2 package Moose::Meta::Attribute;
8 use Scalar::Util 'blessed', 'weaken';
9 use List::MoreUtils 'any';
13 our $VERSION = '1.17';
14 our $AUTHORITY = 'cpan:STEVAN';
16 use Moose::Deprecated;
17 use Moose::Meta::Method::Accessor;
18 use Moose::Meta::Method::Delegation;
20 use Moose::Util::TypeConstraints ();
21 use Class::MOP::MiniTrait;
23 use base 'Class::MOP::Attribute', 'Moose::Meta::Mixin::AttributeCore';
25 Class::MOP::MiniTrait::apply(__PACKAGE__, 'Moose::Meta::Object::Trait');
27 __PACKAGE__->meta->add_attribute('traits' => (
28 reader => 'applied_traits',
29 predicate => 'has_applied_traits',
32 # we need to have a ->does method in here to
33 # more easily support traits, and the introspection
34 # of those traits. We extend the does check to look
35 # for metatrait aliases.
37 my ($self, $role_name) = @_;
39 Moose::Util::resolve_metatrait_alias(Attribute => $role_name)
41 return 0 if !defined($name); # failed to load class
42 return $self->Moose::Object::does($name);
47 my $class = ( ref $self && $self->associated_class ) || "Moose::Meta::Class";
48 unshift @_, "message" if @_ % 2 == 1;
49 unshift @_, attr => $self if ref $self;
51 my $handler = $class->can("throw_error"); # to avoid incrementing depth by 1
56 my ($class, $name, %options) = @_;
57 $class->_process_options($name, \%options) unless $options{__hack_no_process_options}; # used from clone()... YECHKKK FIXME ICKY YUCK GROSS
59 delete $options{__hack_no_process_options};
64 map { $_->init_arg() }
65 $class->meta()->get_all_attributes()
68 my @bad = sort grep { ! $attrs{$_} } keys %options;
72 Carp::cluck "Found unknown argument(s) passed to '$name' attribute constructor in '$class': @bad";
75 return $class->SUPER::new($name, %options);
78 sub interpolate_class_and_new {
79 my ($class, $name, %args) = @_;
81 my ( $new_class, @traits ) = $class->interpolate_class(\%args);
83 $new_class->new($name, %args, ( scalar(@traits) ? ( traits => \@traits ) : () ) );
86 sub interpolate_class {
87 my ($class, $options) = @_;
89 $class = ref($class) || $class;
91 if ( my $metaclass_name = delete $options->{metaclass} ) {
92 my $new_class = Moose::Util::resolve_metaclass_alias( Attribute => $metaclass_name );
94 if ( $class ne $new_class ) {
95 if ( $new_class->can("interpolate_class") ) {
96 return $new_class->interpolate_class($options);
105 if (my $traits = $options->{traits}) {
107 while ($i < @$traits) {
108 my $trait = $traits->[$i++];
109 next if ref($trait); # options to a trait we discarded
111 $trait = Moose::Util::resolve_metatrait_alias(Attribute => $trait)
114 next if $class->does($trait);
116 push @traits, $trait;
119 push @traits, $traits->[$i++]
120 if $traits->[$i] && ref($traits->[$i]);
124 my $anon_class = Moose::Meta::Class->create_anon_class(
125 superclasses => [ $class ],
126 roles => [ @traits ],
130 $class = $anon_class->name;
134 return ( wantarray ? ( $class, @traits ) : $class );
139 # method-generating options shouldn't be overridden
140 sub illegal_options_for_inheritance {
141 qw(reader writer accessor clearer predicate)
145 # This method *must* be able to handle
146 # Class::MOP::Attribute instances as
147 # well. Yes, I know that is wrong, but
148 # apparently we didn't realize it was
149 # doing that and now we have some code
150 # which is dependent on it. The real
151 # solution of course is to push this
152 # feature back up into Class::MOP::Attribute
153 # but I not right now, I am too lazy.
154 # However if you are reading this and
155 # looking for something to do,.. please
158 sub clone_and_inherit_options {
159 my ($self, %options) = @_;
162 # we may want to extends a Class::MOP::Attribute
163 # in which case we need to be able to use the
164 # core set of legal options that have always
165 # been here. But we allows Moose::Meta::Attribute
166 # instances to changes them.
