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, $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 $self->associated_class
76 ->set_slot_value($instance, $self->name, $val);
80 # the next bunch of methods will get bootstrapped
81 # away in the Class::MOP bootstrapping section
83 sub name { $_[0]->{name} }
85 sub associated_class { $_[0]->{associated_class} }
87 sub has_accessor { defined($_[0]->{accessor}) ? 1 : 0 }
88 sub has_reader { defined($_[0]->{reader}) ? 1 : 0 }
89 sub has_writer { defined($_[0]->{writer}) ? 1 : 0 }
90 sub has_predicate { defined($_[0]->{predicate}) ? 1 : 0 }
91 sub has_init_arg { defined($_[0]->{init_arg}) ? 1 : 0 }
92 sub has_default { defined($_[0]->{default}) ? 1 : 0 }
94 sub accessor { $_[0]->{accessor} }
95 sub reader { $_[0]->{reader} }
96 sub writer { $_[0]->{writer} }
97 sub predicate { $_[0]->{predicate} }
98 sub init_arg { $_[0]->{init_arg} }
100 # end bootstrapped away method section.
101 # (all methods below here are kept intact)
105 if (reftype($self->{default}) && reftype($self->{default}) eq 'CODE') {
106 # if the default is a CODE ref, then
107 # we pass in the instance and default
108 # can return a value based on that
109 # instance. Somewhat crude, but works.
110 return $self->{default}->(shift);
117 sub attach_to_class {
118 my ($self, $class) = @_;
119 (blessed($class) && $class->isa('Class::MOP::Class'))
120 || confess "You must pass a Class::MOP::Class instance (or a subclass)";
121 weaken($self->{associated_class} = $class);
124 sub detach_from_class {
126 $self->{associated_class} = undef;
129 ## Method generation helpers
131 sub generate_accessor_method {
133 my $meta_instance = $self->associated_class->get_meta_instance;
134 my $attr_name = $self->name;
136 $meta_instance->set_slot_value($_[0], $attr_name, $_[1]) if scalar(@_) == 2;
137 $meta_instance->get_slot_value($_[0], $attr_name);
141 sub generate_reader_method {
143 my $meta_instance = $self->associated_class->get_meta_instance;
144 my $attr_name = $self->name;
146 confess "Cannot assign a value to a read-only accessor" if @_ > 1;
147 $meta_instance->get_slot_value($_[0], $attr_name);
151 sub generate_writer_method {
153 my $meta_instance = $self->associated_class->get_meta_instance;
154 my $attr_name = $self->name;
156 $meta_instance->set_slot_value($_[0], $attr_name, $_[1]);
160 sub generate_predicate_method {
162 my $meta_instance = $self->associated_class->get_meta_instance;
163 my $attr_name = $self->name;
165 defined $meta_instance->get_slot_value($_[0], $attr_name) ? 1 : 0;
169 sub process_accessors {
170 my ($self, $type, $accessor) = @_;
171 if (reftype($accessor)) {
172 (reftype($accessor) eq 'HASH')
173 || confess "bad accessor/reader/writer/predicate format, must be a HASH ref";
174 my ($name, $method) = each %{$accessor};
175 return ($name, Class::MOP::Attribute::Accessor->wrap($method));
178 my $generator = $self->can('generate_' . $type . '_method');
180 || confess "There is no method generator for the type='$type'";
181 if (my $method = $self->$generator($self->name)) {
182 return ($accessor => Class::MOP::Attribute::Accessor->wrap($method));
184 confess "Could not create the '$type' method for " . $self->name . " because : $@";
188 sub install_accessors {
190 my $class = $self->associated_class;
193 $self->process_accessors('accessor' => $self->accessor())
194 ) if $self->has_accessor();
197 $self->process_accessors('reader' => $self->reader())
198 ) if $self->has_reader();
201 $self->process_accessors('writer' => $self->writer())
202 ) if $self->has_writer();
205 $self->process_accessors('predicate' => $self->predicate())
206 ) if $self->has_predicate();
211 my $_remove_accessor = sub {
212 my ($accessor, $class) = @_;
213 if (reftype($accessor) && reftype($accessor) eq 'HASH') {
214 ($accessor) = keys %{$accessor};
216 my $method = $class->get_method($accessor);
217 $class->remove_method($accessor)
218 if (blessed($method) && $method->isa('Class::MOP::Attribute::Accessor'));
221 sub remove_accessors {
223 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
224 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
225 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
226 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
232 package Class::MOP::Attribute::Accessor;
237 use Class::MOP::Method;
239 our $VERSION = '0.01';
241 our @ISA = ('Class::MOP::Method');
251 Class::MOP::Attribute - Attribute Meta Object
255 Class::MOP::Attribute->new('$foo' => (
256 accessor => 'foo', # dual purpose get/set accessor
257 predicate => 'has_foo' # predicate check for defined-ness
258 init_arg => '-foo', # class->new will look for a -foo key
259 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
262 Class::MOP::Attribute->new('$.bar' => (
263 reader => 'bar', # getter
264 writer => 'set_bar', # setter
265 predicate => 'has_bar' # predicate check for defined-ness
266 init_arg => ':bar', # class->new will look for a :bar key
267 # no default value means it is undef
272 The Attribute Protocol is almost entirely an invention of this module,
273 and is completely optional to this MOP. This is because Perl 5 does not
274 have consistent notion of what is an attribute of a class. There are
275 so many ways in which this is done, and very few (if any) are
276 easily discoverable by this module.
