2 package Moose::Meta::Attribute;
7 use Scalar::Util 'blessed', 'weaken';
8 use List::MoreUtils 'any';
12 our $VERSION = '1.09';
13 our $AUTHORITY = 'cpan:STEVAN';
15 use Moose::Deprecated;
16 use Moose::Meta::Method::Accessor;
17 use Moose::Meta::Method::Delegation;
19 use Moose::Util::TypeConstraints ();
21 use base 'Class::MOP::Attribute', 'Moose::Meta::Mixin::AttributeCore';
23 __PACKAGE__->meta->add_attribute('traits' => (
24 reader => 'applied_traits',
25 predicate => 'has_applied_traits',
28 # we need to have a ->does method in here to
29 # more easily support traits, and the introspection
30 # of those traits. We extend the does check to look
31 # for metatrait aliases.
33 my ($self, $role_name) = @_;
35 Moose::Util::resolve_metatrait_alias(Attribute => $role_name)
37 return 0 if !defined($name); # failed to load class
38 return $self->Moose::Object::does($name);
43 my $class = ( ref $self && $self->associated_class ) || "Moose::Meta::Class";
44 unshift @_, "message" if @_ % 2 == 1;
45 unshift @_, attr => $self if ref $self;
47 my $handler = $class->can("throw_error"); # to avoid incrementing depth by 1
52 my ($class, $name, %options) = @_;
53 $class->_process_options($name, \%options) unless $options{__hack_no_process_options}; # used from clone()... YECHKKK FIXME ICKY YUCK GROSS
55 delete $options{__hack_no_process_options};
60 map { $_->init_arg() }
61 $class->meta()->get_all_attributes()
64 my @bad = sort grep { ! $attrs{$_} } keys %options;
68 Carp::cluck "Found unknown argument(s) passed to '$name' attribute constructor in '$class': @bad";
71 return $class->SUPER::new($name, %options);
74 sub interpolate_class_and_new {
75 my ($class, $name, %args) = @_;
77 my ( $new_class, @traits ) = $class->interpolate_class(\%args);
79 $new_class->new($name, %args, ( scalar(@traits) ? ( traits => \@traits ) : () ) );
82 sub interpolate_class {
83 my ($class, $options) = @_;
85 $class = ref($class) || $class;
87 if ( my $metaclass_name = delete $options->{metaclass} ) {
88 my $new_class = Moose::Util::resolve_metaclass_alias( Attribute => $metaclass_name );
90 if ( $class ne $new_class ) {
91 if ( $new_class->can("interpolate_class") ) {
92 return $new_class->interpolate_class($options);
101 if (my $traits = $options->{traits}) {
103 while ($i < @$traits) {
104 my $trait = $traits->[$i++];
105 next if ref($trait); # options to a trait we discarded
107 $trait = Moose::Util::resolve_metatrait_alias(Attribute => $trait)
110 next if $class->does($trait);
112 push @traits, $trait;
115 push @traits, $traits->[$i++]
116 if $traits->[$i] && ref($traits->[$i]);
120 my $anon_class = Moose::Meta::Class->create_anon_class(
121 superclasses => [ $class ],
122 roles => [ @traits ],
126 $class = $anon_class->name;
130 return ( wantarray ? ( $class, @traits ) : $class );
135 # method-generating options shouldn't be overridden
136 sub illegal_options_for_inheritance {
137 qw(is reader writer accessor clearer predicate)
141 # This method *must* be able to handle
142 # Class::MOP::Attribute instances as
143 # well. Yes, I know that is wrong, but
144 # apparently we didn't realize it was
145 # doing that and now we have some code
146 # which is dependent on it. The real
147 # solution of course is to push this
148 # feature back up into Class::MOP::Attribute
149 # but I not right now, I am too lazy.