168 my @illegal_options = $self->can('illegal_options_for_inheritance')
169 ? $self->illegal_options_for_inheritance
172 my @found_illegal_options = grep { exists $options{$_} && exists $self->{$_} ? $_ : undef } @illegal_options;
173 (scalar @found_illegal_options == 0)
174 || $self->throw_error("Illegal inherited options => (" . (join ', ' => @found_illegal_options) . ")", data => \%options);
178 if (blessed($options{isa}) && $options{isa}->isa('Moose::Meta::TypeConstraint')) {
179 $type_constraint = $options{isa};
182 $type_constraint = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options{isa});
183 (defined $type_constraint)
184 || $self->throw_error("Could not find the type constraint '" . $options{isa} . "'", data => $options{isa});
187 $options{type_constraint} = $type_constraint;
190 if ($options{does}) {
192 if (blessed($options{does}) && $options{does}->isa('Moose::Meta::TypeConstraint')) {
193 $type_constraint = $options{does};
196 $type_constraint = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options{does});
197 (defined $type_constraint)
198 || $self->throw_error("Could not find the type constraint '" . $options{does} . "'", data => $options{does});
201 $options{type_constraint} = $type_constraint;
205 # this doesn't apply to Class::MOP::Attributes,
206 # so we can ignore it for them.
208 if ($self->can('interpolate_class')) {
209 ( $options{metaclass}, my @traits ) = $self->interpolate_class(\%options);
212 my @all_traits = grep { $seen{$_}++ } @{ $self->applied_traits || [] }, @traits;
213 $options{traits} = \@all_traits if @all_traits;
216 $self->_modify_attr_options_for_lazy_build( $self->name, \%options );
218 $self->clone(%options);
222 my ( $self, %params ) = @_;
224 my $class = delete $params{metaclass} || ref $self;
226 my ( @init, @non_init );
228 foreach my $attr ( grep { $_->has_value($self) } Class::MOP::class_of($self)->get_all_attributes ) {
229 push @{ $attr->has_init_arg ? \@init : \@non_init }, $attr;
232 my %new_params = ( ( map { $_->init_arg => $_->get_value($self) } @init ), %params );
234 my $name = delete $new_params{name};
236 my $clone = $class->new($name, %new_params, __hack_no_process_options => 1 );
238 foreach my $attr ( @non_init ) {
239 $attr->set_value($clone, $attr->get_value($self));
245 sub _process_options {
246 my ($class, $name, $options) = @_;
248 if (exists $options->{is}) {
250 ### -------------------------
251 ## is => ro, writer => _foo # turns into (reader => foo, writer => _foo) as before
252 ## is => rw, writer => _foo # turns into (reader => foo, writer => _foo)
253 ## is => rw, accessor => _foo # turns into (accessor => _foo)
254 ## is => ro, accessor => _foo # error, accesor is rw
255 ### -------------------------
257 if ($options->{is} eq 'ro') {
258 $class->throw_error("Cannot define an accessor name on a read-only attribute, accessors are read/write", data => $options)
259 if exists $options->{accessor};
260 $options->{reader} ||= $name;
262 elsif ($options->{is} eq 'rw') {
263 if ($options->{writer}) {
264 $options->{reader} ||= $name;
267 $options->{accessor} ||= $name;
270 elsif ($options->{is} eq 'bare') {
271 # do nothing, but don't complain (later) about missing methods
274 $class->throw_error("I do not understand this option (is => " . $options->{is} . ") on attribute ($name)", data => $options->{is});
278 if (exists $options->{isa}) {
279 if (exists $options->{does}) {
280 if (try { $options->{isa}->can('does') }) {
281 ($options->{isa}->does($options->{does}))
282 || $class->throw_error("Cannot have an isa option and a does option if the isa does not do the does on attribute ($name)", data => $options);
285 $class->throw_error("Cannot have an isa option which cannot ->does() on attribute ($name)", data => $options);
289 # allow for anon-subtypes here ...
