2 package Moose::Meta::Attribute;
7 use Scalar::Util 'blessed', 'weaken';
10 our $VERSION = '0.83';
11 our $AUTHORITY = 'cpan:STEVAN';
13 use Moose::Meta::Method::Accessor;
14 use Moose::Meta::Method::Delegation;
16 use Moose::Util::TypeConstraints ();
18 use base 'Class::MOP::Attribute';
20 # options which are not directly used
21 # but we store them for metadata purposes
22 __PACKAGE__->meta->add_attribute('isa' => (reader => '_isa_metadata'));
23 __PACKAGE__->meta->add_attribute('does' => (reader => '_does_metadata'));
24 __PACKAGE__->meta->add_attribute('is' => (reader => '_is_metadata'));
26 # these are actual options for the attrs
27 __PACKAGE__->meta->add_attribute('required' => (reader => 'is_required' ));
28 __PACKAGE__->meta->add_attribute('lazy' => (reader => 'is_lazy' ));
29 __PACKAGE__->meta->add_attribute('lazy_build' => (reader => 'is_lazy_build' ));
30 __PACKAGE__->meta->add_attribute('coerce' => (reader => 'should_coerce' ));
31 __PACKAGE__->meta->add_attribute('weak_ref' => (reader => 'is_weak_ref' ));
32 __PACKAGE__->meta->add_attribute('auto_deref' => (reader => 'should_auto_deref'));
33 __PACKAGE__->meta->add_attribute('type_constraint' => (
34 reader => 'type_constraint',
35 predicate => 'has_type_constraint',
37 __PACKAGE__->meta->add_attribute('trigger' => (
39 predicate => 'has_trigger',
41 __PACKAGE__->meta->add_attribute('handles' => (
43 predicate => 'has_handles',
45 __PACKAGE__->meta->add_attribute('documentation' => (
46 reader => 'documentation',
47 predicate => 'has_documentation',
49 __PACKAGE__->meta->add_attribute('traits' => (
50 reader => 'applied_traits',
51 predicate => 'has_applied_traits',
54 # we need to have a ->does method in here to
55 # more easily support traits, and the introspection
56 # of those traits. We extend the does check to look
57 # for metatrait aliases.
59 my ($self, $role_name) = @_;
61 Moose::Util::resolve_metatrait_alias(Attribute => $role_name)
63 return 0 if !defined($name); # failed to load class
64 return $self->Moose::Object::does($name);
69 my $class = ( ref $self && $self->associated_class ) || "Moose::Meta::Class";
70 unshift @_, "message" if @_ % 2 == 1;
71 unshift @_, attr => $self if ref $self;
73 my $handler = $class->can("throw_error"); # to avoid incrementing depth by 1
78 my ($class, $name, %options) = @_;
79 $class->_process_options($name, \%options) unless $options{__hack_no_process_options}; # used from clone()... YECHKKK FIXME ICKY YUCK GROSS
80 return $class->SUPER::new($name, %options);
83 sub interpolate_class_and_new {
84 my ($class, $name, @args) = @_;
86 my ( $new_class, @traits ) = $class->interpolate_class(@args);
88 $new_class->new($name, @args, ( scalar(@traits) ? ( traits => \@traits ) : () ) );
91 sub interpolate_class {
92 my ($class, %options) = @_;
94 $class = ref($class) || $class;
96 if ( my $metaclass_name = delete $options{metaclass} ) {
97 my $new_class = Moose::Util::resolve_metaclass_alias( Attribute => $metaclass_name );
99 if ( $class ne $new_class ) {
100 if ( $new_class->can("interpolate_class") ) {
101 return $new_class->interpolate_class(%options);
110 if (my $traits = $options{traits}) {
112 while ($i < @$traits) {
113 my $trait = $traits->[$i++];
114 next if ref($trait); # options to a trait we discarded
116 $trait = Moose::Util::resolve_metatrait_alias(Attribute => $trait)
119 next if $class->does($trait);
121 push @traits, $trait;
124 push @traits, $traits->[$i++]
125 if $traits->[$i] && ref($traits->[$i]);
129 my $anon_class = Moose::Meta::Class->create_anon_class(
130 superclasses => [ $class ],
131 roles => [ @traits ],
135 $class = $anon_class->name;
139 return ( wantarray ? ( $class, @traits ) : $class );
144 my @legal_options_for_inheritance = qw(
145 default coerce required
146 documentation lazy handles
147 builder type_constraint
152 sub legal_options_for_inheritance { @legal_options_for_inheritance }
155 # This method *must* be able to handle
156 # Class::MOP::Attribute instances as
157 # well. Yes, I know that is wrong, but
158 # apparently we didn't realize it was
159 # doing that and now we have some code
160 # which is dependent on it. The real
161 # solution of course is to push this
162 # feature back up into Class::MOP::Attribute
163 # but I not right now, I am too lazy.
