2 package Class::MOP::Attribute;
8 use Scalar::Util 'blessed', 'reftype', 'weaken';
10 our $VERSION = '0.02';
13 require Class::MOP::Class;
14 Class::MOP::Class->initialize($_[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 (!exists $options{reader} && !exists $options{writer})
34 || confess "You cannot declare an accessor and reader and/or writer functions"
35 if exists $options{accessor};
37 $options{init_arg} = $name if not exists $options{init_arg};
41 accessor => $options{accessor},
42 reader => $options{reader},
43 writer => $options{writer},
44 predicate => $options{predicate},
45 init_arg => $options{init_arg},
46 default => $options{default},
47 # keep a weakened link to the
48 # class we are associated with
49 associated_class => undef,
54 # the next bunch of methods will get bootstrapped
55 # away in the Class::MOP bootstrapping section
57 sub name { $_[0]->{name} }
59 sub associated_class { $_[0]->{associated_class} }
61 sub has_accessor { defined($_[0]->{accessor}) ? 1 : 0 }
62 sub has_reader { defined($_[0]->{reader}) ? 1 : 0 }
63 sub has_writer { defined($_[0]->{writer}) ? 1 : 0 }
64 sub has_predicate { defined($_[0]->{predicate}) ? 1 : 0 }
65 sub has_init_arg { defined($_[0]->{init_arg}) ? 1 : 0 }
66 sub has_default { defined($_[0]->{default}) ? 1 : 0 }
68 sub accessor { $_[0]->{accessor} }
69 sub reader { $_[0]->{reader} }
70 sub writer { $_[0]->{writer} }
71 sub predicate { $_[0]->{predicate} }
72 sub init_arg { $_[0]->{init_arg} }
74 # end bootstrapped away method section.
75 # (all methods below here are kept intact)
79 if (reftype($self->{default}) && reftype($self->{default}) eq 'CODE') {
80 # if the default is a CODE ref, then
81 # we pass in the instance and default
82 # can return a value based on that
83 # instance. Somewhat crude, but works.
84 return $self->{default}->(shift);
92 my ($self, $class) = @_;
93 (blessed($class) && $class->isa('Class::MOP::Class'))
94 || confess "You must pass a Class::MOP::Class instance (or a subclass)";
95 weaken($self->{associated_class} = $class);
98 sub detach_from_class {
100 $self->{associated_class} = undef;
103 ## Method generation helpers
105 sub generate_accessor_method {
106 my ($self, $attr_name) = @_;
108 \$_[0]->{'$attr_name'} = \$_[1] if scalar(\@_) == 2;
109 \$_[0]->{'$attr_name'};
113 sub generate_reader_method {
114 my ($self, $attr_name) = @_;
116 \$_[0]->{'$attr_name'};
120 sub generate_writer_method {
121 my ($self, $attr_name) = @_;
123 \$_[0]->{'$attr_name'} = \$_[1];
127 sub generate_predicate_method {
128 my ($self, $attr_name) = @_;
130 defined \$_[0]->{'$attr_name'} ? 1 : 0;
134 sub process_accessors {
135 my ($self, $type, $accessor) = @_;
136 if (reftype($accessor) && reftype($accessor) eq 'HASH') {
137 my ($name, $method) = each %{$accessor};
138 return ($name, Class::MOP::Attribute::Accessor->wrap($method));
141 my $generator = $self->can('generate_' . $type . '_method');
143 || confess "There is no method generator for the type='$type'";
144 if (my $method = $self->$generator($self->name)) {
145 return ($accessor => Class::MOP::Attribute::Accessor->wrap($method));
147 confess "Could not create the '$type' method for " . $self->name . " because : $@";
151 sub install_accessors {
153 my $class = $self->associated_class;
156 $self->process_accessors('accessor' => $self->accessor())
157 ) if $self->has_accessor();
160 $self->process_accessors('reader' => $self->reader())
161 ) if $self->has_reader();
164 $self->process_accessors('writer' => $self->writer())
165 ) if $self->has_writer();
168 $self->process_accessors('predicate' => $self->predicate())
169 ) if $self->has_predicate();
174 my $_remove_accessor = sub {
175 my ($accessor, $class) = @_;
176 if (reftype($accessor) && reftype($accessor) eq 'HASH') {
177 ($accessor) = keys %{$accessor};
179 my $method = $class->get_method($accessor);
180 $class->remove_method($accessor)
181 if (blessed($method) && $method->isa('Class::MOP::Attribute::Accessor'));
184 sub remove_accessors {
186 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
187 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
188 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
189 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
195 package Class::MOP::Attribute::Accessor;
200 use Class::MOP::Method;
202 our $VERSION = '0.01';
204 our @ISA = ('Class::MOP::Method');
214 Class::MOP::Attribute - Attribute Meta Object
218 Class::MOP::Attribute->new('$foo' => (
219 accessor => 'foo', # dual purpose get/set accessor
220 predicate => 'has_foo' # predicate check for defined-ness
221 init_arg => '-foo', # class->new will look for a -foo key
222 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
225 Class::MOP::Attribute->new('$.bar' => (
226 reader => 'bar', # getter
227 writer => 'set_bar', # setter
228 predicate => 'has_bar' # predicate check for defined-ness
229 init_arg => ':bar', # class->new will look for a :bar key
230 # no default value means it is undef
235 The Attribute Protocol is almost entirely an invention of this module,
236 and is completely optional to this MOP. This is because Perl 5 does not
237 have consistent notion of what is an attribute of a class. There are
238 so many ways in which this is done, and very few (if any) are
239 easily discoverable by this module.
