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'}} => $method;
244 my ($self, $instance, $value) = @_;
246 Class::MOP::Class->initialize(blessed($instance))
248 ->set_slot_value($instance, $self->name, $value);
252 my ($self, $instance) = @_;
254 Class::MOP::Class->initialize(blessed($instance))
256 ->get_slot_value($instance, $self->name);
260 my ($self, $instance) = @_;
262 Class::MOP::Class->initialize(blessed($instance))
264 ->is_slot_initialized($instance, $self->name);
268 my ($self, $instance) = @_;
270 Class::MOP::Class->initialize(blessed($instance))
272 ->deinitialize_slot($instance, $self->name);
277 sub accessor_metaclass { 'Class::MOP::Method::Accessor' }
279 sub process_accessors {
280 my ($self, $type, $accessor, $generate_as_inline_methods) = @_;
281 if (reftype($accessor)) {
282 (reftype($accessor) eq 'HASH')
283 || confess "bad accessor/reader/writer/predicate/clearer format, must be a HASH ref";
284 my ($name, $method) = %{$accessor};
285 $method = $self->accessor_metaclass->wrap($method);
286 $self->associate_method($method);
287 return ($name, $method);
290 my $inline_me = ($generate_as_inline_methods && $self->associated_class->instance_metaclass->is_inlinable);
293 $method = $self->accessor_metaclass->new(
295 is_inline => $inline_me,
296 accessor_type => $type,
299 confess "Could not create the '$type' method for " . $self->name . " because : $@" if $@;
300 $self->associate_method($method);
301 return ($accessor, $method);
305 sub install_accessors {
308 my $class = $self->associated_class;
311 $self->process_accessors('accessor' => $self->accessor(), $inline)
312 ) if $self->has_accessor();
315 $self->process_accessors('reader' => $self->reader(), $inline)
316 ) if $self->has_reader();
319 $self->process_accessors('writer' => $self->writer(), $inline)
320 ) if $self->has_writer();
323 $self->process_accessors('predicate' => $self->predicate(), $inline)
324 ) if $self->has_predicate();
327 $self->process_accessors('clearer' => $self->clearer(), $inline)
328 ) if $self->has_clearer();
334 my $_remove_accessor = sub {
335 my ($accessor, $class) = @_;
336 if (reftype($accessor) && reftype($accessor) eq 'HASH') {
337 ($accessor) = keys %{$accessor};
339 my $method = $class->get_method($accessor);
340 $class->remove_method($accessor)
341 if (blessed($method) && $method->isa('Class::MOP::Method::Accessor'));
344 sub remove_accessors {
347 # we really need to make sure to remove from the
348 # associates methods here as well. But this is
349 # such a slimly used method, I am not worried
350 # about it right now.
351 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
352 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
353 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
354 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
355 $_remove_accessor->($self->clearer(), $self->associated_class()) if $self->has_clearer();
369 Class::MOP::Attribute - Attribute Meta Object
373 Class::MOP::Attribute->new('$foo' => (
374 accessor => 'foo', # dual purpose get/set accessor
375 predicate => 'has_foo' # predicate check for defined-ness
376 init_arg => '-foo', # class->new will look for a -foo key
377 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
380 Class::MOP::Attribute->new('$.bar' => (
381 reader => 'bar', # getter
382 writer => 'set_bar', # setter
383 predicate => 'has_bar' # predicate check for defined-ness
384 init_arg => ':bar', # class->new will look for a :bar key
385 # no default value means it is undef
390 The Attribute Protocol is almost entirely an invention of this module,
391 and is completely optional to this MOP. This is because Perl 5 does not
392 have consistent notion of what is an attribute of a class. There are
393 so many ways in which this is done, and very few (if any) are
394 easily discoverable by this module.
396 So, all that said, this module attempts to inject some order into this
397 chaos, by introducing a consistent API which can be used to create
406 =item B<new ($name, ?%options)>
408 An attribute must (at the very least), have a C<$name>. All other
409 C<%options> are contained added as key-value pairs. Acceptable keys
416 This should be a string value representing the expected key in
417 an initialization hash. For instance, if we have an I<init_arg>
418 value of C<-foo>, then the following code will Just Work.
