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 # and a list of the methods
72 # associated with this attr
73 '@!associated_methods' => [],
78 # this is a primative (and kludgy) clone operation
79 # for now, it will be replaced in the Class::MOP
80 # bootstrap with a proper one, however we know
81 # that this one will work fine for now.
86 || confess "Can only clone an instance";
87 return bless { %{$self}, %options } => blessed($self);
90 sub initialize_instance_slot {
91 my ($self, $meta_instance, $instance, $params) = @_;
92 my $init_arg = $self->{'$!init_arg'};
93 # try to fetch the init arg from the %params ...
95 # if nothing was in the %params, we can use the
96 # attribute's default value (if it has one)
97 if(defined $init_arg and exists $params->{$init_arg}){
98 $meta_instance->set_slot_value($instance, $self->name, $params->{$init_arg});
100 elsif (defined $self->{'$!default'}) {
101 $meta_instance->set_slot_value($instance, $self->name, $self->default($instance));
103 elsif (defined( my $builder = $self->{'$!builder'})) {
104 if ($builder = $instance->can($builder)) {
105 $meta_instance->set_slot_value($instance, $self->name, $instance->$builder);
108 confess(blessed($instance)." does not support builder method '". $self->{'$!builder'} ."' for attribute '" . $self->name . "'");
114 # the next bunch of methods will get bootstrapped
115 # away in the Class::MOP bootstrapping section
117 sub name { $_[0]->{'$!name'} }
119 sub associated_class { $_[0]->{'$!associated_class'} }
120 sub associated_methods { $_[0]->{'@!associated_methods'} }
122 sub has_accessor { defined($_[0]->{'$!accessor'}) ? 1 : 0 }
123 sub has_reader { defined($_[0]->{'$!reader'}) ? 1 : 0 }
124 sub has_writer { defined($_[0]->{'$!writer'}) ? 1 : 0 }
125 sub has_predicate { defined($_[0]->{'$!predicate'}) ? 1 : 0 }
126 sub has_clearer { defined($_[0]->{'$!clearer'}) ? 1 : 0 }
127 sub has_builder { defined($_[0]->{'$!builder'}) ? 1 : 0 }
128 sub has_init_arg { defined($_[0]->{'$!init_arg'}) ? 1 : 0 }
129 sub has_default { defined($_[0]->{'$!default'}) ? 1 : 0 }
131 sub accessor { $_[0]->{'$!accessor'} }
132 sub reader { $_[0]->{'$!reader'} }
133 sub writer { $_[0]->{'$!writer'} }
134 sub predicate { $_[0]->{'$!predicate'} }
135 sub clearer { $_[0]->{'$!clearer'} }
136 sub builder { $_[0]->{'$!builder'} }
137 sub init_arg { $_[0]->{'$!init_arg'} }
139 # end bootstrapped away method section.
140 # (all methods below here are kept intact)
142 sub get_read_method {
144 my $reader = $self->reader || $self->accessor;
146 return $reader unless ref $reader;
148 my ($name) = %$reader;
152 sub get_write_method {
154 my $writer = $self->writer || $self->accessor;
156 return $writer unless ref $writer;
158 my ($name) = %$writer;
162 sub get_read_method_ref {
164 if ((my $reader = $self->get_read_method) && $self->associated_class) {
165 return $self->associated_class->get_method($reader);
168 return sub { $self->get_value(@_) };
172 sub get_write_method_ref {
174 if ((my $writer = $self->get_write_method) && $self->associated_class) {
175 return $self->associated_class->get_method($writer);
178 return sub { $self->set_value(@_) };
182 sub is_default_a_coderef {
183 ('CODE' eq (reftype($_[0]->{'$!default'} || $_[0]->{default}) || ''))
187 my ($self, $instance) = @_;
188 if (defined $instance && $self->is_default_a_coderef) {
189 # if the default is a CODE ref, then
190 # we pass in the instance and default
191 # can return a value based on that
192 # instance. Somewhat crude, but works.
