2 package Class::MOP::Attribute;
8 use Scalar::Util 'blessed', 'reftype', 'weaken';
10 our $VERSION = '0.06';
13 require Class::MOP::Class;
14 Class::MOP::Class->initialize(blessed($_[0]) || $_[0]);
17 # NOTE: (meta-circularity)
18 # This method will be replaces in the
19 # boostrap section of Class::MOP, by
20 # a new version which uses the
21 # &Class::MOP::Class::construct_instance
22 # method to build an attribute meta-object
23 # which itself is described with attribute
25 # - Ain't meta-circularity grand? :)
31 (defined $name && $name)
32 || confess "You must provide a name for the attribute";
33 $options{init_arg} = $name
34 if not exists $options{init_arg};
38 accessor => $options{accessor},
39 reader => $options{reader},
40 writer => $options{writer},
41 predicate => $options{predicate},
42 init_arg => $options{init_arg},
43 default => $options{default},
44 # keep a weakened link to the
45 # class we are associated with
46 associated_class => undef,
51 # this is a primative (and kludgy) clone operation
52 # for now, it will be repleace in the Class::MOP
53 # bootstrap with a proper one, however we know
54 # that this one will work fine for now.
59 || confess "Can only clone an instance";
60 return bless { %{$self}, %options } => blessed($self);
63 sub initialize_instance_slot {
64 my ($self, $class, $instance, $params) = @_;
65 my $init_arg = $self->init_arg();
66 # try to fetch the init arg from the %params ...
68 $val = $params->{$init_arg} if exists $params->{$init_arg};
69 # if nothing was in the %params, we can use the
70 # attribute's default value (if it has one)
71 $val = $self->default($instance)
72 if !defined $val && $self->has_default;
73 $instance->{$self->name} = $val;
77 # the next bunch of methods will get bootstrapped
78 # away in the Class::MOP bootstrapping section
80 sub name { $_[0]->{name} }
82 sub associated_class { $_[0]->{associated_class} }
84 sub has_accessor { defined($_[0]->{accessor}) ? 1 : 0 }
85 sub has_reader { defined($_[0]->{reader}) ? 1 : 0 }
86 sub has_writer { defined($_[0]->{writer}) ? 1 : 0 }
87 sub has_predicate { defined($_[0]->{predicate}) ? 1 : 0 }
88 sub has_init_arg { defined($_[0]->{init_arg}) ? 1 : 0 }
89 sub has_default { defined($_[0]->{default}) ? 1 : 0 }
91 sub accessor { $_[0]->{accessor} }
92 sub reader { $_[0]->{reader} }
93 sub writer { $_[0]->{writer} }
94 sub predicate { $_[0]->{predicate} }
95 sub init_arg { $_[0]->{init_arg} }
97 # end bootstrapped away method section.
98 # (all methods below here are kept intact)
102 if (reftype($self->{default}) && reftype($self->{default}) eq 'CODE') {
103 # if the default is a CODE ref, then
104 # we pass in the instance and default
105 # can return a value based on that
106 # instance. Somewhat crude, but works.
