2 package Moose::Meta::Attribute;
7 use Scalar::Util 'blessed', 'weaken';
11 our $VERSION = '0.55';
12 our $AUTHORITY = 'cpan:STEVAN';
14 use Moose::Meta::Method::Accessor;
16 use Moose::Util::TypeConstraints ();
18 use base 'Class::MOP::Attribute';
20 # options which are not directly used
21 # but we store them for metadata purposes
22 __PACKAGE__->meta->add_attribute('isa' => (reader => '_isa_metadata'));
23 __PACKAGE__->meta->add_attribute('does' => (reader => '_does_metadata'));
24 __PACKAGE__->meta->add_attribute('is' => (reader => '_is_metadata'));
26 # these are actual options for the attrs
27 __PACKAGE__->meta->add_attribute('required' => (reader => 'is_required' ));
28 __PACKAGE__->meta->add_attribute('lazy' => (reader => 'is_lazy' ));
29 __PACKAGE__->meta->add_attribute('lazy_build' => (reader => 'is_lazy_build' ));
30 __PACKAGE__->meta->add_attribute('coerce' => (reader => 'should_coerce' ));
31 __PACKAGE__->meta->add_attribute('weak_ref' => (reader => 'is_weak_ref' ));
32 __PACKAGE__->meta->add_attribute('auto_deref' => (reader => 'should_auto_deref'));
33 __PACKAGE__->meta->add_attribute('type_constraint' => (
34 reader => 'type_constraint',
35 predicate => 'has_type_constraint',
37 __PACKAGE__->meta->add_attribute('trigger' => (
39 predicate => 'has_trigger',
41 __PACKAGE__->meta->add_attribute('handles' => (
43 predicate => 'has_handles',
45 __PACKAGE__->meta->add_attribute('documentation' => (
46 reader => 'documentation',
47 predicate => 'has_documentation',
49 __PACKAGE__->meta->add_attribute('traits' => (
50 reader => 'applied_traits',
51 predicate => 'has_applied_traits',
54 # we need to have a ->does method in here to
55 # more easily support traits, and the introspection
56 # of those traits. We extend the does check to look
57 # for metatrait aliases.
59 my ($self, $role_name) = @_;
61 Moose::Util::resolve_metatrait_alias(Attribute => $role_name)
63 return 0 if !defined($name); # failed to load class
64 return Moose::Object::does($self, $name);
68 my ($class, $name, %options) = @_;
69 $class->_process_options($name, \%options) unless $options{__hack_no_process_options}; # used from clone()... YECHKKK FIXME ICKY YUCK GROSS
70 return $class->SUPER::new($name, %options);
73 sub interpolate_class_and_new {
74 my ($class, $name, @args) = @_;
76 my ( $new_class, @traits ) = $class->interpolate_class(@args);
78 $new_class->new($name, @args, ( scalar(@traits) ? ( traits => \@traits ) : () ) );
81 sub interpolate_class {
82 my ($class, %options) = @_;
84 $class = ref($class) || $class;
86 if ( my $metaclass_name = delete $options{metaclass} ) {
87 my $new_class = Moose::Util::resolve_metaclass_alias( Attribute => $metaclass_name );
89 if ( $class ne $new_class ) {
90 if ( $new_class->can("interpolate_class") ) {
91 return $new_class->interpolate_class(%options);
100 if (my $traits = $options{traits}) {
101 if ( @traits = grep { not $class->does($_) } map {
102 Moose::Util::resolve_metatrait_alias( Attribute => $_ )
106 my $anon_class = Moose::Meta::Class->create_anon_class(
107 superclasses => [ $class ],
108 roles => [ @traits ],
112 $class = $anon_class->name;
116 return ( wantarray ? ( $class, @traits ) : $class );
121 my @legal_options_for_inheritance = qw(
122 default coerce required
123 documentation lazy handles
124 builder type_constraint
127 sub legal_options_for_inheritance { @legal_options_for_inheritance }
130 # This method *must* be able to handle
131 # Class::MOP::Attribute instances as
132 # well. Yes, I know that is wrong, but
133 # apparently we didn't realize it was
134 # doing that and now we have some code
135 # which is dependent on it. The real
136 # solution of course is to push this
137 # feature back up into Class::MOP::Attribute
138 # but I not right now, I am too lazy.