290 if (blessed($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 || $class->throw_error("You cannot have coercion without specifying a type constraint on attribute ($name)", data => $options);
310 $class->throw_error("You cannot have a weak reference to a coerced value on attribute ($name)", data => $options)
311 if $options->{weak_ref};
313 unless ( $options->{type_constraint}->has_coercion ) {
314 my $type = $options->{type_constraint}->name;
316 Moose::Deprecated::deprecated(
317 feature => 'coerce without coercion',
319 "You cannot coerce an attribute ($name) unless its type ($type) has a coercion"
324 if (exists $options->{trigger}) {
325 ('CODE' eq ref $options->{trigger})
326 || $class->throw_error("Trigger must be a CODE ref on attribute ($name)", data => $options->{trigger});
329 if (exists $options->{auto_deref} && $options->{auto_deref}) {
330 (exists $options->{type_constraint})
331 || $class->throw_error("You cannot auto-dereference without specifying a type constraint on attribute ($name)", data => $options);
332 ($options->{type_constraint}->is_a_type_of('ArrayRef') ||
333 $options->{type_constraint}->is_a_type_of('HashRef'))
334 || $class->throw_error("You cannot auto-dereference anything other than a ArrayRef or HashRef on attribute ($name)", data => $options);
337 $class->_modify_attr_options_for_lazy_build( $name, $options );
339 if (exists $options->{lazy} && $options->{lazy}) {
340 (exists $options->{default} || defined $options->{builder} )
341 || $class->throw_error("You cannot have lazy attribute ($name) without specifying a default value for it", data => $options);
344 if ( $options->{required} && !( ( !exists $options->{init_arg} || defined $options->{init_arg} ) || exists $options->{default} || defined $options->{builder} ) ) {
345 $class->throw_error("You cannot have a required attribute ($name) without a default, builder, or an init_arg", data => $options);
350 sub _modify_attr_options_for_lazy_build {
351 my ( $class, $name, $options ) = @_;
353 return unless $options->{lazy_build};
356 "You can not use lazy_build and default for the same attribute ($name)",
358 if exists $options->{default};
360 $options->{lazy} = 1;
361 $options->{builder} ||= "_build_${name}";
362 if ( $name =~ /^_/ ) {
363 $options->{clearer} ||= "_clear${name}";
364 $options->{predicate} ||= "_has${name}";
367 $options->{clearer} ||= "clear_${name}";
368 $options->{predicate} ||= "has_${name}";
372 sub initialize_instance_slot {
373 my ($self, $meta_instance, $instance, $params) = @_;
374 my $init_arg = $self->init_arg();
375 # try to fetch the init arg from the %params ...
379 if ( defined($init_arg) and exists $params->{$init_arg}) {
380 $val = $params->{$init_arg};
384 # skip it if it's lazy
385 return if $self->is_lazy;
386 # and die if it's required and doesn't have a default value
387 $self->throw_error("Attribute (" . $self->name . ") is required", object => $instance, data => $params)
388 if $self->is_required && !$self->has_default && !$self->has_builder;
390 # if nothing was in the %params, we can use the
391 # attribute's default value (if it has one)
392 if ($self->has_default) {
393 $val = $self->default($instance);
396 elsif ($self->has_builder) {
397 $val = $self->_call_builder($instance);
402 return unless $value_is_set;
404 $val = $self->_coerce_and_verify( $val, $instance );
406 $self->set_initial_value($instance, $val);
408 if ( ref $val && $self->is_weak_ref ) {
409 $self->_weaken_value($instance);
414 my ( $self, $instance ) = @_;
416 my $builder = $self->builder();
418 return $instance->$builder()
419 if $instance->can( $self->builder );
421 $self->throw_error( blessed($instance)
422 . " does not support builder method '"
424 . "' for attribute '"
434 # this duplicates too much code from
435 # Class::MOP::Attribute, we need to
436 # refactor these bits eventually.
