2 package Class::MOP::Attribute;
7 use Class::MOP::Method::Accessor;
10 use Scalar::Util 'blessed', 'reftype', 'weaken';
12 our $VERSION = '0.20';
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 {
138 my $reader = $self->reader || $self->accessor;
140 return $reader unless ref $reader;
142 my ($name) = %$reader;
146 sub get_write_method {
148 my $writer = $self->writer || $self->accessor;
150 return $writer unless ref $writer;
152 my ($name) = %$writer;
156 sub get_read_method_ref {
158 if ((my $reader = $self->get_read_method) && $self->associated_class) {
159 return $self->associated_class->get_method($reader);
162 return sub { $self->get_value(@_) };
166 sub get_write_method_ref {
168 if ((my $writer = $self->get_write_method) && $self->associated_class) {
169 return $self->associated_class->get_method($writer);
172 return sub { $self->set_value(@_) };
176 sub is_default_a_coderef {
177 ('CODE' eq (reftype($_[0]->{'$!default'} || $_[0]->{default}) || ''))
181 my ($self, $instance) = @_;
182 if (defined $instance && $self->is_default_a_coderef) {
183 # if the default is a CODE ref, then
184 # we pass in the instance and default
185 # can return a value based on that
186 # instance. Somewhat crude, but works.
187 return $self->{'$!default'}->($instance);
189 $self->{'$!default'};
194 sub slots { (shift)->name }
198 sub attach_to_class {
199 my ($self, $class) = @_;
200 (blessed($class) && $class->isa('Class::MOP::Class'))
201 || confess "You must pass a Class::MOP::Class instance (or a subclass)";
202 weaken($self->{'$!associated_class'} = $class);
205 sub detach_from_class {
207 $self->{'$!associated_class'} = undef;
212 sub associate_method {
213 my ($self, $method) = @_;
214 push @{$self->{'@!associated_methods'}} => $method;
220 my ($self, $instance, $value) = @_;
222 Class::MOP::Class->initialize(blessed($instance))
224 ->set_slot_value($instance, $self->name, $value);
228 my ($self, $instance) = @_;
230 Class::MOP::Class->initialize(blessed($instance))
232 ->get_slot_value($instance, $self->name);
236 my ($self, $instance) = @_;
238 Class::MOP::Class->initialize(blessed($instance))
240 ->is_slot_initialized($instance, $self->name);
244 my ($self, $instance) = @_;
246 Class::MOP::Class->initialize(blessed($instance))
248 ->deinitialize_slot($instance, $self->name);
253 sub accessor_metaclass { 'Class::MOP::Method::Accessor' }
255 sub process_accessors {
256 my ($self, $type, $accessor, $generate_as_inline_methods) = @_;
257 if (reftype($accessor)) {
258 (reftype($accessor) eq 'HASH')
259 || confess "bad accessor/reader/writer/predicate/clearer format, must be a HASH ref";
260 my ($name, $method) = %{$accessor};
261 $method = $self->accessor_metaclass->wrap($method);
262 $self->associate_method($method);
263 return ($name, $method);
266 my $inline_me = ($generate_as_inline_methods && $self->associated_class->instance_metaclass->is_inlinable);
269 $method = $self->accessor_metaclass->new(
271 is_inline => $inline_me,
272 accessor_type => $type,
275 confess "Could not create the '$type' method for " . $self->name . " because : $@" if $@;
276 $self->associate_method($method);
277 return ($accessor, $method);
281 sub install_accessors {
284 my $class = $self->associated_class;
287 $self->process_accessors('accessor' => $self->accessor(), $inline)
288 ) if $self->has_accessor();
291 $self->process_accessors('reader' => $self->reader(), $inline)
292 ) if $self->has_reader();
295 $self->process_accessors('writer' => $self->writer(), $inline)
296 ) if $self->has_writer();
299 $self->process_accessors('predicate' => $self->predicate(), $inline)
300 ) if $self->has_predicate();
303 $self->process_accessors('clearer' => $self->clearer(), $inline)
304 ) if $self->has_clearer();
310 my $_remove_accessor = sub {
311 my ($accessor, $class) = @_;
312 if (reftype($accessor) && reftype($accessor) eq 'HASH') {
313 ($accessor) = keys %{$accessor};
315 my $method = $class->get_method($accessor);
316 $class->remove_method($accessor)
317 if (blessed($method) && $method->isa('Class::MOP::Method::Accessor'));
320 sub remove_accessors {
323 # we really need to make sure to remove from the
324 # associates methods here as well. But this is
325 # such a slimly used method, I am not worried
326 # about it right now.