139 # However if you are reading this and
140 # looking for something to do,.. please
143 sub clone_and_inherit_options {
144 my ($self, %options) = @_;
151 # we may want to extends a Class::MOP::Attribute
152 # in which case we need to be able to use the
153 # core set of legal options that have always
154 # been here. But we allows Moose::Meta::Attribute
155 # instances to changes them.
157 my @legal_options = $self->can('legal_options_for_inheritance')
158 ? $self->legal_options_for_inheritance
159 : @legal_options_for_inheritance;
161 foreach my $legal_option (@legal_options) {
162 if (exists $options{$legal_option}) {
163 $actual_options{$legal_option} = $options{$legal_option};
164 delete $options{$legal_option};
170 if (blessed($options{isa}) && $options{isa}->isa('Moose::Meta::TypeConstraint')) {
171 $type_constraint = $options{isa};
174 $type_constraint = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options{isa});
175 (defined $type_constraint)
176 || confess "Could not find the type constraint '" . $options{isa} . "'";
179 $actual_options{type_constraint} = $type_constraint;
180 delete $options{isa};
183 if ($options{does}) {
185 if (blessed($options{does}) && $options{does}->isa('Moose::Meta::TypeConstraint')) {
186 $type_constraint = $options{does};
189 $type_constraint = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options{does});
190 (defined $type_constraint)
191 || confess "Could not find the type constraint '" . $options{does} . "'";
194 $actual_options{type_constraint} = $type_constraint;
195 delete $options{does};
199 # this doesn't apply to Class::MOP::Attributes,
200 # so we can ignore it for them.
202 if ($self->can('interpolate_class')) {
203 ( $actual_options{metaclass}, my @traits ) = $self->interpolate_class(%options);
206 my @all_traits = grep { $seen{$_}++ } @{ $self->applied_traits || [] }, @traits;
207 $actual_options{traits} = \@all_traits if @all_traits;
209 delete @options{qw(metaclass traits)};
212 (scalar keys %options == 0)
213 || confess "Illegal inherited options => (" . (join ', ' => keys %options) . ")";
216 $self->clone(%actual_options);
220 my ( $self, %params ) = @_;
222 my $class = $params{metaclass} || ref $self;
224 if ( 0 and $class eq ref $self ) {
225 return $self->SUPER::clone(%params);
227 my ( @init, @non_init );
229 foreach my $attr ( grep { $_->has_value($self) } $self->meta->compute_all_applicable_attributes ) {
230 push @{ $attr->has_init_arg ? \@init : \@non_init }, $attr;
233 my %new_params = ( ( map { $_->init_arg => $_->get_value($self) } @init ), %params );
235 my $name = delete $new_params{name};
237 my $clone = $class->new($name, %new_params, __hack_no_process_options => 1 );
239 foreach my $attr ( @non_init ) {
240 $attr->set_value($clone, $attr->get_value($self));
248 sub _process_options {
249 my ($class, $name, $options) = @_;
251 if (exists $options->{is}) {
253 ### -------------------------
254 ## is => ro, writer => _foo # turns into (reader => foo, writer => _foo) as before
255 ## is => rw, writer => _foo # turns into (reader => foo, writer => _foo)
256 ## is => rw, accessor => _foo # turns into (accessor => _foo)
257 ## is => ro, accessor => _foo # error, accesor is rw
258 ### -------------------------
260 if ($options->{is} eq 'ro') {
261 confess "Cannot define an accessor name on a read-only attribute, accessors are read/write"
262 if exists $options->{accessor};
263 $options->{reader} ||= $name;
265 elsif ($options->{is} eq 'rw') {
266 if ($options->{writer}) {
267 $options->{reader} ||= $name;
270 $options->{accessor} ||= $name;
274 confess "I do not understand this option (is => " . $options->{is} . ") on attribute ($name)"
278 if (exists $options->{isa}) {
279 if (exists $options->{does}) {
280 if (eval { $options->{isa}->can('does') }) {
281 ($options->{isa}->does($options->{does}))
282 || confess "Cannot have an isa option and a does option if the isa does not do the does on attribute ($name)";
285 confess "Cannot have an isa option which cannot ->does() on attribute ($name)";
289 # allow for anon-subtypes here ...