150 # However if you are reading this and
151 # looking for something to do,.. please
154 sub clone_and_inherit_options {
155 my ($self, %options) = @_;
158 # we may want to extends a Class::MOP::Attribute
159 # in which case we need to be able to use the
160 # core set of legal options that have always
161 # been here. But we allows Moose::Meta::Attribute
162 # instances to changes them.
164 my @illegal_options = $self->can('illegal_options_for_inheritance')
165 ? $self->illegal_options_for_inheritance
168 my @found_illegal_options = grep { exists $options{$_} && exists $self->{$_} ? $_ : undef } @illegal_options;
169 (scalar @found_illegal_options == 0)
170 || $self->throw_error("Illegal inherited options => (" . (join ', ' => @found_illegal_options) . ")", data => \%options);
174 if (blessed($options{isa}) && $options{isa}->isa('Moose::Meta::TypeConstraint')) {
175 $type_constraint = $options{isa};
178 $type_constraint = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options{isa});
179 (defined $type_constraint)
180 || $self->throw_error("Could not find the type constraint '" . $options{isa} . "'", data => $options{isa});
183 $options{type_constraint} = $type_constraint;
186 if ($options{does}) {
188 if (blessed($options{does}) && $options{does}->isa('Moose::Meta::TypeConstraint')) {
189 $type_constraint = $options{does};
192 $type_constraint = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options{does});
193 (defined $type_constraint)
194 || $self->throw_error("Could not find the type constraint '" . $options{does} . "'", data => $options{does});
197 $options{type_constraint} = $type_constraint;
201 # this doesn't apply to Class::MOP::Attributes,
202 # so we can ignore it for them.
204 if ($self->can('interpolate_class')) {
205 ( $options{metaclass}, my @traits ) = $self->interpolate_class(\%options);
208 my @all_traits = grep { $seen{$_}++ } @{ $self->applied_traits || [] }, @traits;
209 $options{traits} = \@all_traits if @all_traits;
212 $self->clone(%options);
216 my ( $self, %params ) = @_;
218 my $class = delete $params{metaclass} || ref $self;
220 my ( @init, @non_init );
222 foreach my $attr ( grep { $_->has_value($self) } Class::MOP::class_of($self)->get_all_attributes ) {
223 push @{ $attr->has_init_arg ? \@init : \@non_init }, $attr;
226 my %new_params = ( ( map { $_->init_arg => $_->get_value($self) } @init ), %params );
228 my $name = delete $new_params{name};
230 my $clone = $class->new($name, %new_params, __hack_no_process_options => 1 );
232 foreach my $attr ( @non_init ) {
233 $attr->set_value($clone, $attr->get_value($self));
239 sub _process_options {
240 my ($class, $name, $options) = @_;
242 if (exists $options->{is}) {
244 ### -------------------------
245 ## is => ro, writer => _foo # turns into (reader => foo, writer => _foo) as before
246 ## is => rw, writer => _foo # turns into (reader => foo, writer => _foo)
247 ## is => rw, accessor => _foo # turns into (accessor => _foo)
248 ## is => ro, accessor => _foo # error, accesor is rw
249 ### -------------------------
251 if ($options->{is} eq 'ro') {
252 $class->throw_error("Cannot define an accessor name on a read-only attribute, accessors are read/write", data => $options)
253 if exists $options->{accessor};
254 $options->{reader} ||= $name;
256 elsif ($options->{is} eq 'rw') {
257 if ($options->{writer}) {
258 $options->{reader} ||= $name;
261 $options->{accessor} ||= $name;
264 elsif ($options->{is} eq 'bare') {
265 # do nothing, but don't complain (later) about missing methods
268 $class->throw_error("I do not understand this option (is => " . $options->{is} . ") on attribute ($name)", data => $options->{is});
272 if (exists $options->{isa}) {
273 if (exists $options->{does}) {
274 if (try { $options->{isa}->can('does') }) {
275 ($options->{isa}->does($options->{does}))
276 || $class->throw_error("Cannot have an isa option and a does option if the isa does not do the does on attribute ($name)", data => $options);
279 $class->throw_error("Cannot have an isa option which cannot ->does() on attribute ($name)", data => $options);
283 # allow for anon-subtypes here ...
