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(
370 package_name => $self->associated_class->name,
372 associated_metaclass => $self->associated_class,
373 definition_context => $method_ctx,
375 $self->associate_method($method);
376 return ($name, $method);
379 my $inline_me = ($generate_as_inline_methods && $self->associated_class->instance_metaclass->is_inlinable);
383 my $desc = "accessor " . $self->associated_class->name . "::$accessor";
384 if ( $accessor ne $self->name ) {
385 $desc .= " of attribute " . $self->name;
388 $method_ctx->{description} = $desc;
391 $method = $self->accessor_metaclass->new(
393 is_inline => $inline_me,
394 accessor_type => $type,
395 package_name => $self->associated_class->name,
397 associated_metaclass => $self->associated_class,
398 definition_context => $method_ctx,
402 confess "Could not create the '$type' method for " . $self->name . " because : $_";
404 $self->associate_method($method);
405 return ($accessor, $method);
409 sub install_accessors {
412 my $class = $self->associated_class;
415 $self->_process_accessors('accessor' => $self->accessor(), $inline)
416 ) if $self->has_accessor();
419 $self->_process_accessors('reader' => $self->reader(), $inline)
420 ) if $self->has_reader();
423 $self->_process_accessors('writer' => $self->writer(), $inline)
424 ) if $self->has_writer();
427 $self->_process_accessors('predicate' => $self->predicate(), $inline)
428 ) if $self->has_predicate();
431 $self->_process_accessors('clearer' => $self->clearer(), $inline)
432 ) if $self->has_clearer();
438 my $_remove_accessor = sub {
439 my ($accessor, $class) = @_;
440 if (ref($accessor) && ref($accessor) eq 'HASH') {
441 ($accessor) = keys %{$accessor};
443 my $method = $class->get_method($accessor);
444 $class->remove_method($accessor)
445 if (ref($method) && $method->isa('Class::MOP::Method::Accessor'));
448 sub remove_accessors {
451 # we really need to make sure to remove from the
452 # associates methods here as well. But this is
453 # such a slimly used method, I am not worried
454 # about it right now.
455 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
456 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
457 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
458 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
459 $_remove_accessor->($self->clearer(), $self->associated_class()) if $self->has_clearer();
467 # ABSTRACT: Attribute Meta Object
475 Class::MOP::Attribute->new(
477 accessor => 'foo', # dual purpose get/set accessor
478 predicate => 'has_foo', # predicate check for defined-ness
479 init_arg => '-foo', # class->new will look for a -foo key
480 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
484 Class::MOP::Attribute->new(
486 reader => 'bar', # getter
487 writer => 'set_bar', # setter
488 predicate => 'has_bar', # predicate check for defined-ness
489 init_arg => ':bar', # class->new will look for a :bar key
490 # no default value means it is undef
496 The Attribute Protocol is almost entirely an invention of
497 C<Class::MOP>. Perl 5 does not have a consistent notion of
498 attributes. There are so many ways in which this is done, and very few
499 (if any) are easily discoverable by this module.
501 With that said, this module attempts to inject some order into this
502 chaos, by introducing a consistent API which can be used to create
511 =item B<< Class::MOP::Attribute->new($name, ?%options) >>
513 An attribute must (at the very least), have a C<$name>. All other
514 C<%options> are added as key-value pairs.
520 This is a string value representing the expected key in an
521 initialization hash. For instance, if we have an C<init_arg> value of
522 C<-foo>, then the following code will Just Work.
524 MyClass->meta->new_object( -foo => 'Hello There' );
526 If an init_arg is not assigned, it will automatically use the
527 attribute's name. If C<init_arg> is explicitly set to C<undef>, the
528 attribute cannot be specified during initialization.
532 This provides the name of a method that will be called to initialize
533 the attribute. This method will be called on the object after it is
534 constructed. It is expected to return a valid value for the attribute.
538 This can be used to provide an explicit default for initializing the
539 attribute. If the default you provide is a subroutine reference, then
540 this reference will be called I<as a method> on the object.
542 If the value is a simple scalar (string or number), then it can be
543 just passed as is. However, if you wish to initialize it with a HASH
544 or ARRAY ref, then you need to wrap that inside a subroutine
547 Class::MOP::Attribute->new(
549 default => sub { [] },
555 Class::MOP::Attribute->new(
557 default => sub { {} },
561 If you wish to initialize an attribute with a subroutine reference
562 itself, then you need to wrap that in a subroutine as well:
564 Class::MOP::Attribute->new(
567 sub { print "Hello World" }
572 And lastly, if the value of your attribute is dependent upon some
573 other aspect of the instance structure, then you can take advantage of
574 the fact that when the C<default> value is called as a method:
576 Class::MOP::Attribute->new(
577 'object_identity' => (
578 default => sub { Scalar::Util::refaddr( $_[0] ) },
582 Note that there is no guarantee that attributes are initialized in any
583 particular order, so you cannot rely on the value of some other
584 attribute when generating the default.
