2 package Moose::Meta::Attribute;
7 use Scalar::Util 'blessed', 'weaken';
10 our $VERSION = '0.64';
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 ) : $class );
144 my @legal_options_for_inheritance = qw(
145 default coerce required
146 documentation lazy handles
147 builder type_constraint
150 sub legal_options_for_inheritance { @legal_options_for_inheritance }
153 # This method *must* be able to handle
154 # Class::MOP::Attribute instances as
155 # well. Yes, I know that is wrong, but
156 # apparently we didn't realize it was
157 # doing that and now we have some code
158 # which is dependent on it. The real
159 # solution of course is to push this
160 # feature back up into Class::MOP::Attribute
161 # but I not right now, I am too lazy.
162 # However if you are reading this and
163 # looking for something to do,.. please
166 sub clone_and_inherit_options {
167 my ($self, %options) = @_;
174 # we may want to extends a Class::MOP::Attribute
175 # in which case we need to be able to use the
176 # core set of legal options that have always
177 # been here. But we allows Moose::Meta::Attribute
178 # instances to changes them.
180 my @legal_options = $self->can('legal_options_for_inheritance')
181 ? $self->legal_options_for_inheritance
182 : @legal_options_for_inheritance;
184 foreach my $legal_option (@legal_options) {
185 if (exists $options{$legal_option}) {
186 $actual_options{$legal_option} = $options{$legal_option};
187 delete $options{$legal_option};
193 if (blessed($options{isa}) && $options{isa}->isa('Moose::Meta::TypeConstraint')) {
194 $type_constraint = $options{isa};
197 $type_constraint = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options{isa});
198 (defined $type_constraint)
199 || $self->throw_error("Could not find the type constraint '" . $options{isa} . "'", data => $options{isa});
202 $actual_options{type_constraint} = $type_constraint;
203 delete $options{isa};
206 if ($options{does}) {
208 if (blessed($options{does}) && $options{does}->isa('Moose::Meta::TypeConstraint')) {
209 $type_constraint = $options{does};
212 $type_constraint = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options{does});
213 (defined $type_constraint)
214 || $self->throw_error("Could not find the type constraint '" . $options{does} . "'", data => $options{does});
217 $actual_options{type_constraint} = $type_constraint;
218 delete $options{does};
222 # this doesn't apply to Class::MOP::Attributes,
223 # so we can ignore it for them.
225 if ($self->can('interpolate_class')) {
226 ( $actual_options{metaclass}, my @traits ) = $self->interpolate_class(%options);
229 my @all_traits = grep { $seen{$_}++ } @{ $self->applied_traits || [] }, @traits;
230 $actual_options{traits} = \@all_traits if @all_traits;
232 delete @options{qw(metaclass traits)};
235 (scalar keys %options == 0)
236 || $self->throw_error("Illegal inherited options => (" . (join ', ' => keys %options) . ")", data => \%options);
239 $self->clone(%actual_options);
243 my ( $self, %params ) = @_;
245 my $class = $params{metaclass} || ref $self;
247 if ( 0 and $class eq ref $self ) {
248 return $self->SUPER::clone(%params);
250 my ( @init, @non_init );
252 foreach my $attr ( grep { $_->has_value($self) } $self->meta->compute_all_applicable_attributes ) {
253 push @{ $attr->has_init_arg ? \@init : \@non_init }, $attr;
256 my %new_params = ( ( map { $_->init_arg => $_->get_value($self) } @init ), %params );
258 my $name = delete $new_params{name};
