2 package Class::MOP::Attribute;
7 use Class::MOP::Method::Accessor;
8 use Class::MOP::Method::Reader;
9 use Class::MOP::Method::Writer;
12 use Scalar::Util 'blessed', 'weaken';
14 our $VERSION = '0.94';
15 $VERSION = eval $VERSION;
16 our $AUTHORITY = 'cpan:STEVAN';
18 use base 'Class::MOP::Object';
20 # NOTE: (meta-circularity)
21 # This method will be replaced in the
22 # boostrap section of Class::MOP, by
23 # a new version which uses the
24 # &Class::MOP::Class::construct_instance
25 # method to build an attribute meta-object
26 # which itself is described with attribute
28 # - Ain't meta-circularity grand? :)
30 my ( $class, @args ) = @_;
32 unshift @args, "name" if @args % 2 == 1;
35 my $name = $options{name};
38 || confess "You must provide a name for the attribute";
40 $options{init_arg} = $name
41 if not exists $options{init_arg};
42 if(exists $options{builder}){
43 confess("builder must be a defined scalar value which is a method name")
44 if ref $options{builder} || !(defined $options{builder});
45 confess("Setting both default and builder is not allowed.")
46 if exists $options{default};
48 (is_default_a_coderef(\%options))
49 || confess("References are not allowed as default values, you must ".
50 "wrap the default of '$name' in a CODE reference (ex: sub { [] } and not [])")
51 if exists $options{default} && ref $options{default};
53 if( $options{required} and not( defined($options{builder}) || defined($options{init_arg}) || exists $options{default} ) ) {
54 confess("A required attribute must have either 'init_arg', 'builder', or 'default'");
57 $class->_new(\%options);
63 return Class::MOP::Class->initialize($class)->new_object(@_)
64 if $class ne __PACKAGE__;
66 my $options = @_ == 1 ? $_[0] : {@_};
69 'name' => $options->{name},
70 'accessor' => $options->{accessor},
71 'reader' => $options->{reader},
72 'writer' => $options->{writer},
73 'predicate' => $options->{predicate},
74 'clearer' => $options->{clearer},
75 'builder' => $options->{builder},
76 'init_arg' => $options->{init_arg},
77 'default' => $options->{default},
78 'initializer' => $options->{initializer},
79 'definition_context' => $options->{definition_context},
80 'lazy' => $options->{lazy},
81 # keep a weakened link to the
82 # class we are associated with
83 'associated_class' => undef,
84 # and a list of the methods
85 # associated with this attr
86 'associated_methods' => [],
87 # this let's us keep track of
88 # our order inside the associated
90 'insertion_order' => undef,
95 # this is a primative (and kludgy) clone operation
96 # for now, it will be replaced in the Class::MOP
97 # bootstrap with a proper one, however we know
98 # that this one will work fine for now.
103 || confess "Can only clone an instance";
104 return bless { %{$self}, %options } => ref($self);
108 my ( $self, $instance ) = @_;
110 my $builder = $self->builder();
112 return $instance->$builder()
113 if $instance->can( $self->builder );
115 $self->throw_error( blessed($instance)
116 . " does not support builder method '"
118 . "' for attribute '"
125 sub initialize_instance_slot {
126 my ($self, $meta_instance, $instance, $params) = @_;
127 my $init_arg = $self->{'init_arg'};
129 my ($val, $value_is_set);
130 # try to fetch the init arg from the %params ...