107 return $self->{default}->(shift);
114 sub attach_to_class {
115 my ($self, $class) = @_;
116 (blessed($class) && $class->isa('Class::MOP::Class'))
117 || confess "You must pass a Class::MOP::Class instance (or a subclass)";
118 weaken($self->{associated_class} = $class);
121 sub detach_from_class {
123 $self->{associated_class} = undef;
126 ## Method generation helpers
128 sub generate_accessor_method {
129 my ($self, $attr_name) = @_;
131 $_[0]->{$attr_name} = $_[1] if scalar(@_) == 2;
136 sub generate_reader_method {
137 my ($self, $attr_name) = @_;
139 confess "Cannot assign a value to a read-only accessor" if @_ > 1;
144 sub generate_writer_method {
145 my ($self, $attr_name) = @_;
146 sub { $_[0]->{$attr_name} = $_[1] };
149 sub generate_predicate_method {
150 my ($self, $attr_name) = @_;
151 sub { defined $_[0]->{$attr_name} ? 1 : 0 };
154 sub process_accessors {
155 my ($self, $type, $accessor) = @_;
156 if (reftype($accessor)) {
157 (reftype($accessor) eq 'HASH')
158 || confess "bad accessor/reader/writer/predicate format, must be a HASH ref";
159 my ($name, $method) = each %{$accessor};
160 return ($name, Class::MOP::Attribute::Accessor->wrap($method));
163 my $generator = $self->can('generate_' . $type . '_method');
165 || confess "There is no method generator for the type='$type'";
166 if (my $method = $self->$generator($self->name)) {
167 return ($accessor => Class::MOP::Attribute::Accessor->wrap($method));
169 confess "Could not create the '$type' method for " . $self->name . " because : $@";
173 sub install_accessors {
175 my $class = $self->associated_class;
178 $self->process_accessors('accessor' => $self->accessor())
179 ) if $self->has_accessor();
182 $self->process_accessors('reader' => $self->reader())
183 ) if $self->has_reader();
186 $self->process_accessors('writer' => $self->writer())
187 ) if $self->has_writer();
190 $self->process_accessors('predicate' => $self->predicate())
191 ) if $self->has_predicate();
196 my $_remove_accessor = sub {
197 my ($accessor, $class) = @_;
198 if (reftype($accessor) && reftype($accessor) eq 'HASH') {
199 ($accessor) = keys %{$accessor};
201 my $method = $class->get_method($accessor);
202 $class->remove_method($accessor)
203 if (blessed($method) && $method->isa('Class::MOP::Attribute::Accessor'));
206 sub remove_accessors {
208 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
209 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
210 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
211 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
217 package Class::MOP::Attribute::Accessor;
222 use Class::MOP::Method;
224 our $VERSION = '0.01';
226 our @ISA = ('Class::MOP::Method');
236 Class::MOP::Attribute - Attribute Meta Object
240 Class::MOP::Attribute->new('$foo' => (
241 accessor => 'foo', # dual purpose get/set accessor
242 predicate => 'has_foo' # predicate check for defined-ness
243 init_arg => '-foo', # class->new will look for a -foo key
244 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
247 Class::MOP::Attribute->new('$.bar' => (
248 reader => 'bar', # getter
249 writer => 'set_bar', # setter
250 predicate => 'has_bar' # predicate check for defined-ness
251 init_arg => ':bar', # class->new will look for a :bar key
252 # no default value means it is undef
257 The Attribute Protocol is almost entirely an invention of this module,
258 and is completely optional to this MOP. This is because Perl 5 does not
259 have consistent notion of what is an attribute of a class. There are
260 so many ways in which this is done, and very few (if any) are
261 easily discoverable by this module.
263 So, all that said, this module attempts to inject some order into this
264 chaos, by introducing a consistent API which can be used to create
273 =item B<new ($name, ?%options)>
275 An attribute must (at the very least), have a C<$name>. All other
276 C<%options> are contained added as key-value pairs. Acceptable keys
283 This should be a string value representing the expected key in
284 an initialization hash. For instance, if we have an I<init_arg>
285 value of C<-foo>, then the following code will Just Work.
287 MyClass->meta->construct_instance(-foo => "Hello There");
289 In an init_arg is not assigned, it will automatically use the
294 The value of this key is the default value which
295 C<Class::MOP::Class::construct_instance> will initialize the
299 If the value is a simple scalar (string or number), then it can
300 be just passed as is. However, if you wish to initialize it with
301 a HASH or ARRAY ref, then you need to wrap that inside a CODE
304 Class::MOP::Attribute->new('@foo' => (
305 default => sub { [] },
310 Class::MOP::Attribute->new('%foo' => (
311 default => sub { {} },
314 If you wish to initialize an attribute with a CODE reference
315 itself, then you need to wrap that in a subroutine as well, like
318 Class::MOP::Attribute->new('&foo' => (
319 default => sub { sub { print "Hello World" } },
322 And lastly, if the value of your attribute is dependent upon
323 some other aspect of the instance structure, then you can take
324 advantage of the fact that when the I<default> value is a CODE
325 reference, it is passed the raw (unblessed) instance structure
326 as it's only argument. So you can do things like this:
328 Class::MOP::Attribute->new('$object_identity' => (
329 default => sub { Scalar::Util::refaddr($_[0]) },
332 This last feature is fairly limited as there is no gurantee of
333 the order of attribute initializations, so you cannot perform
334 any kind of dependent initializations. However, if this is
335 something you need, you could subclass B<Class::MOP::Class> and
336 this class to acheive it. However, this is currently left as
337 an exercise to the reader :).
