2 package Class::MOP::Attribute;
7 use Class::MOP::Method::Accessor;
10 use Scalar::Util 'blessed', 'weaken';
12 our $VERSION = '0.91';
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 if(exists $options{trigger}){
56 ( ref($options{trigger})
57 ? (ref($options{trigger}) eq 'CODE')
58 :(defined $options{trigger} && length $options{trigger}) )
59 || confess("Trigger must be a CODE ref or method name on attribute ($name)");
62 $class->_new(\%options);
68 return Class::MOP::Class->initialize($class)->new_object(@_)
69 if $class ne __PACKAGE__;
71 my $options = @_ == 1 ? $_[0] : {@_};
74 'name' => $options->{name},
75 'accessor' => $options->{accessor},
76 'reader' => $options->{reader},
77 'writer' => $options->{writer},
78 'predicate' => $options->{predicate},
79 'clearer' => $options->{clearer},
80 'builder' => $options->{builder},
81 'init_arg' => $options->{init_arg},
82 'default' => $options->{default},
83 'initializer' => $options->{initializer},
84 'definition_context' => $options->{definition_context},
85 'trigger' => $options->{trigger},
86 # keep a weakened link to the
87 # class we are associated with
88 'associated_class' => undef,
89 # and a list of the methods
90 # associated with this attr
91 'associated_methods' => [],
92 # this let's us keep track of
93 # our order inside the associated
95 'insertion_order' => undef,
100 # this is a primative (and kludgy) clone operation
101 # for now, it will be replaced in the Class::MOP
102 # bootstrap with a proper one, however we know
103 # that this one will work fine for now.
108 || confess "Can only clone an instance";
109 return bless { %{$self}, %options } => ref($self);
112 sub initialize_instance_slot {
113 my ($self, $meta_instance, $instance, $params) = @_;
114 my $init_arg = $self->{'init_arg'};
116 # try to fetch the init arg from the %params ...
118 # if nothing was in the %params, we can use the
119 # attribute's default value (if it has one)
120 if(defined $init_arg and exists $params->{$init_arg}){
121 $self->_set_initial_slot_value(
124 $params->{$init_arg},
127 elsif (defined $self->{'default'}) {
128 $self->_set_initial_slot_value(
131 $self->default($instance),
134 elsif (defined( my $builder = $self->{'builder'})) {
135 if ($builder = $instance->can($builder)) {
136 $self->_set_initial_slot_value(
143 confess(ref($instance)." does not support builder method '". $self->{'builder'} ."' for attribute '" . $self->name . "'");
148 sub _set_initial_slot_value {
149 my ($self, $meta_instance, $instance, $value) = @_;
151 my $slot_name = $self->name;
153 unless($self->has_initializer){
154 $meta_instance->set_slot_value($instance, $slot_name, $value);
155 $self->call_trigger($instance, $value);
160 $meta_instance->set_slot_value($instance, $slot_name, $_[0]);
163 my $initializer = $self->initializer;
165 # most things will just want to set a value, so make it first arg
166 $instance->$initializer($value, $callback, $self);
167 $self->call_trigger($instance, $value);
172 # the next bunch of methods will get bootstrapped
173 # away in the Class::MOP bootstrapping section
175 sub associated_class { $_[0]->{'associated_class'} }
176 sub associated_methods { $_[0]->{'associated_methods'} }
178 sub has_accessor { defined($_[0]->{'accessor'}) }
179 sub has_reader { defined($_[0]->{'reader'}) }
180 sub has_writer { defined($_[0]->{'writer'}) }
181 sub has_predicate { defined($_[0]->{'predicate'}) }
182 sub has_clearer { defined($_[0]->{'clearer'}) }
183 sub has_builder { defined($_[0]->{'builder'}) }
184 sub has_init_arg { defined($_[0]->{'init_arg'}) }
185 sub has_default { defined($_[0]->{'default'}) }
186 sub has_initializer { defined($_[0]->{'initializer'}) }
187 sub has_insertion_order { defined($_[0]->{'insertion_order'}) }
188 sub has_trigger { defined($_[0]->{'trigger'}) }
190 sub accessor { $_[0]->{'accessor'} }
191 sub reader { $_[0]->{'reader'} }
192 sub writer { $_[0]->{'writer'} }
193 sub predicate { $_[0]->{'predicate'} }
194 sub clearer { $_[0]->{'clearer'} }
195 sub builder { $_[0]->{'builder'} }
196 sub init_arg { $_[0]->{'init_arg'} }
197 sub initializer { $_[0]->{'initializer'} }
198 sub definition_context { $_[0]->{'definition_context'} }
199 sub insertion_order { $_[0]->{'insertion_order'} }
200 sub _set_insertion_order { $_[0]->{'insertion_order'} = $_[1] }
201 sub trigger { $_[0]->{'trigger'} }
204 my($self, $instance, $value) = @_;
206 if(defined(my $trigger = $self->{trigger})){
207 $instance->$trigger($value);
211 # end bootstrapped away method section.
