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};
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 $class->_new(\%options);
61 return Class::MOP::Class->initialize($class)->new_object(@_)
62 if $class ne __PACKAGE__;
64 my $options = @_ == 1 ? $_[0] : {@_};
67 'name' => $options->{name},
68 'accessor' => $options->{accessor},
69 'reader' => $options->{reader},
70 'writer' => $options->{writer},
71 'predicate' => $options->{predicate},
72 'clearer' => $options->{clearer},
73 'builder' => $options->{builder},
74 'init_arg' => $options->{init_arg},
75 'default' => $options->{default},
76 'initializer' => $options->{initializer},
77 'definition_context' => $options->{definition_context},
78 # keep a weakened link to the
79 # class we are associated with
80 'associated_class' => undef,
81 # and a list of the methods
82 # associated with this attr
83 'associated_methods' => [],
84 # this let's us keep track of
85 # our order inside the associated
87 'insertion_order' => undef,
92 # this is a primative (and kludgy) clone operation
93 # for now, it will be replaced in the Class::MOP
94 # bootstrap with a proper one, however we know
95 # that this one will work fine for now.
100 || confess "Can only clone an instance";
101 return bless { %{$self}, %options } => ref($self);
104 sub initialize_instance_slot {
105 my ($self, $meta_instance, $instance, $params) = @_;
106 my $init_arg = $self->{'init_arg'};
108 # try to fetch the init arg from the %params ...
110 # if nothing was in the %params, we can use the
111 # attribute's default value (if it has one)
112 if(defined $init_arg and exists $params->{$init_arg}){
113 $self->_set_initial_slot_value(
116 $params->{$init_arg},
119 elsif (defined $self->{'default'}) {
120 $self->_set_initial_slot_value(
123 $self->default($instance),
126 elsif (defined( my $builder = $self->{'builder'})) {
127 if ($builder = $instance->can($builder)) {
128 $self->_set_initial_slot_value(
135 confess(ref($instance)." does not support builder method '". $self->{'builder'} ."' for attribute '" . $self->name . "'");
140 sub _set_initial_slot_value {
141 my ($self, $meta_instance, $instance, $value) = @_;
143 my $slot_name = $self->name;
145 return $meta_instance->set_slot_value($instance, $slot_name, $value)
146 unless $self->has_initializer;
149 $meta_instance->set_slot_value($instance, $slot_name, $_[0]);
152 my $initializer = $self->initializer;
154 # most things will just want to set a value, so make it first arg
155 $instance->$initializer($value, $callback, $self);
159 # the next bunch of methods will get bootstrapped
160 # away in the Class::MOP bootstrapping section
162 sub associated_class { $_[0]->{'associated_class'} }
163 sub associated_methods { $_[0]->{'associated_methods'} }
165 sub has_accessor { defined($_[0]->{'accessor'}) }
166 sub has_reader { defined($_[0]->{'reader'}) }
167 sub has_writer { defined($_[0]->{'writer'}) }
168 sub has_predicate { defined($_[0]->{'predicate'}) }
169 sub has_clearer { defined($_[0]->{'clearer'}) }
170 sub has_builder { defined($_[0]->{'builder'}) }
171 sub has_init_arg { defined($_[0]->{'init_arg'}) }
172 sub has_default { defined($_[0]->{'default'}) }
173 sub has_initializer { defined($_[0]->{'initializer'}) }
174 sub has_insertion_order { defined($_[0]->{'insertion_order'}) }
176 sub accessor { $_[0]->{'accessor'} }
177 sub reader { $_[0]->{'reader'} }
178 sub writer { $_[0]->{'writer'} }
179 sub predicate { $_[0]->{'predicate'} }
180 sub clearer { $_[0]->{'clearer'} }
181 sub builder { $_[0]->{'builder'} }
182 sub init_arg { $_[0]->{'init_arg'} }
183 sub initializer { $_[0]->{'initializer'} }
184 sub definition_context { $_[0]->{'definition_context'} }
185 sub insertion_order { $_[0]->{'insertion_order'} }
186 sub _set_insertion_order { $_[0]->{'insertion_order'} = $_[1] }
188 # end bootstrapped away method section.