290 if (blessed($options->{isa}) && $options->{isa}->isa('Moose::Meta::TypeConstraint')) {
291 $options->{type_constraint} = $options->{isa};
294 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options->{isa});
297 elsif (exists $options->{does}) {
298 # allow for anon-subtypes here ...
299 if (blessed($options->{does}) && $options->{does}->isa('Moose::Meta::TypeConstraint')) {
300 $options->{type_constraint} = $options->{does};
303 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options->{does});
307 if (exists $options->{coerce} && $options->{coerce}) {
308 (exists $options->{type_constraint})
309 || confess "You cannot have coercion without specifying a type constraint on attribute ($name)";
310 confess "You cannot have a weak reference to a coerced value on attribute ($name)"
311 if $options->{weak_ref};
314 if (exists $options->{trigger}) {
315 my $trig = $options->{trigger};
316 if ('HASH' eq ref $trig) {
317 my $legal = qr{^(?:before|after|around)$};
318 foreach my $key (keys %$trig) {
320 || confess "$key is an illegal trigger specifier"
321 . " on attribute ($name)";
322 ('CODE' eq ref $trig->{$key})
323 || confess "$key trigger must be CODE ref"
324 . " on attribute ($name)";
327 elsif ('CODE' ne ref $trig) {
328 confess "Trigger must be a CODE or HASH ref on attribute ($name)";
332 if (exists $options->{auto_deref} && $options->{auto_deref}) {
333 (exists $options->{type_constraint})
334 || confess "You cannot auto-dereference without specifying a type constraint on attribute ($name)";
335 ($options->{type_constraint}->is_a_type_of('ArrayRef') ||
336 $options->{type_constraint}->is_a_type_of('HashRef'))
337 || confess "You cannot auto-dereference anything other than a ArrayRef or HashRef on attribute ($name)";
340 if (exists $options->{lazy_build} && $options->{lazy_build} == 1) {
341 confess("You can not use lazy_build and default for the same attribute ($name)")
342 if exists $options->{default};
343 $options->{lazy} = 1;
344 $options->{required} = 1;
345 $options->{builder} ||= "_build_${name}";
347 $options->{clearer} ||= "_clear${name}";
348 $options->{predicate} ||= "_has${name}";
351 $options->{clearer} ||= "clear_${name}";
352 $options->{predicate} ||= "has_${name}";
356 if (exists $options->{lazy} && $options->{lazy}) {
357 (exists $options->{default} || defined $options->{builder} )
358 || confess "You cannot have lazy attribute ($name) without specifying a default value for it";
361 if ( $options->{required} && !( ( !exists $options->{init_arg} || defined $options->{init_arg} ) || exists $options->{default} || defined $options->{builder} ) ) {
362 confess "You cannot have a required attribute ($name) without a default, builder, or an init_arg";
367 sub _with_inline_triggers {
368 my ($self, $instance, $value, $attr, $gen_code) = @_;