212 # (all methods below here are kept intact)
214 sub has_read_method { $_[0]->has_reader || $_[0]->has_accessor }
215 sub has_write_method { $_[0]->has_writer || $_[0]->has_accessor }
219 sub get_read_method {
221 my $reader = $self->reader || $self->accessor;
223 return $reader unless ref $reader;
225 my ($name) = %$reader;
229 sub get_write_method {
231 my $writer = $self->writer || $self->accessor;
233 return $writer unless ref $writer;
235 my ($name) = %$writer;
239 sub get_read_method_ref {
241 if ((my $reader = $self->get_read_method) && $self->associated_class) {
242 return $self->associated_class->get_method($reader);
245 my $code = sub { $self->get_value(@_) };
246 if (my $class = $self->associated_class) {
247 return $class->method_metaclass->wrap(
249 package_name => $class->name,
259 sub get_write_method_ref {
261 if ((my $writer = $self->get_write_method) && $self->associated_class) {
262 return $self->associated_class->get_method($writer);
265 my $code = sub { $self->set_value(@_) };
266 if (my $class = $self->associated_class) {
267 return $class->method_metaclass->wrap(
269 package_name => $class->name,
279 sub is_default_a_coderef {
280 my ($value) = $_[0]->{'default'};
281 return unless ref($value);
282 return ref($value) eq 'CODE' || (blessed($value) && $value->isa('Class::MOP::Method'));
286 my ($self, $instance) = @_;
287 if (defined $instance && $self->is_default_a_coderef) {
288 # if the default is a CODE ref, then
289 # we pass in the instance and default
290 # can return a value based on that
291 # instance. Somewhat crude, but works.
292 return $self->{'default'}->($instance);
299 sub slots { (shift)->name }
303 sub attach_to_class {
304 my ($self, $class) = @_;
305 (blessed($class) && $class->isa('Class::MOP::Class'))
306 || confess "You must pass a Class::MOP::Class instance (or a subclass)";
307 weaken($self->{'associated_class'} = $class);
310 sub detach_from_class {
312 $self->{'associated_class'} = undef;
317 sub associate_method {
318 my ($self, $method) = @_;
319 push @{$self->{'associated_methods'}} => $method;
324 sub set_initial_value {
325 my ($self, $instance, $value) = @_;
326 $self->_set_initial_slot_value(
327 Class::MOP::Class->initialize(ref($instance))->get_meta_instance,
335 my ($self, $instance, $value) = @_;
337 Class::MOP::Class->initialize(ref($instance))
339 ->set_slot_value($instance, $self->name, $value);
340 $self->call_trigger($instance, $value);
345 my ($self, $instance) = @_;
347 Class::MOP::Class->initialize(ref($instance))
349 ->get_slot_value($instance, $self->name);
353 my ($self, $instance) = @_;
355 Class::MOP::Class->initialize(ref($instance))
357 ->is_slot_initialized($instance, $self->name);
361 my ($self, $instance) = @_;
363 Class::MOP::Class->initialize(ref($instance))
365 ->deinitialize_slot($instance, $self->name);
366 $self->call_trigger($instance);
