2 package Class::MOP::Attribute;
7 use Class::MOP::Method::Accessor;
10 use Scalar::Util 'blessed', 'reftype', 'weaken';
12 our $VERSION = '0.14';
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};
42 (is_default_a_coderef(\%options))
43 || confess("References are not allowed as default values, you must ".
44 "wrap then in a CODE reference (ex: sub { [] } and not [])")
45 if exists $options{default} && ref $options{default};
49 '$!accessor' => $options{accessor},
50 '$!reader' => $options{reader},
51 '$!writer' => $options{writer},
52 '$!predicate' => $options{predicate},
53 '$!clearer' => $options{clearer},
54 '$!init_arg' => $options{init_arg},
55 '$!default' => $options{default},
56 # keep a weakened link to the
57 # class we are associated with
58 '$!associated_class' => undef,
59 # and a list of the methods
60 # associated with this attr
61 '@!associated_methods' => [],
66 # this is a primative (and kludgy) clone operation
67 # for now, it will be replaced in the Class::MOP
68 # bootstrap with a proper one, however we know
69 # that this one will work fine for now.
74 || confess "Can only clone an instance";
75 return bless { %{$self}, %options } => blessed($self);
78 sub initialize_instance_slot {
79 my ($self, $meta_instance, $instance, $params) = @_;
80 my $init_arg = $self->{'$!init_arg'};
81 # try to fetch the init arg from the %params ...
83 $val = $params->{$init_arg} if exists $params->{$init_arg};
84 # if nothing was in the %params, we can use the
85 # attribute's default value (if it has one)
86 if (!defined $val && defined $self->{'$!default'}) {
87 $val = $self->default($instance);
89 $meta_instance->set_slot_value($instance, $self->name, $val);
93 # the next bunch of methods will get bootstrapped
94 # away in the Class::MOP bootstrapping section
96 sub name { $_[0]->{'$!name'} }
98 sub associated_class { $_[0]->{'$!associated_class'} }
99 sub associated_methods { $_[0]->{'@!associated_methods'} }
101 sub has_accessor { defined($_[0]->{'$!accessor'}) ? 1 : 0 }
102 sub has_reader { defined($_[0]->{'$!reader'}) ? 1 : 0 }
103 sub has_writer { defined($_[0]->{'$!writer'}) ? 1 : 0 }
104 sub has_predicate { defined($_[0]->{'$!predicate'}) ? 1 : 0 }
105 sub has_clearer { defined($_[0]->{'$!clearer'}) ? 1 : 0 }
106 sub has_init_arg { defined($_[0]->{'$!init_arg'}) ? 1 : 0 }
107 sub has_default { defined($_[0]->{'$!default'}) ? 1 : 0 }
109 sub accessor { $_[0]->{'$!accessor'} }
110 sub reader { $_[0]->{'$!reader'} }
111 sub writer { $_[0]->{'$!writer'} }
112 sub predicate { $_[0]->{'$!predicate'} }
113 sub clearer { $_[0]->{'$!clearer'} }
114 sub init_arg { $_[0]->{'$!init_arg'} }
116 # end bootstrapped away method section.
117 # (all methods below here are kept intact)
119 sub is_default_a_coderef {
120 ('CODE' eq (reftype($_[0]->{'$!default'} || $_[0]->{default}) || ''))
124 my ($self, $instance) = @_;
125 if (defined $instance && $self->is_default_a_coderef) {
126 # if the default is a CODE ref, then
127 # we pass in the instance and default
128 # can return a value based on that
129 # instance. Somewhat crude, but works.
