2 package Moose::Meta::Attribute;
7 use Scalar::Util 'blessed', 'weaken';
10 our $VERSION = '0.89_02';
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))
500 if ( $self->has_trigger && $self->has_value($instance) ) {
501 @old = $self->get_value($instance, 'for trigger');
504 $meta_instance->set_slot_value($instance, $attr_name, $value);
506 if (ref $value && $self->is_weak_ref) {
507 $meta_instance->weaken_slot_value($instance, $attr_name);
510 if ($self->has_trigger) {
511 $self->trigger->($instance, $value, @old);
516 my ($self, $instance, $for_trigger) = @_;
518 if ($self->is_lazy) {
519 unless ($self->has_value($instance)) {
521 if ($self->has_default) {
522 $value = $self->default($instance);
523 } elsif ( $self->has_builder ) {
524 $value = $self->_call_builder($instance);
527 $value = $self->_coerce_and_verify( $value, $instance );
529 $self->set_initial_value($instance, $value);
533 if ( $self->should_auto_deref && ! $for_trigger ) {
535 my $type_constraint = $self->type_constraint;
537 if ($type_constraint->is_a_type_of('ArrayRef')) {
538 my $rv = $self->SUPER::get_value($instance);
539 return unless defined $rv;
540 return wantarray ? @{ $rv } : $rv;
542 elsif ($type_constraint->is_a_type_of('HashRef')) {
543 my $rv = $self->SUPER::get_value($instance);
544 return unless defined $rv;
545 return wantarray ? %{ $rv } : $rv;
548 $self->throw_error("Can not auto de-reference the type constraint '" . $type_constraint->name . "'", object => $instance, type_constraint => $type_constraint);
554 return $self->SUPER::get_value($instance);
558 ## installing accessors
560 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
562 sub install_accessors {
564 $self->SUPER::install_accessors(@_);
565 $self->install_delegation if $self->has_handles;
569 sub _check_associated_methods {
572 @{ $self->associated_methods }
573 || ($self->_is_metadata || '') eq 'bare'
576 'Attribute (' . $self->name . ') of class '
577 . $self->associated_class->name
578 . ' has no associated methods'
579 . ' (did you mean to provide an "is" argument?)'
585 sub _process_accessors {
587 my ($type, $accessor, $generate_as_inline_methods) = @_;
588 $accessor = (keys %$accessor)[0] if (ref($accessor)||'') eq 'HASH';
589 my $method = $self->associated_class->get_method($accessor);
590 if ($method && !$method->isa('Class::MOP::Method::Accessor')
591 && (!$self->definition_context
592 || $method->package_name eq $self->definition_context->{package})) {
594 "You are overwriting a locally defined method ($accessor) with "
598 $self->SUPER::_process_accessors(@_);
601 sub remove_accessors {
603 $self->SUPER::remove_accessors(@_);
604 $self->remove_delegation if $self->has_handles;
608 sub install_delegation {
612 # Here we canonicalize the 'handles' option
613 # this will sort out any details and always
614 # return an hash of methods which we want
615 # to delagate to, see that method for details
616 my %handles = $self->_canonicalize_handles;
619 # install the delegation ...
620 my $associated_class = $self->associated_class;
621 foreach my $handle (keys %handles) {
622 my $method_to_call = $handles{$handle};
623 my $class_name = $associated_class->name;
624 my $name = "${class_name}::${handle}";
626 (!$associated_class->has_method($handle))
627 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
630 # handles is not allowed to delegate
631 # any of these methods, as they will
632 # override the ones in your class, which
633 # is almost certainly not what you want.
635 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
636 #cluck("Not delegating method '$handle' because it is a core method") and
637 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
639 my $method = $self->_make_delegation_method($handle, $method_to_call);
641 $self->associated_class->add_method($method->name, $method);
642 $self->associate_method($method);
646 sub remove_delegation {
648 my %handles = $self->_canonicalize_handles;
649 my $associated_class = $self->associated_class;
650 foreach my $handle (keys %handles) {
651 $self->associated_class->remove_method($handle);
655 # private methods to help delegation ...