193 return $self->{'$!default'}->($instance);
195 $self->{'$!default'};
200 sub slots { (shift)->name }
204 sub attach_to_class {
205 my ($self, $class) = @_;
206 (blessed($class) && $class->isa('Class::MOP::Class'))
207 || confess "You must pass a Class::MOP::Class instance (or a subclass)";
208 weaken($self->{'$!associated_class'} = $class);
211 sub detach_from_class {
213 $self->{'$!associated_class'} = undef;
218 sub associate_method {
219 my ($self, $method) = @_;
220 push @{$self->{'@!associated_methods'}} => $method;
226 my ($self, $instance, $value) = @_;
228 Class::MOP::Class->initialize(blessed($instance))
230 ->set_slot_value($instance, $self->name, $value);
234 my ($self, $instance) = @_;
236 Class::MOP::Class->initialize(blessed($instance))
238 ->get_slot_value($instance, $self->name);
242 my ($self, $instance) = @_;
244 Class::MOP::Class->initialize(blessed($instance))
246 ->is_slot_initialized($instance, $self->name);
250 my ($self, $instance) = @_;
252 Class::MOP::Class->initialize(blessed($instance))
254 ->deinitialize_slot($instance, $self->name);
259 sub accessor_metaclass { 'Class::MOP::Method::Accessor' }
261 sub process_accessors {
262 my ($self, $type, $accessor, $generate_as_inline_methods) = @_;
263 if (reftype($accessor)) {
264 (reftype($accessor) eq 'HASH')
265 || confess "bad accessor/reader/writer/predicate/clearer format, must be a HASH ref";
266 my ($name, $method) = %{$accessor};
267 $method = $self->accessor_metaclass->wrap($method);
268 $self->associate_method($method);
269 return ($name, $method);
272 my $inline_me = ($generate_as_inline_methods && $self->associated_class->instance_metaclass->is_inlinable);
275 $method = $self->accessor_metaclass->new(
277 is_inline => $inline_me,
278 accessor_type => $type,
281 confess "Could not create the '$type' method for " . $self->name . " because : $@" if $@;
282 $self->associate_method($method);
283 return ($accessor, $method);
287 sub install_accessors {
290 my $class = $self->associated_class;
293 $self->process_accessors('accessor' => $self->accessor(), $inline)
294 ) if $self->has_accessor();
297 $self->process_accessors('reader' => $self->reader(), $inline)
298 ) if $self->has_reader();
301 $self->process_accessors('writer' => $self->writer(), $inline)
302 ) if $self->has_writer();
305 $self->process_accessors('predicate' => $self->predicate(), $inline)
306 ) if $self->has_predicate();
309 $self->process_accessors('clearer' => $self->clearer(), $inline)
310 ) if $self->has_clearer();
316 my $_remove_accessor = sub {
317 my ($accessor, $class) = @_;
318 if (reftype($accessor) && reftype($accessor) eq 'HASH') {
319 ($accessor) = keys %{$accessor};
321 my $method = $class->get_method($accessor);
322 $class->remove_method($accessor)
323 if (blessed($method) && $method->isa('Class::MOP::Method::Accessor'));
326 sub remove_accessors {
329 # we really need to make sure to remove from the
330 # associates methods here as well. But this is
331 # such a slimly used method, I am not worried
332 # about it right now.
333 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
334 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
335 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
336 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
337 $_remove_accessor->($self->clearer(), $self->associated_class()) if $self->has_clearer();
351 Class::MOP::Attribute - Attribute Meta Object
355 Class::MOP::Attribute->new('$foo' => (
356 accessor => 'foo', # dual purpose get/set accessor
357 predicate => 'has_foo' # predicate check for defined-ness
358 init_arg => '-foo', # class->new will look for a -foo key
359 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
362 Class::MOP::Attribute->new('$.bar' => (
363 reader => 'bar', # getter
364 writer => 'set_bar', # setter
365 predicate => 'has_bar' # predicate check for defined-ness
366 init_arg => ':bar', # class->new will look for a :bar key
367 # no default value means it is undef
372 The Attribute Protocol is almost entirely an invention of this module,
373 and is completely optional to this MOP. This is because Perl 5 does not
374 have consistent notion of what is an attribute of a class. There are
375 so many ways in which this is done, and very few (if any) are
376 easily discoverable by this module.
378 So, all that said, this module attempts to inject some order into this
379 chaos, by introducing a consistent API which can be used to create
388 =item B<new ($name, ?%options)>
390 An attribute must (at the very least), have a C<$name>. All other
391 C<%options> are contained added as key-value pairs. Acceptable keys
398 This should be a string value representing the expected key in
399 an initialization hash. For instance, if we have an I<init_arg>
400 value of C<-foo>, then the following code will Just Work.
