2 package Moose::Meta::Attribute;
7 use Scalar::Util 'blessed', 'weaken';
10 our $VERSION = '0.72';
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 if ( 0 and $class eq ref $self ) {
250 return $self->SUPER::clone(%params);
252 my ( @init, @non_init );
254 foreach my $attr ( grep { $_->has_value($self) } $self->meta->compute_all_applicable_attributes ) {
255 push @{ $attr->has_init_arg ? \@init : \@non_init }, $attr;
258 my %new_params = ( ( map { $_->init_arg => $_->get_value($self) } @init ), %params );
260 my $name = delete $new_params{name};
262 my $clone = $class->new($name, %new_params, __hack_no_process_options => 1 );
264 foreach my $attr ( @non_init ) {
265 $attr->set_value($clone, $attr->get_value($self));
273 sub _process_options {
274 my ($class, $name, $options) = @_;
276 if (exists $options->{is}) {
278 ### -------------------------
279 ## is => ro, writer => _foo # turns into (reader => foo, writer => _foo) as before
280 ## is => rw, writer => _foo # turns into (reader => foo, writer => _foo)
281 ## is => rw, accessor => _foo # turns into (accessor => _foo)
282 ## is => ro, accessor => _foo # error, accesor is rw
283 ### -------------------------
285 if ($options->{is} eq 'ro') {
286 $class->throw_error("Cannot define an accessor name on a read-only attribute, accessors are read/write", data => $options)
287 if exists $options->{accessor};
288 $options->{reader} ||= $name;
290 elsif ($options->{is} eq 'rw') {
291 if ($options->{writer}) {
292 $options->{reader} ||= $name;
295 $options->{accessor} ||= $name;
299 $class->throw_error("I do not understand this option (is => " . $options->{is} . ") on attribute ($name)", data => $options->{is});
303 if (exists $options->{isa}) {
304 if (exists $options->{does}) {
305 if (eval { $options->{isa}->can('does') }) {
306 ($options->{isa}->does($options->{does}))
307 || $class->throw_error("Cannot have an isa option and a does option if the isa does not do the does on attribute ($name)", data => $options);
310 $class->throw_error("Cannot have an isa option which cannot ->does() on attribute ($name)", data => $options);
314 # allow for anon-subtypes here ...
315 if (blessed($options->{isa}) && $options->{isa}->isa('Moose::Meta::TypeConstraint')) {
316 $options->{type_constraint} = $options->{isa};
319 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options->{isa});
322 elsif (exists $options->{does}) {
323 # allow for anon-subtypes here ...
324 if (blessed($options->{does}) && $options->{does}->isa('Moose::Meta::TypeConstraint')) {
325 $options->{type_constraint} = $options->{does};
328 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options->{does});
332 if (exists $options->{coerce} && $options->{coerce}) {
333 (exists $options->{type_constraint})
334 || $class->throw_error("You cannot have coercion without specifying a type constraint on attribute ($name)", data => $options);
335 $class->throw_error("You cannot have a weak reference to a coerced value on attribute ($name)", data => $options)
336 if $options->{weak_ref};
339 if (exists $options->{trigger}) {
340 ('CODE' eq ref $options->{trigger})
341 || $class->throw_error("Trigger must be a CODE ref on attribute ($name)", data => $options->{trigger});
344 if (exists $options->{auto_deref} && $options->{auto_deref}) {
345 (exists $options->{type_constraint})
346 || $class->throw_error("You cannot auto-dereference without specifying a type constraint on attribute ($name)", data => $options);
347 ($options->{type_constraint}->is_a_type_of('ArrayRef') ||
348 $options->{type_constraint}->is_a_type_of('HashRef'))
349 || $class->throw_error("You cannot auto-dereference anything other than a ArrayRef or HashRef on attribute ($name)", data => $options);