369 my @ga = ($instance, $value, $attr);
370 return $gen_code->(@ga) unless $self->has_trigger;
372 my $trigger_args = "$instance, $value, $attr";
374 if ('CODE' eq ref $self->trigger) {
375 return $gen_code->(@ga) . "$attr->trigger->($trigger_args);\n";
379 my ($before, $around, $after) = @{$self->trigger}{qw(before around after)};
382 $code .= "$attr->trigger->{before}->($trigger_args);\n";
386 $code .= "$attr->trigger->{around}->(sub {\n"
387 . 'my ($instance, $value, $attr) = @_;' . "\n"
388 . $gen_code->('$instance', '$value', '$attr')
389 . "}, $trigger_args);\n";
392 $code .= $gen_code->(@ga);
396 $code .= "$attr->trigger->{after}->($trigger_args);\n";
403 my ($self, $instance, $value, $fn) = @_;
404 my @trigger_args = ($instance, $value, $self);
405 my ($before, $around, $after);
407 if ($self->has_trigger) {
408 my $trig = $self->trigger;
410 if ('HASH' eq ref $trig) {
411 ($before, $around, $after) = @{$trig}{qw(before around after)}
419 $before->(@trigger_args);
423 $around->($fn, @trigger_args);
426 $fn->(@trigger_args);
430 $after->(@trigger_args);
434 sub initialize_instance_slot {
435 my ($self, $meta_instance, $instance, $params) = @_;
436 my $init_arg = $self->init_arg();
437 # try to fetch the init arg from the %params ...
441 if ( defined($init_arg) and exists $params->{$init_arg}) {
442 $val = $params->{$init_arg};
446 # skip it if it's lazy
447 return if $self->is_lazy;
448 # and die if it's required and doesn't have a default value
449 confess "Attribute (" . $self->name . ") is required"
450 if $self->is_required && !$self->has_default && !$self->has_builder;
452 # if nothing was in the %params, we can use the
453 # attribute's default value (if it has one)
454 if ($self->has_default) {
455 $val = $self->default($instance);
458 elsif ($self->has_builder) {
459 if (my $builder = $instance->can($self->builder)){
460 $val = $instance->$builder;
464 confess(blessed($instance)." does not support builder method '".$self->builder."' for attribute '" . $self->name . "'");
469 return unless $value_is_set;
471 if ($self->has_type_constraint) {
472 my $type_constraint = $self->type_constraint;
473 if ($self->should_coerce && $type_constraint->has_coercion) {
474 $val = $type_constraint->coerce($val);
476 $type_constraint->check($val)
477 || confess "Attribute ("
479 . ") does not pass the type constraint because: "
480 . $type_constraint->get_message($val);
483 $self->_with_triggers($instance, $val, sub {
484 my ($ins, $val, $attr) = @_;
485 my $mi = Class::MOP::Class->initialize(blessed($ins))
487 $attr->set_initial_value($ins, $val);
488 $mi->weaken_slot_value($ins, $attr->name)
489 if ref $val && $attr->is_weak_ref;
496 # this duplicates too much code from
497 # Class::MOP::Attribute, we need to
498 # refactor these bits eventually.