402 MyClass->meta->construct_instance(-foo => "Hello There");
404 In an init_arg is not assigned, it will automatically use the
409 The value of this key is the name of the method that will be
410 called to obtain the value used to initialize the attribute.
411 This should be a method in the class associated with the attribute,
412 not a method in the attribute class itself.
416 The value of this key is the default value which
417 C<Class::MOP::Class::construct_instance> will initialize the
421 If the value is a simple scalar (string or number), then it can
422 be just passed as is. However, if you wish to initialize it with
423 a HASH or ARRAY ref, then you need to wrap that inside a CODE
426 Class::MOP::Attribute->new('@foo' => (
427 default => sub { [] },
432 Class::MOP::Attribute->new('%foo' => (
433 default => sub { {} },
436 If you wish to initialize an attribute with a CODE reference
437 itself, then you need to wrap that in a subroutine as well, like
440 Class::MOP::Attribute->new('&foo' => (
441 default => sub { sub { print "Hello World" } },
444 And lastly, if the value of your attribute is dependent upon
445 some other aspect of the instance structure, then you can take
446 advantage of the fact that when the I<default> value is a CODE
447 reference, it is passed the raw (unblessed) instance structure
448 as it's only argument. So you can do things like this:
450 Class::MOP::Attribute->new('$object_identity' => (
451 default => sub { Scalar::Util::refaddr($_[0]) },
454 This last feature is fairly limited as there is no gurantee of
455 the order of attribute initializations, so you cannot perform
456 any kind of dependent initializations. However, if this is
457 something you need, you could subclass B<Class::MOP::Class> and
458 this class to acheive it. However, this is currently left as
459 an exercise to the reader :).
463 The I<accessor>, I<reader>, I<writer>, I<predicate> and I<clearer> keys can
464 contain either; the name of the method and an appropriate default one will be
465 generated for you, B<or> a HASH ref containing exactly one key (which will be
466 used as the name of the method) and one value, which should contain a CODE
467 reference which will be installed as the method itself.
473 The I<accessor> is a standard perl-style read/write accessor. It will
474 return the value of the attribute, and if a value is passed as an argument,
475 it will assign that value to the attribute.
478 This method will properly handle the following code, by assigning an
479 C<undef> value to the attribute.
481 $object->set_something(undef);
485 This is a basic read-only accessor, it will just return the value of
490 This is a basic write accessor, it accepts a single argument, and
491 assigns that value to the attribute. This method does not intentially
492 return a value, however perl will return the result of the last
493 expression in the subroutine, which returns in this returning the
494 same value that it was passed.
497 This method will properly handle the following code, by assigning an
498 C<undef> value to the attribute.
500 $object->set_something();
504 This is a basic test to see if any value has been set for the
505 attribute. It will return true (C<1>) if the attribute has been set
506 to any value (even C<undef>), and false (C<0>) otherwise.
509 The predicate will return true even when you set an attribute's
510 value to C<undef>. This behaviour has changed as of version 0.43. In
511 older versions, the predicate (erroneously) checked for attribute
512 value definedness, instead of presence as it is now.
514 If you really want to get rid of the value, you have to define and
515 use a I<clearer> (see below).
520 This is the a method that will uninitialize the attr, reverting lazy values
521 back to their "unfulfilled" state.
525 =item B<clone (%options)>
527 =item B<initialize_instance_slot ($instance, $params)>
531 =head2 Value management
533 These methods are basically "backdoors" to the instance, which can be used
534 to bypass the regular accessors, but still stay within the context of the MOP.
536 These methods are not for general use, and should only be used if you really
537 know what you are doing.
541 =item B<set_value ($instance, $value)>
543 Set the value without going through the accessor. Note that this may be done to
544 even attributes with just read only accessors.
546 =item B<get_value ($instance)>
548 Return the value without going through the accessor. Note that this may be done
549 even to attributes with just write only accessors.
551 =item B<has_value ($instance)>
553 Return a boolean indicating if the item in the C<$instance> has a value in it.
554 This is basically what the default C<predicate> method calls.
556 =item B<clear_value ($instance)>
558 This will clear the value in the C<$instance>. This is basically what the default
559 C<clearer> would call. Note that this may be done even if the attirbute does not
560 have any associated read, write or clear methods.
