2 package Class::MOP::Attribute;
7 use Class::MOP::Method::Accessor;
10 use Scalar::Util 'blessed', 'reftype', 'weaken';
12 our $VERSION = '0.17';
13 our $AUTHORITY = 'cpan:STEVAN';
15 use base 'Class::MOP::Object';
18 require Class::MOP::Class;
19 Class::MOP::Class->initialize(blessed($_[0]) || $_[0]);
22 # NOTE: (meta-circularity)
23 # This method will be replaced in the
24 # boostrap section of Class::MOP, by
25 # a new version which uses the
26 # &Class::MOP::Class::construct_instance
27 # method to build an attribute meta-object
28 # which itself is described with attribute
30 # - Ain't meta-circularity grand? :)
36 (defined $name && $name)
37 || confess "You must provide a name for the attribute";
39 $options{init_arg} = $name
40 if not exists $options{init_arg};
41 if(exists $options{builder}){
42 confess("builder must be a defined scalar value which is a method name")
43 if ref $options{builder} || !(defined $options{builder});
44 confess("Setting both default and builder is not allowed.")
45 if exists $options{default};
47 (is_default_a_coderef(\%options))
48 || confess("References are not allowed as default values, you must ".
49 "wrap then in a CODE reference (ex: sub { [] } and not [])")
50 if exists $options{default} && ref $options{default};
54 '$!accessor' => $options{accessor},
55 '$!reader' => $options{reader},
56 '$!writer' => $options{writer},
57 '$!predicate' => $options{predicate},
58 '$!clearer' => $options{clearer},
59 '$!builder' => $options{builder},
60 '$!init_arg' => $options{init_arg},
61 '$!default' => $options{default},
62 # keep a weakened link to the
63 # class we are associated with
64 '$!associated_class' => undef,
65 # and a list of the methods
66 # associated with this attr
67 '@!associated_methods' => [],
72 # this is a primative (and kludgy) clone operation
73 # for now, it will be replaced in the Class::MOP
74 # bootstrap with a proper one, however we know
75 # that this one will work fine for now.
80 || confess "Can only clone an instance";
81 return bless { %{$self}, %options } => blessed($self);
84 sub initialize_instance_slot {
85 my ($self, $meta_instance, $instance, $params) = @_;
86 my $init_arg = $self->{'$!init_arg'};
87 # try to fetch the init arg from the %params ...
89 # if nothing was in the %params, we can use the
90 # attribute's default value (if it has one)
91 if(exists $params->{$init_arg}){
92 $meta_instance->set_slot_value($instance, $self->name, $params->{$init_arg});
94 elsif (defined $self->{'$!default'}) {
95 $meta_instance->set_slot_value($instance, $self->name, $self->default($instance));
97 elsif (defined( my $builder = $self->{'$!builder'})) {
98 if ($builder = $instance->can($builder)) {
99 $meta_instance->set_slot_value($instance, $self->name, $instance->$builder);
102 confess(blessed($instance)." does not support builder method '". $self->{'$!builder'} ."' for attribute '" . $self->name . "'");
108 # the next bunch of methods will get bootstrapped
109 # away in the Class::MOP bootstrapping section
111 sub name { $_[0]->{'$!name'} }
113 sub associated_class { $_[0]->{'$!associated_class'} }
114 sub associated_methods { $_[0]->{'@!associated_methods'} }
116 sub has_accessor { defined($_[0]->{'$!accessor'}) ? 1 : 0 }
117 sub has_reader { defined($_[0]->{'$!reader'}) ? 1 : 0 }
118 sub has_writer { defined($_[0]->{'$!writer'}) ? 1 : 0 }
119 sub has_predicate { defined($_[0]->{'$!predicate'}) ? 1 : 0 }
120 sub has_clearer { defined($_[0]->{'$!clearer'}) ? 1 : 0 }
121 sub has_builder { defined($_[0]->{'$!builder'}) ? 1 : 0 }
122 sub has_init_arg { defined($_[0]->{'$!init_arg'}) ? 1 : 0 }
123 sub has_default { defined($_[0]->{'$!default'}) ? 1 : 0 }
125 sub accessor { $_[0]->{'$!accessor'} }
126 sub reader { $_[0]->{'$!reader'} }
127 sub writer { $_[0]->{'$!writer'} }
128 sub predicate { $_[0]->{'$!predicate'} }
129 sub clearer { $_[0]->{'$!clearer'} }
130 sub builder { $_[0]->{'$!builder'} }
131 sub init_arg { $_[0]->{'$!init_arg'} }
133 # end bootstrapped away method section.