500 sub _set_initial_slot_value {
501 my ($self, $meta_instance, $instance, $value) = @_;
503 my $slot_name = $self->name;
505 return $meta_instance->set_slot_value($instance, $slot_name, $value)
506 unless $self->has_initializer;
508 my ($type_constraint, $can_coerce);
509 if ($self->has_type_constraint) {
510 $type_constraint = $self->type_constraint;
511 $can_coerce = ($self->should_coerce && $type_constraint->has_coercion);
516 if ($type_constraint) {
517 $val = $type_constraint->coerce($val)
519 $type_constraint->check($val)
520 || confess "Attribute ("
522 . ") does not pass the type constraint because: "
523 . $type_constraint->get_message($val);
525 $meta_instance->set_slot_value($instance, $slot_name, $val);
528 my $initializer = $self->initializer;
530 # most things will just want to set a value, so make it first arg
531 $instance->$initializer($value, $callback, $self);
535 my ($self, $instance, @args) = @_;
536 my $value = $args[0];
538 my $attr_name = $self->name;
540 if ($self->is_required and not @args) {
541 confess "Attribute ($attr_name) is required";
544 if ($self->has_type_constraint) {
546 my $type_constraint = $self->type_constraint;
548 if ($self->should_coerce) {
549 $value = $type_constraint->coerce($value);
551 $type_constraint->_compiled_type_constraint->($value)
552 || confess "Attribute ("
554 . ") does not pass the type constraint because "
555 . $type_constraint->get_message($value);
558 $self->_with_triggers($instance, $value, sub {
559 my ($ins, $val, $attr) = @_;
560 my $mi = Class::MOP::Class->initialize(blessed($ins))
562 $mi->set_slot_value($ins, $attr->name, $val);
563 $mi->weaken_slot_value($ins, $attr->name)
564 if (ref $val && $attr->is_weak_ref);
569 my ($self, $instance) = @_;
571 if ($self->is_lazy) {
572 unless ($self->has_value($instance)) {
573 if ($self->has_default) {
574 my $default = $self->default($instance);
575 $self->set_initial_value($instance, $default);
576 } elsif ( $self->has_builder ) {
577 if (my $builder = $instance->can($self->builder)){
578 $self->set_initial_value($instance, $instance->$builder);
581 confess(blessed($instance)
582 . " does not support builder method '"
584 . "' for attribute '"
590 $self->set_initial_value($instance, undef);
595 if ($self->should_auto_deref) {
597 my $type_constraint = $self->type_constraint;
599 if ($type_constraint->is_a_type_of('ArrayRef')) {
600 my $rv = $self->SUPER::get_value($instance);
601 return unless defined $rv;
602 return wantarray ? @{ $rv } : $rv;
604 elsif ($type_constraint->is_a_type_of('HashRef')) {
605 my $rv = $self->SUPER::get_value($instance);
606 return unless defined $rv;
607 return wantarray ? %{ $rv } : $rv;
610 confess "Can not auto de-reference the type constraint '" . $type_constraint->name . "'";
616 return $self->SUPER::get_value($instance);
620 ## installing accessors
622 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
624 sub install_accessors {
626 $self->SUPER::install_accessors(@_);
627 $self->install_delegation if $self->has_handles;
631 sub install_delegation {
635 # Here we canonicalize the 'handles' option
636 # this will sort out any details and always
637 # return an hash of methods which we want
638 # to delagate to, see that method for details
639 my %handles = $self->_canonicalize_handles;
641 # find the accessor method for this attribute
642 my $accessor = $self->_get_delegate_accessor;
644 # install the delegation ...
645 my $associated_class = $self->associated_class;
646 foreach my $handle (keys %handles) {
647 my $method_to_call = $handles{$handle};
648 my $class_name = $associated_class->name;
649 my $name = "${class_name}::${handle}";
651 (!$associated_class->has_method($handle))
652 || confess "You cannot overwrite a locally defined method ($handle) with a delegation";
655 # handles is not allowed to delegate
656 # any of these methods, as they will
657 # override the ones in your class, which
658 # is almost certainly not what you want.
660 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
661 #cluck("Not delegating method '$handle' because it is a core method") and
662 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
664 if ('CODE' eq ref($method_to_call)) {
665 $associated_class->add_method($handle => Class::MOP::subname($name, $method_to_call));
669 # we used to do a goto here, but the
670 # goto didn't handle failure correctly
671 # (it just returned nothing), so I took
672 # that out. However, the more I thought
673 # about it, the less I liked it doing
674 # the goto, and I prefered the act of
675 # delegation being actually represented
676 # in the stack trace.
678 $associated_class->add_method($handle => Class::MOP::subname($name, sub {
679 my $proxy = (shift)->$accessor();
681 || confess "Cannot delegate $handle to $method_to_call because " .
682 "the value of " . $self->name . " is not defined";
683 $proxy->$method_to_call(@_);
689 # private methods to help delegation ...
