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 ) : $class );
134 # method-generating options shouldn't be overridden
135 sub illegal_options_for_inheritance {
136 qw(is reader writer accessor clearer predicate)
140 # This method *must* be able to handle
141 # Class::MOP::Attribute instances as
142 # well. Yes, I know that is wrong, but
143 # apparently we didn't realize it was
144 # doing that and now we have some code
145 # which is dependent on it. The real
146 # solution of course is to push this
147 # feature back up into Class::MOP::Attribute
148 # but I not right now, I am too lazy.
149 # However if you are reading this and
150 # looking for something to do,.. please
153 sub clone_and_inherit_options {
154 my ($self, %options) = @_;
157 # we may want to extends a Class::MOP::Attribute
158 # in which case we need to be able to use the
159 # core set of legal options that have always
160 # been here. But we allows Moose::Meta::Attribute
161 # instances to changes them.
163 my @illegal_options = $self->can('illegal_options_for_inheritance')
164 ? $self->illegal_options_for_inheritance
167 my @found_illegal_options = grep { exists $options{$_} && exists $self->{$_} ? $_ : undef } @illegal_options;
168 (scalar @found_illegal_options == 0)
169 || $self->throw_error("Illegal inherited options => (" . (join ', ' => @found_illegal_options) . ")", data => \%options);
173 if (blessed($options{isa}) && $options{isa}->isa('Moose::Meta::TypeConstraint')) {
174 $type_constraint = $options{isa};
177 $type_constraint = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options{isa});
178 (defined $type_constraint)
179 || $self->throw_error("Could not find the type constraint '" . $options{isa} . "'", data => $options{isa});
182 $options{type_constraint} = $type_constraint;
185 if ($options{does}) {
187 if (blessed($options{does}) && $options{does}->isa('Moose::Meta::TypeConstraint')) {
188 $type_constraint = $options{does};
191 $type_constraint = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options{does});
192 (defined $type_constraint)
193 || $self->throw_error("Could not find the type constraint '" . $options{does} . "'", data => $options{does});
196 $options{type_constraint} = $type_constraint;
200 # this doesn't apply to Class::MOP::Attributes,
201 # so we can ignore it for them.
203 if ($self->can('interpolate_class')) {
204 ( $options{metaclass}, my @traits ) = $self->interpolate_class(\%options);
207 my @all_traits = grep { $seen{$_}++ } @{ $self->applied_traits || [] }, @traits;
208 $options{traits} = \@all_traits if @all_traits;
211 $self->clone(%options);
215 my ( $self, %params ) = @_;
217 my $class = delete $params{metaclass} || ref $self;
219 my ( @init, @non_init );
221 foreach my $attr ( grep { $_->has_value($self) } Class::MOP::class_of($self)->get_all_attributes ) {
222 push @{ $attr->has_init_arg ? \@init : \@non_init }, $attr;
225 my %new_params = ( ( map { $_->init_arg => $_->get_value($self) } @init ), %params );
227 my $name = delete $new_params{name};
229 my $clone = $class->new($name, %new_params, __hack_no_process_options => 1 );
231 foreach my $attr ( @non_init ) {
232 $attr->set_value($clone, $attr->get_value($self));
238 sub _process_options {
239 my ($class, $name, $options) = @_;
241 if (exists $options->{is}) {
243 ### -------------------------
244 ## is => ro, writer => _foo # turns into (reader => foo, writer => _foo) as before
245 ## is => rw, writer => _foo # turns into (reader => foo, writer => _foo)
246 ## is => rw, accessor => _foo # turns into (accessor => _foo)
247 ## is => ro, accessor => _foo # error, accesor is rw
248 ### -------------------------
250 if ($options->{is} eq 'ro') {
251 $class->throw_error("Cannot define an accessor name on a read-only attribute, accessors are read/write", data => $options)
252 if exists $options->{accessor};
253 $options->{reader} ||= $name;
255 elsif ($options->{is} eq 'rw') {
256 if ($options->{writer}) {
257 $options->{reader} ||= $name;
260 $options->{accessor} ||= $name;
263 elsif ($options->{is} eq 'bare') {
264 # do nothing, but don't complain (later) about missing methods
267 $class->throw_error("I do not understand this option (is => " . $options->{is} . ") on attribute ($name)", data => $options->{is});
271 if (exists $options->{isa}) {
272 if (exists $options->{does}) {
273 if (try { $options->{isa}->can('does') }) {
274 ($options->{isa}->does($options->{does}))
275 || $class->throw_error("Cannot have an isa option and a does option if the isa does not do the does on attribute ($name)", data => $options);
278 $class->throw_error("Cannot have an isa option which cannot ->does() on attribute ($name)", data => $options);
282 # allow for anon-subtypes here ...
