2 package Class::MOP::Attribute;
7 use Class::MOP::Method::Accessor;
10 use Scalar::Util 'blessed', 'reftype', 'weaken';
12 our $VERSION = '0.16';
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 $val = $params->{$init_arg} if exists $params->{$init_arg};
90 # if nothing was in the %params, we can use the
91 # attribute's default value (if it has one)
92 if (!defined $val && defined $self->{'$!default'}) {
93 $val = $self->default($instance);
94 } elsif (!defined $val && defined $self->{'$!builder'}) {
95 my $builder = $self->{'$!builder'};
96 confess(blessed($instance)." does not support builder method '$builder' for attribute '" . $self->name . "'")
97 unless $instance->can($builder);
98 $val = $instance->$builder;
100 $meta_instance->set_slot_value($instance, $self->name, $val);
104 # the next bunch of methods will get bootstrapped
105 # away in the Class::MOP bootstrapping section
107 sub name { $_[0]->{'$!name'} }
109 sub associated_class { $_[0]->{'$!associated_class'} }
110 sub associated_methods { $_[0]->{'@!associated_methods'} }
112 sub has_accessor { defined($_[0]->{'$!accessor'}) ? 1 : 0 }
113 sub has_reader { defined($_[0]->{'$!reader'}) ? 1 : 0 }
114 sub has_writer { defined($_[0]->{'$!writer'}) ? 1 : 0 }
115 sub has_predicate { defined($_[0]->{'$!predicate'}) ? 1 : 0 }
116 sub has_clearer { defined($_[0]->{'$!clearer'}) ? 1 : 0 }
117 sub has_builder { defined($_[0]->{'$!builder'}) ? 1 : 0 }
118 sub has_init_arg { defined($_[0]->{'$!init_arg'}) ? 1 : 0 }
119 sub has_default { defined($_[0]->{'$!default'}) ? 1 : 0 }
121 sub accessor { $_[0]->{'$!accessor'} }
122 sub reader { $_[0]->{'$!reader'} }
123 sub writer { $_[0]->{'$!writer'} }
124 sub predicate { $_[0]->{'$!predicate'} }
125 sub clearer { $_[0]->{'$!clearer'} }
126 sub builder { $_[0]->{'$!builder'} }
127 sub init_arg { $_[0]->{'$!init_arg'} }
129 # end bootstrapped away method section.
130 # (all methods below here are kept intact)
132 sub get_read_method { $_[0]->reader || $_[0]->accessor }
133 sub get_write_method { $_[0]->writer || $_[0]->accessor }
135 sub is_default_a_coderef {
136 ('CODE' eq (reftype($_[0]->{'$!default'} || $_[0]->{default}) || ''))
140 my ($self, $instance) = @_;
141 if (defined $instance && $self->is_default_a_coderef) {
142 # if the default is a CODE ref, then
143 # we pass in the instance and default
144 # can return a value based on that
145 # instance. Somewhat crude, but works.
