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, $class, $meta_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 = $self->default($meta_instance->get_instance);
74 $meta_instance->add_slot($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 $self->{default}->(shift);
115 sub attach_to_class {
116 my ($self, $class) = @_;
117 (blessed($class) && $class->isa('Class::MOP::Class'))
118 || confess "You must pass a Class::MOP::Class instance (or a subclass)";
119 weaken($self->{associated_class} = $class);
122 sub detach_from_class {
124 $self->{associated_class} = undef;
127 ## Method generation helpers
129 sub generate_accessor_method {
130 my ($self, $attr_name) = @_;
131 my $meta_instance = $self->associated_class->instance_metaclass;
133 $meta_instance->set_slot_value($_[0], $attr_name, $_[1]) if scalar(@_) == 2;
134 $meta_instance->get_slot_value($_[0], $attr_name);
138 sub generate_reader_method {
139 my ($self, $attr_name) = @_;
140 my $meta_instance = $self->associated_class->instance_metaclass;
142 confess "Cannot assign a value to a read-only accessor" if @_ > 1;
143 $meta_instance->get_slot_value($_[0], $attr_name);
147 sub generate_writer_method {
148 my ($self, $attr_name) = @_;
149 my $meta_instance = $self->associated_class->instance_metaclass;
151 $meta_instance->set_slot_value($_[0], $attr_name, $_[1]);
155 sub generate_predicate_method {
156 my ($self, $attr_name) = @_;
157 my $meta_instance = $self->associated_class->instance_metaclass;
159 $meta_instance->has_slot_value($_[0], $attr_name);
163 sub process_accessors {
164 my ($self, $type, $accessor) = @_;
165 if (reftype($accessor)) {
166 (reftype($accessor) eq 'HASH')
167 || confess "bad accessor/reader/writer/predicate format, must be a HASH ref";
168 my ($name, $method) = each %{$accessor};
169 return ($name, Class::MOP::Attribute::Accessor->wrap($method));
172 my $generator = $self->can('generate_' . $type . '_method');
174 || confess "There is no method generator for the type='$type'";
175 if (my $method = $self->$generator($self->name)) {
176 return ($accessor => Class::MOP::Attribute::Accessor->wrap($method));
178 confess "Could not create the '$type' method for " . $self->name . " because : $@";
182 sub install_accessors {
184 my $class = $self->associated_class;
187 $self->process_accessors('accessor' => $self->accessor())
188 ) if $self->has_accessor();
191 $self->process_accessors('reader' => $self->reader())
192 ) if $self->has_reader();
195 $self->process_accessors('writer' => $self->writer())
196 ) if $self->has_writer();
199 $self->process_accessors('predicate' => $self->predicate())
200 ) if $self->has_predicate();
205 my $_remove_accessor = sub {
206 my ($accessor, $class) = @_;
207 if (reftype($accessor) && reftype($accessor) eq 'HASH') {
208 ($accessor) = keys %{$accessor};
210 my $method = $class->get_method($accessor);
211 $class->remove_method($accessor)
212 if (blessed($method) && $method->isa('Class::MOP::Attribute::Accessor'));
215 sub remove_accessors {
217 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
218 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
219 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
220 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
226 package Class::MOP::Attribute::Accessor;
231 use Class::MOP::Method;
233 our $VERSION = '0.01';
235 our @ISA = ('Class::MOP::Method');
245 Class::MOP::Attribute - Attribute Meta Object
249 Class::MOP::Attribute->new('$foo' => (
250 accessor => 'foo', # dual purpose get/set accessor
251 predicate => 'has_foo' # predicate check for defined-ness
252 init_arg => '-foo', # class->new will look for a -foo key
253 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
256 Class::MOP::Attribute->new('$.bar' => (
257 reader => 'bar', # getter
258 writer => 'set_bar', # setter
259 predicate => 'has_bar' # predicate check for defined-ness
260 init_arg => ':bar', # class->new will look for a :bar key
261 # no default value means it is undef
266 The Attribute Protocol is almost entirely an invention of this module,
267 and is completely optional to this MOP. This is because Perl 5 does not
268 have consistent notion of what is an attribute of a class. There are
269 so many ways in which this is done, and very few (if any) are
270 easily discoverable by this module.
272 So, all that said, this module attempts to inject some order into this
273 chaos, by introducing a consistent API which can be used to create
282 =item B<new ($name, ?%options)>
284 An attribute must (at the very least), have a C<$name>. All other
285 C<%options> are contained added as key-value pairs. Acceptable keys
292 This should be a string value representing the expected key in
293 an initialization hash. For instance, if we have an I<init_arg>
294 value of C<-foo>, then the following code will Just Work.