164 # However if you are reading this and
165 # looking for something to do,.. please
168 sub clone_and_inherit_options {
169 my ($self, %options) = @_;
176 # we may want to extends a Class::MOP::Attribute
177 # in which case we need to be able to use the
178 # core set of legal options that have always
179 # been here. But we allows Moose::Meta::Attribute
180 # instances to changes them.
182 my @legal_options = $self->can('legal_options_for_inheritance')
183 ? $self->legal_options_for_inheritance
184 : @legal_options_for_inheritance;
186 foreach my $legal_option (@legal_options) {
187 if (exists $options{$legal_option}) {
188 $actual_options{$legal_option} = $options{$legal_option};
189 delete $options{$legal_option};
195 if (blessed($options{isa}) && $options{isa}->isa('Moose::Meta::TypeConstraint')) {
196 $type_constraint = $options{isa};
199 $type_constraint = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options{isa});
200 (defined $type_constraint)
201 || $self->throw_error("Could not find the type constraint '" . $options{isa} . "'", data => $options{isa});
204 $actual_options{type_constraint} = $type_constraint;
205 delete $options{isa};
208 if ($options{does}) {
210 if (blessed($options{does}) && $options{does}->isa('Moose::Meta::TypeConstraint')) {
211 $type_constraint = $options{does};
214 $type_constraint = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options{does});
215 (defined $type_constraint)
216 || $self->throw_error("Could not find the type constraint '" . $options{does} . "'", data => $options{does});
219 $actual_options{type_constraint} = $type_constraint;
220 delete $options{does};
224 # this doesn't apply to Class::MOP::Attributes,
225 # so we can ignore it for them.
227 if ($self->can('interpolate_class')) {
228 ( $actual_options{metaclass}, my @traits ) = $self->interpolate_class(%options);
231 my @all_traits = grep { $seen{$_}++ } @{ $self->applied_traits || [] }, @traits;
232 $actual_options{traits} = \@all_traits if @all_traits;
234 delete @options{qw(metaclass traits)};
237 (scalar keys %options == 0)
238 || $self->throw_error("Illegal inherited options => (" . (join ', ' => keys %options) . ")", data => \%options);
241 $self->clone(%actual_options);
245 my ( $self, %params ) = @_;
247 my $class = $params{metaclass} || ref $self;
249 my ( @init, @non_init );
251 foreach my $attr ( grep { $_->has_value($self) } Class::MOP::class_of($self)->get_all_attributes ) {
252 push @{ $attr->has_init_arg ? \@init : \@non_init }, $attr;
255 my %new_params = ( ( map { $_->init_arg => $_->get_value($self) } @init ), %params );
257 my $name = delete $new_params{name};
259 my $clone = $class->new($name, %new_params, __hack_no_process_options => 1 );
261 foreach my $attr ( @non_init ) {
262 $attr->set_value($clone, $attr->get_value($self));
268 sub _process_options {
269 my ($class, $name, $options) = @_;
271 if (exists $options->{is}) {
273 ### -------------------------
274 ## is => ro, writer => _foo # turns into (reader => foo, writer => _foo) as before
275 ## is => rw, writer => _foo # turns into (reader => foo, writer => _foo)
276 ## is => rw, accessor => _foo # turns into (accessor => _foo)
277 ## is => ro, accessor => _foo # error, accesor is rw
278 ### -------------------------
280 if ($options->{is} eq 'ro') {
281 $class->throw_error("Cannot define an accessor name on a read-only attribute, accessors are read/write", data => $options)
282 if exists $options->{accessor};
283 $options->{reader} ||= $name;
285 elsif ($options->{is} eq 'rw') {
286 if ($options->{writer}) {
287 $options->{reader} ||= $name;
290 $options->{accessor} ||= $name;
293 elsif ($options->{is} eq 'bare') {
294 # do nothing, but don't complain (later) about missing methods
297 $class->throw_error("I do not understand this option (is => " . $options->{is} . ") on attribute ($name)", data => $options->{is});
301 if (exists $options->{isa}) {
302 if (exists $options->{does}) {
303 if (eval { $options->{isa}->can('does') }) {
304 ($options->{isa}->does($options->{does}))
305 || $class->throw_error("Cannot have an isa option and a does option if the isa does not do the does on attribute ($name)", data => $options);
308 $class->throw_error("Cannot have an isa option which cannot ->does() on attribute ($name)", data => $options);
312 # allow for anon-subtypes here ...