130 return $self->{'$!default'}->($instance);
132 $self->{'$!default'};
137 sub slots { (shift)->name }
141 sub attach_to_class {
142 my ($self, $class) = @_;
143 (blessed($class) && $class->isa('Class::MOP::Class'))
144 || confess "You must pass a Class::MOP::Class instance (or a subclass)";
145 weaken($self->{'$!associated_class'} = $class);
148 sub detach_from_class {
150 $self->{'$!associated_class'} = undef;
155 sub associate_method {
156 my ($self, $method) = @_;
157 push @{$self->{'@!associated_methods'}} => $method;
163 my ($self, $instance, $value) = @_;
165 Class::MOP::Class->initialize(blessed($instance))
167 ->set_slot_value($instance, $self->name, $value);
171 my ($self, $instance) = @_;
173 Class::MOP::Class->initialize(blessed($instance))
175 ->get_slot_value($instance, $self->name);
179 my ($self, $instance) = @_;
181 defined Class::MOP::Class->initialize(blessed($instance))
183 ->get_slot_value($instance, $self->name) ? 1 : 0;
187 my ($self, $instance) = @_;
189 Class::MOP::Class->initialize(blessed($instance))
191 ->deinitialize_slot($instance, $self->name);
196 sub accessor_metaclass { 'Class::MOP::Method::Accessor' }
198 sub process_accessors {
199 my ($self, $type, $accessor, $generate_as_inline_methods) = @_;
200 if (reftype($accessor)) {
201 (reftype($accessor) eq 'HASH')
202 || confess "bad accessor/reader/writer/predicate/clearer format, must be a HASH ref";
203 my ($name, $method) = %{$accessor};
204 $method = $self->accessor_metaclass->wrap($method);
205 $self->associate_method($method);
206 return ($name, $method);
209 my $inline_me = ($generate_as_inline_methods && $self->associated_class->instance_metaclass->is_inlinable);
212 $method = $self->accessor_metaclass->new(
214 is_inline => $inline_me,
215 accessor_type => $type,
218 confess "Could not create the '$type' method for " . $self->name . " because : $@" if $@;
219 $self->associate_method($method);
220 return ($accessor, $method);
224 sub install_accessors {
227 my $class = $self->associated_class;
230 $self->process_accessors('accessor' => $self->accessor(), $inline)
231 ) if $self->has_accessor();
234 $self->process_accessors('reader' => $self->reader(), $inline)
235 ) if $self->has_reader();
238 $self->process_accessors('writer' => $self->writer(), $inline)
239 ) if $self->has_writer();
242 $self->process_accessors('predicate' => $self->predicate(), $inline)
243 ) if $self->has_predicate();
246 $self->process_accessors('clearer' => $self->clearer(), $inline)
247 ) if $self->has_clearer();
253 my $_remove_accessor = sub {
254 my ($accessor, $class) = @_;
255 if (reftype($accessor) && reftype($accessor) eq 'HASH') {
256 ($accessor) = keys %{$accessor};
258 my $method = $class->get_method($accessor);
259 $class->remove_method($accessor)
260 if (blessed($method) && $method->isa('Class::MOP::Method::Accessor'));
263 sub remove_accessors {
266 # we really need to make sure to remove from the
267 # associates methods here as well. But this is
268 # such a slimly used method, I am not worried
269 # about it right now.
270 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
271 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
272 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
273 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
274 $_remove_accessor->($self->clearer(), $self->associated_class()) if $self->has_clearer();
288 Class::MOP::Attribute - Attribute Meta Object
292 Class::MOP::Attribute->new('$foo' => (
293 accessor => 'foo', # dual purpose get/set accessor
294 predicate => 'has_foo' # predicate check for defined-ness
295 init_arg => '-foo', # class->new will look for a -foo key
296 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
299 Class::MOP::Attribute->new('$.bar' => (
300 reader => 'bar', # getter
301 writer => 'set_bar', # setter
302 predicate => 'has_bar' # predicate check for defined-ness
303 init_arg => ':bar', # class->new will look for a :bar key
304 # no default value means it is undef
309 The Attribute Protocol is almost entirely an invention of this module,
310 and is completely optional to this MOP. This is because Perl 5 does not
311 have consistent notion of what is an attribute of a class. There are
312 so many ways in which this is done, and very few (if any) are
313 easily discoverable by this module.
