2 package Class::MOP::Attribute;
7 use Class::MOP::Method::Accessor;
10 use Scalar::Util 'blessed', 'weaken';
12 our $VERSION = '0.92';
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, $self->name);
342 sub accessor_metaclass { 'Class::MOP::Method::Accessor' }
344 sub _process_accessors {
345 my ($self, $type, $accessor, $generate_as_inline_methods) = @_;
349 if ( my $ctx = $self->definition_context ) {
350 $method_ctx = { %$ctx };
353 if (ref($accessor)) {
354 (ref($accessor) eq 'HASH')
355 || confess "bad accessor/reader/writer/predicate/clearer format, must be a HASH ref";
356 my ($name, $method) = %{$accessor};
357 $method = $self->accessor_metaclass->wrap(
359 package_name => $self->associated_class->name,
361 definition_context => $method_ctx,
363 $self->associate_method($method);
364 return ($name, $method);
367 my $inline_me = ($generate_as_inline_methods && $self->associated_class->instance_metaclass->is_inlinable);
371 my $desc = "accessor $accessor";
372 if ( $accessor ne $self->name ) {
373 $desc .= " of attribute " . $self->name;
376 $method_ctx->{description} = $desc;
379 $method = $self->accessor_metaclass->new(
381 is_inline => $inline_me,
382 accessor_type => $type,
383 package_name => $self->associated_class->name,
385 definition_context => $method_ctx,
388 confess "Could not create the '$type' method for " . $self->name . " because : $@" if $@;
389 $self->associate_method($method);
390 return ($accessor, $method);
394 sub install_accessors {
397 my $class = $self->associated_class;
400 $self->_process_accessors('accessor' => $self->accessor(), $inline)
401 ) if $self->has_accessor();
404 $self->_process_accessors('reader' => $self->reader(), $inline)
405 ) if $self->has_reader();
408 $self->_process_accessors('writer' => $self->writer(), $inline)
409 ) if $self->has_writer();
412 $self->_process_accessors('predicate' => $self->predicate(), $inline)
413 ) if $self->has_predicate();
416 $self->_process_accessors('clearer' => $self->clearer(), $inline)
417 ) if $self->has_clearer();
423 my $_remove_accessor = sub {
424 my ($accessor, $class) = @_;
425 if (ref($accessor) && ref($accessor) eq 'HASH') {
426 ($accessor) = keys %{$accessor};
428 my $method = $class->get_method($accessor);
429 $class->remove_method($accessor)
430 if (ref($method) && $method->isa('Class::MOP::Method::Accessor'));
433 sub remove_accessors {
436 # we really need to make sure to remove from the
437 # associates methods here as well. But this is
438 # such a slimly used method, I am not worried
439 # about it right now.
440 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
441 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
442 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
443 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
444 $_remove_accessor->($self->clearer(), $self->associated_class()) if $self->has_clearer();
458 Class::MOP::Attribute - Attribute Meta Object
462 Class::MOP::Attribute->new(
464 accessor => 'foo', # dual purpose get/set accessor
465 predicate => 'has_foo', # predicate check for defined-ness
466 init_arg => '-foo', # class->new will look for a -foo key
467 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
471 Class::MOP::Attribute->new(
473 reader => 'bar', # getter
474 writer => 'set_bar', # setter
475 predicate => 'has_bar', # predicate check for defined-ness
476 init_arg => ':bar', # class->new will look for a :bar key
477 # no default value means it is undef
483 The Attribute Protocol is almost entirely an invention of
484 C<Class::MOP>. Perl 5 does not have a consistent notion of
485 attributes. There are so many ways in which this is done, and very few
486 (if any) are easily discoverable by this module.
488 With that said, this module attempts to inject some order into this
489 chaos, by introducing a consistent API which can be used to create
498 =item B<< Class::MOP::Attribute->new($name, ?%options) >>
500 An attribute must (at the very least), have a C<$name>. All other
501 C<%options> are added as key-value pairs.
507 This is a string value representing the expected key in an
508 initialization hash. For instance, if we have an C<init_arg> value of
509 C<-foo>, then the following code will Just Work.
511 MyClass->meta->new_object( -foo => 'Hello There' );
513 If an init_arg is not assigned, it will automatically use the
514 attribute's name. If C<init_arg> is explicitly set to C<undef>, the
515 attribute cannot be specified during initialization.
519 This provides the name of a method that will be called to initialize
520 the attribute. This method will be called on the object after it is
521 constructed. It is expected to return a valid value for the attribute.
525 This can be used to provide an explicit default for initializing the
526 attribute. If the default you provide is a subroutine reference, then
527 this reference will be called I<as a method> on the object.