146 return $self->{'$!default'}->($instance);
148 $self->{'$!default'};
153 sub slots { (shift)->name }
157 sub attach_to_class {
158 my ($self, $class) = @_;
159 (blessed($class) && $class->isa('Class::MOP::Class'))
160 || confess "You must pass a Class::MOP::Class instance (or a subclass)";
161 weaken($self->{'$!associated_class'} = $class);
164 sub detach_from_class {
166 $self->{'$!associated_class'} = undef;
171 sub associate_method {
172 my ($self, $method) = @_;
173 push @{$self->{'@!associated_methods'}} => $method;
179 my ($self, $instance, $value) = @_;
181 Class::MOP::Class->initialize(blessed($instance))
183 ->set_slot_value($instance, $self->name, $value);
187 my ($self, $instance) = @_;
189 Class::MOP::Class->initialize(blessed($instance))
191 ->get_slot_value($instance, $self->name);
195 my ($self, $instance) = @_;
197 defined Class::MOP::Class->initialize(blessed($instance))
199 ->get_slot_value($instance, $self->name) ? 1 : 0;
203 my ($self, $instance) = @_;
205 Class::MOP::Class->initialize(blessed($instance))
207 ->deinitialize_slot($instance, $self->name);
212 sub accessor_metaclass { 'Class::MOP::Method::Accessor' }
214 sub process_accessors {
215 my ($self, $type, $accessor, $generate_as_inline_methods) = @_;
216 if (reftype($accessor)) {
217 (reftype($accessor) eq 'HASH')
218 || confess "bad accessor/reader/writer/predicate/clearer format, must be a HASH ref";
219 my ($name, $method) = %{$accessor};
220 $method = $self->accessor_metaclass->wrap($method);
221 $self->associate_method($method);
222 return ($name, $method);
225 my $inline_me = ($generate_as_inline_methods && $self->associated_class->instance_metaclass->is_inlinable);
228 $method = $self->accessor_metaclass->new(
230 is_inline => $inline_me,
231 accessor_type => $type,
234 confess "Could not create the '$type' method for " . $self->name . " because : $@" if $@;
235 $self->associate_method($method);
236 return ($accessor, $method);
240 sub install_accessors {
243 my $class = $self->associated_class;
246 $self->process_accessors('accessor' => $self->accessor(), $inline)
247 ) if $self->has_accessor();
250 $self->process_accessors('reader' => $self->reader(), $inline)
251 ) if $self->has_reader();
254 $self->process_accessors('writer' => $self->writer(), $inline)
255 ) if $self->has_writer();
258 $self->process_accessors('predicate' => $self->predicate(), $inline)
259 ) if $self->has_predicate();
262 $self->process_accessors('clearer' => $self->clearer(), $inline)
263 ) if $self->has_clearer();
269 my $_remove_accessor = sub {
270 my ($accessor, $class) = @_;
271 if (reftype($accessor) && reftype($accessor) eq 'HASH') {
272 ($accessor) = keys %{$accessor};
274 my $method = $class->get_method($accessor);
275 $class->remove_method($accessor)
276 if (blessed($method) && $method->isa('Class::MOP::Method::Accessor'));
279 sub remove_accessors {
282 # we really need to make sure to remove from the
283 # associates methods here as well. But this is
284 # such a slimly used method, I am not worried
285 # about it right now.
286 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
287 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
288 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
289 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
290 $_remove_accessor->($self->clearer(), $self->associated_class()) if $self->has_clearer();
304 Class::MOP::Attribute - Attribute Meta Object
308 Class::MOP::Attribute->new('$foo' => (
309 accessor => 'foo', # dual purpose get/set accessor
310 predicate => 'has_foo' # predicate check for defined-ness
311 init_arg => '-foo', # class->new will look for a -foo key
312 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
315 Class::MOP::Attribute->new('$.bar' => (
316 reader => 'bar', # getter
317 writer => 'set_bar', # setter
318 predicate => 'has_bar' # predicate check for defined-ness
319 init_arg => ':bar', # class->new will look for a :bar key
320 # no default value means it is undef
325 The Attribute Protocol is almost entirely an invention of this module,
326 and is completely optional to this MOP. This is because Perl 5 does not
327 have consistent notion of what is an attribute of a class. There are
328 so many ways in which this is done, and very few (if any) are
329 easily discoverable by this module.
331 So, all that said, this module attempts to inject some order into this
332 chaos, by introducing a consistent API which can be used to create
341 =item B<new ($name, ?%options)>
343 An attribute must (at the very least), have a C<$name>. All other
344 C<%options> are contained added as key-value pairs. Acceptable keys
351 This should be a string value representing the expected key in
352 an initialization hash. For instance, if we have an I<init_arg>
353 value of C<-foo>, then the following code will Just Work.
