2 package Class::MOP::Attribute;
7 use Class::MOP::Method::Accessor;
10 use Scalar::Util 'blessed', 'reftype', 'weaken';
12 our $VERSION = '0.25';
13 our $AUTHORITY = 'cpan:STEVAN';
15 use base 'Class::MOP::Object';
17 # NOTE: (meta-circularity)
18 # This method will be replaced in the
19 # boostrap section of Class::MOP, by
20 # a new version which uses the
21 # &Class::MOP::Class::construct_instance
22 # method to build an attribute meta-object
23 # which itself is described with attribute
25 # - Ain't meta-circularity grand? :)
31 (defined $name && $name)
32 || confess "You must provide a name for the attribute";
34 $options{init_arg} = $name
35 if not exists $options{init_arg};
36 if(exists $options{builder}){
37 confess("builder must be a defined scalar value which is a method name")
38 if ref $options{builder} || !(defined $options{builder});
39 confess("Setting both default and builder is not allowed.")
40 if exists $options{default};
42 (is_default_a_coderef(\%options))
43 || confess("References are not allowed as default values, you must ".
44 "wrap the default of '$name' in a CODE reference (ex: sub { [] } and not [])")
45 if exists $options{default} && ref $options{default};
47 if( $options{required} and not( defined($options{builder}) || defined($options{init_arg}) || exists $options{default} ) ) {
48 confess("A required attribute must have either 'init_arg', 'builder', or 'default'");
52 '$!accessor' => $options{accessor},
53 '$!reader' => $options{reader},
54 '$!writer' => $options{writer},
55 '$!predicate' => $options{predicate},
56 '$!clearer' => $options{clearer},
57 '$!builder' => $options{builder},
58 '$!init_arg' => $options{init_arg},
59 '$!default' => $options{default},
60 '$!initializer' => $options{initializer},
61 # keep a weakened link to the
62 # class we are associated with
63 '$!associated_class' => undef,
64 # and a list of the methods
65 # associated with this attr
66 '@!associated_methods' => [],
68 # protect this from silliness
74 # this is a primative (and kludgy) clone operation
75 # for now, it will be replaced in the Class::MOP
76 # bootstrap with a proper one, however we know
77 # that this one will work fine for now.
82 || confess "Can only clone an instance";
83 return bless { %{$self}, %options } => blessed($self);
86 sub initialize_instance_slot {
87 my ($self, $meta_instance, $instance, $params) = @_;
88 my $init_arg = $self->{'$!init_arg'};
89 # try to fetch the init arg from the %params ...
91 # if nothing was in the %params, we can use the
92 # attribute's default value (if it has one)
93 if(defined $init_arg and exists $params->{$init_arg}){
94 $self->_set_initial_slot_value(
100 elsif (defined $self->{'$!default'}) {
101 $self->_set_initial_slot_value(
104 $self->default($instance),
107 elsif (defined( my $builder = $self->{'$!builder'})) {
108 if ($builder = $instance->can($builder)) {
109 $self->_set_initial_slot_value(
116 confess(blessed($instance)." does not support builder method '". $self->{'$!builder'} ."' for attribute '" . $self->name . "'");
121 sub _set_initial_slot_value {
122 my ($self, $meta_instance, $instance, $value) = @_;
124 my $slot_name = $self->name;
126 return $meta_instance->set_slot_value($instance, $slot_name, $value)
127 unless $self->has_initializer;
130 $meta_instance->set_slot_value($instance, $slot_name, $_[0]);
133 my $initializer = $self->initializer;
135 # most things will just want to set a value, so make it first arg
136 $instance->$initializer($value, $callback, $self);
140 # the next bunch of methods will get bootstrapped
141 # away in the Class::MOP bootstrapping section
143 sub name { $_[0]->{'$!name'} }
145 sub associated_class { $_[0]->{'$!associated_class'} }
146 sub associated_methods { $_[0]->{'@!associated_methods'} }
148 sub has_accessor { defined($_[0]->{'$!accessor'}) ? 1 : 0 }
149 sub has_reader { defined($_[0]->{'$!reader'}) ? 1 : 0 }
150 sub has_writer { defined($_[0]->{'$!writer'}) ? 1 : 0 }
151 sub has_predicate { defined($_[0]->{'$!predicate'}) ? 1 : 0 }
152 sub has_clearer { defined($_[0]->{'$!clearer'}) ? 1 : 0 }
153 sub has_builder { defined($_[0]->{'$!builder'}) ? 1 : 0 }
154 sub has_init_arg { defined($_[0]->{'$!init_arg'}) ? 1 : 0 }
155 sub has_default { defined($_[0]->{'$!default'}) ? 1 : 0 }
156 sub has_initializer { defined($_[0]->{'$!initializer'}) ? 1 : 0 }
158 sub accessor { $_[0]->{'$!accessor'} }
159 sub reader { $_[0]->{'$!reader'} }
160 sub writer { $_[0]->{'$!writer'} }
161 sub predicate { $_[0]->{'$!predicate'} }
162 sub clearer { $_[0]->{'$!clearer'} }
163 sub builder { $_[0]->{'$!builder'} }
164 sub init_arg { $_[0]->{'$!init_arg'} }
165 sub initializer { $_[0]->{'$!initializer'} }
167 # end bootstrapped away method section.
