2 package Class::MOP::Attribute;
7 use Class::MOP::Method::Accessor;
10 use Scalar::Util 'blessed', 'weaken';
13 use base 'Class::MOP::Object', 'Class::MOP::Mixin::AttributeCore';
15 # NOTE: (meta-circularity)
16 # This method will be replaced in the
17 # boostrap section of Class::MOP, by
18 # a new version which uses the
19 # &Class::MOP::Class::construct_instance
20 # method to build an attribute meta-object
21 # which itself is described with attribute
23 # - Ain't meta-circularity grand? :)
25 my ( $class, @args ) = @_;
27 unshift @args, "name" if @args % 2 == 1;
30 my $name = $options{name};
33 || confess "You must provide a name for the attribute";
35 $options{init_arg} = $name
36 if not exists $options{init_arg};
37 if(exists $options{builder}){
38 confess("builder must be a defined scalar value which is a method name")
39 if ref $options{builder} || !(defined $options{builder});
40 confess("Setting both default and builder is not allowed.")
41 if exists $options{default};
43 ($class->is_default_a_coderef(\%options))
44 || confess("References are not allowed as default values, you must ".
45 "wrap the default of '$name' in a CODE reference (ex: sub { [] } and not [])")
46 if exists $options{default} && ref $options{default};
48 if( $options{required} and not( defined($options{builder}) || defined($options{init_arg}) || exists $options{default} ) ) {
49 confess("A required attribute must have either 'init_arg', 'builder', or 'default'");
52 $class->_new(\%options);
58 return Class::MOP::Class->initialize($class)->new_object(@_)
59 if $class ne __PACKAGE__;
61 my $options = @_ == 1 ? $_[0] : {@_};
64 'name' => $options->{name},
65 'accessor' => $options->{accessor},
66 'reader' => $options->{reader},
67 'writer' => $options->{writer},
68 'predicate' => $options->{predicate},
69 'clearer' => $options->{clearer},
70 'builder' => $options->{builder},
71 'init_arg' => $options->{init_arg},
72 exists $options->{default}
73 ? ('default' => $options->{default})
75 'initializer' => $options->{initializer},
76 'definition_context' => $options->{definition_context},
77 # keep a weakened link to the
78 # class we are associated with
79 'associated_class' => undef,
80 # and a list of the methods
81 # associated with this attr
82 'associated_methods' => [],
83 # this let's us keep track of
84 # our order inside the associated
86 'insertion_order' => undef,
91 # this is a primative (and kludgy) clone operation
92 # for now, it will be replaced in the Class::MOP
93 # bootstrap with a proper one, however we know
94 # that this one will work fine for now.
99 || confess "Can only clone an instance";
100 return bless { %{$self}, %options } => ref($self);
103 sub initialize_instance_slot {
104 my ($self, $meta_instance, $instance, $params) = @_;
105 my $init_arg = $self->{'init_arg'};
107 # try to fetch the init arg from the %params ...
109 # if nothing was in the %params, we can use the
110 # attribute's default value (if it has one)
111 if(defined $init_arg and exists $params->{$init_arg}){
112 $self->_set_initial_slot_value(
115 $params->{$init_arg},
118 elsif (exists $self->{'default'}) {
119 $self->_set_initial_slot_value(
122 $self->default($instance),
125 elsif (defined( my $builder = $self->{'builder'})) {
126 if ($builder = $instance->can($builder)) {
127 $self->_set_initial_slot_value(
134 confess(ref($instance)." does not support builder method '". $self->{'builder'} ."' for attribute '" . $self->name . "'");
139 sub _set_initial_slot_value {
140 my ($self, $meta_instance, $instance, $value) = @_;
142 my $slot_name = $self->name;
144 return $meta_instance->set_slot_value($instance, $slot_name, $value)
145 unless $self->has_initializer;
147 my $callback = $self->_make_initializer_writer_callback(
148 $meta_instance, $instance, $slot_name
151 my $initializer = $self->initializer;
153 # most things will just want to set a value, so make it first arg
154 $instance->$initializer($value, $callback, $self);
157 sub _make_initializer_writer_callback {
159 my ($meta_instance, $instance, $slot_name) = @_;
162 $meta_instance->set_slot_value($instance, $slot_name, $_[0]);
166 sub get_read_method {
168 my $reader = $self->reader || $self->accessor;
170 return $reader unless ref $reader;
172 my ($name) = %$reader;
176 sub get_write_method {
178 my $writer = $self->writer || $self->accessor;
180 return $writer unless ref $writer;
182 my ($name) = %$writer;
186 sub get_read_method_ref {
188 if ((my $reader = $self->get_read_method) && $self->associated_class) {
189 return $self->associated_class->get_method($reader);
192 my $code = sub { $self->get_value(@_) };
193 if (my $class = $self->associated_class) {
194 return $class->method_metaclass->wrap(
196 package_name => $class->name,
206 sub get_write_method_ref {
208 if ((my $writer = $self->get_write_method) && $self->associated_class) {