529 If the value is a simple scalar (string or number), then it can be
530 just passed as is. However, if you wish to initialize it with a HASH
531 or ARRAY ref, then you need to wrap that inside a subroutine
534 Class::MOP::Attribute->new(
536 default => sub { [] },
542 Class::MOP::Attribute->new(
544 default => sub { {} },
548 If you wish to initialize an attribute with a subroutine reference
549 itself, then you need to wrap that in a subroutine as well:
551 Class::MOP::Attribute->new(
554 sub { print "Hello World" }
559 And lastly, if the value of your attribute is dependent upon some
560 other aspect of the instance structure, then you can take advantage of
561 the fact that when the C<default> value is called as a method:
563 Class::MOP::Attribute->new(
564 'object_identity' => (
565 default => sub { Scalar::Util::refaddr( $_[0] ) },
569 Note that there is no guarantee that attributes are initialized in any
570 particular order, so you cannot rely on the value of some other
571 attribute when generating the default.
575 This option can be either a method name or a subroutine
576 reference. This method will be called when setting the attribute's
577 value in the constructor. Unlike C<default> and C<builder>, the
578 initializer is only called when a value is provided to the
579 constructor. The initializer allows you to munge this value during
582 The initializer is called as a method with three arguments. The first
583 is the value that was passed to the constructor. The second is a
584 subroutine reference that can be called to actually set the
585 attribute's value, and the last is the associated
586 C<Class::MOP::Attribute> object.
588 This contrived example shows an initializer that sets the attribute to
589 twice the given value.
591 Class::MOP::Attribute->new(
594 my ( $instance, $value, $set ) = @_;
595 $set->( $value * 2 );
600 Since an initializer can be a method name, you can easily make
601 attribute initialization use the writer:
603 Class::MOP::Attribute->new(
605 writer => 'some_attr',
606 initializer => 'some_attr',
610 Your writer will need to examine C<@_> and determine under which
611 context it is being called.
615 The C<accessor>, C<reader>, C<writer>, C<predicate> and C<clearer>
616 options all accept the same parameters. You can provide the name of
617 the method, in which case an appropriate default method will be
618 generated for you. Or instead you can also provide hash reference
619 containing exactly one key (the method name) and one value. The value
620 should be a subroutine reference, which will be installed as the
627 An C<accessor> is a standard Perl-style read/write accessor. It will
628 return the value of the attribute, and if a value is passed as an
629 argument, it will assign that value to the attribute.
631 Note that C<undef> is a legitimate value, so this will work:
633 $object->set_something(undef);
637 This is a basic read-only accessor. It returns the value of the
642 This is a basic write accessor, it accepts a single argument, and
643 assigns that value to the attribute.
645 Note that C<undef> is a legitimate value, so this will work:
647 $object->set_something(undef);
651 The predicate method returns a boolean indicating whether or not the
652 attribute has been explicitly set.
654 Note that the predicate returns true even if the attribute was set to
655 a false value (C<0> or C<undef>).
659 This method will uninitialize the attribute. After an attribute is
660 cleared, its C<predicate> will return false.
662 =item * definition_context
664 Mostly, this exists as a hook for the benefit of Moose.
666 This option should be a hash reference containing several keys which
667 will be used when inlining the attribute's accessors. The keys should
668 include C<line>, the line number where the attribute was created, and
669 either C<file> or C<description>.
671 This information will ultimately be used when eval'ing inlined
672 accessor code so that error messages report a useful line and file
677 =item B<< $attr->clone(%options) >>
679 This clones the attribute. Any options you provide will override the
680 settings of the original attribute. You can change the name of the new
681 attribute by passing a C<name> key in C<%options>.
687 These are all basic read-only accessors for the values passed into
692 =item B<< $attr->name >>
694 Returns the attribute's name.
696 =item B<< $attr->accessor >>
698 =item B<< $attr->reader >>
700 =item B<< $attr->writer >>
702 =item B<< $attr->predicate >>
704 =item B<< $attr->clearer >>
706 The C<accessor>, C<reader>, C<writer>, C<predicate>, and C<clearer>
707 methods all return exactly what was passed to the constructor, so it
708 can be either a string containing a method name, or a hash reference.
710 =item B<< $attr->initializer >>
712 Returns the initializer as passed to the constructor, so this may be
713 either a method name or a subroutine reference.
715 =item B<< $attr->init_arg >>
717 =item B<< $attr->is_default_a_coderef >>
719 =item B<< $attr->default($instance) >>
721 The C<$instance> argument is optional. If you don't pass it, the
722 return value for this method is exactly what was passed to the
723 constructor, either a simple scalar or a subroutine reference.
725 If you I<do> pass an C<$instance> and the default is a subroutine
726 reference, then the reference is called as a method on the
727 C<$instance> and the generated value is returned.
729 =item B<< $attr->slots >>
731 Return a list of slots required by the attribute. This is usually just
732 one, the name of the attribute.
734 A slot is the name of the hash key used to store the attribute in an
737 =item B<< $attr->get_read_method >>
739 =item B<< $attr->get_write_method >>
741 Returns the name of a method suitable for reading or writing the value
742 of the attribute in the associated class.
744 If an attribute is read- or write-only, then these methods can return
745 C<undef> as appropriate.
747 =item B<< $attr->has_read_method >>
749 =item B<< $attr->has_write_method >>
751 This returns a boolean indicating whether the attribute has a I<named>
752 read or write method.
