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 = $options{traits}) {
112 while ($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 $type_constraint->check($val)
415 || $self->throw_error("Attribute ("
417 . ") does not pass the type constraint because: "
418 . $type_constraint->get_message($val), data => $val, object => $instance);
421 $self->set_initial_value($instance, $val);
422 $meta_instance->weaken_slot_value($instance, $self->name)
423 if ref $val && $self->is_weak_ref;
427 my ( $self, $instance ) = @_;
429 my $builder = $self->builder();
431 return $instance->$builder()
432 if $instance->can( $self->builder );
434 $self->throw_error( blessed($instance)
435 . " does not support builder method '"
437 . "' for attribute '"
447 # this duplicates too much code from
448 # Class::MOP::Attribute, we need to
449 # refactor these bits eventually.
451 sub _set_initial_slot_value {
452 my ($self, $meta_instance, $instance, $value) = @_;
454 my $slot_name = $self->name;
456 return $meta_instance->set_slot_value($instance, $slot_name, $value)
457 unless $self->has_initializer;
459 my ($type_constraint, $can_coerce);
460 if ($self->has_type_constraint) {
461 $type_constraint = $self->type_constraint;
462 $can_coerce = ($self->should_coerce && $type_constraint->has_coercion);
467 if ($type_constraint) {
468 $val = $type_constraint->coerce($val)
470 $type_constraint->check($val)
471 || $self->throw_error("Attribute ("
473 . ") does not pass the type constraint because: "
474 . $type_constraint->get_message($val), data => $val, object => $instance);
476 $meta_instance->set_slot_value($instance, $slot_name, $val);
479 my $initializer = $self->initializer;
481 # most things will just want to set a value, so make it first arg
482 $instance->$initializer($value, $callback, $self);
486 my ($self, $instance, @args) = @_;
487 my $value = $args[0];
489 my $attr_name = $self->name;
491 if ($self->is_required and not @args) {
492 $self->throw_error("Attribute ($attr_name) is required", object => $instance);
495 if ($self->has_type_constraint) {
497 my $type_constraint = $self->type_constraint;
499 if ($self->should_coerce) {
500 $value = $type_constraint->coerce($value);
502 $type_constraint->_compiled_type_constraint->($value)
503 || $self->throw_error("Attribute ("
505 . ") does not pass the type constraint because "
506 . $type_constraint->get_message($value), object => $instance, data => $value);
509 my $meta_instance = Class::MOP::Class->initialize(blessed($instance))
512 $meta_instance->set_slot_value($instance, $attr_name, $value);
514 if (ref $value && $self->is_weak_ref) {
515 $meta_instance->weaken_slot_value($instance, $attr_name);
518 if ($self->has_trigger) {
519 $self->trigger->($instance, $value, $self);
524 my ($self, $instance) = @_;
526 if ($self->is_lazy) {
527 unless ($self->has_value($instance)) {
529 if ($self->has_default) {
530 $value = $self->default($instance);
531 } elsif ( $self->has_builder ) {
532 $value = $self->_call_builder($instance);
534 if ($self->has_type_constraint) {
535 my $type_constraint = $self->type_constraint;
536 $value = $type_constraint->coerce($value)
537 if ($self->should_coerce);
538 $type_constraint->check($value)
539 || $self->throw_error("Attribute (" . $self->name
540 . ") does not pass the type constraint because: "
541 . $type_constraint->get_message($value), type_constraint => $type_constraint, data => $value);
543 $self->set_initial_value($instance, $value);
547 if ($self->should_auto_deref) {
549 my $type_constraint = $self->type_constraint;
551 if ($type_constraint->is_a_type_of('ArrayRef')) {
552 my $rv = $self->SUPER::get_value($instance);
553 return unless defined $rv;
554 return wantarray ? @{ $rv } : $rv;
556 elsif ($type_constraint->is_a_type_of('HashRef')) {
557 my $rv = $self->SUPER::get_value($instance);
558 return unless defined $rv;
559 return wantarray ? %{ $rv } : $rv;
562 $self->throw_error("Can not auto de-reference the type constraint '" . $type_constraint->name . "'", object => $instance, type_constraint => $type_constraint);
568 return $self->SUPER::get_value($instance);
572 ## installing accessors
574 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
576 sub install_accessors {
578 $self->SUPER::install_accessors(@_);
579 $self->install_delegation if $self->has_handles;
583 sub remove_accessors {
585 $self->SUPER::remove_accessors(@_);
586 $self->remove_delegation if $self->has_handles;
590 sub install_delegation {
594 # Here we canonicalize the 'handles' option
595 # this will sort out any details and always
596 # return an hash of methods which we want
597 # to delagate to, see that method for details
598 my %handles = $self->_canonicalize_handles;
601 # install the delegation ...