134 # (all methods below here are kept intact)
136 sub get_read_method { $_[0]->reader || $_[0]->accessor }
137 sub get_write_method { $_[0]->writer || $_[0]->accessor }
139 sub is_default_a_coderef {
140 ('CODE' eq (reftype($_[0]->{'$!default'} || $_[0]->{default}) || ''))
144 my ($self, $instance) = @_;
145 if (defined $instance && $self->is_default_a_coderef) {
146 # if the default is a CODE ref, then
147 # we pass in the instance and default
148 # can return a value based on that
149 # instance. Somewhat crude, but works.
150 return $self->{'$!default'}->($instance);
152 $self->{'$!default'};
157 sub slots { (shift)->name }
161 sub attach_to_class {
162 my ($self, $class) = @_;
163 (blessed($class) && $class->isa('Class::MOP::Class'))
164 || confess "You must pass a Class::MOP::Class instance (or a subclass)";
165 weaken($self->{'$!associated_class'} = $class);
168 sub detach_from_class {
170 $self->{'$!associated_class'} = undef;
175 sub associate_method {
176 my ($self, $method) = @_;
177 push @{$self->{'@!associated_methods'}} => $method;
183 my ($self, $instance, $value) = @_;
185 Class::MOP::Class->initialize(blessed($instance))
187 ->set_slot_value($instance, $self->name, $value);
191 my ($self, $instance) = @_;
193 Class::MOP::Class->initialize(blessed($instance))
195 ->get_slot_value($instance, $self->name);
199 my ($self, $instance) = @_;
201 Class::MOP::Class->initialize(blessed($instance))
203 ->is_slot_initialized($instance, $self->name);
207 my ($self, $instance) = @_;
209 Class::MOP::Class->initialize(blessed($instance))
211 ->deinitialize_slot($instance, $self->name);
216 sub accessor_metaclass { 'Class::MOP::Method::Accessor' }
218 sub process_accessors {
219 my ($self, $type, $accessor, $generate_as_inline_methods) = @_;
220 if (reftype($accessor)) {
221 (reftype($accessor) eq 'HASH')
222 || confess "bad accessor/reader/writer/predicate/clearer format, must be a HASH ref";
223 my ($name, $method) = %{$accessor};
224 $method = $self->accessor_metaclass->wrap($method);
225 $self->associate_method($method);
226 return ($name, $method);
229 my $inline_me = ($generate_as_inline_methods && $self->associated_class->instance_metaclass->is_inlinable);
232 $method = $self->accessor_metaclass->new(
234 is_inline => $inline_me,
235 accessor_type => $type,
238 confess "Could not create the '$type' method for " . $self->name . " because : $@" if $@;
239 $self->associate_method($method);
240 return ($accessor, $method);
244 sub install_accessors {
247 my $class = $self->associated_class;
250 $self->process_accessors('accessor' => $self->accessor(), $inline)
251 ) if $self->has_accessor();
254 $self->process_accessors('reader' => $self->reader(), $inline)
255 ) if $self->has_reader();
258 $self->process_accessors('writer' => $self->writer(), $inline)
259 ) if $self->has_writer();
262 $self->process_accessors('predicate' => $self->predicate(), $inline)
263 ) if $self->has_predicate();
266 $self->process_accessors('clearer' => $self->clearer(), $inline)
267 ) if $self->has_clearer();
273 my $_remove_accessor = sub {
274 my ($accessor, $class) = @_;
275 if (reftype($accessor) && reftype($accessor) eq 'HASH') {
276 ($accessor) = keys %{$accessor};
278 my $method = $class->get_method($accessor);
279 $class->remove_method($accessor)
280 if (blessed($method) && $method->isa('Class::MOP::Method::Accessor'));
283 sub remove_accessors {
286 # we really need to make sure to remove from the
287 # associates methods here as well. But this is
288 # such a slimly used method, I am not worried
289 # about it right now.