260 my $clone = $class->new($name, %new_params, __hack_no_process_options => 1 );
262 foreach my $attr ( @non_init ) {
263 $attr->set_value($clone, $attr->get_value($self));
271 sub _process_options {
272 my ($class, $name, $options) = @_;
274 if (exists $options->{is}) {
276 ### -------------------------
277 ## is => ro, writer => _foo # turns into (reader => foo, writer => _foo) as before
278 ## is => rw, writer => _foo # turns into (reader => foo, writer => _foo)
279 ## is => rw, accessor => _foo # turns into (accessor => _foo)
280 ## is => ro, accessor => _foo # error, accesor is rw
281 ### -------------------------
283 if ($options->{is} eq 'ro') {
284 $class->throw_error("Cannot define an accessor name on a read-only attribute, accessors are read/write", data => $options)
285 if exists $options->{accessor};
286 $options->{reader} ||= $name;
288 elsif ($options->{is} eq 'rw') {
289 if ($options->{writer}) {
290 $options->{reader} ||= $name;
293 $options->{accessor} ||= $name;
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->{required} = 1;
355 $options->{builder} ||= "_build_${name}";
357 $options->{clearer} ||= "_clear${name}";
358 $options->{predicate} ||= "_has${name}";
361 $options->{clearer} ||= "clear_${name}";
362 $options->{predicate} ||= "has_${name}";
366 if (exists $options->{lazy} && $options->{lazy}) {
367 (exists $options->{default} || defined $options->{builder} )
368 || $class->throw_error("You cannot have lazy attribute ($name) without specifying a default value for it", data => $options);
371 if ( $options->{required} && !( ( !exists $options->{init_arg} || defined $options->{init_arg} ) || exists $options->{default} || defined $options->{builder} ) ) {
372 $class->throw_error("You cannot have a required attribute ($name) without a default, builder, or an init_arg", data => $options);
377 sub initialize_instance_slot {
378 my ($self, $meta_instance, $instance, $params) = @_;
379 my $init_arg = $self->init_arg();
380 # try to fetch the init arg from the %params ...
384 if ( defined($init_arg) and exists $params->{$init_arg}) {
385 $val = $params->{$init_arg};
389 # skip it if it's lazy
390 return if $self->is_lazy;
391 # and die if it's required and doesn't have a default value
392 $self->throw_error("Attribute (" . $self->name . ") is required", object => $instance, data => $params)
393 if $self->is_required && !$self->has_default && !$self->has_builder;
395 # if nothing was in the %params, we can use the
396 # attribute's default value (if it has one)
397 if ($self->has_default) {
398 $val = $self->default($instance);
401 elsif ($self->has_builder) {
402 $val = $self->_call_builder($instance);
407 return unless $value_is_set;
409 if ($self->has_type_constraint) {
410 my $type_constraint = $self->type_constraint;
411 if ($self->should_coerce && $type_constraint->has_coercion) {
412 $val = $type_constraint->coerce($val);
414 $self->verify_against_type_constraint($val, instance => $instance);
417 $self->set_initial_value($instance, $val);
418 $meta_instance->weaken_slot_value($instance, $self->name)
419 if ref $val && $self->is_weak_ref;
423 my ( $self, $instance ) = @_;
425 my $builder = $self->builder();
427 return $instance->$builder()
428 if $instance->can( $self->builder );
430 $self->throw_error( blessed($instance)
431 . " does not support builder method '"
433 . "' for attribute '"
443 # this duplicates too much code from
444 # Class::MOP::Attribute, we need to
445 # refactor these bits eventually.