602 my $associated_class = $self->associated_class;
603 foreach my $handle (keys %handles) {
604 my $method_to_call = $handles{$handle};
605 my $class_name = $associated_class->name;
606 my $name = "${class_name}::${handle}";
608 (!$associated_class->has_method($handle))
609 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
612 # handles is not allowed to delegate
613 # any of these methods, as they will
614 # override the ones in your class, which
615 # is almost certainly not what you want.
617 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
618 #cluck("Not delegating method '$handle' because it is a core method") and
619 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
621 my $method = $self->_make_delegation_method($handle, $method_to_call);
623 $self->associated_class->add_method($method->name, $method);
627 sub remove_delegation {
629 my %handles = $self->_canonicalize_handles;
630 my $associated_class = $self->associated_class;
631 foreach my $handle (keys %handles) {
632 $self->associated_class->remove_method($handle);
636 # private methods to help delegation ...
638 sub _canonicalize_handles {
640 my $handles = $self->handles;
641 if (my $handle_type = ref($handles)) {
642 if ($handle_type eq 'HASH') {
645 elsif ($handle_type eq 'ARRAY') {
646 return map { $_ => $_ } @{$handles};
648 elsif ($handle_type eq 'Regexp') {
649 ($self->has_type_constraint)
650 || $self->throw_error("Cannot delegate methods based on a RegExpr without a type constraint (isa)", data => $handles);
651 return map { ($_ => $_) }
652 grep { /$handles/ } $self->_get_delegate_method_list;
654 elsif ($handle_type eq 'CODE') {
655 return $handles->($self, $self->_find_delegate_metaclass);
658 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
662 Class::MOP::load_class($handles)
663 unless Class::MOP::is_class_loaded($handles);
665 my $role_meta = eval { $handles->meta };
667 $self->throw_error("Unable to canonicalize the 'handles' option with $handles because : $@", data => $handles, error => $@);
670 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
671 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because ->meta is not a Moose::Meta::Role", data => $handles);
673 return map { $_ => $_ } (
674 $role_meta->get_method_list,
675 $role_meta->get_required_method_list
680 sub _find_delegate_metaclass {
682 if (my $class = $self->_isa_metadata) {
683 # if the class does have
684 # a meta method, use it
685 return $class->meta if $class->can('meta');
686 # otherwise we might be
687 # dealing with a non-Moose
688 # class, and need to make
690 return Moose::Meta::Class->initialize($class);
692 elsif (my $role = $self->_does_metadata) {
693 # our role will always have
698 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
702 sub _get_delegate_method_list {
704 my $meta = $self->_find_delegate_metaclass;
705 if ($meta->isa('Class::MOP::Class')) {
706 return map { $_->name } # NOTE: !never! delegate &meta
707 grep { $_->package_name ne 'Moose::Object' && $_->name ne 'meta' }
708 $meta->get_all_methods;
710 elsif ($meta->isa('Moose::Meta::Role')) {
711 return $meta->get_method_list;
714 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
718 sub _make_delegation_method {
719 my ( $self, $handle_name, $method_to_call ) = @_;
723 $method_body = $method_to_call
724 if 'CODE' eq ref($method_to_call);
726 return Moose::Meta::Method::Delegation->new(
727 name => $handle_name,
728 package_name => $self->associated_class->name,
730 delegate_to_method => $method_to_call,
734 package Moose::Meta::Attribute::Custom::Moose;
735 sub register_implementation { 'Moose::Meta::Attribute' }
745 Moose::Meta::Attribute - The Moose attribute metaclass
749 This is a subclass of L<Class::MOP::Attribute> with Moose specific
752 For the most part, the only time you will ever encounter an
753 instance of this class is if you are doing some serious deep
754 introspection. To really understand this class, you need to refer
755 to the L<Class::MOP::Attribute> documentation.
759 =head2 Overridden methods
761 These methods override methods in L<Class::MOP::Attribute> and add
762 Moose specific features. You can safely assume though that they
763 will behave just as L<Class::MOP::Attribute> does.
773 =item B<initialize_instance_slot>
775 =item B<install_accessors>
777 =item B<remove_accessors>
779 =item B<install_delegation>
781 =item B<remove_delegation>
783 =item B<accessor_metaclass>
789 eval { $point->meta->get_attribute('x')->set_value($point, 'fourty-two') };
794 I<Attribute (x) does not pass the type constraint (Int) with 'fourty-two'>
796 Before setting the value, a check is made on the type constraint of
797 the attribute, if it has one, to see if the value passes it. If the
798 value fails to pass, the set operation dies with a L<throw_error>.
