2 package Moose::Meta::Attribute;
7 use Scalar::Util 'blessed', 'weaken';
8 use List::MoreUtils 'any';
12 our $VERSION = '1.08';
13 our $AUTHORITY = 'cpan:STEVAN';
15 use Moose::Meta::Method::Accessor;
16 use Moose::Meta::Method::Delegation;
18 use Moose::Util::TypeConstraints ();
20 use base 'Class::MOP::Attribute', 'Moose::Meta::Mixin::AttributeCore';
22 __PACKAGE__->meta->add_attribute('traits' => (
23 reader => 'applied_traits',
24 predicate => 'has_applied_traits',
27 # we need to have a ->does method in here to
28 # more easily support traits, and the introspection
29 # of those traits. We extend the does check to look
30 # for metatrait aliases.
32 my ($self, $role_name) = @_;
34 Moose::Util::resolve_metatrait_alias(Attribute => $role_name)
36 return 0 if !defined($name); # failed to load class
37 return $self->Moose::Object::does($name);
42 my $class = ( ref $self && $self->associated_class ) || "Moose::Meta::Class";
43 unshift @_, "message" if @_ % 2 == 1;
44 unshift @_, attr => $self if ref $self;
46 my $handler = $class->can("throw_error"); # to avoid incrementing depth by 1
51 my ($class, $name, %options) = @_;
52 $class->_process_options($name, \%options) unless $options{__hack_no_process_options}; # used from clone()... YECHKKK FIXME ICKY YUCK GROSS
54 delete $options{__hack_no_process_options};
59 map { $_->init_arg() }
60 $class->meta()->get_all_attributes()
63 my @bad = sort grep { ! $attrs{$_} } keys %options;
67 Carp::cluck "Found unknown argument(s) passed to '$name' attribute constructor in '$class': @bad";
70 return $class->SUPER::new($name, %options);
73 sub interpolate_class_and_new {
74 my ($class, $name, %args) = @_;
76 my ( $new_class, @traits ) = $class->interpolate_class(\%args);
78 $new_class->new($name, %args, ( scalar(@traits) ? ( traits => \@traits ) : () ) );
81 sub interpolate_class {
82 my ($class, $options) = @_;
84 $class = ref($class) || $class;
86 if ( my $metaclass_name = delete $options->{metaclass} ) {
87 my $new_class = Moose::Util::resolve_metaclass_alias( Attribute => $metaclass_name );
89 if ( $class ne $new_class ) {
90 if ( $new_class->can("interpolate_class") ) {
91 return $new_class->interpolate_class($options);
100 if (my $traits = $options->{traits}) {
102 while ($i < @$traits) {
103 my $trait = $traits->[$i++];
104 next if ref($trait); # options to a trait we discarded
106 $trait = Moose::Util::resolve_metatrait_alias(Attribute => $trait)
109 next if $class->does($trait);
111 push @traits, $trait;
114 push @traits, $traits->[$i++]
115 if $traits->[$i] && ref($traits->[$i]);
119 my $anon_class = Moose::Meta::Class->create_anon_class(
120 superclasses => [ $class ],
121 roles => [ @traits ],
125 $class = $anon_class->name;
129 return ( wantarray ? ( $class, @traits ) : $class );
134 sub illegal_options_for_inheritance { }
137 # This method *must* be able to handle
138 # Class::MOP::Attribute instances as
139 # well. Yes, I know that is wrong, but
140 # apparently we didn't realize it was
141 # doing that and now we have some code
142 # which is dependent on it. The real
143 # solution of course is to push this
144 # feature back up into Class::MOP::Attribute
145 # but I not right now, I am too lazy.
146 # However if you are reading this and
147 # looking for something to do,.. please
150 sub clone_and_inherit_options {
151 my ($self, %options) = @_;
156 # we may want to extends a Class::MOP::Attribute
157 # in which case we need to be able to use the
158 # core set of legal options that have always
159 # been here. But we allows Moose::Meta::Attribute
160 # instances to changes them.