284 if (blessed($options->{isa}) && $options->{isa}->isa('Moose::Meta::TypeConstraint')) {
285 $options->{type_constraint} = $options->{isa};
288 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_isa_type_constraint($options->{isa});
291 elsif (exists $options->{does}) {
292 # allow for anon-subtypes here ...
293 if (blessed($options->{does}) && $options->{does}->isa('Moose::Meta::TypeConstraint')) {
294 $options->{type_constraint} = $options->{does};
297 $options->{type_constraint} = Moose::Util::TypeConstraints::find_or_create_does_type_constraint($options->{does});
301 if (exists $options->{coerce} && $options->{coerce}) {
302 (exists $options->{type_constraint})
303 || $class->throw_error("You cannot have coercion without specifying a type constraint on attribute ($name)", data => $options);
304 $class->throw_error("You cannot have a weak reference to a coerced value on attribute ($name)", data => $options)
305 if $options->{weak_ref};
307 unless ( $options->{type_constraint}->has_coercion ) {
308 my $type = $options->{type_constraint}->name;
310 Moose::Deprecated::deprecated(
311 feature => 'coerce without coercion',
313 "You cannot coerce an attribute ($name) unless its type ($type) has a coercion"
318 if (exists $options->{trigger}) {
319 ('CODE' eq ref $options->{trigger})
320 || $class->throw_error("Trigger must be a CODE ref on attribute ($name)", data => $options->{trigger});
323 if (exists $options->{auto_deref} && $options->{auto_deref}) {
324 (exists $options->{type_constraint})
325 || $class->throw_error("You cannot auto-dereference without specifying a type constraint on attribute ($name)", data => $options);
326 ($options->{type_constraint}->is_a_type_of('ArrayRef') ||
327 $options->{type_constraint}->is_a_type_of('HashRef'))
328 || $class->throw_error("You cannot auto-dereference anything other than a ArrayRef or HashRef on attribute ($name)", data => $options);
331 if (exists $options->{lazy_build} && $options->{lazy_build} == 1) {
332 $class->throw_error("You can not use lazy_build and default for the same attribute ($name)", data => $options)
333 if exists $options->{default};
334 $options->{lazy} = 1;
335 $options->{builder} ||= "_build_${name}";
337 $options->{clearer} ||= "_clear${name}";
338 $options->{predicate} ||= "_has${name}";
341 $options->{clearer} ||= "clear_${name}";
342 $options->{predicate} ||= "has_${name}";
346 if (exists $options->{lazy} && $options->{lazy}) {
347 (exists $options->{default} || defined $options->{builder} )
348 || $class->throw_error("You cannot have lazy attribute ($name) without specifying a default value for it", data => $options);
351 if ( $options->{required} && !( ( !exists $options->{init_arg} || defined $options->{init_arg} ) || exists $options->{default} || defined $options->{builder} ) ) {
352 $class->throw_error("You cannot have a required attribute ($name) without a default, builder, or an init_arg", data => $options);
357 sub initialize_instance_slot {
358 my ($self, $meta_instance, $instance, $params) = @_;
359 my $init_arg = $self->init_arg();
360 # try to fetch the init arg from the %params ...