657 sub _canonicalize_handles {
659 my $handles = $self->handles;
660 if (my $handle_type = ref($handles)) {
661 if ($handle_type eq 'HASH') {
664 elsif ($handle_type eq 'ARRAY') {
665 return map { $_ => $_ } @{$handles};
667 elsif ($handle_type eq 'Regexp') {
668 ($self->has_type_constraint)
669 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
670 return map { ($_ => $_) }
671 grep { /$handles/ } $self->_get_delegate_method_list;
673 elsif ($handle_type eq 'CODE') {
674 return $handles->($self, $self->_find_delegate_metaclass);
676 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::DuckType')) {
677 return map { $_ => $_ } @{ $handles->methods };
680 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
684 Class::MOP::load_class($handles);
685 my $role_meta = Class::MOP::class_of($handles);
687 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
688 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because its metaclass is not a Moose::Meta::Role", data => $handles);
690 return map { $_ => $_ }
691 grep { $_ ne 'meta' } (
692 $role_meta->get_method_list,
693 map { $_->name } $role_meta->get_required_method_list,
698 sub _find_delegate_metaclass {
700 if (my $class = $self->_isa_metadata) {
701 # we might be dealing with a non-Moose class,
702 # and need to make our own metaclass. if there's
703 # already a metaclass, it will be returned
704 return Moose::Meta::Class->initialize($class);
706 elsif (my $role = $self->_does_metadata) {
707 return Class::MOP::class_of($role);
710 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
714 sub _get_delegate_method_list {
716 my $meta = $self->_find_delegate_metaclass;
717 if ($meta->isa('Class::MOP::Class')) {
718 return map { $_->name } # NOTE: !never! delegate &meta
719 grep { $_->package_name ne 'Moose::Object' && $_->name ne 'meta' }
720 $meta->get_all_methods;
722 elsif ($meta->isa('Moose::Meta::Role')) {
723 return $meta->get_method_list;
726 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
730 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
732 sub _make_delegation_method {
733 my ( $self, $handle_name, $method_to_call ) = @_;
737 $method_body = $method_to_call
738 if 'CODE' eq ref($method_to_call);
740 my @curried_arguments;
742 ($method_to_call, @curried_arguments) = @$method_to_call
743 if 'ARRAY' eq ref($method_to_call);
745 return $self->delegation_metaclass->new(
746 name => $handle_name,
747 package_name => $self->associated_class->name,
749 delegate_to_method => $method_to_call,
750 curried_arguments => \@curried_arguments,
754 sub _coerce_and_verify {
757 my $instance = shift;
759 return $val unless $self->has_type_constraint;
761 my $type_constraint = $self->type_constraint;
762 if ($self->should_coerce && $type_constraint->has_coercion) {
763 $val = $type_constraint->coerce($val);
766 $self->verify_against_type_constraint($val, instance => $instance);
771 sub verify_against_type_constraint {
775 return 1 if !$self->has_type_constraint;
777 my $type_constraint = $self->type_constraint;
779 $type_constraint->check($val)
780 || $self->throw_error("Attribute ("
782 . ") does not pass the type constraint because: "
783 . $type_constraint->get_message($val), data => $val, @_);
786 package Moose::Meta::Attribute::Custom::Moose;
787 sub register_implementation { 'Moose::Meta::Attribute' }
797 Moose::Meta::Attribute - The Moose attribute metaclass
801 This class is a subclass of L<Class::MOP::Attribute> that provides
802 additional Moose-specific functionality.
804 To really understand this class, you will need to start with the
805 L<Class::MOP::Attribute> documentation. This class can be understood
806 as a set of additional features on top of the basic feature provided
807 by that parent class.
811 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
815 Many of the documented below override methods in
816 L<Class::MOP::Attribute> and add Moose specific features.
822 =item B<< Moose::Meta::Attribute->new(%options) >>
824 This method overrides the L<Class::MOP::Attribute> constructor.
826 Many of the options below are described in more detail in the
827 L<Moose::Manual::Attributes> document.
829 It adds the following options to the constructor:
833 =item * is => 'ro', 'rw', 'bare'
835 This provides a shorthand for specifying the C<reader>, C<writer>, or
836 C<accessor> names. If the attribute is read-only ('ro') then it will
837 have a C<reader> method with the same attribute as the name.