372 sub accessor_metaclass { 'Class::MOP::Method::Accessor' }
374 sub process_accessors {
375 Carp::cluck('The process_accessors method has been made private.'
376 . " The public version is deprecated and will be removed in a future release.\n");
377 shift->_process_accessors(@_);
380 sub _process_accessors {
381 my ($self, $type, $accessor, $generate_as_inline_methods) = @_;
385 if ( my $ctx = $self->definition_context ) {
386 $method_ctx = { %$ctx };
389 if (ref($accessor)) {
390 (ref($accessor) eq 'HASH')
391 || confess "bad accessor/reader/writer/predicate/clearer format, must be a HASH ref";
392 my ($name, $method) = %{$accessor};
393 $method = $self->accessor_metaclass->wrap(
395 package_name => $self->associated_class->name,
397 definition_context => $method_ctx,
399 $self->associate_method($method);
400 return ($name, $method);
403 my $inline_me = ($generate_as_inline_methods && $self->associated_class->instance_metaclass->is_inlinable);
407 my $desc = "accessor $accessor";
408 if ( $accessor ne $self->name ) {
409 $desc .= " of attribute " . $self->name;
412 $method_ctx->{description} = $desc;
415 $method = $self->accessor_metaclass->new(
417 is_inline => $inline_me,
418 accessor_type => $type,
419 package_name => $self->associated_class->name,
421 definition_context => $method_ctx,
424 confess "Could not create the '$type' method for " . $self->name . " because : $@" if $@;
425 $self->associate_method($method);
426 return ($accessor, $method);
430 sub install_accessors {
433 my $class = $self->associated_class;
436 $self->_process_accessors('accessor' => $self->accessor(), $inline)
437 ) if $self->has_accessor();
440 $self->_process_accessors('reader' => $self->reader(), $inline)
441 ) if $self->has_reader();
444 $self->_process_accessors('writer' => $self->writer(), $inline)
445 ) if $self->has_writer();
448 $self->_process_accessors('predicate' => $self->predicate(), $inline)
449 ) if $self->has_predicate();
452 $self->_process_accessors('clearer' => $self->clearer(), $inline)
453 ) if $self->has_clearer();
459 my $_remove_accessor = sub {
460 my ($accessor, $class) = @_;
461 if (ref($accessor) && ref($accessor) eq 'HASH') {
462 ($accessor) = keys %{$accessor};
464 my $method = $class->get_method($accessor);
465 $class->remove_method($accessor)
466 if (ref($method) && $method->isa('Class::MOP::Method::Accessor'));
469 sub remove_accessors {
472 # we really need to make sure to remove from the
473 # associates methods here as well. But this is
474 # such a slimly used method, I am not worried
475 # about it right now.
476 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
477 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
478 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
479 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
480 $_remove_accessor->($self->clearer(), $self->associated_class()) if $self->has_clearer();
494 Class::MOP::Attribute - Attribute Meta Object
498 Class::MOP::Attribute->new(
500 accessor => 'foo', # dual purpose get/set accessor
501 predicate => 'has_foo', # predicate check for defined-ness
502 init_arg => '-foo', # class->new will look for a -foo key
503 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
507 Class::MOP::Attribute->new(
509 reader => 'bar', # getter
510 writer => 'set_bar', # setter
511 predicate => 'has_bar', # predicate check for defined-ness
512 init_arg => ':bar', # class->new will look for a :bar key
513 # no default value means it is undef
519 The Attribute Protocol is almost entirely an invention of
520 C<Class::MOP>. Perl 5 does not have a consistent notion of
521 attributes. There are so many ways in which this is done, and very few
522 (if any) are easily discoverable by this module.
524 With that said, this module attempts to inject some order into this
525 chaos, by introducing a consistent API which can be used to create
534 =item B<< Class::MOP::Attribute->new($name, ?%options) >>
536 An attribute must (at the very least), have a C<$name>. All other
537 C<%options> are added as key-value pairs.
543 This is a string value representing the expected key in an
544 initialization hash. For instance, if we have an C<init_arg> value of
545 C<-foo>, then the following code will Just Work.
547 MyClass->meta->new_object( -foo => 'Hello There' );
549 If an init_arg is not assigned, it will automatically use the
550 attribute's name. If C<init_arg> is explicitly set to C<undef>, the
551 attribute cannot be specified during initialization.
555 This provides the name of a method that will be called to initialize
556 the attribute. This method will be called on the object after it is
557 constructed. It is expected to return a valid value for the attribute.
561 This can be used to provide an explicit default for initializing the
562 attribute. If the default you provide is a subroutine reference, then
563 this reference will be called I<as a method> on the object.
565 If the value is a simple scalar (string or number), then it can be
566 just passed as is. However, if you wish to initialize it with a HASH
567 or ARRAY ref, then you need to wrap that inside a subroutine
570 Class::MOP::Attribute->new(
572 default => sub { [] },
578 Class::MOP::Attribute->new(
580 default => sub { {} },
584 If you wish to initialize an attribute with a subroutine reference
585 itself, then you need to wrap that in a subroutine as well:
587 Class::MOP::Attribute->new(
590 sub { print "Hello World" }
595 And lastly, if the value of your attribute is dependent upon some
596 other aspect of the instance structure, then you can take advantage of
597 the fact that when the C<default> value is called as a method:
599 Class::MOP::Attribute->new(
600 'object_identity' => (
601 default => sub { Scalar::Util::refaddr( $_[0] ) },
605 Note that there is no guarantee that attributes are initialized in any
606 particular order, so you cannot rely on the value of some other
607 attribute when generating the default.
