2 package Class::MOP::Attribute;
7 use Class::MOP::Method::Accessor;
10 use Scalar::Util 'blessed', 'weaken';
12 our $VERSION = '0.77';
13 $VERSION = eval $VERSION;
14 our $AUTHORITY = 'cpan:STEVAN';
16 use base 'Class::MOP::Object';
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? :)
28 my ( $class, @args ) = @_;
30 unshift @args, "name" if @args % 2 == 1;
33 my $name = $options{name};
35 (defined $name && $name)
36 || confess "You must provide a name for the attribute";
38 $options{init_arg} = $name
39 if not exists $options{init_arg};
40 if(exists $options{builder}){
41 confess("builder must be a defined scalar value which is a method name")
42 if ref $options{builder} || !(defined $options{builder});
43 confess("Setting both default and builder is not allowed.")
44 if exists $options{default};
46 (is_default_a_coderef(\%options))
47 || confess("References are not allowed as default values, you must ".
48 "wrap the default of '$name' in a CODE reference (ex: sub { [] } and not [])")
49 if exists $options{default} && ref $options{default};
51 if( $options{required} and not( defined($options{builder}) || defined($options{init_arg}) || exists $options{default} ) ) {
52 confess("A required attribute must have either 'init_arg', 'builder', or 'default'");
55 $class->_new(\%options);
60 my $options = @_ == 1 ? $_[0] : {@_};
63 'name' => $options->{name},
64 'accessor' => $options->{accessor},
65 'reader' => $options->{reader},
66 'writer' => $options->{writer},
67 'predicate' => $options->{predicate},
68 'clearer' => $options->{clearer},
69 'builder' => $options->{builder},
70 'init_arg' => $options->{init_arg},
71 'default' => $options->{default},
72 'initializer' => $options->{initializer},
73 'definition_context' => $options->{definition_context},
74 # keep a weakened link to the
75 # class we are associated with
76 'associated_class' => undef,
77 # and a list of the methods
78 # associated with this attr
79 'associated_methods' => [],
84 # this is a primative (and kludgy) clone operation
85 # for now, it will be replaced in the Class::MOP
86 # bootstrap with a proper one, however we know
87 # that this one will work fine for now.
92 || confess "Can only clone an instance";
93 return bless { %{$self}, %options } => ref($self);
96 sub initialize_instance_slot {
97 my ($self, $meta_instance, $instance, $params) = @_;
98 my $init_arg = $self->{'init_arg'};
100 # try to fetch the init arg from the %params ...
102 # if nothing was in the %params, we can use the
103 # attribute's default value (if it has one)
104 if(defined $init_arg and exists $params->{$init_arg}){
105 $self->_set_initial_slot_value(
108 $params->{$init_arg},
111 elsif (defined $self->{'default'}) {
112 $self->_set_initial_slot_value(
115 $self->default($instance),
118 elsif (defined( my $builder = $self->{'builder'})) {
119 if ($builder = $instance->can($builder)) {
120 $self->_set_initial_slot_value(
127 confess(ref($instance)." does not support builder method '". $self->{'builder'} ."' for attribute '" . $self->name . "'");
132 sub _set_initial_slot_value {
133 my ($self, $meta_instance, $instance, $value) = @_;
135 my $slot_name = $self->name;
137 return $meta_instance->set_slot_value($instance, $slot_name, $value)
138 unless $self->has_initializer;
141 $meta_instance->set_slot_value($instance, $slot_name, $_[0]);
144 my $initializer = $self->initializer;
146 # most things will just want to set a value, so make it first arg
147 $instance->$initializer($value, $callback, $self);
151 # the next bunch of methods will get bootstrapped
152 # away in the Class::MOP bootstrapping section
154 sub name { $_[0]->{'name'} }
156 sub associated_class { $_[0]->{'associated_class'} }
157 sub associated_methods { $_[0]->{'associated_methods'} }
159 sub has_accessor { defined($_[0]->{'accessor'}) }
160 sub has_reader { defined($_[0]->{'reader'}) }
161 sub has_writer { defined($_[0]->{'writer'}) }
162 sub has_predicate { defined($_[0]->{'predicate'}) }
163 sub has_clearer { defined($_[0]->{'clearer'}) }
164 sub has_builder { defined($_[0]->{'builder'}) }
165 sub has_init_arg { defined($_[0]->{'init_arg'}) }
166 sub has_default { defined($_[0]->{'default'}) }
167 sub has_initializer { defined($_[0]->{'initializer'}) }
169 sub accessor { $_[0]->{'accessor'} }
170 sub reader { $_[0]->{'reader'} }
171 sub writer { $_[0]->{'writer'} }
172 sub predicate { $_[0]->{'predicate'} }
173 sub clearer { $_[0]->{'clearer'} }
174 sub builder { $_[0]->{'builder'} }
175 sub init_arg { $_[0]->{'init_arg'} }
176 sub initializer { $_[0]->{'initializer'} }
177 sub definition_context { $_[0]->{'definition_context'} }
179 # end bootstrapped away method section.
