2 package Class::MOP::Attribute;
8 use Scalar::Util 'blessed', 'reftype', 'weaken';
10 our $VERSION = '0.08';
13 require Class::MOP::Class;
14 Class::MOP::Class->initialize(blessed($_[0]) || $_[0]);
17 # NOTE: (meta-circularity)
18 # This method will be replaces in the
19 # boostrap section of Class::MOP, by
20 # a new version which uses the
21 # &Class::MOP::Class::construct_instance
22 # method to build an attribute meta-object
23 # which itself is described with attribute
25 # - Ain't meta-circularity grand? :)
31 (defined $name && $name)
32 || confess "You must provide a name for the attribute";
33 $options{init_arg} = $name
34 if not exists $options{init_arg};
38 accessor => $options{accessor},
39 reader => $options{reader},
40 writer => $options{writer},
41 predicate => $options{predicate},
42 init_arg => $options{init_arg},
43 default => $options{default},
44 # keep a weakened link to the
45 # class we are associated with
46 associated_class => undef,
51 # this is a primative (and kludgy) clone operation
52 # for now, it will be repleace in the Class::MOP
53 # bootstrap with a proper one, however we know
54 # that this one will work fine for now.
59 || confess "Can only clone an instance";
60 return bless { %{$self}, %options } => blessed($self);
63 sub initialize_instance_slot {
64 my ($self, $meta_instance, $instance, $params) = @_;
65 my $init_arg = $self->{init_arg};
66 # try to fetch the init arg from the %params ...
68 $val = $params->{$init_arg} if exists $params->{$init_arg};
69 # if nothing was in the %params, we can use the
70 # attribute's default value (if it has one)
71 if (!defined $val && defined $self->{default}) {
72 $val = $self->default($instance);
74 $meta_instance->set_slot_value($instance, $self->name, $val);
78 # the next bunch of methods will get bootstrapped
79 # away in the Class::MOP bootstrapping section
81 sub name { $_[0]->{name} }
83 sub associated_class { $_[0]->{associated_class} }
85 sub has_accessor { defined($_[0]->{accessor}) ? 1 : 0 }
86 sub has_reader { defined($_[0]->{reader}) ? 1 : 0 }
87 sub has_writer { defined($_[0]->{writer}) ? 1 : 0 }
88 sub has_predicate { defined($_[0]->{predicate}) ? 1 : 0 }
89 sub has_init_arg { defined($_[0]->{init_arg}) ? 1 : 0 }
90 sub has_default { defined($_[0]->{default}) ? 1 : 0 }
92 sub accessor { $_[0]->{accessor} }
93 sub reader { $_[0]->{reader} }
94 sub writer { $_[0]->{writer} }
95 sub predicate { $_[0]->{predicate} }
96 sub init_arg { $_[0]->{init_arg} }
98 # end bootstrapped away method section.
99 # (all methods below here are kept intact)
103 if (reftype($self->{default}) && reftype($self->{default}) eq 'CODE') {
104 # if the default is a CODE ref, then
105 # we pass in the instance and default
106 # can return a value based on that
107 # instance. Somewhat crude, but works.
