2 package Class::MOP::Attribute;
8 use Scalar::Util 'blessed', 'reftype', 'weaken';
10 our $VERSION = '0.12';
11 our $AUTHORITY = 'cpan:STEVAN';
14 require Class::MOP::Class;
15 Class::MOP::Class->initialize(blessed($_[0]) || $_[0]);
18 # NOTE: (meta-circularity)
19 # This method will be replaced in the
20 # boostrap section of Class::MOP, by
21 # a new version which uses the
22 # &Class::MOP::Class::construct_instance
23 # method to build an attribute meta-object
24 # which itself is described with attribute
26 # - Ain't meta-circularity grand? :)
32 (defined $name && $name)
33 || confess "You must provide a name for the attribute";
34 $options{init_arg} = $name
35 if not exists $options{init_arg};
37 (is_default_a_coderef(\%options))
38 || confess("References are not allowed as default values, you must ".
39 "wrap then in a CODE reference (ex: sub { [] } and not [])")
40 if exists $options{default} && ref $options{default};
44 accessor => $options{accessor},
45 reader => $options{reader},
46 writer => $options{writer},
47 predicate => $options{predicate},
48 clearer => $options{clearer},
49 init_arg => $options{init_arg},
50 default => $options{default},
51 # keep a weakened link to the
52 # class we are associated with
53 associated_class => undef,
58 # this is a primative (and kludgy) clone operation
59 # for now, it will be replaced in the Class::MOP
60 # bootstrap with a proper one, however we know
61 # that this one will work fine for now.
66 || confess "Can only clone an instance";
67 return bless { %{$self}, %options } => blessed($self);
70 sub initialize_instance_slot {
71 my ($self, $meta_instance, $instance, $params) = @_;
72 my $init_arg = $self->{init_arg};
73 # try to fetch the init arg from the %params ...
75 $val = $params->{$init_arg} if exists $params->{$init_arg};
76 # if nothing was in the %params, we can use the
77 # attribute's default value (if it has one)
78 if (!defined $val && defined $self->{default}) {
79 $val = $self->default($instance);
81 $meta_instance->set_slot_value($instance, $self->name, $val);
85 # the next bunch of methods will get bootstrapped
86 # away in the Class::MOP bootstrapping section
88 sub name { $_[0]->{name} }
90 sub associated_class { $_[0]->{associated_class} }
92 sub has_accessor { defined($_[0]->{accessor}) ? 1 : 0 }
93 sub has_reader { defined($_[0]->{reader}) ? 1 : 0 }
94 sub has_writer { defined($_[0]->{writer}) ? 1 : 0 }
95 sub has_predicate { defined($_[0]->{predicate}) ? 1 : 0 }
96 sub has_clearer { defined($_[0]->{clearer}) ? 1 : 0 }
97 sub has_init_arg { defined($_[0]->{init_arg}) ? 1 : 0 }
98 sub has_default { defined($_[0]->{default}) ? 1 : 0 }
100 sub accessor { $_[0]->{accessor} }
101 sub reader { $_[0]->{reader} }
102 sub writer { $_[0]->{writer} }
103 sub predicate { $_[0]->{predicate} }
104 sub clearer { $_[0]->{clearer} }
105 sub init_arg { $_[0]->{init_arg} }
107 # end bootstrapped away method section.
108 # (all methods below here are kept intact)
110 sub is_default_a_coderef {
111 ('CODE' eq (reftype($_[0]->{default}) || ''))
115 my ($self, $instance) = @_;
116 if ($instance && $self->is_default_a_coderef) {
117 # if the default is a CODE ref, then
118 # we pass in the instance and default
119 # can return a value based on that
120 # instance. Somewhat crude, but works.