209 return $self->associated_class->get_method($writer);
212 my $code = sub { $self->set_value(@_) };
213 if (my $class = $self->associated_class) {
214 return $class->method_metaclass->wrap(
216 package_name => $class->name,
228 sub slots { (shift)->name }
232 sub attach_to_class {
233 my ($self, $class) = @_;
234 (blessed($class) && $class->isa('Class::MOP::Class'))
235 || confess "You must pass a Class::MOP::Class instance (or a subclass)";
236 weaken($self->{'associated_class'} = $class);
239 sub detach_from_class {
241 $self->{'associated_class'} = undef;
246 sub associate_method {
247 my ($self, $method) = @_;
248 push @{$self->{'associated_methods'}} => $method;
253 sub set_initial_value {
254 my ($self, $instance, $value) = @_;
255 $self->_set_initial_slot_value(
256 Class::MOP::Class->initialize(ref($instance))->get_meta_instance,
262 sub set_value { shift->set_raw_value(@_) }
266 my ($instance, $value) = @_;
268 my $mi = Class::MOP::Class->initialize(ref($instance))->get_meta_instance;
269 return $mi->set_slot_value($instance, $self->name, $value);
272 sub _inline_set_value {
274 return $self->_inline_instance_set(@_) . ';';
277 sub _inline_instance_set {
279 my ($instance, $value) = @_;
281 my $mi = $self->associated_class->get_meta_instance;
282 return $mi->inline_set_slot_value($instance, $self->name, $value);
285 sub get_value { shift->get_raw_value(@_) }
291 my $mi = Class::MOP::Class->initialize(ref($instance))->get_meta_instance;
292 return $mi->get_slot_value($instance, $self->name);
295 sub _inline_get_value {
297 return $self->_inline_instance_get(@_) . ';';
300 sub _inline_instance_get {
304 my $mi = $self->associated_class->get_meta_instance;
305 return $mi->inline_get_slot_value($instance, $self->name);
312 my $mi = Class::MOP::Class->initialize(ref($instance))->get_meta_instance;
313 return $mi->is_slot_initialized($instance, $self->name);
316 sub _inline_has_value {
318 return $self->_inline_instance_has(@_) . ';';
321 sub _inline_instance_has {
325 my $mi = $self->associated_class->get_meta_instance;
326 return $mi->inline_is_slot_initialized($instance, $self->name);
333 my $mi = Class::MOP::Class->initialize(ref($instance))->get_meta_instance;
334 return $mi->deinitialize_slot($instance, $self->name);
337 sub _inline_clear_value {
339 return $self->_inline_instance_clear(@_) . ';';
342 sub _inline_instance_clear {
346 my $mi = $self->associated_class->get_meta_instance;
347 return $mi->inline_deinitialize_slot($instance, $self->name);
352 sub accessor_metaclass { 'Class::MOP::Method::Accessor' }
354 sub _process_accessors {
355 my ($self, $type, $accessor, $generate_as_inline_methods) = @_;
359 if ( my $ctx = $self->definition_context ) {
360 $method_ctx = { %$ctx };
363 if (ref($accessor)) {
364 (ref($accessor) eq 'HASH')
365 || confess "bad accessor/reader/writer/predicate/clearer format, must be a HASH ref";
366 my ($name, $method) = %{$accessor};
367 $method = $self->accessor_metaclass->wrap(
369 package_name => $self->associated_class->name,
371 definition_context => $method_ctx,
373 $self->associate_method($method);
374 return ($name, $method);
377 my $inline_me = ($generate_as_inline_methods && $self->associated_class->instance_metaclass->is_inlinable);
381 my $desc = "accessor $accessor";
382 if ( $accessor ne $self->name ) {
383 $desc .= " of attribute " . $self->name;
386 $method_ctx->{description} = $desc;
389 $method = $self->accessor_metaclass->new(
391 is_inline => $inline_me,
392 accessor_type => $type,
393 package_name => $self->associated_class->name,
395 definition_context => $method_ctx,
399 confess "Could not create the '$type' method for " . $self->name . " because : $_";
401 $self->associate_method($method);
402 return ($accessor, $method);
406 sub install_accessors {
409 my $class = $self->associated_class;
412 $self->_process_accessors('accessor' => $self->accessor(), $inline)
413 ) if $self->has_accessor();
416 $self->_process_accessors('reader' => $self->reader(), $inline)
417 ) if $self->has_reader();
420 $self->_process_accessors('writer' => $self->writer(), $inline)
421 ) if $self->has_writer();
424 $self->_process_accessors('predicate' => $self->predicate(), $inline)
425 ) if $self->has_predicate();
428 $self->_process_accessors('clearer' => $self->clearer(), $inline)
429 ) if $self->has_clearer();
435 my $_remove_accessor = sub {
436 my ($accessor, $class) = @_;
437 if (ref($accessor) && ref($accessor) eq 'HASH') {
438 ($accessor) = keys %{$accessor};
440 my $method = $class->get_method($accessor);
441 $class->remove_method($accessor)
442 if (ref($method) && $method->isa('Class::MOP::Method::Accessor'));
445 sub remove_accessors {
448 # we really need to make sure to remove from the
449 # associates methods here as well. But this is
450 # such a slimly used method, I am not worried
451 # about it right now.
