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 attach_to_class {
543 || $self->has_handles
545 || @{ $self->associated_methods }
546 || ($self->_is_metadata || '') eq 'bare'
549 'Attribute (' . $self->name . ') has no associated methods'
550 . ' (did you mean to provide an "is" argument?)'
553 return $self->SUPER::attach_to_class(@_);
556 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
558 sub install_accessors {
560 $self->SUPER::install_accessors(@_);
561 $self->install_delegation if $self->has_handles;
565 sub remove_accessors {
567 $self->SUPER::remove_accessors(@_);
568 $self->remove_delegation if $self->has_handles;
572 sub install_delegation {
576 # Here we canonicalize the 'handles' option
577 # this will sort out any details and always
578 # return an hash of methods which we want
579 # to delagate to, see that method for details
580 my %handles = $self->_canonicalize_handles;
583 # install the delegation ...
584 my $associated_class = $self->associated_class;
585 foreach my $handle (keys %handles) {
586 my $method_to_call = $handles{$handle};
587 my $class_name = $associated_class->name;
588 my $name = "${class_name}::${handle}";
590 (!$associated_class->has_method($handle))
591 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
594 # handles is not allowed to delegate
595 # any of these methods, as they will
596 # override the ones in your class, which
597 # is almost certainly not what you want.
599 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
600 #cluck("Not delegating method '$handle' because it is a core method") and
601 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
603 my $method = $self->_make_delegation_method($handle, $method_to_call);
605 $self->associated_class->add_method($method->name, $method);
609 sub remove_delegation {
611 my %handles = $self->_canonicalize_handles;
612 my $associated_class = $self->associated_class;
613 foreach my $handle (keys %handles) {
614 $self->associated_class->remove_method($handle);
618 # private methods to help delegation ...
620 sub _canonicalize_handles {
622 my $handles = $self->handles;
623 if (my $handle_type = ref($handles)) {
624 if ($handle_type eq 'HASH') {
627 elsif ($handle_type eq 'ARRAY') {
628 return map { $_ => $_ } @{$handles};
630 elsif ($handle_type eq 'Regexp') {
631 ($self->has_type_constraint)
632 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
633 return map { ($_ => $_) }
634 grep { /$handles/ } $self->_get_delegate_method_list;
636 elsif ($handle_type eq 'CODE') {
637 return $handles->($self, $self->_find_delegate_metaclass);
640 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
644 Class::MOP::load_class($handles);
645 my $role_meta = Class::MOP::class_of($handles);
647 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
648 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because its metaclass is not a Moose::Meta::Role", data => $handles);
650 return map { $_ => $_ } (
651 $role_meta->get_method_list,
652 map { $_->name } $role_meta->get_required_method_list,
657 sub _find_delegate_metaclass {
659 if (my $class = $self->_isa_metadata) {
660 # we might be dealing with a non-Moose class,
661 # and need to make our own metaclass. if there's
662 # already a metaclass, it will be returned
663 return Moose::Meta::Class->initialize($class);
665 elsif (my $role = $self->_does_metadata) {
666 return Class::MOP::class_of($role);
669 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
673 sub _get_delegate_method_list {
675 my $meta = $self->_find_delegate_metaclass;
676 if ($meta->isa('Class::MOP::Class')) {
677 return map { $_->name } # NOTE: !never! delegate &meta
678 grep { $_->package_name ne 'Moose::Object' && $_->name ne 'meta' }
679 $meta->get_all_methods;
681 elsif ($meta->isa('Moose::Meta::Role')) {
682 return $meta->get_method_list;
685 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
689 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
691 sub _make_delegation_method {
692 my ( $self, $handle_name, $method_to_call ) = @_;
696 $method_body = $method_to_call
697 if 'CODE' eq ref($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,
707 sub _coerce_and_verify {
710 my $instance = shift;
712 return $val unless $self->has_type_constraint;
714 my $type_constraint = $self->type_constraint;
715 if ($self->should_coerce && $type_constraint->has_coercion) {
716 $val = $type_constraint->coerce($val);
719 $self->verify_against_type_constraint($val, instance => $instance);
724 sub verify_against_type_constraint {
728 return 1 if !$self->has_type_constraint;
730 my $type_constraint = $self->type_constraint;
732 $type_constraint->check($val)
733 || $self->throw_error("Attribute ("
735 . ") does not pass the type constraint because: "
736 . $type_constraint->get_message($val), data => $val, @_);
739 package Moose::Meta::Attribute::Custom::Moose;
740 sub register_implementation { 'Moose::Meta::Attribute' }
750 Moose::Meta::Attribute - The Moose attribute metaclass
754 This class is a subclass of L<Class::MOP::Attribute> that provides
755 additional Moose-specific functionality.
