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 # XXX handles should be in associated_methods
546 || @{ $self->associated_methods }
547 || ($self->_is_metadata || '') eq 'bare'
550 'Attribute (' . $self->name . ') has no associated methods'
551 . ' (did you mean to provide an "is" argument?)'
558 sub remove_accessors {
560 $self->SUPER::remove_accessors(@_);
561 $self->remove_delegation if $self->has_handles;
565 sub install_delegation {
569 # Here we canonicalize the 'handles' option
570 # this will sort out any details and always
571 # return an hash of methods which we want
572 # to delagate to, see that method for details
573 my %handles = $self->_canonicalize_handles;
576 # install the delegation ...
577 my $associated_class = $self->associated_class;
578 foreach my $handle (keys %handles) {
579 my $method_to_call = $handles{$handle};
580 my $class_name = $associated_class->name;
581 my $name = "${class_name}::${handle}";
583 (!$associated_class->has_method($handle))
584 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
587 # handles is not allowed to delegate
588 # any of these methods, as they will
589 # override the ones in your class, which
590 # is almost certainly not what you want.
592 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
593 #cluck("Not delegating method '$handle' because it is a core method") and
594 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
596 my $method = $self->_make_delegation_method($handle, $method_to_call);
598 $self->associated_class->add_method($method->name, $method);
602 sub remove_delegation {
604 my %handles = $self->_canonicalize_handles;
605 my $associated_class = $self->associated_class;
606 foreach my $handle (keys %handles) {
607 $self->associated_class->remove_method($handle);
611 # private methods to help delegation ...
613 sub _canonicalize_handles {
615 my $handles = $self->handles;
616 if (my $handle_type = ref($handles)) {
617 if ($handle_type eq 'HASH') {
620 elsif ($handle_type eq 'ARRAY') {
621 return map { $_ => $_ } @{$handles};
623 elsif ($handle_type eq 'Regexp') {
624 ($self->has_type_constraint)
625 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
626 return map { ($_ => $_) }
627 grep { /$handles/ } $self->_get_delegate_method_list;
629 elsif ($handle_type eq 'CODE') {
630 return $handles->($self, $self->_find_delegate_metaclass);
633 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
637 Class::MOP::load_class($handles);
638 my $role_meta = Class::MOP::class_of($handles);
640 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
641 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because its metaclass is not a Moose::Meta::Role", data => $handles);
643 return map { $_ => $_ } (
644 $role_meta->get_method_list,
645 map { $_->name } $role_meta->get_required_method_list,
650 sub _find_delegate_metaclass {
652 if (my $class = $self->_isa_metadata) {
653 # we might be dealing with a non-Moose class,
654 # and need to make our own metaclass. if there's
655 # already a metaclass, it will be returned
656 return Moose::Meta::Class->initialize($class);
658 elsif (my $role = $self->_does_metadata) {
659 return Class::MOP::class_of($role);
662 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
666 sub _get_delegate_method_list {
668 my $meta = $self->_find_delegate_metaclass;
669 if ($meta->isa('Class::MOP::Class')) {
670 return map { $_->name } # NOTE: !never! delegate &meta
671 grep { $_->package_name ne 'Moose::Object' && $_->name ne 'meta' }
672 $meta->get_all_methods;
674 elsif ($meta->isa('Moose::Meta::Role')) {
675 return $meta->get_method_list;
678 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
682 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
684 sub _make_delegation_method {
685 my ( $self, $handle_name, $method_to_call ) = @_;
689 $method_body = $method_to_call
690 if 'CODE' eq ref($method_to_call);
692 return $self->delegation_metaclass->new(
693 name => $handle_name,
694 package_name => $self->associated_class->name,
696 delegate_to_method => $method_to_call,
700 sub _coerce_and_verify {
703 my $instance = shift;
705 return $val unless $self->has_type_constraint;
707 my $type_constraint = $self->type_constraint;
708 if ($self->should_coerce && $type_constraint->has_coercion) {
709 $val = $type_constraint->coerce($val);
712 $self->verify_against_type_constraint($val, instance => $instance);
717 sub verify_against_type_constraint {
721 return 1 if !$self->has_type_constraint;
723 my $type_constraint = $self->type_constraint;
725 $type_constraint->check($val)
726 || $self->throw_error("Attribute ("
728 . ") does not pass the type constraint because: "
729 . $type_constraint->get_message($val), data => $val, @_);
732 package Moose::Meta::Attribute::Custom::Moose;
733 sub register_implementation { 'Moose::Meta::Attribute' }
743 Moose::Meta::Attribute - The Moose attribute metaclass
747 This class is a subclass of L<Class::MOP::Attribute> that provides
748 additional Moose-specific functionality.