162 my @illegal_options = $self->can('illegal_options_for_inheritance')
163 ? $self->illegal_options_for_inheritance
166 my @found_illegal_options = grep { exists $options{$_} ? $_ : undef } @illegal_options;
167 (scalar @found_illegal_options == 0)
168 || $self->throw_error("Illegal inherited options => (" . (join ', ' => @found_illegal_options) . ")", data => \%options);
172 if (blessed($options{isa}) && $options{isa}->isa('Moose::Meta::TypeConstraint')) {
173 $type_constraint = $options{isa};
176 $type_constraint = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options{isa});
177 (defined $type_constraint)
178 || $self->throw_error("Could not find the type constraint '" . $options{isa} . "'", data => $options{isa});
181 $options{type_constraint} = $type_constraint;
184 if ($options{does}) {
186 if (blessed($options{does}) && $options{does}->isa('Moose::Meta::TypeConstraint')) {
187 $type_constraint = $options{does};
190 $type_constraint = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options{does});
191 (defined $type_constraint)
192 || $self->throw_error("Could not find the type constraint '" . $options{does} . "'", data => $options{does});
195 $options{type_constraint} = $type_constraint;
199 # this doesn't apply to Class::MOP::Attributes,
200 # so we can ignore it for them.
202 if ($self->can('interpolate_class')) {
203 ( $options{metaclass}, my @traits ) = $self->interpolate_class(\%options);
206 my @all_traits = grep { $seen{$_}++ } @{ $self->applied_traits || [] }, @traits;
207 $options{traits} = \@all_traits if @all_traits;
210 $self->clone(%options);
214 my ( $self, %params ) = @_;
216 my $class = delete $params{metaclass} || ref $self;
218 my ( @init, @non_init );
220 foreach my $attr ( grep { $_->has_value($self) } Class::MOP::class_of($self)->get_all_attributes ) {
221 push @{ $attr->has_init_arg ? \@init : \@non_init }, $attr;
224 my %new_params = ( ( map { $_->init_arg => $_->get_value($self) } @init ), %params );
226 my $name = delete $new_params{name};
228 my $clone = $class->new($name, %new_params, __hack_no_process_options => 1 );
230 foreach my $attr ( @non_init ) {
231 $attr->set_value($clone, $attr->get_value($self));
237 sub _process_options {
238 my ($class, $name, $options) = @_;
240 if (exists $options->{is}) {
242 ### -------------------------
243 ## is => ro, writer => _foo # turns into (reader => foo, writer => _foo) as before
244 ## is => rw, writer => _foo # turns into (reader => foo, writer => _foo)
245 ## is => rw, accessor => _foo # turns into (accessor => _foo)
246 ## is => ro, accessor => _foo # error, accesor is rw
247 ### -------------------------
249 if ($options->{is} eq 'ro') {
250 $class->throw_error("Cannot define an accessor name on a read-only attribute, accessors are read/write", data => $options)
251 if exists $options->{accessor};
252 $options->{reader} ||= $name;
254 elsif ($options->{is} eq 'rw') {
255 if ($options->{writer}) {
256 $options->{reader} ||= $name;
259 $options->{accessor} ||= $name;
262 elsif ($options->{is} eq 'bare') {
263 # do nothing, but don't complain (later) about missing methods
266 $class->throw_error("I do not understand this option (is => " . $options->{is} . ") on attribute ($name)", data => $options->{is});
270 if (exists $options->{isa}) {
271 if (exists $options->{does}) {
272 if (try { $options->{isa}->can('does') }) {
273 ($options->{isa}->does($options->{does}))
274 || $class->throw_error("Cannot have an isa option and a does option if the isa does not do the does on attribute ($name)", data => $options);
277 $class->throw_error("Cannot have an isa option which cannot ->does() on attribute ($name)", data => $options);
281 # allow for anon-subtypes here ...
282 if (blessed($options->{isa}) && $options->{isa}->isa('Moose::Meta::TypeConstraint')) {
283 $options->{type_constraint} = $options->{isa};
286 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options->{isa});
289 elsif (exists $options->{does}) {
290 # allow for anon-subtypes here ...