611 This option can be either a method name or a subroutine
612 reference. This method will be called when setting the attribute's
613 value in the constructor. Unlike C<default> and C<builder>, the
614 initializer is only called when a value is provided to the
615 constructor. The initializer allows you to munge this value during
618 The initializer is called as a method with three arguments. The first
619 is the value that was passed to the constructor. The second is a
620 subroutine reference that can be called to actually set the
621 attribute's value, and the last is the associated
622 C<Class::MOP::Attribute> object.
624 This contrived example shows an initializer that sets the attribute to
625 twice the given value.
627 Class::MOP::Attribute->new(
630 my ( $instance, $value, $set ) = @_;
631 $set->( $value * 2 );
636 Since an initializer can be a method name, you can easily make
637 attribute initialization use the writer:
639 Class::MOP::Attribute->new(
641 writer => 'some_attr',
642 initializer => 'some_attr',
646 Your writer will need to examine C<@_> and determine under which
647 context it is being called.
651 The C<accessor>, C<reader>, C<writer>, C<predicate> and C<clearer>
652 options all accept the same parameters. You can provide the name of
653 the method, in which case an appropriate default method will be
654 generated for you. Or instead you can also provide hash reference
655 containing exactly one key (the method name) and one value. The value
656 should be a subroutine reference, which will be installed as the
663 An C<accessor> is a standard Perl-style read/write accessor. It will
664 return the value of the attribute, and if a value is passed as an
665 argument, it will assign that value to the attribute.
667 Note that C<undef> is a legitimate value, so this will work:
669 $object->set_something(undef);
673 This is a basic read-only accessor. It returns the value of the
678 This is a basic write accessor, it accepts a single argument, and
679 assigns that value to the attribute.
681 Note that C<undef> is a legitimate value, so this will work:
683 $object->set_something(undef);
687 The predicate method returns a boolean indicating whether or not the
688 attribute has been explicitly set.
690 Note that the predicate returns true even if the attribute was set to
691 a false value (C<0> or C<undef>).
695 This method will uninitialize the attribute. After an attribute is
696 cleared, its C<predicate> will return false.
698 =item * definition_context
700 Mostly, this exists as a hook for the benefit of Moose.
702 This option should be a hash reference containing several keys which
703 will be used when inlining the attribute's accessors. The keys should
704 include C<line>, the line number where the attribute was created, and
705 either C<file> or C<description>.
707 This information will ultimately be used when eval'ing inlined
708 accessor code so that error messages report a useful line and file
713 =item B<< $attr->clone(%options) >>
715 This clones the attribute. Any options you provide will override the
716 settings of the original attribute. You can change the name of the new
717 attribute by passing a C<name> key in C<%options>.
723 These are all basic read-only accessors for the values passed into
728 =item B<< $attr->name >>
730 Returns the attribute's name.
732 =item B<< $attr->accessor >>
734 =item B<< $attr->reader >>
736 =item B<< $attr->writer >>
738 =item B<< $attr->predicate >>
740 =item B<< $attr->clearer >>
742 The C<accessor>, C<reader>, C<writer>, C<predicate>, and C<clearer>
743 methods all return exactly what was passed to the constructor, so it
744 can be either a string containing a method name, or a hash reference.
746 =item B<< $attr->initializer >>
748 Returns the initializer as passed to the constructor, so this may be
749 either a method name or a subroutine reference.
751 =item B<< $attr->init_arg >>
753 =item B<< $attr->is_default_a_coderef >>
755 =item B<< $attr->default($instance) >>
757 The C<$instance> argument is optional. If you don't pass it, the
758 return value for this method is exactly what was passed to the
759 constructor, either a simple scalar or a subroutine reference.
761 If you I<do> pass an C<$instance> and the default is a subroutine
762 reference, then the reference is called as a method on the
763 C<$instance> and the generated value is returned.
765 =item B<< $attr->slots >>
767 Return a list of slots required by the attribute. This is usually just
768 one, the name of the attribute.
770 A slot is the name of the hash key used to store the attribute in an
773 =item B<< $attr->get_read_method >>
775 =item B<< $attr->get_write_method >>
777 Returns the name of a method suitable for reading or writing the value
778 of the attribute in the associated class.
780 If an attribute is read- or write-only, then these methods can return
781 C<undef> as appropriate.
783 =item B<< $attr->has_read_method >>
785 =item B<< $attr->has_write_method >>
787 This returns a boolean indicating whether the attribute has a I<named>
788 read or write method.
790 =item B<< $attr->get_read_method_ref >>
792 =item B<< $attr->get_write_method_ref >>
794 Returns the subroutine reference of a method suitable for reading or
795 writing the attribute's value in the associated class. These methods
796 always return a subroutine reference, regardless of whether or not the
797 attribute is read- or write-only.