132 # if nothing was in the %params, we can use the
133 # attribute's default value (if it has one)
134 if(defined $init_arg and exists $params->{$init_arg}){
135 $val = $params->{$init_arg};
138 return if $self->is_lazy;
140 if($self->has_default){
141 $val = $self->default($instance);
143 } elsif($self->has_builder){
144 $val = $self->_call_builder($instance);
149 return unless $value_is_set;
151 $self->_set_initial_slot_value(
159 sub _set_initial_slot_value {
160 my ($self, $meta_instance, $instance, $value) = @_;
162 my $slot_name = $self->name;
164 return $meta_instance->set_slot_value($instance, $slot_name, $value)
165 unless $self->has_initializer;
168 $meta_instance->set_slot_value($instance, $slot_name, $_[0]);
171 my $initializer = $self->initializer;
173 # most things will just want to set a value, so make it first arg
174 $instance->$initializer($value, $callback, $self);
178 # the next bunch of methods will get bootstrapped
179 # away in the Class::MOP bootstrapping section
181 sub associated_class { $_[0]->{'associated_class'} }
182 sub associated_methods { $_[0]->{'associated_methods'} }
184 sub has_accessor { defined($_[0]->{'accessor'}) }
185 sub has_reader { defined($_[0]->{'reader'}) }
186 sub has_writer { defined($_[0]->{'writer'}) }
187 sub has_predicate { defined($_[0]->{'predicate'}) }
188 sub has_clearer { defined($_[0]->{'clearer'}) }
189 sub has_builder { defined($_[0]->{'builder'}) }
190 sub has_init_arg { defined($_[0]->{'init_arg'}) }
191 sub has_default { defined($_[0]->{'default'}) }
192 sub has_initializer { defined($_[0]->{'initializer'}) }
193 sub has_insertion_order { defined($_[0]->{'insertion_order'}) }
195 sub accessor { $_[0]->{'accessor'} }
196 sub reader { $_[0]->{'reader'} }
197 sub writer { $_[0]->{'writer'} }
198 sub predicate { $_[0]->{'predicate'} }
199 sub clearer { $_[0]->{'clearer'} }
200 sub builder { $_[0]->{'builder'} }
201 sub init_arg { $_[0]->{'init_arg'} }
202 sub initializer { $_[0]->{'initializer'} }
203 sub definition_context { $_[0]->{'definition_context'} }
204 sub insertion_order { $_[0]->{'insertion_order'} }
205 sub _set_insertion_order { $_[0]->{'insertion_order'} = $_[1] }
206 sub is_lazy { $_[0]->{'lazy'} }
208 # end bootstrapped away method section.
209 # (all methods below here are kept intact)
211 sub has_read_method { $_[0]->has_reader || $_[0]->has_accessor }
212 sub has_write_method { $_[0]->has_writer || $_[0]->has_accessor }
214 sub get_read_method {
216 my $reader = $self->reader || $self->accessor;
218 return $reader unless ref $reader;
220 my ($name) = %$reader;
224 sub get_write_method {
226 my $writer = $self->writer || $self->accessor;
228 return $writer unless ref $writer;
230 my ($name) = %$writer;
234 sub get_read_method_ref {
236 if ((my $reader = $self->get_read_method) && $self->associated_class) {
237 return $self->associated_class->get_method($reader);
240 my $code = sub { $self->get_value(@_) };
241 if (my $class = $self->associated_class) {
242 return $class->method_metaclass->wrap(
244 package_name => $class->name,
254 sub get_write_method_ref {
256 if ((my $writer = $self->get_write_method) && $self->associated_class) {
257 return $self->associated_class->get_method($writer);
260 my $code = sub { $self->set_value(@_) };
261 if (my $class = $self->associated_class) {
262 return $class->method_metaclass->wrap(
264 package_name => $class->name,
274 sub is_default_a_coderef {
275 my ($value) = $_[0]->{'default'};
276 return unless ref($value);
277 return ref($value) eq 'CODE' || (blessed($value) && $value->isa('Class::MOP::Method'));
281 my ($self, $instance) = @_;
282 if (defined $instance && $self->is_default_a_coderef) {
283 # if the default is a CODE ref, then
284 # we pass in the instance and default
285 # can return a value based on that
286 # instance. Somewhat crude, but works.
