2 package Class::MOP::Attribute;
7 use Class::MOP::Method::Accessor;
10 use Scalar::Util 'blessed', 'reftype', 'weaken';
12 our $VERSION = '0.23';
13 our $AUTHORITY = 'cpan:STEVAN';
15 use base 'Class::MOP::Object';
18 require Class::MOP::Class;
19 Class::MOP::Class->initialize(blessed($_[0]) || $_[0]);
22 # NOTE: (meta-circularity)
23 # This method will be replaced in the
24 # boostrap section of Class::MOP, by
25 # a new version which uses the
26 # &Class::MOP::Class::construct_instance
27 # method to build an attribute meta-object
28 # which itself is described with attribute
30 # - Ain't meta-circularity grand? :)
36 (defined $name && $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 (is_default_a_coderef(\%options))
48 || confess("References are not allowed as default values, you must ".
49 "wrap then 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 $options{default} ) ) {
53 confess("A required attribute must have either 'init_arg', 'builder', or 'default'");
57 '$!accessor' => $options{accessor},
58 '$!reader' => $options{reader},
60 # protect this from silliness
61 init_arg => '!............( DO NOT DO THIS )............!',
62 '$!writer' => $options{writer},
63 '$!predicate' => $options{predicate},
64 '$!clearer' => $options{clearer},
65 '$!builder' => $options{builder},
66 '$!init_arg' => $options{init_arg},
67 '$!default' => $options{default},
68 # keep a weakened link to the
69 # class we are associated with
70 '$!associated_class' => undef,
71 '$!initializer' => $options{initializer},
72 # and a list of the methods
73 # associated with this attr
74 '@!associated_methods' => [],
79 # this is a primative (and kludgy) clone operation
80 # for now, it will be replaced in the Class::MOP
81 # bootstrap with a proper one, however we know
82 # that this one will work fine for now.
87 || confess "Can only clone an instance";
88 return bless { %{$self}, %options } => blessed($self);
91 sub initialize_instance_slot {
92 my ($self, $meta_instance, $instance, $params) = @_;
93 my $init_arg = $self->{'$!init_arg'};
94 # try to fetch the init arg from the %params ...
96 # if nothing was in the %params, we can use the
97 # attribute's default value (if it has one)
98 if(defined $init_arg and exists $params->{$init_arg}){
99 $meta_instance->_set_initial_slot_value(
102 $params->{$init_arg},
106 elsif (defined $self->{'$!default'}) {
107 $meta_instance->_set_initial_slot_value(
110 $self->default($instance),
114 elsif (defined( my $builder = $self->{'$!builder'})) {
115 if ($builder = $instance->can($builder)) {
116 $meta_instance->_set_initial_slot_value(
124 confess(blessed($instance)." does not support builder method '". $self->{'$!builder'} ."' for attribute '" . $self->name . "'");
130 # the next bunch of methods will get bootstrapped
131 # away in the Class::MOP bootstrapping section
133 sub name { $_[0]->{'$!name'} }
135 sub associated_class { $_[0]->{'$!associated_class'} }
136 sub associated_methods { $_[0]->{'@!associated_methods'} }
138 sub has_accessor { defined($_[0]->{'$!accessor'}) ? 1 : 0 }
139 sub has_reader { defined($_[0]->{'$!reader'}) ? 1 : 0 }
140 sub has_writer { defined($_[0]->{'$!writer'}) ? 1 : 0 }
141 sub has_predicate { defined($_[0]->{'$!predicate'}) ? 1 : 0 }
142 sub has_clearer { defined($_[0]->{'$!clearer'}) ? 1 : 0 }
143 sub has_builder { defined($_[0]->{'$!builder'}) ? 1 : 0 }
144 sub has_init_arg { defined($_[0]->{'$!init_arg'}) ? 1 : 0 }
145 sub has_default { defined($_[0]->{'$!default'}) ? 1 : 0 }
146 sub has_initializer { defined($_[0]->{'$!initializer'}) ? 1 : 0 }
148 sub accessor { $_[0]->{'$!accessor'} }
149 sub reader { $_[0]->{'$!reader'} }
150 sub writer { $_[0]->{'$!writer'} }
151 sub predicate { $_[0]->{'$!predicate'} }
152 sub clearer { $_[0]->{'$!clearer'} }
153 sub builder { $_[0]->{'$!builder'} }
154 sub init_arg { $_[0]->{'$!init_arg'} }
155 sub initializer { $_[0]->{'$!initializer'} }
157 # end bootstrapped away method section.