420 MyClass->meta->construct_instance(-foo => "Hello There");
422 In an init_arg is not assigned, it will automatically use the
427 The value of this key is the name of the method that will be
428 called to obtain the value used to initialize the attribute.
429 This should be a method in the class associated with the attribute,
430 not a method in the attribute class itself.
434 The value of this key is the default value which
435 C<Class::MOP::Class::construct_instance> will initialize the
439 If the value is a simple scalar (string or number), then it can
440 be just passed as is. However, if you wish to initialize it with
441 a HASH or ARRAY ref, then you need to wrap that inside a CODE
444 Class::MOP::Attribute->new('@foo' => (
445 default => sub { [] },
450 Class::MOP::Attribute->new('%foo' => (
451 default => sub { {} },
454 If you wish to initialize an attribute with a CODE reference
455 itself, then you need to wrap that in a subroutine as well, like
458 Class::MOP::Attribute->new('&foo' => (
459 default => sub { sub { print "Hello World" } },
462 And lastly, if the value of your attribute is dependent upon
463 some other aspect of the instance structure, then you can take
464 advantage of the fact that when the I<default> value is a CODE
465 reference, it is passed the raw (unblessed) instance structure
466 as it's only argument. So you can do things like this:
468 Class::MOP::Attribute->new('$object_identity' => (
469 default => sub { Scalar::Util::refaddr($_[0]) },
472 This last feature is fairly limited as there is no gurantee of
473 the order of attribute initializations, so you cannot perform
474 any kind of dependent initializations. However, if this is
475 something you need, you could subclass B<Class::MOP::Class> and
476 this class to acheive it. However, this is currently left as
477 an exercise to the reader :).
481 The I<accessor>, I<reader>, I<writer>, I<predicate> and I<clearer> keys can
482 contain either; the name of the method and an appropriate default one will be
483 generated for you, B<or> a HASH ref containing exactly one key (which will be
484 used as the name of the method) and one value, which should contain a CODE
485 reference which will be installed as the method itself.
491 The I<accessor> is a standard perl-style read/write accessor. It will
492 return the value of the attribute, and if a value is passed as an argument,
493 it will assign that value to the attribute.
496 This method will properly handle the following code, by assigning an
497 C<undef> value to the attribute.
499 $object->set_something(undef);
503 This is a basic read-only accessor, it will just return the value of
508 This is a basic write accessor, it accepts a single argument, and
509 assigns that value to the attribute. This method does not intentially
510 return a value, however perl will return the result of the last
511 expression in the subroutine, which returns in this returning the
512 same value that it was passed.
515 This method will properly handle the following code, by assigning an
516 C<undef> value to the attribute.
518 $object->set_something();
522 This is a basic test to see if any value has been set for the
523 attribute. It will return true (C<1>) if the attribute has been set
524 to any value (even C<undef>), and false (C<0>) otherwise.
527 The predicate will return true even when you set an attribute's
528 value to C<undef>. This behaviour has changed as of version 0.43. In
529 older versions, the predicate (erroneously) checked for attribute
530 value definedness, instead of presence as it is now.
532 If you really want to get rid of the value, you have to define and
533 use a I<clearer> (see below).
538 This is the a method that will uninitialize the attr, reverting lazy values
539 back to their "unfulfilled" state.
543 =item B<clone (%options)>
545 =item B<initialize_instance_slot ($instance, $params)>
549 =head2 Value management
551 These methods are basically "backdoors" to the instance, which can be used
552 to bypass the regular accessors, but still stay within the context of the MOP.
554 These methods are not for general use, and should only be used if you really
555 know what you are doing.
559 =item B<set_value ($instance, $value)>
561 Set the value without going through the accessor. Note that this may be done to
562 even attributes with just read only accessors.
564 =item B<get_value ($instance)>
566 Return the value without going through the accessor. Note that this may be done
567 even to attributes with just write only accessors.
569 =item B<has_value ($instance)>
571 Return a boolean indicating if the item in the C<$instance> has a value in it.
572 This is basically what the default C<predicate> method calls.
574 =item B<clear_value ($instance)>
576 This will clear the value in the C<$instance>. This is basically what the default
577 C<clearer> would call. Note that this may be done even if the attirbute does not
578 have any associated read, write or clear methods.
