2 package Class::MOP::Attribute;
8 use Scalar::Util 'blessed', 'reftype', 'weaken';
10 our $VERSION = '0.04';
13 require Class::MOP::Class;
14 Class::MOP::Class->initialize(blessed($_[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);
64 # the next bunch of methods will get bootstrapped
65 # away in the Class::MOP bootstrapping section
67 sub name { $_[0]->{name} }
69 sub associated_class { $_[0]->{associated_class} }
71 sub has_accessor { defined($_[0]->{accessor}) ? 1 : 0 }
72 sub has_reader { defined($_[0]->{reader}) ? 1 : 0 }
73 sub has_writer { defined($_[0]->{writer}) ? 1 : 0 }
74 sub has_predicate { defined($_[0]->{predicate}) ? 1 : 0 }
75 sub has_init_arg { defined($_[0]->{init_arg}) ? 1 : 0 }
76 sub has_default { defined($_[0]->{default}) ? 1 : 0 }
78 sub accessor { $_[0]->{accessor} }
79 sub reader { $_[0]->{reader} }
80 sub writer { $_[0]->{writer} }
81 sub predicate { $_[0]->{predicate} }
82 sub init_arg { $_[0]->{init_arg} }
84 # end bootstrapped away method section.
85 # (all methods below here are kept intact)
89 if (reftype($self->{default}) && reftype($self->{default}) eq 'CODE') {
90 # if the default is a CODE ref, then
91 # we pass in the instance and default
92 # can return a value based on that
93 # instance. Somewhat crude, but works.
94 return $self->{default}->(shift);
101 sub attach_to_class {
102 my ($self, $class) = @_;
103 (blessed($class) && $class->isa('Class::MOP::Class'))
104 || confess "You must pass a Class::MOP::Class instance (or a subclass)";
105 weaken($self->{associated_class} = $class);
108 sub detach_from_class {
110 $self->{associated_class} = undef;
113 ## Method generation helpers
115 sub generate_accessor_method {
116 my ($self, $attr_name) = @_;
118 $_[0]->{$attr_name} = $_[1] if scalar(@_) == 2;
123 sub generate_reader_method {
124 my ($self, $attr_name) = @_;
125 sub { $_[0]->{$attr_name} };
128 sub generate_writer_method {
129 my ($self, $attr_name) = @_;
130 sub { $_[0]->{$attr_name} = $_[1] };
133 sub generate_predicate_method {
134 my ($self, $attr_name) = @_;
135 sub { defined $_[0]->{$attr_name} ? 1 : 0 };
138 sub process_accessors {
139 my ($self, $type, $accessor) = @_;
140 if (reftype($accessor)) {
141 (reftype($accessor) eq 'HASH')
142 || confess "bad accessor/reader/writer/predicate format, must be a HASH ref";
143 my ($name, $method) = each %{$accessor};
144 return ($name, Class::MOP::Attribute::Accessor->wrap($method));
147 my $generator = $self->can('generate_' . $type . '_method');
149 || confess "There is no method generator for the type='$type'";
150 if (my $method = $self->$generator($self->name)) {
151 return ($accessor => Class::MOP::Attribute::Accessor->wrap($method));
153 confess "Could not create the '$type' method for " . $self->name . " because : $@";
157 sub install_accessors {
159 my $class = $self->associated_class;
162 $self->process_accessors('accessor' => $self->accessor())
163 ) if $self->has_accessor();
166 $self->process_accessors('reader' => $self->reader())
167 ) if $self->has_reader();
170 $self->process_accessors('writer' => $self->writer())
171 ) if $self->has_writer();
174 $self->process_accessors('predicate' => $self->predicate())
175 ) if $self->has_predicate();
180 my $_remove_accessor = sub {
181 my ($accessor, $class) = @_;
182 if (reftype($accessor) && reftype($accessor) eq 'HASH') {
183 ($accessor) = keys %{$accessor};
185 my $method = $class->get_method($accessor);
186 $class->remove_method($accessor)
187 if (blessed($method) && $method->isa('Class::MOP::Attribute::Accessor'));
190 sub remove_accessors {
192 $_remove_accessor->($self->accessor(), $self->associated_class()) if $self->has_accessor();
193 $_remove_accessor->($self->reader(), $self->associated_class()) if $self->has_reader();
194 $_remove_accessor->($self->writer(), $self->associated_class()) if $self->has_writer();
195 $_remove_accessor->($self->predicate(), $self->associated_class()) if $self->has_predicate();
201 package Class::MOP::Attribute::Accessor;
206 use Class::MOP::Method;
208 our $VERSION = '0.01';
210 our @ISA = ('Class::MOP::Method');
220 Class::MOP::Attribute - Attribute Meta Object
224 Class::MOP::Attribute->new('$foo' => (
225 accessor => 'foo', # dual purpose get/set accessor
226 predicate => 'has_foo' # predicate check for defined-ness
227 init_arg => '-foo', # class->new will look for a -foo key
228 default => 'BAR IS BAZ!' # if no -foo key is provided, use this
231 Class::MOP::Attribute->new('$.bar' => (
232 reader => 'bar', # getter
233 writer => 'set_bar', # setter
234 predicate => 'has_bar' # predicate check for defined-ness
235 init_arg => ':bar', # class->new will look for a :bar key
236 # no default value means it is undef
241 The Attribute Protocol is almost entirely an invention of this module,
242 and is completely optional to this MOP. This is because Perl 5 does not
243 have consistent notion of what is an attribute of a class. There are
244 so many ways in which this is done, and very few (if any) are
245 easily discoverable by this module.