313 if (blessed($options->{isa}) && $options->{isa}->isa('Moose::Meta::TypeConstraint')) {
314 $options->{type_constraint} = $options->{isa};
317 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options->{isa});
320 elsif (exists $options->{does}) {
321 # allow for anon-subtypes here ...
322 if (blessed($options->{does}) && $options->{does}->isa('Moose::Meta::TypeConstraint')) {
323 $options->{type_constraint} = $options->{does};
326 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options->{does});
330 if (exists $options->{coerce} && $options->{coerce}) {
331 (exists $options->{type_constraint})
332 || $class->throw_error("You cannot have coercion without specifying a type constraint on attribute ($name)", data => $options);
333 $class->throw_error("You cannot have a weak reference to a coerced value on attribute ($name)", data => $options)
334 if $options->{weak_ref};
337 if (exists $options->{trigger}) {
338 ('CODE' eq ref $options->{trigger})
339 || $class->throw_error("Trigger must be a CODE ref on attribute ($name)", data => $options->{trigger});
342 if (exists $options->{auto_deref} && $options->{auto_deref}) {
343 (exists $options->{type_constraint})
344 || $class->throw_error("You cannot auto-dereference without specifying a type constraint on attribute ($name)", data => $options);
345 ($options->{type_constraint}->is_a_type_of('ArrayRef') ||
346 $options->{type_constraint}->is_a_type_of('HashRef'))
347 || $class->throw_error("You cannot auto-dereference anything other than a ArrayRef or HashRef on attribute ($name)", data => $options);
350 if (exists $options->{lazy_build} && $options->{lazy_build} == 1) {
351 $class->throw_error("You can not use lazy_build and default for the same attribute ($name)", data => $options)
352 if exists $options->{default};
353 $options->{lazy} = 1;
354 $options->{builder} ||= "_build_${name}";
356 $options->{clearer} ||= "_clear${name}";
357 $options->{predicate} ||= "_has${name}";
360 $options->{clearer} ||= "clear_${name}";
361 $options->{predicate} ||= "has_${name}";
365 if (exists $options->{lazy} && $options->{lazy}) {
366 (exists $options->{default} || defined $options->{builder} )
367 || $class->throw_error("You cannot have lazy attribute ($name) without specifying a default value for it", data => $options);
370 if ( $options->{required} && !( ( !exists $options->{init_arg} || defined $options->{init_arg} ) || exists $options->{default} || defined $options->{builder} ) ) {
371 $class->throw_error("You cannot have a required attribute ($name) without a default, builder, or an init_arg", data => $options);
376 sub initialize_instance_slot {
377 my ($self, $meta_instance, $instance, $params) = @_;
378 my $init_arg = $self->init_arg();
379 # try to fetch the init arg from the %params ...