158 # (all methods below here are kept intact)
160 sub get_read_method {
162 my $reader = $self->reader || $self->accessor;
164 return $reader unless ref $reader;
166 my ($name) = %$reader;
170 sub get_write_method {
172 my $writer = $self->writer || $self->accessor;
174 return $writer unless ref $writer;
176 my ($name) = %$writer;
180 sub get_read_method_ref {
182 if ((my $reader = $self->get_read_method) && $self->associated_class) {
183 return $self->associated_class->get_method($reader);
186 return sub { $self->get_value(@_) };
190 sub get_write_method_ref {
192 if ((my $writer = $self->get_write_method) && $self->associated_class) {
193 return $self->associated_class->get_method($writer);
196 return sub { $self->set_value(@_) };
200 sub is_default_a_coderef {
201 ('CODE' eq (reftype($_[0]->{'$!default'} || $_[0]->{default}) || ''))
205 my ($self, $instance) = @_;
206 if (defined $instance && $self->is_default_a_coderef) {
207 # if the default is a CODE ref, then
208 # we pass in the instance and default
209 # can return a value based on that
210 # instance. Somewhat crude, but works.
211 return $self->{'$!default'}->($instance);
213 $self->{'$!default'};
218 sub slots { (shift)->name }
222 sub attach_to_class {
223 my ($self, $class) = @_;
224 (blessed($class) && $class->isa('Class::MOP::Class'))
225 || confess "You must pass a Class::MOP::Class instance (or a subclass)";
226 weaken($self->{'$!associated_class'} = $class);
229 sub detach_from_class {
231 $self->{'$!associated_class'} = undef;
236 sub associate_method {
237 my ($self, $method) = @_;
238 push @{$self->{'@!associated_methods'}} => $method;
243 sub set_initial_value {
244 my ($self, $instance, $value) = @_;
246 Class::MOP::Class->initialize(blessed($instance))
248 ->_set_initial_slot_value($instance, $self->name, $value, $self->initializer);
252 my ($self, $instance, $value) = @_;
254 Class::MOP::Class->initialize(blessed($instance))
256 ->set_slot_value($instance, $self->name, $value);
260 my ($self, $instance) = @_;
262 Class::MOP::Class->initialize(blessed($instance))
264 ->get_slot_value($instance, $self->name);
268 my ($self, $instance) = @_;
270 Class::MOP::Class->initialize(blessed($instance))
272 ->is_slot_initialized($instance, $self->name);
276 my ($self, $instance) = @_;
278 Class::MOP::Class->initialize(blessed($instance))
280 ->deinitialize_slot($instance, $self->name);
285 sub accessor_metaclass { 'Class::MOP::Method::Accessor' }
287 sub process_accessors {
288 my ($self, $type, $accessor, $generate_as_inline_methods) = @_;
289 if (reftype($accessor)) {
290 (reftype($accessor) eq 'HASH')
291 || confess "bad accessor/reader/writer/predicate/clearer format, must be a HASH ref";
292 my ($name, $method) = %{$accessor};
293 $method = $self->accessor_metaclass->wrap($method);
294 $self->associate_method($method);
295 return ($name, $method);
298 my $inline_me = ($generate_as_inline_methods && $self->associated_class->instance_metaclass->is_inlinable);
301 $method = $self->accessor_metaclass->new(
303 is_inline => $inline_me,
304 accessor_type => $type,
307 confess "Could not create the '$type' method for " . $self->name . " because : $@" if $@;
308 $self->associate_method($method);
309 return ($accessor, $method);
313 sub install_accessors {
316 my $class = $self->associated_class;
319 $self->process_accessors('accessor' => $self->accessor(), $inline)
320 ) if $self->has_accessor();
323 $self->process_accessors('reader' => $self->reader(), $inline)
324 ) if $self->has_reader();
327 $self->process_accessors('writer' => $self->writer(), $inline)
328 ) if $self->has_writer();
331 $self->process_accessors('predicate' => $self->predicate(), $inline)
332 ) if $self->has_predicate();
335 $self->process_accessors('clearer' => $self->clearer(), $inline)
336 ) if $self->has_clearer();
342 my $_remove_accessor = sub {
343 my ($accessor, $class) = @_;
344 if (reftype($accessor) && reftype($accessor) eq 'HASH') {
345 ($accessor) = keys %{$accessor};
347 my $method = $class->get_method($accessor);
348 $class->remove_method($accessor)
349 if (blessed($method) && $method->isa('Class::MOP::Method::Accessor'));
352 sub remove_accessors {
355 # we really need to make sure to remove from the
356 # associates methods here as well. But this is
357 # such a slimly used method, I am not worried
358 # about it right now.