588 This option can be either a method name or a subroutine
589 reference. This method will be called when setting the attribute's
590 value in the constructor. Unlike C<default> and C<builder>, the
591 initializer is only called when a value is provided to the
592 constructor. The initializer allows you to munge this value during
595 The initializer is called as a method with three arguments. The first
596 is the value that was passed to the constructor. The second is a
597 subroutine reference that can be called to actually set the
598 attribute's value, and the last is the associated
599 C<Class::MOP::Attribute> object.
601 This contrived example shows an initializer that sets the attribute to
602 twice the given value.
604 Class::MOP::Attribute->new(
607 my ( $self, $value, $set, $attr ) = @_;
608 $set->( $value * 2 );
613 Since an initializer can be a method name, you can easily make
614 attribute initialization use the writer:
616 Class::MOP::Attribute->new(
618 writer => 'some_attr',
619 initializer => 'some_attr',
623 Your writer (actually, a wrapper around the writer, using
624 L<method modifications|Moose::Manual::MethodModifiers>) will need to examine
625 C<@_> and determine under which
626 context it is being called:
628 around 'some_attr' => sub {
631 # $value is not defined if being called as a reader
632 # $setter and $attr are only defined if being called as an initializer
633 my ($value, $setter, $attr) = @_;
635 # the reader behaves normally
636 return $self->$orig if not @_;
638 # mutate $value as desired
639 # $value = <something($value);
641 # if called as an initializer, set the value and we're done
642 return $setter->($row) if $setter;
644 # otherwise, call the real writer with the new value
651 The C<accessor>, C<reader>, C<writer>, C<predicate> and C<clearer>
652 options all accept the same parameters. You can provide the name of
653 the method, in which case an appropriate default method will be
654 generated for you. Or instead you can also provide hash reference
655 containing exactly one key (the method name) and one value. The value
656 should be a subroutine reference, which will be installed as the
663 An C<accessor> is a standard Perl-style read/write accessor. It will
664 return the value of the attribute, and if a value is passed as an
665 argument, it will assign that value to the attribute.
667 Note that C<undef> is a legitimate value, so this will work:
669 $object->set_something(undef);
673 This is a basic read-only accessor. It returns the value of the
678 This is a basic write accessor, it accepts a single argument, and
679 assigns that value to the attribute.
681 Note that C<undef> is a legitimate value, so this will work:
683 $object->set_something(undef);
687 The predicate method returns a boolean indicating whether or not the
688 attribute has been explicitly set.
690 Note that the predicate returns true even if the attribute was set to
691 a false value (C<0> or C<undef>).
695 This method will uninitialize the attribute. After an attribute is
696 cleared, its C<predicate> will return false.
698 =item * definition_context
700 Mostly, this exists as a hook for the benefit of Moose.
702 This option should be a hash reference containing several keys which
703 will be used when inlining the attribute's accessors. The keys should
704 include C<line>, the line number where the attribute was created, and
705 either C<file> or C<description>.
707 This information will ultimately be used when eval'ing inlined
708 accessor code so that error messages report a useful line and file
713 =item B<< $attr->clone(%options) >>
715 This clones the attribute. Any options you provide will override the
716 settings of the original attribute. You can change the name of the new
717 attribute by passing a C<name> key in C<%options>.
723 These are all basic read-only accessors for the values passed into
728 =item B<< $attr->name >>
730 Returns the attribute's name.
732 =item B<< $attr->accessor >>
734 =item B<< $attr->reader >>
736 =item B<< $attr->writer >>
738 =item B<< $attr->predicate >>
740 =item B<< $attr->clearer >>
742 The C<accessor>, C<reader>, C<writer>, C<predicate>, and C<clearer>
743 methods all return exactly what was passed to the constructor, so it
744 can be either a string containing a method name, or a hash reference.
746 =item B<< $attr->initializer >>
748 Returns the initializer as passed to the constructor, so this may be
749 either a method name or a subroutine reference.
751 =item B<< $attr->init_arg >>
753 =item B<< $attr->is_default_a_coderef >>
755 =item B<< $attr->default($instance) >>
757 The C<$instance> argument is optional. If you don't pass it, the
758 return value for this method is exactly what was passed to the
759 constructor, either a simple scalar or a subroutine reference.
761 If you I<do> pass an C<$instance> and the default is a subroutine
762 reference, then the reference is called as a method on the
763 C<$instance> and the generated value is returned.
765 =item B<< $attr->slots >>
767 Return a list of slots required by the attribute. This is usually just
768 one, the name of the attribute.
770 A slot is the name of the hash key used to store the attribute in an
773 =item B<< $attr->get_read_method >>
775 =item B<< $attr->get_write_method >>
777 Returns the name of a method suitable for reading or writing the value
778 of the attribute in the associated class.
780 If an attribute is read- or write-only, then these methods can return
781 C<undef> as appropriate.
783 =item B<< $attr->has_read_method >>
785 =item B<< $attr->has_write_method >>
787 This returns a boolean indicating whether the attribute has a I<named>
788 read or write method.
790 =item B<< $attr->get_read_method_ref >>
792 =item B<< $attr->get_write_method_ref >>
794 Returns the subroutine reference of a method suitable for reading or
795 writing the attribute's value in the associated class. These methods
796 always return a subroutine reference, regardless of whether or not the
797 attribute is read- or write-only.