438 sub _set_initial_slot_value {
439 my ($self, $meta_instance, $instance, $value) = @_;
441 my $slot_name = $self->name;
443 return $meta_instance->set_slot_value($instance, $slot_name, $value)
444 unless $self->has_initializer;
447 my $val = $self->_coerce_and_verify( shift, $instance );;
449 $meta_instance->set_slot_value($instance, $slot_name, $val);
452 my $initializer = $self->initializer;
454 # most things will just want to set a value, so make it first arg
455 $instance->$initializer($value, $callback, $self);
459 my ($self, $instance, @args) = @_;
460 my $value = $args[0];
462 my $attr_name = $self->name;
464 if ($self->is_required and not @args) {
465 $self->throw_error("Attribute ($attr_name) is required", object => $instance);
468 $value = $self->_coerce_and_verify( $value, $instance );
471 if ( $self->has_trigger && $self->has_value($instance) ) {
472 @old = $self->get_value($instance, 'for trigger');
475 $self->SUPER::set_value($instance, $value);
477 if ( ref $value && $self->is_weak_ref ) {
478 $self->_weaken_value($instance);
481 if ($self->has_trigger) {
482 $self->trigger->($instance, $value, @old);
487 my ( $self, $instance ) = @_;
489 my $meta_instance = Class::MOP::Class->initialize( blessed($instance) )
492 $meta_instance->weaken_slot_value( $instance, $self->name );
496 my ($self, $instance, $for_trigger) = @_;
498 if ($self->is_lazy) {
499 unless ($self->has_value($instance)) {
501 if ($self->has_default) {
502 $value = $self->default($instance);
503 } elsif ( $self->has_builder ) {
504 $value = $self->_call_builder($instance);
507 $value = $self->_coerce_and_verify( $value, $instance );
509 $self->set_initial_value($instance, $value);
513 if ( $self->should_auto_deref && ! $for_trigger ) {
515 my $type_constraint = $self->type_constraint;
517 if ($type_constraint->is_a_type_of('ArrayRef')) {
518 my $rv = $self->SUPER::get_value($instance);
519 return unless defined $rv;
520 return wantarray ? @{ $rv } : $rv;
522 elsif ($type_constraint->is_a_type_of('HashRef')) {
523 my $rv = $self->SUPER::get_value($instance);
524 return unless defined $rv;
525 return wantarray ? %{ $rv } : $rv;
528 $self->throw_error("Can not auto de-reference the type constraint '" . $type_constraint->name . "'", object => $instance, type_constraint => $type_constraint);
534 return $self->SUPER::get_value($instance);
538 ## installing accessors
540 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
542 sub install_accessors {
544 $self->SUPER::install_accessors(@_);
545 $self->install_delegation if $self->has_handles;
549 sub _check_associated_methods {
552 @{ $self->associated_methods }
553 || ($self->_is_metadata || '') eq 'bare'
556 'Attribute (' . $self->name . ') of class '
557 . $self->associated_class->name
558 . ' has no associated methods'
559 . ' (did you mean to provide an "is" argument?)'
565 sub _process_accessors {
567 my ($type, $accessor, $generate_as_inline_methods) = @_;
569 $accessor = ( keys %$accessor )[0] if ( ref($accessor) || '' ) eq 'HASH';
570 my $method = $self->associated_class->get_method($accessor);
574 && !$method->isa('Class::MOP::Method::Accessor')
575 && ( !$self->definition_context
576 || $method->package_name eq $self->definition_context->{package} )
580 "You are overwriting a locally defined method ($accessor) with "
583 if ( !$self->associated_class->has_method($accessor)
584 && $self->associated_class->has_package_symbol( '&' . $accessor ) ) {
587 "You are overwriting a locally defined function ($accessor) with "
591 $self->SUPER::_process_accessors(@_);
594 sub remove_accessors {
596 $self->SUPER::remove_accessors(@_);
597 $self->remove_delegation if $self->has_handles;
603 my ( $instance, $value ) = @_;
605 my $mi = $self->associated_class->get_meta_instance;
608 = $mi->inline_set_slot_value( $instance, $self->slots, $value ) . ";";
610 .= $mi->inline_weaken_slot_value( $instance, $self->slots, $value )
612 if $self->is_weak_ref;
617 sub install_delegation {
621 # Here we canonicalize the 'handles' option
622 # this will sort out any details and always
623 # return an hash of methods which we want
624 # to delagate to, see that method for details
625 my %handles = $self->_canonicalize_handles;
628 # install the delegation ...
629 my $associated_class = $self->associated_class;
630 foreach my $handle (keys %handles) {
631 my $method_to_call = $handles{$handle};
632 my $class_name = $associated_class->name;
633 my $name = "${class_name}::${handle}";
635 (!$associated_class->has_method($handle))
636 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
639 # handles is not allowed to delegate
640 # any of these methods, as they will
641 # override the ones in your class, which
642 # is almost certainly not what you want.
