2 package Class::MOP::Attribute;
7 use Class::MOP::Method::Accessor;
10 use Scalar::Util 'blessed', 'weaken';
13 our $VERSION = '1.11';
14 $VERSION = eval $VERSION;
15 our $AUTHORITY = 'cpan:STEVAN';
17 use base 'Class::MOP::Object', 'Class::MOP::Mixin::AttributeCore';
19 # NOTE: (meta-circularity)
20 # This method will be replaced in the
21 # boostrap section of Class::MOP, by
22 # a new version which uses the
23 # &Class::MOP::Class::construct_instance
24 # method to build an attribute meta-object
25 # which itself is described with attribute
27 # - Ain't meta-circularity grand? :)
29 my ( $class, @args ) = @_;
31 unshift @args, "name" if @args % 2 == 1;
34 my $name = $options{name};
37 || confess "You must provide a name for the attribute";
39 $options{init_arg} = $name
40 if not exists $options{init_arg};
41 if(exists $options{builder}){
42 confess("builder must be a defined scalar value which is a method name")
43 if ref $options{builder} || !(defined $options{builder});
44 confess("Setting both default and builder is not allowed.")
45 if exists $options{default};
47 ($class->is_default_a_coderef(\%options))
48 || confess("References are not allowed as default values, you must ".
49 "wrap the default of '$name' in a CODE reference (ex: sub { [] } and not [])")
50 if exists $options{default} && ref $options{default};
52 if( $options{required} and not( defined($options{builder}) || defined($options{init_arg}) || exists $options{default} ) ) {
53 confess("A required attribute must have either 'init_arg', 'builder', or 'default'");
56 $class->_new(\%options);
62 return Class::MOP::Class->initialize($class)->new_object(@_)
63 if $class ne __PACKAGE__;
65 my $options = @_ == 1 ? $_[0] : {@_};
68 'name' => $options->{name},
69 'accessor' => $options->{accessor},
70 'reader' => $options->{reader},
71 'writer' => $options->{writer},
72 'predicate' => $options->{predicate},
73 'clearer' => $options->{clearer},
74 'builder' => $options->{builder},
75 'init_arg' => $options->{init_arg},
76 exists $options->{default}
77 ? ('default' => $options->{default})
79 'initializer' => $options->{initializer},
80 'definition_context' => $options->{definition_context},
81 # keep a weakened link to the
82 # class we are associated with
83 'associated_class' => undef,
84 # and a list of the methods
85 # associated with this attr
86 'associated_methods' => [],
87 # this let's us keep track of
88 # our order inside the associated
90 'insertion_order' => undef,
95 # this is a primative (and kludgy) clone operation
96 # for now, it will be replaced in the Class::MOP
97 # bootstrap with a proper one, however we know
98 # that this one will work fine for now.
103 || confess "Can only clone an instance";
104 return bless { %{$self}, %options } => ref($self);
107 sub initialize_instance_slot {
108 my ($self, $meta_instance, $instance, $params) = @_;
109 my $init_arg = $self->{'init_arg'};
111 # try to fetch the init arg from the %params ...
113 # if nothing was in the %params, we can use the
114 # attribute's default value (if it has one)
115 if(defined $init_arg and exists $params->{$init_arg}){
116 $self->_set_initial_slot_value(
119 $params->{$init_arg},
122 elsif (exists $self->{'default'}) {
123 $self->_set_initial_slot_value(
126 $self->default($instance),
129 elsif (defined( my $builder = $self->{'builder'})) {
130 if ($builder = $instance->can($builder)) {
131 $self->_set_initial_slot_value(
138 confess(ref($instance)." does not support builder method '". $self->{'builder'} ."' for attribute '" . $self->name . "'");
143 sub _set_initial_slot_value {
144 my ($self, $meta_instance, $instance, $value) = @_;
146 my $slot_name = $self->name;
148 return $meta_instance->set_slot_value($instance, $slot_name, $value)
149 unless $self->has_initializer;
152 $meta_instance->set_slot_value($instance, $slot_name, $_[0]);
155 my $initializer = $self->initializer;
157 # most things will just want to set a value, so make it first arg
158 $instance->$initializer($value, $callback, $self);
161 sub get_read_method {
163 my $reader = $self->reader || $self->accessor;
165 return $reader unless ref $reader;
167 my ($name) = %$reader;
171 sub get_write_method {
173 my $writer = $self->writer || $self->accessor;
175 return $writer unless ref $writer;