839 If it is read-write ('rw') then it will have an C<accessor> method
840 with the same name. If you provide an explicit C<writer> for a
841 read-write attribute, then you will have a C<reader> with the same
842 name as the attribute, and a C<writer> with the name you provided.
844 Use 'bare' when you are deliberately not installing any methods
845 (accessor, reader, etc.) associated with this attribute; otherwise,
846 Moose will issue a deprecation warning when this attribute is added to a
851 This option accepts a type. The type can be a string, which should be
852 a type name. If the type name is unknown, it is assumed to be a class
855 This option can also accept a L<Moose::Meta::TypeConstraint> object.
857 If you I<also> provide a C<does> option, then your C<isa> option must
858 be a class name, and that class must do the role specified with
861 =item * does => $role
863 This is short-hand for saying that the attribute's type must be an
864 object which does the named role.
866 =item * coerce => $bool
868 This option is only valid for objects with a type constraint
869 (C<isa>). If this is true, then coercions will be applied whenever
870 this attribute is set.
872 You can make both this and the C<weak_ref> option true.
874 =item * trigger => $sub
876 This option accepts a subroutine reference, which will be called after
877 the attribute is set.
879 =item * required => $bool
881 An attribute which is required must be provided to the constructor. An
882 attribute which is required can also have a C<default> or C<builder>,
883 which will satisfy its required-ness.
885 A required attribute must have a C<default>, C<builder> or a
886 non-C<undef> C<init_arg>
888 =item * lazy => $bool
890 A lazy attribute must have a C<default> or C<builder>. When an
891 attribute is lazy, the default value will not be calculated until the
894 =item * weak_ref => $bool
896 If this is true, the attribute's value will be stored as a weak
899 =item * auto_deref => $bool
901 If this is true, then the reader will dereference the value when it is
902 called. The attribute must have a type constraint which defines the
903 attribute as an array or hash reference.
905 =item * lazy_build => $bool
907 Setting this to true makes the attribute lazy and provides a number of
915 is equivalent to this:
920 builder => '_build_size',
921 clearer => 'clear_size',
922 predicate => 'has_size',
925 =item * documentation
927 An arbitrary string that can be retrieved later by calling C<<
928 $attr->documentation >>.
932 =item B<< $attr->clone(%options) >>
934 This creates a new attribute based on attribute being cloned. You must
935 supply a C<name> option to provide a new name for the attribute.
937 The C<%options> can only specify options handled by
938 L<Class::MOP::Attribute>.
942 =head2 Value management
946 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
948 This method is used internally to initialize the attribute's slot in
949 the object C<$instance>.
951 This overrides the L<Class::MOP::Attribute> method to handle lazy
952 attributes, weak references, and type constraints.
958 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
963 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
965 Before setting the value, a check is made on the type constraint of
966 the attribute, if it has one, to see if the value passes it. If the
967 value fails to pass, the set operation dies with a L<throw_error>.
969 Any coercion to convert values is done before checking the type constraint.
971 To check a value against a type constraint before setting it, fetch the
972 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
973 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
974 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
979 =head2 Attribute Accessor generation
983 =item B<< $attr->install_accessors >>
985 This method overrides the parent to also install delegation methods.
987 If, after installing all methods, the attribute object has no associated
988 methods, it throws an error unless C<< is => 'bare' >> was passed to the
989 attribute constructor. (Trying to add an attribute that has no associated
990 methods is almost always an error.)
992 =item B<< $attr->remove_accessors >>
994 This method overrides the parent to also remove delegation methods.
996 =item B<< $attr->install_delegation >>
998 This method adds its delegation methods to the attribute's associated
999 class, if it has any to add.