359 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
360 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
361 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
362 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
363 $_remove_accessor->($self->clearer(), $self->associated_class()) if $self->has_clearer();
377 Class::MOP::Attribute - Attribute Meta Object
381 Class::MOP::Attribute->new('$foo' => (
382 accessor => 'foo', # dual purpose get/set accessor
383 predicate => 'has_foo' # predicate check for defined-ness
384 init_arg => '-foo', # class->new will look for a -foo key
385 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
388 Class::MOP::Attribute->new('$.bar' => (
389 reader => 'bar', # getter
390 writer => 'set_bar', # setter
391 predicate => 'has_bar' # predicate check for defined-ness
392 init_arg => ':bar', # class->new will look for a :bar key
393 # no default value means it is undef
398 The Attribute Protocol is almost entirely an invention of this module,
399 and is completely optional to this MOP. This is because Perl 5 does not
400 have consistent notion of what is an attribute of a class. There are
401 so many ways in which this is done, and very few (if any) are
402 easily discoverable by this module.
404 So, all that said, this module attempts to inject some order into this
405 chaos, by introducing a consistent API which can be used to create
414 =item B<new ($name, ?%options)>
416 An attribute must (at the very least), have a C<$name>. All other
417 C<%options> are contained added as key-value pairs. Acceptable keys
424 This should be a string value representing the expected key in
425 an initialization hash. For instance, if we have an I<init_arg>
426 value of C<-foo>, then the following code will Just Work.
428 MyClass->meta->construct_instance(-foo => "Hello There");
430 In an init_arg is not assigned, it will automatically use the
435 The value of this key is the name of the method that will be
436 called to obtain the value used to initialize the attribute.
437 This should be a method in the class associated with the attribute,
438 not a method in the attribute class itself.
442 The value of this key is the default value which
443 C<Class::MOP::Class::construct_instance> will initialize the
447 If the value is a simple scalar (string or number), then it can
448 be just passed as is. However, if you wish to initialize it with
449 a HASH or ARRAY ref, then you need to wrap that inside a CODE
452 Class::MOP::Attribute->new('@foo' => (
453 default => sub { [] },
458 Class::MOP::Attribute->new('%foo' => (
459 default => sub { {} },
462 If you wish to initialize an attribute with a CODE reference
463 itself, then you need to wrap that in a subroutine as well, like
466 Class::MOP::Attribute->new('&foo' => (
467 default => sub { sub { print "Hello World" } },
470 And lastly, if the value of your attribute is dependent upon
471 some other aspect of the instance structure, then you can take
472 advantage of the fact that when the I<default> value is a CODE
473 reference, it is passed the raw (unblessed) instance structure
474 as it's only argument. So you can do things like this:
476 Class::MOP::Attribute->new('$object_identity' => (
477 default => sub { Scalar::Util::refaddr($_[0]) },
480 This last feature is fairly limited as there is no gurantee of
481 the order of attribute initializations, so you cannot perform
482 any kind of dependent initializations. However, if this is
483 something you need, you could subclass B<Class::MOP::Class> and
484 this class to acheive it. However, this is currently left as
485 an exercise to the reader :).
489 The I<accessor>, I<reader>, I<writer>, I<predicate> and I<clearer> keys can
490 contain either; the name of the method and an appropriate default one will be
491 generated for you, B<or> a HASH ref containing exactly one key (which will be
492 used as the name of the method) and one value, which should contain a CODE
493 reference which will be installed as the method itself.
499 The I<accessor> is a standard perl-style read/write accessor. It will
500 return the value of the attribute, and if a value is passed as an argument,
501 it will assign that value to the attribute.
504 This method will properly handle the following code, by assigning an
505 C<undef> value to the attribute.
507 $object->set_something(undef);
511 This is a basic read-only accessor, it will just return the value of
516 This is a basic write accessor, it accepts a single argument, and
517 assigns that value to the attribute. This method does not intentially
518 return a value, however perl will return the result of the last
519 expression in the subroutine, which returns in this returning the
520 same value that it was passed.
523 This method will properly handle the following code, by assigning an
524 C<undef> value to the attribute.
526 $object->set_something();
530 This is a basic test to see if any value has been set for the
531 attribute. It will return true (C<1>) if the attribute has been set
532 to any value (even C<undef>), and false (C<0>) otherwise.
535 The predicate will return true even when you set an attribute's
536 value to C<undef>. This behaviour has changed as of version 0.43. In
537 older versions, the predicate (erroneously) checked for attribute
538 value definedness, instead of presence as it is now.
540 If you really want to get rid of the value, you have to define and
541 use a I<clearer> (see below).
546 This is the a method that will uninitialize the attr, reverting lazy values
547 back to their "unfulfilled" state.
551 =item B<clone (%options)>
553 =item B<initialize_instance_slot ($instance, $params)>
557 =head2 Value management
559 These methods are basically "backdoors" to the instance, which can be used
560 to bypass the regular accessors, but still stay within the context of the MOP.
562 These methods are not for general use, and should only be used if you really
563 know what you are doing.
567 =item B<set_value ($instance, $value)>
569 Set the value without going through the accessor. Note that this may be done to
570 even attributes with just read only accessors.