291 if (blessed($options->{does}) && $options->{does}->isa('Moose::Meta::TypeConstraint')) {
292 $options->{type_constraint} = $options->{does};
295 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options->{does});
299 if (exists $options->{coerce} && $options->{coerce}) {
300 (exists $options->{type_constraint})
301 || $class->throw_error("You cannot have coercion without specifying a type constraint on attribute ($name)", data => $options);
302 $class->throw_error("You cannot have a weak reference to a coerced value on attribute ($name)", data => $options)
303 if $options->{weak_ref};
305 unless ( $options->{type_constraint}->has_coercion ) {
306 my $type = $options->{type_constraint}->name;
307 $class->throw_error("You cannot coerce an attribute ($name) unless its type ($type) has a coercion", data => $options);
311 if (exists $options->{trigger}) {
312 ('CODE' eq ref $options->{trigger})
313 || $class->throw_error("Trigger must be a CODE ref on attribute ($name)", data => $options->{trigger});
316 if (exists $options->{auto_deref} && $options->{auto_deref}) {
317 (exists $options->{type_constraint})
318 || $class->throw_error("You cannot auto-dereference without specifying a type constraint on attribute ($name)", data => $options);
319 ($options->{type_constraint}->is_a_type_of('ArrayRef') ||
320 $options->{type_constraint}->is_a_type_of('HashRef'))
321 || $class->throw_error("You cannot auto-dereference anything other than a ArrayRef or HashRef on attribute ($name)", data => $options);
324 if (exists $options->{lazy_build} && $options->{lazy_build} == 1) {
325 $class->throw_error("You can not use lazy_build and default for the same attribute ($name)", data => $options)
326 if exists $options->{default};
327 $options->{lazy} = 1;
328 $options->{builder} ||= "_build_${name}";
330 $options->{clearer} ||= "_clear${name}";
331 $options->{predicate} ||= "_has${name}";
334 $options->{clearer} ||= "clear_${name}";
335 $options->{predicate} ||= "has_${name}";
339 if (exists $options->{lazy} && $options->{lazy}) {
340 (exists $options->{default} || defined $options->{builder} )
341 || $class->throw_error("You cannot have lazy attribute ($name) without specifying a default value for it", data => $options);
344 if ( $options->{required} && !( ( !exists $options->{init_arg} || defined $options->{init_arg} ) || exists $options->{default} || defined $options->{builder} ) ) {
345 $class->throw_error("You cannot have a required attribute ($name) without a default, builder, or an init_arg", data => $options);
350 sub initialize_instance_slot {
351 my ($self, $meta_instance, $instance, $params) = @_;
352 my $init_arg = $self->init_arg();
353 # try to fetch the init arg from the %params ...
357 if ( defined($init_arg) and exists $params->{$init_arg}) {
358 $val = $params->{$init_arg};
362 # skip it if it's lazy
363 return if $self->is_lazy;
364 # and die if it's required and doesn't have a default value
365 $self->throw_error("Attribute (" . $self->name . ") is required", object => $instance, data => $params)
366 if $self->is_required && !$self->has_default && !$self->has_builder;
368 # if nothing was in the %params, we can use the
369 # attribute's default value (if it has one)
370 if ($self->has_default) {
371 $val = $self->default($instance);
374 elsif ($self->has_builder) {
375 $val = $self->_call_builder($instance);
380 return unless $value_is_set;
382 $val = $self->_coerce_and_verify( $val, $instance );
384 $self->set_initial_value($instance, $val);
386 if ( ref $val && $self->is_weak_ref ) {
387 $self->_weaken_value($instance);
392 my ( $self, $instance ) = @_;
394 my $builder = $self->builder();
396 return $instance->$builder()
397 if $instance->can( $self->builder );
399 $self->throw_error( blessed($instance)
400 . " does not support builder method '"
402 . "' for attribute '"
412 # this duplicates too much code from
413 # Class::MOP::Attribute, we need to
414 # refactor these bits eventually.