750 To really understand this class, you will need to start with the
751 L<Class::MOP::Attribute> documentation. This class can be understood
752 as a set of additional features on top of the basic feature provided
753 by that parent class.
757 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
761 Many of the documented below override methods in
762 L<Class::MOP::Attribute> and add Moose specific features.
768 =item B<< Moose::Meta::Attribute->new(%options) >>
770 This method overrides the L<Class::MOP::Attribute> constructor.
772 Many of the options below are described in more detail in the
773 L<Moose::Manual::Attributes> document.
775 It adds the following options to the constructor:
779 =item * is => 'ro', 'rw', 'bare'
781 This provides a shorthand for specifying the C<reader>, C<writer>, or
782 C<accessor> names. If the attribute is read-only ('ro') then it will
783 have a C<reader> method with the same attribute as the name.
785 If it is read-write ('rw') then it will have an C<accessor> method
786 with the same name. If you provide an explicit C<writer> for a
787 read-write attribute, then you will have a C<reader> with the same
788 name as the attribute, and a C<writer> with the name you provided.
790 Use 'bare' when you are deliberately not installing any methods
791 (accessor, reader, etc.) associated with this attribute; otherwise,
792 Moose will issue a deprecation warning when this attribute is added to a
797 This option accepts a type. The type can be a string, which should be
798 a type name. If the type name is unknown, it is assumed to be a class
801 This option can also accept a L<Moose::Meta::TypeConstraint> object.
803 If you I<also> provide a C<does> option, then your C<isa> option must
804 be a class name, and that class must do the role specified with
807 =item * does => $role
809 This is short-hand for saying that the attribute's type must be an
810 object which does the named role.
812 =item * coerce => $bool
814 This option is only valid for objects with a type constraint
815 (C<isa>). If this is true, then coercions will be applied whenever
816 this attribute is set.
818 You can make both this and the C<weak_ref> option true.
820 =item * trigger => $sub
822 This option accepts a subroutine reference, which will be called after
823 the attribute is set.
825 =item * required => $bool
827 An attribute which is required must be provided to the constructor. An
828 attribute which is required can also have a C<default> or C<builder>,
829 which will satisfy its required-ness.
831 A required attribute must have a C<default>, C<builder> or a
832 non-C<undef> C<init_arg>
834 =item * lazy => $bool
836 A lazy attribute must have a C<default> or C<builder>. When an
837 attribute is lazy, the default value will not be calculated until the
840 =item * weak_ref => $bool
842 If this is true, the attribute's value will be stored as a weak
845 =item * auto_deref => $bool
847 If this is true, then the reader will dereference the value when it is
848 called. The attribute must have a type constraint which defines the
849 attribute as an array or hash reference.
851 =item * lazy_build => $bool
853 Setting this to true makes the attribute lazy and provides a number of
861 is equivalent to this:
866 builder => '_build_size',
867 clearer => 'clear_size',
868 predicate => 'has_size',
871 =item * documentation
873 An arbitrary string that can be retrieved later by calling C<<
874 $attr->documentation >>.
878 =item B<< $attr->clone(%options) >>
880 This creates a new attribute based on attribute being cloned. You must
881 supply a C<name> option to provide a new name for the attribute.
883 The C<%options> can only specify options handled by
884 L<Class::MOP::Attribute>.
888 =head2 Value management
892 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
894 This method is used internally to initialize the attribute's slot in
895 the object C<$instance>.
897 This overrides the L<Class::MOP::Attribute> method to handle lazy
898 attributes, weak references, and type constraints.
904 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
909 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
911 Before setting the value, a check is made on the type constraint of
912 the attribute, if it has one, to see if the value passes it. If the
913 value fails to pass, the set operation dies with a L<throw_error>.
915 Any coercion to convert values is done before checking the type constraint.
917 To check a value against a type constraint before setting it, fetch the
918 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
919 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
920 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
925 =head2 Attribute Accessor generation
929 =item B<< $attr->install_accessors >>
931 This method overrides the parent to also install delegation methods.
933 If, after installing all methods, the attribute object has no associated
934 methods, it throws an error unless C<< is => 'bare' >> was passed to the
935 attribute constructor. (Trying to add an attribute that has no associated
936 methods is almost always an error.)