283 if (blessed($options->{isa}) && $options->{isa}->isa('Moose::Meta::TypeConstraint')) {
284 $options->{type_constraint} = $options->{isa};
287 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options->{isa});
290 elsif (exists $options->{does}) {
291 # allow for anon-subtypes here ...
292 if (blessed($options->{does}) && $options->{does}->isa('Moose::Meta::TypeConstraint')) {
293 $options->{type_constraint} = $options->{does};
296 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options->{does});
300 if (exists $options->{coerce} && $options->{coerce}) {
301 (exists $options->{type_constraint})
302 || $class->throw_error("You cannot have coercion without specifying a type constraint on attribute ($name)", data => $options);
303 $class->throw_error("You cannot have a weak reference to a coerced value on attribute ($name)", data => $options)
304 if $options->{weak_ref};
306 unless ( $options->{type_constraint}->has_coercion ) {
307 my $type = $options->{type_constraint}->name;
308 $class->throw_error("You cannot coerce an attribute ($name) unless its type ($type) has a coercion", data => $options);
312 if (exists $options->{trigger}) {
313 ('CODE' eq ref $options->{trigger})
314 || $class->throw_error("Trigger must be a CODE ref on attribute ($name)", data => $options->{trigger});
317 if (exists $options->{auto_deref} && $options->{auto_deref}) {
318 (exists $options->{type_constraint})
319 || $class->throw_error("You cannot auto-dereference without specifying a type constraint on attribute ($name)", data => $options);
320 ($options->{type_constraint}->is_a_type_of('ArrayRef') ||
321 $options->{type_constraint}->is_a_type_of('HashRef'))
322 || $class->throw_error("You cannot auto-dereference anything other than a ArrayRef or HashRef on attribute ($name)", data => $options);
325 if (exists $options->{lazy_build} && $options->{lazy_build} == 1) {
326 $class->throw_error("You can not use lazy_build and default for the same attribute ($name)", data => $options)
327 if exists $options->{default};
328 $options->{lazy} = 1;
329 $options->{builder} ||= "_build_${name}";
331 $options->{clearer} ||= "_clear${name}";
332 $options->{predicate} ||= "_has${name}";
335 $options->{clearer} ||= "clear_${name}";
336 $options->{predicate} ||= "has_${name}";
340 if (exists $options->{lazy} && $options->{lazy}) {
341 (exists $options->{default} || defined $options->{builder} )
342 || $class->throw_error("You cannot have lazy attribute ($name) without specifying a default value for it", data => $options);
345 if ( $options->{required} && !( ( !exists $options->{init_arg} || defined $options->{init_arg} ) || exists $options->{default} || defined $options->{builder} ) ) {
346 $class->throw_error("You cannot have a required attribute ($name) without a default, builder, or an init_arg", data => $options);
351 sub initialize_instance_slot {
352 my ($self, $meta_instance, $instance, $params) = @_;
353 my $init_arg = $self->init_arg();
354 # try to fetch the init arg from the %params ...
358 if ( defined($init_arg) and exists $params->{$init_arg}) {
359 $val = $params->{$init_arg};
363 # skip it if it's lazy
364 return if $self->is_lazy;
365 # and die if it's required and doesn't have a default value
366 $self->throw_error("Attribute (" . $self->name . ") is required", object => $instance, data => $params)
367 if $self->is_required && !$self->has_default && !$self->has_builder;
369 # if nothing was in the %params, we can use the
370 # attribute's default value (if it has one)
371 if ($self->has_default) {
372 $val = $self->default($instance);
375 elsif ($self->has_builder) {
376 $val = $self->_call_builder($instance);
381 return unless $value_is_set;
383 $val = $self->_coerce_and_verify( $val, $instance );
385 $self->set_initial_value($instance, $val);
387 if ( ref $val && $self->is_weak_ref ) {
388 $self->_weaken_value($instance);
393 my ( $self, $instance ) = @_;
395 my $builder = $self->builder();
397 return $instance->$builder()
398 if $instance->can( $self->builder );
400 $self->throw_error( blessed($instance)
401 . " does not support builder method '"
403 . "' for attribute '"
413 # this duplicates too much code from
414 # Class::MOP::Attribute, we need to
415 # refactor these bits eventually.
