2 package Moose::Meta::Attribute;
7 use Scalar::Util 'blessed', 'weaken';
10 our $VERSION = '0.63';
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 grep { not $class->does($_) }
113 map { Moose::Util::resolve_metatrait_alias(Attribute => $_) || $_ }
117 my $anon_class = Moose::Meta::Class->create_anon_class(
118 superclasses => [ $class ],
119 roles => [ @traits ],
123 $class = $anon_class->name;
127 return ( wantarray ? ( $class, @traits ) : $class );
132 my @legal_options_for_inheritance = qw(
133 default coerce required
134 documentation lazy handles
135 builder type_constraint
138 sub legal_options_for_inheritance { @legal_options_for_inheritance }
141 # This method *must* be able to handle
142 # Class::MOP::Attribute instances as
143 # well. Yes, I know that is wrong, but
144 # apparently we didn't realize it was
145 # doing that and now we have some code
146 # which is dependent on it. The real
147 # solution of course is to push this
148 # feature back up into Class::MOP::Attribute
149 # but I not right now, I am too lazy.
150 # However if you are reading this and
151 # looking for something to do,.. please
154 sub clone_and_inherit_options {
155 my ($self, %options) = @_;
162 # we may want to extends a Class::MOP::Attribute
163 # in which case we need to be able to use the
164 # core set of legal options that have always
165 # been here. But we allows Moose::Meta::Attribute
166 # instances to changes them.
168 my @legal_options = $self->can('legal_options_for_inheritance')
169 ? $self->legal_options_for_inheritance
170 : @legal_options_for_inheritance;
172 foreach my $legal_option (@legal_options) {
173 if (exists $options{$legal_option}) {
174 $actual_options{$legal_option} = $options{$legal_option};
175 delete $options{$legal_option};
181 if (blessed($options{isa}) && $options{isa}->isa('Moose::Meta::TypeConstraint')) {
182 $type_constraint = $options{isa};
185 $type_constraint = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options{isa});
186 (defined $type_constraint)
187 || $self->throw_error("Could not find the type constraint '" . $options{isa} . "'", data => $options{isa});
190 $actual_options{type_constraint} = $type_constraint;
191 delete $options{isa};
194 if ($options{does}) {
196 if (blessed($options{does}) && $options{does}->isa('Moose::Meta::TypeConstraint')) {
197 $type_constraint = $options{does};
200 $type_constraint = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options{does});
201 (defined $type_constraint)
202 || $self->throw_error("Could not find the type constraint '" . $options{does} . "'", data => $options{does});
205 $actual_options{type_constraint} = $type_constraint;
206 delete $options{does};
210 # this doesn't apply to Class::MOP::Attributes,
211 # so we can ignore it for them.
213 if ($self->can('interpolate_class')) {
214 ( $actual_options{metaclass}, my @traits ) = $self->interpolate_class(%options);
217 my @all_traits = grep { $seen{$_}++ } @{ $self->applied_traits || [] }, @traits;
218 $actual_options{traits} = \@all_traits if @all_traits;
220 delete @options{qw(metaclass traits)};
223 (scalar keys %options == 0)
224 || $self->throw_error("Illegal inherited options => (" . (join ', ' => keys %options) . ")", data => \%options);
227 $self->clone(%actual_options);
231 my ( $self, %params ) = @_;
233 my $class = $params{metaclass} || ref $self;
235 if ( 0 and $class eq ref $self ) {
236 return $self->SUPER::clone(%params);
238 my ( @init, @non_init );
240 foreach my $attr ( grep { $_->has_value($self) } $self->meta->compute_all_applicable_attributes ) {
241 push @{ $attr->has_init_arg ? \@init : \@non_init }, $attr;
244 my %new_params = ( ( map { $_->init_arg => $_->get_value($self) } @init ), %params );
246 my $name = delete $new_params{name};
248 my $clone = $class->new($name, %new_params, __hack_no_process_options => 1 );
250 foreach my $attr ( @non_init ) {
251 $attr->set_value($clone, $attr->get_value($self));
259 sub _process_options {
260 my ($class, $name, $options) = @_;
262 if (exists $options->{is}) {
264 ### -------------------------
265 ## is => ro, writer => _foo # turns into (reader => foo, writer => _foo) as before
266 ## is => rw, writer => _foo # turns into (reader => foo, writer => _foo)
267 ## is => rw, accessor => _foo # turns into (accessor => _foo)
268 ## is => ro, accessor => _foo # error, accesor is rw
269 ### -------------------------
271 if ($options->{is} eq 'ro') {
272 $class->throw_error("Cannot define an accessor name on a read-only attribute, accessors are read/write", data => $options)
273 if exists $options->{accessor};
274 $options->{reader} ||= $name;
276 elsif ($options->{is} eq 'rw') {
277 if ($options->{writer}) {
278 $options->{reader} ||= $name;
281 $options->{accessor} ||= $name;
285 $class->throw_error("I do not understand this option (is => " . $options->{is} . ") on attribute ($name)", data => $options->{is});
289 if (exists $options->{isa}) {
290 if (exists $options->{does}) {
291 if (eval { $options->{isa}->can('does') }) {
292 ($options->{isa}->does($options->{does}))
293 || $class->throw_error("Cannot have an isa option and a does option if the isa does not do the does on attribute ($name)", data => $options);
296 $class->throw_error("Cannot have an isa option which cannot ->does() on attribute ($name)", data => $options);
300 # allow for anon-subtypes here ...