691 sub _get_delegate_accessor {
693 # find the accessor method for this attribute
694 my $accessor = $self->get_read_method_ref;
695 # then unpack it if we need too ...
696 $accessor = $accessor->body if blessed $accessor;
697 # return the accessor
701 sub _canonicalize_handles {
703 my $handles = $self->handles;
704 if (my $handle_type = ref($handles)) {
705 if ($handle_type eq 'HASH') {
708 elsif ($handle_type eq 'ARRAY') {
709 return map { $_ => $_ } @{$handles};
711 elsif ($handle_type eq 'Regexp') {
712 ($self->has_type_constraint)
713 || confess "Cannot delegate methods based on a RegExpr without a type constraint (isa)";
714 return map { ($_ => $_) }
715 grep { /$handles/ } $self->_get_delegate_method_list;
717 elsif ($handle_type eq 'CODE') {
718 return $handles->($self, $self->_find_delegate_metaclass);
721 confess "Unable to canonicalize the 'handles' option with $handles";
725 my $role_meta = eval { $handles->meta };
727 confess "Unable to canonicalize the 'handles' option with $handles because : $@";
730 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
731 || confess "Unable to canonicalize the 'handles' option with $handles because ->meta is not a Moose::Meta::Role";
733 return map { $_ => $_ } (
734 $role_meta->get_method_list,
735 $role_meta->get_required_method_list
740 sub _find_delegate_metaclass {
742 if (my $class = $self->_isa_metadata) {
743 # if the class does have
744 # a meta method, use it
745 return $class->meta if $class->can('meta');
746 # otherwise we might be
747 # dealing with a non-Moose
748 # class, and need to make
750 return Moose::Meta::Class->initialize($class);
752 elsif (my $role = $self->_does_metadata) {
753 # our role will always have
758 confess "Cannot find delegate metaclass for attribute " . $self->name;
762 sub _get_delegate_method_list {
764 my $meta = $self->_find_delegate_metaclass;
765 if ($meta->isa('Class::MOP::Class')) {
766 return map { $_->{name} } # NOTE: !never! delegate &meta
767 grep { $_->{class} ne 'Moose::Object' && $_->{name} ne 'meta' }
768 $meta->compute_all_applicable_methods;
770 elsif ($meta->isa('Moose::Meta::Role')) {
771 return $meta->get_method_list;
774 confess "Unable to recognize the delegate metaclass '$meta'";
778 package Moose::Meta::Attribute::Custom::Moose;
779 sub register_implementation { 'Moose::Meta::Attribute' }
789 Moose::Meta::Attribute - The Moose attribute metaclass
793 This is a subclass of L<Class::MOP::Attribute> with Moose specific
796 For the most part, the only time you will ever encounter an
797 instance of this class is if you are doing some serious deep
798 introspection. To really understand this class, you need to refer
799 to the L<Class::MOP::Attribute> documentation.
803 =head2 Overridden methods
805 These methods override methods in L<Class::MOP::Attribute> and add
806 Moose specific features. You can safely assume though that they
807 will behave just as L<Class::MOP::Attribute> does.
817 =item B<initialize_instance_slot>
819 =item B<install_accessors>
821 =item B<install_delegation>
823 =item B<accessor_metaclass>
829 eval { $point->meta->get_attribute('x')->set_value($point, 'fourty-two') };
834 I<Attribute (x) does not pass the type constraint (Int) with 'fourty-two'>
836 Before setting the value, a check is made on the type constraint of
837 the attribute, if it has one, to see if the value passes it. If the
838 value fails to pass, the set operation dies with a L<Carp/confess>.
840 Any coercion to convert values is done before checking the type constraint.
842 To check a value against a type constraint before setting it, fetch the
843 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
844 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
845 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::RecipeX>
850 =head2 Additional Moose features
852 Moose attributes support type-constraint checking, weak reference
853 creation and type coercion.