278 So, all that said, this module attempts to inject some order into this
279 chaos, by introducing a consistent API which can be used to create
288 =item B<new ($name, ?%options)>
290 An attribute must (at the very least), have a C<$name>. All other
291 C<%options> are contained added as key-value pairs. Acceptable keys
298 This should be a string value representing the expected key in
299 an initialization hash. For instance, if we have an I<init_arg>
300 value of C<-foo>, then the following code will Just Work.
302 MyClass->meta->construct_instance(-foo => "Hello There");
304 In an init_arg is not assigned, it will automatically use the
309 The value of this key is the default value which
310 C<Class::MOP::Class::construct_instance> will initialize the
314 If the value is a simple scalar (string or number), then it can
315 be just passed as is. However, if you wish to initialize it with
316 a HASH or ARRAY ref, then you need to wrap that inside a CODE
319 Class::MOP::Attribute->new('@foo' => (
320 default => sub { [] },
325 Class::MOP::Attribute->new('%foo' => (
326 default => sub { {} },
329 If you wish to initialize an attribute with a CODE reference
330 itself, then you need to wrap that in a subroutine as well, like
333 Class::MOP::Attribute->new('&foo' => (
334 default => sub { sub { print "Hello World" } },
337 And lastly, if the value of your attribute is dependent upon
338 some other aspect of the instance structure, then you can take
339 advantage of the fact that when the I<default> value is a CODE
340 reference, it is passed the raw (unblessed) instance structure
341 as it's only argument. So you can do things like this:
343 Class::MOP::Attribute->new('$object_identity' => (
344 default => sub { Scalar::Util::refaddr($_[0]) },
347 This last feature is fairly limited as there is no gurantee of
348 the order of attribute initializations, so you cannot perform
349 any kind of dependent initializations. However, if this is
350 something you need, you could subclass B<Class::MOP::Class> and
351 this class to acheive it. However, this is currently left as
352 an exercise to the reader :).
356 The I<accessor>, I<reader>, I<writer> and I<predicate> keys can
357 contain either; the name of the method and an appropriate default
358 one will be generated for you, B<or> a HASH ref containing exactly one
359 key (which will be used as the name of the method) and one value,
360 which should contain a CODE reference which will be installed as
367 The I<accessor> is a standard perl-style read/write accessor. It will
368 return the value of the attribute, and if a value is passed as an argument,
369 it will assign that value to the attribute.
372 This method will properly handle the following code, by assigning an
373 C<undef> value to the attribute.
375 $object->set_something(undef);
379 This is a basic read-only accessor, it will just return the value of
384 This is a basic write accessor, it accepts a single argument, and
385 assigns that value to the attribute. This method does not intentially
386 return a value, however perl will return the result of the last
387 expression in the subroutine, which returns in this returning the
388 same value that it was passed.
391 This method will properly handle the following code, by assigning an
392 C<undef> value to the attribute.
394 $object->set_something();
398 This is a basic test to see if the value of the attribute is not
399 C<undef>. It will return true (C<1>) if the attribute's value is
400 defined, and false (C<0>) otherwise.
404 =item B<clone (%options)>
406 =item B<initialize_instance_slot ($instance, $params)>
412 These are all basic read-only value accessors for the values
413 passed into C<new>. I think they are pretty much self-explanitory.
429 =item B<default (?$instance)>
431 As noted in the documentation for C<new> above, if the I<default>
432 value is a CODE reference, this accessor will pass a single additional
433 argument C<$instance> into it and return the value.
437 =head2 Informational predicates
439 These are all basic predicate methods for the values passed into C<new>.
443 =item B<has_accessor>
449 =item B<has_predicate>
451 =item B<has_init_arg>
457 =head2 Class association
461 =item B<associated_class>
463 =item B<attach_to_class ($class)>
465 =item B<detach_from_class>
469 =item B<allocate_slots>
471 =item B<deallocate_slots>
475 =head2 Attribute Accessor generation
479 =item B<install_accessors>
481 This allows the attribute to generate and install code for it's own
482 I<accessor/reader/writer/predicate> methods. This is called by
483 C<Class::MOP::Class::add_attribute>.
485 This method will call C<process_accessors> for each of the possible
486 method types (accessor, reader, writer & predicate).
488 =item B<process_accessors ($type, $value)>
490 This takes a C<$type> (accessor, reader, writer or predicate), and
491 a C<$value> (the value passed into the constructor for each of the
492 different types). It will then either generate the method itself
493 (using the C<generate_*_method> methods listed below) or it will
494 use the custom method passed through the constructor.
498 =item B<generate_accessor_method>
500 =item B<generate_predicate_method>
502 =item B<generate_reader_method>
504 =item B<generate_writer_method>
508 =item B<remove_accessors>
510 This allows the attribute to remove the method for it's own
511 I<accessor/reader/writer/predicate>. This is called by
512 C<Class::MOP::Class::remove_attribute>.
522 This will return a B<Class::MOP::Class> instance which is related
525 It should also be noted that B<Class::MOP> will actually bootstrap
526 this module by installing a number of attribute meta-objects into
527 it's metaclass. This will allow this class to reap all the benifits
528 of the MOP when subclassing it.
534 Stevan Little E<lt>stevan@iinteractive.comE<gt>
536 =head1 COPYRIGHT AND LICENSE
538 Copyright 2006 by Infinity Interactive, Inc.
540 L<http://www.iinteractive.com>
542 This library is free software; you can redistribute it and/or modify
543 it under the same terms as Perl itself.