352 if (exists $options->{lazy_build} && $options->{lazy_build} == 1) {
353 $class->throw_error("You can not use lazy_build and default for the same attribute ($name)", data => $options)
354 if exists $options->{default};
355 $options->{lazy} = 1;
356 $options->{required} = 1;
357 $options->{builder} ||= "_build_${name}";
359 $options->{clearer} ||= "_clear${name}";
360 $options->{predicate} ||= "_has${name}";
363 $options->{clearer} ||= "clear_${name}";
364 $options->{predicate} ||= "has_${name}";
368 if (exists $options->{lazy} && $options->{lazy}) {
369 (exists $options->{default} || defined $options->{builder} )
370 || $class->throw_error("You cannot have lazy attribute ($name) without specifying a default value for it", data => $options);
373 if ( $options->{required} && !( ( !exists $options->{init_arg} || defined $options->{init_arg} ) || exists $options->{default} || defined $options->{builder} ) ) {
374 $class->throw_error("You cannot have a required attribute ($name) without a default, builder, or an init_arg", data => $options);
379 sub initialize_instance_slot {
380 my ($self, $meta_instance, $instance, $params) = @_;
381 my $init_arg = $self->init_arg();
382 # try to fetch the init arg from the %params ...
386 if ( defined($init_arg) and exists $params->{$init_arg}) {
387 $val = $params->{$init_arg};
391 # skip it if it's lazy
392 return if $self->is_lazy;
393 # and die if it's required and doesn't have a default value
394 $self->throw_error("Attribute (" . $self->name . ") is required", object => $instance, data => $params)
395 if $self->is_required && !$self->has_default && !$self->has_builder;
397 # if nothing was in the %params, we can use the
398 # attribute's default value (if it has one)
399 if ($self->has_default) {
400 $val = $self->default($instance);
403 elsif ($self->has_builder) {
404 $val = $self->_call_builder($instance);
409 return unless $value_is_set;
411 if ($self->has_type_constraint) {
412 my $type_constraint = $self->type_constraint;
413 if ($self->should_coerce && $type_constraint->has_coercion) {
414 $val = $type_constraint->coerce($val);
416 $self->verify_against_type_constraint($val, instance => $instance);
419 $self->set_initial_value($instance, $val);
420 $meta_instance->weaken_slot_value($instance, $self->name)
421 if ref $val && $self->is_weak_ref;
425 my ( $self, $instance ) = @_;
427 my $builder = $self->builder();
429 return $instance->$builder()
430 if $instance->can( $self->builder );
432 $self->throw_error( blessed($instance)
433 . " does not support builder method '"
435 . "' for attribute '"
445 # this duplicates too much code from
446 # Class::MOP::Attribute, we need to
447 # refactor these bits eventually.
449 sub _set_initial_slot_value {
450 my ($self, $meta_instance, $instance, $value) = @_;
452 my $slot_name = $self->name;
454 return $meta_instance->set_slot_value($instance, $slot_name, $value)
455 unless $self->has_initializer;
457 my ($type_constraint, $can_coerce);
458 if ($self->has_type_constraint) {
459 $type_constraint = $self->type_constraint;
460 $can_coerce = ($self->should_coerce && $type_constraint->has_coercion);
465 if ($type_constraint) {
466 $val = $type_constraint->coerce($val)
468 $self->verify_against_type_constraint($val, object => $instance);
470 $meta_instance->set_slot_value($instance, $slot_name, $val);
473 my $initializer = $self->initializer;
475 # most things will just want to set a value, so make it first arg
476 $instance->$initializer($value, $callback, $self);
480 my ($self, $instance, @args) = @_;
481 my $value = $args[0];
483 my $attr_name = $self->name;
485 if ($self->is_required and not @args) {