447 sub _set_initial_slot_value {
448 my ($self, $meta_instance, $instance, $value) = @_;
450 my $slot_name = $self->name;
452 return $meta_instance->set_slot_value($instance, $slot_name, $value)
453 unless $self->has_initializer;
455 my ($type_constraint, $can_coerce);
456 if ($self->has_type_constraint) {
457 $type_constraint = $self->type_constraint;
458 $can_coerce = ($self->should_coerce && $type_constraint->has_coercion);
463 if ($type_constraint) {
464 $val = $type_constraint->coerce($val)
466 $self->verify_against_type_constraint($val, object => $instance);
468 $meta_instance->set_slot_value($instance, $slot_name, $val);
471 my $initializer = $self->initializer;
473 # most things will just want to set a value, so make it first arg
474 $instance->$initializer($value, $callback, $self);
478 my ($self, $instance, @args) = @_;
479 my $value = $args[0];
481 my $attr_name = $self->name;
483 if ($self->is_required and not @args) {
484 $self->throw_error("Attribute ($attr_name) is required", object => $instance);
487 if ($self->has_type_constraint) {
489 my $type_constraint = $self->type_constraint;
491 if ($self->should_coerce) {
492 $value = $type_constraint->coerce($value);
494 $type_constraint->_compiled_type_constraint->($value)
495 || $self->throw_error("Attribute ("
497 . ") does not pass the type constraint because "
498 . $type_constraint->get_message($value), object => $instance, data => $value);
501 my $meta_instance = Class::MOP::Class->initialize(blessed($instance))
504 $meta_instance->set_slot_value($instance, $attr_name, $value);
506 if (ref $value && $self->is_weak_ref) {
507 $meta_instance->weaken_slot_value($instance, $attr_name);
510 if ($self->has_trigger) {
511 $self->trigger->($instance, $value, $self);
516 my ($self, $instance) = @_;
518 if ($self->is_lazy) {
519 unless ($self->has_value($instance)) {
521 if ($self->has_default) {
522 $value = $self->default($instance);
523 } elsif ( $self->has_builder ) {
524 $value = $self->_call_builder($instance);
526 if ($self->has_type_constraint) {
527 my $type_constraint = $self->type_constraint;
528 $value = $type_constraint->coerce($value)
529 if ($self->should_coerce);
530 $self->verify_against_type_constraint($value);
532 $self->set_initial_value($instance, $value);
536 if ($self->should_auto_deref) {
538 my $type_constraint = $self->type_constraint;
540 if ($type_constraint->is_a_type_of('ArrayRef')) {
541 my $rv = $self->SUPER::get_value($instance);
542 return unless defined $rv;
543 return wantarray ? @{ $rv } : $rv;
545 elsif ($type_constraint->is_a_type_of('HashRef')) {
546 my $rv = $self->SUPER::get_value($instance);
547 return unless defined $rv;
548 return wantarray ? %{ $rv } : $rv;
551 $self->throw_error("Can not auto de-reference the type constraint '" . $type_constraint->name . "'", object => $instance, type_constraint => $type_constraint);
557 return $self->SUPER::get_value($instance);
561 ## installing accessors
563 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
565 sub install_accessors {
567 $self->SUPER::install_accessors(@_);
568 $self->install_delegation if $self->has_handles;
572 sub remove_accessors {
574 $self->SUPER::remove_accessors(@_);
575 $self->remove_delegation if $self->has_handles;
579 sub install_delegation {
583 # Here we canonicalize the 'handles' option
584 # this will sort out any details and always
585 # return an hash of methods which we want
586 # to delagate to, see that method for details
587 my %handles = $self->_canonicalize_handles;
590 # install the delegation ...
591 my $associated_class = $self->associated_class;
592 foreach my $handle (keys %handles) {
593 my $method_to_call = $handles{$handle};
594 my $class_name = $associated_class->name;
595 my $name = "${class_name}::${handle}";
597 (!$associated_class->has_method($handle))
598 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
601 # handles is not allowed to delegate
602 # any of these methods, as they will
603 # override the ones in your class, which
604 # is almost certainly not what you want.
606 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
607 #cluck("Not delegating method '$handle' because it is a core method") and
608 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
610 my $method = $self->_make_delegation_method($handle, $method_to_call);
612 $self->associated_class->add_method($method->name, $method);
616 sub remove_delegation {
618 my %handles = $self->_canonicalize_handles;
619 my $associated_class = $self->associated_class;
620 foreach my $handle (keys %handles) {
621 $self->associated_class->remove_method($handle);
625 # private methods to help delegation ...