452 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
453 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
454 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
455 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
456 $_remove_accessor->($self->clearer(), $self->associated_class()) if $self->has_clearer();
464 # ABSTRACT: Attribute Meta Object
472 Class::MOP::Attribute->new(
474 accessor => 'foo', # dual purpose get/set accessor
475 predicate => 'has_foo', # predicate check for defined-ness
476 init_arg => '-foo', # class->new will look for a -foo key
477 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
481 Class::MOP::Attribute->new(
483 reader => 'bar', # getter
484 writer => 'set_bar', # setter
485 predicate => 'has_bar', # predicate check for defined-ness
486 init_arg => ':bar', # class->new will look for a :bar key
487 # no default value means it is undef
493 The Attribute Protocol is almost entirely an invention of
494 C<Class::MOP>. Perl 5 does not have a consistent notion of
495 attributes. There are so many ways in which this is done, and very few
496 (if any) are easily discoverable by this module.
498 With that said, this module attempts to inject some order into this
499 chaos, by introducing a consistent API which can be used to create
508 =item B<< Class::MOP::Attribute->new($name, ?%options) >>
510 An attribute must (at the very least), have a C<$name>. All other
511 C<%options> are added as key-value pairs.
517 This is a string value representing the expected key in an
518 initialization hash. For instance, if we have an C<init_arg> value of
519 C<-foo>, then the following code will Just Work.
521 MyClass->meta->new_object( -foo => 'Hello There' );
523 If an init_arg is not assigned, it will automatically use the
524 attribute's name. If C<init_arg> is explicitly set to C<undef>, the
525 attribute cannot be specified during initialization.
529 This provides the name of a method that will be called to initialize
530 the attribute. This method will be called on the object after it is
531 constructed. It is expected to return a valid value for the attribute.
535 This can be used to provide an explicit default for initializing the
536 attribute. If the default you provide is a subroutine reference, then
537 this reference will be called I<as a method> on the object.
539 If the value is a simple scalar (string or number), then it can be
540 just passed as is. However, if you wish to initialize it with a HASH
541 or ARRAY ref, then you need to wrap that inside a subroutine
544 Class::MOP::Attribute->new(
546 default => sub { [] },
552 Class::MOP::Attribute->new(
554 default => sub { {} },
558 If you wish to initialize an attribute with a subroutine reference
559 itself, then you need to wrap that in a subroutine as well:
561 Class::MOP::Attribute->new(
564 sub { print "Hello World" }
569 And lastly, if the value of your attribute is dependent upon some
570 other aspect of the instance structure, then you can take advantage of
571 the fact that when the C<default> value is called as a method:
573 Class::MOP::Attribute->new(
574 'object_identity' => (
575 default => sub { Scalar::Util::refaddr( $_[0] ) },
579 Note that there is no guarantee that attributes are initialized in any
580 particular order, so you cannot rely on the value of some other
581 attribute when generating the default.
585 This option can be either a method name or a subroutine
586 reference. This method will be called when setting the attribute's
587 value in the constructor. Unlike C<default> and C<builder>, the
588 initializer is only called when a value is provided to the
589 constructor. The initializer allows you to munge this value during
592 The initializer is called as a method with three arguments. The first
593 is the value that was passed to the constructor. The second is a
594 subroutine reference that can be called to actually set the
595 attribute's value, and the last is the associated
596 C<Class::MOP::Attribute> object.
598 This contrived example shows an initializer that sets the attribute to
599 twice the given value.