121 return $self->{default}->($instance);
128 sub slots { (shift)->name }
132 sub attach_to_class {
133 my ($self, $class) = @_;
134 (blessed($class) && $class->isa('Class::MOP::Class'))
135 || confess "You must pass a Class::MOP::Class instance (or a subclass)";
136 weaken($self->{associated_class} = $class);
139 sub detach_from_class {
141 $self->{associated_class} = undef;
147 my ($self, $instance, $value) = @_;
149 Class::MOP::Class->initialize(Scalar::Util::blessed($instance))
151 ->set_slot_value( $instance, $self->name, $value );
155 my ($self, $instance) = @_;
157 Class::MOP::Class->initialize(Scalar::Util::blessed($instance))
159 ->get_slot_value($instance, $self->name);
162 ## Method generation helpers
164 sub generate_accessor_method {
167 $attr->set_value($_[0], $_[1]) if scalar(@_) == 2;
168 $attr->get_value($_[0]);
172 sub generate_accessor_method_inline {
174 my $attr_name = $self->name;
175 my $meta_instance = $self->associated_class->instance_metaclass;
177 my $code = eval 'sub {'
178 . $meta_instance->inline_set_slot_value('$_[0]', "'$attr_name'", '$_[1]') . ' if scalar(@_) == 2; '
179 . $meta_instance->inline_get_slot_value('$_[0]', "'$attr_name'")
181 confess "Could not generate inline accessor because : $@" if $@;
186 sub generate_reader_method {
189 confess "Cannot assign a value to a read-only accessor" if @_ > 1;
190 $attr->get_value($_[0]);
194 sub generate_reader_method_inline {
196 my $attr_name = $self->name;
197 my $meta_instance = $self->associated_class->instance_metaclass;
199 my $code = eval 'sub {'
200 . 'confess "Cannot assign a value to a read-only accessor" if @_ > 1;'
201 . $meta_instance->inline_get_slot_value('$_[0]', "'$attr_name'")
203 confess "Could not generate inline accessor because : $@" if $@;
208 sub generate_writer_method {
211 $attr->set_value($_[0], $_[1]);
215 sub generate_writer_method_inline {
217 my $attr_name = $self->name;
218 my $meta_instance = $self->associated_class->instance_metaclass;
220 my $code = eval 'sub {'
221 . $meta_instance->inline_set_slot_value('$_[0]', "'$attr_name'", '$_[1]')
223 confess "Could not generate inline accessor because : $@" if $@;
228 sub generate_predicate_method {
230 my $attr_name = $self->name;
232 defined Class::MOP::Class->initialize(Scalar::Util::blessed($_[0]))
234 ->get_slot_value($_[0], $attr_name) ? 1 : 0;
238 sub generate_clearer_method {
240 my $attr_name = $self->name;
242 Class::MOP::Class->initialize(Scalar::Util::blessed($_[0]))
244 ->deinitialize_slot($_[0], $attr_name);
248 sub generate_predicate_method_inline {
250 my $attr_name = $self->name;
251 my $meta_instance = $self->associated_class->instance_metaclass;
253 my $code = eval 'sub {'
254 . 'defined ' . $meta_instance->inline_get_slot_value('$_[0]', "'$attr_name'") . ' ? 1 : 0'
256 confess "Could not generate inline predicate because : $@" if $@;
261 sub generate_clearer_method_inline {
263 my $attr_name = $self->name;
264 my $meta_instance = $self->associated_class->instance_metaclass;
266 my $code = eval 'sub {'
267 . $meta_instance->inline_deinitialize_slot('$_[0]', "'$attr_name'")
269 confess "Could not generate inline clearer because : $@" if $@;
274 sub process_accessors {
275 my ($self, $type, $accessor, $generate_as_inline_methods) = @_;
276 if (reftype($accessor)) {
277 (reftype($accessor) eq 'HASH')
278 || confess "bad accessor/reader/writer/predicate/clearer format, must be a HASH ref";
279 my ($name, $method) = %{$accessor};
280 return ($name, Class::MOP::Attribute::Accessor->wrap($method));
283 my $inline_me = ($generate_as_inline_methods && $self->associated_class->instance_metaclass->is_inlinable);
284 my $generator = $self->can('generate_' . $type . '_method' . ($inline_me ? '_inline' : ''));
286 || confess "There is no method generator for the type='$type'";
287 if (my $method = $self->$generator($self->name)) {
288 return ($accessor => Class::MOP::Attribute::Accessor->wrap($method));
290 confess "Could not create the '$type' method for " . $self->name . " because : $@";
294 sub install_accessors {
297 my $class = $self->associated_class;
300 $self->process_accessors('accessor' => $self->accessor(), $inline)
301 ) if $self->has_accessor();
304 $self->process_accessors('reader' => $self->reader(), $inline)