168 # (all methods below here are kept intact)
170 sub has_read_method { $_[0]->has_reader || $_[0]->has_accessor }
171 sub has_write_method { $_[0]->has_writer || $_[0]->has_accessor }
173 sub get_read_method {
175 my $reader = $self->reader || $self->accessor;
177 return $reader unless ref $reader;
179 my ($name) = %$reader;
183 sub get_write_method {
185 my $writer = $self->writer || $self->accessor;
187 return $writer unless ref $writer;
189 my ($name) = %$writer;
193 sub get_read_method_ref {
195 if ((my $reader = $self->get_read_method) && $self->associated_class) {
196 return $self->associated_class->get_method($reader);
199 my $code = sub { $self->get_value(@_) };
200 if (my $class = $self->associated_class) {
201 return $class->method_metaclass->wrap(
203 package_name => $class->name,
213 sub get_write_method_ref {
215 if ((my $writer = $self->get_write_method) && $self->associated_class) {
216 return $self->associated_class->get_method($writer);
219 my $code = sub { $self->set_value(@_) };
220 if (my $class = $self->associated_class) {
221 return $class->method_metaclass->wrap(
223 package_name => $class->name,
233 sub is_default_a_coderef {
234 ('CODE' eq (reftype($_[0]->{'$!default'} || $_[0]->{default}) || ''))
238 my ($self, $instance) = @_;
239 if (defined $instance && $self->is_default_a_coderef) {
240 # if the default is a CODE ref, then
241 # we pass in the instance and default
242 # can return a value based on that
243 # instance. Somewhat crude, but works.
244 return $self->{'$!default'}->($instance);
246 $self->{'$!default'};
251 sub slots { (shift)->name }
255 sub attach_to_class {
256 my ($self, $class) = @_;
257 (blessed($class) && $class->isa('Class::MOP::Class'))
258 || confess "You must pass a Class::MOP::Class instance (or a subclass)";
259 weaken($self->{'$!associated_class'} = $class);
262 sub detach_from_class {
264 $self->{'$!associated_class'} = undef;
269 sub associate_method {
270 my ($self, $method) = @_;
271 push @{$self->{'@!associated_methods'}} => $method;
276 sub set_initial_value {
277 my ($self, $instance, $value) = @_;
278 $self->_set_initial_slot_value(
279 Class::MOP::Class->initialize(blessed($instance))->get_meta_instance,
286 my ($self, $instance, $value) = @_;
288 Class::MOP::Class->initialize(blessed($instance))
290 ->set_slot_value($instance, $self->name, $value);
294 my ($self, $instance) = @_;
296 Class::MOP::Class->initialize(blessed($instance))
298 ->get_slot_value($instance, $self->name);
302 my ($self, $instance) = @_;
304 Class::MOP::Class->initialize(blessed($instance))
306 ->is_slot_initialized($instance, $self->name);
310 my ($self, $instance) = @_;
312 Class::MOP::Class->initialize(blessed($instance))
314 ->deinitialize_slot($instance, $self->name);
319 sub accessor_metaclass { 'Class::MOP::Method::Accessor' }
321 sub process_accessors {
322 my ($self, $type, $accessor, $generate_as_inline_methods) = @_;
323 if (reftype($accessor)) {
324 (reftype($accessor) eq 'HASH')
325 || confess "bad accessor/reader/writer/predicate/clearer format, must be a HASH ref";
326 my ($name, $method) = %{$accessor};
327 $method = $self->accessor_metaclass->wrap(
329 package_name => $self->associated_class->name,
332 $self->associate_method($method);
333 return ($name, $method);
336 my $inline_me = ($generate_as_inline_methods && $self->associated_class->instance_metaclass->is_inlinable);
339 $method = $self->accessor_metaclass->new(
341 is_inline => $inline_me,
342 accessor_type => $type,
343 package_name => $self->associated_class->name,
347 confess "Could not create the '$type' method for " . $self->name . " because : $@" if $@;
348 $self->associate_method($method);
349 return ($accessor, $method);
353 sub install_accessors {
356 my $class = $self->associated_class;
359 $self->process_accessors('accessor' => $self->accessor(), $inline)
360 ) if $self->has_accessor();
363 $self->process_accessors('reader' => $self->reader(), $inline)
364 ) if $self->has_reader();
367 $self->process_accessors('writer' => $self->writer(), $inline)
368 ) if $self->has_writer();
371 $self->process_accessors('predicate' => $self->predicate(), $inline)
372 ) if $self->has_predicate();
375 $self->process_accessors('clearer' => $self->clearer(), $inline)
376 ) if $self->has_clearer();
382 my $_remove_accessor = sub {