189 # (all methods below here are kept intact)
191 sub has_read_method { $_[0]->has_reader || $_[0]->has_accessor }
192 sub has_write_method { $_[0]->has_writer || $_[0]->has_accessor }
194 sub get_read_method {
196 my $reader = $self->reader || $self->accessor;
198 return $reader unless ref $reader;
200 my ($name) = %$reader;
204 sub get_write_method {
206 my $writer = $self->writer || $self->accessor;
208 return $writer unless ref $writer;
210 my ($name) = %$writer;
214 sub get_read_method_ref {
216 if ((my $reader = $self->get_read_method) && $self->associated_class) {
217 return $self->associated_class->get_method($reader);
220 my $code = sub { $self->get_value(@_) };
221 if (my $class = $self->associated_class) {
222 return $class->method_metaclass->wrap(
224 package_name => $class->name,
234 sub get_write_method_ref {
236 if ((my $writer = $self->get_write_method) && $self->associated_class) {
237 return $self->associated_class->get_method($writer);
240 my $code = sub { $self->set_value(@_) };
241 if (my $class = $self->associated_class) {
242 return $class->method_metaclass->wrap(
244 package_name => $class->name,
254 sub is_default_a_coderef {
255 my ($value) = $_[0]->{'default'};
256 return unless ref($value);
257 return ref($value) eq 'CODE' || (blessed($value) && $value->isa('Class::MOP::Method'));
261 my ($self, $instance) = @_;
262 if (defined $instance && $self->is_default_a_coderef) {
263 # if the default is a CODE ref, then
264 # we pass in the instance and default
265 # can return a value based on that
266 # instance. Somewhat crude, but works.
267 return $self->{'default'}->($instance);
274 sub slots { (shift)->name }
278 sub attach_to_class {
279 my ($self, $class) = @_;
280 (blessed($class) && $class->isa('Class::MOP::Class'))
281 || confess "You must pass a Class::MOP::Class instance (or a subclass)";
282 weaken($self->{'associated_class'} = $class);
285 sub detach_from_class {
287 $self->{'associated_class'} = undef;
292 sub associate_method {
293 my ($self, $method) = @_;
294 push @{$self->{'associated_methods'}} => $method;
299 sub set_initial_value {
300 my ($self, $instance, $value) = @_;
301 $self->_set_initial_slot_value(
302 Class::MOP::Class->initialize(ref($instance))->get_meta_instance,
309 my ($self, $instance, $value) = @_;
311 Class::MOP::Class->initialize(ref($instance))
313 ->set_slot_value($instance, $self->name, $value);
317 my ($self, $instance) = @_;
319 Class::MOP::Class->initialize(ref($instance))
321 ->get_slot_value($instance, $self->name);
325 my ($self, $instance) = @_;
327 Class::MOP::Class->initialize(ref($instance))
329 ->is_slot_initialized($instance, $self->name);
333 my ($self, $instance) = @_;
335 Class::MOP::Class->initialize(ref($instance))
337 ->deinitialize_slot($instance, $self->name);
342 sub accessor_metaclass { 'Class::MOP::Method::Accessor' }
344 sub process_accessors {
345 Carp::cluck('The process_accessors method has been made private.'
346 . " The public version is deprecated and will be removed in a future release.\n");
347 shift->_process_accessors(@_);
350 sub _process_accessors {
351 my ($self, $type, $accessor, $generate_as_inline_methods) = @_;
355 if ( my $ctx = $self->definition_context ) {
356 $method_ctx = { %$ctx };
359 if (ref($accessor)) {
360 (ref($accessor) eq 'HASH')
361 || confess "bad accessor/reader/writer/predicate/clearer format, must be a HASH ref";
362 my ($name, $method) = %{$accessor};
363 $method = $self->accessor_metaclass->wrap(
365 package_name => $self->associated_class->name,
367 definition_context => $method_ctx,
369 $self->associate_method($method);
370 return ($name, $method);
373 my $inline_me = ($generate_as_inline_methods && $self->associated_class->instance_metaclass->is_inlinable);
377 my $desc = "accessor $accessor";
378 if ( $accessor ne $self->name ) {
379 $desc .= " of attribute " . $self->name;
382 $method_ctx->{description} = $desc;
385 $method = $self->accessor_metaclass->new(
387 is_inline => $inline_me,
388 accessor_type => $type,
389 package_name => $self->associated_class->name,
391 definition_context => $method_ctx,
394 confess "Could not create the '$type' method for " . $self->name . " because : $@" if $@;
395 $self->associate_method($method);
396 return ($accessor, $method);
400 sub install_accessors {
403 my $class = $self->associated_class;
405 $inline = 1 unless defined $inline;
408 $self->_process_accessors('accessor' => $self->accessor(), $inline)
409 ) if $self->has_accessor();
412 $self->_process_accessors('reader' => $self->reader(), $inline)
413 ) if $self->has_reader();
416 $self->_process_accessors('writer' => $self->writer(), $inline)
417 ) if $self->has_writer();
420 $self->_process_accessors('predicate' => $self->predicate(), $inline)
421 ) if $self->has_predicate();
424 $self->_process_accessors('clearer' => $self->clearer(), $inline)
425 ) if $self->has_clearer();
431 my $_remove_accessor = sub {
432 my ($accessor, $class) = @_;
433 if (ref($accessor) && ref($accessor) eq 'HASH') {
434 ($accessor) = keys %{$accessor};
436 my $method = $class->get_method($accessor);
437 $class->remove_method($accessor)
438 if (ref($method) && $method->isa('Class::MOP::Method::Accessor'));
441 sub remove_accessors {
444 # we really need to make sure to remove from the
445 # associates methods here as well. But this is
446 # such a slimly used method, I am not worried
447 # about it right now.