177 my ($name) = %$writer;
181 sub get_read_method_ref {
183 if ((my $reader = $self->get_read_method) && $self->associated_class) {
184 return $self->associated_class->get_method($reader);
187 my $code = sub { $self->get_value(@_) };
188 if (my $class = $self->associated_class) {
189 return $class->method_metaclass->wrap(
191 package_name => $class->name,
201 sub get_write_method_ref {
203 if ((my $writer = $self->get_write_method) && $self->associated_class) {
204 return $self->associated_class->get_method($writer);
207 my $code = sub { $self->set_value(@_) };
208 if (my $class = $self->associated_class) {
209 return $class->method_metaclass->wrap(
211 package_name => $class->name,
223 sub slots { (shift)->name }
227 sub attach_to_class {
228 my ($self, $class) = @_;
229 (blessed($class) && $class->isa('Class::MOP::Class'))
230 || confess "You must pass a Class::MOP::Class instance (or a subclass)";
231 weaken($self->{'associated_class'} = $class);
234 sub detach_from_class {
236 $self->{'associated_class'} = undef;
241 sub associate_method {
242 my ($self, $method) = @_;
243 push @{$self->{'associated_methods'}} => $method;
248 sub set_initial_value {
249 my ($self, $instance, $value) = @_;
250 $self->_set_initial_slot_value(
251 Class::MOP::Class->initialize(ref($instance))->get_meta_instance,
257 sub set_value { shift->set_raw_value(@_) }
258 sub get_value { shift->get_raw_value(@_) }
261 my ($self, $instance, $value) = @_;
263 Class::MOP::Class->initialize(ref($instance))
265 ->set_slot_value($instance, $self->name, $value);
269 my ($self, $instance) = @_;
271 Class::MOP::Class->initialize(ref($instance))
273 ->get_slot_value($instance, $self->name);
277 my ($self, $instance) = @_;
279 Class::MOP::Class->initialize(ref($instance))
281 ->is_slot_initialized($instance, $self->name);
285 my ($self, $instance) = @_;
287 Class::MOP::Class->initialize(ref($instance))
289 ->deinitialize_slot($instance, $self->name);
294 sub accessor_metaclass { 'Class::MOP::Method::Accessor' }
296 sub _process_accessors {
297 my ($self, $type, $accessor, $generate_as_inline_methods) = @_;
301 if ( my $ctx = $self->definition_context ) {
302 $method_ctx = { %$ctx };
305 if (ref($accessor)) {
306 (ref($accessor) eq 'HASH')
307 || confess "bad accessor/reader/writer/predicate/clearer format, must be a HASH ref";
308 my ($name, $method) = %{$accessor};
309 $method = $self->accessor_metaclass->wrap(
311 package_name => $self->associated_class->name,
313 definition_context => $method_ctx,
315 $self->associate_method($method);
316 return ($name, $method);
319 my $inline_me = ($generate_as_inline_methods && $self->associated_class->instance_metaclass->is_inlinable);
323 my $desc = "accessor $accessor";
324 if ( $accessor ne $self->name ) {
325 $desc .= " of attribute " . $self->name;
328 $method_ctx->{description} = $desc;
331 $method = $self->accessor_metaclass->new(
333 is_inline => $inline_me,
334 accessor_type => $type,
335 package_name => $self->associated_class->name,
337 definition_context => $method_ctx,
341 confess "Could not create the '$type' method for " . $self->name . " because : $_";
343 $self->associate_method($method);
344 return ($accessor, $method);
348 sub install_accessors {
351 my $class = $self->associated_class;
354 $self->_process_accessors('accessor' => $self->accessor(), $inline)
355 ) if $self->has_accessor();
358 $self->_process_accessors('reader' => $self->reader(), $inline)
359 ) if $self->has_reader();
362 $self->_process_accessors('writer' => $self->writer(), $inline)
363 ) if $self->has_writer();
366 $self->_process_accessors('predicate' => $self->predicate(), $inline)
367 ) if $self->has_predicate();
370 $self->_process_accessors('clearer' => $self->clearer(), $inline)
371 ) if $self->has_clearer();
377 my $_remove_accessor = sub {
378 my ($accessor, $class) = @_;
379 if (ref($accessor) && ref($accessor) eq 'HASH') {
380 ($accessor) = keys %{$accessor};
382 my $method = $class->get_method($accessor);
383 $class->remove_method($accessor)
384 if (ref($method) && $method->isa('Class::MOP::Method::Accessor'));
387 sub remove_accessors {
390 # we really need to make sure to remove from the
391 # associates methods here as well. But this is
392 # such a slimly used method, I am not worried
393 # about it right now.