417 sub _set_initial_slot_value {
418 my ($self, $meta_instance, $instance, $value) = @_;
420 my $slot_name = $self->name;
422 return $meta_instance->set_slot_value($instance, $slot_name, $value)
423 unless $self->has_initializer;
426 my $val = $self->_coerce_and_verify( shift, $instance );;
428 $meta_instance->set_slot_value($instance, $slot_name, $val);
431 my $initializer = $self->initializer;
433 # most things will just want to set a value, so make it first arg
434 $instance->$initializer($value, $callback, $self);
438 my ($self, $instance, @args) = @_;
439 my $value = $args[0];
441 my $attr_name = $self->name;
443 if ($self->is_required and not @args) {
444 $self->throw_error("Attribute ($attr_name) is required", object => $instance);
447 $value = $self->_coerce_and_verify( $value, $instance );
450 if ( $self->has_trigger && $self->has_value($instance) ) {
451 @old = $self->get_value($instance, 'for trigger');
454 $self->SUPER::set_value($instance, $value);
456 if ( ref $value && $self->is_weak_ref ) {
457 $self->_weaken_value($instance);
460 if ($self->has_trigger) {
461 $self->trigger->($instance, $value, @old);
466 my ( $self, $instance ) = @_;
468 my $meta_instance = Class::MOP::Class->initialize( blessed($instance) )
471 $meta_instance->weaken_slot_value( $instance, $self->name );
475 my ($self, $instance, $for_trigger) = @_;
477 if ($self->is_lazy) {
478 unless ($self->has_value($instance)) {
480 if ($self->has_default) {
481 $value = $self->default($instance);
482 } elsif ( $self->has_builder ) {
483 $value = $self->_call_builder($instance);
486 $value = $self->_coerce_and_verify( $value, $instance );
488 $self->set_initial_value($instance, $value);
492 if ( $self->should_auto_deref && ! $for_trigger ) {
494 my $type_constraint = $self->type_constraint;
496 if ($type_constraint->is_a_type_of('ArrayRef')) {
497 my $rv = $self->SUPER::get_value($instance);
498 return unless defined $rv;
499 return wantarray ? @{ $rv } : $rv;
501 elsif ($type_constraint->is_a_type_of('HashRef')) {
502 my $rv = $self->SUPER::get_value($instance);
503 return unless defined $rv;
504 return wantarray ? %{ $rv } : $rv;
507 $self->throw_error("Can not auto de-reference the type constraint '" . $type_constraint->name . "'", object => $instance, type_constraint => $type_constraint);
513 return $self->SUPER::get_value($instance);
517 ## installing accessors
519 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
521 sub install_accessors {
523 $self->SUPER::install_accessors(@_);
524 $self->install_delegation if $self->has_handles;
528 sub _check_associated_methods {
531 @{ $self->associated_methods }
532 || ($self->_is_metadata || '') eq 'bare'
535 'Attribute (' . $self->name . ') of class '
536 . $self->associated_class->name
537 . ' has no associated methods'
538 . ' (did you mean to provide an "is" argument?)'
544 sub _process_accessors {
546 my ($type, $accessor, $generate_as_inline_methods) = @_;
547 $accessor = (keys %$accessor)[0] if (ref($accessor)||'') eq 'HASH';
548 my $method = $self->associated_class->get_method($accessor);
549 if ($method && !$method->isa('Class::MOP::Method::Accessor')
550 && (!$self->definition_context
551 || $method->package_name eq $self->definition_context->{package})) {
553 "You are overwriting a locally defined method ($accessor) with "
557 if (!$self->associated_class->has_method($accessor)
558 && $self->associated_class->has_package_symbol('&' . $accessor)) {
560 "You are overwriting a locally defined function ($accessor) with "
564 $self->SUPER::_process_accessors(@_);
567 sub remove_accessors {
569 $self->SUPER::remove_accessors(@_);
570 $self->remove_delegation if $self->has_handles;
574 sub install_delegation {
578 # Here we canonicalize the 'handles' option
579 # this will sort out any details and always
580 # return an hash of methods which we want
581 # to delagate to, see that method for details
582 my %handles = $self->_canonicalize_handles;
585 # install the delegation ...