1001 =item B<< $attr->remove_delegation >>
1003 This method remove its delegation methods from the attribute's
1006 =item B<< $attr->accessor_metaclass >>
1008 Returns the accessor metaclass name, which defaults to
1009 L<Moose::Meta::Method::Accessor>.
1011 =item B<< $attr->delegation_metaclass >>
1013 Returns the delegation metaclass name, which defaults to
1014 L<Moose::Meta::Method::Delegation>.
1018 =head2 Additional Moose features
1020 These methods are not found in the superclass. They support features
1025 =item B<< $attr->does($role) >>
1027 This indicates whether the I<attribute itself> does the given
1028 role. The role can be given as a full class name, or as a resolvable
1031 Note that this checks the attribute itself, not its type constraint,
1032 so it is checking the attribute's metaclass and any traits applied to
1035 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
1037 This is an alternate constructor that handles the C<metaclass> and
1040 Effectively, this method is a factory that finds or creates the
1041 appropriate class for the given C<metaclass> and/or C<traits>.
1043 Once it has the appropriate class, it will call C<< $class->new($name,
1044 %options) >> on that class.
1046 =item B<< $attr->clone_and_inherit_options(%options) >>
1048 This method supports the C<has '+foo'> feature. It does various bits
1049 of processing on the supplied C<%options> before ultimately calling
1050 the C<clone> method.
1052 One of its main tasks is to make sure that the C<%options> provided
1053 only includes the options returned by the
1054 C<legal_options_for_inheritance> method.
1056 =item B<< $attr->legal_options_for_inheritance >>
1058 This returns a whitelist of options that can be overridden in a
1059 subclass's attribute definition.
1061 This exists to allow a custom metaclass to change or add to the list
1062 of options which can be changed.
1064 =item B<< $attr->type_constraint >>
1066 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1069 =item B<< $attr->has_type_constraint >>
1071 Returns true if this attribute has a type constraint.
1073 =item B<< $attr->verify_against_type_constraint($value) >>
1075 Given a value, this method returns true if the value is valid for the
1076 attribute's type constraint. If the value is not valid, it throws an
1079 =item B<< $attr->handles >>
1081 This returns the value of the C<handles> option passed to the
1084 =item B<< $attr->has_handles >>
1086 Returns true if this attribute performs delegation.
1088 =item B<< $attr->is_weak_ref >>
1090 Returns true if this attribute stores its value as a weak reference.
1092 =item B<< $attr->is_required >>
1094 Returns true if this attribute is required to have a value.
1096 =item B<< $attr->is_lazy >>
1098 Returns true if this attribute is lazy.
1100 =item B<< $attr->is_lazy_build >>
1102 Returns true if the C<lazy_build> option was true when passed to the
1105 =item B<< $attr->should_coerce >>
1107 Returns true if the C<coerce> option passed to the constructor was
1110 =item B<< $attr->should_auto_deref >>
1112 Returns true if the C<auto_deref> option passed to the constructor was
1115 =item B<< $attr->trigger >>
1117 This is the subroutine reference that was in the C<trigger> option
1118 passed to the constructor, if any.
1120 =item B<< $attr->has_trigger >>
1122 Returns true if this attribute has a trigger set.
1124 =item B<< $attr->documentation >>
1126 Returns the value that was in the C<documentation> option passed to
1127 the constructor, if any.
1129 =item B<< $attr->has_documentation >>
1131 Returns true if this attribute has any documentation.
1133 =item B<< $attr->applied_traits >>
1135 This returns an array reference of all the traits which were applied
1136 to this attribute. If none were applied, this returns C<undef>.
1138 =item B<< $attr->has_applied_traits >>
1140 Returns true if this attribute has any traits applied.
1146 All complex software has bugs lurking in it, and this module is no
1147 exception. If you find a bug please either email me, or add the bug
1152 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1154 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1156 =head1 COPYRIGHT AND LICENSE
1158 Copyright 2006-2009 by Infinity Interactive, Inc.
1160 L<http://www.iinteractive.com>
1162 This library is free software; you can redistribute it and/or modify
1163 it under the same terms as Perl itself.