394 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
395 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
396 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
397 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
398 $_remove_accessor->($self->clearer(), $self->associated_class()) if $self->has_clearer();
408 return $self->associated_class->get_meta_instance->inline_get_slot_value(
409 $instance, $self->name );
414 my ( $instance, $value ) = @_;
416 return $self->associated_class->get_meta_instance->inline_set_slot_value(
417 $instance, $self->name, $value );
425 $self->associated_class->get_meta_instance
426 ->inline_is_slot_initialized( $instance, $self->name );
434 $self->associated_class->get_meta_instance
435 ->inline_deinitialize_slot( $instance, $self->name );
446 Class::MOP::Attribute - Attribute Meta Object
450 Class::MOP::Attribute->new(
452 accessor => 'foo', # dual purpose get/set accessor
453 predicate => 'has_foo', # predicate check for defined-ness
454 init_arg => '-foo', # class->new will look for a -foo key
455 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
459 Class::MOP::Attribute->new(
461 reader => 'bar', # getter
462 writer => 'set_bar', # setter
463 predicate => 'has_bar', # predicate check for defined-ness
464 init_arg => ':bar', # class->new will look for a :bar key
465 # no default value means it is undef
471 The Attribute Protocol is almost entirely an invention of
472 C<Class::MOP>. Perl 5 does not have a consistent notion of
473 attributes. There are so many ways in which this is done, and very few
474 (if any) are easily discoverable by this module.
476 With that said, this module attempts to inject some order into this
477 chaos, by introducing a consistent API which can be used to create
486 =item B<< Class::MOP::Attribute->new($name, ?%options) >>
488 An attribute must (at the very least), have a C<$name>. All other
489 C<%options> are added as key-value pairs.
495 This is a string value representing the expected key in an
496 initialization hash. For instance, if we have an C<init_arg> value of
497 C<-foo>, then the following code will Just Work.
499 MyClass->meta->new_object( -foo => 'Hello There' );
501 If an init_arg is not assigned, it will automatically use the
502 attribute's name. If C<init_arg> is explicitly set to C<undef>, the
503 attribute cannot be specified during initialization.
507 This provides the name of a method that will be called to initialize
508 the attribute. This method will be called on the object after it is
509 constructed. It is expected to return a valid value for the attribute.
513 This can be used to provide an explicit default for initializing the
514 attribute. If the default you provide is a subroutine reference, then
515 this reference will be called I<as a method> on the object.
517 If the value is a simple scalar (string or number), then it can be
518 just passed as is. However, if you wish to initialize it with a HASH
519 or ARRAY ref, then you need to wrap that inside a subroutine
522 Class::MOP::Attribute->new(
524 default => sub { [] },
530 Class::MOP::Attribute->new(
532 default => sub { {} },
536 If you wish to initialize an attribute with a subroutine reference
537 itself, then you need to wrap that in a subroutine as well:
539 Class::MOP::Attribute->new(
542 sub { print "Hello World" }
547 And lastly, if the value of your attribute is dependent upon some
548 other aspect of the instance structure, then you can take advantage of
549 the fact that when the C<default> value is called as a method:
551 Class::MOP::Attribute->new(
552 'object_identity' => (
553 default => sub { Scalar::Util::refaddr( $_[0] ) },
557 Note that there is no guarantee that attributes are initialized in any
558 particular order, so you cannot rely on the value of some other
559 attribute when generating the default.
563 This option can be either a method name or a subroutine
564 reference. This method will be called when setting the attribute's
565 value in the constructor. Unlike C<default> and C<builder>, the
566 initializer is only called when a value is provided to the
567 constructor. The initializer allows you to munge this value during
570 The initializer is called as a method with three arguments. The first
571 is the value that was passed to the constructor. The second is a
572 subroutine reference that can be called to actually set the
573 attribute's value, and the last is the associated
574 C<Class::MOP::Attribute> object.
576 This contrived example shows an initializer that sets the attribute to
577 twice the given value.
579 Class::MOP::Attribute->new(
582 my ( $self, $value, $set, $attr ) = @_;
583 $set->( $value * 2 );
588 Since an initializer can be a method name, you can easily make
589 attribute initialization use the writer:
591 Class::MOP::Attribute->new(
593 writer => 'some_attr',
594 initializer => 'some_attr',
598 Your writer will need to examine C<@_> and determine under which
599 context it is being called.