364 if ( defined($init_arg) and exists $params->{$init_arg}) {
365 $val = $params->{$init_arg};
369 # skip it if it's lazy
370 return if $self->is_lazy;
371 # and die if it's required and doesn't have a default value
372 $self->throw_error("Attribute (" . $self->name . ") is required", object => $instance, data => $params)
373 if $self->is_required && !$self->has_default && !$self->has_builder;
375 # if nothing was in the %params, we can use the
376 # attribute's default value (if it has one)
377 if ($self->has_default) {
378 $val = $self->default($instance);
381 elsif ($self->has_builder) {
382 $val = $self->_call_builder($instance);
387 return unless $value_is_set;
389 $val = $self->_coerce_and_verify( $val, $instance );
391 $self->set_initial_value($instance, $val);
393 if ( ref $val && $self->is_weak_ref ) {
394 $self->_weaken_value($instance);
399 my ( $self, $instance ) = @_;
401 my $builder = $self->builder();
403 return $instance->$builder()
404 if $instance->can( $self->builder );
406 $self->throw_error( blessed($instance)
407 . " does not support builder method '"
409 . "' for attribute '"
419 # this duplicates too much code from
420 # Class::MOP::Attribute, we need to
421 # refactor these bits eventually.
423 sub _set_initial_slot_value {
424 my ($self, $meta_instance, $instance, $value) = @_;
426 my $slot_name = $self->name;
428 return $meta_instance->set_slot_value($instance, $slot_name, $value)
429 unless $self->has_initializer;
432 my $val = $self->_coerce_and_verify( shift, $instance );;
434 $meta_instance->set_slot_value($instance, $slot_name, $val);
437 my $initializer = $self->initializer;
439 # most things will just want to set a value, so make it first arg
440 $instance->$initializer($value, $callback, $self);
444 my ($self, $instance, @args) = @_;
445 my $value = $args[0];
447 my $attr_name = $self->name;
449 if ($self->is_required and not @args) {
450 $self->throw_error("Attribute ($attr_name) is required", object => $instance);
453 $value = $self->_coerce_and_verify( $value, $instance );
456 if ( $self->has_trigger && $self->has_value($instance) ) {
457 @old = $self->get_value($instance, 'for trigger');
460 $self->SUPER::set_value($instance, $value);
462 if ( ref $value && $self->is_weak_ref ) {
463 $self->_weaken_value($instance);
466 if ($self->has_trigger) {
467 $self->trigger->($instance, $value, @old);
472 my ( $self, $instance ) = @_;
474 my $meta_instance = Class::MOP::Class->initialize( blessed($instance) )
477 $meta_instance->weaken_slot_value( $instance, $self->name );
481 my ($self, $instance, $for_trigger) = @_;
483 if ($self->is_lazy) {
484 unless ($self->has_value($instance)) {
486 if ($self->has_default) {
487 $value = $self->default($instance);
488 } elsif ( $self->has_builder ) {
489 $value = $self->_call_builder($instance);
492 $value = $self->_coerce_and_verify( $value, $instance );
494 $self->set_initial_value($instance, $value);
498 if ( $self->should_auto_deref && ! $for_trigger ) {
500 my $type_constraint = $self->type_constraint;
502 if ($type_constraint->is_a_type_of('ArrayRef')) {
503 my $rv = $self->SUPER::get_value($instance);
504 return unless defined $rv;
505 return wantarray ? @{ $rv } : $rv;
507 elsif ($type_constraint->is_a_type_of('HashRef')) {
508 my $rv = $self->SUPER::get_value($instance);
509 return unless defined $rv;
510 return wantarray ? %{ $rv } : $rv;
513 $self->throw_error("Can not auto de-reference the type constraint '" . $type_constraint->name . "'", object => $instance, type_constraint => $type_constraint);
519 return $self->SUPER::get_value($instance);
523 ## installing accessors
525 sub accessor_metaclass { 'Moose::Meta::Method::Accessor' }
527 sub install_accessors {
529 $self->SUPER::install_accessors(@_);
530 $self->install_delegation if $self->has_handles;
534 sub _check_associated_methods {
537 @{ $self->associated_methods }
538 || ($self->_is_metadata || '') eq 'bare'
541 'Attribute (' . $self->name . ') of class '
542 . $self->associated_class->name
543 . ' has no associated methods'
544 . ' (did you mean to provide an "is" argument?)'