383 my ($accessor, $class) = @_;
384 if (reftype($accessor) && reftype($accessor) eq 'HASH') {
385 ($accessor) = keys %{$accessor};
387 my $method = $class->get_method($accessor);
388 $class->remove_method($accessor)
389 if (blessed($method) && $method->isa('Class::MOP::Method::Accessor'));
392 sub remove_accessors {
395 # we really need to make sure to remove from the
396 # associates methods here as well. But this is
397 # such a slimly used method, I am not worried
398 # about it right now.
399 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
400 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
401 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
402 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
403 $_remove_accessor->($self->clearer(), $self->associated_class()) if $self->has_clearer();
417 Class::MOP::Attribute - Attribute Meta Object
421 Class::MOP::Attribute->new('$foo' => (
422 accessor => 'foo', # dual purpose get/set accessor
423 predicate => 'has_foo' # predicate check for defined-ness
424 init_arg => '-foo', # class->new will look for a -foo key
425 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
428 Class::MOP::Attribute->new('$.bar' => (
429 reader => 'bar', # getter
430 writer => 'set_bar', # setter
431 predicate => 'has_bar' # predicate check for defined-ness
432 init_arg => ':bar', # class->new will look for a :bar key
433 # no default value means it is undef
438 The Attribute Protocol is almost entirely an invention of this module,
439 and is completely optional to this MOP. This is because Perl 5 does not
440 have consistent notion of what is an attribute of a class. There are
441 so many ways in which this is done, and very few (if any) are
442 easily discoverable by this module.
444 So, all that said, this module attempts to inject some order into this
445 chaos, by introducing a consistent API which can be used to create
454 =item B<new ($name, ?%options)>
456 An attribute must (at the very least), have a C<$name>. All other
457 C<%options> are contained added as key-value pairs. Acceptable keys
464 This should be a string value representing the expected key in
465 an initialization hash. For instance, if we have an I<init_arg>
466 value of C<-foo>, then the following code will Just Work.
468 MyClass->meta->construct_instance(-foo => "Hello There");
470 In an init_arg is not assigned, it will automatically use the
471 value of C<$name>. If an explicit C<undef> is given for an init_arg,
472 an attribute value can't be specified during initialization.
476 The value of this key is the name of the method that will be
477 called to obtain the value used to initialize the attribute.
478 This should be a method in the class associated with the attribute,
479 not a method in the attribute class itself.
483 The value of this key is the default value which
484 C<Class::MOP::Class::construct_instance> will initialize the
488 If the value is a simple scalar (string or number), then it can
489 be just passed as is. However, if you wish to initialize it with
490 a HASH or ARRAY ref, then you need to wrap that inside a CODE
493 Class::MOP::Attribute->new('@foo' => (
494 default => sub { [] },
499 Class::MOP::Attribute->new('%foo' => (
500 default => sub { {} },
503 If you wish to initialize an attribute with a CODE reference
504 itself, then you need to wrap that in a subroutine as well, like
507 Class::MOP::Attribute->new('&foo' => (
508 default => sub { sub { print "Hello World" } },
511 And lastly, if the value of your attribute is dependent upon
512 some other aspect of the instance structure, then you can take
513 advantage of the fact that when the I<default> value is a CODE
514 reference, it is passed the (as yet unfinished) instance structure
515 as it's only argument. So you can do things like this:
517 Class::MOP::Attribute->new('$object_identity' => (
518 default => sub { Scalar::Util::refaddr($_[0]) },
521 This last feature is fairly limited as there is no gurantee of
522 the order of attribute initializations, so you cannot perform
523 any kind of dependent initializations. However, if this is
524 something you need, you could subclass B<Class::MOP::Class> and
525 this class to acheive it. However, this is currently left as
526 an exercise to the reader :).