180 # (all methods below here are kept intact)
182 sub has_read_method { $_[0]->has_reader || $_[0]->has_accessor }
183 sub has_write_method { $_[0]->has_writer || $_[0]->has_accessor }
185 sub get_read_method {
187 my $reader = $self->reader || $self->accessor;
189 return $reader unless ref $reader;
191 my ($name) = %$reader;
195 sub get_write_method {
197 my $writer = $self->writer || $self->accessor;
199 return $writer unless ref $writer;
201 my ($name) = %$writer;
205 sub get_read_method_ref {
207 if ((my $reader = $self->get_read_method) && $self->associated_class) {
208 return $self->associated_class->get_method($reader);
211 my $code = sub { $self->get_value(@_) };
212 if (my $class = $self->associated_class) {
213 return $class->method_metaclass->wrap(
215 package_name => $class->name,
225 sub get_write_method_ref {
227 if ((my $writer = $self->get_write_method) && $self->associated_class) {
228 return $self->associated_class->get_method($writer);
231 my $code = sub { $self->set_value(@_) };
232 if (my $class = $self->associated_class) {
233 return $class->method_metaclass->wrap(
235 package_name => $class->name,
245 sub is_default_a_coderef {
246 ('CODE' eq ref($_[0]->{'default'}))
250 my ($self, $instance) = @_;
251 if (defined $instance && $self->is_default_a_coderef) {
252 # if the default is a CODE ref, then
253 # we pass in the instance and default
254 # can return a value based on that
255 # instance. Somewhat crude, but works.
256 return $self->{'default'}->($instance);
263 sub slots { (shift)->name }
267 sub attach_to_class {
268 my ($self, $class) = @_;
269 (blessed($class) && $class->isa('Class::MOP::Class'))
270 || confess "You must pass a Class::MOP::Class instance (or a subclass)";
271 weaken($self->{'associated_class'} = $class);
274 sub detach_from_class {
276 $self->{'associated_class'} = undef;
281 sub associate_method {
282 my ($self, $method) = @_;
283 push @{$self->{'associated_methods'}} => $method;
288 sub set_initial_value {
289 my ($self, $instance, $value) = @_;
290 $self->_set_initial_slot_value(
291 Class::MOP::Class->initialize(ref($instance))->get_meta_instance,
298 my ($self, $instance, $value) = @_;
300 Class::MOP::Class->initialize(ref($instance))
302 ->set_slot_value($instance, $self->name, $value);
306 my ($self, $instance) = @_;
308 Class::MOP::Class->initialize(ref($instance))
310 ->get_slot_value($instance, $self->name);
314 my ($self, $instance) = @_;
316 Class::MOP::Class->initialize(ref($instance))
318 ->is_slot_initialized($instance, $self->name);
322 my ($self, $instance) = @_;
324 Class::MOP::Class->initialize(ref($instance))
326 ->deinitialize_slot($instance, $self->name);
331 sub accessor_metaclass { 'Class::MOP::Method::Accessor' }
333 sub process_accessors {
334 my ($self, $type, $accessor, $generate_as_inline_methods) = @_;
338 if ( my $ctx = $self->definition_context ) {
339 $method_ctx = { %$ctx };
342 if (ref($accessor)) {
343 (ref($accessor) eq 'HASH')
344 || confess "bad accessor/reader/writer/predicate/clearer format, must be a HASH ref";
345 my ($name, $method) = %{$accessor};
346 $method = $self->accessor_metaclass->wrap(
348 package_name => $self->associated_class->name,
350 definition_context => $method_ctx,
352 $self->associate_method($method);
353 return ($name, $method);
356 my $inline_me = ($generate_as_inline_methods && $self->associated_class->instance_metaclass->is_inlinable);
360 my $desc = "accessor $accessor";
361 if ( $accessor ne $self->name ) {
362 $desc .= " of attribute " . $self->name;
365 $method_ctx->{description} = $desc;
368 $method = $self->accessor_metaclass->new(
370 is_inline => $inline_me,
371 accessor_type => $type,
372 package_name => $self->associated_class->name,
374 definition_context => $method_ctx,
377 confess "Could not create the '$type' method for " . $self->name . " because : $@" if $@;
378 $self->associate_method($method);
379 return ($accessor, $method);
383 sub install_accessors {
386 my $class = $self->associated_class;
389 $self->process_accessors('accessor' => $self->accessor(), $inline)
390 ) if $self->has_accessor();
393 $self->process_accessors('reader' => $self->reader(), $inline)
394 ) if $self->has_reader();
397 $self->process_accessors('writer' => $self->writer(), $inline)
398 ) if $self->has_writer();
401 $self->process_accessors('predicate' => $self->predicate(), $inline)
402 ) if $self->has_predicate();
