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 { $_[0]->{init_arg} }
98 # end bootstrapped away method section.
99 # (all methods below here are kept intact)
101 sub is_default_a_coderef {
102 (reftype($_[0]->{default}) && reftype($_[0]->{default}) eq 'CODE')
106 my ($self, $instance) = @_;
107 if ($instance && $self->is_default_a_coderef) {
108 # if the default is a CODE ref, then
109 # we pass in the instance and default
110 # can return a value based on that
111 # instance. Somewhat crude, but works.
112 return $self->{default}->($instance);
119 sub slots { (shift)->name }
123 sub attach_to_class {
124 my ($self, $class) = @_;
125 (blessed($class) && $class->isa('Class::MOP::Class'))
126 || confess "You must pass a Class::MOP::Class instance (or a subclass)";
127 weaken($self->{associated_class} = $class);
130 sub detach_from_class {
132 $self->{associated_class} = undef;
135 ## Method generation helpers
137 sub generate_accessor_method {
139 my $attr_name = $self->name;
141 my $meta_instance = Class::MOP::Class->initialize(Scalar::Util::blessed($_[0]))->get_meta_instance;
142 $meta_instance->set_slot_value($_[0], $attr_name, $_[1]) if scalar(@_) == 2;
143 $meta_instance->get_slot_value($_[0], $attr_name);
147 sub generate_accessor_method_inline {
149 my $attr_name = $self->name;
150 my $meta_instance = $self->associated_class->instance_metaclass;
152 my $code = eval 'sub {'
153 . $meta_instance->inline_set_slot_value('$_[0]', $attr_name, '$_[1]') . ' if scalar(@_) == 2; '
154 . $meta_instance->inline_get_slot_value('$_[0]', $attr_name)
156 confess "Could not generate inline accessor because : $@" if $@;
161 sub generate_reader_method {
163 my $attr_name = $self->name;
165 confess "Cannot assign a value to a read-only accessor" if @_ > 1;
166 Class::MOP::Class->initialize(Scalar::Util::blessed($_[0]))
168 ->get_slot_value($_[0], $attr_name);
172 sub generate_reader_method_inline {
174 my $attr_name = $self->name;
175 my $meta_instance = $self->associated_class->instance_metaclass;
177 my $code = eval 'sub {'
178 . 'confess "Cannot assign a value to a read-only accessor" if @_ > 1;'
179 . $meta_instance->inline_get_slot_value('$_[0]', $attr_name)
181 confess "Could not generate inline accessor because : $@" if $@;
186 sub generate_writer_method {
188 my $attr_name = $self->name;
190 Class::MOP::Class->initialize(Scalar::Util::blessed($_[0]))
192 ->set_slot_value($_[0], $attr_name, $_[1]);
196 sub generate_writer_method_inline {
198 my $attr_name = $self->name;
199 my $meta_instance = $self->associated_class->instance_metaclass;
201 my $code = eval 'sub {'
202 . $meta_instance->inline_set_slot_value('$_[0]', $attr_name, '$_[1]')
204 confess "Could not generate inline accessor because : $@" if $@;
209 sub generate_predicate_method {
211 my $attr_name = $self->name;
213 defined Class::MOP::Class->initialize(Scalar::Util::blessed($_[0]))
215 ->get_slot_value($_[0], $attr_name) ? 1 : 0;
219 sub generate_predicate_method_inline {
221 my $attr_name = $self->name;
222 my $meta_instance = $self->associated_class->instance_metaclass;
224 my $code = eval 'sub {'
225 . 'defined ' . $meta_instance->inline_get_slot_value('$_[0]', $attr_name) . ' ? 1 : 0'
227 confess "Could not generate inline accessor because : $@" if $@;
232 sub process_accessors {
233 my ($self, $type, $accessor, $generate_as_inline_methods) = @_;
234 if (reftype($accessor)) {
235 (reftype($accessor) eq 'HASH')
236 || confess "bad accessor/reader/writer/predicate format, must be a HASH ref";
237 my ($name, $method) = each %{$accessor};
238 return ($name, Class::MOP::Attribute::Accessor->wrap($method));
241 my $inline_me = ($generate_as_inline_methods && $self->associated_class->instance_metaclass->is_inlinable);
242 my $generator = $self->can('generate_' . $type . '_method' . ($inline_me ? '_inline' : ''));
244 || confess "There is no method generator for the type='$type'";
245 if (my $method = $self->$generator($self->name)) {
246 return ($accessor => Class::MOP::Attribute::Accessor->wrap($method));
248 confess "Could not create the '$type' method for " . $self->name . " because : $@";
252 sub install_accessors {
255 my $class = $self->associated_class;
