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});
93 } elsif (defined $self->{'$!default'}) {
94 $meta_instance->set_slot_value($instance, $self->name, $self->default($instance));
95 } elsif (defined( my $builder = $self->{'$!builder'})) {
96 if($builder = $instance->can($builder) ){
97 $meta_instance->set_slot_value($instance, $self->name, $instance->$builder);
99 confess(blessed($instance)." does not support builder method '". $self->{'$!builder'} ."' for attribute '" . $self->name . "'");
105 # the next bunch of methods will get bootstrapped
106 # away in the Class::MOP bootstrapping section
108 sub name { $_[0]->{'$!name'} }
110 sub associated_class { $_[0]->{'$!associated_class'} }
111 sub associated_methods { $_[0]->{'@!associated_methods'} }
113 sub has_accessor { defined($_[0]->{'$!accessor'}) ? 1 : 0 }
114 sub has_reader { defined($_[0]->{'$!reader'}) ? 1 : 0 }
115 sub has_writer { defined($_[0]->{'$!writer'}) ? 1 : 0 }
116 sub has_predicate { defined($_[0]->{'$!predicate'}) ? 1 : 0 }
117 sub has_clearer { defined($_[0]->{'$!clearer'}) ? 1 : 0 }
118 sub has_builder { defined($_[0]->{'$!builder'}) ? 1 : 0 }
119 sub has_init_arg { defined($_[0]->{'$!init_arg'}) ? 1 : 0 }
120 sub has_default { defined($_[0]->{'$!default'}) ? 1 : 0 }
122 sub accessor { $_[0]->{'$!accessor'} }
123 sub reader { $_[0]->{'$!reader'} }
124 sub writer { $_[0]->{'$!writer'} }
125 sub predicate { $_[0]->{'$!predicate'} }
126 sub clearer { $_[0]->{'$!clearer'} }
127 sub builder { $_[0]->{'$!builder'} }
128 sub init_arg { $_[0]->{'$!init_arg'} }
130 # end bootstrapped away method section.
131 # (all methods below here are kept intact)
133 sub get_read_method { $_[0]->reader || $_[0]->accessor }
134 sub get_write_method { $_[0]->writer || $_[0]->accessor }
136 sub is_default_a_coderef {
137 ('CODE' eq (reftype($_[0]->{'$!default'} || $_[0]->{default}) || ''))
141 my ($self, $instance) = @_;
142 if (defined $instance && $self->is_default_a_coderef) {
143 # if the default is a CODE ref, then
144 # we pass in the instance and default
145 # can return a value based on that
146 # instance. Somewhat crude, but works.
147 return $self->{'$!default'}->($instance);
149 $self->{'$!default'};
154 sub slots { (shift)->name }
158 sub attach_to_class {
159 my ($self, $class) = @_;
160 (blessed($class) && $class->isa('Class::MOP::Class'))
161 || confess "You must pass a Class::MOP::Class instance (or a subclass)";
162 weaken($self->{'$!associated_class'} = $class);
165 sub detach_from_class {
167 $self->{'$!associated_class'} = undef;
172 sub associate_method {
173 my ($self, $method) = @_;
174 push @{$self->{'@!associated_methods'}} => $method;
180 my ($self, $instance, $value) = @_;
182 Class::MOP::Class->initialize(blessed($instance))
184 ->set_slot_value($instance, $self->name, $value);
188 my ($self, $instance) = @_;
190 Class::MOP::Class->initialize(blessed($instance))
192 ->get_slot_value($instance, $self->name);
196 my ($self, $instance) = @_;
198 Class::MOP::Class->initialize(blessed($instance))
200 ->is_slot_initialized($instance, $self->name);
204 my ($self, $instance) = @_;
206 Class::MOP::Class->initialize(blessed($instance))
208 ->deinitialize_slot($instance, $self->name);
213 sub accessor_metaclass { 'Class::MOP::Method::Accessor' }
215 sub process_accessors {
216 my ($self, $type, $accessor, $generate_as_inline_methods) = @_;
217 if (reftype($accessor)) {
218 (reftype($accessor) eq 'HASH')
219 || confess "bad accessor/reader/writer/predicate/clearer format, must be a HASH ref";
220 my ($name, $method) = %{$accessor};
221 $method = $self->accessor_metaclass->wrap($method);
222 $self->associate_method($method);
223 return ($name, $method);
226 my $inline_me = ($generate_as_inline_methods && $self->associated_class->instance_metaclass->is_inlinable);
229 $method = $self->accessor_metaclass->new(
231 is_inline => $inline_me,
232 accessor_type => $type,
235 confess "Could not create the '$type' method for " . $self->name . " because : $@" if $@;
236 $self->associate_method($method);
237 return ($accessor, $method);
241 sub install_accessors {
244 my $class = $self->associated_class;
247 $self->process_accessors('accessor' => $self->accessor(), $inline)
248 ) if $self->has_accessor();
251 $self->process_accessors('reader' => $self->reader(), $inline)
252 ) if $self->has_reader();
255 $self->process_accessors('writer' => $self->writer(), $inline)
256 ) if $self->has_writer();
259 $self->process_accessors('predicate' => $self->predicate(), $inline)
260 ) if $self->has_predicate();
263 $self->process_accessors('clearer' => $self->clearer(), $inline)
264 ) if $self->has_clearer();
270 my $_remove_accessor = sub {
271 my ($accessor, $class) = @_;
272 if (reftype($accessor) && reftype($accessor) eq 'HASH') {
273 ($accessor) = keys %{$accessor};
275 my $method = $class->get_method($accessor);
276 $class->remove_method($accessor)
277 if (blessed($method) && $method->isa('Class::MOP::Method::Accessor'));
280 sub remove_accessors {
283 # we really need to make sure to remove from the
284 # associates methods here as well. But this is
285 # such a slimly used method, I am not worried
286 # about it right now.