405 $self->process_accessors('clearer' => $self->clearer(), $inline)
406 ) if $self->has_clearer();
412 my $_remove_accessor = sub {
413 my ($accessor, $class) = @_;
414 if (ref($accessor) && ref($accessor) eq 'HASH') {
415 ($accessor) = keys %{$accessor};
417 my $method = $class->get_method($accessor);
418 $class->remove_method($accessor)
419 if (ref($method) && $method->isa('Class::MOP::Method::Accessor'));
422 sub remove_accessors {
425 # we really need to make sure to remove from the
426 # associates methods here as well. But this is
427 # such a slimly used method, I am not worried
428 # about it right now.
429 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
430 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
431 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
432 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
433 $_remove_accessor->($self->clearer(), $self->associated_class()) if $self->has_clearer();
447 Class::MOP::Attribute - Attribute Meta Object
451 Class::MOP::Attribute->new( foo => (
452 accessor => 'foo', # dual purpose get/set accessor
453 predicate => 'has_foo' # predicate check for defined-ness
454 init_arg => '-foo', # class->new will look for a -foo key
455 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
458 Class::MOP::Attribute->new( bar => (
459 reader => 'bar', # getter
460 writer => 'set_bar', # setter
461 predicate => 'has_bar' # predicate check for defined-ness
462 init_arg => ':bar', # class->new will look for a :bar key
463 # no default value means it is undef
468 The Attribute Protocol is almost entirely an invention of this module,
469 and is completely optional to this MOP. This is because Perl 5 does not
470 have consistent notion of what is an attribute of a class. There are
471 so many ways in which this is done, and very few (if any) are
472 easily discoverable by this module.
474 So, all that said, this module attempts to inject some order into this
475 chaos, by introducing a consistent API which can be used to create
484 =item B<new ($name, ?%options)>
486 An attribute must (at the very least), have a C<$name>. All other
487 C<%options> are contained added as key-value pairs. Acceptable keys
494 This should be a string value representing the expected key in
495 an initialization hash. For instance, if we have an I<init_arg>
496 value of C<-foo>, then the following code will Just Work.
498 MyClass->meta->construct_instance(-foo => "Hello There");
500 In an init_arg is not assigned, it will automatically use the
501 value of C<$name>. If an explicit C<undef> is given for an init_arg,
502 an attribute value can't be specified during initialization.
506 The value of this key is the name of the method that will be
507 called to obtain the value used to initialize the attribute.
508 This should be a method in the class associated with the attribute,
509 not a method in the attribute class itself.
513 The value of this key is the default value which
514 C<Class::MOP::Class::construct_instance> will initialize the
518 If the value is a simple scalar (string or number), then it can
519 be just passed as is. However, if you wish to initialize it with
520 a HASH or ARRAY ref, then you need to wrap that inside a CODE
523 Class::MOP::Attribute->new('@foo' => (
524 default => sub { [] },
529 Class::MOP::Attribute->new('%foo' => (
530 default => sub { {} },
533 If you wish to initialize an attribute with a CODE reference
534 itself, then you need to wrap that in a subroutine as well, like
537 Class::MOP::Attribute->new('&foo' => (
538 default => sub { sub { print "Hello World" } },
541 And lastly, if the value of your attribute is dependent upon
542 some other aspect of the instance structure, then you can take
543 advantage of the fact that when the I<default> value is a CODE
544 reference, it is passed the (as yet unfinished) instance structure
545 as it's only argument. So you can do things like this:
547 Class::MOP::Attribute->new('$object_identity' => (
548 default => sub { Scalar::Util::refaddr($_[0]) },
551 This last feature is fairly limited as there is no gurantee of
552 the order of attribute initializations, so you cannot perform
553 any kind of dependent initializations. However, if this is
554 something you need, you could subclass B<Class::MOP::Class> and
555 this class to acheive it. However, this is currently left as
556 an exercise to the reader :).