305 ) if $self->has_reader();
308 $self->process_accessors('writer' => $self->writer(), $inline)
309 ) if $self->has_writer();
312 $self->process_accessors('predicate' => $self->predicate(), $inline)
313 ) if $self->has_predicate();
316 $self->process_accessors('clearer' => $self->clearer(), $inline)
317 ) if $self->has_clearer();
323 my $_remove_accessor = sub {
324 my ($accessor, $class) = @_;
325 if (reftype($accessor) && reftype($accessor) eq 'HASH') {
326 ($accessor) = keys %{$accessor};
328 my $method = $class->get_method($accessor);
329 $class->remove_method($accessor)
330 if (blessed($method) && $method->isa('Class::MOP::Attribute::Accessor'));
333 sub remove_accessors {
335 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
336 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
337 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
338 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
339 $_remove_accessor->($self->clearer(), $self->associated_class()) if $self->has_clearer();
345 package Class::MOP::Attribute::Accessor;
350 use Class::MOP::Method;
352 our $VERSION = '0.02';
353 our $AUTHORITY = 'cpan:STEVAN';
355 use base 'Class::MOP::Method';
365 Class::MOP::Attribute - Attribute Meta Object
369 Class::MOP::Attribute->new('$foo' => (
370 accessor => 'foo', # dual purpose get/set accessor
371 predicate => 'has_foo' # predicate check for defined-ness
372 init_arg => '-foo', # class->new will look for a -foo key
373 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
376 Class::MOP::Attribute->new('$.bar' => (
377 reader => 'bar', # getter
378 writer => 'set_bar', # setter
379 predicate => 'has_bar' # predicate check for defined-ness
380 init_arg => ':bar', # class->new will look for a :bar key
381 # no default value means it is undef
386 The Attribute Protocol is almost entirely an invention of this module,
387 and is completely optional to this MOP. This is because Perl 5 does not
388 have consistent notion of what is an attribute of a class. There are
389 so many ways in which this is done, and very few (if any) are
390 easily discoverable by this module.
392 So, all that said, this module attempts to inject some order into this
393 chaos, by introducing a consistent API which can be used to create
402 =item B<new ($name, ?%options)>
404 An attribute must (at the very least), have a C<$name>. All other
405 C<%options> are contained added as key-value pairs. Acceptable keys
412 This should be a string value representing the expected key in
413 an initialization hash. For instance, if we have an I<init_arg>
414 value of C<-foo>, then the following code will Just Work.
416 MyClass->meta->construct_instance(-foo => "Hello There");
418 In an init_arg is not assigned, it will automatically use the
423 The value of this key is the default value which
424 C<Class::MOP::Class::construct_instance> will initialize the
428 If the value is a simple scalar (string or number), then it can
429 be just passed as is. However, if you wish to initialize it with
430 a HASH or ARRAY ref, then you need to wrap that inside a CODE
433 Class::MOP::Attribute->new('@foo' => (
434 default => sub { [] },
439 Class::MOP::Attribute->new('%foo' => (
440 default => sub { {} },
443 If you wish to initialize an attribute with a CODE reference
444 itself, then you need to wrap that in a subroutine as well, like
447 Class::MOP::Attribute->new('&foo' => (
448 default => sub { sub { print "Hello World" } },
451 And lastly, if the value of your attribute is dependent upon
452 some other aspect of the instance structure, then you can take
453 advantage of the fact that when the I<default> value is a CODE
454 reference, it is passed the raw (unblessed) instance structure
455 as it's only argument. So you can do things like this:
457 Class::MOP::Attribute->new('$object_identity' => (
458 default => sub { Scalar::Util::refaddr($_[0]) },
461 This last feature is fairly limited as there is no gurantee of
462 the order of attribute initializations, so you cannot perform
463 any kind of dependent initializations. However, if this is
464 something you need, you could subclass B<Class::MOP::Class> and
465 this class to acheive it. However, this is currently left as
466 an exercise to the reader :).