315 So, all that said, this module attempts to inject some order into this
316 chaos, by introducing a consistent API which can be used to create
325 =item B<new ($name, ?%options)>
327 An attribute must (at the very least), have a C<$name>. All other
328 C<%options> are contained added as key-value pairs. Acceptable keys
335 This should be a string value representing the expected key in
336 an initialization hash. For instance, if we have an I<init_arg>
337 value of C<-foo>, then the following code will Just Work.
339 MyClass->meta->construct_instance(-foo => "Hello There");
341 In an init_arg is not assigned, it will automatically use the
346 The value of this key is the default value which
347 C<Class::MOP::Class::construct_instance> will initialize the
351 If the value is a simple scalar (string or number), then it can
352 be just passed as is. However, if you wish to initialize it with
353 a HASH or ARRAY ref, then you need to wrap that inside a CODE
356 Class::MOP::Attribute->new('@foo' => (
357 default => sub { [] },
362 Class::MOP::Attribute->new('%foo' => (
363 default => sub { {} },
366 If you wish to initialize an attribute with a CODE reference
367 itself, then you need to wrap that in a subroutine as well, like
370 Class::MOP::Attribute->new('&foo' => (
371 default => sub { sub { print "Hello World" } },
374 And lastly, if the value of your attribute is dependent upon
375 some other aspect of the instance structure, then you can take
376 advantage of the fact that when the I<default> value is a CODE
377 reference, it is passed the raw (unblessed) instance structure
378 as it's only argument. So you can do things like this:
380 Class::MOP::Attribute->new('$object_identity' => (
381 default => sub { Scalar::Util::refaddr($_[0]) },
384 This last feature is fairly limited as there is no gurantee of
385 the order of attribute initializations, so you cannot perform
386 any kind of dependent initializations. However, if this is
387 something you need, you could subclass B<Class::MOP::Class> and
388 this class to acheive it. However, this is currently left as
389 an exercise to the reader :).
393 The I<accessor>, I<reader>, I<writer>, I<predicate> and I<clearer> keys can
394 contain either; the name of the method and an appropriate default one will be
395 generated for you, B<or> a HASH ref containing exactly one key (which will be
396 used as the name of the method) and one value, which should contain a CODE
397 reference which will be installed as the method itself.
403 The I<accessor> is a standard perl-style read/write accessor. It will
404 return the value of the attribute, and if a value is passed as an argument,
405 it will assign that value to the attribute.
408 This method will properly handle the following code, by assigning an
409 C<undef> value to the attribute.
411 $object->set_something(undef);
415 This is a basic read-only accessor, it will just return the value of
420 This is a basic write accessor, it accepts a single argument, and
421 assigns that value to the attribute. This method does not intentially
422 return a value, however perl will return the result of the last
423 expression in the subroutine, which returns in this returning the
424 same value that it was passed.
427 This method will properly handle the following code, by assigning an
428 C<undef> value to the attribute.
430 $object->set_something();
434 This is a basic test to see if the value of the attribute is not
435 C<undef>. It will return true (C<1>) if the attribute's value is
436 defined, and false (C<0>) otherwise.
440 This is the a method that will uninitialize the attr, reverting lazy values
441 back to their "unfulfilled" state.
445 =item B<clone (%options)>
447 =item B<initialize_instance_slot ($instance, $params)>
451 =head2 Value management
453 These methods are basically "backdoors" to the instance, which can be used
454 to bypass the regular accessors, but still stay within the context of the MOP.
456 These methods are not for general use, and should only be used if you really
457 know what you are doing.
461 =item B<set_value ($instance, $value)>
463 Set the value without going through the accessor. Note that this may be done to
464 even attributes with just read only accessors.
466 =item B<get_value ($instance)>
468 Return the value without going through the accessor. Note that this may be done
469 even to attributes with just write only accessors.