416 sub _set_initial_slot_value {
417 my ($self, $meta_instance, $instance, $value) = @_;
419 my $slot_name = $self->name;
421 return $meta_instance->set_slot_value($instance, $slot_name, $value)
422 unless $self->has_initializer;
425 my $val = $self->_coerce_and_verify( shift, $instance );;
427 $meta_instance->set_slot_value($instance, $slot_name, $val);
430 my $initializer = $self->initializer;
432 # most things will just want to set a value, so make it first arg
433 $instance->$initializer($value, $callback, $self);
437 my ($self, $instance, @args) = @_;
438 my $value = $args[0];
440 my $attr_name = $self->name;
442 if ($self->is_required and not @args) {
443 $self->throw_error("Attribute ($attr_name) is required", object => $instance);
446 $value = $self->_coerce_and_verify( $value, $instance );
449 if ( $self->has_trigger && $self->has_value($instance) ) {
450 @old = $self->get_value($instance, 'for trigger');
453 $self->SUPER::set_value($instance, $value);
455 if ( ref $value && $self->is_weak_ref ) {
456 $self->_weaken_value($instance);
459 if ($self->has_trigger) {
460 $self->trigger->($instance, $value, @old);
465 my ( $self, $instance ) = @_;
467 my $meta_instance = Class::MOP::Class->initialize( blessed($instance) )
470 $meta_instance->weaken_slot_value( $instance, $self->name );
474 my ($self, $instance, $for_trigger) = @_;
476 if ($self->is_lazy) {
477 unless ($self->has_value($instance)) {
479 if ($self->has_default) {
480 $value = $self->default($instance);
481 } elsif ( $self->has_builder ) {
482 $value = $self->_call_builder($instance);
485 $value = $self->_coerce_and_verify( $value, $instance );
487 $self->set_initial_value($instance, $value);
491 if ( $self->should_auto_deref && ! $for_trigger ) {
493 my $type_constraint = $self->type_constraint;
495 if ($type_constraint->is_a_type_of('ArrayRef')) {
496 my $rv = $self->SUPER::get_value($instance);
497 return unless defined $rv;
498 return wantarray ? @{ $rv } : $rv;
500 elsif ($type_constraint->is_a_type_of('HashRef')) {
501 my $rv = $self->SUPER::get_value($instance);
502 return unless defined $rv;
503 return wantarray ? %{ $rv } : $rv;
506 $self->throw_error("Can not auto de-reference the type constraint '" . $type_constraint->name . "'", object => $instance, type_constraint => $type_constraint);
512 return $self->SUPER::get_value($instance);
516 ## installing accessors
518 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
520 sub install_accessors {
522 $self->SUPER::install_accessors(@_);
523 $self->install_delegation if $self->has_handles;
527 sub _check_associated_methods {
530 @{ $self->associated_methods }
531 || ($self->_is_metadata || '') eq 'bare'
534 'Attribute (' . $self->name . ') of class '
535 . $self->associated_class->name
536 . ' has no associated methods'
537 . ' (did you mean to provide an "is" argument?)'
543 sub _process_accessors {
545 my ($type, $accessor, $generate_as_inline_methods) = @_;
546 $accessor = (keys %$accessor)[0] if (ref($accessor)||'') eq 'HASH';
547 my $method = $self->associated_class->get_method($accessor);
548 if ($method && !$method->isa('Class::MOP::Method::Accessor')
549 && (!$self->definition_context
550 || $method->package_name eq $self->definition_context->{package})) {
552 "You are overwriting a locally defined method ($accessor) with "
556 $self->SUPER::_process_accessors(@_);
559 sub remove_accessors {
561 $self->SUPER::remove_accessors(@_);
562 $self->remove_delegation if $self->has_handles;
566 sub install_delegation {
570 # Here we canonicalize the 'handles' option
571 # this will sort out any details and always
572 # return an hash of methods which we want
573 # to delagate to, see that method for details
574 my %handles = $self->_canonicalize_handles;
577 # install the delegation ...
578 my $associated_class = $self->associated_class;
579 foreach my $handle (keys %handles) {
580 my $method_to_call = $handles{$handle};
581 my $class_name = $associated_class->name;
582 my $name = "${class_name}::${handle}";
584 (!$associated_class->has_method($handle))
585 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
588 # handles is not allowed to delegate
589 # any of these methods, as they will
590 # override the ones in your class, which
591 # is almost certainly not what you want.