601 Class::MOP::Attribute->new(
604 my ( $self, $value, $set, $attr ) = @_;
605 $set->( $value * 2 );
610 Since an initializer can be a method name, you can easily make
611 attribute initialization use the writer:
613 Class::MOP::Attribute->new(
615 writer => 'some_attr',
616 initializer => 'some_attr',
620 Your writer will need to examine C<@_> and determine under which
621 context it is being called.
625 The C<accessor>, C<reader>, C<writer>, C<predicate> and C<clearer>
626 options all accept the same parameters. You can provide the name of
627 the method, in which case an appropriate default method will be
628 generated for you. Or instead you can also provide hash reference
629 containing exactly one key (the method name) and one value. The value
630 should be a subroutine reference, which will be installed as the
637 An C<accessor> is a standard Perl-style read/write accessor. It will
638 return the value of the attribute, and if a value is passed as an
639 argument, it will assign that value to the attribute.
641 Note that C<undef> is a legitimate value, so this will work:
643 $object->set_something(undef);
647 This is a basic read-only accessor. It returns the value of the
652 This is a basic write accessor, it accepts a single argument, and
653 assigns that value to the attribute.
655 Note that C<undef> is a legitimate value, so this will work:
657 $object->set_something(undef);
661 The predicate method returns a boolean indicating whether or not the
662 attribute has been explicitly set.
664 Note that the predicate returns true even if the attribute was set to
665 a false value (C<0> or C<undef>).
669 This method will uninitialize the attribute. After an attribute is
670 cleared, its C<predicate> will return false.
672 =item * definition_context
674 Mostly, this exists as a hook for the benefit of Moose.
676 This option should be a hash reference containing several keys which
677 will be used when inlining the attribute's accessors. The keys should
678 include C<line>, the line number where the attribute was created, and
679 either C<file> or C<description>.
681 This information will ultimately be used when eval'ing inlined
682 accessor code so that error messages report a useful line and file
687 =item B<< $attr->clone(%options) >>
689 This clones the attribute. Any options you provide will override the
690 settings of the original attribute. You can change the name of the new
691 attribute by passing a C<name> key in C<%options>.
697 These are all basic read-only accessors for the values passed into
702 =item B<< $attr->name >>
704 Returns the attribute's name.
706 =item B<< $attr->accessor >>
708 =item B<< $attr->reader >>
710 =item B<< $attr->writer >>
712 =item B<< $attr->predicate >>
714 =item B<< $attr->clearer >>
716 The C<accessor>, C<reader>, C<writer>, C<predicate>, and C<clearer>
717 methods all return exactly what was passed to the constructor, so it
718 can be either a string containing a method name, or a hash reference.
720 =item B<< $attr->initializer >>
722 Returns the initializer as passed to the constructor, so this may be
723 either a method name or a subroutine reference.
725 =item B<< $attr->init_arg >>
727 =item B<< $attr->is_default_a_coderef >>
729 =item B<< $attr->default($instance) >>
731 The C<$instance> argument is optional. If you don't pass it, the
732 return value for this method is exactly what was passed to the
733 constructor, either a simple scalar or a subroutine reference.
735 If you I<do> pass an C<$instance> and the default is a subroutine
736 reference, then the reference is called as a method on the
737 C<$instance> and the generated value is returned.
739 =item B<< $attr->slots >>
741 Return a list of slots required by the attribute. This is usually just
742 one, the name of the attribute.
744 A slot is the name of the hash key used to store the attribute in an
747 =item B<< $attr->get_read_method >>
749 =item B<< $attr->get_write_method >>
751 Returns the name of a method suitable for reading or writing the value
752 of the attribute in the associated class.
754 If an attribute is read- or write-only, then these methods can return
755 C<undef> as appropriate.
757 =item B<< $attr->has_read_method >>
759 =item B<< $attr->has_write_method >>
761 This returns a boolean indicating whether the attribute has a I<named>
762 read or write method.
764 =item B<< $attr->get_read_method_ref >>
766 =item B<< $attr->get_write_method_ref >>
768 Returns the subroutine reference of a method suitable for reading or
769 writing the attribute's value in the associated class. These methods
770 always return a subroutine reference, regardless of whether or not the
771 attribute is read- or write-only.
773 =item B<< $attr->insertion_order >>
775 If this attribute has been inserted into a class, this returns a zero
776 based index regarding the order of insertion.