603 The C<accessor>, C<reader>, C<writer>, C<predicate> and C<clearer>
604 options all accept the same parameters. You can provide the name of
605 the method, in which case an appropriate default method will be
606 generated for you. Or instead you can also provide hash reference
607 containing exactly one key (the method name) and one value. The value
608 should be a subroutine reference, which will be installed as the
615 An C<accessor> is a standard Perl-style read/write accessor. It will
616 return the value of the attribute, and if a value is passed as an
617 argument, it will assign that value to the attribute.
619 Note that C<undef> is a legitimate value, so this will work:
621 $object->set_something(undef);
625 This is a basic read-only accessor. It returns the value of the
630 This is a basic write accessor, it accepts a single argument, and
631 assigns that value to the attribute.
633 Note that C<undef> is a legitimate value, so this will work:
635 $object->set_something(undef);
639 The predicate method returns a boolean indicating whether or not the
640 attribute has been explicitly set.
642 Note that the predicate returns true even if the attribute was set to
643 a false value (C<0> or C<undef>).
647 This method will uninitialize the attribute. After an attribute is
648 cleared, its C<predicate> will return false.
650 =item * definition_context
652 Mostly, this exists as a hook for the benefit of Moose.
654 This option should be a hash reference containing several keys which
655 will be used when inlining the attribute's accessors. The keys should
656 include C<line>, the line number where the attribute was created, and
657 either C<file> or C<description>.
659 This information will ultimately be used when eval'ing inlined
660 accessor code so that error messages report a useful line and file
665 =item B<< $attr->clone(%options) >>
667 This clones the attribute. Any options you provide will override the
668 settings of the original attribute. You can change the name of the new
669 attribute by passing a C<name> key in C<%options>.
675 These are all basic read-only accessors for the values passed into
680 =item B<< $attr->name >>
682 Returns the attribute's name.
684 =item B<< $attr->accessor >>
686 =item B<< $attr->reader >>
688 =item B<< $attr->writer >>
690 =item B<< $attr->predicate >>
692 =item B<< $attr->clearer >>
694 The C<accessor>, C<reader>, C<writer>, C<predicate>, and C<clearer>
695 methods all return exactly what was passed to the constructor, so it
696 can be either a string containing a method name, or a hash reference.
698 =item B<< $attr->initializer >>
700 Returns the initializer as passed to the constructor, so this may be
701 either a method name or a subroutine reference.
703 =item B<< $attr->init_arg >>
705 =item B<< $attr->is_default_a_coderef >>
707 =item B<< $attr->default($instance) >>
709 The C<$instance> argument is optional. If you don't pass it, the
710 return value for this method is exactly what was passed to the
711 constructor, either a simple scalar or a subroutine reference.
713 If you I<do> pass an C<$instance> and the default is a subroutine
714 reference, then the reference is called as a method on the
715 C<$instance> and the generated value is returned.
717 =item B<< $attr->slots >>
719 Return a list of slots required by the attribute. This is usually just
720 one, the name of the attribute.
722 A slot is the name of the hash key used to store the attribute in an
725 =item B<< $attr->get_read_method >>
727 =item B<< $attr->get_write_method >>
729 Returns the name of a method suitable for reading or writing the value
730 of the attribute in the associated class.
732 If an attribute is read- or write-only, then these methods can return
733 C<undef> as appropriate.
735 =item B<< $attr->has_read_method >>
737 =item B<< $attr->has_write_method >>
739 This returns a boolean indicating whether the attribute has a I<named>
740 read or write method.
742 =item B<< $attr->get_read_method_ref >>
744 =item B<< $attr->get_write_method_ref >>
746 Returns the subroutine reference of a method suitable for reading or
747 writing the attribute's value in the associated class. These methods
748 always return a subroutine reference, regardless of whether or not the
749 attribute is read- or write-only.
751 =item B<< $attr->insertion_order >>
753 If this attribute has been inserted into a class, this returns a zero
754 based index regarding the order of insertion.
758 =head2 Informational predicates
760 These are all basic predicate methods for the values passed into C<new>.
764 =item B<< $attr->has_accessor >>
766 =item B<< $attr->has_reader >>
768 =item B<< $attr->has_writer >>
770 =item B<< $attr->has_predicate >>
772 =item B<< $attr->has_clearer >>
774 =item B<< $attr->has_initializer >>
776 =item B<< $attr->has_init_arg >>
778 This will be I<false> if the C<init_arg> was set to C<undef>.
780 =item B<< $attr->has_default >>
782 This will be I<false> if the C<default> was set to C<undef>, since
783 C<undef> is the default C<default> anyway.
785 =item B<< $attr->has_builder >>
787 =item B<< $attr->has_insertion_order >>
789 This will be I<false> if this attribute has not be inserted into a class
793 =head2 Value management
795 These methods are basically "back doors" to the instance, and can be
796 used to bypass the regular accessors, but still stay within the MOP.