938 =item B<< $attr->remove_accessors >>
940 This method overrides the parent to also remove delegation methods.
942 =item B<< $attr->install_delegation >>
944 This method adds its delegation methods to the attribute's associated
945 class, if it has any to add.
947 =item B<< $attr->remove_delegation >>
949 This method remove its delegation methods from the attribute's
952 =item B<< $attr->accessor_metaclass >>
954 Returns the accessor metaclass name, which defaults to
955 L<Moose::Meta::Method::Accessor>.
957 =item B<< $attr->delegation_metaclass >>
959 Returns the delegation metaclass name, which defaults to
960 L<Moose::Meta::Method::Delegation>.
964 =head2 Additional Moose features
966 These methods are not found in the superclass. They support features
971 =item B<< $attr->does($role) >>
973 This indicates whether the I<attribute itself> does the given
974 role. The role can be given as a full class name, or as a resolvable
977 Note that this checks the attribute itself, not its type constraint,
978 so it is checking the attribute's metaclass and any traits applied to
981 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
983 This is an alternate constructor that handles the C<metaclass> and
986 Effectively, this method is a factory that finds or creates the
987 appropriate class for the given C<metaclass> and/or C<traits>.
989 Once it has the appropriate class, it will call C<< $class->new($name,
990 %options) >> on that class.
992 =item B<< $attr->clone_and_inherit_options(%options) >>
994 This method supports the C<has '+foo'> feature. It does various bits
995 of processing on the supplied C<%options> before ultimately calling
998 One of its main tasks is to make sure that the C<%options> provided
999 only includes the options returned by the
1000 C<legal_options_for_inheritance> method.
1002 =item B<< $attr->legal_options_for_inheritance >>
1004 This returns a whitelist of options that can be overridden in a
1005 subclass's attribute definition.
1007 This exists to allow a custom metaclass to change or add to the list
1008 of options which can be changed.
1010 =item B<< $attr->type_constraint >>
1012 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1015 =item B<< $attr->has_type_constraint >>
1017 Returns true if this attribute has a type constraint.
1019 =item B<< $attr->verify_against_type_constraint($value) >>
1021 Given a value, this method returns true if the value is valid for the
1022 attribute's type constraint. If the value is not valid, it throws an
1025 =item B<< $attr->handles >>
1027 This returns the value of the C<handles> option passed to the
1030 =item B<< $attr->has_handles >>
1032 Returns true if this attribute performs delegation.
1034 =item B<< $attr->is_weak_ref >>
1036 Returns true if this attribute stores its value as a weak reference.
1038 =item B<< $attr->is_required >>
1040 Returns true if this attribute is required to have a value.
1042 =item B<< $attr->is_lazy >>
1044 Returns true if this attribute is lazy.
1046 =item B<< $attr->is_lazy_build >>
1048 Returns true if the C<lazy_build> option was true when passed to the
1051 =item B<< $attr->should_coerce >>
1053 Returns true if the C<coerce> option passed to the constructor was
1056 =item B<< $attr->should_auto_deref >>
1058 Returns true if the C<auto_deref> option passed to the constructor was
1061 =item B<< $attr->trigger >>
1063 This is the subroutine reference that was in the C<trigger> option
1064 passed to the constructor, if any.
1066 =item B<< $attr->has_trigger >>
1068 Returns true if this attribute has a trigger set.
1070 =item B<< $attr->documentation >>
1072 Returns the value that was in the C<documentation> option passed to
1073 the constructor, if any.
1075 =item B<< $attr->has_documentation >>
1077 Returns true if this attribute has any documentation.
1079 =item B<< $attr->applied_traits >>
1081 This returns an array reference of all the traits which were applied
1082 to this attribute. If none were applied, this returns C<undef>.
1084 =item B<< $attr->has_applied_traits >>
1086 Returns true if this attribute has any traits applied.
1092 All complex software has bugs lurking in it, and this module is no
1093 exception. If you find a bug please either email me, or add the bug
1098 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1100 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1102 =head1 COPYRIGHT AND LICENSE
1104 Copyright 2006-2009 by Infinity Interactive, Inc.
1106 L<http://www.iinteractive.com>
1108 This library is free software; you can redistribute it and/or modify
1109 it under the same terms as Perl itself.