799 =item B<< $attr->insertion_order >>
801 If this attribute has been inserted into a class, this returns a zero
802 based index regarding the order of insertion.
806 =head2 Informational predicates
808 These are all basic predicate methods for the values passed into C<new>.
812 =item B<< $attr->has_accessor >>
814 =item B<< $attr->has_reader >>
816 =item B<< $attr->has_writer >>
818 =item B<< $attr->has_predicate >>
820 =item B<< $attr->has_clearer >>
822 =item B<< $attr->has_initializer >>
824 =item B<< $attr->has_init_arg >>
826 This will be I<false> if the C<init_arg> was set to C<undef>.
828 =item B<< $attr->has_default >>
830 This will be I<false> if the C<default> was set to C<undef>, since
831 C<undef> is the default C<default> anyway.
833 =item B<< $attr->has_builder >>
835 =item B<< $attr->has_insertion_order >>
837 This will be I<false> if this attribute has not be inserted into a class
841 =head2 Value management
843 These methods are basically "back doors" to the instance, and can be
844 used to bypass the regular accessors, but still stay within the MOP.
846 These methods are not for general use, and should only be used if you
847 really know what you are doing.
851 =item B<< $attr->initialize_instance_slot($meta_instance, $instance, $params) >>
853 This method is used internally to initialize the attribute's slot in
854 the object C<$instance>.
856 The C<$params> is a hash reference of the values passed to the object
859 It's unlikely that you'll need to call this method yourself.
861 =item B<< $attr->set_value($instance, $value) >>
863 Sets the value without going through the accessor. Note that this
864 works even with read-only attributes.
866 =item B<< $attr->set_raw_value($instance, $value) >>
868 Sets the value with no side effects such as a trigger.
870 This doesn't actually apply to Class::MOP attributes, only to subclasses.
872 =item B<< $attr->set_initial_value($instance, $value) >>
874 Sets the value without going through the accessor. This method is only
875 called when the instance is first being initialized.
877 =item B<< $attr->get_value($instance) >>
879 Returns the value without going through the accessor. Note that this
880 works even with write-only accessors.
882 =item B<< $attr->get_raw_value($instance) >>
884 Returns the value without any side effects such as lazy attributes.
886 Doesn't actually apply to Class::MOP attributes, only to subclasses.
888 =item B<< $attr->has_value($instance) >>
890 Return a boolean indicating whether the attribute has been set in
891 C<$instance>. This how the default C<predicate> method works.
893 =item B<< $attr->clear_value($instance) >>
895 This will clear the attribute's value in C<$instance>. This is what
896 the default C<clearer> calls.
898 Note that this works even if the attribute does not have any
899 associated read, write or clear methods.
903 =head2 Class association
905 These methods allow you to manage the attributes association with
906 the class that contains it. These methods should not be used
907 lightly, nor are they very magical, they are mostly used internally
908 and by metaclass instances.
912 =item B<< $attr->associated_class >>
914 This returns the C<Class::MOP::Class> with which this attribute is
917 =item B<< $attr->attach_to_class($metaclass) >>
919 This method stores a weakened reference to the C<$metaclass> object
922 This method does not remove the attribute from its old class,
923 nor does it create any accessors in the new class.
925 It is probably best to use the L<Class::MOP::Class> C<add_attribute>
928 =item B<< $attr->detach_from_class >>
930 This method removes the associate metaclass object from the attribute
933 This method does not remove the attribute itself from the class, or
934 remove its accessors.
936 It is probably best to use the L<Class::MOP::Class>
937 C<remove_attribute> method instead.
941 =head2 Attribute Accessor generation
945 =item B<< $attr->accessor_metaclass >>
947 Accessor methods are generated using an accessor metaclass. By
948 default, this is L<Class::MOP::Method::Accessor>. This method returns
949 the name of the accessor metaclass that this attribute uses.
951 =item B<< $attr->associate_method($method) >>
953 This associates a L<Class::MOP::Method> object with the
954 attribute. Typically, this is called internally when an attribute
955 generates its accessors.
957 =item B<< $attr->associated_methods >>
959 This returns the list of methods which have been associated with the
962 =item B<< $attr->install_accessors >>
964 This method generates and installs code the attributes various
965 accessors. It is typically called from the L<Class::MOP::Class>
966 C<add_attribute> method.
968 =item B<< $attr->remove_accessors >>
970 This method removes all of the accessors associated with the
973 This does not currently remove methods from the list returned by
974 C<associated_methods>.
976 =item B<< $attr->inline_get >>
978 =item B<< $attr->inline_set >>
980 =item B<< $attr->inline_has >>
982 =item B<< $attr->inline_clear >>
984 These methods return a code snippet suitable for inlining the relevant
985 operation. They expect strings containing variable names to be used in the
986 inlining, like C<'$self'> or C<'$_[1]'>.
994 =item B<< Class::MOP::Attribute->meta >>
996 This will return a L<Class::MOP::Class> instance for this class.
998 It should also be noted that L<Class::MOP> will actually bootstrap
999 this module by installing a number of attribute meta-objects into its