287 return $self->{'default'}->($instance);
294 sub slots { (shift)->name }
298 sub attach_to_class {
299 my ($self, $class) = @_;
300 (blessed($class) && $class->isa('Class::MOP::Class'))
301 || confess "You must pass a Class::MOP::Class instance (or a subclass)";
302 weaken($self->{'associated_class'} = $class);
305 sub detach_from_class {
307 $self->{'associated_class'} = undef;
312 sub associate_method {
313 my ($self, $method) = @_;
314 push @{$self->{'associated_methods'}} => $method;
319 sub set_initial_value {
320 my ($self, $instance, $value) = @_;
321 $self->_set_initial_slot_value(
322 Class::MOP::Class->initialize(ref($instance))->get_meta_instance,
328 sub set_value { shift->set_raw_value(@_) }
329 sub get_value { shift->get_raw_value(@_) }
332 my ($self, $instance, $value) = @_;
334 Class::MOP::Class->initialize(ref($instance))
336 ->set_slot_value($instance, $self->name, $value);
340 my ($self, $instance) = @_;
342 if($self->is_lazy && !$self->has_value($instance)){
345 if($self->has_default){
346 $val = $self->default($instance);
347 } elsif($self->has_builder){
348 $val = $self->_call_builder($instance);
351 $self->set_initial_value(
357 Class::MOP::Class->initialize(ref($instance))
359 ->get_slot_value($instance, $self->name);
363 my ($self, $instance) = @_;
365 Class::MOP::Class->initialize(ref($instance))
367 ->is_slot_initialized($instance, $self->name);
371 my ($self, $instance) = @_;
373 Class::MOP::Class->initialize(ref($instance))
375 ->deinitialize_slot($instance, $self->name);
380 sub accessor_metaclass { 'Class::MOP::Method::Accessor' }
381 sub method_metaclasses {
383 reader => 'Class::MOP::Method::Reader',
384 writer => 'Class::MOP::Method::Writer',
388 sub _process_accessors {
389 my ($self, $type, $accessor, $generate_as_inline_methods) = @_;
393 if ( my $ctx = $self->definition_context ) {
394 $method_ctx = { %$ctx };
397 if (ref($accessor)) {
398 (ref($accessor) eq 'HASH')
399 || confess "bad accessor/reader/writer/predicate/clearer format, must be a HASH ref";
400 my ($name, $method) = %{$accessor};
401 $method = $self->accessor_metaclass->wrap(
403 package_name => $self->associated_class->name,
405 definition_context => $method_ctx,
407 $self->associate_method($method);
408 return ($name, $method);
411 my $inline_me = ($generate_as_inline_methods && $self->associated_class->instance_metaclass->is_inlinable);
415 my $desc = "accessor $accessor";
416 if ( $accessor ne $self->name ) {
417 $desc .= " of attribute " . $self->name;
420 $method_ctx->{description} = $desc;
423 my $method_metaclass = $self->method_metaclasses->{$type} || $self->accessor_metaclass;
425 $method = $method_metaclass->new(
427 is_inline => $inline_me,
428 accessor_type => $type,
429 package_name => $self->associated_class->name,
431 definition_context => $method_ctx,
434 confess "Could not create the '$type' method for " . $self->name . " because : $@" if $@;
435 $self->associate_method($method);
436 return ($accessor, $method);
440 sub install_accessors {
443 my $class = $self->associated_class;
446 $self->_process_accessors('accessor' => $self->accessor(), $inline)
447 ) if $self->has_accessor();
450 $self->_process_accessors('reader' => $self->reader(), $inline)
451 ) if $self->has_reader();
454 $self->_process_accessors('writer' => $self->writer(), $inline)
455 ) if $self->has_writer();
458 $self->_process_accessors('predicate' => $self->predicate(), $inline)
459 ) if $self->has_predicate();
462 $self->_process_accessors('clearer' => $self->clearer(), $inline)
463 ) if $self->has_clearer();
469 my $_remove_accessor = sub {
470 my ($accessor, $class) = @_;
471 if (ref($accessor) && ref($accessor) eq 'HASH') {
472 ($accessor) = keys %{$accessor};
474 my $method = $class->get_method($accessor);
475 $class->remove_method($accessor)
476 if (ref($method) && $method->isa('Class::MOP::Method::Attribute'));
479 sub remove_accessors {
482 # we really need to make sure to remove from the
483 # associates methods here as well. But this is
484 # such a slimly used method, I am not worried
485 # about it right now.