486 $self->throw_error("Attribute ($attr_name) is required", object => $instance);
489 if ($self->has_type_constraint) {
491 my $type_constraint = $self->type_constraint;
493 if ($self->should_coerce) {
494 $value = $type_constraint->coerce($value);
496 $type_constraint->_compiled_type_constraint->($value)
497 || $self->throw_error("Attribute ("
499 . ") does not pass the type constraint because "
500 . $type_constraint->get_message($value), object => $instance, data => $value);
503 my $meta_instance = Class::MOP::Class->initialize(blessed($instance))
506 $meta_instance->set_slot_value($instance, $attr_name, $value);
508 if (ref $value && $self->is_weak_ref) {
509 $meta_instance->weaken_slot_value($instance, $attr_name);
512 if ($self->has_trigger) {
513 $self->trigger->($instance, $value);
518 my ($self, $instance) = @_;
520 if ($self->is_lazy) {
521 unless ($self->has_value($instance)) {
523 if ($self->has_default) {
524 $value = $self->default($instance);
525 } elsif ( $self->has_builder ) {
526 $value = $self->_call_builder($instance);
528 if ($self->has_type_constraint) {
529 my $type_constraint = $self->type_constraint;
530 $value = $type_constraint->coerce($value)
531 if ($self->should_coerce);
532 $self->verify_against_type_constraint($value);
534 $self->set_initial_value($instance, $value);
538 if ($self->should_auto_deref) {
540 my $type_constraint = $self->type_constraint;
542 if ($type_constraint->is_a_type_of('ArrayRef')) {
543 my $rv = $self->SUPER::get_value($instance);
544 return unless defined $rv;
545 return wantarray ? @{ $rv } : $rv;
547 elsif ($type_constraint->is_a_type_of('HashRef')) {
548 my $rv = $self->SUPER::get_value($instance);
549 return unless defined $rv;
550 return wantarray ? %{ $rv } : $rv;
553 $self->throw_error("Can not auto de-reference the type constraint '" . $type_constraint->name . "'", object => $instance, type_constraint => $type_constraint);
559 return $self->SUPER::get_value($instance);
563 ## installing accessors
565 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
567 sub install_accessors {
569 $self->SUPER::install_accessors(@_);
570 $self->install_delegation if $self->has_handles;
574 sub remove_accessors {
576 $self->SUPER::remove_accessors(@_);
577 $self->remove_delegation if $self->has_handles;
581 sub install_delegation {
585 # Here we canonicalize the 'handles' option
586 # this will sort out any details and always
587 # return an hash of methods which we want
588 # to delagate to, see that method for details
589 my %handles = $self->_canonicalize_handles;
592 # install the delegation ...
593 my $associated_class = $self->associated_class;
594 foreach my $handle (keys %handles) {
595 my $method_to_call = $handles{$handle};
596 my $class_name = $associated_class->name;
597 my $name = "${class_name}::${handle}";
599 (!$associated_class->has_method($handle))
600 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
603 # handles is not allowed to delegate
604 # any of these methods, as they will
605 # override the ones in your class, which
606 # is almost certainly not what you want.
608 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
609 #cluck("Not delegating method '$handle' because it is a core method") and
610 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
612 my $method = $self->_make_delegation_method($handle, $method_to_call);
614 $self->associated_class->add_method($method->name, $method);
618 sub remove_delegation {
620 my %handles = $self->_canonicalize_handles;
621 my $associated_class = $self->associated_class;
622 foreach my $handle (keys %handles) {
623 $self->associated_class->remove_method($handle);
627 # private methods to help delegation ...