800 Any coercion to convert values is done before checking the type constraint.
802 To check a value against a type constraint before setting it, fetch the
803 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
804 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
805 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
810 =head2 Additional Moose features
812 Moose attributes support type-constraint checking, weak reference
813 creation and type coercion.
819 Delegates to C<associated_class> or C<Moose::Meta::Class> if there is none.
821 =item B<interpolate_class_and_new>
823 =item B<interpolate_class>
825 When called as a class method causes interpretation of the C<metaclass> and
828 =item B<clone_and_inherit_options>
830 This is to support the C<has '+foo'> feature, it clones an attribute
831 from a superclass and allows a very specific set of changes to be made
834 =item B<legal_options_for_inheritance>
836 Whitelist with options you can change. You can overload it in your custom
837 metaclass to allow your options be inheritable.
839 =item B<has_type_constraint>
841 Returns true if this meta-attribute has a type constraint.
843 =item B<type_constraint>
845 A read-only accessor for this meta-attribute's type constraint. For
846 more information on what you can do with this, see the documentation
847 for L<Moose::Meta::TypeConstraint>.
851 Returns true if this meta-attribute performs delegation.
855 This returns the value which was passed into the handles option.
859 Returns true if this meta-attribute produces a weak reference.
863 Returns true if this meta-attribute is required to have a value.
867 Returns true if this meta-attribute should be initialized lazily.
869 NOTE: lazy attributes, B<must> have a C<default> or C<builder> field set.
871 =item B<is_lazy_build>
873 Returns true if this meta-attribute should be initialized lazily through
874 the builder generated by lazy_build. Using C<lazy_build =E<gt> 1> will
875 make your attribute required and lazy. In addition it will set the builder, clearer
876 and predicate options for you using the following convention.
878 #If your attribute name starts with an underscore:
879 has '_foo' => (lazy_build => 1);
881 has '_foo' => (lazy => 1, required => 1, predicate => '_has_foo', clearer => '_clear_foo', builder => '_build__foo');
883 has '_foo' => (lazy => 1, required => 1, predicate => '_has_foo', clearer => '_clear_foo', default => sub{shift->_build__foo});
885 #If your attribute name does not start with an underscore:
886 has 'foo' => (lazy_build => 1);
888 has 'foo' => (lazy => 1, required => 1, predicate => 'has_foo', clearer => 'clear_foo', builder => '_build_foo');
890 has 'foo' => (lazy => 1, required => 1, predicate => 'has_foo', clearer => 'clear_foo', default => sub{shift->_build_foo});
892 The reason for the different naming of the C<builder> is that the C<builder>
893 method is a private method while the C<clearer> and C<predicate> methods
896 NOTE: This means your class should provide a method whose name matches the value
897 of the builder part, in this case _build__foo or _build_foo.
899 =item B<should_coerce>
901 Returns true if this meta-attribute should perform type coercion.
903 =item B<should_auto_deref>
905 Returns true if this meta-attribute should perform automatic
908 NOTE: This can only be done for attributes whose type constraint is
909 either I<ArrayRef> or I<HashRef>.
913 Returns true if this meta-attribute has a trigger set.
917 This is a CODE reference which will be executed every time the
918 value of an attribute is assigned. The CODE ref will get two values,
919 the invocant and the new value. This can be used to handle I<basic>
920 bi-directional relations.
922 =item B<documentation>
924 This is a string which contains the documentation for this attribute.
925 It serves no direct purpose right now, but it might in the future
926 in some kind of automated documentation system perhaps.
928 =item B<has_documentation>
930 Returns true if this meta-attribute has any documentation.
932 =item B<applied_traits>
934 This will return the ARRAY ref of all the traits applied to this
935 attribute, or if no traits have been applied, it returns C<undef>.
937 =item B<has_applied_traits>
939 Returns true if this meta-attribute has any traits applied.
945 All complex software has bugs lurking in it, and this module is no
946 exception. If you find a bug please either email me, or add the bug
951 Stevan Little E<lt>stevan@iinteractive.comE<gt>
953 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
955 =head1 COPYRIGHT AND LICENSE
957 Copyright 2006-2008 by Infinity Interactive, Inc.
959 L<http://www.iinteractive.com>
961 This library is free software; you can redistribute it and/or modify
962 it under the same terms as Perl itself.