550 sub _process_accessors {
552 my ($type, $accessor, $generate_as_inline_methods) = @_;
553 $accessor = (keys %$accessor)[0] if (ref($accessor)||'') eq 'HASH';
554 my $method = $self->associated_class->get_method($accessor);
555 if ($method && !$method->isa('Class::MOP::Method::Accessor')
556 && (!$self->definition_context
557 || $method->package_name eq $self->definition_context->{package})) {
559 "You are overwriting a locally defined method ($accessor) with "
563 if (!$self->associated_class->has_method($accessor)
564 && $self->associated_class->has_package_symbol('&' . $accessor)) {
566 "You are overwriting a locally defined function ($accessor) with "
570 $self->SUPER::_process_accessors(@_);
573 sub remove_accessors {
575 $self->SUPER::remove_accessors(@_);
576 $self->remove_delegation if $self->has_handles;
580 sub install_delegation {
584 # Here we canonicalize the 'handles' option
585 # this will sort out any details and always
586 # return an hash of methods which we want
587 # to delagate to, see that method for details
588 my %handles = $self->_canonicalize_handles;
591 # install the delegation ...
592 my $associated_class = $self->associated_class;
593 foreach my $handle (keys %handles) {
594 my $method_to_call = $handles{$handle};
595 my $class_name = $associated_class->name;
596 my $name = "${class_name}::${handle}";
598 (!$associated_class->has_method($handle))
599 || $self->throw_error("You cannot overwrite a locally defined method ($handle) with a delegation", method_name => $handle);
602 # handles is not allowed to delegate
603 # any of these methods, as they will
604 # override the ones in your class, which
605 # is almost certainly not what you want.
607 # FIXME warn when $handle was explicitly specified, but not if the source is a regex or something
608 #cluck("Not delegating method '$handle' because it is a core method") and
609 next if $class_name->isa("Moose::Object") and $handle =~ /^BUILD|DEMOLISH$/ || Moose::Object->can($handle);
611 my $method = $self->_make_delegation_method($handle, $method_to_call);
613 $self->associated_class->add_method($method->name, $method);
614 $self->associate_method($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 next unless any { $handle eq $_ }
625 @{ $self->associated_methods };
626 $self->associated_class->remove_method($handle);
630 # private methods to help delegation ...
632 sub _canonicalize_handles {
634 my $handles = $self->handles;
635 if (my $handle_type = ref($handles)) {
636 if ($handle_type eq 'HASH') {
639 elsif ($handle_type eq 'ARRAY') {
640 return map { $_ => $_ } @{$handles};
642 elsif ($handle_type eq 'Regexp') {
643 ($self->has_type_constraint)
644 || $self->throw_error("Cannot delegate methods based on a Regexp without a type constraint (isa)", data => $handles);
645 return map { ($_ => $_) }
646 grep { /$handles/ } $self->_get_delegate_method_list;
648 elsif ($handle_type eq 'CODE') {
649 return $handles->($self, $self->_find_delegate_metaclass);
651 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::DuckType')) {
652 return map { $_ => $_ } @{ $handles->methods };
654 elsif (blessed($handles) && $handles->isa('Moose::Meta::TypeConstraint::Role')) {
655 $handles = $handles->role;
658 $self->throw_error("Unable to canonicalize the 'handles' option with $handles", data => $handles);
662 Class::MOP::load_class($handles);
663 my $role_meta = Class::MOP::class_of($handles);
665 (blessed $role_meta && $role_meta->isa('Moose::Meta::Role'))
666 || $self->throw_error("Unable to canonicalize the 'handles' option with $handles because its metaclass is not a Moose::Meta::Role", data => $handles);
668 return map { $_ => $_ }