247 So, all that said, this module attempts to inject some order into this
248 chaos, by introducing a consistent API which can be used to create
257 =item B<new ($name, ?%options)>
259 An attribute must (at the very least), have a C<$name>. All other
260 C<%options> are contained added as key-value pairs. Acceptable keys
263 =item B<clone (%options)>
269 This should be a string value representing the expected key in
270 an initialization hash. For instance, if we have an I<init_arg>
271 value of C<-foo>, then the following code will Just Work.
273 MyClass->meta->construct_instance(-foo => "Hello There");
275 In an init_arg is not assigned, it will automatically use the
280 The value of this key is the default value which
281 C<Class::MOP::Class::construct_instance> will initialize the
285 If the value is a simple scalar (string or number), then it can
286 be just passed as is. However, if you wish to initialize it with
287 a HASH or ARRAY ref, then you need to wrap that inside a CODE
290 Class::MOP::Attribute->new('@foo' => (
291 default => sub { [] },
296 Class::MOP::Attribute->new('%foo' => (
297 default => sub { {} },
300 If you wish to initialize an attribute with a CODE reference
301 itself, then you need to wrap that in a subroutine as well, like
304 Class::MOP::Attribute->new('&foo' => (
305 default => sub { sub { print "Hello World" } },
308 And lastly, if the value of your attribute is dependent upon
309 some other aspect of the instance structure, then you can take
310 advantage of the fact that when the I<default> value is a CODE
311 reference, it is passed the raw (unblessed) instance structure
312 as it's only argument. So you can do things like this:
314 Class::MOP::Attribute->new('$object_identity' => (
315 default => sub { Scalar::Util::refaddr($_[0]) },
318 This last feature is fairly limited as there is no gurantee of
319 the order of attribute initializations, so you cannot perform
320 any kind of dependent initializations. However, if this is
321 something you need, you could subclass B<Class::MOP::Class> and
322 this class to acheive it. However, this is currently left as
323 an exercise to the reader :).
327 The I<accessor>, I<reader>, I<writer> and I<predicate> keys can
328 contain either; the name of the method and an appropriate default
329 one will be generated for you, B<or> a HASH ref containing exactly one
330 key (which will be used as the name of the method) and one value,
331 which should contain a CODE reference which will be installed as
338 The I<accessor> is a standard perl-style read/write accessor. It will
339 return the value of the attribute, and if a value is passed as an argument,
340 it will assign that value to the attribute.
343 This method will properly handle the following code, by assigning an
344 C<undef> value to the attribute.
346 $object->set_something(undef);
350 This is a basic read-only accessor, it will just return the value of
355 This is a basic write accessor, it accepts a single argument, and
356 assigns that value to the attribute. This method does not intentially
357 return a value, however perl will return the result of the last
358 expression in the subroutine, which returns in this returning the
359 same value that it was passed.
362 This method will properly handle the following code, by assigning an
363 C<undef> value to the attribute.
365 $object->set_something();
369 This is a basic test to see if the value of the attribute is not
370 C<undef>. It will return true (C<1>) if the attribute's value is
371 defined, and false (C<0>) otherwise.
379 These are all basic read-only value accessors for the values
380 passed into C<new>. I think they are pretty much self-explanitory.
396 =item B<default (?$instance)>
398 As noted in the documentation for C<new> above, if the I<default>
399 value is a CODE reference, this accessor will pass a single additional
400 argument C<$instance> into it and return the value.
404 =head2 Informational predicates
406 These are all basic predicate methods for the values passed into C<new>.
410 =item B<has_accessor>
416 =item B<has_predicate>
418 =item B<has_init_arg>
424 =head2 Class association
428 =item B<associated_class>
430 =item B<attach_to_class ($class)>
432 =item B<detach_from_class>
436 =head2 Attribute Accessor generation
440 =item B<install_accessors>
442 This allows the attribute to generate and install code for it's own
443 I<accessor/reader/writer/predicate> methods. This is called by
444 C<Class::MOP::Class::add_attribute>.
446 This method will call C<process_accessors> for each of the possible
447 method types (accessor, reader, writer & predicate).
449 =item B<process_accessors ($type, $value)>
451 This takes a C<$type> (accessor, reader, writer or predicate), and
452 a C<$value> (the value passed into the constructor for each of the
453 different types). It will then either generate the method itself
454 (using the C<generate_*_method> methods listed below) or it will
455 use the custom method passed through the constructor.
459 =item B<generate_accessor_method ($attr_name)>
461 =item B<generate_predicate_method ($attr_name)>
463 =item B<generate_reader_method ($attr_name)>
465 =item B<generate_writer_method ($attr_name)>
469 =item B<remove_accessors>
471 This allows the attribute to remove the method for it's own
472 I<accessor/reader/writer/predicate>. This is called by
473 C<Class::MOP::Class::remove_attribute>.
483 This will return a B<Class::MOP::Class> instance which is related
486 It should also be noted that B<Class::MOP> will actually bootstrap
487 this module by installing a number of attribute meta-objects into
488 it's metaclass. This will allow this class to reap all the benifits
489 of the MOP when subclassing it.
495 Stevan Little E<lt>stevan@iinteractive.comE<gt>
497 =head1 COPYRIGHT AND LICENSE
499 Copyright 2006 by Infinity Interactive, Inc.
501 L<http://www.iinteractive.com>
503 This library is free software; you can redistribute it and/or modify
504 it under the same terms as Perl itself.