486 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
487 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
488 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
489 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
490 $_remove_accessor->($self->clearer(), $self->associated_class()) if $self->has_clearer();
504 Class::MOP::Attribute - Attribute Meta Object
508 Class::MOP::Attribute->new(
510 accessor => 'foo', # dual purpose get/set accessor
511 predicate => 'has_foo', # predicate check for defined-ness
512 init_arg => '-foo', # class->new will look for a -foo key
513 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
517 Class::MOP::Attribute->new(
519 reader => 'bar', # getter
520 writer => 'set_bar', # setter
521 predicate => 'has_bar', # predicate check for defined-ness
522 init_arg => ':bar', # class->new will look for a :bar key
523 # no default value means it is undef
529 The Attribute Protocol is almost entirely an invention of
530 C<Class::MOP>. Perl 5 does not have a consistent notion of
531 attributes. There are so many ways in which this is done, and very few
532 (if any) are easily discoverable by this module.
534 With that said, this module attempts to inject some order into this
535 chaos, by introducing a consistent API which can be used to create
544 =item B<< Class::MOP::Attribute->new($name, ?%options) >>
546 An attribute must (at the very least), have a C<$name>. All other
547 C<%options> are added as key-value pairs.
553 This is a string value representing the expected key in an
554 initialization hash. For instance, if we have an C<init_arg> value of
555 C<-foo>, then the following code will Just Work.
557 MyClass->meta->new_object( -foo => 'Hello There' );
559 If an init_arg is not assigned, it will automatically use the
560 attribute's name. If C<init_arg> is explicitly set to C<undef>, the
561 attribute cannot be specified during initialization.
565 This provides the name of a method that will be called to initialize
566 the attribute. This method will be called on the object after it is
567 constructed. It is expected to return a valid value for the attribute.
571 This can be used to provide an explicit default for initializing the
572 attribute. If the default you provide is a subroutine reference, then
573 this reference will be called I<as a method> on the object.
575 If the value is a simple scalar (string or number), then it can be
576 just passed as is. However, if you wish to initialize it with a HASH
577 or ARRAY ref, then you need to wrap that inside a subroutine
580 Class::MOP::Attribute->new(
582 default => sub { [] },
588 Class::MOP::Attribute->new(
590 default => sub { {} },
594 If you wish to initialize an attribute with a subroutine reference
595 itself, then you need to wrap that in a subroutine as well:
597 Class::MOP::Attribute->new(
600 sub { print "Hello World" }
605 And lastly, if the value of your attribute is dependent upon some
606 other aspect of the instance structure, then you can take advantage of
607 the fact that when the C<default> value is called as a method:
609 Class::MOP::Attribute->new(
610 'object_identity' => (
611 default => sub { Scalar::Util::refaddr( $_[0] ) },
615 Note that there is no guarantee that attributes are initialized in any
616 particular order, so you cannot rely on the value of some other
617 attribute when generating the default.
621 This option can be either a method name or a subroutine
622 reference. This method will be called when setting the attribute's
623 value in the constructor. Unlike C<default> and C<builder>, the
624 initializer is only called when a value is provided to the
625 constructor. The initializer allows you to munge this value during
628 The initializer is called as a method with three arguments. The first
629 is the value that was passed to the constructor. The second is a
630 subroutine reference that can be called to actually set the
631 attribute's value, and the last is the associated
632 C<Class::MOP::Attribute> object.
634 This contrived example shows an initializer that sets the attribute to
635 twice the given value.
637 Class::MOP::Attribute->new(
640 my ( $self, $value, $set, $attr ) = @_;
641 $set->( $value * 2 );
646 Since an initializer can be a method name, you can easily make
647 attribute initialization use the writer:
649 Class::MOP::Attribute->new(
651 writer => 'some_attr',
652 initializer => 'some_attr',
656 Your writer will need to examine C<@_> and determine under which
657 context it is being called.
661 The C<accessor>, C<reader>, C<writer>, C<predicate> and C<clearer>
662 options all accept the same parameters. You can provide the name of
663 the method, in which case an appropriate default method will be
664 generated for you. Or instead you can also provide hash reference
665 containing exactly one key (the method name) and one value. The value
666 should be a subroutine reference, which will be installed as the
673 An C<accessor> is a standard Perl-style read/write accessor. It will
674 return the value of the attribute, and if a value is passed as an
675 argument, it will assign that value to the attribute.