627 sub _canonicalize_handles {
629 my $handles = $self->handles;
630 if (my $handle_type = ref($handles)) {
631 if ($handle_type eq 'HASH') {
634 elsif ($handle_type eq 'ARRAY') {
635 return map { $_ => $_ } @{$handles};
637 elsif ($handle_type eq 'Regexp') {
638 ($self->has_type_constraint)
639 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
640 return map { ($_ => $_) }
641 grep { /$handles/ } $self->_get_delegate_method_list;
643 elsif ($handle_type eq 'CODE') {
644 return $handles->($self, $self->_find_delegate_metaclass);
647 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
651 Class::MOP::load_class($handles)
652 unless Class::MOP::is_class_loaded($handles);
654 my $role_meta = eval { $handles->meta };
656 $self->throw_error("Unable to canonicalize the 'handles' option with $handles because : $@", data => $handles, error => $@);
659 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
660 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because ->meta is not a Moose::Meta::Role", data => $handles);
662 return map { $_ => $_ } (
663 $role_meta->get_method_list,
664 $role_meta->get_required_method_list
669 sub _find_delegate_metaclass {
671 if (my $class = $self->_isa_metadata) {
672 # if the class does have
673 # a meta method, use it
674 return $class->meta if $class->can('meta');
675 # otherwise we might be
676 # dealing with a non-Moose
677 # class, and need to make
679 return Moose::Meta::Class->initialize($class);
681 elsif (my $role = $self->_does_metadata) {
682 # our role will always have
687 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
691 sub _get_delegate_method_list {
693 my $meta = $self->_find_delegate_metaclass;
694 if ($meta->isa('Class::MOP::Class')) {
695 return map { $_->name } # NOTE: !never! delegate &meta
696 grep { $_->package_name ne 'Moose::Object' && $_->name ne 'meta' }
697 $meta->get_all_methods;
699 elsif ($meta->isa('Moose::Meta::Role')) {
700 return $meta->get_method_list;
703 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
707 sub _make_delegation_method {
708 my ( $self, $handle_name, $method_to_call ) = @_;
712 $method_body = $method_to_call
713 if 'CODE' eq ref($method_to_call);
715 return Moose::Meta::Method::Delegation->new(
716 name => $handle_name,
717 package_name => $self->associated_class->name,
719 delegate_to_method => $method_to_call,
723 sub verify_against_type_constraint {
727 return 1 if !$self->has_type_constraint;
729 my $type_constraint = $self->type_constraint;
731 $type_constraint->check($val)
732 || $self->throw_error("Attribute ("
734 . ") does not pass the type constraint because: "
735 . $type_constraint->get_message($val), data => $val, @_);
738 package Moose::Meta::Attribute::Custom::Moose;
739 sub register_implementation { 'Moose::Meta::Attribute' }
749 Moose::Meta::Attribute - The Moose attribute metaclass
753 This is a subclass of L<Class::MOP::Attribute> with Moose specific
756 For the most part, the only time you will ever encounter an
757 instance of this class is if you are doing some serious deep
758 introspection. To really understand this class, you need to refer
759 to the L<Class::MOP::Attribute> documentation.
763 =head2 Overridden methods
765 These methods override methods in L<Class::MOP::Attribute> and add
766 Moose specific features. You can safely assume though that they
767 will behave just as L<Class::MOP::Attribute> does.
777 =item B<initialize_instance_slot>
779 =item B<install_accessors>
781 =item B<remove_accessors>
783 =item B<install_delegation>
785 =item B<remove_delegation>
787 =item B<accessor_metaclass>
793 eval { $point->meta->get_attribute('x')->set_value($point, 'fourty-two') };
798 I<Attribute (x) does not pass the type constraint (Int) with 'fourty-two'>
800 Before setting the value, a check is made on the type constraint of
801 the attribute, if it has one, to see if the value passes it. If the
802 value fails to pass, the set operation dies with a L<throw_error>.
804 Any coercion to convert values is done before checking the type constraint.
806 To check a value against a type constraint before setting it, fetch the
807 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
808 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
809 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
814 =head2 Additional Moose features
816 Moose attributes support type-constraint checking, weak reference
817 creation and type coercion.