108 return $self->{default}->(shift);
115 sub slots { (shift)->name }
119 sub attach_to_class {
120 my ($self, $class) = @_;
121 (blessed($class) && $class->isa('Class::MOP::Class'))
122 || confess "You must pass a Class::MOP::Class instance (or a subclass)";
123 weaken($self->{associated_class} = $class);
126 sub detach_from_class {
128 $self->{associated_class} = undef;
131 ## Method generation helpers
133 sub generate_accessor_method {
135 my $attr_name = $self->name;
137 my $meta_instance = Class::MOP::Class->initialize(Scalar::Util::blessed($_[0]))->get_meta_instance;
138 $meta_instance->set_slot_value($_[0], $attr_name, $_[1]) if scalar(@_) == 2;
139 $meta_instance->get_slot_value($_[0], $attr_name);
143 sub generate_reader_method {
145 my $attr_name = $self->name;
147 confess "Cannot assign a value to a read-only accessor" if @_ > 1;
148 Class::MOP::Class->initialize(Scalar::Util::blessed($_[0]))
150 ->get_slot_value($_[0], $attr_name);
154 sub generate_writer_method {
156 my $attr_name = $self->name;
158 Class::MOP::Class->initialize(Scalar::Util::blessed($_[0]))
160 ->set_slot_value($_[0], $attr_name, $_[1]);
164 sub generate_predicate_method {
166 my $attr_name = $self->name;
168 defined Class::MOP::Class->initialize(Scalar::Util::blessed($_[0]))
170 ->get_slot_value($_[0], $attr_name) ? 1 : 0;
174 sub process_accessors {
175 my ($self, $type, $accessor) = @_;
176 if (reftype($accessor)) {
177 (reftype($accessor) eq 'HASH')
178 || confess "bad accessor/reader/writer/predicate format, must be a HASH ref";
179 my ($name, $method) = each %{$accessor};
180 return ($name, Class::MOP::Attribute::Accessor->wrap($method));
183 my $generator = $self->can('generate_' . $type . '_method');
185 || confess "There is no method generator for the type='$type'";
186 if (my $method = $self->$generator($self->name)) {
187 return ($accessor => Class::MOP::Attribute::Accessor->wrap($method));
189 confess "Could not create the '$type' method for " . $self->name . " because : $@";
193 sub install_accessors {
195 my $class = $self->associated_class;
198 $self->process_accessors('accessor' => $self->accessor())
199 ) if $self->has_accessor();
202 $self->process_accessors('reader' => $self->reader())
203 ) if $self->has_reader();
206 $self->process_accessors('writer' => $self->writer())
207 ) if $self->has_writer();
210 $self->process_accessors('predicate' => $self->predicate())
211 ) if $self->has_predicate();
216 my $_remove_accessor = sub {
217 my ($accessor, $class) = @_;
218 if (reftype($accessor) && reftype($accessor) eq 'HASH') {
219 ($accessor) = keys %{$accessor};
221 my $method = $class->get_method($accessor);
222 $class->remove_method($accessor)
223 if (blessed($method) && $method->isa('Class::MOP::Attribute::Accessor'));
226 sub remove_accessors {
228 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
229 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
230 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
231 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
237 package Class::MOP::Attribute::Accessor;
242 use Class::MOP::Method;
244 our $VERSION = '0.01';
246 our @ISA = ('Class::MOP::Method');
256 Class::MOP::Attribute - Attribute Meta Object
260 Class::MOP::Attribute->new('$foo' => (
261 accessor => 'foo', # dual purpose get/set accessor
262 predicate => 'has_foo' # predicate check for defined-ness
263 init_arg => '-foo', # class->new will look for a -foo key
264 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
267 Class::MOP::Attribute->new('$.bar' => (
268 reader => 'bar', # getter
269 writer => 'set_bar', # setter
270 predicate => 'has_bar' # predicate check for defined-ness
271 init_arg => ':bar', # class->new will look for a :bar key
272 # no default value means it is undef
277 The Attribute Protocol is almost entirely an invention of this module,
278 and is completely optional to this MOP. This is because Perl 5 does not
279 have consistent notion of what is an attribute of a class. There are
280 so many ways in which this is done, and very few (if any) are
281 easily discoverable by this module.
283 So, all that said, this module attempts to inject some order into this
284 chaos, by introducing a consistent API which can be used to create
293 =item B<new ($name, ?%options)>
295 An attribute must (at the very least), have a C<$name>. All other
296 C<%options> are contained added as key-value pairs. Acceptable keys
303 This should be a string value representing the expected key in
304 an initialization hash. For instance, if we have an I<init_arg>
305 value of C<-foo>, then the following code will Just Work.
307 MyClass->meta->construct_instance(-foo => "Hello There");
309 In an init_arg is not assigned, it will automatically use the
314 The value of this key is the default value which
315 C<Class::MOP::Class::construct_instance> will initialize the
319 If the value is a simple scalar (string or number), then it can
320 be just passed as is. However, if you wish to initialize it with
321 a HASH or ARRAY ref, then you need to wrap that inside a CODE
324 Class::MOP::Attribute->new('@foo' => (
325 default => sub { [] },
330 Class::MOP::Attribute->new('%foo' => (
331 default => sub { {} },
334 If you wish to initialize an attribute with a CODE reference
335 itself, then you need to wrap that in a subroutine as well, like
338 Class::MOP::Attribute->new('&foo' => (
339 default => sub { sub { print "Hello World" } },
342 And lastly, if the value of your attribute is dependent upon
343 some other aspect of the instance structure, then you can take
344 advantage of the fact that when the I<default> value is a CODE
345 reference, it is passed the raw (unblessed) instance structure
346 as it's only argument. So you can do things like this:
348 Class::MOP::Attribute->new('$object_identity' => (
349 default => sub { Scalar::Util::refaddr($_[0]) },
352 This last feature is fairly limited as there is no gurantee of
353 the order of attribute initializations, so you cannot perform
354 any kind of dependent initializations. However, if this is
355 something you need, you could subclass B<Class::MOP::Class> and
356 this class to acheive it. However, this is currently left as
357 an exercise to the reader :).