355 MyClass->meta->construct_instance(-foo => "Hello There");
357 In an init_arg is not assigned, it will automatically use the
362 The value of this key is the default value which
363 C<Class::MOP::Class::construct_instance> will initialize the
368 The value of this key is the name of the method that will be
369 called to obtain the value used to initialize the attribute.
370 This should be a method in the class associated with the attribute,
371 not a method in the attribute class itself.
374 If the value is a simple scalar (string or number), then it can
375 be just passed as is. However, if you wish to initialize it with
376 a HASH or ARRAY ref, then you need to wrap that inside a CODE
379 Class::MOP::Attribute->new('@foo' => (
380 default => sub { [] },
385 Class::MOP::Attribute->new('%foo' => (
386 default => sub { {} },
389 If you wish to initialize an attribute with a CODE reference
390 itself, then you need to wrap that in a subroutine as well, like
393 Class::MOP::Attribute->new('&foo' => (
394 default => sub { sub { print "Hello World" } },
397 And lastly, if the value of your attribute is dependent upon
398 some other aspect of the instance structure, then you can take
399 advantage of the fact that when the I<default> value is a CODE
400 reference, it is passed the raw (unblessed) instance structure
401 as it's only argument. So you can do things like this:
403 Class::MOP::Attribute->new('$object_identity' => (
404 default => sub { Scalar::Util::refaddr($_[0]) },
407 This last feature is fairly limited as there is no gurantee of
408 the order of attribute initializations, so you cannot perform
409 any kind of dependent initializations. However, if this is
410 something you need, you could subclass B<Class::MOP::Class> and
411 this class to acheive it. However, this is currently left as
412 an exercise to the reader :).
416 The I<accessor>, I<reader>, I<writer>, I<predicate> and I<clearer> keys can
417 contain either; the name of the method and an appropriate default one will be
418 generated for you, B<or> a HASH ref containing exactly one key (which will be
419 used as the name of the method) and one value, which should contain a CODE
420 reference which will be installed as the method itself.
426 The I<accessor> is a standard perl-style read/write accessor. It will
427 return the value of the attribute, and if a value is passed as an argument,
428 it will assign that value to the attribute.
431 This method will properly handle the following code, by assigning an
432 C<undef> value to the attribute.
434 $object->set_something(undef);
438 This is a basic read-only accessor, it will just return the value of
443 This is a basic write accessor, it accepts a single argument, and
444 assigns that value to the attribute. This method does not intentially
445 return a value, however perl will return the result of the last
446 expression in the subroutine, which returns in this returning the
447 same value that it was passed.
450 This method will properly handle the following code, by assigning an
451 C<undef> value to the attribute.
453 $object->set_something();
457 This is a basic test to see if the value of the attribute is not
458 C<undef>. It will return true (C<1>) if the attribute's value is
459 defined, and false (C<0>) otherwise.
463 This is the a method that will uninitialize the attr, reverting lazy values
464 back to their "unfulfilled" state.
468 =item B<clone (%options)>
470 =item B<initialize_instance_slot ($instance, $params)>
474 =head2 Value management
476 These methods are basically "backdoors" to the instance, which can be used
477 to bypass the regular accessors, but still stay within the context of the MOP.
479 These methods are not for general use, and should only be used if you really
480 know what you are doing.
484 =item B<set_value ($instance, $value)>
486 Set the value without going through the accessor. Note that this may be done to
487 even attributes with just read only accessors.
489 =item B<get_value ($instance)>
491 Return the value without going through the accessor. Note that this may be done
492 even to attributes with just write only accessors.
494 =item B<has_value ($instance)>
496 Returns a boolean indicating if the item in the C<$instance> has a value in it.
497 This is basically what the default C<predicate> method calls.
499 =item B<clear_value ($instance)>
501 This will clear the value in the C<$instance>. This is basically what the default
502 C<clearer> would call. Note that this may be done even if the attirbute does not
503 have any associated read, write or clear methods.