383 if ( defined($init_arg) and exists $params->{$init_arg}) {
384 $val = $params->{$init_arg};
388 # skip it if it's lazy
389 return if $self->is_lazy;
390 # and die if it's required and doesn't have a default value
391 $self->throw_error("Attribute (" . $self->name . ") is required", object => $instance, data => $params)
392 if $self->is_required && !$self->has_default && !$self->has_builder;
394 # if nothing was in the %params, we can use the
395 # attribute's default value (if it has one)
396 if ($self->has_default) {
397 $val = $self->default($instance);
400 elsif ($self->has_builder) {
401 $val = $self->_call_builder($instance);
406 return unless $value_is_set;
408 $val = $self->_coerce_and_verify( $val, $instance );
410 $self->set_initial_value($instance, $val);
411 $meta_instance->weaken_slot_value($instance, $self->name)
412 if ref $val && $self->is_weak_ref;
416 my ( $self, $instance ) = @_;
418 my $builder = $self->builder();
420 return $instance->$builder()
421 if $instance->can( $self->builder );
423 $self->throw_error( blessed($instance)
424 . " does not support builder method '"
426 . "' for attribute '"
436 # this duplicates too much code from
437 # Class::MOP::Attribute, we need to
438 # refactor these bits eventually.
440 sub _set_initial_slot_value {
441 my ($self, $meta_instance, $instance, $value) = @_;
443 my $slot_name = $self->name;
445 return $meta_instance->set_slot_value($instance, $slot_name, $value)
446 unless $self->has_initializer;
448 my ($type_constraint, $can_coerce);
449 if ($self->has_type_constraint) {
450 $type_constraint = $self->type_constraint;
451 $can_coerce = ($self->should_coerce && $type_constraint->has_coercion);
455 my $val = $self->_coerce_and_verify( shift, $instance );;
457 $meta_instance->set_slot_value($instance, $slot_name, $val);
460 my $initializer = $self->initializer;
462 # most things will just want to set a value, so make it first arg
463 $instance->$initializer($value, $callback, $self);
467 my ($self, $instance, @args) = @_;
468 my $value = $args[0];
470 my $attr_name = $self->name;
472 if ($self->is_required and not @args) {
473 $self->throw_error("Attribute ($attr_name) is required", object => $instance);
476 $value = $self->_coerce_and_verify( $value, $instance );
478 my $meta_instance = Class::MOP::Class->initialize(blessed($instance))
481 $meta_instance->set_slot_value($instance, $attr_name, $value);
483 if (ref $value && $self->is_weak_ref) {
484 $meta_instance->weaken_slot_value($instance, $attr_name);
487 if ($self->has_trigger) {
488 $self->trigger->($instance, $value);
493 my ($self, $instance) = @_;
495 if ($self->is_lazy) {
496 unless ($self->has_value($instance)) {
498 if ($self->has_default) {
499 $value = $self->default($instance);
500 } elsif ( $self->has_builder ) {
501 $value = $self->_call_builder($instance);
504 $value = $self->_coerce_and_verify( $value, $instance );
506 $self->set_initial_value($instance, $value);
510 if ($self->should_auto_deref) {
512 my $type_constraint = $self->type_constraint;
514 if ($type_constraint->is_a_type_of('ArrayRef')) {
515 my $rv = $self->SUPER::get_value($instance);
516 return unless defined $rv;
517 return wantarray ? @{ $rv } : $rv;
519 elsif ($type_constraint->is_a_type_of('HashRef')) {
520 my $rv = $self->SUPER::get_value($instance);
521 return unless defined $rv;
522 return wantarray ? %{ $rv } : $rv;
525 $self->throw_error("Can not auto de-reference the type constraint '" . $type_constraint->name . "'", object => $instance, type_constraint => $type_constraint);
531 return $self->SUPER::get_value($instance);
535 ## installing accessors
537 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
539 sub install_accessors {
541 $self->SUPER::install_accessors(@_);
542 $self->install_delegation if $self->has_handles;
544 @{ $self->associated_methods }
545 || ($self->_is_metadata || '') eq 'bare'
548 'Attribute (' . $self->name . ') has no associated methods'
549 . ' (did you mean to provide an "is" argument?)'
556 sub remove_accessors {
558 $self->SUPER::remove_accessors(@_);
559 $self->remove_delegation if $self->has_handles;
563 sub install_delegation {
567 # Here we canonicalize the 'handles' option
568 # this will sort out any details and always
569 # return an hash of methods which we want
570 # to delagate to, see that method for details
571 my %handles = $self->_canonicalize_handles;
574 # install the delegation ...
575 my $associated_class = $self->associated_class;
576 foreach my $handle (keys %handles) {
577 my $method_to_call = $handles{$handle};
578 my $class_name = $associated_class->name;
579 my $name = "${class_name}::${handle}";
581 (!$associated_class->has_method($handle))
582 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
585 # handles is not allowed to delegate
586 # any of these methods, as they will
587 # override the ones in your class, which
588 # is almost certainly not what you want.