361 The I<accessor>, I<reader>, I<writer> and I<predicate> keys can
362 contain either; the name of the method and an appropriate default
363 one will be generated for you, B<or> a HASH ref containing exactly one
364 key (which will be used as the name of the method) and one value,
365 which should contain a CODE reference which will be installed as
372 The I<accessor> is a standard perl-style read/write accessor. It will
373 return the value of the attribute, and if a value is passed as an argument,
374 it will assign that value to the attribute.
377 This method will properly handle the following code, by assigning an
378 C<undef> value to the attribute.
380 $object->set_something(undef);
384 This is a basic read-only accessor, it will just return the value of
389 This is a basic write accessor, it accepts a single argument, and
390 assigns that value to the attribute. This method does not intentially
391 return a value, however perl will return the result of the last
392 expression in the subroutine, which returns in this returning the
393 same value that it was passed.
396 This method will properly handle the following code, by assigning an
397 C<undef> value to the attribute.
399 $object->set_something();
403 This is a basic test to see if the value of the attribute is not
404 C<undef>. It will return true (C<1>) if the attribute's value is
405 defined, and false (C<0>) otherwise.
409 =item B<clone (%options)>
411 =item B<initialize_instance_slot ($instance, $params)>
417 These are all basic read-only value accessors for the values
418 passed into C<new>. I think they are pretty much self-explanitory.
434 =item B<default (?$instance)>
436 As noted in the documentation for C<new> above, if the I<default>
437 value is a CODE reference, this accessor will pass a single additional
438 argument C<$instance> into it and return the value.
442 Returns a list of slots required by the attribute. This is usually
443 just one, which is the name of the attribute.
447 =head2 Informational predicates
449 These are all basic predicate methods for the values passed into C<new>.
453 =item B<has_accessor>
459 =item B<has_predicate>
461 =item B<has_init_arg>
467 =head2 Class association
471 =item B<associated_class>
473 =item B<attach_to_class ($class)>
475 =item B<detach_from_class>
479 =item B<allocate_slots>
481 =item B<deallocate_slots>
485 =head2 Attribute Accessor generation
489 =item B<install_accessors>
491 This allows the attribute to generate and install code for it's own
492 I<accessor/reader/writer/predicate> methods. This is called by
493 C<Class::MOP::Class::add_attribute>.
495 This method will call C<process_accessors> for each of the possible
496 method types (accessor, reader, writer & predicate).
498 =item B<process_accessors ($type, $value)>
500 This takes a C<$type> (accessor, reader, writer or predicate), and
501 a C<$value> (the value passed into the constructor for each of the
502 different types). It will then either generate the method itself
503 (using the C<generate_*_method> methods listed below) or it will
504 use the custom method passed through the constructor.
508 =item B<generate_accessor_method>
510 =item B<generate_predicate_method>
512 =item B<generate_reader_method>
514 =item B<generate_writer_method>
518 =item B<remove_accessors>
520 This allows the attribute to remove the method for it's own
521 I<accessor/reader/writer/predicate>. This is called by
522 C<Class::MOP::Class::remove_attribute>.
532 This will return a B<Class::MOP::Class> instance which is related
535 It should also be noted that B<Class::MOP> will actually bootstrap
536 this module by installing a number of attribute meta-objects into
537 it's metaclass. This will allow this class to reap all the benifits
538 of the MOP when subclassing it.
544 Stevan Little E<lt>stevan@iinteractive.comE<gt>
546 =head1 COPYRIGHT AND LICENSE
548 Copyright 2006 by Infinity Interactive, Inc.
550 L<http://www.iinteractive.com>
552 This library is free software; you can redistribute it and/or modify
553 it under the same terms as Perl itself.