757 To really understand this class, you will need to start with the
758 L<Class::MOP::Attribute> documentation. This class can be understood
759 as a set of additional features on top of the basic feature provided
760 by that parent class.
764 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
768 Many of the documented below override methods in
769 L<Class::MOP::Attribute> and add Moose specific features.
775 =item B<< Moose::Meta::Attribute->new(%options) >>
777 This method overrides the L<Class::MOP::Attribute> constructor.
779 Many of the options below are described in more detail in the
780 L<Moose::Manual::Attributes> document.
782 It adds the following options to the constructor:
786 =item * is => 'ro' or 'rw'
788 This provides a shorthand for specifying the C<reader>, C<writer>, or
789 C<accessor> names. If the attribute is read-only ('ro') then it will
790 have a C<reader> method with the same attribute as the name.
792 If it is read-write ('rw') then it will have an C<accessor> method
793 with the same name. If you provide an explicit C<writer> for a
794 read-write attribute, then you will have a C<reader> with the same
795 name as the attribute, and a C<writer> with the name you provided.
799 This option accepts a type. The type can be a string, which should be
800 a type name. If the type name is unknown, it is assumed to be a class
803 This option can also accept a L<Moose::Meta::TypeConstraint> object.
805 If you I<also> provide a C<does> option, then your C<isa> option must
806 be a class name, and that class must do the role specified with
809 =item * does => $role
811 This is short-hand for saying that the attribute's type must be an
812 object which does the named role.
814 =item * coerce => $bool
816 This option is only valid for objects with a type constraint
817 (C<isa>). If this is true, then coercions will be applied whenever
818 this attribute is set.
820 You can make both this and the C<weak_ref> option true.
822 =item * trigger => $sub
824 This option accepts a subroutine reference, which will be called after
825 the attribute is set.
827 =item * required => $bool
829 An attribute which is required must be provided to the constructor. An
830 attribute which is required can also have a C<default> or C<builder>,
831 which will satisfy its required-ness.
833 A required attribute must have a C<default>, C<builder> or a
834 non-C<undef> C<init_arg>
836 =item * lazy => $bool
838 A lazy attribute must have a C<default> or C<builder>. When an
839 attribute is lazy, the default value will not be calculated until the
842 =item * weak_ref => $bool
844 If this is true, the attribute's value will be stored as a weak
847 =item * auto_deref => $bool
849 If this is true, then the reader will dereference the value when it is
850 called. The attribute must have a type constraint which defines the
851 attribute as an array or hash reference.
853 =item * lazy_build => $bool
855 Setting this to true makes the attribute lazy and provides a number of
863 is equivalent to this:
868 builder => '_build_size',
869 clearer => 'clear_size',
870 predicate => 'has_size',
873 =item * documentation
875 An arbitrary string that can be retrieved later by calling C<<
876 $attr->documentation >>.
880 =item B<< $attr->clone(%options) >>
882 This creates a new attribute based on attribute being cloned. You must
883 supply a C<name> option to provide a new name for the attribute.
885 The C<%options> can only specify options handled by
886 L<Class::MOP::Attribute>.
890 =head2 Value management
894 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
896 This method is used internally to initialize the attribute's slot in
897 the object C<$instance>.
899 This overrides the L<Class::MOP::Attribute> method to handle lazy
900 attributes, weak references, and type constraints.
906 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
911 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
913 Before setting the value, a check is made on the type constraint of
914 the attribute, if it has one, to see if the value passes it. If the
915 value fails to pass, the set operation dies with a L<throw_error>.
917 Any coercion to convert values is done before checking the type constraint.
919 To check a value against a type constraint before setting it, fetch the
920 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
921 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
922 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
927 =head2 Attribute Accessor generation
931 =item B<< $attr->install_accessors >>
933 This method overrides the parent to also install delegation methods.
935 =item B<< $attr->remove_accessors >>
937 This method overrides the parent to also remove delegation methods.
939 =item B<< $attr->install_delegation >>
941 This method adds its delegation methods to the attribute's associated
942 class, if it has any to add.