590 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
591 #cluck("Not delegating method '$handle' because it is a core method") and
592 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
594 my $method = $self->_make_delegation_method($handle, $method_to_call);
596 $self->associated_class->add_method($method->name, $method);
597 $self->associate_method($method);
601 sub remove_delegation {
603 my %handles = $self->_canonicalize_handles;
604 my $associated_class = $self->associated_class;
605 foreach my $handle (keys %handles) {
606 $self->associated_class->remove_method($handle);
610 # private methods to help delegation ...
612 sub _canonicalize_handles {
614 my $handles = $self->handles;
615 if (my $handle_type = ref($handles)) {
616 if ($handle_type eq 'HASH') {
619 elsif ($handle_type eq 'ARRAY') {
620 return map { $_ => $_ } @{$handles};
622 elsif ($handle_type eq 'Regexp') {
623 ($self->has_type_constraint)
624 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
625 return map { ($_ => $_) }
626 grep { /$handles/ } $self->_get_delegate_method_list;
628 elsif ($handle_type eq 'CODE') {
629 return $handles->($self, $self->_find_delegate_metaclass);
631 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::DuckType')) {
632 return map { $_ => $_ } @{ $handles->methods };
635 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
639 Class::MOP::load_class($handles);
640 my $role_meta = Class::MOP::class_of($handles);
642 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
643 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because its metaclass is not a Moose::Meta::Role", data => $handles);
645 return map { $_ => $_ } (
646 $role_meta->get_method_list,
647 map { $_->name } $role_meta->get_required_method_list,
652 sub _find_delegate_metaclass {
654 if (my $class = $self->_isa_metadata) {
655 # we might be dealing with a non-Moose class,
656 # and need to make our own metaclass. if there's
657 # already a metaclass, it will be returned
658 return Moose::Meta::Class->initialize($class);
660 elsif (my $role = $self->_does_metadata) {
661 return Class::MOP::class_of($role);
664 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
668 sub _get_delegate_method_list {
670 my $meta = $self->_find_delegate_metaclass;
671 if ($meta->isa('Class::MOP::Class')) {
672 return map { $_->name } # NOTE: !never! delegate &meta
673 grep { $_->package_name ne 'Moose::Object' && $_->name ne 'meta' }
674 $meta->get_all_methods;
676 elsif ($meta->isa('Moose::Meta::Role')) {
677 return $meta->get_method_list;
680 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
684 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
686 sub _make_delegation_method {
687 my ( $self, $handle_name, $method_to_call ) = @_;
691 $method_body = $method_to_call
692 if 'CODE' eq ref($method_to_call);
694 my $curried_arguments = [];
696 ($method_to_call, $curried_arguments) = @$method_to_call
697 if 'ARRAY' eq ref($method_to_call);
699 return $self->delegation_metaclass->new(
700 name => $handle_name,
701 package_name => $self->associated_class->name,
703 delegate_to_method => $method_to_call,
704 curried_arguments => $curried_arguments || [],
708 sub _coerce_and_verify {
711 my $instance = shift;
713 return $val unless $self->has_type_constraint;
715 my $type_constraint = $self->type_constraint;
716 if ($self->should_coerce && $type_constraint->has_coercion) {
717 $val = $type_constraint->coerce($val);
720 $self->verify_against_type_constraint($val, instance => $instance);
725 sub verify_against_type_constraint {
729 return 1 if !$self->has_type_constraint;
731 my $type_constraint = $self->type_constraint;
733 $type_constraint->check($val)
734 || $self->throw_error("Attribute ("
736 . ") does not pass the type constraint because: "
737 . $type_constraint->get_message($val), data => $val, @_);
740 package Moose::Meta::Attribute::Custom::Moose;
741 sub register_implementation { 'Moose::Meta::Attribute' }
751 Moose::Meta::Attribute - The Moose attribute metaclass
755 This class is a subclass of L<Class::MOP::Attribute> that provides
756 additional Moose-specific functionality.