677 Note that C<undef> is a legitimate value, so this will work:
679 $object->set_something(undef);
683 This is a basic read-only accessor. It returns the value of the
688 This is a basic write accessor, it accepts a single argument, and
689 assigns that value to the attribute.
691 Note that C<undef> is a legitimate value, so this will work:
693 $object->set_something(undef);
697 The predicate method returns a boolean indicating whether or not the
698 attribute has been explicitly set.
700 Note that the predicate returns true even if the attribute was set to
701 a false value (C<0> or C<undef>).
705 This method will uninitialize the attribute. After an attribute is
706 cleared, its C<predicate> will return false.
708 =item * definition_context
710 Mostly, this exists as a hook for the benefit of Moose.
712 This option should be a hash reference containing several keys which
713 will be used when inlining the attribute's accessors. The keys should
714 include C<line>, the line number where the attribute was created, and
715 either C<file> or C<description>.
717 This information will ultimately be used when eval'ing inlined
718 accessor code so that error messages report a useful line and file
723 =item B<< $attr->clone(%options) >>
725 This clones the attribute. Any options you provide will override the
726 settings of the original attribute. You can change the name of the new
727 attribute by passing a C<name> key in C<%options>.
733 These are all basic read-only accessors for the values passed into
738 =item B<< $attr->name >>
740 Returns the attribute's name.
742 =item B<< $attr->accessor >>
744 =item B<< $attr->reader >>
746 =item B<< $attr->writer >>
748 =item B<< $attr->predicate >>
750 =item B<< $attr->clearer >>
752 The C<accessor>, C<reader>, C<writer>, C<predicate>, and C<clearer>
753 methods all return exactly what was passed to the constructor, so it
754 can be either a string containing a method name, or a hash reference.
756 =item B<< $attr->initializer >>
758 Returns the initializer as passed to the constructor, so this may be
759 either a method name or a subroutine reference.
761 =item B<< $attr->init_arg >>
763 =item B<< $attr->is_default_a_coderef >>
765 =item B<< $attr->default($instance) >>
767 The C<$instance> argument is optional. If you don't pass it, the
768 return value for this method is exactly what was passed to the
769 constructor, either a simple scalar or a subroutine reference.
771 If you I<do> pass an C<$instance> and the default is a subroutine
772 reference, then the reference is called as a method on the
773 C<$instance> and the generated value is returned.
775 =item B<< $attr->slots >>
777 Return a list of slots required by the attribute. This is usually just
778 one, the name of the attribute.
780 A slot is the name of the hash key used to store the attribute in an
783 =item B<< $attr->get_read_method >>
785 =item B<< $attr->get_write_method >>
787 Returns the name of a method suitable for reading or writing the value
788 of the attribute in the associated class.
790 If an attribute is read- or write-only, then these methods can return
791 C<undef> as appropriate.
793 =item B<< $attr->has_read_method >>
795 =item B<< $attr->has_write_method >>
797 This returns a boolean indicating whether the attribute has a I<named>
798 read or write method.
800 =item B<< $attr->get_read_method_ref >>
802 =item B<< $attr->get_write_method_ref >>
804 Returns the subroutine reference of a method suitable for reading or
805 writing the attribute's value in the associated class. These methods
806 always return a subroutine reference, regardless of whether or not the
807 attribute is read- or write-only.
809 =item B<< $attr->insertion_order >>
811 If this attribute has been inserted into a class, this returns a zero
812 based index regarding the order of insertion.
816 =head2 Informational predicates
818 These are all basic predicate methods for the values passed into C<new>.
822 =item B<< $attr->has_accessor >>
824 =item B<< $attr->has_reader >>
826 =item B<< $attr->has_writer >>
828 =item B<< $attr->has_predicate >>
830 =item B<< $attr->has_clearer >>
832 =item B<< $attr->has_initializer >>
834 =item B<< $attr->has_init_arg >>
836 This will be I<false> if the C<init_arg> was set to C<undef>.
838 =item B<< $attr->has_default >>
840 This will be I<false> if the C<default> was set to C<undef>, since
841 C<undef> is the default C<default> anyway.
843 =item B<< $attr->has_builder >>
845 =item B<< $attr->has_insertion_order >>
847 This will be I<false> if this attribute has not be inserted into a class
851 =head2 Value management
853 These methods are basically "back doors" to the instance, and can be
854 used to bypass the regular accessors, but still stay within the MOP.