572 =item B<get_value ($instance)>
574 Return the value without going through the accessor. Note that this may be done
575 even to attributes with just write only accessors.
577 =item B<has_value ($instance)>
579 Return a boolean indicating if the item in the C<$instance> has a value in it.
580 This is basically what the default C<predicate> method calls.
582 =item B<clear_value ($instance)>
584 This will clear the value in the C<$instance>. This is basically what the default
585 C<clearer> would call. Note that this may be done even if the attirbute does not
586 have any associated read, write or clear methods.
592 These are all basic read-only value accessors for the values
593 passed into C<new>. I think they are pretty much self-explanitory.
613 =item B<is_default_a_coderef>
615 =item B<default (?$instance)>
617 Return the default value for the attribute.
619 If you pass in an C<$instance> argument to this accessor and the
620 I<default> is a CODE reference, then the CODE reference will be
621 executed with the C<$instance> as its argument.
625 Return a list of slots required by the attribute. This is usually
626 just one, which is the name of the attribute.
628 =item B<get_read_method>
630 =item B<get_write_method>
632 Return the name of a method name suitable for reading / writing the value
633 of the attribute in the associated class. Suitable for use whether
634 C<reader> and C<writer> or C<accessor> was used.
636 =item B<get_read_method_ref>
638 =item B<get_write_method_ref>
640 Return the CODE reference of a method suitable for reading / writing the
641 value of the attribute in the associated class. Suitable for use whether
642 C<reader> and C<writer> or C<accessor> was specified or not.
644 NOTE: If not reader/writer/accessor was specified, this will use the
645 attribute get_value/set_value methods, which can be very inefficient.
649 =head2 Informational predicates
651 These are all basic predicate methods for the values passed into C<new>.
655 =item B<has_accessor>
661 =item B<has_predicate>
665 =item B<has_initializer>
667 =item B<has_init_arg>
675 =head2 Class association
677 These methods allow you to manage the attributes association with
678 the class that contains it. These methods should not be used
679 lightly, nor are they very magical, they are mostly used internally
680 and by metaclass instances.
684 =item B<associated_class>
686 This returns the metaclass this attribute is associated with.
688 =item B<attach_to_class ($class)>
690 This will store a weaken reference to C<$class> internally. You should
691 note that just changing the class assocation will not remove the attribute
692 from it's old class, and initialize it (and it's accessors) in the new
693 C<$class>. It is up to you to do this manually.
695 =item B<detach_from_class>
697 This will remove the weakened reference to the class. It does B<not>
698 remove the attribute itself from the class (or remove it's accessors),
699 you must do that yourself if you want too. Actually if that is what
700 you want to do, you should probably be looking at
701 L<Class::MOP::Class::remove_attribute> instead.
705 =head2 Attribute Accessor generation
709 =item B<accessor_metaclass>
711 Accessors are generated by an accessor metaclass, which is usually
712 a subclass of C<Class::MOP::Method::Accessor>. This method returns
713 the name of the accessor metaclass that this attribute uses.
715 =item B<associate_method ($method)>
717 This will associate a C<$method> with the given attribute which is
718 used internally by the accessor generator.
720 =item B<associated_methods>
722 This will return the list of methods which have been associated with
723 the C<associate_method> methods.
725 =item B<install_accessors>
727 This allows the attribute to generate and install code for it's own
728 I<accessor/reader/writer/predicate> methods. This is called by
729 C<Class::MOP::Class::add_attribute>.
731 This method will call C<process_accessors> for each of the possible
732 method types (accessor, reader, writer & predicate).
734 =item B<process_accessors ($type, $value)>
736 This takes a C<$type> (accessor, reader, writer or predicate), and
737 a C<$value> (the value passed into the constructor for each of the
738 different types). It will then either generate the method itself
739 (using the C<generate_*_method> methods listed below) or it will
740 use the custom method passed through the constructor.
742 =item B<remove_accessors>
744 This allows the attribute to remove the method for it's own
745 I<accessor/reader/writer/predicate/clearer>. This is called by
746 C<Class::MOP::Class::remove_attribute>.
748 NOTE: This does not currently remove methods from the list returned
749 by C<associated_methods>, that is on the TODO list.
759 This will return a B<Class::MOP::Class> instance which is related
762 It should also be noted that B<Class::MOP> will actually bootstrap
763 this module by installing a number of attribute meta-objects into
764 it's metaclass. This will allow this class to reap all the benifits
765 of the MOP when subclassing it.
771 Stevan Little E<lt>stevan@iinteractive.comE<gt>
773 =head1 COPYRIGHT AND LICENSE
775 Copyright 2006-2008 by Infinity Interactive, Inc.
777 L<http://www.iinteractive.com>
779 This library is free software; you can redistribute it and/or modify
780 it under the same terms as Perl itself.