301 if (blessed($options->{isa}) && $options->{isa}->isa('Moose::Meta::TypeConstraint')) {
302 $options->{type_constraint} = $options->{isa};
305 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options->{isa});
308 elsif (exists $options->{does}) {
309 # allow for anon-subtypes here ...
310 if (blessed($options->{does}) && $options->{does}->isa('Moose::Meta::TypeConstraint')) {
311 $options->{type_constraint} = $options->{does};
314 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options->{does});
318 if (exists $options->{coerce} && $options->{coerce}) {
319 (exists $options->{type_constraint})
320 || $class->throw_error("You cannot have coercion without specifying a type constraint on attribute ($name)", data => $options);
321 $class->throw_error("You cannot have a weak reference to a coerced value on attribute ($name)", data => $options)
322 if $options->{weak_ref};
325 if (exists $options->{trigger}) {
326 ('CODE' eq ref $options->{trigger})
327 || $class->throw_error("Trigger must be a CODE ref on attribute ($name)", data => $options->{trigger});
330 if (exists $options->{auto_deref} && $options->{auto_deref}) {
331 (exists $options->{type_constraint})
332 || $class->throw_error("You cannot auto-dereference without specifying a type constraint on attribute ($name)", data => $options);
333 ($options->{type_constraint}->is_a_type_of('ArrayRef') ||
334 $options->{type_constraint}->is_a_type_of('HashRef'))
335 || $class->throw_error("You cannot auto-dereference anything other than a ArrayRef or HashRef on attribute ($name)", data => $options);
338 if (exists $options->{lazy_build} && $options->{lazy_build} == 1) {
339 $class->throw_error("You can not use lazy_build and default for the same attribute ($name)", data => $options)
340 if exists $options->{default};
341 $options->{lazy} = 1;
342 $options->{required} = 1;
343 $options->{builder} ||= "_build_${name}";
345 $options->{clearer} ||= "_clear${name}";
346 $options->{predicate} ||= "_has${name}";
349 $options->{clearer} ||= "clear_${name}";
350 $options->{predicate} ||= "has_${name}";
354 if (exists $options->{lazy} && $options->{lazy}) {
355 (exists $options->{default} || defined $options->{builder} )
356 || $class->throw_error("You cannot have lazy attribute ($name) without specifying a default value for it", data => $options);
359 if ( $options->{required} && !( ( !exists $options->{init_arg} || defined $options->{init_arg} ) || exists $options->{default} || defined $options->{builder} ) ) {
360 $class->throw_error("You cannot have a required attribute ($name) without a default, builder, or an init_arg", data => $options);
365 sub initialize_instance_slot {
366 my ($self, $meta_instance, $instance, $params) = @_;
367 my $init_arg = $self->init_arg();
368 # try to fetch the init arg from the %params ...