669 grep { $_ ne 'meta' } (
670 $role_meta->get_method_list,
671 map { $_->name } $role_meta->get_required_method_list,
675 sub _find_delegate_metaclass {
677 if (my $class = $self->_isa_metadata) {
678 # we might be dealing with a non-Moose class,
679 # and need to make our own metaclass. if there's
680 # already a metaclass, it will be returned
681 return Class::MOP::Class->initialize($class);
683 elsif (my $role = $self->_does_metadata) {
684 return Class::MOP::class_of($role);
687 $self->throw_error("Cannot find delegate metaclass for attribute " . $self->name);
691 sub _get_delegate_method_list {
693 my $meta = $self->_find_delegate_metaclass;
694 if ($meta->isa('Class::MOP::Class')) {
695 return map { $_->name } # NOTE: !never! delegate &meta
696 grep { $_->package_name ne 'Moose::Object' && $_->name ne 'meta' }
697 $meta->get_all_methods;
699 elsif ($meta->isa('Moose::Meta::Role')) {
700 return $meta->get_method_list;
703 $self->throw_error("Unable to recognize the delegate metaclass '$meta'", data => $meta);
707 sub delegation_metaclass { 'Moose::Meta::Method::Delegation' }
709 sub _make_delegation_method {
710 my ( $self, $handle_name, $method_to_call ) = @_;
712 my @curried_arguments;
714 ($method_to_call, @curried_arguments) = @$method_to_call
715 if 'ARRAY' eq ref($method_to_call);
717 return $self->delegation_metaclass->new(
718 name => $handle_name,
719 package_name => $self->associated_class->name,
721 delegate_to_method => $method_to_call,
722 curried_arguments => \@curried_arguments,
726 sub _coerce_and_verify {
729 my $instance = shift;
731 return $val unless $self->has_type_constraint;
733 $val = $self->type_constraint->coerce($val)
734 if $self->should_coerce && $self->type_constraint->has_coercion;
736 $self->verify_against_type_constraint($val, instance => $instance);
741 sub verify_against_type_constraint {
745 return 1 if !$self->has_type_constraint;
747 my $type_constraint = $self->type_constraint;
749 $type_constraint->check($val)
750 || $self->throw_error("Attribute ("
752 . ") does not pass the type constraint because: "
753 . $type_constraint->get_message($val), data => $val, @_);
756 package Moose::Meta::Attribute::Custom::Moose;
757 sub register_implementation { 'Moose::Meta::Attribute' }
767 Moose::Meta::Attribute - The Moose attribute metaclass
771 This class is a subclass of L<Class::MOP::Attribute> that provides
772 additional Moose-specific functionality.
774 To really understand this class, you will need to start with the
775 L<Class::MOP::Attribute> documentation. This class can be understood
776 as a set of additional features on top of the basic feature provided
777 by that parent class.
781 C<Moose::Meta::Attribute> is a subclass of L<Class::MOP::Attribute>.
785 Many of the documented below override methods in
786 L<Class::MOP::Attribute> and add Moose specific features.
792 =item B<< Moose::Meta::Attribute->new(%options) >>
794 This method overrides the L<Class::MOP::Attribute> constructor.
796 Many of the options below are described in more detail in the
797 L<Moose::Manual::Attributes> document.
799 It adds the following options to the constructor:
803 =item * is => 'ro', 'rw', 'bare'
805 This provides a shorthand for specifying the C<reader>, C<writer>, or
806 C<accessor> names. If the attribute is read-only ('ro') then it will
807 have a C<reader> method with the same attribute as the name.
809 If it is read-write ('rw') then it will have an C<accessor> method
810 with the same name. If you provide an explicit C<writer> for a
811 read-write attribute, then you will have a C<reader> with the same
812 name as the attribute, and a C<writer> with the name you provided.