560 This may be a method name (referring to a method on the class with this
561 attribute) or a CODE ref. The initializer is used to set the attribute value
562 on an instance when the attribute is set during instance initialization. When
563 called, it is passed the instance (as the invocant), the value to set, a
564 slot-setting CODE ref, and the attribute meta-instance. The slot-setting code
565 is provided to make it easy to set the (possibly altered) value on the instance
566 without going through several more method calls.
568 This contrived example shows an initializer that sets the attribute to twice
571 Class::MOP::Attribute->new('$doubled' => (
573 my ($instance, $value, $set) = @_;
578 As method names can be given as initializers, one can easily make
579 attribute initialization use the writer:
581 Class::MOP::Attribute->new('$some_attr' => (
582 writer => 'some_attr',
583 initializer => 'some_attr',
586 Your writer will simply need to examine it's C<@_> and determine under
587 which context it is being called.
591 The I<accessor>, I<reader>, I<writer>, I<predicate> and I<clearer> keys can
592 contain either; the name of the method and an appropriate default one will be
593 generated for you, B<or> a HASH ref containing exactly one key (which will be
594 used as the name of the method) and one value, which should contain a CODE
595 reference which will be installed as the method itself.
601 The I<accessor> is a standard perl-style read/write accessor. It will
602 return the value of the attribute, and if a value is passed as an argument,
603 it will assign that value to the attribute.
606 This method will properly handle the following code, by assigning an
607 C<undef> value to the attribute.
609 $object->set_something(undef);
613 This is a basic read-only accessor, it will just return the value of
618 This is a basic write accessor, it accepts a single argument, and
619 assigns that value to the attribute. This method does not intentially
620 return a value, however perl will return the result of the last
621 expression in the subroutine, which returns in this returning the
622 same value that it was passed.
625 This method will properly handle the following code, by assigning an
626 C<undef> value to the attribute.
628 $object->set_something();
632 This is a basic test to see if any value has been set for the
633 attribute. It will return true (C<1>) if the attribute has been set
634 to any value (even C<undef>), and false (C<0>) otherwise.
637 The predicate will return true even when you set an attribute's
638 value to C<undef>. This behaviour has changed as of version 0.43. In
639 older versions, the predicate (erroneously) checked for attribute
640 value definedness, instead of presence as it is now.
642 If you really want to get rid of the value, you have to define and
643 use a I<clearer> (see below).
647 This is the a method that will uninitialize the attr, reverting lazy values
648 back to their "unfulfilled" state.
652 =item B<clone (%options)>
654 This will return a clone of the attribute instance, allowing the overriding
655 of various attributes through the C<%options> supplied.
657 =item B<initialize_instance_slot ($instance, $params)>
659 This method is used internally to initialize the approriate slot for this
660 attribute in a given C<$instance>, the C<$params> passed are those that were
661 passed to the constructor.
665 =head2 Value management
667 These methods are basically "backdoors" to the instance, which can be used
668 to bypass the regular accessors, but still stay within the context of the MOP.
670 These methods are not for general use, and should only be used if you really
671 know what you are doing.
675 =item B<set_value ($instance, $value)>
677 Set the value without going through the accessor. Note that this may be done to
678 even attributes with just read only accessors.
680 =item B<set_initial_value ($instance, $value)>
682 This method sets the value without going through the accessor -- but it is only
683 called when the instance data is first initialized.
685 =item B<get_value ($instance)>
687 Return the value without going through the accessor. Note that this may be done
688 even to attributes with just write only accessors.
690 =item B<has_value ($instance)>
692 Return a boolean indicating if the item in the C<$instance> has a value in it.
693 This is basically what the default C<predicate> method calls.
695 =item B<clear_value ($instance)>
697 This will clear the value in the C<$instance>. This is basically what the default
698 C<clearer> would call. Note that this may be done even if the attirbute does not
699 have any associated read, write or clear methods.
705 These are all basic read-only value accessors for the values
706 passed into C<new>. I think they are pretty much self-explanitory.