258 $self->process_accessors('accessor' => $self->accessor(), $inline)
259 ) if $self->has_accessor();
262 $self->process_accessors('reader' => $self->reader(), $inline)
263 ) if $self->has_reader();
266 $self->process_accessors('writer' => $self->writer(), $inline)
267 ) if $self->has_writer();
270 $self->process_accessors('predicate' => $self->predicate(), $inline)
271 ) if $self->has_predicate();
277 my $_remove_accessor = sub {
278 my ($accessor, $class) = @_;
279 if (reftype($accessor) && reftype($accessor) eq 'HASH') {
280 ($accessor) = keys %{$accessor};
282 my $method = $class->get_method($accessor);
283 $class->remove_method($accessor)
284 if (blessed($method) && $method->isa('Class::MOP::Attribute::Accessor'));
287 sub remove_accessors {
289 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
290 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
291 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
292 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
298 package Class::MOP::Attribute::Accessor;
303 use Class::MOP::Method;
305 our $VERSION = '0.01';
307 our @ISA = ('Class::MOP::Method');
317 Class::MOP::Attribute - Attribute Meta Object
321 Class::MOP::Attribute->new('$foo' => (
322 accessor => 'foo', # dual purpose get/set accessor
323 predicate => 'has_foo' # predicate check for defined-ness
324 init_arg => '-foo', # class->new will look for a -foo key
325 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
328 Class::MOP::Attribute->new('$.bar' => (
329 reader => 'bar', # getter
330 writer => 'set_bar', # setter
331 predicate => 'has_bar' # predicate check for defined-ness
332 init_arg => ':bar', # class->new will look for a :bar key
333 # no default value means it is undef
338 The Attribute Protocol is almost entirely an invention of this module,
339 and is completely optional to this MOP. This is because Perl 5 does not
340 have consistent notion of what is an attribute of a class. There are
341 so many ways in which this is done, and very few (if any) are
342 easily discoverable by this module.
344 So, all that said, this module attempts to inject some order into this
345 chaos, by introducing a consistent API which can be used to create
354 =item B<new ($name, ?%options)>
356 An attribute must (at the very least), have a C<$name>. All other
357 C<%options> are contained added as key-value pairs. Acceptable keys
364 This should be a string value representing the expected key in
365 an initialization hash. For instance, if we have an I<init_arg>
366 value of C<-foo>, then the following code will Just Work.
368 MyClass->meta->construct_instance(-foo => "Hello There");
370 In an init_arg is not assigned, it will automatically use the
375 The value of this key is the default value which
376 C<Class::MOP::Class::construct_instance> will initialize the
380 If the value is a simple scalar (string or number), then it can
381 be just passed as is. However, if you wish to initialize it with
382 a HASH or ARRAY ref, then you need to wrap that inside a CODE
385 Class::MOP::Attribute->new('@foo' => (
386 default => sub { [] },
391 Class::MOP::Attribute->new('%foo' => (
392 default => sub { {} },
395 If you wish to initialize an attribute with a CODE reference
396 itself, then you need to wrap that in a subroutine as well, like
399 Class::MOP::Attribute->new('&foo' => (
400 default => sub { sub { print "Hello World" } },
403 And lastly, if the value of your attribute is dependent upon
404 some other aspect of the instance structure, then you can take
405 advantage of the fact that when the I<default> value is a CODE
406 reference, it is passed the raw (unblessed) instance structure
407 as it's only argument. So you can do things like this:
409 Class::MOP::Attribute->new('$object_identity' => (
410 default => sub { Scalar::Util::refaddr($_[0]) },
413 This last feature is fairly limited as there is no gurantee of
414 the order of attribute initializations, so you cannot perform
415 any kind of dependent initializations. However, if this is
416 something you need, you could subclass B<Class::MOP::Class> and
417 this class to acheive it. However, this is currently left as
418 an exercise to the reader :).