780 =head2 Informational predicates
782 These are all basic predicate methods for the values passed into C<new>.
786 =item B<< $attr->has_accessor >>
788 =item B<< $attr->has_reader >>
790 =item B<< $attr->has_writer >>
792 =item B<< $attr->has_predicate >>
794 =item B<< $attr->has_clearer >>
796 =item B<< $attr->has_initializer >>
798 =item B<< $attr->has_init_arg >>
800 This will be I<false> if the C<init_arg> was set to C<undef>.
802 =item B<< $attr->has_default >>
804 This will be I<false> if the C<default> was set to C<undef>, since
805 C<undef> is the default C<default> anyway.
807 =item B<< $attr->has_builder >>
809 =item B<< $attr->has_insertion_order >>
811 This will be I<false> if this attribute has not be inserted into a class
815 =head2 Value management
817 These methods are basically "back doors" to the instance, and can be
818 used to bypass the regular accessors, but still stay within the MOP.
820 These methods are not for general use, and should only be used if you
821 really know what you are doing.
825 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
827 This method is used internally to initialize the attribute's slot in
828 the object C<$instance>.
830 The C<$params> is a hash reference of the values passed to the object
833 It's unlikely that you'll need to call this method yourself.
835 =item B<< $attr->set_value($instance, $value) >>
837 Sets the value without going through the accessor. Note that this
838 works even with read-only attributes.
840 =item B<< $attr->set_raw_value($instance, $value) >>
842 Sets the value with no side effects such as a trigger.
844 This doesn't actually apply to Class::MOP attributes, only to subclasses.
846 =item B<< $attr->set_initial_value($instance, $value) >>
848 Sets the value without going through the accessor. This method is only
849 called when the instance is first being initialized.
851 =item B<< $attr->get_value($instance) >>
853 Returns the value without going through the accessor. Note that this
854 works even with write-only accessors.
856 =item B<< $attr->get_raw_value($instance) >>
858 Returns the value without any side effects such as lazy attributes.
860 Doesn't actually apply to Class::MOP attributes, only to subclasses.
862 =item B<< $attr->has_value($instance) >>
864 Return a boolean indicating whether the attribute has been set in
865 C<$instance>. This how the default C<predicate> method works.
867 =item B<< $attr->clear_value($instance) >>
869 This will clear the attribute's value in C<$instance>. This is what
870 the default C<clearer> calls.
872 Note that this works even if the attribute does not have any
873 associated read, write or clear methods.
877 =head2 Class association
879 These methods allow you to manage the attributes association with
880 the class that contains it. These methods should not be used
881 lightly, nor are they very magical, they are mostly used internally
882 and by metaclass instances.
886 =item B<< $attr->associated_class >>
888 This returns the C<Class::MOP::Class> with which this attribute is
891 =item B<< $attr->attach_to_class($metaclass) >>
893 This method stores a weakened reference to the C<$metaclass> object
896 This method does not remove the attribute from its old class,
897 nor does it create any accessors in the new class.
899 It is probably best to use the L<Class::MOP::Class> C<add_attribute>
902 =item B<< $attr->detach_from_class >>
904 This method removes the associate metaclass object from the attribute
907 This method does not remove the attribute itself from the class, or
908 remove its accessors.
910 It is probably best to use the L<Class::MOP::Class>
911 C<remove_attribute> method instead.
915 =head2 Attribute Accessor generation
919 =item B<< $attr->accessor_metaclass >>
921 Accessor methods are generated using an accessor metaclass. By
922 default, this is L<Class::MOP::Method::Accessor>. This method returns
923 the name of the accessor metaclass that this attribute uses.
925 =item B<< $attr->associate_method($method) >>
927 This associates a L<Class::MOP::Method> object with the
928 attribute. Typically, this is called internally when an attribute
929 generates its accessors.
931 =item B<< $attr->associated_methods >>
933 This returns the list of methods which have been associated with the
936 =item B<< $attr->install_accessors >>
938 This method generates and installs code the attributes various
939 accessors. It is typically called from the L<Class::MOP::Class>
940 C<add_attribute> method.
942 =item B<< $attr->remove_accessors >>
944 This method removes all of the accessors associated with the
947 This does not currently remove methods from the list returned by
948 C<associated_methods>.
950 =item B<< $attr->inline_get >>
952 =item B<< $attr->inline_set >>
954 =item B<< $attr->inline_has >>
956 =item B<< $attr->inline_clear >>
958 These methods return a code snippet suitable for inlining the relevant
959 operation. They expect strings containing variable names to be used in the
960 inlining, like C<'$self'> or C<'$_[1]'>.
968 =item B<< Class::MOP::Attribute->meta >>
970 This will return a L<Class::MOP::Class> instance for this class.
972 It should also be noted that L<Class::MOP> will actually bootstrap
973 this module by installing a number of attribute meta-objects into its