644 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
645 #cluck("Not delegating method '$handle' because it is a core method") and
646 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
648 my $method = $self->_make_delegation_method($handle, $method_to_call);
650 $self->associated_class->add_method($method->name, $method);
651 $self->associate_method($method);
655 sub remove_delegation {
657 my %handles = $self->_canonicalize_handles;
658 my $associated_class = $self->associated_class;
659 foreach my $handle (keys %handles) {
660 next unless any { $handle eq $_ }
662 @{ $self->associated_methods };
663 $self->associated_class->remove_method($handle);
667 # private methods to help delegation ...
669 sub _canonicalize_handles {
671 my $handles = $self->handles;
672 if (my $handle_type = ref($handles)) {
673 if ($handle_type eq 'HASH') {
676 elsif ($handle_type eq 'ARRAY') {
677 return map { $_ => $_ } @{$handles};
679 elsif ($handle_type eq 'Regexp') {
680 ($self->has_type_constraint)
681 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
682 return map { ($_ => $_) }
683 grep { /$handles/ } $self->_get_delegate_method_list;
685 elsif ($handle_type eq 'CODE') {
686 return $handles->($self, $self->_find_delegate_metaclass);
688 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::DuckType')) {
689 return map { $_ => $_ } @{ $handles->methods };
691 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::Role')) {
692 $handles = $handles->role;
695 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
699 Class::MOP::load_class($handles);
700 my $role_meta = Class::MOP::class_of($handles);
702 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
703 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because its metaclass is not a Moose::Meta::Role", data => $handles);
705 return map { $_ => $_ }
707 grep { !$_->isa('Class::MOP::Method::Meta') } (
708 $role_meta->_get_local_methods,
709 $role_meta->get_required_method_list,
713 sub _get_delegate_method_list {
715 my $meta = $self->_find_delegate_metaclass;
716 if ($meta->isa('Class::MOP::Class')) {
717 return map { $_->name } # NOTE: !never! delegate &meta
718 grep { $_->package_name ne 'Moose::Object' && !$_->isa('Class::MOP::Method::Meta') }
719 $meta->get_all_methods;
721 elsif ($meta->isa('Moose::Meta::Role')) {
722 return $meta->get_method_list;
725 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
729 sub _find_delegate_metaclass {
731 if (my $class = $self->_isa_metadata) {
732 unless ( Class::MOP::is_class_loaded($class) ) {
735 'The %s attribute is trying to delegate to a class which has not been loaded - %s',
740 # we might be dealing with a non-Moose class,
741 # and need to make our own metaclass. if there's
742 # already a metaclass, it will be returned
743 return Class::MOP::Class->initialize($class);
745 elsif (my $role = $self->_does_metadata) {
746 unless ( Class::MOP::is_class_loaded($class) ) {
749 'The %s attribute is trying to delegate to a role which has not been loaded - %s',
755 return Class::MOP::class_of($role);
758 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
762 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
764 sub _make_delegation_method {
765 my ( $self, $handle_name, $method_to_call ) = @_;
767 my @curried_arguments;
769 ($method_to_call, @curried_arguments) = @$method_to_call
770 if 'ARRAY' eq ref($method_to_call);
772 return $self->delegation_metaclass->new(
773 name => $handle_name,
774 package_name => $self->associated_class->name,
776 delegate_to_method => $method_to_call,
777 curried_arguments => \@curried_arguments,
781 sub _coerce_and_verify {
784 my $instance = shift;
786 return $val unless $self->has_type_constraint;
788 $val = $self->type_constraint->coerce($val)
789 if $self->should_coerce && $self->type_constraint->has_coercion;
791 $self->verify_against_type_constraint($val, instance => $instance);
796 sub verify_against_type_constraint {
800 return 1 if !$self->has_type_constraint;
802 my $type_constraint = $self->type_constraint;
804 $type_constraint->check($val)
805 || $self->throw_error("Attribute ("
807 . ") does not pass the type constraint because: "
808 . $type_constraint->get_message($val), data => $val, @_);
811 package Moose::Meta::Attribute::Custom::Moose;
812 sub register_implementation { 'Moose::Meta::Attribute' }
822 Moose::Meta::Attribute - The Moose attribute metaclass
826 This class is a subclass of L<Class::MOP::Attribute> that provides
827 additional Moose-specific functionality.
829 To really understand this class, you will need to start with the
830 L<Class::MOP::Attribute> documentation. This class can be understood
831 as a set of additional features on top of the basic feature provided
832 by that parent class.