593 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
594 #cluck("Not delegating method '$handle' because it is a core method") and
595 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
597 my $method = $self->_make_delegation_method($handle, $method_to_call);
599 $self->associated_class->add_method($method->name, $method);
600 $self->associate_method($method);
604 sub remove_delegation {
606 my %handles = $self->_canonicalize_handles;
607 my $associated_class = $self->associated_class;
608 foreach my $handle (keys %handles) {
609 next unless any { $handle eq $_ }
611 @{ $self->associated_methods };
612 $self->associated_class->remove_method($handle);
616 # private methods to help delegation ...
618 sub _canonicalize_handles {
620 my $handles = $self->handles;
621 if (my $handle_type = ref($handles)) {
622 if ($handle_type eq 'HASH') {
625 elsif ($handle_type eq 'ARRAY') {
626 return map { $_ => $_ } @{$handles};
628 elsif ($handle_type eq 'Regexp') {
629 ($self->has_type_constraint)
630 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
631 return map { ($_ => $_) }
632 grep { /$handles/ } $self->_get_delegate_method_list;
634 elsif ($handle_type eq 'CODE') {
635 return $handles->($self, $self->_find_delegate_metaclass);
637 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::DuckType')) {
638 return map { $_ => $_ } @{ $handles->methods };
640 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::Role')) {
641 $handles = $handles->role;
644 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
648 Class::MOP::load_class($handles);
649 my $role_meta = Class::MOP::class_of($handles);
651 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
652 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because its metaclass is not a Moose::Meta::Role", data => $handles);
654 return map { $_ => $_ }
655 grep { $_ ne 'meta' } (
656 $role_meta->get_method_list,
657 map { $_->name } $role_meta->get_required_method_list,
661 sub _find_delegate_metaclass {
663 if (my $class = $self->_isa_metadata) {
664 # we might be dealing with a non-Moose class,
665 # and need to make our own metaclass. if there's
666 # already a metaclass, it will be returned
667 return Class::MOP::Class->initialize($class);
669 elsif (my $role = $self->_does_metadata) {
670 return Class::MOP::class_of($role);
673 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
677 sub _get_delegate_method_list {
679 my $meta = $self->_find_delegate_metaclass;
680 if ($meta->isa('Class::MOP::Class')) {
681 return map { $_->name } # NOTE: !never! delegate &meta
682 grep { $_->package_name ne 'Moose::Object' && $_->name ne 'meta' }
683 $meta->get_all_methods;
685 elsif ($meta->isa('Moose::Meta::Role')) {
686 return $meta->get_method_list;
689 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
693 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
695 sub _make_delegation_method {
696 my ( $self, $handle_name, $method_to_call ) = @_;
698 my @curried_arguments;
700 ($method_to_call, @curried_arguments) = @$method_to_call
701 if 'ARRAY' eq ref($method_to_call);
703 return $self->delegation_metaclass->new(
704 name => $handle_name,
705 package_name => $self->associated_class->name,
707 delegate_to_method => $method_to_call,
708 curried_arguments => \@curried_arguments,
712 sub _coerce_and_verify {
715 my $instance = shift;
717 return $val unless $self->has_type_constraint;
719 $val = $self->type_constraint->coerce($val)
720 if $self->should_coerce;
722 $self->verify_against_type_constraint($val, instance => $instance);
727 sub verify_against_type_constraint {
731 return 1 if !$self->has_type_constraint;
733 my $type_constraint = $self->type_constraint;
735 $type_constraint->check($val)
736 || $self->throw_error("Attribute ("
738 . ") does not pass the type constraint because: "
739 . $type_constraint->get_message($val), data => $val, @_);
742 package Moose::Meta::Attribute::Custom::Moose;
743 sub register_implementation { 'Moose::Meta::Attribute' }
753 Moose::Meta::Attribute - The Moose attribute metaclass
757 This class is a subclass of L<Class::MOP::Attribute> that provides
758 additional Moose-specific functionality.