448 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
449 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
450 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
451 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
452 $_remove_accessor->($self->clearer(), $self->associated_class()) if $self->has_clearer();
466 Class::MOP::Attribute - Attribute Meta Object
470 Class::MOP::Attribute->new(
472 accessor => 'foo', # dual purpose get/set accessor
473 predicate => 'has_foo', # predicate check for defined-ness
474 init_arg => '-foo', # class->new will look for a -foo key
475 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
479 Class::MOP::Attribute->new(
481 reader => 'bar', # getter
482 writer => 'set_bar', # setter
483 predicate => 'has_bar', # predicate check for defined-ness
484 init_arg => ':bar', # class->new will look for a :bar key
485 # no default value means it is undef
491 The Attribute Protocol is almost entirely an invention of
492 C<Class::MOP>. Perl 5 does not have a consistent notion of
493 attributes. There are so many ways in which this is done, and very few
494 (if any) are easily discoverable by this module.
496 With that said, this module attempts to inject some order into this
497 chaos, by introducing a consistent API which can be used to create
506 =item B<< Class::MOP::Attribute->new($name, ?%options) >>
508 An attribute must (at the very least), have a C<$name>. All other
509 C<%options> are added as key-value pairs.
515 This is a string value representing the expected key in an
516 initialization hash. For instance, if we have an C<init_arg> value of
517 C<-foo>, then the following code will Just Work.
519 MyClass->meta->new_object( -foo => 'Hello There' );
521 If an init_arg is not assigned, it will automatically use the
522 attribute's name. If C<init_arg> is explicitly set to C<undef>, the
523 attribute cannot be specified during initialization.
527 This provides the name of a method that will be called to initialize
528 the attribute. This method will be called on the object after it is
529 constructed. It is expected to return a valid value for the attribute.
533 This can be used to provide an explicit default for initializing the
534 attribute. If the default you provide is a subroutine reference, then
535 this reference will be called I<as a method> on the object.
537 If the value is a simple scalar (string or number), then it can be
538 just passed as is. However, if you wish to initialize it with a HASH
539 or ARRAY ref, then you need to wrap that inside a subroutine
542 Class::MOP::Attribute->new(
544 default => sub { [] },
550 Class::MOP::Attribute->new(
552 default => sub { {} },
556 If you wish to initialize an attribute with a subroutine reference
557 itself, then you need to wrap that in a subroutine as well:
559 Class::MOP::Attribute->new(
562 sub { print "Hello World" }
567 And lastly, if the value of your attribute is dependent upon some
568 other aspect of the instance structure, then you can take advantage of
569 the fact that when the C<default> value is called as a method:
571 Class::MOP::Attribute->new(
572 'object_identity' => (
573 default => sub { Scalar::Util::refaddr( $_[0] ) },
577 Note that there is no guarantee that attributes are initialized in any
578 particular order, so you cannot rely on the value of some other
579 attribute when generating the default.
583 This option can be either a method name or a subroutine
584 reference. This method will be called when setting the attribute's
585 value in the constructor. Unlike C<default> and C<builder>, the
586 initializer is only called when a value is provided to the
587 constructor. The initializer allows you to munge this value during
590 The initializer is called as a method with three arguments. The first
591 is the value that was passed to the constructor. The second is a
592 subroutine reference that can be called to actually set the
593 attribute's value, and the last is the associated
594 C<Class::MOP::Attribute> object.
596 This contrived example shows an initializer that sets the attribute to
597 twice the given value.