372 if ( defined($init_arg) and exists $params->{$init_arg}) {
373 $val = $params->{$init_arg};
377 # skip it if it's lazy
378 return if $self->is_lazy;
379 # and die if it's required and doesn't have a default value
380 $self->throw_error("Attribute (" . $self->name . ") is required", object => $instance, data => $params)
381 if $self->is_required && !$self->has_default && !$self->has_builder;
383 # if nothing was in the %params, we can use the
384 # attribute's default value (if it has one)
385 if ($self->has_default) {
386 $val = $self->default($instance);
389 elsif ($self->has_builder) {
390 $val = $self->_call_builder($instance);
395 return unless $value_is_set;
397 if ($self->has_type_constraint) {
398 my $type_constraint = $self->type_constraint;
399 if ($self->should_coerce && $type_constraint->has_coercion) {
400 $val = $type_constraint->coerce($val);
402 $type_constraint->check($val)
403 || $self->throw_error("Attribute ("
405 . ") does not pass the type constraint because: "
406 . $type_constraint->get_message($val), data => $val, object => $instance);
409 $self->set_initial_value($instance, $val);
410 $meta_instance->weaken_slot_value($instance, $self->name)
411 if ref $val && $self->is_weak_ref;
415 my ( $self, $instance ) = @_;
417 my $builder = $self->builder();
419 return $instance->$builder()
420 if $instance->can( $self->builder );
422 $self->throw_error( blessed($instance)
423 . " does not support builder method '"
425 . "' for attribute '"
435 # this duplicates too much code from
436 # Class::MOP::Attribute, we need to
437 # refactor these bits eventually.
439 sub _set_initial_slot_value {
440 my ($self, $meta_instance, $instance, $value) = @_;
442 my $slot_name = $self->name;
444 return $meta_instance->set_slot_value($instance, $slot_name, $value)
445 unless $self->has_initializer;
447 my ($type_constraint, $can_coerce);
448 if ($self->has_type_constraint) {
449 $type_constraint = $self->type_constraint;
450 $can_coerce = ($self->should_coerce && $type_constraint->has_coercion);
455 if ($type_constraint) {
456 $val = $type_constraint->coerce($val)
458 $type_constraint->check($val)
459 || $self->throw_error("Attribute ("
461 . ") does not pass the type constraint because: "
462 . $type_constraint->get_message($val), data => $val, object => $instance);
464 $meta_instance->set_slot_value($instance, $slot_name, $val);
467 my $initializer = $self->initializer;
469 # most things will just want to set a value, so make it first arg
470 $instance->$initializer($value, $callback, $self);
474 my ($self, $instance, @args) = @_;
475 my $value = $args[0];
477 my $attr_name = $self->name;
479 if ($self->is_required and not @args) {
480 $self->throw_error("Attribute ($attr_name) is required", object => $instance);
483 if ($self->has_type_constraint) {
485 my $type_constraint = $self->type_constraint;
487 if ($self->should_coerce) {
488 $value = $type_constraint->coerce($value);
490 $type_constraint->_compiled_type_constraint->($value)
491 || $self->throw_error("Attribute ("
493 . ") does not pass the type constraint because "
494 . $type_constraint->get_message($value), object => $instance, data => $value);
497 my $meta_instance = Class::MOP::Class->initialize(blessed($instance))
500 $meta_instance->set_slot_value($instance, $attr_name, $value);
502 if (ref $value && $self->is_weak_ref) {
503 $meta_instance->weaken_slot_value($instance, $attr_name);
506 if ($self->has_trigger) {
507 $self->trigger->($instance, $value, $self);
512 my ($self, $instance) = @_;
514 if ($self->is_lazy) {
515 unless ($self->has_value($instance)) {
517 if ($self->has_default) {
518 $value = $self->default($instance);
519 } elsif ( $self->has_builder ) {
520 $value = $self->_call_builder($instance);
522 if ($self->has_type_constraint) {
523 my $type_constraint = $self->type_constraint;
524 $value = $type_constraint->coerce($value)
525 if ($self->should_coerce);
526 $type_constraint->check($value)
527 || $self->throw_error("Attribute (" . $self->name
528 . ") does not pass the type constraint because: "
529 . $type_constraint->get_message($value), type_constraint => $type_constraint, data => $value);
531 $self->set_initial_value($instance, $value);
535 if ($self->should_auto_deref) {
537 my $type_constraint = $self->type_constraint;
539 if ($type_constraint->is_a_type_of('ArrayRef')) {
540 my $rv = $self->SUPER::get_value($instance);
541 return unless defined $rv;
542 return wantarray ? @{ $rv } : $rv;
544 elsif ($type_constraint->is_a_type_of('HashRef')) {
545 my $rv = $self->SUPER::get_value($instance);
546 return unless defined $rv;
547 return wantarray ? %{ $rv } : $rv;
550 $self->throw_error("Can not auto de-reference the type constraint '" . $type_constraint->name . "'", object => $instance, type_constraint => $type_constraint);
556 return $self->SUPER::get_value($instance);
560 ## installing accessors
562 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
564 sub install_accessors {
566 $self->SUPER::install_accessors(@_);
567 $self->install_delegation if $self->has_handles;
571 sub remove_accessors {
573 $self->SUPER::remove_accessors(@_);
574 $self->remove_delegation if $self->has_handles;
578 sub install_delegation {
582 # Here we canonicalize the 'handles' option
583 # this will sort out any details and always
584 # return an hash of methods which we want
585 # to delagate to, see that method for details
586 my %handles = $self->_canonicalize_handles;
589 # install the delegation ...