726 =item B<is_default_a_coderef>
728 =item B<default (?$instance)>
730 Return the default value for the attribute.
732 If you pass in an C<$instance> argument to this accessor and the
733 I<default> is a CODE reference, then the CODE reference will be
734 executed with the C<$instance> as its argument.
738 Return a list of slots required by the attribute. This is usually
739 just one, which is the name of the attribute.
741 =item B<get_read_method>
743 =item B<get_write_method>
745 Return the name of a method name suitable for reading / writing the value
746 of the attribute in the associated class. Suitable for use whether
747 C<reader> and C<writer> or C<accessor> was used.
749 =item B<get_read_method_ref>
751 =item B<get_write_method_ref>
753 Return the CODE reference of a method suitable for reading / writing the
754 value of the attribute in the associated class. Suitable for use whether
755 C<reader> and C<writer> or C<accessor> was specified or not.
757 NOTE: If no reader/writer/accessor was specified, this will use the
758 attribute get_value/set_value methods, which can be very inefficient.
760 =item B<has_read_method>
762 =item B<has_write_method>
764 Return whether a method exists suitable for reading / writing the value
765 of the attribute in the associated class. Suitable for use whether
766 C<reader> and C<writer> or C<accessor> was used.
770 =head2 Informational predicates
772 These are all basic predicate methods for the values passed into C<new>.
776 =item B<has_accessor>
782 =item B<has_predicate>
786 =item B<has_initializer>
788 =item B<has_init_arg>
796 =head2 Class association
798 These methods allow you to manage the attributes association with
799 the class that contains it. These methods should not be used
800 lightly, nor are they very magical, they are mostly used internally
801 and by metaclass instances.
805 =item B<associated_class>
807 This returns the metaclass this attribute is associated with.
809 =item B<attach_to_class ($class)>
811 This will store a weaken reference to C<$class> internally. You should
812 note that just changing the class assocation will not remove the attribute
813 from it's old class, and initialize it (and it's accessors) in the new
814 C<$class>. It is up to you to do this manually.
816 =item B<detach_from_class>
818 This will remove the weakened reference to the class. It does B<not>
819 remove the attribute itself from the class (or remove it's accessors),
820 you must do that yourself if you want too. Actually if that is what
821 you want to do, you should probably be looking at
822 L<Class::MOP::Class::remove_attribute> instead.
826 =head2 Attribute Accessor generation
830 =item B<accessor_metaclass>
832 Accessors are generated by an accessor metaclass, which is usually
833 a subclass of C<Class::MOP::Method::Accessor>. This method returns
834 the name of the accessor metaclass that this attribute uses.
836 =item B<associate_method ($method)>
838 This will associate a C<$method> with the given attribute which is
839 used internally by the accessor generator.
841 =item B<associated_methods>
843 This will return the list of methods which have been associated with
844 the C<associate_method> methods. This is a good way of seeing what
845 methods are used to manage a given attribute.
847 =item B<install_accessors>
849 This allows the attribute to generate and install code for it's own
850 I<accessor/reader/writer/predicate> methods. This is called by
851 C<Class::MOP::Class::add_attribute>.
853 This method will call C<process_accessors> for each of the possible
854 method types (accessor, reader, writer & predicate).
856 =item B<process_accessors ($type, $value)>
858 This takes a C<$type> (accessor, reader, writer or predicate), and
859 a C<$value> (the value passed into the constructor for each of the
860 different types). It will then either generate the method itself
861 (using the C<generate_*_method> methods listed below) or it will
862 use the custom method passed through the constructor.
864 =item B<remove_accessors>
866 This allows the attribute to remove the method for it's own
867 I<accessor/reader/writer/predicate/clearer>. This is called by
868 C<Class::MOP::Class::remove_attribute>.
870 NOTE: This does not currently remove methods from the list returned
871 by C<associated_methods>, that is on the TODO list.
881 This will return a B<Class::MOP::Class> instance which is related
884 It should also be noted that B<Class::MOP> will actually bootstrap
885 this module by installing a number of attribute meta-objects into
886 it's metaclass. This will allow this class to reap all the benefits
887 of the MOP when subclassing it.
893 Stevan Little E<lt>stevan@iinteractive.comE<gt>
895 =head1 COPYRIGHT AND LICENSE
897 Copyright 2006-2008 by Infinity Interactive, Inc.
899 L<http://www.iinteractive.com>
901 This library is free software; you can redistribute it and/or modify
902 it under the same terms as Perl itself.