566 These are all basic read-only value accessors for the values
567 passed into C<new>. I think they are pretty much self-explanitory.
585 =item B<is_default_a_coderef>
587 =item B<default (?$instance)>
589 Return the default value for the attribute.
591 If you pass in an C<$instance> argument to this accessor and the
592 I<default> is a CODE reference, then the CODE reference will be
593 executed with the C<$instance> as its argument.
597 Return a list of slots required by the attribute. This is usually
598 just one, which is the name of the attribute.
600 =item B<get_read_method>
602 =item B<get_write_method>
604 Return the name of a method name suitable for reading / writing the value
605 of the attribute in the associated class. Suitable for use whether
606 C<reader> and C<writer> or C<accessor> was used.
608 =item B<get_read_method_ref>
610 =item B<get_write_method_ref>
612 Return the CODE reference of a method suitable for reading / writing the
613 value of the attribute in the associated class. Suitable for use whether
614 C<reader> and C<writer> or C<accessor> was specified or not.
616 NOTE: If not reader/writer/accessor was specified, this will use the
617 attribute get_value/set_value methods, which can be very inefficient.
621 =head2 Informational predicates
623 These are all basic predicate methods for the values passed into C<new>.
627 =item B<has_accessor>
633 =item B<has_predicate>
637 =item B<has_init_arg>
645 =head2 Class association
647 These methods allow you to manage the attributes association with
648 the class that contains it. These methods should not be used
649 lightly, nor are they very magical, they are mostly used internally
650 and by metaclass instances.
654 =item B<associated_class>
656 This returns the metaclass this attribute is associated with.
658 =item B<attach_to_class ($class)>
660 This will store a weaken reference to C<$class> internally. You should
661 note that just changing the class assocation will not remove the attribute
662 from it's old class, and initialize it (and it's accessors) in the new
663 C<$class>. It is up to you to do this manually.
665 =item B<detach_from_class>
667 This will remove the weakened reference to the class. It does B<not>
668 remove the attribute itself from the class (or remove it's accessors),
669 you must do that yourself if you want too. Actually if that is what
670 you want to do, you should probably be looking at
671 L<Class::MOP::Class::remove_attribute> instead.
675 =head2 Attribute Accessor generation
679 =item B<accessor_metaclass>
681 Accessors are generated by an accessor metaclass, which is usually
682 a subclass of C<Class::MOP::Method::Accessor>. This method returns
683 the name of the accessor metaclass that this attribute uses.
685 =item B<associate_method ($method)>
687 This will associate a C<$method> with the given attribute which is
688 used internally by the accessor generator.
690 =item B<associated_methods>
692 This will return the list of methods which have been associated with
693 the C<associate_method> methods.
695 =item B<install_accessors>
697 This allows the attribute to generate and install code for it's own
698 I<accessor/reader/writer/predicate> methods. This is called by
699 C<Class::MOP::Class::add_attribute>.
701 This method will call C<process_accessors> for each of the possible
702 method types (accessor, reader, writer & predicate).
704 =item B<process_accessors ($type, $value)>
706 This takes a C<$type> (accessor, reader, writer or predicate), and
707 a C<$value> (the value passed into the constructor for each of the
708 different types). It will then either generate the method itself
709 (using the C<generate_*_method> methods listed below) or it will
710 use the custom method passed through the constructor.
712 =item B<remove_accessors>
714 This allows the attribute to remove the method for it's own
715 I<accessor/reader/writer/predicate/clearer>. This is called by
716 C<Class::MOP::Class::remove_attribute>.
718 NOTE: This does not currently remove methods from the list returned
719 by C<associated_methods>, that is on the TODO list.
729 This will return a B<Class::MOP::Class> instance which is related
732 It should also be noted that B<Class::MOP> will actually bootstrap
733 this module by installing a number of attribute meta-objects into
734 it's metaclass. This will allow this class to reap all the benifits
735 of the MOP when subclassing it.
741 Stevan Little E<lt>stevan@iinteractive.comE<gt>
743 =head1 COPYRIGHT AND LICENSE
745 Copyright 2006-2008 by Infinity Interactive, Inc.
747 L<http://www.iinteractive.com>
749 This library is free software; you can redistribute it and/or modify
750 it under the same terms as Perl itself.