758 To really understand this class, you will need to start with the
759 L<Class::MOP::Attribute> documentation. This class can be understood
760 as a set of additional features on top of the basic feature provided
761 by that parent class.
765 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
769 Many of the documented below override methods in
770 L<Class::MOP::Attribute> and add Moose specific features.
776 =item B<< Moose::Meta::Attribute->new(%options) >>
778 This method overrides the L<Class::MOP::Attribute> constructor.
780 Many of the options below are described in more detail in the
781 L<Moose::Manual::Attributes> document.
783 It adds the following options to the constructor:
787 =item * is => 'ro', 'rw', 'bare'
789 This provides a shorthand for specifying the C<reader>, C<writer>, or
790 C<accessor> names. If the attribute is read-only ('ro') then it will
791 have a C<reader> method with the same attribute as the name.
793 If it is read-write ('rw') then it will have an C<accessor> method
794 with the same name. If you provide an explicit C<writer> for a
795 read-write attribute, then you will have a C<reader> with the same
796 name as the attribute, and a C<writer> with the name you provided.
798 Use 'bare' when you are deliberately not installing any methods
799 (accessor, reader, etc.) associated with this attribute; otherwise,
800 Moose will issue a deprecation warning when this attribute is added to a
805 This option accepts a type. The type can be a string, which should be
806 a type name. If the type name is unknown, it is assumed to be a class
809 This option can also accept a L<Moose::Meta::TypeConstraint> object.
811 If you I<also> provide a C<does> option, then your C<isa> option must
812 be a class name, and that class must do the role specified with
815 =item * does => $role
817 This is short-hand for saying that the attribute's type must be an
818 object which does the named role.
820 =item * coerce => $bool
822 This option is only valid for objects with a type constraint
823 (C<isa>). If this is true, then coercions will be applied whenever
824 this attribute is set.
826 You can make both this and the C<weak_ref> option true.
828 =item * trigger => $sub
830 This option accepts a subroutine reference, which will be called after
831 the attribute is set.
833 =item * required => $bool
835 An attribute which is required must be provided to the constructor. An
836 attribute which is required can also have a C<default> or C<builder>,
837 which will satisfy its required-ness.
839 A required attribute must have a C<default>, C<builder> or a
840 non-C<undef> C<init_arg>
842 =item * lazy => $bool
844 A lazy attribute must have a C<default> or C<builder>. When an
845 attribute is lazy, the default value will not be calculated until the
848 =item * weak_ref => $bool
850 If this is true, the attribute's value will be stored as a weak
853 =item * auto_deref => $bool
855 If this is true, then the reader will dereference the value when it is
856 called. The attribute must have a type constraint which defines the
857 attribute as an array or hash reference.
859 =item * lazy_build => $bool
861 Setting this to true makes the attribute lazy and provides a number of
869 is equivalent to this:
874 builder => '_build_size',
875 clearer => 'clear_size',
876 predicate => 'has_size',
879 =item * documentation
881 An arbitrary string that can be retrieved later by calling C<<
882 $attr->documentation >>.
886 =item B<< $attr->clone(%options) >>
888 This creates a new attribute based on attribute being cloned. You must
889 supply a C<name> option to provide a new name for the attribute.
891 The C<%options> can only specify options handled by
892 L<Class::MOP::Attribute>.
896 =head2 Value management
900 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
902 This method is used internally to initialize the attribute's slot in
903 the object C<$instance>.
905 This overrides the L<Class::MOP::Attribute> method to handle lazy
906 attributes, weak references, and type constraints.
912 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
917 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
919 Before setting the value, a check is made on the type constraint of
920 the attribute, if it has one, to see if the value passes it. If the
921 value fails to pass, the set operation dies with a L<throw_error>.
923 Any coercion to convert values is done before checking the type constraint.
925 To check a value against a type constraint before setting it, fetch the
926 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
927 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
928 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
933 =head2 Attribute Accessor generation
937 =item B<< $attr->install_accessors >>
939 This method overrides the parent to also install delegation methods.
941 If, after installing all methods, the attribute object has no associated
942 methods, it throws an error unless C<< is => 'bare' >> was passed to the
943 attribute constructor. (Trying to add an attribute that has no associated
944 methods is almost always an error.)