836 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
840 Many of the documented below override methods in
841 L<Class::MOP::Attribute> and add Moose specific features.
847 =item B<< Moose::Meta::Attribute->new(%options) >>
849 This method overrides the L<Class::MOP::Attribute> constructor.
851 Many of the options below are described in more detail in the
852 L<Moose::Manual::Attributes> document.
854 It adds the following options to the constructor:
858 =item * is => 'ro', 'rw', 'bare'
860 This provides a shorthand for specifying the C<reader>, C<writer>, or
861 C<accessor> names. If the attribute is read-only ('ro') then it will
862 have a C<reader> method with the same attribute as the name.
864 If it is read-write ('rw') then it will have an C<accessor> method
865 with the same name. If you provide an explicit C<writer> for a
866 read-write attribute, then you will have a C<reader> with the same
867 name as the attribute, and a C<writer> with the name you provided.
869 Use 'bare' when you are deliberately not installing any methods
870 (accessor, reader, etc.) associated with this attribute; otherwise,
871 Moose will issue a deprecation warning when this attribute is added to a
876 This option accepts a type. The type can be a string, which should be
877 a type name. If the type name is unknown, it is assumed to be a class
880 This option can also accept a L<Moose::Meta::TypeConstraint> object.
882 If you I<also> provide a C<does> option, then your C<isa> option must
883 be a class name, and that class must do the role specified with
886 =item * does => $role
888 This is short-hand for saying that the attribute's type must be an
889 object which does the named role.
891 =item * coerce => $bool
893 This option is only valid for objects with a type constraint
894 (C<isa>) that defined a coercion. If this is true, then coercions will be applied whenever
895 this attribute is set.
897 You can make both this and the C<weak_ref> option true.
899 =item * trigger => $sub
901 This option accepts a subroutine reference, which will be called after
902 the attribute is set.
904 =item * required => $bool
906 An attribute which is required must be provided to the constructor. An
907 attribute which is required can also have a C<default> or C<builder>,
908 which will satisfy its required-ness.
910 A required attribute must have a C<default>, C<builder> or a
911 non-C<undef> C<init_arg>
913 =item * lazy => $bool
915 A lazy attribute must have a C<default> or C<builder>. When an
916 attribute is lazy, the default value will not be calculated until the
919 =item * weak_ref => $bool
921 If this is true, the attribute's value will be stored as a weak
924 =item * auto_deref => $bool
926 If this is true, then the reader will dereference the value when it is
927 called. The attribute must have a type constraint which defines the
928 attribute as an array or hash reference.
930 =item * lazy_build => $bool
932 Setting this to true makes the attribute lazy and provides a number of
940 is equivalent to this:
945 builder => '_build_size',
946 clearer => 'clear_size',
947 predicate => 'has_size',
950 =item * documentation
952 An arbitrary string that can be retrieved later by calling C<<
953 $attr->documentation >>.
957 =item B<< $attr->clone(%options) >>
959 This creates a new attribute based on attribute being cloned. You must
960 supply a C<name> option to provide a new name for the attribute.
962 The C<%options> can only specify options handled by
963 L<Class::MOP::Attribute>.
967 =head2 Value management
971 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
973 This method is used internally to initialize the attribute's slot in
974 the object C<$instance>.
976 This overrides the L<Class::MOP::Attribute> method to handle lazy
977 attributes, weak references, and type constraints.
983 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
988 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
990 Before setting the value, a check is made on the type constraint of
991 the attribute, if it has one, to see if the value passes it. If the
992 value fails to pass, the set operation dies with a L</throw_error>.
994 Any coercion to convert values is done before checking the type constraint.
996 To check a value against a type constraint before setting it, fetch the
997 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
998 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
999 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
1004 =head2 Attribute Accessor generation
1008 =item B<< $attr->install_accessors >>
1010 This method overrides the parent to also install delegation methods.
1012 If, after installing all methods, the attribute object has no associated
1013 methods, it throws an error unless C<< is => 'bare' >> was passed to the
1014 attribute constructor. (Trying to add an attribute that has no associated
1015 methods is almost always an error.)
1017 =item B<< $attr->remove_accessors >>
1019 This method overrides the parent to also remove delegation methods.
1021 =item B<< $attr->inline_set($instance_var, $value_var) >>
1023 This method return a code snippet suitable for inlining the relevant
1024 operation. It expect strings containing variable names to be used in the
1025 inlining, like C<'$self'> or C<'$_[1]'>.