241 So, all that said, this module attempts to inject some order into this
242 chaos, by introducing a consistent API which can be used to create
251 =item B<new ($name, ?%options)>
253 An attribute must (at the very least), have a C<$name>. All other
254 C<%options> are contained added as key-value pairs. Acceptable keys
261 This should be a string value representing the expected key in
262 an initialization hash. For instance, if we have an I<init_arg>
263 value of C<-foo>, then the following code will Just Work.
265 MyClass->meta->construct_instance(-foo => "Hello There");
267 In an init_arg is not assigned, it will automatically use the
272 The value of this key is the default value which
273 C<Class::MOP::Class::construct_instance> will initialize the
277 If the value is a simple scalar (string or number), then it can
278 be just passed as is. However, if you wish to initialize it with
279 a HASH or ARRAY ref, then you need to wrap that inside a CODE
282 Class::MOP::Attribute->new('@foo' => (
283 default => sub { [] },
288 Class::MOP::Attribute->new('%foo' => (
289 default => sub { {} },
292 If you wish to initialize an attribute with a CODE reference
293 itself, then you need to wrap that in a subroutine as well, like
296 Class::MOP::Attribute->new('&foo' => (
297 default => sub { sub { print "Hello World" } },
300 And lastly, if the value of your attribute is dependent upon
301 some other aspect of the instance structure, then you can take
302 advantage of the fact that when the I<default> value is a CODE
303 reference, it is passed the raw (unblessed) instance structure
304 as it's only argument. So you can do things like this:
306 Class::MOP::Attribute->new('$object_identity' => (
307 default => sub { Scalar::Util::refaddr($_[0]) },
310 This last feature is fairly limited as there is no gurantee of
311 the order of attribute initializations, so you cannot perform
312 any kind of dependent initializations. However, if this is
313 something you need, you could subclass B<Class::MOP::Class> and
314 this class to acheive it. However, this is currently left as
315 an exercise to the reader :).
319 The I<accessor>, I<reader>, I<writer> and I<predicate> keys can
320 contain either; the name of the method and an appropriate default
321 one will be generated for you, B<or> a HASH ref containing exactly one
322 key (which will be used as the name of the method) and one value,
323 which should contain a CODE reference which will be installed as
330 The I<accessor> is a standard perl-style read/write accessor. It will
331 return the value of the attribute, and if a value is passed as an argument,
332 it will assign that value to the attribute.
335 This method will properly handle the following code, by assigning an
336 C<undef> value to the attribute.
338 $object->set_something(undef);
342 This is a basic read-only accessor, it will just return the value of
347 This is a basic write accessor, it accepts a single argument, and
348 assigns that value to the attribute. This method does not intentially
349 return a value, however perl will return the result of the last
350 expression in the subroutine, which returns in this returning the
351 same value that it was passed.
354 This method will properly handle the following code, by assigning an
355 C<undef> value to the attribute.
357 $object->set_something();
361 This is a basic test to see if the value of the attribute is not
362 C<undef>. It will return true (C<1>) if the attribute's value is
363 defined, and false (C<0>) otherwise.
371 These are all basic read-only value accessors for the values
372 passed into C<new>. I think they are pretty much self-explanitory.
388 =item B<default (?$instance)>
390 As noted in the documentation for C<new> above, if the I<default>
391 value is a CODE reference, this accessor will pass a single additional
392 argument C<$instance> into it and return the value.
396 =head2 Informational predicates
398 These are all basic predicate methods for the values passed into C<new>.
402 =item B<has_accessor>
408 =item B<has_predicate>
410 =item B<has_init_arg>
416 =head2 Class association
420 =item B<associated_class>
422 =item B<attach_to_class ($class)>
424 =item B<detach_from_class>
428 =head2 Attribute Accessor generation
432 =item B<install_accessors>
434 This allows the attribute to generate and install code for it's own
435 I<accessor/reader/writer/predicate> methods. This is called by
436 C<Class::MOP::Class::add_attribute>.
438 This method will call C<process_accessors> for each of the possible
439 method types (accessor, reader, writer & predicate).
441 =item B<process_accessors ($type, $value)>
443 This takes a C<$type> (accessor, reader, writer or predicate), and
444 a C<$value> (the value passed into the constructor for each of the
445 different types). It will then either generate the method itself
446 (using the C<generate_*_method> methods listed below) or it will
447 use the custom method passed through the constructor.
451 =item B<generate_accessor_method ($attr_name)>
453 =item B<generate_predicate_method ($attr_name)>
455 =item B<generate_reader_method ($attr_name)>
457 =item B<generate_writer_method ($attr_name)>
461 =item B<remove_accessors>
463 This allows the attribute to remove the method for it's own
464 I<accessor/reader/writer/predicate>. This is called by
465 C<Class::MOP::Class::remove_attribute>.
475 This will return a B<Class::MOP::Class> instance which is related
478 It should also be noted that B<Class::MOP> will actually bootstrap
479 this module by installing a number of attribute meta-objects into
480 it's metaclass. This will allow this class to reap all the benifits
481 of the MOP when subclassing it.
487 Stevan Little E<lt>stevan@iinteractive.comE<gt>
489 =head1 COPYRIGHT AND LICENSE
491 Copyright 2006 by Infinity Interactive, Inc.
493 L<http://www.iinteractive.com>
495 This library is free software; you can redistribute it and/or modify
496 it under the same terms as Perl itself.