823 Delegates to C<associated_class> or C<Moose::Meta::Class> if there is none.
825 =item B<interpolate_class_and_new>
827 =item B<interpolate_class>
829 When called as a class method causes interpretation of the C<metaclass> and
832 =item B<clone_and_inherit_options>
834 This is to support the C<has '+foo'> feature, it clones an attribute
835 from a superclass and allows a very specific set of changes to be made
838 =item B<legal_options_for_inheritance>
840 Whitelist with options you can change. You can overload it in your custom
841 metaclass to allow your options be inheritable.
843 =item B<has_type_constraint>
845 Returns true if this meta-attribute has a type constraint.
847 =item B<type_constraint>
849 A read-only accessor for this meta-attribute's type constraint. For
850 more information on what you can do with this, see the documentation
851 for L<Moose::Meta::TypeConstraint>.
853 =item B<verify_against_type_constraint>
855 Verifies that the given value is valid under this attribute's type
856 constraint, otherwise throws an error.
860 Returns true if this meta-attribute performs delegation.
864 This returns the value which was passed into the handles option.
868 Returns true if this meta-attribute produces a weak reference.
872 Returns true if this meta-attribute is required to have a value.
876 Returns true if this meta-attribute should be initialized lazily.
878 NOTE: lazy attributes, B<must> have a C<default> or C<builder> field set.
880 =item B<is_lazy_build>
882 Returns true if this meta-attribute should be initialized lazily through
883 the builder generated by lazy_build. Using C<lazy_build =E<gt> 1> will
884 make your attribute required and lazy. In addition it will set the builder, clearer
885 and predicate options for you using the following convention.
887 #If your attribute name starts with an underscore:
888 has '_foo' => (lazy_build => 1);
890 has '_foo' => (lazy => 1, required => 1, predicate => '_has_foo', clearer => '_clear_foo', builder => '_build__foo');
892 has '_foo' => (lazy => 1, required => 1, predicate => '_has_foo', clearer => '_clear_foo', default => sub{shift->_build__foo});
894 #If your attribute name does not start with an underscore:
895 has 'foo' => (lazy_build => 1);
897 has 'foo' => (lazy => 1, required => 1, predicate => 'has_foo', clearer => 'clear_foo', builder => '_build_foo');
899 has 'foo' => (lazy => 1, required => 1, predicate => 'has_foo', clearer => 'clear_foo', default => sub{shift->_build_foo});
901 The reason for the different naming of the C<builder> is that the C<builder>
902 method is a private method while the C<clearer> and C<predicate> methods
905 NOTE: This means your class should provide a method whose name matches the value
906 of the builder part, in this case _build__foo or _build_foo.
908 =item B<should_coerce>
910 Returns true if this meta-attribute should perform type coercion.
912 =item B<should_auto_deref>
914 Returns true if this meta-attribute should perform automatic
917 NOTE: This can only be done for attributes whose type constraint is
918 either I<ArrayRef> or I<HashRef>.
922 Returns true if this meta-attribute has a trigger set.
926 This is a CODE reference which will be executed every time the
927 value of an attribute is assigned. The CODE ref will get two values,
928 the invocant and the new value. This can be used to handle I<basic>
929 bi-directional relations.
931 =item B<documentation>
933 This is a string which contains the documentation for this attribute.
934 It serves no direct purpose right now, but it might in the future
935 in some kind of automated documentation system perhaps.
937 =item B<has_documentation>
939 Returns true if this meta-attribute has any documentation.
941 =item B<applied_traits>
943 This will return the ARRAY ref of all the traits applied to this
944 attribute, or if no traits have been applied, it returns C<undef>.
946 =item B<has_applied_traits>
948 Returns true if this meta-attribute has any traits applied.
954 All complex software has bugs lurking in it, and this module is no
955 exception. If you find a bug please either email me, or add the bug
960 Stevan Little E<lt>stevan@iinteractive.comE<gt>
962 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
964 =head1 COPYRIGHT AND LICENSE
966 Copyright 2006-2008 by Infinity Interactive, Inc.
968 L<http://www.iinteractive.com>
970 This library is free software; you can redistribute it and/or modify
971 it under the same terms as Perl itself.