760 To really understand this class, you will need to start with the
761 L<Class::MOP::Attribute> documentation. This class can be understood
762 as a set of additional features on top of the basic feature provided
763 by that parent class.
767 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
771 Many of the documented below override methods in
772 L<Class::MOP::Attribute> and add Moose specific features.
778 =item B<< Moose::Meta::Attribute->new(%options) >>
780 This method overrides the L<Class::MOP::Attribute> constructor.
782 Many of the options below are described in more detail in the
783 L<Moose::Manual::Attributes> document.
785 It adds the following options to the constructor:
789 =item * is => 'ro', 'rw', 'bare'
791 This provides a shorthand for specifying the C<reader>, C<writer>, or
792 C<accessor> names. If the attribute is read-only ('ro') then it will
793 have a C<reader> method with the same attribute as the name.
795 If it is read-write ('rw') then it will have an C<accessor> method
796 with the same name. If you provide an explicit C<writer> for a
797 read-write attribute, then you will have a C<reader> with the same
798 name as the attribute, and a C<writer> with the name you provided.
800 Use 'bare' when you are deliberately not installing any methods
801 (accessor, reader, etc.) associated with this attribute; otherwise,
802 Moose will issue a deprecation warning when this attribute is added to a
807 This option accepts a type. The type can be a string, which should be
808 a type name. If the type name is unknown, it is assumed to be a class
811 This option can also accept a L<Moose::Meta::TypeConstraint> object.
813 If you I<also> provide a C<does> option, then your C<isa> option must
814 be a class name, and that class must do the role specified with
817 =item * does => $role
819 This is short-hand for saying that the attribute's type must be an
820 object which does the named role.
822 =item * coerce => $bool
824 This option is only valid for objects with a type constraint
825 (C<isa>). If this is true, then coercions will be applied whenever
826 this attribute is set.
828 You can make both this and the C<weak_ref> option true.
830 =item * trigger => $sub
832 This option accepts a subroutine reference, which will be called after
833 the attribute is set.
835 =item * required => $bool
837 An attribute which is required must be provided to the constructor. An
838 attribute which is required can also have a C<default> or C<builder>,
839 which will satisfy its required-ness.
841 A required attribute must have a C<default>, C<builder> or a
842 non-C<undef> C<init_arg>
844 =item * lazy => $bool
846 A lazy attribute must have a C<default> or C<builder>. When an
847 attribute is lazy, the default value will not be calculated until the
850 =item * weak_ref => $bool
852 If this is true, the attribute's value will be stored as a weak
855 =item * auto_deref => $bool
857 If this is true, then the reader will dereference the value when it is
858 called. The attribute must have a type constraint which defines the
859 attribute as an array or hash reference.
861 =item * lazy_build => $bool
863 Setting this to true makes the attribute lazy and provides a number of
871 is equivalent to this:
876 builder => '_build_size',
877 clearer => 'clear_size',
878 predicate => 'has_size',
881 =item * documentation
883 An arbitrary string that can be retrieved later by calling C<<
884 $attr->documentation >>.
888 =item B<< $attr->clone(%options) >>
890 This creates a new attribute based on attribute being cloned. You must
891 supply a C<name> option to provide a new name for the attribute.
893 The C<%options> can only specify options handled by
894 L<Class::MOP::Attribute>.
898 =head2 Value management
902 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
904 This method is used internally to initialize the attribute's slot in
905 the object C<$instance>.
907 This overrides the L<Class::MOP::Attribute> method to handle lazy
908 attributes, weak references, and type constraints.
914 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
919 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
921 Before setting the value, a check is made on the type constraint of
922 the attribute, if it has one, to see if the value passes it. If the
923 value fails to pass, the set operation dies with a L</throw_error>.
925 Any coercion to convert values is done before checking the type constraint.
927 To check a value against a type constraint before setting it, fetch the
928 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
929 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
930 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
935 =head2 Attribute Accessor generation
939 =item B<< $attr->install_accessors >>
941 This method overrides the parent to also install delegation methods.
943 If, after installing all methods, the attribute object has no associated
944 methods, it throws an error unless C<< is => 'bare' >> was passed to the
945 attribute constructor. (Trying to add an attribute that has no associated
946 methods is almost always an error.)