287 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
288 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
289 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
290 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
291 $_remove_accessor->($self->clearer(), $self->associated_class()) if $self->has_clearer();
305 Class::MOP::Attribute - Attribute Meta Object
309 Class::MOP::Attribute->new('$foo' => (
310 accessor => 'foo', # dual purpose get/set accessor
311 predicate => 'has_foo' # predicate check for defined-ness
312 init_arg => '-foo', # class->new will look for a -foo key
313 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
316 Class::MOP::Attribute->new('$.bar' => (
317 reader => 'bar', # getter
318 writer => 'set_bar', # setter
319 predicate => 'has_bar' # predicate check for defined-ness
320 init_arg => ':bar', # class->new will look for a :bar key
321 # no default value means it is undef
326 The Attribute Protocol is almost entirely an invention of this module,
327 and is completely optional to this MOP. This is because Perl 5 does not
328 have consistent notion of what is an attribute of a class. There are
329 so many ways in which this is done, and very few (if any) are
330 easily discoverable by this module.
332 So, all that said, this module attempts to inject some order into this
333 chaos, by introducing a consistent API which can be used to create
342 =item B<new ($name, ?%options)>
344 An attribute must (at the very least), have a C<$name>. All other
345 C<%options> are contained added as key-value pairs. Acceptable keys
352 This should be a string value representing the expected key in
353 an initialization hash. For instance, if we have an I<init_arg>
354 value of C<-foo>, then the following code will Just Work.
356 MyClass->meta->construct_instance(-foo => "Hello There");
358 In an init_arg is not assigned, it will automatically use the
363 The value of this key is the default value which
364 C<Class::MOP::Class::construct_instance> will initialize the
369 The value of this key is the name of the method that will be
370 called to obtain the value used to initialize the attribute.
371 This should be a method in the class associated with the attribute,
372 not a method in the attribute class itself.
375 If the value is a simple scalar (string or number), then it can
376 be just passed as is. However, if you wish to initialize it with
377 a HASH or ARRAY ref, then you need to wrap that inside a CODE
380 Class::MOP::Attribute->new('@foo' => (
381 default => sub { [] },
386 Class::MOP::Attribute->new('%foo' => (
387 default => sub { {} },
390 If you wish to initialize an attribute with a CODE reference
391 itself, then you need to wrap that in a subroutine as well, like
394 Class::MOP::Attribute->new('&foo' => (
395 default => sub { sub { print "Hello World" } },
398 And lastly, if the value of your attribute is dependent upon
399 some other aspect of the instance structure, then you can take
400 advantage of the fact that when the I<default> value is a CODE
401 reference, it is passed the raw (unblessed) instance structure
402 as it's only argument. So you can do things like this:
404 Class::MOP::Attribute->new('$object_identity' => (
405 default => sub { Scalar::Util::refaddr($_[0]) },
408 This last feature is fairly limited as there is no gurantee of
409 the order of attribute initializations, so you cannot perform
410 any kind of dependent initializations. However, if this is
411 something you need, you could subclass B<Class::MOP::Class> and
412 this class to acheive it. However, this is currently left as
413 an exercise to the reader :).
417 The I<accessor>, I<reader>, I<writer>, I<predicate> and I<clearer> keys can
418 contain either; the name of the method and an appropriate default one will be
419 generated for you, B<or> a HASH ref containing exactly one key (which will be
420 used as the name of the method) and one value, which should contain a CODE
421 reference which will be installed as the method itself.
427 The I<accessor> is a standard perl-style read/write accessor. It will
428 return the value of the attribute, and if a value is passed as an argument,
429 it will assign that value to the attribute.
432 This method will properly handle the following code, by assigning an
433 C<undef> value to the attribute.
435 $object->set_something(undef);
439 This is a basic read-only accessor, it will just return the value of
444 This is a basic write accessor, it accepts a single argument, and
445 assigns that value to the attribute. This method does not intentially
446 return a value, however perl will return the result of the last
447 expression in the subroutine, which returns in this returning the
448 same value that it was passed.
451 This method will properly handle the following code, by assigning an
452 C<undef> value to the attribute.
454 $object->set_something();
458 This is a basic test to see if the value of the attribute is not
459 C<undef>. It will return true (C<1>) if the attribute's value is
460 defined, and false (C<0>) otherwise.