530 This may be a method name (referring to a method on the class with this
531 attribute) or a CODE ref. The initializer is used to set the attribute value
532 on an instance when the attribute is set during instance initialization. When
533 called, it is passed the instance (as the invocant), the value to set, a
534 slot-setting CODE ref, and the attribute meta-instance. The slot-setting code
535 is provided to make it easy to set the (possibly altered) value on the instance
536 without going through several more method calls.
538 This contrived example shows an initializer that sets the attribute to twice
541 Class::MOP::Attribute->new('$doubled' => (
543 my ($instance, $value, $set) = @_;
548 As method names can be given as initializers, one can easily make
549 attribute initialization use the writer:
551 Class::MOP::Attribute->new('$some_attr' => (
552 writer => 'some_attr',
553 initializer => 'some_attr',
556 Your writer will simply need to examine it's C<@_> and determine under
557 which context it is being called.
561 The I<accessor>, I<reader>, I<writer>, I<predicate> and I<clearer> keys can
562 contain either; the name of the method and an appropriate default one will be
563 generated for you, B<or> a HASH ref containing exactly one key (which will be
564 used as the name of the method) and one value, which should contain a CODE
565 reference which will be installed as the method itself.
571 The I<accessor> is a standard perl-style read/write accessor. It will
572 return the value of the attribute, and if a value is passed as an argument,
573 it will assign that value to the attribute.
576 This method will properly handle the following code, by assigning an
577 C<undef> value to the attribute.
579 $object->set_something(undef);
583 This is a basic read-only accessor, it will just return the value of
588 This is a basic write accessor, it accepts a single argument, and
589 assigns that value to the attribute. This method does not intentially
590 return a value, however perl will return the result of the last
591 expression in the subroutine, which returns in this returning the
592 same value that it was passed.
595 This method will properly handle the following code, by assigning an
596 C<undef> value to the attribute.
598 $object->set_something();
602 This is a basic test to see if any value has been set for the
603 attribute. It will return true (C<1>) if the attribute has been set
604 to any value (even C<undef>), and false (C<0>) otherwise.
607 The predicate will return true even when you set an attribute's
608 value to C<undef>. This behaviour has changed as of version 0.43. In
609 older versions, the predicate (erroneously) checked for attribute
610 value definedness, instead of presence as it is now.
612 If you really want to get rid of the value, you have to define and
613 use a I<clearer> (see below).
617 This is the a method that will uninitialize the attr, reverting lazy values
618 back to their "unfulfilled" state.
622 =item B<clone (%options)>
624 This will return a clone of the attribute instance, allowing the overriding
625 of various attributes through the C<%options> supplied.
627 =item B<initialize_instance_slot ($instance, $params)>
629 This method is used internally to initialize the approriate slot for this
630 attribute in a given C<$instance>, the C<$params> passed are those that were
631 passed to the constructor.
635 =head2 Value management
637 These methods are basically "backdoors" to the instance, which can be used
638 to bypass the regular accessors, but still stay within the context of the MOP.
640 These methods are not for general use, and should only be used if you really
641 know what you are doing.
645 =item B<set_value ($instance, $value)>
647 Set the value without going through the accessor. Note that this may be done to
648 even attributes with just read only accessors.
650 =item B<set_initial_value ($instance, $value)>
652 This method sets the value without going through the accessor -- but it is only
653 called when the instance data is first initialized.
655 =item B<get_value ($instance)>
657 Return the value without going through the accessor. Note that this may be done
658 even to attributes with just write only accessors.
660 =item B<has_value ($instance)>
662 Return a boolean indicating if the item in the C<$instance> has a value in it.
663 This is basically what the default C<predicate> method calls.
665 =item B<clear_value ($instance)>
667 This will clear the value in the C<$instance>. This is basically what the default
668 C<clearer> would call. Note that this may be done even if the attirbute does not
669 have any associated read, write or clear methods.
675 These are all basic read-only value accessors for the values
676 passed into C<new>. I think they are pretty much self-explanitory.