857 =item B<interpolate_class_and_new>
859 =item B<interpolate_class>
861 When called as a class method causes interpretation of the C<metaclass> and
864 =item B<clone_and_inherit_options>
866 This is to support the C<has '+foo'> feature, it clones an attribute
867 from a superclass and allows a very specific set of changes to be made
870 =item B<legal_options_for_inheritance>
872 Whitelist with options you can change. You can overload it in your custom
873 metaclass to allow your options be inheritable.
875 =item B<has_type_constraint>
877 Returns true if this meta-attribute has a type constraint.
879 =item B<type_constraint>
881 A read-only accessor for this meta-attribute's type constraint. For
882 more information on what you can do with this, see the documentation
883 for L<Moose::Meta::TypeConstraint>.
887 Returns true if this meta-attribute performs delegation.
891 This returns the value which was passed into the handles option.
895 Returns true if this meta-attribute produces a weak reference.
899 Returns true if this meta-attribute is required to have a value.
903 Returns true if this meta-attribute should be initialized lazily.
905 NOTE: lazy attributes, B<must> have a C<default> or C<builder> field set.
907 =item B<is_lazy_build>
909 Returns true if this meta-attribute should be initialized lazily through
910 the builder generated by lazy_build. Using C<lazy_build =E<gt> 1> will
911 make your attribute required and lazy. In addition it will set the builder, clearer
912 and predicate options for you using the following convention.
914 #If your attribute name starts with an underscore:
915 has '_foo' => (lazy_build => 1);
917 has '_foo' => (lazy => 1, required => 1, predicate => '_has_foo', clearer => '_clear_foo', builder => '_build__foo);
919 has '_foo' => (lazy => 1, required => 1, predicate => '_has_foo', clearer => '_clear_foo', default => sub{shift->_build__foo});
921 #If your attribute name does not start with an underscore:
922 has 'foo' => (lazy_build => 1);
924 has 'foo' => (lazy => 1, required => 1, predicate => 'has_foo', clearer => 'clear_foo', builder => '_build_foo);
926 has 'foo' => (lazy => 1, required => 1, predicate => 'has_foo', clearer => 'clear_foo', default => sub{shift->_build_foo});
928 The reason for the different naming of the C<builder> is that the C<builder>
929 method is a private method while the C<clearer> and C<predicate> methods
932 NOTE: This means your class should provide a method whose name matches the value
933 of the builder part, in this case _build__foo or _build_foo.
935 =item B<should_coerce>
937 Returns true if this meta-attribute should perform type coercion.
939 =item B<should_auto_deref>
941 Returns true if this meta-attribute should perform automatic
944 NOTE: This can only be done for attributes whose type constraint is
945 either I<ArrayRef> or I<HashRef>.
949 Returns true if this meta-attribute has a trigger set.
953 This is a CODE reference which will be executed every time the
954 value of an attribute is assigned. The CODE ref will get two values,
955 the invocant and the new value. This can be used to handle I<basic>
956 bi-directional relations.
958 =item B<documentation>
960 This is a string which contains the documentation for this attribute.
961 It serves no direct purpose right now, but it might in the future
962 in some kind of automated documentation system perhaps.
964 =item B<has_documentation>
966 Returns true if this meta-attribute has any documentation.
968 =item B<applied_traits>
970 This will return the ARRAY ref of all the traits applied to this
971 attribute, or if no traits have been applied, it returns C<undef>.
973 =item B<has_applied_traits>
975 Returns true if this meta-attribute has any traits applied.
981 All complex software has bugs lurking in it, and this module is no
982 exception. If you find a bug please either email me, or add the bug
987 Stevan Little E<lt>stevan@iinteractive.comE<gt>
989 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
991 =head1 COPYRIGHT AND LICENSE
993 Copyright 2006-2008 by Infinity Interactive, Inc.
995 L<http://www.iinteractive.com>
997 This library is free software; you can redistribute it and/or modify
998 it under the same terms as Perl itself.