754 =item B<< $attr->get_read_method_ref >>
756 =item B<< $attr->get_write_method_ref >>
758 Returns the subroutine reference of a method suitable for reading or
759 writing the attribute's value in the associated class. These methods
760 always return a subroutine reference, regardless of whether or not the
761 attribute is read- or write-only.
763 =item B<< $attr->insertion_order >>
765 If this attribute has been inserted into a class, this returns a zero
766 based index regarding the order of insertion.
770 =head2 Informational predicates
772 These are all basic predicate methods for the values passed into C<new>.
776 =item B<< $attr->has_accessor >>
778 =item B<< $attr->has_reader >>
780 =item B<< $attr->has_writer >>
782 =item B<< $attr->has_predicate >>
784 =item B<< $attr->has_clearer >>
786 =item B<< $attr->has_initializer >>
788 =item B<< $attr->has_init_arg >>
790 This will be I<false> if the C<init_arg> was set to C<undef>.
792 =item B<< $attr->has_default >>
794 This will be I<false> if the C<default> was set to C<undef>, since
795 C<undef> is the default C<default> anyway.
797 =item B<< $attr->has_builder >>
799 =item B<< $attr->has_insertion_order >>
801 This will be I<false> if this attribute has not be inserted into a class
805 =head2 Value management
807 These methods are basically "back doors" to the instance, and can be
808 used to bypass the regular accessors, but still stay within the MOP.
810 These methods are not for general use, and should only be used if you
811 really know what you are doing.
815 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
817 This method is used internally to initialize the attribute's slot in
818 the object C<$instance>.
820 The C<$params> is a hash reference of the values passed to the object
823 It's unlikely that you'll need to call this method yourself.
825 =item B<< $attr->set_value($instance, $value) >>
827 Sets the value without going through the accessor. Note that this
828 works even with read-only attributes.
830 =item B<< $attr->set_initial_value($instance, $value) >>
832 Sets the value without going through the accessor. This method is only
833 called when the instance is first being initialized.
835 =item B<< $attr->get_value($instance) >>
837 Returns the value without going through the accessor. Note that this
838 works even with write-only accessors.
840 =item B<< $attr->has_value($instance) >>
842 Return a boolean indicating whether the attribute has been set in
843 C<$instance>. This how the default C<predicate> method works.
845 =item B<< $attr->clear_value($instance) >>
847 This will clear the attribute's value in C<$instance>. This is what
848 the default C<clearer> calls.
850 Note that this works even if the attribute does not have any
851 associated read, write or clear methods.
855 =head2 Class association
857 These methods allow you to manage the attributes association with
858 the class that contains it. These methods should not be used
859 lightly, nor are they very magical, they are mostly used internally
860 and by metaclass instances.
864 =item B<< $attr->associated_class >>
866 This returns the C<Class::MOP::Class> with which this attribute is
869 =item B<< $attr->attach_to_class($metaclass) >>
871 This method stores a weakened reference to the C<$metaclass> object
874 This method does not remove the attribute from its old class,
875 nor does it create any accessors in the new class.
877 It is probably best to use the L<Class::MOP::Class> C<add_attribute>
880 =item B<< $attr->detach_from_class >>
882 This method removes the associate metaclass object from the attribute
885 This method does not remove the attribute itself from the class, or
886 remove its accessors.
888 It is probably best to use the L<Class::MOP::Class>
889 C<remove_attribute> method instead.
893 =head2 Attribute Accessor generation
897 =item B<< $attr->accessor_metaclass >>
899 Accessor methods are generated using an accessor metaclass. By
900 default, this is L<Class::MOP::Method::Accessor>. This method returns
901 the name of the accessor metaclass that this attribute uses.
903 =item B<< $attr->associate_method($method) >>
905 This associates a L<Class::MOP::Method> object with the
906 attribute. Typically, this is called internally when an attribute
907 generates its accessors.
909 =item B<< $attr->associated_methods >>
911 This returns the list of methods which have been associated with the
914 =item B<< $attr->install_accessors >>
916 This method generates and installs code the attributes various
917 accessors. It is typically called from the L<Class::MOP::Class>
918 C<add_attribute> method.
920 =item B<< $attr->remove_accessors >>
922 This method removes all of the accessors associated with the
925 This does not currently remove methods from the list returned by
926 C<associated_methods>.
934 =item B<< Class::MOP::Attribute->meta >>
936 This will return a L<Class::MOP::Class> instance for this class.
938 It should also be noted that L<Class::MOP> will actually bootstrap
939 this module by installing a number of attribute meta-objects into its
946 Stevan Little E<lt>stevan@iinteractive.comE<gt>
948 =head1 COPYRIGHT AND LICENSE
950 Copyright 2006-2009 by Infinity Interactive, Inc.
952 L<http://www.iinteractive.com>
954 This library is free software; you can redistribute it and/or modify
955 it under the same terms as Perl itself.