599 Class::MOP::Attribute->new(
602 my ( $instance, $value, $set ) = @_;
603 $set->( $value * 2 );
608 Since an initializer can be a method name, you can easily make
609 attribute initialization use the writer:
611 Class::MOP::Attribute->new(
613 writer => 'some_attr',
614 initializer => 'some_attr',
618 Your writer will need to examine C<@_> and determine under which
619 context it is being called.
623 The C<accessor>, C<reader>, C<writer>, C<predicate> and C<clearer>
624 options all accept the same parameters. You can provide the name of
625 the method, in which case an appropriate default method will be
626 generated for you. Or instead you can also provide hash reference
627 containing exactly one key (the method name) and one value. The value
628 should be a subroutine reference, which will be installed as the
635 An C<accessor> is a standard Perl-style read/write accessor. It will
636 return the value of the attribute, and if a value is passed as an
637 argument, it will assign that value to the attribute.
639 Note that C<undef> is a legitimate value, so this will work:
641 $object->set_something(undef);
645 This is a basic read-only accessor. It returns the value of the
650 This is a basic write accessor, it accepts a single argument, and
651 assigns that value to the attribute.
653 Note that C<undef> is a legitimate value, so this will work:
655 $object->set_something(undef);
659 The predicate method returns a boolean indicating whether or not the
660 attribute has been explicitly set.
662 Note that the predicate returns true even if the attribute was set to
663 a false value (C<0> or C<undef>).
667 This method will uninitialize the attribute. After an attribute is
668 cleared, its C<predicate> will return false.
670 =item * definition_context
672 Mostly, this exists as a hook for the benefit of Moose.
674 This option should be a hash reference containing several keys which
675 will be used when inlining the attribute's accessors. The keys should
676 include C<line>, the line number where the attribute was created, and
677 either C<file> or C<description>.
679 This information will ultimately be used when eval'ing inlined
680 accessor code so that error messages report a useful line and file
685 =item B<< $attr->clone(%options) >>
687 This clones the attribute. Any options you provide will override the
688 settings of the original attribute. You can change the name of the new
689 attribute by passing a C<name> key in C<%options>.
695 These are all basic read-only accessors for the values passed into
700 =item B<< $attr->name >>
702 Returns the attribute's name.
704 =item B<< $attr->accessor >>
706 =item B<< $attr->reader >>
708 =item B<< $attr->writer >>
710 =item B<< $attr->predicate >>
712 =item B<< $attr->clearer >>
714 The C<accessor>, C<reader>, C<writer>, C<predicate>, and C<clearer>
715 methods all return exactly what was passed to the constructor, so it
716 can be either a string containing a method name, or a hash reference.
718 =item B<< $attr->initializer >>
720 Returns the initializer as passed to the constructor, so this may be
721 either a method name or a subroutine reference.
723 =item B<< $attr->init_arg >>
725 =item B<< $attr->is_default_a_coderef >>
727 =item B<< $attr->default($instance) >>
729 The C<$instance> argument is optional. If you don't pass it, the
730 return value for this method is exactly what was passed to the
731 constructor, either a simple scalar or a subroutine reference.
733 If you I<do> pass an C<$instance> and the default is a subroutine
734 reference, then the reference is called as a method on the
735 C<$instance> and the generated value is returned.
737 =item B<< $attr->slots >>
739 Return a list of slots required by the attribute. This is usually just
740 one, the name of the attribute.
742 A slot is the name of the hash key used to store the attribute in an
745 =item B<< $attr->get_read_method >>
747 =item B<< $attr->get_write_method >>
749 Returns the name of a method suitable for reading or writing the value
750 of the attribute in the associated class.
752 If an attribute is read- or write-only, then these methods can return
753 C<undef> as appropriate.
755 =item B<< $attr->has_read_method >>
757 =item B<< $attr->has_write_method >>
759 This returns a boolean indicating whether the attribute has a I<named>
760 read or write method.
762 =item B<< $attr->get_read_method_ref >>
764 =item B<< $attr->get_write_method_ref >>
766 Returns the subroutine reference of a method suitable for reading or
767 writing the attribute's value in the associated class. These methods
768 always return a subroutine reference, regardless of whether or not the
769 attribute is read- or write-only.
771 =item B<< $attr->insertion_order >>
773 If this attribute has been inserted into a class, this returns a zero
774 based index regarding the order of insertion.