799 =item B<< $attr->insertion_order >>
801 If this attribute has been inserted into a class, this returns a zero
802 based index regarding the order of insertion.
806 =head2 Informational predicates
808 These are all basic predicate methods for the values passed into C<new>.
812 =item B<< $attr->has_accessor >>
814 =item B<< $attr->has_reader >>
816 =item B<< $attr->has_writer >>
818 =item B<< $attr->has_predicate >>
820 =item B<< $attr->has_clearer >>
822 =item B<< $attr->has_initializer >>
824 =item B<< $attr->has_init_arg >>
826 This will be I<false> if the C<init_arg> was set to C<undef>.
828 =item B<< $attr->has_default >>
830 This will be I<false> if the C<default> was set to C<undef>, since
831 C<undef> is the default C<default> anyway.
833 =item B<< $attr->has_builder >>
835 =item B<< $attr->has_insertion_order >>
837 This will be I<false> if this attribute has not be inserted into a class
841 =head2 Value management
843 These methods are basically "back doors" to the instance, and can be
844 used to bypass the regular accessors, but still stay within the MOP.
846 These methods are not for general use, and should only be used if you
847 really know what you are doing.
851 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
853 This method is used internally to initialize the attribute's slot in
854 the object C<$instance>.
856 The C<$params> is a hash reference of the values passed to the object
859 It's unlikely that you'll need to call this method yourself.
861 =item B<< $attr->set_value($instance, $value) >>
863 Sets the value without going through the accessor. Note that this
864 works even with read-only attributes.
866 =item B<< $attr->set_initial_value($instance, $value) >>
868 Sets the value without going through the accessor. This method is only
869 called when the instance is first being initialized.
871 =item B<< $attr->get_value($instance) >>
873 Returns the value without going through the accessor. Note that this
874 works even with write-only accessors.
876 =item B<< $attr->has_value($instance) >>
878 Return a boolean indicating whether the attribute has been set in
879 C<$instance>. This how the default C<predicate> method works.
881 =item B<< $attr->clear_value($instance) >>
883 This will clear the attribute's value in C<$instance>. This is what
884 the default C<clearer> calls.
886 Note that this works even if the attribute does not have any
887 associated read, write or clear methods.
891 =head2 Class association
893 These methods allow you to manage the attributes association with
894 the class that contains it. These methods should not be used
895 lightly, nor are they very magical, they are mostly used internally
896 and by metaclass instances.
900 =item B<< $attr->associated_class >>
902 This returns the C<Class::MOP::Class> with which this attribute is
905 =item B<< $attr->attach_to_class($metaclass) >>
907 This method stores a weakened reference to the C<$metaclass> object
910 This method does not remove the attribute from its old class,
911 nor does it create any accessors in the new class.
913 It is probably best to use the L<Class::MOP::Class> C<add_attribute>
916 =item B<< $attr->detach_from_class >>
918 This method removes the associate metaclass object from the attribute
921 This method does not remove the attribute itself from the class, or
922 remove its accessors.
924 It is probably best to use the L<Class::MOP::Class>
925 C<remove_attribute> method instead.
929 =head2 Attribute Accessor generation
933 =item B<< $attr->accessor_metaclass >>
935 Accessor methods are generated using an accessor metaclass. By
936 default, this is L<Class::MOP::Method::Accessor>. This method returns
937 the name of the accessor metaclass that this attribute uses.
939 =item B<< $attr->associate_method($method) >>
941 This associates a L<Class::MOP::Method> object with the
942 attribute. Typically, this is called internally when an attribute
943 generates its accessors.
945 =item B<< $attr->associated_methods >>
947 This returns the list of methods which have been associated with the
950 =item B<< $attr->install_accessors >>
952 This method generates and installs code the attributes various
953 accessors. It is typically called from the L<Class::MOP::Class>
954 C<add_attribute> method.
956 =item B<< $attr->remove_accessors >>
958 This method removes all of the accessors associated with the
961 This does not currently remove methods from the list returned by
962 C<associated_methods>.
970 =item B<< Class::MOP::Attribute->meta >>
972 This will return a L<Class::MOP::Class> instance for this class.
974 It should also be noted that L<Class::MOP> will actually bootstrap
975 this module by installing a number of attribute meta-objects into its
982 Stevan Little E<lt>stevan@iinteractive.comE<gt>
984 =head1 COPYRIGHT AND LICENSE
986 Copyright 2006-2009 by Infinity Interactive, Inc.
988 L<http://www.iinteractive.com>
990 This library is free software; you can redistribute it and/or modify
991 it under the same terms as Perl itself.