296 MyClass->meta->construct_instance(-foo => "Hello There");
298 In an init_arg is not assigned, it will automatically use the
303 The value of this key is the default value which
304 C<Class::MOP::Class::construct_instance> will initialize the
308 If the value is a simple scalar (string or number), then it can
309 be just passed as is. However, if you wish to initialize it with
310 a HASH or ARRAY ref, then you need to wrap that inside a CODE
313 Class::MOP::Attribute->new('@foo' => (
314 default => sub { [] },
319 Class::MOP::Attribute->new('%foo' => (
320 default => sub { {} },
323 If you wish to initialize an attribute with a CODE reference
324 itself, then you need to wrap that in a subroutine as well, like
327 Class::MOP::Attribute->new('&foo' => (
328 default => sub { sub { print "Hello World" } },
331 And lastly, if the value of your attribute is dependent upon
332 some other aspect of the instance structure, then you can take
333 advantage of the fact that when the I<default> value is a CODE
334 reference, it is passed the raw (unblessed) instance structure
335 as it's only argument. So you can do things like this:
337 Class::MOP::Attribute->new('$object_identity' => (
338 default => sub { Scalar::Util::refaddr($_[0]) },
341 This last feature is fairly limited as there is no gurantee of
342 the order of attribute initializations, so you cannot perform
343 any kind of dependent initializations. However, if this is
344 something you need, you could subclass B<Class::MOP::Class> and
345 this class to acheive it. However, this is currently left as
346 an exercise to the reader :).
350 The I<accessor>, I<reader>, I<writer> and I<predicate> keys can
351 contain either; the name of the method and an appropriate default
352 one will be generated for you, B<or> a HASH ref containing exactly one
353 key (which will be used as the name of the method) and one value,
354 which should contain a CODE reference which will be installed as
361 The I<accessor> is a standard perl-style read/write accessor. It will
362 return the value of the attribute, and if a value is passed as an argument,
363 it will assign that value to the attribute.
366 This method will properly handle the following code, by assigning an
367 C<undef> value to the attribute.
369 $object->set_something(undef);
373 This is a basic read-only accessor, it will just return the value of
378 This is a basic write accessor, it accepts a single argument, and
379 assigns that value to the attribute. This method does not intentially
380 return a value, however perl will return the result of the last
381 expression in the subroutine, which returns in this returning the
382 same value that it was passed.
385 This method will properly handle the following code, by assigning an
386 C<undef> value to the attribute.
388 $object->set_something();
392 This is a basic test to see if the value of the attribute is not
393 C<undef>. It will return true (C<1>) if the attribute's value is
394 defined, and false (C<0>) otherwise.
398 =item B<clone (%options)>
400 =item B<initialize_instance_slot ($instance, $params)>
406 These are all basic read-only value accessors for the values
407 passed into C<new>. I think they are pretty much self-explanitory.
423 =item B<default (?$instance)>
425 As noted in the documentation for C<new> above, if the I<default>
426 value is a CODE reference, this accessor will pass a single additional
427 argument C<$instance> into it and return the value.
431 =head2 Informational predicates
433 These are all basic predicate methods for the values passed into C<new>.
437 =item B<has_accessor>
443 =item B<has_predicate>
445 =item B<has_init_arg>
451 =head2 Class association
455 =item B<associated_class>
457 =item B<attach_to_class ($class)>
459 =item B<detach_from_class>
463 =head2 Attribute Accessor generation
467 =item B<install_accessors>
469 This allows the attribute to generate and install code for it's own
470 I<accessor/reader/writer/predicate> methods. This is called by
471 C<Class::MOP::Class::add_attribute>.
473 This method will call C<process_accessors> for each of the possible
474 method types (accessor, reader, writer & predicate).
476 =item B<process_accessors ($type, $value)>
478 This takes a C<$type> (accessor, reader, writer or predicate), and
479 a C<$value> (the value passed into the constructor for each of the
480 different types). It will then either generate the method itself
481 (using the C<generate_*_method> methods listed below) or it will
482 use the custom method passed through the constructor.
486 =item B<generate_accessor_method ($attr_name)>
488 =item B<generate_predicate_method ($attr_name)>
490 =item B<generate_reader_method ($attr_name)>
492 =item B<generate_writer_method ($attr_name)>
496 =item B<remove_accessors>
498 This allows the attribute to remove the method for it's own
499 I<accessor/reader/writer/predicate>. This is called by
500 C<Class::MOP::Class::remove_attribute>.
510 This will return a B<Class::MOP::Class> instance which is related
513 It should also be noted that B<Class::MOP> will actually bootstrap
514 this module by installing a number of attribute meta-objects into
515 it's metaclass. This will allow this class to reap all the benifits
516 of the MOP when subclassing it.
522 Stevan Little E<lt>stevan@iinteractive.comE<gt>
524 =head1 COPYRIGHT AND LICENSE
526 Copyright 2006 by Infinity Interactive, Inc.
528 L<http://www.iinteractive.com>
530 This library is free software; you can redistribute it and/or modify
531 it under the same terms as Perl itself.