584 These are all basic read-only value accessors for the values
585 passed into C<new>. I think they are pretty much self-explanitory.
605 =item B<is_default_a_coderef>
607 =item B<default (?$instance)>
609 Return the default value for the attribute.
611 If you pass in an C<$instance> argument to this accessor and the
612 I<default> is a CODE reference, then the CODE reference will be
613 executed with the C<$instance> as its argument.
617 Return a list of slots required by the attribute. This is usually
618 just one, which is the name of the attribute.
620 =item B<get_read_method>
622 =item B<get_write_method>
624 Return the name of a method name suitable for reading / writing the value
625 of the attribute in the associated class. Suitable for use whether
626 C<reader> and C<writer> or C<accessor> was used.
628 =item B<get_read_method_ref>
630 =item B<get_write_method_ref>
632 Return the CODE reference of a method suitable for reading / writing the
633 value of the attribute in the associated class. Suitable for use whether
634 C<reader> and C<writer> or C<accessor> was specified or not.
636 NOTE: If not reader/writer/accessor was specified, this will use the
637 attribute get_value/set_value methods, which can be very inefficient.
641 =head2 Informational predicates
643 These are all basic predicate methods for the values passed into C<new>.
647 =item B<has_accessor>
653 =item B<has_predicate>
657 =item B<has_initializer>
659 =item B<has_init_arg>
667 =head2 Class association
669 These methods allow you to manage the attributes association with
670 the class that contains it. These methods should not be used
671 lightly, nor are they very magical, they are mostly used internally
672 and by metaclass instances.
676 =item B<associated_class>
678 This returns the metaclass this attribute is associated with.
680 =item B<attach_to_class ($class)>
682 This will store a weaken reference to C<$class> internally. You should
683 note that just changing the class assocation will not remove the attribute
684 from it's old class, and initialize it (and it's accessors) in the new
685 C<$class>. It is up to you to do this manually.
687 =item B<detach_from_class>
689 This will remove the weakened reference to the class. It does B<not>
690 remove the attribute itself from the class (or remove it's accessors),
691 you must do that yourself if you want too. Actually if that is what
692 you want to do, you should probably be looking at
693 L<Class::MOP::Class::remove_attribute> instead.
697 =head2 Attribute Accessor generation
701 =item B<accessor_metaclass>
703 Accessors are generated by an accessor metaclass, which is usually
704 a subclass of C<Class::MOP::Method::Accessor>. This method returns
705 the name of the accessor metaclass that this attribute uses.
707 =item B<associate_method ($method)>
709 This will associate a C<$method> with the given attribute which is
710 used internally by the accessor generator.
712 =item B<associated_methods>
714 This will return the list of methods which have been associated with
715 the C<associate_method> methods.
717 =item B<install_accessors>
719 This allows the attribute to generate and install code for it's own
720 I<accessor/reader/writer/predicate> methods. This is called by
721 C<Class::MOP::Class::add_attribute>.
723 This method will call C<process_accessors> for each of the possible
724 method types (accessor, reader, writer & predicate).
726 =item B<process_accessors ($type, $value)>
728 This takes a C<$type> (accessor, reader, writer or predicate), and
729 a C<$value> (the value passed into the constructor for each of the
730 different types). It will then either generate the method itself
731 (using the C<generate_*_method> methods listed below) or it will
732 use the custom method passed through the constructor.
734 =item B<remove_accessors>
736 This allows the attribute to remove the method for it's own
737 I<accessor/reader/writer/predicate/clearer>. This is called by
738 C<Class::MOP::Class::remove_attribute>.
740 NOTE: This does not currently remove methods from the list returned
741 by C<associated_methods>, that is on the TODO list.
751 This will return a B<Class::MOP::Class> instance which is related
754 It should also be noted that B<Class::MOP> will actually bootstrap
755 this module by installing a number of attribute meta-objects into
756 it's metaclass. This will allow this class to reap all the benifits
757 of the MOP when subclassing it.
763 Stevan Little E<lt>stevan@iinteractive.comE<gt>
765 =head1 COPYRIGHT AND LICENSE
767 Copyright 2006-2008 by Infinity Interactive, Inc.
769 L<http://www.iinteractive.com>
771 This library is free software; you can redistribute it and/or modify
772 it under the same terms as Perl itself.