586 my $associated_class = $self->associated_class;
587 foreach my $handle (keys %handles) {
588 my $method_to_call = $handles{$handle};
589 my $class_name = $associated_class->name;
590 my $name = "${class_name}::${handle}";
592 (!$associated_class->has_method($handle))
593 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
596 # handles is not allowed to delegate
597 # any of these methods, as they will
598 # override the ones in your class, which
599 # is almost certainly not what you want.
601 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
602 #cluck("Not delegating method '$handle' because it is a core method") and
603 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
605 my $method = $self->_make_delegation_method($handle, $method_to_call);
607 $self->associated_class->add_method($method->name, $method);
608 $self->associate_method($method);
612 sub remove_delegation {
614 my %handles = $self->_canonicalize_handles;
615 my $associated_class = $self->associated_class;
616 foreach my $handle (keys %handles) {
617 next unless any { $handle eq $_ }
619 @{ $self->associated_methods };
620 $self->associated_class->remove_method($handle);
624 # private methods to help delegation ...
626 sub _canonicalize_handles {
628 my $handles = $self->handles;
629 if (my $handle_type = ref($handles)) {
630 if ($handle_type eq 'HASH') {
633 elsif ($handle_type eq 'ARRAY') {
634 return map { $_ => $_ } @{$handles};
636 elsif ($handle_type eq 'Regexp') {
637 ($self->has_type_constraint)
638 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
639 return map { ($_ => $_) }
640 grep { /$handles/ } $self->_get_delegate_method_list;
642 elsif ($handle_type eq 'CODE') {
643 return $handles->($self, $self->_find_delegate_metaclass);
645 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::DuckType')) {
646 return map { $_ => $_ } @{ $handles->methods };
648 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::Role')) {
649 $handles = $handles->role;
652 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
656 Class::MOP::load_class($handles);
657 my $role_meta = Class::MOP::class_of($handles);
659 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
660 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because its metaclass is not a Moose::Meta::Role", data => $handles);
662 return map { $_ => $_ }
663 grep { $_ ne 'meta' } (
664 $role_meta->get_method_list,
665 map { $_->name } $role_meta->get_required_method_list,
669 sub _find_delegate_metaclass {
671 if (my $class = $self->_isa_metadata) {
672 # we might be dealing with a non-Moose class,
673 # and need to make our own metaclass. if there's
674 # already a metaclass, it will be returned
675 return Class::MOP::Class->initialize($class);
677 elsif (my $role = $self->_does_metadata) {
678 return Class::MOP::class_of($role);
681 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
685 sub _get_delegate_method_list {
687 my $meta = $self->_find_delegate_metaclass;
688 if ($meta->isa('Class::MOP::Class')) {
689 return map { $_->name } # NOTE: !never! delegate &meta
690 grep { $_->package_name ne 'Moose::Object' && $_->name ne 'meta' }
691 $meta->get_all_methods;
693 elsif ($meta->isa('Moose::Meta::Role')) {
694 return $meta->get_method_list;
697 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
701 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
703 sub _make_delegation_method {
704 my ( $self, $handle_name, $method_to_call ) = @_;
706 my @curried_arguments;
708 ($method_to_call, @curried_arguments) = @$method_to_call
709 if 'ARRAY' eq ref($method_to_call);
711 return $self->delegation_metaclass->new(
712 name => $handle_name,
713 package_name => $self->associated_class->name,
715 delegate_to_method => $method_to_call,
716 curried_arguments => \@curried_arguments,
720 sub _coerce_and_verify {
723 my $instance = shift;
725 return $val unless $self->has_type_constraint;
727 $val = $self->type_constraint->coerce($val)
728 if $self->should_coerce;
730 $self->verify_against_type_constraint($val, instance => $instance);
735 sub verify_against_type_constraint {
739 return 1 if !$self->has_type_constraint;
741 my $type_constraint = $self->type_constraint;
743 $type_constraint->check($val)
744 || $self->throw_error("Attribute ("
746 . ") does not pass the type constraint because: "
747 . $type_constraint->get_message($val), data => $val, @_);
750 package Moose::Meta::Attribute::Custom::Moose;
751 sub register_implementation { 'Moose::Meta::Attribute' }
761 Moose::Meta::Attribute - The Moose attribute metaclass
765 This class is a subclass of L<Class::MOP::Attribute> that provides
766 additional Moose-specific functionality.