464 This is the a method that will uninitialize the attr, reverting lazy values
465 back to their "unfulfilled" state.
469 =item B<clone (%options)>
471 =item B<initialize_instance_slot ($instance, $params)>
475 =head2 Value management
477 These methods are basically "backdoors" to the instance, which can be used
478 to bypass the regular accessors, but still stay within the context of the MOP.
480 These methods are not for general use, and should only be used if you really
481 know what you are doing.
485 =item B<set_value ($instance, $value)>
487 Set the value without going through the accessor. Note that this may be done to
488 even attributes with just read only accessors.
490 =item B<get_value ($instance)>
492 Return the value without going through the accessor. Note that this may be done
493 even to attributes with just write only accessors.
495 =item B<has_value ($instance)>
497 Returns a boolean indicating if the item in the C<$instance> has a value in it.
498 This is basically what the default C<predicate> method calls.
500 =item B<clear_value ($instance)>
502 This will clear the value in the C<$instance>. This is basically what the default
503 C<clearer> would call. Note that this may be done even if the attirbute does not
504 have any associated read, write or clear methods.
510 These are all basic read-only value accessors for the values
511 passed into C<new>. I think they are pretty much self-explanitory.
529 =item B<is_default_a_coderef>
531 =item B<default (?$instance)>
533 As noted in the documentation for C<new> above, if the I<default>
534 value is a CODE reference, this accessor will pass a single additional
535 argument C<$instance> into it and return the value.
539 Returns a list of slots required by the attribute. This is usually
540 just one, which is the name of the attribute.
542 =item B<get_read_method>
544 =item B<get_write_method>
546 Return the name of a method suitable for reading / writing the value of the
547 attribute in the associated class. Suitable for use whether C<reader> and
548 C<writer> or C<accessor> was used.
552 =head2 Informational predicates
554 These are all basic predicate methods for the values passed into C<new>.
558 =item B<has_accessor>
564 =item B<has_predicate>
568 =item B<has_init_arg>
574 =head2 Class association
576 These methods allow you to manage the attributes association with
577 the class that contains it. These methods should not be used
578 lightly, nor are they very magical, they are mostly used internally
579 and by metaclass instances.
583 =item B<associated_class>
585 This returns the metaclass this attribute is associated with.
587 =item B<attach_to_class ($class)>
589 This will store a weaken reference to C<$class> internally. You should
590 note that just changing the class assocation will not remove the attribute
591 from it's old class, and initialize it (and it's accessors) in the new
592 C<$class>. It is up to you to do this manually.
594 =item B<detach_from_class>
596 This will remove the weakened reference to the class. It does B<not>
597 remove the attribute itself from the class (or remove it's accessors),
598 you must do that yourself if you want too. Actually if that is what
599 you want to do, you should probably be looking at
600 L<Class::MOP::Class::remove_attribute> instead.
604 =head2 Attribute Accessor generation
608 =item B<accessor_metaclass>
610 Accessors are generated by an accessor metaclass, which is usually
611 a subclass of C<Class::MOP::Method::Accessor>. This method returns
612 the name of the accessor metaclass that this attribute uses.
614 =item B<associate_method ($method)>
616 This will associate a C<$method> with the given attribute which is
617 used internally by the accessor generator.
619 =item B<associated_methods>
621 This will return the list of methods which have been associated with
622 the C<associate_method> methods.
624 =item B<install_accessors>
626 This allows the attribute to generate and install code for it's own
627 I<accessor/reader/writer/predicate> methods. This is called by
628 C<Class::MOP::Class::add_attribute>.
630 This method will call C<process_accessors> for each of the possible
631 method types (accessor, reader, writer & predicate).
633 =item B<process_accessors ($type, $value)>
635 This takes a C<$type> (accessor, reader, writer or predicate), and
636 a C<$value> (the value passed into the constructor for each of the
637 different types). It will then either generate the method itself
638 (using the C<generate_*_method> methods listed below) or it will
639 use the custom method passed through the constructor.
641 =item B<remove_accessors>
643 This allows the attribute to remove the method for it's own
644 I<accessor/reader/writer/predicate/clearer>. This is called by
645 C<Class::MOP::Class::remove_attribute>.
647 NOTE: This does not currently remove methods from the list returned
648 by C<associated_methods>, that is on the TODO list.
658 This will return a B<Class::MOP::Class> instance which is related
661 It should also be noted that B<Class::MOP> will actually bootstrap
662 this module by installing a number of attribute meta-objects into
663 it's metaclass. This will allow this class to reap all the benifits
664 of the MOP when subclassing it.
670 Stevan Little E<lt>stevan@iinteractive.comE<gt>
672 =head1 COPYRIGHT AND LICENSE
674 Copyright 2006, 2007 by Infinity Interactive, Inc.
676 L<http://www.iinteractive.com>
678 This library is free software; you can redistribute it and/or modify
679 it under the same terms as Perl itself.