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 $VERSION = '0.01';
354 use base 'Class::MOP::Method';
364 Class::MOP::Attribute - Attribute Meta Object
368 Class::MOP::Attribute->new('$foo' => (
369 accessor => 'foo', # dual purpose get/set accessor
370 predicate => 'has_foo' # predicate check for defined-ness
371 init_arg => '-foo', # class->new will look for a -foo key
372 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
375 Class::MOP::Attribute->new('$.bar' => (
376 reader => 'bar', # getter
377 writer => 'set_bar', # setter
378 predicate => 'has_bar' # predicate check for defined-ness
379 init_arg => ':bar', # class->new will look for a :bar key
380 # no default value means it is undef
385 The Attribute Protocol is almost entirely an invention of this module,
386 and is completely optional to this MOP. This is because Perl 5 does not
387 have consistent notion of what is an attribute of a class. There are
388 so many ways in which this is done, and very few (if any) are
389 easily discoverable by this module.
391 So, all that said, this module attempts to inject some order into this
392 chaos, by introducing a consistent API which can be used to create
401 =item B<new ($name, ?%options)>
403 An attribute must (at the very least), have a C<$name>. All other
404 C<%options> are contained added as key-value pairs. Acceptable keys
411 This should be a string value representing the expected key in
412 an initialization hash. For instance, if we have an I<init_arg>
413 value of C<-foo>, then the following code will Just Work.
415 MyClass->meta->construct_instance(-foo => "Hello There");
417 In an init_arg is not assigned, it will automatically use the
422 The value of this key is the default value which
423 C<Class::MOP::Class::construct_instance> will initialize the
427 If the value is a simple scalar (string or number), then it can
428 be just passed as is. However, if you wish to initialize it with
429 a HASH or ARRAY ref, then you need to wrap that inside a CODE
432 Class::MOP::Attribute->new('@foo' => (
433 default => sub { [] },
438 Class::MOP::Attribute->new('%foo' => (
439 default => sub { {} },
442 If you wish to initialize an attribute with a CODE reference
443 itself, then you need to wrap that in a subroutine as well, like
446 Class::MOP::Attribute->new('&foo' => (
447 default => sub { sub { print "Hello World" } },
450 And lastly, if the value of your attribute is dependent upon
451 some other aspect of the instance structure, then you can take
452 advantage of the fact that when the I<default> value is a CODE
453 reference, it is passed the raw (unblessed) instance structure
454 as it's only argument. So you can do things like this:
456 Class::MOP::Attribute->new('$object_identity' => (
457 default => sub { Scalar::Util::refaddr($_[0]) },
460 This last feature is fairly limited as there is no gurantee of
461 the order of attribute initializations, so you cannot perform
462 any kind of dependent initializations. However, if this is
463 something you need, you could subclass B<Class::MOP::Class> and
464 this class to acheive it. However, this is currently left as
465 an exercise to the reader :).
469 The I<accessor>, I<reader>, I<writer>, I<predicate> and I<clearer> keys can
470 contain either; the name of the method and an appropriate default one will be
471 generated for you, B<or> a HASH ref containing exactly one key (which will be
472 used as the name of the method) and one value, which should contain a CODE
473 reference which will be installed as the method itself.
479 The I<accessor> is a standard perl-style read/write accessor. It will
480 return the value of the attribute, and if a value is passed as an argument,
481 it will assign that value to the attribute.
484 This method will properly handle the following code, by assigning an
485 C<undef> value to the attribute.
487 $object->set_something(undef);
491 This is a basic read-only accessor, it will just return the value of
496 This is a basic write accessor, it accepts a single argument, and
497 assigns that value to the attribute. This method does not intentially
498 return a value, however perl will return the result of the last
499 expression in the subroutine, which returns in this returning the
500 same value that it was passed.
503 This method will properly handle the following code, by assigning an
504 C<undef> value to the attribute.
506 $object->set_something();
510 This is a basic test to see if the value of the attribute is not
511 C<undef>. It will return true (C<1>) if the attribute's value is
512 defined, and false (C<0>) otherwise.
516 This is the a method that will uninitialize the attr, reverting lazy values
517 back to their "unfulfilled" state.
521 =item B<clone (%options)>
523 =item B<initialize_instance_slot ($instance, $params)>
527 =head2 Value management
531 =item set_value $instance, $value
533 Set the value without going through the accessor. Note that this may be done to
534 even attributes with just read only accessors.
536 =item get_value $instance
538 Return the value without going through the accessor. Note that this may be done
539 even to attributes with just write only accessors.
545 These are all basic read-only value accessors for the values
546 passed into C<new>. I think they are pretty much self-explanitory.
564 =item B<is_default_a_coderef>
566 =item B<default (?$instance)>
568 As noted in the documentation for C<new> above, if the I<default>
569 value is a CODE reference, this accessor will pass a single additional
570 argument C<$instance> into it and return the value.
574 Returns a list of slots required by the attribute. This is usually
575 just one, which is the name of the attribute.
579 =head2 Informational predicates
581 These are all basic predicate methods for the values passed into C<new>.
585 =item B<has_accessor>
591 =item B<has_predicate>
595 =item B<has_init_arg>
601 =head2 Class association
605 =item B<associated_class>
607 =item B<attach_to_class ($class)>
609 =item B<detach_from_class>
613 =item B<allocate_slots>
615 =item B<deallocate_slots>
619 =head2 Attribute Accessor generation
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.
642 =item B<generate_accessor_method>
644 =item B<generate_predicate_method>
646 =item B<generate_clearer_method>
648 =item B<generate_reader_method>
650 =item B<generate_writer_method>
656 =item B<generate_accessor_method_inline>
658 =item B<generate_predicate_method_inline>
660 =item B<generate_clearer_method_inline>
662 =item B<generate_reader_method_inline>
664 =item B<generate_writer_method_inline>
668 =item B<remove_accessors>
670 This allows the attribute to remove the method for it's own
671 I<accessor/reader/writer/predicate/clearer>. This is called by
672 C<Class::MOP::Class::remove_attribute>.
682 This will return a B<Class::MOP::Class> instance which is related
685 It should also be noted that B<Class::MOP> will actually bootstrap
686 this module by installing a number of attribute meta-objects into
687 it's metaclass. This will allow this class to reap all the benifits
688 of the MOP when subclassing it.
694 Stevan Little E<lt>stevan@iinteractive.comE<gt>
696 Yuval Kogman E<lt>nothingmuch@woobling.comE<gt>
698 =head1 COPYRIGHT AND LICENSE
700 Copyright 2006 by Infinity Interactive, Inc.
702 L<http://www.iinteractive.com>
704 This library is free software; you can redistribute it and/or modify
705 it under the same terms as Perl itself.