting it, fetch the
966 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
967 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
968 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
973 =head2 Attribute Accessor generation
977 =item B<< $attr->install_accessors >>
979 This method overrides the parent to also install delegation methods.
981 If, after installing all methods, the attribute object has no associated
982 methods, it throws an error unless C<< is => 'bare' >> was passed to the
983 attribute constructor. (Trying to add an attribute that has no associated
984 methods is almost always an error.)
986 =item B<< $attr->remove_accessors >>
988 This method overrides the parent to also remove delegation methods.
990 =item B<< $attr->install_delegation >>
992 This method adds its delegation methods to the attribute's associated
993 class, if it has any to add.
995 =item B<< $attr->remove_delegation >>
997 This method remove its delegation methods from the attribute's
1000 =item B<< $attr->accessor_metaclass >>
1002 Returns the accessor metaclass name, which defaults to
1003 L<Moose::Meta::Method::Accessor>.
1005 =item B<< $attr->delegation_metaclass >>
1007 Returns the delegation metaclass name, which defaults to
1008 L<Moose::Meta::Method::Delegation>.
1012 =head2 Additional Moose features
1014 These methods are not found in the superclass. They support features
1019 =item B<< $attr->does($role) >>
1021 This indicates whether the I<attribute itself> does the given
1022 role. The role can be given as a full class name, or as a resolvable
1025 Note that this checks the attribute itself, not its type constraint,
1026 so it is checking the attribute's metaclass and any traits applied to
1029 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
1031 This is an alternate constructor that handles the C<metaclass> and
1034 Effectively, this method is a factory that finds or creates the
1035 appropriate class for the given C<metaclass> and/or C<traits>.
1037 Once it has the appropriate class, it will call C<< $class->new($name,
1038 %options) >> on that class.
1040 =item B<< $attr->clone_and_inherit_options(%options) >>
1042 This method supports the C<has '+foo'> feature. It does various bits
1043 of processing on the supplied C<%options> before ultimately calling
1044 the C<clone> method.
1046 One of its main tasks is to make sure that the C<%options> provided
1047 only includes the options returned by the
1048 C<legal_options_for_inheritance> method.
1050 =item B<< $attr->legal_options_for_inheritance >>
1052 This returns a whitelist of options that can be overridden in a
1053 subclass's attribute definition.
1055 This exists to allow a custom metaclass to change or add to the list
1056 of options which can be changed.
1058 =item B<< $attr->type_constraint >>
1060 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1063 =item B<< $attr->has_type_constraint >>
1065 Returns true if this attribute has a type constraint.
1067 =item B<< $attr->verify_against_type_constraint($value) >>
1069 Given a value, this method returns true if the value is valid for the
1070 attribute's type constraint. If the value is not valid, it throws an
1073 =item B<< $attr->handles >>
1075 This returns the value of the C<handles> option passed to the
1078 =item B<< $attr->has_handles >>
1080 Returns true if this attribute performs delegation.
1082 =item B<< $attr->is_weak_ref >>
1084 Returns true if this attribute stores its value as a weak reference.
1086 =item B<< $attr->is_required >>
1088 Returns true if this attribute is required to have a value.
1090 =item B<< $attr->is_lazy >>
1092 Returns true if this attribute is lazy.
1094 =item B<< $attr->is_lazy_build >>
1096 Returns true if the C<lazy_build> option was true when passed to the
1099 =item B<< $attr->should_coerce >>
1101 Returns true if the C<coerce> option passed to the constructor was
1104 =item B<< $attr->should_auto_deref >>
1106 Returns true if the C<auto_deref> option passed to the constructor was
1109 =item B<< $attr->trigger >>
1111 This is the subroutine reference that was in the C<trigger> option
1112 passed to the constructor, if any.
1114 =item B<< $attr->has_trigger >>
1116 Returns true if this attribute has a trigger set.
1118 =item B<< $attr->documentation >>
1120 Returns the value that was in the C<documentation> option passed to
1121 the constructor, if any.
1123 =item B<< $attr->has_documentation >>
1125 Returns true if this attribute has any documentation.
1127 =item B<< $attr->applied_traits >>
1129 This returns an array reference of all the traits which were applied
1130 to this attribute. If none were applied, this returns C<undef>.
1132 =item B<< $attr->has_applied_traits >>
1134 Returns true if this attribute has any traits applied.
1140 All complex software has bugs lurking in it, and this module is no
1141 exception. If you find a bug please either email me, or add the bug
1146 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1148 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1150 =head1 COPYRIGHT AND LICENSE
1152 Copyright 2006-2009 by Infinity Interactive, Inc.
1154 L<http://www.iinteractive.com>
1156 This library is free software; you can redistribute it and/or modify
1157 it under the same terms as Perl itself.