290 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
291 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
292 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
293 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
294 $_remove_accessor->($self->clearer(), $self->associated_class()) if $self->has_clearer();
308 Class::MOP::Attribute - Attribute Meta Object
312 Class::MOP::Attribute->new('$foo' => (
313 accessor => 'foo', # dual purpose get/set accessor
314 predicate => 'has_foo' # predicate check for defined-ness
315 init_arg => '-foo', # class->new will look for a -foo key
316 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
319 Class::MOP::Attribute->new('$.bar' => (
320 reader => 'bar', # getter
321 writer => 'set_bar', # setter
322 predicate => 'has_bar' # predicate check for defined-ness
323 init_arg => ':bar', # class->new will look for a :bar key
324 # no default value means it is undef
329 The Attribute Protocol is almost entirely an invention of this module,
330 and is completely optional to this MOP. This is because Perl 5 does not
331 have consistent notion of what is an attribute of a class. There are
332 so many ways in which this is done, and very few (if any) are
333 easily discoverable by this module.
335 So, all that said, this module attempts to inject some order into this
336 chaos, by introducing a consistent API which can be used to create
345 =item B<new ($name, ?%options)>
347 An attribute must (at the very least), have a C<$name>. All other
348 C<%options> are contained added as key-value pairs. Acceptable keys
355 This should be a string value representing the expected key in
356 an initialization hash. For instance, if we have an I<init_arg>
357 value of C<-foo>, then the following code will Just Work.
359 MyClass->meta->construct_instance(-foo => "Hello There");
361 In an init_arg is not assigned, it will automatically use the
366 The value of this key is the default value which
367 C<Class::MOP::Class::construct_instance> will initialize the
372 The value of this key is the name of the method that will be
373 called to obtain the value used to initialize the attribute.
374 This should be a method in the class associated with the attribute,
375 not a method in the attribute class itself.
378 If the value is a simple scalar (string or number), then it can
379 be just passed as is. However, if you wish to initialize it with
380 a HASH or ARRAY ref, then you need to wrap that inside a CODE
383 Class::MOP::Attribute->new('@foo' => (
384 default => sub { [] },
389 Class::MOP::Attribute->new('%foo' => (
390 default => sub { {} },
393 If you wish to initialize an attribute with a CODE reference
394 itself, then you need to wrap that in a subroutine as well, like
397 Class::MOP::Attribute->new('&foo' => (
398 default => sub { sub { print "Hello World" } },
401 And lastly, if the value of your attribute is dependent upon
402 some other aspect of the instance structure, then you can take
403 advantage of the fact that when the I<default> value is a CODE
404 reference, it is passed the raw (unblessed) instance structure
405 as it's only argument. So you can do things like this:
407 Class::MOP::Attribute->new('$object_identity' => (
408 default => sub { Scalar::Util::refaddr($_[0]) },
411 This last feature is fairly limited as there is no gurantee of
412 the order of attribute initializations, so you cannot perform
413 any kind of dependent initializations. However, if this is
414 something you need, you could subclass B<Class::MOP::Class> and
415 this class to acheive it. However, this is currently left as
416 an exercise to the reader :).
420 The I<accessor>, I<reader>, I<writer>, I<predicate> and I<clearer> keys can
421 contain either; the name of the method and an appropriate default one will be
422 generated for you, B<or> a HASH ref containing exactly one key (which will be
423 used as the name of the method) and one value, which should contain a CODE
424 reference which will be installed as the method itself.
430 The I<accessor> is a standard perl-style read/write accessor. It will
431 return the value of the attribute, and if a value is passed as an argument,
432 it will assign that value to the attribute.
435 This method will properly handle the following code, by assigning an
436 C<undef> value to the attribute.
438 $object->set_something(undef);
442 This is a basic read-only accessor, it will just return the value of
447 This is a basic write accessor, it accepts a single argument, and
448 assigns that value to the attribute. This method does not intentially
449 return a value, however perl will return the result of the last
450 expression in the subroutine, which returns in this returning the
451 same value that it was passed.
454 This method will properly handle the following code, by assigning an
455 C<undef> value to the attribute.
457 $object->set_something();
461 This is a basic test to see if the value of the attribute is not
462 C<undef>. It will return true (C<1>) if the attribute's value is
463 defined, and false (C<0>) otherwise.
467 This is the a method that will uninitialize the attr, reverting lazy values
468 back to their "unfulfilled" state.
472 =item B<clone (%options)>
474 =item B<initialize_instance_slot ($instance, $params)>
478 =head2 Value management
480 These methods are basically "backdoors" to the instance, which can be used
481 to bypass the regular accessors, but still stay within the context of the MOP.
483 These methods are not for general use, and should only be used if you really
484 know what you are doing.