798 These methods are not for general use, and should only be used if you
799 really know what you are doing.
803 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
805 This method is used internally to initialize the attribute's slot in
806 the object C<$instance>.
808 The C<$params> is a hash reference of the values passed to the object
811 It's unlikely that you'll need to call this method yourself.
813 =item B<< $attr->set_value($instance, $value) >>
815 Sets the value without going through the accessor. Note that this
816 works even with read-only attributes.
818 =item B<< $attr->set_raw_value($instance, $value) >>
820 Sets the value with no side effects such as a trigger.
822 This doesn't actually apply to Class::MOP attributes, only to subclasses.
824 =item B<< $attr->set_initial_value($instance, $value) >>
826 Sets the value without going through the accessor. This method is only
827 called when the instance is first being initialized.
829 =item B<< $attr->get_value($instance) >>
831 Returns the value without going through the accessor. Note that this
832 works even with write-only accessors.
834 =item B<< $attr->get_raw_value($instance) >>
836 Returns the value without any side effects such as lazy attributes.
838 Doesn't actually apply to Class::MOP attributes, only to subclasses.
840 =item B<< $attr->has_value($instance) >>
842 Return a boolean indicating whether the attribute has been set in
843 C<$instance>. This how the default C<predicate> method works.
845 =item B<< $attr->clear_value($instance) >>
847 This will clear the attribute's value in C<$instance>. This is what
848 the default C<clearer> calls.
850 Note that this works even if the attribute does not have any
851 associated read, write or clear methods.
855 =head2 Class association
857 These methods allow you to manage the attributes association with
858 the class that contains it. These methods should not be used
859 lightly, nor are they very magical, they are mostly used internally
860 and by metaclass instances.
864 =item B<< $attr->associated_class >>
866 This returns the C<Class::MOP::Class> with which this attribute is
869 =item B<< $attr->attach_to_class($metaclass) >>
871 This method stores a weakened reference to the C<$metaclass> object
874 This method does not remove the attribute from its old class,
875 nor does it create any accessors in the new class.
877 It is probably best to use the L<Class::MOP::Class> C<add_attribute>
880 =item B<< $attr->detach_from_class >>
882 This method removes the associate metaclass object from the attribute
885 This method does not remove the attribute itself from the class, or
886 remove its accessors.
888 It is probably best to use the L<Class::MOP::Class>
889 C<remove_attribute> method instead.
893 =head2 Attribute Accessor generation
897 =item B<< $attr->accessor_metaclass >>
899 Accessor methods are generated using an accessor metaclass. By
900 default, this is L<Class::MOP::Method::Accessor>. This method returns
901 the name of the accessor metaclass that this attribute uses.
903 =item B<< $attr->associate_method($method) >>
905 This associates a L<Class::MOP::Method> object with the
906 attribute. Typically, this is called internally when an attribute
907 generates its accessors.
909 =item B<< $attr->associated_methods >>
911 This returns the list of methods which have been associated with the
914 =item B<< $attr->install_accessors >>
916 This method generates and installs code the attributes various
917 accessors. It is typically called from the L<Class::MOP::Class>
918 C<add_attribute> method.
920 =item B<< $attr->remove_accessors >>
922 This method removes all of the accessors associated with the
925 This does not currently remove methods from the list returned by
926 C<associated_methods>.
928 =item B<< $attr->inline_get >>
930 =item B<< $attr->inline_set >>
932 =item B<< $attr->inline_has >>
934 =item B<< $attr->inline_clear >>
936 These methods return a code snippet suitable for inlining the relevant
937 operation. They expect strings containing variable names to be used in the
938 inlining, like C<'$self'> or C<'$_[1]'>.
946 =item B<< Class::MOP::Attribute->meta >>
948 This will return a L<Class::MOP::Class> instance for this class.
950 It should also be noted that L<Class::MOP> will actually bootstrap
951 this module by installing a number of attribute meta-objects into its
958 Stevan Little E<lt>stevan@iinteractive.comE<gt>
960 =head1 COPYRIGHT AND LICENSE
962 Copyright 2006-2010 by Infinity Interactive, Inc.
964 L<http://www.iinteractive.com>
966 This library is free software; you can redistribute it and/or modify
967 it under the same terms as Perl itself.