768 To really understand this class, you will need to start with the
769 L<Class::MOP::Attribute> documentation. This class can be understood
770 as a set of additional features on top of the basic feature provided
771 by that parent class.
775 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
779 Many of the documented below override methods in
780 L<Class::MOP::Attribute> and add Moose specific features.
786 =item B<< Moose::Meta::Attribute->new(%options) >>
788 This method overrides the L<Class::MOP::Attribute> constructor.
790 Many of the options below are described in more detail in the
791 L<Moose::Manual::Attributes> document.
793 It adds the following options to the constructor:
797 =item * is => 'ro', 'rw', 'bare'
799 This provides a shorthand for specifying the C<reader>, C<writer>, or
800 C<accessor> names. If the attribute is read-only ('ro') then it will
801 have a C<reader> method with the same attribute as the name.
803 If it is read-write ('rw') then it will have an C<accessor> method
804 with the same name. If you provide an explicit C<writer> for a
805 read-write attribute, then you will have a C<reader> with the same
806 name as the attribute, and a C<writer> with the name you provided.
808 Use 'bare' when you are deliberately not installing any methods
809 (accessor, reader, etc.) associated with this attribute; otherwise,
810 Moose will issue a deprecation warning when this attribute is added to a
815 This option accepts a type. The type can be a string, which should be
816 a type name. If the type name is unknown, it is assumed to be a class
819 This option can also accept a L<Moose::Meta::TypeConstraint> object.
821 If you I<also> provide a C<does> option, then your C<isa> option must
822 be a class name, and that class must do the role specified with
825 =item * does => $role
827 This is short-hand for saying that the attribute's type must be an
828 object which does the named role.
830 =item * coerce => $bool
832 This option is only valid for objects with a type constraint
833 (C<isa>). If this is true, then coercions will be applied whenever
834 this attribute is set.
836 You can make both this and the C<weak_ref> option true.
838 =item * trigger => $sub
840 This option accepts a subroutine reference, which will be called after
841 the attribute is set.
843 =item * required => $bool
845 An attribute which is required must be provided to the constructor. An
846 attribute which is required can also have a C<default> or C<builder>,
847 which will satisfy its required-ness.
849 A required attribute must have a C<default>, C<builder> or a
850 non-C<undef> C<init_arg>
852 =item * lazy => $bool
854 A lazy attribute must have a C<default> or C<builder>. When an
855 attribute is lazy, the default value will not be calculated until the
858 =item * weak_ref => $bool
860 If this is true, the attribute's value will be stored as a weak
863 =item * auto_deref => $bool
865 If this is true, then the reader will dereference the value when it is
866 called. The attribute must have a type constraint which defines the
867 attribute as an array or hash reference.
869 =item * lazy_build => $bool
871 Setting this to true makes the attribute lazy and provides a number of
879 is equivalent to this:
884 builder => '_build_size',
885 clearer => 'clear_size',
886 predicate => 'has_size',
889 =item * documentation
891 An arbitrary string that can be retrieved later by calling C<<
892 $attr->documentation >>.
896 =item B<< $attr->clone(%options) >>
898 This creates a new attribute based on attribute being cloned. You must
899 supply a C<name> option to provide a new name for the attribute.
901 The C<%options> can only specify options handled by
902 L<Class::MOP::Attribute>.
906 =head2 Value management
910 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
912 This method is used internally to initialize the attribute's slot in
913 the object C<$instance>.
915 This overrides the L<Class::MOP::Attribute> method to handle lazy
916 attributes, weak references, and type constraints.
922 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
927 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
929 Before setting the value, a check is made on the type constraint of
930 the attribute, if it has one, to see if the value passes it. If the
931 value fails to pass, the set operation dies with a L</throw_error>.
933 Any coercion to convert values is done before checking the type constraint.
935 To check a value against a type constraint before setting it, fetch the
936 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
937 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
938 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
943 =head2 Attribute Accessor generation
947 =item B<< $attr->install_accessors >>
949 This method overrides the parent to also install delegation methods.
951 If, after installing all methods, the attribute object has no associated
952 methods, it throws an error unless C<< is => 'bare' >> was passed to the
953 attribute constructor. (Trying to add an attribute that has no associated
954 methods is almost always an error.)