327 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
328 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
329 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
330 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
331 $_remove_accessor->($self->clearer(), $self->associated_class()) if $self->has_clearer();
345 Class::MOP::Attribute - Attribute Meta Object
349 Class::MOP::Attribute->new('$foo' => (
350 accessor => 'foo', # dual purpose get/set accessor
351 predicate => 'has_foo' # predicate check for defined-ness
352 init_arg => '-foo', # class->new will look for a -foo key
353 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
356 Class::MOP::Attribute->new('$.bar' => (
357 reader => 'bar', # getter
358 writer => 'set_bar', # setter
359 predicate => 'has_bar' # predicate check for defined-ness
360 init_arg => ':bar', # class->new will look for a :bar key
361 # no default value means it is undef
366 The Attribute Protocol is almost entirely an invention of this module,
367 and is completely optional to this MOP. This is because Perl 5 does not
368 have consistent notion of what is an attribute of a class. There are
369 so many ways in which this is done, and very few (if any) are
370 easily discoverable by this module.
372 So, all that said, this module attempts to inject some order into this
373 chaos, by introducing a consistent API which can be used to create
382 =item B<new ($name, ?%options)>
384 An attribute must (at the very least), have a C<$name>. All other
385 C<%options> are contained added as key-value pairs. Acceptable keys
392 This should be a string value representing the expected key in
393 an initialization hash. For instance, if we have an I<init_arg>
394 value of C<-foo>, then the following code will Just Work.
396 MyClass->meta->construct_instance(-foo => "Hello There");
398 In an init_arg is not assigned, it will automatically use the
403 The value of this key is the default value which
404 C<Class::MOP::Class::construct_instance> will initialize the
409 The value of this key is the name of the method that will be
410 called to obtain the value used to initialize the attribute.
411 This should be a method in the class associated with the attribute,
412 not a method in the attribute class itself.
415 If the value is a simple scalar (string or number), then it can
416 be just passed as is. However, if you wish to initialize it with
417 a HASH or ARRAY ref, then you need to wrap that inside a CODE
420 Class::MOP::Attribute->new('@foo' => (
421 default => sub { [] },
426 Class::MOP::Attribute->new('%foo' => (
427 default => sub { {} },
430 If you wish to initialize an attribute with a CODE reference
431 itself, then you need to wrap that in a subroutine as well, like
434 Class::MOP::Attribute->new('&foo' => (
435 default => sub { sub { print "Hello World" } },
438 And lastly, if the value of your attribute is dependent upon
439 some other aspect of the instance structure, then you can take
440 advantage of the fact that when the I<default> value is a CODE
441 reference, it is passed the raw (unblessed) instance structure
442 as it's only argument. So you can do things like this:
444 Class::MOP::Attribute->new('$object_identity' => (
445 default => sub { Scalar::Util::refaddr($_[0]) },
448 This last feature is fairly limited as there is no gurantee of
449 the order of attribute initializations, so you cannot perform
450 any kind of dependent initializations. However, if this is
451 something you need, you could subclass B<Class::MOP::Class> and
452 this class to acheive it. However, this is currently left as
453 an exercise to the reader :).
457 The I<accessor>, I<reader>, I<writer>, I<predicate> and I<clearer> keys can
458 contain either; the name of the method and an appropriate default one will be
459 generated for you, B<or> a HASH ref containing exactly one key (which will be
460 used as the name of the method) and one value, which should contain a CODE
461 reference which will be installed as the method itself.
467 The I<accessor> is a standard perl-style read/write accessor. It will
468 return the value of the attribute, and if a value is passed as an argument,
469 it will assign that value to the attribute.
472 This method will properly handle the following code, by assigning an
473 C<undef> value to the attribute.
475 $object->set_something(undef);
479 This is a basic read-only accessor, it will just return the value of
484 This is a basic write accessor, it accepts a single argument, and
485 assigns that value to the attribute. This method does not intentially
486 return a value, however perl will return the result of the last
487 expression in the subroutine, which returns in this returning the
488 same value that it was passed.
491 This method will properly handle the following code, by assigning an
492 C<undef> value to the attribute.
494 $object->set_something();
498 This is a basic test to see if the value of the attribute is not
499 C<undef>. It will return true (C<1>) if the attribute's value is
500 defined, and false (C<0>) otherwise.
504 This is the a method that will uninitialize the attr, reverting lazy values
505 back to their "unfulfilled" state.
509 =item B<clone (%options)>
511 =item B<initialize_instance_slot ($instance, $params)>
515 =head2 Value management
517 These methods are basically "backdoors" to the instance, which can be used
518 to bypass the regular accessors, but still stay within the context of the MOP.
520 These methods are not for general use, and should only be used if you really
521 know what you are doing.
525 =item B<set_value ($instance, $value)>
527 Set the value without going through the accessor. Note that this may be done to
528 even attributes with just read only accessors.