814 Use 'bare' when you are deliberately not installing any methods
815 (accessor, reader, etc.) associated with this attribute; otherwise,
816 Moose will issue a deprecation warning when this attribute is added to a
821 This option accepts a type. The type can be a string, which should be
822 a type name. If the type name is unknown, it is assumed to be a class
825 This option can also accept a L<Moose::Meta::TypeConstraint> object.
827 If you I<also> provide a C<does> option, then your C<isa> option must
828 be a class name, and that class must do the role specified with
831 =item * does => $role
833 This is short-hand for saying that the attribute's type must be an
834 object which does the named role.
836 =item * coerce => $bool
838 This option is only valid for objects with a type constraint
839 (C<isa>). If this is true, then coercions will be applied whenever
840 this attribute is set.
842 You can make both this and the C<weak_ref> option true.
844 =item * trigger => $sub
846 This option accepts a subroutine reference, which will be called after
847 the attribute is set.
849 =item * required => $bool
851 An attribute which is required must be provided to the constructor. An
852 attribute which is required can also have a C<default> or C<builder>,
853 which will satisfy its required-ness.
855 A required attribute must have a C<default>, C<builder> or a
856 non-C<undef> C<init_arg>
858 =item * lazy => $bool
860 A lazy attribute must have a C<default> or C<builder>. When an
861 attribute is lazy, the default value will not be calculated until the
864 =item * weak_ref => $bool
866 If this is true, the attribute's value will be stored as a weak
869 =item * auto_deref => $bool
871 If this is true, then the reader will dereference the value when it is
872 called. The attribute must have a type constraint which defines the
873 attribute as an array or hash reference.
875 =item * lazy_build => $bool
877 Setting this to true makes the attribute lazy and provides a number of
885 is equivalent to this:
890 builder => '_build_size',
891 clearer => 'clear_size',
892 predicate => 'has_size',
895 =item * documentation
897 An arbitrary string that can be retrieved later by calling C<<
898 $attr->documentation >>.
902 =item B<< $attr->clone(%options) >>
904 This creates a new attribute based on attribute being cloned. You must
905 supply a C<name> option to provide a new name for the attribute.
907 The C<%options> can only specify options handled by
908 L<Class::MOP::Attribute>.
912 =head2 Value management
916 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
918 This method is used internally to initialize the attribute's slot in
919 the object C<$instance>.
921 This overrides the L<Class::MOP::Attribute> method to handle lazy
922 attributes, weak references, and type constraints.
928 eval { $point->meta->get_attribute('x')->set_value($point, 'forty-two') };
933 I<Attribute (x) does not pass the type constraint (Int) with 'forty-two'>
935 Before setting the value, a check is made on the type constraint of
936 the attribute, if it has one, to see if the value passes it. If the
937 value fails to pass, the set operation dies with a L</throw_error>.
939 Any coercion to convert values is done before checking the type constraint.
941 To check a value against a type constraint before setting it, fetch the
942 attribute instance using L<Class::MOP::Class/find_attribute_by_name>,
943 fetch the type_constraint from the attribute using L<Moose::Meta::Attribute/type_constraint>
944 and call L<Moose::Meta::TypeConstraint/check>. See L<Moose::Cookbook::Basics::Recipe4>
949 =head2 Attribute Accessor generation
953 =item B<< $attr->install_accessors >>
955 This method overrides the parent to also install delegation methods.
957 If, after installing all methods, the attribute object has no associated
958 methods, it throws an error unless C<< is => 'bare' >> was passed to the
959 attribute constructor. (Trying to add an attribute that has no associated
960 methods is almost always an error.)
962 =item B<< $attr->remove_accessors >>
964 This method overrides the parent to also remove delegation methods.
966 =item B<< $attr->install_delegation >>
968 This method adds its delegation methods to the attribute's associated
969 class, if it has any to add.