696 =item B<is_default_a_coderef>
698 =item B<default (?$instance)>
700 Return the default value for the attribute.
702 If you pass in an C<$instance> argument to this accessor and the
703 I<default> is a CODE reference, then the CODE reference will be
704 executed with the C<$instance> as its argument.
708 Return a list of slots required by the attribute. This is usually
709 just one, which is the name of the attribute.
711 =item B<get_read_method>
713 =item B<get_write_method>
715 Return the name of a method name suitable for reading / writing the value
716 of the attribute in the associated class. Suitable for use whether
717 C<reader> and C<writer> or C<accessor> was used.
719 =item B<get_read_method_ref>
721 =item B<get_write_method_ref>
723 Return the CODE reference of a method suitable for reading / writing the
724 value of the attribute in the associated class. Suitable for use whether
725 C<reader> and C<writer> or C<accessor> was specified or not.
727 NOTE: If no reader/writer/accessor was specified, this will use the
728 attribute get_value/set_value methods, which can be very inefficient.
730 =item B<has_read_method>
732 =item B<has_write_method>
734 Return whether a method exists suitable for reading / writing the value
735 of the attribute in the associated class. Suitable for use whether
736 C<reader> and C<writer> or C<accessor> was used.
740 =head2 Informational predicates
742 These are all basic predicate methods for the values passed into C<new>.
746 =item B<has_accessor>
752 =item B<has_predicate>
756 =item B<has_initializer>
758 =item B<has_init_arg>
766 =head2 Class association
768 These methods allow you to manage the attributes association with
769 the class that contains it. These methods should not be used
770 lightly, nor are they very magical, they are mostly used internally
771 and by metaclass instances.
775 =item B<associated_class>
777 This returns the metaclass this attribute is associated with.
779 =item B<attach_to_class ($class)>
781 This will store a weaken reference to C<$class> internally. You should
782 note that just changing the class assocation will not remove the attribute
783 from it's old class, and initialize it (and it's accessors) in the new
784 C<$class>. It is up to you to do this manually.
786 =item B<detach_from_class>
788 This will remove the weakened reference to the class. It does B<not>
789 remove the attribute itself from the class (or remove it's accessors),
790 you must do that yourself if you want too. Actually if that is what
791 you want to do, you should probably be looking at
792 L<Class::MOP::Class::remove_attribute> instead.
796 =head2 Attribute Accessor generation
800 =item B<accessor_metaclass>
802 Accessors are generated by an accessor metaclass, which is usually
803 a subclass of C<Class::MOP::Method::Accessor>. This method returns
804 the name of the accessor metaclass that this attribute uses.
806 =item B<associate_method ($method)>
808 This will associate a C<$method> with the given attribute which is
809 used internally by the accessor generator.
811 =item B<associated_methods>
813 This will return the list of methods which have been associated with
814 the C<associate_method> methods. This is a good way of seeing what
815 methods are used to manage a given attribute.
817 =item B<install_accessors>
819 This allows the attribute to generate and install code for it's own
820 I<accessor/reader/writer/predicate> methods. This is called by
821 C<Class::MOP::Class::add_attribute>.
823 This method will call C<process_accessors> for each of the possible
824 method types (accessor, reader, writer & predicate).
826 =item B<process_accessors ($type, $value)>
828 This takes a C<$type> (accessor, reader, writer or predicate), and
829 a C<$value> (the value passed into the constructor for each of the
830 different types). It will then either generate the method itself
831 (using the C<generate_*_method> methods listed below) or it will
832 use the custom method passed through the constructor.
834 =item B<remove_accessors>
836 This allows the attribute to remove the method for it's own
837 I<accessor/reader/writer/predicate/clearer>. This is called by
838 C<Class::MOP::Class::remove_attribute>.
840 NOTE: This does not currently remove methods from the list returned
841 by C<associated_methods>, that is on the TODO list.
851 This will return a B<Class::MOP::Class> instance which is related
854 It should also be noted that B<Class::MOP> will actually bootstrap
855 this module by installing a number of attribute meta-objects into
856 it's metaclass. This will allow this class to reap all the benefits
857 of the MOP when subclassing it.
863 Stevan Little E<lt>stevan@iinteractive.comE<gt>
865 =head1 COPYRIGHT AND LICENSE
867 Copyright 2006-2008 by Infinity Interactive, Inc.
869 L<http://www.iinteractive.com>
871 This library is free software; you can redistribute it and/or modify
872 it under the same terms as Perl itself.