944 =item B<< $attr->remove_delegation >>
946 This method remove its delegation methods from the attribute's
949 =item B<< $attr->accessor_metaclass >>
951 Returns the accessor metaclass name, which defaults to
952 L<Moose::Meta::Method::Accessor>.
954 =item B<< $attr->delegation_metaclass >>
956 Returns the delegation metaclass name, which defaults to
957 L<Moose::Meta::Method::Delegation>.
961 =head2 Additional Moose features
963 These methods are not found in the superclass. They support features
968 =item B<< $attr->does($role) >>
970 This indicates whether the I<attribute itself> does the given
971 role. The role can be given as a full class name, or as a resolvable
974 Note that this checks the attribute itself, not its type constraint,
975 so it is checking the attribute's metaclass and any traits applied to
978 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
980 This is an alternate constructor that handles the C<metaclass> and
983 Effectively, this method is a factory that finds or creates the
984 appropriate class for the given C<metaclass> and/or C<traits>.
986 Once it has the appropriate class, it will call C<< $class->new($name,
987 %options) >> on that class.
989 =item B<< $attr->clone_and_inherit_options(%options) >>
991 This method supports the C<has '+foo'> feature. It does various bits
992 of processing on the supplied C<%options> before ultimately calling
995 One of its main tasks is to make sure that the C<%options> provided
996 only includes the options returned by the
997 C<legal_options_for_inheritance> method.
999 =item B<< $attr->legal_options_for_inheritance >>
1001 This returns a whitelist of options that can be overridden in a
1002 subclass's attribute definition.
1004 This exists to allow a custom metaclass to change or add to the list
1005 of options which can be changed.
1007 =item B<< $attr->type_constraint >>
1009 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1012 =item B<< $attr->has_type_constraint >>
1014 Returns true if this attribute has a type constraint.
1016 =item B<< $attr->verify_against_type_constraint($value) >>
1018 Given a value, this method returns true if the value is valid for the
1019 attribute's type constraint. If the value is not valid, it throws an
1022 =item B<< $attr->handles >>
1024 This returns the value of the C<handles> option passed to the
1027 =item B<< $attr->has_handles >>
1029 Returns true if this attribute performs delegation.
1031 =item B<< $attr->is_weak_ref >>
1033 Returns true if this attribute stores its value as a weak reference.
1035 =item B<< $attr->is_required >>
1037 Returns true if this attribute is required to have a value.
1039 =item B<< $attr->is_lazy >>
1041 Returns true if this attribute is lazy.
1043 =item B<< $attr->is_lazy_build >>
1045 Returns true if the C<lazy_build> option was true when passed to the
1048 =item B<< $attr->should_coerce >>
1050 Returns true if the C<coerce> option passed to the constructor was
1053 =item B<< $attr->should_auto_deref >>
1055 Returns true if the C<auto_deref> option passed to the constructor was
1058 =item B<< $attr->trigger >>
1060 This is the subroutine reference that was in the C<trigger> option
1061 passed to the constructor, if any.
1063 =item B<< $attr->has_trigger >>
1065 Returns true if this attribute has a trigger set.
1067 =item B<< $attr->documentation >>
1069 Returns the value that was in the C<documentation> option passed to
1070 the constructor, if any.
1072 =item B<< $attr->has_documentation >>
1074 Returns true if this attribute has any documentation.
1076 =item B<< $attr->applied_traits >>
1078 This returns an array reference of all the traits which were applied
1079 to this attribute. If none were applied, this returns C<undef>.
1081 =item B<< $attr->has_applied_traits >>
1083 Returns true if this attribute has any traits applied.
1089 All complex software has bugs lurking in it, and this module is no
1090 exception. If you find a bug please either email me, or add the bug
1095 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1097 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1099 =head1 COPYRIGHT AND LICENSE
1101 Copyright 2006-2009 by Infinity Interactive, Inc.
1103 L<http://www.iinteractive.com>
1105 This library is free software; you can redistribute it and/or modify
1106 it under the same terms as Perl itself.