422 The I<accessor>, I<reader>, I<writer> and I<predicate> keys can
423 contain either; the name of the method and an appropriate default
424 one will be generated for you, B<or> a HASH ref containing exactly one
425 key (which will be used as the name of the method) and one value,
426 which should contain a CODE reference which will be installed as
433 The I<accessor> is a standard perl-style read/write accessor. It will
434 return the value of the attribute, and if a value is passed as an argument,
435 it will assign that value to the attribute.
438 This method will properly handle the following code, by assigning an
439 C<undef> value to the attribute.
441 $object->set_something(undef);
445 This is a basic read-only accessor, it will just return the value of
450 This is a basic write accessor, it accepts a single argument, and
451 assigns that value to the attribute. This method does not intentially
452 return a value, however perl will return the result of the last
453 expression in the subroutine, which returns in this returning the
454 same value that it was passed.
457 This method will properly handle the following code, by assigning an
458 C<undef> value to the attribute.
460 $object->set_something();
464 This is a basic test to see if the value of the attribute is not
465 C<undef>. It will return true (C<1>) if the attribute's value is
466 defined, and false (C<0>) otherwise.
470 =item B<clone (%options)>
472 =item B<initialize_instance_slot ($instance, $params)>
478 These are all basic read-only value accessors for the values
479 passed into C<new>. I think they are pretty much self-explanitory.
495 =item B<default (?$instance)>
497 As noted in the documentation for C<new> above, if the I<default>
498 value is a CODE reference, this accessor will pass a single additional
499 argument C<$instance> into it and return the value.
503 Returns a list of slots required by the attribute. This is usually
504 just one, which is the name of the attribute.
508 =head2 Informational predicates
510 These are all basic predicate methods for the values passed into C<new>.
514 =item B<has_accessor>
520 =item B<has_predicate>
522 =item B<has_init_arg>
528 =head2 Class association
532 =item B<associated_class>
534 =item B<attach_to_class ($class)>
536 =item B<detach_from_class>
540 =item B<allocate_slots>
542 =item B<deallocate_slots>
546 =head2 Attribute Accessor generation
550 =item B<install_accessors>
552 This allows the attribute to generate and install code for it's own
553 I<accessor/reader/writer/predicate> methods. This is called by
554 C<Class::MOP::Class::add_attribute>.
556 This method will call C<process_accessors> for each of the possible
557 method types (accessor, reader, writer & predicate).
559 =item B<process_accessors ($type, $value)>
561 This takes a C<$type> (accessor, reader, writer or predicate), and
562 a C<$value> (the value passed into the constructor for each of the
563 different types). It will then either generate the method itself
564 (using the C<generate_*_method> methods listed below) or it will
565 use the custom method passed through the constructor.
569 =item B<generate_accessor_method>
571 =item B<generate_predicate_method>
573 =item B<generate_reader_method>
575 =item B<generate_writer_method>
579 =item B<remove_accessors>
581 This allows the attribute to remove the method for it's own
582 I<accessor/reader/writer/predicate>. This is called by
583 C<Class::MOP::Class::remove_attribute>.
593 This will return a B<Class::MOP::Class> instance which is related
596 It should also be noted that B<Class::MOP> will actually bootstrap
597 this module by installing a number of attribute meta-objects into
598 it's metaclass. This will allow this class to reap all the benifits
599 of the MOP when subclassing it.
605 Stevan Little E<lt>stevan@iinteractive.comE<gt>
607 =head1 COPYRIGHT AND LICENSE
609 Copyright 2006 by Infinity Interactive, Inc.
611 L<http://www.iinteractive.com>
613 This library is free software; you can redistribute it and/or modify
614 it under the same terms as Perl itself.