971 =item B<< $attr->remove_delegation >>
973 This method remove its delegation methods from the attribute's
976 =item B<< $attr->accessor_metaclass >>
978 Returns the accessor metaclass name, which defaults to
979 L<Moose::Meta::Method::Accessor>.
981 =item B<< $attr->delegation_metaclass >>
983 Returns the delegation metaclass name, which defaults to
984 L<Moose::Meta::Method::Delegation>.
988 =head2 Additional Moose features
990 These methods are not found in the superclass. They support features
995 =item B<< $attr->does($role) >>
997 This indicates whether the I<attribute itself> does the given
998 role. The role can be given as a full class name, or as a resolvable
1001 Note that this checks the attribute itself, not its type constraint,
1002 so it is checking the attribute's metaclass and any traits applied to
1005 =item B<< Moose::Meta::Class->interpolate_class_and_new($name, %options) >>
1007 This is an alternate constructor that handles the C<metaclass> and
1010 Effectively, this method is a factory that finds or creates the
1011 appropriate class for the given C<metaclass> and/or C<traits>.
1013 Once it has the appropriate class, it will call C<< $class->new($name,
1014 %options) >> on that class.
1016 =item B<< $attr->clone_and_inherit_options(%options) >>
1018 This method supports the C<has '+foo'> feature. It does various bits
1019 of processing on the supplied C<%options> before ultimately calling
1020 the C<clone> method.
1022 One of its main tasks is to make sure that the C<%options> provided
1023 does not include the options returned by the
1024 C<illegal_options_for_inheritance> method.
1026 =item B<< $attr->illegal_options_for_inheritance >>
1028 This returns a blacklist of options that can not be overridden in a
1029 subclass's attribute definition.
1031 This exists to allow a custom metaclass to change or add to the list
1032 of options which can not be changed.
1034 =item B<< $attr->type_constraint >>
1036 Returns the L<Moose::Meta::TypeConstraint> object for this attribute,
1039 =item B<< $attr->has_type_constraint >>
1041 Returns true if this attribute has a type constraint.
1043 =item B<< $attr->verify_against_type_constraint($value) >>
1045 Given a value, this method returns true if the value is valid for the
1046 attribute's type constraint. If the value is not valid, it throws an
1049 =item B<< $attr->handles >>
1051 This returns the value of the C<handles> option passed to the
1054 =item B<< $attr->has_handles >>
1056 Returns true if this attribute performs delegation.
1058 =item B<< $attr->is_weak_ref >>
1060 Returns true if this attribute stores its value as a weak reference.
1062 =item B<< $attr->is_required >>
1064 Returns true if this attribute is required to have a value.
1066 =item B<< $attr->is_lazy >>
1068 Returns true if this attribute is lazy.
1070 =item B<< $attr->is_lazy_build >>
1072 Returns true if the C<lazy_build> option was true when passed to the
1075 =item B<< $attr->should_coerce >>
1077 Returns true if the C<coerce> option passed to the constructor was
1080 =item B<< $attr->should_auto_deref >>
1082 Returns true if the C<auto_deref> option passed to the constructor was
1085 =item B<< $attr->trigger >>
1087 This is the subroutine reference that was in the C<trigger> option
1088 passed to the constructor, if any.
1090 =item B<< $attr->has_trigger >>
1092 Returns true if this attribute has a trigger set.
1094 =item B<< $attr->documentation >>
1096 Returns the value that was in the C<documentation> option passed to
1097 the constructor, if any.
1099 =item B<< $attr->has_documentation >>
1101 Returns true if this attribute has any documentation.
1103 =item B<< $attr->applied_traits >>
1105 This returns an array reference of all the traits which were applied
1106 to this attribute. If none were applied, this returns C<undef>.
1108 =item B<< $attr->has_applied_traits >>
1110 Returns true if this attribute has any traits applied.
1116 See L<Moose/BUGS> for details on reporting bugs.
1120 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1122 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
1124 =head1 COPYRIGHT AND LICENSE
1126 Copyright 2006-2010 by Infinity Interactive, Inc.
1128 L<http://www.iinteractive.com>
1130 This library is free software; you can redistribute it and/or modify
1131 it under the same terms as Perl itself.