946 =item B<< $attr->remove_accessors >>
948 This method overrides the parent to also remove delegation methods.
950 =item B<< $attr->install_delegation >>
952 This method adds its delegation methods to the attribute's associated
953 class, if it has any to add.
955 =item B<< $attr->remove_delegation >>
957 This method remove its delegation methods from the attribute's
960 =item B<< $attr->accessor_metaclass >>
962 Returns the accessor metaclass name, which defaults to
963 L<Moose::Meta::Method::Accessor>.
965 =item B<< $attr->delegation_metaclass >>
967 Returns the delegation metaclass name, which defaults to
968 L<Moose::Meta::Method::Delegation>.
972 =head2 Additional Moose features
974 These methods are not found in the superclass. They support features
979 =item B<< $attr->does($role) >>
981 This indicates whether the I<attribute itself> does the given
982 role. The role can be given as a full class name, or as a resolvable
985 Note that this checks the attribute itself, not its type constraint,
986 so it is checking the attribute's metaclass and any traits applied to
989 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
991 This is an alternate constructor that handles the C<metaclass> and
994 Effectively, this method is a factory that finds or creates the
995 appropriate class for the given C<metaclass> and/or C<traits>.
997 Once it has the appropriate class, it will call C<< $class->new($name,
998 %options) >> on that class.
1000 =item B<< $attr->clone_and_inherit_options(%options) >>
1002 This method supports the C<has '+foo'> feature. It does various bits
1003 of processing on the supplied C<%options> before ultimately calling
1004 the C<clone> method.
1006 One of its main tasks is to make sure that the C<%options> provided
1007 only includes the options returned by the
1008 C<legal_options_for_inheritance> method.
1010 =item B<< $attr->legal_options_for_inheritance >>
1012 This returns a whitelist of options that can be overridden in a
1013 subclass's attribute definition.
1015 This exists to allow a custom metaclass to change or add to the list
1016 of options which can be changed.
1018 =item B<< $attr->type_constraint >>
1020 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1023 =item B<< $attr->has_type_constraint >>
1025 Returns true if this attribute has a type constraint.
1027 =item B<< $attr->verify_against_type_constraint($value) >>
1029 Given a value, this method returns true if the value is valid for the
1030 attribute's type constraint. If the value is not valid, it throws an
1033 =item B<< $attr->handles >>
1035 This returns the value of the C<handles> option passed to the
1038 =item B<< $attr->has_handles >>
1040 Returns true if this attribute performs delegation.
1042 =item B<< $attr->is_weak_ref >>
1044 Returns true if this attribute stores its value as a weak reference.
1046 =item B<< $attr->is_required >>
1048 Returns true if this attribute is required to have a value.
1050 =item B<< $attr->is_lazy >>
1052 Returns true if this attribute is lazy.
1054 =item B<< $attr->is_lazy_build >>
1056 Returns true if the C<lazy_build> option was true when passed to the
1059 =item B<< $attr->should_coerce >>
1061 Returns true if the C<coerce> option passed to the constructor was
1064 =item B<< $attr->should_auto_deref >>
1066 Returns true if the C<auto_deref> option passed to the constructor was
1069 =item B<< $attr->trigger >>
1071 This is the subroutine reference that was in the C<trigger> option
1072 passed to the constructor, if any.
1074 =item B<< $attr->has_trigger >>
1076 Returns true if this attribute has a trigger set.
1078 =item B<< $attr->documentation >>
1080 Returns the value that was in the C<documentation> option passed to
1081 the constructor, if any.
1083 =item B<< $attr->has_documentation >>
1085 Returns true if this attribute has any documentation.
1087 =item B<< $attr->applied_traits >>
1089 This returns an array reference of all the traits which were applied
1090 to this attribute. If none were applied, this returns C<undef>.
1092 =item B<< $attr->has_applied_traits >>
1094 Returns true if this attribute has any traits applied.
1100 All complex software has bugs lurking in it, and this module is no
1101 exception. If you find a bug please either email me, or add the bug
1106 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1108 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1110 =head1 COPYRIGHT AND LICENSE
1112 Copyright 2006-2009 by Infinity Interactive, Inc.
1114 L<http://www.iinteractive.com>
1116 This library is free software; you can redistribute it and/or modify
1117 it under the same terms as Perl itself.