778 =head2 Informational predicates
780 These are all basic predicate methods for the values passed into C<new>.
784 =item B<< $attr->has_accessor >>
786 =item B<< $attr->has_reader >>
788 =item B<< $attr->has_writer >>
790 =item B<< $attr->has_predicate >>
792 =item B<< $attr->has_clearer >>
794 =item B<< $attr->has_initializer >>
796 =item B<< $attr->has_init_arg >>
798 This will be I<false> if the C<init_arg> was set to C<undef>.
800 =item B<< $attr->has_default >>
802 This will be I<false> if the C<default> was set to C<undef>, since
803 C<undef> is the default C<default> anyway.
805 =item B<< $attr->has_builder >>
807 =item B<< $attr->has_insertion_order >>
809 This will be I<false> if this attribute has not be inserted into a class
813 =head2 Value management
815 These methods are basically "back doors" to the instance, and can be
816 used to bypass the regular accessors, but still stay within the MOP.
818 These methods are not for general use, and should only be used if you
819 really know what you are doing.
823 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
825 This method is used internally to initialize the attribute's slot in
826 the object C<$instance>.
828 The C<$params> is a hash reference of the values passed to the object
831 It's unlikely that you'll need to call this method yourself.
833 =item B<< $attr->set_value($instance, $value) >>
835 Sets the value without going through the accessor. Note that this
836 works even with read-only attributes.
838 =item B<< $attr->set_initial_value($instance, $value) >>
840 Sets the value without going through the accessor. This method is only
841 called when the instance is first being initialized.
843 =item B<< $attr->get_value($instance) >>
845 Returns the value without going through the accessor. Note that this
846 works even with write-only accessors.
848 =item B<< $attr->has_value($instance) >>
850 Return a boolean indicating whether the attribute has been set in
851 C<$instance>. This how the default C<predicate> method works.
853 =item B<< $attr->clear_value($instance) >>
855 This will clear the attribute's value in C<$instance>. This is what
856 the default C<clearer> calls.
858 Note that this works even if the attribute does not have any
859 associated read, write or clear methods.
863 =head2 Class association
865 These methods allow you to manage the attributes association with
866 the class that contains it. These methods should not be used
867 lightly, nor are they very magical, they are mostly used internally
868 and by metaclass instances.
872 =item B<< $attr->associated_class >>
874 This returns the C<Class::MOP::Class> with which this attribute is
877 =item B<< $attr->attach_to_class($metaclass) >>
879 This method stores a weakened reference to the C<$metaclass> object
882 This method does not remove the attribute from its old class,
883 nor does it create any accessors in the new class.
885 It is probably best to use the L<Class::MOP::Class> C<add_attribute>
888 =item B<< $attr->detach_from_class >>
890 This method removes the associate metaclass object from the attribute
893 This method does not remove the attribute itself from the class, or
894 remove its accessors.
896 It is probably best to use the L<Class::MOP::Class>
897 C<remove_attribute> method instead.
901 =head2 Attribute Accessor generation
905 =item B<< $attr->accessor_metaclass >>
907 Accessor methods are generated using an accessor metaclass. By
908 default, this is L<Class::MOP::Method::Accessor>. This method returns
909 the name of the accessor metaclass that this attribute uses.
911 =item B<< $attr->associate_method($method) >>
913 This associates a L<Class::MOP::Method> object with the
914 attribute. Typically, this is called internally when an attribute
915 generates its accessors.
917 =item B<< $attr->associated_methods >>
919 This returns the list of methods which have been associated with the
922 =item B<< $attr->install_accessors >>
924 This method generates and installs code the attributes various
925 accessors. It is typically called from the L<Class::MOP::Class>
926 C<add_attribute> method.
928 =item B<< $attr->remove_accessors >>
930 This method removes all of the accessors associated with the
933 This does not currently remove methods from the list returned by
934 C<associated_methods>.
942 =item B<< Class::MOP::Attribute->meta >>
944 This will return a L<Class::MOP::Class> instance for this class.
946 It should also be noted that L<Class::MOP> will actually bootstrap
947 this module by installing a number of attribute meta-objects into its
954 Stevan Little E<lt>stevan@iinteractive.comE<gt>
956 =head1 COPYRIGHT AND LICENSE
958 Copyright 2006-2009 by Infinity Interactive, Inc.
960 L<http://www.iinteractive.com>
962 This library is free software; you can redistribute it and/or modify
963 it under the same terms as Perl itself.