629 sub _canonicalize_handles {
631 my $handles = $self->handles;
632 if (my $handle_type = ref($handles)) {
633 if ($handle_type eq 'HASH') {
636 elsif ($handle_type eq 'ARRAY') {
637 return map { $_ => $_ } @{$handles};
639 elsif ($handle_type eq 'Regexp') {
640 ($self->has_type_constraint)
641 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
642 return map { ($_ => $_) }
643 grep { /$handles/ } $self->_get_delegate_method_list;
645 elsif ($handle_type eq 'CODE') {
646 return $handles->($self, $self->_find_delegate_metaclass);
649 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
653 Class::MOP::load_class($handles)
654 unless Class::MOP::is_class_loaded($handles);
656 my $role_meta = eval { $handles->meta };
658 $self->throw_error("Unable to canonicalize the 'handles' option with $handles because : $@", data => $handles, error => $@);
661 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
662 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because ->meta is not a Moose::Meta::Role", data => $handles);
664 return map { $_ => $_ } (
665 $role_meta->get_method_list,
666 $role_meta->get_required_method_list
671 sub _find_delegate_metaclass {
673 if (my $class = $self->_isa_metadata) {
674 # if the class does have
675 # a meta method, use it
676 return $class->meta if $class->can('meta');
677 # otherwise we might be
678 # dealing with a non-Moose
679 # class, and need to make
681 return Moose::Meta::Class->initialize($class);
683 elsif (my $role = $self->_does_metadata) {
684 # our role will always have
689 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
693 sub _get_delegate_method_list {
695 my $meta = $self->_find_delegate_metaclass;
696 if ($meta->isa('Class::MOP::Class')) {
697 return map { $_->name } # NOTE: !never! delegate &meta
698 grep { $_->package_name ne 'Moose::Object' && $_->name ne 'meta' }
699 $meta->get_all_methods;
701 elsif ($meta->isa('Moose::Meta::Role')) {
702 return $meta->get_method_list;
705 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
709 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
711 sub _make_delegation_method {
712 my ( $self, $handle_name, $method_to_call ) = @_;
716 $method_body = $method_to_call
717 if 'CODE' eq ref($method_to_call);
719 return $self->delegation_metaclass->new(
720 name => $handle_name,
721 package_name => $self->associated_class->name,
723 delegate_to_method => $method_to_call,
727 sub verify_against_type_constraint {
731 return 1 if !$self->has_type_constraint;
733 my $type_constraint = $self->type_constraint;
735 $type_constraint->check($val)
736 || $self->throw_error("Attribute ("
738 . ") does not pass the type constraint because: "
739 . $type_constraint->get_message($val), data => $val, @_);
742 package Moose::Meta::Attribute::Custom::Moose;
743 sub register_implementation { 'Moose::Meta::Attribute' }
753 Moose::Meta::Attribute - The Moose attribute metaclass
757 This is a subclass of L<Class::MOP::Attribute> with Moose specific
760 For the most part, the only time you will ever encounter an
761 instance of this class is if you are doing some serious deep
762 introspection. To really understand this class, you need to refer
763 to the L<Class::MOP::Attribute> documentation.
767 =head2 Overridden methods
769 These methods override methods in L<Class::MOP::Attribute> and add
770 Moose specific features. You can safely assume though that they
771 will behave just as L<Class::MOP::Attribute> does.
781 =item B<initialize_instance_slot>
783 =item B<install_accessors>
785 =item B<remove_accessors>
787 =item B<install_delegation>
789 =item B<remove_delegation>
791 =item B<accessor_metaclass>
793 =item B<delegation_metaclass>
799 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
804 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
806 Before setting the value, a check is made on the type constraint of
807 the attribute, if it has one, to see if the value passes it. If the
808 value fails to pass, the set operation dies with a L<throw_error>.
810 Any coercion to convert values is done before checking the type constraint.
812 To check a value against a type constraint before setting it, fetch the
813 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
814 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
815 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
820 =head2 Additional Moose features
822 Moose attributes support type-constraint checking, weak reference
823 creation and type coercion.
829 Delegates to C<associated_class> or C<Moose::Meta::Class> if there is none.
831 =item B<interpolate_class_and_new>
833 =item B<interpolate_class>
835 When called as a class method causes interpretation of the C<metaclass> and
838 =item B<clone_and_inherit_options>
840 This is to support the C<has '+foo'> feature, it clones an attribute
841 from a superclass and allows a very specific set of changes to be made
844 =item B<legal_options_for_inheritance>
846 Whitelist with options you can change. You can overload it in your custom
847 metaclass to allow your options be inheritable.