1027 =item B<< $attr->install_delegation >>
1029 This method adds its delegation methods to the attribute's associated
1030 class, if it has any to add.
1032 =item B<< $attr->remove_delegation >>
1034 This method remove its delegation methods from the attribute's
1037 =item B<< $attr->accessor_metaclass >>
1039 Returns the accessor metaclass name, which defaults to
1040 L<Moose::Meta::Method::Accessor>.
1042 =item B<< $attr->delegation_metaclass >>
1044 Returns the delegation metaclass name, which defaults to
1045 L<Moose::Meta::Method::Delegation>.
1049 =head2 Additional Moose features
1051 These methods are not found in the superclass. They support features
1056 =item B<< $attr->does($role) >>
1058 This indicates whether the I<attribute itself> does the given
1059 role. The role can be given as a full class name, or as a resolvable
1062 Note that this checks the attribute itself, not its type constraint,
1063 so it is checking the attribute's metaclass and any traits applied to
1066 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
1068 This is an alternate constructor that handles the C<metaclass> and
1071 Effectively, this method is a factory that finds or creates the
1072 appropriate class for the given C<metaclass> and/or C<traits>.
1074 Once it has the appropriate class, it will call C<< $class->new($name,
1075 %options) >> on that class.
1077 =item B<< $attr->clone_and_inherit_options(%options) >>
1079 This method supports the C<has '+foo'> feature. It does various bits
1080 of processing on the supplied C<%options> before ultimately calling
1081 the C<clone> method.
1083 One of its main tasks is to make sure that the C<%options> provided
1084 does not include the options returned by the
1085 C<illegal_options_for_inheritance> method.
1087 =item B<< $attr->illegal_options_for_inheritance >>
1089 This returns a blacklist of options that can not be overridden in a
1090 subclass's attribute definition.
1092 This exists to allow a custom metaclass to change or add to the list
1093 of options which can not be changed.
1095 =item B<< $attr->type_constraint >>
1097 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1100 =item B<< $attr->has_type_constraint >>
1102 Returns true if this attribute has a type constraint.
1104 =item B<< $attr->verify_against_type_constraint($value) >>
1106 Given a value, this method returns true if the value is valid for the
1107 attribute's type constraint. If the value is not valid, it throws an
1110 =item B<< $attr->handles >>
1112 This returns the value of the C<handles> option passed to the
1115 =item B<< $attr->has_handles >>
1117 Returns true if this attribute performs delegation.
1119 =item B<< $attr->is_weak_ref >>
1121 Returns true if this attribute stores its value as a weak reference.
1123 =item B<< $attr->is_required >>
1125 Returns true if this attribute is required to have a value.
1127 =item B<< $attr->is_lazy >>
1129 Returns true if this attribute is lazy.
1131 =item B<< $attr->is_lazy_build >>
1133 Returns true if the C<lazy_build> option was true when passed to the
1136 =item B<< $attr->should_coerce >>
1138 Returns true if the C<coerce> option passed to the constructor was
1141 =item B<< $attr->should_auto_deref >>
1143 Returns true if the C<auto_deref> option passed to the constructor was
1146 =item B<< $attr->trigger >>
1148 This is the subroutine reference that was in the C<trigger> option
1149 passed to the constructor, if any.
1151 =item B<< $attr->has_trigger >>
1153 Returns true if this attribute has a trigger set.
1155 =item B<< $attr->documentation >>
1157 Returns the value that was in the C<documentation> option passed to
1158 the constructor, if any.
1160 =item B<< $attr->has_documentation >>
1162 Returns true if this attribute has any documentation.
1164 =item B<< $attr->applied_traits >>
1166 This returns an array reference of all the traits which were applied
1167 to this attribute. If none were applied, this returns C<undef>.
1169 =item B<< $attr->has_applied_traits >>
1171 Returns true if this attribute has any traits applied.
1177 See L<Moose/BUGS> for details on reporting bugs.
1181 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1183 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1185 =head1 COPYRIGHT AND LICENSE
1187 Copyright 2006-2010 by Infinity Interactive, Inc.
1189 L<http://www.iinteractive.com>
1191 This library is free software; you can redistribute it and/or modify
1192 it under the same terms as Perl itself.