856 These methods are not for general use, and should only be used if you
857 really know what you are doing.
861 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
863 This method is used internally to initialize the attribute's slot in
864 the object C<$instance>.
866 The C<$params> is a hash reference of the values passed to the object
869 It's unlikely that you'll need to call this method yourself.
871 =item B<< $attr->set_value($instance, $value) >>
873 Sets the value without going through the accessor. Note that this
874 works even with read-only attributes.
876 =item B<< $attr->set_raw_value($instance, $value) >>
878 Sets the value with no side effects such as a trigger.
880 This doesn't actually apply to Class::MOP attributes, only to subclasses.
882 =item B<< $attr->set_initial_value($instance, $value) >>
884 Sets the value without going through the accessor. This method is only
885 called when the instance is first being initialized.
887 =item B<< $attr->get_value($instance) >>
889 Returns the value without going through the accessor. Note that this
890 works even with write-only accessors.
892 =item B<< $sttr->get_raw_value($instance) >>
894 Returns the value without any side effects such as lazy attributes.
896 Doesn't actually apply to Class::MOP attributes, only to subclasses.
898 =item B<< $attr->has_value($instance) >>
900 Return a boolean indicating whether the attribute has been set in
901 C<$instance>. This how the default C<predicate> method works.
903 =item B<< $attr->clear_value($instance) >>
905 This will clear the attribute's value in C<$instance>. This is what
906 the default C<clearer> calls.
908 Note that this works even if the attribute does not have any
909 associated read, write or clear methods.
913 =head2 Class association
915 These methods allow you to manage the attributes association with
916 the class that contains it. These methods should not be used
917 lightly, nor are they very magical, they are mostly used internally
918 and by metaclass instances.
922 =item B<< $attr->associated_class >>
924 This returns the C<Class::MOP::Class> with which this attribute is
927 =item B<< $attr->attach_to_class($metaclass) >>
929 This method stores a weakened reference to the C<$metaclass> object
932 This method does not remove the attribute from its old class,
933 nor does it create any accessors in the new class.
935 It is probably best to use the L<Class::MOP::Class> C<add_attribute>
938 =item B<< $attr->detach_from_class >>
940 This method removes the associate metaclass object from the attribute
943 This method does not remove the attribute itself from the class, or
944 remove its accessors.
946 It is probably best to use the L<Class::MOP::Class>
947 C<remove_attribute> method instead.
951 =head2 Attribute Accessor generation
955 =item B<< $attr->accessor_metaclass >>
957 Accessor methods are generated using an accessor metaclass. By
958 default, this is L<Class::MOP::Method::Accessor>. This method returns
959 the name of the accessor metaclass that this attribute uses.
961 =item B<< $attr->associate_method($method) >>
963 This associates a L<Class::MOP::Method> object with the
964 attribute. Typically, this is called internally when an attribute
965 generates its accessors.
967 =item B<< $attr->associated_methods >>
969 This returns the list of methods which have been associated with the
972 =item B<< $attr->install_accessors >>
974 This method generates and installs code the attributes various
975 accessors. It is typically called from the L<Class::MOP::Class>
976 C<add_attribute> method.
978 =item B<< $attr->remove_accessors >>
980 This method removes all of the accessors associated with the
983 This does not currently remove methods from the list returned by
984 C<associated_methods>.
992 =item B<< Class::MOP::Attribute->meta >>
994 This will return a L<Class::MOP::Class> instance for this class.
996 It should also be noted that L<Class::MOP> will actually bootstrap
997 this module by installing a number of attribute meta-objects into its
1004 Stevan Little E<lt>stevan@iinteractive.comE<gt>
1006 =head1 COPYRIGHT AND LICENSE
1008 Copyright 2006-2009 by Infinity Interactive, Inc.
1010 L<http://www.iinteractive.com>
1012 This library is free software; you can redistribute it and/or modify
1013 it under the same terms as Perl itself.