470 The I<accessor>, I<reader>, I<writer>, I<predicate> and I<clearer> keys can
471 contain either; the name of the method and an appropriate default one will be
472 generated for you, B<or> a HASH ref containing exactly one key (which will be
473 used as the name of the method) and one value, which should contain a CODE
474 reference which will be installed as the method itself.
480 The I<accessor> is a standard perl-style read/write accessor. It will
481 return the value of the attribute, and if a value is passed as an argument,
482 it will assign that value to the attribute.
485 This method will properly handle the following code, by assigning an
486 C<undef> value to the attribute.
488 $object->set_something(undef);
492 This is a basic read-only accessor, it will just return the value of
497 This is a basic write accessor, it accepts a single argument, and
498 assigns that value to the attribute. This method does not intentially
499 return a value, however perl will return the result of the last
500 expression in the subroutine, which returns in this returning the
501 same value that it was passed.
504 This method will properly handle the following code, by assigning an
505 C<undef> value to the attribute.
507 $object->set_something();
511 This is a basic test to see if the value of the attribute is not
512 C<undef>. It will return true (C<1>) if the attribute's value is
513 defined, and false (C<0>) otherwise.
517 This is the a method that will uninitialize the attr, reverting lazy values
518 back to their "unfulfilled" state.
522 =item B<clone (%options)>
524 =item B<initialize_instance_slot ($instance, $params)>
528 =head2 Value management
532 =item set_value $instance, $value
534 Set the value without going through the accessor. Note that this may be done to
535 even attributes with just read only accessors.
537 =item get_value $instance
539 Return the value without going through the accessor. Note that this may be done
540 even to attributes with just write only accessors.
546 These are all basic read-only value accessors for the values
547 passed into C<new>. I think they are pretty much self-explanitory.
565 =item B<is_default_a_coderef>
567 =item B<default (?$instance)>
569 As noted in the documentation for C<new> above, if the I<default>
570 value is a CODE reference, this accessor will pass a single additional
571 argument C<$instance> into it and return the value.
575 Returns a list of slots required by the attribute. This is usually
576 just one, which is the name of the attribute.
580 =head2 Informational predicates
582 These are all basic predicate methods for the values passed into C<new>.
586 =item B<has_accessor>
592 =item B<has_predicate>
596 =item B<has_init_arg>
602 =head2 Class association
606 =item B<associated_class>
608 =item B<attach_to_class ($class)>
610 =item B<detach_from_class>
614 =item B<allocate_slots>
616 =item B<deallocate_slots>
620 =head2 Attribute Accessor generation
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.
643 =item B<generate_accessor_method>
645 =item B<generate_predicate_method>
647 =item B<generate_clearer_method>
649 =item B<generate_reader_method>
651 =item B<generate_writer_method>
657 =item B<generate_accessor_method_inline>
659 =item B<generate_predicate_method_inline>
661 =item B<generate_clearer_method_inline>
663 =item B<generate_reader_method_inline>
665 =item B<generate_writer_method_inline>
669 =item B<remove_accessors>
671 This allows the attribute to remove the method for it's own
672 I<accessor/reader/writer/predicate/clearer>. This is called by
673 C<Class::MOP::Class::remove_attribute>.
683 This will return a B<Class::MOP::Class> instance which is related
686 It should also be noted that B<Class::MOP> will actually bootstrap
687 this module by installing a number of attribute meta-objects into
688 it's metaclass. This will allow this class to reap all the benifits
689 of the MOP when subclassing it.
695 Stevan Little E<lt>stevan@iinteractive.comE<gt>
697 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
699 =head1 COPYRIGHT AND LICENSE
701 Copyright 2006 by Infinity Interactive, Inc.
703 L<http://www.iinteractive.com>
705 This library is free software; you can redistribute it and/or modify
706 it under the same terms as Perl itself.