471 =item B<has_value ($instance)>
473 Returns a boolean indicating if the item in the C<$instance> has a value in it.
474 This is basically what the default C<predicate> method calls.
476 =item B<clear_value ($instance)>
478 This will clear the value in the C<$instance>. This is basically what the default
479 C<clearer> would call. Note that this may be done even if the attirbute does not
480 have any associated read, write or clear methods.
486 These are all basic read-only value accessors for the values
487 passed into C<new>. I think they are pretty much self-explanitory.
505 =item B<is_default_a_coderef>
507 =item B<default (?$instance)>
509 As noted in the documentation for C<new> above, if the I<default>
510 value is a CODE reference, this accessor will pass a single additional
511 argument C<$instance> into it and return the value.
515 Returns a list of slots required by the attribute. This is usually
516 just one, which is the name of the attribute.
520 =head2 Informational predicates
522 These are all basic predicate methods for the values passed into C<new>.
526 =item B<has_accessor>
532 =item B<has_predicate>
536 =item B<has_init_arg>
542 =head2 Class association
544 These methods allow you to manage the attributes association with
545 the class that contains it. These methods should not be used
546 lightly, nor are they very magical, they are mostly used internally
547 and by metaclass instances.
551 =item B<associated_class>
553 This returns the metaclass this attribute is associated with.
555 =item B<attach_to_class ($class)>
557 This will store a weaken reference to C<$class> internally. You should
558 note that just changing the class assocation will not remove the attribute
559 from it's old class, and initialize it (and it's accessors) in the new
560 C<$class>. It is up to you to do this manually.
562 =item B<detach_from_class>
564 This will remove the weakened reference to the class. It does B<not>
565 remove the attribute itself from the class (or remove it's accessors),
566 you must do that yourself if you want too. Actually if that is what
567 you want to do, you should probably be looking at
568 L<Class::MOP::Class::remove_attribute> instead.
572 =head2 Attribute Accessor generation
576 =item B<accessor_metaclass>
578 Accessors are generated by an accessor metaclass, which is usually
579 a subclass of C<Class::MOP::Method::Accessor>. This method returns
580 the name of the accessor metaclass that this attribute uses.
582 =item B<associate_method ($method)>
584 This will associate a C<$method> with the given attribute which is
585 used internally by the accessor generator.
587 =item B<associated_methods>
589 This will return the list of methods which have been associated with
590 the C<associate_method> methods.
592 =item B<install_accessors>
594 This allows the attribute to generate and install code for it's own
595 I<accessor/reader/writer/predicate> methods. This is called by
596 C<Class::MOP::Class::add_attribute>.
598 This method will call C<process_accessors> for each of the possible
599 method types (accessor, reader, writer & predicate).
601 =item B<process_accessors ($type, $value)>
603 This takes a C<$type> (accessor, reader, writer or predicate), and
604 a C<$value> (the value passed into the constructor for each of the
605 different types). It will then either generate the method itself
606 (using the C<generate_*_method> methods listed below) or it will
607 use the custom method passed through the constructor.
609 =item B<remove_accessors>
611 This allows the attribute to remove the method for it's own
612 I<accessor/reader/writer/predicate/clearer>. This is called by
613 C<Class::MOP::Class::remove_attribute>.
615 NOTE: This does not currently remove methods from the list returned
616 by C<associated_methods>, that is on the TODO list.
626 This will return a B<Class::MOP::Class> instance which is related
629 It should also be noted that B<Class::MOP> will actually bootstrap
630 this module by installing a number of attribute meta-objects into
631 it's metaclass. This will allow this class to reap all the benifits
632 of the MOP when subclassing it.
638 Stevan Little E<lt>stevan@iinteractive.comE<gt>
640 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
642 =head1 COPYRIGHT AND LICENSE
644 Copyright 2006, 2007 by Infinity Interactive, Inc.
646 L<http://www.iinteractive.com>
648 This library is free software; you can redistribute it and/or modify
649 it under the same terms as Perl itself.