488 =item B<set_value ($instance, $value)>
490 Set the value without going through the accessor. Note that this may be done to
491 even attributes with just read only accessors.
493 =item B<get_value ($instance)>
495 Return the value without going through the accessor. Note that this may be done
496 even to attributes with just write only accessors.
498 =item B<has_value ($instance)>
500 Returns a boolean indicating if the item in the C<$instance> has a value in it.
501 This is basically what the default C<predicate> method calls.
503 =item B<clear_value ($instance)>
505 This will clear the value in the C<$instance>. This is basically what the default
506 C<clearer> would call. Note that this may be done even if the attirbute does not
507 have any associated read, write or clear methods.
513 These are all basic read-only value accessors for the values
514 passed into C<new>. I think they are pretty much self-explanitory.
532 =item B<is_default_a_coderef>
534 =item B<default (?$instance)>
536 As noted in the documentation for C<new> above, if the I<default>
537 value is a CODE reference, this accessor will pass a single additional
538 argument C<$instance> into it and return the value.
542 Returns a list of slots required by the attribute. This is usually
543 just one, which is the name of the attribute.
545 =item B<get_read_method>
547 =item B<get_write_method>
549 Return the name of a method suitable for reading / writing the value of the
550 attribute in the associated class. Suitable for use whether C<reader> and
551 C<writer> or C<accessor> was used.
555 =head2 Informational predicates
557 These are all basic predicate methods for the values passed into C<new>.
561 =item B<has_accessor>
567 =item B<has_predicate>
571 =item B<has_init_arg>
579 =head2 Class association
581 These methods allow you to manage the attributes association with
582 the class that contains it. These methods should not be used
583 lightly, nor are they very magical, they are mostly used internally
584 and by metaclass instances.
588 =item B<associated_class>
590 This returns the metaclass this attribute is associated with.
592 =item B<attach_to_class ($class)>
594 This will store a weaken reference to C<$class> internally. You should
595 note that just changing the class assocation will not remove the attribute
596 from it's old class, and initialize it (and it's accessors) in the new
597 C<$class>. It is up to you to do this manually.
599 =item B<detach_from_class>
601 This will remove the weakened reference to the class. It does B<not>
602 remove the attribute itself from the class (or remove it's accessors),
603 you must do that yourself if you want too. Actually if that is what
604 you want to do, you should probably be looking at
605 L<Class::MOP::Class::remove_attribute> instead.
609 =head2 Attribute Accessor generation
613 =item B<accessor_metaclass>
615 Accessors are generated by an accessor metaclass, which is usually
616 a subclass of C<Class::MOP::Method::Accessor>. This method returns
617 the name of the accessor metaclass that this attribute uses.
619 =item B<associate_method ($method)>
621 This will associate a C<$method> with the given attribute which is
622 used internally by the accessor generator.
624 =item B<associated_methods>
626 This will return the list of methods which have been associated with
627 the C<associate_method> methods.
629 =item B<install_accessors>
631 This allows the attribute to generate and install code for it's own
632 I<accessor/reader/writer/predicate> methods. This is called by
633 C<Class::MOP::Class::add_attribute>.
635 This method will call C<process_accessors> for each of the possible
636 method types (accessor, reader, writer & predicate).
638 =item B<process_accessors ($type, $value)>
640 This takes a C<$type> (accessor, reader, writer or predicate), and
641 a C<$value> (the value passed into the constructor for each of the
642 different types). It will then either generate the method itself
643 (using the C<generate_*_method> methods listed below) or it will
644 use the custom method passed through the constructor.
646 =item B<remove_accessors>
648 This allows the attribute to remove the method for it's own
649 I<accessor/reader/writer/predicate/clearer>. This is called by
650 C<Class::MOP::Class::remove_attribute>.
652 NOTE: This does not currently remove methods from the list returned
653 by C<associated_methods>, that is on the TODO list.
663 This will return a B<Class::MOP::Class> instance which is related
666 It should also be noted that B<Class::MOP> will actually bootstrap
667 this module by installing a number of attribute meta-objects into
668 it's metaclass. This will allow this class to reap all the benifits
669 of the MOP when subclassing it.
675 Stevan Little E<lt>stevan@iinteractive.comE<gt>
677 =head1 COPYRIGHT AND LICENSE
679 Copyright 2006, 2007 by Infinity Interactive, Inc.
681 L<http://www.iinteractive.com>
683 This library is free software; you can redistribute it and/or modify
684 it under the same terms as Perl itself.