530 =item B<get_value ($instance)>
532 Return the value without going through the accessor. Note that this may be done
533 even to attributes with just write only accessors.
535 =item B<has_value ($instance)>
537 Returns a boolean indicating if the item in the C<$instance> has a value in it.
538 This is basically what the default C<predicate> method calls.
540 =item B<clear_value ($instance)>
542 This will clear the value in the C<$instance>. This is basically what the default
543 C<clearer> would call. Note that this may be done even if the attirbute does not
544 have any associated read, write or clear methods.
550 These are all basic read-only value accessors for the values
551 passed into C<new>. I think they are pretty much self-explanitory.
569 =item B<is_default_a_coderef>
571 =item B<default (?$instance)>
573 As noted in the documentation for C<new> above, if the I<default>
574 value is a CODE reference, this accessor will pass a single additional
575 argument C<$instance> into it and return the value.
579 Returns a list of slots required by the attribute. This is usually
580 just one, which is the name of the attribute.
582 =item B<get_read_method>
584 =item B<get_write_method>
586 Return the name of a method name suitable for reading / writing the value
587 of the attribute in the associated class. Suitable for use whether
588 C<reader> and C<writer> or C<accessor> was used.
590 =item B<get_read_method_ref>
592 =item B<get_write_method_ref>
594 Return the CODE reference of a method suitable for reading / writing the
595 value of the attribute in the associated class. Suitable for use whether
596 C<reader> and C<writer> or C<accessor> was specified or not.
598 NOTE: If not reader/writer/accessor was specified, this will use the
599 attribute get_value/set_value methods, which can be very inefficient.
603 =head2 Informational predicates
605 These are all basic predicate methods for the values passed into C<new>.
609 =item B<has_accessor>
615 =item B<has_predicate>
619 =item B<has_init_arg>
627 =head2 Class association
629 These methods allow you to manage the attributes association with
630 the class that contains it. These methods should not be used
631 lightly, nor are they very magical, they are mostly used internally
632 and by metaclass instances.
636 =item B<associated_class>
638 This returns the metaclass this attribute is associated with.
640 =item B<attach_to_class ($class)>
642 This will store a weaken reference to C<$class> internally. You should
643 note that just changing the class assocation will not remove the attribute
644 from it's old class, and initialize it (and it's accessors) in the new
645 C<$class>. It is up to you to do this manually.
647 =item B<detach_from_class>
649 This will remove the weakened reference to the class. It does B<not>
650 remove the attribute itself from the class (or remove it's accessors),
651 you must do that yourself if you want too. Actually if that is what
652 you want to do, you should probably be looking at
653 L<Class::MOP::Class::remove_attribute> instead.
657 =head2 Attribute Accessor generation
661 =item B<accessor_metaclass>
663 Accessors are generated by an accessor metaclass, which is usually
664 a subclass of C<Class::MOP::Method::Accessor>. This method returns
665 the name of the accessor metaclass that this attribute uses.
667 =item B<associate_method ($method)>
669 This will associate a C<$method> with the given attribute which is
670 used internally by the accessor generator.
672 =item B<associated_methods>
674 This will return the list of methods which have been associated with
675 the C<associate_method> methods.
677 =item B<install_accessors>
679 This allows the attribute to generate and install code for it's own
680 I<accessor/reader/writer/predicate> methods. This is called by
681 C<Class::MOP::Class::add_attribute>.
683 This method will call C<process_accessors> for each of the possible
684 method types (accessor, reader, writer & predicate).
686 =item B<process_accessors ($type, $value)>
688 This takes a C<$type> (accessor, reader, writer or predicate), and
689 a C<$value> (the value passed into the constructor for each of the
690 different types). It will then either generate the method itself
691 (using the C<generate_*_method> methods listed below) or it will
692 use the custom method passed through the constructor.
694 =item B<remove_accessors>
696 This allows the attribute to remove the method for it's own
697 I<accessor/reader/writer/predicate/clearer>. This is called by
698 C<Class::MOP::Class::remove_attribute>.
700 NOTE: This does not currently remove methods from the list returned
701 by C<associated_methods>, that is on the TODO list.
711 This will return a B<Class::MOP::Class> instance which is related
714 It should also be noted that B<Class::MOP> will actually bootstrap
715 this module by installing a number of attribute meta-objects into
716 it's metaclass. This will allow this class to reap all the benifits
717 of the MOP when subclassing it.
723 Stevan Little E<lt>stevan@iinteractive.comE<gt>
725 =head1 COPYRIGHT AND LICENSE
727 Copyright 2006, 2007 by Infinity Interactive, Inc.
729 L<http://www.iinteractive.com>
731 This library is free software; you can redistribute it and/or modify
732 it under the same terms as Perl itself.