590 my $associated_class = $self->associated_class;
591 foreach my $handle (keys %handles) {
592 my $method_to_call = $handles{$handle};
593 my $class_name = $associated_class->name;
594 my $name = "${class_name}::${handle}";
596 (!$associated_class->has_method($handle))
597 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
600 # handles is not allowed to delegate
601 # any of these methods, as they will
602 # override the ones in your class, which
603 # is almost certainly not what you want.
605 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
606 #cluck("Not delegating method '$handle' because it is a core method") and
607 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
609 my $method = $self->_make_delegation_method($handle, $method_to_call);
611 $self->associated_class->add_method($method->name, $method);
615 sub remove_delegation {
617 my %handles = $self->_canonicalize_handles;
618 my $associated_class = $self->associated_class;
619 foreach my $handle (keys %handles) {
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 RegExpr 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);
646 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
650 Class::MOP::load_class($handles)
651 unless Class::MOP::is_class_loaded($handles);
653 my $role_meta = eval { $handles->meta };
655 $self->throw_error("Unable to canonicalize the 'handles' option with $handles because : $@", data => $handles, error => $@);
658 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
659 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because ->meta is not a Moose::Meta::Role", data => $handles);
661 return map { $_ => $_ } (
662 $role_meta->get_method_list,
663 $role_meta->get_required_method_list
668 sub _find_delegate_metaclass {
670 if (my $class = $self->_isa_metadata) {
671 # if the class does have
672 # a meta method, use it
673 return $class->meta if $class->can('meta');
674 # otherwise we might be
675 # dealing with a non-Moose
676 # class, and need to make
678 return Moose::Meta::Class->initialize($class);
680 elsif (my $role = $self->_does_metadata) {
681 # our role will always have
686 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
690 sub _get_delegate_method_list {
692 my $meta = $self->_find_delegate_metaclass;
693 if ($meta->isa('Class::MOP::Class')) {
694 return map { $_->name } # NOTE: !never! delegate &meta
695 grep { $_->package_name ne 'Moose::Object' && $_->name ne 'meta' }
696 $meta->get_all_methods;
698 elsif ($meta->isa('Moose::Meta::Role')) {
699 return $meta->get_method_list;
702 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
706 sub _make_delegation_method {
707 my ( $self, $handle_name, $method_to_call ) = @_;
711 $method_body = $method_to_call
712 if 'CODE' eq ref($method_to_call);
714 return Moose::Meta::Method::Delegation->new(
715 name => $handle_name,
716 package_name => $self->associated_class->name,
718 delegate_to_method => $method_to_call,
722 package Moose::Meta::Attribute::Custom::Moose;
723 sub register_implementation { 'Moose::Meta::Attribute' }
733 Moose::Meta::Attribute - The Moose attribute metaclass
737 This is a subclass of L<Class::MOP::Attribute> with Moose specific
740 For the most part, the only time you will ever encounter an
741 instance of this class is if you are doing some serious deep
742 introspection. To really understand this class, you need to refer
743 to the L<Class::MOP::Attribute> documentation.
747 =head2 Overridden methods
749 These methods override methods in L<Class::MOP::Attribute> and add
750 Moose specific features. You can safely assume though that they
751 will behave just as L<Class::MOP::Attribute> does.
761 =item B<initialize_instance_slot>
763 =item B<install_accessors>
765 =item B<remove_accessors>
767 =item B<install_delegation>
769 =item B<remove_delegation>
771 =item B<accessor_metaclass>
777 eval { $point->meta->get_attribute('x')->set_value($point, 'fourty-two') };
782 I<Attribute (x) does not pass the type constraint (Int) with 'fourty-two'>
784 Before setting the value, a check is made on the type constraint of
785 the attribute, if it has one, to see if the value passes it. If the
786 value fails to pass, the set operation dies with a L<throw_error>.