849 =item B<has_type_constraint>
851 Returns true if this meta-attribute has a type constraint.
853 =item B<type_constraint>
855 A read-only accessor for this meta-attribute's type constraint. For
856 more information on what you can do with this, see the documentation
857 for L<Moose::Meta::TypeConstraint>.
859 =item B<verify_against_type_constraint>
861 Verifies that the given value is valid under this attribute's type
862 constraint, otherwise throws an error.
866 Returns true if this meta-attribute performs delegation.
870 This returns the value which was passed into the handles option.
874 Returns true if this meta-attribute produces a weak reference.
878 Returns true if this meta-attribute is required to have a value.
882 Returns true if this meta-attribute should be initialized lazily.
884 NOTE: lazy attributes, B<must> have a C<default> or C<builder> field set.
886 =item B<is_lazy_build>
888 Returns true if this meta-attribute should be initialized lazily through
889 the builder generated by lazy_build. Using C<lazy_build =E<gt> 1> will
890 make your attribute required and lazy. In addition it will set the builder, clearer
891 and predicate options for you using the following convention.
893 #If your attribute name starts with an underscore:
894 has '_foo' => (lazy_build => 1);
896 has '_foo' => (lazy => 1, required => 1, predicate => '_has_foo', clearer => '_clear_foo', builder => '_build__foo');
898 has '_foo' => (lazy => 1, required => 1, predicate => '_has_foo', clearer => '_clear_foo', default => sub{shift->_build__foo});
900 #If your attribute name does not start with an underscore:
901 has 'foo' => (lazy_build => 1);
903 has 'foo' => (lazy => 1, required => 1, predicate => 'has_foo', clearer => 'clear_foo', builder => '_build_foo');
905 has 'foo' => (lazy => 1, required => 1, predicate => 'has_foo', clearer => 'clear_foo', default => sub{shift->_build_foo});
907 The reason for the different naming of the C<builder> is that the C<builder>
908 method is a private method while the C<clearer> and C<predicate> methods
911 NOTE: This means your class should provide a method whose name matches the value
912 of the builder part, in this case _build__foo or _build_foo.
914 =item B<should_coerce>
916 Returns true if this meta-attribute should perform type coercion.
918 =item B<should_auto_deref>
920 Returns true if this meta-attribute should perform automatic
923 NOTE: This can only be done for attributes whose type constraint is
924 either I<ArrayRef> or I<HashRef>.
928 Returns true if this meta-attribute has a trigger set.
932 This is a CODE reference which will be executed every time the
933 value of an attribute is assigned. The CODE ref will get two values,
934 the invocant and the new value. This can be used to handle I<basic>
935 bi-directional relations.
937 =item B<documentation>
939 This is a string which contains the documentation for this attribute.
940 It serves no direct purpose right now, but it might in the future
941 in some kind of automated documentation system perhaps.
943 =item B<has_documentation>
945 Returns true if this meta-attribute has any documentation.
947 =item B<applied_traits>
949 This will return the ARRAY ref of all the traits applied to this
950 attribute, or if no traits have been applied, it returns C<undef>.
952 =item B<has_applied_traits>
954 Returns true if this meta-attribute has any traits applied.
960 All complex software has bugs lurking in it, and this module is no
961 exception. If you find a bug please either email me, or add the bug
966 Stevan Little E<lt>stevan@iinteractive.comE<gt>
968 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
970 =head1 COPYRIGHT AND LICENSE
972 Copyright 2006-2009 by Infinity Interactive, Inc.
974 L<http://www.iinteractive.com>
976 This library is free software; you can redistribute it and/or modify
977 it under the same terms as Perl itself.