948 =item B<< $attr->remove_accessors >>
950 This method overrides the parent to also remove delegation methods.
952 =item B<< $attr->install_delegation >>
954 This method adds its delegation methods to the attribute's associated
955 class, if it has any to add.
957 =item B<< $attr->remove_delegation >>
959 This method remove its delegation methods from the attribute's
962 =item B<< $attr->accessor_metaclass >>
964 Returns the accessor metaclass name, which defaults to
965 L<Moose::Meta::Method::Accessor>.
967 =item B<< $attr->delegation_metaclass >>
969 Returns the delegation metaclass name, which defaults to
970 L<Moose::Meta::Method::Delegation>.
974 =head2 Additional Moose features
976 These methods are not found in the superclass. They support features
981 =item B<< $attr->does($role) >>
983 This indicates whether the I<attribute itself> does the given
984 role. The role can be given as a full class name, or as a resolvable
987 Note that this checks the attribute itself, not its type constraint,
988 so it is checking the attribute's metaclass and any traits applied to
991 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
993 This is an alternate constructor that handles the C<metaclass> and
996 Effectively, this method is a factory that finds or creates the
997 appropriate class for the given C<metaclass> and/or C<traits>.
999 Once it has the appropriate class, it will call C<< $class->new($name,
1000 %options) >> on that class.
1002 =item B<< $attr->clone_and_inherit_options(%options) >>
1004 This method supports the C<has '+foo'> feature. It does various bits
1005 of processing on the supplied C<%options> before ultimately calling
1006 the C<clone> method.
1008 One of its main tasks is to make sure that the C<%options> provided
1009 does not include the options returned by the
1010 C<illegal_options_for_inheritance> method.
1012 =item B<< $attr->illegal_options_for_inheritance >>
1014 This returns a blacklist of options that can not be overridden in a
1015 subclass's attribute definition.
1017 This exists to allow a custom metaclass to change or add to the list
1018 of options which can not be changed.
1020 =item B<< $attr->type_constraint >>
1022 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1025 =item B<< $attr->has_type_constraint >>
1027 Returns true if this attribute has a type constraint.
1029 =item B<< $attr->verify_against_type_constraint($value) >>
1031 Given a value, this method returns true if the value is valid for the
1032 attribute's type constraint. If the value is not valid, it throws an
1035 =item B<< $attr->handles >>
1037 This returns the value of the C<handles> option passed to the
1040 =item B<< $attr->has_handles >>
1042 Returns true if this attribute performs delegation.
1044 =item B<< $attr->is_weak_ref >>
1046 Returns true if this attribute stores its value as a weak reference.
1048 =item B<< $attr->is_required >>
1050 Returns true if this attribute is required to have a value.
1052 =item B<< $attr->is_lazy >>
1054 Returns true if this attribute is lazy.
1056 =item B<< $attr->is_lazy_build >>
1058 Returns true if the C<lazy_build> option was true when passed to the
1061 =item B<< $attr->should_coerce >>
1063 Returns true if the C<coerce> option passed to the constructor was
1066 =item B<< $attr->should_auto_deref >>
1068 Returns true if the C<auto_deref> option passed to the constructor was
1071 =item B<< $attr->trigger >>
1073 This is the subroutine reference that was in the C<trigger> option
1074 passed to the constructor, if any.
1076 =item B<< $attr->has_trigger >>
1078 Returns true if this attribute has a trigger set.
1080 =item B<< $attr->documentation >>
1082 Returns the value that was in the C<documentation> option passed to
1083 the constructor, if any.
1085 =item B<< $attr->has_documentation >>
1087 Returns true if this attribute has any documentation.
1089 =item B<< $attr->applied_traits >>
1091 This returns an array reference of all the traits which were applied
1092 to this attribute. If none were applied, this returns C<undef>.
1094 =item B<< $attr->has_applied_traits >>
1096 Returns true if this attribute has any traits applied.
1102 See L<Moose/BUGS> for details on reporting bugs.
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 2006-2010 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.