509 These are all basic read-only value accessors for the values
510 passed into C<new>. I think they are pretty much self-explanitory.
528 =item B<is_default_a_coderef>
530 =item B<default (?$instance)>
532 As noted in the documentation for C<new> above, if the I<default>
533 value is a CODE reference, this accessor will pass a single additional
534 argument C<$instance> into it and return the value.
538 Returns a list of slots required by the attribute. This is usually
539 just one, which is the name of the attribute.
541 =item B<get_read_method>
543 =item B<get_write_method>
545 Return the name of a method suitable for reading / writing the value of the
546 attribute in the associated class. Suitable for use whether C<reader> and
547 C<writer> or C<accessor> was used.
551 =head2 Informational predicates
553 These are all basic predicate methods for the values passed into C<new>.
557 =item B<has_accessor>
563 =item B<has_predicate>
567 =item B<has_init_arg>
573 =head2 Class association
575 These methods allow you to manage the attributes association with
576 the class that contains it. These methods should not be used
577 lightly, nor are they very magical, they are mostly used internally
578 and by metaclass instances.
582 =item B<associated_class>
584 This returns the metaclass this attribute is associated with.
586 =item B<attach_to_class ($class)>
588 This will store a weaken reference to C<$class> internally. You should
589 note that just changing the class assocation will not remove the attribute
590 from it's old class, and initialize it (and it's accessors) in the new
591 C<$class>. It is up to you to do this manually.
593 =item B<detach_from_class>
595 This will remove the weakened reference to the class. It does B<not>
596 remove the attribute itself from the class (or remove it's accessors),
597 you must do that yourself if you want too. Actually if that is what
598 you want to do, you should probably be looking at
599 L<Class::MOP::Class::remove_attribute> instead.
603 =head2 Attribute Accessor generation
607 =item B<accessor_metaclass>
609 Accessors are generated by an accessor metaclass, which is usually
610 a subclass of C<Class::MOP::Method::Accessor>. This method returns
611 the name of the accessor metaclass that this attribute uses.
613 =item B<associate_method ($method)>
615 This will associate a C<$method> with the given attribute which is
616 used internally by the accessor generator.
618 =item B<associated_methods>
620 This will return the list of methods which have been associated with
621 the C<associate_method> methods.
623 =item B<install_accessors>
625 This allows the attribute to generate and install code for it's own
626 I<accessor/reader/writer/predicate> methods. This is called by
627 C<Class::MOP::Class::add_attribute>.
629 This method will call C<process_accessors> for each of the possible
630 method types (accessor, reader, writer & predicate).
632 =item B<process_accessors ($type, $value)>
634 This takes a C<$type> (accessor, reader, writer or predicate), and
635 a C<$value> (the value passed into the constructor for each of the
636 different types). It will then either generate the method itself
637 (using the C<generate_*_method> methods listed below) or it will
638 use the custom method passed through the constructor.
640 =item B<remove_accessors>
642 This allows the attribute to remove the method for it's own
643 I<accessor/reader/writer/predicate/clearer>. This is called by
644 C<Class::MOP::Class::remove_attribute>.
646 NOTE: This does not currently remove methods from the list returned
647 by C<associated_methods>, that is on the TODO list.
657 This will return a B<Class::MOP::Class> instance which is related
660 It should also be noted that B<Class::MOP> will actually bootstrap
661 this module by installing a number of attribute meta-objects into
662 it's metaclass. This will allow this class to reap all the benifits
663 of the MOP when subclassing it.
669 Stevan Little E<lt>stevan@iinteractive.comE<gt>
671 =head1 COPYRIGHT AND LICENSE
673 Copyright 2006, 2007 by Infinity Interactive, Inc.
675 L<http://www.iinteractive.com>
677 This library is free software; you can redistribute it and/or modify
678 it under the same terms as Perl itself.