341 The I<accessor>, I<reader>, I<writer> and I<predicate> keys can
342 contain either; the name of the method and an appropriate default
343 one will be generated for you, B<or> a HASH ref containing exactly one
344 key (which will be used as the name of the method) and one value,
345 which should contain a CODE reference which will be installed as
352 The I<accessor> is a standard perl-style read/write accessor. It will
353 return the value of the attribute, and if a value is passed as an argument,
354 it will assign that value to the attribute.
357 This method will properly handle the following code, by assigning an
358 C<undef> value to the attribute.
360 $object->set_something(undef);
364 This is a basic read-only accessor, it will just return the value of
369 This is a basic write accessor, it accepts a single argument, and
370 assigns that value to the attribute. This method does not intentially
371 return a value, however perl will return the result of the last
372 expression in the subroutine, which returns in this returning the
373 same value that it was passed.
376 This method will properly handle the following code, by assigning an
377 C<undef> value to the attribute.
379 $object->set_something();
383 This is a basic test to see if the value of the attribute is not
384 C<undef>. It will return true (C<1>) if the attribute's value is
385 defined, and false (C<0>) otherwise.
389 =item B<clone (%options)>
391 =item B<initialize_instance_slot ($instance, $params)>
397 These are all basic read-only value accessors for the values
398 passed into C<new>. I think they are pretty much self-explanitory.
414 =item B<default (?$instance)>
416 As noted in the documentation for C<new> above, if the I<default>
417 value is a CODE reference, this accessor will pass a single additional
418 argument C<$instance> into it and return the value.
422 =head2 Informational predicates
424 These are all basic predicate methods for the values passed into C<new>.
428 =item B<has_accessor>
434 =item B<has_predicate>
436 =item B<has_init_arg>
442 =head2 Class association
446 =item B<associated_class>
448 =item B<attach_to_class ($class)>
450 =item B<detach_from_class>
454 =head2 Attribute Accessor generation
458 =item B<install_accessors>
460 This allows the attribute to generate and install code for it's own
461 I<accessor/reader/writer/predicate> methods. This is called by
462 C<Class::MOP::Class::add_attribute>.
464 This method will call C<process_accessors> for each of the possible
465 method types (accessor, reader, writer & predicate).
467 =item B<process_accessors ($type, $value)>
469 This takes a C<$type> (accessor, reader, writer or predicate), and
470 a C<$value> (the value passed into the constructor for each of the
471 different types). It will then either generate the method itself
472 (using the C<generate_*_method> methods listed below) or it will
473 use the custom method passed through the constructor.
477 =item B<generate_accessor_method ($attr_name)>
479 =item B<generate_predicate_method ($attr_name)>
481 =item B<generate_reader_method ($attr_name)>
483 =item B<generate_writer_method ($attr_name)>
487 =item B<remove_accessors>
489 This allows the attribute to remove the method for it's own
490 I<accessor/reader/writer/predicate>. This is called by
491 C<Class::MOP::Class::remove_attribute>.
501 This will return a B<Class::MOP::Class> instance which is related
504 It should also be noted that B<Class::MOP> will actually bootstrap
505 this module by installing a number of attribute meta-objects into
506 it's metaclass. This will allow this class to reap all the benifits
507 of the MOP when subclassing it.
513 Stevan Little E<lt>stevan@iinteractive.comE<gt>
515 =head1 COPYRIGHT AND LICENSE
517 Copyright 2006 by Infinity Interactive, Inc.
519 L<http://www.iinteractive.com>
521 This library is free software; you can redistribute it and/or modify
522 it under the same terms as Perl itself.