788 Any coercion to convert values is done before checking the type constraint.
790 To check a value against a type constraint before setting it, fetch the
791 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
792 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
793 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
798 =head2 Additional Moose features
800 Moose attributes support type-constraint checking, weak reference
801 creation and type coercion.
807 Delegates to C<associated_class> or C<Moose::Meta::Class> if there is none.
809 =item B<interpolate_class_and_new>
811 =item B<interpolate_class>
813 When called as a class method causes interpretation of the C<metaclass> and
816 =item B<clone_and_inherit_options>
818 This is to support the C<has '+foo'> feature, it clones an attribute
819 from a superclass and allows a very specific set of changes to be made
822 =item B<legal_options_for_inheritance>
824 Whitelist with options you can change. You can overload it in your custom
825 metaclass to allow your options be inheritable.
827 =item B<has_type_constraint>
829 Returns true if this meta-attribute has a type constraint.
831 =item B<type_constraint>
833 A read-only accessor for this meta-attribute's type constraint. For
834 more information on what you can do with this, see the documentation
835 for L<Moose::Meta::TypeConstraint>.
839 Returns true if this meta-attribute performs delegation.
843 This returns the value which was passed into the handles option.
847 Returns true if this meta-attribute produces a weak reference.
851 Returns true if this meta-attribute is required to have a value.
855 Returns true if this meta-attribute should be initialized lazily.
857 NOTE: lazy attributes, B<must> have a C<default> or C<builder> field set.
859 =item B<is_lazy_build>
861 Returns true if this meta-attribute should be initialized lazily through
862 the builder generated by lazy_build. Using C<lazy_build =E<gt> 1> will
863 make your attribute required and lazy. In addition it will set the builder, clearer
864 and predicate options for you using the following convention.
866 #If your attribute name starts with an underscore:
867 has '_foo' => (lazy_build => 1);
869 has '_foo' => (lazy => 1, required => 1, predicate => '_has_foo', clearer => '_clear_foo', builder => '_build__foo');
871 has '_foo' => (lazy => 1, required => 1, predicate => '_has_foo', clearer => '_clear_foo', default => sub{shift->_build__foo});
873 #If your attribute name does not start with an underscore:
874 has 'foo' => (lazy_build => 1);
876 has 'foo' => (lazy => 1, required => 1, predicate => 'has_foo', clearer => 'clear_foo', builder => '_build_foo');
878 has 'foo' => (lazy => 1, required => 1, predicate => 'has_foo', clearer => 'clear_foo', default => sub{shift->_build_foo});
880 The reason for the different naming of the C<builder> is that the C<builder>
881 method is a private method while the C<clearer> and C<predicate> methods
884 NOTE: This means your class should provide a method whose name matches the value
885 of the builder part, in this case _build__foo or _build_foo.
887 =item B<should_coerce>
889 Returns true if this meta-attribute should perform type coercion.
891 =item B<should_auto_deref>
893 Returns true if this meta-attribute should perform automatic
896 NOTE: This can only be done for attributes whose type constraint is
897 either I<ArrayRef> or I<HashRef>.
901 Returns true if this meta-attribute has a trigger set.
905 This is a CODE reference which will be executed every time the
906 value of an attribute is assigned. The CODE ref will get two values,
907 the invocant and the new value. This can be used to handle I<basic>
908 bi-directional relations.
910 =item B<documentation>
912 This is a string which contains the documentation for this attribute.
913 It serves no direct purpose right now, but it might in the future
914 in some kind of automated documentation system perhaps.
916 =item B<has_documentation>
918 Returns true if this meta-attribute has any documentation.
920 =item B<applied_traits>
922 This will return the ARRAY ref of all the traits applied to this
923 attribute, or if no traits have been applied, it returns C<undef>.
925 =item B<has_applied_traits>
927 Returns true if this meta-attribute has any traits applied.
933 All complex software has bugs lurking in it, and this module is no
934 exception. If you find a bug please either email me, or add the bug
939 Stevan Little E<lt>stevan@iinteractive.comE<gt>
941 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
943 =head1 COPYRIGHT AND LICENSE
945 Copyright 2006-2008 by Infinity Interactive, Inc.
947 L<http://www.iinteractive.com>
949 This library is free software; you can redistribute it and/or modify
950 it under the same terms as Perl itself.