956 =item B<< $attr->remove_accessors >>
958 This method overrides the parent to also remove delegation methods.
960 =item B<< $attr->install_delegation >>
962 This method adds its delegation methods to the attribute's associated
963 class, if it has any to add.
965 =item B<< $attr->remove_delegation >>
967 This method remove its delegation methods from the attribute's
970 =item B<< $attr->accessor_metaclass >>
972 Returns the accessor metaclass name, which defaults to
973 L<Moose::Meta::Method::Accessor>.
975 =item B<< $attr->delegation_metaclass >>
977 Returns the delegation metaclass name, which defaults to
978 L<Moose::Meta::Method::Delegation>.
982 =head2 Additional Moose features
984 These methods are not found in the superclass. They support features
989 =item B<< $attr->does($role) >>
991 This indicates whether the I<attribute itself> does the given
992 role. The role can be given as a full class name, or as a resolvable
995 Note that this checks the attribute itself, not its type constraint,
996 so it is checking the attribute's metaclass and any traits applied to
999 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
1001 This is an alternate constructor that handles the C<metaclass> and
1004 Effectively, this method is a factory that finds or creates the
1005 appropriate class for the given C<metaclass> and/or C<traits>.
1007 Once it has the appropriate class, it will call C<< $class->new($name,
1008 %options) >> on that class.
1010 =item B<< $attr->clone_and_inherit_options(%options) >>
1012 This method supports the C<has '+foo'> feature. It does various bits
1013 of processing on the supplied C<%options> before ultimately calling
1014 the C<clone> method.
1016 One of its main tasks is to make sure that the C<%options> provided
1017 does not include the options returned by the
1018 C<illegal_options_for_inheritance> method.
1020 =item B<< $attr->illegal_options_for_inheritance >>
1022 This returns a blacklist of options that can not be overridden in a
1023 subclass's attribute definition.
1025 This exists to allow a custom metaclass to change or add to the list
1026 of options which can not be changed.
1028 =item B<< $attr->type_constraint >>
1030 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1033 =item B<< $attr->has_type_constraint >>
1035 Returns true if this attribute has a type constraint.
1037 =item B<< $attr->verify_against_type_constraint($value) >>
1039 Given a value, this method returns true if the value is valid for the
1040 attribute's type constraint. If the value is not valid, it throws an
1043 =item B<< $attr->handles >>
1045 This returns the value of the C<handles> option passed to the
1048 =item B<< $attr->has_handles >>
1050 Returns true if this attribute performs delegation.
1052 =item B<< $attr->is_weak_ref >>
1054 Returns true if this attribute stores its value as a weak reference.
1056 =item B<< $attr->is_required >>
1058 Returns true if this attribute is required to have a value.
1060 =item B<< $attr->is_lazy >>
1062 Returns true if this attribute is lazy.
1064 =item B<< $attr->is_lazy_build >>
1066 Returns true if the C<lazy_build> option was true when passed to the
1069 =item B<< $attr->should_coerce >>
1071 Returns true if the C<coerce> option passed to the constructor was
1074 =item B<< $attr->should_auto_deref >>
1076 Returns true if the C<auto_deref> option passed to the constructor was
1079 =item B<< $attr->trigger >>
1081 This is the subroutine reference that was in the C<trigger> option
1082 passed to the constructor, if any.
1084 =item B<< $attr->has_trigger >>
1086 Returns true if this attribute has a trigger set.
1088 =item B<< $attr->documentation >>
1090 Returns the value that was in the C<documentation> option passed to
1091 the constructor, if any.
1093 =item B<< $attr->has_documentation >>
1095 Returns true if this attribute has any documentation.
1097 =item B<< $attr->applied_traits >>
1099 This returns an array reference of all the traits which were applied
1100 to this attribute. If none were applied, this returns C<undef>.
1102 =item B<< $attr->has_applied_traits >>
1104 Returns true if this attribute has any traits applied.
1110 See L<Moose/BUGS> for details on reporting bugs.
1114 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1116 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1118 =head1 COPYRIGHT AND LICENSE
1120 Copyright 2006-2010 by Infinity Interactive, Inc.
1122 L<http://www.iinteractive.com>
1124 This library is free software; you can redistribute it and/or modify
1125 it under the same terms as Perl itself.